1 <section xmlns="http://docbook.org/ns/docbook" version="5.0"
2 xml:id="appendix.porting.abi" xreflabel="abi">
3 <?dbhtml filename="abi.html"?>
5 <info><title>ABI Policy and Guidelines</title>
9 <keyword>version</keyword>
10 <keyword>dynamic</keyword>
11 <keyword>shared</keyword>
12 <keyword>compatibility</keyword>
21 <section xml:id="abi.cxx_interface"><info><title>The C++ Interface</title></info>
25 C++ applications often depend on specific language support
26 routines, say for throwing exceptions, or catching exceptions, and
27 perhaps also depend on features in the C++ Standard Library.
31 The C++ Standard Library has many include files, types defined in
32 those include files, specific named functions, and other
33 behavior. The text of these behaviors, as written in source include
34 files, is called the Application Programing Interface, or API.
38 Furthermore, C++ source that is compiled into object files is
39 transformed by the compiler: it arranges objects with specific
40 alignment and in a particular layout, mangling names according to a
41 well-defined algorithm, has specific arrangements for the support of
42 virtual functions, etc. These details are defined as the compiler
43 Application Binary Interface, or ABI. From GCC version 3 onwards the
44 GNU C++ compiler uses an industry-standard C++ ABI, the
45 <link linkend="biblio.cxxabi">Itanium C++ ABI</link>.
49 The GNU C++ compiler, g++, has a compiler command line option to
50 switch between various different C++ ABIs. This explicit version
51 switch is the flag <code>-fabi-version</code>. In addition, some
52 g++ command line options may change the ABI as a side-effect of
53 use. Such flags include <code>-fpack-struct</code> and
54 <code>-fno-exceptions</code>, but include others: see the complete
55 list in the GCC manual under the heading <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html#Code%20Gen%20Options">Options
56 for Code Generation Conventions</link>.
60 The configure options used when building a specific libstdc++
61 version may also impact the resulting library ABI. The available
62 configure options, and their impact on the library ABI, are
64 <link linkend="manual.intro.setup.configure">here</link>.
67 <para> Putting all of these ideas together results in the C++ Standard
68 Library ABI, which is the compilation of a given library API by a
69 given compiler ABI. In a nutshell:
74 library API + compiler ABI = library ABI
79 The library ABI is mostly of interest for end-users who have
80 unresolved symbols and are linking dynamically to the C++ Standard
81 library, and who thus must be careful to compile their application
82 with a compiler that is compatible with the available C++ Standard
83 library binary. In this case, compatible is defined with the equation
84 above: given an application compiled with a given compiler ABI and
85 library API, it will work correctly with a Standard C++ Library
86 created with the same constraints.
90 To use a specific version of the C++ ABI, one must use a
91 corresponding GNU C++ toolchain (i.e., g++ and libstdc++) that
92 implements the C++ ABI in question.
97 <section xml:id="abi.versioning"><info><title>Versioning</title></info>
100 <para> The C++ interface has evolved throughout the history of the GNU
101 C++ toolchain. With each release, various details have been changed so
102 as to give distinct versions to the C++ interface.
105 <section xml:id="abi.versioning.goals"><info><title>Goals</title></info>
108 <para>Extending existing, stable ABIs. Versioning gives subsequent
109 releases of library binaries the ability to add new symbols and add
110 functionality, all the while retaining compatibility with the previous
111 releases in the series. Thus, program binaries linked with the initial
112 release of a library binary will still run correctly if the library
113 binary is replaced by carefully-managed subsequent library
114 binaries. This is called forward compatibility.
117 The reverse (backwards compatibility) is not true. It is not possible
118 to take program binaries linked with the latest version of a library
119 binary in a release series (with additional symbols added), substitute
120 in the initial release of the library binary, and remain link
124 <para>Allows multiple, incompatible ABIs to coexist at the same time.
