14158 lines
537 KiB
Plaintext
14158 lines
537 KiB
Plaintext
@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
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@c 2000, 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
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@c This is part of the GCC manual.
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@c For copying conditions, see the file gcc.texi.
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@ignore
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@c man begin INCLUDE
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@include gcc-vers.texi
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@c man end
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@c man begin COPYRIGHT
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Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
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1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.2 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``GNU General Public License'' and ``Funding
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Free Software'', the Front-Cover texts being (a) (see below), and with
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the Back-Cover Texts being (b) (see below). A copy of the license is
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included in the gfdl(7) man page.
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development.
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@c man end
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@c Set file name and title for the man page.
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@setfilename gcc
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@settitle GNU project C and C++ compiler
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@c man begin SYNOPSIS
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gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
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[@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
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[@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
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[@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
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[@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
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[@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
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[@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
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Only the most useful options are listed here; see below for the
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remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
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@c man end
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@c man begin SEEALSO
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gpl(7), gfdl(7), fsf-funding(7),
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cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
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and the Info entries for @file{gcc}, @file{cpp}, @file{as},
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@file{ld}, @file{binutils} and @file{gdb}.
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@c man end
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@c man begin BUGS
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For instructions on reporting bugs, see
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@w{@uref{http://gcc.gnu.org/bugs.html}}.
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@c man end
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@c man begin AUTHOR
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See the Info entry for @command{gcc}, or
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@w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
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for contributors to GCC@.
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@c man end
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@end ignore
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@node Invoking GCC
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@chapter GCC Command Options
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@cindex GCC command options
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@cindex command options
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@cindex options, GCC command
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@c man begin DESCRIPTION
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When you invoke GCC, it normally does preprocessing, compilation,
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assembly and linking. The ``overall options'' allow you to stop this
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process at an intermediate stage. For example, the @option{-c} option
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says not to run the linker. Then the output consists of object files
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output by the assembler.
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Other options are passed on to one stage of processing. Some options
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control the preprocessor and others the compiler itself. Yet other
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options control the assembler and linker; most of these are not
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documented here, since you rarely need to use any of them.
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@cindex C compilation options
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Most of the command line options that you can use with GCC are useful
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for C programs; when an option is only useful with another language
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(usually C++), the explanation says so explicitly. If the description
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for a particular option does not mention a source language, you can use
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that option with all supported languages.
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@cindex C++ compilation options
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@xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
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options for compiling C++ programs.
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@cindex grouping options
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@cindex options, grouping
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The @command{gcc} program accepts options and file names as operands. Many
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options have multi-letter names; therefore multiple single-letter options
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may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
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-r}}.
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@cindex order of options
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@cindex options, order
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You can mix options and other arguments. For the most part, the order
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you use doesn't matter. Order does matter when you use several options
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of the same kind; for example, if you specify @option{-L} more than once,
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the directories are searched in the order specified.
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Many options have long names starting with @samp{-f} or with
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@samp{-W}---for example,
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@option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
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these have both positive and negative forms; the negative form of
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@option{-ffoo} would be @option{-fno-foo}. This manual documents
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only one of these two forms, whichever one is not the default.
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@c man end
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@xref{Option Index}, for an index to GCC's options.
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@menu
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* Option Summary:: Brief list of all options, without explanations.
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* Overall Options:: Controlling the kind of output:
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an executable, object files, assembler files,
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or preprocessed source.
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* Invoking G++:: Compiling C++ programs.
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* C Dialect Options:: Controlling the variant of C language compiled.
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* C++ Dialect Options:: Variations on C++.
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* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
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and Objective-C++.
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* Language Independent Options:: Controlling how diagnostics should be
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formatted.
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* Warning Options:: How picky should the compiler be?
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* Debugging Options:: Symbol tables, measurements, and debugging dumps.
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* Optimize Options:: How much optimization?
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* Preprocessor Options:: Controlling header files and macro definitions.
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Also, getting dependency information for Make.
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* Assembler Options:: Passing options to the assembler.
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* Link Options:: Specifying libraries and so on.
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* Directory Options:: Where to find header files and libraries.
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Where to find the compiler executable files.
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* Spec Files:: How to pass switches to sub-processes.
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* Target Options:: Running a cross-compiler, or an old version of GCC.
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* Submodel Options:: Specifying minor hardware or convention variations,
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such as 68010 vs 68020.
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* Code Gen Options:: Specifying conventions for function calls, data layout
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and register usage.
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* Environment Variables:: Env vars that affect GCC.
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* Precompiled Headers:: Compiling a header once, and using it many times.
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* Running Protoize:: Automatically adding or removing function prototypes.
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@end menu
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@c man begin OPTIONS
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@node Option Summary
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@section Option Summary
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Here is a summary of all the options, grouped by type. Explanations are
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in the following sections.
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@table @emph
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@item Overall Options
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@xref{Overall Options,,Options Controlling the Kind of Output}.
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@gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol
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-x @var{language} -v -### --help --target-help --version @@@var{file}}
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@item C Language Options
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@xref{C Dialect Options,,Options Controlling C Dialect}.
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@gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol
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-aux-info @var{filename} @gol
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-fno-asm -fno-builtin -fno-builtin-@var{function} @gol
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-fhosted -ffreestanding -fopenmp -fms-extensions @gol
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-trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
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-fallow-single-precision -fcond-mismatch @gol
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-fsigned-bitfields -fsigned-char @gol
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-funsigned-bitfields -funsigned-char}
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@item C++ Language Options
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@xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
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@gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
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-fconserve-space -ffriend-injection @gol
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-fno-elide-constructors @gol
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-fno-enforce-eh-specs @gol
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-ffor-scope -fno-for-scope -fno-gnu-keywords @gol
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-fno-implicit-templates @gol
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-fno-implicit-inline-templates @gol
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-fno-implement-inlines -fms-extensions @gol
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-fno-nonansi-builtins -fno-operator-names @gol
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-fno-optional-diags -fpermissive @gol
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-frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
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-fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
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-fno-default-inline -fvisibility-inlines-hidden @gol
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-Wabi -Wctor-dtor-privacy @gol
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-Wnon-virtual-dtor -Wreorder @gol
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-Weffc++ -Wno-deprecated -Wstrict-null-sentinel @gol
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-Wno-non-template-friend -Wold-style-cast @gol
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-Woverloaded-virtual -Wno-pmf-conversions @gol
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-Wsign-promo}
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@item Objective-C and Objective-C++ Language Options
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@xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
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Objective-C and Objective-C++ Dialects}.
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@gccoptlist{-fconstant-string-class=@var{class-name} @gol
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-fgnu-runtime -fnext-runtime @gol
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-fno-nil-receivers @gol
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-fobjc-call-cxx-cdtors @gol
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-fobjc-direct-dispatch @gol
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-fobjc-exceptions @gol
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-fobjc-gc @gol
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-freplace-objc-classes @gol
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-fzero-link @gol
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-gen-decls @gol
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-Wassign-intercept @gol
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-Wno-protocol -Wselector @gol
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-Wstrict-selector-match @gol
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-Wundeclared-selector}
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@item Language Independent Options
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@xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
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@gccoptlist{-fmessage-length=@var{n} @gol
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-fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
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-fdiagnostics-show-option}
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@item Warning Options
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@xref{Warning Options,,Options to Request or Suppress Warnings}.
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@gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
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-w -Wextra -Wall -Waddress -Waggregate-return -Wno-attributes @gol
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-Wc++-compat -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
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-Wconversion -Wno-deprecated-declarations @gol
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-Wdisabled-optimization -Wno-div-by-zero -Wno-endif-labels @gol
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-Werror -Werror=* -Werror-implicit-function-declaration @gol
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-Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
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-Wno-format-extra-args -Wformat-nonliteral @gol
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-Wformat-security -Wformat-y2k @gol
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-Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
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-Wimport -Wno-import -Winit-self -Winline @gol
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-Wno-int-to-pointer-cast @gol
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-Wno-invalid-offsetof -Winvalid-pch @gol
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-Wlarger-than-@var{len} -Wunsafe-loop-optimizations -Wlong-long @gol
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-Wmain -Wmissing-braces -Wmissing-field-initializers @gol
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-Wmissing-format-attribute -Wmissing-include-dirs @gol
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-Wmissing-noreturn @gol
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-Wno-multichar -Wnonnull -Wno-overflow @gol
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-Woverlength-strings -Wpacked -Wpadded @gol
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-Wparentheses -Wpointer-arith -Wno-pointer-to-int-cast @gol
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-Wredundant-decls @gol
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-Wreturn-type -Wsequence-point -Wshadow @gol
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-Wsign-compare -Wstack-protector @gol
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-Wstrict-aliasing -Wstrict-aliasing=2 @gol
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-Wstrict-overflow -Wstrict-overflow=@var{n} @gol
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-Wswitch -Wswitch-default -Wswitch-enum @gol
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-Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
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-Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
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-Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
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-Wunused-value -Wunused-variable -Wvariadic-macros @gol
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-Wvolatile-register-var -Wwrite-strings}
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@item C-only Warning Options
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@gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
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-Wmissing-prototypes -Wnested-externs -Wold-style-definition @gol
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-Wstrict-prototypes -Wtraditional @gol
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-Wdeclaration-after-statement -Wpointer-sign}
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@item Debugging Options
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@xref{Debugging Options,,Options for Debugging Your Program or GCC}.
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@gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
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-fdump-noaddr -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
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-fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
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-fdump-ipa-all -fdump-ipa-cgraph @gol
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-fdump-tree-all @gol
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-fdump-tree-original@r{[}-@var{n}@r{]} @gol
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-fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
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-fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
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-fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
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-fdump-tree-ch @gol
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-fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
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-fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
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-fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
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-fdump-tree-dom@r{[}-@var{n}@r{]} @gol
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-fdump-tree-dse@r{[}-@var{n}@r{]} @gol
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-fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
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-fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
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-fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
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-fdump-tree-nrv -fdump-tree-vect @gol
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-fdump-tree-sink @gol
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-fdump-tree-sra@r{[}-@var{n}@r{]} @gol
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-fdump-tree-salias @gol
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-fdump-tree-fre@r{[}-@var{n}@r{]} @gol
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-fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
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-ftree-vectorizer-verbose=@var{n} @gol
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-fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
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-feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
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-feliminate-unused-debug-symbols -femit-class-debug-always @gol
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-fmem-report -fprofile-arcs @gol
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-frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
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-ftest-coverage -ftime-report -fvar-tracking @gol
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-g -g@var{level} -gcoff -gdwarf-2 @gol
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-ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
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-p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
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-print-multi-directory -print-multi-lib @gol
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-print-prog-name=@var{program} -print-search-dirs -Q @gol
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-save-temps -time}
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@item Optimization Options
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@xref{Optimize Options,,Options that Control Optimization}.
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@gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
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-falign-labels=@var{n} -falign-loops=@var{n} @gol
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-fbounds-check -fmudflap -fmudflapth -fmudflapir @gol
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|
-fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize @gol
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|
-fbranch-target-load-optimize2 -fbtr-bb-exclusive @gol
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|
-fcaller-saves -fcprop-registers -fcse-follow-jumps @gol
|
|
-fcse-skip-blocks -fcx-limited-range -fdata-sections @gol
|
|
-fdelayed-branch -fdelete-null-pointer-checks -fearly-inlining @gol
|
|
-fexpensive-optimizations -ffast-math -ffloat-store @gol
|
|
-fforce-addr -ffunction-sections @gol
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|
-fgcse -fgcse-lm -fgcse-sm -fgcse-las -fgcse-after-reload @gol
|
|
-fcrossjumping -fif-conversion -fif-conversion2 @gol
|
|
-finline-functions -finline-functions-called-once @gol
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|
-finline-limit=@var{n} -fkeep-inline-functions @gol
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|
-fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
|
|
-fmodulo-sched -fno-branch-count-reg @gol
|
|
-fno-default-inline -fno-defer-pop -fmove-loop-invariants @gol
|
|
-fno-function-cse -fno-guess-branch-probability @gol
|
|
-fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
|
|
-funsafe-math-optimizations -funsafe-loop-optimizations -ffinite-math-only @gol
|
|
-fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
|
|
-fomit-frame-pointer -foptimize-register-move @gol
|
|
-foptimize-sibling-calls -fprefetch-loop-arrays @gol
|
|
-fprofile-generate -fprofile-use @gol
|
|
-fregmove -frename-registers @gol
|
|
-freorder-blocks -freorder-blocks-and-partition -freorder-functions @gol
|
|
-frerun-cse-after-loop @gol
|
|
-frounding-math -frtl-abstract-sequences @gol
|
|
-fschedule-insns -fschedule-insns2 @gol
|
|
-fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
|
|
-fsched-spec-load-dangerous @gol
|
|
-fsched-stalled-insns=@var{n} -fsched-stalled-insns-dep=@var{n} @gol
|
|
-fsched2-use-superblocks @gol
|
|
-fsched2-use-traces -fsee -freschedule-modulo-scheduled-loops @gol
|
|
-fsection-anchors -fsignaling-nans -fsingle-precision-constant @gol
|
|
-fstack-protector -fstack-protector-all @gol
|
|
-fstrict-aliasing -fstrict-overflow -ftracer -fthread-jumps @gol
|
|
-funroll-all-loops -funroll-loops -fpeel-loops @gol
|
|
-fsplit-ivs-in-unroller -funswitch-loops @gol
|
|
-fvariable-expansion-in-unroller @gol
|
|
-ftree-pre -ftree-ccp -ftree-dce -ftree-loop-optimize @gol
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|
-ftree-loop-linear -ftree-loop-im -ftree-loop-ivcanon -fivopts @gol
|
|
-ftree-dominator-opts -ftree-dse -ftree-copyrename -ftree-sink @gol
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|
-ftree-ch -ftree-sra -ftree-ter -ftree-lrs -ftree-fre -ftree-vectorize @gol
|
|
-ftree-vect-loop-version -ftree-salias -fipa-pta -fweb @gol
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|
-ftree-copy-prop -ftree-store-ccp -ftree-store-copy-prop -fwhole-program @gol
|
|
--param @var{name}=@var{value}
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|
-O -O0 -O1 -O2 -O3 -Os}
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|
|
|
@item Preprocessor Options
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|
@xref{Preprocessor Options,,Options Controlling the Preprocessor}.
|
|
@gccoptlist{-A@var{question}=@var{answer} @gol
|
|
-A-@var{question}@r{[}=@var{answer}@r{]} @gol
|
|
-C -dD -dI -dM -dN @gol
|
|
-D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
|
|
-idirafter @var{dir} @gol
|
|
-include @var{file} -imacros @var{file} @gol
|
|
-iprefix @var{file} -iwithprefix @var{dir} @gol
|
|
-iwithprefixbefore @var{dir} -isystem @var{dir} @gol
|
|
-imultilib @var{dir} -isysroot @var{dir} @gol
|
|
-M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
|
|
-P -fworking-directory -remap @gol
|
|
-trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
|
|
-Xpreprocessor @var{option}}
|
|
|
|
@item Assembler Option
|
|
@xref{Assembler Options,,Passing Options to the Assembler}.
|
|
@gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
|
|
|
|
@item Linker Options
|
|
@xref{Link Options,,Options for Linking}.
|
|
@gccoptlist{@var{object-file-name} -l@var{library} @gol
|
|
-nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
|
|
-s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
|
|
-Wl,@var{option} -Xlinker @var{option} @gol
|
|
-u @var{symbol}}
|
|
|
|
@item Directory Options
|
|
@xref{Directory Options,,Options for Directory Search}.
|
|
@gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
|
|
-specs=@var{file} -I- --sysroot=@var{dir}}
|
|
|
|
@item Target Options
|
|
@c I wrote this xref this way to avoid overfull hbox. -- rms
|
|
@xref{Target Options}.
|
|
@gccoptlist{-V @var{version} -b @var{machine}}
|
|
|
|
@item Machine Dependent Options
|
|
@xref{Submodel Options,,Hardware Models and Configurations}.
|
|
@c This list is ordered alphanumerically by subsection name.
|
|
@c Try and put the significant identifier (CPU or system) first,
|
|
@c so users have a clue at guessing where the ones they want will be.
|
|
|
|
@emph{ARC Options}
|
|
@gccoptlist{-EB -EL @gol
|
|
-mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
|
|
-mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
|
|
|
|
@emph{ARM Options}
|
|
@gccoptlist{-mapcs-frame -mno-apcs-frame @gol
|
|
-mabi=@var{name} @gol
|
|
-mapcs-stack-check -mno-apcs-stack-check @gol
|
|
-mapcs-float -mno-apcs-float @gol
|
|
-mapcs-reentrant -mno-apcs-reentrant @gol
|
|
-msched-prolog -mno-sched-prolog @gol
|
|
-mlittle-endian -mbig-endian -mwords-little-endian @gol
|
|
-mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
|
|
-mthumb-interwork -mno-thumb-interwork @gol
|
|
-mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
|
|
-mstructure-size-boundary=@var{n} @gol
|
|
-mabort-on-noreturn @gol
|
|
-mlong-calls -mno-long-calls @gol
|
|
-msingle-pic-base -mno-single-pic-base @gol
|
|
-mpic-register=@var{reg} @gol
|
|
-mnop-fun-dllimport @gol
|
|
-mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
|
|
-mpoke-function-name @gol
|
|
-mthumb -marm @gol
|
|
-mtpcs-frame -mtpcs-leaf-frame @gol
|
|
-mcaller-super-interworking -mcallee-super-interworking @gol
|
|
-mtp=@var{name}}
|
|
|
|
@emph{AVR Options}
|
|
@gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
|
|
-mcall-prologues -mno-tablejump -mtiny-stack -mint8}
|
|
|
|
@emph{Blackfin Options}
|
|
@gccoptlist{-momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
|
|
-mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
|
|
-mlow-64k -mno-low64k -mid-shared-library @gol
|
|
-mno-id-shared-library -mshared-library-id=@var{n} @gol
|
|
-mlong-calls -mno-long-calls}
|
|
|
|
@emph{CRIS Options}
|
|
@gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
|
|
-mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
|
|
-metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
|
|
-mstack-align -mdata-align -mconst-align @gol
|
|
-m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
|
|
-melf -maout -melinux -mlinux -sim -sim2 @gol
|
|
-mmul-bug-workaround -mno-mul-bug-workaround}
|
|
|
|
@emph{CRX Options}
|
|
@gccoptlist{-mmac -mpush-args}
|
|
|
|
@emph{Darwin Options}
|
|
@gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
|
|
-arch_only -bind_at_load -bundle -bundle_loader @gol
|
|
-client_name -compatibility_version -current_version @gol
|
|
-dead_strip @gol
|
|
-dependency-file -dylib_file -dylinker_install_name @gol
|
|
-dynamic -dynamiclib -exported_symbols_list @gol
|
|
-filelist -flat_namespace -force_cpusubtype_ALL @gol
|
|
-force_flat_namespace -headerpad_max_install_names @gol
|
|
-image_base -init -install_name -keep_private_externs @gol
|
|
-multi_module -multiply_defined -multiply_defined_unused @gol
|
|
-noall_load -no_dead_strip_inits_and_terms @gol
|
|
-nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
|
|
-pagezero_size -prebind -prebind_all_twolevel_modules @gol
|
|
-private_bundle -read_only_relocs -sectalign @gol
|
|
-sectobjectsymbols -whyload -seg1addr @gol
|
|
-sectcreate -sectobjectsymbols -sectorder @gol
|
|
-segaddr -segs_read_only_addr -segs_read_write_addr @gol
|
|
-seg_addr_table -seg_addr_table_filename -seglinkedit @gol
|
|
-segprot -segs_read_only_addr -segs_read_write_addr @gol
|
|
-single_module -static -sub_library -sub_umbrella @gol
|
|
-twolevel_namespace -umbrella -undefined @gol
|
|
-unexported_symbols_list -weak_reference_mismatches @gol
|
|
-whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
|
|
-mkernel -mone-byte-bool}
|
|
|
|
@emph{DEC Alpha Options}
|
|
@gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
|
|
-mieee -mieee-with-inexact -mieee-conformant @gol
|
|
-mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
|
|
-mtrap-precision=@var{mode} -mbuild-constants @gol
|
|
-mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
|
|
-mbwx -mmax -mfix -mcix @gol
|
|
-mfloat-vax -mfloat-ieee @gol
|
|
-mexplicit-relocs -msmall-data -mlarge-data @gol
|
|
-msmall-text -mlarge-text @gol
|
|
-mmemory-latency=@var{time}}
|
|
|
|
@emph{DEC Alpha/VMS Options}
|
|
@gccoptlist{-mvms-return-codes}
|
|
|
|
@emph{FRV Options}
|
|
@gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
|
|
-mhard-float -msoft-float @gol
|
|
-malloc-cc -mfixed-cc -mdword -mno-dword @gol
|
|
-mdouble -mno-double @gol
|
|
-mmedia -mno-media -mmuladd -mno-muladd @gol
|
|
-mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
|
|
-mlinked-fp -mlong-calls -malign-labels @gol
|
|
-mlibrary-pic -macc-4 -macc-8 @gol
|
|
-mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
|
|
-moptimize-membar -mno-optimize-membar @gol
|
|
-mscc -mno-scc -mcond-exec -mno-cond-exec @gol
|
|
-mvliw-branch -mno-vliw-branch @gol
|
|
-mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
|
|
-mno-nested-cond-exec -mtomcat-stats @gol
|
|
-mTLS -mtls @gol
|
|
-mcpu=@var{cpu}}
|
|
|
|
@emph{GNU/Linux Options}
|
|
@gccoptlist{-muclibc}
|
|
|
|
@emph{H8/300 Options}
|
|
@gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
|
|
|
|
@emph{HPPA Options}
|
|
@gccoptlist{-march=@var{architecture-type} @gol
|
|
-mbig-switch -mdisable-fpregs -mdisable-indexing @gol
|
|
-mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
|
|
-mfixed-range=@var{register-range} @gol
|
|
-mjump-in-delay -mlinker-opt -mlong-calls @gol
|
|
-mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
|
|
-mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
|
|
-mno-jump-in-delay -mno-long-load-store @gol
|
|
-mno-portable-runtime -mno-soft-float @gol
|
|
-mno-space-regs -msoft-float -mpa-risc-1-0 @gol
|
|
-mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
|
|
-mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
|
|
-munix=@var{unix-std} -nolibdld -static -threads}
|
|
|
|
@emph{i386 and x86-64 Options}
|
|
@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
|
|
-mfpmath=@var{unit} @gol
|
|
-masm=@var{dialect} -mno-fancy-math-387 @gol
|
|
-mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
|
|
-mno-wide-multiply -mrtd -malign-double @gol
|
|
-mpreferred-stack-boundary=@var{num} @gol
|
|
-mmmx -msse -msse2 -msse3 -m3dnow @gol
|
|
-mthreads -mno-align-stringops -minline-all-stringops @gol
|
|
-mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
|
|
-m96bit-long-double -mregparm=@var{num} -msseregparm @gol
|
|
-mstackrealign @gol
|
|
-momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
|
|
-mcmodel=@var{code-model} @gol
|
|
-m32 -m64 -mlarge-data-threshold=@var{num}}
|
|
|
|
@emph{IA-64 Options}
|
|
@gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
|
|
-mvolatile-asm-stop -mregister-names -mno-sdata @gol
|
|
-mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
|
|
-minline-float-divide-max-throughput @gol
|
|
-minline-int-divide-min-latency @gol
|
|
-minline-int-divide-max-throughput @gol
|
|
-minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
|
|
-mno-dwarf2-asm -mearly-stop-bits @gol
|
|
-mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
|
|
-mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64 @gol
|
|
-mno-sched-br-data-spec -msched-ar-data-spec -mno-sched-control-spec @gol
|
|
-msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
|
|
-msched-ldc -mno-sched-control-ldc -mno-sched-spec-verbose @gol
|
|
-mno-sched-prefer-non-data-spec-insns @gol
|
|
-mno-sched-prefer-non-control-spec-insns @gol
|
|
-mno-sched-count-spec-in-critical-path}
|
|
|
|
@emph{M32R/D Options}
|
|
@gccoptlist{-m32r2 -m32rx -m32r @gol
|
|
-mdebug @gol
|
|
-malign-loops -mno-align-loops @gol
|
|
-missue-rate=@var{number} @gol
|
|
-mbranch-cost=@var{number} @gol
|
|
-mmodel=@var{code-size-model-type} @gol
|
|
-msdata=@var{sdata-type} @gol
|
|
-mno-flush-func -mflush-func=@var{name} @gol
|
|
-mno-flush-trap -mflush-trap=@var{number} @gol
|
|
-G @var{num}}
|
|
|
|
@emph{M32C Options}
|
|
@gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
|
|
|
|
@emph{M680x0 Options}
|
|
@gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
|
|
-m68060 -mcpu32 -m5200 -mcfv4e -m68881 -mbitfield @gol
|
|
-mc68000 -mc68020 @gol
|
|
-mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
|
|
-malign-int -mstrict-align -msep-data -mno-sep-data @gol
|
|
-mshared-library-id=n -mid-shared-library -mno-id-shared-library}
|
|
|
|
@emph{M68hc1x Options}
|
|
@gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
|
|
-mauto-incdec -minmax -mlong-calls -mshort @gol
|
|
-msoft-reg-count=@var{count}}
|
|
|
|
@emph{MCore Options}
|
|
@gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
|
|
-mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
|
|
-m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
|
|
-mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
|
|
-mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
|
|
|
|
@emph{MIPS Options}
|
|
@gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
|
|
-mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
|
|
-mips16 -mno-mips16 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
|
|
-mshared -mno-shared -mxgot -mno-xgot -mgp32 -mgp64 @gol
|
|
-mfp32 -mfp64 -mhard-float -msoft-float @gol
|
|
-msingle-float -mdouble-float -mdsp -mpaired-single -mips3d @gol
|
|
-mlong64 -mlong32 -msym32 -mno-sym32 @gol
|
|
-G@var{num} -membedded-data -mno-embedded-data @gol
|
|
-muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
|
|
-msplit-addresses -mno-split-addresses @gol
|
|
-mexplicit-relocs -mno-explicit-relocs @gol
|
|
-mcheck-zero-division -mno-check-zero-division @gol
|
|
-mdivide-traps -mdivide-breaks @gol
|
|
-mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
|
|
-mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
|
|
-mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
|
|
-mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 @gol
|
|
-mfix-sb1 -mno-fix-sb1 @gol
|
|
-mflush-func=@var{func} -mno-flush-func @gol
|
|
-mbranch-likely -mno-branch-likely @gol
|
|
-mfp-exceptions -mno-fp-exceptions @gol
|
|
-mvr4130-align -mno-vr4130-align}
|
|
|
|
@emph{MMIX Options}
|
|
@gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
|
|
-mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
|
|
-melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
|
|
-mno-base-addresses -msingle-exit -mno-single-exit}
|
|
|
|
@emph{MN10300 Options}
|
|
@gccoptlist{-mmult-bug -mno-mult-bug @gol
|
|
-mam33 -mno-am33 @gol
|
|
-mam33-2 -mno-am33-2 @gol
|
|
-mreturn-pointer-on-d0 @gol
|
|
-mno-crt0 -mrelax}
|
|
|
|
@emph{MT Options}
|
|
@gccoptlist{-mno-crt0 -mbacc -msim @gol
|
|
-march=@var{cpu-type} }
|
|
|
|
@emph{PDP-11 Options}
|
|
@gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
|
|
-mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
|
|
-mint16 -mno-int32 -mfloat32 -mno-float64 @gol
|
|
-mfloat64 -mno-float32 -mabshi -mno-abshi @gol
|
|
-mbranch-expensive -mbranch-cheap @gol
|
|
-msplit -mno-split -munix-asm -mdec-asm}
|
|
|
|
@emph{PowerPC Options}
|
|
See RS/6000 and PowerPC Options.
|
|
|
|
@emph{RS/6000 and PowerPC Options}
|
|
@gccoptlist{-mcpu=@var{cpu-type} @gol
|
|
-mtune=@var{cpu-type} @gol
|
|
-mpower -mno-power -mpower2 -mno-power2 @gol
|
|
-mpowerpc -mpowerpc64 -mno-powerpc @gol
|
|
-maltivec -mno-altivec @gol
|
|
-mpowerpc-gpopt -mno-powerpc-gpopt @gol
|
|
-mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
|
|
-mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol
|
|
-mnew-mnemonics -mold-mnemonics @gol
|
|
-mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
|
|
-m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
|
|
-malign-power -malign-natural @gol
|
|
-msoft-float -mhard-float -mmultiple -mno-multiple @gol
|
|
-mstring -mno-string -mupdate -mno-update @gol
|
|
-mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
|
|
-mstrict-align -mno-strict-align -mrelocatable @gol
|
|
-mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
|
|
-mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
|
|
-mdynamic-no-pic -maltivec -mswdiv @gol
|
|
-mprioritize-restricted-insns=@var{priority} @gol
|
|
-msched-costly-dep=@var{dependence_type} @gol
|
|
-minsert-sched-nops=@var{scheme} @gol
|
|
-mcall-sysv -mcall-netbsd @gol
|
|
-maix-struct-return -msvr4-struct-return @gol
|
|
-mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
|
|
-misel -mno-isel @gol
|
|
-misel=yes -misel=no @gol
|
|
-mspe -mno-spe @gol
|
|
-mspe=yes -mspe=no @gol
|
|
-mvrsave -mno-vrsave @gol
|
|
-mmulhw -mno-mulhw @gol
|
|
-mdlmzb -mno-dlmzb @gol
|
|
-mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
|
|
-mprototype -mno-prototype @gol
|
|
-msim -mmvme -mads -myellowknife -memb -msdata @gol
|
|
-msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
|
|
|
|
@emph{S/390 and zSeries Options}
|
|
@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
|
|
-mhard-float -msoft-float -mlong-double-64 -mlong-double-128 @gol
|
|
-mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
|
|
-msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
|
|
-m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
|
|
-mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
|
|
-mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
|
|
|
|
@emph{Score Options}
|
|
@gccoptlist{-meb -mel @gol
|
|
-mnhwloop @gol
|
|
-muls @gol
|
|
-mmac @gol
|
|
-mscore5 -mscore5u -mscore7 -mscore7d}
|
|
|
|
@emph{SH Options}
|
|
@gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
|
|
-m4-nofpu -m4-single-only -m4-single -m4 @gol
|
|
-m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
|
|
-m5-64media -m5-64media-nofpu @gol
|
|
-m5-32media -m5-32media-nofpu @gol
|
|
-m5-compact -m5-compact-nofpu @gol
|
|
-mb -ml -mdalign -mrelax @gol
|
|
-mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
|
|
-mieee -misize -mpadstruct -mspace @gol
|
|
-mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
|
|
-mdivsi3_libfunc=@var{name} @gol
|
|
-madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
|
|
-minvalid-symbols}
|
|
|
|
@emph{SPARC Options}
|
|
@gccoptlist{-mcpu=@var{cpu-type} @gol
|
|
-mtune=@var{cpu-type} @gol
|
|
-mcmodel=@var{code-model} @gol
|
|
-m32 -m64 -mapp-regs -mno-app-regs @gol
|
|
-mfaster-structs -mno-faster-structs @gol
|
|
-mfpu -mno-fpu -mhard-float -msoft-float @gol
|
|
-mhard-quad-float -msoft-quad-float @gol
|
|
-mimpure-text -mno-impure-text -mlittle-endian @gol
|
|
-mstack-bias -mno-stack-bias @gol
|
|
-munaligned-doubles -mno-unaligned-doubles @gol
|
|
-mv8plus -mno-v8plus -mvis -mno-vis
|
|
-threads -pthreads -pthread}
|
|
|
|
@emph{System V Options}
|
|
@gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
|
|
|
|
@emph{TMS320C3x/C4x Options}
|
|
@gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
|
|
-mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
|
|
-mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
|
|
-mparallel-insns -mparallel-mpy -mpreserve-float}
|
|
|
|
@emph{V850 Options}
|
|
@gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
|
|
-mprolog-function -mno-prolog-function -mspace @gol
|
|
-mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
|
|
-mapp-regs -mno-app-regs @gol
|
|
-mdisable-callt -mno-disable-callt @gol
|
|
-mv850e1 @gol
|
|
-mv850e @gol
|
|
-mv850 -mbig-switch}
|
|
|
|
@emph{VAX Options}
|
|
@gccoptlist{-mg -mgnu -munix}
|
|
|
|
@emph{x86-64 Options}
|
|
See i386 and x86-64 Options.
|
|
|
|
@emph{Xstormy16 Options}
|
|
@gccoptlist{-msim}
|
|
|
|
@emph{Xtensa Options}
|
|
@gccoptlist{-mconst16 -mno-const16 @gol
|
|
-mfused-madd -mno-fused-madd @gol
|
|
-mtext-section-literals -mno-text-section-literals @gol
|
|
-mtarget-align -mno-target-align @gol
|
|
-mlongcalls -mno-longcalls}
|
|
|
|
@emph{zSeries Options}
|
|
See S/390 and zSeries Options.
|
|
|
|
@item Code Generation Options
|
|
@xref{Code Gen Options,,Options for Code Generation Conventions}.
|
|
@gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
|
|
-ffixed-@var{reg} -fexceptions @gol
|
|
-fnon-call-exceptions -funwind-tables @gol
|
|
-fasynchronous-unwind-tables @gol
|
|
-finhibit-size-directive -finstrument-functions @gol
|
|
-fno-common -fno-ident @gol
|
|
-fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
|
|
-fno-jump-tables @gol
|
|
-freg-struct-return -fshort-enums @gol
|
|
-fshort-double -fshort-wchar @gol
|
|
-fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
|
|
-fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
|
|
-fargument-alias -fargument-noalias @gol
|
|
-fargument-noalias-global -fargument-noalias-anything
|
|
-fleading-underscore -ftls-model=@var{model} @gol
|
|
-ftrapv -fwrapv -fbounds-check @gol
|
|
-fvisibility}
|
|
@end table
|
|
|
|
@menu
|
|
* Overall Options:: Controlling the kind of output:
|
|
an executable, object files, assembler files,
|
|
or preprocessed source.
|
|
* C Dialect Options:: Controlling the variant of C language compiled.
|
|
* C++ Dialect Options:: Variations on C++.
|
|
* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
|
|
and Objective-C++.
|
|
* Language Independent Options:: Controlling how diagnostics should be
|
|
formatted.
|
|
* Warning Options:: How picky should the compiler be?
|
|
* Debugging Options:: Symbol tables, measurements, and debugging dumps.
|
|
* Optimize Options:: How much optimization?
|
|
* Preprocessor Options:: Controlling header files and macro definitions.
|
|
Also, getting dependency information for Make.
|
|
* Assembler Options:: Passing options to the assembler.
|
|
* Link Options:: Specifying libraries and so on.
|
|
* Directory Options:: Where to find header files and libraries.
|
|
Where to find the compiler executable files.
|
|
* Spec Files:: How to pass switches to sub-processes.
|
|
* Target Options:: Running a cross-compiler, or an old version of GCC.
|
|
@end menu
|
|
|
|
@node Overall Options
|
|
@section Options Controlling the Kind of Output
|
|
|
|
Compilation can involve up to four stages: preprocessing, compilation
|
|
proper, assembly and linking, always in that order. GCC is capable of
|
|
preprocessing and compiling several files either into several
|
|
assembler input files, or into one assembler input file; then each
|
|
assembler input file produces an object file, and linking combines all
|
|
the object files (those newly compiled, and those specified as input)
|
|
into an executable file.
|
|
|
|
@cindex file name suffix
|
|
For any given input file, the file name suffix determines what kind of
|
|
compilation is done:
|
|
|
|
@table @gcctabopt
|
|
@item @var{file}.c
|
|
C source code which must be preprocessed.
|
|
|
|
@item @var{file}.i
|
|
C source code which should not be preprocessed.
|
|
|
|
@item @var{file}.ii
|
|
C++ source code which should not be preprocessed.
|
|
|
|
@item @var{file}.m
|
|
Objective-C source code. Note that you must link with the @file{libobjc}
|
|
library to make an Objective-C program work.
|
|
|
|
@item @var{file}.mi
|
|
Objective-C source code which should not be preprocessed.
|
|
|
|
@item @var{file}.mm
|
|
@itemx @var{file}.M
|
|
Objective-C++ source code. Note that you must link with the @file{libobjc}
|
|
library to make an Objective-C++ program work. Note that @samp{.M} refers
|
|
to a literal capital M@.
|
|
|
|
@item @var{file}.mii
|
|
Objective-C++ source code which should not be preprocessed.
|
|
|
|
@item @var{file}.h
|
|
C, C++, Objective-C or Objective-C++ header file to be turned into a
|
|
precompiled header.
|
|
|
|
@item @var{file}.cc
|
|
@itemx @var{file}.cp
|
|
@itemx @var{file}.cxx
|
|
@itemx @var{file}.cpp
|
|
@itemx @var{file}.CPP
|
|
@itemx @var{file}.c++
|
|
@itemx @var{file}.C
|
|
C++ source code which must be preprocessed. Note that in @samp{.cxx},
|
|
the last two letters must both be literally @samp{x}. Likewise,
|
|
@samp{.C} refers to a literal capital C@.
|
|
|
|
@item @var{file}.mm
|
|
@itemx @var{file}.M
|
|
Objective-C++ source code which must be preprocessed.
|
|
|
|
@item @var{file}.mii
|
|
Objective-C++ source code which should not be preprocessed.
|
|
|
|
@item @var{file}.hh
|
|
@itemx @var{file}.H
|
|
C++ header file to be turned into a precompiled header.
|
|
|
|
@item @var{file}.f
|
|
@itemx @var{file}.for
|
|
@itemx @var{file}.FOR
|
|
Fixed form Fortran source code which should not be preprocessed.
|
|
|
|
@item @var{file}.F
|
|
@itemx @var{file}.fpp
|
|
@itemx @var{file}.FPP
|
|
Fixed form Fortran source code which must be preprocessed (with the traditional
|
|
preprocessor).
|
|
|
|
@item @var{file}.f90
|
|
@itemx @var{file}.f95
|
|
Free form Fortran source code which should not be preprocessed.
|
|
|
|
@item @var{file}.F90
|
|
@itemx @var{file}.F95
|
|
Free form Fortran source code which must be preprocessed (with the
|
|
traditional preprocessor).
|
|
|
|
@c FIXME: Descriptions of Java file types.
|
|
@c @var{file}.java
|
|
@c @var{file}.class
|
|
@c @var{file}.zip
|
|
@c @var{file}.jar
|
|
|
|
@item @var{file}.ads
|
|
Ada source code file which contains a library unit declaration (a
|
|
declaration of a package, subprogram, or generic, or a generic
|
|
instantiation), or a library unit renaming declaration (a package,
|
|
generic, or subprogram renaming declaration). Such files are also
|
|
called @dfn{specs}.
|
|
|
|
@itemx @var{file}.adb
|
|
Ada source code file containing a library unit body (a subprogram or
|
|
package body). Such files are also called @dfn{bodies}.
|
|
|
|
@c GCC also knows about some suffixes for languages not yet included:
|
|
@c Pascal:
|
|
@c @var{file}.p
|
|
@c @var{file}.pas
|
|
@c Ratfor:
|
|
@c @var{file}.r
|
|
|
|
@item @var{file}.s
|
|
Assembler code.
|
|
|
|
@item @var{file}.S
|
|
Assembler code which must be preprocessed.
|
|
|
|
@item @var{other}
|
|
An object file to be fed straight into linking.
|
|
Any file name with no recognized suffix is treated this way.
|
|
@end table
|
|
|
|
@opindex x
|
|
You can specify the input language explicitly with the @option{-x} option:
|
|
|
|
@table @gcctabopt
|
|
@item -x @var{language}
|
|
Specify explicitly the @var{language} for the following input files
|
|
(rather than letting the compiler choose a default based on the file
|
|
name suffix). This option applies to all following input files until
|
|
the next @option{-x} option. Possible values for @var{language} are:
|
|
@smallexample
|
|
c c-header c-cpp-output
|
|
c++ c++-header c++-cpp-output
|
|
objective-c objective-c-header objective-c-cpp-output
|
|
objective-c++ objective-c++-header objective-c++-cpp-output
|
|
assembler assembler-with-cpp
|
|
ada
|
|
f95 f95-cpp-input
|
|
java
|
|
treelang
|
|
@end smallexample
|
|
|
|
@item -x none
|
|
Turn off any specification of a language, so that subsequent files are
|
|
handled according to their file name suffixes (as they are if @option{-x}
|
|
has not been used at all).
|
|
|
|
@item -pass-exit-codes
|
|
@opindex pass-exit-codes
|
|
Normally the @command{gcc} program will exit with the code of 1 if any
|
|
phase of the compiler returns a non-success return code. If you specify
|
|
@option{-pass-exit-codes}, the @command{gcc} program will instead return with
|
|
numerically highest error produced by any phase that returned an error
|
|
indication. The C, C++, and Fortran frontends return 4, if an internal
|
|
compiler error is encountered.
|
|
@end table
|
|
|
|
If you only want some of the stages of compilation, you can use
|
|
@option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
|
|
one of the options @option{-c}, @option{-S}, or @option{-E} to say where
|
|
@command{gcc} is to stop. Note that some combinations (for example,
|
|
@samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
|
|
|
|
@table @gcctabopt
|
|
@item -c
|
|
@opindex c
|
|
Compile or assemble the source files, but do not link. The linking
|
|
stage simply is not done. The ultimate output is in the form of an
|
|
object file for each source file.
|
|
|
|
By default, the object file name for a source file is made by replacing
|
|
the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
|
|
|
|
Unrecognized input files, not requiring compilation or assembly, are
|
|
ignored.
|
|
|
|
@item -S
|
|
@opindex S
|
|
Stop after the stage of compilation proper; do not assemble. The output
|
|
is in the form of an assembler code file for each non-assembler input
|
|
file specified.
|
|
|
|
By default, the assembler file name for a source file is made by
|
|
replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
|
|
|
|
Input files that don't require compilation are ignored.
|
|
|
|
@item -E
|
|
@opindex E
|
|
Stop after the preprocessing stage; do not run the compiler proper. The
|
|
output is in the form of preprocessed source code, which is sent to the
|
|
standard output.
|
|
|
|
Input files which don't require preprocessing are ignored.
|
|
|
|
@cindex output file option
|
|
@item -o @var{file}
|
|
@opindex o
|
|
Place output in file @var{file}. This applies regardless to whatever
|
|
sort of output is being produced, whether it be an executable file,
|
|
an object file, an assembler file or preprocessed C code.
|
|
|
|
If @option{-o} is not specified, the default is to put an executable
|
|
file in @file{a.out}, the object file for
|
|
@file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
|
|
assembler file in @file{@var{source}.s}, a precompiled header file in
|
|
@file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
|
|
standard output.
|
|
|
|
@item -v
|
|
@opindex v
|
|
Print (on standard error output) the commands executed to run the stages
|
|
of compilation. Also print the version number of the compiler driver
|
|
program and of the preprocessor and the compiler proper.
|
|
|
|
@item -###
|
|
@opindex ###
|
|
Like @option{-v} except the commands are not executed and all command
|
|
arguments are quoted. This is useful for shell scripts to capture the
|
|
driver-generated command lines.
|
|
|
|
@item -pipe
|
|
@opindex pipe
|
|
Use pipes rather than temporary files for communication between the
|
|
various stages of compilation. This fails to work on some systems where
|
|
the assembler is unable to read from a pipe; but the GNU assembler has
|
|
no trouble.
|
|
|
|
@item -combine
|
|
@opindex combine
|
|
If you are compiling multiple source files, this option tells the driver
|
|
to pass all the source files to the compiler at once (for those
|
|
languages for which the compiler can handle this). This will allow
|
|
intermodule analysis (IMA) to be performed by the compiler. Currently the only
|
|
language for which this is supported is C@. If you pass source files for
|
|
multiple languages to the driver, using this option, the driver will invoke
|
|
the compiler(s) that support IMA once each, passing each compiler all the
|
|
source files appropriate for it. For those languages that do not support
|
|
IMA this option will be ignored, and the compiler will be invoked once for
|
|
each source file in that language. If you use this option in conjunction
|
|
with @option{-save-temps}, the compiler will generate multiple
|
|
pre-processed files
|
|
(one for each source file), but only one (combined) @file{.o} or
|
|
@file{.s} file.
|
|
|
|
@item --help
|
|
@opindex help
|
|
Print (on the standard output) a description of the command line options
|
|
understood by @command{gcc}. If the @option{-v} option is also specified
|
|
then @option{--help} will also be passed on to the various processes
|
|
invoked by @command{gcc}, so that they can display the command line options
|
|
they accept. If the @option{-Wextra} option is also specified then command
|
|
line options which have no documentation associated with them will also
|
|
be displayed.
|
|
|
|
@item --target-help
|
|
@opindex target-help
|
|
Print (on the standard output) a description of target specific command
|
|
line options for each tool.
|
|
|
|
@item --version
|
|
@opindex version
|
|
Display the version number and copyrights of the invoked GCC@.
|
|
|
|
@include @value{srcdir}/../libiberty/at-file.texi
|
|
@end table
|
|
|
|
@node Invoking G++
|
|
@section Compiling C++ Programs
|
|
|
|
@cindex suffixes for C++ source
|
|
@cindex C++ source file suffixes
|
|
C++ source files conventionally use one of the suffixes @samp{.C},
|
|
@samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
|
|
@samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
|
|
preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
|
|
files with these names and compiles them as C++ programs even if you
|
|
call the compiler the same way as for compiling C programs (usually
|
|
with the name @command{gcc}).
|
|
|
|
@findex g++
|
|
@findex c++
|
|
However, the use of @command{gcc} does not add the C++ library.
|
|
@command{g++} is a program that calls GCC and treats @samp{.c},
|
|
@samp{.h} and @samp{.i} files as C++ source files instead of C source
|
|
files unless @option{-x} is used, and automatically specifies linking
|
|
against the C++ library. This program is also useful when
|
|
precompiling a C header file with a @samp{.h} extension for use in C++
|
|
compilations. On many systems, @command{g++} is also installed with
|
|
the name @command{c++}.
|
|
|
|
@cindex invoking @command{g++}
|
|
When you compile C++ programs, you may specify many of the same
|
|
command-line options that you use for compiling programs in any
|
|
language; or command-line options meaningful for C and related
|
|
languages; or options that are meaningful only for C++ programs.
|
|
@xref{C Dialect Options,,Options Controlling C Dialect}, for
|
|
explanations of options for languages related to C@.
|
|
@xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
|
|
explanations of options that are meaningful only for C++ programs.
|
|
|
|
@node C Dialect Options
|
|
@section Options Controlling C Dialect
|
|
@cindex dialect options
|
|
@cindex language dialect options
|
|
@cindex options, dialect
|
|
|
|
The following options control the dialect of C (or languages derived
|
|
from C, such as C++, Objective-C and Objective-C++) that the compiler
|
|
accepts:
|
|
|
|
@table @gcctabopt
|
|
@cindex ANSI support
|
|
@cindex ISO support
|
|
@item -ansi
|
|
@opindex ansi
|
|
In C mode, support all ISO C90 programs. In C++ mode,
|
|
remove GNU extensions that conflict with ISO C++.
|
|
|
|
This turns off certain features of GCC that are incompatible with ISO
|
|
C90 (when compiling C code), or of standard C++ (when compiling C++ code),
|
|
such as the @code{asm} and @code{typeof} keywords, and
|
|
predefined macros such as @code{unix} and @code{vax} that identify the
|
|
type of system you are using. It also enables the undesirable and
|
|
rarely used ISO trigraph feature. For the C compiler,
|
|
it disables recognition of C++ style @samp{//} comments as well as
|
|
the @code{inline} keyword.
|
|
|
|
The alternate keywords @code{__asm__}, @code{__extension__},
|
|
@code{__inline__} and @code{__typeof__} continue to work despite
|
|
@option{-ansi}. You would not want to use them in an ISO C program, of
|
|
course, but it is useful to put them in header files that might be included
|
|
in compilations done with @option{-ansi}. Alternate predefined macros
|
|
such as @code{__unix__} and @code{__vax__} are also available, with or
|
|
without @option{-ansi}.
|
|
|
|
The @option{-ansi} option does not cause non-ISO programs to be
|
|
rejected gratuitously. For that, @option{-pedantic} is required in
|
|
addition to @option{-ansi}. @xref{Warning Options}.
|
|
|
|
The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
|
|
option is used. Some header files may notice this macro and refrain
|
|
from declaring certain functions or defining certain macros that the
|
|
ISO standard doesn't call for; this is to avoid interfering with any
|
|
programs that might use these names for other things.
|
|
|
|
Functions which would normally be built in but do not have semantics
|
|
defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
|
|
functions with @option{-ansi} is used. @xref{Other Builtins,,Other
|
|
built-in functions provided by GCC}, for details of the functions
|
|
affected.
|
|
|
|
@item -std=
|
|
@opindex std
|
|
Determine the language standard. This option is currently only
|
|
supported when compiling C or C++. A value for this option must be
|
|
provided; possible values are
|
|
|
|
@table @samp
|
|
@item c89
|
|
@itemx iso9899:1990
|
|
ISO C90 (same as @option{-ansi}).
|
|
|
|
@item iso9899:199409
|
|
ISO C90 as modified in amendment 1.
|
|
|
|
@item c99
|
|
@itemx c9x
|
|
@itemx iso9899:1999
|
|
@itemx iso9899:199x
|
|
ISO C99. Note that this standard is not yet fully supported; see
|
|
@w{@uref{http://gcc.gnu.org/gcc-4.2/c99status.html}} for more information. The
|
|
names @samp{c9x} and @samp{iso9899:199x} are deprecated.
|
|
|
|
@item gnu89
|
|
Default, ISO C90 plus GNU extensions (including some C99 features).
|
|
|
|
@item gnu99
|
|
@itemx gnu9x
|
|
ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
|
|
this will become the default. The name @samp{gnu9x} is deprecated.
|
|
|
|
@item c++98
|
|
The 1998 ISO C++ standard plus amendments.
|
|
|
|
@item gnu++98
|
|
The same as @option{-std=c++98} plus GNU extensions. This is the
|
|
default for C++ code.
|
|
@end table
|
|
|
|
Even when this option is not specified, you can still use some of the
|
|
features of newer standards in so far as they do not conflict with
|
|
previous C standards. For example, you may use @code{__restrict__} even
|
|
when @option{-std=c99} is not specified.
|
|
|
|
The @option{-std} options specifying some version of ISO C have the same
|
|
effects as @option{-ansi}, except that features that were not in ISO C90
|
|
but are in the specified version (for example, @samp{//} comments and
|
|
the @code{inline} keyword in ISO C99) are not disabled.
|
|
|
|
@xref{Standards,,Language Standards Supported by GCC}, for details of
|
|
these standard versions.
|
|
|
|
@item -fgnu89-inline
|
|
@opindex fgnu89-inline
|
|
The option @option{-fgnu89-inline} tells GCC to use the traditional
|
|
GNU semantics for @code{inline} functions when in C99 mode.
|
|
@xref{Inline,,An Inline Function is As Fast As a Macro}. Using this
|
|
option is roughly equivalent to adding the @code{gnu_inline} function
|
|
attribute to all inline functions (@pxref{Function Attributes}).
|
|
|
|
This option is accepted by GCC versions 4.1.3 and up. In GCC versions
|
|
prior to 4.3, C99 inline semantics are not supported, and thus this
|
|
option is effectively assumed to be present regardless of whether or not
|
|
it is specified; the only effect of specifying it explicitly is to
|
|
disable warnings about using inline functions in C99 mode. Likewise,
|
|
the option @option{-fno-gnu89-inline} is not supported in versions of
|
|
GCC before 4.3. It will be supported only in C99 or gnu99 mode, not in
|
|
C89 or gnu89 mode.
|
|
|
|
The preprocesor macros @code{__GNUC_GNU_INLINE__} and
|
|
@code{__GNUC_STDC_INLINE__} may be used to check which semantics are
|
|
in effect for @code{inline} functions. @xref{Common Predefined
|
|
Macros,,,cpp,The C Preprocessor}.
|
|
|
|
@item -aux-info @var{filename}
|
|
@opindex aux-info
|
|
Output to the given filename prototyped declarations for all functions
|
|
declared and/or defined in a translation unit, including those in header
|
|
files. This option is silently ignored in any language other than C@.
|
|
|
|
Besides declarations, the file indicates, in comments, the origin of
|
|
each declaration (source file and line), whether the declaration was
|
|
implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
|
|
@samp{O} for old, respectively, in the first character after the line
|
|
number and the colon), and whether it came from a declaration or a
|
|
definition (@samp{C} or @samp{F}, respectively, in the following
|
|
character). In the case of function definitions, a K&R-style list of
|
|
arguments followed by their declarations is also provided, inside
|
|
comments, after the declaration.
|
|
|
|
@item -fno-asm
|
|
@opindex fno-asm
|
|
Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
|
|
keyword, so that code can use these words as identifiers. You can use
|
|
the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
|
|
instead. @option{-ansi} implies @option{-fno-asm}.
|
|
|
|
In C++, this switch only affects the @code{typeof} keyword, since
|
|
@code{asm} and @code{inline} are standard keywords. You may want to
|
|
use the @option{-fno-gnu-keywords} flag instead, which has the same
|
|
effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
|
|
switch only affects the @code{asm} and @code{typeof} keywords, since
|
|
@code{inline} is a standard keyword in ISO C99.
|
|
|
|
@item -fno-builtin
|
|
@itemx -fno-builtin-@var{function}
|
|
@opindex fno-builtin
|
|
@cindex built-in functions
|
|
Don't recognize built-in functions that do not begin with
|
|
@samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
|
|
functions provided by GCC}, for details of the functions affected,
|
|
including those which are not built-in functions when @option{-ansi} or
|
|
@option{-std} options for strict ISO C conformance are used because they
|
|
do not have an ISO standard meaning.
|
|
|
|
GCC normally generates special code to handle certain built-in functions
|
|
more efficiently; for instance, calls to @code{alloca} may become single
|
|
instructions that adjust the stack directly, and calls to @code{memcpy}
|
|
may become inline copy loops. The resulting code is often both smaller
|
|
and faster, but since the function calls no longer appear as such, you
|
|
cannot set a breakpoint on those calls, nor can you change the behavior
|
|
of the functions by linking with a different library. In addition,
|
|
when a function is recognized as a built-in function, GCC may use
|
|
information about that function to warn about problems with calls to
|
|
that function, or to generate more efficient code, even if the
|
|
resulting code still contains calls to that function. For example,
|
|
warnings are given with @option{-Wformat} for bad calls to
|
|
@code{printf}, when @code{printf} is built in, and @code{strlen} is
|
|
known not to modify global memory.
|
|
|
|
With the @option{-fno-builtin-@var{function}} option
|
|
only the built-in function @var{function} is
|
|
disabled. @var{function} must not begin with @samp{__builtin_}. If a
|
|
function is named this is not built-in in this version of GCC, this
|
|
option is ignored. There is no corresponding
|
|
@option{-fbuiltin-@var{function}} option; if you wish to enable
|
|
built-in functions selectively when using @option{-fno-builtin} or
|
|
@option{-ffreestanding}, you may define macros such as:
|
|
|
|
@smallexample
|
|
#define abs(n) __builtin_abs ((n))
|
|
#define strcpy(d, s) __builtin_strcpy ((d), (s))
|
|
@end smallexample
|
|
|
|
@item -fhosted
|
|
@opindex fhosted
|
|
@cindex hosted environment
|
|
|
|
Assert that compilation takes place in a hosted environment. This implies
|
|
@option{-fbuiltin}. A hosted environment is one in which the
|
|
entire standard library is available, and in which @code{main} has a return
|
|
type of @code{int}. Examples are nearly everything except a kernel.
|
|
This is equivalent to @option{-fno-freestanding}.
|
|
|
|
@item -ffreestanding
|
|
@opindex ffreestanding
|
|
@cindex hosted environment
|
|
|
|
Assert that compilation takes place in a freestanding environment. This
|
|
implies @option{-fno-builtin}. A freestanding environment
|
|
is one in which the standard library may not exist, and program startup may
|
|
not necessarily be at @code{main}. The most obvious example is an OS kernel.
|
|
This is equivalent to @option{-fno-hosted}.
|
|
|
|
@xref{Standards,,Language Standards Supported by GCC}, for details of
|
|
freestanding and hosted environments.
|
|
|
|
@item -fopenmp
|
|
@opindex fopenmp
|
|
@cindex openmp parallel
|
|
Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
|
|
@code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
|
|
compiler generates parallel code according to the OpenMP Application
|
|
Program Interface v2.5 @w{@uref{http://www.openmp.org/}}.
|
|
|
|
@item -fms-extensions
|
|
@opindex fms-extensions
|
|
Accept some non-standard constructs used in Microsoft header files.
|
|
|
|
Some cases of unnamed fields in structures and unions are only
|
|
accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
|
|
fields within structs/unions}, for details.
|
|
|
|
@item -trigraphs
|
|
@opindex trigraphs
|
|
Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
|
|
options for strict ISO C conformance) implies @option{-trigraphs}.
|
|
|
|
@item -no-integrated-cpp
|
|
@opindex no-integrated-cpp
|
|
Performs a compilation in two passes: preprocessing and compiling. This
|
|
option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
|
|
@option{-B} option. The user supplied compilation step can then add in
|
|
an additional preprocessing step after normal preprocessing but before
|
|
compiling. The default is to use the integrated cpp (internal cpp)
|
|
|
|
The semantics of this option will change if "cc1", "cc1plus", and
|
|
"cc1obj" are merged.
|
|
|
|
@cindex traditional C language
|
|
@cindex C language, traditional
|
|
@item -traditional
|
|
@itemx -traditional-cpp
|
|
@opindex traditional-cpp
|
|
@opindex traditional
|
|
Formerly, these options caused GCC to attempt to emulate a pre-standard
|
|
C compiler. They are now only supported with the @option{-E} switch.
|
|
The preprocessor continues to support a pre-standard mode. See the GNU
|
|
CPP manual for details.
|
|
|
|
@item -fcond-mismatch
|
|
@opindex fcond-mismatch
|
|
Allow conditional expressions with mismatched types in the second and
|
|
third arguments. The value of such an expression is void. This option
|
|
is not supported for C++.
|
|
|
|
@item -funsigned-char
|
|
@opindex funsigned-char
|
|
Let the type @code{char} be unsigned, like @code{unsigned char}.
|
|
|
|
Each kind of machine has a default for what @code{char} should
|
|
be. It is either like @code{unsigned char} by default or like
|
|
@code{signed char} by default.
|
|
|
|
Ideally, a portable program should always use @code{signed char} or
|
|
@code{unsigned char} when it depends on the signedness of an object.
|
|
But many programs have been written to use plain @code{char} and
|
|
expect it to be signed, or expect it to be unsigned, depending on the
|
|
machines they were written for. This option, and its inverse, let you
|
|
make such a program work with the opposite default.
|
|
|
|
The type @code{char} is always a distinct type from each of
|
|
@code{signed char} or @code{unsigned char}, even though its behavior
|
|
is always just like one of those two.
|
|
|
|
@item -fsigned-char
|
|
@opindex fsigned-char
|
|
Let the type @code{char} be signed, like @code{signed char}.
|
|
|
|
Note that this is equivalent to @option{-fno-unsigned-char}, which is
|
|
the negative form of @option{-funsigned-char}. Likewise, the option
|
|
@option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
|
|
|
|
@item -fsigned-bitfields
|
|
@itemx -funsigned-bitfields
|
|
@itemx -fno-signed-bitfields
|
|
@itemx -fno-unsigned-bitfields
|
|
@opindex fsigned-bitfields
|
|
@opindex funsigned-bitfields
|
|
@opindex fno-signed-bitfields
|
|
@opindex fno-unsigned-bitfields
|
|
These options control whether a bit-field is signed or unsigned, when the
|
|
declaration does not use either @code{signed} or @code{unsigned}. By
|
|
default, such a bit-field is signed, because this is consistent: the
|
|
basic integer types such as @code{int} are signed types.
|
|
@end table
|
|
|
|
@node C++ Dialect Options
|
|
@section Options Controlling C++ Dialect
|
|
|
|
@cindex compiler options, C++
|
|
@cindex C++ options, command line
|
|
@cindex options, C++
|
|
This section describes the command-line options that are only meaningful
|
|
for C++ programs; but you can also use most of the GNU compiler options
|
|
regardless of what language your program is in. For example, you
|
|
might compile a file @code{firstClass.C} like this:
|
|
|
|
@smallexample
|
|
g++ -g -frepo -O -c firstClass.C
|
|
@end smallexample
|
|
|
|
@noindent
|
|
In this example, only @option{-frepo} is an option meant
|
|
only for C++ programs; you can use the other options with any
|
|
language supported by GCC@.
|
|
|
|
Here is a list of options that are @emph{only} for compiling C++ programs:
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -fabi-version=@var{n}
|
|
@opindex fabi-version
|
|
Use version @var{n} of the C++ ABI@. Version 2 is the version of the
|
|
C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
|
|
the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
|
|
the version that conforms most closely to the C++ ABI specification.
|
|
Therefore, the ABI obtained using version 0 will change as ABI bugs
|
|
are fixed.
|
|
|
|
The default is version 2.
|
|
|
|
@item -fno-access-control
|
|
@opindex fno-access-control
|
|
Turn off all access checking. This switch is mainly useful for working
|
|
around bugs in the access control code.
|
|
|
|
@item -fcheck-new
|
|
@opindex fcheck-new
|
|
Check that the pointer returned by @code{operator new} is non-null
|
|
before attempting to modify the storage allocated. This check is
|
|
normally unnecessary because the C++ standard specifies that
|
|
@code{operator new} will only return @code{0} if it is declared
|
|
@samp{throw()}, in which case the compiler will always check the
|
|
return value even without this option. In all other cases, when
|
|
@code{operator new} has a non-empty exception specification, memory
|
|
exhaustion is signalled by throwing @code{std::bad_alloc}. See also
|
|
@samp{new (nothrow)}.
|
|
|
|
@item -fconserve-space
|
|
@opindex fconserve-space
|
|
Put uninitialized or runtime-initialized global variables into the
|
|
common segment, as C does. This saves space in the executable at the
|
|
cost of not diagnosing duplicate definitions. If you compile with this
|
|
flag and your program mysteriously crashes after @code{main()} has
|
|
completed, you may have an object that is being destroyed twice because
|
|
two definitions were merged.
|
|
|
|
This option is no longer useful on most targets, now that support has
|
|
been added for putting variables into BSS without making them common.
|
|
|
|
@item -ffriend-injection
|
|
@opindex ffriend-injection
|
|
Inject friend functions into the enclosing namespace, so that they are
|
|
visible outside the scope of the class in which they are declared.
|
|
Friend functions were documented to work this way in the old Annotated
|
|
C++ Reference Manual, and versions of G++ before 4.1 always worked
|
|
that way. However, in ISO C++ a friend function which is not declared
|
|
in an enclosing scope can only be found using argument dependent
|
|
lookup. This option causes friends to be injected as they were in
|
|
earlier releases.
|
|
|
|
This option is for compatibility, and may be removed in a future
|
|
release of G++.
|
|
|
|
@item -fno-elide-constructors
|
|
@opindex fno-elide-constructors
|
|
The C++ standard allows an implementation to omit creating a temporary
|
|
which is only used to initialize another object of the same type.
|
|
Specifying this option disables that optimization, and forces G++ to
|
|
call the copy constructor in all cases.
|
|
|
|
@item -fno-enforce-eh-specs
|
|
@opindex fno-enforce-eh-specs
|
|
Don't generate code to check for violation of exception specifications
|
|
at runtime. This option violates the C++ standard, but may be useful
|
|
for reducing code size in production builds, much like defining
|
|
@samp{NDEBUG}. This does not give user code permission to throw
|
|
exceptions in violation of the exception specifications; the compiler
|
|
will still optimize based on the specifications, so throwing an
|
|
unexpected exception will result in undefined behavior.
|
|
|
|
@item -ffor-scope
|
|
@itemx -fno-for-scope
|
|
@opindex ffor-scope
|
|
@opindex fno-for-scope
|
|
If @option{-ffor-scope} is specified, the scope of variables declared in
|
|
a @i{for-init-statement} is limited to the @samp{for} loop itself,
|
|
as specified by the C++ standard.
|
|
If @option{-fno-for-scope} is specified, the scope of variables declared in
|
|
a @i{for-init-statement} extends to the end of the enclosing scope,
|
|
as was the case in old versions of G++, and other (traditional)
|
|
implementations of C++.
|
|
|
|
The default if neither flag is given to follow the standard,
|
|
but to allow and give a warning for old-style code that would
|
|
otherwise be invalid, or have different behavior.
|
|
|
|
@item -fno-gnu-keywords
|
|
@opindex fno-gnu-keywords
|
|
Do not recognize @code{typeof} as a keyword, so that code can use this
|
|
word as an identifier. You can use the keyword @code{__typeof__} instead.
|
|
@option{-ansi} implies @option{-fno-gnu-keywords}.
|
|
|
|
@item -fno-implicit-templates
|
|
@opindex fno-implicit-templates
|
|
Never emit code for non-inline templates which are instantiated
|
|
implicitly (i.e.@: by use); only emit code for explicit instantiations.
|
|
@xref{Template Instantiation}, for more information.
|
|
|
|
@item -fno-implicit-inline-templates
|
|
@opindex fno-implicit-inline-templates
|
|
Don't emit code for implicit instantiations of inline templates, either.
|
|
The default is to handle inlines differently so that compiles with and
|
|
without optimization will need the same set of explicit instantiations.
|
|
|
|
@item -fno-implement-inlines
|
|
@opindex fno-implement-inlines
|
|
To save space, do not emit out-of-line copies of inline functions
|
|
controlled by @samp{#pragma implementation}. This will cause linker
|
|
errors if these functions are not inlined everywhere they are called.
|
|
|
|
@item -fms-extensions
|
|
@opindex fms-extensions
|
|
Disable pedantic warnings about constructs used in MFC, such as implicit
|
|
int and getting a pointer to member function via non-standard syntax.
|
|
|
|
@item -fno-nonansi-builtins
|
|
@opindex fno-nonansi-builtins
|
|
Disable built-in declarations of functions that are not mandated by
|
|
ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
|
|
@code{index}, @code{bzero}, @code{conjf}, and other related functions.
|
|
|
|
@item -fno-operator-names
|
|
@opindex fno-operator-names
|
|
Do not treat the operator name keywords @code{and}, @code{bitand},
|
|
@code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
|
|
synonyms as keywords.
|
|
|
|
@item -fno-optional-diags
|
|
@opindex fno-optional-diags
|
|
Disable diagnostics that the standard says a compiler does not need to
|
|
issue. Currently, the only such diagnostic issued by G++ is the one for
|
|
a name having multiple meanings within a class.
|
|
|
|
@item -fpermissive
|
|
@opindex fpermissive
|
|
Downgrade some diagnostics about nonconformant code from errors to
|
|
warnings. Thus, using @option{-fpermissive} will allow some
|
|
nonconforming code to compile.
|
|
|
|
@item -frepo
|
|
@opindex frepo
|
|
Enable automatic template instantiation at link time. This option also
|
|
implies @option{-fno-implicit-templates}. @xref{Template
|
|
Instantiation}, for more information.
|
|
|
|
@item -fno-rtti
|
|
@opindex fno-rtti
|
|
Disable generation of information about every class with virtual
|
|
functions for use by the C++ runtime type identification features
|
|
(@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
|
|
of the language, you can save some space by using this flag. Note that
|
|
exception handling uses the same information, but it will generate it as
|
|
needed. The @samp{dynamic_cast} operator can still be used for casts that
|
|
do not require runtime type information, i.e. casts to @code{void *} or to
|
|
unambiguous base classes.
|
|
|
|
@item -fstats
|
|
@opindex fstats
|
|
Emit statistics about front-end processing at the end of the compilation.
|
|
This information is generally only useful to the G++ development team.
|
|
|
|
@item -ftemplate-depth-@var{n}
|
|
@opindex ftemplate-depth
|
|
Set the maximum instantiation depth for template classes to @var{n}.
|
|
A limit on the template instantiation depth is needed to detect
|
|
endless recursions during template class instantiation. ANSI/ISO C++
|
|
conforming programs must not rely on a maximum depth greater than 17.
|
|
|
|
@item -fno-threadsafe-statics
|
|
@opindex fno-threadsafe-statics
|
|
Do not emit the extra code to use the routines specified in the C++
|
|
ABI for thread-safe initialization of local statics. You can use this
|
|
option to reduce code size slightly in code that doesn't need to be
|
|
thread-safe.
|
|
|
|
@item -fuse-cxa-atexit
|
|
@opindex fuse-cxa-atexit
|
|
Register destructors for objects with static storage duration with the
|
|
@code{__cxa_atexit} function rather than the @code{atexit} function.
|
|
This option is required for fully standards-compliant handling of static
|
|
destructors, but will only work if your C library supports
|
|
@code{__cxa_atexit}.
|
|
|
|
@item -fno-use-cxa-get-exception-ptr
|
|
@opindex fno-use-cxa-get-exception-ptr
|
|
Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
|
|
will cause @code{std::uncaught_exception} to be incorrect, but is necessary
|
|
if the runtime routine is not available.
|
|
|
|
@item -fvisibility-inlines-hidden
|
|
@opindex fvisibility-inlines-hidden
|
|
This switch declares that the user does not attempt to compare
|
|
pointers to inline methods where the addresses of the two functions
|
|
were taken in different shared objects.
|
|
|
|
The effect of this is that GCC may, effectively, mark inline methods with
|
|
@code{__attribute__ ((visibility ("hidden")))} so that they do not
|
|
appear in the export table of a DSO and do not require a PLT indirection
|
|
when used within the DSO@. Enabling this option can have a dramatic effect
|
|
on load and link times of a DSO as it massively reduces the size of the
|
|
dynamic export table when the library makes heavy use of templates.
|
|
|
|
The behaviour of this switch is not quite the same as marking the
|
|
methods as hidden directly, because it does not affect static variables
|
|
local to the function or cause the compiler to deduce that
|
|
the function is defined in only one shared object.
|
|
|
|
You may mark a method as having a visibility explicitly to negate the
|
|
effect of the switch for that method. For example, if you do want to
|
|
compare pointers to a particular inline method, you might mark it as
|
|
having default visibility. Marking the enclosing class with explicit
|
|
visibility will have no effect.
|
|
|
|
Explicitly instantiated inline methods are unaffected by this option
|
|
as their linkage might otherwise cross a shared library boundary.
|
|
@xref{Template Instantiation}.
|
|
|
|
@item -fno-weak
|
|
@opindex fno-weak
|
|
Do not use weak symbol support, even if it is provided by the linker.
|
|
By default, G++ will use weak symbols if they are available. This
|
|
option exists only for testing, and should not be used by end-users;
|
|
it will result in inferior code and has no benefits. This option may
|
|
be removed in a future release of G++.
|
|
|
|
@item -nostdinc++
|
|
@opindex nostdinc++
|
|
Do not search for header files in the standard directories specific to
|
|
C++, but do still search the other standard directories. (This option
|
|
is used when building the C++ library.)
|
|
@end table
|
|
|
|
In addition, these optimization, warning, and code generation options
|
|
have meanings only for C++ programs:
|
|
|
|
@table @gcctabopt
|
|
@item -fno-default-inline
|
|
@opindex fno-default-inline
|
|
Do not assume @samp{inline} for functions defined inside a class scope.
|
|
@xref{Optimize Options,,Options That Control Optimization}. Note that these
|
|
functions will have linkage like inline functions; they just won't be
|
|
inlined by default.
|
|
|
|
@item -Wabi @r{(C++ only)}
|
|
@opindex Wabi
|
|
Warn when G++ generates code that is probably not compatible with the
|
|
vendor-neutral C++ ABI@. Although an effort has been made to warn about
|
|
all such cases, there are probably some cases that are not warned about,
|
|
even though G++ is generating incompatible code. There may also be
|
|
cases where warnings are emitted even though the code that is generated
|
|
will be compatible.
|
|
|
|
You should rewrite your code to avoid these warnings if you are
|
|
concerned about the fact that code generated by G++ may not be binary
|
|
compatible with code generated by other compilers.
