libstdc++-v3/doc/html/manual/abi.html

   1 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
   2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
   3 <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 V1.75.2" /><meta name="keywords" content="&#10;      C++&#10;    , &#10;      ABI&#10;    , &#10;      version&#10;    , &#10;      dynamic&#10;    , &#10;      shared&#10;    , &#10;      compatibility&#10;    " /><meta name="keywords" content="&#10;      ISO C++&#10;    , &#10;      library&#10;    " /><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="test.html" title="Test" /><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="test.html">Prev</a> </td><th width="60%" align="center">Appendix B.
   4   Porting and Maintenance
   5
   6 </th><td width="20%" align="right"> <a accesskey="n" href="api.html">Next</a></td></tr></table><hr /></div><div class="sect1" title="ABI Policy and Guidelines"><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>
   7 </p><div class="sect2" title="The C++ Interface"><div class="titlepage"><div><div><h3 class="title"><a id="abi.cxx_interface"></a>The C++ Interface</h3></div></div></div><p>
   8   C++ applications often depend on specific language support
   9   routines, say for throwing exceptions, or catching exceptions, and
  10   perhaps also depend on features in the C++ Standard Library.
  11 </p><p>
  12   The C++ Standard Library has many include files, types defined in
  13   those include files, specific named functions, and other
  14   behavior. The text of these behaviors, as written in source include
  15   files, is called the Application Programing Interface, or API.
  16 </p><p>
  17   Furthermore, C++ source that is compiled into object files is
  18   transformed by the compiler: it arranges objects with specific
  19   alignment and in a particular layout, mangling names according to a
  20   well-defined algorithm, has specific arrangements for the support of
  21   virtual functions, etc. These details are defined as the compiler
  22   Application Binary Interface, or ABI. The GNU C++ compiler uses an
  23   industry-standard C++ ABI starting with version 3. Details can be
  24   found in the <a class="ulink" href="http://www.codesourcery.com/cxx-abi/abi.html" target="_top"> ABI
  25   specification</a>.
  26 </p><p>
  27  The GNU C++ compiler, g++, has a compiler command line option to
  28   switch between various different C++ ABIs. This explicit version
  29   switch is the flag <code class="code">-fabi-version</code>. In addition, some
  30   g++ command line options may change the ABI as a side-effect of
  31   use. Such flags include <code class="code">-fpack-struct</code> and
  32   <code class="code">-fno-exceptions</code>, but include others: see the complete
  33   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
  34   for Code Generation Conventions</a>.
  35 </p><p>
  36   The configure options used when building a specific libstdc++
  37   version may also impact the resulting library ABI. The available
  38   configure options, and their impact on the library ABI, are
  39   documented
  40 <a class="link" href="configure.html" title="Configure">here</a>.
  41 </p><p> Putting all of these ideas together results in the C++ Standard
  42 library ABI, which is the compilation of a given library API by a
  43 given compiler ABI. In a nutshell:
  44 </p><p>
  45   <span class="quote">“<span class="quote">
  46     library API + compiler ABI = library ABI
  47   </span>”</span>
  48 </p><p>
  49  The library ABI is mostly of interest for end-users who have
  50  unresolved symbols and are linking dynamically to the C++ Standard
  51  library, and who thus must be careful to compile their application
  52  with a compiler that is compatible with the available C++ Standard
  53  library binary. In this case, compatible is defined with the equation
  54  above: given an application compiled with a given compiler ABI and
  55  library API, it will work correctly with a Standard C++ Library
  56  created with the same constraints.
  57 </p><p>
  58   To use a specific version of the C++ ABI, one must use a
  59   corresponding GNU C++ toolchain (i.e., g++ and libstdc++) that
  60   implements the C++ ABI in question.
  61 </p></div><div class="sect2" title="Versioning"><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
  62 C++ toolchain. With each release, various details have been changed so
  63 as to give distinct versions to the C++ interface.
  64 </p><div class="sect3" title="Goals"><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
  65 releases of library binaries the ability to add new symbols and add
  66 functionality, all the while retaining compatibility with the previous
  67 releases in the series. Thus, program binaries linked with the initial
  68 release of a library binary will still run correctly if the library
  69 binary is replaced by carefully-managed subsequent library
  70 binaries. This is called forward compatibility.
  71 </p><p>
  72 The reverse (backwards compatibility) is not true. It is not possible
  73 to take program binaries linked with the latest version of a library
  74 binary in a release series (with additional symbols added), substitute
  75 in the initial release of the library binary, and remain link
  76 compatible.
  77 </p><p>Allows multiple, incompatible ABIs to coexist at the same time.
  78 </p></div><div class="sect3" title="History"><div class="titlepage"><div><div><h4 class="title"><a id="abi.versioning.history"></a>History</h4></div></div></div><p>
  79  How can this complexity be managed? What does C++ versioning mean?
  80   Because library and compiler changes often make binaries compiled
  81   with one version of the GNU tools incompatible with binaries
  82   compiled with other (either newer or older) versions of the same GNU
  83   tools, specific techniques are used to make managing this complexity
  84   easier.