128 <section xml:id="abi.versioning.history"><info><title>History</title></info>
132 How can this complexity be managed? What does C++ versioning mean?
133 Because library and compiler changes often make binaries compiled
134 with one version of the GNU tools incompatible with binaries
135 compiled with other (either newer or older) versions of the same GNU
136 tools, specific techniques are used to make managing this complexity
141 The following techniques are used:
146 <listitem><para>Release versioning on the libgcc_s.so binary. </para>
148 <para>This is implemented via file names and the ELF
149 <constant>DT_SONAME</constant> mechanism (at least on ELF
150 systems). It is versioned as follows:
154 <listitem><para>GCC 3.x: libgcc_s.so.1</para></listitem>
155 <listitem><para>GCC 4.x: libgcc_s.so.1</para></listitem>
158 <para>For m68k-linux the versions differ as follows: </para>
161 <listitem><para>GCC 3.4, GCC 4.x: libgcc_s.so.1
162 when configuring <code>--with-sjlj-exceptions</code>, or
163 libgcc_s.so.2 </para> </listitem>
166 <para>For hppa-linux the versions differ as follows: </para>
169 <listitem><para>GCC 3.4, GCC 4.[0-1]: either libgcc_s.so.1
170 when configuring <code>--with-sjlj-exceptions</code>, or
171 libgcc_s.so.2 </para> </listitem>
172 <listitem><para>GCC 4.[2-7]: either libgcc_s.so.3 when configuring
173 <code>--with-sjlj-exceptions</code>) or libgcc_s.so.4
179 <listitem><para>Symbol versioning on the libgcc_s.so binary.</para>
181 <para>It is versioned with the following labels and version
182 definitions, where the version definition is the maximum for a
183 particular release. Labels are cumulative. If a particular release
184 is not listed, it has the same version labels as the preceding
187 <para>This corresponds to the mapfile: gcc/libgcc-std.ver</para>
189 <listitem><para>GCC 3.0.0: GCC_3.0</para></listitem>
190 <listitem><para>GCC 3.3.0: GCC_3.3</para></listitem>
191 <listitem><para>GCC 3.3.1: GCC_3.3.1</para></listitem>
192 <listitem><para>GCC 3.3.2: GCC_3.3.2</para></listitem>
193 <listitem><para>GCC 3.3.4: GCC_3.3.4</para></listitem>
194 <listitem><para>GCC 3.4.0: GCC_3.4</para></listitem>
195 <listitem><para>GCC 3.4.2: GCC_3.4.2</para></listitem>
196 <listitem><para>GCC 3.4.4: GCC_3.4.4</para></listitem>
197 <listitem><para>GCC 4.0.0: GCC_4.0.0</para></listitem>
198 <listitem><para>GCC 4.1.0: GCC_4.1.0</para></listitem>
199 <listitem><para>GCC 4.2.0: GCC_4.2.0</para></listitem>
200 <listitem><para>GCC 4.3.0: GCC_4.3.0</para></listitem>
201 <listitem><para>GCC 4.4.0: GCC_4.4.0</para></listitem>
202 <listitem><para>GCC 4.5.0: GCC_4.5.0</para></listitem>
203 <listitem><para>GCC 4.6.0: GCC_4.6.0</para></listitem>
204 <listitem><para>GCC 4.7.0: GCC_4.7.0</para></listitem>
205 <listitem><para>GCC 4.8.0: GCC_4.8.0</para></listitem>
211 Release versioning on the libstdc++.so binary, implemented in
212 the same way as the libgcc_s.so binary above. Listed is the
213 filename: <constant>DT_SONAME</constant> can be deduced from
214 the filename by removing the last two period-delimited numbers. For
215 example, filename <filename>libstdc++.so.5.0.4</filename>
216 corresponds to a <constant>DT_SONAME</constant> of
217 <constant>libstdc++.so.5</constant>. Binaries with equivalent
218 <constant>DT_SONAME</constant>s are forward-compatibile: in
219 the table below, releases incompatible with the previous
220 one are explicitly noted.
221 If a particular release is not listed, its libstdc++.so binary
222 has the same filename and <constant>DT_SONAME</constant> as the
226 <para>It is versioned as follows:
229 <listitem><para>GCC 3.0.0: libstdc++.so.3.0.0</para></listitem>
230 <listitem><para>GCC 3.0.1: libstdc++.so.3.0.1</para></listitem>
231 <listitem><para>GCC 3.0.2: libstdc++.so.3.0.2</para></listitem>
232 <listitem><para>GCC 3.0.3: libstdc++.so.3.0.2 (See Note 1)</para></listitem>
233 <listitem><para>GCC 3.0.4: libstdc++.so.3.0.4</para></listitem>
234 <listitem><para>GCC 3.1.0: libstdc++.so.4.0.0 <emphasis>(Incompatible with previous)</emphasis></para></listitem>
235 <listitem><para>GCC 3.1.1: libstdc++.so.4.0.1</para></listitem>
236 <listitem><para>GCC 3.2.0: libstdc++.so.5.0.0 <emphasis>(Incompatible with previous)</emphasis></para></listitem>
237 <listitem><para>GCC 3.2.1: libstdc++.so.5.0.1</para></listitem>
238 <listitem><para>GCC 3.2.2: libstdc++.so.5.0.2</para></listitem>