|
|
|
|
The known incompatibilities at this point include:
|
|
|
|
@itemize @bullet
|
|
|
|
@item
|
|
Incorrect handling of tail-padding for bit-fields. G++ may attempt to
|
|
pack data into the same byte as a base class. For example:
|
|
|
|
@smallexample
|
|
struct A @{ virtual void f(); int f1 : 1; @};
|
|
struct B : public A @{ int f2 : 1; @};
|
|
@end smallexample
|
|
|
|
@noindent
|
|
In this case, G++ will place @code{B::f2} into the same byte
|
|
as@code{A::f1}; other compilers will not. You can avoid this problem
|
|
by explicitly padding @code{A} so that its size is a multiple of the
|
|
byte size on your platform; that will cause G++ and other compilers to
|
|
layout @code{B} identically.
|
|
|
|
@item
|
|
Incorrect handling of tail-padding for virtual bases. G++ does not use
|
|
tail padding when laying out virtual bases. For example:
|
|
|
|
@smallexample
|
|
struct A @{ virtual void f(); char c1; @};
|
|
struct B @{ B(); char c2; @};
|
|
struct C : public A, public virtual B @{@};
|
|
@end smallexample
|
|
|
|
@noindent
|
|
In this case, G++ will not place @code{B} into the tail-padding for
|
|
@code{A}; other compilers will. You can avoid this problem by
|
|
explicitly padding @code{A} so that its size is a multiple of its
|
|
alignment (ignoring virtual base classes); that will cause G++ and other
|
|
compilers to layout @code{C} identically.
|
|
|
|
@item
|
|
Incorrect handling of bit-fields with declared widths greater than that
|
|
of their underlying types, when the bit-fields appear in a union. For
|
|
example:
|
|
|
|
@smallexample
|
|
union U @{ int i : 4096; @};
|
|
@end smallexample
|
|
|
|
@noindent
|
|
Assuming that an @code{int} does not have 4096 bits, G++ will make the
|
|
union too small by the number of bits in an @code{int}.
|
|
|
|
@item
|
|
Empty classes can be placed at incorrect offsets. For example:
|
|
|
|
@smallexample
|
|
struct A @{@};
|
|
|
|
struct B @{
|
|
A a;
|
|
virtual void f ();
|
|
@};
|
|
|
|
struct C : public B, public A @{@};
|
|
@end smallexample
|
|
|
|
@noindent
|
|
G++ will place the @code{A} base class of @code{C} at a nonzero offset;
|
|
it should be placed at offset zero. G++ mistakenly believes that the
|
|
@code{A} data member of @code{B} is already at offset zero.
|
|
|
|
@item
|
|
Names of template functions whose types involve @code{typename} or
|
|
template template parameters can be mangled incorrectly.
|
|
|
|
@smallexample
|
|
template <typename Q>
|
|
void f(typename Q::X) @{@}
|
|
|
|
template <template <typename> class Q>
|
|
void f(typename Q<int>::X) @{@}
|
|
@end smallexample
|
|
|
|
@noindent
|
|
Instantiations of these templates may be mangled incorrectly.
|
|
|
|
@end itemize
|
|
|
|
@item -Wctor-dtor-privacy @r{(C++ only)}
|
|
@opindex Wctor-dtor-privacy
|
|
Warn when a class seems unusable because all the constructors or
|
|
destructors in that class are private, and it has neither friends nor
|
|
public static member functions.
|
|
|
|
@item -Wnon-virtual-dtor @r{(C++ only)}
|
|
@opindex Wnon-virtual-dtor
|
|
Warn when a class appears to be polymorphic, thereby requiring a virtual
|
|
destructor, yet it declares a non-virtual one. This warning is also
|
|
enabled if -Weffc++ is specified.
|
|
|
|
@item -Wreorder @r{(C++ only)}
|
|
@opindex Wreorder
|
|
@cindex reordering, warning
|
|
@cindex warning for reordering of member initializers
|
|
Warn when the order of member initializers given in the code does not
|
|
match the order in which they must be executed. For instance:
|
|
|
|
@smallexample
|
|
struct A @{
|
|
int i;
|
|
int j;
|
|
A(): j (0), i (1) @{ @}
|
|
@};
|
|
@end smallexample
|
|
|
|
The compiler will rearrange the member initializers for @samp{i}
|
|
and @samp{j} to match the declaration order of the members, emitting
|
|
a warning to that effect. This warning is enabled by @option{-Wall}.
|
|
@end table
|
|
|
|
The following @option{-W@dots{}} options are not affected by @option{-Wall}.
|
|
|
|
@table @gcctabopt
|
|
@item -Weffc++ @r{(C++ only)}
|
|
@opindex Weffc++
|
|
Warn about violations of the following style guidelines from Scott Meyers'
|
|
@cite{Effective C++} book:
|
|
|
|
@itemize @bullet
|
|
@item
|
|
Item 11: Define a copy constructor and an assignment operator for classes
|
|
with dynamically allocated memory.
|
|
|
|
@item
|
|
Item 12: Prefer initialization to assignment in constructors.
|
|
|
|
@item
|
|
Item 14: Make destructors virtual in base classes.
|
|
|
|
@item
|
|
Item 15: Have @code{operator=} return a reference to @code{*this}.
|
|
|
|
@item
|
|
Item 23: Don't try to return a reference when you must return an object.
|
|
|
|
@end itemize
|
|
|
|
Also warn about violations of the following style guidelines from
|
|
Scott Meyers' @cite{More Effective C++} book:
|
|
|
|
@itemize @bullet
|
|
@item
|
|
Item 6: Distinguish between prefix and postfix forms of increment and
|
|
decrement operators.
|
|
|
|
@item
|
|
Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
|
|
|
|
@end itemize
|
|
|
|
When selecting this option, be aware that the standard library
|
|
headers do not obey all of these guidelines; use @samp{grep -v}
|
|
to filter out those warnings.
|
|
|
|
@item -Wno-deprecated @r{(C++ only)}
|
|
@opindex Wno-deprecated
|
|
Do not warn about usage of deprecated features. @xref{Deprecated Features}.
|
|
|
|
@item -Wstrict-null-sentinel @r{(C++ only)}
|
|
@opindex Wstrict-null-sentinel
|
|
Warn also about the use of an uncasted @code{NULL} as sentinel. When
|
|
compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
|
|
to @code{__null}. Although it is a null pointer constant not a null pointer,
|
|
it is guaranteed to of the same size as a pointer. But this use is
|
|
not portable across different compilers.
|
|
|
|
@item -Wno-non-template-friend @r{(C++ only)}
|
|
@opindex Wno-non-template-friend
|
|
Disable warnings when non-templatized friend functions are declared
|
|
within a template. Since the advent of explicit template specification
|
|
support in G++, if the name of the friend is an unqualified-id (i.e.,
|
|
@samp{friend foo(int)}), the C++ language specification demands that the
|
|
friend declare or define an ordinary, nontemplate function. (Section
|
|
14.5.3). Before G++ implemented explicit specification, unqualified-ids
|
|
could be interpreted as a particular specialization of a templatized
|
|
function. Because this non-conforming behavior is no longer the default
|
|
behavior for G++, @option{-Wnon-template-friend} allows the compiler to
|
|
check existing code for potential trouble spots and is on by default.
|
|
This new compiler behavior can be turned off with
|
|
@option{-Wno-non-template-friend} which keeps the conformant compiler code
|
|
but disables the helpful warning.
|
|
|
|
@item -Wold-style-cast @r{(C++ only)}
|
|
@opindex Wold-style-cast
|
|
Warn if an old-style (C-style) cast to a non-void type is used within
|
|
a C++ program. The new-style casts (@samp{dynamic_cast},
|
|
@samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
|
|
less vulnerable to unintended effects and much easier to search for.
|
|
|
|
@item -Woverloaded-virtual @r{(C++ only)}
|
|
@opindex Woverloaded-virtual
|
|
@cindex overloaded virtual fn, warning
|
|
@cindex warning for overloaded virtual fn
|
|
Warn when a function declaration hides virtual functions from a
|
|
base class. For example, in:
|
|
|
|
@smallexample
|
|
struct A @{
|
|
virtual void f();
|
|
@};
|
|
|
|
struct B: public A @{
|
|
void f(int);
|
|
@};
|
|
@end smallexample
|
|
|
|
the @code{A} class version of @code{f} is hidden in @code{B}, and code
|
|
like:
|
|
|
|
@smallexample
|
|
B* b;
|
|
b->f();
|
|
@end smallexample
|
|
|
|
will fail to compile.
|
|
|
|
@item -Wno-pmf-conversions @r{(C++ only)}
|
|
@opindex Wno-pmf-conversions
|
|
Disable the diagnostic for converting a bound pointer to member function
|
|
to a plain pointer.
|
|
|
|
@item -Wsign-promo @r{(C++ only)}
|
|
@opindex Wsign-promo
|
|
Warn when overload resolution chooses a promotion from unsigned or
|
|
enumerated type to a signed type, over a conversion to an unsigned type of
|
|
the same size. Previous versions of G++ would try to preserve
|
|
unsignedness, but the standard mandates the current behavior.
|
|
|
|
@smallexample
|
|
struct A @{
|
|
operator int ();
|
|
A& operator = (int);
|
|
@};
|
|
|
|
main ()
|
|
@{
|
|
A a,b;
|
|
a = b;
|
|
@}
|
|
@end smallexample
|
|
|
|
In this example, G++ will synthesize a default @samp{A& operator =
|
|
(const A&);}, while cfront will use the user-defined @samp{operator =}.
|
|
@end table
|
|
|
|
@node Objective-C and Objective-C++ Dialect Options
|
|
@section Options Controlling Objective-C and Objective-C++ Dialects
|
|
|
|
@cindex compiler options, Objective-C and Objective-C++
|
|
@cindex Objective-C and Objective-C++ options, command line
|
|
@cindex options, Objective-C and Objective-C++
|
|
(NOTE: This manual does not describe the Objective-C and Objective-C++
|
|
languages themselves. See @xref{Standards,,Language Standards
|
|
Supported by GCC}, for references.)
|
|
|
|
This section describes the command-line options that are only meaningful
|
|
for Objective-C and Objective-C++ programs, but you can also use most of
|
|
the language-independent GNU compiler options.
|
|
For example, you might compile a file @code{some_class.m} like this:
|
|
|
|
@smallexample
|
|
gcc -g -fgnu-runtime -O -c some_class.m
|
|
@end smallexample
|
|
|
|
@noindent
|
|
In this example, @option{-fgnu-runtime} is an option meant only for
|
|
Objective-C and Objective-C++ programs; you can use the other options with
|
|
any language supported by GCC@.
|
|
|
|
Note that since Objective-C is an extension of the C language, Objective-C
|
|
compilations may also use options specific to the C front-end (e.g.,
|
|
@option{-Wtraditional}). Similarly, Objective-C++ compilations may use
|
|
C++-specific options (e.g., @option{-Wabi}).
|
|
|
|
Here is a list of options that are @emph{only} for compiling Objective-C
|
|
and Objective-C++ programs:
|
|
|
|
@table @gcctabopt
|
|
@item -fconstant-string-class=@var{class-name}
|
|
@opindex fconstant-string-class
|
|
Use @var{class-name} as the name of the class to instantiate for each
|
|
literal string specified with the syntax @code{@@"@dots{}"}. The default
|
|
class name is @code{NXConstantString} if the GNU runtime is being used, and
|
|
@code{NSConstantString} if the NeXT runtime is being used (see below). The
|
|
@option{-fconstant-cfstrings} option, if also present, will override the
|
|
@option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
|
|
to be laid out as constant CoreFoundation strings.
|
|
|
|
@item -fgnu-runtime
|
|
@opindex fgnu-runtime
|
|
Generate object code compatible with the standard GNU Objective-C
|
|
runtime. This is the default for most types of systems.
|
|
|
|
@item -fnext-runtime
|
|
@opindex fnext-runtime
|
|
Generate output compatible with the NeXT runtime. This is the default
|
|
for NeXT-based systems, including Darwin and Mac OS X@. The macro
|
|
@code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
|
|
used.
|
|
|
|
@item -fno-nil-receivers
|
|
@opindex fno-nil-receivers
|
|
Assume that all Objective-C message dispatches (e.g.,
|
|
@code{[receiver message:arg]}) in this translation unit ensure that the receiver
|
|
is not @code{nil}. This allows for more efficient entry points in the runtime
|
|
to be used. Currently, this option is only available in conjunction with
|
|
the NeXT runtime on Mac OS X 10.3 and later.
|
|
|
|
@item -fobjc-call-cxx-cdtors
|
|
@opindex fobjc-call-cxx-cdtors
|
|
For each Objective-C class, check if any of its instance variables is a
|
|
C++ object with a non-trivial default constructor. If so, synthesize a
|
|
special @code{- (id) .cxx_construct} instance method that will run
|
|
non-trivial default constructors on any such instance variables, in order,
|
|
and then return @code{self}. Similarly, check if any instance variable
|
|
is a C++ object with a non-trivial destructor, and if so, synthesize a
|
|
special @code{- (void) .cxx_destruct} method that will run
|
|
all such default destructors, in reverse order.
|
|
|
|
The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
|
|
thusly generated will only operate on instance variables declared in the
|
|
current Objective-C class, and not those inherited from superclasses. It
|
|
is the responsibility of the Objective-C runtime to invoke all such methods
|
|
in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
|
|
will be invoked by the runtime immediately after a new object
|
|
instance is allocated; the @code{- (void) .cxx_destruct} methods will
|
|
be invoked immediately before the runtime deallocates an object instance.
|
|
|
|
As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
|
|
support for invoking the @code{- (id) .cxx_construct} and
|
|
@code{- (void) .cxx_destruct} methods.
|
|
|
|
@item -fobjc-direct-dispatch
|
|
@opindex fobjc-direct-dispatch
|
|
Allow fast jumps to the message dispatcher. On Darwin this is
|
|
accomplished via the comm page.
|
|
|
|
@item -fobjc-exceptions
|
|
@opindex fobjc-exceptions
|
|
Enable syntactic support for structured exception handling in Objective-C,
|
|
similar to what is offered by C++ and Java. This option is
|
|
unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and
|
|
earlier.
|
|
|
|
@smallexample
|
|
@@try @{
|
|
@dots{}
|
|
@@throw expr;
|
|
@dots{}
|
|
@}
|
|
@@catch (AnObjCClass *exc) @{
|
|
@dots{}
|
|
@@throw expr;
|
|
@dots{}
|
|
@@throw;
|
|
@dots{}
|
|
@}
|
|
@@catch (AnotherClass *exc) @{
|
|
@dots{}
|
|
@}
|
|
@@catch (id allOthers) @{
|
|
@dots{}
|
|
@}
|
|
@@finally @{
|
|
@dots{}
|
|
@@throw expr;
|
|
@dots{}
|
|
@}
|
|
@end smallexample
|
|
|
|
The @code{@@throw} statement may appear anywhere in an Objective-C or
|
|
Objective-C++ program; when used inside of a @code{@@catch} block, the
|
|
@code{@@throw} may appear without an argument (as shown above), in which case
|
|
the object caught by the @code{@@catch} will be rethrown.
|
|
|
|
Note that only (pointers to) Objective-C objects may be thrown and
|
|
caught using this scheme. When an object is thrown, it will be caught
|
|
by the nearest @code{@@catch} clause capable of handling objects of that type,
|
|
analogously to how @code{catch} blocks work in C++ and Java. A
|
|
@code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
|
|
any and all Objective-C exceptions not caught by previous @code{@@catch}
|
|
clauses (if any).
|
|
|
|
The @code{@@finally} clause, if present, will be executed upon exit from the
|
|
immediately preceding @code{@@try @dots{} @@catch} section. This will happen
|
|
regardless of whether any exceptions are thrown, caught or rethrown
|
|
inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
|
|
of the @code{finally} clause in Java.
|
|
|
|
There are several caveats to using the new exception mechanism:
|
|
|
|
@itemize @bullet
|
|
@item
|
|
Although currently designed to be binary compatible with @code{NS_HANDLER}-style
|
|
idioms provided by the @code{NSException} class, the new
|
|
exceptions can only be used on Mac OS X 10.3 (Panther) and later
|
|
systems, due to additional functionality needed in the (NeXT) Objective-C
|
|
runtime.
|
|
|
|
@item
|
|
As mentioned above, the new exceptions do not support handling
|
|
types other than Objective-C objects. Furthermore, when used from
|
|
Objective-C++, the Objective-C exception model does not interoperate with C++
|
|
exceptions at this time. This means you cannot @code{@@throw} an exception
|
|
from Objective-C and @code{catch} it in C++, or vice versa
|
|
(i.e., @code{throw @dots{} @@catch}).
|
|
@end itemize
|
|
|
|
The @option{-fobjc-exceptions} switch also enables the use of synchronization
|
|
blocks for thread-safe execution:
|
|
|
|
@smallexample
|
|
@@synchronized (ObjCClass *guard) @{
|
|
@dots{}
|
|
@}
|
|
@end smallexample
|
|
|
|
Upon entering the @code{@@synchronized} block, a thread of execution shall
|
|
first check whether a lock has been placed on the corresponding @code{guard}
|
|
object by another thread. If it has, the current thread shall wait until
|
|
the other thread relinquishes its lock. Once @code{guard} becomes available,
|
|
the current thread will place its own lock on it, execute the code contained in
|
|
the @code{@@synchronized} block, and finally relinquish the lock (thereby
|
|
making @code{guard} available to other threads).
|
|
|
|
Unlike Java, Objective-C does not allow for entire methods to be marked
|
|
@code{@@synchronized}. Note that throwing exceptions out of
|
|
@code{@@synchronized} blocks is allowed, and will cause the guarding object
|
|
to be unlocked properly.
|
|
|
|
@item -fobjc-gc
|
|
@opindex fobjc-gc
|
|
Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
|
|
|
|
@item -freplace-objc-classes
|
|
@opindex freplace-objc-classes
|
|
Emit a special marker instructing @command{ld(1)} not to statically link in
|
|
the resulting object file, and allow @command{dyld(1)} to load it in at
|
|
run time instead. This is used in conjunction with the Fix-and-Continue
|
|
debugging mode, where the object file in question may be recompiled and
|
|
dynamically reloaded in the course of program execution, without the need
|
|
to restart the program itself. Currently, Fix-and-Continue functionality
|
|
is only available in conjunction with the NeXT runtime on Mac OS X 10.3
|
|
and later.
|
|
|
|
@item -fzero-link
|
|
@opindex fzero-link
|
|
When compiling for the NeXT runtime, the compiler ordinarily replaces calls
|
|
to @code{objc_getClass("@dots{}")} (when the name of the class is known at
|
|
compile time) with static class references that get initialized at load time,
|
|
which improves run-time performance. Specifying the @option{-fzero-link} flag
|
|
suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
|
|
to be retained. This is useful in Zero-Link debugging mode, since it allows
|
|
for individual class implementations to be modified during program execution.
|
|
|
|
@item -gen-decls
|
|
@opindex gen-decls
|
|
Dump interface declarations for all classes seen in the source file to a
|
|
file named @file{@var{sourcename}.decl}.
|
|
|
|
@item -Wassign-intercept
|
|
@opindex Wassign-intercept
|
|
Warn whenever an Objective-C assignment is being intercepted by the
|
|
garbage collector.
|
|
|
|
@item -Wno-protocol
|
|
@opindex Wno-protocol
|
|
If a class is declared to implement a protocol, a warning is issued for
|
|
every method in the protocol that is not implemented by the class. The
|
|
default behavior is to issue a warning for every method not explicitly
|
|
implemented in the class, even if a method implementation is inherited
|
|
from the superclass. If you use the @option{-Wno-protocol} option, then
|
|
methods inherited from the superclass are considered to be implemented,
|
|
and no warning is issued for them.
|
|
|
|
@item -Wselector
|
|
@opindex Wselector
|
|
Warn if multiple methods of different types for the same selector are
|
|
found during compilation. The check is performed on the list of methods
|
|
in the final stage of compilation. Additionally, a check is performed
|
|
for each selector appearing in a @code{@@selector(@dots{})}
|
|
expression, and a corresponding method for that selector has been found
|
|
during compilation. Because these checks scan the method table only at
|
|
the end of compilation, these warnings are not produced if the final
|
|
stage of compilation is not reached, for example because an error is
|
|
found during compilation, or because the @option{-fsyntax-only} option is
|
|
being used.
|
|
|
|
@item -Wstrict-selector-match
|
|
@opindex Wstrict-selector-match
|
|
Warn if multiple methods with differing argument and/or return types are
|
|
found for a given selector when attempting to send a message using this
|
|
selector to a receiver of type @code{id} or @code{Class}. When this flag
|
|
is off (which is the default behavior), the compiler will omit such warnings
|
|
if any differences found are confined to types which share the same size
|
|
and alignment.
|
|
|
|
@item -Wundeclared-selector
|
|
@opindex Wundeclared-selector
|
|
Warn if a @code{@@selector(@dots{})} expression referring to an
|
|
undeclared selector is found. A selector is considered undeclared if no
|
|
method with that name has been declared before the
|
|
@code{@@selector(@dots{})} expression, either explicitly in an
|
|
@code{@@interface} or @code{@@protocol} declaration, or implicitly in
|
|
an @code{@@implementation} section. This option always performs its
|
|
checks as soon as a @code{@@selector(@dots{})} expression is found,
|
|
while @option{-Wselector} only performs its checks in the final stage of
|
|
compilation. This also enforces the coding style convention
|
|
that methods and selectors must be declared before being used.
|
|
|
|
@item -print-objc-runtime-info
|
|
@opindex print-objc-runtime-info
|
|
Generate C header describing the largest structure that is passed by
|
|
value, if any.
|
|
|
|
@end table
|
|
|
|
@node Language Independent Options
|
|
@section Options to Control Diagnostic Messages Formatting
|
|
@cindex options to control diagnostics formatting
|
|
@cindex diagnostic messages
|
|
@cindex message formatting
|
|
|
|
Traditionally, diagnostic messages have been formatted irrespective of
|
|
the output device's aspect (e.g.@: its width, @dots{}). The options described
|
|
below can be used to control the diagnostic messages formatting
|
|
algorithm, e.g.@: how many characters per line, how often source location
|
|
information should be reported. Right now, only the C++ front end can
|
|
honor these options. However it is expected, in the near future, that
|
|
the remaining front ends would be able to digest them correctly.
|
|
|
|
@table @gcctabopt
|
|
@item -fmessage-length=@var{n}
|
|
@opindex fmessage-length
|
|
Try to format error messages so that they fit on lines of about @var{n}
|
|
characters. The default is 72 characters for @command{g++} and 0 for the rest of
|
|
the front ends supported by GCC@. If @var{n} is zero, then no
|
|
line-wrapping will be done; each error message will appear on a single
|
|
line.
|
|
|
|
@opindex fdiagnostics-show-location
|
|
@item -fdiagnostics-show-location=once
|
|
Only meaningful in line-wrapping mode. Instructs the diagnostic messages
|
|
reporter to emit @emph{once} source location information; that is, in
|
|
case the message is too long to fit on a single physical line and has to
|
|
be wrapped, the source location won't be emitted (as prefix) again,
|
|
over and over, in subsequent continuation lines. This is the default
|
|
behavior.
|
|
|
|
@item -fdiagnostics-show-location=every-line
|
|
Only meaningful in line-wrapping mode. Instructs the diagnostic
|
|
messages reporter to emit the same source location information (as
|
|
prefix) for physical lines that result from the process of breaking
|
|
a message which is too long to fit on a single line.
|
|
|
|
@item -fdiagnostics-show-option
|
|
@opindex fdiagnostics-show-option
|
|
This option instructs the diagnostic machinery to add text to each
|
|
diagnostic emitted, which indicates which command line option directly
|
|
controls that diagnostic, when such an option is known to the
|
|
diagnostic machinery.
|
|
|
|
@end table
|
|
|
|
@node Warning Options
|
|
@section Options to Request or Suppress Warnings
|
|
@cindex options to control warnings
|
|
@cindex warning messages
|
|
@cindex messages, warning
|
|
@cindex suppressing warnings
|
|
|
|
Warnings are diagnostic messages that report constructions which
|
|
are not inherently erroneous but which are risky or suggest there
|
|
may have been an error.
|
|
|
|
You can request many specific warnings with options beginning @samp{-W},
|
|
for example @option{-Wimplicit} to request warnings on implicit
|
|
declarations. Each of these specific warning options also has a
|
|
negative form beginning @samp{-Wno-} to turn off warnings;
|
|
for example, @option{-Wno-implicit}. This manual lists only one of the
|
|
two forms, whichever is not the default.
|
|
|
|
The following options control the amount and kinds of warnings produced
|
|
by GCC; for further, language-specific options also refer to
|
|
@ref{C++ Dialect Options} and @ref{Objective-C and Objective-C++ Dialect
|
|
Options}.
|
|
|
|
@table @gcctabopt
|
|
@cindex syntax checking
|
|
@item -fsyntax-only
|
|
@opindex fsyntax-only
|
|
Check the code for syntax errors, but don't do anything beyond that.
|
|
|
|
@item -pedantic
|
|
@opindex pedantic
|
|
Issue all the warnings demanded by strict ISO C and ISO C++;
|
|
reject all programs that use forbidden extensions, and some other
|
|
programs that do not follow ISO C and ISO C++. For ISO C, follows the
|
|
version of the ISO C standard specified by any @option{-std} option used.
|
|
|
|
Valid ISO C and ISO C++ programs should compile properly with or without
|
|
this option (though a rare few will require @option{-ansi} or a
|
|
@option{-std} option specifying the required version of ISO C)@. However,
|
|
without this option, certain GNU extensions and traditional C and C++
|
|
features are supported as well. With this option, they are rejected.
|
|
|
|
@option{-pedantic} does not cause warning messages for use of the
|
|
alternate keywords whose names begin and end with @samp{__}. Pedantic
|
|
warnings are also disabled in the expression that follows
|
|
@code{__extension__}. However, only system header files should use
|
|
these escape routes; application programs should avoid them.
|
|
@xref{Alternate Keywords}.
|
|
|
|
Some users try to use @option{-pedantic} to check programs for strict ISO
|
|
C conformance. They soon find that it does not do quite what they want:
|
|
it finds some non-ISO practices, but not all---only those for which
|
|
ISO C @emph{requires} a diagnostic, and some others for which
|
|
diagnostics have been added.
|
|
|
|
A feature to report any failure to conform to ISO C might be useful in
|
|
some instances, but would require considerable additional work and would
|
|
be quite different from @option{-pedantic}. We don't have plans to
|
|
support such a feature in the near future.
|
|
|
|
Where the standard specified with @option{-std} represents a GNU
|
|
extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
|
|
corresponding @dfn{base standard}, the version of ISO C on which the GNU
|
|
extended dialect is based. Warnings from @option{-pedantic} are given
|
|
where they are required by the base standard. (It would not make sense
|
|
for such warnings to be given only for features not in the specified GNU
|
|
C dialect, since by definition the GNU dialects of C include all
|
|
features the compiler supports with the given option, and there would be
|
|
nothing to warn about.)
|
|
|
|
@item -pedantic-errors
|
|
@opindex pedantic-errors
|
|
Like @option{-pedantic}, except that errors are produced rather than
|
|
warnings.
|
|
|
|
@item -w
|
|
@opindex w
|
|
Inhibit all warning messages.
|
|
|
|
@item -Wno-import
|
|
@opindex Wno-import
|
|
Inhibit warning messages about the use of @samp{#import}.
|
|
|
|
@item -Wchar-subscripts
|
|
@opindex Wchar-subscripts
|
|
Warn if an array subscript has type @code{char}. This is a common cause
|
|
of error, as programmers often forget that this type is signed on some
|
|
machines.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wcomment
|
|
@opindex Wcomment
|
|
Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
|
|
comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wfatal-errors
|
|
@opindex Wfatal-errors
|
|
This option causes the compiler to abort compilation on the first error
|
|
occurred rather than trying to keep going and printing further error
|
|
messages.
|
|
|
|
@item -Wformat
|
|
@opindex Wformat
|
|
@opindex ffreestanding
|
|
@opindex fno-builtin
|
|
Check calls to @code{printf} and @code{scanf}, etc., to make sure that
|
|
the arguments supplied have types appropriate to the format string
|
|
specified, and that the conversions specified in the format string make
|
|
sense. This includes standard functions, and others specified by format
|
|
attributes (@pxref{Function Attributes}), in the @code{printf},
|
|
@code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
|
|
not in the C standard) families (or other target-specific families).
|
|
Which functions are checked without format attributes having been
|
|
specified depends on the standard version selected, and such checks of
|
|
functions without the attribute specified are disabled by
|
|
@option{-ffreestanding} or @option{-fno-builtin}.
|
|
|
|
The formats are checked against the format features supported by GNU
|
|
libc version 2.2. These include all ISO C90 and C99 features, as well
|
|
as features from the Single Unix Specification and some BSD and GNU
|
|
extensions. Other library implementations may not support all these
|
|
features; GCC does not support warning about features that go beyond a
|
|
particular library's limitations. However, if @option{-pedantic} is used
|
|
with @option{-Wformat}, warnings will be given about format features not
|
|
in the selected standard version (but not for @code{strfmon} formats,
|
|
since those are not in any version of the C standard). @xref{C Dialect
|
|
Options,,Options Controlling C Dialect}.
|
|
|
|
Since @option{-Wformat} also checks for null format arguments for
|
|
several functions, @option{-Wformat} also implies @option{-Wnonnull}.
|
|
|
|
@option{-Wformat} is included in @option{-Wall}. For more control over some
|
|
aspects of format checking, the options @option{-Wformat-y2k},
|
|
@option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
|
|
@option{-Wformat-nonliteral}, @option{-Wformat-security}, and
|
|
@option{-Wformat=2} are available, but are not included in @option{-Wall}.
|
|
|
|
@item -Wformat-y2k
|
|
@opindex Wformat-y2k
|
|
If @option{-Wformat} is specified, also warn about @code{strftime}
|
|
formats which may yield only a two-digit year.
|
|
|
|
@item -Wno-format-extra-args
|
|
@opindex Wno-format-extra-args
|
|
If @option{-Wformat} is specified, do not warn about excess arguments to a
|
|
@code{printf} or @code{scanf} format function. The C standard specifies
|
|
that such arguments are ignored.
|
|
|
|
Where the unused arguments lie between used arguments that are
|
|
specified with @samp{$} operand number specifications, normally
|
|
warnings are still given, since the implementation could not know what
|
|
type to pass to @code{va_arg} to skip the unused arguments. However,
|
|
in the case of @code{scanf} formats, this option will suppress the
|
|
warning if the unused arguments are all pointers, since the Single
|
|
Unix Specification says that such unused arguments are allowed.
|
|
|
|
@item -Wno-format-zero-length
|
|
@opindex Wno-format-zero-length
|
|
If @option{-Wformat} is specified, do not warn about zero-length formats.
|
|
The C standard specifies that zero-length formats are allowed.
|
|
|
|
@item -Wformat-nonliteral
|
|
@opindex Wformat-nonliteral
|
|
If @option{-Wformat} is specified, also warn if the format string is not a
|
|
string literal and so cannot be checked, unless the format function
|
|
takes its format arguments as a @code{va_list}.
|
|
|
|
@item -Wformat-security
|
|
@opindex Wformat-security
|
|
If @option{-Wformat} is specified, also warn about uses of format
|
|
functions that represent possible security problems. At present, this
|
|
warns about calls to @code{printf} and @code{scanf} functions where the
|
|
format string is not a string literal and there are no format arguments,
|
|
as in @code{printf (foo);}. This may be a security hole if the format
|
|
string came from untrusted input and contains @samp{%n}. (This is
|
|
currently a subset of what @option{-Wformat-nonliteral} warns about, but
|
|
in future warnings may be added to @option{-Wformat-security} that are not
|
|
included in @option{-Wformat-nonliteral}.)
|
|
|
|
@item -Wformat=2
|
|
@opindex Wformat=2
|
|
Enable @option{-Wformat} plus format checks not included in
|
|
@option{-Wformat}. Currently equivalent to @samp{-Wformat
|
|
-Wformat-nonliteral -Wformat-security -Wformat-y2k}.
|
|
|
|
@item -Wnonnull
|
|
@opindex Wnonnull
|
|
Warn about passing a null pointer for arguments marked as
|
|
requiring a non-null value by the @code{nonnull} function attribute.
|
|
|
|
@option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
|
|
can be disabled with the @option{-Wno-nonnull} option.
|
|
|
|
@item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
|
|
@opindex Winit-self
|
|
Warn about uninitialized variables which are initialized with themselves.
|
|
Note this option can only be used with the @option{-Wuninitialized} option,
|
|
which in turn only works with @option{-O1} and above.
|
|
|
|
For example, GCC will warn about @code{i} being uninitialized in the
|
|
following snippet only when @option{-Winit-self} has been specified:
|
|
@smallexample
|
|
@group
|
|
int f()
|
|
@{
|
|
int i = i;
|
|
return i;
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
|
|
@item -Wimplicit-int
|
|
@opindex Wimplicit-int
|
|
Warn when a declaration does not specify a type.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wimplicit-function-declaration
|
|
@itemx -Werror-implicit-function-declaration
|
|
@opindex Wimplicit-function-declaration
|
|
@opindex Werror-implicit-function-declaration
|
|
Give a warning (or error) whenever a function is used before being
|
|
declared. The form @option{-Wno-error-implicit-function-declaration}
|
|
is not supported.
|
|
This warning is enabled by @option{-Wall} (as a warning, not an error).
|
|
|
|
@item -Wimplicit
|
|
@opindex Wimplicit
|
|
Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wmain
|
|
@opindex Wmain
|
|
Warn if the type of @samp{main} is suspicious. @samp{main} should be a
|
|
function with external linkage, returning int, taking either zero
|
|
arguments, two, or three arguments of appropriate types.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wmissing-braces
|
|
@opindex Wmissing-braces
|
|
Warn if an aggregate or union initializer is not fully bracketed. In
|
|
the following example, the initializer for @samp{a} is not fully
|
|
bracketed, but that for @samp{b} is fully bracketed.
|
|
|
|
@smallexample
|
|
int a[2][2] = @{ 0, 1, 2, 3 @};
|
|
int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
|
|
@end smallexample
|
|
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
|
|
@opindex Wmissing-include-dirs
|
|
Warn if a user-supplied include directory does not exist.
|
|
|
|
@item -Wparentheses
|
|
@opindex Wparentheses
|
|
Warn if parentheses are omitted in certain contexts, such
|
|
as when there is an assignment in a context where a truth value
|
|
is expected, or when operators are nested whose precedence people
|
|
often get confused about. Only the warning for an assignment used as
|
|
a truth value is supported when compiling C++; the other warnings are
|
|
only supported when compiling C@.
|
|
|
|
Also warn if a comparison like @samp{x<=y<=z} appears; this is
|
|
equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
|
|
interpretation from that of ordinary mathematical notation.
|
|
|
|
Also warn about constructions where there may be confusion to which
|
|
@code{if} statement an @code{else} branch belongs. Here is an example of
|
|
such a case:
|
|
|
|
@smallexample
|
|
@group
|
|
@{
|
|
if (a)
|
|
if (b)
|
|
foo ();
|
|
else
|
|
bar ();
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
|
|
In C, every @code{else} branch belongs to the innermost possible @code{if}
|
|
statement, which in this example is @code{if (b)}. This is often not
|
|
what the programmer expected, as illustrated in the above example by
|
|
indentation the programmer chose. When there is the potential for this
|
|
confusion, GCC will issue a warning when this flag is specified.
|
|
To eliminate the warning, add explicit braces around the innermost
|
|
@code{if} statement so there is no way the @code{else} could belong to
|
|
the enclosing @code{if}. The resulting code would look like this:
|
|
|
|
@smallexample
|
|
@group
|
|
@{
|
|
if (a)
|
|
@{
|
|
if (b)
|
|
foo ();
|
|
else
|
|
bar ();
|
|
@}
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wsequence-point
|
|
@opindex Wsequence-point
|
|
Warn about code that may have undefined semantics because of violations
|
|
of sequence point rules in the C and C++ standards.
|
|
|
|
The C and C++ standards defines the order in which expressions in a C/C++
|
|
program are evaluated in terms of @dfn{sequence points}, which represent
|
|
a partial ordering between the execution of parts of the program: those
|
|
executed before the sequence point, and those executed after it. These
|
|
occur after the evaluation of a full expression (one which is not part
|
|
of a larger expression), after the evaluation of the first operand of a
|
|
@code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
|
|
function is called (but after the evaluation of its arguments and the
|
|
expression denoting the called function), and in certain other places.
|
|
Other than as expressed by the sequence point rules, the order of
|
|
evaluation of subexpressions of an expression is not specified. All
|
|
these rules describe only a partial order rather than a total order,
|
|
since, for example, if two functions are called within one expression
|
|
with no sequence point between them, the order in which the functions
|
|
are called is not specified. However, the standards committee have
|
|
ruled that function calls do not overlap.
|
|
|
|
It is not specified when between sequence points modifications to the
|
|
values of objects take effect. Programs whose behavior depends on this
|
|
have undefined behavior; the C and C++ standards specify that ``Between
|
|
the previous and next sequence point an object shall have its stored
|
|
value modified at most once by the evaluation of an expression.
|
|
Furthermore, the prior value shall be read only to determine the value
|
|
to be stored.''. If a program breaks these rules, the results on any
|
|
particular implementation are entirely unpredictable.
|
|
|
|
Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
|
|
= b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
|
|
diagnosed by this option, and it may give an occasional false positive
|
|
result, but in general it has been found fairly effective at detecting
|
|
this sort of problem in programs.
|
|
|
|
The standard is worded confusingly, therefore there is some debate
|
|
over the precise meaning of the sequence point rules in subtle cases.
|
|
Links to discussions of the problem, including proposed formal
|
|
definitions, may be found on the GCC readings page, at
|
|
@w{@uref{http://gcc.gnu.org/readings.html}}.
|
|
|
|
This warning is enabled by @option{-Wall} for C and C++.
|
|
|
|
@item -Wreturn-type
|
|
@opindex Wreturn-type
|
|
Warn whenever a function is defined with a return-type that defaults to
|
|
@code{int}. Also warn about any @code{return} statement with no
|
|
return-value in a function whose return-type is not @code{void}.
|
|
|
|
For C, also warn if the return type of a function has a type qualifier
|
|
such as @code{const}. Such a type qualifier has no effect, since the
|
|
value returned by a function is not an lvalue. ISO C prohibits
|
|
qualified @code{void} return types on function definitions, so such
|
|
return types always receive a warning even without this option.
|
|
|
|
For C++, a function without return type always produces a diagnostic
|
|
message, even when @option{-Wno-return-type} is specified. The only
|
|
exceptions are @samp{main} and functions defined in system headers.
|
|
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wswitch
|
|
@opindex Wswitch
|
|
Warn whenever a @code{switch} statement has an index of enumerated type
|
|
and lacks a @code{case} for one or more of the named codes of that
|
|
enumeration. (The presence of a @code{default} label prevents this
|
|
warning.) @code{case} labels outside the enumeration range also
|
|
provoke warnings when this option is used.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wswitch-default
|
|
@opindex Wswitch-switch
|
|
Warn whenever a @code{switch} statement does not have a @code{default}
|
|
case.
|
|
|
|
@item -Wswitch-enum
|
|
@opindex Wswitch-enum
|
|
Warn whenever a @code{switch} statement has an index of enumerated type
|
|
and lacks a @code{case} for one or more of the named codes of that
|
|
enumeration. @code{case} labels outside the enumeration range also
|
|
provoke warnings when this option is used.
|
|
|
|
@item -Wtrigraphs
|
|
@opindex Wtrigraphs
|
|
Warn if any trigraphs are encountered that might change the meaning of
|
|
the program (trigraphs within comments are not warned about).
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wunused-function
|
|
@opindex Wunused-function
|
|
Warn whenever a static function is declared but not defined or a
|
|
non-inline static function is unused.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wunused-label
|
|
@opindex Wunused-label
|
|
Warn whenever a label is declared but not used.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
To suppress this warning use the @samp{unused} attribute
|
|
(@pxref{Variable Attributes}).
|
|
|
|
@item -Wunused-parameter
|
|
@opindex Wunused-parameter
|
|
Warn whenever a function parameter is unused aside from its declaration.
|
|
|
|
To suppress this warning use the @samp{unused} attribute
|
|
(@pxref{Variable Attributes}).
|
|
|
|
@item -Wunused-variable
|
|
@opindex Wunused-variable
|
|
Warn whenever a local variable or non-constant static variable is unused
|
|
aside from its declaration.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
To suppress this warning use the @samp{unused} attribute
|
|
(@pxref{Variable Attributes}).
|
|
|
|
@item -Wunused-value
|
|
@opindex Wunused-value
|
|
Warn whenever a statement computes a result that is explicitly not used.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
To suppress this warning cast the expression to @samp{void}.
|
|
|
|
@item -Wunused
|
|
@opindex Wunused
|
|
All the above @option{-Wunused} options combined.
|
|
|
|
In order to get a warning about an unused function parameter, you must
|
|
either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
|
|
@samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
|
|
|
|
@item -Wuninitialized
|
|
@opindex Wuninitialized
|
|
Warn if an automatic variable is used without first being initialized or
|
|
if a variable may be clobbered by a @code{setjmp} call.
|
|
|
|
These warnings are possible only in optimizing compilation,
|
|
because they require data flow information that is computed only
|
|
when optimizing. If you do not specify @option{-O}, you will not get
|
|
these warnings. Instead, GCC will issue a warning about @option{-Wuninitialized}
|
|
requiring @option{-O}.
|
|
|
|
If you want to warn about code which uses the uninitialized value of the
|
|
variable in its own initializer, use the @option{-Winit-self} option.
|
|
|
|
These warnings occur for individual uninitialized or clobbered
|
|
elements of structure, union or array variables as well as for
|
|
variables which are uninitialized or clobbered as a whole. They do
|
|
not occur for variables or elements declared @code{volatile}. Because
|
|
these warnings depend on optimization, the exact variables or elements
|
|
for which there are warnings will depend on the precise optimization
|
|
options and version of GCC used.
|
|
|
|
Note that there may be no warning about a variable that is used only
|
|
to compute a value that itself is never used, because such
|
|
computations may be deleted by data flow analysis before the warnings
|
|
are printed.
|
|
|
|
These warnings are made optional because GCC is not smart
|
|
enough to see all the reasons why the code might be correct
|
|
despite appearing to have an error. Here is one example of how
|
|
this can happen:
|
|
|
|
@smallexample
|
|
@group
|
|
@{
|
|
int x;
|
|
switch (y)
|
|
@{
|
|
case 1: x = 1;
|
|
break;
|
|
case 2: x = 4;
|
|
break;
|
|
case 3: x = 5;
|
|
@}
|
|
foo (x);
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
|
|
@noindent
|
|
If the value of @code{y} is always 1, 2 or 3, then @code{x} is
|
|
always initialized, but GCC doesn't know this. Here is
|
|
another common case:
|
|
|
|
@smallexample
|
|
@{
|
|
int save_y;
|
|
if (change_y) save_y = y, y = new_y;
|
|
@dots{}
|
|
if (change_y) y = save_y;
|
|
@}
|
|
@end smallexample
|
|
|
|
@noindent
|
|
This has no bug because @code{save_y} is used only if it is set.
|
|
|
|
@cindex @code{longjmp} warnings
|
|
This option also warns when a non-volatile automatic variable might be
|
|
changed by a call to @code{longjmp}. These warnings as well are possible
|
|
only in optimizing compilation.
|
|
|
|
The compiler sees only the calls to @code{setjmp}. It cannot know
|
|
where @code{longjmp} will be called; in fact, a signal handler could
|
|
call it at any point in the code. As a result, you may get a warning
|
|
even when there is in fact no problem because @code{longjmp} cannot
|
|
in fact be called at the place which would cause a problem.
|
|
|
|
Some spurious warnings can be avoided if you declare all the functions
|
|
you use that never return as @code{noreturn}. @xref{Function
|
|
Attributes}.
|
|
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wunknown-pragmas
|
|
@opindex Wunknown-pragmas
|
|
@cindex warning for unknown pragmas
|
|
@cindex unknown pragmas, warning
|
|
@cindex pragmas, warning of unknown
|
|
Warn when a #pragma directive is encountered which is not understood by
|
|
GCC@. If this command line option is used, warnings will even be issued
|
|
for unknown pragmas in system header files. This is not the case if
|
|
the warnings were only enabled by the @option{-Wall} command line option.
|
|
|
|
@item -Wno-pragmas
|
|
@opindex Wno-pragmas
|
|
@opindex Wpragmas
|
|
Do not warn about misuses of pragmas, such as incorrect parameters,
|
|
invalid syntax, or conflicts between pragmas. See also
|
|
@samp{-Wunknown-pragmas}.
|
|
|
|
@item -Wstrict-aliasing
|
|
@opindex Wstrict-aliasing
|
|
This option is only active when @option{-fstrict-aliasing} is active.
|
|
It warns about code which might break the strict aliasing rules that the
|
|
compiler is using for optimization. The warning does not catch all
|
|
cases, but does attempt to catch the more common pitfalls. It is
|
|
included in @option{-Wall}.
|
|
|
|
@item -Wstrict-aliasing=2
|
|
@opindex Wstrict-aliasing=2
|
|
This option is only active when @option{-fstrict-aliasing} is active.
|
|
It warns about code which might break the strict aliasing rules that the
|
|
compiler is using for optimization. This warning catches more cases than
|
|
@option{-Wstrict-aliasing}, but it will also give a warning for some ambiguous
|
|
cases that are safe.
|
|
|
|
@item -Wstrict-overflow
|
|
@item -Wstrict-overflow=@var{n}
|
|
@opindex Wstrict-overflow
|
|
This option is only active when @option{-fstrict-overflow} is active.
|
|
It warns about cases where the compiler optimizes based on the
|
|
assumption that signed overflow does not occur. Note that it does not
|
|
warn about all cases where the code might overflow: it only warns
|
|
about cases where the compiler implements some optimization. Thus
|
|
this warning depends on the optimization level.
|
|
|
|
An optimization which assumes that signed overflow does not occur is
|
|
perfectly safe if the values of the variables involved are such that
|
|
overflow never does, in fact, occur. Therefore this warning can
|
|
easily give a false positive: a warning about code which is not
|
|
actually a problem. To help focus on important issues, several
|
|
warning levels are defined. No warnings are issued for the use of
|
|
undefined signed overflow when estimating how many iterations a loop
|
|
will require, in particular when determining whether a loop will be
|
|
executed at all.
|
|
|
|
@table @option
|
|
@item -Wstrict-overflow=1
|
|
Warn about cases which are both questionable and easy to avoid. For
|
|
example: @code{x + 1 > x}; with @option{-fstrict-overflow}, the
|
|
compiler will simplify this to @code{1}. This level of
|
|
@option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels
|
|
are not, and must be explicitly requested.
|
|
|
|
@item -Wstrict-overflow=2
|
|
Also warn about other cases where a comparison is simplified to a
|
|
constant. For example: @code{abs (x) >= 0}. This can only be
|
|
simplified when @option{-fstrict-overflow} is in effect, because
|
|
@code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than
|
|
zero. @option{-Wstrict-overflow} (with no level) is the same as
|
|
@option{-Wstrict-overflow=2}.
|
|
|
|
@item -Wstrict-overflow=3
|
|
Also warn about other cases where a comparison is simplified. For
|
|
example: @code{x + 1 > 1} will be simplified to @code{x > 0}.
|
|
|
|
@item -Wstrict-overflow=4
|
|
Also warn about other simplifications not covered by the above cases.
|
|
For example: @code{(x * 10) / 5} will be simplified to @code{x * 2}.
|
|
|
|
@item -Wstrict-overflow=5
|
|
Also warn about cases where the compiler reduces the magnitude of a
|
|
constant involved in a comparison. For example: @code{x + 2 > y} will
|
|
be simplified to @code{x + 1 >= y}. This is reported only at the
|
|
highest warning level because this simplification applies to many
|
|
comparisons, so this warning level will give a very large number of
|
|
false positives.
|
|
@end table
|
|
|
|
@item -Wall
|
|
@opindex Wall
|
|
All of the above @samp{-W} options combined. This enables all the
|
|
warnings about constructions that some users consider questionable, and
|
|
that are easy to avoid (or modify to prevent the warning), even in
|
|
conjunction with macros. This also enables some language-specific
|
|
warnings described in @ref{C++ Dialect Options} and
|
|
@ref{Objective-C and Objective-C++ Dialect Options}.
|
|
@end table
|
|
|
|
The following @option{-W@dots{}} options are not implied by @option{-Wall}.
|
|
Some of them warn about constructions that users generally do not
|
|
consider questionable, but which occasionally you might wish to check
|
|
for; others warn about constructions that are necessary or hard to avoid
|
|
in some cases, and there is no simple way to modify the code to suppress
|
|
the warning.
|
|
|
|
@table @gcctabopt
|
|
@item -Wextra
|
|
@opindex W
|
|
@opindex Wextra
|
|
(This option used to be called @option{-W}. The older name is still
|
|
supported, but the newer name is more descriptive.) Print extra warning
|
|
messages for these events:
|
|
|
|
@itemize @bullet
|
|
@item
|
|
A function can return either with or without a value. (Falling
|
|
off the end of the function body is considered returning without
|
|
a value.) For example, this function would evoke such a
|
|
warning:
|
|
|
|
@smallexample
|
|
@group
|
|
foo (a)
|
|
@{
|
|
if (a > 0)
|
|
return a;
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
|
|
@item
|
|
An expression-statement or the left-hand side of a comma expression
|
|
contains no side effects.
|
|
To suppress the warning, cast the unused expression to void.
|
|
For example, an expression such as @samp{x[i,j]} will cause a warning,
|
|
but @samp{x[(void)i,j]} will not.
|
|
|
|
@item
|
|
An unsigned value is compared against zero with @samp{<} or @samp{>=}.
|
|
|
|
@item
|
|
Storage-class specifiers like @code{static} are not the first things in
|
|
a declaration. According to the C Standard, this usage is obsolescent.
|
|
|
|
@item
|
|
If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
|
|
arguments.
|
|
|
|
@item
|
|
A comparison between signed and unsigned values could produce an
|
|
incorrect result when the signed value is converted to unsigned.
|
|
(But don't warn if @option{-Wno-sign-compare} is also specified.)
|
|
|
|
@item
|
|
An aggregate has an initializer which does not initialize all members.
|
|
This warning can be independently controlled by
|
|
@option{-Wmissing-field-initializers}.
|
|
|
|
@item
|
|
An initialized field without side effects is overridden when using
|
|
designated initializers (@pxref{Designated Inits, , Designated
|
|
Initializers}). This warning can be independently controlled by
|
|
@option{-Woverride-init}.
|
|
|
|
@item
|
|
A function parameter is declared without a type specifier in K&R-style
|
|
functions:
|
|
|
|
@smallexample
|
|
void foo(bar) @{ @}
|
|
@end smallexample
|
|
|
|
@item
|
|
An empty body occurs in an @samp{if} or @samp{else} statement.
|
|
|
|
@item
|
|
A pointer is compared against integer zero with @samp{<}, @samp{<=},
|
|
@samp{>}, or @samp{>=}.
|
|
|
|
@item
|
|
A variable might be changed by @samp{longjmp} or @samp{vfork}.
|
|
|
|
@item @r{(C++ only)}
|
|
An enumerator and a non-enumerator both appear in a conditional expression.
|
|
|
|
@item @r{(C++ only)}
|
|
A non-static reference or non-static @samp{const} member appears in a
|
|
class without constructors.
|
|
|
|
@item @r{(C++ only)}
|
|
Ambiguous virtual bases.
|
|
|
|
@item @r{(C++ only)}
|
|
Subscripting an array which has been declared @samp{register}.
|
|
|
|
@item @r{(C++ only)}
|
|
Taking the address of a variable which has been declared @samp{register}.
|
|
|
|
@item @r{(C++ only)}
|
|
A base class is not initialized in a derived class' copy constructor.
|
|
@end itemize
|
|
|
|
@item -Wno-div-by-zero
|
|
@opindex Wno-div-by-zero
|
|
@opindex Wdiv-by-zero
|
|
Do not warn about compile-time integer division by zero. Floating point
|
|
division by zero is not warned about, as it can be a legitimate way of
|
|
obtaining infinities and NaNs.
|
|
|
|
@item -Wsystem-headers
|
|
@opindex Wsystem-headers
|
|
@cindex warnings from system headers
|
|
@cindex system headers, warnings from
|
|
Print warning messages for constructs found in system header files.
|
|
Warnings from system headers are normally suppressed, on the assumption
|
|
that they usually do not indicate real problems and would only make the
|
|
compiler output harder to read. Using this command line option tells
|
|
GCC to emit warnings from system headers as if they occurred in user
|
|
code. However, note that using @option{-Wall} in conjunction with this
|
|
option will @emph{not} warn about unknown pragmas in system
|
|
headers---for that, @option{-Wunknown-pragmas} must also be used.
|
|
|
|
@item -Wfloat-equal
|
|
@opindex Wfloat-equal
|
|
Warn if floating point values are used in equality comparisons.
|
|
|
|
The idea behind this is that sometimes it is convenient (for the
|
|
programmer) to consider floating-point values as approximations to
|
|
infinitely precise real numbers. If you are doing this, then you need
|
|
to compute (by analyzing the code, or in some other way) the maximum or
|
|
likely maximum error that the computation introduces, and allow for it
|
|
when performing comparisons (and when producing output, but that's a
|
|
different problem). In particular, instead of testing for equality, you
|
|
would check to see whether the two values have ranges that overlap; and
|
|
this is done with the relational operators, so equality comparisons are
|
|
probably mistaken.
|
|
|
|
@item -Wtraditional @r{(C only)}
|
|
@opindex Wtraditional
|
|
Warn about certain constructs that behave differently in traditional and
|
|
ISO C@. Also warn about ISO C constructs that have no traditional C
|
|
equivalent, and/or problematic constructs which should be avoided.
|
|
|
|
@itemize @bullet
|
|
@item
|
|
Macro parameters that appear within string literals in the macro body.
|
|
In traditional C macro replacement takes place within string literals,
|
|
but does not in ISO C@.
|
|
|
|
@item
|
|
In traditional C, some preprocessor directives did not exist.
|
|
Traditional preprocessors would only consider a line to be a directive
|
|
if the @samp{#} appeared in column 1 on the line. Therefore
|
|
@option{-Wtraditional} warns about directives that traditional C
|
|
understands but would ignore because the @samp{#} does not appear as the
|
|
first character on the line. It also suggests you hide directives like
|
|
@samp{#pragma} not understood by traditional C by indenting them. Some
|
|
traditional implementations would not recognize @samp{#elif}, so it
|
|
suggests avoiding it altogether.
|
|
|
|
@item
|
|
A function-like macro that appears without arguments.
|
|
|
|
@item
|
|
The unary plus operator.
|
|
|
|
@item
|
|
The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
|
|
constant suffixes. (Traditional C does support the @samp{L} suffix on integer
|
|
constants.) Note, these suffixes appear in macros defined in the system
|
|
headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
|
|
Use of these macros in user code might normally lead to spurious
|
|
warnings, however GCC's integrated preprocessor has enough context to
|
|
avoid warning in these cases.
|
|
|
|
@item
|
|
A function declared external in one block and then used after the end of
|
|
the block.
|
|
|
|
@item
|
|
A @code{switch} statement has an operand of type @code{long}.
|
|
|
|
@item
|
|
A non-@code{static} function declaration follows a @code{static} one.
|
|
This construct is not accepted by some traditional C compilers.
|
|
|
|
@item
|
|
The ISO type of an integer constant has a different width or
|
|
signedness from its traditional type. This warning is only issued if
|
|
the base of the constant is ten. I.e.@: hexadecimal or octal values, which
|
|
typically represent bit patterns, are not warned about.
|
|
|
|
@item
|
|
Usage of ISO string concatenation is detected.
|
|
|
|
@item
|
|
Initialization of automatic aggregates.
|
|
|
|
@item
|
|
Identifier conflicts with labels. Traditional C lacks a separate
|
|
namespace for labels.
|
|
|
|
@item
|
|
Initialization of unions. If the initializer is zero, the warning is
|
|
omitted. This is done under the assumption that the zero initializer in
|
|
user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
|
|
initializer warnings and relies on default initialization to zero in the
|
|
traditional C case.
|
|
|
|
@item
|
|
Conversions by prototypes between fixed/floating point values and vice
|
|
versa. The absence of these prototypes when compiling with traditional
|
|
C would cause serious problems. This is a subset of the possible
|
|
conversion warnings, for the full set use @option{-Wconversion}.
|
|
|
|
@item
|
|
Use of ISO C style function definitions. This warning intentionally is
|
|
@emph{not} issued for prototype declarations or variadic functions
|
|
because these ISO C features will appear in your code when using
|
|
libiberty's traditional C compatibility macros, @code{PARAMS} and
|
|
@code{VPARAMS}. This warning is also bypassed for nested functions
|
|
because that feature is already a GCC extension and thus not relevant to
|
|
traditional C compatibility.
|
|
@end itemize
|
|
|
|
@item -Wdeclaration-after-statement @r{(C only)}
|
|
@opindex Wdeclaration-after-statement
|
|
Warn when a declaration is found after a statement in a block. This
|
|
construct, known from C++, was introduced with ISO C99 and is by default
|
|
allowed in GCC@. It is not supported by ISO C90 and was not supported by
|
|
GCC versions before GCC 3.0. @xref{Mixed Declarations}.
|
|
|
|
@item -Wundef
|
|
@opindex Wundef
|
|
Warn if an undefined identifier is evaluated in an @samp{#if} directive.
|
|
|
|
@item -Wno-endif-labels
|
|
@opindex Wno-endif-labels
|
|
@opindex Wendif-labels
|
|
Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
|
|
|
|
@item -Wshadow
|
|
@opindex Wshadow
|
|
Warn whenever a local variable shadows another local variable, parameter or
|
|
global variable or whenever a built-in function is shadowed.
|
|
|
|
@item -Wlarger-than-@var{len}
|
|
@opindex Wlarger-than
|
|
Warn whenever an object of larger than @var{len} bytes is defined.
|
|
|
|
@item -Wunsafe-loop-optimizations
|
|
@opindex Wunsafe-loop-optimizations
|
|
Warn if the loop cannot be optimized because the compiler could not
|
|
assume anything on the bounds of the loop indices. With
|
|
@option{-funsafe-loop-optimizations} warn if the compiler made
|
|
such assumptions.
|
|
|
|
@item -Wpointer-arith
|
|
@opindex Wpointer-arith
|
|
Warn about anything that depends on the ``size of'' a function type or
|
|
of @code{void}. GNU C assigns these types a size of 1, for
|
|
convenience in calculations with @code{void *} pointers and pointers
|
|
to functions.
|
|
|
|
@item -Wbad-function-cast @r{(C only)}
|
|
@opindex Wbad-function-cast
|
|
Warn whenever a function call is cast to a non-matching type.
|
|
For example, warn if @code{int malloc()} is cast to @code{anything *}.
|
|
|
|
@item -Wc++-compat
|
|
Warn about ISO C constructs that are outside of the common subset of
|
|
ISO C and ISO C++, e.g.@: request for implicit conversion from
|
|
@code{void *} to a pointer to non-@code{void} type.
|
|
|
|
@item -Wcast-qual
|
|
@opindex Wcast-qual
|
|
Warn whenever a pointer is cast so as to remove a type qualifier from
|
|
the target type. For example, warn if a @code{const char *} is cast
|
|
to an ordinary @code{char *}.
|
|
|
|
@item -Wcast-align
|
|
@opindex Wcast-align
|
|
Warn whenever a pointer is cast such that the required alignment of the
|
|
target is increased. For example, warn if a @code{char *} is cast to
|
|
an @code{int *} on machines where integers can only be accessed at
|
|
two- or four-byte boundaries.
|
|
|
|
@item -Wwrite-strings
|
|
@opindex Wwrite-strings
|
|
When compiling C, give string constants the type @code{const
|
|
char[@var{length}]} so that
|
|
copying the address of one into a non-@code{const} @code{char *}
|
|
pointer will get a warning; when compiling C++, warn about the
|
|
deprecated conversion from string literals to @code{char *}. This
|
|
warning, by default, is enabled for C++ programs.
|
|
These warnings will help you find at
|
|
compile time code that can try to write into a string constant, but
|
|
only if you have been very careful about using @code{const} in
|
|
declarations and prototypes. Otherwise, it will just be a nuisance;
|
|
this is why we did not make @option{-Wall} request these warnings.
|
|
|
|
@item -Wconversion
|
|
@opindex Wconversion
|
|
Warn if a prototype causes a type conversion that is different from what
|
|
would happen to the same argument in the absence of a prototype. This
|
|
includes conversions of fixed point to floating and vice versa, and
|
|
conversions changing the width or signedness of a fixed point argument
|
|
except when the same as the default promotion.
|
|
|
|
Also, warn if a negative integer constant expression is implicitly
|
|
converted to an unsigned type. For example, warn about the assignment
|
|
@code{x = -1} if @code{x} is unsigned. But do not warn about explicit
|
|
casts like @code{(unsigned) -1}.
|
|
|
|
@item -Wsign-compare
|
|
@opindex Wsign-compare
|
|
@cindex warning for comparison of signed and unsigned values
|
|
@cindex comparison of signed and unsigned values, warning
|
|
@cindex signed and unsigned values, comparison warning
|
|
Warn when a comparison between signed and unsigned values could produce
|
|
an incorrect result when the signed value is converted to unsigned.
|
|
This warning is also enabled by @option{-Wextra}; to get the other warnings
|
|
of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
|
|
|
|
@item -Waddress
|
|
@opindex Waddress
|
|
@opindex Wno-address
|
|
Warn about suspicious uses of memory addresses. These include using
|
|
the address of a function in a conditional expression, such as
|
|
@code{void func(void); if (func)}, and comparisons against the memory
|
|
address of a string literal, such as @code{if (x == "abc")}. Such
|
|
uses typically indicate a programmer error: the address of a function
|
|
always evaluates to true, so their use in a conditional usually
|
|
indicate that the programmer forgot the parentheses in a function
|
|
call; and comparisons against string literals result in unspecified
|
|
behavior and are not portable in C, so they usually indicate that the
|
|
programmer intended to use @code{strcmp}. This warning is enabled by
|
|
@option{-Wall}.
|
|
|
|
@item -Waggregate-return
|
|
@opindex Waggregate-return
|
|
Warn if any functions that return structures or unions are defined or
|
|
called. (In languages where you can return an array, this also elicits
|
|
a warning.)
|
|
|
|
@item -Wno-attributes
|
|
@opindex Wno-attributes
|
|
@opindex Wattributes
|
|
Do not warn if an unexpected @code{__attribute__} is used, such as
|
|
unrecognized attributes, function attributes applied to variables,
|
|
etc. This will not stop errors for incorrect use of supported
|
|
attributes.
|
|
|
|
@item -Wstrict-prototypes @r{(C only)}
|
|
@opindex Wstrict-prototypes
|
|
Warn if a function is declared or defined without specifying the
|
|
argument types. (An old-style function definition is permitted without
|
|
a warning if preceded by a declaration which specifies the argument
|
|
types.)
|
|
|
|
@item -Wold-style-definition @r{(C only)}
|
|
@opindex Wold-style-definition
|
|
Warn if an old-style function definition is used. A warning is given
|
|
even if there is a previous prototype.
|
|
|
|
@item -Wmissing-prototypes @r{(C only)}
|
|
@opindex Wmissing-prototypes
|
|
Warn if a global function is defined without a previous prototype
|
|
declaration. This warning is issued even if the definition itself
|
|
provides a prototype. The aim is to detect global functions that fail
|
|
to be declared in header files.
|
|
|
|
@item -Wmissing-declarations @r{(C only)}
|
|
@opindex Wmissing-declarations
|
|
Warn if a global function is defined without a previous declaration.
|
|
Do so even if the definition itself provides a prototype.
|
|
Use this option to detect global functions that are not declared in
|
|
header files.
|
|
|
|
@item -Wmissing-field-initializers
|
|
@opindex Wmissing-field-initializers
|
|
@opindex W
|
|
@opindex Wextra
|
|
Warn if a structure's initializer has some fields missing. For
|
|
example, the following code would cause such a warning, because
|
|
@code{x.h} is implicitly zero:
|
|
|
|
@smallexample
|
|
struct s @{ int f, g, h; @};
|
|
struct s x = @{ 3, 4 @};
|
|
@end smallexample
|
|
|
|
This option does not warn about designated initializers, so the following
|
|
modification would not trigger a warning:
|
|
|
|
@smallexample
|
|
struct s @{ int f, g, h; @};
|
|
struct s x = @{ .f = 3, .g = 4 @};
|
|
@end smallexample
|
|
|
|
This warning is included in @option{-Wextra}. To get other @option{-Wextra}
|
|
warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
|
|
|
|
@item -Wmissing-noreturn
|
|
@opindex Wmissing-noreturn
|
|
Warn about functions which might be candidates for attribute @code{noreturn}.
|
|
Note these are only possible candidates, not absolute ones. Care should
|
|
be taken to manually verify functions actually do not ever return before
|
|
adding the @code{noreturn} attribute, otherwise subtle code generation
|
|
bugs could be introduced. You will not get a warning for @code{main} in
|
|
hosted C environments.
|
|
|
|
@item -Wmissing-format-attribute
|
|
@opindex Wmissing-format-attribute
|
|
@opindex Wformat
|
|
Warn about function pointers which might be candidates for @code{format}
|
|
attributes. Note these are only possible candidates, not absolute ones.
|
|
GCC will guess that function pointers with @code{format} attributes that
|
|
are used in assignment, initialization, parameter passing or return
|
|
statements should have a corresponding @code{format} attribute in the
|
|
resulting type. I.e.@: the left-hand side of the assignment or
|
|
initialization, the type of the parameter variable, or the return type
|
|
of the containing function respectively should also have a @code{format}
|
|
attribute to avoid the warning.
|
|
|
|
GCC will also warn about function definitions which might be
|
|
candidates for @code{format} attributes. Again, these are only
|
|
possible candidates. GCC will guess that @code{format} attributes
|
|
might be appropriate for any function that calls a function like
|
|
@code{vprintf} or @code{vscanf}, but this might not always be the
|
|
case, and some functions for which @code{format} attributes are
|
|
appropriate may not be detected.
|
|
|
|
@item -Wno-multichar
|
|
@opindex Wno-multichar
|
|
@opindex Wmultichar
|
|
Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
|
|
Usually they indicate a typo in the user's code, as they have
|
|
implementation-defined values, and should not be used in portable code.
|
|
|
|
@item -Wnormalized=<none|id|nfc|nfkc>
|
|
@opindex Wnormalized
|
|
@cindex NFC
|
|
@cindex NFKC
|
|
@cindex character set, input normalization
|
|
In ISO C and ISO C++, two identifiers are different if they are
|
|
different sequences of characters. However, sometimes when characters
|
|
outside the basic ASCII character set are used, you can have two
|
|
different character sequences that look the same. To avoid confusion,
|
|
the ISO 10646 standard sets out some @dfn{normalization rules} which
|
|
when applied ensure that two sequences that look the same are turned into
|
|
the same sequence. GCC can warn you if you are using identifiers which
|
|
have not been normalized; this option controls that warning.
|
|
|
|
There are four levels of warning that GCC supports. The default is
|
|
@option{-Wnormalized=nfc}, which warns about any identifier which is
|
|
not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
|
|
recommended form for most uses.
|
|
|
|
Unfortunately, there are some characters which ISO C and ISO C++ allow
|
|
in identifiers that when turned into NFC aren't allowable as
|
|
identifiers. That is, there's no way to use these symbols in portable
|
|
ISO C or C++ and have all your identifiers in NFC.
|
|
@option{-Wnormalized=id} suppresses the warning for these characters.
|
|
It is hoped that future versions of the standards involved will correct
|
|
this, which is why this option is not the default.
|
|
|
|
You can switch the warning off for all characters by writing
|
|
@option{-Wnormalized=none}. You would only want to do this if you
|
|
were using some other normalization scheme (like ``D''), because
|
|
otherwise you can easily create bugs that are literally impossible to see.
|
|
|
|
Some characters in ISO 10646 have distinct meanings but look identical
|
|
in some fonts or display methodologies, especially once formatting has
|
|
been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
|
|
LETTER N'', will display just like a regular @code{n} which has been
|
|
placed in a superscript. ISO 10646 defines the @dfn{NFKC}
|
|
normalization scheme to convert all these into a standard form as
|
|
well, and GCC will warn if your code is not in NFKC if you use
|
|
@option{-Wnormalized=nfkc}. This warning is comparable to warning
|
|
about every identifier that contains the letter O because it might be
|
|
confused with the digit 0, and so is not the default, but may be
|
|
useful as a local coding convention if the programming environment is
|
|
unable to be fixed to display these characters distinctly.
|
|
|
|
@item -Wno-deprecated-declarations
|
|
@opindex Wno-deprecated-declarations
|
|
Do not warn about uses of functions (@pxref{Function Attributes}),
|
|
variables (@pxref{Variable Attributes}), and types (@pxref{Type
|
|
Attributes}) marked as deprecated by using the @code{deprecated}
|
|
attribute.
|
|
|
|
@item -Wno-overflow
|
|
@opindex Wno-overflow
|
|
Do not warn about compile-time overflow in constant expressions.
|
|
|
|
@item -Woverride-init
|
|
@opindex Woverride-init
|
|
@opindex W
|
|
@opindex Wextra
|
|
Warn if an initialized field without side effects is overridden when
|
|
using designated initializers (@pxref{Designated Inits, , Designated
|
|
Initializers}).
|
|
|
|
This warning is included in @option{-Wextra}. To get other
|
|
@option{-Wextra} warnings without this one, use @samp{-Wextra
|
|
-Wno-override-init}.
|
|
|
|
@item -Wpacked
|
|
@opindex Wpacked
|
|
Warn if a structure is given the packed attribute, but the packed
|
|
attribute has no effect on the layout or size of the structure.
|
|
Such structures may be mis-aligned for little benefit. For
|
|
instance, in this code, the variable @code{f.x} in @code{struct bar}
|
|
will be misaligned even though @code{struct bar} does not itself
|
|
have the packed attribute:
|
|
|
|
@smallexample
|
|
@group
|
|
struct foo @{
|
|
int x;
|
|
char a, b, c, d;
|
|
@} __attribute__((packed));
|
|
struct bar @{
|
|
char z;
|
|
struct foo f;
|
|
@};
|
|
@end group
|
|
@end smallexample
|
|
|
|
@item -Wpadded
|
|
@opindex Wpadded
|
|
Warn if padding is included in a structure, either to align an element
|
|
of the structure or to align the whole structure. Sometimes when this
|
|
happens it is possible to rearrange the fields of the structure to
|
|
reduce the padding and so make the structure smaller.
|
|
|
|
@item -Wredundant-decls
|
|
@opindex Wredundant-decls
|
|
Warn if anything is declared more than once in the same scope, even in
|
|
cases where multiple declaration is valid and changes nothing.
|
|
|
|
@item -Wnested-externs @r{(C only)}
|
|
@opindex Wnested-externs
|
|
Warn if an @code{extern} declaration is encountered within a function.
|
|
|
|
@item -Wunreachable-code
|
|
@opindex Wunreachable-code
|
|
Warn if the compiler detects that code will never be executed.
|
|
|
|
This option is intended to warn when the compiler detects that at
|
|
least a whole line of source code will never be executed, because
|
|
some condition is never satisfied or because it is after a
|
|
procedure that never returns.
|
|
|
|
It is possible for this option to produce a warning even though there
|
|
are circumstances under which part of the affected line can be executed,
|
|
so care should be taken when removing apparently-unreachable code.
|
|
|
|
For instance, when a function is inlined, a warning may mean that the
|
|
line is unreachable in only one inlined copy of the function.
|
|
|
|
This option is not made part of @option{-Wall} because in a debugging
|
|
version of a program there is often substantial code which checks
|
|
correct functioning of the program and is, hopefully, unreachable
|
|
because the program does work. Another common use of unreachable
|
|
code is to provide behavior which is selectable at compile-time.
|
|
|
|
@item -Winline
|
|
@opindex Winline
|
|
Warn if a function can not be inlined and it was declared as inline.