  85 </p><p>
  86   The following techniques are used:
  87 </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>Release versioning on the libgcc_s.so binary. </p><p>This is implemented via file names and the ELF
  88     <code class="constant">DT_SONAME</code> mechanism (at least on ELF
  89     systems). It is versioned as follows:
  90     </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>gcc-3.0.0: libgcc_s.so.1</p></li><li class="listitem"><p>gcc-3.0.1: libgcc_s.so.1</p></li><li class="listitem"><p>gcc-3.0.2: libgcc_s.so.1</p></li><li class="listitem"><p>gcc-3.0.3: libgcc_s.so.1</p></li><li class="listitem"><p>gcc-3.0.4: libgcc_s.so.1</p></li><li class="listitem"><p>gcc-3.1.0: libgcc_s.so.1</p></li><li class="listitem"><p>gcc-3.1.1: libgcc_s.so.1</p></li><li class="listitem"><p>gcc-3.2.0: libgcc_s.so.1</p></li><li class="listitem"><p>gcc-3.2.1: libgcc_s.so.1</p></li><li class="listitem"><p>gcc-3.2.2: libgcc_s.so.1</p></li><li class="listitem"><p>gcc-3.2.3: libgcc_s.so.1</p></li><li class="listitem"><p>gcc-3.3.0: libgcc_s.so.1</p></li><li class="listitem"><p>gcc-3.3.1: libgcc_s.so.1</p></li><li class="listitem"><p>gcc-3.3.2: libgcc_s.so.1</p></li><li class="listitem"><p>gcc-3.3.3: libgcc_s.so.1</p></li><li class="listitem"><p>gcc-3.4.x, gcc-4.[0-5].x: libgcc_s.so.1</p></li></ul></div><p>For m68k-linux the versions differ as follows: </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>gcc-3.4.x, gcc-4.[0-5].x: libgcc_s.so.1
  91     when configuring <code class="code">--with-sjlj-exceptions</code>, or
  92     libgcc_s.so.2 </p></li></ul></div><p>For hppa-linux the versions differ as follows: </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>gcc-3.4.x, gcc-4.[0-1].x: either libgcc_s.so.1
  93     when configuring <code class="code">--with-sjlj-exceptions</code>, or
  94     libgcc_s.so.2 </p></li><li class="listitem"><p>gcc-4.[2-5].x: either libgcc_s.so.3 when configuring
  95     <code class="code">--with-sjlj-exceptions</code>) or libgcc_s.so.4
  96     </p></li></ul></div></li><li class="listitem"><p>Symbol versioning on the libgcc_s.so binary.</p><p>It is versioned with the following labels and version
  97    definitions, where the version definition is the maximum for a
  98    particular release. Labels are cumulative. If a particular release
  99    is not listed, it has the same version labels as the preceding
 100    release.</p><p>This corresponds to the mapfile: gcc/libgcc-std.ver</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>gcc-3.0.0: GCC_3.0</p></li><li class="listitem"><p>gcc-3.3.0: GCC_3.3</p></li><li class="listitem"><p>gcc-3.3.1: GCC_3.3.1</p></li><li class="listitem"><p>gcc-3.3.2: GCC_3.3.2</p></li><li class="listitem"><p>gcc-3.3.4: GCC_3.3.4</p></li><li class="listitem"><p>gcc-3.4.0: GCC_3.4</p></li><li class="listitem"><p>gcc-3.4.2: GCC_3.4.2</p></li><li class="listitem"><p>gcc-3.4.4: GCC_3.4.4</p></li><li class="listitem"><p>gcc-4.0.0: GCC_4.0.0</p></li><li class="listitem"><p>gcc-4.1.0: GCC_4.1.0</p></li><li class="listitem"><p>gcc-4.2.0: GCC_4.2.0</p></li><li class="listitem"><p>gcc-4.3.0: GCC_4.3.0</p></li><li class="listitem"><p>gcc-4.4.0: GCC_4.4.0</p></li></ul></div></li><li class="listitem"><p>
 101         Release versioning on the libstdc++.so binary, implemented in
 102         the same way as the libgcc_s.so binary above. Listed is the
 103         filename: <code class="constant">DT_SONAME</code> can be deduced from
 104         the filename by removing the last two period-delimited numbers. For
 105         example, filename <code class="filename">libstdc++.so.5.0.4</code>
 106         corresponds to a <code class="constant">DT_SONAME</code> of
 107         <code class="constant">libstdc++.so.5</code>. Binaries with equivalent
 108         <code class="constant">DT_SONAME</code>s are forward-compatibile: in
 109         the table below, releases incompatible with the previous
 110         one are explicitly noted.
 111       </p><p>It is versioned as follows:
 112     </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>gcc-3.0.0: libstdc++.so.3.0.0</p></li><li class="listitem"><p>gcc-3.0.1: libstdc++.so.3.0.1</p></li><li class="listitem"><p>gcc-3.0.2: libstdc++.so.3.0.2</p></li><li class="listitem"><p>gcc-3.0.3: libstdc++.so.3.0.2 (See Note 1)</p></li><li class="listitem"><p>gcc-3.0.4: libstdc++.so.3.0.4</p></li><li class="listitem"><p>gcc-3.1.0: libstdc++.so.4.0.0 <span class="emphasis"><em>(Incompatible with previous)</em></span></p></li><li class="listitem"><p>gcc-3.1.1: libstdc++.so.4.0.1</p></li><li class="listitem"><p>gcc-3.2.0: libstdc++.so.5.0.0 <span class="emphasis"><em>(Incompatible with previous)</em></span></p></li><li class="listitem"><p>gcc-3.2.1: libstdc++.so.5.0.1</p></li><li class="listitem"><p>gcc-3.2.2: libstdc++.so.5.0.2</p></li><li class="listitem"><p>gcc-3.2.3: libstdc++.so.5.0.3 (See Note 2)</p></li><li class="listitem"><p>gcc-3.3.0: libstdc++.so.5.0.4</p></li><li class="listitem"><p>gcc-3.3.1: libstdc++.so.5.0.5</p></li><li class="listitem"><p>gcc-3.3.2: libstdc++.so.5.0.5</p></li><li class="listitem"><p>gcc-3.3.3: libstdc++.so.5.0.5</p></li><li class="listitem"><p>gcc-3.4.0: libstdc++.so.6.0.0 <span class="emphasis"><em>(Incompatible with previous)</em></span></p></li><li class="listitem"><p>gcc-3.4.1: libstdc++.so.6.0.1</p></li><li class="listitem"><p>gcc-3.4.2: libstdc++.so.6.0.2</p></li><li class="listitem"><p>gcc-3.4.3: libstdc++.so.6.0.3</p></li><li class="listitem"><p>gcc-3.4.4: libstdc++.so.6.0.3</p></li><li class="listitem"><p>gcc-3.4.5: libstdc++.so.6.0.3</p></li><li class="listitem"><p>gcc-3.4.6: libstdc++.so.6.0.3</p></li><li class="listitem"><p>gcc-4.0.0: libstdc++.so.6.0.4</p></li><li class="listitem"><p>gcc-4.0.1: libstdc++.so.6.0.5</p></li><li class="listitem"><p>gcc-4.0.2: libstdc++.so.6.0.6</p></li><li class="listitem"><p>gcc-4.0.3: libstdc++.so.6.0.7</p></li><li class="listitem"><p>gcc-4.1.0: libstdc++.so.6.0.7</p></li><li class="listitem"><p>gcc-4.1.1: libstdc++.so.6.0.8</p></li><li class="listitem"><p>gcc-4.1.2: libstdc++.so.6.0.8</p></li><li class="listitem"><p>gcc-4.2.0: libstdc++.so.6.0.9</p></li><li class="listitem"><p>gcc-4.2.1: libstdc++.so.6.0.9 (See Note 3)</p></li><li class="listitem"><p>gcc-4.2.2: libstdc++.so.6.0.9</p></li><li class="listitem"><p>gcc-4.2.3: libstdc++.so.6.0.9</p></li><li class="listitem"><p>gcc-4.2.4: libstdc++.so.6.0.9</p></li><li class="listitem"><p>gcc-4.3.0: libstdc++.so.6.0.10</p></li><li class="listitem"><p>gcc-4.3.1: libstdc++.so.6.0.10</p></li><li class="listitem"><p>gcc-4.3.2: libstdc++.so.6.0.10</p></li><li class="listitem"><p>gcc-4.3.3: libstdc++.so.6.0.10</p></li><li class="listitem"><p>gcc-4.3.4: libstdc++.so.6.0.10</p></li><li class="listitem"><p>gcc-4.4.0: libstdc++.so.6.0.11</p></li><li class="listitem"><p>gcc-4.4.1: libstdc++.so.6.0.12</p></li><li class="listitem"><p>gcc-4.4.2: libstdc++.so.6.0.13</p></li><li class="listitem"><p>gcc-4.5.0: libstdc++.so.6.0.14</p></li></ul></div><p>
