| <sect1 id="appendix.porting.abi" xreflabel="abi"> |
| <?dbhtml filename="abi.html"?> |
| |
| <sect1info> |
| <keywordset> |
| <keyword> |
| C++ |
| </keyword> |
| <keyword> |
| ABI |
| </keyword> |
| <keyword> |
| version |
| </keyword> |
| <keyword> |
| dynamic |
| </keyword> |
| <keyword> |
| shared |
| </keyword> |
| </keywordset> |
| </sect1info> |
| |
| <title>ABI Policy and Guidelines</title> |
| |
| <para> |
| </para> |
| |
| <sect2 id="abi.cxx_interface" xreflabel="abi.cxx_interface"> |
| <title>The C++ Interface</title> |
| |
| <para> |
| C++ applications often dependent on specific language support |
| routines, say for throwing exceptions, or catching exceptions, and |
| perhaps also dependent on features in the C++ Standard Library. |
| </para> |
| |
| <para> |
| The C++ Standard Library has many include files, types defined in |
| those include files, specific named functions, and other |
| behavior. The text of these behaviors, as written in source include |
| files, is called the Application Programing Interface, or API. |
| </para> |
| |
| <para> |
| Furthermore, C++ source that is compiled into object files is |
| transformed by the compiler: it arranges objects with specific |
| alignment and in a particular layout, mangling names according to a |
| well-defined algorithm, has specific arrangements for the support of |
| virtual functions, etc. These details are defined as the compiler |
| Application Binary Interface, or ABI. The GNU C++ compiler uses an |
| industry-standard C++ ABI starting with version 3. Details can be |
| found in the <ulink |
| url="http://www.codesourcery.com/cxx-abi/abi.html"> ABI |
| specification</ulink>. |
| </para> |
| |
| <para> |
| The GNU C++ compiler, g++, has a compiler command line option to |
| switch between various different C++ ABIs. This explicit version |
| switch is the flag <code>-fabi-version</code>. In addition, some |
| g++ command line options may change the ABI as a side-effect of |
| use. Such flags include <code>-fpack-struct</code> and |
| <code>-fno-exceptions</code>, but include others: see the complete |
| list in the GCC manual under the heading <ulink url="http://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html#Code%20Gen%20Options">Options |
| for Code Generation Conventions</ulink>. |
| </para> |
| |
| <para> |
| The configure options used when building a specific libstdc++ |
| version may also impact the resulting library ABI. The available |
| configure options, and their impact on the library ABI, are |
| documented |
| <ulink url="http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html"> |
| here</ulink>. |
| </para> |
| |
| <para> Putting all of these ideas together results in the C++ Standard |
| library ABI, which is the compilation of a given library API by a |
| given compiler ABI. In a nutshell: |
| </para> |
| |
| <para> |
| <quote> |
| library API + compiler ABI = library ABI |
| </quote> |
| </para> |
| |
| <para> |
| The library ABI is mostly of interest for end-users who have |
| unresolved symbols and are linking dynamically to the C++ Standard |
| library, and who thus must be careful to compile their application |
| with a compiler that is compatible with the available C++ Standard |
| library binary. In this case, compatible is defined with the equation |
| above: given an application compiled with a given compiler ABI and |
| library API, it will work correctly with a Standard C++ Library |
| created with the same constraints. |
| </para> |
| |
| <para> |
| To use a specific version of the C++ ABI, one must use a |
| corresponding GNU C++ toolchain (i.e., g++ and libstdc++) that |
| implements the C++ ABI in question. |
| </para> |
| |
| </sect2> |
| |
| <sect2 id="abi.versioning" xreflabel="abi.versioning"> |
| <title>Versioning</title> |
| |
| <para> The C++ interface has evolved throughout the history of the GNU |
| C++ toolchain. With each release, various details have been changed so |
| as to give distinct versions to the C++ interface. |
| </para> |
| |
| <sect3 id="abi.versioning.goals" xreflabel="abi.versioning.goals"> |
| <title>Goals</title> |
| |
| <para>Extending existing, stable ABIs. Versioning gives subsequent stable |
| releases series libraries the ability to add new symbols and add |
| functionality, all the while retaining backwards compatibility with |
| the previous releases in the series. Note: the reverse is not true. It |
| is not possible to take binaries linked with the latest version of a |
| release series (if symbols have been added) and expect the initial |
| release of the series to remain link compatible. |
| </para> |
| |