|
|
Even with this option, the compiler will not warn about failures to
|
|
inline functions declared in system headers.
|
|
|
|
The compiler uses a variety of heuristics to determine whether or not
|
|
to inline a function. For example, the compiler takes into account
|
|
the size of the function being inlined and the amount of inlining
|
|
that has already been done in the current function. Therefore,
|
|
seemingly insignificant changes in the source program can cause the
|
|
warnings produced by @option{-Winline} to appear or disappear.
|
|
|
|
@item -Wno-invalid-offsetof @r{(C++ only)}
|
|
@opindex Wno-invalid-offsetof
|
|
Suppress warnings from applying the @samp{offsetof} macro to a non-POD
|
|
type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
|
|
to a non-POD type is undefined. In existing C++ implementations,
|
|
however, @samp{offsetof} typically gives meaningful results even when
|
|
applied to certain kinds of non-POD types. (Such as a simple
|
|
@samp{struct} that fails to be a POD type only by virtue of having a
|
|
constructor.) This flag is for users who are aware that they are
|
|
writing nonportable code and who have deliberately chosen to ignore the
|
|
warning about it.
|
|
|
|
The restrictions on @samp{offsetof} may be relaxed in a future version
|
|
of the C++ standard.
|
|
|
|
@item -Wno-int-to-pointer-cast @r{(C only)}
|
|
@opindex Wno-int-to-pointer-cast
|
|
Suppress warnings from casts to pointer type of an integer of a
|
|
different size.
|
|
|
|
@item -Wno-pointer-to-int-cast @r{(C only)}
|
|
@opindex Wno-pointer-to-int-cast
|
|
Suppress warnings from casts from a pointer to an integer type of a
|
|
different size.
|
|
|
|
@item -Winvalid-pch
|
|
@opindex Winvalid-pch
|
|
Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
|
|
the search path but can't be used.
|
|
|
|
@item -Wlong-long
|
|
@opindex Wlong-long
|
|
@opindex Wno-long-long
|
|
Warn if @samp{long long} type is used. This is default. To inhibit
|
|
the warning messages, use @option{-Wno-long-long}. Flags
|
|
@option{-Wlong-long} and @option{-Wno-long-long} are taken into account
|
|
only when @option{-pedantic} flag is used.
|
|
|
|
@item -Wvariadic-macros
|
|
@opindex Wvariadic-macros
|
|
@opindex Wno-variadic-macros
|
|
Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
|
|
alternate syntax when in pedantic ISO C99 mode. This is default.
|
|
To inhibit the warning messages, use @option{-Wno-variadic-macros}.
|
|
|
|
@item -Wvolatile-register-var
|
|
@opindex Wvolatile-register-var
|
|
@opindex Wno-volatile-register-var
|
|
Warn if a register variable is declared volatile. The volatile
|
|
modifier does not inhibit all optimizations that may eliminate reads
|
|
and/or writes to register variables.
|
|
|
|
@item -Wdisabled-optimization
|
|
@opindex Wdisabled-optimization
|
|
Warn if a requested optimization pass is disabled. This warning does
|
|
not generally indicate that there is anything wrong with your code; it
|
|
merely indicates that GCC's optimizers were unable to handle the code
|
|
effectively. Often, the problem is that your code is too big or too
|
|
complex; GCC will refuse to optimize programs when the optimization
|
|
itself is likely to take inordinate amounts of time.
|
|
|
|
@item -Wpointer-sign
|
|
@opindex Wpointer-sign
|
|
@opindex Wno-pointer-sign
|
|
Warn for pointer argument passing or assignment with different signedness.
|
|
This option is only supported for C and Objective-C@. It is implied by
|
|
@option{-Wall} and by @option{-pedantic}, which can be disabled with
|
|
@option{-Wno-pointer-sign}.
|
|
|
|
@item -Werror
|
|
@opindex Werror
|
|
Make all warnings into errors.
|
|
|
|
@item -Werror=
|
|
@opindex Werror=
|
|
Make the specified warning into an errors. The specifier for a
|
|
warning is appended, for example @option{-Werror=switch} turns the
|
|
warnings controlled by @option{-Wswitch} into errors. This switch
|
|
takes a negative form, to be used to negate @option{-Werror} for
|
|
specific warnings, for example @option{-Wno-error=switch} makes
|
|
@option{-Wswitch} warnings not be errors, even when @option{-Werror}
|
|
is in effect. You can use the @option{-fdiagnostics-show-option}
|
|
option to have each controllable warning amended with the option which
|
|
controls it, to determine what to use with this option.
|
|
|
|
Note that specifying @option{-Werror=}@var{foo} automatically implies
|
|
@option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
|
|
imply anything.
|
|
|
|
@item -Wstack-protector
|
|
@opindex Wstack-protector
|
|
This option is only active when @option{-fstack-protector} is active. It
|
|
warns about functions that will not be protected against stack smashing.
|
|
|
|
@item -Woverlength-strings
|
|
@opindex Woverlength-strings
|
|
Warn about string constants which are longer than the ``minimum
|
|
maximum'' length specified in the C standard. Modern compilers
|
|
generally allow string constants which are much longer than the
|
|
standard's minimum limit, but very portable programs should avoid
|
|
using longer strings.
|
|
|
|
The limit applies @emph{after} string constant concatenation, and does
|
|
not count the trailing NUL@. In C89, the limit was 509 characters; in
|
|
C99, it was raised to 4095. C++98 does not specify a normative
|
|
minimum maximum, so we do not diagnose overlength strings in C++@.
|
|
|
|
This option is implied by @option{-pedantic}, and can be disabled with
|
|
@option{-Wno-overlength-strings}.
|
|
@end table
|
|
|
|
@node Debugging Options
|
|
@section Options for Debugging Your Program or GCC
|
|
@cindex options, debugging
|
|
@cindex debugging information options
|
|
|
|
GCC has various special options that are used for debugging
|
|
either your program or GCC:
|
|
|
|
@table @gcctabopt
|
|
@item -g
|
|
@opindex g
|
|
Produce debugging information in the operating system's native format
|
|
(stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
|
|
information.
|
|
|
|
On most systems that use stabs format, @option{-g} enables use of extra
|
|
debugging information that only GDB can use; this extra information
|
|
makes debugging work better in GDB but will probably make other debuggers
|
|
crash or
|
|
refuse to read the program. If you want to control for certain whether
|
|
to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
|
|
@option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
|
|
|
|
GCC allows you to use @option{-g} with
|
|
@option{-O}. The shortcuts taken by optimized code may occasionally
|
|
produce surprising results: some variables you declared may not exist
|
|
at all; flow of control may briefly move where you did not expect it;
|
|
some statements may not be executed because they compute constant
|
|
results or their values were already at hand; some statements may
|
|
execute in different places because they were moved out of loops.
|
|
|
|
Nevertheless it proves possible to debug optimized output. This makes
|
|
it reasonable to use the optimizer for programs that might have bugs.
|
|
|
|
The following options are useful when GCC is generated with the
|
|
capability for more than one debugging format.
|
|
|
|
@item -ggdb
|
|
@opindex ggdb
|
|
Produce debugging information for use by GDB@. This means to use the
|
|
most expressive format available (DWARF 2, stabs, or the native format
|
|
if neither of those are supported), including GDB extensions if at all
|
|
possible.
|
|
|
|
@item -gstabs
|
|
@opindex gstabs
|
|
Produce debugging information in stabs format (if that is supported),
|
|
without GDB extensions. This is the format used by DBX on most BSD
|
|
systems. On MIPS, Alpha and System V Release 4 systems this option
|
|
produces stabs debugging output which is not understood by DBX or SDB@.
|
|
On System V Release 4 systems this option requires the GNU assembler.
|
|
|
|
@item -feliminate-unused-debug-symbols
|
|
@opindex feliminate-unused-debug-symbols
|
|
Produce debugging information in stabs format (if that is supported),
|
|
for only symbols that are actually used.
|
|
|
|
@item -femit-class-debug-always
|
|
Instead of emitting debugging information for a C++ class in only one
|
|
object file, emit it in all object files using the class. This option
|
|
should be used only with debuggers that are unable to handle the way GCC
|
|
normally emits debugging information for classes because using this
|
|
option will increase the size of debugging information by as much as a
|
|
factor of two.
|
|
|
|
@item -gstabs+
|
|
@opindex gstabs+
|
|
Produce debugging information in stabs format (if that is supported),
|
|
using GNU extensions understood only by the GNU debugger (GDB)@. The
|
|
use of these extensions is likely to make other debuggers crash or
|
|
refuse to read the program.
|
|
|
|
@item -gcoff
|
|
@opindex gcoff
|
|
Produce debugging information in COFF format (if that is supported).
|
|
This is the format used by SDB on most System V systems prior to
|
|
System V Release 4.
|
|
|
|
@item -gxcoff
|
|
@opindex gxcoff
|
|
Produce debugging information in XCOFF format (if that is supported).
|
|
This is the format used by the DBX debugger on IBM RS/6000 systems.
|
|
|
|
@item -gxcoff+
|
|
@opindex gxcoff+
|
|
Produce debugging information in XCOFF format (if that is supported),
|
|
using GNU extensions understood only by the GNU debugger (GDB)@. The
|
|
use of these extensions is likely to make other debuggers crash or
|
|
refuse to read the program, and may cause assemblers other than the GNU
|
|
assembler (GAS) to fail with an error.
|
|
|
|
@item -gdwarf-2
|
|
@opindex gdwarf-2
|
|
Produce debugging information in DWARF version 2 format (if that is
|
|
supported). This is the format used by DBX on IRIX 6. With this
|
|
option, GCC uses features of DWARF version 3 when they are useful;
|
|
version 3 is upward compatible with version 2, but may still cause
|
|
problems for older debuggers.
|
|
|
|
@item -gvms
|
|
@opindex gvms
|
|
Produce debugging information in VMS debug format (if that is
|
|
supported). This is the format used by DEBUG on VMS systems.
|
|
|
|
@item -g@var{level}
|
|
@itemx -ggdb@var{level}
|
|
@itemx -gstabs@var{level}
|
|
@itemx -gcoff@var{level}
|
|
@itemx -gxcoff@var{level}
|
|
@itemx -gvms@var{level}
|
|
Request debugging information and also use @var{level} to specify how
|
|
much information. The default level is 2.
|
|
|
|
Level 1 produces minimal information, enough for making backtraces in
|
|
parts of the program that you don't plan to debug. This includes
|
|
descriptions of functions and external variables, but no information
|
|
about local variables and no line numbers.
|
|
|
|
Level 3 includes extra information, such as all the macro definitions
|
|
present in the program. Some debuggers support macro expansion when
|
|
you use @option{-g3}.
|
|
|
|
@option{-gdwarf-2} does not accept a concatenated debug level, because
|
|
GCC used to support an option @option{-gdwarf} that meant to generate
|
|
debug information in version 1 of the DWARF format (which is very
|
|
different from version 2), and it would have been too confusing. That
|
|
debug format is long obsolete, but the option cannot be changed now.
|
|
Instead use an additional @option{-g@var{level}} option to change the
|
|
debug level for DWARF2.
|
|
|
|
@item -feliminate-dwarf2-dups
|
|
@opindex feliminate-dwarf2-dups
|
|
Compress DWARF2 debugging information by eliminating duplicated
|
|
information about each symbol. This option only makes sense when
|
|
generating DWARF2 debugging information with @option{-gdwarf-2}.
|
|
|
|
@cindex @command{prof}
|
|
@item -p
|
|
@opindex p
|
|
Generate extra code to write profile information suitable for the
|
|
analysis program @command{prof}. You must use this option when compiling
|
|
the source files you want data about, and you must also use it when
|
|
linking.
|
|
|
|
@cindex @command{gprof}
|
|
@item -pg
|
|
@opindex pg
|
|
Generate extra code to write profile information suitable for the
|
|
analysis program @command{gprof}. You must use this option when compiling
|
|
the source files you want data about, and you must also use it when
|
|
linking.
|
|
|
|
@item -Q
|
|
@opindex Q
|
|
Makes the compiler print out each function name as it is compiled, and
|
|
print some statistics about each pass when it finishes.
|
|
|
|
@item -ftime-report
|
|
@opindex ftime-report
|
|
Makes the compiler print some statistics about the time consumed by each
|
|
pass when it finishes.
|
|
|
|
@item -fmem-report
|
|
@opindex fmem-report
|
|
Makes the compiler print some statistics about permanent memory
|
|
allocation when it finishes.
|
|
|
|
@item -fprofile-arcs
|
|
@opindex fprofile-arcs
|
|
Add code so that program flow @dfn{arcs} are instrumented. During
|
|
execution the program records how many times each branch and call is
|
|
executed and how many times it is taken or returns. When the compiled
|
|
program exits it saves this data to a file called
|
|
@file{@var{auxname}.gcda} for each source file. The data may be used for
|
|
profile-directed optimizations (@option{-fbranch-probabilities}), or for
|
|
test coverage analysis (@option{-ftest-coverage}). Each object file's
|
|
@var{auxname} is generated from the name of the output file, if
|
|
explicitly specified and it is not the final executable, otherwise it is
|
|
the basename of the source file. In both cases any suffix is removed
|
|
(e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
|
|
@file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
|
|
@xref{Cross-profiling}.
|
|
|
|
@cindex @command{gcov}
|
|
@item --coverage
|
|
@opindex coverage
|
|
|
|
This option is used to compile and link code instrumented for coverage
|
|
analysis. The option is a synonym for @option{-fprofile-arcs}
|
|
@option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
|
|
linking). See the documentation for those options for more details.
|
|
|
|
@itemize
|
|
|
|
@item
|
|
Compile the source files with @option{-fprofile-arcs} plus optimization
|
|
and code generation options. For test coverage analysis, use the
|
|
additional @option{-ftest-coverage} option. You do not need to profile
|
|
every source file in a program.
|
|
|
|
@item
|
|
Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
|
|
(the latter implies the former).
|
|
|
|
@item
|
|
Run the program on a representative workload to generate the arc profile
|
|
information. This may be repeated any number of times. You can run
|
|
concurrent instances of your program, and provided that the file system
|
|
supports locking, the data files will be correctly updated. Also
|
|
@code{fork} calls are detected and correctly handled (double counting
|
|
will not happen).
|
|
|
|
@item
|
|
For profile-directed optimizations, compile the source files again with
|
|
the same optimization and code generation options plus
|
|
@option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
|
|
Control Optimization}).
|
|
|
|
@item
|
|
For test coverage analysis, use @command{gcov} to produce human readable
|
|
information from the @file{.gcno} and @file{.gcda} files. Refer to the
|
|
@command{gcov} documentation for further information.
|
|
|
|
@end itemize
|
|
|
|
With @option{-fprofile-arcs}, for each function of your program GCC
|
|
creates a program flow graph, then finds a spanning tree for the graph.
|
|
Only arcs that are not on the spanning tree have to be instrumented: the
|
|
compiler adds code to count the number of times that these arcs are
|
|
executed. When an arc is the only exit or only entrance to a block, the
|
|
instrumentation code can be added to the block; otherwise, a new basic
|
|
block must be created to hold the instrumentation code.
|
|
|
|
@need 2000
|
|
@item -ftest-coverage
|
|
@opindex ftest-coverage
|
|
Produce a notes file that the @command{gcov} code-coverage utility
|
|
(@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
|
|
show program coverage. Each source file's note file is called
|
|
@file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
|
|
above for a description of @var{auxname} and instructions on how to
|
|
generate test coverage data. Coverage data will match the source files
|
|
more closely, if you do not optimize.
|
|
|
|
@item -d@var{letters}
|
|
@item -fdump-rtl-@var{pass}
|
|
@opindex d
|
|
Says to make debugging dumps during compilation at times specified by
|
|
@var{letters}. This is used for debugging the RTL-based passes of the
|
|
compiler. The file names for most of the dumps are made by appending a
|
|
pass number and a word to the @var{dumpname}. @var{dumpname} is generated
|
|
from the name of the output file, if explicitly specified and it is not
|
|
an executable, otherwise it is the basename of the source file.
|
|
|
|
Most debug dumps can be enabled either passing a letter to the @option{-d}
|
|
option, or with a long @option{-fdump-rtl} switch; here are the possible
|
|
letters for use in @var{letters} and @var{pass}, and their meanings:
|
|
|
|
@table @gcctabopt
|
|
@item -dA
|
|
@opindex dA
|
|
Annotate the assembler output with miscellaneous debugging information.
|
|
|
|
@item -dB
|
|
@itemx -fdump-rtl-bbro
|
|
@opindex dB
|
|
@opindex fdump-rtl-bbro
|
|
Dump after block reordering, to @file{@var{file}.148r.bbro}.
|
|
|
|
@item -dc
|
|
@itemx -fdump-rtl-combine
|
|
@opindex dc
|
|
@opindex fdump-rtl-combine
|
|
Dump after instruction combination, to the file @file{@var{file}.129r.combine}.
|
|
|
|
@item -dC
|
|
@itemx -fdump-rtl-ce1
|
|
@itemx -fdump-rtl-ce2
|
|
@opindex dC
|
|
@opindex fdump-rtl-ce1
|
|
@opindex fdump-rtl-ce2
|
|
@option{-dC} and @option{-fdump-rtl-ce1} enable dumping after the
|
|
first if conversion, to the file @file{@var{file}.117r.ce1}. @option{-dC}
|
|
and @option{-fdump-rtl-ce2} enable dumping after the second if
|
|
conversion, to the file @file{@var{file}.130r.ce2}.
|
|
|
|
@item -dd
|
|
@itemx -fdump-rtl-btl
|
|
@itemx -fdump-rtl-dbr
|
|
@opindex dd
|
|
@opindex fdump-rtl-btl
|
|
@opindex fdump-rtl-dbr
|
|
@option{-dd} and @option{-fdump-rtl-btl} enable dumping after branch
|
|
target load optimization, to @file{@var{file}.31.btl}. @option{-dd}
|
|
and @option{-fdump-rtl-dbr} enable dumping after delayed branch
|
|
scheduling, to @file{@var{file}.36.dbr}.
|
|
|
|
@item -dD
|
|
@opindex dD
|
|
Dump all macro definitions, at the end of preprocessing, in addition to
|
|
normal output.
|
|
|
|
@item -dE
|
|
@itemx -fdump-rtl-ce3
|
|
@opindex dE
|
|
@opindex fdump-rtl-ce3
|
|
Dump after the third if conversion, to @file{@var{file}.146r.ce3}.
|
|
|
|
@item -df
|
|
@itemx -fdump-rtl-cfg
|
|
@itemx -fdump-rtl-life
|
|
@opindex df
|
|
@opindex fdump-rtl-cfg
|
|
@opindex fdump-rtl-life
|
|
@option{-df} and @option{-fdump-rtl-cfg} enable dumping after control
|
|
and data flow analysis, to @file{@var{file}.116r.cfg}. @option{-df}
|
|
and @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
|
|
to @file{@var{file}.128r.life1} and @file{@var{file}.135r.life2}.
|
|
|
|
@item -dg
|
|
@itemx -fdump-rtl-greg
|
|
@opindex dg
|
|
@opindex fdump-rtl-greg
|
|
Dump after global register allocation, to @file{@var{file}.139r.greg}.
|
|
|
|
@item -dG
|
|
@itemx -fdump-rtl-gcse
|
|
@itemx -fdump-rtl-bypass
|
|
@opindex dG
|
|
@opindex fdump-rtl-gcse
|
|
@opindex fdump-rtl-bypass
|
|
@option{-dG} and @option{-fdump-rtl-gcse} enable dumping after GCSE, to
|
|
@file{@var{file}.114r.gcse}. @option{-dG} and @option{-fdump-rtl-bypass}
|
|
enable dumping after jump bypassing and control flow optimizations, to
|
|
@file{@var{file}.115r.bypass}.
|
|
|
|
@item -dh
|
|
@itemx -fdump-rtl-eh
|
|
@opindex dh
|
|
@opindex fdump-rtl-eh
|
|
Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
|
|
|
|
@item -di
|
|
@itemx -fdump-rtl-sibling
|
|
@opindex di
|
|
@opindex fdump-rtl-sibling
|
|
Dump after sibling call optimizations, to @file{@var{file}.106r.sibling}.
|
|
|
|
@item -dj
|
|
@itemx -fdump-rtl-jump
|
|
@opindex dj
|
|
@opindex fdump-rtl-jump
|
|
Dump after the first jump optimization, to @file{@var{file}.112r.jump}.
|
|
|
|
@item -dk
|
|
@itemx -fdump-rtl-stack
|
|
@opindex dk
|
|
@opindex fdump-rtl-stack
|
|
Dump after conversion from registers to stack, to @file{@var{file}.152r.stack}.
|
|
|
|
@item -dl
|
|
@itemx -fdump-rtl-lreg
|
|
@opindex dl
|
|
@opindex fdump-rtl-lreg
|
|
Dump after local register allocation, to @file{@var{file}.138r.lreg}.
|
|
|
|
@item -dL
|
|
@itemx -fdump-rtl-loop2
|
|
@opindex dL
|
|
@opindex fdump-rtl-loop2
|
|
@option{-dL} and @option{-fdump-rtl-loop2} enable dumping after the
|
|
loop optimization pass, to @file{@var{file}.119r.loop2},
|
|
@file{@var{file}.120r.loop2_init},
|
|
@file{@var{file}.121r.loop2_invariant}, and
|
|
@file{@var{file}.125r.loop2_done}.
|
|
|
|
@item -dm
|
|
@itemx -fdump-rtl-sms
|
|
@opindex dm
|
|
@opindex fdump-rtl-sms
|
|
Dump after modulo scheduling, to @file{@var{file}.136r.sms}.
|
|
|
|
@item -dM
|
|
@itemx -fdump-rtl-mach
|
|
@opindex dM
|
|
@opindex fdump-rtl-mach
|
|
Dump after performing the machine dependent reorganization pass, to
|
|
@file{@var{file}.155r.mach}.
|
|
|
|
@item -dn
|
|
@itemx -fdump-rtl-rnreg
|
|
@opindex dn
|
|
@opindex fdump-rtl-rnreg
|
|
Dump after register renumbering, to @file{@var{file}.147r.rnreg}.
|
|
|
|
@item -dN
|
|
@itemx -fdump-rtl-regmove
|
|
@opindex dN
|
|
@opindex fdump-rtl-regmove
|
|
Dump after the register move pass, to @file{@var{file}.132r.regmove}.
|
|
|
|
@item -do
|
|
@itemx -fdump-rtl-postreload
|
|
@opindex do
|
|
@opindex fdump-rtl-postreload
|
|
Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
|
|
|
|
@item -dr
|
|
@itemx -fdump-rtl-expand
|
|
@opindex dr
|
|
@opindex fdump-rtl-expand
|
|
Dump after RTL generation, to @file{@var{file}.104r.expand}.
|
|
|
|
@item -dR
|
|
@itemx -fdump-rtl-sched2
|
|
@opindex dR
|
|
@opindex fdump-rtl-sched2
|
|
Dump after the second scheduling pass, to @file{@var{file}.150r.sched2}.
|
|
|
|
@item -ds
|
|
@itemx -fdump-rtl-cse
|
|
@opindex ds
|
|
@opindex fdump-rtl-cse
|
|
Dump after CSE (including the jump optimization that sometimes follows
|
|
CSE), to @file{@var{file}.113r.cse}.
|
|
|
|
@item -dS
|
|
@itemx -fdump-rtl-sched
|
|
@opindex dS
|
|
@opindex fdump-rtl-sched
|
|
Dump after the first scheduling pass, to @file{@var{file}.21.sched}.
|
|
|
|
@item -dt
|
|
@itemx -fdump-rtl-cse2
|
|
@opindex dt
|
|
@opindex fdump-rtl-cse2
|
|
Dump after the second CSE pass (including the jump optimization that
|
|
sometimes follows CSE), to @file{@var{file}.127r.cse2}.
|
|
|
|
@item -dT
|
|
@itemx -fdump-rtl-tracer
|
|
@opindex dT
|
|
@opindex fdump-rtl-tracer
|
|
Dump after running tracer, to @file{@var{file}.118r.tracer}.
|
|
|
|
@item -dV
|
|
@itemx -fdump-rtl-vpt
|
|
@itemx -fdump-rtl-vartrack
|
|
@opindex dV
|
|
@opindex fdump-rtl-vpt
|
|
@opindex fdump-rtl-vartrack
|
|
@option{-dV} and @option{-fdump-rtl-vpt} enable dumping after the value
|
|
profile transformations, to @file{@var{file}.10.vpt}. @option{-dV}
|
|
and @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
|
|
to @file{@var{file}.154r.vartrack}.
|
|
|
|
@item -dw
|
|
@itemx -fdump-rtl-flow2
|
|
@opindex dw
|
|
@opindex fdump-rtl-flow2
|
|
Dump after the second flow pass, to @file{@var{file}.142r.flow2}.
|
|
|
|
@item -dz
|
|
@itemx -fdump-rtl-peephole2
|
|
@opindex dz
|
|
@opindex fdump-rtl-peephole2
|
|
Dump after the peephole pass, to @file{@var{file}.145r.peephole2}.
|
|
|
|
@item -dZ
|
|
@itemx -fdump-rtl-web
|
|
@opindex dZ
|
|
@opindex fdump-rtl-web
|
|
Dump after live range splitting, to @file{@var{file}.126r.web}.
|
|
|
|
@item -da
|
|
@itemx -fdump-rtl-all
|
|
@opindex da
|
|
@opindex fdump-rtl-all
|
|
Produce all the dumps listed above.
|
|
|
|
@item -dH
|
|
@opindex dH
|
|
Produce a core dump whenever an error occurs.
|
|
|
|
@item -dm
|
|
@opindex dm
|
|
Print statistics on memory usage, at the end of the run, to
|
|
standard error.
|
|
|
|
@item -dp
|
|
@opindex dp
|
|
Annotate the assembler output with a comment indicating which
|
|
pattern and alternative was used. The length of each instruction is
|
|
also printed.
|
|
|
|
@item -dP
|
|
@opindex dP
|
|
Dump the RTL in the assembler output as a comment before each instruction.
|
|
Also turns on @option{-dp} annotation.
|
|
|
|
@item -dv
|
|
@opindex dv
|
|
For each of the other indicated dump files (either with @option{-d} or
|
|
@option{-fdump-rtl-@var{pass}}), dump a representation of the control flow
|
|
graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
|
|
|
|
@item -dx
|
|
@opindex dx
|
|
Just generate RTL for a function instead of compiling it. Usually used
|
|
with @samp{r} (@option{-fdump-rtl-expand}).
|
|
|
|
@item -dy
|
|
@opindex dy
|
|
Dump debugging information during parsing, to standard error.
|
|
@end table
|
|
|
|
@item -fdump-noaddr
|
|
@opindex fdump-noaddr
|
|
When doing debugging dumps (see @option{-d} option above), suppress
|
|
address output. This makes it more feasible to use diff on debugging
|
|
dumps for compiler invocations with different compiler binaries and/or
|
|
different text / bss / data / heap / stack / dso start locations.
|
|
|
|
@item -fdump-unnumbered
|
|
@opindex fdump-unnumbered
|
|
When doing debugging dumps (see @option{-d} option above), suppress instruction
|
|
numbers, line number note and address output. This makes it more feasible to
|
|
use diff on debugging dumps for compiler invocations with different
|
|
options, in particular with and without @option{-g}.
|
|
|
|
@item -fdump-translation-unit @r{(C++ only)}
|
|
@itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
|
|
@opindex fdump-translation-unit
|
|
Dump a representation of the tree structure for the entire translation
|
|
unit to a file. The file name is made by appending @file{.tu} to the
|
|
source file name. If the @samp{-@var{options}} form is used, @var{options}
|
|
controls the details of the dump as described for the
|
|
@option{-fdump-tree} options.
|
|
|
|
@item -fdump-class-hierarchy @r{(C++ only)}
|
|
@itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
|
|
@opindex fdump-class-hierarchy
|
|
Dump a representation of each class's hierarchy and virtual function
|
|
table layout to a file. The file name is made by appending @file{.class}
|
|
to the source file name. If the @samp{-@var{options}} form is used,
|
|
@var{options} controls the details of the dump as described for the
|
|
@option{-fdump-tree} options.
|
|
|
|
@item -fdump-ipa-@var{switch}
|
|
@opindex fdump-ipa
|
|
Control the dumping at various stages of inter-procedural analysis
|
|
language tree to a file. The file name is generated by appending a switch
|
|
specific suffix to the source file name. The following dumps are possible:
|
|
|
|
@table @samp
|
|
@item all
|
|
Enables all inter-procedural analysis dumps; currently the only produced
|
|
dump is the @samp{cgraph} dump.
|
|
|
|
@item cgraph
|
|
Dumps information about call-graph optimization, unused function removal,
|
|
and inlining decisions.
|
|
@end table
|
|
|
|
@item -fdump-tree-@var{switch}
|
|
@itemx -fdump-tree-@var{switch}-@var{options}
|
|
@opindex fdump-tree
|
|
Control the dumping at various stages of processing the intermediate
|
|
language tree to a file. The file name is generated by appending a switch
|
|
specific suffix to the source file name. If the @samp{-@var{options}}
|
|
form is used, @var{options} is a list of @samp{-} separated options that
|
|
control the details of the dump. Not all options are applicable to all
|
|
dumps, those which are not meaningful will be ignored. The following
|
|
options are available
|
|
|
|
@table @samp
|
|
@item address
|
|
Print the address of each node. Usually this is not meaningful as it
|
|
changes according to the environment and source file. Its primary use
|
|
is for tying up a dump file with a debug environment.
|
|
@item slim
|
|
Inhibit dumping of members of a scope or body of a function merely
|
|
because that scope has been reached. Only dump such items when they
|
|
are directly reachable by some other path. When dumping pretty-printed
|
|
trees, this option inhibits dumping the bodies of control structures.
|
|
@item raw
|
|
Print a raw representation of the tree. By default, trees are
|
|
pretty-printed into a C-like representation.
|
|
@item details
|
|
Enable more detailed dumps (not honored by every dump option).
|
|
@item stats
|
|
Enable dumping various statistics about the pass (not honored by every dump
|
|
option).
|
|
@item blocks
|
|
Enable showing basic block boundaries (disabled in raw dumps).
|
|
@item vops
|
|
Enable showing virtual operands for every statement.
|
|
@item lineno
|
|
Enable showing line numbers for statements.
|
|
@item uid
|
|
Enable showing the unique ID (@code{DECL_UID}) for each variable.
|
|
@item all
|
|
Turn on all options, except @option{raw}, @option{slim} and @option{lineno}.
|
|
@end table
|
|
|
|
The following tree dumps are possible:
|
|
@table @samp
|
|
|
|
@item original
|
|
Dump before any tree based optimization, to @file{@var{file}.original}.
|
|
|
|
@item optimized
|
|
Dump after all tree based optimization, to @file{@var{file}.optimized}.
|
|
|
|
@item inlined
|
|
Dump after function inlining, to @file{@var{file}.inlined}.
|
|
|
|
@item gimple
|
|
@opindex fdump-tree-gimple
|
|
Dump each function before and after the gimplification pass to a file. The
|
|
file name is made by appending @file{.gimple} to the source file name.
|
|
|
|
@item cfg
|
|
@opindex fdump-tree-cfg
|
|
Dump the control flow graph of each function to a file. The file name is
|
|
made by appending @file{.cfg} to the source file name.
|
|
|
|
@item vcg
|
|
@opindex fdump-tree-vcg
|
|
Dump the control flow graph of each function to a file in VCG format. The
|
|
file name is made by appending @file{.vcg} to the source file name. Note
|
|
that if the file contains more than one function, the generated file cannot
|
|
be used directly by VCG@. You will need to cut and paste each function's
|
|
graph into its own separate file first.
|
|
|
|
@item ch
|
|
@opindex fdump-tree-ch
|
|
Dump each function after copying loop headers. The file name is made by
|
|
appending @file{.ch} to the source file name.
|
|
|
|
@item ssa
|
|
@opindex fdump-tree-ssa
|
|
Dump SSA related information to a file. The file name is made by appending
|
|
@file{.ssa} to the source file name.
|
|
|
|
@item salias
|
|
@opindex fdump-tree-salias
|
|
Dump structure aliasing variable information to a file. This file name
|
|
is made by appending @file{.salias} to the source file name.
|
|
|
|
@item alias
|
|
@opindex fdump-tree-alias
|
|
Dump aliasing information for each function. The file name is made by
|
|
appending @file{.alias} to the source file name.
|
|
|
|
@item ccp
|
|
@opindex fdump-tree-ccp
|
|
Dump each function after CCP@. The file name is made by appending
|
|
@file{.ccp} to the source file name.
|
|
|
|
@item storeccp
|
|
@opindex fdump-tree-storeccp
|
|
Dump each function after STORE-CCP. The file name is made by appending
|
|
@file{.storeccp} to the source file name.
|
|
|
|
@item pre
|
|
@opindex fdump-tree-pre
|
|
Dump trees after partial redundancy elimination. The file name is made
|
|
by appending @file{.pre} to the source file name.
|
|
|
|
@item fre
|
|
@opindex fdump-tree-fre
|
|
Dump trees after full redundancy elimination. The file name is made
|
|
by appending @file{.fre} to the source file name.
|
|
|
|
@item copyprop
|
|
@opindex fdump-tree-copyprop
|
|
Dump trees after copy propagation. The file name is made
|
|
by appending @file{.copyprop} to the source file name.
|
|
|
|
@item store_copyprop
|
|
@opindex fdump-tree-store_copyprop
|
|
Dump trees after store copy-propagation. The file name is made
|
|
by appending @file{.store_copyprop} to the source file name.
|
|
|
|
@item dce
|
|
@opindex fdump-tree-dce
|
|
Dump each function after dead code elimination. The file name is made by
|
|
appending @file{.dce} to the source file name.
|
|
|
|
@item mudflap
|
|
@opindex fdump-tree-mudflap
|
|
Dump each function after adding mudflap instrumentation. The file name is
|
|
made by appending @file{.mudflap} to the source file name.
|
|
|
|
@item sra
|
|
@opindex fdump-tree-sra
|
|
Dump each function after performing scalar replacement of aggregates. The
|
|
file name is made by appending @file{.sra} to the source file name.
|
|
|
|
@item sink
|
|
@opindex fdump-tree-sink
|
|
Dump each function after performing code sinking. The file name is made
|
|
by appending @file{.sink} to the source file name.
|
|
|
|
@item dom
|
|
@opindex fdump-tree-dom
|
|
Dump each function after applying dominator tree optimizations. The file
|
|
name is made by appending @file{.dom} to the source file name.
|
|
|
|
@item dse
|
|
@opindex fdump-tree-dse
|
|
Dump each function after applying dead store elimination. The file
|
|
name is made by appending @file{.dse} to the source file name.
|
|
|
|
@item phiopt
|
|
@opindex fdump-tree-phiopt
|
|
Dump each function after optimizing PHI nodes into straightline code. The file
|
|
name is made by appending @file{.phiopt} to the source file name.
|
|
|
|
@item forwprop
|
|
@opindex fdump-tree-forwprop
|
|
Dump each function after forward propagating single use variables. The file
|
|
name is made by appending @file{.forwprop} to the source file name.
|
|
|
|
@item copyrename
|
|
@opindex fdump-tree-copyrename
|
|
Dump each function after applying the copy rename optimization. The file
|
|
name is made by appending @file{.copyrename} to the source file name.
|
|
|
|
@item nrv
|
|
@opindex fdump-tree-nrv
|
|
Dump each function after applying the named return value optimization on
|
|
generic trees. The file name is made by appending @file{.nrv} to the source
|
|
file name.
|
|
|
|
@item vect
|
|
@opindex fdump-tree-vect
|
|
Dump each function after applying vectorization of loops. The file name is
|
|
made by appending @file{.vect} to the source file name.
|
|
|
|
@item vrp
|
|
@opindex fdump-tree-vrp
|
|
Dump each function after Value Range Propagation (VRP). The file name
|
|
is made by appending @file{.vrp} to the source file name.
|
|
|
|
@item all
|
|
@opindex fdump-tree-all
|
|
Enable all the available tree dumps with the flags provided in this option.
|
|
@end table
|
|
|
|
@item -ftree-vectorizer-verbose=@var{n}
|
|
@opindex ftree-vectorizer-verbose
|
|
This option controls the amount of debugging output the vectorizer prints.
|
|
This information is written to standard error, unless
|
|
@option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified,
|
|
in which case it is output to the usual dump listing file, @file{.vect}.
|
|
For @var{n}=0 no diagnostic information is reported.
|
|
If @var{n}=1 the vectorizer reports each loop that got vectorized,
|
|
and the total number of loops that got vectorized.
|
|
If @var{n}=2 the vectorizer also reports non-vectorized loops that passed
|
|
the first analysis phase (vect_analyze_loop_form) - i.e. countable,
|
|
inner-most, single-bb, single-entry/exit loops. This is the same verbosity
|
|
level that @option{-fdump-tree-vect-stats} uses.
|
|
Higher verbosity levels mean either more information dumped for each
|
|
reported loop, or same amount of information reported for more loops:
|
|
If @var{n}=3, alignment related information is added to the reports.
|
|
If @var{n}=4, data-references related information (e.g. memory dependences,
|
|
memory access-patterns) is added to the reports.
|
|
If @var{n}=5, the vectorizer reports also non-vectorized inner-most loops
|
|
that did not pass the first analysis phase (i.e. may not be countable, or
|
|
may have complicated control-flow).
|
|
If @var{n}=6, the vectorizer reports also non-vectorized nested loops.
|
|
For @var{n}=7, all the information the vectorizer generates during its
|
|
analysis and transformation is reported. This is the same verbosity level
|
|
that @option{-fdump-tree-vect-details} uses.
|
|
|
|
@item -frandom-seed=@var{string}
|
|
@opindex frandom-string
|
|
This option provides a seed that GCC uses when it would otherwise use
|
|
random numbers. It is used to generate certain symbol names
|
|
that have to be different in every compiled file. It is also used to
|
|
place unique stamps in coverage data files and the object files that
|
|
produce them. You can use the @option{-frandom-seed} option to produce
|
|
reproducibly identical object files.
|
|
|
|
The @var{string} should be different for every file you compile.
|
|
|
|
@item -fsched-verbose=@var{n}
|
|
@opindex fsched-verbose
|
|
On targets that use instruction scheduling, this option controls the
|
|
amount of debugging output the scheduler prints. This information is
|
|
written to standard error, unless @option{-dS} or @option{-dR} is
|
|
specified, in which case it is output to the usual dump
|
|
listing file, @file{.sched} or @file{.sched2} respectively. However
|
|
for @var{n} greater than nine, the output is always printed to standard
|
|
error.
|
|
|
|
For @var{n} greater than zero, @option{-fsched-verbose} outputs the
|
|
same information as @option{-dRS}. For @var{n} greater than one, it
|
|
also output basic block probabilities, detailed ready list information
|
|
and unit/insn info. For @var{n} greater than two, it includes RTL
|
|
at abort point, control-flow and regions info. And for @var{n} over
|
|
four, @option{-fsched-verbose} also includes dependence info.
|
|
|
|
@item -save-temps
|
|
@opindex save-temps
|
|
Store the usual ``temporary'' intermediate files permanently; place them
|
|
in the current directory and name them based on the source file. Thus,
|
|
compiling @file{foo.c} with @samp{-c -save-temps} would produce files
|
|
@file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
|
|
preprocessed @file{foo.i} output file even though the compiler now
|
|
normally uses an integrated preprocessor.
|
|
|
|
When used in combination with the @option{-x} command line option,
|
|
@option{-save-temps} is sensible enough to avoid over writing an
|
|
input source file with the same extension as an intermediate file.
|
|
The corresponding intermediate file may be obtained by renaming the
|
|
source file before using @option{-save-temps}.
|
|
|
|
@item -time
|
|
@opindex time
|
|
Report the CPU time taken by each subprocess in the compilation
|
|
sequence. For C source files, this is the compiler proper and assembler
|
|
(plus the linker if linking is done). The output looks like this:
|
|
|
|
@smallexample
|
|
# cc1 0.12 0.01
|
|
# as 0.00 0.01
|
|
@end smallexample
|
|
|
|
The first number on each line is the ``user time'', that is time spent
|
|
executing the program itself. The second number is ``system time'',
|
|
time spent executing operating system routines on behalf of the program.
|
|
Both numbers are in seconds.
|
|
|
|
@item -fvar-tracking
|
|
@opindex fvar-tracking
|
|
Run variable tracking pass. It computes where variables are stored at each
|
|
position in code. Better debugging information is then generated
|
|
(if the debugging information format supports this information).
|
|
|
|
It is enabled by default when compiling with optimization (@option{-Os},
|
|
@option{-O}, @option{-O2}, ...), debugging information (@option{-g}) and
|
|
the debug info format supports it.
|
|
|
|
@item -print-file-name=@var{library}
|
|
@opindex print-file-name
|
|
Print the full absolute name of the library file @var{library} that
|
|
would be used when linking---and don't do anything else. With this
|
|
option, GCC does not compile or link anything; it just prints the
|
|
file name.
|
|
|
|
@item -print-multi-directory
|
|
@opindex print-multi-directory
|
|
Print the directory name corresponding to the multilib selected by any
|
|
other switches present in the command line. This directory is supposed
|
|
to exist in @env{GCC_EXEC_PREFIX}.
|
|
|
|
@item -print-multi-lib
|
|
@opindex print-multi-lib
|
|
Print the mapping from multilib directory names to compiler switches
|
|
that enable them. The directory name is separated from the switches by
|
|
@samp{;}, and each switch starts with an @samp{@@} instead of the
|
|
@samp{-}, without spaces between multiple switches. This is supposed to
|
|
ease shell-processing.
|
|
|
|
@item -print-prog-name=@var{program}
|
|
@opindex print-prog-name
|
|
Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
|
|
|
|
@item -print-libgcc-file-name
|
|
@opindex print-libgcc-file-name
|
|
Same as @option{-print-file-name=libgcc.a}.
|
|
|
|
This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
|
|
but you do want to link with @file{libgcc.a}. You can do
|
|
|
|
@smallexample
|
|
gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
|
|
@end smallexample
|
|
|
|
@item -print-search-dirs
|
|
@opindex print-search-dirs
|
|
Print the name of the configured installation directory and a list of
|
|
program and library directories @command{gcc} will search---and don't do anything else.
|
|
|
|
This is useful when @command{gcc} prints the error message
|
|
@samp{installation problem, cannot exec cpp0: No such file or directory}.
|
|
To resolve this you either need to put @file{cpp0} and the other compiler
|
|
components where @command{gcc} expects to find them, or you can set the environment
|
|
variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
|
|
Don't forget the trailing @samp{/}.
|
|
@xref{Environment Variables}.
|
|
|
|
@item -dumpmachine
|
|
@opindex dumpmachine
|
|
Print the compiler's target machine (for example,
|
|
@samp{i686-pc-linux-gnu})---and don't do anything else.
|
|
|
|
@item -dumpversion
|
|
@opindex dumpversion
|
|
Print the compiler version (for example, @samp{3.0})---and don't do
|
|
anything else.
|
|
|
|
@item -dumpspecs
|
|
@opindex dumpspecs
|
|
Print the compiler's built-in specs---and don't do anything else. (This
|
|
is used when GCC itself is being built.) @xref{Spec Files}.
|
|
|
|
@item -feliminate-unused-debug-types
|
|
@opindex feliminate-unused-debug-types
|
|
Normally, when producing DWARF2 output, GCC will emit debugging
|
|
information for all types declared in a compilation
|
|
unit, regardless of whether or not they are actually used
|
|
in that compilation unit. Sometimes this is useful, such as
|
|
if, in the debugger, you want to cast a value to a type that is
|
|
not actually used in your program (but is declared). More often,
|
|
however, this results in a significant amount of wasted space.
|
|
With this option, GCC will avoid producing debug symbol output
|
|
for types that are nowhere used in the source file being compiled.
|
|
@end table
|
|
|
|
@node Optimize Options
|
|
@section Options That Control Optimization
|
|
@cindex optimize options
|
|
@cindex options, optimization
|
|
|
|
These options control various sorts of optimizations.
|
|
|
|
Without any optimization option, the compiler's goal is to reduce the
|
|
cost of compilation and to make debugging produce the expected
|
|
results. Statements are independent: if you stop the program with a
|
|
breakpoint between statements, you can then assign a new value to any
|
|
variable or change the program counter to any other statement in the
|
|
function and get exactly the results you would expect from the source
|
|
code.
|
|
|
|
Turning on optimization flags makes the compiler attempt to improve
|
|
the performance and/or code size at the expense of compilation time
|
|
and possibly the ability to debug the program.
|
|
|
|
The compiler performs optimization based on the knowledge it has of
|
|
the program. Optimization levels @option{-O} and above, in
|
|
particular, enable @emph{unit-at-a-time} mode, which allows the
|
|
compiler to consider information gained from later functions in
|
|
the file when compiling a function. Compiling multiple files at
|
|
once to a single output file in @emph{unit-at-a-time} mode allows
|
|
the compiler to use information gained from all of the files when
|
|
compiling each of them.
|
|
|
|
Not all optimizations are controlled directly by a flag. Only
|
|
optimizations that have a flag are listed.
|
|
|
|
@table @gcctabopt
|
|
@item -O
|
|
@itemx -O1
|
|
@opindex O
|
|
@opindex O1
|
|
Optimize. Optimizing compilation takes somewhat more time, and a lot
|
|
more memory for a large function.
|
|
|
|
With @option{-O}, the compiler tries to reduce code size and execution
|
|
time, without performing any optimizations that take a great deal of
|
|
compilation time.
|
|
|
|
@option{-O} turns on the following optimization flags:
|
|
@gccoptlist{-fdefer-pop @gol
|
|
-fdelayed-branch @gol
|
|
-fguess-branch-probability @gol
|
|
-fcprop-registers @gol
|
|
-fif-conversion @gol
|
|
-fif-conversion2 @gol
|
|
-ftree-ccp @gol
|
|
-ftree-dce @gol
|
|
-ftree-dominator-opts @gol
|
|
-ftree-dse @gol
|
|
-ftree-ter @gol
|
|
-ftree-lrs @gol
|
|
-ftree-sra @gol
|
|
-ftree-copyrename @gol
|
|
-ftree-fre @gol
|
|
-ftree-ch @gol
|
|
-funit-at-a-time @gol
|
|
-fmerge-constants}
|
|
|
|
@option{-O} also turns on @option{-fomit-frame-pointer} on machines
|
|
where doing so does not interfere with debugging.
|
|
|
|
@item -O2
|
|
@opindex O2
|
|
Optimize even more. GCC performs nearly all supported optimizations
|
|
that do not involve a space-speed tradeoff. The compiler does not
|
|
perform loop unrolling or function inlining when you specify @option{-O2}.
|
|
As compared to @option{-O}, this option increases both compilation time
|
|
and the performance of the generated code.
|
|
|
|
@option{-O2} turns on all optimization flags specified by @option{-O}. It
|
|
also turns on the following optimization flags:
|
|
@gccoptlist{-fthread-jumps @gol
|
|
-fcrossjumping @gol
|
|
-foptimize-sibling-calls @gol
|
|
-fcse-follow-jumps -fcse-skip-blocks @gol
|
|
-fgcse -fgcse-lm @gol
|
|
-fexpensive-optimizations @gol
|
|
-frerun-cse-after-loop @gol
|
|
-fcaller-saves @gol
|
|
-fpeephole2 @gol
|
|
-fschedule-insns -fschedule-insns2 @gol
|
|
-fsched-interblock -fsched-spec @gol
|
|
-fregmove @gol
|
|
-fstrict-aliasing -fstrict-overflow @gol
|
|
-fdelete-null-pointer-checks @gol
|
|
-freorder-blocks -freorder-functions @gol
|
|
-falign-functions -falign-jumps @gol
|
|
-falign-loops -falign-labels @gol
|
|
-ftree-vrp @gol
|
|
-ftree-pre}
|
|
|
|
Please note the warning under @option{-fgcse} about
|
|
invoking @option{-O2} on programs that use computed gotos.
|
|
|
|
@option{-O2} doesn't turn on @option{-ftree-vrp} for the Ada compiler.
|
|
This option must be explicitly specified on the command line to be
|
|
enabled for the Ada compiler.
|
|
|
|
@item -O3
|
|
@opindex O3
|
|
Optimize yet more. @option{-O3} turns on all optimizations specified by
|
|
@option{-O2} and also turns on the @option{-finline-functions},
|
|
@option{-funswitch-loops} and @option{-fgcse-after-reload} options.
|
|
|
|
@item -O0
|
|
@opindex O0
|
|
Do not optimize. This is the default.
|
|
|
|
@item -Os
|
|
@opindex Os
|
|
Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
|
|
do not typically increase code size. It also performs further
|
|
optimizations designed to reduce code size.
|
|
|
|
@option{-Os} disables the following optimization flags:
|
|
@gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
|
|
-falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
|
|
-fprefetch-loop-arrays -ftree-vect-loop-version}
|
|
|
|
If you use multiple @option{-O} options, with or without level numbers,
|
|
the last such option is the one that is effective.
|
|
@end table
|
|
|
|
Options of the form @option{-f@var{flag}} specify machine-independent
|
|
flags. Most flags have both positive and negative forms; the negative
|
|
form of @option{-ffoo} would be @option{-fno-foo}. In the table
|
|
below, only one of the forms is listed---the one you typically will
|
|
use. You can figure out the other form by either removing @samp{no-}
|
|
or adding it.
|
|
|
|
The following options control specific optimizations. They are either
|
|
activated by @option{-O} options or are related to ones that are. You
|
|
can use the following flags in the rare cases when ``fine-tuning'' of
|
|
optimizations to be performed is desired.
|
|
|
|
@table @gcctabopt
|
|
@item -fno-default-inline
|
|
@opindex fno-default-inline
|
|
Do not make member functions inline by default merely because they are
|
|
defined inside the class scope (C++ only). Otherwise, when you specify
|
|
@w{@option{-O}}, member functions defined inside class scope are compiled
|
|
inline by default; i.e., you don't need to add @samp{inline} in front of
|
|
the member function name.
|
|
|
|
@item -fno-defer-pop
|
|
@opindex fno-defer-pop
|
|
Always pop the arguments to each function call as soon as that function
|
|
returns. For machines which must pop arguments after a function call,
|
|
the compiler normally lets arguments accumulate on the stack for several
|
|
function calls and pops them all at once.
|
|
|
|
Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fforce-mem
|
|
@opindex fforce-mem
|
|
Force memory operands to be copied into registers before doing
|
|
arithmetic on them. This produces better code by making all memory
|
|
references potential common subexpressions. When they are not common
|
|
subexpressions, instruction combination should eliminate the separate
|
|
register-load. This option is now a nop and will be removed in 4.3.
|
|
|
|
@item -fforce-addr
|
|
@opindex fforce-addr
|
|
Force memory address constants to be copied into registers before
|
|
doing arithmetic on them.
|
|
|
|
@item -fomit-frame-pointer
|
|
@opindex fomit-frame-pointer
|
|
Don't keep the frame pointer in a register for functions that
|
|
don't need one. This avoids the instructions to save, set up and
|
|
restore frame pointers; it also makes an extra register available
|
|
in many functions. @strong{It also makes debugging impossible on
|
|
some machines.}
|
|
|
|
On some machines, such as the VAX, this flag has no effect, because
|
|
the standard calling sequence automatically handles the frame pointer
|
|
and nothing is saved by pretending it doesn't exist. The
|
|
machine-description macro @code{FRAME_POINTER_REQUIRED} controls
|
|
whether a target machine supports this flag. @xref{Registers,,Register
|
|
Usage, gccint, GNU Compiler Collection (GCC) Internals}.
|
|
|
|
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -foptimize-sibling-calls
|
|
@opindex foptimize-sibling-calls
|
|
Optimize sibling and tail recursive calls.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fno-inline
|
|
@opindex fno-inline
|
|
Don't pay attention to the @code{inline} keyword. Normally this option
|
|
is used to keep the compiler from expanding any functions inline.
|
|
Note that if you are not optimizing, no functions can be expanded inline.
|
|
|
|
@item -finline-functions
|
|
@opindex finline-functions
|
|
Integrate all simple functions into their callers. The compiler
|
|
heuristically decides which functions are simple enough to be worth
|
|
integrating in this way.
|
|
|
|
If all calls to a given function are integrated, and the function is
|
|
declared @code{static}, then the function is normally not output as
|
|
assembler code in its own right.
|
|
|
|
Enabled at level @option{-O3}.
|
|
|
|
@item -finline-functions-called-once
|
|
@opindex finline-functions-called-once
|
|
Consider all @code{static} functions called once for inlining into their
|
|
caller even if they are not marked @code{inline}. If a call to a given
|
|
function is integrated, then the function is not output as assembler code
|
|
in its own right.
|
|
|
|
Enabled if @option{-funit-at-a-time} is enabled.
|
|
|
|
@item -fearly-inlining
|
|
@opindex fearly-inlining
|
|
Inline functions marked by @code{always_inline} and functions whose body seems
|
|
smaller than the function call overhead early before doing
|
|
@option{-fprofile-generate} instrumentation and real inlining pass. Doing so
|
|
makes profiling significantly cheaper and usually inlining faster on programs
|
|
having large chains of nested wrapper functions.
|
|
|
|
Enabled by default.
|
|
|
|
@item -finline-limit=@var{n}
|
|
@opindex finline-limit
|
|
By default, GCC limits the size of functions that can be inlined. This flag
|
|
allows the control of this limit for functions that are explicitly marked as
|
|
inline (i.e., marked with the inline keyword or defined within the class
|
|
definition in c++). @var{n} is the size of functions that can be inlined in
|
|
number of pseudo instructions (not counting parameter handling). The default
|
|
value of @var{n} is 600.
|
|
Increasing this value can result in more inlined code at
|
|
the cost of compilation time and memory consumption. Decreasing usually makes
|
|
the compilation faster and less code will be inlined (which presumably
|
|
means slower programs). This option is particularly useful for programs that
|
|
use inlining heavily such as those based on recursive templates with C++.
|
|
|
|
Inlining is actually controlled by a number of parameters, which may be
|
|
specified individually by using @option{--param @var{name}=@var{value}}.
|
|
The @option{-finline-limit=@var{n}} option sets some of these parameters
|
|
as follows:
|
|
|
|
@table @gcctabopt
|
|
@item max-inline-insns-single
|
|
is set to @var{n}/2.
|
|
@item max-inline-insns-auto
|
|
is set to @var{n}/2.
|
|
@item min-inline-insns
|
|
is set to 130 or @var{n}/4, whichever is smaller.
|
|
@item max-inline-insns-rtl
|
|
is set to @var{n}.
|
|
@end table
|
|
|
|
See below for a documentation of the individual
|
|
parameters controlling inlining.
|
|
|
|
@emph{Note:} pseudo instruction represents, in this particular context, an
|
|
abstract measurement of function's size. In no way does it represent a count
|
|
of assembly instructions and as such its exact meaning might change from one
|
|
release to an another.
|
|
|
|
@item -fkeep-inline-functions
|
|
@opindex fkeep-inline-functions
|
|
In C, emit @code{static} functions that are declared @code{inline}
|
|
into the object file, even if the function has been inlined into all
|
|
of its callers. This switch does not affect functions using the
|
|
@code{extern inline} extension in GNU C@. In C++, emit any and all
|
|
inline functions into the object file.
|
|
|
|
@item -fkeep-static-consts
|
|
@opindex fkeep-static-consts
|
|
Emit variables declared @code{static const} when optimization isn't turned
|
|
on, even if the variables aren't referenced.
|
|
|
|
GCC enables this option by default. If you want to force the compiler to
|
|
check if the variable was referenced, regardless of whether or not
|
|
optimization is turned on, use the @option{-fno-keep-static-consts} option.
|
|
|
|
@item -fmerge-constants
|
|
Attempt to merge identical constants (string constants and floating point
|
|
constants) across compilation units.
|
|
|
|
This option is the default for optimized compilation if the assembler and
|
|
linker support it. Use @option{-fno-merge-constants} to inhibit this
|
|
behavior.
|
|
|
|
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fmerge-all-constants
|
|
Attempt to merge identical constants and identical variables.
|
|
|
|
This option implies @option{-fmerge-constants}. In addition to
|
|
@option{-fmerge-constants} this considers e.g.@: even constant initialized
|
|
arrays or initialized constant variables with integral or floating point
|
|
types. Languages like C or C++ require each non-automatic variable to
|
|
have distinct location, so using this option will result in non-conforming
|
|
behavior.
|
|
|
|
@item -fmodulo-sched
|
|
@opindex fmodulo-sched
|
|
Perform swing modulo scheduling immediately before the first scheduling
|
|
pass. This pass looks at innermost loops and reorders their
|
|
instructions by overlapping different iterations.
|
|
|
|
@item -fno-branch-count-reg
|
|
@opindex fno-branch-count-reg
|
|
Do not use ``decrement and branch'' instructions on a count register,
|
|
but instead generate a sequence of instructions that decrement a
|
|
register, compare it against zero, then branch based upon the result.
|
|
This option is only meaningful on architectures that support such
|
|
instructions, which include x86, PowerPC, IA-64 and S/390.
|
|
|
|
The default is @option{-fbranch-count-reg}.
|
|
|
|
@item -fno-function-cse
|
|
@opindex fno-function-cse
|
|
Do not put function addresses in registers; make each instruction that
|
|
calls a constant function contain the function's address explicitly.
|
|
|
|
This option results in less efficient code, but some strange hacks
|
|
that alter the assembler output may be confused by the optimizations
|
|
performed when this option is not used.
|
|
|
|
The default is @option{-ffunction-cse}
|
|
|
|
@item -fno-zero-initialized-in-bss
|
|
@opindex fno-zero-initialized-in-bss
|
|
If the target supports a BSS section, GCC by default puts variables that
|
|
are initialized to zero into BSS@. This can save space in the resulting
|
|
code.
|
|
|
|
This option turns off this behavior because some programs explicitly
|
|
rely on variables going to the data section. E.g., so that the
|
|
resulting executable can find the beginning of that section and/or make
|
|
assumptions based on that.
|
|
|
|
The default is @option{-fzero-initialized-in-bss}.
|
|
|
|
@item -fbounds-check
|
|
@opindex fbounds-check
|
|
For front-ends that support it, generate additional code to check that
|
|
indices used to access arrays are within the declared range. This is
|
|
currently only supported by the Java and Fortran front-ends, where
|
|
this option defaults to true and false respectively.
|
|
|
|
@item -fmudflap -fmudflapth -fmudflapir
|
|
@opindex fmudflap
|
|
@opindex fmudflapth
|
|
@opindex fmudflapir
|
|
@cindex bounds checking
|
|
@cindex mudflap
|
|
For front-ends that support it (C and C++), instrument all risky
|
|
pointer/array dereferencing operations, some standard library
|
|
string/heap functions, and some other associated constructs with
|
|
range/validity tests. Modules so instrumented should be immune to
|
|
buffer overflows, invalid heap use, and some other classes of C/C++
|
|
programming errors. The instrumentation relies on a separate runtime
|
|
library (@file{libmudflap}), which will be linked into a program if
|
|
@option{-fmudflap} is given at link time. Run-time behavior of the
|
|
instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
|
|
environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
|
|
for its options.
|
|
|
|
Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
|
|
link if your program is multi-threaded. Use @option{-fmudflapir}, in
|
|
addition to @option{-fmudflap} or @option{-fmudflapth}, if
|
|
instrumentation should ignore pointer reads. This produces less
|
|
instrumentation (and therefore faster execution) and still provides
|
|
some protection against outright memory corrupting writes, but allows
|
|
erroneously read data to propagate within a program.
|
|
|
|
@item -fthread-jumps
|
|
@opindex fthread-jumps
|
|
Perform optimizations where we check to see if a jump branches to a
|
|
location where another comparison subsumed by the first is found. If
|
|
so, the first branch is redirected to either the destination of the
|
|
second branch or a point immediately following it, depending on whether
|
|
the condition is known to be true or false.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fcse-follow-jumps
|
|
@opindex fcse-follow-jumps
|
|
In common subexpression elimination, scan through jump instructions
|
|
when the target of the jump is not reached by any other path. For
|
|
example, when CSE encounters an @code{if} statement with an
|
|
@code{else} clause, CSE will follow the jump when the condition
|
|
tested is false.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fcse-skip-blocks
|
|
@opindex fcse-skip-blocks
|
|
This is similar to @option{-fcse-follow-jumps}, but causes CSE to
|
|
follow jumps which conditionally skip over blocks. When CSE
|
|
encounters a simple @code{if} statement with no else clause,
|
|
@option{-fcse-skip-blocks} causes CSE to follow the jump around the
|
|
body of the @code{if}.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -frerun-cse-after-loop
|
|
@opindex frerun-cse-after-loop
|
|
Re-run common subexpression elimination after loop optimizations has been
|
|
performed.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fgcse
|
|
@opindex fgcse
|
|
Perform a global common subexpression elimination pass.
|
|
This pass also performs global constant and copy propagation.
|
|
|
|
@emph{Note:} When compiling a program using computed gotos, a GCC
|
|
extension, you may get better runtime performance if you disable
|
|
the global common subexpression elimination pass by adding
|
|
@option{-fno-gcse} to the command line.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fgcse-lm
|
|
@opindex fgcse-lm
|
|
When @option{-fgcse-lm} is enabled, global common subexpression elimination will
|
|
attempt to move loads which are only killed by stores into themselves. This
|
|
allows a loop containing a load/store sequence to be changed to a load outside
|
|
the loop, and a copy/store within the loop.
|
|
|
|
Enabled by default when gcse is enabled.
|
|
|
|
@item -fgcse-sm
|
|
@opindex fgcse-sm
|
|
When @option{-fgcse-sm} is enabled, a store motion pass is run after
|
|
global common subexpression elimination. This pass will attempt to move
|
|
stores out of loops. When used in conjunction with @option{-fgcse-lm},
|
|
loops containing a load/store sequence can be changed to a load before
|
|
the loop and a store after the loop.
|
|
|
|
Not enabled at any optimization level.
|
|
|
|
@item -fgcse-las
|
|
@opindex fgcse-las
|
|
When @option{-fgcse-las} is enabled, the global common subexpression
|
|
elimination pass eliminates redundant loads that come after stores to the
|
|
same memory location (both partial and full redundancies).
|
|
|
|
Not enabled at any optimization level.
|
|
|
|
@item -fgcse-after-reload
|
|
@opindex fgcse-after-reload
|
|
When @option{-fgcse-after-reload} is enabled, a redundant load elimination
|
|
pass is performed after reload. The purpose of this pass is to cleanup
|
|
redundant spilling.
|
|
|
|
@item -funsafe-loop-optimizations
|
|
@opindex funsafe-loop-optimizations
|
|
If given, the loop optimizer will assume that loop indices do not
|
|
overflow, and that the loops with nontrivial exit condition are not
|
|
infinite. This enables a wider range of loop optimizations even if
|
|
the loop optimizer itself cannot prove that these assumptions are valid.
|
|
Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
|
|
if it finds this kind of loop.
|
|
|
|
@item -fcrossjumping
|
|
@opindex crossjumping
|
|
Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
|
|
resulting code may or may not perform better than without cross-jumping.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fif-conversion
|
|
@opindex if-conversion
|
|
Attempt to transform conditional jumps into branch-less equivalents. This
|
|
include use of conditional moves, min, max, set flags and abs instructions, and
|
|
some tricks doable by standard arithmetics. The use of conditional execution
|
|
on chips where it is available is controlled by @code{if-conversion2}.
|
|
|
|
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fif-conversion2
|
|
@opindex if-conversion2
|
|
Use conditional execution (where available) to transform conditional jumps into
|
|
branch-less equivalents.
|
|
|
|
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fdelete-null-pointer-checks
|
|
@opindex fdelete-null-pointer-checks
|
|
Use global dataflow analysis to identify and eliminate useless checks
|
|
for null pointers. The compiler assumes that dereferencing a null
|
|
pointer would have halted the program. If a pointer is checked after
|
|
it has already been dereferenced, it cannot be null.
|
|
|
|
In some environments, this assumption is not true, and programs can
|
|
safely dereference null pointers. Use
|
|
@option{-fno-delete-null-pointer-checks} to disable this optimization
|
|
for programs which depend on that behavior.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fexpensive-optimizations
|
|
@opindex fexpensive-optimizations
|
|
Perform a number of minor optimizations that are relatively expensive.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -foptimize-register-move
|
|
@itemx -fregmove
|
|
@opindex foptimize-register-move
|
|
@opindex fregmove
|
|
Attempt to reassign register numbers in move instructions and as
|
|
operands of other simple instructions in order to maximize the amount of
|
|
register tying. This is especially helpful on machines with two-operand
|
|
instructions.
|
|
|
|
Note @option{-fregmove} and @option{-foptimize-register-move} are the same
|
|
optimization.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fdelayed-branch
|
|
@opindex fdelayed-branch
|
|
If supported for the target machine, attempt to reorder instructions
|
|
to exploit instruction slots available after delayed branch
|
|
instructions.
|
|
|
|
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fschedule-insns
|
|
@opindex fschedule-insns
|
|
If supported for the target machine, attempt to reorder instructions to
|
|
eliminate execution stalls due to required data being unavailable. This
|
|
helps machines that have slow floating point or memory load instructions
|
|
by allowing other instructions to be issued until the result of the load
|
|
or floating point instruction is required.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fschedule-insns2
|
|
@opindex fschedule-insns2
|
|
Similar to @option{-fschedule-insns}, but requests an additional pass of
|
|
instruction scheduling after register allocation has been done. This is
|
|
especially useful on machines with a relatively small number of
|
|
registers and where memory load instructions take more than one cycle.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fno-sched-interblock
|
|
@opindex fno-sched-interblock
|
|
Don't schedule instructions across basic blocks. This is normally
|
|
enabled by default when scheduling before register allocation, i.e.@:
|
|
with @option{-fschedule-insns} or at @option{-O2} or higher.
|
|
|
|
@item -fno-sched-spec
|
|
@opindex fno-sched-spec
|
|
Don't allow speculative motion of non-load instructions. This is normally
|
|
enabled by default when scheduling before register allocation, i.e.@:
|
|
with @option{-fschedule-insns} or at @option{-O2} or higher.
|
|
|
|
@item -fsched-spec-load
|
|
@opindex fsched-spec-load
|
|
Allow speculative motion of some load instructions. This only makes
|
|
sense when scheduling before register allocation, i.e.@: with
|
|
@option{-fschedule-insns} or at @option{-O2} or higher.
|
|
|
|
@item -fsched-spec-load-dangerous
|
|
@opindex fsched-spec-load-dangerous
|
|
Allow speculative motion of more load instructions. This only makes
|
|
sense when scheduling before register allocation, i.e.@: with
|
|
@option{-fschedule-insns} or at @option{-O2} or higher.
|
|
|
|
@item -fsched-stalled-insns=@var{n}
|
|
@opindex fsched-stalled-insns
|
|
Define how many insns (if any) can be moved prematurely from the queue
|
|
of stalled insns into the ready list, during the second scheduling pass.
|
|
|
|
@item -fsched-stalled-insns-dep=@var{n}
|
|
@opindex fsched-stalled-insns-dep
|
|
Define how many insn groups (cycles) will be examined for a dependency
|
|
on a stalled insn that is candidate for premature removal from the queue
|
|
of stalled insns. Has an effect only during the second scheduling pass,
|
|
and only if @option{-fsched-stalled-insns} is used and its value is not zero.
|
|
|
|
@item -fsched2-use-superblocks
|
|
@opindex fsched2-use-superblocks
|
|
When scheduling after register allocation, do use superblock scheduling
|
|
algorithm. Superblock scheduling allows motion across basic block boundaries
|
|
resulting on faster schedules. This option is experimental, as not all machine
|
|
descriptions used by GCC model the CPU closely enough to avoid unreliable
|
|
results from the algorithm.
|
|
|
|
This only makes sense when scheduling after register allocation, i.e.@: with
|
|
@option{-fschedule-insns2} or at @option{-O2} or higher.
|
|
|
|
@item -fsched2-use-traces
|
|
@opindex fsched2-use-traces
|
|
Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
|
|
allocation and additionally perform code duplication in order to increase the
|
|
size of superblocks using tracer pass. See @option{-ftracer} for details on
|
|
trace formation.
|
|
|
|
This mode should produce faster but significantly longer programs. Also
|
|
without @option{-fbranch-probabilities} the traces constructed may not
|
|
match the reality and hurt the performance. This only makes
|
|
sense when scheduling after register allocation, i.e.@: with
|
|
@option{-fschedule-insns2} or at @option{-O2} or higher.
|
|
|
|
@item -fsee
|
|
@opindex fsee
|
|
Eliminates redundant extension instructions and move the non redundant
|
|
ones to optimal placement using LCM.
|
|
|
|
@item -freschedule-modulo-scheduled-loops
|
|
@opindex fscheduling-in-modulo-scheduled-loops
|
|
The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled
|
|
we may want to prevent the later scheduling passes from changing its schedule, we use this
|
|
option to control that.
|
|
|
|
@item -fcaller-saves
|
|
@opindex fcaller-saves
|
|
Enable values to be allocated in registers that will be clobbered by
|
|
function calls, by emitting extra instructions to save and restore the
|
|
registers around such calls. Such allocation is done only when it
|
|
seems to result in better code than would otherwise be produced.
|
|
|
|
This option is always enabled by default on certain machines, usually
|
|
those which have no call-preserved registers to use instead.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -ftree-pre
|
|
Perform Partial Redundancy Elimination (PRE) on trees. This flag is
|
|
enabled by default at @option{-O2} and @option{-O3}.
|
|
|
|
@item -ftree-fre
|
|
Perform Full Redundancy Elimination (FRE) on trees. The difference
|
|
between FRE and PRE is that FRE only considers expressions
|
|
that are computed on all paths leading to the redundant computation.
|
|
This analysis faster than PRE, though it exposes fewer redundancies.
|
|
This flag is enabled by default at @option{-O} and higher.
|
|
|
|
@item -ftree-copy-prop
|
|
Perform copy propagation on trees. This pass eliminates unnecessary
|
|
copy operations. This flag is enabled by default at @option{-O} and
|
|
higher.
|
|
|
|
@item -ftree-store-copy-prop
|
|
Perform copy propagation of memory loads and stores. This pass
|
|
eliminates unnecessary copy operations in memory references
|
|
(structures, global variables, arrays, etc). This flag is enabled by
|
|
default at @option{-O2} and higher.
|
|
|
|
@item -ftree-salias
|
|
Perform structural alias analysis on trees. This flag
|
|
is enabled by default at @option{-O} and higher.
|
|
|
|
@item -fipa-pta
|
|
Perform interprocedural pointer analysis.
|
|
|
|
@item -ftree-sink
|
|
Perform forward store motion on trees. This flag is
|
|
enabled by default at @option{-O} and higher.
|
|
|
|
@item -ftree-ccp
|
|
Perform sparse conditional constant propagation (CCP) on trees. This
|
|
pass only operates on local scalar variables and is enabled by default
|
|
at @option{-O} and higher.
|
|
|
|
@item -ftree-store-ccp
|
|
Perform sparse conditional constant propagation (CCP) on trees. This
|
|
pass operates on both local scalar variables and memory stores and
|
|
loads (global variables, structures, arrays, etc). This flag is
|
|
enabled by default at @option{-O2} and higher.
|
|
|
|
@item -ftree-dce
|
|
Perform dead code elimination (DCE) on trees. This flag is enabled by
|
|
default at @option{-O} and higher.
|
|
|
|
@item -ftree-dominator-opts
|
|
Perform a variety of simple scalar cleanups (constant/copy
|
|
propagation, redundancy elimination, range propagation and expression
|
|
simplification) based on a dominator tree traversal. This also
|
|
performs jump threading (to reduce jumps to jumps). This flag is
|
|
enabled by default at @option{-O} and higher.
|
|
|
|
@item -ftree-ch
|
|
Perform loop header copying on trees. This is beneficial since it increases
|
|
effectiveness of code motion optimizations. It also saves one jump. This flag
|
|
is enabled by default at @option{-O} and higher. It is not enabled
|
|
for @option{-Os}, since it usually increases code size.
|
|
|
|
@item -ftree-loop-optimize
|
|
Perform loop optimizations on trees. This flag is enabled by default
|
|
at @option{-O} and higher.