 113       Note 1: Error should be libstdc++.so.3.0.3.
 114     </p><p>
 115       Note 2: Not strictly required.
 116     </p><p>
 117       Note 3: This release (but not previous or subsequent) has one
 118       known incompatibility, see <a class="ulink" href="http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33678" target="_top">33678</a>
 119       in the GCC bug database.
 120     </p></li><li class="listitem"><p>Symbol versioning on the libstdc++.so binary.</p><p>mapfile: libstdc++-v3/config/abi/pre/gnu.ver</p><p>It is versioned with the following labels and version
 121    definitions, where the version definition is the maximum for a
 122    particular release. Note, only symbols which are newly introduced
 123    will use the maximum version definition. Thus, for release series
 124    with the same label, but incremented version definitions, the later
 125    release has both versions. (An example of this would be the
 126    gcc-3.2.1 release, which has GLIBCPP_3.2.1 for new symbols and
 127    GLIBCPP_3.2 for symbols that were introduced in the gcc-3.2.0
 128    release.) If a particular release is not listed, it has the same
 129    version labels as the preceding release.
 130    </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>gcc-3.0.0: (Error, not versioned)</p></li><li class="listitem"><p>gcc-3.0.1: (Error, not versioned)</p></li><li class="listitem"><p>gcc-3.0.2: (Error, not versioned)</p></li><li class="listitem"><p>gcc-3.0.3: (Error, not versioned)</p></li><li class="listitem"><p>gcc-3.0.4: (Error, not versioned)</p></li><li class="listitem"><p>gcc-3.1.0: GLIBCPP_3.1, CXXABI_1</p></li><li class="listitem"><p>gcc-3.1.1: GLIBCPP_3.1, CXXABI_1</p></li><li class="listitem"><p>gcc-3.2.0: GLIBCPP_3.2, CXXABI_1.2</p></li><li class="listitem"><p>gcc-3.2.1: GLIBCPP_3.2.1, CXXABI_1.2</p></li><li class="listitem"><p>gcc-3.2.2: GLIBCPP_3.2.2, CXXABI_1.2</p></li><li class="listitem"><p>gcc-3.2.3: GLIBCPP_3.2.2, CXXABI_1.2</p></li><li class="listitem"><p>gcc-3.3.0: GLIBCPP_3.2.2, CXXABI_1.2.1</p></li><li class="listitem"><p>gcc-3.3.1: GLIBCPP_3.2.3, CXXABI_1.2.1</p></li><li class="listitem"><p>gcc-3.3.2: GLIBCPP_3.2.3, CXXABI_1.2.1</p></li><li class="listitem"><p>gcc-3.3.3: GLIBCPP_3.2.3, CXXABI_1.2.1</p></li><li class="listitem"><p>gcc-3.4.0: GLIBCXX_3.4, CXXABI_1.3</p></li><li class="listitem"><p>gcc-3.4.1: GLIBCXX_3.4.1, CXXABI_1.3</p></li><li class="listitem"><p>gcc-3.4.2: GLIBCXX_3.4.2</p></li><li class="listitem"><p>gcc-3.4.3: GLIBCXX_3.4.3</p></li><li class="listitem"><p>gcc-4.0.0: GLIBCXX_3.4.4, CXXABI_1.3.1</p></li><li class="listitem"><p>gcc-4.0.1: GLIBCXX_3.4.5</p></li><li class="listitem"><p>gcc-4.0.2: GLIBCXX_3.4.6</p></li><li class="listitem"><p>gcc-4.0.3: GLIBCXX_3.4.7</p></li><li class="listitem"><p>gcc-4.1.1: GLIBCXX_3.4.8</p></li><li class="listitem"><p>gcc-4.2.0: GLIBCXX_3.4.9</p></li><li class="listitem"><p>gcc-4.3.0: GLIBCXX_3.4.10, CXXABI_1.3.2</p></li><li class="listitem"><p>gcc-4.4.0: GLIBCXX_3.4.11, CXXABI_1.3.3</p></li><li class="listitem"><p>gcc-4.4.1: GLIBCXX_3.4.12, CXXABI_1.3.3</p></li><li class="listitem"><p>gcc-4.4.2: GLIBCXX_3.4.13, CXXABI_1.3.3</p></li><li class="listitem"><p>gcc-4.5.0: GLIBCXX_3.4.14, CXXABI_1.3.4</p></li></ul></div></li><li class="listitem"><p>Incremental bumping of a compiler pre-defined macro,
 131     __GXX_ABI_VERSION. This macro is defined as the version of the
 132     compiler v3 ABI, with g++ 3.0.x being version 100. This macro will
 133     be automatically defined whenever g++ is used (the curious can
 134     test this by invoking g++ with the '-v' flag.)
 135     </p><p>
 136     This macro was defined in the file "lang-specs.h" in the gcc/cp directory.
 137     Later versions defined it in "c-common.c" in the gcc directory, and from
 138     G++ 3.4 it is defined in c-cppbuiltin.c and its value determined by the
 139     '-fabi-version' command line option.
 140     </p><p>
 141     It is versioned as follows, where 'n' is given by '-fabi-version=n':
 142     </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>gcc-3.0.x: 100</p></li><li class="listitem"><p>gcc-3.1.x: 100 (Error, should be 101)</p></li><li class="listitem"><p>gcc-3.2.x: 102</p></li><li class="listitem"><p>gcc-3.3.x: 102</p></li><li class="listitem"><p>gcc-3.4.x, gcc-4.[0-5].x: 102 (when n=1)</p></li><li class="listitem"><p>gcc-3.4.x, gcc-4.[0-5].x: 1000 + n (when n&gt;1) </p></li><li class="listitem"><p>gcc-3.4.x, gcc-4.[0-5].x: 999999 (when n=0)</p></li></ul></div><p></p></li><li class="listitem"><p>Changes to the default compiler option for
 143     <code class="code">-fabi-version</code>.