| <para>Allows multiple, incompatible ABIs to coexist at the same time. |
| </para> |
| </sect3> |
| |
| <sect3 id="abi.versioning.history" xreflabel="abi.versioning.history"> |
| <title>History</title> |
| |
| <para> |
| How can this complexity be managed? What does C++ versioning mean? |
| Because library and compiler changes often make binaries compiled |
| with one version of the GNU tools incompatible with binaries |
| compiled with other (either newer or older) versions of the same GNU |
| tools, specific techniques are used to make managing this complexity |
| easier. |
| </para> |
| |
| <para> |
| The following techniques are used: |
| </para> |
| |
| <orderedlist> |
| |
| <listitem><para>Release versioning on the libgcc_s.so binary. </para> |
| |
| <para>This is implemented via file names and the ELF DT_SONAME |
| mechanism (at least on ELF systems). It is versioned as follows: |
| </para> |
| |
| <itemizedlist> |
| <listitem><para>gcc-3.0.0: libgcc_s.so.1</para></listitem> |
| <listitem><para>gcc-3.0.1: libgcc_s.so.1</para></listitem> |
| <listitem><para>gcc-3.0.2: libgcc_s.so.1</para></listitem> |
| <listitem><para>gcc-3.0.3: libgcc_s.so.1</para></listitem> |
| <listitem><para>gcc-3.0.4: libgcc_s.so.1</para></listitem> |
| <listitem><para>gcc-3.1.0: libgcc_s.so.1</para></listitem> |
| <listitem><para>gcc-3.1.1: libgcc_s.so.1</para></listitem> |
| <listitem><para>gcc-3.2.0: libgcc_s.so.1</para></listitem> |
| <listitem><para>gcc-3.2.1: libgcc_s.so.1</para></listitem> |
| <listitem><para>gcc-3.2.2: libgcc_s.so.1</para></listitem> |
| <listitem><para>gcc-3.2.3: libgcc_s.so.1</para></listitem> |
| <listitem><para>gcc-3.3.0: libgcc_s.so.1</para></listitem> |
| <listitem><para>gcc-3.3.1: libgcc_s.so.1</para></listitem> |
| <listitem><para>gcc-3.3.2: libgcc_s.so.1</para></listitem> |
| <listitem><para>gcc-3.3.3: libgcc_s.so.1</para></listitem> |
| <listitem><para>gcc-3.4.x, gcc-4.0.x, gcc-4.1.x, gcc-4.2.x: on m68k-linux and |
| hppa-linux this is either libgcc_s.so.1 (when configuring |
| <code>--with-sjlj-exceptions</code>) or libgcc_s.so.2. For all |
| others, this is libgcc_s.so.1. </para> |
| </listitem> |
| </itemizedlist> |
| |
| </listitem> |
| |
| <listitem><para>Symbol versioning on the libgcc_s.so binary.</para> |
| |
| <para>It is versioned with the following labels and version |
| definitions, where the version definition is the maximum for a |
| particular release. Labels are cumulative. If a particular release |
| is not listed, it has the same version labels as the preceding |
| release.</para> |
| |
| <para>This corresponds to the mapfile: gcc/libgcc-std.ver</para> |
| <itemizedlist> |
| <listitem><para>gcc-3.0.0: GCC_3.0</para></listitem> |
| <listitem><para>gcc-3.3.0: GCC_3.3</para></listitem> |
| <listitem><para>gcc-3.3.1: GCC_3.3.1</para></listitem> |
| <listitem><para>gcc-3.3.2: GCC_3.3.2</para></listitem> |
| <listitem><para>gcc-3.3.4: GCC_3.3.4</para></listitem> |
| <listitem><para>gcc-3.4.0: GCC_3.4</para></listitem> |
| <listitem><para>gcc-3.4.2: GCC_3.4.2</para></listitem> |
| <listitem><para>gcc-3.4.4: GCC_3.4.4</para></listitem> |
| <listitem><para>gcc-4.0.0: GCC_4.0.0</para></listitem> |
| <listitem><para>gcc-4.1.0: GCC_4.1.0</para></listitem> |
| <listitem><para>gcc-4.2.0: GCC_4.2.0</para></listitem> |
| </itemizedlist> |
| </listitem> |
| |
| <listitem><para>Release versioning on the libstdc++.so binary, implemented in the same was as the libgcc_s.so binary, above.</para> |
| |
| <para>It is versioned as follows: |
| </para> |
| <itemizedlist> |
| <listitem><para>gcc-3.0.0: libstdc++.so.3.0.0</para></listitem> |
| <listitem><para>gcc-3.0.1: libstdc++.so.3.0.1</para></listitem> |
| <listitem><para>gcc-3.0.2: libstdc++.so.3.0.2</para></listitem> |
| <listitem><para>gcc-3.0.3: libstdc++.so.3.0.2 (Error should be libstdc++.so.3.0.3)</para></listitem> |
| <listitem><para>gcc-3.0.4: libstdc++.so.3.0.4</para></listitem> |
| <listitem><para>gcc-3.1.0: libstdc++.so.4.0.0</para></listitem> |
| <listitem><para>gcc-3.1.1: libstdc++.so.4.0.1</para></listitem> |
| <listitem><para>gcc-3.2.0: libstdc++.so.5.0.0</para></listitem> |
| <listitem><para>gcc-3.2.1: libstdc++.so.5.0.1</para></listitem> |
| <listitem><para>gcc-3.2.2: libstdc++.so.5.0.2</para></listitem> |
| <listitem><para>gcc-3.2.3: libstdc++.so.5.0.3 (Not strictly required)</para></listitem> |
| <listitem><para>gcc-3.3.0: libstdc++.so.5.0.4</para></listitem> |
| <listitem><para>gcc-3.3.1: libstdc++.so.5.0.5</para></listitem> |
| <listitem><para>gcc-3.3.2: libstdc++.so.5.0.5</para></listitem> |
| <listitem><para>gcc-3.3.3: libstdc++.so.5.0.5</para></listitem> |
| <listitem><para>gcc-3.4.0: libstdc++.so.6.0.0</para></listitem> |
