mirror of git://gcc.gnu.org/git/gcc.git
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!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 Vsnapshot" /><meta name="keywords" content="C++, ABI, version, dynamic, shared, compatibility" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="appendix_porting.html" title="Appendix B. Porting and Maintenance" /><link rel="prev" href="test.html" title="Testing" /><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.
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Porting and Maintenance
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</th><td width="20%" align="right"> <a accesskey="n" href="api.html">Next</a></td></tr></table><hr /></div><div class="section"><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>
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</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="abi.cxx_interface"></a>The C++ Interface</h3></div></div></div><p>
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C++ applications often depend on specific language support
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routines, say for throwing exceptions, or catching exceptions, and
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perhaps also depend on features in the C++ Standard Library.
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</p><p>
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The C++ Standard Library has many include files, types defined in
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those include files, specific named functions, and other
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behavior. The text of these behaviors, as written in source include
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files, is called the Application Programing Interface, or API.
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</p><p>
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Furthermore, C++ source that is compiled into object files is
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transformed by the compiler: it arranges objects with specific
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alignment and in a particular layout, mangling names according to a
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well-defined algorithm, has specific arrangements for the support of
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virtual functions, etc. These details are defined as the compiler
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Application Binary Interface, or ABI. From GCC version 3 onwards the
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GNU C++ compiler uses an industry-standard C++ ABI, the
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<a class="link" href="abi.html#biblio.cxxabi" title="Itanium C++ ABI">Itanium C++ ABI</a>.
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</p><p>
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The GNU C++ compiler, g++, has a compiler command line option to
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switch between various different C++ ABIs. This explicit version
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switch is the flag <code class="code">-fabi-version</code>. In addition, some
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g++ command line options may change the ABI as a side-effect of
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use. Such flags include <code class="code">-fpack-struct</code> and
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<code class="code">-fno-exceptions</code>, but include others: see the complete
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list in the GCC manual under the heading <a class="link" href="http://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html#Code%20Gen%20Options" target="_top">Options
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for Code Generation Conventions</a>.
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</p><p>
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The configure options used when building a specific libstdc++
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version may also impact the resulting library ABI. The available
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configure options, and their impact on the library ABI, are
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documented
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<a class="link" href="configure.html" title="Configure">here</a>.
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</p><p> Putting all of these ideas together results in the C++ Standard
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Library ABI, which is the compilation of a given library API by a
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given compiler ABI. In a nutshell:
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</p><p>
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<span class="quote">“<span class="quote">
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library API + compiler ABI = library ABI
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</span>”</span>
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</p><p>
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The library ABI is mostly of interest for end-users who have
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unresolved symbols and are linking dynamically to the C++ Standard
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library, and who thus must be careful to compile their application
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with a compiler that is compatible with the available C++ Standard
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library binary. In this case, compatible is defined with the equation
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above: given an application compiled with a given compiler ABI and
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library API, it will work correctly with a Standard C++ Library
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created with the same constraints.
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</p><p>
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To use a specific version of the C++ ABI, one must use a
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corresponding GNU C++ toolchain (i.e., g++ and libstdc++) that
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implements the C++ ABI in question.
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</p></div><div class="section"><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
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C++ toolchain. With each release, various details have been changed so
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as to give distinct versions to the C++ interface.
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</p><div class="section"><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
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releases of library binaries the ability to add new symbols and add
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functionality, all the while retaining compatibility with the previous
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releases in the series. Thus, program binaries linked with the initial
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release of a library binary will still run correctly if the library
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binary is replaced by carefully-managed subsequent library
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binaries. This is called forward compatibility.
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</p><p>
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The reverse (backwards compatibility) is not true. It is not possible
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to take program binaries linked with the latest version of a library
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binary in a release series (with additional symbols added), substitute
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in the initial release of the library binary, and remain link
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compatible.
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</p><p>Allows multiple, incompatible ABIs to coexist at the same time.
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</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="abi.versioning.history"></a>History</h4></div></div></div><p>
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How can this complexity be managed? What does C++ versioning mean?