 144     </p><p>
 145     It is versioned as follows:
 146     </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>gcc-3.0.x: (Error, not versioned) </p></li><li class="listitem"><p>gcc-3.1.x: (Error, not versioned) </p></li><li class="listitem"><p>gcc-3.2.x: <code class="code">-fabi-version=1</code></p></li><li class="listitem"><p>gcc-3.3.x: <code class="code">-fabi-version=1</code></p></li><li class="listitem"><p>gcc-3.4.x, gcc-4.[0-5].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 class="listitem"><p>Incremental bumping of a library pre-defined macro. For releases
 147     before 3.4.0, the macro is __GLIBCPP__. For later releases, it's
 148     __GLIBCXX__. (The libstdc++ project generously changed from CPP to
 149     CXX throughout its source to allow the "C" pre-processor the CPP
 150     macro namespace.) These macros are defined as the date the library
 151     was released, in compressed ISO date format, as an unsigned long.
 152     </p><p>
 153     This macro is defined in the file "c++config" in the
 154     "libstdc++-v3/include/bits" directory. (Up to gcc-4.1.0, it was
 155     changed every night by an automated script. Since gcc-4.1.0, it is
 156     the same value as gcc/DATESTAMP.)
 157     </p><p>
 158     It is versioned as follows:
 159     </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>gcc-3.0.0: 20010615</p></li><li class="listitem"><p>gcc-3.0.1: 20010819</p></li><li class="listitem"><p>gcc-3.0.2: 20011023</p></li><li class="listitem"><p>gcc-3.0.3: 20011220</p></li><li class="listitem"><p>gcc-3.0.4: 20020220</p></li><li class="listitem"><p>gcc-3.1.0: 20020514</p></li><li class="listitem"><p>gcc-3.1.1: 20020725</p></li><li class="listitem"><p>gcc-3.2.0: 20020814</p></li><li class="listitem"><p>gcc-3.2.1: 20021119</p></li><li class="listitem"><p>gcc-3.2.2: 20030205</p></li><li class="listitem"><p>gcc-3.2.3: 20030422</p></li><li class="listitem"><p>gcc-3.3.0: 20030513</p></li><li class="listitem"><p>gcc-3.3.1: 20030804</p></li><li class="listitem"><p>gcc-3.3.2: 20031016</p></li><li class="listitem"><p>gcc-3.3.3: 20040214</p></li><li class="listitem"><p>gcc-3.4.0: 20040419</p></li><li class="listitem"><p>gcc-3.4.1: 20040701</p></li><li class="listitem"><p>gcc-3.4.2: 20040906</p></li><li class="listitem"><p>gcc-3.4.3: 20041105</p></li><li class="listitem"><p>gcc-3.4.4: 20050519</p></li><li class="listitem"><p>gcc-3.4.5: 20051201</p></li><li class="listitem"><p>gcc-3.4.6: 20060306</p></li><li class="listitem"><p>gcc-4.0.0: 20050421</p></li><li class="listitem"><p>gcc-4.0.1: 20050707</p></li><li class="listitem"><p>gcc-4.0.2: 20050921</p></li><li class="listitem"><p>gcc-4.0.3: 20060309</p></li><li class="listitem"><p>gcc-4.1.0: 20060228</p></li><li class="listitem"><p>gcc-4.1.1: 20060524</p></li><li class="listitem"><p>gcc-4.1.2: 20070214</p></li><li class="listitem"><p>gcc-4.2.0: 20070514</p></li><li class="listitem"><p>gcc-4.2.1: 20070719</p></li><li class="listitem"><p>gcc-4.2.2: 20071007</p></li><li class="listitem"><p>gcc-4.2.3: 20080201</p></li><li class="listitem"><p>gcc-4.2.4: 20080519</p></li><li class="listitem"><p>gcc-4.3.0: 20080306</p></li><li class="listitem"><p>gcc-4.3.1: 20080606</p></li><li class="listitem"><p>gcc-4.3.2: 20080827</p></li><li class="listitem"><p>gcc-4.3.3: 20090124</p></li><li class="listitem"><p>gcc-4.4.0: 20090421</p></li><li class="listitem"><p>gcc-4.4.1: 20090722</p></li><li class="listitem"><p>gcc-4.4.2: 20091015</p></li></ul></div><p></p></li><li class="listitem"><p>
 160     Incremental bumping of a library pre-defined macro,
 161     _GLIBCPP_VERSION. This macro is defined as the released version of
 162     the library, as a string literal. This is only implemented in
 163     gcc-3.1.0 releases and higher, and is deprecated in 3.4 (where it
 164     is called _GLIBCXX_VERSION).
 165     </p><p>
 166     This macro is defined in the file "c++config" in the
 167     "libstdc++-v3/include/bits" directory and is generated
 168     automatically by autoconf as part of the configure-time generation
 169     of config.h.
 170     </p><p>
 171     It is versioned as follows:
 172     </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>gcc-3.0.0: "3.0.0"</p></li><li class="listitem"><p>gcc-3.0.1: "3.0.0" (Error, should be "3.0.1")</p></li><li class="listitem"><p>gcc-3.0.2: "3.0.0" (Error, should be "3.0.2")</p></li><li class="listitem"><p>gcc-3.0.3: "3.0.0" (Error, should be "3.0.3")</p></li><li class="listitem"><p>gcc-3.0.4: "3.0.0" (Error, should be "3.0.4")</p></li><li class="listitem"><p>gcc-3.1.0: "3.1.0"</p></li><li class="listitem"><p>gcc-3.1.1: "3.1.1"</p></li><li class="listitem"><p>gcc-3.2.0: "3.2"</p></li><li class="listitem"><p>gcc-3.2.1: "3.2.1"</p></li><li class="listitem"><p>gcc-3.2.2: "3.2.2"</p></li><li class="listitem"><p>gcc-3.2.3: "3.2.3"</p></li><li class="listitem"><p>gcc-3.3.0: "3.3"</p></li><li class="listitem"><p>gcc-3.3.1: "3.3.1"</p></li><li class="listitem"><p>gcc-3.3.2: "3.3.2"</p></li><li class="listitem"><p>gcc-3.3.3: "3.3.3"</p></li><li class="listitem"><p>gcc-3.4.x: "version-unused"</p></li><li class="listitem"><p>gcc-4.[0-5].x: "version-unused"</p></li></ul></div><p></p></li><li class="listitem"><p>
 173     Matching each specific C++ compiler release to a specific set of
 174     C++ include files. This is only implemented in gcc-3.1.1 releases
 175     and higher.