| <listitem><para>gcc-3.4.1: libstdc++.so.6.0.1</para></listitem> |
| <listitem><para>gcc-3.4.2: libstdc++.so.6.0.2</para></listitem> |
| <listitem><para>gcc-3.4.3: libstdc++.so.6.0.3</para></listitem> |
| <listitem><para>gcc-3.4.4: libstdc++.so.6.0.3</para></listitem> |
| <listitem><para>gcc-3.4.5: libstdc++.so.6.0.3</para></listitem> |
| <listitem><para>gcc-3.4.6: libstdc++.so.6.0.3</para></listitem> |
| <listitem><para>gcc-4.0.0: libstdc++.so.6.0.4</para></listitem> |
| <listitem><para>gcc-4.0.1: libstdc++.so.6.0.5</para></listitem> |
| <listitem><para>gcc-4.0.2: libstdc++.so.6.0.6</para></listitem> |
| <listitem><para>gcc-4.0.3: libstdc++.so.6.0.7</para></listitem> |
| <listitem><para>gcc-4.1.0: libstdc++.so.6.0.7</para></listitem> |
| <listitem><para>gcc-4.1.1: libstdc++.so.6.0.8</para></listitem> |
| <listitem><para>gcc-4.1.2: libstdc++.so.6.0.8</para></listitem> |
| <listitem><para>gcc-4.2.0: libstdc++.so.6.0.9</para></listitem> |
| </itemizedlist> |
| </listitem> |
| |
| <listitem><para>Symbol versioning on the libstdc++.so binary.</para> |
| |
| <para>mapfile: libstdc++/config/linker-map.gnu</para> |
| <para>It is versioned with the following labels and version |
| definitions, where the version definition is the maximum for a |
| particular release. Note, only symbol which are newly introduced |
| will use the maximum version definition. Thus, for release series |
| with the same label, but incremented version definitions, the later |
| release has both versions. (An example of this would be the |
| gcc-3.2.1 release, which has GLIBCPP_3.2.1 for new symbols and |
| GLIBCPP_3.2 for symbols that were introduced in the gcc-3.2.0 |
| release.) If a particular release is not listed, it has the same |
| version labels as the preceding release. |
| </para> |
| <itemizedlist> |
| <listitem><para>gcc-3.0.0: (Error, not versioned)</para></listitem> |
| <listitem><para>gcc-3.0.1: (Error, not versioned)</para></listitem> |
| <listitem><para>gcc-3.0.2: (Error, not versioned)</para></listitem> |
| <listitem><para>gcc-3.0.3: (Error, not versioned)</para></listitem> |
| <listitem><para>gcc-3.0.4: (Error, not versioned)</para></listitem> |
| <listitem><para>gcc-3.1.0: GLIBCPP_3.1, CXXABI_1</para></listitem> |
| <listitem><para>gcc-3.1.1: GLIBCPP_3.1, CXXABI_1</para></listitem> |
| <listitem><para>gcc-3.2.0: GLIBCPP_3.2, CXXABI_1.2</para></listitem> |
| <listitem><para>gcc-3.2.1: GLIBCPP_3.2.1, CXXABI_1.2</para></listitem> |
| <listitem><para>gcc-3.2.2: GLIBCPP_3.2.2, CXXABI_1.2</para></listitem> |
| <listitem><para>gcc-3.2.3: GLIBCPP_3.2.2, CXXABI_1.2</para></listitem> |
| <listitem><para>gcc-3.3.0: GLIBCPP_3.2.2, CXXABI_1.2.1</para></listitem> |
| <listitem><para>gcc-3.3.1: GLIBCPP_3.2.3, CXXABI_1.2.1</para></listitem> |
| <listitem><para>gcc-3.3.2: GLIBCPP_3.2.3, CXXABI_1.2.1</para></listitem> |
| <listitem><para>gcc-3.3.3: GLIBCPP_3.2.3, CXXABI_1.2.1</para></listitem> |
| <listitem><para>gcc-3.4.0: GLIBCXX_3.4, CXXABI_1.3</para></listitem> |
| <listitem><para>gcc-3.4.1: GLIBCXX_3.4.1, CXXABI_1.3</para></listitem> |
| <listitem><para>gcc-3.4.2: GLIBCXX_3.4.2</para></listitem> |
| <listitem><para>gcc-3.4.3: GLIBCXX_3.4.3</para></listitem> |
| <listitem><para>gcc-4.0.0: GLIBCXX_3.4.4, CXXABI_1.3.1</para></listitem> |
| <listitem><para>gcc-4.0.1: GLIBCXX_3.4.5</para></listitem> |
| <listitem><para>gcc-4.0.2: GLIBCXX_3.4.6</para></listitem> |
| <listitem><para>gcc-4.0.3: GLIBCXX_3.4.7</para></listitem> |
| <listitem><para>gcc-4.1.1: GLIBCXX_3.4.8</para></listitem> |
| <listitem><para>gcc-4.2.0: GLIBCXX_3.4.9</para></listitem> |
| </itemizedlist> |
| </listitem> |
| |
| <listitem> |
| <para>Incremental bumping of a compiler pre-defined macro, |
| __GXX_ABI_VERSION. This macro is defined as the version of the |
| compiler v3 ABI, with g++ 3.0.x being version 100. This macro will |
| be automatically defined whenever g++ is used (the curious can |
| test this by invoking g++ with the '-v' flag.) |
| </para> |
| |
| <para> |
| This macro was defined in the file "lang-specs.h" in the gcc/cp directory. |
| Later versions defined it in "c-common.c" in the gcc directory, and from |
| G++ 3.4 it is defined in c-cppbuiltin.c and its value determined by the |
| '-fabi-version' command line option. |
| </para> |
| |
| <para> |
| It is versioned as follows, where 'n' is given by '-fabi-version=n': |
| </para> |
| <itemizedlist> |
| <listitem><para>gcc-3.0.x: 100</para></listitem> |
| <listitem><para>gcc-3.1.x: 100 (Error, should be 101)</para></listitem> |
| <listitem><para>gcc-3.2.x: 102</para></listitem> |
| <listitem><para>gcc-3.3.x: 102</para></listitem> |
| <listitem><para>gcc-3.4.x, gcc-4.0.x, gcc-4.1.x, gcc-4.2.x: 102 (when n=1)</para></listitem> |