239 <listitem><para>GCC 3.2.3: libstdc++.so.5.0.3 (See Note 2)</para></listitem>
240 <listitem><para>GCC 3.3.0: libstdc++.so.5.0.4</para></listitem>
241 <listitem><para>GCC 3.3.1: libstdc++.so.5.0.5</para></listitem>
242 <listitem><para>GCC 3.4.0: libstdc++.so.6.0.0 <emphasis>(Incompatible with previous)</emphasis></para></listitem>
243 <listitem><para>GCC 3.4.1: libstdc++.so.6.0.1</para></listitem>
244 <listitem><para>GCC 3.4.2: libstdc++.so.6.0.2</para></listitem>
245 <listitem><para>GCC 3.4.3: libstdc++.so.6.0.3</para></listitem>
246 <listitem><para>GCC 4.0.0: libstdc++.so.6.0.4</para></listitem>
247 <listitem><para>GCC 4.0.1: libstdc++.so.6.0.5</para></listitem>
248 <listitem><para>GCC 4.0.2: libstdc++.so.6.0.6</para></listitem>
249 <listitem><para>GCC 4.0.3: libstdc++.so.6.0.7</para></listitem>
250 <listitem><para>GCC 4.1.0: libstdc++.so.6.0.7</para></listitem>
251 <listitem><para>GCC 4.1.1: libstdc++.so.6.0.8</para></listitem>
252 <listitem><para>GCC 4.2.0: libstdc++.so.6.0.9</para></listitem>
253 <listitem><para>GCC 4.2.1: libstdc++.so.6.0.9 (See Note 3)</para></listitem>
254 <listitem><para>GCC 4.2.2: libstdc++.so.6.0.9</para></listitem>
255 <listitem><para>GCC 4.3.0: libstdc++.so.6.0.10</para></listitem>
256 <listitem><para>GCC 4.4.0: libstdc++.so.6.0.11</para></listitem>
257 <listitem><para>GCC 4.4.1: libstdc++.so.6.0.12</para></listitem>
258 <listitem><para>GCC 4.4.2: libstdc++.so.6.0.13</para></listitem>
259 <listitem><para>GCC 4.5.0: libstdc++.so.6.0.14</para></listitem>
260 <listitem><para>GCC 4.6.0: libstdc++.so.6.0.15</para></listitem>
261 <listitem><para>GCC 4.6.1: libstdc++.so.6.0.16</para></listitem>
262 <listitem><para>GCC 4.7.0: libstdc++.so.6.0.17</para></listitem>
263 <listitem><para>GCC 4.8.0: libstdc++.so.6.0.18</para></listitem>
264 <listitem><para>GCC 4.8.3: libstdc++.so.6.0.19</para></listitem>
265 <listitem><para>GCC 4.9.0: libstdc++.so.6.0.20</para></listitem>
266 <listitem><para>GCC 5.1.0: libstdc++.so.6.0.21</para></listitem>
267 <listitem><para>GCC 6.1.0: libstdc++.so.6.0.22</para></listitem>
268 <listitem><para>GCC 7.1.0: libstdc++.so.6.0.23</para></listitem>
269 <listitem><para>GCC 7.2.0: libstdc++.so.6.0.24</para></listitem>
270 <listitem><para>GCC 8.0.0: libstdc++.so.6.0.25</para></listitem>
273 Note 1: Error should be libstdc++.so.3.0.3.
276 Note 2: Not strictly required.
279 Note 3: This release (but not previous or subsequent) has one
280 known incompatibility, see <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33678">33678</link>
281 in the GCC bug database.
285 <listitem><para>Symbol versioning on the libstdc++.so binary.</para>
287 <para>mapfile: libstdc++-v3/config/abi/pre/gnu.ver</para>
288 <para>It is versioned with the following labels and version
289 definitions, where the version definition is the maximum for a
290 particular release. Note, only symbols which are newly introduced
291 will use the maximum version definition. Thus, for release series
292 with the same label, but incremented version definitions, the later
293 release has both versions. (An example of this would be the
294 GCC 3.2.1 release, which has GLIBCPP_3.2.1 for new symbols and
295 GLIBCPP_3.2 for symbols that were introduced in the GCC 3.2.0
296 release.) If a particular release is not listed, it has the same
297 version labels as the preceding release.
300 <listitem><para>GCC 3.0.0: (Error, not versioned)</para></listitem>
301 <listitem><para>GCC 3.0.1: (Error, not versioned)</para></listitem>
302 <listitem><para>GCC 3.0.2: (Error, not versioned)</para></listitem>
303 <listitem><para>GCC 3.0.3: (Error, not versioned)</para></listitem>
304 <listitem><para>GCC 3.0.4: (Error, not versioned)</para></listitem>
305 <listitem><para>GCC 3.1.0: GLIBCPP_3.1, CXXABI_1</para></listitem>
306 <listitem><para>GCC 3.1.1: GLIBCPP_3.1, CXXABI_1</para></listitem>
307 <listitem><para>GCC 3.2.0: GLIBCPP_3.2, CXXABI_1.2</para></listitem>
308 <listitem><para>GCC 3.2.1: GLIBCPP_3.2.1, CXXABI_1.2</para></listitem>
309 <listitem><para>GCC 3.2.2: GLIBCPP_3.2.2, CXXABI_1.2</para></listitem>
310 <listitem><para>GCC 3.2.3: GLIBCPP_3.2.2, CXXABI_1.2</para></listitem>
311 <listitem><para>GCC 3.3.0: GLIBCPP_3.2.2, CXXABI_1.2.1</para></listitem>
312 <listitem><para>GCC 3.3.1: GLIBCPP_3.2.3, CXXABI_1.2.1</para></listitem>