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Because library and compiler changes often make binaries compiled
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with one version of the GNU tools incompatible with binaries
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compiled with other (either newer or older) versions of the same GNU
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tools, specific techniques are used to make managing this complexity
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easier.
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</p><p>
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The following techniques are used:
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</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
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<code class="constant">DT_SONAME</code> mechanism (at least on ELF
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systems). It is versioned as follows:
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</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>GCC 3.x: libgcc_s.so.1</p></li><li class="listitem"><p>GCC 4.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" style="list-style-type: disc; "><li class="listitem"><p>GCC 3.4, GCC 4.x: libgcc_s.so.1
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when configuring <code class="code">--with-sjlj-exceptions</code>, or
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libgcc_s.so.2 </p></li></ul></div><p>For hppa-linux the versions differ as follows: </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>GCC 3.4, GCC 4.[0-1]: either libgcc_s.so.1
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when configuring <code class="code">--with-sjlj-exceptions</code>, or
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libgcc_s.so.2 </p></li><li class="listitem"><p>GCC 4.[2-7]: either libgcc_s.so.3 when configuring
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<code class="code">--with-sjlj-exceptions</code>) or libgcc_s.so.4
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</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
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definitions, where the version definition is the maximum for a
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particular release. Labels are cumulative. If a particular release
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is not listed, it has the same version labels as the preceding
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release.</p><p>This corresponds to the mapfile: gcc/libgcc-std.ver</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-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><li class="listitem"><p>GCC 4.5.0: GCC_4.5.0</p></li><li class="listitem"><p>GCC 4.6.0: GCC_4.6.0</p></li><li class="listitem"><p>GCC 4.7.0: GCC_4.7.0</p></li><li class="listitem"><p>GCC 4.8.0: GCC_4.8.0</p></li></ul></div></li><li class="listitem"><p>
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Release versioning on the libstdc++.so binary, implemented in
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the same way as the libgcc_s.so binary above. Listed is the
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filename: <code class="constant">DT_SONAME</code> can be deduced from
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the filename by removing the last two period-delimited numbers. For
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example, filename <code class="filename">libstdc++.so.5.0.4</code>
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corresponds to a <code class="constant">DT_SONAME</code> of
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<code class="constant">libstdc++.so.5</code>. Binaries with equivalent
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<code class="constant">DT_SONAME</code>s are forward-compatibile: in
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the table below, releases incompatible with the previous
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one are explicitly noted.
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If a particular release is not listed, its libstdc++.so binary
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has the same filename and <code class="constant">DT_SONAME</code> as the
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preceding release.
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</p><p>It is versioned as follows:
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</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-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 3.4.0: 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 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 4.2.0: 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 4.3.0: 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><li class="listitem"><p>GCC 4.6.0: libstdc++.so.6.0.15</p></li><li class="listitem"><p>GCC 4.6.1: libstdc++.so.6.0.16</p></li><li class="listitem"><p>GCC 4.7.0: libstdc++.so.6.0.17</p></li><li class="listitem"><p>GCC 4.8.0: libstdc++.so.6.0.18</p></li><li class="listitem"><p>GCC 4.8.3: libstdc++.so.6.0.19</p></li><li class="listitem"><p>GCC 4.9.0: libstdc++.so.6.0.20</p></li><li class="listitem"><p>GCC 5.1.0: libstdc++.so.6.0.21</p></li><li class="listitem"><p>GCC 6.1.0: libstdc++.so.6.0.22</p></li><li class="listitem"><p>GCC 7.1.0: libstdc++.so.6.0.23</p></li><li class="listitem"><p>GCC 7.2.0: libstdc++.so.6.0.24</p></li><li class="listitem"><p>GCC 8.0.0: libstdc++.so.6.0.25</p></li><li class="listitem"><p>GCC 9.0.0: libstdc++.so.6.0.26</p></li></ul></div><p>
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Note 1: Error should be libstdc++.so.3.0.3.
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</p><p>
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Note 2: Not strictly required.