| <listitem><para>gcc-3.4.x, gcc-4.0.x, gcc-4.1.x, gcc-4.2.x: 1000 + n (when n>1)</para></listitem> |
| <listitem><para>gcc-3.4.x, gcc-4.0.x, gcc-4.1.x, gcc-4.2.x: 999999 (when n=0)</para></listitem> |
| </itemizedlist> |
| <para></para> |
| </listitem> |
| |
| <listitem> |
| <para>Changes to the default compiler option for |
| <code>-fabi-version</code>. |
| </para> |
| <para> |
| It is versioned as follows: |
| </para> |
| <itemizedlist> |
| <listitem><para>gcc-3.0.x: (Error, not versioned) </para></listitem> |
| <listitem><para>gcc-3.1.x: (Error, not versioned) </para></listitem> |
| <listitem><para>gcc-3.2.x: <code>-fabi-version=1</code></para></listitem> |
| <listitem><para>gcc-3.3.x: <code>-fabi-version=1</code></para></listitem> |
| <listitem><para>gcc-3.4.x, gcc-4.0.x, gcc-4.1.x, gcc-4.2.x: <code>-fabi-version=2</code></para></listitem> |
| </itemizedlist> |
| <para></para> |
| </listitem> |
| |
| <listitem> |
| <para>Incremental bumping of a library pre-defined macro. For releases |
| before 3.4.0, the macro is __GLIBCPP__. For later releases, it's |
| __GLIBCXX__. (The libstdc++ project generously changed from CPP to |
| CXX throughout its source to allow the "C" pre-processor the CPP |
| macro namespace.) These macros are defined as the date the library |
| was released, in compressed ISO date format, as an unsigned long. |
| </para> |
| |
| <para> |
| This macro is defined in the file "c++config" in the |
| "libstdc++/include/bits" directory. (Up to gcc-4.1.0, it was |
| changed every night by an automated script. Since gcc-4.1.0, it is |
| the same value as gcc/DATESTAMP.) |
| </para> |
| <para> |
| It is versioned as follows: |
| </para> |
| <itemizedlist> |
| <listitem><para>gcc-3.0.0: 20010615</para></listitem> |
| <listitem><para>gcc-3.0.1: 20010819</para></listitem> |
| <listitem><para>gcc-3.0.2: 20011023</para></listitem> |
| <listitem><para>gcc-3.0.3: 20011220</para></listitem> |
| <listitem><para>gcc-3.0.4: 20020220</para></listitem> |
| <listitem><para>gcc-3.1.0: 20020514</para></listitem> |
| <listitem><para>gcc-3.1.1: 20020725</para></listitem> |
| <listitem><para>gcc-3.2.0: 20020814</para></listitem> |
| <listitem><para>gcc-3.2.1: 20021119</para></listitem> |
| <listitem><para>gcc-3.2.2: 20030205</para></listitem> |
| <listitem><para>gcc-3.2.3: 20030422</para></listitem> |
| <listitem><para>gcc-3.3.0: 20030513</para></listitem> |
| <listitem><para>gcc-3.3.1: 20030804</para></listitem> |
| <listitem><para>gcc-3.3.2: 20031016</para></listitem> |
| <listitem><para>gcc-3.3.3: 20040214</para></listitem> |
| <listitem><para>gcc-3.4.0: 20040419</para></listitem> |
| <listitem><para>gcc-3.4.1: 20040701</para></listitem> |
| <listitem><para>gcc-3.4.2: 20040906</para></listitem> |
| <listitem><para>gcc-3.4.3: 20041105</para></listitem> |
| <listitem><para>gcc-3.4.4: 20050519</para></listitem> |
| <listitem><para>gcc-3.4.5: 20051201</para></listitem> |
| <listitem><para>gcc-3.4.6: 20060306</para></listitem> |
| <listitem><para>gcc-4.0.0: 20050421</para></listitem> |
| <listitem><para>gcc-4.0.1: 20050707</para></listitem> |
| <listitem><para>gcc-4.0.2: 20050921</para></listitem> |
| <listitem><para>gcc-4.0.3: 20060309</para></listitem> |
| <listitem><para>gcc-4.1.0: 20060228</para></listitem> |
| <listitem><para>gcc-4.1.1: 20060524</para></listitem> |
| <listitem><para>gcc-4.1.2: 20070214</para></listitem> |
| <listitem><para>gcc-4.2.0: 20070514</para></listitem> |
| </itemizedlist> |
| <para></para> |
| </listitem> |
| |
| <listitem> |
| <para> |
| Incremental bumping of a library pre-defined macro, |
| _GLIBCPP_VERSION. This macro is defined as the released version of |
| the library, as a string literal. This is only implemented in |
| gcc-3.1.0 releases and higher, and is deprecated in 3.4 (where it |
| is called _GLIBCXX_VERSION). |
| </para> |
| |
| <para> |
| This macro is defined in the file "c++config" in the |
| "libstdc++/include/bits" directory and is generated |
| automatically by autoconf as part of the configure-time generation |
| of config.h. |
| </para> |
| |
| <para> |
| It is versioned as follows: |
| </para> |
| <itemizedlist> |
| <listitem><para>gcc-3.0.0: "3.0.0"</para></listitem> |
| <listitem><para>gcc-3.0.1: "3.0.0" (Error, should be "3.0.1")</para></listitem> |
| <listitem><para>gcc-3.0.2: "3.0.0" (Error, should be "3.0.2")</para></listitem> |
| <listitem><para>gcc-3.0.3: "3.0.0" (Error, should be "3.0.3")</para></listitem> |
| <listitem><para>gcc-3.0.4: "3.0.0" (Error, should be "3.0.4")</para></listitem> |
| <listitem><para>gcc-3.1.0: "3.1.0"</para></listitem> |
| <listitem><para>gcc-3.1.1: "3.1.1"</para></listitem> |