313 <listitem><para>GCC 3.3.2: GLIBCPP_3.2.3, CXXABI_1.2.1</para></listitem>
314 <listitem><para>GCC 3.3.3: GLIBCPP_3.2.3, CXXABI_1.2.1</para></listitem>
315 <listitem><para>GCC 3.4.0: GLIBCXX_3.4, CXXABI_1.3</para></listitem>
316 <listitem><para>GCC 3.4.1: GLIBCXX_3.4.1, CXXABI_1.3</para></listitem>
317 <listitem><para>GCC 3.4.2: GLIBCXX_3.4.2</para></listitem>
318 <listitem><para>GCC 3.4.3: GLIBCXX_3.4.3</para></listitem>
319 <listitem><para>GCC 4.0.0: GLIBCXX_3.4.4, CXXABI_1.3.1</para></listitem>
320 <listitem><para>GCC 4.0.1: GLIBCXX_3.4.5</para></listitem>
321 <listitem><para>GCC 4.0.2: GLIBCXX_3.4.6</para></listitem>
322 <listitem><para>GCC 4.0.3: GLIBCXX_3.4.7</para></listitem>
323 <listitem><para>GCC 4.1.1: GLIBCXX_3.4.8</para></listitem>
324 <listitem><para>GCC 4.2.0: GLIBCXX_3.4.9</para></listitem>
325 <listitem><para>GCC 4.3.0: GLIBCXX_3.4.10, CXXABI_1.3.2</para></listitem>
326 <listitem><para>GCC 4.4.0: GLIBCXX_3.4.11, CXXABI_1.3.3</para></listitem>
327 <listitem><para>GCC 4.4.1: GLIBCXX_3.4.12, CXXABI_1.3.3</para></listitem>
328 <listitem><para>GCC 4.4.2: GLIBCXX_3.4.13, CXXABI_1.3.3</para></listitem>
329 <listitem><para>GCC 4.5.0: GLIBCXX_3.4.14, CXXABI_1.3.4</para></listitem>
330 <listitem><para>GCC 4.6.0: GLIBCXX_3.4.15, CXXABI_1.3.5</para></listitem>
331 <listitem><para>GCC 4.6.1: GLIBCXX_3.4.16, CXXABI_1.3.5</para></listitem>
332 <listitem><para>GCC 4.7.0: GLIBCXX_3.4.17, CXXABI_1.3.6</para></listitem>
333 <listitem><para>GCC 4.8.0: GLIBCXX_3.4.18, CXXABI_1.3.7</para></listitem>
334 <listitem><para>GCC 4.8.3: GLIBCXX_3.4.19, CXXABI_1.3.7</para></listitem>
335 <listitem><para>GCC 4.9.0: GLIBCXX_3.4.20, CXXABI_1.3.8</para></listitem>
336 <listitem><para>GCC 5.1.0: GLIBCXX_3.4.21, CXXABI_1.3.9</para></listitem>
337 <listitem><para>GCC 6.1.0: GLIBCXX_3.4.22, CXXABI_1.3.10</para></listitem>
338 <listitem><para>GCC 7.1.0: GLIBCXX_3.4.23, CXXABI_1.3.11</para></listitem>
339 <listitem><para>GCC 7.2.0: GLIBCXX_3.4.24, CXXABI_1.3.11</para></listitem>
340 <listitem><para>GCC 8.0.0: GLIBCXX_3.4.25, CXXABI_1.3.11</para></listitem>
345 <para>Incremental bumping of a compiler pre-defined macro,
346 __GXX_ABI_VERSION. This macro is defined as the version of the
347 compiler v3 ABI, with g++ 3.0 being version 100. This macro will
348 be automatically defined whenever g++ is used (the curious can
349 test this by invoking g++ with the '-v' flag.)
353 This macro was defined in the file "lang-specs.h" in the gcc/cp directory.
354 Later versions defined it in "c-common.c" in the gcc directory, and from
355 G++ 3.4 it is defined in c-cppbuiltin.c and its value determined by the
356 '-fabi-version' command line option.
360 It is versioned as follows, where 'n' is given by '-fabi-version=n':
363 <listitem><para>GCC 3.0: 100</para></listitem>
364 <listitem><para>GCC 3.1: 100 (Error, should be 101)</para></listitem>
365 <listitem><para>GCC 3.2: 102</para></listitem>
366 <listitem><para>GCC 3.3: 102</para></listitem>
367 <listitem><para>GCC 3.4, GCC 4.x: 102 (when n=1)</para></listitem>
368 <listitem><para>GCC 3.4, GCC 4.x: 1000 + n (when n>1) </para></listitem>
369 <listitem><para>GCC 3.4, GCC 4.x: 999999 (when n=0)</para></listitem>
375 <para>Changes to the default compiler option for
376 <code>-fabi-version</code>.
379 It is versioned as follows:
382 <listitem><para>GCC 3.0: (Error, not versioned) </para></listitem>
383 <listitem><para>GCC 3.1: (Error, not versioned) </para></listitem>
384 <listitem><para>GCC 3.2: <code>-fabi-version=1</code></para></listitem>
385 <listitem><para>GCC 3.3: <code>-fabi-version=1</code></para></listitem>
386 <listitem><para>GCC 3.4, GCC 4.x: <code>-fabi-version=2</code> <emphasis>(Incompatible with previous)</emphasis></para></listitem>
387 <listitem><para>GCC 5 and higher: <code>-fabi-version=0</code> <emphasis>(See GCC manual for meaning)</emphasis></para></listitem>
392 <listitem xml:id="abi.versioning.__GLIBCXX__">
393 <para>Incremental bumping of a library pre-defined macro. For releases
394 before 3.4.0, the macro is <symbol>__GLIBCPP__</symbol>. For later
395 releases, it's <symbol>__GLIBCXX__</symbol>. (The libstdc++ project
396 generously changed from CPP to CXX throughout its source to allow the
397 "C" pre-processor the CPP macro namespace.) These macros are defined
398 as the date the library was released, in compressed ISO date format,
399 as an integer constant.
