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diff --git a/gcc-4.4.3/libstdc++-v3/doc/html/manual/abi.html b/gcc-4.4.3/libstdc++-v3/doc/html/manual/abi.html new file mode 100644 index 000000000..71fe6c05c --- /dev/null +++ b/gcc-4.4.3/libstdc++-v3/doc/html/manual/abi.html @@ -0,0 +1,521 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>ABI Policy and Guidelines</title><meta name="generator" content="DocBook XSL Stylesheets V1.74.0" /><meta name="keywords" content=" C++ , ABI , version , dynamic , shared " /><meta name="keywords" content=" ISO C++ , library " /><link rel="home" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="appendix_porting.html" title="Appendix B. Porting and Maintenance" /><link rel="prev" href="internals.html" title="Porting to New Hardware or Operating Systems" /><link rel="next" href="api.html" title="API Evolution and Deprecation History" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">ABI Policy and Guidelines</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="internals.html">Prev</a> </td><th width="60%" align="center">Appendix B. + Porting and Maintenance + +</th><td width="20%" align="right"> <a accesskey="n" href="api.html">Next</a></td></tr></table><hr /></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="appendix.porting.abi"></a>ABI Policy and Guidelines</h2></div></div></div><p> +</p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="abi.cxx_interface"></a>The C++ Interface</h3></div></div></div><p> + C++ applications often dependent on specific language support + routines, say for throwing exceptions, or catching exceptions, and + perhaps also dependent on features in the C++ Standard Library. +</p><p> + The C++ Standard Library has many include files, types defined in + those include files, specific named functions, and other + behavior. The text of these behaviors, as written in source include + files, is called the Application Programing Interface, or API. +</p><p> + Furthermore, C++ source that is compiled into object files is + transformed by the compiler: it arranges objects with specific + alignment and in a particular layout, mangling names according to a + well-defined algorithm, has specific arrangements for the support of + virtual functions, etc. These details are defined as the compiler + Application Binary Interface, or ABI. The GNU C++ compiler uses an + industry-standard C++ ABI starting with version 3. Details can be + found in the <a class="ulink" href="http://www.codesourcery.com/cxx-abi/abi.html" target="_top"> ABI + specification</a>. +</p><p> + The GNU C++ compiler, g++, has a compiler command line option to + switch between various different C++ ABIs. This explicit version + switch is the flag <code class="code">-fabi-version</code>. In addition, some + g++ command line options may change the ABI as a side-effect of + use. Such flags include <code class="code">-fpack-struct</code> and + <code class="code">-fno-exceptions</code>, but include others: see the complete + list in the GCC manual under the heading <a class="ulink" href="http://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html#Code%20Gen%20Options" target="_top">Options + for Code Generation Conventions</a>. +</p><p> + The configure options used when building a specific libstdc++ + version may also impact the resulting library ABI. The available + configure options, and their impact on the library ABI, are + documented +<a class="link" href="configure.html" title="Configure">here</a>. +</p><p> Putting all of these ideas together results in the C++ Standard +library ABI, which is the compilation of a given library API by a +given compiler ABI. In a nutshell: +</p><p> + “<span class="quote"> + library API + compiler ABI = library ABI + </span>” +</p><p> + The library ABI is mostly of interest for end-users who have + unresolved symbols and are linking dynamically to the C++ Standard + library, and who thus must be careful to compile their application + with a compiler that is compatible with the available C++ Standard + library binary. In this case, compatible is defined with the equation + above: given an application compiled with a given compiler ABI and + library API, it will work correctly with a Standard C++ Library + created with the same constraints. +</p><p> + To use a specific version of the C++ ABI, one must use a + corresponding GNU C++ toolchain (i.e., g++ and libstdc++) that + implements the C++ ABI in question. +</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="abi.versioning"></a>Versioning</h3></div></div></div><p> The C++ interface has evolved throughout the history of the GNU +C++ toolchain. With each release, various details have been changed so +as to give distinct versions to the C++ interface. +</p><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="abi.versioning.goals"></a>Goals</h4></div></div></div><p>Extending existing, stable ABIs. Versioning gives subsequent +releases of library binaries the ability to add new symbols and add +functionality, all the while retaining