|
|
|
|
@item -ftree-loop-linear
|
|
Perform linear loop transformations on tree. This flag can improve cache
|
|
performance and allow further loop optimizations to take place.
|
|
|
|
@item -ftree-loop-im
|
|
Perform loop invariant motion on trees. This pass moves only invariants that
|
|
would be hard to handle at RTL level (function calls, operations that expand to
|
|
nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
|
|
operands of conditions that are invariant out of the loop, so that we can use
|
|
just trivial invariantness analysis in loop unswitching. The pass also includes
|
|
store motion.
|
|
|
|
@item -ftree-loop-ivcanon
|
|
Create a canonical counter for number of iterations in the loop for that
|
|
determining number of iterations requires complicated analysis. Later
|
|
optimizations then may determine the number easily. Useful especially
|
|
in connection with unrolling.
|
|
|
|
@item -fivopts
|
|
Perform induction variable optimizations (strength reduction, induction
|
|
variable merging and induction variable elimination) on trees.
|
|
|
|
@item -ftree-sra
|
|
Perform scalar replacement of aggregates. This pass replaces structure
|
|
references with scalars to prevent committing structures to memory too
|
|
early. This flag is enabled by default at @option{-O} and higher.
|
|
|
|
@item -ftree-copyrename
|
|
Perform copy renaming on trees. This pass attempts to rename compiler
|
|
temporaries to other variables at copy locations, usually resulting in
|
|
variable names which more closely resemble the original variables. This flag
|
|
is enabled by default at @option{-O} and higher.
|
|
|
|
@item -ftree-ter
|
|
Perform temporary expression replacement during the SSA->normal phase. Single
|
|
use/single def temporaries are replaced at their use location with their
|
|
defining expression. This results in non-GIMPLE code, but gives the expanders
|
|
much more complex trees to work on resulting in better RTL generation. This is
|
|
enabled by default at @option{-O} and higher.
|
|
|
|
@item -ftree-lrs
|
|
Perform live range splitting during the SSA->normal phase. Distinct live
|
|
ranges of a variable are split into unique variables, allowing for better
|
|
optimization later. This is enabled by default at @option{-O} and higher.
|
|
|
|
@item -ftree-vectorize
|
|
Perform loop vectorization on trees.
|
|
|
|
@item -ftree-vect-loop-version
|
|
@opindex ftree-vect-loop-version
|
|
Perform loop versioning when doing loop vectorization on trees. When a loop
|
|
appears to be vectorizable except that data alignment or data dependence cannot
|
|
be determined at compile time then vectorized and non-vectorized versions of
|
|
the loop are generated along with runtime checks for alignment or dependence
|
|
to control which version is executed. This option is enabled by default
|
|
except at level @option{-Os} where it is disabled.
|
|
|
|
@item -ftree-vrp
|
|
Perform Value Range Propagation on trees. This is similar to the
|
|
constant propagation pass, but instead of values, ranges of values are
|
|
propagated. This allows the optimizers to remove unnecessary range
|
|
checks like array bound checks and null pointer checks. This is
|
|
enabled by default at @option{-O2} and higher. Null pointer check
|
|
elimination is only done if @option{-fdelete-null-pointer-checks} is
|
|
enabled.
|
|
|
|
@item -ftracer
|
|
@opindex ftracer
|
|
Perform tail duplication to enlarge superblock size. This transformation
|
|
simplifies the control flow of the function allowing other optimizations to do
|
|
better job.
|
|
|
|
@item -funroll-loops
|
|
@opindex funroll-loops
|
|
Unroll loops whose number of iterations can be determined at compile
|
|
time or upon entry to the loop. @option{-funroll-loops} implies
|
|
@option{-frerun-cse-after-loop}. This option makes code larger,
|
|
and may or may not make it run faster.
|
|
|
|
@item -funroll-all-loops
|
|
@opindex funroll-all-loops
|
|
Unroll all loops, even if their number of iterations is uncertain when
|
|
the loop is entered. This usually makes programs run more slowly.
|
|
@option{-funroll-all-loops} implies the same options as
|
|
@option{-funroll-loops},
|
|
|
|
@item -fsplit-ivs-in-unroller
|
|
@opindex fsplit-ivs-in-unroller
|
|
Enables expressing of values of induction variables in later iterations
|
|
of the unrolled loop using the value in the first iteration. This breaks
|
|
long dependency chains, thus improving efficiency of the scheduling passes.
|
|
|
|
Combination of @option{-fweb} and CSE is often sufficient to obtain the
|
|
same effect. However in cases the loop body is more complicated than
|
|
a single basic block, this is not reliable. It also does not work at all
|
|
on some of the architectures due to restrictions in the CSE pass.
|
|
|
|
This optimization is enabled by default.
|
|
|
|
@item -fvariable-expansion-in-unroller
|
|
@opindex fvariable-expansion-in-unroller
|
|
With this option, the compiler will create multiple copies of some
|
|
local variables when unrolling a loop which can result in superior code.
|
|
|
|
@item -fprefetch-loop-arrays
|
|
@opindex fprefetch-loop-arrays
|
|
If supported by the target machine, generate instructions to prefetch
|
|
memory to improve the performance of loops that access large arrays.
|
|
|
|
This option may generate better or worse code; results are highly
|
|
dependent on the structure of loops within the source code.
|
|
|
|
Disabled at level @option{-Os}.
|
|
|
|
@item -fno-peephole
|
|
@itemx -fno-peephole2
|
|
@opindex fno-peephole
|
|
@opindex fno-peephole2
|
|
Disable any machine-specific peephole optimizations. The difference
|
|
between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
|
|
are implemented in the compiler; some targets use one, some use the
|
|
other, a few use both.
|
|
|
|
@option{-fpeephole} is enabled by default.
|
|
@option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fno-guess-branch-probability
|
|
@opindex fno-guess-branch-probability
|
|
Do not guess branch probabilities using heuristics.
|
|
|
|
GCC will use heuristics to guess branch probabilities if they are
|
|
not provided by profiling feedback (@option{-fprofile-arcs}). These
|
|
heuristics are based on the control flow graph. If some branch probabilities
|
|
are specified by @samp{__builtin_expect}, then the heuristics will be
|
|
used to guess branch probabilities for the rest of the control flow graph,
|
|
taking the @samp{__builtin_expect} info into account. The interactions
|
|
between the heuristics and @samp{__builtin_expect} can be complex, and in
|
|
some cases, it may be useful to disable the heuristics so that the effects
|
|
of @samp{__builtin_expect} are easier to understand.
|
|
|
|
The default is @option{-fguess-branch-probability} at levels
|
|
@option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -freorder-blocks
|
|
@opindex freorder-blocks
|
|
Reorder basic blocks in the compiled function in order to reduce number of
|
|
taken branches and improve code locality.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}.
|
|
|
|
@item -freorder-blocks-and-partition
|
|
@opindex freorder-blocks-and-partition
|
|
In addition to reordering basic blocks in the compiled function, in order
|
|
to reduce number of taken branches, partitions hot and cold basic blocks
|
|
into separate sections of the assembly and .o files, to improve
|
|
paging and cache locality performance.
|
|
|
|
This optimization is automatically turned off in the presence of
|
|
exception handling, for linkonce sections, for functions with a user-defined
|
|
section attribute and on any architecture that does not support named
|
|
sections.
|
|
|
|
@item -freorder-functions
|
|
@opindex freorder-functions
|
|
Reorder functions in the object file in order to
|
|
improve code locality. This is implemented by using special
|
|
subsections @code{.text.hot} for most frequently executed functions and
|
|
@code{.text.unlikely} for unlikely executed functions. Reordering is done by
|
|
the linker so object file format must support named sections and linker must
|
|
place them in a reasonable way.
|
|
|
|
Also profile feedback must be available in to make this option effective. See
|
|
@option{-fprofile-arcs} for details.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fstrict-aliasing
|
|
@opindex fstrict-aliasing
|
|
Allows the compiler to assume the strictest aliasing rules applicable to
|
|
the language being compiled. For C (and C++), this activates
|
|
optimizations based on the type of expressions. In particular, an
|
|
object of one type is assumed never to reside at the same address as an
|
|
object of a different type, unless the types are almost the same. For
|
|
example, an @code{unsigned int} can alias an @code{int}, but not a
|
|
@code{void*} or a @code{double}. A character type may alias any other
|
|
type.
|
|
|
|
Pay special attention to code like this:
|
|
@smallexample
|
|
union a_union @{
|
|
int i;
|
|
double d;
|
|
@};
|
|
|
|
int f() @{
|
|
a_union t;
|
|
t.d = 3.0;
|
|
return t.i;
|
|
@}
|
|
@end smallexample
|
|
The practice of reading from a different union member than the one most
|
|
recently written to (called ``type-punning'') is common. Even with
|
|
@option{-fstrict-aliasing}, type-punning is allowed, provided the memory
|
|
is accessed through the union type. So, the code above will work as
|
|
expected. However, this code might not:
|
|
@smallexample
|
|
int f() @{
|
|
a_union t;
|
|
int* ip;
|
|
t.d = 3.0;
|
|
ip = &t.i;
|
|
return *ip;
|
|
@}
|
|
@end smallexample
|
|
|
|
Every language that wishes to perform language-specific alias analysis
|
|
should define a function that computes, given an @code{tree}
|
|
node, an alias set for the node. Nodes in different alias sets are not
|
|
allowed to alias. For an example, see the C front-end function
|
|
@code{c_get_alias_set}.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fstrict-overflow
|
|
@opindex fstrict-overflow
|
|
Allow the compiler to assume strict signed overflow rules, depending
|
|
on the language being compiled. For C (and C++) this means that
|
|
overflow when doing arithmetic with signed numbers is undefined, which
|
|
means that the compiler may assume that it will not happen. This
|
|
permits various optimizations. For example, the compiler will assume
|
|
that an expression like @code{i + 10 > i} will always be true for
|
|
signed @code{i}. This assumption is only valid if signed overflow is
|
|
undefined, as the expression is false if @code{i + 10} overflows when
|
|
using twos complement arithmetic. When this option is in effect any
|
|
attempt to determine whether an operation on signed numbers will
|
|
overflow must be written carefully to not actually involve overflow.
|
|
|
|
See also the @option{-fwrapv} option. Using @option{-fwrapv} means
|
|
that signed overflow is fully defined: it wraps. When
|
|
@option{-fwrapv} is used, there is no difference between
|
|
@option{-fstrict-overflow} and @option{-fno-strict-overflow}. With
|
|
@option{-fwrapv} certain types of overflow are permitted. For
|
|
example, if the compiler gets an overflow when doing arithmetic on
|
|
constants, the overflowed value can still be used with
|
|
@option{-fwrapv}, but not otherwise.
|
|
|
|
The @option{-fstrict-overflow} option is enabled at levels
|
|
@option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -falign-functions
|
|
@itemx -falign-functions=@var{n}
|
|
@opindex falign-functions
|
|
Align the start of functions to the next power-of-two greater than
|
|
@var{n}, skipping up to @var{n} bytes. For instance,
|
|
@option{-falign-functions=32} aligns functions to the next 32-byte
|
|
boundary, but @option{-falign-functions=24} would align to the next
|
|
32-byte boundary only if this can be done by skipping 23 bytes or less.
|
|
|
|
@option{-fno-align-functions} and @option{-falign-functions=1} are
|
|
equivalent and mean that functions will not be aligned.
|
|
|
|
Some assemblers only support this flag when @var{n} is a power of two;
|
|
in that case, it is rounded up.
|
|
|
|
If @var{n} is not specified or is zero, use a machine-dependent default.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}.
|
|
|
|
@item -falign-labels
|
|
@itemx -falign-labels=@var{n}
|
|
@opindex falign-labels
|
|
Align all branch targets to a power-of-two boundary, skipping up to
|
|
@var{n} bytes like @option{-falign-functions}. This option can easily
|
|
make code slower, because it must insert dummy operations for when the
|
|
branch target is reached in the usual flow of the code.
|
|
|
|
@option{-fno-align-labels} and @option{-falign-labels=1} are
|
|
equivalent and mean that labels will not be aligned.
|
|
|
|
If @option{-falign-loops} or @option{-falign-jumps} are applicable and
|
|
are greater than this value, then their values are used instead.
|
|
|
|
If @var{n} is not specified or is zero, use a machine-dependent default
|
|
which is very likely to be @samp{1}, meaning no alignment.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}.
|
|
|
|
@item -falign-loops
|
|
@itemx -falign-loops=@var{n}
|
|
@opindex falign-loops
|
|
Align loops to a power-of-two boundary, skipping up to @var{n} bytes
|
|
like @option{-falign-functions}. The hope is that the loop will be
|
|
executed many times, which will make up for any execution of the dummy
|
|
operations.
|
|
|
|
@option{-fno-align-loops} and @option{-falign-loops=1} are
|
|
equivalent and mean that loops will not be aligned.
|
|
|
|
If @var{n} is not specified or is zero, use a machine-dependent default.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}.
|
|
|
|
@item -falign-jumps
|
|
@itemx -falign-jumps=@var{n}
|
|
@opindex falign-jumps
|
|
Align branch targets to a power-of-two boundary, for branch targets
|
|
where the targets can only be reached by jumping, skipping up to @var{n}
|
|
bytes like @option{-falign-functions}. In this case, no dummy operations
|
|
need be executed.
|
|
|
|
@option{-fno-align-jumps} and @option{-falign-jumps=1} are
|
|
equivalent and mean that loops will not be aligned.
|
|
|
|
If @var{n} is not specified or is zero, use a machine-dependent default.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}.
|
|
|
|
@item -funit-at-a-time
|
|
@opindex funit-at-a-time
|
|
Parse the whole compilation unit before starting to produce code.
|
|
This allows some extra optimizations to take place but consumes
|
|
more memory (in general). There are some compatibility issues
|
|
with @emph{unit-at-a-time} mode:
|
|
@itemize @bullet
|
|
@item
|
|
enabling @emph{unit-at-a-time} mode may change the order
|
|
in which functions, variables, and top-level @code{asm} statements
|
|
are emitted, and will likely break code relying on some particular
|
|
ordering. The majority of such top-level @code{asm} statements,
|
|
though, can be replaced by @code{section} attributes. The
|
|
@option{fno-toplevel-reorder} option may be used to keep the ordering
|
|
used in the input file, at the cost of some optimizations.
|
|
|
|
@item
|
|
@emph{unit-at-a-time} mode removes unreferenced static variables
|
|
and functions. This may result in undefined references
|
|
when an @code{asm} statement refers directly to variables or functions
|
|
that are otherwise unused. In that case either the variable/function
|
|
shall be listed as an operand of the @code{asm} statement operand or,
|
|
in the case of top-level @code{asm} statements the attribute @code{used}
|
|
shall be used on the declaration.
|
|
|
|
@item
|
|
Static functions now can use non-standard passing conventions that
|
|
may break @code{asm} statements calling functions directly. Again,
|
|
attribute @code{used} will prevent this behavior.
|
|
@end itemize
|
|
|
|
As a temporary workaround, @option{-fno-unit-at-a-time} can be used,
|
|
but this scheme may not be supported by future releases of GCC@.
|
|
|
|
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fno-toplevel-reorder
|
|
Do not reorder top-level functions, variables, and @code{asm}
|
|
statements. Output them in the same order that they appear in the
|
|
input file. When this option is used, unreferenced static variables
|
|
will not be removed. This option is intended to support existing code
|
|
which relies on a particular ordering. For new code, it is better to
|
|
use attributes.
|
|
|
|
@item -fweb
|
|
@opindex fweb
|
|
Constructs webs as commonly used for register allocation purposes and assign
|
|
each web individual pseudo register. This allows the register allocation pass
|
|
to operate on pseudos directly, but also strengthens several other optimization
|
|
passes, such as CSE, loop optimizer and trivial dead code remover. It can,
|
|
however, make debugging impossible, since variables will no longer stay in a
|
|
``home register''.
|
|
|
|
Enabled by default with @option{-funroll-loops}.
|
|
|
|
@item -fwhole-program
|
|
@opindex fwhole-program
|
|
Assume that the current compilation unit represents whole program being
|
|
compiled. All public functions and variables with the exception of @code{main}
|
|
and those merged by attribute @code{externally_visible} become static functions
|
|
and in a affect gets more aggressively optimized by interprocedural optimizers.
|
|
While this option is equivalent to proper use of @code{static} keyword for
|
|
programs consisting of single file, in combination with option
|
|
@option{--combine} this flag can be used to compile most of smaller scale C
|
|
programs since the functions and variables become local for the whole combined
|
|
compilation unit, not for the single source file itself.
|
|
|
|
|
|
@item -fno-cprop-registers
|
|
@opindex fno-cprop-registers
|
|
After register allocation and post-register allocation instruction splitting,
|
|
we perform a copy-propagation pass to try to reduce scheduling dependencies
|
|
and occasionally eliminate the copy.
|
|
|
|
Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fprofile-generate
|
|
@opindex fprofile-generate
|
|
|
|
Enable options usually used for instrumenting application to produce
|
|
profile useful for later recompilation with profile feedback based
|
|
optimization. You must use @option{-fprofile-generate} both when
|
|
compiling and when linking your program.
|
|
|
|
The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
|
|
|
|
@item -fprofile-use
|
|
@opindex fprofile-use
|
|
Enable profile feedback directed optimizations, and optimizations
|
|
generally profitable only with profile feedback available.
|
|
|
|
The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
|
|
@code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}
|
|
|
|
@end table
|
|
|
|
The following options control compiler behavior regarding floating
|
|
point arithmetic. These options trade off between speed and
|
|
correctness. All must be specifically enabled.
|
|
|
|
@table @gcctabopt
|
|
@item -ffloat-store
|
|
@opindex ffloat-store
|
|
Do not store floating point variables in registers, and inhibit other
|
|
options that might change whether a floating point value is taken from a
|
|
register or memory.
|
|
|
|
@cindex floating point precision
|
|
This option prevents undesirable excess precision on machines such as
|
|
the 68000 where the floating registers (of the 68881) keep more
|
|
precision than a @code{double} is supposed to have. Similarly for the
|
|
x86 architecture. For most programs, the excess precision does only
|
|
good, but a few programs rely on the precise definition of IEEE floating
|
|
point. Use @option{-ffloat-store} for such programs, after modifying
|
|
them to store all pertinent intermediate computations into variables.
|
|
|
|
@item -ffast-math
|
|
@opindex ffast-math
|
|
Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
|
|
@option{-fno-trapping-math}, @option{-ffinite-math-only},
|
|
@option{-fno-rounding-math}, @option{-fno-signaling-nans}
|
|
and @option{fcx-limited-range}.
|
|
|
|
This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
|
|
|
|
This option should never be turned on by any @option{-O} option since
|
|
it can result in incorrect output for programs which depend on
|
|
an exact implementation of IEEE or ISO rules/specifications for
|
|
math functions.
|
|
|
|
@item -fno-math-errno
|
|
@opindex fno-math-errno
|
|
Do not set ERRNO after calling math functions that are executed
|
|
with a single instruction, e.g., sqrt. A program that relies on
|
|
IEEE exceptions for math error handling may want to use this flag
|
|
for speed while maintaining IEEE arithmetic compatibility.
|
|
|
|
This option should never be turned on by any @option{-O} option since
|
|
it can result in incorrect output for programs which depend on
|
|
an exact implementation of IEEE or ISO rules/specifications for
|
|
math functions.
|
|
|
|
The default is @option{-fmath-errno}.
|
|
|
|
On Darwin and FreeBSD systems, the math library never sets @code{errno}.
|
|
There is therefore
|
|
no reason for the compiler to consider the possibility that it might,
|
|
and @option{-fno-math-errno} is the default.
|
|
|
|
@item -funsafe-math-optimizations
|
|
@opindex funsafe-math-optimizations
|
|
Allow optimizations for floating-point arithmetic that (a) assume
|
|
that arguments and results are valid and (b) may violate IEEE or
|
|
ANSI standards. When used at link-time, it may include libraries
|
|
or startup files that change the default FPU control word or other
|
|
similar optimizations.
|
|
|
|
This option should never be turned on by any @option{-O} option since
|
|
it can result in incorrect output for programs which depend on
|
|
an exact implementation of IEEE or ISO rules/specifications for
|
|
math functions.
|
|
|
|
The default is @option{-fno-unsafe-math-optimizations}.
|
|
|
|
@item -ffinite-math-only
|
|
@opindex ffinite-math-only
|
|
Allow optimizations for floating-point arithmetic that assume
|
|
that arguments and results are not NaNs or +-Infs.
|
|
|
|
This option should never be turned on by any @option{-O} option since
|
|
it can result in incorrect output for programs which depend on
|
|
an exact implementation of IEEE or ISO rules/specifications.
|
|
|
|
The default is @option{-fno-finite-math-only}.
|
|
|
|
@item -fno-trapping-math
|
|
@opindex fno-trapping-math
|
|
Compile code assuming that floating-point operations cannot generate
|
|
user-visible traps. These traps include division by zero, overflow,
|
|
underflow, inexact result and invalid operation. This option implies
|
|
@option{-fno-signaling-nans}. Setting this option may allow faster
|
|
code if one relies on ``non-stop'' IEEE arithmetic, for example.
|
|
|
|
This option should never be turned on by any @option{-O} option since
|
|
it can result in incorrect output for programs which depend on
|
|
an exact implementation of IEEE or ISO rules/specifications for
|
|
math functions.
|
|
|
|
The default is @option{-ftrapping-math}.
|
|
|
|
@item -frounding-math
|
|
@opindex frounding-math
|
|
Disable transformations and optimizations that assume default floating
|
|
point rounding behavior. This is round-to-zero for all floating point
|
|
to integer conversions, and round-to-nearest for all other arithmetic
|
|
truncations. This option should be specified for programs that change
|
|
the FP rounding mode dynamically, or that may be executed with a
|
|
non-default rounding mode. This option disables constant folding of
|
|
floating point expressions at compile-time (which may be affected by
|
|
rounding mode) and arithmetic transformations that are unsafe in the
|
|
presence of sign-dependent rounding modes.
|
|
|
|
The default is @option{-fno-rounding-math}.
|
|
|
|
This option is experimental and does not currently guarantee to
|
|
disable all GCC optimizations that are affected by rounding mode.
|
|
Future versions of GCC may provide finer control of this setting
|
|
using C99's @code{FENV_ACCESS} pragma. This command line option
|
|
will be used to specify the default state for @code{FENV_ACCESS}.
|
|
|
|
@item -frtl-abstract-sequences
|
|
@opindex frtl-abstract-sequences
|
|
It is a size optimization method. This option is to find identical
|
|
sequences of code, which can be turned into pseudo-procedures and
|
|
then replace all occurrences with calls to the newly created
|
|
subroutine. It is kind of an opposite of @option{-finline-functions}.
|
|
This optimization runs at RTL level.
|
|
|
|
@item -fsignaling-nans
|
|
@opindex fsignaling-nans
|
|
Compile code assuming that IEEE signaling NaNs may generate user-visible
|
|
traps during floating-point operations. Setting this option disables
|
|
optimizations that may change the number of exceptions visible with
|
|
signaling NaNs. This option implies @option{-ftrapping-math}.
|
|
|
|
This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
|
|
be defined.
|
|
|
|
The default is @option{-fno-signaling-nans}.
|
|
|
|
This option is experimental and does not currently guarantee to
|
|
disable all GCC optimizations that affect signaling NaN behavior.
|
|
|
|
@item -fsingle-precision-constant
|
|
@opindex fsingle-precision-constant
|
|
Treat floating point constant as single precision constant instead of
|
|
implicitly converting it to double precision constant.
|
|
|
|
@item -fcx-limited-range
|
|
@itemx -fno-cx-limited-range
|
|
@opindex fcx-limited-range
|
|
@opindex fno-cx-limited-range
|
|
When enabled, this option states that a range reduction step is not
|
|
needed when performing complex division. The default is
|
|
@option{-fno-cx-limited-range}, but is enabled by @option{-ffast-math}.
|
|
|
|
This option controls the default setting of the ISO C99
|
|
@code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
|
|
all languages.
|
|
|
|
@end table
|
|
|
|
The following options control optimizations that may improve
|
|
performance, but are not enabled by any @option{-O} options. This
|
|
section includes experimental options that may produce broken code.
|
|
|
|
@table @gcctabopt
|
|
@item -fbranch-probabilities
|
|
@opindex fbranch-probabilities
|
|
After running a program compiled with @option{-fprofile-arcs}
|
|
(@pxref{Debugging Options,, Options for Debugging Your Program or
|
|
@command{gcc}}), you can compile it a second time using
|
|
@option{-fbranch-probabilities}, to improve optimizations based on
|
|
the number of times each branch was taken. When the program
|
|
compiled with @option{-fprofile-arcs} exits it saves arc execution
|
|
counts to a file called @file{@var{sourcename}.gcda} for each source
|
|
file The information in this data file is very dependent on the
|
|
structure of the generated code, so you must use the same source code
|
|
and the same optimization options for both compilations.
|
|
|
|
With @option{-fbranch-probabilities}, GCC puts a
|
|
@samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
|
|
These can be used to improve optimization. Currently, they are only
|
|
used in one place: in @file{reorg.c}, instead of guessing which path a
|
|
branch is mostly to take, the @samp{REG_BR_PROB} values are used to
|
|
exactly determine which path is taken more often.
|
|
|
|
@item -fprofile-values
|
|
@opindex fprofile-values
|
|
If combined with @option{-fprofile-arcs}, it adds code so that some
|
|
data about values of expressions in the program is gathered.
|
|
|
|
With @option{-fbranch-probabilities}, it reads back the data gathered
|
|
from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
|
|
notes to instructions for their later usage in optimizations.
|
|
|
|
Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
|
|
|
|
@item -fvpt
|
|
@opindex fvpt
|
|
If combined with @option{-fprofile-arcs}, it instructs the compiler to add
|
|
a code to gather information about values of expressions.
|
|
|
|
With @option{-fbranch-probabilities}, it reads back the data gathered
|
|
and actually performs the optimizations based on them.
|
|
Currently the optimizations include specialization of division operation
|
|
using the knowledge about the value of the denominator.
|
|
|
|
@item -frename-registers
|
|
@opindex frename-registers
|
|
Attempt to avoid false dependencies in scheduled code by making use
|
|
of registers left over after register allocation. This optimization
|
|
will most benefit processors with lots of registers. Depending on the
|
|
debug information format adopted by the target, however, it can
|
|
make debugging impossible, since variables will no longer stay in
|
|
a ``home register''.
|
|
|
|
Enabled by default with @option{-funroll-loops}.
|
|
|
|
@item -ftracer
|
|
@opindex ftracer
|
|
Perform tail duplication to enlarge superblock size. This transformation
|
|
simplifies the control flow of the function allowing other optimizations to do
|
|
better job.
|
|
|
|
Enabled with @option{-fprofile-use}.
|
|
|
|
@item -funroll-loops
|
|
@opindex funroll-loops
|
|
Unroll loops whose number of iterations can be determined at compile time or
|
|
upon entry to the loop. @option{-funroll-loops} implies
|
|
@option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
|
|
It also turns on complete loop peeling (i.e.@: complete removal of loops with
|
|
small constant number of iterations). This option makes code larger, and may
|
|
or may not make it run faster.
|
|
|
|
Enabled with @option{-fprofile-use}.
|
|
|
|
@item -funroll-all-loops
|
|
@opindex funroll-all-loops
|
|
Unroll all loops, even if their number of iterations is uncertain when
|
|
the loop is entered. This usually makes programs run more slowly.
|
|
@option{-funroll-all-loops} implies the same options as
|
|
@option{-funroll-loops}.
|
|
|
|
@item -fpeel-loops
|
|
@opindex fpeel-loops
|
|
Peels the loops for that there is enough information that they do not
|
|
roll much (from profile feedback). It also turns on complete loop peeling
|
|
(i.e.@: complete removal of loops with small constant number of iterations).
|
|
|
|
Enabled with @option{-fprofile-use}.
|
|
|
|
@item -fmove-loop-invariants
|
|
@opindex fmove-loop-invariants
|
|
Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
|
|
at level @option{-O1}
|
|
|
|
@item -funswitch-loops
|
|
@opindex funswitch-loops
|
|
Move branches with loop invariant conditions out of the loop, with duplicates
|
|
of the loop on both branches (modified according to result of the condition).
|
|
|
|
@item -ffunction-sections
|
|
@itemx -fdata-sections
|
|
@opindex ffunction-sections
|
|
@opindex fdata-sections
|
|
Place each function or data item into its own section in the output
|
|
file if the target supports arbitrary sections. The name of the
|
|
function or the name of the data item determines the section's name
|
|
in the output file.
|
|
|
|
Use these options on systems where the linker can perform optimizations
|
|
to improve locality of reference in the instruction space. Most systems
|
|
using the ELF object format and SPARC processors running Solaris 2 have
|
|
linkers with such optimizations. AIX may have these optimizations in
|
|
the future.
|
|
|
|
Only use these options when there are significant benefits from doing
|
|
so. When you specify these options, the assembler and linker will
|
|
create larger object and executable files and will also be slower.
|
|
You will not be able to use @code{gprof} on all systems if you
|
|
specify this option and you may have problems with debugging if
|
|
you specify both this option and @option{-g}.
|
|
|
|
@item -fbranch-target-load-optimize
|
|
@opindex fbranch-target-load-optimize
|
|
Perform branch target register load optimization before prologue / epilogue
|
|
threading.
|
|
The use of target registers can typically be exposed only during reload,
|
|
thus hoisting loads out of loops and doing inter-block scheduling needs
|
|
a separate optimization pass.
|
|
|
|
@item -fbranch-target-load-optimize2
|
|
@opindex fbranch-target-load-optimize2
|
|
Perform branch target register load optimization after prologue / epilogue
|
|
threading.
|
|
|
|
@item -fbtr-bb-exclusive
|
|
@opindex fbtr-bb-exclusive
|
|
When performing branch target register load optimization, don't reuse
|
|
branch target registers in within any basic block.
|
|
|
|
@item -fstack-protector
|
|
Emit extra code to check for buffer overflows, such as stack smashing
|
|
attacks. This is done by adding a guard variable to functions with
|
|
vulnerable objects. This includes functions that call alloca, and
|
|
functions with buffers larger than 8 bytes. The guards are initialized
|
|
when a function is entered and then checked when the function exits.
|
|
If a guard check fails, an error message is printed and the program exits.
|
|
|
|
@item -fstack-protector-all
|
|
Like @option{-fstack-protector} except that all functions are protected.
|
|
|
|
@item -fsection-anchors
|
|
@opindex fsection-anchors
|
|
Try to reduce the number of symbolic address calculations by using
|
|
shared ``anchor'' symbols to address nearby objects. This transformation
|
|
can help to reduce the number of GOT entries and GOT accesses on some
|
|
targets.
|
|
|
|
For example, the implementation of the following function @code{foo}:
|
|
|
|
@smallexample
|
|
static int a, b, c;
|
|
int foo (void) @{ return a + b + c; @}
|
|
@end smallexample
|
|
|
|
would usually calculate the addresses of all three variables, but if you
|
|
compile it with @option{-fsection-anchors}, it will access the variables
|
|
from a common anchor point instead. The effect is similar to the
|
|
following pseudocode (which isn't valid C):
|
|
|
|
@smallexample
|
|
int foo (void)
|
|
@{
|
|
register int *xr = &x;
|
|
return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
|
|
@}
|
|
@end smallexample
|
|
|
|
Not all targets support this option.
|
|
|
|
@item --param @var{name}=@var{value}
|
|
@opindex param
|
|
In some places, GCC uses various constants to control the amount of
|
|
optimization that is done. For example, GCC will not inline functions
|
|
that contain more that a certain number of instructions. You can
|
|
control some of these constants on the command-line using the
|
|
@option{--param} option.
|
|
|
|
The names of specific parameters, and the meaning of the values, are
|
|
tied to the internals of the compiler, and are subject to change
|
|
without notice in future releases.
|
|
|
|
In each case, the @var{value} is an integer. The allowable choices for
|
|
@var{name} are given in the following table:
|
|
|
|
@table @gcctabopt
|
|
@item salias-max-implicit-fields
|
|
The maximum number of fields in a variable without direct
|
|
structure accesses for which structure aliasing will consider trying
|
|
to track each field. The default is 5
|
|
|
|
@item salias-max-array-elements
|
|
The maximum number of elements an array can have and its elements
|
|
still be tracked individually by structure aliasing. The default is 4
|
|
|
|
@item sra-max-structure-size
|
|
The maximum structure size, in bytes, at which the scalar replacement
|
|
of aggregates (SRA) optimization will perform block copies. The
|
|
default value, 0, implies that GCC will select the most appropriate
|
|
size itself.
|
|
|
|
@item sra-field-structure-ratio
|
|
The threshold ratio (as a percentage) between instantiated fields and
|
|
the complete structure size. We say that if the ratio of the number
|
|
of bytes in instantiated fields to the number of bytes in the complete
|
|
structure exceeds this parameter, then block copies are not used. The
|
|
default is 75.
|
|
|
|
@item max-crossjump-edges
|
|
The maximum number of incoming edges to consider for crossjumping.
|
|
The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
|
|
the number of edges incoming to each block. Increasing values mean
|
|
more aggressive optimization, making the compile time increase with
|
|
probably small improvement in executable size.
|
|
|
|
@item min-crossjump-insns
|
|
The minimum number of instructions which must be matched at the end
|
|
of two blocks before crossjumping will be performed on them. This
|
|
value is ignored in the case where all instructions in the block being
|
|
crossjumped from are matched. The default value is 5.
|
|
|
|
@item max-grow-copy-bb-insns
|
|
The maximum code size expansion factor when copying basic blocks
|
|
instead of jumping. The expansion is relative to a jump instruction.
|
|
The default value is 8.
|
|
|
|
@item max-goto-duplication-insns
|
|
The maximum number of instructions to duplicate to a block that jumps
|
|
to a computed goto. To avoid @math{O(N^2)} behavior in a number of
|
|
passes, GCC factors computed gotos early in the compilation process,
|
|
and unfactors them as late as possible. Only computed jumps at the
|
|
end of a basic blocks with no more than max-goto-duplication-insns are
|
|
unfactored. The default value is 8.
|
|
|
|
@item max-delay-slot-insn-search
|
|
The maximum number of instructions to consider when looking for an
|
|
instruction to fill a delay slot. If more than this arbitrary number of
|
|
instructions is searched, the time savings from filling the delay slot
|
|
will be minimal so stop searching. Increasing values mean more
|
|
aggressive optimization, making the compile time increase with probably
|
|
small improvement in executable run time.
|
|
|
|
@item max-delay-slot-live-search
|
|
When trying to fill delay slots, the maximum number of instructions to
|
|
consider when searching for a block with valid live register
|
|
information. Increasing this arbitrarily chosen value means more
|
|
aggressive optimization, increasing the compile time. This parameter
|
|
should be removed when the delay slot code is rewritten to maintain the
|
|
control-flow graph.
|
|
|
|
@item max-gcse-memory
|
|
The approximate maximum amount of memory that will be allocated in
|
|
order to perform the global common subexpression elimination
|
|
optimization. If more memory than specified is required, the
|
|
optimization will not be done.
|
|
|
|
@item max-gcse-passes
|
|
The maximum number of passes of GCSE to run. The default is 1.
|
|
|
|
@item max-pending-list-length
|
|
The maximum number of pending dependencies scheduling will allow
|
|
before flushing the current state and starting over. Large functions
|
|
with few branches or calls can create excessively large lists which
|
|
needlessly consume memory and resources.
|
|
|
|
@item max-inline-insns-single
|
|
Several parameters control the tree inliner used in gcc.
|
|
This number sets the maximum number of instructions (counted in GCC's
|
|
internal representation) in a single function that the tree inliner
|
|
will consider for inlining. This only affects functions declared
|
|
inline and methods implemented in a class declaration (C++).
|
|
The default value is 450.
|
|
|
|
@item max-inline-insns-auto
|
|
When you use @option{-finline-functions} (included in @option{-O3}),
|
|
a lot of functions that would otherwise not be considered for inlining
|
|
by the compiler will be investigated. To those functions, a different
|
|
(more restrictive) limit compared to functions declared inline can
|
|
be applied.
|
|
The default value is 90.
|
|
|
|
@item large-function-insns
|
|
The limit specifying really large functions. For functions larger than this
|
|
limit after inlining inlining is constrained by
|
|
@option{--param large-function-growth}. This parameter is useful primarily
|
|
to avoid extreme compilation time caused by non-linear algorithms used by the
|
|
backend.
|
|
This parameter is ignored when @option{-funit-at-a-time} is not used.
|
|
The default value is 2700.
|
|
|
|
@item large-function-growth
|
|
Specifies maximal growth of large function caused by inlining in percents.
|
|
This parameter is ignored when @option{-funit-at-a-time} is not used.
|
|
The default value is 100 which limits large function growth to 2.0 times
|
|
the original size.
|
|
|
|
@item large-unit-insns
|
|
The limit specifying large translation unit. Growth caused by inlining of
|
|
units larger than this limit is limited by @option{--param inline-unit-growth}.
|
|
For small units this might be too tight (consider unit consisting of function A
|
|
that is inline and B that just calls A three time. If B is small relative to
|
|
A, the growth of unit is 300\% and yet such inlining is very sane. For very
|
|
large units consisting of small inlininable functions however the overall unit
|
|
growth limit is needed to avoid exponential explosion of code size. Thus for
|
|
smaller units, the size is increased to @option{--param large-unit-insns}
|
|
before applying @option{--param inline-unit-growth}. The default is 10000
|
|
|
|
@item inline-unit-growth
|
|
Specifies maximal overall growth of the compilation unit caused by inlining.
|
|
This parameter is ignored when @option{-funit-at-a-time} is not used.
|
|
The default value is 50 which limits unit growth to 1.5 times the original
|
|
size.
|
|
|
|
@item max-inline-insns-recursive
|
|
@itemx max-inline-insns-recursive-auto
|
|
Specifies maximum number of instructions out-of-line copy of self recursive inline
|
|
function can grow into by performing recursive inlining.
|
|
|
|
For functions declared inline @option{--param max-inline-insns-recursive} is
|
|
taken into account. For function not declared inline, recursive inlining
|
|
happens only when @option{-finline-functions} (included in @option{-O3}) is
|
|
enabled and @option{--param max-inline-insns-recursive-auto} is used. The
|
|
default value is 450.
|
|
|
|
@item max-inline-recursive-depth
|
|
@itemx max-inline-recursive-depth-auto
|
|
Specifies maximum recursion depth used by the recursive inlining.
|
|
|
|
For functions declared inline @option{--param max-inline-recursive-depth} is
|
|
taken into account. For function not declared inline, recursive inlining
|
|
happens only when @option{-finline-functions} (included in @option{-O3}) is
|
|
enabled and @option{--param max-inline-recursive-depth-auto} is used. The
|
|
default value is 450.
|
|
|
|
@item min-inline-recursive-probability
|
|
Recursive inlining is profitable only for function having deep recursion
|
|
in average and can hurt for function having little recursion depth by
|
|
increasing the prologue size or complexity of function body to other
|
|
optimizers.
|
|
|
|
When profile feedback is available (see @option{-fprofile-generate}) the actual
|
|
recursion depth can be guessed from probability that function will recurse via
|
|
given call expression. This parameter limits inlining only to call expression
|
|
whose probability exceeds given threshold (in percents). The default value is
|
|
10.
|
|
|
|
@item inline-call-cost
|
|
Specify cost of call instruction relative to simple arithmetics operations
|
|
(having cost of 1). Increasing this cost disqualifies inlining of non-leaf
|
|
functions and at the same time increases size of leaf function that is believed to
|
|
reduce function size by being inlined. In effect it increases amount of
|
|
inlining for code having large abstraction penalty (many functions that just
|
|
pass the arguments to other functions) and decrease inlining for code with low
|
|
abstraction penalty. The default value is 16.
|
|
|
|
@item max-unrolled-insns
|
|
The maximum number of instructions that a loop should have if that loop
|
|
is unrolled, and if the loop is unrolled, it determines how many times
|
|
the loop code is unrolled.
|
|
|
|
@item max-average-unrolled-insns
|
|
The maximum number of instructions biased by probabilities of their execution
|
|
that a loop should have if that loop is unrolled, and if the loop is unrolled,
|
|
it determines how many times the loop code is unrolled.
|
|
|
|
@item max-unroll-times
|
|
The maximum number of unrollings of a single loop.
|
|
|
|
@item max-peeled-insns
|
|
The maximum number of instructions that a loop should have if that loop
|
|
is peeled, and if the loop is peeled, it determines how many times
|
|
the loop code is peeled.
|
|
|
|
@item max-peel-times
|
|
The maximum number of peelings of a single loop.
|
|
|
|
@item max-completely-peeled-insns
|
|
The maximum number of insns of a completely peeled loop.
|
|
|
|
@item max-completely-peel-times
|
|
The maximum number of iterations of a loop to be suitable for complete peeling.
|
|
|
|
@item max-unswitch-insns
|
|
The maximum number of insns of an unswitched loop.
|
|
|
|
@item max-unswitch-level
|
|
The maximum number of branches unswitched in a single loop.
|
|
|
|
@item lim-expensive
|
|
The minimum cost of an expensive expression in the loop invariant motion.
|
|
|
|
@item iv-consider-all-candidates-bound
|
|
Bound on number of candidates for induction variables below that
|
|
all candidates are considered for each use in induction variable
|
|
optimizations. Only the most relevant candidates are considered
|
|
if there are more candidates, to avoid quadratic time complexity.
|
|
|
|
@item iv-max-considered-uses
|
|
The induction variable optimizations give up on loops that contain more
|
|
induction variable uses.
|
|
|
|
@item iv-always-prune-cand-set-bound
|
|
If number of candidates in the set is smaller than this value,
|
|
we always try to remove unnecessary ivs from the set during its
|
|
optimization when a new iv is added to the set.
|
|
|
|
@item scev-max-expr-size
|
|
Bound on size of expressions used in the scalar evolutions analyzer.
|
|
Large expressions slow the analyzer.
|
|
|
|
@item vect-max-version-checks
|
|
The maximum number of runtime checks that can be performed when doing
|
|
loop versioning in the vectorizer. See option ftree-vect-loop-version
|
|
for more information.
|
|
|
|
@item max-iterations-to-track
|
|
|
|
The maximum number of iterations of a loop the brute force algorithm
|
|
for analysis of # of iterations of the loop tries to evaluate.
|
|
|
|
@item hot-bb-count-fraction
|
|
Select fraction of the maximal count of repetitions of basic block in program
|
|
given basic block needs to have to be considered hot.
|
|
|
|
@item hot-bb-frequency-fraction
|
|
Select fraction of the maximal frequency of executions of basic block in
|
|
function given basic block needs to have to be considered hot
|
|
|
|
@item max-predicted-iterations
|
|
The maximum number of loop iterations we predict statically. This is useful
|
|
in cases where function contain single loop with known bound and other loop
|
|
with unknown. We predict the known number of iterations correctly, while
|
|
the unknown number of iterations average to roughly 10. This means that the
|
|
loop without bounds would appear artificially cold relative to the other one.
|
|
|
|
@item tracer-dynamic-coverage
|
|
@itemx tracer-dynamic-coverage-feedback
|
|
|
|
This value is used to limit superblock formation once the given percentage of
|
|
executed instructions is covered. This limits unnecessary code size
|
|
expansion.
|
|
|
|
The @option{tracer-dynamic-coverage-feedback} is used only when profile
|
|
feedback is available. The real profiles (as opposed to statically estimated
|
|
ones) are much less balanced allowing the threshold to be larger value.
|
|
|
|
@item tracer-max-code-growth
|
|
Stop tail duplication once code growth has reached given percentage. This is
|
|
rather hokey argument, as most of the duplicates will be eliminated later in
|
|
cross jumping, so it may be set to much higher values than is the desired code
|
|
growth.
|
|
|
|
@item tracer-min-branch-ratio
|
|
|
|
Stop reverse growth when the reverse probability of best edge is less than this
|
|
threshold (in percent).
|
|
|
|
@item tracer-min-branch-ratio
|
|
@itemx tracer-min-branch-ratio-feedback
|
|
|
|
Stop forward growth if the best edge do have probability lower than this
|
|
threshold.
|
|
|
|
Similarly to @option{tracer-dynamic-coverage} two values are present, one for
|
|
compilation for profile feedback and one for compilation without. The value
|
|
for compilation with profile feedback needs to be more conservative (higher) in
|
|
order to make tracer effective.
|
|
|
|
@item max-cse-path-length
|
|
|
|
Maximum number of basic blocks on path that cse considers. The default is 10.
|
|
|
|
@item max-cse-insns
|
|
The maximum instructions CSE process before flushing. The default is 1000.
|
|
|
|
@item global-var-threshold
|
|
|
|
Counts the number of function calls (@var{n}) and the number of
|
|
call-clobbered variables (@var{v}). If @var{n}x@var{v} is larger than this limit, a
|
|
single artificial variable will be created to represent all the
|
|
call-clobbered variables at function call sites. This artificial
|
|
variable will then be made to alias every call-clobbered variable.
|
|
(done as @code{int * size_t} on the host machine; beware overflow).
|
|
|
|
@item max-aliased-vops
|
|
|
|
Maximum number of virtual operands allowed to represent aliases
|
|
before triggering the alias grouping heuristic. Alias grouping
|
|
reduces compile times and memory consumption needed for aliasing at
|
|
the expense of precision loss in alias information.
|
|
|
|
@item ggc-min-expand
|
|
|
|
GCC uses a garbage collector to manage its own memory allocation. This
|
|
parameter specifies the minimum percentage by which the garbage
|
|
collector's heap should be allowed to expand between collections.
|
|
Tuning this may improve compilation speed; it has no effect on code
|
|
generation.
|
|
|
|
The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
|
|
RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
|
|
the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
|
|
GCC is not able to calculate RAM on a particular platform, the lower
|
|
bound of 30% is used. Setting this parameter and
|
|
@option{ggc-min-heapsize} to zero causes a full collection to occur at
|
|
every opportunity. This is extremely slow, but can be useful for
|
|
debugging.
|
|
|
|
@item ggc-min-heapsize
|
|
|
|
Minimum size of the garbage collector's heap before it begins bothering
|
|
to collect garbage. The first collection occurs after the heap expands
|
|
by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
|
|
tuning this may improve compilation speed, and has no effect on code
|
|
generation.
|
|
|
|
The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
|
|
tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
|
|
with a lower bound of 4096 (four megabytes) and an upper bound of
|
|
131072 (128 megabytes). If GCC is not able to calculate RAM on a
|
|
particular platform, the lower bound is used. Setting this parameter
|
|
very large effectively disables garbage collection. Setting this
|
|
parameter and @option{ggc-min-expand} to zero causes a full collection
|
|
to occur at every opportunity.
|
|
|
|
@item max-reload-search-insns
|
|
The maximum number of instruction reload should look backward for equivalent
|
|
register. Increasing values mean more aggressive optimization, making the
|
|
compile time increase with probably slightly better performance. The default
|
|
value is 100.
|
|
|
|
@item max-cselib-memory-locations
|
|
The maximum number of memory locations cselib should take into account.
|
|
Increasing values mean more aggressive optimization, making the compile time
|
|
increase with probably slightly better performance. The default value is 500.
|
|
|
|
@item max-flow-memory-locations
|
|
Similar as @option{max-cselib-memory-locations} but for dataflow liveness.
|
|
The default value is 100.
|
|
|
|
@item reorder-blocks-duplicate
|
|
@itemx reorder-blocks-duplicate-feedback
|
|
|
|
Used by basic block reordering pass to decide whether to use unconditional
|
|
branch or duplicate the code on its destination. Code is duplicated when its
|
|
estimated size is smaller than this value multiplied by the estimated size of
|
|
unconditional jump in the hot spots of the program.
|
|
|
|
The @option{reorder-block-duplicate-feedback} is used only when profile
|
|
feedback is available and may be set to higher values than
|
|
@option{reorder-block-duplicate} since information about the hot spots is more
|
|
accurate.
|
|
|
|
@item max-sched-ready-insns
|
|
The maximum number of instructions ready to be issued the scheduler should
|
|
consider at any given time during the first scheduling pass. Increasing
|
|
values mean more thorough searches, making the compilation time increase
|
|
with probably little benefit. The default value is 100.
|
|
|
|
@item max-sched-region-blocks
|
|
The maximum number of blocks in a region to be considered for
|
|
interblock scheduling. The default value is 10.
|
|
|
|
@item max-sched-region-insns
|
|
The maximum number of insns in a region to be considered for
|
|
interblock scheduling. The default value is 100.
|
|
|
|
@item min-spec-prob
|
|
The minimum probability (in percents) of reaching a source block
|
|
for interblock speculative scheduling. The default value is 40.
|
|
|
|
@item max-sched-extend-regions-iters
|
|
The maximum number of iterations through CFG to extend regions.
|
|
0 - disable region extension,
|
|
N - do at most N iterations.
|
|
The default value is 0.
|
|
|
|
@item max-sched-insn-conflict-delay
|
|
The maximum conflict delay for an insn to be considered for speculative motion.
|
|
The default value is 3.
|
|
|
|
@item sched-spec-prob-cutoff
|
|
The minimal probability of speculation success (in percents), so that
|
|
speculative insn will be scheduled.
|
|
The default value is 40.
|
|
|
|
@item max-last-value-rtl
|
|
|
|
The maximum size measured as number of RTLs that can be recorded in an expression
|
|
in combiner for a pseudo register as last known value of that register. The default
|
|
is 10000.
|
|
|
|
@item integer-share-limit
|
|
Small integer constants can use a shared data structure, reducing the
|
|
compiler's memory usage and increasing its speed. This sets the maximum
|
|
value of a shared integer constant's. The default value is 256.
|
|
|
|
@item min-virtual-mappings
|
|
Specifies the minimum number of virtual mappings in the incremental
|
|
SSA updater that should be registered to trigger the virtual mappings
|
|
heuristic defined by virtual-mappings-ratio. The default value is
|
|
100.
|
|
|
|
@item virtual-mappings-ratio
|
|
If the number of virtual mappings is virtual-mappings-ratio bigger
|
|
than the number of virtual symbols to be updated, then the incremental
|
|
SSA updater switches to a full update for those symbols. The default
|
|
ratio is 3.
|
|
|
|
@item ssp-buffer-size
|
|
The minimum size of buffers (i.e. arrays) that will receive stack smashing
|
|
protection when @option{-fstack-protection} is used.
|
|
|
|
@item max-jump-thread-duplication-stmts
|
|
Maximum number of statements allowed in a block that needs to be
|
|
duplicated when threading jumps.
|
|
|
|
@item max-fields-for-field-sensitive
|
|
Maximum number of fields in a structure we will treat in
|
|
a field sensitive manner during pointer analysis.
|
|
|
|
@end table
|
|
@end table
|
|
|
|
@node Preprocessor Options
|
|
@section Options Controlling the Preprocessor
|
|
@cindex preprocessor options
|
|
@cindex options, preprocessor
|
|
|
|
These options control the C preprocessor, which is run on each C source
|
|
file before actual compilation.
|
|
|
|
If you use the @option{-E} option, nothing is done except preprocessing.
|
|
Some of these options make sense only together with @option{-E} because
|
|
they cause the preprocessor output to be unsuitable for actual
|
|
compilation.
|
|
|
|
@table @gcctabopt
|
|
@opindex Wp
|
|
You can use @option{-Wp,@var{option}} to bypass the compiler driver
|
|
and pass @var{option} directly through to the preprocessor. If
|
|
@var{option} contains commas, it is split into multiple options at the
|
|
commas. However, many options are modified, translated or interpreted
|
|
by the compiler driver before being passed to the preprocessor, and
|
|
@option{-Wp} forcibly bypasses this phase. The preprocessor's direct
|
|
interface is undocumented and subject to change, so whenever possible
|
|
you should avoid using @option{-Wp} and let the driver handle the
|
|
options instead.
|
|
|
|
@item -Xpreprocessor @var{option}
|
|
@opindex preprocessor
|
|
Pass @var{option} as an option to the preprocessor. You can use this to
|
|
supply system-specific preprocessor options which GCC does not know how to
|
|
recognize.
|
|
|
|
If you want to pass an option that takes an argument, you must use
|
|
@option{-Xpreprocessor} twice, once for the option and once for the argument.
|
|
@end table
|
|
|
|
@include cppopts.texi
|
|
|
|
@node Assembler Options
|
|
@section Passing Options to the Assembler
|
|
|
|
@c prevent bad page break with this line
|
|
You can pass options to the assembler.
|
|
|
|
@table @gcctabopt
|
|
@item -Wa,@var{option}
|
|
@opindex Wa
|
|
Pass @var{option} as an option to the assembler. If @var{option}
|
|
contains commas, it is split into multiple options at the commas.
|
|
|
|
@item -Xassembler @var{option}
|
|
@opindex Xassembler
|
|
Pass @var{option} as an option to the assembler. You can use this to
|
|
supply system-specific assembler options which GCC does not know how to
|
|
recognize.
|
|
|
|
If you want to pass an option that takes an argument, you must use
|
|
@option{-Xassembler} twice, once for the option and once for the argument.
|
|
|
|
@end table
|
|
|
|
@node Link Options
|
|
@section Options for Linking
|
|
@cindex link options
|
|
@cindex options, linking
|
|
|
|
These options come into play when the compiler links object files into
|
|
an executable output file. They are meaningless if the compiler is
|
|
not doing a link step.
|
|
|
|
@table @gcctabopt
|
|
@cindex file names
|
|
@item @var{object-file-name}
|
|
A file name that does not end in a special recognized suffix is
|
|
considered to name an object file or library. (Object files are
|
|
distinguished from libraries by the linker according to the file
|
|
contents.) If linking is done, these object files are used as input
|
|
to the linker.
|
|
|
|
@item -c
|
|
@itemx -S
|
|
@itemx -E
|
|
@opindex c
|
|
@opindex S
|
|
@opindex E
|
|
If any of these options is used, then the linker is not run, and
|
|
object file names should not be used as arguments. @xref{Overall
|
|
Options}.
|
|
|
|
@cindex Libraries
|
|
@item -l@var{library}
|
|
@itemx -l @var{library}
|
|
@opindex l
|
|
Search the library named @var{library} when linking. (The second
|
|
alternative with the library as a separate argument is only for
|
|
POSIX compliance and is not recommended.)
|
|
|
|
It makes a difference where in the command you write this option; the
|
|
linker searches and processes libraries and object files in the order they
|
|
are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
|
|
after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
|
|
to functions in @samp{z}, those functions may not be loaded.
|
|
|
|
The linker searches a standard list of directories for the library,
|
|
which is actually a file named @file{lib@var{library}.a}. The linker
|
|
then uses this file as if it had been specified precisely by name.
|
|
|
|
The directories searched include several standard system directories
|
|
plus any that you specify with @option{-L}.
|
|
|
|
Normally the files found this way are library files---archive files
|
|
whose members are object files. The linker handles an archive file by
|
|
scanning through it for members which define symbols that have so far
|
|
been referenced but not defined. But if the file that is found is an
|
|
ordinary object file, it is linked in the usual fashion. The only
|
|
difference between using an @option{-l} option and specifying a file name
|
|
is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
|
|
and searches several directories.
|
|
|
|
@item -lobjc
|
|
@opindex lobjc
|
|
You need this special case of the @option{-l} option in order to
|
|
link an Objective-C or Objective-C++ program.
|
|
|
|
@item -nostartfiles
|
|
@opindex nostartfiles
|
|
Do not use the standard system startup files when linking.
|
|
The standard system libraries are used normally, unless @option{-nostdlib}
|
|
or @option{-nodefaultlibs} is used.
|
|
|
|
@item -nodefaultlibs
|
|
@opindex nodefaultlibs
|
|
Do not use the standard system libraries when linking.
|
|
Only the libraries you specify will be passed to the linker.
|
|
The standard startup files are used normally, unless @option{-nostartfiles}
|
|
is used. The compiler may generate calls to @code{memcmp},
|
|
@code{memset}, @code{memcpy} and @code{memmove}.
|
|
These entries are usually resolved by entries in
|
|
libc. These entry points should be supplied through some other
|
|
mechanism when this option is specified.
|
|
|
|
@item -nostdlib
|
|
@opindex nostdlib
|
|
Do not use the standard system startup files or libraries when linking.
|
|
No startup files and only the libraries you specify will be passed to
|
|
the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
|
|
@code{memcpy} and @code{memmove}.
|
|
These entries are usually resolved by entries in
|
|
libc. These entry points should be supplied through some other
|
|
mechanism when this option is specified.
|
|
|
|
@cindex @option{-lgcc}, use with @option{-nostdlib}
|
|
@cindex @option{-nostdlib} and unresolved references
|
|
@cindex unresolved references and @option{-nostdlib}
|
|
@cindex @option{-lgcc}, use with @option{-nodefaultlibs}
|
|
@cindex @option{-nodefaultlibs} and unresolved references
|
|
@cindex unresolved references and @option{-nodefaultlibs}
|
|
One of the standard libraries bypassed by @option{-nostdlib} and
|
|
@option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
|
|
that GCC uses to overcome shortcomings of particular machines, or special
|
|
needs for some languages.
|
|
(@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
|
|
Collection (GCC) Internals},
|
|
for more discussion of @file{libgcc.a}.)
|
|
In most cases, you need @file{libgcc.a} even when you want to avoid
|
|
other standard libraries. In other words, when you specify @option{-nostdlib}
|
|
or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
|
|
This ensures that you have no unresolved references to internal GCC
|
|
library subroutines. (For example, @samp{__main}, used to ensure C++
|
|
constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
|
|
GNU Compiler Collection (GCC) Internals}.)
|
|
|
|
@item -pie
|
|
@opindex pie
|
|
Produce a position independent executable on targets which support it.
|
|
For predictable results, you must also specify the same set of options
|
|
that were used to generate code (@option{-fpie}, @option{-fPIE},
|
|
or model suboptions) when you specify this option.
|
|
|
|
@item -rdynamic
|
|
@opindex rdynamic
|
|
Pass the flag @option{-export-dynamic} to the ELF linker, on targets
|
|
that support it. This instructs the linker to add all symbols, not
|
|
only used ones, to the dynamic symbol table. This option is needed
|
|
for some uses of @code{dlopen} or to allow obtaining backtraces
|
|
from within a program.
|
|
|
|
@item -s
|
|
@opindex s
|
|
Remove all symbol table and relocation information from the executable.
|
|
|
|
@item -static
|
|
@opindex static
|
|
On systems that support dynamic linking, this prevents linking with the shared
|
|
libraries. On other systems, this option has no effect.
|
|
|
|
@item -shared
|
|
@opindex shared
|
|
Produce a shared object which can then be linked with other objects to
|
|
form an executable. Not all systems support this option. For predictable
|
|
results, you must also specify the same set of options that were used to
|
|
generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
|
|
when you specify this option.@footnote{On some systems, @samp{gcc -shared}
|
|
needs to build supplementary stub code for constructors to work. On
|
|
multi-libbed systems, @samp{gcc -shared} must select the correct support
|
|
libraries to link against. Failing to supply the correct flags may lead
|
|
to subtle defects. Supplying them in cases where they are not necessary
|
|
is innocuous.}
|
|
|
|
@item -shared-libgcc
|
|
@itemx -static-libgcc
|
|
@opindex shared-libgcc
|
|
@opindex static-libgcc
|
|
On systems that provide @file{libgcc} as a shared library, these options
|
|
force the use of either the shared or static version respectively.
|
|
If no shared version of @file{libgcc} was built when the compiler was
|
|
configured, these options have no effect.
|
|
|
|
There are several situations in which an application should use the
|
|
shared @file{libgcc} instead of the static version. The most common
|
|
of these is when the application wishes to throw and catch exceptions
|
|
across different shared libraries. In that case, each of the libraries
|
|
as well as the application itself should use the shared @file{libgcc}.
|
|
|
|
Therefore, the G++ and GCJ drivers automatically add
|
|
@option{-shared-libgcc} whenever you build a shared library or a main
|
|
executable, because C++ and Java programs typically use exceptions, so
|
|
this is the right thing to do.
|
|
|
|
If, instead, you use the GCC driver to create shared libraries, you may
|
|
find that they will not always be linked with the shared @file{libgcc}.
|
|
If GCC finds, at its configuration time, that you have a non-GNU linker
|
|
or a GNU linker that does not support option @option{--eh-frame-hdr},
|
|
it will link the shared version of @file{libgcc} into shared libraries
|
|
by default. Otherwise, it will take advantage of the linker and optimize
|
|
away the linking with the shared version of @file{libgcc}, linking with
|
|
the static version of libgcc by default. This allows exceptions to
|
|
propagate through such shared libraries, without incurring relocation
|
|
costs at library load time.
|
|
|
|
However, if a library or main executable is supposed to throw or catch
|
|
exceptions, you must link it using the G++ or GCJ driver, as appropriate
|
|
for the languages used in the program, or using the option
|
|
@option{-shared-libgcc}, such that it is linked with the shared
|
|
@file{libgcc}.
|
|
|
|
@item -symbolic
|
|
@opindex symbolic
|
|
Bind references to global symbols when building a shared object. Warn
|
|
about any unresolved references (unless overridden by the link editor
|
|
option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
|
|
this option.
|
|
|
|
@item -Xlinker @var{option}
|
|
@opindex Xlinker
|
|
Pass @var{option} as an option to the linker. You can use this to
|
|
supply system-specific linker options which GCC does not know how to
|
|
recognize.
|
|
|
|
If you want to pass an option that takes an argument, you must use
|
|
@option{-Xlinker} twice, once for the option and once for the argument.
|
|
For example, to pass @option{-assert definitions}, you must write
|
|
@samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
|
|
@option{-Xlinker "-assert definitions"}, because this passes the entire
|
|
string as a single argument, which is not what the linker expects.
|
|
|
|
@item -Wl,@var{option}
|
|
@opindex Wl
|
|
Pass @var{option} as an option to the linker. If @var{option} contains
|
|
commas, it is split into multiple options at the commas.
|
|
|
|
@item -u @var{symbol}
|
|
@opindex u
|
|
Pretend the symbol @var{symbol} is undefined, to force linking of
|
|
library modules to define it. You can use @option{-u} multiple times with
|
|
different symbols to force loading of additional library modules.
|
|
@end table
|
|
|
|
@node Directory Options
|
|
@section Options for Directory Search
|
|
@cindex directory options
|
|
@cindex options, directory search
|
|
@cindex search path
|
|
|
|
These options specify directories to search for header files, for
|
|
libraries and for parts of the compiler:
|
|
|
|
@table @gcctabopt
|
|
@item -I@var{dir}
|
|
@opindex I
|
|
Add the directory @var{dir} to the head of the list of directories to be
|
|
searched for header files. This can be used to override a system header
|
|
file, substituting your own version, since these directories are
|
|
searched before the system header file directories. However, you should
|
|
not use this option to add directories that contain vendor-supplied
|
|
system header files (use @option{-isystem} for that). If you use more than
|
|
one @option{-I} option, the directories are scanned in left-to-right
|
|
order; the standard system directories come after.
|
|
|
|
If a standard system include directory, or a directory specified with
|
|
@option{-isystem}, is also specified with @option{-I}, the @option{-I}
|
|
option will be ignored. The directory will still be searched but as a
|
|
system directory at its normal position in the system include chain.
|
|
This is to ensure that GCC's procedure to fix buggy system headers and
|
|
the ordering for the include_next directive are not inadvertently changed.
|
|
If you really need to change the search order for system directories,
|
|
use the @option{-nostdinc} and/or @option{-isystem} options.
|
|
|
|
@item -iquote@var{dir}
|
|
@opindex iquote
|
|
Add the directory @var{dir} to the head of the list of directories to
|
|
be searched for header files only for the case of @samp{#include
|
|
"@var{file}"}; they are not searched for @samp{#include <@var{file}>},
|
|
otherwise just like @option{-I}.
|
|
|
|
@item -L@var{dir}
|
|
@opindex L
|
|
Add directory @var{dir} to the list of directories to be searched
|
|
for @option{-l}.
|
|
|
|
@item -B@var{prefix}
|
|
@opindex B
|
|
This option specifies where to find the executables, libraries,
|
|
include files, and data files of the compiler itself.
|
|
|
|
The compiler driver program runs one or more of the subprograms
|
|
@file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
|
|
@var{prefix} as a prefix for each program it tries to run, both with and
|
|
without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
|
|
|
|
For each subprogram to be run, the compiler driver first tries the
|
|
@option{-B} prefix, if any. If that name is not found, or if @option{-B}
|
|
was not specified, the driver tries two standard prefixes, which are
|
|
@file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
|
|
those results in a file name that is found, the unmodified program
|
|
name is searched for using the directories specified in your
|
|
@env{PATH} environment variable.
|
|
|
|
The compiler will check to see if the path provided by the @option{-B}
|
|
refers to a directory, and if necessary it will add a directory
|
|
separator character at the end of the path.
|
|
|
|
@option{-B} prefixes that effectively specify directory names also apply
|
|
to libraries in the linker, because the compiler translates these
|
|
options into @option{-L} options for the linker. They also apply to
|
|
includes files in the preprocessor, because the compiler translates these
|
|
options into @option{-isystem} options for the preprocessor. In this case,
|
|
the compiler appends @samp{include} to the prefix.
|
|
|
|
The run-time support file @file{libgcc.a} can also be searched for using
|
|
the @option{-B} prefix, if needed. If it is not found there, the two
|
|
standard prefixes above are tried, and that is all. The file is left
|
|
out of the link if it is not found by those means.
|
|
|
|
Another way to specify a prefix much like the @option{-B} prefix is to use
|
|
the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
|
|
Variables}.
|
|
|
|
As a special kludge, if the path provided by @option{-B} is
|
|
@file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
|
|
9, then it will be replaced by @file{[dir/]include}. This is to help
|
|
with boot-strapping the compiler.
|
|
|
|
@item -specs=@var{file}
|
|
@opindex specs
|
|
Process @var{file} after the compiler reads in the standard @file{specs}
|
|
file, in order to override the defaults that the @file{gcc} driver
|
|
program uses when determining what switches to pass to @file{cc1},
|
|
@file{cc1plus}, @file{as}, @file{ld}, etc. More than one
|
|
@option{-specs=@var{file}} can be specified on the command line, and they
|
|
are processed in order, from left to right.
|
|
|
|
@item --sysroot=@var{dir}
|
|
@opindex sysroot
|
|
Use @var{dir} as the logical root directory for headers and libraries.
|
|
For example, if the compiler would normally search for headers in
|
|
@file{/usr/include} and libraries in @file{/usr/lib}, it will instead
|
|
search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
|
|
|
|
If you use both this option and the @option{-isysroot} option, then
|
|
the @option{--sysroot} option will apply to libraries, but the
|
|
@option{-isysroot} option will apply to header files.
|
|
|
|
The GNU linker (beginning with version 2.16) has the necessary support
|
|
for this option. If your linker does not support this option, the
|
|
header file aspect of @option{--sysroot} will still work, but the
|
|
library aspect will not.
|
|
|
|
@item -I-
|
|
@opindex I-
|
|
This option has been deprecated. Please use @option{-iquote} instead for
|
|
@option{-I} directories before the @option{-I-} and remove the @option{-I-}.
|
|
Any directories you specify with @option{-I} options before the @option{-I-}
|
|
option are searched only for the case of @samp{#include "@var{file}"};
|
|
they are not searched for @samp{#include <@var{file}>}.
|
|
|
|
If additional directories are specified with @option{-I} options after
|
|
the @option{-I-}, these directories are searched for all @samp{#include}
|
|
directives. (Ordinarily @emph{all} @option{-I} directories are used
|
|
this way.)
|
|
|
|
In addition, the @option{-I-} option inhibits the use of the current
|
|
directory (where the current input file came from) as the first search
|
|
directory for @samp{#include "@var{file}"}. There is no way to
|
|
override this effect of @option{-I-}. With @option{-I.} you can specify
|
|
searching the directory which was current when the compiler was
|
|
invoked. That is not exactly the same as what the preprocessor does
|
|
by default, but it is often satisfactory.
|
|
|
|
@option{-I-} does not inhibit the use of the standard system directories
|
|
for header files. Thus, @option{-I-} and @option{-nostdinc} are
|
|
independent.
|
|
@end table
|
|
|
|
@c man end
|
|
|
|
@node Spec Files
|
|
@section Specifying subprocesses and the switches to pass to them
|
|
@cindex Spec Files
|
|
|
|
@command{gcc} is a driver program. It performs its job by invoking a
|
|
sequence of other programs to do the work of compiling, assembling and
|
|
linking. GCC interprets its command-line parameters and uses these to
|
|
deduce which programs it should invoke, and which command-line options
|
|
it ought to place on their command lines. This behavior is controlled
|
|
by @dfn{spec strings}. In most cases there is one spec string for each
|
|
program that GCC can invoke, but a few programs have multiple spec
|
|
strings to control their behavior. The spec strings built into GCC can
|
|
be overridden by using the @option{-specs=} command-line switch to specify
|
|
a spec file.
|
|
|
|
@dfn{Spec files} are plaintext files that are used to construct spec
|
|
strings. They consist of a sequence of directives separated by blank
|
|
lines. The type of directive is determined by the first non-whitespace
|
|
character on the line and it can be one of the following:
|
|
|
|
@table @code
|
|
@item %@var{command}
|
|
Issues a @var{command} to the spec file processor. The commands that can
|
|
appear here are:
|
|
|
|
@table @code
|
|
@item %include <@var{file}>
|
|
@cindex %include
|
|
Search for @var{file} and insert its text at the current point in the
|
|
specs file.
|
|
|
|
@item %include_noerr <@var{file}>
|
|
@cindex %include_noerr
|
|
Just like @samp{%include}, but do not generate an error message if the include
|
|
file cannot be found.
|
|
|
|
@item %rename @var{old_name} @var{new_name}
|
|
@cindex %rename
|
|
Rename the spec string @var{old_name} to @var{new_name}.
|
|
|
|
@end table
|
|
|
|
@item *[@var{spec_name}]:
|
|
This tells the compiler to create, override or delete the named spec
|
|
string. All lines after this directive up to the next directive or
|
|
blank line are considered to be the text for the spec string. If this
|
|
results in an empty string then the spec will be deleted. (Or, if the
|
|
spec did not exist, then nothing will happened.) Otherwise, if the spec
|
|
does not currently exist a new spec will be created. If the spec does
|
|
exist then its contents will be overridden by the text of this
|
|
directive, unless the first character of that text is the @samp{+}
|
|
character, in which case the text will be appended to the spec.
|
|
|
|
@item [@var{suffix}]:
|
|
Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
|
|
and up to the next directive or blank line are considered to make up the
|
|
spec string for the indicated suffix. When the compiler encounters an
|
|
input file with the named suffix, it will processes the spec string in
|
|
order to work out how to compile that file. For example:
|
|
|
|
@smallexample
|
|
.ZZ:
|
|
z-compile -input %i
|
|
@end smallexample
|
|
|
|
This says that any input file whose name ends in @samp{.ZZ} should be
|
|
passed to the program @samp{z-compile}, which should be invoked with the
|
|
command-line switch @option{-input} and with the result of performing the
|
|
@samp{%i} substitution. (See below.)
|
|
|
|
As an alternative to providing a spec string, the text that follows a
|
|
suffix directive can be one of the following:
|
|
|
|
@table @code
|
|
@item @@@var{language}
|
|
This says that the suffix is an alias for a known @var{language}. This is
|
|
similar to using the @option{-x} command-line switch to GCC to specify a
|
|
language explicitly. For example:
|
|
|
|
@smallexample
|
|
.ZZ:
|
|
@@c++
|
|
@end smallexample
|
|
|
|
Says that .ZZ files are, in fact, C++ source files.
|
|
|
|
@item #@var{name}
|
|
This causes an error messages saying:
|
|
|
|
@smallexample
|
|
@var{name} compiler not installed on this system.
|
|
@end smallexample
|
|
@end table
|
|
|
|
GCC already has an extensive list of suffixes built into it.
|
|
This directive will add an entry to the end of the list of suffixes, but
|
|
since the list is searched from the end backwards, it is effectively
|
|
possible to override earlier entries using this technique.
|
|
|
|
@end table
|
|
|
|
GCC has the following spec strings built into it. Spec files can
|
|
override these strings or create their own. Note that individual
|
|
targets can also add their own spec strings to this list.