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</p><p>
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Note 3: This release (but not previous or subsequent) has one
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known incompatibility, see <a class="link" href="http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33678" target="_top">33678</a>
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in the GCC bug database.
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</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
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definitions, where the version definition is the maximum for a
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particular release. Note, only symbols which are newly introduced
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will use the maximum version definition. Thus, for release series
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with the same label, but incremented version definitions, the later
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release has both versions. (An example of this would be the
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GCC 3.2.1 release, which has GLIBCPP_3.2.1 for new symbols and
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GLIBCPP_3.2 for symbols that were introduced in the GCC 3.2.0
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release.) If a particular release is not listed, it has the same
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version labels as the preceding release.
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</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-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><li class="listitem"><p>GCC 4.6.0: GLIBCXX_3.4.15, CXXABI_1.3.5</p></li><li class="listitem"><p>GCC 4.6.1: GLIBCXX_3.4.16, CXXABI_1.3.5</p></li><li class="listitem"><p>GCC 4.7.0: GLIBCXX_3.4.17, CXXABI_1.3.6</p></li><li class="listitem"><p>GCC 4.8.0: GLIBCXX_3.4.18, CXXABI_1.3.7</p></li><li class="listitem"><p>GCC 4.8.3: GLIBCXX_3.4.19, CXXABI_1.3.7</p></li><li class="listitem"><p>GCC 4.9.0: GLIBCXX_3.4.20, CXXABI_1.3.8</p></li><li class="listitem"><p>GCC 5.1.0: GLIBCXX_3.4.21, CXXABI_1.3.9</p></li><li class="listitem"><p>GCC 6.1.0: GLIBCXX_3.4.22, CXXABI_1.3.10</p></li><li class="listitem"><p>GCC 7.1.0: GLIBCXX_3.4.23, CXXABI_1.3.11</p></li><li class="listitem"><p>GCC 7.2.0: GLIBCXX_3.4.24, CXXABI_1.3.11</p></li><li class="listitem"><p>GCC 8.0.0: GLIBCXX_3.4.25, CXXABI_1.3.11</p></li><li class="listitem"><p>GCC 9.0.0: GLIBCXX_3.4.26, CXXABI_1.3.11</p></li></ul></div></li><li class="listitem"><p>Incremental bumping of a compiler pre-defined macro,
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__GXX_ABI_VERSION. This macro is defined as the version of the
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compiler v3 ABI, with g++ 3.0 being version 100. This macro will
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||
be automatically defined whenever g++ is used (the curious can
|
||
test this by invoking g++ with the '-v' flag.)
|
||
</p><p>
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This macro was defined in the file "lang-specs.h" in the gcc/cp directory.
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Later versions defined it in "c-common.c" in the gcc directory, and from
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G++ 3.4 it is defined in c-cppbuiltin.c and its value determined by the
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'-fabi-version' command line option.
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||
</p><p>
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It is versioned as follows, where 'n' is given by '-fabi-version=n':
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||
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>GCC 3.0: 100</p></li><li class="listitem"><p>GCC 3.1: 100 (Error, should be 101)</p></li><li class="listitem"><p>GCC 3.2: 102</p></li><li class="listitem"><p>GCC 3.3: 102</p></li><li class="listitem"><p>GCC 3.4, GCC 4.x: 102 (when n=1)</p></li><li class="listitem"><p>GCC 3.4, GCC 4.x: 1000 + n (when n>1) </p></li><li class="listitem"><p>GCC 3.4, GCC 4.x: 999999 (when n=0)</p></li></ul></div><p></p></li><li class="listitem"><p>Changes to the default compiler option for
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<code class="code">-fabi-version</code>.