 176     </p><p>
 177     All C++ includes are installed in include/c++, then nest in a
 178     directory hierarchy corresponding to the C++ compiler's released
 179     version. This version corresponds to the variable "gcc_version" in
 180     "libstdc++-v3/acinclude.m4," and more details can be found in that
 181     file's macro GLIBCXX_CONFIGURE (GLIBCPP_CONFIGURE before gcc-3.4.0).
 182     </p><p>
 183     C++ includes are versioned as follows:
 184     </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>gcc-3.0.0: include/g++-v3</p></li><li class="listitem"><p>gcc-3.0.1: include/g++-v3</p></li><li class="listitem"><p>gcc-3.0.2: include/g++-v3</p></li><li class="listitem"><p>gcc-3.0.3: include/g++-v3</p></li><li class="listitem"><p>gcc-3.0.4: include/g++-v3</p></li><li class="listitem"><p>gcc-3.1.0: include/g++-v3</p></li><li class="listitem"><p>gcc-3.1.1: include/c++/3.1.1</p></li><li class="listitem"><p>gcc-3.2.0: include/c++/3.2</p></li><li class="listitem"><p>gcc-3.2.1: include/c++/3.2.1</p></li><li class="listitem"><p>gcc-3.2.2: include/c++/3.2.2</p></li><li class="listitem"><p>gcc-3.2.3: include/c++/3.2.3</p></li><li class="listitem"><p>gcc-3.3.0: include/c++/3.3</p></li><li class="listitem"><p>gcc-3.3.1: include/c++/3.3.1</p></li><li class="listitem"><p>gcc-3.3.2: include/c++/3.3.2</p></li><li class="listitem"><p>gcc-3.3.3: include/c++/3.3.3</p></li><li class="listitem"><p>gcc-3.4.0: include/c++/3.4.0</p></li><li class="listitem"><p>gcc-3.4.1: include/c++/3.4.1</p></li><li class="listitem"><p>gcc-3.4.2: include/c++/3.4.2</p></li><li class="listitem"><p>gcc-3.4.3: include/c++/3.4.3</p></li><li class="listitem"><p>gcc-3.4.4: include/c++/3.4.4</p></li><li class="listitem"><p>gcc-3.4.5: include/c++/3.4.5</p></li><li class="listitem"><p>gcc-3.4.6: include/c++/3.4.6</p></li><li class="listitem"><p>gcc-4.0.0: include/c++/4.0.0</p></li><li class="listitem"><p>gcc-4.0.1: include/c++/4.0.1</p></li><li class="listitem"><p>gcc-4.0.2: include/c++/4.0.2</p></li><li class="listitem"><p>gcc-4.0.3: include/c++/4.0.3</p></li><li class="listitem"><p>gcc-4.1.0: include/c++/4.1.0</p></li><li class="listitem"><p>gcc-4.1.1: include/c++/4.1.1</p></li><li class="listitem"><p>gcc-4.1.2: include/c++/4.1.2</p></li><li class="listitem"><p>gcc-4.2.0: include/c++/4.2.0</p></li><li class="listitem"><p>gcc-4.2.1: include/c++/4.2.1</p></li><li class="listitem"><p>gcc-4.2.2: include/c++/4.2.2</p></li><li class="listitem"><p>gcc-4.2.3: include/c++/4.2.3</p></li><li class="listitem"><p>gcc-4.2.4: include/c++/4.2.4</p></li><li class="listitem"><p>gcc-4.3.0: include/c++/4.3.0</p></li><li class="listitem"><p>gcc-4.3.1: include/c++/4.3.1</p></li><li class="listitem"><p>gcc-4.3.3: include/c++/4.3.3</p></li><li class="listitem"><p>gcc-4.3.4: include/c++/4.3.4</p></li><li class="listitem"><p>gcc-4.4.0: include/c++/4.4.0</p></li><li class="listitem"><p>gcc-4.4.1: include/c++/4.4.1</p></li><li class="listitem"><p>gcc-4.4.2: include/c++/4.4.2</p></li><li class="listitem"><p>gcc-4.5.0: include/c++/4.5.0</p></li></ul></div><p></p></li></ol></div><p>
 185   Taken together, these techniques can accurately specify interface
 186   and implementation changes in the GNU C++ tools themselves. Used
 187   properly, they allow both the GNU C++ tools implementation, and
 188   programs using them, an evolving yet controlled development that
 189   maintains backward compatibility.
 190 </p></div><div class="sect3" title="Prerequisites"><div class="titlepage"><div><div><h4 class="title"><a id="abi.versioning.prereq"></a>Prerequisites</h4></div></div></div><p>
 191       Minimum environment that supports a versioned ABI: A supported
 192       dynamic linker, a GNU linker of sufficient vintage to understand
 193       demangled C++ name globbing (ld) or the Sun linker, a shared
 194       executable compiled
 195       with g++, and shared libraries (libgcc_s, libstdc++) compiled by
 196       a compiler (g++) with a compatible ABI. Phew.
 197     </p><p>
 198       On top of all that, an additional constraint: libstdc++ did not
 199       attempt to version symbols (or age gracefully, really) until
 200       version 3.1.0.
 201     </p><p>
 202       Most modern Linux and BSD versions, particularly ones using
 203       gcc-3.1.x tools and more recent vintages, will meet the
 204       requirements above, as does Solaris 2.5 and up.
 205     </p></div><div class="sect3" title="Configuring"><div class="titlepage"><div><div><h4 class="title"><a id="abi.versioning.config"></a>Configuring</h4></div></div></div><p>
 206       It turns out that most of the configure options that change
 207       default behavior will impact the mangled names of exported
 208       symbols, and thus impact versioning and compatibility.
 209     </p><p>
 210       For more information on configure options, including ABI
 211       impacts, see:
 212       <a class="link" href="configure.html" title="Configure">here</a>
 213     </p><p>
 214       There is one flag that explicitly deals with symbol versioning:
 215       --enable-symvers.
 216     </p><p>
 217       In particular, libstdc++-v3/acinclude.m4 has a macro called
 218       GLIBCXX_ENABLE_SYMVERS that defaults to yes (or the argument
 219       passed in via --enable-symvers=foo). At that point, the macro
 220       attempts to make sure that all the requirement for symbol
 221       versioning are in place. For more information, please consult
 222       acinclude.m4.
