215 lines
8.6 KiB
Plaintext
215 lines
8.6 KiB
Plaintext
@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
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@c 1999, 2000, 2001, 2003 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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@node Fragments
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@chapter Makefile Fragments
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@cindex makefile fragment
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When you configure GCC using the @file{configure} script, it will
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construct the file @file{Makefile} from the template file
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@file{Makefile.in}. When it does this, it can incorporate makefile
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fragments from the @file{config} directory. These are used to set
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Makefile parameters that are not amenable to being calculated by
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autoconf. The list of fragments to incorporate is set by
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@file{config.gcc} (and occasionally @file{config.build}
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and @file{config.host}); @xref{System Config}.
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Fragments are named either @file{t-@var{target}} or @file{x-@var{host}},
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depending on whether they are relevant to configuring GCC to produce
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code for a particular target, or to configuring GCC to run on a
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particular host. Here @var{target} and @var{host} are mnemonics
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which usually have some relationship to the canonical system name, but
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no formal connection.
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If these files do not exist, it means nothing needs to be added for a
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given target or host. Most targets need a few @file{t-@var{target}}
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fragments, but needing @file{x-@var{host}} fragments is rare.
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@menu
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* Target Fragment:: Writing @file{t-@var{target}} files.
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* Host Fragment:: Writing @file{x-@var{host}} files.
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@end menu
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@node Target Fragment
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@section Target Makefile Fragments
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@cindex target makefile fragment
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@cindex @file{t-@var{target}}
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Target makefile fragments can set these Makefile variables.
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@table @code
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@findex LIBGCC2_CFLAGS
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@item LIBGCC2_CFLAGS
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Compiler flags to use when compiling @file{libgcc2.c}.
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@findex LIB2FUNCS_EXTRA
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@item LIB2FUNCS_EXTRA
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A list of source file names to be compiled or assembled and inserted
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into @file{libgcc.a}.
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@findex Floating Point Emulation
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@item Floating Point Emulation
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To have GCC include software floating point libraries in @file{libgcc.a}
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define @code{FPBIT} and @code{DPBIT} along with a few rules as follows:
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@smallexample
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# We want fine grained libraries, so use the new code
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# to build the floating point emulation libraries.
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FPBIT = fp-bit.c
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DPBIT = dp-bit.c
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fp-bit.c: $(srcdir)/config/fp-bit.c
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echo '#define FLOAT' > fp-bit.c
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cat $(srcdir)/config/fp-bit.c >> fp-bit.c
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dp-bit.c: $(srcdir)/config/fp-bit.c
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cat $(srcdir)/config/fp-bit.c > dp-bit.c
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@end smallexample
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You may need to provide additional #defines at the beginning of @file{fp-bit.c}
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and @file{dp-bit.c} to control target endianness and other options.
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@findex CRTSTUFF_T_CFLAGS
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@item CRTSTUFF_T_CFLAGS
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Special flags used when compiling @file{crtstuff.c}.
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@xref{Initialization}.
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@findex CRTSTUFF_T_CFLAGS_S
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@item CRTSTUFF_T_CFLAGS_S
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Special flags used when compiling @file{crtstuff.c} for shared
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linking. Used if you use @file{crtbeginS.o} and @file{crtendS.o}
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in @code{EXTRA-PARTS}.
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@xref{Initialization}.
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@findex MULTILIB_OPTIONS
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@item MULTILIB_OPTIONS
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For some targets, invoking GCC in different ways produces objects
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that can not be linked together. For example, for some targets GCC
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produces both big and little endian code. For these targets, you must
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arrange for multiple versions of @file{libgcc.a} to be compiled, one for
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each set of incompatible options. When GCC invokes the linker, it
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arranges to link in the right version of @file{libgcc.a}, based on
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the command line options used.
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The @code{MULTILIB_OPTIONS} macro lists the set of options for which
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special versions of @file{libgcc.a} must be built. Write options that
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are mutually incompatible side by side, separated by a slash. Write
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options that may be used together separated by a space. The build
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procedure will build all combinations of compatible options.
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For example, if you set @code{MULTILIB_OPTIONS} to @samp{m68000/m68020
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msoft-float}, @file{Makefile} will build special versions of
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@file{libgcc.a} using the following sets of options: @option{-m68000},
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@option{-m68020}, @option{-msoft-float}, @samp{-m68000 -msoft-float}, and
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@samp{-m68020 -msoft-float}.
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@findex MULTILIB_DIRNAMES
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@item MULTILIB_DIRNAMES
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If @code{MULTILIB_OPTIONS} is used, this variable specifies the
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directory names that should be used to hold the various libraries.