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||
</p><p>
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||
It is versioned as follows:
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</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>GCC 3.0: (Error, not versioned) </p></li><li class="listitem"><p>GCC 3.1: (Error, not versioned) </p></li><li class="listitem"><p>GCC 3.2: <code class="code">-fabi-version=1</code></p></li><li class="listitem"><p>GCC 3.3: <code class="code">-fabi-version=1</code></p></li><li class="listitem"><p>GCC 3.4, GCC 4.x: <code class="code">-fabi-version=2</code> <span class="emphasis"><em>(Incompatible with previous)</em></span></p></li><li class="listitem"><p>GCC 5 and higher: <code class="code">-fabi-version=0</code> <span class="emphasis"><em>(See GCC manual for meaning)</em></span></p></li></ul></div><p></p></li><li class="listitem"><p><a id="abi.versioning.__GLIBCXX__"></a>Incremental bumping of a library pre-defined macro. For releases
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before 3.4.0, the macro is <span class="symbol">__GLIBCPP__</span>. For later
|
||
releases, it's <span class="symbol">__GLIBCXX__</span>. (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 integer constant.
|
||
</p><p>
|
||
This macro is defined in the file
|
||
<code class="filename">c++config</code> in the
|
||
<code class="filename">libstdc++-v3/include/bits</code>
|
||
directory. Up to GCC 4.1.0, it was
|
||
changed every night by an automated script. Since GCC 4.1.0 it is set
|
||
during configuration to the same value as
|
||
<code class="filename">gcc/DATESTAMP</code>, so for an official release its value
|
||
is the same as the date of the release, which is given in the <a class="link" href="https://gcc.gnu.org/develop.html#timeline" target="_top">GCC Release
|
||
Timeline</a>.
|
||
</p><p>
|
||
This macro can be used in code to detect whether the C++ Standard Library
|
||
implementation in use is libstdc++, but is not useful for detecting the
|
||
libstdc++ version, nor whether particular features are supported.
|
||
The macro value might be a date after a feature was added to the
|
||
development trunk, but the release could be from an older branch without
|
||
the feature. For example, in the 5.4.0 release the macro has the value
|
||
<code class="literal">20160603</code> which is greater than the
|
||
<code class="literal">20160427</code> value of the macro in the 6.1.0 release,
|
||
but there are features supported in the 6.1.0 release that are not
|
||
supported in 5.4.0 release.
|
||
You also can't test for the exact values listed below to try and
|
||
identify a release, because a snapshot taken from the gcc-5-branch on
|
||
2016-04-27 would have the same value for the macro as the 6.1.0 release
|
||
despite being a different version.
|
||
Many GNU/Linux distributions build their GCC packages from snapshots, so
|
||
the macro can have dates that don't correspond to official releases.
|
||
</p><p>
|
||
It is versioned as follows:
|
||