 223     </p></div><div class="sect3" title="Checking Active"><div class="titlepage"><div><div><h4 class="title"><a id="abi.versioning.active"></a>Checking Active</h4></div></div></div><p>
 224       When the GNU C++ library is being built with symbol versioning
 225       on, you should see the following at configure time for
 226       libstdc++:
 227     </p><pre class="screen">
 228 <code class="computeroutput">
 229   checking versioning on shared library symbols... gnu
 230 </code>
 231 </pre><p>
 232   or another of the supported styles.
 233   If you don't see this line in the configure output, or if this line
 234   appears but the last word is 'no', then you are out of luck.
 235 </p><p>
 236   If the compiler is pre-installed, a quick way to test is to compile
 237   the following (or any) simple C++ file and link it to the shared
 238   libstdc++ library:
 239 </p><pre class="programlisting">
 240 #include &lt;iostream&gt;
 241
 242 int main()
 243 { std::cout &lt;&lt; "hello" &lt;&lt; std::endl; return 0; }
 244
 245 %g++ hello.cc -o hello.out
 246
 247 %ldd hello.out
 248         libstdc++.so.5 =&gt; /usr/lib/libstdc++.so.5 (0x00764000)
 249         libm.so.6 =&gt; /lib/tls/libm.so.6 (0x004a8000)
 250         libgcc_s.so.1 =&gt; /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x40016000)
 251         libc.so.6 =&gt; /lib/tls/libc.so.6 (0x0036d000)
 252         /lib/ld-linux.so.2 =&gt; /lib/ld-linux.so.2 (0x00355000)
 253
 254 %nm hello.out
 255 </pre><p>
 256 If you see symbols in the resulting output with "GLIBCXX_3" as part
 257 of the name, then the executable is versioned. Here's an example:
 258 </p><p>
 259    <code class="code">U _ZNSt8ios_base4InitC1Ev@@GLIBCXX_3.4</code>
 260 </p><p>
 261 On Solaris 2, you can use <code class="code">pvs -r</code> instead:
 262 </p><pre class="programlisting">
 263 %g++ hello.cc -o hello.out
 264
 265 %pvs -r hello.out
 266         libstdc++.so.6 (GLIBCXX_3.4, GLIBCXX_3.4.12);
 267         libgcc_s.so.1 (GCC_3.0);
 268         libc.so.1 (SUNWprivate_1.1, SYSVABI_1.3);
 269 </pre><p>
 270 <code class="code">ldd -v</code> works too, but is very verbose.
 271 </p></div></div><div class="sect2" title="Allowed Changes"><div class="titlepage"><div><div><h3 class="title"><a id="abi.changes_allowed"></a>Allowed Changes</h3></div></div></div><p>
 272 The following will cause the library minor version number to
 273 increase, say from "libstdc++.so.3.0.4" to "libstdc++.so.3.0.5".
 274 </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>Adding an exported global or static data member</p></li><li class="listitem"><p>Adding an exported function, static or non-virtual member function</p></li><li class="listitem"><p>Adding an exported symbol or symbols by additional instantiations</p></li></ol></div><p>
 275 Other allowed changes are possible.
 276 </p></div><div class="sect2" title="Prohibited Changes"><div class="titlepage"><div><div><h3 class="title"><a id="abi.changes_no"></a>Prohibited Changes</h3></div></div></div><p>
 277 The following non-exhaustive list will cause the library major version
 278 number to increase, say from "libstdc++.so.3.0.4" to
 279 "libstdc++.so.4.0.0".
 280 </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>Changes in the gcc/g++ compiler ABI</p></li><li class="listitem"><p>Changing size of an exported symbol</p></li><li class="listitem"><p>Changing alignment of an exported symbol</p></li><li class="listitem"><p>Changing the layout of an exported symbol</p></li><li class="listitem"><p>Changing mangling on an exported symbol</p></li><li class="listitem"><p>Deleting an exported symbol</p></li><li class="listitem"><p>Changing the inheritance properties of a type by adding or removing
 281     base classes</p></li><li class="listitem"><p>
 282   Changing the size, alignment, or layout of types
 283   specified in the C++ standard. These may not necessarily be
 284   instantiated or otherwise exported in the library binary, and
 285   include all the required locale facets, as well as things like
 286   std::basic_streambuf, et al.
 287 </p></li><li class="listitem"><p> Adding an explicit copy constructor or destructor to a
 288 class that would otherwise have implicit versions. This will change
 289 the way the compiler deals with this class in by-value return
 290 statements or parameters: instead of passing instances of this
 291 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>
 292  of the C++ ABI documentation for further details.
 293  </p></li></ol></div></div><div class="sect2" title="Implementation"><div class="titlepage"><div><div><h3 class="title"><a id="abi.impl"></a>Implementation</h3></div></div></div><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
 294      Separation of interface and implementation
 295    </p><p>
 296      This is accomplished by two techniques that separate the API from
 297      the ABI: forcing undefined references to link against a library
 298      binary for definitions.
 299    </p><div class="variablelist"><dl><dt><span class="term">Include files have declarations, source files have defines</span></dt><dd><p>
 300         For non-templatized types, such as much of <code class="code">class
 301         locale</code>, the appropriate standard C++ include, say
 302         <code class="code">locale</code>, can contain full declarations, while
 303         various source files (say <code class="code"> locale.cc, locale_init.cc,
 304         localename.cc</code>) contain definitions.
 305       </p></dd><dt><span class="term">Extern template on required types</span></dt><dd><p>
 306        For parts of the standard that have an explicit list of
 307        required instantiations, the GNU extension syntax <code class="code"> extern
 308        template </code> can be used to control where template
 309        definitions reside. By marking required instantiations as
 310        <code class="code"> extern template </code> in include files, and providing
 311        explicit instantiations in the appropriate instantiation files,
 312        non-inlined template functions can be versioned. This technique
 313        is mostly used on parts of the standard that require <code class="code">
 314        char</code> and <code class="code"> wchar_t</code> instantiations, and
 315        includes <code class="code"> basic_string</code>, the locale facets, and the
 316        types in <code class="code"> iostreams</code>.
 317      </p></dd></dl></div><p>
 318    In addition, these techniques have the additional benefit that they
 319    reduce binary size, which can increase runtime performance.