|
|
|
|
@smallexample
|
|
asm Options to pass to the assembler
|
|
asm_final Options to pass to the assembler post-processor
|
|
cpp Options to pass to the C preprocessor
|
|
cc1 Options to pass to the C compiler
|
|
cc1plus Options to pass to the C++ compiler
|
|
endfile Object files to include at the end of the link
|
|
link Options to pass to the linker
|
|
lib Libraries to include on the command line to the linker
|
|
libgcc Decides which GCC support library to pass to the linker
|
|
linker Sets the name of the linker
|
|
predefines Defines to be passed to the C preprocessor
|
|
signed_char Defines to pass to CPP to say whether @code{char} is signed
|
|
by default
|
|
startfile Object files to include at the start of the link
|
|
@end smallexample
|
|
|
|
Here is a small example of a spec file:
|
|
|
|
@smallexample
|
|
%rename lib old_lib
|
|
|
|
*lib:
|
|
--start-group -lgcc -lc -leval1 --end-group %(old_lib)
|
|
@end smallexample
|
|
|
|
This example renames the spec called @samp{lib} to @samp{old_lib} and
|
|
then overrides the previous definition of @samp{lib} with a new one.
|
|
The new definition adds in some extra command-line options before
|
|
including the text of the old definition.
|
|
|
|
@dfn{Spec strings} are a list of command-line options to be passed to their
|
|
corresponding program. In addition, the spec strings can contain
|
|
@samp{%}-prefixed sequences to substitute variable text or to
|
|
conditionally insert text into the command line. Using these constructs
|
|
it is possible to generate quite complex command lines.
|
|
|
|
Here is a table of all defined @samp{%}-sequences for spec
|
|
strings. Note that spaces are not generated automatically around the
|
|
results of expanding these sequences. Therefore you can concatenate them
|
|
together or combine them with constant text in a single argument.
|
|
|
|
@table @code
|
|
@item %%
|
|
Substitute one @samp{%} into the program name or argument.
|
|
|
|
@item %i
|
|
Substitute the name of the input file being processed.
|
|
|
|
@item %b
|
|
Substitute the basename of the input file being processed.
|
|
This is the substring up to (and not including) the last period
|
|
and not including the directory.
|
|
|
|
@item %B
|
|
This is the same as @samp{%b}, but include the file suffix (text after
|
|
the last period).
|
|
|
|
@item %d
|
|
Marks the argument containing or following the @samp{%d} as a
|
|
temporary file name, so that that file will be deleted if GCC exits
|
|
successfully. Unlike @samp{%g}, this contributes no text to the
|
|
argument.
|
|
|
|
@item %g@var{suffix}
|
|
Substitute a file name that has suffix @var{suffix} and is chosen
|
|
once per compilation, and mark the argument in the same way as
|
|
@samp{%d}. To reduce exposure to denial-of-service attacks, the file
|
|
name is now chosen in a way that is hard to predict even when previously
|
|
chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
|
|
might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
|
|
the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
|
|
treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
|
|
was simply substituted with a file name chosen once per compilation,
|
|
without regard to any appended suffix (which was therefore treated
|
|
just like ordinary text), making such attacks more likely to succeed.
|
|
|
|
@item %u@var{suffix}
|
|
Like @samp{%g}, but generates a new temporary file name even if
|
|
@samp{%u@var{suffix}} was already seen.
|
|
|
|
@item %U@var{suffix}
|
|
Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
|
|
new one if there is no such last file name. In the absence of any
|
|
@samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
|
|
the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
|
|
would involve the generation of two distinct file names, one
|
|
for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
|
|
simply substituted with a file name chosen for the previous @samp{%u},
|
|
without regard to any appended suffix.
|
|
|
|
@item %j@var{suffix}
|
|
Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
|
|
writable, and if save-temps is off; otherwise, substitute the name
|
|
of a temporary file, just like @samp{%u}. This temporary file is not
|
|
meant for communication between processes, but rather as a junk
|
|
disposal mechanism.
|
|
|
|
@item %|@var{suffix}
|
|
@itemx %m@var{suffix}
|
|
Like @samp{%g}, except if @option{-pipe} is in effect. In that case
|
|
@samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
|
|
all. These are the two most common ways to instruct a program that it
|
|
should read from standard input or write to standard output. If you
|
|
need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
|
|
construct: see for example @file{f/lang-specs.h}.
|
|
|
|
@item %.@var{SUFFIX}
|
|
Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
|
|
when it is subsequently output with @samp{%*}. @var{SUFFIX} is
|
|
terminated by the next space or %.
|
|
|
|
@item %w
|
|
Marks the argument containing or following the @samp{%w} as the
|
|
designated output file of this compilation. This puts the argument
|
|
into the sequence of arguments that @samp{%o} will substitute later.
|
|
|
|
@item %o
|
|
Substitutes the names of all the output files, with spaces
|
|
automatically placed around them. You should write spaces
|
|
around the @samp{%o} as well or the results are undefined.
|
|
@samp{%o} is for use in the specs for running the linker.
|
|
Input files whose names have no recognized suffix are not compiled
|
|
at all, but they are included among the output files, so they will
|
|
be linked.
|
|
|
|
@item %O
|
|
Substitutes the suffix for object files. Note that this is
|
|
handled specially when it immediately follows @samp{%g, %u, or %U},
|
|
because of the need for those to form complete file names. The
|
|
handling is such that @samp{%O} is treated exactly as if it had already
|
|
been substituted, except that @samp{%g, %u, and %U} do not currently
|
|
support additional @var{suffix} characters following @samp{%O} as they would
|
|
following, for example, @samp{.o}.
|
|
|
|
@item %p
|
|
Substitutes the standard macro predefinitions for the
|
|
current target machine. Use this when running @code{cpp}.
|
|
|
|
@item %P
|
|
Like @samp{%p}, but puts @samp{__} before and after the name of each
|
|
predefined macro, except for macros that start with @samp{__} or with
|
|
@samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
|
|
C@.
|
|
|
|
@item %I
|
|
Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
|
|
@option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
|
|
@option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
|
|
and @option{-imultilib} as necessary.
|
|
|
|
@item %s
|
|
Current argument is the name of a library or startup file of some sort.
|
|
Search for that file in a standard list of directories and substitute
|
|
the full name found.
|
|
|
|
@item %e@var{str}
|
|
Print @var{str} as an error message. @var{str} is terminated by a newline.
|
|
Use this when inconsistent options are detected.
|
|
|
|
@item %(@var{name})
|
|
Substitute the contents of spec string @var{name} at this point.
|
|
|
|
@item %[@var{name}]
|
|
Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
|
|
|
|
@item %x@{@var{option}@}
|
|
Accumulate an option for @samp{%X}.
|
|
|
|
@item %X
|
|
Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
|
|
spec string.
|
|
|
|
@item %Y
|
|
Output the accumulated assembler options specified by @option{-Wa}.
|
|
|
|
@item %Z
|
|
Output the accumulated preprocessor options specified by @option{-Wp}.
|
|
|
|
@item %a
|
|
Process the @code{asm} spec. This is used to compute the
|
|
switches to be passed to the assembler.
|
|
|
|
@item %A
|
|
Process the @code{asm_final} spec. This is a spec string for
|
|
passing switches to an assembler post-processor, if such a program is
|
|
needed.
|
|
|
|
@item %l
|
|
Process the @code{link} spec. This is the spec for computing the
|
|
command line passed to the linker. Typically it will make use of the
|
|
@samp{%L %G %S %D and %E} sequences.
|
|
|
|
@item %D
|
|
Dump out a @option{-L} option for each directory that GCC believes might
|
|
contain startup files. If the target supports multilibs then the
|
|
current multilib directory will be prepended to each of these paths.
|
|
|
|
@item %L
|
|
Process the @code{lib} spec. This is a spec string for deciding which
|
|
libraries should be included on the command line to the linker.
|
|
|
|
@item %G
|
|
Process the @code{libgcc} spec. This is a spec string for deciding
|
|
which GCC support library should be included on the command line to the linker.
|
|
|
|
@item %S
|
|
Process the @code{startfile} spec. This is a spec for deciding which
|
|
object files should be the first ones passed to the linker. Typically
|
|
this might be a file named @file{crt0.o}.
|
|
|
|
@item %E
|
|
Process the @code{endfile} spec. This is a spec string that specifies
|
|
the last object files that will be passed to the linker.
|
|
|
|
@item %C
|
|
Process the @code{cpp} spec. This is used to construct the arguments
|
|
to be passed to the C preprocessor.
|
|
|
|
@item %1
|
|
Process the @code{cc1} spec. This is used to construct the options to be
|
|
passed to the actual C compiler (@samp{cc1}).
|
|
|
|
@item %2
|
|
Process the @code{cc1plus} spec. This is used to construct the options to be
|
|
passed to the actual C++ compiler (@samp{cc1plus}).
|
|
|
|
@item %*
|
|
Substitute the variable part of a matched option. See below.
|
|
Note that each comma in the substituted string is replaced by
|
|
a single space.
|
|
|
|
@item %<@code{S}
|
|
Remove all occurrences of @code{-S} from the command line. Note---this
|
|
command is position dependent. @samp{%} commands in the spec string
|
|
before this one will see @code{-S}, @samp{%} commands in the spec string
|
|
after this one will not.
|
|
|
|
@item %:@var{function}(@var{args})
|
|
Call the named function @var{function}, passing it @var{args}.
|
|
@var{args} is first processed as a nested spec string, then split
|
|
into an argument vector in the usual fashion. The function returns
|
|
a string which is processed as if it had appeared literally as part
|
|
of the current spec.
|
|
|
|
The following built-in spec functions are provided:
|
|
|
|
@table @code
|
|
@item @code{if-exists}
|
|
The @code{if-exists} spec function takes one argument, an absolute
|
|
pathname to a file. If the file exists, @code{if-exists} returns the
|
|
pathname. Here is a small example of its usage:
|
|
|
|
@smallexample
|
|
*startfile:
|
|
crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
|
|
@end smallexample
|
|
|
|
@item @code{if-exists-else}
|
|
The @code{if-exists-else} spec function is similar to the @code{if-exists}
|
|
spec function, except that it takes two arguments. The first argument is
|
|
an absolute pathname to a file. If the file exists, @code{if-exists-else}
|
|
returns the pathname. If it does not exist, it returns the second argument.
|
|
This way, @code{if-exists-else} can be used to select one file or another,
|
|
based on the existence of the first. Here is a small example of its usage:
|
|
|
|
@smallexample
|
|
*startfile:
|
|
crt0%O%s %:if-exists(crti%O%s) \
|
|
%:if-exists-else(crtbeginT%O%s crtbegin%O%s)
|
|
@end smallexample
|
|
|
|
@item @code{replace-outfile}
|
|
The @code{replace-outfile} spec function takes two arguments. It looks for the
|
|
first argument in the outfiles array and replaces it with the second argument. Here
|
|
is a small example of its usage:
|
|
|
|
@smallexample
|
|
%@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
|
|
@end smallexample
|
|
|
|
@end table
|
|
|
|
@item %@{@code{S}@}
|
|
Substitutes the @code{-S} switch, if that switch was given to GCC@.
|
|
If that switch was not specified, this substitutes nothing. Note that
|
|
the leading dash is omitted when specifying this option, and it is
|
|
automatically inserted if the substitution is performed. Thus the spec
|
|
string @samp{%@{foo@}} would match the command-line option @option{-foo}
|
|
and would output the command line option @option{-foo}.
|
|
|
|
@item %W@{@code{S}@}
|
|
Like %@{@code{S}@} but mark last argument supplied within as a file to be
|
|
deleted on failure.
|
|
|
|
@item %@{@code{S}*@}
|
|
Substitutes all the switches specified to GCC whose names start
|
|
with @code{-S}, but which also take an argument. This is used for
|
|
switches like @option{-o}, @option{-D}, @option{-I}, etc.
|
|
GCC considers @option{-o foo} as being
|
|
one switch whose names starts with @samp{o}. %@{o*@} would substitute this
|
|
text, including the space. Thus two arguments would be generated.
|
|
|
|
@item %@{@code{S}*&@code{T}*@}
|
|
Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
|
|
(the order of @code{S} and @code{T} in the spec is not significant).
|
|
There can be any number of ampersand-separated variables; for each the
|
|
wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
|
|
|
|
@item %@{@code{S}:@code{X}@}
|
|
Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
|
|
|
|
@item %@{!@code{S}:@code{X}@}
|
|
Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
|
|
|
|
@item %@{@code{S}*:@code{X}@}
|
|
Substitutes @code{X} if one or more switches whose names start with
|
|
@code{-S} are specified to GCC@. Normally @code{X} is substituted only
|
|
once, no matter how many such switches appeared. However, if @code{%*}
|
|
appears somewhere in @code{X}, then @code{X} will be substituted once
|
|
for each matching switch, with the @code{%*} replaced by the part of
|
|
that switch that matched the @code{*}.
|
|
|
|
@item %@{.@code{S}:@code{X}@}
|
|
Substitutes @code{X}, if processing a file with suffix @code{S}.
|
|
|
|
@item %@{!.@code{S}:@code{X}@}
|
|
Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
|
|
|
|
@item %@{@code{S}|@code{P}:@code{X}@}
|
|
Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
|
|
This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
|
|
although they have a stronger binding than the @samp{|}. If @code{%*}
|
|
appears in @code{X}, all of the alternatives must be starred, and only
|
|
the first matching alternative is substituted.
|
|
|
|
For example, a spec string like this:
|
|
|
|
@smallexample
|
|
%@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
|
|
@end smallexample
|
|
|
|
will output the following command-line options from the following input
|
|
command-line options:
|
|
|
|
@smallexample
|
|
fred.c -foo -baz
|
|
jim.d -bar -boggle
|
|
-d fred.c -foo -baz -boggle
|
|
-d jim.d -bar -baz -boggle
|
|
@end smallexample
|
|
|
|
@item %@{S:X; T:Y; :D@}
|
|
|
|
If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
|
|
given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
|
|
be as many clauses as you need. This may be combined with @code{.},
|
|
@code{!}, @code{|}, and @code{*} as needed.
|
|
|
|
|
|
@end table
|
|
|
|
The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
|
|
construct may contain other nested @samp{%} constructs or spaces, or
|
|
even newlines. They are processed as usual, as described above.
|
|
Trailing white space in @code{X} is ignored. White space may also
|
|
appear anywhere on the left side of the colon in these constructs,
|
|
except between @code{.} or @code{*} and the corresponding word.
|
|
|
|
The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
|
|
handled specifically in these constructs. If another value of
|
|
@option{-O} or the negated form of a @option{-f}, @option{-m}, or
|
|
@option{-W} switch is found later in the command line, the earlier
|
|
switch value is ignored, except with @{@code{S}*@} where @code{S} is
|
|
just one letter, which passes all matching options.
|
|
|
|
The character @samp{|} at the beginning of the predicate text is used to
|
|
indicate that a command should be piped to the following command, but
|
|
only if @option{-pipe} is specified.
|
|
|
|
It is built into GCC which switches take arguments and which do not.
|
|
(You might think it would be useful to generalize this to allow each
|
|
compiler's spec to say which switches take arguments. But this cannot
|
|
be done in a consistent fashion. GCC cannot even decide which input
|
|
files have been specified without knowing which switches take arguments,
|
|
and it must know which input files to compile in order to tell which
|
|
compilers to run).
|
|
|
|
GCC also knows implicitly that arguments starting in @option{-l} are to be
|
|
treated as compiler output files, and passed to the linker in their
|
|
proper position among the other output files.
|
|
|
|
@c man begin OPTIONS
|
|
|
|
@node Target Options
|
|
@section Specifying Target Machine and Compiler Version
|
|
@cindex target options
|
|
@cindex cross compiling
|
|
@cindex specifying machine version
|
|
@cindex specifying compiler version and target machine
|
|
@cindex compiler version, specifying
|
|
@cindex target machine, specifying
|
|
|
|
The usual way to run GCC is to run the executable called @file{gcc}, or
|
|
@file{<machine>-gcc} when cross-compiling, or
|
|
@file{<machine>-gcc-<version>} to run a version other than the one that
|
|
was installed last. Sometimes this is inconvenient, so GCC provides
|
|
options that will switch to another cross-compiler or version.
|
|
|
|
@table @gcctabopt
|
|
@item -b @var{machine}
|
|
@opindex b
|
|
The argument @var{machine} specifies the target machine for compilation.
|
|
|
|
The value to use for @var{machine} is the same as was specified as the
|
|
machine type when configuring GCC as a cross-compiler. For
|
|
example, if a cross-compiler was configured with @samp{configure
|
|
arm-elf}, meaning to compile for an arm processor with elf binaries,
|
|
then you would specify @option{-b arm-elf} to run that cross compiler.
|
|
Because there are other options beginning with @option{-b}, the
|
|
configuration must contain a hyphen.
|
|
|
|
@item -V @var{version}
|
|
@opindex V
|
|
The argument @var{version} specifies which version of GCC to run.
|
|
This is useful when multiple versions are installed. For example,
|
|
@var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
|
|
@end table
|
|
|
|
The @option{-V} and @option{-b} options work by running the
|
|
@file{<machine>-gcc-<version>} executable, so there's no real reason to
|
|
use them if you can just run that directly.
|
|
|
|
@node Submodel Options
|
|
@section Hardware Models and Configurations
|
|
@cindex submodel options
|
|
@cindex specifying hardware config
|
|
@cindex hardware models and configurations, specifying
|
|
@cindex machine dependent options
|
|
|
|
Earlier we discussed the standard option @option{-b} which chooses among
|
|
different installed compilers for completely different target
|
|
machines, such as VAX vs.@: 68000 vs.@: 80386.
|
|
|
|
In addition, each of these target machine types can have its own
|
|
special options, starting with @samp{-m}, to choose among various
|
|
hardware models or configurations---for example, 68010 vs 68020,
|
|
floating coprocessor or none. A single installed version of the
|
|
compiler can compile for any model or configuration, according to the
|
|
options specified.
|
|
|
|
Some configurations of the compiler also support additional special
|
|
options, usually for compatibility with other compilers on the same
|
|
platform.
|
|
|
|
@c This list is ordered alphanumerically by subsection name.
|
|
@c It should be the same order and spelling as these options are listed
|
|
@c in Machine Dependent Options
|
|
|
|
@menu
|
|
* ARC Options::
|
|
* ARM Options::
|
|
* AVR Options::
|
|
* Blackfin Options::
|
|
* CRIS Options::
|
|
* CRX Options::
|
|
* Darwin Options::
|
|
* DEC Alpha Options::
|
|
* DEC Alpha/VMS Options::
|
|
* FRV Options::
|
|
* GNU/Linux Options::
|
|
* H8/300 Options::
|
|
* HPPA Options::
|
|
* i386 and x86-64 Options::
|
|
* IA-64 Options::
|
|
* M32C Options::
|
|
* M32R/D Options::
|
|
* M680x0 Options::
|
|
* M68hc1x Options::
|
|
* MCore Options::
|
|
* MIPS Options::
|
|
* MMIX Options::
|
|
* MN10300 Options::
|
|
* MT Options::
|
|
* PDP-11 Options::
|
|
* PowerPC Options::
|
|
* RS/6000 and PowerPC Options::
|
|
* S/390 and zSeries Options::
|
|
* Score Options::
|
|
* SH Options::
|
|
* SPARC Options::
|
|
* System V Options::
|
|
* TMS320C3x/C4x Options::
|
|
* V850 Options::
|
|
* VAX Options::
|
|
* x86-64 Options::
|
|
* Xstormy16 Options::
|
|
* Xtensa Options::
|
|
* zSeries Options::
|
|
@end menu
|
|
|
|
@node ARC Options
|
|
@subsection ARC Options
|
|
@cindex ARC Options
|
|
|
|
These options are defined for ARC implementations:
|
|
|
|
@table @gcctabopt
|
|
@item -EL
|
|
@opindex EL
|
|
Compile code for little endian mode. This is the default.
|
|
|
|
@item -EB
|
|
@opindex EB
|
|
Compile code for big endian mode.
|
|
|
|
@item -mmangle-cpu
|
|
@opindex mmangle-cpu
|
|
Prepend the name of the cpu to all public symbol names.
|
|
In multiple-processor systems, there are many ARC variants with different
|
|
instruction and register set characteristics. This flag prevents code
|
|
compiled for one cpu to be linked with code compiled for another.
|
|
No facility exists for handling variants that are ``almost identical''.
|
|
This is an all or nothing option.
|
|
|
|
@item -mcpu=@var{cpu}
|
|
@opindex mcpu
|
|
Compile code for ARC variant @var{cpu}.
|
|
Which variants are supported depend on the configuration.
|
|
All variants support @option{-mcpu=base}, this is the default.
|
|
|
|
@item -mtext=@var{text-section}
|
|
@itemx -mdata=@var{data-section}
|
|
@itemx -mrodata=@var{readonly-data-section}
|
|
@opindex mtext
|
|
@opindex mdata
|
|
@opindex mrodata
|
|
Put functions, data, and readonly data in @var{text-section},
|
|
@var{data-section}, and @var{readonly-data-section} respectively
|
|
by default. This can be overridden with the @code{section} attribute.
|
|
@xref{Variable Attributes}.
|
|
|
|
@end table
|
|
|
|
@node ARM Options
|
|
@subsection ARM Options
|
|
@cindex ARM options
|
|
|
|
These @samp{-m} options are defined for Advanced RISC Machines (ARM)
|
|
architectures:
|
|
|
|
@table @gcctabopt
|
|
@item -mabi=@var{name}
|
|
@opindex mabi
|
|
Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
|
|
@samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
|
|
|
|
@item -mapcs-frame
|
|
@opindex mapcs-frame
|
|
Generate a stack frame that is compliant with the ARM Procedure Call
|
|
Standard for all functions, even if this is not strictly necessary for
|
|
correct execution of the code. Specifying @option{-fomit-frame-pointer}
|
|
with this option will cause the stack frames not to be generated for
|
|
leaf functions. The default is @option{-mno-apcs-frame}.
|
|
|
|
@item -mapcs
|
|
@opindex mapcs
|
|
This is a synonym for @option{-mapcs-frame}.
|
|
|
|
@ignore
|
|
@c not currently implemented
|
|
@item -mapcs-stack-check
|
|
@opindex mapcs-stack-check
|
|
Generate code to check the amount of stack space available upon entry to
|
|
every function (that actually uses some stack space). If there is
|
|
insufficient space available then either the function
|
|
@samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
|
|
called, depending upon the amount of stack space required. The run time
|
|
system is required to provide these functions. The default is
|
|
@option{-mno-apcs-stack-check}, since this produces smaller code.
|
|
|
|
@c not currently implemented
|
|
@item -mapcs-float
|
|
@opindex mapcs-float
|
|
Pass floating point arguments using the float point registers. This is
|
|
one of the variants of the APCS@. This option is recommended if the
|
|
target hardware has a floating point unit or if a lot of floating point
|
|
arithmetic is going to be performed by the code. The default is
|
|
@option{-mno-apcs-float}, since integer only code is slightly increased in
|
|
size if @option{-mapcs-float} is used.
|
|
|
|
@c not currently implemented
|
|
@item -mapcs-reentrant
|
|
@opindex mapcs-reentrant
|
|
Generate reentrant, position independent code. The default is
|
|
@option{-mno-apcs-reentrant}.
|
|
@end ignore
|
|
|
|
@item -mthumb-interwork
|
|
@opindex mthumb-interwork
|
|
Generate code which supports calling between the ARM and Thumb
|
|
instruction sets. Without this option the two instruction sets cannot
|
|
be reliably used inside one program. The default is
|
|
@option{-mno-thumb-interwork}, since slightly larger code is generated
|
|
when @option{-mthumb-interwork} is specified.
|
|
|
|
@item -mno-sched-prolog
|
|
@opindex mno-sched-prolog
|
|
Prevent the reordering of instructions in the function prolog, or the
|
|
merging of those instruction with the instructions in the function's
|
|
body. This means that all functions will start with a recognizable set
|
|
of instructions (or in fact one of a choice from a small set of
|
|
different function prologues), and this information can be used to
|
|
locate the start if functions inside an executable piece of code. The
|
|
default is @option{-msched-prolog}.
|
|
|
|
@item -mhard-float
|
|
@opindex mhard-float
|
|
Generate output containing floating point instructions. This is the
|
|
default.
|
|
|
|
@item -msoft-float
|
|
@opindex msoft-float
|
|
Generate output containing library calls for floating point.
|
|
@strong{Warning:} the requisite libraries are not available for all ARM
|
|
targets. Normally the facilities of the machine's usual C compiler are
|
|
used, but this cannot be done directly in cross-compilation. You must make
|
|
your own arrangements to provide suitable library functions for
|
|
cross-compilation.
|
|
|
|
@option{-msoft-float} changes the calling convention in the output file;
|
|
therefore, it is only useful if you compile @emph{all} of a program with
|
|
this option. In particular, you need to compile @file{libgcc.a}, the
|
|
library that comes with GCC, with @option{-msoft-float} in order for
|
|
this to work.
|
|
|
|
@item -mfloat-abi=@var{name}
|
|
@opindex mfloat-abi
|
|
Specifies which ABI to use for floating point values. Permissible values
|
|
are: @samp{soft}, @samp{softfp} and @samp{hard}.
|
|
|
|
@samp{soft} and @samp{hard} are equivalent to @option{-msoft-float}
|
|
and @option{-mhard-float} respectively. @samp{softfp} allows the generation
|
|
of floating point instructions, but still uses the soft-float calling
|
|
conventions.
|
|
|
|
@item -mlittle-endian
|
|
@opindex mlittle-endian
|
|
Generate code for a processor running in little-endian mode. This is
|
|
the default for all standard configurations.
|
|
|
|
@item -mbig-endian
|
|
@opindex mbig-endian
|
|
Generate code for a processor running in big-endian mode; the default is
|
|
to compile code for a little-endian processor.
|
|
|
|
@item -mwords-little-endian
|
|
@opindex mwords-little-endian
|
|
This option only applies when generating code for big-endian processors.
|
|
Generate code for a little-endian word order but a big-endian byte
|
|
order. That is, a byte order of the form @samp{32107654}. Note: this
|
|
option should only be used if you require compatibility with code for
|
|
big-endian ARM processors generated by versions of the compiler prior to
|
|
2.8.
|
|
|
|
@item -mcpu=@var{name}
|
|
@opindex mcpu
|
|
This specifies the name of the target ARM processor. GCC uses this name
|
|
to determine what kind of instructions it can emit when generating
|
|
assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
|
|
@samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
|
|
@samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
|
|
@samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
|
|
@samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
|
|
@samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
|
|
@samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
|
|
@samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
|
|
@samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
|
|
@samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
|
|
@samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
|
|
@samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
|
|
@samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
|
|
@samp{arm1176jz-s}, @samp{arm1176jzf-s}, @samp{xscale}, @samp{iwmmxt},
|
|
@samp{ep9312}.
|
|
|
|
@itemx -mtune=@var{name}
|
|
@opindex mtune
|
|
This option is very similar to the @option{-mcpu=} option, except that
|
|
instead of specifying the actual target processor type, and hence
|
|
restricting which instructions can be used, it specifies that GCC should
|
|
tune the performance of the code as if the target were of the type
|
|
specified in this option, but still choosing the instructions that it
|
|
will generate based on the cpu specified by a @option{-mcpu=} option.
|
|
For some ARM implementations better performance can be obtained by using
|
|
this option.
|
|
|
|
@item -march=@var{name}
|
|
@opindex march
|
|
This specifies the name of the target ARM architecture. GCC uses this
|
|
name to determine what kind of instructions it can emit when generating
|
|
assembly code. This option can be used in conjunction with or instead
|
|
of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
|
|
@samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
|
|
@samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
|
|
@samp{iwmmxt}, @samp{ep9312}.
|
|
|
|
@item -mfpu=@var{name}
|
|
@itemx -mfpe=@var{number}
|
|
@itemx -mfp=@var{number}
|
|
@opindex mfpu
|
|
@opindex mfpe
|
|
@opindex mfp
|
|
This specifies what floating point hardware (or hardware emulation) is
|
|
available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
|
|
@samp{fpe3}, @samp{maverick}, @samp{vfp}. @option{-mfp} and @option{-mfpe}
|
|
are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
|
|
with older versions of GCC@.
|
|
|
|
If @option{-msoft-float} is specified this specifies the format of
|
|
floating point values.
|
|
|
|
@item -mstructure-size-boundary=@var{n}
|
|
@opindex mstructure-size-boundary
|
|
The size of all structures and unions will be rounded up to a multiple
|
|
of the number of bits set by this option. Permissible values are 8, 32
|
|
and 64. The default value varies for different toolchains. For the COFF
|
|
targeted toolchain the default value is 8. A value of 64 is only allowed
|
|
if the underlying ABI supports it.
|
|
|
|
Specifying the larger number can produce faster, more efficient code, but
|
|
can also increase the size of the program. Different values are potentially
|
|
incompatible. Code compiled with one value cannot necessarily expect to
|
|
work with code or libraries compiled with another value, if they exchange
|
|
information using structures or unions.
|
|
|
|
@item -mabort-on-noreturn
|
|
@opindex mabort-on-noreturn
|
|
Generate a call to the function @code{abort} at the end of a
|
|
@code{noreturn} function. It will be executed if the function tries to
|
|
return.
|
|
|
|
@item -mlong-calls
|
|
@itemx -mno-long-calls
|
|
@opindex mlong-calls
|
|
@opindex mno-long-calls
|
|
Tells the compiler to perform function calls by first loading the
|
|
address of the function into a register and then performing a subroutine
|
|
call on this register. This switch is needed if the target function
|
|
will lie outside of the 64 megabyte addressing range of the offset based
|
|
version of subroutine call instruction.
|
|
|
|
Even if this switch is enabled, not all function calls will be turned
|
|
into long calls. The heuristic is that static functions, functions
|
|
which have the @samp{short-call} attribute, functions that are inside
|
|
the scope of a @samp{#pragma no_long_calls} directive and functions whose
|
|
definitions have already been compiled within the current compilation
|
|
unit, will not be turned into long calls. The exception to this rule is
|
|
that weak function definitions, functions with the @samp{long-call}
|
|
attribute or the @samp{section} attribute, and functions that are within
|
|
the scope of a @samp{#pragma long_calls} directive, will always be
|
|
turned into long calls.
|
|
|
|
This feature is not enabled by default. Specifying
|
|
@option{-mno-long-calls} will restore the default behavior, as will
|
|
placing the function calls within the scope of a @samp{#pragma
|
|
long_calls_off} directive. Note these switches have no effect on how
|
|
the compiler generates code to handle function calls via function
|
|
pointers.
|
|
|
|
@item -mnop-fun-dllimport
|
|
@opindex mnop-fun-dllimport
|
|
Disable support for the @code{dllimport} attribute.
|
|
|
|
@item -msingle-pic-base
|
|
@opindex msingle-pic-base
|
|
Treat the register used for PIC addressing as read-only, rather than
|
|
loading it in the prologue for each function. The run-time system is
|
|
responsible for initializing this register with an appropriate value
|
|
before execution begins.
|
|
|
|
@item -mpic-register=@var{reg}
|
|
@opindex mpic-register
|
|
Specify the register to be used for PIC addressing. The default is R10
|
|
unless stack-checking is enabled, when R9 is used.
|
|
|
|
@item -mcirrus-fix-invalid-insns
|
|
@opindex mcirrus-fix-invalid-insns
|
|
@opindex mno-cirrus-fix-invalid-insns
|
|
Insert NOPs into the instruction stream to in order to work around
|
|
problems with invalid Maverick instruction combinations. This option
|
|
is only valid if the @option{-mcpu=ep9312} option has been used to
|
|
enable generation of instructions for the Cirrus Maverick floating
|
|
point co-processor. This option is not enabled by default, since the
|
|
problem is only present in older Maverick implementations. The default
|
|
can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
|
|
switch.
|
|
|
|
@item -mpoke-function-name
|
|
@opindex mpoke-function-name
|
|
Write the name of each function into the text section, directly
|
|
preceding the function prologue. The generated code is similar to this:
|
|
|
|
@smallexample
|
|
t0
|
|
.ascii "arm_poke_function_name", 0
|
|
.align
|
|
t1
|
|
.word 0xff000000 + (t1 - t0)
|
|
arm_poke_function_name
|
|
mov ip, sp
|
|
stmfd sp!, @{fp, ip, lr, pc@}
|
|
sub fp, ip, #4
|
|
@end smallexample
|
|
|
|
When performing a stack backtrace, code can inspect the value of
|
|
@code{pc} stored at @code{fp + 0}. If the trace function then looks at
|
|
location @code{pc - 12} and the top 8 bits are set, then we know that
|
|
there is a function name embedded immediately preceding this location
|
|
and has length @code{((pc[-3]) & 0xff000000)}.
|
|
|
|
@item -mthumb
|
|
@opindex mthumb
|
|
Generate code for the 16-bit Thumb instruction set. The default is to
|
|
use the 32-bit ARM instruction set.
|
|
|
|
@item -mtpcs-frame
|
|
@opindex mtpcs-frame
|
|
Generate a stack frame that is compliant with the Thumb Procedure Call
|
|
Standard for all non-leaf functions. (A leaf function is one that does
|
|
not call any other functions.) The default is @option{-mno-tpcs-frame}.
|
|
|
|
@item -mtpcs-leaf-frame
|
|
@opindex mtpcs-leaf-frame
|
|
Generate a stack frame that is compliant with the Thumb Procedure Call
|
|
Standard for all leaf functions. (A leaf function is one that does
|
|
not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
|
|
|
|
@item -mcallee-super-interworking
|
|
@opindex mcallee-super-interworking
|
|
Gives all externally visible functions in the file being compiled an ARM
|
|
instruction set header which switches to Thumb mode before executing the
|
|
rest of the function. This allows these functions to be called from
|
|
non-interworking code.
|
|
|
|
@item -mcaller-super-interworking
|
|
@opindex mcaller-super-interworking
|
|
Allows calls via function pointers (including virtual functions) to
|
|
execute correctly regardless of whether the target code has been
|
|
compiled for interworking or not. There is a small overhead in the cost
|
|
of executing a function pointer if this option is enabled.
|
|
|
|
@item -mtp=@var{name}
|
|
@opindex mtp
|
|
Specify the access model for the thread local storage pointer. The valid
|
|
models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
|
|
@option{cp15}, which fetches the thread pointer from @code{cp15} directly
|
|
(supported in the arm6k architecture), and @option{auto}, which uses the
|
|
best available method for the selected processor. The default setting is
|
|
@option{auto}.
|
|
|
|
@end table
|
|
|
|
@node AVR Options
|
|
@subsection AVR Options
|
|
@cindex AVR Options
|
|
|
|
These options are defined for AVR implementations:
|
|
|
|
@table @gcctabopt
|
|
@item -mmcu=@var{mcu}
|
|
@opindex mmcu
|
|
Specify ATMEL AVR instruction set or MCU type.
|
|
|
|
Instruction set avr1 is for the minimal AVR core, not supported by the C
|
|
compiler, only for assembler programs (MCU types: at90s1200, attiny10,
|
|
attiny11, attiny12, attiny15, attiny28).
|
|
|
|
Instruction set avr2 (default) is for the classic AVR core with up to
|
|
8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
|
|
at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
|
|
at90c8534, at90s8535).
|
|
|
|
Instruction set avr3 is for the classic AVR core with up to 128K program
|
|
memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
|
|
|
|
Instruction set avr4 is for the enhanced AVR core with up to 8K program
|
|
memory space (MCU types: atmega8, atmega83, atmega85).
|
|
|
|
Instruction set avr5 is for the enhanced AVR core with up to 128K program
|
|
memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
|
|
atmega64, atmega128, at43usb355, at94k).
|
|
|
|
@item -msize
|
|
@opindex msize
|
|
Output instruction sizes to the asm file.
|
|
|
|
@item -minit-stack=@var{N}
|
|
@opindex minit-stack
|
|
Specify the initial stack address, which may be a symbol or numeric value,
|
|
@samp{__stack} is the default.
|
|
|
|
@item -mno-interrupts
|
|
@opindex mno-interrupts
|
|
Generated code is not compatible with hardware interrupts.
|
|
Code size will be smaller.
|
|
|
|
@item -mcall-prologues
|
|
@opindex mcall-prologues
|
|
Functions prologues/epilogues expanded as call to appropriate
|
|
subroutines. Code size will be smaller.
|
|
|
|
@item -mno-tablejump
|
|
@opindex mno-tablejump
|
|
Do not generate tablejump insns which sometimes increase code size.
|
|
|
|
@item -mtiny-stack
|
|
@opindex mtiny-stack
|
|
Change only the low 8 bits of the stack pointer.
|
|
|
|
@item -mint8
|
|
@opindex mint8
|
|
Assume int to be 8 bit integer. This affects the sizes of all types: A
|
|
char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
|
|
and long long will be 4 bytes. Please note that this option does not
|
|
comply to the C standards, but it will provide you with smaller code
|
|
size.
|
|
@end table
|
|
|
|
@node Blackfin Options
|
|
@subsection Blackfin Options
|
|
@cindex Blackfin Options
|
|
|
|
@table @gcctabopt
|
|
@item -momit-leaf-frame-pointer
|
|
@opindex momit-leaf-frame-pointer
|
|
Don't keep the frame pointer in a register for leaf functions. This
|
|
avoids the instructions to save, set up and restore frame pointers and
|
|
makes an extra register available in leaf functions. The option
|
|
@option{-fomit-frame-pointer} removes the frame pointer for all functions
|
|
which might make debugging harder.
|
|
|
|
@item -mspecld-anomaly
|
|
@opindex mspecld-anomaly
|
|
When enabled, the compiler will ensure that the generated code does not
|
|
contain speculative loads after jump instructions. This option is enabled
|
|
by default.
|
|
|
|
@item -mno-specld-anomaly
|
|
@opindex mno-specld-anomaly
|
|
Don't generate extra code to prevent speculative loads from occurring.
|
|
|
|
@item -mcsync-anomaly
|
|
@opindex mcsync-anomaly
|
|
When enabled, the compiler will ensure that the generated code does not
|
|
contain CSYNC or SSYNC instructions too soon after conditional branches.
|
|
This option is enabled by default.
|
|
|
|
@item -mno-csync-anomaly
|
|
@opindex mno-csync-anomaly
|
|
Don't generate extra code to prevent CSYNC or SSYNC instructions from
|
|
occurring too soon after a conditional branch.
|
|
|
|
@item -mlow-64k
|
|
@opindex mlow-64k
|
|
When enabled, the compiler is free to take advantage of the knowledge that
|
|
the entire program fits into the low 64k of memory.
|
|
|
|
@item -mno-low-64k
|
|
@opindex mno-low-64k
|
|
Assume that the program is arbitrarily large. This is the default.
|
|
|
|
@item -mid-shared-library
|
|
@opindex mid-shared-library
|
|
Generate code that supports shared libraries via the library ID method.
|
|
This allows for execute in place and shared libraries in an environment
|
|
without virtual memory management. This option implies @option{-fPIC}.
|
|
|
|
@item -mno-id-shared-library
|
|
@opindex mno-id-shared-library
|
|
Generate code that doesn't assume ID based shared libraries are being used.
|
|
This is the default.
|
|
|
|
@item -mshared-library-id=n
|
|
@opindex mshared-library-id
|
|
Specified the identification number of the ID based shared library being
|
|
compiled. Specifying a value of 0 will generate more compact code, specifying
|
|
other values will force the allocation of that number to the current
|
|
library but is no more space or time efficient than omitting this option.
|
|
|
|
@item -mlong-calls
|
|
@itemx -mno-long-calls
|
|
@opindex mlong-calls
|
|
@opindex mno-long-calls
|
|
Tells the compiler to perform function calls by first loading the
|
|
address of the function into a register and then performing a subroutine
|
|
call on this register. This switch is needed if the target function
|
|
will lie outside of the 24 bit addressing range of the offset based
|
|
version of subroutine call instruction.
|
|
|
|
This feature is not enabled by default. Specifying
|
|
@option{-mno-long-calls} will restore the default behavior. Note these
|
|
switches have no effect on how the compiler generates code to handle
|
|
function calls via function pointers.
|
|
@end table
|
|
|
|
@node CRIS Options
|
|
@subsection CRIS Options
|
|
@cindex CRIS Options
|
|
|
|
These options are defined specifically for the CRIS ports.
|
|
|
|
@table @gcctabopt
|
|
@item -march=@var{architecture-type}
|
|
@itemx -mcpu=@var{architecture-type}
|
|
@opindex march
|
|
@opindex mcpu
|
|
Generate code for the specified architecture. The choices for
|
|
@var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
|
|
respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
|
|
Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
|
|
@samp{v10}.
|
|
|
|
@item -mtune=@var{architecture-type}
|
|
@opindex mtune
|
|
Tune to @var{architecture-type} everything applicable about the generated
|
|
code, except for the ABI and the set of available instructions. The
|
|
choices for @var{architecture-type} are the same as for
|
|
@option{-march=@var{architecture-type}}.
|
|
|
|
@item -mmax-stack-frame=@var{n}
|
|
@opindex mmax-stack-frame
|
|
Warn when the stack frame of a function exceeds @var{n} bytes.
|
|
|
|
@item -melinux-stacksize=@var{n}
|
|
@opindex melinux-stacksize
|
|
Only available with the @samp{cris-axis-aout} target. Arranges for
|
|
indications in the program to the kernel loader that the stack of the
|
|
program should be set to @var{n} bytes.
|
|
|
|
@item -metrax4
|
|
@itemx -metrax100
|
|
@opindex metrax4
|
|
@opindex metrax100
|
|
The options @option{-metrax4} and @option{-metrax100} are synonyms for
|
|
@option{-march=v3} and @option{-march=v8} respectively.
|
|
|
|
@item -mmul-bug-workaround
|
|
@itemx -mno-mul-bug-workaround
|
|
@opindex mmul-bug-workaround
|
|
@opindex mno-mul-bug-workaround
|
|
Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
|
|
models where it applies. This option is active by default.
|
|
|
|
@item -mpdebug
|
|
@opindex mpdebug
|
|
Enable CRIS-specific verbose debug-related information in the assembly
|
|
code. This option also has the effect to turn off the @samp{#NO_APP}
|
|
formatted-code indicator to the assembler at the beginning of the
|
|
assembly file.
|
|
|
|
@item -mcc-init
|
|
@opindex mcc-init
|
|
Do not use condition-code results from previous instruction; always emit
|
|
compare and test instructions before use of condition codes.
|
|
|
|
@item -mno-side-effects
|
|
@opindex mno-side-effects
|
|
Do not emit instructions with side-effects in addressing modes other than
|
|
post-increment.
|
|
|
|
@item -mstack-align
|
|
@itemx -mno-stack-align
|
|
@itemx -mdata-align
|
|
@itemx -mno-data-align
|
|
@itemx -mconst-align
|
|
@itemx -mno-const-align
|
|
@opindex mstack-align
|
|
@opindex mno-stack-align
|
|
@opindex mdata-align
|
|
@opindex mno-data-align
|
|
@opindex mconst-align
|
|
@opindex mno-const-align
|
|
These options (no-options) arranges (eliminate arrangements) for the
|
|
stack-frame, individual data and constants to be aligned for the maximum
|
|
single data access size for the chosen CPU model. The default is to
|
|
arrange for 32-bit alignment. ABI details such as structure layout are
|
|
not affected by these options.
|
|
|
|
@item -m32-bit
|
|
@itemx -m16-bit
|
|
@itemx -m8-bit
|
|
@opindex m32-bit
|
|
@opindex m16-bit
|
|
@opindex m8-bit
|
|
Similar to the stack- data- and const-align options above, these options
|
|
arrange for stack-frame, writable data and constants to all be 32-bit,
|
|
16-bit or 8-bit aligned. The default is 32-bit alignment.
|
|
|
|
@item -mno-prologue-epilogue
|
|
@itemx -mprologue-epilogue
|
|
@opindex mno-prologue-epilogue
|
|
@opindex mprologue-epilogue
|
|
With @option{-mno-prologue-epilogue}, the normal function prologue and
|
|
epilogue that sets up the stack-frame are omitted and no return
|
|
instructions or return sequences are generated in the code. Use this
|
|
option only together with visual inspection of the compiled code: no
|
|
warnings or errors are generated when call-saved registers must be saved,
|
|
or storage for local variable needs to be allocated.
|
|
|
|
@item -mno-gotplt
|
|
@itemx -mgotplt
|
|
@opindex mno-gotplt
|
|
@opindex mgotplt
|
|
With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
|
|
instruction sequences that load addresses for functions from the PLT part
|
|
of the GOT rather than (traditional on other architectures) calls to the
|
|
PLT@. The default is @option{-mgotplt}.
|
|
|
|
@item -maout
|
|
@opindex maout
|
|
Legacy no-op option only recognized with the cris-axis-aout target.
|
|
|
|
@item -melf
|
|
@opindex melf
|
|
Legacy no-op option only recognized with the cris-axis-elf and
|
|
cris-axis-linux-gnu targets.
|
|
|
|
@item -melinux
|
|
@opindex melinux
|
|
Only recognized with the cris-axis-aout target, where it selects a
|
|
GNU/linux-like multilib, include files and instruction set for
|
|
@option{-march=v8}.
|
|
|
|
@item -mlinux
|
|
@opindex mlinux
|
|
Legacy no-op option only recognized with the cris-axis-linux-gnu target.
|
|
|
|
@item -sim
|
|
@opindex sim
|
|
This option, recognized for the cris-axis-aout and cris-axis-elf arranges
|
|
to link with input-output functions from a simulator library. Code,
|
|
initialized data and zero-initialized data are allocated consecutively.
|
|
|
|
@item -sim2
|
|
@opindex sim2
|
|
Like @option{-sim}, but pass linker options to locate initialized data at
|
|
0x40000000 and zero-initialized data at 0x80000000.
|
|
@end table
|
|
|
|
@node CRX Options
|
|
@subsection CRX Options
|
|
@cindex CRX Options
|
|
|
|
These options are defined specifically for the CRX ports.
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -mmac
|
|
@opindex mmac
|
|
Enable the use of multiply-accumulate instructions. Disabled by default.
|
|
|
|
@item -mpush-args
|
|
@opindex mpush-args
|
|
Push instructions will be used to pass outgoing arguments when functions
|
|
are called. Enabled by default.
|
|
@end table
|
|
|
|
@node Darwin Options
|
|
@subsection Darwin Options
|
|
@cindex Darwin options
|
|
|
|
These options are defined for all architectures running the Darwin operating
|
|
system.
|
|
|
|
FSF GCC on Darwin does not create ``fat'' object files; it will create
|
|
an object file for the single architecture that it was built to
|
|
target. Apple's GCC on Darwin does create ``fat'' files if multiple
|
|
@option{-arch} options are used; it does so by running the compiler or
|
|
linker multiple times and joining the results together with
|
|
@file{lipo}.
|
|
|
|
The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
|
|
@samp{i686}) is determined by the flags that specify the ISA
|
|
that GCC is targetting, like @option{-mcpu} or @option{-march}. The
|
|
@option{-force_cpusubtype_ALL} option can be used to override this.
|
|
|
|
The Darwin tools vary in their behavior when presented with an ISA
|
|
mismatch. The assembler, @file{as}, will only permit instructions to
|
|
be used that are valid for the subtype of the file it is generating,
|
|
so you cannot put 64-bit instructions in an @samp{ppc750} object file.
|
|
The linker for shared libraries, @file{/usr/bin/libtool}, will fail
|
|
and print an error if asked to create a shared library with a less
|
|
restrictive subtype than its input files (for instance, trying to put
|
|
a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
|
|
for executables, @file{ld}, will quietly give the executable the most
|
|
restrictive subtype of any of its input files.
|
|
|
|
@table @gcctabopt
|
|
@item -F@var{dir}
|
|
@opindex F
|
|
Add the framework directory @var{dir} to the head of the list of
|
|
directories to be searched for header files. These directories are
|
|
interleaved with those specified by @option{-I} options and are
|
|
scanned in a left-to-right order.
|
|
|
|
A framework directory is a directory with frameworks in it. A
|
|
framework is a directory with a @samp{"Headers"} and/or
|
|
@samp{"PrivateHeaders"} directory contained directly in it that ends
|
|
in @samp{".framework"}. The name of a framework is the name of this
|
|
directory excluding the @samp{".framework"}. Headers associated with
|
|
the framework are found in one of those two directories, with
|
|
@samp{"Headers"} being searched first. A subframework is a framework
|
|
directory that is in a framework's @samp{"Frameworks"} directory.
|
|
Includes of subframework headers can only appear in a header of a
|
|
framework that contains the subframework, or in a sibling subframework
|
|
header. Two subframeworks are siblings if they occur in the same
|
|
framework. A subframework should not have the same name as a
|
|
framework, a warning will be issued if this is violated. Currently a
|
|
subframework cannot have subframeworks, in the future, the mechanism
|
|
may be extended to support this. The standard frameworks can be found
|
|
in @samp{"/System/Library/Frameworks"} and
|
|
@samp{"/Library/Frameworks"}. An example include looks like
|
|
@code{#include <Framework/header.h>}, where @samp{Framework} denotes
|
|
the name of the framework and header.h is found in the
|
|
@samp{"PrivateHeaders"} or @samp{"Headers"} directory.
|
|
|
|
@item -gused
|
|
@opindex gused
|
|
Emit debugging information for symbols that are used. For STABS
|
|
debugging format, this enables @option{-feliminate-unused-debug-symbols}.
|
|
This is by default ON@.
|
|
|
|
@item -gfull
|
|
@opindex gfull
|
|
Emit debugging information for all symbols and types.
|
|
|
|
@item -mmacosx-version-min=@var{version}
|
|
The earliest version of MacOS X that this executable will run on
|
|
is @var{version}. Typical values of @var{version} include @code{10.1},
|
|
@code{10.2}, and @code{10.3.9}.
|
|
|
|
The default for this option is to make choices that seem to be most
|
|
useful.
|
|
|
|
@item -mkernel
|
|
@opindex mkernel
|
|
Enable kernel development mode. The @option{-mkernel} option sets
|
|
@option{-static}, @option{-fno-common}, @option{-fno-cxa-atexit},
|
|
@option{-fno-exceptions}, @option{-fno-non-call-exceptions},
|
|
@option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
|
|
applicable. This mode also sets @option{-mno-altivec},
|
|
@option{-msoft-float}, @option{-fno-builtin} and
|
|
@option{-mlong-branch} for PowerPC targets.
|
|
|
|
@item -mone-byte-bool
|
|
@opindex mone-byte-bool
|
|
Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
|
|
By default @samp{sizeof(bool)} is @samp{4} when compiling for
|
|
Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
|
|
option has no effect on x86.
|
|
|
|
@strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
|
|
to generate code that is not binary compatible with code generated
|
|
without that switch. Using this switch may require recompiling all
|
|
other modules in a program, including system libraries. Use this
|
|
switch to conform to a non-default data model.
|
|
|
|
@item -mfix-and-continue
|
|
@itemx -ffix-and-continue
|
|
@itemx -findirect-data
|
|
@opindex mfix-and-continue
|
|
@opindex ffix-and-continue
|
|
@opindex findirect-data
|
|
Generate code suitable for fast turn around development. Needed to
|
|
enable gdb to dynamically load @code{.o} files into already running
|
|
programs. @option{-findirect-data} and @option{-ffix-and-continue}
|
|
are provided for backwards compatibility.
|
|
|
|
@item -all_load
|
|
@opindex all_load
|
|
Loads all members of static archive libraries.
|
|
See man ld(1) for more information.
|
|
|
|
@item -arch_errors_fatal
|
|
@opindex arch_errors_fatal
|
|
Cause the errors having to do with files that have the wrong architecture
|
|
to be fatal.
|
|
|
|
@item -bind_at_load
|
|
@opindex bind_at_load
|
|
Causes the output file to be marked such that the dynamic linker will
|
|
bind all undefined references when the file is loaded or launched.
|
|
|
|
@item -bundle
|
|
@opindex bundle
|
|
Produce a Mach-o bundle format file.
|
|
See man ld(1) for more information.
|
|
|
|
@item -bundle_loader @var{executable}
|
|
@opindex bundle_loader
|
|
This option specifies the @var{executable} that will be loading the build
|
|
output file being linked. See man ld(1) for more information.
|
|
|
|
@item -dynamiclib
|
|
@opindex dynamiclib
|
|
When passed this option, GCC will produce a dynamic library instead of
|
|
an executable when linking, using the Darwin @file{libtool} command.
|
|
|
|
@item -force_cpusubtype_ALL
|
|
@opindex force_cpusubtype_ALL
|
|
This causes GCC's output file to have the @var{ALL} subtype, instead of
|
|
one controlled by the @option{-mcpu} or @option{-march} option.
|
|
|
|
@item -allowable_client @var{client_name}
|
|
@itemx -client_name
|
|
@itemx -compatibility_version
|
|
@itemx -current_version
|
|
@itemx -dead_strip
|
|
@itemx -dependency-file
|
|
@itemx -dylib_file
|
|
@itemx -dylinker_install_name
|
|
@itemx -dynamic
|
|
@itemx -exported_symbols_list
|
|
@itemx -filelist
|
|
@itemx -flat_namespace
|
|
@itemx -force_flat_namespace
|
|
@itemx -headerpad_max_install_names
|
|
@itemx -image_base
|
|
@itemx -init
|
|
@itemx -install_name
|
|
@itemx -keep_private_externs
|
|
@itemx -multi_module
|
|
@itemx -multiply_defined
|
|
@itemx -multiply_defined_unused
|
|
@itemx -noall_load
|
|
@itemx -no_dead_strip_inits_and_terms
|
|
@itemx -nofixprebinding
|
|
@itemx -nomultidefs
|
|
@itemx -noprebind
|
|
@itemx -noseglinkedit
|
|
@itemx -pagezero_size
|
|
@itemx -prebind
|
|
@itemx -prebind_all_twolevel_modules
|
|
@itemx -private_bundle
|
|
@itemx -read_only_relocs
|
|
@itemx -sectalign
|
|
@itemx -sectobjectsymbols
|
|
@itemx -whyload
|
|
@itemx -seg1addr
|
|
@itemx -sectcreate
|
|
@itemx -sectobjectsymbols
|
|
@itemx -sectorder
|
|
@itemx -segaddr
|
|
@itemx -segs_read_only_addr
|
|
@itemx -segs_read_write_addr
|
|
@itemx -seg_addr_table
|
|
@itemx -seg_addr_table_filename
|
|
@itemx -seglinkedit
|
|
@itemx -segprot
|
|
@itemx -segs_read_only_addr
|
|
@itemx -segs_read_write_addr
|
|
@itemx -single_module
|
|
@itemx -static
|
|
@itemx -sub_library
|
|
@itemx -sub_umbrella
|
|
@itemx -twolevel_namespace
|
|
@itemx -umbrella
|
|
@itemx -undefined
|
|
@itemx -unexported_symbols_list
|
|
@itemx -weak_reference_mismatches
|
|
@itemx -whatsloaded
|
|
|
|
@opindex allowable_client
|
|
@opindex client_name
|
|
@opindex compatibility_version
|
|
@opindex current_version
|
|
@opindex dead_strip
|
|
@opindex dependency-file
|
|
@opindex dylib_file
|
|
@opindex dylinker_install_name
|
|
@opindex dynamic
|
|
@opindex exported_symbols_list
|
|
@opindex filelist
|
|
@opindex flat_namespace
|
|
@opindex force_flat_namespace
|
|
@opindex headerpad_max_install_names
|
|
@opindex image_base
|
|
@opindex init
|
|
@opindex install_name
|
|
@opindex keep_private_externs
|
|
@opindex multi_module
|
|
@opindex multiply_defined
|
|
@opindex multiply_defined_unused
|
|
@opindex noall_load
|
|
@opindex no_dead_strip_inits_and_terms
|
|
@opindex nofixprebinding
|
|
@opindex nomultidefs
|
|
@opindex noprebind
|
|
@opindex noseglinkedit
|
|
@opindex pagezero_size
|
|
@opindex prebind
|
|
@opindex prebind_all_twolevel_modules
|
|
@opindex private_bundle
|
|
@opindex read_only_relocs
|
|
@opindex sectalign
|
|
@opindex sectobjectsymbols
|
|
@opindex whyload
|
|
@opindex seg1addr
|
|
@opindex sectcreate
|
|
@opindex sectobjectsymbols
|
|
@opindex sectorder
|
|
@opindex segaddr
|
|
@opindex segs_read_only_addr
|
|
@opindex segs_read_write_addr
|
|
@opindex seg_addr_table
|
|
@opindex seg_addr_table_filename
|
|
@opindex seglinkedit
|
|
@opindex segprot
|
|
@opindex segs_read_only_addr
|
|
@opindex segs_read_write_addr
|
|
@opindex single_module
|
|
@opindex static
|
|
@opindex sub_library
|
|
@opindex sub_umbrella
|
|
@opindex twolevel_namespace
|
|
@opindex umbrella
|
|
@opindex undefined
|
|
@opindex unexported_symbols_list
|
|
@opindex weak_reference_mismatches
|
|
@opindex whatsloaded
|
|
|
|
These options are passed to the Darwin linker. The Darwin linker man page
|
|
describes them in detail.
|
|
@end table
|
|
|
|
@node DEC Alpha Options
|
|
@subsection DEC Alpha Options
|
|
|
|
These @samp{-m} options are defined for the DEC Alpha implementations:
|
|
|
|
@table @gcctabopt
|
|
@item -mno-soft-float
|
|
@itemx -msoft-float
|
|
@opindex mno-soft-float
|
|
@opindex msoft-float
|
|
Use (do not use) the hardware floating-point instructions for
|
|
floating-point operations. When @option{-msoft-float} is specified,
|
|
functions in @file{libgcc.a} will be used to perform floating-point
|
|
operations. Unless they are replaced by routines that emulate the
|
|
floating-point operations, or compiled in such a way as to call such
|
|
emulations routines, these routines will issue floating-point
|
|
operations. If you are compiling for an Alpha without floating-point
|
|
operations, you must ensure that the library is built so as not to call
|
|
them.
|
|
|
|
Note that Alpha implementations without floating-point operations are
|
|
required to have floating-point registers.
|
|
|
|
@item -mfp-reg
|
|
@itemx -mno-fp-regs
|
|
@opindex mfp-reg
|
|
@opindex mno-fp-regs
|
|
Generate code that uses (does not use) the floating-point register set.
|
|
@option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
|
|
register set is not used, floating point operands are passed in integer
|
|
registers as if they were integers and floating-point results are passed
|
|
in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
|
|
so any function with a floating-point argument or return value called by code
|
|
compiled with @option{-mno-fp-regs} must also be compiled with that
|
|
option.
|
|
|
|
A typical use of this option is building a kernel that does not use,
|
|
and hence need not save and restore, any floating-point registers.
|
|
|
|
@item -mieee
|
|
@opindex mieee
|
|
The Alpha architecture implements floating-point hardware optimized for
|
|
maximum performance. It is mostly compliant with the IEEE floating
|
|
point standard. However, for full compliance, software assistance is
|
|
required. This option generates code fully IEEE compliant code
|
|
@emph{except} that the @var{inexact-flag} is not maintained (see below).
|
|
If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
|
|
defined during compilation. The resulting code is less efficient but is
|
|
able to correctly support denormalized numbers and exceptional IEEE
|
|
values such as not-a-number and plus/minus infinity. Other Alpha
|
|
compilers call this option @option{-ieee_with_no_inexact}.
|
|
|
|
@item -mieee-with-inexact
|
|
@opindex mieee-with-inexact
|
|
This is like @option{-mieee} except the generated code also maintains
|
|
the IEEE @var{inexact-flag}. Turning on this option causes the
|
|
generated code to implement fully-compliant IEEE math. In addition to
|
|
@code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
|
|
macro. On some Alpha implementations the resulting code may execute
|
|
significantly slower than the code generated by default. Since there is
|
|
very little code that depends on the @var{inexact-flag}, you should
|
|
normally not specify this option. Other Alpha compilers call this
|
|
option @option{-ieee_with_inexact}.
|
|
|
|
@item -mfp-trap-mode=@var{trap-mode}
|
|
@opindex mfp-trap-mode
|
|
This option controls what floating-point related traps are enabled.
|
|
Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
|
|
The trap mode can be set to one of four values:
|
|
|
|
@table @samp
|
|
@item n
|
|
This is the default (normal) setting. The only traps that are enabled
|
|
are the ones that cannot be disabled in software (e.g., division by zero
|
|
trap).
|
|
|
|
@item u
|
|
In addition to the traps enabled by @samp{n}, underflow traps are enabled
|
|
as well.
|
|
|
|
@item su
|
|
Like @samp{u}, but the instructions are marked to be safe for software
|
|
completion (see Alpha architecture manual for details).
|
|
|
|
@item sui
|
|
Like @samp{su}, but inexact traps are enabled as well.
|
|
@end table
|
|
|
|
@item -mfp-rounding-mode=@var{rounding-mode}
|
|
@opindex mfp-rounding-mode
|
|
Selects the IEEE rounding mode. Other Alpha compilers call this option
|
|
@option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
|
|
of:
|
|
|
|
@table @samp
|
|
@item n
|
|
Normal IEEE rounding mode. Floating point numbers are rounded towards
|
|
the nearest machine number or towards the even machine number in case
|
|
of a tie.
|
|
|
|
@item m
|
|
Round towards minus infinity.
|
|
|
|
@item c
|
|
Chopped rounding mode. Floating point numbers are rounded towards zero.
|
|
|
|
@item d
|
|
Dynamic rounding mode. A field in the floating point control register
|
|
(@var{fpcr}, see Alpha architecture reference manual) controls the
|
|
rounding mode in effect. The C library initializes this register for
|
|
rounding towards plus infinity. Thus, unless your program modifies the
|
|
@var{fpcr}, @samp{d} corresponds to round towards plus infinity.
|
|
@end table
|
|
|
|
@item -mtrap-precision=@var{trap-precision}
|
|
@opindex mtrap-precision
|
|
In the Alpha architecture, floating point traps are imprecise. This
|
|
means without software assistance it is impossible to recover from a
|
|
floating trap and program execution normally needs to be terminated.
|
|
GCC can generate code that can assist operating system trap handlers
|
|
in determining the exact location that caused a floating point trap.
|
|
Depending on the requirements of an application, different levels of
|
|
precisions can be selected:
|
|
|
|
@table @samp
|
|
@item p
|
|
Program precision. This option is the default and means a trap handler
|
|
can only identify which program caused a floating point exception.
|
|
|
|
@item f
|
|
Function precision. The trap handler can determine the function that
|
|
caused a floating point exception.
|
|
|
|
@item i
|
|
Instruction precision. The trap handler can determine the exact
|
|
instruction that caused a floating point exception.
|
|
@end table
|
|
|
|
Other Alpha compilers provide the equivalent options called
|
|
@option{-scope_safe} and @option{-resumption_safe}.
|
|
|
|
@item -mieee-conformant
|
|
@opindex mieee-conformant
|
|
This option marks the generated code as IEEE conformant. You must not
|
|
use this option unless you also specify @option{-mtrap-precision=i} and either
|
|
@option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
|
|
is to emit the line @samp{.eflag 48} in the function prologue of the
|
|
generated assembly file. Under DEC Unix, this has the effect that
|
|
IEEE-conformant math library routines will be linked in.
|
|
|
|
@item -mbuild-constants
|
|
@opindex mbuild-constants
|
|
Normally GCC examines a 32- or 64-bit integer constant to
|
|
see if it can construct it from smaller constants in two or three
|
|
instructions. If it cannot, it will output the constant as a literal and
|
|
generate code to load it from the data segment at runtime.
|
|
|
|
Use this option to require GCC to construct @emph{all} integer constants
|
|
using code, even if it takes more instructions (the maximum is six).
|
|
|
|
You would typically use this option to build a shared library dynamic
|
|
loader. Itself a shared library, it must relocate itself in memory
|
|
before it can find the variables and constants in its own data segment.
|
|
|
|
@item -malpha-as
|
|
@itemx -mgas
|
|
@opindex malpha-as
|
|
@opindex mgas
|
|
Select whether to generate code to be assembled by the vendor-supplied
|
|
assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
|
|
|
|
@item -mbwx
|
|
@itemx -mno-bwx
|
|
@itemx -mcix
|
|
@itemx -mno-cix
|
|
@itemx -mfix
|
|
@itemx -mno-fix
|
|
@itemx -mmax
|
|
@itemx -mno-max
|
|
@opindex mbwx
|
|
@opindex mno-bwx
|
|
@opindex mcix
|
|
@opindex mno-cix
|
|
@opindex mfix
|
|
@opindex mno-fix
|
|
@opindex mmax
|
|
@opindex mno-max
|
|
Indicate whether GCC should generate code to use the optional BWX,
|
|
CIX, FIX and MAX instruction sets. The default is to use the instruction
|
|
sets supported by the CPU type specified via @option{-mcpu=} option or that
|
|
of the CPU on which GCC was built if none was specified.
|
|
|
|
@item -mfloat-vax
|
|
@itemx -mfloat-ieee
|
|
@opindex mfloat-vax
|
|
@opindex mfloat-ieee
|
|
Generate code that uses (does not use) VAX F and G floating point
|
|
arithmetic instead of IEEE single and double precision.
|
|
|
|
@item -mexplicit-relocs
|
|
@itemx -mno-explicit-relocs
|
|
@opindex mexplicit-relocs
|
|
@opindex mno-explicit-relocs
|
|
Older Alpha assemblers provided no way to generate symbol relocations
|
|
except via assembler macros. Use of these macros does not allow
|
|
optimal instruction scheduling. GNU binutils as of version 2.12
|
|
supports a new syntax that allows the compiler to explicitly mark
|
|
which relocations should apply to which instructions. This option
|
|
is mostly useful for debugging, as GCC detects the capabilities of
|
|
the assembler when it is built and sets the default accordingly.
|
|
|
|
@item -msmall-data
|
|
@itemx -mlarge-data
|
|
@opindex msmall-data
|
|
@opindex mlarge-data
|
|
When @option{-mexplicit-relocs} is in effect, static data is
|
|
accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
|
|
is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
|
|
(the @code{.sdata} and @code{.sbss} sections) and are accessed via
|
|
16-bit relocations off of the @code{$gp} register. This limits the
|
|
size of the small data area to 64KB, but allows the variables to be
|
|
directly accessed via a single instruction.
|
|
|
|
The default is @option{-mlarge-data}. With this option the data area
|
|
is limited to just below 2GB@. Programs that require more than 2GB of
|
|
data must use @code{malloc} or @code{mmap} to allocate the data in the
|
|
heap instead of in the program's data segment.
|
|
|
|
When generating code for shared libraries, @option{-fpic} implies
|
|
@option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
|
|
|
|
@item -msmall-text
|
|
@itemx -mlarge-text
|
|
@opindex msmall-text
|
|
@opindex mlarge-text
|
|
When @option{-msmall-text} is used, the compiler assumes that the
|
|
code of the entire program (or shared library) fits in 4MB, and is
|
|
thus reachable with a branch instruction. When @option{-msmall-data}
|
|
is used, the compiler can assume that all local symbols share the
|
|
same @code{$gp} value, and thus reduce the number of instructions
|
|
required for a function call from 4 to 1.
|
|
|
|
The default is @option{-mlarge-text}.
|
|
|
|
@item -mcpu=@var{cpu_type}
|
|
@opindex mcpu
|
|
Set the instruction set and instruction scheduling parameters for
|
|
machine type @var{cpu_type}. You can specify either the @samp{EV}
|
|
style name or the corresponding chip number. GCC supports scheduling
|
|
parameters for the EV4, EV5 and EV6 family of processors and will
|
|
choose the default values for the instruction set from the processor
|
|
you specify. If you do not specify a processor type, GCC will default
|
|
to the processor on which the compiler was built.
|
|
|
|
Supported values for @var{cpu_type} are
|
|
|
|
@table @samp
|
|
@item ev4
|
|
@itemx ev45
|
|
@itemx 21064
|
|
Schedules as an EV4 and has no instruction set extensions.
|
|
|
|
@item ev5
|
|
@itemx 21164
|
|
Schedules as an EV5 and has no instruction set extensions.
|
|
|
|
@item ev56
|
|
@itemx 21164a
|
|
Schedules as an EV5 and supports the BWX extension.
|
|
|
|
@item pca56
|
|
@itemx 21164pc
|
|
@itemx 21164PC
|
|
Schedules as an EV5 and supports the BWX and MAX extensions.
|
|
|
|
@item ev6
|
|
@itemx 21264
|
|
Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
|
|
|
|
@item ev67
|
|
@itemx 21264a
|
|
Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
|
|
@end table
|
|
|
|
@item -mtune=@var{cpu_type}
|
|
@opindex mtune
|
|
Set only the instruction scheduling parameters for machine type
|
|
@var{cpu_type}. The instruction set is not changed.
|
|
|
|
@item -mmemory-latency=@var{time}
|
|
@opindex mmemory-latency
|
|
Sets the latency the scheduler should assume for typical memory
|
|
references as seen by the application. This number is highly
|
|
dependent on the memory access patterns used by the application
|
|
and the size of the external cache on the machine.
|
|
|
|
Valid options for @var{time} are
|
|
|
|
@table @samp
|
|
@item @var{number}
|
|
A decimal number representing clock cycles.
|
|
|
|
@item L1
|
|
@itemx L2
|
|
@itemx L3
|
|
@itemx main
|
|
The compiler contains estimates of the number of clock cycles for
|
|
``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
|
|
(also called Dcache, Scache, and Bcache), as well as to main memory.
|
|
Note that L3 is only valid for EV5.
|
|
|
|
@end table
|
|
@end table
|
|
|
|
@node DEC Alpha/VMS Options
|
|
@subsection DEC Alpha/VMS Options
|
|
|
|
These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
|
|
|
|
@table @gcctabopt
|
|
@item -mvms-return-codes
|
|
@opindex mvms-return-codes
|
|
Return VMS condition codes from main. The default is to return POSIX
|
|
style condition (e.g.@ error) codes.
|
|
@end table
|
|
|
|
@node FRV Options
|
|
@subsection FRV Options
|
|
@cindex FRV Options
|
|
|
|
@table @gcctabopt
|
|
@item -mgpr-32
|
|
@opindex mgpr-32
|
|
|
|
Only use the first 32 general purpose registers.
|
|
|
|
@item -mgpr-64
|
|
@opindex mgpr-64
|
|
|
|
Use all 64 general purpose registers.
|
|
|
|
@item -mfpr-32
|
|
@opindex mfpr-32
|
|
|
|
Use only the first 32 floating point registers.
|
|
|
|
@item -mfpr-64
|
|
@opindex mfpr-64
|
|
|
|
Use all 64 floating point registers
|
|
|
|
@item -mhard-float
|
|
@opindex mhard-float
|
|
|
|
Use hardware instructions for floating point operations.
|
|
|
|
@item -msoft-float
|
|
@opindex msoft-float
|
|
|
|
Use library routines for floating point operations.
|
|
|
|
@item -malloc-cc
|
|
@opindex malloc-cc
|
|
|
|
Dynamically allocate condition code registers.
|
|
|
|
@item -mfixed-cc
|
|
@opindex mfixed-cc
|
|
|
|
Do not try to dynamically allocate condition code registers, only
|
|
use @code{icc0} and @code{fcc0}.
|
|
|
|
@item -mdword
|
|
@opindex mdword
|
|
|
|
Change ABI to use double word insns.
|
|
|
|
@item -mno-dword
|
|
@opindex mno-dword
|
|
|
|
Do not use double word instructions.
|
|
|
|
@item -mdouble
|
|
@opindex mdouble
|
|
|
|
Use floating point double instructions.
|
|
|
|
@item -mno-double
|
|
@opindex mno-double
|
|
|
|
Do not use floating point double instructions.
|
|
|
|
@item -mmedia
|
|
@opindex mmedia
|
|
|
|
Use media instructions.
|
|
|
|
@item -mno-media
|
|
@opindex mno-media
|
|
|
|
Do not use media instructions.
|
|
|
|
@item -mmuladd
|
|
@opindex mmuladd
|
|
|
|
Use multiply and add/subtract instructions.
|
|
|
|
@item -mno-muladd
|
|
@opindex mno-muladd
|
|
|
|
Do not use multiply and add/subtract instructions.
|
|
|
|
@item -mfdpic
|
|
@opindex mfdpic
|
|
|
|
Select the FDPIC ABI, that uses function descriptors to represent
|
|
pointers to functions. Without any PIC/PIE-related options, it
|
|
implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
|
|
assumes GOT entries and small data are within a 12-bit range from the
|
|
GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
|
|
are computed with 32 bits.
|
|
|
|
@item -minline-plt
|
|
@opindex minline-plt
|
|
|
|
Enable inlining of PLT entries in function calls to functions that are
|
|
not known to bind locally. It has no effect without @option{-mfdpic}.
|
|
It's enabled by default if optimizing for speed and compiling for
|
|
shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
|
|
optimization option such as @option{-O3} or above is present in the
|
|
command line.
|
|
|
|
@item -mTLS
|
|
@opindex TLS
|
|
|
|
Assume a large TLS segment when generating thread-local code.
|
|
|
|
@item -mtls
|
|
@opindex tls
|
|
|
|
Do not assume a large TLS segment when generating thread-local code.
|
|
|
|
@item -mgprel-ro
|
|
@opindex mgprel-ro
|
|
|
|
Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
|
|
that is known to be in read-only sections. It's enabled by default,
|
|
except for @option{-fpic} or @option{-fpie}: even though it may help
|
|
make the global offset table smaller, it trades 1 instruction for 4.
|
|
With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
|
|
one of which may be shared by multiple symbols, and it avoids the need
|
|
for a GOT entry for the referenced symbol, so it's more likely to be a
|
|
win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
|
|
|
|
@item -multilib-library-pic
|
|
@opindex multilib-library-pic
|
|
|
|
Link with the (library, not FD) pic libraries. It's implied by
|
|
@option{-mlibrary-pic}, as well as by @option{-fPIC} and
|
|
@option{-fpic} without @option{-mfdpic}. You should never have to use
|
|
it explicitly.
|
|
|
|
@item -mlinked-fp
|
|
@opindex mlinked-fp
|
|
|
|
Follow the EABI requirement of always creating a frame pointer whenever
|
|
a stack frame is allocated. This option is enabled by default and can
|
|
be disabled with @option{-mno-linked-fp}.
|
|
|
|
@item -mlong-calls
|
|
@opindex mlong-calls
|
|
|
|
Use indirect addressing to call functions outside the current
|
|
compilation unit. This allows the functions to be placed anywhere
|
|
within the 32-bit address space.
|
|
|
|
@item -malign-labels
|
|
@opindex malign-labels
|
|
|
|
Try to align labels to an 8-byte boundary by inserting nops into the
|
|
previous packet. This option only has an effect when VLIW packing
|
|
is enabled. It doesn't create new packets; it merely adds nops to
|
|
existing ones.
|
|
|
|
@item -mlibrary-pic
|
|
@opindex mlibrary-pic
|
|
|
|
Generate position-independent EABI code.
|
|
|
|
@item -macc-4
|
|
@opindex macc-4
|
|
|
|
Use only the first four media accumulator registers.
|
|
|
|
@item -macc-8
|
|
@opindex macc-8
|
|
|
|
Use all eight media accumulator registers.
|
|
|
|
@item -mpack
|
|
@opindex mpack
|
|
|
|
Pack VLIW instructions.
|
|
|
|
@item -mno-pack
|
|
@opindex mno-pack
|
|
|
|
Do not pack VLIW instructions.
|
|
|
|
@item -mno-eflags
|
|
@opindex mno-eflags
|
|
|
|
Do not mark ABI switches in e_flags.
|
|
|
|
@item -mcond-move
|
|
@opindex mcond-move
|
|
|
|
Enable the use of conditional-move instructions (default).
