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189 lines
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189 lines
9.2 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Compatibility - Using the GNU Compiler Collection (GCC)</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="Using the GNU Compiler Collection (GCC)">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="prev" href="Objective_002dC.html#Objective_002dC" title="Objective-C">
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<link rel="next" href="Gcov.html#Gcov" title="Gcov">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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Copyright (C) 1988-2015 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 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``Funding Free Software'', the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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``GNU Free Documentation License''.
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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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</head>
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<body>
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<div class="node">
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<a name="Compatibility"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Gcov.html#Gcov">Gcov</a>,
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Previous: <a rel="previous" accesskey="p" href="Objective_002dC.html#Objective_002dC">Objective-C</a>,
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Up: <a rel="up" accesskey="u" href="index.html#Top">Top</a>
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<hr>
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</div>
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<h2 class="chapter">9 Binary Compatibility</h2>
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<p><a name="index-binary-compatibility-4238"></a><a name="index-ABI-4239"></a><a name="index-application-binary-interface-4240"></a>
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Binary compatibility encompasses several related concepts:
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<dl>
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<dt><dfn>application binary interface (ABI)</dfn><dd>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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<br><dt><dfn>ABI conformance</dfn><dd>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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<br><dt><dfn>calling conventions</dfn><dd>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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<br><dt><dfn>interoperability</dfn><dd>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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<br><dt><dfn>intercallability</dfn><dd>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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<br><dt><dfn>implementation-defined features</dfn><dd>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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<br><dt><dfn>compatibility</dfn><dd>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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</dl>
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<p>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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<ul>
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<li>size and alignment of data types
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<li>layout of structured types
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<li>calling conventions
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<li>register usage conventions
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<li>interfaces for runtime arithmetic support
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<li>object file formats
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</ul>
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<p>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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<ul>
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<li>name mangling
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<li>exception handling
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<li>invoking constructors and destructors
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<li>layout, alignment, and padding of classes
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<li>layout and alignment of virtual tables
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</ul>
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<p>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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<p>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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<p>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 <samp><span class="option">-Wabi</span></samp> switch warns when G++ generates code that is
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probably not compatible with the C++ ABI.
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<p>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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<p>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++ <samp><span class="option">-v</span></samp> 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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<pre class="smallexample"> -I<var>gcc_install_directory</var>/include/c++/3.3
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</pre>
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<p>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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<p>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 <samp><span class="command">g++</span></samp> driver, for example, tells the linker where
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to find GCC's C++ library (<samp><span class="file">libstdc++</span></samp>) plus the other libraries
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and startup files it needs, in the proper order.
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<p>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 <samp><span class="command">g++</span></samp> 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 <samp><span class="option">-nostdlib</span></samp>,
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<samp><span class="option">-nostartfiles</span></samp>, and <samp><span class="option">-nodefaultlibs</span></samp>.
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<!-- Copyright (C) 1996-2015 Free Software Foundation, Inc. -->
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<!-- This is part of the GCC manual. -->
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<!-- For copying conditions, see the file gcc.texi. -->
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</body></html>
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