 320  </p></li><li class="listitem"><p>
 321      Namespaces linking symbol definitions to export mapfiles
 322    </p><p>
 323      All symbols in the shared library binary are processed by a
 324      linker script at build time that either allows or disallows
 325      external linkage. Because of this, some symbols, regardless of
 326      normal C/C++ linkage, are not visible. Symbols that are internal
 327      have several appealing characteristics: by not exporting the
 328      symbols, there are no relocations when the shared library is
 329      started and thus this makes for faster runtime loading
 330      performance by the underlying dynamic loading mechanism. In
 331      addition, they have the possibility of changing without impacting
 332      ABI compatibility.
 333    </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
 334 <code class="code">GLIBCXX</code> that do not begin with an underscore, i.e.,
 335 <code class="code">__test_func</code> would not be exported by default. Select
 336 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
 337 <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
 338 <code class="code">CXXABI</code>, select items are allowed to be visible.</p></dd></dl></div><p>
 339 </p></li><li class="listitem"><p>Freezing the API</p><p>Disallowed changes, as above, are not made on a stable release
 340 branch. Enforcement tends to be less strict with GNU extensions that
 341 standard includes.</p></li></ol></div></div><div class="sect2" title="Testing"><div class="titlepage"><div><div><h3 class="title"><a id="abi.testing"></a>Testing</h3></div></div></div><div class="sect3" title="Single ABI Testing"><div class="titlepage"><div><div><h4 class="title"><a id="abi.testing.single"></a>Single ABI Testing</h4></div></div></div><p>
 342       Testing for GNU C++ ABI changes is composed of two distinct
 343       areas: testing the C++ compiler (g++) for compiler changes, and
 344       testing the C++ library (libstdc++) for library changes.
 345     </p><p>
 346       Testing the C++ compiler ABI can be done various ways.
 347     </p><p>
 348       One.  Intel ABI checker.
 349     </p><p>
 350 Two.
 351 The second is yet unreleased, but has been announced on the gcc
 352 mailing list. It is yet unspecified if these tools will be freely
 353 available, and able to be included in a GNU project. Please contact
 354 Mark Mitchell (mark@codesourcery.com) for more details, and current
 355 status.
 356 </p><p>
 357 Three.
 358 Involves using the vlad.consistency test framework. This has also been
 359 discussed on the gcc mailing lists.
 360 </p><p>
 361 Testing the C++ library ABI can also be done various ways.
 362 </p><p>
 363 One.
 364 (Brendan Kehoe, Jeff Law suggestion to run 'make check-c++' two ways,
 365 one with a new compiler and an old library, and the other with an old
 366 compiler and a new library, and look for testsuite regressions)
 367 </p><p>
 368 Details on how to set this kind of test up can be found here:
 369 http://gcc.gnu.org/ml/gcc/2002-08/msg00142.html
 370 </p><p>
 371 Two.
 372 Use the 'make check-abi' rule in the libstdc++ Makefile.
 373 </p><p>
 374 This is a proactive check of the library ABI. Currently, exported symbol
 375 names that are either weak or defined are checked against a last known
 376 good baseline. Currently, this baseline is keyed off of 3.4.0
 377 binaries, as this was the last time the .so number was incremented. In
 378 addition, all exported names are demangled, and the exported objects
 379 are checked to make sure they are the same size as the same object in
 380 the baseline.
 381
 382 Notice that each baseline is relative to a <span class="emphasis"><em>default</em></span>
 383 configured library and compiler: in particular, if options such as
 384 --enable-clocale, or --with-cpu, in case of multilibs, are used at
 385 configure time, the check may fail, either because of substantive
 386 differences or because of limitations of the current checking
 387 machinery.
 388 </p><p>
 389 This dataset is insufficient, yet a start. Also needed is a
 390 comprehensive check for all user-visible types part of the standard
 391 library for sizeof() and alignof() changes.
 392 </p><p>
 393 Verifying compatible layouts of objects is not even attempted.  It
 394 should be possible to use sizeof, alignof, and offsetof to compute
 395 offsets for each structure and type in the standard library, saving to
 396 another datafile. Then, compute this in a similar way for new
 397 binaries, and look for differences.
 398 </p><p>
 399 Another approach might be to use the -fdump-class-hierarchy flag to
 400 get information. However, currently this approach gives insufficient
 401 data for use in library testing, as class data members, their offsets,
 402 and other detailed data is not displayed with this flag.
 403 (See PR g++/7470 on how this was used to find bugs.)
 404 </p><p>
 405 Perhaps there are other C++ ABI checkers. If so, please notify
 406 us. We'd like to know about them!
 407 </p></div><div class="sect3" title="Multiple ABI Testing"><div class="titlepage"><div><div><h4 class="title"><a id="abi.testing.multi"></a>Multiple ABI Testing</h4></div></div></div><p>
 408 A "C" application, dynamically linked to two shared libraries, liba,
 409 libb. The dependent library liba is a C++ shared library compiled with
 410 gcc-3.3.x, and uses io, exceptions, locale, etc. The dependent library
 411 libb is a C++ shared library compiled with gcc-3.4.x, and also uses io,
 412 exceptions, locale, etc.
 413 </p><p> As above, libone is constructed as follows: </p><pre class="programlisting">
 414 %$bld/H-x86-gcc-3.4.0/bin/g++ -fPIC -DPIC -c a.cc
 415
 416 %$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
 417
 418 %ln -s libone.so.1.0.0 libone.so
 419
 420 %$bld/H-x86-gcc-3.4.0/bin/g++ -c a.cc
 421
 422 %ar cru libone.a a.o
 423 </pre><p> And, libtwo is constructed as follows: </p><pre class="programlisting">
 424 %$bld/H-x86-gcc-3.3.3/bin/g++ -fPIC -DPIC -c b.cc
 425
 426 %$bld/H-x86-gcc-3.3.3/bin/g++ -shared -Wl,-soname -Wl,libtwo.so.1 -Wl,-O1 -Wl,-z,defs b.o -o libtwo.so.1.0.0
 427
 428 %ln -s libtwo.so.1.0.0 libtwo.so
 429
 430 %$bld/H-x86-gcc-3.3.3/bin/g++ -c b.cc
 431
 432 %ar cru libtwo.a b.o
 433 </pre><p> ...with the resulting libraries looking like </p><pre class="screen">
 434 <code class="computeroutput">
 435 %ldd libone.so.1.0.0
 436         libstdc++.so.6 =&gt; /usr/lib/libstdc++.so.6 (0x40016000)
 437         libm.so.6 =&gt; /lib/tls/libm.so.6 (0x400fa000)
 438         libgcc_s.so.1 =&gt; /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x4011c000)
 439         libc.so.6 =&gt; /lib/tls/libc.so.6 (0x40125000)
 440         /lib/ld-linux.so.2 =&gt; /lib/ld-linux.so.2 (0x00355000)
 441
 442 %ldd libtwo.so.1.0.0
 443         libstdc++.so.5 =&gt; /usr/lib/libstdc++.so.5 (0x40027000)
 444         libm.so.6 =&gt; /lib/tls/libm.so.6 (0x400e1000)
 445         libgcc_s.so.1 =&gt; /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x40103000)
 446         libc.so.6 =&gt; /lib/tls/libc.so.6 (0x4010c000)
 447         /lib/ld-linux.so.2 =&gt; /lib/ld-linux.so.2 (0x00355000)
 448 </code>
 449 </pre><p>
 450   Then, the "C" compiler is used to compile a source file that uses
 451   functions from each library.