compatibility with the previous +releases in the series. Thus, program binaries linked with the initial +release of a library binary will still link correctly if the library +binary is replaced by carefully-managed subsequent library +binaries. This is called forward compatibility. +</p><p> +The reverse (backwards compatibility) is not true. It is not possible +to take program binaries linked with the latest version of a library +binary in a release series (with additional symbols added), substitute +in the initial release of the library binary, and remain link +compatible. +</p><p>Allows multiple, incompatible ABIs to coexist at the same time. +</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="abi.versioning.history"></a>History</h4></div></div></div><p> + How can this complexity be managed? What does C++ versioning mean? + Because library and compiler changes often make binaries compiled + with one version of the GNU tools incompatible with binaries + compiled with other (either newer or older) versions of the same GNU + tools, specific techniques are used to make managing this complexity + easier. +</p><p> + The following techniques are used: +</p><div class="orderedlist"><ol type="1"><li><p>Release versioning on the libgcc_s.so binary. </p><p>This is implemented via file names and the ELF + <code class="constant">DT_SONAME</code> mechanism (at least on ELF + systems). It is versioned as follows: + </p><div class="itemizedlist"><ul type="disc"><li><p>gcc-3.0.0: libgcc_s.so.1</p></li><li><p>gcc-3.0.1: libgcc_s.so.1</p></li><li><p>gcc-3.0.2: libgcc_s.so.1</p></li><li><p>gcc-3.0.3: libgcc_s.so.1</p></li><li><p>gcc-3.0.4: libgcc_s.so.1</p></li><li><p>gcc-3.1.0: libgcc_s.so.1</p></li><li><p>gcc-3.1.1: libgcc_s.so.1</p></li><li><p>gcc-3.2.0: libgcc_s.so.1</p></li><li><p>gcc-3.2.1: libgcc_s.so.1</p></li><li><p>gcc-3.2.2: libgcc_s.so.1</p></li><li><p>gcc-3.2.3: libgcc_s.so.1</p></li><li><p>gcc-3.3.0: libgcc_s.so.1</p></li><li><p>gcc-3.3.1: libgcc_s.so.1</p></li><li><p>gcc-3.3.2: libgcc_s.so.1</p></li><li><p>gcc-3.3.3: libgcc_s.so.1</p></li><li><p>gcc-3.4.x, gcc-4.[0-3].x: on m68k-linux and + hppa-linux this is either libgcc_s.so.1 (when configuring + <code class="code">--with-sjlj-exceptions</code>) or libgcc_s.so.2. For all + others, this is libgcc_s.so.1. </p></li></ul></div></li><li><p>Symbol versioning on the libgcc_s.so binary.</p><p>It is versioned with the following labels and version + definitions, where the version definition is the maximum for a + particular release. Labels are cumulative. If a particular release + is not listed, it has the same version labels as the preceding + release.</p><p>This corresponds to the mapfile: gcc/libgcc-std.ver</p><div class="itemizedlist"><ul type="disc"><li><p>gcc-3.0.0: GCC_3.0</p></li><li><p>gcc-3.3.0: GCC_3.3</p></li><li><p>gcc-3.3.1: GCC_3.3.1</p></li><li><p>gcc-3.3.2: GCC_3.3.2</p></li><li><p>gcc-3.3.4: GCC_3.3.4</p></li><li><p>gcc-3.4.0: GCC_3.4</p></li><li><p>gcc-3.4.2: GCC_3.4.2</p></li><li><p>gcc-3.4.4: GCC_3.4.4</p></li><li><p>gcc-4.0.0: GCC_4.0.0</p></li><li><p>gcc-4.1.0: GCC_4.1.0</p></li><li><p>gcc-4.2.0: GCC_4.2.0</p></li><li><p>gcc-4.3.0: GCC_4.3.0</p></li></ul></div></li><li><p> + Release versioning on the libstdc++.so binary, implemented in + the same was as the libgcc_s.so binary above. Listed is the + filename: <code class="constant">DT_SONAME</code> can be deduced from + the filename by removing the last two period-delimited numbers. For + example, filename <code class="filename">libstdc++.so.5.0.4</code> + corresponds to a <code class="constant">DT_SONAME</code> of + <code class="constant">libstdc++.so.5</code>. Binaries with equivalent + <code class="constant">DT_SONAME</code>s are forward-compatibile: in + the table below, releases incompatible with the previous + one are explicitly noted. + </p><p>It is versioned as follows: + </p><div class="itemizedlist"><ul type="disc"><li><p>gcc-3.0.0: libstdc++.so.3.0.0</p></li><li><p>gcc-3.0.1: libstdc++.so.3.0.1</p></li><li><p>gcc-3.0.2: libstdc++.so.3.0.2</p></li><li><p>gcc-3.0.3: libstdc++.so.3.0.2 (See Note 1)</p></li><li><p>gcc-3.0.4: libstdc++.so.3.0.4</p></li><li><p>gcc-3.1.0: libstdc++.so.4.0.0 <span class="emphasis"><em>(Incompatible with previous)</em></span></p></li><li><p>gcc-3.1.1: libstdc++.so.4.0.1</p></li><li><p>gcc-3.2.0: libstdc++.so.5.0.0 <span class="emphasis"><em>(Incompatible with previous)</em></span></p></li><li><p>gcc-3.2.1: libstdc++.so.5.0.1</p></li><li><p>gcc-3.2.2: libstdc++.so.5.0.2</p></li><li><p>gcc-3.2.3: libstdc++.so.5.0.3 (See Note 2)</p></li><li><p>gcc-3.3.0: libstdc++.so.5.0.4</p></li><li><p>gcc-3.3.1: libstdc++.so.5.0.5</p></li><li><p>gcc-3.3.2: libstdc++.so.5.0.5</p></li><li><p>gcc-3.3.3: libstdc++.so.5.0.5</p></li><li><p>gcc-3.4.0: libstdc++.so.6.0.0 <span class="emphasis"><em>(Incompatible with previous)</em></span></p></li><li><p>gcc-3.4.1: libstdc++.so.6.0.1</p></li><li><p>gcc-3.4.2: libstdc++.so.6.0.2</p></li><li><p>gcc-3.4.3: libstdc++.so.6.0.3</p></li><li><p>gcc-3.4.4: libstdc++.so.6.0.3</p></li><li><p>gcc-3.4.5: libstdc++.so.6.0.3</p></li><li><p>gcc-3.4.6: libstdc++.so.6.0.3</p></li><li><p>gcc-4.0.0: libstdc++.so.6.0.4</p></li><li><p>gcc-4.0.1: libstdc++.so.6.0.5</p></li><li><p>gcc-4.0.2: libstdc++.so.6.0.6</p></li><li><p>gcc-4.0.3: libstdc++.so.6.0.7</p></li><li><p>gcc-4.1.0: libstdc++.so.6.0.7</p></li><li><p>gcc-4.1.1: libstdc++.so.6.0.8</p></li><li><p>gcc-4.1.2: libstdc++.so.6.0.8</p></li><li><p>gcc-4.2.0: libstdc++.so.6.0.9</p></li><li><p>gcc-4.2.1: libstdc++.so.6.0.9 (See Note 3)</p></li><li><p>gcc-4.2.2: libstdc++.so.6.0.9</p></li><li><p>gcc-4.2.3: libstdc++.so.6.0.9</p></li><li><p>gcc-4.2.4: libstdc++.so.6.0.9</p></li><li><p>gcc-4.3.0: libstdc++.so.6.0.10</p></li><li><p>gcc-4.3.1: libstdc++.so.6.0.10</p></li><li><p>gcc-4.3.2: libstdc++.so.6.0.10</p></li></ul></div><p> + Note 1: Error should be libstdc++.so.3.0.3. + </p><p> + Note 2: Not strictly required. + </p><p> + Note 3: This release (but not previous or subsequent) has one + known incompatibility, see <a class="ulink" href="http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33678" target="_top">33678</a> + in the GCC bug database. + </p></li><li><p>Symbol versioning on the libstdc++.so binary.</p><p>mapfile: libstdc++/config/linker-map.gnu</p><p>It is versioned with the following labels and version + definitions, where the version definition is the maximum for a + particular release. Note, only symbol which are newly introduced + will use the maximum version definition. Thus, for release series + with the same label, but incremented version definitions, the later + release has both versions. (An example of this would be the + gcc-3.2.1 release, which has GLIBCPP_3.2.1 for new symbols and + GLIBCPP_3.2 for symbols that were introduced in the gcc-3.2.0 + release.) If a particular release is not listed, it has the same + version labels as the preceding release. + </p><div class="itemizedlist"><ul type="disc"><li><p>gcc-3.0.0: (Error, not versioned)</p></li><li><p>gcc-3.0.1: (Error, not versioned)</p></li><li><p>gcc-3.0.2: (Error, not versioned)</p></li><li><p>gcc-3.0.3: (Error, not versioned)</p></li><li><p>gcc-3.0.4: (Error, not versioned)</p></li><li><p>gcc-3.1.0: GLIBCPP_3.1, CXXABI_1</p></li><li><p>gcc-3.1.1: GLIBCPP_3.1, CXXABI_1</p></li><li><p>gcc-3.2.0: GLIBCPP_3.2, CXXABI_1.2</p></li><li><p>gcc-3.2.1: GLIBCPP_3.2.1, CXXABI_1.2</p></li><li><p>gcc-3.2.2: GLIBCPP_3.2.2, CXXABI_1.2</p></li><li><p>gcc-3.2.3: GLIBCPP_3.2.2, CXXABI_1.2</p></li><li><p>gcc-3.3.0: GLIBCPP_3.2.2, CXXABI_1.2.1</p></li><li><p>gcc-3.3.1: GLIBCPP_3.2.3, CXXABI_1.2.1</p></li><li><p>gcc-3.3.2: GLIBCPP_3.2.3, CXXABI_1.2.1</p></li><li><p>gcc-3.3.3: GLIBCPP_3.2.3, CXXABI_1.2.1</p></li><li><p>gcc-3.4.0: GLIBCXX_3.4, CXXABI_1.3</p></li><li><p>gcc-3.4.1: GLIBCXX_3.4.1, CXXABI_1.3</p></li><li><p>gcc-3.4.2: GLIBCXX_3.4.2</p></li><li><p>gcc-3.4.3: GLIBCXX_3.4.3</p></li><li><p>gcc-4.0.0: GLIBCXX_3.4.4, CXXABI_1.3.1</p></li><li><p>gcc-4.0.1: GLIBCXX_3.4.5</p></li><li><p>gcc-4.0.2: GLIBCXX_3.4.6</p></li><li><p>gcc-4.0.3: GLIBCXX_3.4.7</p></li><li><p>gcc-4.1.1: GLIBCXX_3.4.8</p></li><li><p>gcc-4.2.0: GLIBCXX_3.4.9</p></li><li><p>gcc-4.3.0: GLIBCXX_3.4.10, CXXABI_1.3.2</p></li></ul></div></li><li><p>Incremental bumping of a compiler pre-defined macro, + __GXX_ABI_VERSION. This macro is defined as the version of the + compiler v3 ABI, with g++ 3.0.x being version 100. This macro will + be automatically defined whenever g++ is used (the curious can + test this by invoking g++ with the '-v' flag.) + </p><p> + This macro was defined in the file "lang-specs.h" in the gcc/cp directory. + Later versions defined it in "c-common.c" in the gcc directory, and from + G++ 3.4 it is defined in c-cppbuiltin.c and its value determined by the + '-fabi-version' command line option. + </p><p> + It is versioned as follows, where 'n' is given by '-fabi-version=n': + </p><div class="itemizedlist"><ul type="disc"><li><p>gcc-3.0.x: 100</p></li><li><p>gcc-3.1.x: 100 (Error, should be 101)</p></li><li><p>gcc-3.2.x: 102</p></li><li><p>gcc-3.3.x: 102</p></li><li><p>gcc-3.4.x, gcc-4.[0-3].x: 102 (when n=1)</p></li><li><p>gcc-3.4.x, gcc-4.[0-3].x: 1000 + n (when n>1) </p></li><li><p>gcc-3.4.x, gcc-4.[0-3].x: 999999 (when n=0)</p></li></ul></div><p></p></li><li><p>Changes to the default compiler option for + <code class="code">-fabi-version</code>. + </p><p> + It is versioned as follows: + </p><div class="itemizedlist"><ul type="disc"><li><p>gcc-3.0.x: (Error, not versioned) </p></li><li><p>gcc-3.1.x: (Error, not versioned) </p></li><li><p>gcc-3.2.x: <code class="code">-fabi-version=1</code></p></li><li><p>gcc-3.3.x: <code class="code">-fabi-version=1</code></p></li><li><p>gcc-3.4.x, gcc-4.