| <listitem><para>gcc-3.2.0: "3.2"</para></listitem> |
| <listitem><para>gcc-3.2.1: "3.2.1"</para></listitem> |
| <listitem><para>gcc-3.2.2: "3.2.2"</para></listitem> |
| <listitem><para>gcc-3.2.3: "3.2.3"</para></listitem> |
| <listitem><para>gcc-3.3.0: "3.3"</para></listitem> |
| <listitem><para>gcc-3.3.1: "3.3.1"</para></listitem> |
| <listitem><para>gcc-3.3.2: "3.3.2"</para></listitem> |
| <listitem><para>gcc-3.3.3: "3.3.3"</para></listitem> |
| <listitem><para>gcc-3.4.x: "version-unused"</para></listitem> |
| <listitem><para>gcc-4.0.x: "version-unused"</para></listitem> |
| <listitem><para>gcc-4.1.x: "version-unused"</para></listitem> |
| <listitem><para>gcc-4.2.x: "version-unused"</para></listitem> |
| </itemizedlist> |
| <para></para> |
| </listitem> |
| |
| <listitem> |
| <para> |
| 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. |
| </para> |
| <para> |
| All C++ includes are installed in include/c++, then nest in a |
| directory hierarchy corresponding to the C++ compiler's released |
| version. This version corresponds to the variable "gcc_version" in |
| "libstdc++/acinclude.m4," and more details can be found in that |
| file's macro GLIBCXX_CONFIGURE (GLIBCPP_CONFIGURE before gcc-3.4.0). |
| </para> |
| <para> |
| C++ includes are versioned as follows: |
| </para> |
| <itemizedlist> |
| <listitem><para>gcc-3.0.0: include/g++-v3</para></listitem> |
| <listitem><para>gcc-3.0.1: include/g++-v3</para></listitem> |
| <listitem><para>gcc-3.0.2: include/g++-v3</para></listitem> |
| <listitem><para>gcc-3.0.3: include/g++-v3</para></listitem> |
| <listitem><para>gcc-3.0.4: include/g++-v3</para></listitem> |
| <listitem><para>gcc-3.1.0: include/g++-v3</para></listitem> |
| <listitem><para>gcc-3.1.1: include/c++/3.1.1</para></listitem> |
| <listitem><para>gcc-3.2.0: include/c++/3.2</para></listitem> |
| <listitem><para>gcc-3.2.1: include/c++/3.2.1</para></listitem> |
| <listitem><para>gcc-3.2.2: include/c++/3.2.2</para></listitem> |
| <listitem><para>gcc-3.2.3: include/c++/3.2.3</para></listitem> |
| <listitem><para>gcc-3.3.0: include/c++/3.3</para></listitem> |
| <listitem><para>gcc-3.3.1: include/c++/3.3.1</para></listitem> |
| <listitem><para>gcc-3.3.2: include/c++/3.3.2</para></listitem> |
| <listitem><para>gcc-3.3.3: include/c++/3.3.3</para></listitem> |
| <listitem><para>gcc-3.4.0: include/c++/3.4.0</para></listitem> |
| <listitem><para>gcc-3.4.1: include/c++/3.4.1</para></listitem> |
| <listitem><para>gcc-3.4.2: include/c++/3.4.2</para></listitem> |
| <listitem><para>gcc-3.4.3: include/c++/3.4.3</para></listitem> |
| <listitem><para>gcc-3.4.4: include/c++/3.4.4</para></listitem> |
| <listitem><para>gcc-3.4.5: include/c++/3.4.5</para></listitem> |
| <listitem><para>gcc-3.4.6: include/c++/3.4.6</para></listitem> |
| <listitem><para>gcc-4.0.0: include/c++/4.0.0</para></listitem> |
| <listitem><para>gcc-4.0.1: include/c++/4.0.1</para></listitem> |
| <listitem><para>gcc-4.0.2: include/c++/4.0.2</para></listitem> |
| <listitem><para>gcc-4.0.3: include/c++/4.0.3</para></listitem> |
| <listitem><para>gcc-4.1.0: include/c++/4.1.0</para></listitem> |
| <listitem><para>gcc-4.1.1: include/c++/4.1.1</para></listitem> |
| <listitem><para>gcc-4.1.2: include/c++/4.1.2</para></listitem> |
| <listitem><para>gcc-4.2.0: include/c++/4.2.0</para></listitem> |
| </itemizedlist> |
| <para></para> |
| </listitem> |
| </orderedlist> |
| |
| <para> |
| 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. |
| </para> |
| |
| |
| </sect3> |
| |
| <sect3 id="abi.versioning.prereq" xreflabel="abi.versioning.prereq"> |
| <title>Prerequisites</title> |
| <para> |
| Minimum environment that supports a versioned ABI: A supported |
| dynamic linker, a GNU linker of sufficient vintage to understand |
| demangled C++ name globbing (ld), a shared executable compiled |
| with g++, and shared libraries (libgcc_s, libstdc++) compiled by |
| a compiler (g++) with a compatible ABI. Phew. |
| </para> |
| |
| <para> |
| On top of all that, an additional constraint: libstdc++ did not |
| attempt to version symbols (or age gracefully, really) until |
| version 3.1.0. |
| </para> |
| |
| <para> |
| Most modern Linux and BSD versions, particularly ones using |
| gcc-3.1.x tools and more recent vintages, will meet the |
| requirements above. |
| </para> |
| </sect3> |
| |
| <sect3 id="abi.versioning.config" xreflabel="abi.versioning.config"> |
| <title>Configuring</title> |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| For more information on configure options, including ABI |
| impacts, see: |
| http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html |
| </para> |
| |
| <para> |
| There is one flag that explicitly deals with symbol versioning: |