 452 </p><pre class="programlisting">
 453 gcc test.c -g -O2 -L. -lone -ltwo /usr/lib/libstdc++.so.5 /usr/lib/libstdc++.so.6
 454 </pre><p>
 455   Which gives the expected:
 456 </p><pre class="screen">
 457 <code class="computeroutput">
 458 %ldd a.out
 459         libstdc++.so.5 =&gt; /usr/lib/libstdc++.so.5 (0x00764000)
 460         libstdc++.so.6 =&gt; /usr/lib/libstdc++.so.6 (0x40015000)
 461         libc.so.6 =&gt; /lib/tls/libc.so.6 (0x0036d000)
 462         libm.so.6 =&gt; /lib/tls/libm.so.6 (0x004a8000)
 463         libgcc_s.so.1 =&gt; /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x400e5000)
 464         /lib/ld-linux.so.2 =&gt; /lib/ld-linux.so.2 (0x00355000)
 465 </code>
 466 </pre><p>
 467   This resulting binary, when executed, will be able to safely use
 468   code from both liba, and the dependent libstdc++.so.6, and libb,
 469   with the dependent libstdc++.so.5.
 470 </p></div></div><div class="sect2" title="Outstanding Issues"><div class="titlepage"><div><div><h3 class="title"><a id="abi.issues"></a>Outstanding Issues</h3></div></div></div><p>
 471   Some features in the C++ language make versioning especially
 472   difficult. In particular, compiler generated constructs such as
 473   implicit instantiations for templates, typeinfo information, and
 474   virtual tables all may cause ABI leakage across shared library
 475   boundaries. Because of this, mixing C++ ABIs is not recommended at
 476   this time.
 477 </p><p>
 478   For more background on this issue, see these bugzilla entries:
 479 </p><p>
 480 <a class="ulink" href="http://gcc.gnu.org/PR24660" target="_top">24660: versioning weak symbols in libstdc++</a>
 481 </p><p>
 482 <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>
 483 </p></div><div class="bibliography" title="Bibliography"><div class="titlepage"><div><div><h3 class="title"><a id="abi.biblio"></a>Bibliography</h3></div></div></div><div class="biblioentry"><a id="id396917"></a><p><span class="biblioid">
 484       <a class="ulink" href="http://abicheck.sourceforge.net/" target="_top">
 485         <em class="citetitle">
 486           ABIcheck, a vague idea of checking ABI compatibility
 487         </em>
 488       </a>
 489     . </span></p></div><div class="biblioentry"><a id="id396937"></a><p><span class="biblioid">
 490       <a class="ulink" href="http://www.codesourcery.com/public/cxx-abi/" target="_top">
 491         <em class="citetitle">
 492           C++ ABI Reference
 493         </em>
 494       </a>
 495     . </span></p></div><div class="biblioentry"><a id="id396956"></a><p><span class="biblioid">
 496       <a class="ulink" href="http://www.intel.com/cd/software/products/asmo-na/eng/284736.htm" target="_top">
 497         <em class="citetitle">
 498           Intel Compilers for Linux Compatibility with the GNU Compilers
 499         </em>
 500       </a>
 501     . </span></p></div><div class="biblioentry"><a id="id396976"></a><p><span class="biblioid">
 502       <a class="ulink" href="http://docs.sun.com/app/docs/doc/819-0690" target="_top">
 503         <em class="citetitle">
 504           Linker and Libraries Guide (document 819-0690)
 505         </em>
 506       </a>
 507     . </span></p></div><div class="biblioentry"><a id="id396995"></a><p><span class="biblioid">
 508       <a class="ulink" href="http://docs.sun.com/app/docs/doc/819-3689" target="_top">
 509         <em class="citetitle">
 510           Sun Studio 11: C++ Migration Guide (document 819-3689)
 511         </em>
 512       </a>
 513     . </span></p></div><div class="biblioentry"><a id="id397015"></a><p><span class="biblioid">
 514       <a class="ulink" href="http://people.redhat.com/drepper/dsohowto.pdf" target="_top">
 515         <em class="citetitle">
 516           How to Write Shared Libraries
 517         </em>
 518       </a>
 519     . </span><span class="author"><span class="firstname">Ulrich</span> <span class="surname">Drepper</span>. </span></p></div><div class="biblioentry"><a id="id397046"></a><p><span class="biblioid">
 520       <a class="ulink" href="http://www.arm.com/miscPDFs/8033.pdf" target="_top">
 521         <em class="citetitle">
 522           C++ ABI for the ARM Architecture
 523         </em>
 524       </a>
 525     . </span></p></div><div class="biblioentry"><a id="id397065"></a><p><span class="biblioid">
 526       <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1976.html" target="_top">
 527         <em class="citetitle">
 528           Dynamic Shared Objects: Survey and Issues
 529         </em>
 530       </a>
 531     . </span><span class="subtitle">
 532       ISO C++ J16/06-0046
 533     . </span><span class="author"><span class="firstname">Benjamin</span> <span class="surname">Kosnik</span>. </span></p></div><div class="biblioentry"><a id="id397100"></a><p><span class="biblioid">
 534       <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2013.html" target="_top">
 535         <em class="citetitle">
 536           Versioning With Namespaces
 537         </em>
 538       </a>
 539     . </span><span class="subtitle">
 540       ISO C++ J16/06-0083
 541     . </span><span class="author"><span class="firstname">Benjamin</span> <span class="surname">Kosnik</span>. </span></p></div><div class="biblioentry"><a id="id397135"></a><p><span class="biblioid">
 542       <a class="ulink" href="http://syrcose.ispras.ru/2009/files/SYRCoSE2009-CfP.pdf" target="_top">
 543         <em class="citetitle">
 544           Binary Compatibility of Shared Libraries Implemented in C++
 545           on GNU/Linux Systems
 546         </em>
 547       </a>
 548     . </span><span class="subtitle">
 549       SYRCoSE 2009
 550     . </span><span class="author"><span class="firstname">Pavel</span> <span class="surname">Shved</span>. </span><span class="author"><span class="firstname">Denis</span> <span class="surname">Silakov</span>. </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="test.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">Test </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>