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Write one element in @code{MULTILIB_DIRNAMES} for each element in
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@code{MULTILIB_OPTIONS}. If @code{MULTILIB_DIRNAMES} is not used, the
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default value will be @code{MULTILIB_OPTIONS}, with all slashes treated
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as spaces.
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For example, if @code{MULTILIB_OPTIONS} is set to @samp{m68000/m68020
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msoft-float}, then the default value of @code{MULTILIB_DIRNAMES} is
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@samp{m68000 m68020 msoft-float}. You may specify a different value if
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you desire a different set of directory names.
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@findex MULTILIB_MATCHES
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@item MULTILIB_MATCHES
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Sometimes the same option may be written in two different ways. If an
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option is listed in @code{MULTILIB_OPTIONS}, GCC needs to know about
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any synonyms. In that case, set @code{MULTILIB_MATCHES} to a list of
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items of the form @samp{option=option} to describe all relevant
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synonyms. For example, @samp{m68000=mc68000 m68020=mc68020}.
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@findex MULTILIB_EXCEPTIONS
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@item MULTILIB_EXCEPTIONS
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Sometimes when there are multiple sets of @code{MULTILIB_OPTIONS} being
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specified, there are combinations that should not be built. In that
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case, set @code{MULTILIB_EXCEPTIONS} to be all of the switch exceptions
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in shell case syntax that should not be built.
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For example the ARM processor cannot execute both hardware floating
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point instructions and the reduced size THUMB instructions at the same
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time, so there is no need to build libraries with both of these
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options enabled. Therefore @code{MULTILIB_EXCEPTIONS} is set to:
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@smallexample
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*mthumb/*mhard-float*
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@end smallexample
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@findex MULTILIB_EXTRA_OPTS
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@item MULTILIB_EXTRA_OPTS
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Sometimes it is desirable that when building multiple versions of
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@file{libgcc.a} certain options should always be passed on to the
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compiler. In that case, set @code{MULTILIB_EXTRA_OPTS} to be the list
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of options to be used for all builds. If you set this, you should
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probably set @code{CRTSTUFF_T_CFLAGS} to a dash followed by it.
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@findex NATIVE_SYSTEM_HEADER_DIR
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@item NATIVE_SYSTEM_HEADER_DIR
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If the default location for system headers is not @file{/usr/include},
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you must set this to the directory containing the headers. This value
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should match the value of the @code{SYSTEM_INCLUDE_DIR} macro.
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@findex SPECS
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@item SPECS
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Unfortunately, setting @code{MULTILIB_EXTRA_OPTS} is not enough, since
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it does not affect the build of target libraries, at least not the
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build of the default multilib. One possible work-around is to use
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@code{DRIVER_SELF_SPECS} to bring options from the @file{specs} file
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as if they had been passed in the compiler driver command line.
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However, you don't want to be adding these options after the toolchain
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is installed, so you can instead tweak the @file{specs} file that will
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be used during the toolchain build, while you still install the
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original, built-in @file{specs}. The trick is to set @code{SPECS} to
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some other filename (say @file{specs.install}), that will then be
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created out of the built-in specs, and introduce a @file{Makefile}
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rule to generate the @file{specs} file that's going to be used at
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build time out of your @file{specs.install}.
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@end table
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@node Host Fragment
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@section Host Makefile Fragments
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@cindex host makefile fragment
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@cindex @file{x-@var{host}}
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The use of @file{x-@var{host}} fragments is discouraged. You should do
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so only if there is no other mechanism to get the behavior desired.
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Host fragments should never forcibly override variables set by the
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configure script, as they may have been adjusted by the user.
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Variables provided for host fragments to set include:
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@table @code
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@item X_CFLAGS
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@itemx X_CPPFLAGS
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These are extra flags to pass to the C compiler and preprocessor,
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respectively. They are used both when building GCC, and when compiling
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things with the just-built GCC@.
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@item XCFLAGS
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These are extra flags to use when building the compiler. They are not
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used when compiling @file{libgcc.a}. However, they @emph{are} used when
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recompiling the compiler with itself in later stages of a bootstrap.
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@item BOOT_LDFLAGS
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Flags to be passed to the linker when recompiling the compiler with
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itself in later stages of a bootstrap. You might need to use this if,
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for instance, one of the front ends needs more text space than the
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linker provides by default.
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@item EXTRA_PROGRAMS
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A list of additional programs required to use the compiler on this host,
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which should be compiled with GCC and installed alongside the front
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ends. If you set this variable, you must also provide rules to build
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the extra programs.
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@end table
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