| --enable-symvers. |
| </para> |
| |
| <para> |
| In particular, libstdc++/acinclude.m4 has a macro called |
| GLIBCXX_ENABLE_SYMVERS that defaults to yes (or the argument |
| passed in via --enable-symvers=foo). At that point, the macro |
| attempts to make sure that all the requirement for symbol |
| versioning are in place. For more information, please consult |
| acinclude.m4. |
| </para> |
| </sect3> |
| |
| <sect3 id="abi.versioning.active" xreflabel="abi.versioning.active"> |
| <title>Checking Active</title> |
| |
| <para> |
| When the GNU C++ library is being built with symbol versioning |
| on, you should see the following at configure time for |
| libstdc++: |
| </para> |
| |
| <screen> |
| <computeroutput> |
| checking versioning on shared library symbols... gnu |
| </computeroutput> |
| </screen> |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| 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: |
| </para> |
| |
| <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 |
| </programlisting> |
| |
| <para> |
| 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: |
| </para> |
| |
| <para> |
| <code>U _ZNSt8ios_base4InitC1Ev@@GLIBCXX_3.4</code> |
| </para> |
| |
| </sect3> |
| </sect2> |
| |
| <sect2 id="abi.changes_allowed" xreflabel="abi.changes_allowed"> |
| <title>Allowed Changes</title> |
| |
| <para> |
| The following will cause the library minor version number to |
| increase, say from "libstdc++.so.3.0.4" to "libstdc++.so.3.0.5". |
| </para> |
| <orderedlist> |
| <listitem><para>Adding an exported global or static data member</para></listitem> |
| <listitem><para>Adding an exported function, static or non-virtual member function</para></listitem> |
| <listitem><para>Adding an exported symbol or symbols by additional instantiations</para></listitem> |
| </orderedlist> |
| <para> |
| Other allowed changes are possible. |
| </para> |
| |
| </sect2> |
| |
| <sect2 id="abi.changes_no" xreflabel="abi.changes_no"> |
| <title>Prohibited Changes</title> |
| |
| <para> |
| 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". |
| </para> |
| |
| <orderedlist> |
| <listitem><para>Changes in the gcc/g++ compiler ABI</para></listitem> |
| <listitem><para>Changing size of an exported symbol</para></listitem> |
| <listitem><para>Changing alignment of an exported symbol</para></listitem> |
| <listitem><para>Changing the layout of an exported symbol</para></listitem> |
| <listitem><para>Changing mangling on an exported symbol</para></listitem> |
| <listitem><para>Deleting an exported symbol</para></listitem> |
| <listitem><para>Changing the inheritance properties of a type by adding or removing |
| base classes</para></listitem> |
| <listitem><para> |
| 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. |
| </para></listitem> |
| |
| <listitem><para> Adding an explicit copy constructor or destructor to a |
| class that would otherwise have implicit versions. This will change |
| the way the compiler deals with this class in by-value return |
| statements or parameters: instead of being passing instances of this |
| class in registers, the compiler will be forced to use memory. See <ulink url="http://www.codesourcery.com/cxx-abi/abi.html#calls"> this part</ulink> |
| of the C++ ABI documentation for further details. |
| </para></listitem> |
| |
| </orderedlist> |
| |
| </sect2> |
| |
| |
| |
| <sect2 id="abi.impl" xreflabel="abi.impl"> |
| <title>Implementation</title> |
| |
| <orderedlist> |
| <listitem> |
| <para> |
| Separation of interface and implementation |
| </para> |
| <para> |
| This is accomplished by two techniques that separate the API from |
| the ABI: forcing undefined references to link against a library |
| binary for definitions. |
| </para> |
| |
| <variablelist> |
| <varlistentry> |
| <term>Include files have declarations, source files have defines</term> |
| |
| <listitem> |
| <para> |
| For non-templatized types, such as much of <code>class |
| locale</code>, the appropriate standard C++ include, say |
| <code>locale</code>, can contain full declarations, while |
| various source files (say <code> locale.cc, locale_init.cc, |
| localename.cc</code>) contain definitions. |
| </para> |
| </listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term>Extern template on required types</term> |
| |
| <listitem> |
| <para> |
| For parts of the standard that have an explicit list of |
| required instantiations, the GNU extension syntax <code> extern |
| template </code> can be used to control where template |
| definitions reside. By marking required instantiations as |
| <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> |