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>GCC 3.0.0: <code class="literal">20010615</code></p></li><li class="listitem"><p>GCC 3.0.1: <code class="literal">20010819</code></p></li><li class="listitem"><p>GCC 3.0.2: <code class="literal">20011023</code></p></li><li class="listitem"><p>GCC 3.0.3: <code class="literal">20011220</code></p></li><li class="listitem"><p>GCC 3.0.4: <code class="literal">20020220</code></p></li><li class="listitem"><p>GCC 3.1.0: <code class="literal">20020514</code></p></li><li class="listitem"><p>GCC 3.1.1: <code class="literal">20020725</code></p></li><li class="listitem"><p>GCC 3.2.0: <code class="literal">20020814</code></p></li><li class="listitem"><p>GCC 3.2.1: <code class="literal">20021119</code></p></li><li class="listitem"><p>GCC 3.2.2: <code class="literal">20030205</code></p></li><li class="listitem"><p>GCC 3.2.3: <code class="literal">20030422</code></p></li><li class="listitem"><p>GCC 3.3.0: <code class="literal">20030513</code></p></li><li class="listitem"><p>GCC 3.3.1: <code class="literal">20030804</code></p></li><li class="listitem"><p>GCC 3.3.2: <code class="literal">20031016</code></p></li><li class="listitem"><p>GCC 3.3.3: <code class="literal">20040214</code></p></li><li class="listitem"><p>GCC 3.4.0: <code class="literal">20040419</code></p></li><li class="listitem"><p>GCC 3.4.1: <code class="literal">20040701</code></p></li><li class="listitem"><p>GCC 3.4.2: <code class="literal">20040906</code></p></li><li class="listitem"><p>GCC 3.4.3: <code class="literal">20041105</code></p></li><li class="listitem"><p>GCC 3.4.4: <code class="literal">20050519</code></p></li><li class="listitem"><p>GCC 3.4.5: <code class="literal">20051201</code></p></li><li class="listitem"><p>GCC 3.4.6: <code class="literal">20060306</code></p></li><li class="listitem"><p>GCC 4.0.0: <code class="literal">20050421</code></p></li><li class="listitem"><p>GCC 4.0.1: <code class="literal">20050707</code></p></li><li class="listitem"><p>GCC 4.0.2: <code class="literal">20050921</code></p></li><li class="listitem"><p>GCC 4.0.3: <code class="literal">20060309</code></p></li><li class="listitem"><p>
|
||
GCC 4.1.0 and later: the GCC release date, as shown in the
|
||
<a class="link" href="https://gcc.gnu.org/develop.html#timeline" target="_top">GCC
|
||
Release Timeline</a>
|
||
</p></li></ul></div><p></p></li><li class="listitem"><p>
|
||
Since GCC 7, incremental bumping of a library pre-defined macro,
|
||
<span class="symbol">_GLIBCXX_RELEASE</span>. This macro is defined to the GCC
|
||
major version that the libstdc++ headers belong to, as an integer constant.
|
||
When compiling with GCC it has the same value as GCC's pre-defined
|
||
macro <span class="symbol">__GNUC__</span>.
|
||
This macro can be used when libstdc++ is used with a non-GNU
|
||
compiler where <span class="symbol">__GNUC__</span> is not defined, or has a
|
||
different value that doesn't correspond to the libstdc++ version.
|
||
</p><p>
|
||
This macro is defined in the file
|
||
<code class="filename">c++config</code> in the
|
||
<code class="filename">libstdc++-v3/include/bits</code>
|
||
directory and is generated automatically by autoconf as part of the
|
||
configure-time generation of
|
||
<code class="filename">config.h</code> and subsequently
|
||
<code class="filename"><bits/c++config.h></code>.
|
||
</p></li><li class="listitem"><p>
|
||
Historically, incremental bumping of a library pre-defined macro,
|
||
<span class="symbol">_GLIBCPP_VERSION</span>. This macro was defined as the
|
||
released version of the library, as a string literal. This was only
|
||
implemented in GCC 3.1.0 releases and higher, and was deprecated in
|
||
3.4.x (where it was called <span class="symbol">_GLIBCXX_VERSION</span>),
|
||
and is not defined in 4.0.0 and higher.
|
||
</p><p>
|
||
This macro is defined in the same file as
|
||
<span class="symbol">_GLIBCXX_RELEASE</span>, described above.