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mno-cond-move
|
|
@opindex mno-cond-move
|
|
|
|
Disable the use of conditional-move instructions.
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mscc
|
|
@opindex mscc
|
|
|
|
Enable the use of conditional set instructions (default).
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mno-scc
|
|
@opindex mno-scc
|
|
|
|
Disable the use of conditional set instructions.
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mcond-exec
|
|
@opindex mcond-exec
|
|
|
|
Enable the use of conditional execution (default).
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mno-cond-exec
|
|
@opindex mno-cond-exec
|
|
|
|
Disable the use of conditional execution.
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mvliw-branch
|
|
@opindex mvliw-branch
|
|
|
|
Run a pass to pack branches into VLIW instructions (default).
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mno-vliw-branch
|
|
@opindex mno-vliw-branch
|
|
|
|
Do not run a pass to pack branches into VLIW instructions.
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mmulti-cond-exec
|
|
@opindex mmulti-cond-exec
|
|
|
|
Enable optimization of @code{&&} and @code{||} in conditional execution
|
|
(default).
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mno-multi-cond-exec
|
|
@opindex mno-multi-cond-exec
|
|
|
|
Disable optimization of @code{&&} and @code{||} in conditional execution.
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mnested-cond-exec
|
|
@opindex mnested-cond-exec
|
|
|
|
Enable nested conditional execution optimizations (default).
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mno-nested-cond-exec
|
|
@opindex mno-nested-cond-exec
|
|
|
|
Disable nested conditional execution optimizations.
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -moptimize-membar
|
|
@opindex moptimize-membar
|
|
|
|
This switch removes redundant @code{membar} instructions from the
|
|
compiler generated code. It is enabled by default.
|
|
|
|
@item -mno-optimize-membar
|
|
@opindex mno-optimize-membar
|
|
|
|
This switch disables the automatic removal of redundant @code{membar}
|
|
instructions from the generated code.
|
|
|
|
@item -mtomcat-stats
|
|
@opindex mtomcat-stats
|
|
|
|
Cause gas to print out tomcat statistics.
|
|
|
|
@item -mcpu=@var{cpu}
|
|
@opindex mcpu
|
|
|
|
Select the processor type for which to generate code. Possible values are
|
|
@samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
|
|
@samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
|
|
|
|
@end table
|
|
|
|
@node GNU/Linux Options
|
|
@subsection GNU/Linux Options
|
|
|
|
These @samp{-m} options are defined for GNU/Linux targets:
|
|
|
|
@table @gcctabopt
|
|
@item -mglibc
|
|
@opindex mglibc
|
|
Use the GNU C library instead of uClibc. This is the default except
|
|
on @samp{*-*-linux-*uclibc*} targets.
|
|
|
|
@item -muclibc
|
|
@opindex muclibc
|
|
Use uClibc instead of the GNU C library. This is the default on
|
|
@samp{*-*-linux-*uclibc*} targets.
|
|
@end table
|
|
|
|
@node H8/300 Options
|
|
@subsection H8/300 Options
|
|
|
|
These @samp{-m} options are defined for the H8/300 implementations:
|
|
|
|
@table @gcctabopt
|
|
@item -mrelax
|
|
@opindex mrelax
|
|
Shorten some address references at link time, when possible; uses the
|
|
linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
|
|
ld, Using ld}, for a fuller description.
|
|
|
|
@item -mh
|
|
@opindex mh
|
|
Generate code for the H8/300H@.
|
|
|
|
@item -ms
|
|
@opindex ms
|
|
Generate code for the H8S@.
|
|
|
|
@item -mn
|
|
@opindex mn
|
|
Generate code for the H8S and H8/300H in the normal mode. This switch
|
|
must be used either with @option{-mh} or @option{-ms}.
|
|
|
|
@item -ms2600
|
|
@opindex ms2600
|
|
Generate code for the H8S/2600. This switch must be used with @option{-ms}.
|
|
|
|
@item -mint32
|
|
@opindex mint32
|
|
Make @code{int} data 32 bits by default.
|
|
|
|
@item -malign-300
|
|
@opindex malign-300
|
|
On the H8/300H and H8S, use the same alignment rules as for the H8/300.
|
|
The default for the H8/300H and H8S is to align longs and floats on 4
|
|
byte boundaries.
|
|
@option{-malign-300} causes them to be aligned on 2 byte boundaries.
|
|
This option has no effect on the H8/300.
|
|
@end table
|
|
|
|
@node HPPA Options
|
|
@subsection HPPA Options
|
|
@cindex HPPA Options
|
|
|
|
These @samp{-m} options are defined for the HPPA family of computers:
|
|
|
|
@table @gcctabopt
|
|
@item -march=@var{architecture-type}
|
|
@opindex march
|
|
Generate code for the specified architecture. The choices for
|
|
@var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
|
|
1.1, and @samp{2.0} for PA 2.0 processors. Refer to
|
|
@file{/usr/lib/sched.models} on an HP-UX system to determine the proper
|
|
architecture option for your machine. Code compiled for lower numbered
|
|
architectures will run on higher numbered architectures, but not the
|
|
other way around.
|
|
|
|
@item -mpa-risc-1-0
|
|
@itemx -mpa-risc-1-1
|
|
@itemx -mpa-risc-2-0
|
|
@opindex mpa-risc-1-0
|
|
@opindex mpa-risc-1-1
|
|
@opindex mpa-risc-2-0
|
|
Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
|
|
|
|
@item -mbig-switch
|
|
@opindex mbig-switch
|
|
Generate code suitable for big switch tables. Use this option only if
|
|
the assembler/linker complain about out of range branches within a switch
|
|
table.
|
|
|
|
@item -mjump-in-delay
|
|
@opindex mjump-in-delay
|
|
Fill delay slots of function calls with unconditional jump instructions
|
|
by modifying the return pointer for the function call to be the target
|
|
of the conditional jump.
|
|
|
|
@item -mdisable-fpregs
|
|
@opindex mdisable-fpregs
|
|
Prevent floating point registers from being used in any manner. This is
|
|
necessary for compiling kernels which perform lazy context switching of
|
|
floating point registers. If you use this option and attempt to perform
|
|
floating point operations, the compiler will abort.
|
|
|
|
@item -mdisable-indexing
|
|
@opindex mdisable-indexing
|
|
Prevent the compiler from using indexing address modes. This avoids some
|
|
rather obscure problems when compiling MIG generated code under MACH@.
|
|
|
|
@item -mno-space-regs
|
|
@opindex mno-space-regs
|
|
Generate code that assumes the target has no space registers. This allows
|
|
GCC to generate faster indirect calls and use unscaled index address modes.
|
|
|
|
Such code is suitable for level 0 PA systems and kernels.
|
|
|
|
@item -mfast-indirect-calls
|
|
@opindex mfast-indirect-calls
|
|
Generate code that assumes calls never cross space boundaries. This
|
|
allows GCC to emit code which performs faster indirect calls.
|
|
|
|
This option will not work in the presence of shared libraries or nested
|
|
functions.
|
|
|
|
@item -mfixed-range=@var{register-range}
|
|
@opindex mfixed-range
|
|
Generate code treating the given register range as fixed registers.
|
|
A fixed register is one that the register allocator can not use. This is
|
|
useful when compiling kernel code. A register range is specified as
|
|
two registers separated by a dash. Multiple register ranges can be
|
|
specified separated by a comma.
|
|
|
|
@item -mlong-load-store
|
|
@opindex mlong-load-store
|
|
Generate 3-instruction load and store sequences as sometimes required by
|
|
the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
|
|
the HP compilers.
|
|
|
|
@item -mportable-runtime
|
|
@opindex mportable-runtime
|
|
Use the portable calling conventions proposed by HP for ELF systems.
|
|
|
|
@item -mgas
|
|
@opindex mgas
|
|
Enable the use of assembler directives only GAS understands.
|
|
|
|
@item -mschedule=@var{cpu-type}
|
|
@opindex mschedule
|
|
Schedule code according to the constraints for the machine type
|
|
@var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
|
|
@samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
|
|
to @file{/usr/lib/sched.models} on an HP-UX system to determine the
|
|
proper scheduling option for your machine. The default scheduling is
|
|
@samp{8000}.
|
|
|
|
@item -mlinker-opt
|
|
@opindex mlinker-opt
|
|
Enable the optimization pass in the HP-UX linker. Note this makes symbolic
|
|
debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
|
|
linkers in which they give bogus error messages when linking some programs.
|
|
|
|
@item -msoft-float
|
|
@opindex msoft-float
|
|
Generate output containing library calls for floating point.
|
|
@strong{Warning:} the requisite libraries are not available for all HPPA
|
|
targets. Normally the facilities of the machine's usual C compiler are
|
|
used, but this cannot be done directly in cross-compilation. You must make
|
|
your own arrangements to provide suitable library functions for
|
|
cross-compilation. The embedded target @samp{hppa1.1-*-pro}
|
|
does provide software floating point support.
|
|
|
|
@option{-msoft-float} changes the calling convention in the output file;
|
|
therefore, it is only useful if you compile @emph{all} of a program with
|
|
this option. In particular, you need to compile @file{libgcc.a}, the
|
|
library that comes with GCC, with @option{-msoft-float} in order for
|
|
this to work.
|
|
|
|
@item -msio
|
|
@opindex msio
|
|
Generate the predefine, @code{_SIO}, for server IO@. The default is
|
|
@option{-mwsio}. This generates the predefines, @code{__hp9000s700},
|
|
@code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
|
|
options are available under HP-UX and HI-UX@.
|
|
|
|
@item -mgnu-ld
|
|
@opindex gnu-ld
|
|
Use GNU ld specific options. This passes @option{-shared} to ld when
|
|
building a shared library. It is the default when GCC is configured,
|
|
explicitly or implicitly, with the GNU linker. This option does not
|
|
have any affect on which ld is called, it only changes what parameters
|
|
are passed to that ld. The ld that is called is determined by the
|
|
@option{--with-ld} configure option, GCC's program search path, and
|
|
finally by the user's @env{PATH}. The linker used by GCC can be printed
|
|
using @samp{which `gcc -print-prog-name=ld`}. This option is only available
|
|
on the 64 bit HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
|
|
|
|
@item -mhp-ld
|
|
@opindex hp-ld
|
|
Use HP ld specific options. This passes @option{-b} to ld when building
|
|
a shared library and passes @option{+Accept TypeMismatch} to ld on all
|
|
links. It is the default when GCC is configured, explicitly or
|
|
implicitly, with the HP linker. This option does not have any affect on
|
|
which ld is called, it only changes what parameters are passed to that
|
|
ld. The ld that is called is determined by the @option{--with-ld}
|
|
configure option, GCC's program search path, and finally by the user's
|
|
@env{PATH}. The linker used by GCC can be printed using @samp{which
|
|
`gcc -print-prog-name=ld`}. This option is only available on the 64 bit
|
|
HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
|
|
|
|
@item -mlong-calls
|
|
@opindex mno-long-calls
|
|
Generate code that uses long call sequences. This ensures that a call
|
|
is always able to reach linker generated stubs. The default is to generate
|
|
long calls only when the distance from the call site to the beginning
|
|
of the function or translation unit, as the case may be, exceeds a
|
|
predefined limit set by the branch type being used. The limits for
|
|
normal calls are 7,600,000 and 240,000 bytes, respectively for the
|
|
PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
|
|
240,000 bytes.
|
|
|
|
Distances are measured from the beginning of functions when using the
|
|
@option{-ffunction-sections} option, or when using the @option{-mgas}
|
|
and @option{-mno-portable-runtime} options together under HP-UX with
|
|
the SOM linker.
|
|
|
|
It is normally not desirable to use this option as it will degrade
|
|
performance. However, it may be useful in large applications,
|
|
particularly when partial linking is used to build the application.
|
|
|
|
The types of long calls used depends on the capabilities of the
|
|
assembler and linker, and the type of code being generated. The
|
|
impact on systems that support long absolute calls, and long pic
|
|
symbol-difference or pc-relative calls should be relatively small.
|
|
However, an indirect call is used on 32-bit ELF systems in pic code
|
|
and it is quite long.
|
|
|
|
@item -munix=@var{unix-std}
|
|
@opindex march
|
|
Generate compiler predefines and select a startfile for the specified
|
|
UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
|
|
and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
|
|
is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
|
|
11.11 and later. The default values are @samp{93} for HP-UX 10.00,
|
|
@samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
|
|
and later.
|
|
|
|
@option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
|
|
@option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
|
|
and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
|
|
@option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
|
|
@code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
|
|
@code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
|
|
|
|
It is @emph{important} to note that this option changes the interfaces
|
|
for various library routines. It also affects the operational behavior
|
|
of the C library. Thus, @emph{extreme} care is needed in using this
|
|
option.
|
|
|
|
Library code that is intended to operate with more than one UNIX
|
|
standard must test, set and restore the variable @var{__xpg4_extended_mask}
|
|
as appropriate. Most GNU software doesn't provide this capability.
|
|
|
|
@item -nolibdld
|
|
@opindex nolibdld
|
|
Suppress the generation of link options to search libdld.sl when the
|
|
@option{-static} option is specified on HP-UX 10 and later.
|
|
|
|
@item -static
|
|
@opindex static
|
|
The HP-UX implementation of setlocale in libc has a dependency on
|
|
libdld.sl. There isn't an archive version of libdld.sl. Thus,
|
|
when the @option{-static} option is specified, special link options
|
|
are needed to resolve this dependency.
|
|
|
|
On HP-UX 10 and later, the GCC driver adds the necessary options to
|
|
link with libdld.sl when the @option{-static} option is specified.
|
|
This causes the resulting binary to be dynamic. On the 64-bit port,
|
|
the linkers generate dynamic binaries by default in any case. The
|
|
@option{-nolibdld} option can be used to prevent the GCC driver from
|
|
adding these link options.
|
|
|
|
@item -threads
|
|
@opindex threads
|
|
Add support for multithreading with the @dfn{dce thread} library
|
|
under HP-UX@. This option sets flags for both the preprocessor and
|
|
linker.
|
|
@end table
|
|
|
|
@node i386 and x86-64 Options
|
|
@subsection Intel 386 and AMD x86-64 Options
|
|
@cindex i386 Options
|
|
@cindex x86-64 Options
|
|
@cindex Intel 386 Options
|
|
@cindex AMD x86-64 Options
|
|
|
|
These @samp{-m} options are defined for the i386 and x86-64 family of
|
|
computers:
|
|
|
|
@table @gcctabopt
|
|
@item -mtune=@var{cpu-type}
|
|
@opindex mtune
|
|
Tune to @var{cpu-type} everything applicable about the generated code, except
|
|
for the ABI and the set of available instructions. The choices for
|
|
@var{cpu-type} are:
|
|
@table @emph
|
|
@item generic
|
|
Produce code optimized for the most common IA32/AMD64/EM64T processors.
|
|
If you know the CPU on which your code will run, then you should use
|
|
the corresponding @option{-mtune} option instead of
|
|
@option{-mtune=generic}. But, if you do not know exactly what CPU users
|
|
of your application will have, then you should use this option.
|
|
|
|
As new processors are deployed in the marketplace, the behavior of this
|
|
option will change. Therefore, if you upgrade to a newer version of
|
|
GCC, the code generated option will change to reflect the processors
|
|
that were most common when that version of GCC was released.
|
|
|
|
There is no @option{-march=generic} option because @option{-march}
|
|
indicates the instruction set the compiler can use, and there is no
|
|
generic instruction set applicable to all processors. In contrast,
|
|
@option{-mtune} indicates the processor (or, in this case, collection of
|
|
processors) for which the code is optimized.
|
|
@item native
|
|
This selects the CPU to tune for at compilation time by determining
|
|
the processor type of the compiling machine. Using @option{-mtune=native}
|
|
will produce code optimized for the local machine under the constraints
|
|
of the selected instruction set. Using @option{-march=native} will
|
|
enable all instruction subsets supported by the local machine (hence
|
|
the result might not run on different machines).
|
|
@item i386
|
|
Original Intel's i386 CPU@.
|
|
@item i486
|
|
Intel's i486 CPU@. (No scheduling is implemented for this chip.)
|
|
@item i586, pentium
|
|
Intel Pentium CPU with no MMX support.
|
|
@item pentium-mmx
|
|
Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
|
|
@item pentiumpro
|
|
Intel PentiumPro CPU@.
|
|
@item i686
|
|
Same as @code{generic}, but when used as @code{march} option, PentiumPro
|
|
instruction set will be used, so the code will run on all i686 family chips.
|
|
@item pentium2
|
|
Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
|
|
@item pentium3, pentium3m
|
|
Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
|
|
support.
|
|
@item pentium-m
|
|
Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
|
|
support. Used by Centrino notebooks.
|
|
@item pentium4, pentium4m
|
|
Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
|
|
@item prescott
|
|
Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
|
|
set support.
|
|
@item nocona
|
|
Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
|
|
SSE2 and SSE3 instruction set support.
|
|
@item k6
|
|
AMD K6 CPU with MMX instruction set support.
|
|
@item k6-2, k6-3
|
|
Improved versions of AMD K6 CPU with MMX and 3dNOW! instruction set support.
|
|
@item athlon, athlon-tbird
|
|
AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE prefetch instructions
|
|
support.
|
|
@item athlon-4, athlon-xp, athlon-mp
|
|
Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and full SSE
|
|
instruction set support.
|
|
@item k8, opteron, athlon64, athlon-fx
|
|
AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
|
|
MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and 64-bit instruction set extensions.)
|
|
@item winchip-c6
|
|
IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
|
|
set support.
|
|
@item winchip2
|
|
IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!
|
|
instruction set support.
|
|
@item c3
|
|
Via C3 CPU with MMX and 3dNOW! instruction set support. (No scheduling is
|
|
implemented for this chip.)
|
|
@item c3-2
|
|
Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
|
|
implemented for this chip.)
|
|
@end table
|
|
|
|
While picking a specific @var{cpu-type} will schedule things appropriately
|
|
for that particular chip, the compiler will not generate any code that
|
|
does not run on the i386 without the @option{-march=@var{cpu-type}} option
|
|
being used.
|
|
|
|
@item -march=@var{cpu-type}
|
|
@opindex march
|
|
Generate instructions for the machine type @var{cpu-type}. The choices
|
|
for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
|
|
specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
|
|
|
|
@item -mcpu=@var{cpu-type}
|
|
@opindex mcpu
|
|
A deprecated synonym for @option{-mtune}.
|
|
|
|
@item -m386
|
|
@itemx -m486
|
|
@itemx -mpentium
|
|
@itemx -mpentiumpro
|
|
@opindex m386
|
|
@opindex m486
|
|
@opindex mpentium
|
|
@opindex mpentiumpro
|
|
These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
|
|
@option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
|
|
These synonyms are deprecated.
|
|
|
|
@item -mfpmath=@var{unit}
|
|
@opindex march
|
|
Generate floating point arithmetics for selected unit @var{unit}. The choices
|
|
for @var{unit} are:
|
|
|
|
@table @samp
|
|
@item 387
|
|
Use the standard 387 floating point coprocessor present majority of chips and
|
|
emulated otherwise. Code compiled with this option will run almost everywhere.
|
|
The temporary results are computed in 80bit precision instead of precision
|
|
specified by the type resulting in slightly different results compared to most
|
|
of other chips. See @option{-ffloat-store} for more detailed description.
|
|
|
|
This is the default choice for i386 compiler.
|
|
|
|
@item sse
|
|
Use scalar floating point instructions present in the SSE instruction set.
|
|
This instruction set is supported by Pentium3 and newer chips, in the AMD line
|
|
by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
|
|
instruction set supports only single precision arithmetics, thus the double and
|
|
extended precision arithmetics is still done using 387. Later version, present
|
|
only in Pentium4 and the future AMD x86-64 chips supports double precision
|
|
arithmetics too.
|
|
|
|
For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
|
|
or @option{-msse2} switches to enable SSE extensions and make this option
|
|
effective. For the x86-64 compiler, these extensions are enabled by default.
|
|
|
|
The resulting code should be considerably faster in the majority of cases and avoid
|
|
the numerical instability problems of 387 code, but may break some existing
|
|
code that expects temporaries to be 80bit.
|
|
|
|
This is the default choice for the x86-64 compiler.
|
|
|
|
@item sse,387
|
|
Attempt to utilize both instruction sets at once. This effectively double the
|
|
amount of available registers and on chips with separate execution units for
|
|
387 and SSE the execution resources too. Use this option with care, as it is
|
|
still experimental, because the GCC register allocator does not model separate
|
|
functional units well resulting in instable performance.
|
|
@end table
|
|
|
|
@item -masm=@var{dialect}
|
|
@opindex masm=@var{dialect}
|
|
Output asm instructions using selected @var{dialect}. Supported
|
|
choices are @samp{intel} or @samp{att} (the default one). Darwin does
|
|
not support @samp{intel}.
|
|
|
|
@item -mieee-fp
|
|
@itemx -mno-ieee-fp
|
|
@opindex mieee-fp
|
|
@opindex mno-ieee-fp
|
|
Control whether or not the compiler uses IEEE floating point
|
|
comparisons. These handle correctly the case where the result of a
|
|
comparison is unordered.
|
|
|
|
@item -msoft-float
|
|
@opindex msoft-float
|
|
Generate output containing library calls for floating point.
|
|
@strong{Warning:} the requisite libraries are not part of GCC@.
|
|
Normally the facilities of the machine's usual C compiler are used, but
|
|
this can't be done directly in cross-compilation. You must make your
|
|
own arrangements to provide suitable library functions for
|
|
cross-compilation.
|
|
|
|
On machines where a function returns floating point results in the 80387
|
|
register stack, some floating point opcodes may be emitted even if
|
|
@option{-msoft-float} is used.
|
|
|
|
@item -mno-fp-ret-in-387
|
|
@opindex mno-fp-ret-in-387
|
|
Do not use the FPU registers for return values of functions.
|
|
|
|
The usual calling convention has functions return values of types
|
|
@code{float} and @code{double} in an FPU register, even if there
|
|
is no FPU@. The idea is that the operating system should emulate
|
|
an FPU@.
|
|
|
|
The option @option{-mno-fp-ret-in-387} causes such values to be returned
|
|
in ordinary CPU registers instead.
|
|
|
|
@item -mno-fancy-math-387
|
|
@opindex mno-fancy-math-387
|
|
Some 387 emulators do not support the @code{sin}, @code{cos} and
|
|
@code{sqrt} instructions for the 387. Specify this option to avoid
|
|
generating those instructions. This option is the default on
|
|
OpenBSD and NetBSD@. This option is overridden when @option{-march}
|
|
indicates that the target cpu will always have an FPU and so the
|
|
instruction will not need emulation. As of revision 2.6.1, these
|
|
instructions are not generated unless you also use the
|
|
@option{-funsafe-math-optimizations} switch.
|
|
|
|
@item -malign-double
|
|
@itemx -mno-align-double
|
|
@opindex malign-double
|
|
@opindex mno-align-double
|
|
Control whether GCC aligns @code{double}, @code{long double}, and
|
|
@code{long long} variables on a two word boundary or a one word
|
|
boundary. Aligning @code{double} variables on a two word boundary will
|
|
produce code that runs somewhat faster on a @samp{Pentium} at the
|
|
expense of more memory.
|
|
|
|
On x86-64, @option{-malign-double} is enabled by default.
|
|
|
|
@strong{Warning:} if you use the @option{-malign-double} switch,
|
|
structures containing the above types will be aligned differently than
|
|
the published application binary interface specifications for the 386
|
|
and will not be binary compatible with structures in code compiled
|
|
without that switch.
|
|
|
|
@item -m96bit-long-double
|
|
@itemx -m128bit-long-double
|
|
@opindex m96bit-long-double
|
|
@opindex m128bit-long-double
|
|
These switches control the size of @code{long double} type. The i386
|
|
application binary interface specifies the size to be 96 bits,
|
|
so @option{-m96bit-long-double} is the default in 32 bit mode.
|
|
|
|
Modern architectures (Pentium and newer) would prefer @code{long double}
|
|
to be aligned to an 8 or 16 byte boundary. In arrays or structures
|
|
conforming to the ABI, this would not be possible. So specifying a
|
|
@option{-m128bit-long-double} will align @code{long double}
|
|
to a 16 byte boundary by padding the @code{long double} with an additional
|
|
32 bit zero.
|
|
|
|
In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
|
|
its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
|
|
|
|
Notice that neither of these options enable any extra precision over the x87
|
|
standard of 80 bits for a @code{long double}.
|
|
|
|
@strong{Warning:} if you override the default value for your target ABI, the
|
|
structures and arrays containing @code{long double} variables will change
|
|
their size as well as function calling convention for function taking
|
|
@code{long double} will be modified. Hence they will not be binary
|
|
compatible with arrays or structures in code compiled without that switch.
|
|
|
|
@item -mmlarge-data-threshold=@var{number}
|
|
@opindex mlarge-data-threshold=@var{number}
|
|
When @option{-mcmodel=medium} is specified, the data greater than
|
|
@var{threshold} are placed in large data section. This value must be the
|
|
same across all object linked into the binary and defaults to 65535.
|
|
|
|
@item -msvr3-shlib
|
|
@itemx -mno-svr3-shlib
|
|
@opindex msvr3-shlib
|
|
@opindex mno-svr3-shlib
|
|
Control whether GCC places uninitialized local variables into the
|
|
@code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
|
|
into @code{bss}. These options are meaningful only on System V Release 3.
|
|
|
|
@item -mrtd
|
|
@opindex mrtd
|
|
Use a different function-calling convention, in which functions that
|
|
take a fixed number of arguments return with the @code{ret} @var{num}
|
|
instruction, which pops their arguments while returning. This saves one
|
|
instruction in the caller since there is no need to pop the arguments
|
|
there.
|
|
|
|
You can specify that an individual function is called with this calling
|
|
sequence with the function attribute @samp{stdcall}. You can also
|
|
override the @option{-mrtd} option by using the function attribute
|
|
@samp{cdecl}. @xref{Function Attributes}.
|
|
|
|
@strong{Warning:} this calling convention is incompatible with the one
|
|
normally used on Unix, so you cannot use it if you need to call
|
|
libraries compiled with the Unix compiler.
|
|
|
|
Also, you must provide function prototypes for all functions that
|
|
take variable numbers of arguments (including @code{printf});
|
|
otherwise incorrect code will be generated for calls to those
|
|
functions.
|
|
|
|
In addition, seriously incorrect code will result if you call a
|
|
function with too many arguments. (Normally, extra arguments are
|
|
harmlessly ignored.)
|
|
|
|
@item -mregparm=@var{num}
|
|
@opindex mregparm
|
|
Control how many registers are used to pass integer arguments. By
|
|
default, no registers are used to pass arguments, and at most 3
|
|
registers can be used. You can control this behavior for a specific
|
|
function by using the function attribute @samp{regparm}.
|
|
@xref{Function Attributes}.
|
|
|
|
@strong{Warning:} if you use this switch, and
|
|
@var{num} is nonzero, then you must build all modules with the same
|
|
value, including any libraries. This includes the system libraries and
|
|
startup modules.
|
|
|
|
@item -msseregparm
|
|
@opindex msseregparm
|
|
Use SSE register passing conventions for float and double arguments
|
|
and return values. You can control this behavior for a specific
|
|
function by using the function attribute @samp{sseregparm}.
|
|
@xref{Function Attributes}.
|
|
|
|
@strong{Warning:} if you use this switch then you must build all
|
|
modules with the same value, including any libraries. This includes
|
|
the system libraries and startup modules.
|
|
|
|
@item -mstackrealign
|
|
@opindex mstackrealign
|
|
Realign the stack at entry. On the Intel x86, the
|
|
@option{-mstackrealign} option will generate an alternate prologue and
|
|
epilogue that realigns the runtime stack. This supports mixing legacy
|
|
codes that keep a 4-byte aligned stack with modern codes that keep a
|
|
16-byte stack for SSE compatibility. The alternate prologue and
|
|
epilogue are slower and bigger than the regular ones, and the
|
|
alternate prologue requires an extra scratch register; this lowers the
|
|
number of registers available if used in conjunction with the
|
|
@code{regparm} attribute. The @option{-mstackrealign} option is
|
|
incompatible with the nested function prologue; this is considered a
|
|
hard error. See also the attribute @code{force_align_arg_pointer},
|
|
applicable to individual functions.
|
|
|
|
@item -mpreferred-stack-boundary=@var{num}
|
|
@opindex mpreferred-stack-boundary
|
|
Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
|
|
byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
|
|
the default is 4 (16 bytes or 128 bits).
|
|
|
|
On Pentium and PentiumPro, @code{double} and @code{long double} values
|
|
should be aligned to an 8 byte boundary (see @option{-malign-double}) or
|
|
suffer significant run time performance penalties. On Pentium III, the
|
|
Streaming SIMD Extension (SSE) data type @code{__m128} may not work
|
|
properly if it is not 16 byte aligned.
|
|
|
|
To ensure proper alignment of this values on the stack, the stack boundary
|
|
must be as aligned as that required by any value stored on the stack.
|
|
Further, every function must be generated such that it keeps the stack
|
|
aligned. Thus calling a function compiled with a higher preferred
|
|
stack boundary from a function compiled with a lower preferred stack
|
|
boundary will most likely misalign the stack. It is recommended that
|
|
libraries that use callbacks always use the default setting.
|
|
|
|
This extra alignment does consume extra stack space, and generally
|
|
increases code size. Code that is sensitive to stack space usage, such
|
|
as embedded systems and operating system kernels, may want to reduce the
|
|
preferred alignment to @option{-mpreferred-stack-boundary=2}.
|
|
|
|
@item -mmmx
|
|
@itemx -mno-mmx
|
|
@item -msse
|
|
@itemx -mno-sse
|
|
@item -msse2
|
|
@itemx -mno-sse2
|
|
@item -msse3
|
|
@itemx -mno-sse3
|
|
@item -m3dnow
|
|
@itemx -mno-3dnow
|
|
@opindex mmmx
|
|
@opindex mno-mmx
|
|
@opindex msse
|
|
@opindex mno-sse
|
|
@opindex m3dnow
|
|
@opindex mno-3dnow
|
|
These switches enable or disable the use of instructions in the MMX,
|
|
SSE, SSE2 or 3DNow! extended instruction sets. These extensions are
|
|
also available as built-in functions: see @ref{X86 Built-in Functions},
|
|
for details of the functions enabled and disabled by these switches.
|
|
|
|
To have SSE/SSE2 instructions generated automatically from floating-point
|
|
code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
|
|
|
|
These options will enable GCC to use these extended instructions in
|
|
generated code, even without @option{-mfpmath=sse}. Applications which
|
|
perform runtime CPU detection must compile separate files for each
|
|
supported architecture, using the appropriate flags. In particular,
|
|
the file containing the CPU detection code should be compiled without
|
|
these options.
|
|
|
|
@item -mpush-args
|
|
@itemx -mno-push-args
|
|
@opindex mpush-args
|
|
@opindex mno-push-args
|
|
Use PUSH operations to store outgoing parameters. This method is shorter
|
|
and usually equally fast as method using SUB/MOV operations and is enabled
|
|
by default. In some cases disabling it may improve performance because of
|
|
improved scheduling and reduced dependencies.
|
|
|
|
@item -maccumulate-outgoing-args
|
|
@opindex maccumulate-outgoing-args
|
|
If enabled, the maximum amount of space required for outgoing arguments will be
|
|
computed in the function prologue. This is faster on most modern CPUs
|
|
because of reduced dependencies, improved scheduling and reduced stack usage
|
|
when preferred stack boundary is not equal to 2. The drawback is a notable
|
|
increase in code size. This switch implies @option{-mno-push-args}.
|
|
|
|
@item -mthreads
|
|
@opindex mthreads
|
|
Support thread-safe exception handling on @samp{Mingw32}. Code that relies
|
|
on thread-safe exception handling must compile and link all code with the
|
|
@option{-mthreads} option. When compiling, @option{-mthreads} defines
|
|
@option{-D_MT}; when linking, it links in a special thread helper library
|
|
@option{-lmingwthrd} which cleans up per thread exception handling data.
|
|
|
|
@item -mno-align-stringops
|
|
@opindex mno-align-stringops
|
|
Do not align destination of inlined string operations. This switch reduces
|
|
code size and improves performance in case the destination is already aligned,
|
|
but GCC doesn't know about it.
|
|
|
|
@item -minline-all-stringops
|
|
@opindex minline-all-stringops
|
|
By default GCC inlines string operations only when destination is known to be
|
|
aligned at least to 4 byte boundary. This enables more inlining, increase code
|
|
size, but may improve performance of code that depends on fast memcpy, strlen
|
|
and memset for short lengths.
|
|
|
|
@item -momit-leaf-frame-pointer
|
|
@opindex momit-leaf-frame-pointer
|
|
Don't keep the frame pointer in a register for leaf functions. This
|
|
avoids the instructions to save, set up and restore frame pointers and
|
|
makes an extra register available in leaf functions. The option
|
|
@option{-fomit-frame-pointer} removes the frame pointer for all functions
|
|
which might make debugging harder.
|
|
|
|
@item -mtls-direct-seg-refs
|
|
@itemx -mno-tls-direct-seg-refs
|
|
@opindex mtls-direct-seg-refs
|
|
Controls whether TLS variables may be accessed with offsets from the
|
|
TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
|
|
or whether the thread base pointer must be added. Whether or not this
|
|
is legal depends on the operating system, and whether it maps the
|
|
segment to cover the entire TLS area.
|
|
|
|
For systems that use GNU libc, the default is on.
|
|
@end table
|
|
|
|
These @samp{-m} switches are supported in addition to the above
|
|
on AMD x86-64 processors in 64-bit environments.
|
|
|
|
@table @gcctabopt
|
|
@item -m32
|
|
@itemx -m64
|
|
@opindex m32
|
|
@opindex m64
|
|
Generate code for a 32-bit or 64-bit environment.
|
|
The 32-bit environment sets int, long and pointer to 32 bits and
|
|
generates code that runs on any i386 system.
|
|
The 64-bit environment sets int to 32 bits and long and pointer
|
|
to 64 bits and generates code for AMD's x86-64 architecture. For
|
|
darwin only the -m64 option turns off the @option{-fno-pic} and
|
|
@option{-mdynamic-no-pic} options.
|
|
|
|
@item -mno-red-zone
|
|
@opindex no-red-zone
|
|
Do not use a so called red zone for x86-64 code. The red zone is mandated
|
|
by the x86-64 ABI, it is a 128-byte area beyond the location of the
|
|
stack pointer that will not be modified by signal or interrupt handlers
|
|
and therefore can be used for temporary data without adjusting the stack
|
|
pointer. The flag @option{-mno-red-zone} disables this red zone.
|
|
|
|
@item -mcmodel=small
|
|
@opindex mcmodel=small
|
|
Generate code for the small code model: the program and its symbols must
|
|
be linked in the lower 2 GB of the address space. Pointers are 64 bits.
|
|
Programs can be statically or dynamically linked. This is the default
|
|
code model.
|
|
|
|
@item -mcmodel=kernel
|
|
@opindex mcmodel=kernel
|
|
Generate code for the kernel code model. The kernel runs in the
|
|
negative 2 GB of the address space.
|
|
This model has to be used for Linux kernel code.
|
|
|
|
@item -mcmodel=medium
|
|
@opindex mcmodel=medium
|
|
Generate code for the medium model: The program is linked in the lower 2
|
|
GB of the address space but symbols can be located anywhere in the
|
|
address space. Programs can be statically or dynamically linked, but
|
|
building of shared libraries are not supported with the medium model.
|
|
|
|
@item -mcmodel=large
|
|
@opindex mcmodel=large
|
|
Generate code for the large model: This model makes no assumptions
|
|
about addresses and sizes of sections. Currently GCC does not implement
|
|
this model.
|
|
@end table
|
|
|
|
@node IA-64 Options
|
|
@subsection IA-64 Options
|
|
@cindex IA-64 Options
|
|
|
|
These are the @samp{-m} options defined for the Intel IA-64 architecture.
|
|
|
|
@table @gcctabopt
|
|
@item -mbig-endian
|
|
@opindex mbig-endian
|
|
Generate code for a big endian target. This is the default for HP-UX@.
|
|
|
|
@item -mlittle-endian
|
|
@opindex mlittle-endian
|
|
Generate code for a little endian target. This is the default for AIX5
|
|
and GNU/Linux.
|
|
|
|
@item -mgnu-as
|
|
@itemx -mno-gnu-as
|
|
@opindex mgnu-as
|
|
@opindex mno-gnu-as
|
|
Generate (or don't) code for the GNU assembler. This is the default.
|
|
@c Also, this is the default if the configure option @option{--with-gnu-as}
|
|
@c is used.
|
|
|
|
@item -mgnu-ld
|
|
@itemx -mno-gnu-ld
|
|
@opindex mgnu-ld
|
|
@opindex mno-gnu-ld
|
|
Generate (or don't) code for the GNU linker. This is the default.
|
|
@c Also, this is the default if the configure option @option{--with-gnu-ld}
|
|
@c is used.
|
|
|
|
@item -mno-pic
|
|
@opindex mno-pic
|
|
Generate code that does not use a global pointer register. The result
|
|
is not position independent code, and violates the IA-64 ABI@.
|
|
|
|
@item -mvolatile-asm-stop
|
|
@itemx -mno-volatile-asm-stop
|
|
@opindex mvolatile-asm-stop
|
|
@opindex mno-volatile-asm-stop
|
|
Generate (or don't) a stop bit immediately before and after volatile asm
|
|
statements.
|
|
|
|
@item -mregister-names
|
|
@itemx -mno-register-names
|
|
@opindex mregister-names
|
|
@opindex mno-register-names
|
|
Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
|
|
the stacked registers. This may make assembler output more readable.
|
|
|
|
@item -mno-sdata
|
|
@itemx -msdata
|
|
@opindex mno-sdata
|
|
@opindex msdata
|
|
Disable (or enable) optimizations that use the small data section. This may
|
|
be useful for working around optimizer bugs.
|
|
|
|
@item -mconstant-gp
|
|
@opindex mconstant-gp
|
|
Generate code that uses a single constant global pointer value. This is
|
|
useful when compiling kernel code.
|
|
|
|
@item -mauto-pic
|
|
@opindex mauto-pic
|
|
Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
|
|
This is useful when compiling firmware code.
|
|
|
|
@item -minline-float-divide-min-latency
|
|
@opindex minline-float-divide-min-latency
|
|
Generate code for inline divides of floating point values
|
|
using the minimum latency algorithm.
|
|
|
|
@item -minline-float-divide-max-throughput
|
|
@opindex minline-float-divide-max-throughput
|
|
Generate code for inline divides of floating point values
|
|
using the maximum throughput algorithm.
|
|
|
|
@item -minline-int-divide-min-latency
|
|
@opindex minline-int-divide-min-latency
|
|
Generate code for inline divides of integer values
|
|
using the minimum latency algorithm.
|
|
|
|
@item -minline-int-divide-max-throughput
|
|
@opindex minline-int-divide-max-throughput
|
|
Generate code for inline divides of integer values
|
|
using the maximum throughput algorithm.
|
|
|
|
@item -minline-sqrt-min-latency
|
|
@opindex minline-sqrt-min-latency
|
|
Generate code for inline square roots
|
|
using the minimum latency algorithm.
|
|
|
|
@item -minline-sqrt-max-throughput
|
|
@opindex minline-sqrt-max-throughput
|
|
Generate code for inline square roots
|
|
using the maximum throughput algorithm.
|
|
|
|
@item -mno-dwarf2-asm
|
|
@itemx -mdwarf2-asm
|
|
@opindex mno-dwarf2-asm
|
|
@opindex mdwarf2-asm
|
|
Don't (or do) generate assembler code for the DWARF2 line number debugging
|
|
info. This may be useful when not using the GNU assembler.
|
|
|
|
@item -mearly-stop-bits
|
|
@itemx -mno-early-stop-bits
|
|
@opindex mearly-stop-bits
|
|
@opindex mno-early-stop-bits
|
|
Allow stop bits to be placed earlier than immediately preceding the
|
|
instruction that triggered the stop bit. This can improve instruction
|
|
scheduling, but does not always do so.
|
|
|
|
@item -mfixed-range=@var{register-range}
|
|
@opindex mfixed-range
|
|
Generate code treating the given register range as fixed registers.
|
|
A fixed register is one that the register allocator can not use. This is
|
|
useful when compiling kernel code. A register range is specified as
|
|
two registers separated by a dash. Multiple register ranges can be
|
|
specified separated by a comma.
|
|
|
|
@item -mtls-size=@var{tls-size}
|
|
@opindex mtls-size
|
|
Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
|
|
64.
|
|
|
|
@item -mtune=@var{cpu-type}
|
|
@opindex mtune
|
|
Tune the instruction scheduling for a particular CPU, Valid values are
|
|
itanium, itanium1, merced, itanium2, and mckinley.
|
|
|
|
@item -mt
|
|
@itemx -pthread
|
|
@opindex mt
|
|
@opindex pthread
|
|
Add support for multithreading using the POSIX threads library. This
|
|
option sets flags for both the preprocessor and linker. It does
|
|
not affect the thread safety of object code produced by the compiler or
|
|
that of libraries supplied with it. These are HP-UX specific flags.
|
|
|
|
@item -milp32
|
|
@itemx -mlp64
|
|
@opindex milp32
|
|
@opindex mlp64
|
|
Generate code for a 32-bit or 64-bit environment.
|
|
The 32-bit environment sets int, long and pointer to 32 bits.
|
|
The 64-bit environment sets int to 32 bits and long and pointer
|
|
to 64 bits. These are HP-UX specific flags.
|
|
|
|
@item -mno-sched-br-data-spec
|
|
@itemx -msched-br-data-spec
|
|
@opindex mno-sched-br-data-spec
|
|
@opindex msched-br-data-spec
|
|
(Dis/En)able data speculative scheduling before reload.
|
|
This will result in generation of the ld.a instructions and
|
|
the corresponding check instructions (ld.c / chk.a).
|
|
The default is 'disable'.
|
|
|
|
@item -msched-ar-data-spec
|
|
@itemx -mno-sched-ar-data-spec
|
|
@opindex msched-ar-data-spec
|
|
@opindex mno-sched-ar-data-spec
|
|
(En/Dis)able data speculative scheduling after reload.
|
|
This will result in generation of the ld.a instructions and
|
|
the corresponding check instructions (ld.c / chk.a).
|
|
The default is 'enable'.
|
|
|
|
@item -mno-sched-control-spec
|
|
@itemx -msched-control-spec
|
|
@opindex mno-sched-control-spec
|
|
@opindex msched-control-spec
|
|
(Dis/En)able control speculative scheduling. This feature is
|
|
available only during region scheduling (i.e. before reload).
|
|
This will result in generation of the ld.s instructions and
|
|
the corresponding check instructions chk.s .
|
|
The default is 'disable'.
|
|
|
|
@item -msched-br-in-data-spec
|
|
@itemx -mno-sched-br-in-data-spec
|
|
@opindex msched-br-in-data-spec
|
|
@opindex mno-sched-br-in-data-spec
|
|
(En/Dis)able speculative scheduling of the instructions that
|
|
are dependent on the data speculative loads before reload.
|
|
This is effective only with @option{-msched-br-data-spec} enabled.
|
|
The default is 'enable'.
|
|
|
|
@item -msched-ar-in-data-spec
|
|
@itemx -mno-sched-ar-in-data-spec
|
|
@opindex msched-ar-in-data-spec
|
|
@opindex mno-sched-ar-in-data-spec
|
|
(En/Dis)able speculative scheduling of the instructions that
|
|
are dependent on the data speculative loads after reload.
|
|
This is effective only with @option{-msched-ar-data-spec} enabled.
|
|
The default is 'enable'.
|
|
|
|
@item -msched-in-control-spec
|
|
@itemx -mno-sched-in-control-spec
|
|
@opindex msched-in-control-spec
|
|
@opindex mno-sched-in-control-spec
|
|
(En/Dis)able speculative scheduling of the instructions that
|
|
are dependent on the control speculative loads.
|
|
This is effective only with @option{-msched-control-spec} enabled.
|
|
The default is 'enable'.
|
|
|
|
@item -msched-ldc
|
|
@itemx -mno-sched-ldc
|
|
@opindex msched-ldc
|
|
@opindex mno-sched-ldc
|
|
(En/Dis)able use of simple data speculation checks ld.c .
|
|
If disabled, only chk.a instructions will be emitted to check
|
|
data speculative loads.
|
|
The default is 'enable'.
|
|
|
|
@item -mno-sched-control-ldc
|
|
@itemx -msched-control-ldc
|
|
@opindex mno-sched-control-ldc
|
|
@opindex msched-control-ldc
|
|
(Dis/En)able use of ld.c instructions to check control speculative loads.
|
|
If enabled, in case of control speculative load with no speculatively
|
|
scheduled dependent instructions this load will be emitted as ld.sa and
|
|
ld.c will be used to check it.
|
|
The default is 'disable'.
|
|
|
|
@item -mno-sched-spec-verbose
|
|
@itemx -msched-spec-verbose
|
|
@opindex mno-sched-spec-verbose
|
|
@opindex msched-spec-verbose
|
|
(Dis/En)able printing of the information about speculative motions.
|
|
|
|
@item -mno-sched-prefer-non-data-spec-insns
|
|
@itemx -msched-prefer-non-data-spec-insns
|
|
@opindex mno-sched-prefer-non-data-spec-insns
|
|
@opindex msched-prefer-non-data-spec-insns
|
|
If enabled, data speculative instructions will be chosen for schedule
|
|
only if there are no other choices at the moment. This will make
|
|
the use of the data speculation much more conservative.
|
|
The default is 'disable'.
|
|
|
|
@item -mno-sched-prefer-non-control-spec-insns
|
|
@itemx -msched-prefer-non-control-spec-insns
|
|
@opindex mno-sched-prefer-non-control-spec-insns
|
|
@opindex msched-prefer-non-control-spec-insns
|
|
If enabled, control speculative instructions will be chosen for schedule
|
|
only if there are no other choices at the moment. This will make
|
|
the use of the control speculation much more conservative.
|
|
The default is 'disable'.
|
|
|
|
@item -mno-sched-count-spec-in-critical-path
|
|
@itemx -msched-count-spec-in-critical-path
|
|
@opindex mno-sched-count-spec-in-critical-path
|
|
@opindex msched-count-spec-in-critical-path
|
|
If enabled, speculative dependencies will be considered during
|
|
computation of the instructions priorities. This will make the use of the
|
|
speculation a bit more conservative.
|
|
The default is 'disable'.
|
|
|
|
@end table
|
|
|
|
@node M32C Options
|
|
@subsection M32C Options
|
|
@cindex M32C options
|
|
|
|
@table @gcctabopt
|
|
@item -mcpu=@var{name}
|
|
@opindex mcpu=
|
|
Select the CPU for which code is generated. @var{name} may be one of
|
|
@samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
|
|
/60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
|
|
the M32C/80 series.
|
|
|
|
@item -msim
|
|
@opindex msim
|
|
Specifies that the program will be run on the simulator. This causes
|
|
an alternate runtime library to be linked in which supports, for
|
|
example, file I/O. You must not use this option when generating
|
|
programs that will run on real hardware; you must provide your own
|
|
runtime library for whatever I/O functions are needed.
|
|
|
|
@item -memregs=@var{number}
|
|
@opindex memregs=
|
|
Specifies the number of memory-based pseudo-registers GCC will use
|
|
during code generation. These pseudo-registers will be used like real
|
|
registers, so there is a tradeoff between GCC's ability to fit the
|
|
code into available registers, and the performance penalty of using
|
|
memory instead of registers. Note that all modules in a program must
|
|
be compiled with the same value for this option. Because of that, you
|
|
must not use this option with the default runtime libraries gcc
|
|
builds.
|
|
|
|
@end table
|
|
|
|
@node M32R/D Options
|
|
@subsection M32R/D Options
|
|
@cindex M32R/D options
|
|
|
|
These @option{-m} options are defined for Renesas M32R/D architectures:
|
|
|
|
@table @gcctabopt
|
|
@item -m32r2
|
|
@opindex m32r2
|
|
Generate code for the M32R/2@.
|
|
|
|
@item -m32rx
|
|
@opindex m32rx
|
|
Generate code for the M32R/X@.
|
|
|
|
@item -m32r
|
|
@opindex m32r
|
|
Generate code for the M32R@. This is the default.
|
|
|
|
@item -mmodel=small
|
|
@opindex mmodel=small
|
|
Assume all objects live in the lower 16MB of memory (so that their addresses
|
|
can be loaded with the @code{ld24} instruction), and assume all subroutines
|
|
are reachable with the @code{bl} instruction.
|
|
This is the default.
|
|
|
|
The addressability of a particular object can be set with the
|
|
@code{model} attribute.
|
|
|
|
@item -mmodel=medium
|
|
@opindex mmodel=medium
|
|
Assume objects may be anywhere in the 32-bit address space (the compiler
|
|
will generate @code{seth/add3} instructions to load their addresses), and
|
|
assume all subroutines are reachable with the @code{bl} instruction.
|
|
|
|
@item -mmodel=large
|
|
@opindex mmodel=large
|
|
Assume objects may be anywhere in the 32-bit address space (the compiler
|
|
will generate @code{seth/add3} instructions to load their addresses), and
|
|
assume subroutines may not be reachable with the @code{bl} instruction
|
|
(the compiler will generate the much slower @code{seth/add3/jl}
|
|
instruction sequence).
|
|
|
|
@item -msdata=none
|
|
@opindex msdata=none
|
|
Disable use of the small data area. Variables will be put into
|
|
one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
|
|
@code{section} attribute has been specified).
|
|
This is the default.
|
|
|
|
The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
|
|
Objects may be explicitly put in the small data area with the
|
|
@code{section} attribute using one of these sections.
|
|
|
|
@item -msdata=sdata
|
|
@opindex msdata=sdata
|
|
Put small global and static data in the small data area, but do not
|
|
generate special code to reference them.
|
|
|
|
@item -msdata=use
|
|
@opindex msdata=use
|
|
Put small global and static data in the small data area, and generate
|
|
special instructions to reference them.
|
|
|
|
@item -G @var{num}
|
|
@opindex G
|
|
@cindex smaller data references
|
|
Put global and static objects less than or equal to @var{num} bytes
|
|
into the small data or bss sections instead of the normal data or bss
|
|
sections. The default value of @var{num} is 8.
|
|
The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
|
|
for this option to have any effect.
|
|
|
|
All modules should be compiled with the same @option{-G @var{num}} value.
|
|
Compiling with different values of @var{num} may or may not work; if it
|
|
doesn't the linker will give an error message---incorrect code will not be
|
|
generated.
|
|
|
|
@item -mdebug
|
|
@opindex mdebug
|
|
Makes the M32R specific code in the compiler display some statistics
|
|
that might help in debugging programs.
|
|
|
|
@item -malign-loops
|
|
@opindex malign-loops
|
|
Align all loops to a 32-byte boundary.
|
|
|
|
@item -mno-align-loops
|
|
@opindex mno-align-loops
|
|
Do not enforce a 32-byte alignment for loops. This is the default.
|
|
|
|
@item -missue-rate=@var{number}
|
|
@opindex missue-rate=@var{number}
|
|
Issue @var{number} instructions per cycle. @var{number} can only be 1
|
|
or 2.
|
|
|
|
@item -mbranch-cost=@var{number}
|
|
@opindex mbranch-cost=@var{number}
|
|
@var{number} can only be 1 or 2. If it is 1 then branches will be
|
|
preferred over conditional code, if it is 2, then the opposite will
|
|
apply.
|
|
|
|
@item -mflush-trap=@var{number}
|
|
@opindex mflush-trap=@var{number}
|
|
Specifies the trap number to use to flush the cache. The default is
|
|
12. Valid numbers are between 0 and 15 inclusive.
|
|
|
|
@item -mno-flush-trap
|
|
@opindex mno-flush-trap
|
|
Specifies that the cache cannot be flushed by using a trap.
|
|
|
|
@item -mflush-func=@var{name}
|
|
@opindex mflush-func=@var{name}
|
|
Specifies the name of the operating system function to call to flush
|
|
the cache. The default is @emph{_flush_cache}, but a function call
|
|
will only be used if a trap is not available.
|
|
|
|
@item -mno-flush-func
|
|
@opindex mno-flush-func
|
|
Indicates that there is no OS function for flushing the cache.
|
|
|
|
@end table
|
|
|
|
@node M680x0 Options
|
|
@subsection M680x0 Options
|
|
@cindex M680x0 options
|
|
|
|
These are the @samp{-m} options defined for the 68000 series. The default
|
|
values for these options depends on which style of 68000 was selected when
|
|
the compiler was configured; the defaults for the most common choices are
|
|
given below.
|
|
|
|
@table @gcctabopt
|
|
@item -m68000
|
|
@itemx -mc68000
|
|
@opindex m68000
|
|
@opindex mc68000
|
|
Generate output for a 68000. This is the default
|
|
when the compiler is configured for 68000-based systems.
|
|
|
|
Use this option for microcontrollers with a 68000 or EC000 core,
|
|
including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
|
|
|
|
@item -m68020
|
|
@itemx -mc68020
|
|
@opindex m68020
|
|
@opindex mc68020
|
|
Generate output for a 68020. This is the default
|
|
when the compiler is configured for 68020-based systems.
|
|
|
|
@item -m68881
|
|
@opindex m68881
|
|
Generate output containing 68881 instructions for floating point.
|
|
This is the default for most 68020 systems unless @option{--nfp} was
|
|
specified when the compiler was configured.
|
|
|
|
@item -m68030
|
|
@opindex m68030
|
|
Generate output for a 68030. This is the default when the compiler is
|
|
configured for 68030-based systems.
|
|
|
|
@item -m68040
|
|
@opindex m68040
|
|
Generate output for a 68040. This is the default when the compiler is
|
|
configured for 68040-based systems.
|
|
|
|
This option inhibits the use of 68881/68882 instructions that have to be
|
|
emulated by software on the 68040. Use this option if your 68040 does not
|
|
have code to emulate those instructions.
|
|
|
|
@item -m68060
|
|
@opindex m68060
|
|
Generate output for a 68060. This is the default when the compiler is
|
|
configured for 68060-based systems.
|
|
|
|
This option inhibits the use of 68020 and 68881/68882 instructions that
|
|
have to be emulated by software on the 68060. Use this option if your 68060
|
|
does not have code to emulate those instructions.
|
|
|
|
@item -mcpu32
|
|
@opindex mcpu32
|
|
Generate output for a CPU32. This is the default
|
|
when the compiler is configured for CPU32-based systems.
|
|
|
|
Use this option for microcontrollers with a
|
|
CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
|
|
68336, 68340, 68341, 68349 and 68360.
|
|
|
|
@item -m5200
|
|
@opindex m5200
|
|
Generate output for a 520X ``coldfire'' family cpu. This is the default
|
|
when the compiler is configured for 520X-based systems.
|
|
|
|
Use this option for microcontroller with a 5200 core, including
|
|
the MCF5202, MCF5203, MCF5204 and MCF5202.
|
|
|
|
@item -mcfv4e
|
|
@opindex mcfv4e
|
|
Generate output for a ColdFire V4e family cpu (e.g.@: 547x/548x).
|
|
This includes use of hardware floating point instructions.
|
|
|
|
@item -m68020-40
|
|
@opindex m68020-40
|
|
Generate output for a 68040, without using any of the new instructions.
|
|
This results in code which can run relatively efficiently on either a
|
|
68020/68881 or a 68030 or a 68040. The generated code does use the
|
|
68881 instructions that are emulated on the 68040.
|
|
|
|
@item -m68020-60
|
|
@opindex m68020-60
|
|
Generate output for a 68060, without using any of the new instructions.
|
|
This results in code which can run relatively efficiently on either a
|
|
68020/68881 or a 68030 or a 68040. The generated code does use the
|
|
68881 instructions that are emulated on the 68060.
|
|
|
|
@item -msoft-float
|
|
@opindex msoft-float
|
|
Generate output containing library calls for floating point.
|
|
@strong{Warning:} the requisite libraries are not available for all m68k
|
|
targets. Normally the facilities of the machine's usual C compiler are
|
|
used, but this can't be done directly in cross-compilation. You must
|
|
make your own arrangements to provide suitable library functions for
|
|
cross-compilation. The embedded targets @samp{m68k-*-aout} and
|
|
@samp{m68k-*-coff} do provide software floating point support.
|
|
|
|
@item -mshort
|
|
@opindex mshort
|
|
Consider type @code{int} to be 16 bits wide, like @code{short int}.
|
|
Additionally, parameters passed on the stack are also aligned to a
|
|
16-bit boundary even on targets whose API mandates promotion to 32-bit.
|
|
|
|
@item -mnobitfield
|
|
@opindex mnobitfield
|
|
Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
|
|
and @option{-m5200} options imply @w{@option{-mnobitfield}}.
|
|
|
|
@item -mbitfield
|
|
@opindex mbitfield
|
|
Do use the bit-field instructions. The @option{-m68020} option implies
|
|
@option{-mbitfield}. This is the default if you use a configuration
|
|
designed for a 68020.
|
|
|
|
@item -mrtd
|
|
@opindex mrtd
|
|
Use a different function-calling convention, in which functions
|
|
that take a fixed number of arguments return with the @code{rtd}
|
|
instruction, which pops their arguments while returning. This
|
|
saves one instruction in the caller since there is no need to pop
|
|
the arguments there.
|
|
|
|
This calling convention is incompatible with the one normally
|
|
used on Unix, so you cannot use it if you need to call libraries
|
|
compiled with the Unix compiler.
|
|
|
|
Also, you must provide function prototypes for all functions that
|
|
take variable numbers of arguments (including @code{printf});
|
|
otherwise incorrect code will be generated for calls to those
|
|
functions.
|
|
|
|
In addition, seriously incorrect code will result if you call a
|
|
function with too many arguments. (Normally, extra arguments are
|
|
harmlessly ignored.)
|
|
|
|
The @code{rtd} instruction is supported by the 68010, 68020, 68030,
|
|
68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
|
|
|
|
@item -malign-int
|
|
@itemx -mno-align-int
|
|
@opindex malign-int
|
|
@opindex mno-align-int
|
|
Control whether GCC aligns @code{int}, @code{long}, @code{long long},
|
|
@code{float}, @code{double}, and @code{long double} variables on a 32-bit
|
|
boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
|
|
Aligning variables on 32-bit boundaries produces code that runs somewhat
|
|
faster on processors with 32-bit busses at the expense of more memory.
|
|
|
|
@strong{Warning:} if you use the @option{-malign-int} switch, GCC will
|
|
align structures containing the above types differently than
|
|
most published application binary interface specifications for the m68k.
|
|
|
|
@item -mpcrel
|
|
@opindex mpcrel
|
|
Use the pc-relative addressing mode of the 68000 directly, instead of
|
|
using a global offset table. At present, this option implies @option{-fpic},
|
|
allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
|
|
not presently supported with @option{-mpcrel}, though this could be supported for
|
|
68020 and higher processors.
|
|
|
|
@item -mno-strict-align
|
|
@itemx -mstrict-align
|
|
@opindex mno-strict-align
|
|
@opindex mstrict-align
|
|
Do not (do) assume that unaligned memory references will be handled by
|
|
the system.
|
|
|
|
@item -msep-data
|
|
Generate code that allows the data segment to be located in a different
|
|
area of memory from the text segment. This allows for execute in place in
|
|
an environment without virtual memory management. This option implies
|
|
@option{-fPIC}.
|
|
|
|
@item -mno-sep-data
|
|
Generate code that assumes that the data segment follows the text segment.
|
|
This is the default.
|
|
|
|
@item -mid-shared-library
|
|
Generate code that supports shared libraries via the library ID method.
|
|
This allows for execute in place and shared libraries in an environment
|
|
without virtual memory management. This option implies @option{-fPIC}.
|
|
|
|
@item -mno-id-shared-library
|
|
Generate code that doesn't assume ID based shared libraries are being used.
|
|
This is the default.
|
|
|
|
@item -mshared-library-id=n
|
|
Specified the identification number of the ID based shared library being
|
|
compiled. Specifying a value of 0 will generate more compact code, specifying
|
|
other values will force the allocation of that number to the current
|
|
library but is no more space or time efficient than omitting this option.
|
|
|
|
@end table
|
|
|
|
@node M68hc1x Options
|
|
@subsection M68hc1x Options
|
|
@cindex M68hc1x options
|
|
|
|
These are the @samp{-m} options defined for the 68hc11 and 68hc12
|
|
microcontrollers. The default values for these options depends on
|
|
which style of microcontroller was selected when the compiler was configured;
|
|
the defaults for the most common choices are given below.
|
|
|
|
@table @gcctabopt
|
|
@item -m6811
|
|
@itemx -m68hc11
|
|
@opindex m6811
|
|
@opindex m68hc11
|
|
Generate output for a 68HC11. This is the default
|
|
when the compiler is configured for 68HC11-based systems.
|
|
|
|
@item -m6812
|
|
@itemx -m68hc12
|
|
@opindex m6812
|
|
@opindex m68hc12
|
|
Generate output for a 68HC12. This is the default
|
|
when the compiler is configured for 68HC12-based systems.
|
|
|
|
@item -m68S12
|
|
@itemx -m68hcs12
|
|
@opindex m68S12
|
|
@opindex m68hcs12
|
|
Generate output for a 68HCS12.
|
|
|
|
@item -mauto-incdec
|
|
@opindex mauto-incdec
|
|
Enable the use of 68HC12 pre and post auto-increment and auto-decrement
|
|
addressing modes.
|
|
|
|
@item -minmax
|
|
@itemx -nominmax
|
|
@opindex minmax
|
|
@opindex mnominmax
|
|
Enable the use of 68HC12 min and max instructions.
|
|
|
|
@item -mlong-calls
|
|
@itemx -mno-long-calls
|
|
@opindex mlong-calls
|
|
@opindex mno-long-calls
|
|
Treat all calls as being far away (near). If calls are assumed to be
|
|
far away, the compiler will use the @code{call} instruction to
|
|
call a function and the @code{rtc} instruction for returning.
|
|
|
|
@item -mshort
|
|
@opindex mshort
|
|
Consider type @code{int} to be 16 bits wide, like @code{short int}.
|
|
|
|
@item -msoft-reg-count=@var{count}
|
|
@opindex msoft-reg-count
|
|
Specify the number of pseudo-soft registers which are used for the
|
|
code generation. The maximum number is 32. Using more pseudo-soft
|
|
register may or may not result in better code depending on the program.
|
|
The default is 4 for 68HC11 and 2 for 68HC12.
|
|
|
|
@end table
|
|
|
|
@node MCore Options
|
|
@subsection MCore Options
|
|
@cindex MCore options
|
|
|
|
These are the @samp{-m} options defined for the Motorola M*Core
|
|
processors.