403 This macro is defined in the file
404 <filename class="headerfile">c++config</filename> in the
405 <filename class="directory">libstdc++-v3/include/bits</filename>
406 directory. Up to GCC 4.1.0, it was
407 changed every night by an automated script. Since GCC 4.1.0 it is set
408 during configuration to the same value as
409 <filename>gcc/DATESTAMP</filename>, so for an official release its value
410 is the same as the date of the release, which is given in the <link
411 xmlns:xlink="http://www.w3.org/1999/xlink"
412 xlink:href="https://gcc.gnu.org/develop.html#timeline">GCC Release
417 This macro can be used in code to detect whether the C++ Standard Library
418 implementation in use is libstdc++, but is not useful for detecting the
419 libstdc++ version, nor whether particular features are supported.
420 The macro value might be a date after a feature was added to the
421 development trunk, but the release could be from an older branch without
422 the feature. For example, in the 5.4.0 release the macro has the value
423 <literal>20160603</literal> which is greater than the
424 <literal>20160427</literal> value of the macro in the 6.1.0 release,
425 but there are features supported in the 6.1.0 release that are not
426 supported in 5.4.0 release.
427 You also can't test for the exact values listed below to try and
428 identify a release, because a snapshot taken from the gcc-5-branch on
429 2016-04-27 would have the same value for the macro as the 6.1.0 release
430 despite being a different version.
431 Many GNU/Linux distributions build their GCC packages from snapshots, so
432 the macro can have dates that don't correspond to official releases.
436 It is versioned as follows:
439 <listitem><para>GCC 3.0.0: <literal>20010615</literal></para></listitem>
440 <listitem><para>GCC 3.0.1: <literal>20010819</literal></para></listitem>
441 <listitem><para>GCC 3.0.2: <literal>20011023</literal></para></listitem>
442 <listitem><para>GCC 3.0.3: <literal>20011220</literal></para></listitem>
443 <listitem><para>GCC 3.0.4: <literal>20020220</literal></para></listitem>
444 <listitem><para>GCC 3.1.0: <literal>20020514</literal></para></listitem>
445 <listitem><para>GCC 3.1.1: <literal>20020725</literal></para></listitem>
446 <listitem><para>GCC 3.2.0: <literal>20020814</literal></para></listitem>
447 <listitem><para>GCC 3.2.1: <literal>20021119</literal></para></listitem>
448 <listitem><para>GCC 3.2.2: <literal>20030205</literal></para></listitem>
449 <listitem><para>GCC 3.2.3: <literal>20030422</literal></para></listitem>
450 <listitem><para>GCC 3.3.0: <literal>20030513</literal></para></listitem>
451 <listitem><para>GCC 3.3.1: <literal>20030804</literal></para></listitem>
452 <listitem><para>GCC 3.3.2: <literal>20031016</literal></para></listitem>
453 <listitem><para>GCC 3.3.3: <literal>20040214</literal></para></listitem>
454 <listitem><para>GCC 3.4.0: <literal>20040419</literal></para></listitem>
455 <listitem><para>GCC 3.4.1: <literal>20040701</literal></para></listitem>
456 <listitem><para>GCC 3.4.2: <literal>20040906</literal></para></listitem>
457 <listitem><para>GCC 3.4.3: <literal>20041105</literal></para></listitem>
458 <listitem><para>GCC 3.4.4: <literal>20050519</literal></para></listitem>
459 <listitem><para>GCC 3.4.5: <literal>20051201</literal></para></listitem>
460 <listitem><para>GCC 3.4.6: <literal>20060306</literal></para></listitem>
461 <listitem><para>GCC 4.0.0: <literal>20050421</literal></para></listitem>
462 <listitem><para>GCC 4.0.1: <literal>20050707</literal></para></listitem>
463 <listitem><para>GCC 4.0.2: <literal>20050921</literal></para></listitem>
464 <listitem><para>GCC 4.0.3: <literal>20060309</literal></para></listitem>
466 GCC 4.1.0 and later: the GCC release date, as shown in the
467 <link xmlns:xlink="http://www.w3.org/1999/xlink"
468 xlink:href="https://gcc.gnu.org/develop.html#timeline">GCC
469 Release Timeline</link>
477 Since GCC 7, incremental bumping of a library pre-defined macro,
478 <symbol>_GLIBCXX_RELEASE</symbol>. This macro is defined to the GCC
479 major version that the libstdc++ headers belong to, as an integer constant.
480 When compiling with GCC it has the same value as GCC's pre-defined
481 macro <symbol>__GNUC__</symbol>.
482 This macro can be used when libstdc++ is used with a non-GNU
483 compiler where <symbol>__GNUC__</symbol> is not defined, or has a
484 different value that doesn't correspond to the libstdc++ version.
488 This macro is defined in the file
489 <filename class="headerfile">c++config</filename> in the
490 <filename class="directory">libstdc++-v3/include/bits</filename>
491 directory and is generated automatically by autoconf as part of the
492 configure-time generation of
493 <filename class="headerfile">config.h</filename> and subsequently
494 <filename class="headerfile"><bits/c++config.h></filename>.
500 Historically, incremental bumping of a library pre-defined macro,
501 <symbol>_GLIBCPP_VERSION</symbol>. This macro was defined as the
502 released version of the library, as a string literal. This was only
503 implemented in GCC 3.1.0 releases and higher, and was deprecated in
504 3.4.x (where it was called <symbol>_GLIBCXX_VERSION</symbol>),
505 and is not defined in 4.0.0 and higher.