| char</code> and <code> wchar_t</code> instantiations, and |
| includes <code> basic_string</code>, the locale facets, and the |
| types in <code> iostreams</code>. |
| </para> |
| </listitem> |
| </varlistentry> |
| |
| </variablelist> |
| |
| <para> |
| In addition, these techniques have the additional benefit that they |
| reduce binary size, which can increase runtime performance. |
| </para> |
| </listitem> |
| |
| <listitem> |
| <para> |
| Namespaces linking symbol definitions to export mapfiles |
| </para> |
| <para> |
| 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. |
| </para> |
| |
| <para>The following namespaces are transformed by the mapfile:</para> |
| |
| <variablelist> |
| |
| <varlistentry> |
| <term><code>namespace std</code></term> |
| <listitem><para> Defaults to exporting all symbols in label |
| <code>GLIBCXX</code> that do not begin with an underscore, i.e., |
| <code>__test_func</code> would not be exported by default. Select |
| exceptional symbols are allowed to be visible.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><code>namespace __gnu_cxx</code></term> |
| <listitem><para> Defaults to not exporting any symbols in label |
| <code>GLIBCXX</code>, select items are allowed to be visible.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><code>namespace __gnu_internal</code></term> |
| <listitem><para> Defaults to not exported, no items are allowed to be visible.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><code>namespace __cxxabiv1</code>, aliased to <code> namespace abi</code></term> |
| <listitem><para> Defaults to not exporting any symbols in label |
| <code>CXXABI</code>, select items are allowed to be visible.</para></listitem> |
| </varlistentry> |
| |
| </variablelist> |
| <para> |
| </para> |
| </listitem> |
| |
| <listitem><para>Freezing the API</para> |
| <para>Disallowed changes, as above, are not made on a stable release |
| branch. Enforcement tends to be less strict with GNU extensions that |
| standard includes.</para> |
| </listitem> |
| </orderedlist> |
| |
| </sect2> |
| |
| <sect2 id="abi.testing" xreflabel="abi.testing"> |
| <title>Testing</title> |
| |
| <sect3 id="abi.testing.single" xreflabel="abi.testing.single"> |
| <title>Single ABI Testing</title> |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| Testing the C++ compiler ABI can be done various ways. |
| </para> |
| |
| <para> |
| One. Intel ABI checker. More information can be obtained <ulink |
| url="http://developer.intel.com/software/products/opensource/">here.</ulink> |
| </para> |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| Three. |
| Involves using the vlad.consistency test framework. This has also been |
| discussed on the gcc mailing lists. |
| </para> |
| |
| <para> |
| Testing the C++ library ABI can also be done various ways. |
| </para> |
| |
| <para> |
| 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) |
| </para> |
| |
| <para> |
| Details on how to set this kind of test up can be found here: |
| http://gcc.gnu.org/ml/gcc/2002-08/msg00142.html |
| </para> |
| |
| <para> |
| Two. |
| Use the 'make check-abi' rule in the libstdc++ Makefile. |
| </para> |
| |
| <para> |
| This is a proactive check the library ABI. Currently, exported symbol |
| names that are either weak or defined are checked against a last known |
| good baseline. Currently, this baseline is keyed off of 3.4.0 |
| binaries, as this was the last time the .so number was incremented. In |
| addition, all exported names are demangled, and the exported objects |
| are checked to make sure they are the same size as the same object in |
| the baseline. |
| |
| Notice that each baseline is relative to a <emphasis>default</emphasis> |
| 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. |
| </para> |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| Another approach might be to use the -fdump-class-hierarchy flag to |
| get information. However, currently this approach gives insufficient |
| data for use in library testing, as class data members, their offsets, |
| and other detailed data is not displayed with this flag. |
| (See g++/7470 on how this was used to find bugs.) |
| </para> |
| |
| <para> |
| Perhaps there are other C++ ABI checkers. If so, please notify |
| us. We'd like to know about them! |
| </para> |
| |
| </sect3> |
| <sect3 id="abi.testing.multi" xreflabel="abi.testing.multi"> |
| <title>Multiple ABI Testing</title> |
| <para> |
| A "C" application, dynamically linked to two shared libraries, liba, |
| libb. The dependent library liba is C++ shared library compiled with |
| gcc-3.3.x, and uses io, exceptions, locale, etc. The dependent library |