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -mhardlit
|
|
@itemx -mno-hardlit
|
|
@opindex mhardlit
|
|
@opindex mno-hardlit
|
|
Inline constants into the code stream if it can be done in two
|
|
instructions or less.
|
|
|
|
@item -mdiv
|
|
@itemx -mno-div
|
|
@opindex mdiv
|
|
@opindex mno-div
|
|
Use the divide instruction. (Enabled by default).
|
|
|
|
@item -mrelax-immediate
|
|
@itemx -mno-relax-immediate
|
|
@opindex mrelax-immediate
|
|
@opindex mno-relax-immediate
|
|
Allow arbitrary sized immediates in bit operations.
|
|
|
|
@item -mwide-bitfields
|
|
@itemx -mno-wide-bitfields
|
|
@opindex mwide-bitfields
|
|
@opindex mno-wide-bitfields
|
|
Always treat bit-fields as int-sized.
|
|
|
|
@item -m4byte-functions
|
|
@itemx -mno-4byte-functions
|
|
@opindex m4byte-functions
|
|
@opindex mno-4byte-functions
|
|
Force all functions to be aligned to a four byte boundary.
|
|
|
|
@item -mcallgraph-data
|
|
@itemx -mno-callgraph-data
|
|
@opindex mcallgraph-data
|
|
@opindex mno-callgraph-data
|
|
Emit callgraph information.
|
|
|
|
@item -mslow-bytes
|
|
@itemx -mno-slow-bytes
|
|
@opindex mslow-bytes
|
|
@opindex mno-slow-bytes
|
|
Prefer word access when reading byte quantities.
|
|
|
|
@item -mlittle-endian
|
|
@itemx -mbig-endian
|
|
@opindex mlittle-endian
|
|
@opindex mbig-endian
|
|
Generate code for a little endian target.
|
|
|
|
@item -m210
|
|
@itemx -m340
|
|
@opindex m210
|
|
@opindex m340
|
|
Generate code for the 210 processor.
|
|
@end table
|
|
|
|
@node MIPS Options
|
|
@subsection MIPS Options
|
|
@cindex MIPS options
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -EB
|
|
@opindex EB
|
|
Generate big-endian code.
|
|
|
|
@item -EL
|
|
@opindex EL
|
|
Generate little-endian code. This is the default for @samp{mips*el-*-*}
|
|
configurations.
|
|
|
|
@item -march=@var{arch}
|
|
@opindex march
|
|
Generate code that will run on @var{arch}, which can be the name of a
|
|
generic MIPS ISA, or the name of a particular processor.
|
|
The ISA names are:
|
|
@samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
|
|
@samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
|
|
The processor names are:
|
|
@samp{4kc}, @samp{4km}, @samp{4kp},
|
|
@samp{5kc}, @samp{5kf},
|
|
@samp{20kc},
|
|
@samp{24k}, @samp{24kc}, @samp{24kf}, @samp{24kx},
|
|
@samp{m4k},
|
|
@samp{orion},
|
|
@samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
|
|
@samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
|
|
@samp{rm7000}, @samp{rm9000},
|
|
@samp{sb1},
|
|
@samp{sr71000},
|
|
@samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
|
|
@samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
|
|
The special value @samp{from-abi} selects the
|
|
most compatible architecture for the selected ABI (that is,
|
|
@samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
|
|
|
|
In processor names, a final @samp{000} can be abbreviated as @samp{k}
|
|
(for example, @samp{-march=r2k}). Prefixes are optional, and
|
|
@samp{vr} may be written @samp{r}.
|
|
|
|
GCC defines two macros based on the value of this option. The first
|
|
is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
|
|
a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
|
|
where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
|
|
For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
|
|
to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
|
|
|
|
Note that the @samp{_MIPS_ARCH} macro uses the processor names given
|
|
above. In other words, it will have the full prefix and will not
|
|
abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
|
|
the macro names the resolved architecture (either @samp{"mips1"} or
|
|
@samp{"mips3"}). It names the default architecture when no
|
|
@option{-march} option is given.
|
|
|
|
@item -mtune=@var{arch}
|
|
@opindex mtune
|
|
Optimize for @var{arch}. Among other things, this option controls
|
|
the way instructions are scheduled, and the perceived cost of arithmetic
|
|
operations. The list of @var{arch} values is the same as for
|
|
@option{-march}.
|
|
|
|
When this option is not used, GCC will optimize for the processor
|
|
specified by @option{-march}. By using @option{-march} and
|
|
@option{-mtune} together, it is possible to generate code that will
|
|
run on a family of processors, but optimize the code for one
|
|
particular member of that family.
|
|
|
|
@samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
|
|
@samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
|
|
@samp{-march} ones described above.
|
|
|
|
@item -mips1
|
|
@opindex mips1
|
|
Equivalent to @samp{-march=mips1}.
|
|
|
|
@item -mips2
|
|
@opindex mips2
|
|
Equivalent to @samp{-march=mips2}.
|
|
|
|
@item -mips3
|
|
@opindex mips3
|
|
Equivalent to @samp{-march=mips3}.
|
|
|
|
@item -mips4
|
|
@opindex mips4
|
|
Equivalent to @samp{-march=mips4}.
|
|
|
|
@item -mips32
|
|
@opindex mips32
|
|
Equivalent to @samp{-march=mips32}.
|
|
|
|
@item -mips32r2
|
|
@opindex mips32r2
|
|
Equivalent to @samp{-march=mips32r2}.
|
|
|
|
@item -mips64
|
|
@opindex mips64
|
|
Equivalent to @samp{-march=mips64}.
|
|
|
|
@item -mips16
|
|
@itemx -mno-mips16
|
|
@opindex mips16
|
|
@opindex mno-mips16
|
|
Generate (do not generate) MIPS16 code. If GCC is targetting a
|
|
MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
|
|
|
|
@item -mabi=32
|
|
@itemx -mabi=o64
|
|
@itemx -mabi=n32
|
|
@itemx -mabi=64
|
|
@itemx -mabi=eabi
|
|
@opindex mabi=32
|
|
@opindex mabi=o64
|
|
@opindex mabi=n32
|
|
@opindex mabi=64
|
|
@opindex mabi=eabi
|
|
Generate code for the given ABI@.
|
|
|
|
Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
|
|
generates 64-bit code when you select a 64-bit architecture, but you
|
|
can use @option{-mgp32} to get 32-bit code instead.
|
|
|
|
For information about the O64 ABI, see
|
|
@w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
|
|
|
|
@item -mabicalls
|
|
@itemx -mno-abicalls
|
|
@opindex mabicalls
|
|
@opindex mno-abicalls
|
|
Generate (do not generate) code that is suitable for SVR4-style
|
|
dynamic objects. @option{-mabicalls} is the default for SVR4-based
|
|
systems.
|
|
|
|
@item -mshared
|
|
@itemx -mno-shared
|
|
Generate (do not generate) code that is fully position-independent,
|
|
and that can therefore be linked into shared libraries. This option
|
|
only affects @option{-mabicalls}.
|
|
|
|
All @option{-mabicalls} code has traditionally been position-independent,
|
|
regardless of options like @option{-fPIC} and @option{-fpic}. However,
|
|
as an extension, the GNU toolchain allows executables to use absolute
|
|
accesses for locally-binding symbols. It can also use shorter GP
|
|
initialization sequences and generate direct calls to locally-defined
|
|
functions. This mode is selected by @option{-mno-shared}.
|
|
|
|
@option{-mno-shared} depends on binutils 2.16 or higher and generates
|
|
objects that can only be linked by the GNU linker. However, the option
|
|
does not affect the ABI of the final executable; it only affects the ABI
|
|
of relocatable objects. Using @option{-mno-shared} will generally make
|
|
executables both smaller and quicker.
|
|
|
|
@option{-mshared} is the default.
|
|
|
|
@item -mxgot
|
|
@itemx -mno-xgot
|
|
@opindex mxgot
|
|
@opindex mno-xgot
|
|
Lift (do not lift) the usual restrictions on the size of the global
|
|
offset table.
|
|
|
|
GCC normally uses a single instruction to load values from the GOT@.
|
|
While this is relatively efficient, it will only work if the GOT
|
|
is smaller than about 64k. Anything larger will cause the linker
|
|
to report an error such as:
|
|
|
|
@cindex relocation truncated to fit (MIPS)
|
|
@smallexample
|
|
relocation truncated to fit: R_MIPS_GOT16 foobar
|
|
@end smallexample
|
|
|
|
If this happens, you should recompile your code with @option{-mxgot}.
|
|
It should then work with very large GOTs, although it will also be
|
|
less efficient, since it will take three instructions to fetch the
|
|
value of a global symbol.
|
|
|
|
Note that some linkers can create multiple GOTs. If you have such a
|
|
linker, you should only need to use @option{-mxgot} when a single object
|
|
file accesses more than 64k's worth of GOT entries. Very few do.
|
|
|
|
These options have no effect unless GCC is generating position
|
|
independent code.
|
|
|
|
@item -mgp32
|
|
@opindex mgp32
|
|
Assume that general-purpose registers are 32 bits wide.
|
|
|
|
@item -mgp64
|
|
@opindex mgp64
|
|
Assume that general-purpose registers are 64 bits wide.
|
|
|
|
@item -mfp32
|
|
@opindex mfp32
|
|
Assume that floating-point registers are 32 bits wide.
|
|
|
|
@item -mfp64
|
|
@opindex mfp64
|
|
Assume that floating-point registers are 64 bits wide.
|
|
|
|
@item -mhard-float
|
|
@opindex mhard-float
|
|
Use floating-point coprocessor instructions.
|
|
|
|
@item -msoft-float
|
|
@opindex msoft-float
|
|
Do not use floating-point coprocessor instructions. Implement
|
|
floating-point calculations using library calls instead.
|
|
|
|
@item -msingle-float
|
|
@opindex msingle-float
|
|
Assume that the floating-point coprocessor only supports single-precision
|
|
operations.
|
|
|
|
@itemx -mdouble-float
|
|
@opindex mdouble-float
|
|
Assume that the floating-point coprocessor supports double-precision
|
|
operations. This is the default.
|
|
|
|
@itemx -mdsp
|
|
@itemx -mno-dsp
|
|
@opindex mdsp
|
|
@opindex mno-dsp
|
|
Use (do not use) the MIPS DSP ASE. @xref{MIPS DSP Built-in Functions}.
|
|
|
|
@itemx -mpaired-single
|
|
@itemx -mno-paired-single
|
|
@opindex mpaired-single
|
|
@opindex mno-paired-single
|
|
Use (do not use) paired-single floating-point instructions.
|
|
@xref{MIPS Paired-Single Support}. This option can only be used
|
|
when generating 64-bit code and requires hardware floating-point
|
|
support to be enabled.
|
|
|
|
@itemx -mips3d
|
|
@itemx -mno-mips3d
|
|
@opindex mips3d
|
|
@opindex mno-mips3d
|
|
Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
|
|
The option @option{-mips3d} implies @option{-mpaired-single}.
|
|
|
|
@item -mlong64
|
|
@opindex mlong64
|
|
Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
|
|
an explanation of the default and the way that the pointer size is
|
|
determined.
|
|
|
|
@item -mlong32
|
|
@opindex mlong32
|
|
Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
|
|
|
|
The default size of @code{int}s, @code{long}s and pointers depends on
|
|
the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
|
|
uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
|
|
32-bit @code{long}s. Pointers are the same size as @code{long}s,
|
|
or the same size as integer registers, whichever is smaller.
|
|
|
|
@item -msym32
|
|
@itemx -mno-sym32
|
|
@opindex msym32
|
|
@opindex mno-sym32
|
|
Assume (do not assume) that all symbols have 32-bit values, regardless
|
|
of the selected ABI@. This option is useful in combination with
|
|
@option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
|
|
to generate shorter and faster references to symbolic addresses.
|
|
|
|
@item -G @var{num}
|
|
@opindex G
|
|
@cindex smaller data references (MIPS)
|
|
@cindex gp-relative references (MIPS)
|
|
Put global and static items less than or equal to @var{num} bytes into
|
|
the small data or bss section instead of the normal data or bss section.
|
|
This allows the data to be accessed using a single instruction.
|
|
|
|
All modules should be compiled with the same @option{-G @var{num}}
|
|
value.
|
|
|
|
@item -membedded-data
|
|
@itemx -mno-embedded-data
|
|
@opindex membedded-data
|
|
@opindex mno-embedded-data
|
|
Allocate variables to the read-only data section first if possible, then
|
|
next in the small data section if possible, otherwise in data. This gives
|
|
slightly slower code than the default, but reduces the amount of RAM required
|
|
when executing, and thus may be preferred for some embedded systems.
|
|
|
|
@item -muninit-const-in-rodata
|
|
@itemx -mno-uninit-const-in-rodata
|
|
@opindex muninit-const-in-rodata
|
|
@opindex mno-uninit-const-in-rodata
|
|
Put uninitialized @code{const} variables in the read-only data section.
|
|
This option is only meaningful in conjunction with @option{-membedded-data}.
|
|
|
|
@item -msplit-addresses
|
|
@itemx -mno-split-addresses
|
|
@opindex msplit-addresses
|
|
@opindex mno-split-addresses
|
|
Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
|
|
relocation operators. This option has been superseded by
|
|
@option{-mexplicit-relocs} but is retained for backwards compatibility.
|
|
|
|
@item -mexplicit-relocs
|
|
@itemx -mno-explicit-relocs
|
|
@opindex mexplicit-relocs
|
|
@opindex mno-explicit-relocs
|
|
Use (do not use) assembler relocation operators when dealing with symbolic
|
|
addresses. The alternative, selected by @option{-mno-explicit-relocs},
|
|
is to use assembler macros instead.
|
|
|
|
@option{-mexplicit-relocs} is the default if GCC was configured
|
|
to use an assembler that supports relocation operators.
|
|
|
|
@item -mcheck-zero-division
|
|
@itemx -mno-check-zero-division
|
|
@opindex mcheck-zero-division
|
|
@opindex mno-check-zero-division
|
|
Trap (do not trap) on integer division by zero. The default is
|
|
@option{-mcheck-zero-division}.
|
|
|
|
@item -mdivide-traps
|
|
@itemx -mdivide-breaks
|
|
@opindex mdivide-traps
|
|
@opindex mdivide-breaks
|
|
MIPS systems check for division by zero by generating either a
|
|
conditional trap or a break instruction. Using traps results in
|
|
smaller code, but is only supported on MIPS II and later. Also, some
|
|
versions of the Linux kernel have a bug that prevents trap from
|
|
generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
|
|
allow conditional traps on architectures that support them and
|
|
@option{-mdivide-breaks} to force the use of breaks.
|
|
|
|
The default is usually @option{-mdivide-traps}, but this can be
|
|
overridden at configure time using @option{--with-divide=breaks}.
|
|
Divide-by-zero checks can be completely disabled using
|
|
@option{-mno-check-zero-division}.
|
|
|
|
@item -mmemcpy
|
|
@itemx -mno-memcpy
|
|
@opindex mmemcpy
|
|
@opindex mno-memcpy
|
|
Force (do not force) the use of @code{memcpy()} for non-trivial block
|
|
moves. The default is @option{-mno-memcpy}, which allows GCC to inline
|
|
most constant-sized copies.
|
|
|
|
@item -mlong-calls
|
|
@itemx -mno-long-calls
|
|
@opindex mlong-calls
|
|
@opindex mno-long-calls
|
|
Disable (do not disable) use of the @code{jal} instruction. Calling
|
|
functions using @code{jal} is more efficient but requires the caller
|
|
and callee to be in the same 256 megabyte segment.
|
|
|
|
This option has no effect on abicalls code. The default is
|
|
@option{-mno-long-calls}.
|
|
|
|
@item -mmad
|
|
@itemx -mno-mad
|
|
@opindex mmad
|
|
@opindex mno-mad
|
|
Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
|
|
instructions, as provided by the R4650 ISA@.
|
|
|
|
@item -mfused-madd
|
|
@itemx -mno-fused-madd
|
|
@opindex mfused-madd
|
|
@opindex mno-fused-madd
|
|
Enable (disable) use of the floating point multiply-accumulate
|
|
instructions, when they are available. The default is
|
|
@option{-mfused-madd}.
|
|
|
|
When multiply-accumulate instructions are used, the intermediate
|
|
product is calculated to infinite precision and is not subject to
|
|
the FCSR Flush to Zero bit. This may be undesirable in some
|
|
circumstances.
|
|
|
|
@item -nocpp
|
|
@opindex nocpp
|
|
Tell the MIPS assembler to not run its preprocessor over user
|
|
assembler files (with a @samp{.s} suffix) when assembling them.
|
|
|
|
@item -mfix-r4000
|
|
@itemx -mno-fix-r4000
|
|
@opindex mfix-r4000
|
|
@opindex mno-fix-r4000
|
|
Work around certain R4000 CPU errata:
|
|
@itemize @minus
|
|
@item
|
|
A double-word or a variable shift may give an incorrect result if executed
|
|
immediately after starting an integer division.
|
|
@item
|
|
A double-word or a variable shift may give an incorrect result if executed
|
|
while an integer multiplication is in progress.
|
|
@item
|
|
An integer division may give an incorrect result if started in a delay slot
|
|
of a taken branch or a jump.
|
|
@end itemize
|
|
|
|
@item -mfix-r4400
|
|
@itemx -mno-fix-r4400
|
|
@opindex mfix-r4400
|
|
@opindex mno-fix-r4400
|
|
Work around certain R4400 CPU errata:
|
|
@itemize @minus
|
|
@item
|
|
A double-word or a variable shift may give an incorrect result if executed
|
|
immediately after starting an integer division.
|
|
@end itemize
|
|
|
|
@item -mfix-vr4120
|
|
@itemx -mno-fix-vr4120
|
|
@opindex mfix-vr4120
|
|
Work around certain VR4120 errata:
|
|
@itemize @minus
|
|
@item
|
|
@code{dmultu} does not always produce the correct result.
|
|
@item
|
|
@code{div} and @code{ddiv} do not always produce the correct result if one
|
|
of the operands is negative.
|
|
@end itemize
|
|
The workarounds for the division errata rely on special functions in
|
|
@file{libgcc.a}. At present, these functions are only provided by
|
|
the @code{mips64vr*-elf} configurations.
|
|
|
|
Other VR4120 errata require a nop to be inserted between certain pairs of
|
|
instructions. These errata are handled by the assembler, not by GCC itself.
|
|
|
|
@item -mfix-vr4130
|
|
@opindex mfix-vr4130
|
|
Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
|
|
workarounds are implemented by the assembler rather than by GCC,
|
|
although GCC will avoid using @code{mflo} and @code{mfhi} if the
|
|
VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
|
|
instructions are available instead.
|
|
|
|
@item -mfix-sb1
|
|
@itemx -mno-fix-sb1
|
|
@opindex mfix-sb1
|
|
Work around certain SB-1 CPU core errata.
|
|
(This flag currently works around the SB-1 revision 2
|
|
``F1'' and ``F2'' floating point errata.)
|
|
|
|
@item -mflush-func=@var{func}
|
|
@itemx -mno-flush-func
|
|
@opindex mflush-func
|
|
Specifies the function to call to flush the I and D caches, or to not
|
|
call any such function. If called, the function must take the same
|
|
arguments as the common @code{_flush_func()}, that is, the address of the
|
|
memory range for which the cache is being flushed, the size of the
|
|
memory range, and the number 3 (to flush both caches). The default
|
|
depends on the target GCC was configured for, but commonly is either
|
|
@samp{_flush_func} or @samp{__cpu_flush}.
|
|
|
|
@item -mbranch-likely
|
|
@itemx -mno-branch-likely
|
|
@opindex mbranch-likely
|
|
@opindex mno-branch-likely
|
|
Enable or disable use of Branch Likely instructions, regardless of the
|
|
default for the selected architecture. By default, Branch Likely
|
|
instructions may be generated if they are supported by the selected
|
|
architecture. An exception is for the MIPS32 and MIPS64 architectures
|
|
and processors which implement those architectures; for those, Branch
|
|
Likely instructions will not be generated by default because the MIPS32
|
|
and MIPS64 architectures specifically deprecate their use.
|
|
|
|
@item -mfp-exceptions
|
|
@itemx -mno-fp-exceptions
|
|
@opindex mfp-exceptions
|
|
Specifies whether FP exceptions are enabled. This affects how we schedule
|
|
FP instructions for some processors. The default is that FP exceptions are
|
|
enabled.
|
|
|
|
For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
|
|
64-bit code, then we can use both FP pipes. Otherwise, we can only use one
|
|
FP pipe.
|
|
|
|
@item -mvr4130-align
|
|
@itemx -mno-vr4130-align
|
|
@opindex mvr4130-align
|
|
The VR4130 pipeline is two-way superscalar, but can only issue two
|
|
instructions together if the first one is 8-byte aligned. When this
|
|
option is enabled, GCC will align pairs of instructions that it
|
|
thinks should execute in parallel.
|
|
|
|
This option only has an effect when optimizing for the VR4130.
|
|
It normally makes code faster, but at the expense of making it bigger.
|
|
It is enabled by default at optimization level @option{-O3}.
|
|
@end table
|
|
|
|
@node MMIX Options
|
|
@subsection MMIX Options
|
|
@cindex MMIX Options
|
|
|
|
These options are defined for the MMIX:
|
|
|
|
@table @gcctabopt
|
|
@item -mlibfuncs
|
|
@itemx -mno-libfuncs
|
|
@opindex mlibfuncs
|
|
@opindex mno-libfuncs
|
|
Specify that intrinsic library functions are being compiled, passing all
|
|
values in registers, no matter the size.
|
|
|
|
@item -mepsilon
|
|
@itemx -mno-epsilon
|
|
@opindex mepsilon
|
|
@opindex mno-epsilon
|
|
Generate floating-point comparison instructions that compare with respect
|
|
to the @code{rE} epsilon register.
|
|
|
|
@item -mabi=mmixware
|
|
@itemx -mabi=gnu
|
|
@opindex mabi-mmixware
|
|
@opindex mabi=gnu
|
|
Generate code that passes function parameters and return values that (in
|
|
the called function) are seen as registers @code{$0} and up, as opposed to
|
|
the GNU ABI which uses global registers @code{$231} and up.
|
|
|
|
@item -mzero-extend
|
|
@itemx -mno-zero-extend
|
|
@opindex mzero-extend
|
|
@opindex mno-zero-extend
|
|
When reading data from memory in sizes shorter than 64 bits, use (do not
|
|
use) zero-extending load instructions by default, rather than
|
|
sign-extending ones.
|
|
|
|
@item -mknuthdiv
|
|
@itemx -mno-knuthdiv
|
|
@opindex mknuthdiv
|
|
@opindex mno-knuthdiv
|
|
Make the result of a division yielding a remainder have the same sign as
|
|
the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
|
|
remainder follows the sign of the dividend. Both methods are
|
|
arithmetically valid, the latter being almost exclusively used.
|
|
|
|
@item -mtoplevel-symbols
|
|
@itemx -mno-toplevel-symbols
|
|
@opindex mtoplevel-symbols
|
|
@opindex mno-toplevel-symbols
|
|
Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
|
|
code can be used with the @code{PREFIX} assembly directive.
|
|
|
|
@item -melf
|
|
@opindex melf
|
|
Generate an executable in the ELF format, rather than the default
|
|
@samp{mmo} format used by the @command{mmix} simulator.
|
|
|
|
@item -mbranch-predict
|
|
@itemx -mno-branch-predict
|
|
@opindex mbranch-predict
|
|
@opindex mno-branch-predict
|
|
Use (do not use) the probable-branch instructions, when static branch
|
|
prediction indicates a probable branch.
|
|
|
|
@item -mbase-addresses
|
|
@itemx -mno-base-addresses
|
|
@opindex mbase-addresses
|
|
@opindex mno-base-addresses
|
|
Generate (do not generate) code that uses @emph{base addresses}. Using a
|
|
base address automatically generates a request (handled by the assembler
|
|
and the linker) for a constant to be set up in a global register. The
|
|
register is used for one or more base address requests within the range 0
|
|
to 255 from the value held in the register. The generally leads to short
|
|
and fast code, but the number of different data items that can be
|
|
addressed is limited. This means that a program that uses lots of static
|
|
data may require @option{-mno-base-addresses}.
|
|
|
|
@item -msingle-exit
|
|
@itemx -mno-single-exit
|
|
@opindex msingle-exit
|
|
@opindex mno-single-exit
|
|
Force (do not force) generated code to have a single exit point in each
|
|
function.
|
|
@end table
|
|
|
|
@node MN10300 Options
|
|
@subsection MN10300 Options
|
|
@cindex MN10300 options
|
|
|
|
These @option{-m} options are defined for Matsushita MN10300 architectures:
|
|
|
|
@table @gcctabopt
|
|
@item -mmult-bug
|
|
@opindex mmult-bug
|
|
Generate code to avoid bugs in the multiply instructions for the MN10300
|
|
processors. This is the default.
|
|
|
|
@item -mno-mult-bug
|
|
@opindex mno-mult-bug
|
|
Do not generate code to avoid bugs in the multiply instructions for the
|
|
MN10300 processors.
|
|
|
|
@item -mam33
|
|
@opindex mam33
|
|
Generate code which uses features specific to the AM33 processor.
|
|
|
|
@item -mno-am33
|
|
@opindex mno-am33
|
|
Do not generate code which uses features specific to the AM33 processor. This
|
|
is the default.
|
|
|
|
@item -mreturn-pointer-on-d0
|
|
@opindex mreturn-pointer-on-d0
|
|
When generating a function which returns a pointer, return the pointer
|
|
in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
|
|
only in a0, and attempts to call such functions without a prototype
|
|
would result in errors. Note that this option is on by default; use
|
|
@option{-mno-return-pointer-on-d0} to disable it.
|
|
|
|
@item -mno-crt0
|
|
@opindex mno-crt0
|
|
Do not link in the C run-time initialization object file.
|
|
|
|
@item -mrelax
|
|
@opindex mrelax
|
|
Indicate to the linker that it should perform a relaxation optimization pass
|
|
to shorten branches, calls and absolute memory addresses. This option only
|
|
has an effect when used on the command line for the final link step.
|
|
|
|
This option makes symbolic debugging impossible.
|
|
@end table
|
|
|
|
@node MT Options
|
|
@subsection MT Options
|
|
@cindex MT options
|
|
|
|
These @option{-m} options are defined for Morpho MT architectures:
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -march=@var{cpu-type}
|
|
@opindex march
|
|
Generate code that will run on @var{cpu-type}, which is the name of a system
|
|
representing a certain processor type. Possible values for
|
|
@var{cpu-type} are @samp{ms1-64-001}, @samp{ms1-16-002},
|
|
@samp{ms1-16-003} and @samp{ms2}.
|
|
|
|
When this option is not used, the default is @option{-march=ms1-16-002}.
|
|
|
|
@item -mbacc
|
|
@opindex mbacc
|
|
Use byte loads and stores when generating code.
|
|
|
|
@item -mno-bacc
|
|
@opindex mno-bacc
|
|
Do not use byte loads and stores when generating code.
|
|
|
|
@item -msim
|
|
@opindex msim
|
|
Use simulator runtime
|
|
|
|
@item -mno-crt0
|
|
@opindex mno-crt0
|
|
Do not link in the C run-time initialization object file
|
|
@file{crti.o}. Other run-time initialization and termination files
|
|
such as @file{startup.o} and @file{exit.o} are still included on the
|
|
linker command line.
|
|
|
|
@end table
|
|
|
|
@node PDP-11 Options
|
|
@subsection PDP-11 Options
|
|
@cindex PDP-11 Options
|
|
|
|
These options are defined for the PDP-11:
|
|
|
|
@table @gcctabopt
|
|
@item -mfpu
|
|
@opindex mfpu
|
|
Use hardware FPP floating point. This is the default. (FIS floating
|
|
point on the PDP-11/40 is not supported.)
|
|
|
|
@item -msoft-float
|
|
@opindex msoft-float
|
|
Do not use hardware floating point.
|
|
|
|
@item -mac0
|
|
@opindex mac0
|
|
Return floating-point results in ac0 (fr0 in Unix assembler syntax).
|
|
|
|
@item -mno-ac0
|
|
@opindex mno-ac0
|
|
Return floating-point results in memory. This is the default.
|
|
|
|
@item -m40
|
|
@opindex m40
|
|
Generate code for a PDP-11/40.
|
|
|
|
@item -m45
|
|
@opindex m45
|
|
Generate code for a PDP-11/45. This is the default.
|
|
|
|
@item -m10
|
|
@opindex m10
|
|
Generate code for a PDP-11/10.
|
|
|
|
@item -mbcopy-builtin
|
|
@opindex bcopy-builtin
|
|
Use inline @code{movmemhi} patterns for copying memory. This is the
|
|
default.
|
|
|
|
@item -mbcopy
|
|
@opindex mbcopy
|
|
Do not use inline @code{movmemhi} patterns for copying memory.
|
|
|
|
@item -mint16
|
|
@itemx -mno-int32
|
|
@opindex mint16
|
|
@opindex mno-int32
|
|
Use 16-bit @code{int}. This is the default.
|
|
|
|
@item -mint32
|
|
@itemx -mno-int16
|
|
@opindex mint32
|
|
@opindex mno-int16
|
|
Use 32-bit @code{int}.
|
|
|
|
@item -mfloat64
|
|
@itemx -mno-float32
|
|
@opindex mfloat64
|
|
@opindex mno-float32
|
|
Use 64-bit @code{float}. This is the default.
|
|
|
|
@item -mfloat32
|
|
@itemx -mno-float64
|
|
@opindex mfloat32
|
|
@opindex mno-float64
|
|
Use 32-bit @code{float}.
|
|
|
|
@item -mabshi
|
|
@opindex mabshi
|
|
Use @code{abshi2} pattern. This is the default.
|
|
|
|
@item -mno-abshi
|
|
@opindex mno-abshi
|
|
Do not use @code{abshi2} pattern.
|
|
|
|
@item -mbranch-expensive
|
|
@opindex mbranch-expensive
|
|
Pretend that branches are expensive. This is for experimenting with
|
|
code generation only.
|
|
|
|
@item -mbranch-cheap
|
|
@opindex mbranch-cheap
|
|
Do not pretend that branches are expensive. This is the default.
|
|
|
|
@item -msplit
|
|
@opindex msplit
|
|
Generate code for a system with split I&D@.
|
|
|
|
@item -mno-split
|
|
@opindex mno-split
|
|
Generate code for a system without split I&D@. This is the default.
|
|
|
|
@item -munix-asm
|
|
@opindex munix-asm
|
|
Use Unix assembler syntax. This is the default when configured for
|
|
@samp{pdp11-*-bsd}.
|
|
|
|
@item -mdec-asm
|
|
@opindex mdec-asm
|
|
Use DEC assembler syntax. This is the default when configured for any
|
|
PDP-11 target other than @samp{pdp11-*-bsd}.
|
|
@end table
|
|
|
|
@node PowerPC Options
|
|
@subsection PowerPC Options
|
|
@cindex PowerPC options
|
|
|
|
These are listed under @xref{RS/6000 and PowerPC Options}.
|
|
|
|
@node RS/6000 and PowerPC Options
|
|
@subsection IBM RS/6000 and PowerPC Options
|
|
@cindex RS/6000 and PowerPC Options
|
|
@cindex IBM RS/6000 and PowerPC Options
|
|
|
|
These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
|
|
@table @gcctabopt
|
|
@item -mpower
|
|
@itemx -mno-power
|
|
@itemx -mpower2
|
|
@itemx -mno-power2
|
|
@itemx -mpowerpc
|
|
@itemx -mno-powerpc
|
|
@itemx -mpowerpc-gpopt
|
|
@itemx -mno-powerpc-gpopt
|
|
@itemx -mpowerpc-gfxopt
|
|
@itemx -mno-powerpc-gfxopt
|
|
@itemx -mpowerpc64
|
|
@itemx -mno-powerpc64
|
|
@itemx -mmfcrf
|
|
@itemx -mno-mfcrf
|
|
@itemx -mpopcntb
|
|
@itemx -mno-popcntb
|
|
@itemx -mfprnd
|
|
@itemx -mno-fprnd
|
|
@opindex mpower
|
|
@opindex mno-power
|
|
@opindex mpower2
|
|
@opindex mno-power2
|
|
@opindex mpowerpc
|
|
@opindex mno-powerpc
|
|
@opindex mpowerpc-gpopt
|
|
@opindex mno-powerpc-gpopt
|
|
@opindex mpowerpc-gfxopt
|
|
@opindex mno-powerpc-gfxopt
|
|
@opindex mpowerpc64
|
|
@opindex mno-powerpc64
|
|
@opindex mmfcrf
|
|
@opindex mno-mfcrf
|
|
@opindex mpopcntb
|
|
@opindex mno-popcntb
|
|
@opindex mfprnd
|
|
@opindex mno-fprnd
|
|
GCC supports two related instruction set architectures for the
|
|
RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
|
|
instructions supported by the @samp{rios} chip set used in the original
|
|
RS/6000 systems and the @dfn{PowerPC} instruction set is the
|
|
architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
|
|
the IBM 4xx, 6xx, and follow-on microprocessors.
|
|
|
|
Neither architecture is a subset of the other. However there is a
|
|
large common subset of instructions supported by both. An MQ
|
|
register is included in processors supporting the POWER architecture.
|
|
|
|
You use these options to specify which instructions are available on the
|
|
processor you are using. The default value of these options is
|
|
determined when configuring GCC@. Specifying the
|
|
@option{-mcpu=@var{cpu_type}} overrides the specification of these
|
|
options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
|
|
rather than the options listed above.
|
|
|
|
The @option{-mpower} option allows GCC to generate instructions that
|
|
are found only in the POWER architecture and to use the MQ register.
|
|
Specifying @option{-mpower2} implies @option{-power} and also allows GCC
|
|
to generate instructions that are present in the POWER2 architecture but
|
|
not the original POWER architecture.
|
|
|
|
The @option{-mpowerpc} option allows GCC to generate instructions that
|
|
are found only in the 32-bit subset of the PowerPC architecture.
|
|
Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
|
|
GCC to use the optional PowerPC architecture instructions in the
|
|
General Purpose group, including floating-point square root. Specifying
|
|
@option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
|
|
use the optional PowerPC architecture instructions in the Graphics
|
|
group, including floating-point select.
|
|
|
|
The @option{-mmfcrf} option allows GCC to generate the move from
|
|
condition register field instruction implemented on the POWER4
|
|
processor and other processors that support the PowerPC V2.01
|
|
architecture.
|
|
The @option{-mpopcntb} option allows GCC to generate the popcount and
|
|
double precision FP reciprocal estimate instruction implemented on the
|
|
POWER5 processor and other processors that support the PowerPC V2.02
|
|
architecture.
|
|
The @option{-mfprnd} option allows GCC to generate the FP round to
|
|
integer instructions implemented on the POWER5+ processor and other
|
|
processors that support the PowerPC V2.03 architecture.
|
|
|
|
The @option{-mpowerpc64} option allows GCC to generate the additional
|
|
64-bit instructions that are found in the full PowerPC64 architecture
|
|
and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
|
|
@option{-mno-powerpc64}.
|
|
|
|
If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
|
|
will use only the instructions in the common subset of both
|
|
architectures plus some special AIX common-mode calls, and will not use
|
|
the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
|
|
permits GCC to use any instruction from either architecture and to
|
|
allow use of the MQ register; specify this for the Motorola MPC601.
|
|
|
|
@item -mnew-mnemonics
|
|
@itemx -mold-mnemonics
|
|
@opindex mnew-mnemonics
|
|
@opindex mold-mnemonics
|
|
Select which mnemonics to use in the generated assembler code. With
|
|
@option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
|
|
the PowerPC architecture. With @option{-mold-mnemonics} it uses the
|
|
assembler mnemonics defined for the POWER architecture. Instructions
|
|
defined in only one architecture have only one mnemonic; GCC uses that
|
|
mnemonic irrespective of which of these options is specified.
|
|
|
|
GCC defaults to the mnemonics appropriate for the architecture in
|
|
use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
|
|
value of these option. Unless you are building a cross-compiler, you
|
|
should normally not specify either @option{-mnew-mnemonics} or
|
|
@option{-mold-mnemonics}, but should instead accept the default.
|
|
|
|
@item -mcpu=@var{cpu_type}
|
|
@opindex mcpu
|
|
Set architecture type, register usage, choice of mnemonics, and
|
|
instruction scheduling parameters for machine type @var{cpu_type}.
|
|
Supported values for @var{cpu_type} are @samp{401}, @samp{403},
|
|
@samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{505},
|
|
@samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
|
|
@samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
|
|
@samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
|
|
@samp{860}, @samp{970}, @samp{8540}, @samp{ec603e}, @samp{G3},
|
|
@samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3},
|
|
@samp{power4}, @samp{power5}, @samp{power5+}, @samp{power6},
|
|
@samp{common}, @samp{powerpc}, @samp{powerpc64},
|
|
@samp{rios}, @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
|
|
|
|
@option{-mcpu=common} selects a completely generic processor. Code
|
|
generated under this option will run on any POWER or PowerPC processor.
|
|
GCC will use only the instructions in the common subset of both
|
|
architectures, and will not use the MQ register. GCC assumes a generic
|
|
processor model for scheduling purposes.
|
|
|
|
@option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
|
|
@option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
|
|
PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
|
|
types, with an appropriate, generic processor model assumed for
|
|
scheduling purposes.
|
|
|
|
The other options specify a specific processor. Code generated under
|
|
those options will run best on that processor, and may not run at all on
|
|
others.
|
|
|
|
The @option{-mcpu} options automatically enable or disable the
|
|
following options: @option{-maltivec}, @option{-mfprnd},
|
|
@option{-mhard-float}, @option{-mmfcrf}, @option{-mmultiple},
|
|
@option{-mnew-mnemonics}, @option{-mpopcntb}, @option{-mpower},
|
|
@option{-mpower2}, @option{-mpowerpc64}, @option{-mpowerpc-gpopt},
|
|
@option{-mpowerpc-gfxopt}, @option{-mstring}, @option{-mmulhw}, @option{-mdlmzb}.
|
|
The particular options
|
|
set for any particular CPU will vary between compiler versions,
|
|
depending on what setting seems to produce optimal code for that CPU;
|
|
it doesn't necessarily reflect the actual hardware's capabilities. If
|
|
you wish to set an individual option to a particular value, you may
|
|
specify it after the @option{-mcpu} option, like @samp{-mcpu=970
|
|
-mno-altivec}.
|
|
|
|
On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
|
|
not enabled or disabled by the @option{-mcpu} option at present because
|
|
AIX does not have full support for these options. You may still
|
|
enable or disable them individually if you're sure it'll work in your
|
|
environment.
|
|
|
|
@item -mtune=@var{cpu_type}
|
|
@opindex mtune
|
|
Set the instruction scheduling parameters for machine type
|
|
@var{cpu_type}, but do not set the architecture type, register usage, or
|
|
choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
|
|
values for @var{cpu_type} are used for @option{-mtune} as for
|
|
@option{-mcpu}. If both are specified, the code generated will use the
|
|
architecture, registers, and mnemonics set by @option{-mcpu}, but the
|
|
scheduling parameters set by @option{-mtune}.
|
|
|
|
@item -mswdiv
|
|
@itemx -mno-swdiv
|
|
@opindex mswdiv
|
|
@opindex mno-swdiv
|
|
Generate code to compute division as reciprocal estimate and iterative
|
|
refinement, creating opportunities for increased throughput. This
|
|
feature requires: optional PowerPC Graphics instruction set for single
|
|
precision and FRE instruction for double precision, assuming divides
|
|
cannot generate user-visible traps, and the domain values not include
|
|
Infinities, denormals or zero denominator.
|
|
|
|
@item -maltivec
|
|
@itemx -mno-altivec
|
|
@opindex maltivec
|
|
@opindex mno-altivec
|
|
Generate code that uses (does not use) AltiVec instructions, and also
|
|
enable the use of built-in functions that allow more direct access to
|
|
the AltiVec instruction set. You may also need to set
|
|
@option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
|
|
enhancements.
|
|
|
|
@item -mvrsave
|
|
@item -mno-vrsave
|
|
@opindex mvrsave
|
|
@opindex mno-vrsave
|
|
Generate VRSAVE instructions when generating AltiVec code.
|
|
|
|
@item -msecure-plt
|
|
@opindex msecure-plt
|
|
Generate code that allows ld and ld.so to build executables and shared
|
|
libraries with non-exec .plt and .got sections. This is a PowerPC
|
|
32-bit SYSV ABI option.
|
|
|
|
@item -mbss-plt
|
|
@opindex mbss-plt
|
|
Generate code that uses a BSS .plt section that ld.so fills in, and
|
|
requires .plt and .got sections that are both writable and executable.
|
|
This is a PowerPC 32-bit SYSV ABI option.
|
|
|
|
@item -misel
|
|
@itemx -mno-isel
|
|
@opindex misel
|
|
@opindex mno-isel
|
|
This switch enables or disables the generation of ISEL instructions.
|
|
|
|
@item -misel=@var{yes/no}
|
|
This switch has been deprecated. Use @option{-misel} and
|
|
@option{-mno-isel} instead.
|
|
|
|
@item -mspe
|
|
@itemx -mno-spe
|
|
@opindex mspe
|
|
@opindex mno-spe
|
|
This switch enables or disables the generation of SPE simd
|
|
instructions.
|
|
|
|
@item -mspe=@var{yes/no}
|
|
This option has been deprecated. Use @option{-mspe} and
|
|
@option{-mno-spe} instead.
|
|
|
|
@item -mfloat-gprs=@var{yes/single/double/no}
|
|
@itemx -mfloat-gprs
|
|
@opindex mfloat-gprs
|
|
This switch enables or disables the generation of floating point
|
|
operations on the general purpose registers for architectures that
|
|
support it.
|
|
|
|
The argument @var{yes} or @var{single} enables the use of
|
|
single-precision floating point operations.
|
|
|
|
The argument @var{double} enables the use of single and
|
|
double-precision floating point operations.
|
|
|
|
The argument @var{no} disables floating point operations on the
|
|
general purpose registers.
|
|
|
|
This option is currently only available on the MPC854x.
|
|
|
|
@item -m32
|
|
@itemx -m64
|
|
@opindex m32
|
|
@opindex m64
|
|
Generate code for 32-bit or 64-bit environments of Darwin and SVR4
|
|
targets (including GNU/Linux). The 32-bit environment sets int, long
|
|
and pointer to 32 bits and generates code that runs on any PowerPC
|
|
variant. The 64-bit environment sets int to 32 bits and long and
|
|
pointer to 64 bits, and generates code for PowerPC64, as for
|
|
@option{-mpowerpc64}.
|
|
|
|
@item -mfull-toc
|
|
@itemx -mno-fp-in-toc
|
|
@itemx -mno-sum-in-toc
|
|
@itemx -mminimal-toc
|
|
@opindex mfull-toc
|
|
@opindex mno-fp-in-toc
|
|
@opindex mno-sum-in-toc
|
|
@opindex mminimal-toc
|
|
Modify generation of the TOC (Table Of Contents), which is created for
|
|
every executable file. The @option{-mfull-toc} option is selected by
|
|
default. In that case, GCC will allocate at least one TOC entry for
|
|
each unique non-automatic variable reference in your program. GCC
|
|
will also place floating-point constants in the TOC@. However, only
|
|
16,384 entries are available in the TOC@.
|
|
|
|
If you receive a linker error message that saying you have overflowed
|
|
the available TOC space, you can reduce the amount of TOC space used
|
|
with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
|
|
@option{-mno-fp-in-toc} prevents GCC from putting floating-point
|
|
constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
|
|
generate code to calculate the sum of an address and a constant at
|
|
run-time instead of putting that sum into the TOC@. You may specify one
|
|
or both of these options. Each causes GCC to produce very slightly
|
|
slower and larger code at the expense of conserving TOC space.
|
|
|
|
If you still run out of space in the TOC even when you specify both of
|
|
these options, specify @option{-mminimal-toc} instead. This option causes
|
|
GCC to make only one TOC entry for every file. When you specify this
|
|
option, GCC will produce code that is slower and larger but which
|
|
uses extremely little TOC space. You may wish to use this option
|
|
only on files that contain less frequently executed code.
|
|
|
|
@item -maix64
|
|
@itemx -maix32
|
|
@opindex maix64
|
|
@opindex maix32
|
|
Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
|
|
@code{long} type, and the infrastructure needed to support them.
|
|
Specifying @option{-maix64} implies @option{-mpowerpc64} and
|
|
@option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
|
|
implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
|
|
|
|
@item -mxl-compat
|
|
@itemx -mno-xl-compat
|
|
@opindex mxl-compat
|
|
@opindex mno-xl-compat
|
|
Produce code that conforms more closely to IBM XL compiler semantics
|
|
when using AIX-compatible ABI. Pass floating-point arguments to
|
|
prototyped functions beyond the register save area (RSA) on the stack
|
|
in addition to argument FPRs. Do not assume that most significant
|
|
double in 128-bit long double value is properly rounded when comparing
|
|
values and converting to double. Use XL symbol names for long double
|
|
support routines.
|
|
|
|
The AIX calling convention was extended but not initially documented to
|
|
handle an obscure K&R C case of calling a function that takes the
|
|
address of its arguments with fewer arguments than declared. IBM XL
|
|
compilers access floating point arguments which do not fit in the
|
|
RSA from the stack when a subroutine is compiled without
|
|
optimization. Because always storing floating-point arguments on the
|
|
stack is inefficient and rarely needed, this option is not enabled by
|
|
default and only is necessary when calling subroutines compiled by IBM
|
|
XL compilers without optimization.
|
|
|
|
@item -mpe
|
|
@opindex mpe
|
|
Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
|
|
application written to use message passing with special startup code to
|
|
enable the application to run. The system must have PE installed in the
|
|
standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
|
|
must be overridden with the @option{-specs=} option to specify the
|
|
appropriate directory location. The Parallel Environment does not
|
|
support threads, so the @option{-mpe} option and the @option{-pthread}
|
|
option are incompatible.
|
|
|
|
@item -malign-natural
|
|
@itemx -malign-power
|
|
@opindex malign-natural
|
|
@opindex malign-power
|
|
On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
|
|
@option{-malign-natural} overrides the ABI-defined alignment of larger
|
|
types, such as floating-point doubles, on their natural size-based boundary.
|
|
The option @option{-malign-power} instructs GCC to follow the ABI-specified
|
|
alignment rules. GCC defaults to the standard alignment defined in the ABI@.
|
|
|
|
On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
|
|
is not supported.
|
|
|
|
@item -msoft-float
|
|
@itemx -mhard-float
|
|
@opindex msoft-float
|
|
@opindex mhard-float
|
|
Generate code that does not use (uses) the floating-point register set.
|
|
Software floating point emulation is provided if you use the
|
|
@option{-msoft-float} option, and pass the option to GCC when linking.
|
|
|
|
@item -mmultiple
|
|
@itemx -mno-multiple
|
|
@opindex mmultiple
|
|
@opindex mno-multiple
|
|
Generate code that uses (does not use) the load multiple word
|
|
instructions and the store multiple word instructions. These
|
|
instructions are generated by default on POWER systems, and not
|
|
generated on PowerPC systems. Do not use @option{-mmultiple} on little
|
|
endian PowerPC systems, since those instructions do not work when the
|
|
processor is in little endian mode. The exceptions are PPC740 and
|
|
PPC750 which permit the instructions usage in little endian mode.
|
|
|
|
@item -mstring
|
|
@itemx -mno-string
|
|
@opindex mstring
|
|
@opindex mno-string
|
|
Generate code that uses (does not use) the load string instructions
|
|
and the store string word instructions to save multiple registers and
|
|
do small block moves. These instructions are generated by default on
|
|
POWER systems, and not generated on PowerPC systems. Do not use
|
|
@option{-mstring} on little endian PowerPC systems, since those
|
|
instructions do not work when the processor is in little endian mode.
|
|
The exceptions are PPC740 and PPC750 which permit the instructions
|
|
usage in little endian mode.
|
|
|
|
@item -mupdate
|
|
@itemx -mno-update
|
|
@opindex mupdate
|
|
@opindex mno-update
|
|
Generate code that uses (does not use) the load or store instructions
|
|
that update the base register to the address of the calculated memory
|
|
location. These instructions are generated by default. If you use
|
|
@option{-mno-update}, there is a small window between the time that the
|
|
stack pointer is updated and the address of the previous frame is
|
|
stored, which means code that walks the stack frame across interrupts or
|
|
signals may get corrupted data.
|
|
|
|
@item -mfused-madd
|
|
@itemx -mno-fused-madd
|
|
@opindex mfused-madd
|
|
@opindex mno-fused-madd
|
|
Generate code that uses (does not use) the floating point multiply and
|
|
accumulate instructions. These instructions are generated by default if
|
|
hardware floating is used.
|
|
|
|
@item -mmulhw
|
|
@itemx -mno-mulhw
|
|
@opindex mmulhw
|
|
@opindex mno-mulhw
|
|
Generate code that uses (does not use) the half-word multiply and
|
|
multiply-accumulate instructions on the IBM 405 and 440 processors.
|
|
These instructions are generated by default when targetting those
|
|
processors.
|
|
|
|
@item -mdlmzb
|
|
@itemx -mno-dlmzb
|
|
@opindex mdlmzb
|
|
@opindex mno-dlmzb
|
|
Generate code that uses (does not use) the string-search @samp{dlmzb}
|
|
instruction on the IBM 405 and 440 processors. This instruction is
|
|
generated by default when targetting those processors.
|
|
|
|
@item -mno-bit-align
|
|
@itemx -mbit-align
|
|
@opindex mno-bit-align
|
|
@opindex mbit-align
|
|
On System V.4 and embedded PowerPC systems do not (do) force structures
|
|
and unions that contain bit-fields to be aligned to the base type of the
|
|
bit-field.
|
|
|
|
For example, by default a structure containing nothing but 8
|
|
@code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
|
|
boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
|
|
the structure would be aligned to a 1 byte boundary and be one byte in
|
|
size.
|
|
|
|
@item -mno-strict-align
|
|
@itemx -mstrict-align
|
|
@opindex mno-strict-align
|
|
@opindex mstrict-align
|
|
On System V.4 and embedded PowerPC systems do not (do) assume that
|
|
unaligned memory references will be handled by the system.
|
|
|
|
@item -mrelocatable
|
|
@itemx -mno-relocatable
|
|
@opindex mrelocatable
|
|
@opindex mno-relocatable
|
|
On embedded PowerPC systems generate code that allows (does not allow)
|
|
the program to be relocated to a different address at runtime. If you
|
|
use @option{-mrelocatable} on any module, all objects linked together must
|
|
be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
|
|
|
|
@item -mrelocatable-lib
|
|
@itemx -mno-relocatable-lib
|
|
@opindex mrelocatable-lib
|
|
@opindex mno-relocatable-lib
|
|
On embedded PowerPC systems generate code that allows (does not allow)
|
|
the program to be relocated to a different address at runtime. Modules
|
|
compiled with @option{-mrelocatable-lib} can be linked with either modules
|
|
compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
|
|
with modules compiled with the @option{-mrelocatable} options.
|
|
|
|
@item -mno-toc
|
|
@itemx -mtoc
|
|
@opindex mno-toc
|
|
@opindex mtoc
|
|
On System V.4 and embedded PowerPC systems do not (do) assume that
|
|
register 2 contains a pointer to a global area pointing to the addresses
|
|
used in the program.
|
|
|
|
@item -mlittle
|
|
@itemx -mlittle-endian
|
|
@opindex mlittle
|
|
@opindex mlittle-endian
|
|
On System V.4 and embedded PowerPC systems compile code for the
|
|
processor in little endian mode. The @option{-mlittle-endian} option is
|
|
the same as @option{-mlittle}.
|
|
|
|
@item -mbig
|
|
@itemx -mbig-endian
|
|
@opindex mbig
|
|
@opindex mbig-endian
|
|
On System V.4 and embedded PowerPC systems compile code for the
|
|
processor in big endian mode. The @option{-mbig-endian} option is
|
|
the same as @option{-mbig}.
|
|
|
|
@item -mdynamic-no-pic
|
|
@opindex mdynamic-no-pic
|
|
On Darwin and Mac OS X systems, compile code so that it is not
|
|
relocatable, but that its external references are relocatable. The
|
|
resulting code is suitable for applications, but not shared
|
|
libraries.
|
|
|
|
@item -mprioritize-restricted-insns=@var{priority}
|
|
@opindex mprioritize-restricted-insns
|
|
This option controls the priority that is assigned to
|
|
dispatch-slot restricted instructions during the second scheduling
|
|
pass. The argument @var{priority} takes the value @var{0/1/2} to assign
|
|
@var{no/highest/second-highest} priority to dispatch slot restricted
|
|
instructions.
|
|
|
|
@item -msched-costly-dep=@var{dependence_type}
|
|
@opindex msched-costly-dep
|
|
This option controls which dependences are considered costly
|
|
by the target during instruction scheduling. The argument
|
|
@var{dependence_type} takes one of the following values:
|
|
@var{no}: no dependence is costly,
|
|
@var{all}: all dependences are costly,
|
|
@var{true_store_to_load}: a true dependence from store to load is costly,
|
|
@var{store_to_load}: any dependence from store to load is costly,
|
|
@var{number}: any dependence which latency >= @var{number} is costly.
|
|
|
|
@item -minsert-sched-nops=@var{scheme}
|
|
@opindex minsert-sched-nops
|
|
This option controls which nop insertion scheme will be used during
|
|
the second scheduling pass. The argument @var{scheme} takes one of the
|
|
following values:
|
|
@var{no}: Don't insert nops.
|
|
@var{pad}: Pad with nops any dispatch group which has vacant issue slots,
|
|
according to the scheduler's grouping.
|
|
@var{regroup_exact}: Insert nops to force costly dependent insns into
|
|
separate groups. Insert exactly as many nops as needed to force an insn
|
|
to a new group, according to the estimated processor grouping.
|
|
@var{number}: Insert nops to force costly dependent insns into
|
|
separate groups. Insert @var{number} nops to force an insn to a new group.
|
|
|
|
@item -mcall-sysv
|
|
@opindex mcall-sysv
|
|
On System V.4 and embedded PowerPC systems compile code using calling
|
|
conventions that adheres to the March 1995 draft of the System V
|
|
Application Binary Interface, PowerPC processor supplement. This is the
|
|
default unless you configured GCC using @samp{powerpc-*-eabiaix}.
|
|
|
|
@item -mcall-sysv-eabi
|
|
@opindex mcall-sysv-eabi
|
|
Specify both @option{-mcall-sysv} and @option{-meabi} options.
|
|
|
|
@item -mcall-sysv-noeabi
|
|
@opindex mcall-sysv-noeabi
|
|
Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
|
|
|
|
@item -mcall-solaris
|
|
@opindex mcall-solaris
|
|
On System V.4 and embedded PowerPC systems compile code for the Solaris
|
|
operating system.
|
|
|
|
@item -mcall-linux
|
|
@opindex mcall-linux
|
|
On System V.4 and embedded PowerPC systems compile code for the
|
|
Linux-based GNU system.
|
|
|
|
@item -mcall-gnu
|
|
@opindex mcall-gnu
|
|
On System V.4 and embedded PowerPC systems compile code for the
|
|
Hurd-based GNU system.
|
|
|
|
@item -mcall-netbsd
|
|
@opindex mcall-netbsd
|
|
On System V.4 and embedded PowerPC systems compile code for the
|
|
NetBSD operating system.
|
|
|
|
@item -maix-struct-return
|
|
@opindex maix-struct-return
|
|
Return all structures in memory (as specified by the AIX ABI)@.
|
|
|
|
@item -msvr4-struct-return
|
|
@opindex msvr4-struct-return
|
|
Return structures smaller than 8 bytes in registers (as specified by the
|
|
SVR4 ABI)@.
|
|
|
|
@item -mabi=@var{abi-type}
|
|
@opindex mabi
|
|
Extend the current ABI with a particular extension, or remove such extension.
|
|
Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
|
|
@var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@.
|
|
|
|
@item -mabi=spe
|
|
@opindex mabi=spe
|
|
Extend the current ABI with SPE ABI extensions. This does not change
|
|
the default ABI, instead it adds the SPE ABI extensions to the current
|
|
ABI@.
|
|
|
|
@item -mabi=no-spe
|
|
@opindex mabi=no-spe
|
|
Disable Booke SPE ABI extensions for the current ABI@.
|
|
|
|
@item -mabi=ibmlongdouble
|
|
@opindex mabi=ibmlongdouble
|
|
Change the current ABI to use IBM extended precision long double.
|
|
This is a PowerPC 32-bit SYSV ABI option.
|
|
|
|
@item -mabi=ieeelongdouble
|
|
@opindex mabi=ieeelongdouble
|
|
Change the current ABI to use IEEE extended precision long double.
|
|
This is a PowerPC 32-bit Linux ABI option.
|
|
|
|
@item -mprototype
|
|
@itemx -mno-prototype
|
|
@opindex mprototype
|
|
@opindex mno-prototype
|
|
On System V.4 and embedded PowerPC systems assume that all calls to
|
|
variable argument functions are properly prototyped. Otherwise, the
|
|
compiler must insert an instruction before every non prototyped call to
|
|
set or clear bit 6 of the condition code register (@var{CR}) to
|
|
indicate whether floating point values were passed in the floating point
|
|
registers in case the function takes a variable arguments. With
|
|
@option{-mprototype}, only calls to prototyped variable argument functions
|
|
will set or clear the bit.
|
|
|
|
@item -msim
|
|
@opindex msim
|
|
On embedded PowerPC systems, assume that the startup module is called
|
|
@file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
|
|
@file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
|
|
configurations.
|
|
|
|
@item -mmvme
|
|
@opindex mmvme
|
|
On embedded PowerPC systems, assume that the startup module is called
|
|
@file{crt0.o} and the standard C libraries are @file{libmvme.a} and
|
|
@file{libc.a}.
|
|
|
|
@item -mads
|
|
@opindex mads
|
|
On embedded PowerPC systems, assume that the startup module is called
|
|
@file{crt0.o} and the standard C libraries are @file{libads.a} and
|
|
@file{libc.a}.
|
|
|
|
@item -myellowknife
|
|
@opindex myellowknife
|
|
On embedded PowerPC systems, assume that the startup module is called
|
|
@file{crt0.o} and the standard C libraries are @file{libyk.a} and
|
|
@file{libc.a}.
|
|
|
|
@item -mvxworks
|
|
@opindex mvxworks
|
|
On System V.4 and embedded PowerPC systems, specify that you are
|
|
compiling for a VxWorks system.
|
|
|
|
@item -mwindiss
|
|
@opindex mwindiss
|
|
Specify that you are compiling for the WindISS simulation environment.
|
|
|
|
@item -memb
|
|
@opindex memb
|
|
On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
|
|
header to indicate that @samp{eabi} extended relocations are used.
|
|
|
|
@item -meabi
|
|
@itemx -mno-eabi
|
|
@opindex meabi
|
|
@opindex mno-eabi
|
|
On System V.4 and embedded PowerPC systems do (do not) adhere to the
|
|
Embedded Applications Binary Interface (eabi) which is a set of
|
|
modifications to the System V.4 specifications. Selecting @option{-meabi}
|
|
means that the stack is aligned to an 8 byte boundary, a function
|
|
@code{__eabi} is called to from @code{main} to set up the eabi
|
|
environment, and the @option{-msdata} option can use both @code{r2} and
|
|
@code{r13} to point to two separate small data areas. Selecting
|
|
@option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
|
|
do not call an initialization function from @code{main}, and the
|
|
@option{-msdata} option will only use @code{r13} to point to a single
|
|
small data area. The @option{-meabi} option is on by default if you
|
|
configured GCC using one of the @samp{powerpc*-*-eabi*} options.
|
|
|
|
@item -msdata=eabi
|
|
@opindex msdata=eabi
|
|
On System V.4 and embedded PowerPC systems, put small initialized
|
|
@code{const} global and static data in the @samp{.sdata2} section, which
|
|
is pointed to by register @code{r2}. Put small initialized
|
|
non-@code{const} global and static data in the @samp{.sdata} section,
|
|
which is pointed to by register @code{r13}. Put small uninitialized
|
|
global and static data in the @samp{.sbss} section, which is adjacent to
|
|
the @samp{.sdata} section. The @option{-msdata=eabi} option is
|
|
incompatible with the @option{-mrelocatable} option. The
|
|
@option{-msdata=eabi} option also sets the @option{-memb} option.
|
|
|
|
@item -msdata=sysv
|
|
@opindex msdata=sysv
|
|
On System V.4 and embedded PowerPC systems, put small global and static
|
|
data in the @samp{.sdata} section, which is pointed to by register
|
|
@code{r13}. Put small uninitialized global and static data in the
|
|
@samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
|
|
The @option{-msdata=sysv} option is incompatible with the
|
|
@option{-mrelocatable} option.
|
|
|
|
@item -msdata=default
|
|
@itemx -msdata
|
|
@opindex msdata=default
|
|
@opindex msdata
|
|
On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
|
|
compile code the same as @option{-msdata=eabi}, otherwise compile code the
|
|
same as @option{-msdata=sysv}.
|
|
|
|
@item -msdata-data
|
|
@opindex msdata-data
|
|
On System V.4 and embedded PowerPC systems, put small global
|
|
data in the @samp{.sdata} section. Put small uninitialized global
|
|
data in the @samp{.sbss} section. Do not use register @code{r13}
|
|
to address small data however. This is the default behavior unless
|
|
other @option{-msdata} options are used.
|
|
|
|
@item -msdata=none
|
|
@itemx -mno-sdata
|
|
@opindex msdata=none
|
|
@opindex mno-sdata
|
|
On embedded PowerPC systems, put all initialized global and static data
|
|
in the @samp{.data} section, and all uninitialized data in the
|
|
@samp{.bss} section.
|
|
|
|
@item -G @var{num}
|
|
@opindex G
|
|
@cindex smaller data references (PowerPC)
|
|
@cindex .sdata/.sdata2 references (PowerPC)
|
|
On embedded PowerPC systems, put global and static items less than or
|
|
equal to @var{num} bytes into the small data or bss sections instead of
|
|
the normal data or bss section. By default, @var{num} is 8. The
|
|
@option{-G @var{num}} switch is also passed to the linker.
|
|
All modules should be compiled with the same @option{-G @var{num}} value.
|
|
|
|
@item -mregnames
|
|
@itemx -mno-regnames
|
|
@opindex mregnames
|
|
@opindex mno-regnames
|
|
On System V.4 and embedded PowerPC systems do (do not) emit register
|
|
names in the assembly language output using symbolic forms.
|
|
|
|
@item -mlongcall
|
|
@itemx -mno-longcall
|
|
@opindex mlongcall
|
|
@opindex mno-longcall
|
|
By default assume that all calls are far away so that a longer more
|
|
expensive calling sequence is required. This is required for calls
|
|
further than 32 megabytes (33,554,432 bytes) from the current location.
|
|
A short call will be generated if the compiler knows
|
|
the call cannot be that far away. This setting can be overridden by
|
|
the @code{shortcall} function attribute, or by @code{#pragma
|
|
longcall(0)}.
|
|
|
|
Some linkers are capable of detecting out-of-range calls and generating
|
|
glue code on the fly. On these systems, long calls are unnecessary and
|
|
generate slower code. As of this writing, the AIX linker can do this,
|
|
as can the GNU linker for PowerPC/64. It is planned to add this feature
|
|
to the GNU linker for 32-bit PowerPC systems as well.
|
|
|
|
On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
|
|
callee, L42'', plus a ``branch island'' (glue code). The two target
|
|
addresses represent the callee and the ``branch island''. The
|
|
Darwin/PPC linker will prefer the first address and generate a ``bl
|
|
callee'' if the PPC ``bl'' instruction will reach the callee directly;
|
|
otherwise, the linker will generate ``bl L42'' to call the ``branch
|
|
island''. The ``branch island'' is appended to the body of the
|
|
calling function; it computes the full 32-bit address of the callee
|
|
and jumps to it.
|
|
|
|
On Mach-O (Darwin) systems, this option directs the compiler emit to
|
|
the glue for every direct call, and the Darwin linker decides whether
|
|
to use or discard it.
|
|
|
|
In the future, we may cause GCC to ignore all longcall specifications
|
|
when the linker is known to generate glue.
|
|
|
|
@item -pthread
|
|
@opindex pthread
|
|
Adds support for multithreading with the @dfn{pthreads} library.
|
|
This option sets flags for both the preprocessor and linker.
|
|
|
|
@end table
|
|
|
|
@node S/390 and zSeries Options
|
|
@subsection S/390 and zSeries Options
|
|
@cindex S/390 and zSeries Options
|
|
|
|
These are the @samp{-m} options defined for the S/390 and zSeries architecture.
|
|
|
|
@table @gcctabopt
|
|
@item -mhard-float
|
|
@itemx -msoft-float
|
|
@opindex mhard-float
|
|
@opindex msoft-float
|
|
Use (do not use) the hardware floating-point instructions and registers
|
|
for floating-point operations. When @option{-msoft-float} is specified,
|
|
functions in @file{libgcc.a} will be used to perform floating-point
|
|
operations. When @option{-mhard-float} is specified, the compiler
|
|
generates IEEE floating-point instructions. This is the default.
|
|
|
|
@item -mlong-double-64
|
|
@itemx -mlong-double-128
|
|
@opindex mlong-double-64
|
|
@opindex mlong-double-128
|
|
These switches control the size of @code{long double} type. A size
|
|
of 64bit makes the @code{long double} type equivalent to the @code{double}
|
|
type. This is the default.
|
|
|
|
@item -mbackchain
|
|
@itemx -mno-backchain
|
|
@opindex mbackchain
|
|
@opindex mno-backchain
|
|
Store (do not store) the address of the caller's frame as backchain pointer
|
|
into the callee's stack frame.
|
|
A backchain may be needed to allow debugging using tools that do not understand
|
|
DWARF-2 call frame information.
|
|
When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
|
|
at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
|
|
the backchain is placed into the topmost word of the 96/160 byte register
|
|
save area.
|
|
|
|
In general, code compiled with @option{-mbackchain} is call-compatible with
|
|
code compiled with @option{-mmo-backchain}; however, use of the backchain
|
|
for debugging purposes usually requires that the whole binary is built with
|
|
@option{-mbackchain}. Note that the combination of @option{-mbackchain},
|
|
@option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
|
|
to build a linux kernel use @option{-msoft-float}.
|
|
|
|
The default is to not maintain the backchain.
|
|
|
|
@item -mpacked-stack
|
|
@item -mno-packed-stack
|
|
@opindex mpacked-stack
|
|
@opindex mno-packed-stack
|
|
Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
|
|
specified, the compiler uses the all fields of the 96/160 byte register save
|
|
area only for their default purpose; unused fields still take up stack space.
|
|
When @option{-mpacked-stack} is specified, register save slots are densely
|
|
packed at the top of the register save area; unused space is reused for other
|
|
purposes, allowing for more efficient use of the available stack space.
|
|
However, when @option{-mbackchain} is also in effect, the topmost word of
|
|
the save area is always used to store the backchain, and the return address
|
|
register is always saved two words below the backchain.
|
|
|
|
As long as the stack frame backchain is not used, code generated with
|
|
@option{-mpacked-stack} is call-compatible with code generated with
|
|
@option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
|
|
S/390 or zSeries generated code that uses the stack frame backchain at run
|
|
time, not just for debugging purposes. Such code is not call-compatible
|
|
with code compiled with @option{-mpacked-stack}. Also, note that the
|
|
combination of @option{-mbackchain},
|
|
@option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
|
|
to build a linux kernel use @option{-msoft-float}.
|
|
|
|
The default is to not use the packed stack layout.
|
|
|
|
@item -msmall-exec
|
|
@itemx -mno-small-exec
|
|
@opindex msmall-exec
|
|
@opindex mno-small-exec
|
|
Generate (or do not generate) code using the @code{bras} instruction
|
|
to do subroutine calls.
|
|
This only works reliably if the total executable size does not
|
|
exceed 64k. The default is to use the @code{basr} instruction instead,
|
|
which does not have this limitation.
|
|
|
|
@item -m64
|
|
@itemx -m31
|
|
@opindex m64
|
|
@opindex m31
|
|
When @option{-m31} is specified, generate code compliant to the
|
|
GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
|
|
code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
|
|
particular to generate 64-bit instructions. For the @samp{s390}
|
|
targets, the default is @option{-m31}, while the @samp{s390x}
|
|
targets default to @option{-m64}.
|
|
|
|
@item -mzarch
|
|
@itemx -mesa
|
|
@opindex mzarch
|
|
@opindex mesa
|
|
When @option{-mzarch} is specified, generate code using the
|
|
instructions available on z/Architecture.
|
|
When @option{-mesa} is specified, generate code using the
|
|
instructions available on ESA/390. Note that @option{-mesa} is
|
|
not possible with @option{-m64}.
|
|
When generating code compliant to the GNU/Linux for S/390 ABI,
|
|
the default is @option{-mesa}. When generating code compliant
|
|
to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
|
|
|
|
@item -mmvcle
|
|
@itemx -mno-mvcle
|
|
@opindex mmvcle
|
|
@opindex mno-mvcle
|
|
Generate (or do not generate) code using the @code{mvcle} instruction
|
|
to perform block moves. When @option{-mno-mvcle} is specified,
|
|
use a @code{mvc} loop instead. This is the default unless optimizing for
|
|
size.
|
|
|
|
@item -mdebug
|
|
@itemx -mno-debug
|
|
@opindex mdebug
|
|
@opindex mno-debug
|
|
Print (or do not print) additional debug information when compiling.
|
|
The default is to not print debug information.
|
|
|
|
@item -march=@var{cpu-type}
|
|
@opindex march
|
|
Generate code that will run on @var{cpu-type}, which is the name of a system
|
|
representing a certain processor type. Possible values for
|
|
@var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
|
|
When generating code using the instructions available on z/Architecture,
|
|
the default is @option{-march=z900}. Otherwise, the default is
|
|
@option{-march=g5}.
|
|
|
|
@item -mtune=@var{cpu-type}
|
|
@opindex mtune
|
|
Tune to @var{cpu-type} everything applicable about the generated code,
|
|
except for the ABI and the set of available instructions.
|
|
The list of @var{cpu-type} values is the same as for @option{-march}.
|
|
The default is the value used for @option{-march}.
|
|
|
|
@item -mtpf-trace
|
|
@itemx -mno-tpf-trace
|
|
@opindex mtpf-trace
|
|
@opindex mno-tpf-trace
|
|
Generate code that adds (does not add) in TPF OS specific branches to trace
|
|
routines in the operating system. This option is off by default, even
|
|
when compiling for the TPF OS@.
|
|
|
|
@item -mfused-madd
|
|
@itemx -mno-fused-madd
|
|
@opindex mfused-madd
|
|
@opindex mno-fused-madd
|
|
Generate code that uses (does not use) the floating point multiply and
|
|
accumulate instructions. These instructions are generated by default if
|
|
hardware floating point is used.
|
|
|
|
@item -mwarn-framesize=@var{framesize}
|
|
@opindex mwarn-framesize
|
|
Emit a warning if the current function exceeds the given frame size. Because
|
|
this is a compile time check it doesn't need to be a real problem when the program
|
|
runs. It is intended to identify functions which most probably cause
|
|
a stack overflow. It is useful to be used in an environment with limited stack
|
|
size e.g.@: the linux kernel.
|
|
|
|
@item -mwarn-dynamicstack
|
|
@opindex mwarn-dynamicstack
|
|
Emit a warning if the function calls alloca or uses dynamically
|
|
sized arrays. This is generally a bad idea with a limited stack size.
|
|
|
|
@item -mstack-guard=@var{stack-guard}
|
|
@item -mstack-size=@var{stack-size}
|
|
@opindex mstack-guard
|
|
@opindex mstack-size
|
|
These arguments always have to be used in conjunction. If they are present the s390
|
|
back end emits additional instructions in the function prologue which trigger a trap
|
|
if the stack size is @var{stack-guard} bytes above the @var{stack-size}
|
|
(remember that the stack on s390 grows downward). These options are intended to
|
|
be used to help debugging stack overflow problems. The additionally emitted code
|
|
causes only little overhead and hence can also be used in production like systems
|
|
without greater performance degradation. The given values have to be exact
|
|
powers of 2 and @var{stack-size} has to be greater than @var{stack-guard} without
|
|
exceeding 64k.
|
|
In order to be efficient the extra code makes the assumption that the stack starts
|
|
at an address aligned to the value given by @var{stack-size}.
|
|
@end table
|
|
|
|
@node Score Options
|
|
@subsection Score Options
|
|
@cindex Score Options
|
|
|
|
These options are defined for Score implementations:
|
|
|
|
@table @gcctabopt
|
|
@item -meb
|
|
@opindex meb
|
|
Compile code for big endian mode. This is the default.
|
|
|
|
@item -mel
|
|
@opindex mel
|
|
Compile code for little endian mode.
|
|
|
|
@item -mnhwloop
|
|
@opindex mnhwloop
|
|
Disable generate bcnz instruction.
|
|
|
|
@item -muls
|
|
@opindex muls
|
|
Enable generate unaligned load and store instruction.
|
|
|
|
@item -mmac
|
|
@opindex mmac
|
|
Enable the use of multiply-accumulate instructions. Disabled by default.
|
|
|
|
@item -mscore5
|
|
@opindex mscore5
|
|
Specify the SCORE5 as the target architecture.
|
|
|
|
@item -mscore5u
|
|
@opindex mscore5u
|
|
Specify the SCORE5U of the target architecture.
|
|
|
|
@item -mscore7
|
|
@opindex mscore7
|
|
Specify the SCORE7 as the target architecture. This is the default.
|
|
|
|
@item -mscore7d
|
|
@opindex mscore7d
|
|
Specify the SCORE7D as the target architecture.
|
|
@end table
|
|
|
|
@node SH Options
|
|
@subsection SH Options
|
|
|
|
These @samp{-m} options are defined for the SH implementations:
|
|
|
|
@table @gcctabopt
|
|
@item -m1
|
|
@opindex m1
|
|
Generate code for the SH1.
|
|
|
|
@item -m2
|
|
@opindex m2
|
|
Generate code for the SH2.
|
|
|
|
@item -m2e
|
|
Generate code for the SH2e.
|
|
|
|
@item -m3
|
|
@opindex m3
|
|
Generate code for the SH3.
|
|
|
|
@item -m3e
|
|
@opindex m3e
|
|
Generate code for the SH3e.
|
|
|
|
@item -m4-nofpu
|
|
@opindex m4-nofpu
|
|
Generate code for the SH4 without a floating-point unit.
|
|
|
|
@item -m4-single-only
|
|
@opindex m4-single-only
|
|
Generate code for the SH4 with a floating-point unit that only
|
|
supports single-precision arithmetic.
|
|
|
|
@item -m4-single
|
|
@opindex m4-single
|
|
Generate code for the SH4 assuming the floating-point unit is in
|
|
single-precision mode by default.
|
|
|
|
@item -m4
|
|
@opindex m4
|
|
Generate code for the SH4.
|
|
|
|
@item -m4a-nofpu
|
|
@opindex m4a-nofpu
|
|
Generate code for the SH4al-dsp, or for a SH4a in such a way that the
|
|
floating-point unit is not used.
|
|
|
|
@item -m4a-single-only
|
|
@opindex m4a-single-only
|
|
Generate code for the SH4a, in such a way that no double-precision
|
|
floating point operations are used.
|
|
|
|
@item -m4a-single
|
|
@opindex m4a-single
|
|
Generate code for the SH4a assuming the floating-point unit is in
|
|
single-precision mode by default.
|
|
|
|
@item -m4a
|
|
@opindex m4a
|
|
Generate code for the SH4a.
|
|
|
|
@item -m4al
|
|
@opindex m4al
|
|
Same as @option{-m4a-nofpu}, except that it implicitly passes
|
|
@option{-dsp} to the assembler. GCC doesn't generate any DSP
|
|
instructions at the moment.
|
|
|
|
@item -mb
|
|
@opindex mb
|
|
Compile code for the processor in big endian mode.
|
|
|
|
@item -ml
|
|
@opindex ml
|
|
Compile code for the processor in little endian mode.
|
|
|
|
@item -mdalign
|
|
@opindex mdalign
|
|
Align doubles at 64-bit boundaries. Note that this changes the calling
|
|
conventions, and thus some functions from the standard C library will
|
|
not work unless you recompile it first with @option{-mdalign}.
|
|
|
|
@item -mrelax
|
|
@opindex mrelax
|
|
Shorten some address references at link time, when possible; uses the
|
|
linker option @option{-relax}.
|
|
|
|
@item -mbigtable
|
|
@opindex mbigtable
|
|
Use 32-bit offsets in @code{switch} tables. The default is to use
|
|
16-bit offsets.
|
|
|
|
@item -mfmovd
|
|
@opindex mfmovd
|
|
Enable the use of the instruction @code{fmovd}.
|
|
|
|
@item -mhitachi
|
|
@opindex mhitachi
|
|
Comply with the calling conventions defined by Renesas.
|
|
|
|
@item -mrenesas
|
|
@opindex mhitachi
|
|
Comply with the calling conventions defined by Renesas.
|
|
|
|
@item -mno-renesas
|
|
@opindex mhitachi
|
|
Comply with the calling conventions defined for GCC before the Renesas
|
|
conventions were available. This option is the default for all
|
|
targets of the SH toolchain except for @samp{sh-symbianelf}.
|
|
|
|
@item -mnomacsave
|
|
@opindex mnomacsave
|
|
Mark the @code{MAC} register as call-clobbered, even if
|
|
@option{-mhitachi} is given.
|
|
|
|
@item -mieee
|
|
@opindex mieee
|
|
Increase IEEE-compliance of floating-point code.
|
|
At the moment, this is equivalent to @option{-fno-finite-math-only}.
|
|
When generating 16 bit SH opcodes, getting IEEE-conforming results for
|
|
comparisons of NANs / infinities incurs extra overhead in every
|
|
floating point comparison, therefore the default is set to
|
|
@option{-ffinite-math-only}.
|
|
|
|
@item -misize
|
|
@opindex misize
|
|
Dump instruction size and location in the assembly code.
|
|
|
|
@item -mpadstruct
|
|
@opindex mpadstruct
|
|
This option is deprecated. It pads structures to multiple of 4 bytes,
|
|
which is incompatible with the SH ABI@.