[0-3].x: <code class="code">-fabi-version=2</code> <span class="emphasis"><em>(Incompatible with previous)</em></span></p></li></ul></div><p></p></li><li><p>Incremental bumping of a library pre-defined macro. For releases + before 3.4.0, the macro is __GLIBCPP__. For later releases, it's + __GLIBCXX__. (The libstdc++ project generously changed from CPP to + CXX throughout its source to allow the "C" pre-processor the CPP + macro namespace.) These macros are defined as the date the library + was released, in compressed ISO date format, as an unsigned long. + </p><p> + This macro is defined in the file "c++config" in the + "libstdc++/include/bits" directory. (Up to gcc-4.1.0, it was + changed every night by an automated script. Since gcc-4.1.0, it is + the same value as gcc/DATESTAMP.) + </p><p> + It is versioned as follows: + </p><div class="itemizedlist"><ul type="disc"><li><p>gcc-3.0.0: 20010615</p></li><li><p>gcc-3.0.1: 20010819</p></li><li><p>gcc-3.0.2: 20011023</p></li><li><p>gcc-3.0.3: 20011220</p></li><li><p>gcc-3.0.4: 20020220</p></li><li><p>gcc-3.1.0: 20020514</p></li><li><p>gcc-3.1.1: 20020725</p></li><li><p>gcc-3.2.0: 20020814</p></li><li><p>gcc-3.2.1: 20021119</p></li><li><p>gcc-3.2.2: 20030205</p></li><li><p>gcc-3.2.3: 20030422</p></li><li><p>gcc-3.3.0: 20030513</p></li><li><p>gcc-3.3.1: 20030804</p></li><li><p>gcc-3.3.2: 20031016</p></li><li><p>gcc-3.3.3: 20040214</p></li><li><p>gcc-3.4.0: 20040419</p></li><li><p>gcc-3.4.1: 20040701</p></li><li><p>gcc-3.4.2: 20040906</p></li><li><p>gcc-3.4.3: 20041105</p></li><li><p>gcc-3.4.4: 20050519</p></li><li><p>gcc-3.4.5: 20051201</p></li><li><p>gcc-3.4.6: 20060306</p></li><li><p>gcc-4.0.0: 20050421</p></li><li><p>gcc-4.0.1: 20050707</p></li><li><p>gcc-4.0.2: 20050921</p></li><li><p>gcc-4.0.3: 20060309</p></li><li><p>gcc-4.1.0: 20060228</p></li><li><p>gcc-4.1.1: 20060524</p></li><li><p>gcc-4.1.2: 20070214</p></li><li><p>gcc-4.2.0: 20070514</p></li><li><p>gcc-4.2.1: 20070719</p></li><li><p>gcc-4.2.2: 20071007</p></li><li><p>gcc-4.2.3: 20080201</p></li><li><p>gcc-4.2.4: 20080519</p></li><li><p>gcc-4.3.0: 20080306</p></li><li><p>gcc-4.3.1: 20080606</p></li><li><p>gcc-4.3.2: 20080827</p></li></ul></div><p></p></li><li><p> + Incremental bumping of a library pre-defined macro, + _GLIBCPP_VERSION. This macro is defined as the released version of + the library, as a string literal. This is only implemented in + gcc-3.1.0 releases and higher, and is deprecated in 3.4 (where it + is called _GLIBCXX_VERSION). + </p><p> + This macro is defined in the file "c++config" in the + "libstdc++/include/bits" directory and is generated + automatically by autoconf as part of the configure-time generation + of config.h. + </p><p> + It is versioned as follows: + </p><div class="itemizedlist"><ul type="disc"><li><p>gcc-3.0.0: "3.0.0"</p></li><li><p>gcc-3.0.1: "3.0.0" (Error, should be "3.0.1")</p></li><li><p>gcc-3.0.2: "3.0.0" (Error, should be "3.0.2")</p></li><li><p>gcc-3.0.3: "3.0.0" (Error, should be "3.0.3")</p></li><li><p>gcc-3.0.4: "3.0.0" (Error, should be "3.0.4")</p></li><li><p>gcc-3.1.0: "3.1.0"</p></li><li><p>gcc-3.1.1: "3.1.1"</p></li><li><p>gcc-3.2.0: "3.2"</p></li><li><p>gcc-3.2.1: "3.2.1"</p></li><li><p>gcc-3.2.2: "3.2.2"</p></li><li><p>gcc-3.2.3: "3.2.3"</p></li><li><p>gcc-3.3.0: "3.3"</p></li><li><p>gcc-3.3.1: "3.3.1"</p></li><li><p>gcc-3.3.2: "3.3.2"</p></li><li><p>gcc-3.3.3: "3.3.3"</p></li><li><p>gcc-3.4.x: "version-unused"</p></li><li><p>gcc-4.[0-3].x: "version-unused"</p></li></ul></div><p></p></li><li><p> + Matching each specific C++ compiler release to a specific set of + C++ include files. This is only implemented in gcc-3.1.1 releases + and higher. + </p><p> + All C++ includes are installed in include/c++, then nest in a + directory hierarchy corresponding to the C++ compiler's released + version. This version corresponds to the variable "gcc_version" in + "libstdc++/acinclude.m4," and more details can be found in that + file's macro GLIBCXX_CONFIGURE (GLIBCPP_CONFIGURE before gcc-3.4.0). + </p><p> + C++ includes are versioned as follows: + </p><div class="itemizedlist"><ul type="disc"><li><p>gcc-3.0.0: include/g++-v3</p></li><li><p>gcc-3.0.1: include/g++-v3</p></li><li><p>gcc-3.0.2: include/g++-v3</p></li><li><p>gcc-3.0.3: include/g++-v3</p></li><li><p>gcc-3.0.4: include/g++-v3</p></li><li><p>gcc-3.1.0: include/g++-v3</p></li><li><p>gcc-3.1.1: include/c++/3.1.1</p></li><li><p>gcc-3.2.0: include/c++/3.2</p></li><li><p>gcc-3.2.1: include/c++/3.2.1</p></li><li><p>gcc-3.2.2: include/c++/3.2.2</p></li><li><p>gcc-3.2.3: include/c++/3.2.3</p></li><li><p>gcc-3.3.0: include/c++/3.3</p></li><li><p>gcc-3.3.1: include/c++/3.3.1</p></li><li><p>gcc-3.3.2: include/c++/3.3.2</p></li><li><p>gcc-3.3.3: include/c++/3.3.3</p></li><li><p>gcc-3.4.0: include/c++/3.4.0</p></li><li><p>gcc-3.4.1: include/c++/3.4.1</p></li><li><p>gcc-3.4.2: include/c++/3.4.2</p></li><li><p>gcc-3.4.3: include/c++/3.4.3</p></li><li><p>gcc-3.4.4: include/c++/3.4.4</p></li><li><p>gcc-3.4.5: include/c++/3.4.5</p></li><li><p>gcc-3.4.6: include/c++/3.4.6</p></li><li><p>gcc-4.0.0: include/c++/4.0.0</p></li><li><p>gcc-4.0.1: include/c++/4.0.1</p></li><li><p>gcc-4.0.2: include/c++/4.0.2</p></li><li><p>gcc-4.0.3: include/c++/4.0.3</p></li><li><p>gcc-4.1.0: include/c++/4.1.0</p></li><li><p>gcc-4.1.1: include/c++/4.1.1</p></li><li><p>gcc-4.1.2: include/c++/4.1.2</p></li><li><p>gcc-4.2.0: include/c++/4.2.0</p></li><li><p>gcc-4.2.1: include/c++/4.2.1</p></li><li><p>gcc-4.2.2: include/c++/4.2.2</p></li><li><p>gcc-4.2.3: include/c++/4.2.3</p></li><li><p>gcc-4.2.4: include/c++/4.2.4</p></li><li><p>gcc-4.3.0: include/c++/4.3.0</p></li><li><p>gcc-4.3.1: include/c++/4.3.1</p></li><li><p>gcc-4.3.2: include/c++/4.3.2</p></li></ul></div><p></p></li></ol></div><p> + Taken together, these techniques can accurately specify interface + and implementation changes in the GNU C++ tools themselves. Used + properly, they allow both the GNU C++ tools implementation, and + programs using them, an evolving yet controlled development that + maintains backward compatibility. +</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="abi.versioning.prereq"></a>Prerequisites</h4></div></div></div><p> + Minimum environment that supports a versioned ABI: A supported + dynamic linker, a GNU linker of sufficient vintage to understand + demangled C++ name globbing (ld), a shared executable compiled + with g++, and shared libraries (libgcc_s, libstdc++) compiled by + a compiler (g++) with a compatible ABI. Phew. + </p><p> + On top of all that, an additional constraint: libstdc++ did not + attempt to version symbols (or age gracefully, really) until + version 3.1.0. + </p><p> + Most modern Linux and BSD versions, particularly ones using + gcc-3.1.x tools and more recent vintages, will meet the + requirements above. + </p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="abi.versioning.config"></a>Configuring</h4></div></div></div><p> + It turns out that most of the configure options that change + default behavior will impact the mangled names of exported + symbols, and thus impact versioning and compatibility. + </p><p> + For more information on configure options, including ABI + impacts, see: + http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html + </p><p> + There is one flag that explicitly deals with symbol versioning: + --enable-symvers. + </p><p> + In particular, libstdc++/acinclude.m4 has a macro called + GLIBCXX_ENABLE_SYMVERS that defaults to yes (or the argument + passed in via --enable-symvers=foo). At that point, the macro + attempts to make sure that all the requirement for symbol + versioning are in place. For more information, please consult + acinclude.m4. + </p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="abi.versioning.active"></a>Checking Active</h4></div></div></div><p> + When the GNU C++ library is being built with symbol versioning + on, you should see the following at configure time for + libstdc++: + </p><pre class="screen"> +<code class="computeroutput"> + checking versioning on shared library symbols... gnu +</code> +</pre><p> + If you don't see this line in the configure output, or if this line + appears but the last word is 'no', then you are out of luck. +</p><p> + If the compiler is pre-installed, a quick way to test is to compile + the following (or any) simple C++ file and link it to the shared + libstdc++ library: +</p><pre class="programlisting"> +#include <iostream> + +int main() +{ std::cout << "hello" << std::endl; return 0; } + +%g++ hello.cc -o hello.out + +%ldd hello.out + libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x00764000) + libm.so.6 => /lib/tls/libm.so.6 (0x004a8000) + libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x40016000) + libc.so.6 => /lib/tls/libc.so.6 (0x0036d000) + /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000) + +%nm hello.out +</pre><p> +If you see symbols in the resulting output with "GLIBCXX_3" as part +of the name, then the executable is versioned. Here's an example: +</p><p> + <code class="code">U _ZNSt8ios_base4InitC1Ev@@GLIBCXX_3.4</code> +</p></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="abi.changes_allowed"></a>Allowed Changes</h3></div></div></div><p> +The following will cause the library minor version number to +increase, say from "libstdc++.so.3.0.4" to "libstdc++.so.3.0.5". +</p><div class="orderedlist"><ol type="1"><li><p>Adding an exported global or static data member</p></li><li><p>Adding an exported function, static or non-virtual member function</p></li><li><p>Adding an exported symbol or symbols by additional instantiations</p></li></ol></div><p> +Other allowed changes are possible. +</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="abi.changes_no"></a>Prohibited Changes</h3></div></div></div><p> +The following non-exhaustive list will cause the library major version +number to increase, say from "libstdc++.so.3.0.4" to +"libstdc++.so.4.0.0". +</p><div class="orderedlist"><ol type="1"><li><p>Changes in the gcc/g++ compiler ABI</p></li><li><p>Changing size of an exported symbol</p></li><li><p>Changing alignment of an exported symbol</p></li><li><p>Changing the layout of an exported symbol</p></li><li><p>Changing mangling on an exported symbol</p></li><li><p>Deleting an exported symbol</p></li><li><p>Changing the inheritance properties of a type by adding or removing + base classes</p></li><li><p> + Changing the size, alignment, or layout of types + specified in the C++ standard. These may not necessarily be + instantiated or otherwise exported in the library binary, and + include all the required locale facets, as well as things like + std::basic_streambuf, et al. +</p></li><li><p> Adding an explicit copy constructor or destructor to a +class that would otherwise have implicit versions. This will change +the way the compiler deals with this class in by-value return +statements or parameters: instead of being passing instances of this +class in registers, the compiler will be forced to use memory. See <a class="ulink" href="http://www.codesourcery.com/cxx-abi/abi.html#calls" target="_top"> this part</a> + of the C++ ABI documentation for further details. + </p></li></ol></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="abi.impl"></a>Implementation</h3></div></div></div><div class="orderedlist"><ol type="1"><li><p> + Separation of interface and implementation + </p><p> + This is accomplished by two techniques that separate the API from + the ABI: forcing undefined references to link against a library + binary for definitions. + </p><div class="variablelist"><dl><dt><span class="term">Include files have declarations, source files have defines</span></dt><dd><p> + For non-templatized types, such as much of <code class="code">class + locale</code>, the appropriate standard C++ include, say + <code class="code">locale</code>, can contain full declarations, while + various source files (say <code class="code"> locale.cc, locale_init.cc, + localename.cc</code>) contain definitions. + </p></dd><dt><span class="term">Extern template on required types</span></dt><dd><p> + For parts of the standard that have an explicit list of + required instantiations, the GNU extension syntax <code class="code"> extern + template </code> can be used to control where template + definitions reside. By marking required instantiations as + <code class="code"> extern template </code> in include files, and providing + explicit instantiations in the appropriate instantiation files, + non-inlined template functions can be versioned. This technique + is mostly used on parts of the standard that require <code class="code"> + char</code> and <code class="code"> wchar_t</code> instantiations, and + includes <code class="code"> basic_string</code>, the locale facets, and the + types in <code class="code"> iostreams</code>. + </p></dd></dl></div><p> + In addition, these techniques have the additional benefit that they + reduce binary size, which can increase runtime performance. + </p></li><li><p> + Namespaces linking symbol definitions to export mapfiles + </p><p> + All symbols in the shared library binary are processed by a + linker script at build time that either allows or disallows + external linkage. Because of this, some symbols, regardless of + normal C/C++ linkage, are not visible. Symbols that are internal + have several appealing characteristics: by not exporting the + symbols, there are no relocations when the shared library is + started and thus this makes for faster runtime loading + performance by the underlying dynamic loading mechanism. In + addition, they have the possibility of changing without impacting + ABI compatibility. + </p><p>The following namespaces are transformed by the mapfile:</p><div class="variablelist"><dl><dt><span class="term"><code class="code">namespace std</code></span></dt><dd><p> Defaults to exporting all symbols in label +<code class="code">GLIBCXX</code> that do not begin with an underscore, i.e., +<code class="code">__test_func</code> would not be exported by default. Select +exceptional symbols are allowed to be visible.</p></dd><dt><span class="term"><code class="code">namespace __gnu_cxx</code></span></dt><dd><p> Defaults to not exporting any symbols in label +<code class="code">GLIBCXX</code>, select items are allowed to be visible.</p></dd><dt><span class="term"><code class="code">namespace __gnu_internal</code></span></dt><dd><p> Defaults to not exported, no items are allowed to be visible.</p></dd><dt><span class="term"><code class="code">namespace __cxxabiv1</code>, aliased to <code class="code"> namespace abi</code></span></dt><dd><p> Defaults to not exporting any symbols in label +<code class="code">CXXABI</code>, select items are allowed to be visible.</p></dd></dl></div><p> +</p></li><li><p>Freezing the API</p><p>Disallowed changes, as above, are not made on a stable release +branch. Enforcement tends to be less strict with GNU extensions that +standard includes.</p></li></ol></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="abi.testing"></a>Testing</h3></div></div></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="abi.testing.single"></a>Single ABI Testing</h4></div></div></div><p> + Testing for GNU C++ ABI changes is composed of two distinct + areas: testing the C++ compiler (g++) for compiler changes, and + testing the C++ library (libstdc++) for library changes. + </p><p> + Testing the C++ compiler ABI can be done various ways. + </p><p> + One. Intel ABI checker. More information can be obtained <a class="ulink" href="http://developer.intel.com/software/products/opensource/" target="_top">here.