509 This macro is defined in the same file as
510 <symbol>_GLIBCXX_RELEASE</symbol>, described above.
514 It is versioned as follows:
517 <listitem><para>GCC 3.0.0: <literal>"3.0.0"</literal></para></listitem>
518 <listitem><para>GCC 3.0.1: <literal>"3.0.0"</literal> (Error, should be <literal>"3.0.1"</literal>)</para></listitem>
519 <listitem><para>GCC 3.0.2: <literal>"3.0.0"</literal> (Error, should be <literal>"3.0.2"</literal>)</para></listitem>
520 <listitem><para>GCC 3.0.3: <literal>"3.0.0"</literal> (Error, should be <literal>"3.0.3"</literal>)</para></listitem>
521 <listitem><para>GCC 3.0.4: <literal>"3.0.0"</literal> (Error, should be <literal>"3.0.4"</literal>)</para></listitem>
522 <listitem><para>GCC 3.1.0: <literal>"3.1.0"</literal></para></listitem>
523 <listitem><para>GCC 3.1.1: <literal>"3.1.1"</literal></para></listitem>
524 <listitem><para>GCC 3.2.0: <literal>"3.2"</literal></para></listitem>
525 <listitem><para>GCC 3.2.1: <literal>"3.2.1"</literal></para></listitem>
526 <listitem><para>GCC 3.2.2: <literal>"3.2.2"</literal></para></listitem>
527 <listitem><para>GCC 3.2.3: <literal>"3.2.3"</literal></para></listitem>
528 <listitem><para>GCC 3.3.0: <literal>"3.3"</literal></para></listitem>
529 <listitem><para>GCC 3.3.1: <literal>"3.3.1"</literal></para></listitem>
530 <listitem><para>GCC 3.3.2: <literal>"3.3.2"</literal></para></listitem>
531 <listitem><para>GCC 3.3.3: <literal>"3.3.3"</literal></para></listitem>
532 <listitem><para>GCC 3.4: <literal>"version-unused"</literal></para></listitem>
533 <listitem><para>GCC 4 and later: not defined</para></listitem>
540 Matching each specific C++ compiler release to a specific set of
541 C++ include files. This is only implemented in GCC 3.1.1 releases
545 All C++ includes are installed in
546 <filename class="directory">include/c++</filename>, then nested in a
547 directory hierarchy corresponding to the C++ compiler's released
548 version. This version corresponds to the variable "gcc_version" in
549 "libstdc++-v3/acinclude.m4," and more details can be found in that
550 file's macro GLIBCXX_CONFIGURE (GLIBCPP_CONFIGURE before GCC 3.4.0).
553 C++ includes are versioned as follows:
556 <listitem><para>GCC 3.0.0: include/g++-v3</para></listitem>
557 <listitem><para>GCC 3.0.1: include/g++-v3</para></listitem>
558 <listitem><para>GCC 3.0.2: include/g++-v3</para></listitem>
559 <listitem><para>GCC 3.0.3: include/g++-v3</para></listitem>
560 <listitem><para>GCC 3.0.4: include/g++-v3</para></listitem>
561 <listitem><para>GCC 3.1.0: include/g++-v3</para></listitem>
562 <listitem><para>GCC 3.1.1: include/c++/3.1.1</para></listitem>
563 <listitem><para>GCC 3.2.0: include/c++/3.2</para></listitem>
564 <listitem><para>GCC 3.2.1: include/c++/3.2.1</para></listitem>
565 <listitem><para>GCC 3.2.2: include/c++/3.2.2</para></listitem>
566 <listitem><para>GCC 3.2.3: include/c++/3.2.3</para></listitem>
567 <listitem><para>GCC 3.3.0: include/c++/3.3</para></listitem>
568 <listitem><para>GCC 3.3.1: include/c++/3.3.1</para></listitem>
569 <listitem><para>GCC 3.3.2: include/c++/3.3.2</para></listitem>
570 <listitem><para>GCC 3.3.3: include/c++/3.3.3</para></listitem>
571 <listitem><para>GCC 3.4.x: include/c++/3.4.x</para></listitem>
572 <listitem><para>GCC 4.x.y: include/c++/4.x.y</para></listitem>
573 <listitem><para>GCC 5.x.0: include/c++/5.x.0</para></listitem>
574 <listitem><para>GCC 6.x.0: include/c++/6.x.0</para></listitem>
575 <listitem><para>GCC 7.x.0: include/c++/7.x.0</para></listitem>
576 <listitem><para>GCC 8.x.0: include/c++/8.x.0</para></listitem>
583 Taken together, these techniques can accurately specify interface
584 and implementation changes in the GNU C++ tools themselves. Used
585 properly, they allow both the GNU C++ tools implementation, and
586 programs using them, an evolving yet controlled development that
587 maintains backward compatibility.
593 <section xml:id="abi.versioning.prereq"><info><title>Prerequisites</title></info>
596 Minimum environment that supports a versioned ABI: A supported
597 dynamic linker, a GNU linker of sufficient vintage to understand
598 demangled C++ name globbing (ld) or the Sun linker, a shared
600 with g++, and shared libraries (libgcc_s, libstdc++) compiled by
601 a compiler (g++) with a compatible ABI. Phew.