|
|
|
|
@item -mspace
|
|
@opindex mspace
|
|
Optimize for space instead of speed. Implied by @option{-Os}.
|
|
|
|
@item -mprefergot
|
|
@opindex mprefergot
|
|
When generating position-independent code, emit function calls using
|
|
the Global Offset Table instead of the Procedure Linkage Table.
|
|
|
|
@item -musermode
|
|
@opindex musermode
|
|
Generate a library function call to invalidate instruction cache
|
|
entries, after fixing up a trampoline. This library function call
|
|
doesn't assume it can write to the whole memory address space. This
|
|
is the default when the target is @code{sh-*-linux*}.
|
|
|
|
@item -multcost=@var{number}
|
|
@opindex multcost=@var{number}
|
|
Set the cost to assume for a multiply insn.
|
|
|
|
@item -mdiv=@var{strategy}
|
|
@opindex mdiv=@var{strategy}
|
|
Set the division strategy to use for SHmedia code. @var{strategy} must be
|
|
one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
|
|
inv:call2, inv:fp .
|
|
"fp" performs the operation in floating point. This has a very high latency,
|
|
but needs only a few instructions, so it might be a good choice if
|
|
your code has enough easily exploitable ILP to allow the compiler to
|
|
schedule the floating point instructions together with other instructions.
|
|
Division by zero causes a floating point exception.
|
|
"inv" uses integer operations to calculate the inverse of the divisor,
|
|
and then multiplies the dividend with the inverse. This strategy allows
|
|
cse and hoisting of the inverse calculation. Division by zero calculates
|
|
an unspecified result, but does not trap.
|
|
"inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
|
|
have been found, or if the entire operation has been hoisted to the same
|
|
place, the last stages of the inverse calculation are intertwined with the
|
|
final multiply to reduce the overall latency, at the expense of using a few
|
|
more instructions, and thus offering fewer scheduling opportunities with
|
|
other code.
|
|
"call" calls a library function that usually implements the inv:minlat
|
|
strategy.
|
|
This gives high code density for m5-*media-nofpu compilations.
|
|
"call2" uses a different entry point of the same library function, where it
|
|
assumes that a pointer to a lookup table has already been set up, which
|
|
exposes the pointer load to cse / code hoisting optimizations.
|
|
"inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
|
|
code generation, but if the code stays unoptimized, revert to the "call",
|
|
"call2", or "fp" strategies, respectively. Note that the
|
|
potentially-trapping side effect of division by zero is carried by a
|
|
separate instruction, so it is possible that all the integer instructions
|
|
are hoisted out, but the marker for the side effect stays where it is.
|
|
A recombination to fp operations or a call is not possible in that case.
|
|
"inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
|
|
that the inverse calculation was nor separated from the multiply, they speed
|
|
up division where the dividend fits into 20 bits (plus sign where applicable),
|
|
by inserting a test to skip a number of operations in this case; this test
|
|
slows down the case of larger dividends. inv20u assumes the case of a such
|
|
a small dividend to be unlikely, and inv20l assumes it to be likely.
|
|
|
|
@item -mdivsi3_libfunc=@var{name}
|
|
@opindex mdivsi3_libfunc=@var{name}
|
|
Set the name of the library function used for 32 bit signed division to
|
|
@var{name}. This only affect the name used in the call and inv:call
|
|
division strategies, and the compiler will still expect the same
|
|
sets of input/output/clobbered registers as if this option was not present.
|
|
|
|
@item -madjust-unroll
|
|
@opindex madjust-unroll
|
|
Throttle unrolling to avoid thrashing target registers.
|
|
This option only has an effect if the gcc code base supports the
|
|
TARGET_ADJUST_UNROLL_MAX target hook.
|
|
|
|
@item -mindexed-addressing
|
|
@opindex mindexed-addressing
|
|
Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
|
|
This is only safe if the hardware and/or OS implement 32 bit wrap-around
|
|
semantics for the indexed addressing mode. The architecture allows the
|
|
implementation of processors with 64 bit MMU, which the OS could use to
|
|
get 32 bit addressing, but since no current hardware implementation supports
|
|
this or any other way to make the indexed addressing mode safe to use in
|
|
the 32 bit ABI, the default is -mno-indexed-addressing.
|
|
|
|
@item -mgettrcost=@var{number}
|
|
@opindex mgettrcost=@var{number}
|
|
Set the cost assumed for the gettr instruction to @var{number}.
|
|
The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
|
|
|
|
@item -mpt-fixed
|
|
@opindex mpt-fixed
|
|
Assume pt* instructions won't trap. This will generally generate better
|
|
scheduled code, but is unsafe on current hardware. The current architecture
|
|
definition says that ptabs and ptrel trap when the target anded with 3 is 3.
|
|
This has the unintentional effect of making it unsafe to schedule ptabs /
|
|
ptrel before a branch, or hoist it out of a loop. For example,
|
|
__do_global_ctors, a part of libgcc that runs constructors at program
|
|
startup, calls functions in a list which is delimited by -1. With the
|
|
-mpt-fixed option, the ptabs will be done before testing against -1.
|
|
That means that all the constructors will be run a bit quicker, but when
|
|
the loop comes to the end of the list, the program crashes because ptabs
|
|
loads -1 into a target register. Since this option is unsafe for any
|
|
hardware implementing the current architecture specification, the default
|
|
is -mno-pt-fixed. Unless the user specifies a specific cost with
|
|
@option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
|
|
this deters register allocation using target registers for storing
|
|
ordinary integers.
|
|
|
|
@item -minvalid-symbols
|
|
@opindex minvalid-symbols
|
|
Assume symbols might be invalid. Ordinary function symbols generated by
|
|
the compiler will always be valid to load with movi/shori/ptabs or
|
|
movi/shori/ptrel, but with assembler and/or linker tricks it is possible
|
|
to generate symbols that will cause ptabs / ptrel to trap.
|
|
This option is only meaningful when @option{-mno-pt-fixed} is in effect.
|
|
It will then prevent cross-basic-block cse, hoisting and most scheduling
|
|
of symbol loads. The default is @option{-mno-invalid-symbols}.
|
|
@end table
|
|
|
|
@node SPARC Options
|
|
@subsection SPARC Options
|
|
@cindex SPARC options
|
|
|
|
These @samp{-m} options are supported on the SPARC:
|
|
|
|
@table @gcctabopt
|
|
@item -mno-app-regs
|
|
@itemx -mapp-regs
|
|
@opindex mno-app-regs
|
|
@opindex mapp-regs
|
|
Specify @option{-mapp-regs} to generate output using the global registers
|
|
2 through 4, which the SPARC SVR4 ABI reserves for applications. This
|
|
is the default.
|
|
|
|
To be fully SVR4 ABI compliant at the cost of some performance loss,
|
|
specify @option{-mno-app-regs}. You should compile libraries and system
|
|
software with this option.
|
|
|
|
@item -mfpu
|
|
@itemx -mhard-float
|
|
@opindex mfpu
|
|
@opindex mhard-float
|
|
Generate output containing floating point instructions. This is the
|
|
default.
|
|
|
|
@item -mno-fpu
|
|
@itemx -msoft-float
|
|
@opindex mno-fpu
|
|
@opindex msoft-float
|
|
Generate output containing library calls for floating point.
|
|
@strong{Warning:} the requisite libraries are not available for all SPARC
|
|
targets. Normally the facilities of the machine's usual C compiler are
|
|
used, but this cannot be done directly in cross-compilation. You must make
|
|
your own arrangements to provide suitable library functions for
|
|
cross-compilation. The embedded targets @samp{sparc-*-aout} and
|
|
@samp{sparclite-*-*} do provide software floating point support.
|
|
|
|
@option{-msoft-float} changes the calling convention in the output file;
|
|
therefore, it is only useful if you compile @emph{all} of a program with
|
|
this option. In particular, you need to compile @file{libgcc.a}, the
|
|
library that comes with GCC, with @option{-msoft-float} in order for
|
|
this to work.
|
|
|
|
@item -mhard-quad-float
|
|
@opindex mhard-quad-float
|
|
Generate output containing quad-word (long double) floating point
|
|
instructions.
|
|
|
|
@item -msoft-quad-float
|
|
@opindex msoft-quad-float
|
|
Generate output containing library calls for quad-word (long double)
|
|
floating point instructions. The functions called are those specified
|
|
in the SPARC ABI@. This is the default.
|
|
|
|
As of this writing, there are no SPARC implementations that have hardware
|
|
support for the quad-word floating point instructions. They all invoke
|
|
a trap handler for one of these instructions, and then the trap handler
|
|
emulates the effect of the instruction. Because of the trap handler overhead,
|
|
this is much slower than calling the ABI library routines. Thus the
|
|
@option{-msoft-quad-float} option is the default.
|
|
|
|
@item -mno-unaligned-doubles
|
|
@itemx -munaligned-doubles
|
|
@opindex mno-unaligned-doubles
|
|
@opindex munaligned-doubles
|
|
Assume that doubles have 8 byte alignment. This is the default.
|
|
|
|
With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
|
|
alignment only if they are contained in another type, or if they have an
|
|
absolute address. Otherwise, it assumes they have 4 byte alignment.
|
|
Specifying this option avoids some rare compatibility problems with code
|
|
generated by other compilers. It is not the default because it results
|
|
in a performance loss, especially for floating point code.
|
|
|
|
@item -mno-faster-structs
|
|
@itemx -mfaster-structs
|
|
@opindex mno-faster-structs
|
|
@opindex mfaster-structs
|
|
With @option{-mfaster-structs}, the compiler assumes that structures
|
|
should have 8 byte alignment. This enables the use of pairs of
|
|
@code{ldd} and @code{std} instructions for copies in structure
|
|
assignment, in place of twice as many @code{ld} and @code{st} pairs.
|
|
However, the use of this changed alignment directly violates the SPARC
|
|
ABI@. Thus, it's intended only for use on targets where the developer
|
|
acknowledges that their resulting code will not be directly in line with
|
|
the rules of the ABI@.
|
|
|
|
@item -mimpure-text
|
|
@opindex mimpure-text
|
|
@option{-mimpure-text}, used in addition to @option{-shared}, tells
|
|
the compiler to not pass @option{-z text} to the linker when linking a
|
|
shared object. Using this option, you can link position-dependent
|
|
code into a shared object.
|
|
|
|
@option{-mimpure-text} suppresses the ``relocations remain against
|
|
allocatable but non-writable sections'' linker error message.
|
|
However, the necessary relocations will trigger copy-on-write, and the
|
|
shared object is not actually shared across processes. Instead of
|
|
using @option{-mimpure-text}, you should compile all source code with
|
|
@option{-fpic} or @option{-fPIC}.
|
|
|
|
This option is only available on SunOS and Solaris.
|
|
|
|
@item -mcpu=@var{cpu_type}
|
|
@opindex mcpu
|
|
Set the instruction set, register set, and instruction scheduling parameters
|
|
for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
|
|
@samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
|
|
@samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
|
|
@samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc},
|
|
@samp{ultrasparc3}, and @samp{niagara}.
|
|
|
|
Default instruction scheduling parameters are used for values that select
|
|
an architecture and not an implementation. These are @samp{v7}, @samp{v8},
|
|
@samp{sparclite}, @samp{sparclet}, @samp{v9}.
|
|
|
|
Here is a list of each supported architecture and their supported
|
|
implementations.
|
|
|
|
@smallexample
|
|
v7: cypress
|
|
v8: supersparc, hypersparc
|
|
sparclite: f930, f934, sparclite86x
|
|
sparclet: tsc701
|
|
v9: ultrasparc, ultrasparc3, niagara
|
|
@end smallexample
|
|
|
|
By default (unless configured otherwise), GCC generates code for the V7
|
|
variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
|
|
additionally optimizes it for the Cypress CY7C602 chip, as used in the
|
|
SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
|
|
SPARCStation 1, 2, IPX etc.
|
|
|
|
With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
|
|
architecture. The only difference from V7 code is that the compiler emits
|
|
the integer multiply and integer divide instructions which exist in SPARC-V8
|
|
but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
|
|
optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
|
|
2000 series.
|
|
|
|
With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
|
|
the SPARC architecture. This adds the integer multiply, integer divide step
|
|
and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
|
|
With @option{-mcpu=f930}, the compiler additionally optimizes it for the
|
|
Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
|
|
@option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
|
|
MB86934 chip, which is the more recent SPARClite with FPU@.
|
|
|
|
With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
|
|
the SPARC architecture. This adds the integer multiply, multiply/accumulate,
|
|
integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
|
|
but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
|
|
optimizes it for the TEMIC SPARClet chip.
|
|
|
|
With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
|
|
architecture. This adds 64-bit integer and floating-point move instructions,
|
|
3 additional floating-point condition code registers and conditional move
|
|
instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
|
|
optimizes it for the Sun UltraSPARC I/II/IIi chips. With
|
|
@option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
|
|
Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
|
|
@option{-mcpu=niagara}, the compiler additionally optimizes it for
|
|
Sun UltraSPARC T1 chips.
|
|
|
|
@item -mtune=@var{cpu_type}
|
|
@opindex mtune
|
|
Set the instruction scheduling parameters for machine type
|
|
@var{cpu_type}, but do not set the instruction set or register set that the
|
|
option @option{-mcpu=@var{cpu_type}} would.
|
|
|
|
The same values for @option{-mcpu=@var{cpu_type}} can be used for
|
|
@option{-mtune=@var{cpu_type}}, but the only useful values are those
|
|
that select a particular cpu implementation. Those are @samp{cypress},
|
|
@samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
|
|
@samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc},
|
|
@samp{ultrasparc3}, and @samp{niagara}.
|
|
|
|
@item -mv8plus
|
|
@itemx -mno-v8plus
|
|
@opindex mv8plus
|
|
@opindex mno-v8plus
|
|
With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
|
|
difference from the V8 ABI is that the global and out registers are
|
|
considered 64-bit wide. This is enabled by default on Solaris in 32-bit
|
|
mode for all SPARC-V9 processors.
|
|
|
|
@item -mvis
|
|
@itemx -mno-vis
|
|
@opindex mvis
|
|
@opindex mno-vis
|
|
With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
|
|
Visual Instruction Set extensions. The default is @option{-mno-vis}.
|
|
@end table
|
|
|
|
These @samp{-m} options are supported in addition to the above
|
|
on SPARC-V9 processors in 64-bit environments:
|
|
|
|
@table @gcctabopt
|
|
@item -mlittle-endian
|
|
@opindex mlittle-endian
|
|
Generate code for a processor running in little-endian mode. It is only
|
|
available for a few configurations and most notably not on Solaris and Linux.
|
|
|
|
@item -m32
|
|
@itemx -m64
|
|
@opindex m32
|
|
@opindex m64
|
|
Generate code for a 32-bit or 64-bit environment.
|
|
The 32-bit environment sets int, long and pointer to 32 bits.
|
|
The 64-bit environment sets int to 32 bits and long and pointer
|
|
to 64 bits.
|
|
|
|
@item -mcmodel=medlow
|
|
@opindex mcmodel=medlow
|
|
Generate code for the Medium/Low code model: 64-bit addresses, programs
|
|
must be linked in the low 32 bits of memory. Programs can be statically
|
|
or dynamically linked.
|
|
|
|
@item -mcmodel=medmid
|
|
@opindex mcmodel=medmid
|
|
Generate code for the Medium/Middle code model: 64-bit addresses, programs
|
|
must be linked in the low 44 bits of memory, the text and data segments must
|
|
be less than 2GB in size and the data segment must be located within 2GB of
|
|
the text segment.
|
|
|
|
@item -mcmodel=medany
|
|
@opindex mcmodel=medany
|
|
Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
|
|
may be linked anywhere in memory, the text and data segments must be less
|
|
than 2GB in size and the data segment must be located within 2GB of the
|
|
text segment.
|
|
|
|
@item -mcmodel=embmedany
|
|
@opindex mcmodel=embmedany
|
|
Generate code for the Medium/Anywhere code model for embedded systems:
|
|
64-bit addresses, the text and data segments must be less than 2GB in
|
|
size, both starting anywhere in memory (determined at link time). The
|
|
global register %g4 points to the base of the data segment. Programs
|
|
are statically linked and PIC is not supported.
|
|
|
|
@item -mstack-bias
|
|
@itemx -mno-stack-bias
|
|
@opindex mstack-bias
|
|
@opindex mno-stack-bias
|
|
With @option{-mstack-bias}, GCC assumes that the stack pointer, and
|
|
frame pointer if present, are offset by @minus{}2047 which must be added back
|
|
when making stack frame references. This is the default in 64-bit mode.
|
|
Otherwise, assume no such offset is present.
|
|
@end table
|
|
|
|
These switches are supported in addition to the above on Solaris:
|
|
|
|
@table @gcctabopt
|
|
@item -threads
|
|
@opindex threads
|
|
Add support for multithreading using the Solaris threads library. This
|
|
option sets flags for both the preprocessor and linker. This option does
|
|
not affect the thread safety of object code produced by the compiler or
|
|
that of libraries supplied with it.
|
|
|
|
@item -pthreads
|
|
@opindex pthreads
|
|
Add support for multithreading using the POSIX threads library. This
|
|
option sets flags for both the preprocessor and linker. This option does
|
|
not affect the thread safety of object code produced by the compiler or
|
|
that of libraries supplied with it.
|
|
|
|
@item -pthread
|
|
@opindex pthread
|
|
This is a synonym for @option{-pthreads}.
|
|
@end table
|
|
|
|
@node System V Options
|
|
@subsection Options for System V
|
|
|
|
These additional options are available on System V Release 4 for
|
|
compatibility with other compilers on those systems:
|
|
|
|
@table @gcctabopt
|
|
@item -G
|
|
@opindex G
|
|
Create a shared object.
|
|
It is recommended that @option{-symbolic} or @option{-shared} be used instead.
|
|
|
|
@item -Qy
|
|
@opindex Qy
|
|
Identify the versions of each tool used by the compiler, in a
|
|
@code{.ident} assembler directive in the output.
|
|
|
|
@item -Qn
|
|
@opindex Qn
|
|
Refrain from adding @code{.ident} directives to the output file (this is
|
|
the default).
|
|
|
|
@item -YP,@var{dirs}
|
|
@opindex YP
|
|
Search the directories @var{dirs}, and no others, for libraries
|
|
specified with @option{-l}.
|
|
|
|
@item -Ym,@var{dir}
|
|
@opindex Ym
|
|
Look in the directory @var{dir} to find the M4 preprocessor.
|
|
The assembler uses this option.
|
|
@c This is supposed to go with a -Yd for predefined M4 macro files, but
|
|
@c the generic assembler that comes with Solaris takes just -Ym.
|
|
@end table
|
|
|
|
@node TMS320C3x/C4x Options
|
|
@subsection TMS320C3x/C4x Options
|
|
@cindex TMS320C3x/C4x Options
|
|
|
|
These @samp{-m} options are defined for TMS320C3x/C4x implementations:
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -mcpu=@var{cpu_type}
|
|
@opindex mcpu
|
|
Set the instruction set, register set, and instruction scheduling
|
|
parameters for machine type @var{cpu_type}. Supported values for
|
|
@var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
|
|
@samp{c44}. The default is @samp{c40} to generate code for the
|
|
TMS320C40.
|
|
|
|
@item -mbig-memory
|
|
@itemx -mbig
|
|
@itemx -msmall-memory
|
|
@itemx -msmall
|
|
@opindex mbig-memory
|
|
@opindex mbig
|
|
@opindex msmall-memory
|
|
@opindex msmall
|
|
Generates code for the big or small memory model. The small memory
|
|
model assumed that all data fits into one 64K word page. At run-time
|
|
the data page (DP) register must be set to point to the 64K page
|
|
containing the .bss and .data program sections. The big memory model is
|
|
the default and requires reloading of the DP register for every direct
|
|
memory access.
|
|
|
|
@item -mbk
|
|
@itemx -mno-bk
|
|
@opindex mbk
|
|
@opindex mno-bk
|
|
Allow (disallow) allocation of general integer operands into the block
|
|
count register BK@.
|
|
|
|
@item -mdb
|
|
@itemx -mno-db
|
|
@opindex mdb
|
|
@opindex mno-db
|
|
Enable (disable) generation of code using decrement and branch,
|
|
DBcond(D), instructions. This is enabled by default for the C4x. To be
|
|
on the safe side, this is disabled for the C3x, since the maximum
|
|
iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
|
|
@math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
|
|
that it can utilize the decrement and branch instruction, but will give
|
|
up if there is more than one memory reference in the loop. Thus a loop
|
|
where the loop counter is decremented can generate slightly more
|
|
efficient code, in cases where the RPTB instruction cannot be utilized.
|
|
|
|
@item -mdp-isr-reload
|
|
@itemx -mparanoid
|
|
@opindex mdp-isr-reload
|
|
@opindex mparanoid
|
|
Force the DP register to be saved on entry to an interrupt service
|
|
routine (ISR), reloaded to point to the data section, and restored on
|
|
exit from the ISR@. This should not be required unless someone has
|
|
violated the small memory model by modifying the DP register, say within
|
|
an object library.
|
|
|
|
@item -mmpyi
|
|
@itemx -mno-mpyi
|
|
@opindex mmpyi
|
|
@opindex mno-mpyi
|
|
For the C3x use the 24-bit MPYI instruction for integer multiplies
|
|
instead of a library call to guarantee 32-bit results. Note that if one
|
|
of the operands is a constant, then the multiplication will be performed
|
|
using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
|
|
then squaring operations are performed inline instead of a library call.
|
|
|
|
@item -mfast-fix
|
|
@itemx -mno-fast-fix
|
|
@opindex mfast-fix
|
|
@opindex mno-fast-fix
|
|
The C3x/C4x FIX instruction to convert a floating point value to an
|
|
integer value chooses the nearest integer less than or equal to the
|
|
floating point value rather than to the nearest integer. Thus if the
|
|
floating point number is negative, the result will be incorrectly
|
|
truncated an additional code is necessary to detect and correct this
|
|
case. This option can be used to disable generation of the additional
|
|
code required to correct the result.
|
|
|
|
@item -mrptb
|
|
@itemx -mno-rptb
|
|
@opindex mrptb
|
|
@opindex mno-rptb
|
|
Enable (disable) generation of repeat block sequences using the RPTB
|
|
instruction for zero overhead looping. The RPTB construct is only used
|
|
for innermost loops that do not call functions or jump across the loop
|
|
boundaries. There is no advantage having nested RPTB loops due to the
|
|
overhead required to save and restore the RC, RS, and RE registers.
|
|
This is enabled by default with @option{-O2}.
|
|
|
|
@item -mrpts=@var{count}
|
|
@itemx -mno-rpts
|
|
@opindex mrpts
|
|
@opindex mno-rpts
|
|
Enable (disable) the use of the single instruction repeat instruction
|
|
RPTS@. If a repeat block contains a single instruction, and the loop
|
|
count can be guaranteed to be less than the value @var{count}, GCC will
|
|
emit a RPTS instruction instead of a RPTB@. If no value is specified,
|
|
then a RPTS will be emitted even if the loop count cannot be determined
|
|
at compile time. Note that the repeated instruction following RPTS does
|
|
not have to be reloaded from memory each iteration, thus freeing up the
|
|
CPU buses for operands. However, since interrupts are blocked by this
|
|
instruction, it is disabled by default.
|
|
|
|
@item -mloop-unsigned
|
|
@itemx -mno-loop-unsigned
|
|
@opindex mloop-unsigned
|
|
@opindex mno-loop-unsigned
|
|
The maximum iteration count when using RPTS and RPTB (and DB on the C40)
|
|
is @math{2^{31} + 1} since these instructions test if the iteration count is
|
|
negative to terminate the loop. If the iteration count is unsigned
|
|
there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
|
|
exceeded. This switch allows an unsigned iteration count.
|
|
|
|
@item -mti
|
|
@opindex mti
|
|
Try to emit an assembler syntax that the TI assembler (asm30) is happy
|
|
with. This also enforces compatibility with the API employed by the TI
|
|
C3x C compiler. For example, long doubles are passed as structures
|
|
rather than in floating point registers.
|
|
|
|
@item -mregparm
|
|
@itemx -mmemparm
|
|
@opindex mregparm
|
|
@opindex mmemparm
|
|
Generate code that uses registers (stack) for passing arguments to functions.
|
|
By default, arguments are passed in registers where possible rather
|
|
than by pushing arguments on to the stack.
|
|
|
|
@item -mparallel-insns
|
|
@itemx -mno-parallel-insns
|
|
@opindex mparallel-insns
|
|
@opindex mno-parallel-insns
|
|
Allow the generation of parallel instructions. This is enabled by
|
|
default with @option{-O2}.
|
|
|
|
@item -mparallel-mpy
|
|
@itemx -mno-parallel-mpy
|
|
@opindex mparallel-mpy
|
|
@opindex mno-parallel-mpy
|
|
Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
|
|
provided @option{-mparallel-insns} is also specified. These instructions have
|
|
tight register constraints which can pessimize the code generation
|
|
of large functions.
|
|
|
|
@end table
|
|
|
|
@node V850 Options
|
|
@subsection V850 Options
|
|
@cindex V850 Options
|
|
|
|
These @samp{-m} options are defined for V850 implementations:
|
|
|
|
@table @gcctabopt
|
|
@item -mlong-calls
|
|
@itemx -mno-long-calls
|
|
@opindex mlong-calls
|
|
@opindex mno-long-calls
|
|
Treat all calls as being far away (near). If calls are assumed to be
|
|
far away, the compiler will always load the functions address up into a
|
|
register, and call indirect through the pointer.
|
|
|
|
@item -mno-ep
|
|
@itemx -mep
|
|
@opindex mno-ep
|
|
@opindex mep
|
|
Do not optimize (do optimize) basic blocks that use the same index
|
|
pointer 4 or more times to copy pointer into the @code{ep} register, and
|
|
use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
|
|
option is on by default if you optimize.
|
|
|
|
@item -mno-prolog-function
|
|
@itemx -mprolog-function
|
|
@opindex mno-prolog-function
|
|
@opindex mprolog-function
|
|
Do not use (do use) external functions to save and restore registers
|
|
at the prologue and epilogue of a function. The external functions
|
|
are slower, but use less code space if more than one function saves
|
|
the same number of registers. The @option{-mprolog-function} option
|
|
is on by default if you optimize.
|
|
|
|
@item -mspace
|
|
@opindex mspace
|
|
Try to make the code as small as possible. At present, this just turns
|
|
on the @option{-mep} and @option{-mprolog-function} options.
|
|
|
|
@item -mtda=@var{n}
|
|
@opindex mtda
|
|
Put static or global variables whose size is @var{n} bytes or less into
|
|
the tiny data area that register @code{ep} points to. The tiny data
|
|
area can hold up to 256 bytes in total (128 bytes for byte references).
|
|
|
|
@item -msda=@var{n}
|
|
@opindex msda
|
|
Put static or global variables whose size is @var{n} bytes or less into
|
|
the small data area that register @code{gp} points to. The small data
|
|
area can hold up to 64 kilobytes.
|
|
|
|
@item -mzda=@var{n}
|
|
@opindex mzda
|
|
Put static or global variables whose size is @var{n} bytes or less into
|
|
the first 32 kilobytes of memory.
|
|
|
|
@item -mv850
|
|
@opindex mv850
|
|
Specify that the target processor is the V850.
|
|
|
|
@item -mbig-switch
|
|
@opindex mbig-switch
|
|
Generate code suitable for big switch tables. Use this option only if
|
|
the assembler/linker complain about out of range branches within a switch
|
|
table.
|
|
|
|
@item -mapp-regs
|
|
@opindex mapp-regs
|
|
This option will cause r2 and r5 to be used in the code generated by
|
|
the compiler. This setting is the default.
|
|
|
|
@item -mno-app-regs
|
|
@opindex mno-app-regs
|
|
This option will cause r2 and r5 to be treated as fixed registers.
|
|
|
|
@item -mv850e1
|
|
@opindex mv850e1
|
|
Specify that the target processor is the V850E1. The preprocessor
|
|
constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
|
|
this option is used.
|
|
|
|
@item -mv850e
|
|
@opindex mv850e
|
|
Specify that the target processor is the V850E@. The preprocessor
|
|
constant @samp{__v850e__} will be defined if this option is used.
|
|
|
|
If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
|
|
are defined then a default target processor will be chosen and the
|
|
relevant @samp{__v850*__} preprocessor constant will be defined.
|
|
|
|
The preprocessor constants @samp{__v850} and @samp{__v851__} are always
|
|
defined, regardless of which processor variant is the target.
|
|
|
|
@item -mdisable-callt
|
|
@opindex mdisable-callt
|
|
This option will suppress generation of the CALLT instruction for the
|
|
v850e and v850e1 flavors of the v850 architecture. The default is
|
|
@option{-mno-disable-callt} which allows the CALLT instruction to be used.
|
|
|
|
@end table
|
|
|
|
@node VAX Options
|
|
@subsection VAX Options
|
|
@cindex VAX options
|
|
|
|
These @samp{-m} options are defined for the VAX:
|
|
|
|
@table @gcctabopt
|
|
@item -munix
|
|
@opindex munix
|
|
Do not output certain jump instructions (@code{aobleq} and so on)
|
|
that the Unix assembler for the VAX cannot handle across long
|
|
ranges.
|
|
|
|
@item -mgnu
|
|
@opindex mgnu
|
|
Do output those jump instructions, on the assumption that you
|
|
will assemble with the GNU assembler.
|
|
|
|
@item -mg
|
|
@opindex mg
|
|
Output code for g-format floating point numbers instead of d-format.
|
|
@end table
|
|
|
|
@node x86-64 Options
|
|
@subsection x86-64 Options
|
|
@cindex x86-64 options
|
|
|
|
These are listed under @xref{i386 and x86-64 Options}.
|
|
|
|
@node Xstormy16 Options
|
|
@subsection Xstormy16 Options
|
|
@cindex Xstormy16 Options
|
|
|
|
These options are defined for Xstormy16:
|
|
|
|
@table @gcctabopt
|
|
@item -msim
|
|
@opindex msim
|
|
Choose startup files and linker script suitable for the simulator.
|
|
@end table
|
|
|
|
@node Xtensa Options
|
|
@subsection Xtensa Options
|
|
@cindex Xtensa Options
|
|
|
|
These options are supported for Xtensa targets:
|
|
|
|
@table @gcctabopt
|
|
@item -mconst16
|
|
@itemx -mno-const16
|
|
@opindex mconst16
|
|
@opindex mno-const16
|
|
Enable or disable use of @code{CONST16} instructions for loading
|
|
constant values. The @code{CONST16} instruction is currently not a
|
|
standard option from Tensilica. When enabled, @code{CONST16}
|
|
instructions are always used in place of the standard @code{L32R}
|
|
instructions. The use of @code{CONST16} is enabled by default only if
|
|
the @code{L32R} instruction is not available.
|
|
|
|
@item -mfused-madd
|
|
@itemx -mno-fused-madd
|
|
@opindex mfused-madd
|
|
@opindex mno-fused-madd
|
|
Enable or disable use of fused multiply/add and multiply/subtract
|
|
instructions in the floating-point option. This has no effect if the
|
|
floating-point option is not also enabled. Disabling fused multiply/add
|
|
and multiply/subtract instructions forces the compiler to use separate
|
|
instructions for the multiply and add/subtract operations. This may be
|
|
desirable in some cases where strict IEEE 754-compliant results are
|
|
required: the fused multiply add/subtract instructions do not round the
|
|
intermediate result, thereby producing results with @emph{more} bits of
|
|
precision than specified by the IEEE standard. Disabling fused multiply
|
|
add/subtract instructions also ensures that the program output is not
|
|
sensitive to the compiler's ability to combine multiply and add/subtract
|
|
operations.
|
|
|
|
@item -mtext-section-literals
|
|
@itemx -mno-text-section-literals
|
|
@opindex mtext-section-literals
|
|
@opindex mno-text-section-literals
|
|
Control the treatment of literal pools. The default is
|
|
@option{-mno-text-section-literals}, which places literals in a separate
|
|
section in the output file. This allows the literal pool to be placed
|
|
in a data RAM/ROM, and it also allows the linker to combine literal
|
|
pools from separate object files to remove redundant literals and
|
|
improve code size. With @option{-mtext-section-literals}, the literals
|
|
are interspersed in the text section in order to keep them as close as
|
|
possible to their references. This may be necessary for large assembly
|
|
files.
|
|
|
|
@item -mtarget-align
|
|
@itemx -mno-target-align
|
|
@opindex mtarget-align
|
|
@opindex mno-target-align
|
|
When this option is enabled, GCC instructs the assembler to
|
|
automatically align instructions to reduce branch penalties at the
|
|
expense of some code density. The assembler attempts to widen density
|
|
instructions to align branch targets and the instructions following call
|
|
instructions. If there are not enough preceding safe density
|
|
instructions to align a target, no widening will be performed. The
|
|
default is @option{-mtarget-align}. These options do not affect the
|
|
treatment of auto-aligned instructions like @code{LOOP}, which the
|
|
assembler will always align, either by widening density instructions or
|
|
by inserting no-op instructions.
|
|
|
|
@item -mlongcalls
|
|
@itemx -mno-longcalls
|
|
@opindex mlongcalls
|
|
@opindex mno-longcalls
|
|
When this option is enabled, GCC instructs the assembler to translate
|
|
direct calls to indirect calls unless it can determine that the target
|
|
of a direct call is in the range allowed by the call instruction. This
|
|
translation typically occurs for calls to functions in other source
|
|
files. Specifically, the assembler translates a direct @code{CALL}
|
|
instruction into an @code{L32R} followed by a @code{CALLX} instruction.
|
|
The default is @option{-mno-longcalls}. This option should be used in
|
|
programs where the call target can potentially be out of range. This
|
|
option is implemented in the assembler, not the compiler, so the
|
|
assembly code generated by GCC will still show direct call
|
|
instructions---look at the disassembled object code to see the actual
|
|
instructions. Note that the assembler will use an indirect call for
|
|
every cross-file call, not just those that really will be out of range.
|
|
@end table
|
|
|
|
@node zSeries Options
|
|
@subsection zSeries Options
|
|
@cindex zSeries options
|
|
|
|
These are listed under @xref{S/390 and zSeries Options}.
|
|
|
|
@node Code Gen Options
|
|
@section Options for Code Generation Conventions
|
|
@cindex code generation conventions
|
|
@cindex options, code generation
|
|
@cindex run-time options
|
|
|
|
These machine-independent options control the interface conventions
|
|
used in code generation.
|
|
|
|
Most of them have both positive and negative forms; the negative form
|
|
of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
|
|
one of the forms is listed---the one which is not the default. You
|
|
can figure out the other form by either removing @samp{no-} or adding
|
|
it.
|
|
|
|
@table @gcctabopt
|
|
@item -fbounds-check
|
|
@opindex fbounds-check
|
|
For front-ends that support it, generate additional code to check that
|
|
indices used to access arrays are within the declared range. This is
|
|
currently only supported by the Java and Fortran front-ends, where
|
|
this option defaults to true and false respectively.
|
|
|
|
@item -ftrapv
|
|
@opindex ftrapv
|
|
This option generates traps for signed overflow on addition, subtraction,
|
|
multiplication operations.
|
|
|
|
@item -fwrapv
|
|
@opindex fwrapv
|
|
This option instructs the compiler to assume that signed arithmetic
|
|
overflow of addition, subtraction and multiplication wraps around
|
|
using twos-complement representation. This flag enables some optimizations
|
|
and disables others. This option is enabled by default for the Java
|
|
front-end, as required by the Java language specification.
|
|
|
|
@item -fexceptions
|
|
@opindex fexceptions
|
|
Enable exception handling. Generates extra code needed to propagate
|
|
exceptions. For some targets, this implies GCC will generate frame
|
|
unwind information for all functions, which can produce significant data
|
|
size overhead, although it does not affect execution. If you do not
|
|
specify this option, GCC will enable it by default for languages like
|
|
C++ which normally require exception handling, and disable it for
|
|
languages like C that do not normally require it. However, you may need
|
|
to enable this option when compiling C code that needs to interoperate
|
|
properly with exception handlers written in C++. You may also wish to
|
|
disable this option if you are compiling older C++ programs that don't
|
|
use exception handling.
|
|
|
|
@item -fnon-call-exceptions
|
|
@opindex fnon-call-exceptions
|
|
Generate code that allows trapping instructions to throw exceptions.
|
|
Note that this requires platform-specific runtime support that does
|
|
not exist everywhere. Moreover, it only allows @emph{trapping}
|
|
instructions to throw exceptions, i.e.@: memory references or floating
|
|
point instructions. It does not allow exceptions to be thrown from
|
|
arbitrary signal handlers such as @code{SIGALRM}.
|
|
|
|
@item -funwind-tables
|
|
@opindex funwind-tables
|
|
Similar to @option{-fexceptions}, except that it will just generate any needed
|
|
static data, but will not affect the generated code in any other way.
|
|
You will normally not enable this option; instead, a language processor
|
|
that needs this handling would enable it on your behalf.
|
|
|
|
@item -fasynchronous-unwind-tables
|
|
@opindex fasynchronous-unwind-tables
|
|
Generate unwind table in dwarf2 format, if supported by target machine. The
|
|
table is exact at each instruction boundary, so it can be used for stack
|
|
unwinding from asynchronous events (such as debugger or garbage collector).
|
|
|
|
@item -fpcc-struct-return
|
|
@opindex fpcc-struct-return
|
|
Return ``short'' @code{struct} and @code{union} values in memory like
|
|
longer ones, rather than in registers. This convention is less
|
|
efficient, but it has the advantage of allowing intercallability between
|
|
GCC-compiled files and files compiled with other compilers, particularly
|
|
the Portable C Compiler (pcc).
|
|
|
|
The precise convention for returning structures in memory depends
|
|
on the target configuration macros.
|
|
|
|
Short structures and unions are those whose size and alignment match
|
|
that of some integer type.
|
|
|
|
@strong{Warning:} code compiled with the @option{-fpcc-struct-return}
|
|
switch is not binary compatible with code compiled with the
|
|
@option{-freg-struct-return} switch.
|
|
Use it to conform to a non-default application binary interface.
|
|
|
|
@item -freg-struct-return
|
|
@opindex freg-struct-return
|
|
Return @code{struct} and @code{union} values in registers when possible.
|
|
This is more efficient for small structures than
|
|
@option{-fpcc-struct-return}.
|
|
|
|
If you specify neither @option{-fpcc-struct-return} nor
|
|
@option{-freg-struct-return}, GCC defaults to whichever convention is
|
|
standard for the target. If there is no standard convention, GCC
|
|
defaults to @option{-fpcc-struct-return}, except on targets where GCC is
|
|
the principal compiler. In those cases, we can choose the standard, and
|
|
we chose the more efficient register return alternative.
|
|
|
|
@strong{Warning:} code compiled with the @option{-freg-struct-return}
|
|
switch is not binary compatible with code compiled with the
|
|
@option{-fpcc-struct-return} switch.
|
|
Use it to conform to a non-default application binary interface.
|
|
|
|
@item -fshort-enums
|
|
@opindex fshort-enums
|
|
Allocate to an @code{enum} type only as many bytes as it needs for the
|
|
declared range of possible values. Specifically, the @code{enum} type
|
|
will be equivalent to the smallest integer type which has enough room.
|
|
|
|
@strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
|
|
code that is not binary compatible with code generated without that switch.
|
|
Use it to conform to a non-default application binary interface.
|
|
|
|
@item -fshort-double
|
|
@opindex fshort-double
|
|
Use the same size for @code{double} as for @code{float}.
|
|
|
|
@strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
|
|
code that is not binary compatible with code generated without that switch.
|
|
Use it to conform to a non-default application binary interface.
|
|
|
|
@item -fshort-wchar
|
|
@opindex fshort-wchar
|
|
Override the underlying type for @samp{wchar_t} to be @samp{short
|
|
unsigned int} instead of the default for the target. This option is
|
|
useful for building programs to run under WINE@.
|
|
|
|
@strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
|
|
code that is not binary compatible with code generated without that switch.
|
|
Use it to conform to a non-default application binary interface.
|
|
|
|
@item -fno-common
|
|
@opindex fno-common
|
|
In C, allocate even uninitialized global variables in the data section of the
|
|
object file, rather than generating them as common blocks. This has the
|
|
effect that if the same variable is declared (without @code{extern}) in
|
|
two different compilations, you will get an error when you link them.
|
|
The only reason this might be useful is if you wish to verify that the
|
|
program will work on other systems which always work this way.
|
|
|
|
@item -fno-ident
|
|
@opindex fno-ident
|
|
Ignore the @samp{#ident} directive.
|
|
|
|
@item -finhibit-size-directive
|
|
@opindex finhibit-size-directive
|
|
Don't output a @code{.size} assembler directive, or anything else that
|
|
would cause trouble if the function is split in the middle, and the
|
|
two halves are placed at locations far apart in memory. This option is
|
|
used when compiling @file{crtstuff.c}; you should not need to use it
|
|
for anything else.
|
|
|
|
@item -fverbose-asm
|
|
@opindex fverbose-asm
|
|
Put extra commentary information in the generated assembly code to
|
|
make it more readable. This option is generally only of use to those
|
|
who actually need to read the generated assembly code (perhaps while
|
|
debugging the compiler itself).
|
|
|
|
@option{-fno-verbose-asm}, the default, causes the
|
|
extra information to be omitted and is useful when comparing two assembler
|
|
files.
|
|
|
|
@item -fpic
|
|
@opindex fpic
|
|
@cindex global offset table
|
|
@cindex PIC
|
|
Generate position-independent code (PIC) suitable for use in a shared
|
|
library, if supported for the target machine. Such code accesses all
|
|
constant addresses through a global offset table (GOT)@. The dynamic
|
|
loader resolves the GOT entries when the program starts (the dynamic
|
|
loader is not part of GCC; it is part of the operating system). If
|
|
the GOT size for the linked executable exceeds a machine-specific
|
|
maximum size, you get an error message from the linker indicating that
|
|
@option{-fpic} does not work; in that case, recompile with @option{-fPIC}
|
|
instead. (These maximums are 8k on the SPARC and 32k
|
|
on the m68k and RS/6000. The 386 has no such limit.)
|
|
|
|
Position-independent code requires special support, and therefore works
|
|
only on certain machines. For the 386, GCC supports PIC for System V
|
|
but not for the Sun 386i. Code generated for the IBM RS/6000 is always
|
|
position-independent.
|
|
|
|
When this flag is set, the macros @code{__pic__} and @code{__PIC__}
|
|
are defined to 1.
|
|
|
|
@item -fPIC
|
|
@opindex fPIC
|
|
If supported for the target machine, emit position-independent code,
|
|
suitable for dynamic linking and avoiding any limit on the size of the
|
|
global offset table. This option makes a difference on the m68k,
|
|
PowerPC and SPARC@.
|
|
|
|
Position-independent code requires special support, and therefore works
|
|
only on certain machines.
|
|
|
|
When this flag is set, the macros @code{__pic__} and @code{__PIC__}
|
|
are defined to 2.
|
|
|
|
@item -fpie
|
|
@itemx -fPIE
|
|
@opindex fpie
|
|
@opindex fPIE
|
|
These options are similar to @option{-fpic} and @option{-fPIC}, but
|
|
generated position independent code can be only linked into executables.
|
|
Usually these options are used when @option{-pie} GCC option will be
|
|
used during linking.
|
|
|
|
@item -fno-jump-tables
|
|
@opindex fno-jump-tables
|
|
Do not use jump tables for switch statements even where it would be
|
|
more efficient than other code generation strategies. This option is
|
|
of use in conjunction with @option{-fpic} or @option{-fPIC} for
|
|
building code which forms part of a dynamic linker and cannot
|
|
reference the address of a jump table. On some targets, jump tables
|
|
do not require a GOT and this option is not needed.
|
|
|
|
@item -ffixed-@var{reg}
|
|
@opindex ffixed
|
|
Treat the register named @var{reg} as a fixed register; generated code
|
|
should never refer to it (except perhaps as a stack pointer, frame
|
|
pointer or in some other fixed role).
|
|
|
|
@var{reg} must be the name of a register. The register names accepted
|
|
are machine-specific and are defined in the @code{REGISTER_NAMES}
|
|
macro in the machine description macro file.
|
|
|
|
This flag does not have a negative form, because it specifies a
|
|
three-way choice.
|
|
|
|
@item -fcall-used-@var{reg}
|
|
@opindex fcall-used
|
|
Treat the register named @var{reg} as an allocable register that is
|
|
clobbered by function calls. It may be allocated for temporaries or
|
|
variables that do not live across a call. Functions compiled this way
|
|
will not save and restore the register @var{reg}.
|
|
|
|
It is an error to used this flag with the frame pointer or stack pointer.
|
|
Use of this flag for other registers that have fixed pervasive roles in
|
|
the machine's execution model will produce disastrous results.
|
|
|
|
This flag does not have a negative form, because it specifies a
|
|
three-way choice.
|
|
|
|
@item -fcall-saved-@var{reg}
|
|
@opindex fcall-saved
|
|
Treat the register named @var{reg} as an allocable register saved by
|
|
functions. It may be allocated even for temporaries or variables that
|
|
live across a call. Functions compiled this way will save and restore
|
|
the register @var{reg} if they use it.
|
|
|
|
It is an error to used this flag with the frame pointer or stack pointer.
|
|
Use of this flag for other registers that have fixed pervasive roles in
|
|
the machine's execution model will produce disastrous results.
|
|
|
|
A different sort of disaster will result from the use of this flag for
|
|
a register in which function values may be returned.
|
|
|
|
This flag does not have a negative form, because it specifies a
|
|
three-way choice.
|
|
|
|
@item -fpack-struct[=@var{n}]
|
|
@opindex fpack-struct
|
|
Without a value specified, pack all structure members together without
|
|
holes. When a value is specified (which must be a small power of two), pack
|
|
structure members according to this value, representing the maximum
|
|
alignment (that is, objects with default alignment requirements larger than
|
|
this will be output potentially unaligned at the next fitting location.
|
|
|
|
@strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
|
|
code that is not binary compatible with code generated without that switch.
|
|
Additionally, it makes the code suboptimal.
|
|
Use it to conform to a non-default application binary interface.
|
|
|
|
@item -finstrument-functions
|
|
@opindex finstrument-functions
|
|
Generate instrumentation calls for entry and exit to functions. Just
|
|
after function entry and just before function exit, the following
|
|
profiling functions will be called with the address of the current
|
|
function and its call site. (On some platforms,
|
|
@code{__builtin_return_address} does not work beyond the current
|
|
function, so the call site information may not be available to the
|
|
profiling functions otherwise.)
|
|
|
|
@smallexample
|
|
void __cyg_profile_func_enter (void *this_fn,
|
|
void *call_site);
|
|
void __cyg_profile_func_exit (void *this_fn,
|
|
void *call_site);
|
|
@end smallexample
|
|
|
|
The first argument is the address of the start of the current function,
|
|
which may be looked up exactly in the symbol table.
|
|
|
|
This instrumentation is also done for functions expanded inline in other
|
|
functions. The profiling calls will indicate where, conceptually, the
|
|
inline function is entered and exited. This means that addressable
|
|
versions of such functions must be available. If all your uses of a
|
|
function are expanded inline, this may mean an additional expansion of
|
|
code size. If you use @samp{extern inline} in your C code, an
|
|
addressable version of such functions must be provided. (This is
|
|
normally the case anyways, but if you get lucky and the optimizer always
|
|
expands the functions inline, you might have gotten away without
|
|
providing static copies.)
|
|
|
|
A function may be given the attribute @code{no_instrument_function}, in
|
|
which case this instrumentation will not be done. This can be used, for
|
|
example, for the profiling functions listed above, high-priority
|
|
interrupt routines, and any functions from which the profiling functions
|
|
cannot safely be called (perhaps signal handlers, if the profiling
|
|
routines generate output or allocate memory).
|
|
|
|
@item -fstack-check
|
|
@opindex fstack-check
|
|
Generate code to verify that you do not go beyond the boundary of the
|
|
stack. You should specify this flag if you are running in an
|
|
environment with multiple threads, but only rarely need to specify it in
|
|
a single-threaded environment since stack overflow is automatically
|
|
detected on nearly all systems if there is only one stack.
|
|
|
|
Note that this switch does not actually cause checking to be done; the
|
|
operating system must do that. The switch causes generation of code
|
|
to ensure that the operating system sees the stack being extended.
|
|
|
|
@item -fstack-limit-register=@var{reg}
|
|
@itemx -fstack-limit-symbol=@var{sym}
|
|
@itemx -fno-stack-limit
|
|
@opindex fstack-limit-register
|
|
@opindex fstack-limit-symbol
|
|
@opindex fno-stack-limit
|
|
Generate code to ensure that the stack does not grow beyond a certain value,
|
|
either the value of a register or the address of a symbol. If the stack
|
|
would grow beyond the value, a signal is raised. For most targets,
|
|
the signal is raised before the stack overruns the boundary, so
|
|
it is possible to catch the signal without taking special precautions.
|
|
|
|
For instance, if the stack starts at absolute address @samp{0x80000000}
|
|
and grows downwards, you can use the flags
|
|
@option{-fstack-limit-symbol=__stack_limit} and
|
|
@option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
|
|
of 128KB@. Note that this may only work with the GNU linker.
|
|
|
|
@cindex aliasing of parameters
|
|
@cindex parameters, aliased
|
|
@item -fargument-alias
|
|
@itemx -fargument-noalias
|
|
@itemx -fargument-noalias-global
|
|
@itemx -fargument-noalias-anything
|
|
@opindex fargument-alias
|
|
@opindex fargument-noalias
|
|
@opindex fargument-noalias-global
|
|
@opindex fargument-noalias-anything
|
|
Specify the possible relationships among parameters and between
|
|
parameters and global data.
|
|
|
|
@option{-fargument-alias} specifies that arguments (parameters) may
|
|
alias each other and may alias global storage.@*
|
|
@option{-fargument-noalias} specifies that arguments do not alias
|
|
each other, but may alias global storage.@*
|
|
@option{-fargument-noalias-global} specifies that arguments do not
|
|
alias each other and do not alias global storage.
|
|
@option{-fargument-noalias-anything} specifies that arguments do not
|
|
alias any other storage.
|
|
|
|
Each language will automatically use whatever option is required by
|
|
the language standard. You should not need to use these options yourself.
|
|
|
|
@item -fleading-underscore
|
|
@opindex fleading-underscore
|
|
This option and its counterpart, @option{-fno-leading-underscore}, forcibly
|
|
change the way C symbols are represented in the object file. One use
|
|
is to help link with legacy assembly code.
|
|
|
|
@strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
|
|
generate code that is not binary compatible with code generated without that
|
|
switch. Use it to conform to a non-default application binary interface.
|
|
Not all targets provide complete support for this switch.
|
|
|
|
@item -ftls-model=@var{model}
|
|
Alter the thread-local storage model to be used (@pxref{Thread-Local}).
|
|
The @var{model} argument should be one of @code{global-dynamic},
|
|
@code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
|
|
|
|
The default without @option{-fpic} is @code{initial-exec}; with
|
|
@option{-fpic} the default is @code{global-dynamic}.
|
|
|
|
@item -fvisibility=@var{default|internal|hidden|protected}
|
|
@opindex fvisibility
|
|
Set the default ELF image symbol visibility to the specified option---all
|
|
symbols will be marked with this unless overridden within the code.
|
|
Using this feature can very substantially improve linking and
|
|
load times of shared object libraries, produce more optimized
|
|
code, provide near-perfect API export and prevent symbol clashes.
|
|
It is @strong{strongly} recommended that you use this in any shared objects
|
|
you distribute.
|
|
|
|
Despite the nomenclature, @code{default} always means public ie;
|
|
available to be linked against from outside the shared object.
|
|
@code{protected} and @code{internal} are pretty useless in real-world
|
|
usage so the only other commonly used option will be @code{hidden}.
|
|
The default if @option{-fvisibility} isn't specified is
|
|
@code{default}, i.e., make every
|
|
symbol public---this causes the same behavior as previous versions of
|
|
GCC@.
|
|
|
|
A good explanation of the benefits offered by ensuring ELF
|
|
symbols have the correct visibility is given by ``How To Write
|
|
Shared Libraries'' by Ulrich Drepper (which can be found at
|
|
@w{@uref{http://people.redhat.com/~drepper/}})---however a superior
|
|
solution made possible by this option to marking things hidden when
|
|
the default is public is to make the default hidden and mark things
|
|
public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
|
|
and @code{__attribute__ ((visibility("default")))} instead of
|
|
@code{__declspec(dllexport)} you get almost identical semantics with
|
|
identical syntax. This is a great boon to those working with
|
|
cross-platform projects.
|
|
|
|
For those adding visibility support to existing code, you may find
|
|
@samp{#pragma GCC visibility} of use. This works by you enclosing
|
|
the declarations you wish to set visibility for with (for example)
|
|
@samp{#pragma GCC visibility push(hidden)} and
|
|
@samp{#pragma GCC visibility pop}.
|
|
Bear in mind that symbol visibility should be viewed @strong{as
|
|
part of the API interface contract} and thus all new code should
|
|
always specify visibility when it is not the default ie; declarations
|
|
only for use within the local DSO should @strong{always} be marked explicitly
|
|
as hidden as so to avoid PLT indirection overheads---making this
|
|
abundantly clear also aids readability and self-documentation of the code.
|
|
Note that due to ISO C++ specification requirements, operator new and
|
|
operator delete must always be of default visibility.
|
|
|
|
Be aware that headers from outside your project, in particular system
|
|
headers and headers from any other library you use, may not be
|
|
expecting to be compiled with visibility other than the default. You
|
|
may need to explicitly say @samp{#pragma GCC visibility push(default)}
|
|
before including any such headers.
|
|
|
|
@samp{extern} declarations are not affected by @samp{-fvisibility}, so
|
|
a lot of code can be recompiled with @samp{-fvisibility=hidden} with
|
|
no modifications. However, this means that calls to @samp{extern}
|
|
functions with no explicit visibility will use the PLT, so it is more
|
|
effective to use @samp{__attribute ((visibility))} and/or
|
|
@samp{#pragma GCC visibility} to tell the compiler which @samp{extern}
|
|
declarations should be treated as hidden.
|
|
|
|
Note that @samp{-fvisibility} does affect C++ vague linkage
|
|
entities. This means that, for instance, an exception class that will
|
|
be thrown between DSOs must be explicitly marked with default
|
|
visibility so that the @samp{type_info} nodes will be unified between
|
|
the DSOs.
|
|
|
|
An overview of these techniques, their benefits and how to use them
|
|
is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
|
|
|
|
@end table
|
|
|
|
@c man end
|
|
|
|
@node Environment Variables
|
|
@section Environment Variables Affecting GCC
|
|
@cindex environment variables
|
|
|
|
@c man begin ENVIRONMENT
|
|
This section describes several environment variables that affect how GCC
|
|
operates. Some of them work by specifying directories or prefixes to use
|
|
when searching for various kinds of files. Some are used to specify other
|
|
aspects of the compilation environment.
|
|
|
|
Note that you can also specify places to search using options such as
|
|
@option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
|
|
take precedence over places specified using environment variables, which
|
|
in turn take precedence over those specified by the configuration of GCC@.
|
|
@xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
|
|
GNU Compiler Collection (GCC) Internals}.
|
|
|
|
@table @env
|
|
@item LANG
|
|
@itemx LC_CTYPE
|
|
@c @itemx LC_COLLATE
|
|
@itemx LC_MESSAGES
|
|
@c @itemx LC_MONETARY
|
|
@c @itemx LC_NUMERIC
|
|
@c @itemx LC_TIME
|
|
@itemx LC_ALL
|
|
@findex LANG
|
|
@findex LC_CTYPE
|
|
@c @findex LC_COLLATE
|
|
@findex LC_MESSAGES
|
|
@c @findex LC_MONETARY
|
|
@c @findex LC_NUMERIC
|
|
@c @findex LC_TIME
|
|
@findex LC_ALL
|
|
@cindex locale
|
|
These environment variables control the way that GCC uses
|
|
localization information that allow GCC to work with different
|
|
national conventions. GCC inspects the locale categories
|
|
@env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
|
|
so. These locale categories can be set to any value supported by your
|
|
installation. A typical value is @samp{en_GB.UTF-8} for English in the United
|
|
Kingdom encoded in UTF-8.
|
|
|
|
The @env{LC_CTYPE} environment variable specifies character
|
|
classification. GCC uses it to determine the character boundaries in
|
|
a string; this is needed for some multibyte encodings that contain quote
|
|
and escape characters that would otherwise be interpreted as a string
|
|
end or escape.
|
|
|
|
The @env{LC_MESSAGES} environment variable specifies the language to
|
|
use in diagnostic messages.
|
|
|
|
If the @env{LC_ALL} environment variable is set, it overrides the value
|
|
of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
|
|
and @env{LC_MESSAGES} default to the value of the @env{LANG}
|
|
environment variable. If none of these variables are set, GCC
|
|
defaults to traditional C English behavior.
|
|
|
|
@item TMPDIR
|
|
@findex TMPDIR
|
|
If @env{TMPDIR} is set, it specifies the directory to use for temporary
|
|
files. GCC uses temporary files to hold the output of one stage of
|
|
compilation which is to be used as input to the next stage: for example,
|
|
the output of the preprocessor, which is the input to the compiler
|
|
proper.
|
|
|
|
@item GCC_EXEC_PREFIX
|
|
@findex GCC_EXEC_PREFIX
|
|
If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
|
|
names of the subprograms executed by the compiler. No slash is added
|
|
when this prefix is combined with the name of a subprogram, but you can
|
|
specify a prefix that ends with a slash if you wish.
|
|
|
|
If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
|
|
an appropriate prefix to use based on the pathname it was invoked with.
|
|
|
|
If GCC cannot find the subprogram using the specified prefix, it
|
|
tries looking in the usual places for the subprogram.
|
|
|
|
The default value of @env{GCC_EXEC_PREFIX} is
|
|
@file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
|
|
of @code{prefix} when you ran the @file{configure} script.
|
|
|
|
Other prefixes specified with @option{-B} take precedence over this prefix.
|
|
|
|
This prefix is also used for finding files such as @file{crt0.o} that are
|
|
used for linking.
|
|
|
|
In addition, the prefix is used in an unusual way in finding the
|
|
directories to search for header files. For each of the standard
|
|
directories whose name normally begins with @samp{/usr/local/lib/gcc}
|
|
(more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
|
|
replacing that beginning with the specified prefix to produce an
|
|
alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
|
|
@file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
|
|
These alternate directories are searched first; the standard directories
|
|
come next.
|
|
|
|
@item COMPILER_PATH
|
|
@findex COMPILER_PATH
|
|
The value of @env{COMPILER_PATH} is a colon-separated list of
|
|
directories, much like @env{PATH}. GCC tries the directories thus
|
|
specified when searching for subprograms, if it can't find the
|
|
subprograms using @env{GCC_EXEC_PREFIX}.
|
|
|
|
@item LIBRARY_PATH
|
|
@findex LIBRARY_PATH
|
|
The value of @env{LIBRARY_PATH} is a colon-separated list of
|
|
directories, much like @env{PATH}. When configured as a native compiler,
|
|
GCC tries the directories thus specified when searching for special
|
|
linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
|
|
using GCC also uses these directories when searching for ordinary
|
|
libraries for the @option{-l} option (but directories specified with
|
|
@option{-L} come first).
|
|
|
|
@item LANG
|
|
@findex LANG
|
|
@cindex locale definition
|
|
This variable is used to pass locale information to the compiler. One way in
|
|
which this information is used is to determine the character set to be used
|
|
when character literals, string literals and comments are parsed in C and C++.
|
|
When the compiler is configured to allow multibyte characters,
|
|
the following values for @env{LANG} are recognized:
|
|
|
|
@table @samp
|
|
@item C-JIS
|
|
Recognize JIS characters.
|
|
@item C-SJIS
|
|
Recognize SJIS characters.
|
|
@item C-EUCJP
|
|
Recognize EUCJP characters.
|
|
@end table
|
|
|
|
If @env{LANG} is not defined, or if it has some other value, then the
|
|
compiler will use mblen and mbtowc as defined by the default locale to
|
|
recognize and translate multibyte characters.
|
|
@end table
|
|
|
|
@noindent
|
|
Some additional environments variables affect the behavior of the
|
|
preprocessor.
|
|
|
|
@include cppenv.texi
|
|
|
|
@c man end
|
|
|
|
@node Precompiled Headers
|
|
@section Using Precompiled Headers
|
|
@cindex precompiled headers
|
|
@cindex speed of compilation
|
|
|
|
Often large projects have many header files that are included in every
|
|
source file. The time the compiler takes to process these header files
|
|
over and over again can account for nearly all of the time required to
|
|
build the project. To make builds faster, GCC allows users to
|
|
`precompile' a header file; then, if builds can use the precompiled
|
|
header file they will be much faster.
|
|
|
|
To create a precompiled header file, simply compile it as you would any
|
|
other file, if necessary using the @option{-x} option to make the driver
|
|
treat it as a C or C++ header file. You will probably want to use a
|
|
tool like @command{make} to keep the precompiled header up-to-date when
|
|
the headers it contains change.
|
|
|
|
A precompiled header file will be searched for when @code{#include} is
|
|
seen in the compilation. As it searches for the included file
|
|
(@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
|
|
compiler looks for a precompiled header in each directory just before it
|
|
looks for the include file in that directory. The name searched for is
|
|
the name specified in the @code{#include} with @samp{.gch} appended. If
|
|
the precompiled header file can't be used, it is ignored.
|
|
|
|
For instance, if you have @code{#include "all.h"}, and you have
|
|
@file{all.h.gch} in the same directory as @file{all.h}, then the
|
|
precompiled header file will be used if possible, and the original
|
|
header will be used otherwise.
|
|
|
|
Alternatively, you might decide to put the precompiled header file in a
|
|
directory and use @option{-I} to ensure that directory is searched
|
|
before (or instead of) the directory containing the original header.
|
|
Then, if you want to check that the precompiled header file is always
|
|
used, you can put a file of the same name as the original header in this
|
|
directory containing an @code{#error} command.
|
|
|
|
This also works with @option{-include}. So yet another way to use
|
|
precompiled headers, good for projects not designed with precompiled
|
|
header files in mind, is to simply take most of the header files used by
|
|
a project, include them from another header file, precompile that header
|
|
file, and @option{-include} the precompiled header. If the header files
|
|
have guards against multiple inclusion, they will be skipped because
|
|
they've already been included (in the precompiled header).
|
|
|
|
If you need to precompile the same header file for different
|
|
languages, targets, or compiler options, you can instead make a
|
|
@emph{directory} named like @file{all.h.gch}, and put each precompiled
|
|
header in the directory, perhaps using @option{-o}. It doesn't matter
|
|
what you call the files in the directory, every precompiled header in
|
|
the directory will be considered. The first precompiled header
|
|
encountered in the directory that is valid for this compilation will
|
|
be used; they're searched in no particular order.
|
|
|
|
There are many other possibilities, limited only by your imagination,
|
|
good sense, and the constraints of your build system.
|
|
|
|
A precompiled header file can be used only when these conditions apply:
|
|
|
|
@itemize
|
|
@item
|
|
Only one precompiled header can be used in a particular compilation.
|
|
|
|
@item
|
|
A precompiled header can't be used once the first C token is seen. You
|
|
can have preprocessor directives before a precompiled header; you can
|
|
even include a precompiled header from inside another header, so long as
|
|
there are no C tokens before the @code{#include}.
|
|
|
|
@item
|
|
The precompiled header file must be produced for the same language as
|
|
the current compilation. You can't use a C precompiled header for a C++
|
|
compilation.
|
|
|
|
@item
|
|
The precompiled header file must have been produced by the same compiler
|
|
binary as the current compilation is using.
|
|
|
|
@item
|
|
Any macros defined before the precompiled header is included must
|
|
either be defined in the same way as when the precompiled header was
|
|
generated, or must not affect the precompiled header, which usually
|
|
means that they don't appear in the precompiled header at all.
|
|
|
|
The @option{-D} option is one way to define a macro before a
|
|
precompiled header is included; using a @code{#define} can also do it.
|
|
There are also some options that define macros implicitly, like
|
|
@option{-O} and @option{-Wdeprecated}; the same rule applies to macros
|
|
defined this way.
|
|
|
|
@item If debugging information is output when using the precompiled
|
|
header, using @option{-g} or similar, the same kind of debugging information
|
|
must have been output when building the precompiled header. However,
|
|
a precompiled header built using @option{-g} can be used in a compilation
|
|
when no debugging information is being output.
|
|
|
|
@item The same @option{-m} options must generally be used when building
|
|
and using the precompiled header. @xref{Submodel Options},
|
|
for any cases where this rule is relaxed.
|
|
|
|
@item Each of the following options must be the same when building and using
|
|
the precompiled header:
|
|
|
|
@gccoptlist{-fexceptions -funit-at-a-time}
|
|
|
|
@item
|
|
Some other command-line options starting with @option{-f},
|
|
@option{-p}, or @option{-O} must be defined in the same way as when
|
|
the precompiled header was generated. At present, it's not clear
|
|
which options are safe to change and which are not; the safest choice
|
|
is to use exactly the same options when generating and using the
|
|
precompiled header. The following are known to be safe:
|
|
|
|
@gccoptlist{-fmessage-length= -fpreprocessed
|
|
-fsched-interblock -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous
|
|
-fsched-verbose=<number> -fschedule-insns -fvisibility=
|
|
-pedantic-errors}
|
|
|
|
@end itemize
|
|
|
|
For all of these except the last, the compiler will automatically
|
|
ignore the precompiled header if the conditions aren't met. If you
|
|
find an option combination that doesn't work and doesn't cause the
|
|
precompiled header to be ignored, please consider filing a bug report,
|
|
see @ref{Bugs}.
|
|
|
|
If you do use differing options when generating and using the
|
|
precompiled header, the actual behavior will be a mixture of the
|
|
behavior for the options. For instance, if you use @option{-g} to
|
|
generate the precompiled header but not when using it, you may or may
|
|
not get debugging information for routines in the precompiled header.
|
|
|
|
@node Running Protoize
|
|
@section Running Protoize
|
|
|
|
The program @code{protoize} is an optional part of GCC@. You can use
|
|
it to add prototypes to a program, thus converting the program to ISO
|
|
C in one respect. The companion program @code{unprotoize} does the
|
|
reverse: it removes argument types from any prototypes that are found.
|
|
|
|
When you run these programs, you must specify a set of source files as
|
|
command line arguments. The conversion programs start out by compiling
|
|
these files to see what functions they define. The information gathered
|
|
about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
|
|
|
|
After scanning comes actual conversion. The specified files are all
|
|
eligible to be converted; any files they include (whether sources or
|
|
just headers) are eligible as well.
|
|
|
|
But not all the eligible files are converted. By default,
|
|
@code{protoize} and @code{unprotoize} convert only source and header
|
|
files in the current directory. You can specify additional directories
|
|
whose files should be converted with the @option{-d @var{directory}}
|
|
option. You can also specify particular files to exclude with the
|
|
@option{-x @var{file}} option. A file is converted if it is eligible, its
|
|
directory name matches one of the specified directory names, and its
|
|
name within the directory has not been excluded.
|
|
|
|
Basic conversion with @code{protoize} consists of rewriting most
|
|
function definitions and function declarations to specify the types of
|
|
the arguments. The only ones not rewritten are those for varargs
|
|
functions.
|
|
|
|
@code{protoize} optionally inserts prototype declarations at the
|
|
beginning of the source file, to make them available for any calls that
|
|
precede the function's definition. Or it can insert prototype
|
|
declarations with block scope in the blocks where undeclared functions
|
|
are called.
|
|
|
|
Basic conversion with @code{unprotoize} consists of rewriting most
|
|
function declarations to remove any argument types, and rewriting
|
|
function definitions to the old-style pre-ISO form.
|
|
|
|
Both conversion programs print a warning for any function declaration or
|
|
definition that they can't convert. You can suppress these warnings
|
|
with @option{-q}.
|
|
|
|
The output from @code{protoize} or @code{unprotoize} replaces the
|
|
original source file. The original file is renamed to a name ending
|
|
with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
|
|
without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
|
|
for DOS) file already exists, then the source file is simply discarded.
|
|
|
|
@code{protoize} and @code{unprotoize} both depend on GCC itself to
|
|
scan the program and collect information about the functions it uses.
|
|
So neither of these programs will work until GCC is installed.
|
|
|
|
Here is a table of the options you can use with @code{protoize} and
|
|
@code{unprotoize}. Each option works with both programs unless
|
|
otherwise stated.
|
|
|
|
@table @code
|
|
@item -B @var{directory}
|
|
Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
|
|
usual directory (normally @file{/usr/local/lib}). This file contains
|
|
prototype information about standard system functions. This option
|
|
applies only to @code{protoize}.
|
|
|
|
@item -c @var{compilation-options}
|
|
Use @var{compilation-options} as the options when running @command{gcc} to
|
|
produce the @samp{.X} files. The special option @option{-aux-info} is
|
|
always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
|
|
|
|
Note that the compilation options must be given as a single argument to
|
|
@code{protoize} or @code{unprotoize}. If you want to specify several
|
|
@command{gcc} options, you must quote the entire set of compilation options
|
|
to make them a single word in the shell.
|
|
|
|
There are certain @command{gcc} arguments that you cannot use, because they
|
|
would produce the wrong kind of output. These include @option{-g},
|
|
@option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
|
|
the @var{compilation-options}, they are ignored.
|
|
|
|
@item -C
|
|
Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
|
|
systems) instead of @samp{.c}. This is convenient if you are converting
|
|
a C program to C++. This option applies only to @code{protoize}.
|
|
|
|
@item -g
|
|
Add explicit global declarations. This means inserting explicit
|
|
declarations at the beginning of each source file for each function
|
|
that is called in the file and was not declared. These declarations
|
|
precede the first function definition that contains a call to an
|
|
undeclared function. This option applies only to @code{protoize}.
|
|
|
|
@item -i @var{string}
|
|
Indent old-style parameter declarations with the string @var{string}.
|
|
This option applies only to @code{protoize}.
|
|
|
|
@code{unprotoize} converts prototyped function definitions to old-style
|
|
function definitions, where the arguments are declared between the
|
|
argument list and the initial @samp{@{}. By default, @code{unprotoize}
|
|
uses five spaces as the indentation. If you want to indent with just
|
|
one space instead, use @option{-i " "}.
|
|
|
|
@item -k
|
|
Keep the @samp{.X} files. Normally, they are deleted after conversion
|
|
is finished.
|
|
|
|
@item -l
|
|
Add explicit local declarations. @code{protoize} with @option{-l} inserts
|
|
a prototype declaration for each function in each block which calls the
|
|
function without any declaration. This option applies only to
|
|
@code{protoize}.
|
|
|
|
@item -n
|
|
Make no real changes. This mode just prints information about the conversions
|
|
that would have been done without @option{-n}.
|
|
|
|
@item -N
|
|
Make no @samp{.save} files. The original files are simply deleted.
|
|
Use this option with caution.
|
|
|
|
@item -p @var{program}
|
|
Use the program @var{program} as the compiler. Normally, the name
|
|
@file{gcc} is used.
|
|
|
|
@item -q
|
|
Work quietly. Most warnings are suppressed.
|
|
|
|
@item -v
|
|
Print the version number, just like @option{-v} for @command{gcc}.
|
|
@end table
|
|
|
|
If you need special compiler options to compile one of your program's
|
|
source files, then you should generate that file's @samp{.X} file
|
|
specially, by running @command{gcc} on that source file with the
|
|
appropriate options and the option @option{-aux-info}. Then run
|
|
@code{protoize} on the entire set of files. @code{protoize} will use
|
|
the existing @samp{.X} file because it is newer than the source file.
|
|
For example:
|
|
|
|
@smallexample
|
|
gcc -Dfoo=bar file1.c -aux-info file1.X
|
|
protoize *.c
|
|
@end smallexample
|
|
|
|
@noindent
|
|
You need to include the special files along with the rest in the
|
|
@code{protoize} command, even though their @samp{.X} files already
|
|
exist, because otherwise they won't get converted.
|
|
|
|
@xref{Protoize Caveats}, for more information on how to use
|
|
@code{protoize} successfully.
|