|
||
</p><p>
|
||
It is versioned as follows:
|
||
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>GCC 3.0.0: <code class="literal">"3.0.0"</code></p></li><li class="listitem"><p>GCC 3.0.1: <code class="literal">"3.0.0"</code> (Error, should be <code class="literal">"3.0.1"</code>)</p></li><li class="listitem"><p>GCC 3.0.2: <code class="literal">"3.0.0"</code> (Error, should be <code class="literal">"3.0.2"</code>)</p></li><li class="listitem"><p>GCC 3.0.3: <code class="literal">"3.0.0"</code> (Error, should be <code class="literal">"3.0.3"</code>)</p></li><li class="listitem"><p>GCC 3.0.4: <code class="literal">"3.0.0"</code> (Error, should be <code class="literal">"3.0.4"</code>)</p></li><li class="listitem"><p>GCC 3.1.0: <code class="literal">"3.1.0"</code></p></li><li class="listitem"><p>GCC 3.1.1: <code class="literal">"3.1.1"</code></p></li><li class="listitem"><p>GCC 3.2.0: <code class="literal">"3.2"</code></p></li><li class="listitem"><p>GCC 3.2.1: <code class="literal">"3.2.1"</code></p></li><li class="listitem"><p>GCC 3.2.2: <code class="literal">"3.2.2"</code></p></li><li class="listitem"><p>GCC 3.2.3: <code class="literal">"3.2.3"</code></p></li><li class="listitem"><p>GCC 3.3.0: <code class="literal">"3.3"</code></p></li><li class="listitem"><p>GCC 3.3.1: <code class="literal">"3.3.1"</code></p></li><li class="listitem"><p>GCC 3.3.2: <code class="literal">"3.3.2"</code></p></li><li class="listitem"><p>GCC 3.3.3: <code class="literal">"3.3.3"</code></p></li><li class="listitem"><p>GCC 3.4: <code class="literal">"version-unused"</code></p></li><li class="listitem"><p>GCC 4 and later: not defined</p></li></ul></div><p></p></li><li class="listitem"><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
|
||
<code class="filename">include/c++</code>, then nested in a
|
||
directory hierarchy corresponding to the C++ compiler's released
|
||
version. This version corresponds to the variable "gcc_version" in
|
||
"libstdc++-v3/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 class="itemizedlist" style="list-style-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.x: include/c++/3.4.x</p></li><li class="listitem"><p>GCC 4.x.y: include/c++/4.x.y</p></li><li class="listitem"><p>GCC 5.x.0: include/c++/5.x.0</p></li><li class="listitem"><p>GCC 6.x.0: include/c++/6.x.0</p></li><li class="listitem"><p>GCC 7.x.0: include/c++/7.x.0</p></li><li class="listitem"><p>GCC 8.x.0: include/c++/8.x.0</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="section"><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) or the Sun linker, 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 GNU/Linux and BSD versions, particularly ones using
|
||
GCC 3.1 and later, will meet the
|
||
requirements above, as does Solaris 2.5 and up.
|
||
</p></div><div class="section"><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:
|
||
<a class="link" href="configure.html" title="Configure">here</a>
|
||
</p><p>
|
||
There is one flag that explicitly deals with symbol versioning:
|
||
--enable-symvers.
|
||
</p><p>
|
||
In particular, libstdc++-v3/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="section"><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++ (showing either 'gnu' or another of the supported styles):
|
||
</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><p>
|
||
On Solaris 2, you can use <code class="code">pvs -r</code> instead:
|
||
</p><pre class="programlisting">
|
||
%g++ hello.cc -o hello.out
|
||
|
||
%pvs -r hello.out
|
||
libstdc++.so.6 (GLIBCXX_3.4, GLIBCXX_3.4.12);
|
||
libgcc_s.so.1 (GCC_3.0);
|
||
libc.so.1 (SUNWprivate_1.1, SYSVABI_1.3);
|
||
</pre><p>
|
||
<code class="code">ldd -v</code> works too, but is very verbose.
|
||
</p></div></div><div class="section"><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 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>
|
||
Other allowed changes are possible.
|
||
</p></div><div class="section"><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 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
|
||
base classes</p></li><li class="listitem"><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 class="listitem"><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 passing instances of this
|
||
class in registers, the compiler will be forced to use memory. See the
|
||
section on <a class="link" href="https://itanium-cxx-abi.github.io/cxx-abi/abi.html#calls" target="_top">Function
|
||
Calling Conventions and APIs</a>
|
||
of the C++ ABI documentation for further details.
|
||
</p></li></ol></div></div><div class="section"><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>
|
||
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 class="variablelist"><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 class="listitem"><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 class="variablelist"><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 class="listitem"><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="section"><div class="titlepage"><div><div><h3 class="title"><a id="abi.testing"></a>Testing</h3></div></div></div><div class="section"><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.