605 On top of all that, an additional constraint: libstdc++ did not
606 attempt to version symbols (or age gracefully, really) until
611 Most modern GNU/Linux and BSD versions, particularly ones using
612 GCC 3.1 and later, will meet the
613 requirements above, as does Solaris 2.5 and up.
617 <section xml:id="abi.versioning.config"><info><title>Configuring</title></info>
621 It turns out that most of the configure options that change
622 default behavior will impact the mangled names of exported
623 symbols, and thus impact versioning and compatibility.
627 For more information on configure options, including ABI
629 <link linkend="manual.intro.setup.configure">here</link>
633 There is one flag that explicitly deals with symbol versioning:
638 In particular, libstdc++-v3/acinclude.m4 has a macro called
639 GLIBCXX_ENABLE_SYMVERS that defaults to yes (or the argument
640 passed in via --enable-symvers=foo). At that point, the macro
641 attempts to make sure that all the requirement for symbol
642 versioning are in place. For more information, please consult
647 <section xml:id="abi.versioning.active"><info><title>Checking Active</title></info>
651 When the GNU C++ library is being built with symbol versioning
652 on, you should see the following at configure time for
653 libstdc++ (showing either 'gnu' or another of the supported styles):
658 checking versioning on shared library symbols... gnu
663 If you don't see this line in the configure output, or if this line
664 appears but the last word is 'no', then you are out of luck.
668 If the compiler is pre-installed, a quick way to test is to compile
669 the following (or any) simple C++ file and link it to the shared
674 #include <iostream>
677 { std::cout << "hello" << std::endl; return 0; }
679 %g++ hello.cc -o hello.out
682 libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x00764000)
683 libm.so.6 => /lib/tls/libm.so.6 (0x004a8000)
684 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x40016000)
685 libc.so.6 => /lib/tls/libc.so.6 (0x0036d000)
686 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
692 If you see symbols in the resulting output with "GLIBCXX_3" as part
693 of the name, then the executable is versioned. Here's an example:
697 <code>U _ZNSt8ios_base4InitC1Ev@@GLIBCXX_3.4</code>
701 On Solaris 2, you can use <code>pvs -r</code> instead:
705 %g++ hello.cc -o hello.out
708 libstdc++.so.6 (GLIBCXX_3.4, GLIBCXX_3.4.12);
709 libgcc_s.so.1 (GCC_3.0);
710 libc.so.1 (SUNWprivate_1.1, SYSVABI_1.3);
714 <code>ldd -v</code> works too, but is very verbose.
720 <section xml:id="abi.changes_allowed"><info><title>Allowed Changes</title></info>
724 The following will cause the library minor version number to
725 increase, say from "libstdc++.so.3.0.4" to "libstdc++.so.3.0.5".
728 <listitem><para>Adding an exported global or static data member</para></listitem>
729 <listitem><para>Adding an exported function, static or non-virtual member function</para></listitem>
730 <listitem><para>Adding an exported symbol or symbols by additional instantiations</para></listitem>
733 Other allowed changes are possible.
738 <section xml:id="abi.changes_no"><info><title>Prohibited Changes</title></info>
742 The following non-exhaustive list will cause the library major version
743 number to increase, say from "libstdc++.so.3.0.4" to
744 "libstdc++.so.4.0.0".
748 <listitem><para>Changes in the gcc/g++ compiler ABI</para></listitem>
749 <listitem><para>Changing size of an exported symbol</para></listitem>
750 <listitem><para>Changing alignment of an exported symbol</para></listitem>
751 <listitem><para>Changing the layout of an exported symbol</para></listitem>
752 <listitem><para>Changing mangling on an exported symbol</para></listitem>
753 <listitem><para>Deleting an exported symbol</para></listitem>
754 <listitem><para>Changing the inheritance properties of a type by adding or removing
755 base classes</para></listitem>
757 Changing the size, alignment, or layout of types
758 specified in the C++ standard. These may not necessarily be
759 instantiated or otherwise exported in the library binary, and
760 include all the required locale facets, as well as things like
761 std::basic_streambuf, et al.
764 <listitem><para> Adding an explicit copy constructor or destructor to a
765 class that would otherwise have implicit versions. This will change
766 the way the compiler deals with this class in by-value return
767 statements or parameters: instead of passing instances of this
768 class in registers, the compiler will be forced to use memory. See the
769 section on <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://itanium-cxx-abi.github.io/cxx-abi/abi.html#calls">Function
770 Calling Conventions and APIs</link>
771 of the C++ ABI documentation for further details.
780 <section xml:id="abi.impl"><info><title>Implementation</title></info>
786 Separation of interface and implementation
789 This is accomplished by two techniques that separate the API from
790 the ABI: forcing undefined references to link against a library
791 binary for definitions.
796 <term>Include files have declarations, source files have defines</term>
800 For non-templatized types, such as much of <code>class
801 locale</code>, the appropriate standard C++ include, say
802 <code>locale</code>, can contain full declarations, while
803 various source files (say <code> locale.cc, locale_init.cc,
804 localename.cc</code>) contain definitions.
