157 lines
6.6 KiB
Plaintext
157 lines
6.6 KiB
Plaintext
@c Copyright (C) 2002, 2004 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 Compatibility
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@chapter Binary Compatibility
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@cindex binary compatibility
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@cindex ABI
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@cindex application binary interface
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Binary compatibility encompasses several related concepts:
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@table @dfn
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@item application binary interface (ABI)
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The set of runtime conventions followed by all of the tools that deal
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with binary representations of a program, including compilers, assemblers,
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linkers, and language runtime support.
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Some ABIs are formal with a written specification, possibly designed
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by multiple interested parties. Others are simply the way things are
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actually done by a particular set of tools.
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@item ABI conformance
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A compiler conforms to an ABI if it generates code that follows all of
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the specifications enumerated by that ABI@.
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A library conforms to an ABI if it is implemented according to that ABI@.
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An application conforms to an ABI if it is built using tools that conform
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to that ABI and does not contain source code that specifically changes
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behavior specified by the ABI@.
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@item calling conventions
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Calling conventions are a subset of an ABI that specify of how arguments
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are passed and function results are returned.
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@item interoperability
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Different sets of tools are interoperable if they generate files that
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can be used in the same program. The set of tools includes compilers,
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assemblers, linkers, libraries, header files, startup files, and debuggers.
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Binaries produced by different sets of tools are not interoperable unless
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they implement the same ABI@. This applies to different versions of the
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same tools as well as tools from different vendors.
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@item intercallability
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Whether a function in a binary built by one set of tools can call a
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function in a binary built by a different set of tools is a subset
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of interoperability.
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@item implementation-defined features
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Language standards include lists of implementation-defined features whose
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behavior can vary from one implementation to another. Some of these
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features are normally covered by a platform's ABI and others are not.
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The features that are not covered by an ABI generally affect how a
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program behaves, but not intercallability.
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@item compatibility
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Conformance to the same ABI and the same behavior of implementation-defined
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features are both relevant for compatibility.
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@end table
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The application binary interface implemented by a C or C++ compiler
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affects code generation and runtime support for:
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@itemize @bullet
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@item
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size and alignment of data types
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@item
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layout of structured types
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@item
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calling conventions
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@item
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register usage conventions
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@item
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interfaces for runtime arithmetic support
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@item
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object file formats
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@end itemize
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In addition, the application binary interface implemented by a C++ compiler
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affects code generation and runtime support for:
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@itemize @bullet
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@item
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name mangling
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@item
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exception handling
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@item
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invoking constructors and destructors
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@item
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layout, alignment, and padding of classes
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@item
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layout and alignment of virtual tables
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@end itemize
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Some GCC compilation options cause the compiler to generate code that
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does not conform to the platform's default ABI@. Other options cause
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different program behavior for implementation-defined features that are
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not covered by an ABI@. These options are provided for consistency with
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other compilers that do not follow the platform's default ABI or the
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usual behavior of implementation-defined features for the platform.
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Be very careful about using such options.
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Most platforms have a well-defined ABI that covers C code, but ABIs
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that cover C++ functionality are not yet common.
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Starting with GCC 3.2, GCC binary conventions for C++ are based on a
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written, vendor-neutral C++ ABI that was designed to be specific to
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64-bit Itanium but also includes generic specifications that apply to
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any platform.
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This C++ ABI is also implemented by other compiler vendors on some
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platforms, notably GNU/Linux and BSD systems.
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We have tried hard to provide a stable ABI that will be compatible with
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future GCC releases, but it is possible that we will encounter problems
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that make this difficult. Such problems could include different
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interpretations of the C++ ABI by different vendors, bugs in the ABI, or
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bugs in the implementation of the ABI in different compilers.
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GCC's @option{-Wabi} switch warns when G++ generates code that is
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probably not compatible with the C++ ABI@.
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The C++ library used with a C++ compiler includes the Standard C++
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Library, with functionality defined in the C++ Standard, plus language
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runtime support. The runtime support is included in a C++ ABI, but there
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is no formal ABI for the Standard C++ Library. Two implementations
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of that library are interoperable if one follows the de-facto ABI of the
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other and if they are both built with the same compiler, or with compilers
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that conform to the same ABI for C++ compiler and runtime support.
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When G++ and another C++ compiler conform to the same C++ ABI, but the
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implementations of the Standard C++ Library that they normally use do not
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follow the same ABI for the Standard C++ Library, object files built with
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those compilers can be used in the same program only if they use the same
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C++ library. This requires specifying the location of the C++ library
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header files when invoking the compiler whose usual library is not being
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used. The location of GCC's C++ header files depends on how the GCC
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build was configured, but can be seen by using the G++ @option{-v} option.
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With default configuration options for G++ 3.3 the compile line for a
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different C++ compiler needs to include
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@smallexample
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-I@var{gcc_install_directory}/include/c++/3.3
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@end smallexample
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Similarly, compiling code with G++ that must use a C++ library other
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than the GNU C++ library requires specifying the location of the header
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files for that other library.
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The most straightforward way to link a program to use a particular
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C++ library is to use a C++ driver that specifies that C++ library by
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default. The @command{g++} driver, for example, tells the linker where
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to find GCC's C++ library (@file{libstdc++}) plus the other libraries
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and startup files it needs, in the proper order.
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If a program must use a different C++ library and it's not possible
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to do the final link using a C++ driver that uses that library by default,
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it is necessary to tell @command{g++} the location and name of that
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library. It might also be necessary to specify different startup files
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and other runtime support libraries, and to suppress the use of GCC's
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support libraries with one or more of the options @option{-nostdlib},
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@option{-nostartfiles}, and @option{-nodefaultlibs}.
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