|
||
</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 of 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 PR 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="section"><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 a C++ shared library compiled with
|
||
GCC 3.3, and uses io, exceptions, locale, etc. The dependent library
|
||
libb is a C++ shared library compiled with GCC 3.4, 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="section"><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="link" href="http://gcc.gnu.org/PR24660" target="_top">24660: versioning weak symbols in libstdc++</a>
|
||
</p><p>
|
||
<a class="link" 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="biblio.abicheck"></a><p>[biblio.abicheck] <span class="title"><em>
|
||
<a class="link" href="http://abicheck.sourceforge.net" target="_top">
|
||
ABIcheck
|
||
</a>
|
||
</em>. </span></p></div><div class="biblioentry"><a id="biblio.cxxabi"></a><p>[biblio.cxxabi] <span class="title"><em>
|
||
<a class="link" href="https://itanium-cxx-abi.github.io/cxx-abi/" target="_top">
|
||
Itanium C++ ABI
|
||
</a>
|
||
</em>. </span></p></div><div class="biblioentry"><a id="id-1.3.6.3.6.10.4"></a><p><span class="title"><em>
|
||
<a class="link" href="https://software.intel.com/en-us/articles/intel-compilers-for-linux-compatibility-with-gnu-compilers" target="_top">
|
||
Intel Compilers for Linux: Compatibility with GNU Compilers
|
||
</a>
|
||
</em>. </span></p></div><div class="biblioentry"><a id="id-1.3.6.3.6.10.5"></a><p><span class="title"><em>
|
||
<a class="link" href="https://docs.oracle.com/cd/E23824_01/html/819-0690/index.html" target="_top">
|
||
Linker and Libraries Guide (document 819-0690)
|
||
</a>
|
||
</em>. </span></p></div><div class="biblioentry"><a id="id-1.3.6.3.6.10.6"></a><p><span class="title"><em>
|
||
<a class="link" href="https://docs.oracle.com/cd/E19422-01/819-3689/" target="_top">
|
||
Sun Studio 11: C++ Migration Guide (document 819-3689)
|
||
</a>
|
||
</em>. </span></p></div><div class="biblioentry"><a id="id-1.3.6.3.6.10.7"></a><p><span class="title"><em>
|
||
<a class="link" href="https://www.akkadia.org/drepper/dsohowto.pdf" target="_top">
|
||
How to Write Shared Libraries
|
||
</a>
|
||
</em>. </span><span class="author"><span class="firstname">Ulrich</span> <span class="surname">Drepper</span>. </span></p></div><div class="biblioentry"><a id="id-1.3.6.3.6.10.8"></a><p><span class="title"><em>
|
||
<a class="link" href="http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ihi0036b/index.html" target="_top">
|
||
C++ ABI for the ARM Architecture
|
||
</a>
|
||
</em>. </span></p></div><div class="biblioentry"><a id="id-1.3.6.3.6.10.9"></a><p><span class="title"><em>
|
||
<a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1976.html" target="_top">
|
||
Dynamic Shared Objects: Survey and Issues
|
||
</a>
|
||
</em>. </span><span class="subtitle">
|
||
ISO C++ J16/06-0046
|
||
. </span><span class="author"><span class="firstname">Benjamin</span> <span class="surname">Kosnik</span>. </span></p></div><div class="biblioentry"><a id="id-1.3.6.3.6.10.10"></a><p><span class="title"><em>
|
||
<a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2013.html" target="_top">
|
||
Versioning With Namespaces
|
||
</a>
|
||
</em>. </span><span class="subtitle">
|
||
ISO C++ J16/06-0083
|
||
. </span><span class="author"><span class="firstname">Benjamin</span> <span class="surname">Kosnik</span>. </span></p></div><div class="biblioentry"><a id="id-1.3.6.3.6.10.11"></a><p><span class="title"><em>
|
||
<a class="link" href="http://syrcose.ispras.ru/2009/files/02_paper.pdf" target="_top">
|
||
Binary Compatibility of Shared Libraries Implemented in C++
|
||
on GNU/Linux Systems
|
||
</a>
|
||
</em>. </span><span class="subtitle">
|
||
SYRCoSE 2009
|
||
. </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">Testing </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> API Evolution and Deprecation History</td></tr></table></div></body></html> |