</a> + </p><p> +Two. +The second is yet unreleased, but has been announced on the gcc +mailing list. It is yet unspecified if these tools will be freely +available, and able to be included in a GNU project. Please contact +Mark Mitchell (mark@codesourcery.com) for more details, and current +status. +</p><p> +Three. +Involves using the vlad.consistency test framework. This has also been +discussed on the gcc mailing lists. +</p><p> +Testing the C++ library ABI can also be done various ways. +</p><p> +One. +(Brendan Kehoe, Jeff Law suggestion to run 'make check-c++' two ways, +one with a new compiler and an old library, and the other with an old +compiler and a new library, and look for testsuite regressions) +</p><p> +Details on how to set this kind of test up can be found here: +http://gcc.gnu.org/ml/gcc/2002-08/msg00142.html +</p><p> +Two. +Use the 'make check-abi' rule in the libstdc++ Makefile. +</p><p> +This is a proactive check the library ABI. Currently, exported symbol +names that are either weak or defined are checked against a last known +good baseline. Currently, this baseline is keyed off of 3.4.0 +binaries, as this was the last time the .so number was incremented. In +addition, all exported names are demangled, and the exported objects +are checked to make sure they are the same size as the same object in +the baseline. + +Notice that each baseline is relative to a <span class="emphasis"><em>default</em></span> +configured library and compiler: in particular, if options such as +--enable-clocale, or --with-cpu, in case of multilibs, are used at +configure time, the check may fail, either because of substantive +differences or because of limitations of the current checking +machinery. +</p><p> +This dataset is insufficient, yet a start. Also needed is a +comprehensive check for all user-visible types part of the standard +library for sizeof() and alignof() changes. +</p><p> +Verifying compatible layouts of objects is not even attempted. It +should be possible to use sizeof, alignof, and offsetof to compute +offsets for each structure and type in the standard library, saving to +another datafile. Then, compute this in a similar way for new +binaries, and look for differences. +</p><p> +Another approach might be to use the -fdump-class-hierarchy flag to +get information. However, currently this approach gives insufficient +data for use in library testing, as class data members, their offsets, +and other detailed data is not displayed with this flag. +(See g++/7470 on how this was used to find bugs.) +</p><p> +Perhaps there are other C++ ABI checkers. If so, please notify +us. We'd like to know about them! +</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="abi.testing.multi"></a>Multiple ABI Testing</h4></div></div></div><p> +A "C" application, dynamically linked to two shared libraries, liba, +libb. The dependent library liba is C++ shared library compiled with +gcc-3.3.x, and uses io, exceptions, locale, etc. The dependent library +libb is a C++ shared library compiled with gcc-3.4.x, and also uses io, +exceptions, locale, etc. +</p><p> As above, libone is constructed as follows: </p><pre class="programlisting"> +%$bld/H-x86-gcc-3.4.0/bin/g++ -fPIC -DPIC -c a.cc + +%$bld/H-x86-gcc-3.4.0/bin/g++ -shared -Wl,-soname -Wl,libone.so.1 -Wl,-O1 -Wl,-z,defs a.o -o libone.so.1.0.0 + +%ln -s libone.so.1.0.0 libone.so + +%$bld/H-x86-gcc-3.4.0/bin/g++ -c a.cc + +%ar cru libone.a a.o +</pre><p> And, libtwo is constructed as follows: </p><pre class="programlisting"> +%$bld/H-x86-gcc-3.3.3/bin/g++ -fPIC -DPIC -c b.cc + +%$bld/H-x86-gcc-3.3.3/bin/g++ -shared -Wl,-soname -Wl,libtwo.so.1 -Wl,-O1 -Wl,-z,defs b.o -o libtwo.so.1.0.0 + +%ln -s libtwo.so.1.0.0 libtwo.so + +%$bld/H-x86-gcc-3.3.3/bin/g++ -c b.cc + +%ar cru libtwo.a b.o +</pre><p> ...with the resulting libraries looking like </p><pre class="screen"> +<code class="computeroutput"> +%ldd libone.so.1.0.0 + libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x40016000) + libm.so.6 => /lib/tls/libm.so.6 (0x400fa000) + libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x4011c000) + libc.so.6 => /lib/tls/libc.so.6 (0x40125000) + /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000) + +%ldd libtwo.so.1.0.0 + libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x40027000) + libm.so.6 => /lib/tls/libm.so.6 (0x400e1000) + libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x40103000) + libc.so.6 => /lib/tls/libc.so.6 (0x4010c000) + /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000) +</code> +</pre><p> + Then, the "C" compiler is used to compile a source file that uses + functions from each library. +</p><pre class="programlisting"> +gcc test.c -g -O2 -L. -lone -ltwo /usr/lib/libstdc++.so.5 /usr/lib/libstdc++.so.6 +</pre><p> + Which gives the expected: +</p><pre class="screen"> +<code class="computeroutput"> +%ldd a.out + libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x00764000) + libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x40015000) + libc.so.6 => /lib/tls/libc.so.6 (0x0036d000) + libm.so.6 => /lib/tls/libm.so.6 (0x004a8000) + libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x400e5000) + /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000) +</code> +</pre><p> + This resulting binary, when executed, will be able to safely use + code from both liba, and the dependent libstdc++.so.6, and libb, + with the dependent libstdc++.so.5. +</p></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="abi.issues"></a>Outstanding Issues</h3></div></div></div><p> + Some features in the C++ language make versioning especially + difficult. In particular, compiler generated constructs such as + implicit instantiations for templates, typeinfo information, and + virtual tables all may cause ABI leakage across shared library + boundaries. Because of this, mixing C++ ABIs is not recommended at + this time. +</p><p> + For more background on this issue, see these bugzilla entries: +</p><p> +<a class="ulink" href="http://gcc.gnu.org/PR24660" target="_top">24660: versioning weak symbols in libstdc++</a> +</p><p> +<a class="ulink" href="http://gcc.gnu.org/PR19664" target="_top">19664: libstdc++ headers should have pop/push of the visibility around the declarations</a> +</p></div><div class="bibliography"><div class="titlepage"><div><div><h3 class="title"><a id="abi.biblio"></a>Bibliography</h3></div></div></div><div class="biblioentry"><a id="id430252"></a><p><span class="title"><i> + ABIcheck, a vague idea of checking ABI compatibility + </i>. </span><span class="biblioid"> + <a class="ulink" href="http://abicheck.sourceforge.net/" target="_top"> + </a> + . </span></p></div><div class="biblioentry"><a id="id430269"></a><p><span class="title"><i> + C++ ABI Reference + </i>. </span><span class="biblioid"> + <a class="ulink" href="http://www.codesourcery.com/cxx-abi" target="_top"> + </a> + . </span></p></div><div class="biblioentry"><a id="id430287"></a><p><span class="title"><i> + Intel® Compilers for Linux* -Compatibility with the GNU Compilers + </i>. </span><span class="biblioid"> + <a class="ulink" href="http://developer.intel.com/software/products/compilers/techtopics/LinuxCompilersCompatibility.htm" target="_top"> + </a> + . </span></p></div><div class="biblioentry"><a id="id430304"></a><p><span class="title"><i> + Intel® Compilers for Linux* -Compatibility with the GNU Compilers + </i>. </span><span class="biblioid"> + <a class="ulink" href="http://developer.intel.com/software/products/compilers/techtopics/LinuxCompilersCompatibility.htm" target="_top"> + </a> + . </span></p></div><div class="biblioentry"><a id="id430322"></a><p><span class="title"><i> + Sun Solaris 2.9 : Linker and Libraries Guide (document 816-1386) + </i>. </span><span class="biblioid"> + <a class="ulink" href="http://docs.sun.com/?p=/doc/816-1386&a=load" target="_top"> + </a> + . </span></p></div><div class="biblioentry"><a id="id430339"></a><p><span class="title"><i> + Sun Solaris 2.9 : C++ Migration Guide (document 816-2459) + </i>. </span><span class="biblioid"> + <a class="ulink" href="http://docs.sun.com/db/prod/solaris.9" target="_top"> + </a> + . </span></p></div><div class="biblioentry"><a id="id430356"></a><p><span class="title"><i> + ELF Symbol Versioning + </i>. </span><span class="author"><span class="firstname">Ulrich</span> <span class="surname">Drepper</span>. </span><span class="biblioid"> + <a class="ulink" href="http://people.redhat.com/drepper/symbol-versioning" target="_top"> + </a> + . </span></p></div><div class="biblioentry"><a id="id430385"></a><p><span class="title"><i> + C++ ABI for the ARM Architecture + </i>. </span><span class="biblioid"> + <a class="ulink" href="http://www.arm.com/miscPDFs/8033.pdf" target="_top"> + </a> + . </span></p></div><div class="biblioentry"><a id="id430402"></a><p><span class="title"><i> + Dynamic Shared Objects: Survey and Issues + </i>. </span><span class="subtitle"> + ISO C++ J16/06-0046 + . </span><span class="author"><span class="firstname">Benjamin</span> <span class="surname">Kosnik</span>. </span><span class="biblioid"> + <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1976.html" target="_top"> + </a> + . </span></p></div><div class="biblioentry"><a id="id430434"></a><p><span class="title"><i> + Versioning With Namespaces + </i>. </span><span class="subtitle"> + ISO C++ J16/06-0083 + . </span><span class="author"><span class="firstname">Benjamin</span> <span class="surname">Kosnik</span>. </span><span class="biblioid"> + <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2013.html" target="_top"> + </a> + . </span></p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="internals.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="appendix_porting.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="api.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Porting to New Hardware or Operating Systems </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> API Evolution and Deprecation History</td></tr></table></div></body></html> |