| libb is a C++ shared library compiled with gcc-3.4.x, and also uses io, |
| exceptions, locale, etc. |
| </para> |
| |
| <para> As above, libone is constructed as follows: </para> |
| <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 |
| |
| %$bld/H-x86-gcc-3.4.0/bin/g++ -c a.cc |
| |
| %ar cru libone.a a.o |
| </programlisting> |
| |
| <para> And, libtwo is constructed as follows: </para> |
| |
| <programlisting> |
| %$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 |
| </programlisting> |
| |
| <para> ...with the resulting libraries looking like </para> |
| |
| <screen> |
| <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) |
| </computeroutput> |
| </screen> |
| |
| <para> |
| Then, the "C" compiler is used to compile a source file that uses |
| functions from each library. |
| </para> |
| <programlisting> |
| gcc test.c -g -O2 -L. -lone -ltwo /usr/lib/libstdc++.so.5 /usr/lib/libstdc++.so.6 |
| </programlisting> |
| |
| <para> |
| Which gives the expected: |
| </para> |
| |
| <screen> |
| <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) |
| </computeroutput> |
| </screen> |
| |
| <para> |
| 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. |
| </para> |
| </sect3> |
| </sect2> |
| |
| <sect2 id="abi.issues" xreflabel="abi.issues"> |
| <title>Outstanding Issues</title> |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| For more background on this issue, see these bugzilla entries: |
| </para> |
| |
| <para> |
| <ulink url="http://gcc.gnu.org/PR24660">24660: versioning weak symbols in libstdc++</ulink> |
| </para> |
| |
| <para> |
| <ulink url="http://gcc.gnu.org/PR19664">19664: libstdc++ headers should have pop/push of the visibility around the declarations</ulink> |
| </para> |
| |
| </sect2> |
| |
| <bibliography id="abi.biblio" xreflabel="abi.biblio"> |
| <title>Bibliography</title> |
| |
| <biblioentry> |
| <title> |
| ABIcheck, a vague idea of checking ABI compatibility |
| </title> |
| |
| <biblioid> |
| <ulink url="http://abicheck.sourceforge.net/"> |
| </ulink> |
| </biblioid> |
| </biblioentry> |
| |
| <biblioentry> |
| <title> |
| C++ ABI Reference |
| </title> |
| |
| <biblioid> |
| <ulink url="http://www.codesourcery.com/cxx-abi"> |
| </ulink> |
| </biblioid> |
| </biblioentry> |
| |
| <biblioentry> |
| <title> |
| IntelĀ® Compilers for Linux* -Compatibility with the GNU Compilers |
| </title> |
| |
| <biblioid> |
| <ulink url="http://developer.intel.com/software/products/compilers/techtopics/LinuxCompilersCompatibility.htm"> |
| </ulink> |
| </biblioid> |
| </biblioentry> |
| |
| <biblioentry> |
| <title> |
| IntelĀ® Compilers for Linux* -Compatibility with the GNU Compilers |
| </title> |
| |
| <biblioid> |
| <ulink url="http://developer.intel.com/software/products/compilers/techtopics/LinuxCompilersCompatibility.htm"> |
| </ulink> |
| </biblioid> |
| </biblioentry> |
| |
| <biblioentry> |
| <title> |
| Sun Solaris 2.9 : Linker and Libraries Guide (document 816-1386) |
| </title> |
| |
| <biblioid> |
| <ulink url="http://docs.sun.com/?p=/doc/816-1386&a=load"> |
| </ulink> |
| </biblioid> |
| </biblioentry> |
| |
| |
| <biblioentry> |
| <title> |
| Sun Solaris 2.9 : C++ Migration Guide (document 816-2459) |
| </title> |
| |
| <biblioid> |
| <ulink url="http://docs.sun.com/db/prod/solaris.9"> |
| </ulink> |
| </biblioid> |
| </biblioentry> |
| |
| <biblioentry> |
| <title> |
| ELF Symbol Versioning |
| </title> |
| |
| <author> |
| <firstname>Ulrich</firstname> |
| <surname>Drepper</surname> |
| </author> |
| |
| <biblioid> |
| <ulink url="http://people.redhat.com/drepper/symbol-versioning"> |
| </ulink> |
| </biblioid> |
| </biblioentry> |
| |
| <biblioentry> |
| <title> |
| C++ ABI for the ARM Architecture |
| </title> |
| |
| <biblioid> |
| <ulink url="http://www.arm.com/miscPDFs/8033.pdf"> |
| </ulink> |
| </biblioid> |
| </biblioentry> |
| |
| <biblioentry> |
| <title> |
| Dynamic Shared Objects: Survey and Issues |
| </title> |
| <subtitle> |
| ISO C++ J16/06-0046 |
| </subtitle> |
| |
| <author> |
| <firstname>Benjamin</firstname> |
| <surname>Kosnik</surname> |
| </author> |
| |
| <biblioid> |
| <ulink url="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1976.html"> |
| </ulink> |
| </biblioid> |
| </biblioentry> |
| |
| <biblioentry> |
| <title> |
| Versioning With Namespaces |
| </title> |
| <subtitle> |
| ISO C++ J16/06-0083 |
| </subtitle> |
| |
| <author> |
| <firstname>Benjamin</firstname> |
| <surname>Kosnik</surname> |
| </author> |
| |
| <biblioid> |
| <ulink url="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2013.html"> |
| </ulink> |
| </biblioid> |
| </biblioentry> |
| |
| </bibliography> |
| |
| </sect1> |