810 <term>Extern template on required types</term>
814 For parts of the standard that have an explicit list of
815 required instantiations, the GNU extension syntax <code> extern
816 template </code> can be used to control where template
817 definitions reside. By marking required instantiations as
818 <code> extern template </code> in include files, and providing
819 explicit instantiations in the appropriate instantiation files,
820 non-inlined template functions can be versioned. This technique
821 is mostly used on parts of the standard that require <code>
822 char</code> and <code> wchar_t</code> instantiations, and
823 includes <code> basic_string</code>, the locale facets, and the
824 types in <code> iostreams</code>.
832 In addition, these techniques have the additional benefit that they
833 reduce binary size, which can increase runtime performance.
839 Namespaces linking symbol definitions to export mapfiles
842 All symbols in the shared library binary are processed by a
843 linker script at build time that either allows or disallows
844 external linkage. Because of this, some symbols, regardless of
845 normal C/C++ linkage, are not visible. Symbols that are internal
846 have several appealing characteristics: by not exporting the
847 symbols, there are no relocations when the shared library is
848 started and thus this makes for faster runtime loading
849 performance by the underlying dynamic loading mechanism. In
850 addition, they have the possibility of changing without impacting
854 <para>The following namespaces are transformed by the mapfile:</para>
859 <term><code>namespace std</code></term>
860 <listitem><para> Defaults to exporting all symbols in label
861 <code>GLIBCXX</code> that do not begin with an underscore, i.e.,
862 <code>__test_func</code> would not be exported by default. Select
863 exceptional symbols are allowed to be visible.</para></listitem>
867 <term><code>namespace __gnu_cxx</code></term>
868 <listitem><para> Defaults to not exporting any symbols in label
869 <code>GLIBCXX</code>, select items are allowed to be visible.</para></listitem>
873 <term><code>namespace __gnu_internal</code></term>
874 <listitem><para> Defaults to not exported, no items are allowed to be visible.</para></listitem>
878 <term><code>namespace __cxxabiv1</code>, aliased to <code> namespace abi</code></term>
879 <listitem><para> Defaults to not exporting any symbols in label
880 <code>CXXABI</code>, select items are allowed to be visible.</para></listitem>
888 <listitem><para>Freezing the API</para>
889 <para>Disallowed changes, as above, are not made on a stable release
890 branch. Enforcement tends to be less strict with GNU extensions that
891 standard includes.</para>
897 <section xml:id="abi.testing"><info><title>Testing</title></info>
900 <section xml:id="abi.testing.single"><info><title>Single ABI Testing</title></info>
904 Testing for GNU C++ ABI changes is composed of two distinct
905 areas: testing the C++ compiler (g++) for compiler changes, and
906 testing the C++ library (libstdc++) for library changes.
910 Testing the C++ compiler ABI can be done various ways.
914 One. Intel ABI checker.
919 The second is yet unreleased, but has been announced on the gcc
920 mailing list. It is yet unspecified if these tools will be freely
921 available, and able to be included in a GNU project. Please contact
922 Mark Mitchell (mark@codesourcery.com) for more details, and current
928 Involves using the vlad.consistency test framework. This has also been
929 discussed on the gcc mailing lists.
933 Testing the C++ library ABI can also be done various ways.
938 (Brendan Kehoe, Jeff Law suggestion to run 'make check-c++' two ways,
939 one with a new compiler and an old library, and the other with an old
940 compiler and a new library, and look for testsuite regressions)
944 Details on how to set this kind of test up can be found here:
945 http://gcc.gnu.org/ml/gcc/2002-08/msg00142.html
950 Use the 'make check-abi' rule in the libstdc++ Makefile.
954 This is a proactive check of the library ABI. Currently, exported symbol
955 names that are either weak or defined are checked against a last known
956 good baseline. Currently, this baseline is keyed off of 3.4.0
957 binaries, as this was the last time the .so number was incremented. In
958 addition, all exported names are demangled, and the exported objects
959 are checked to make sure they are the same size as the same object in
962 Notice that each baseline is relative to a <emphasis>default</emphasis>
963 configured library and compiler: in particular, if options such as
964 --enable-clocale, or --with-cpu, in case of multilibs, are used at
965 configure time, the check may fail, either because of substantive
966 differences or because of limitations of the current checking
971 This dataset is insufficient, yet a start. Also needed is a
972 comprehensive check for all user-visible types part of the standard
973 library for sizeof() and alignof() changes.
977 Verifying compatible layouts of objects is not even attempted. It
978 should be possible to use sizeof, alignof, and offsetof to compute
979 offsets for each structure and type in the standard library, saving to
980 another datafile. Then, compute this in a similar way for new
981 binaries, and look for differences.
985 Another approach might be to use the -fdump-class-hierarchy flag to
986 get information. However, currently this approach gives insufficient
987 data for use in library testing, as class data members, their offsets,
988 and other detailed data is not displayed with this flag.
989 (See PR g++/7470 on how this was used to find bugs.)
993 Perhaps there are other C++ ABI checkers. If so, please notify
994 us. We'd like to know about them!
998 <section xml:id="abi.testing.multi"><info><title>Multiple ABI Testing</title></info>
1001 A "C" application, dynamically linked to two shared libraries, liba,
1002 libb. The dependent library liba is a C++ shared library compiled with
1003 GCC 3.3, and uses io, exceptions, locale, etc. The dependent library
1004 libb is a C++ shared library compiled with GCC 3.4, and also uses io,
1005 exceptions, locale, etc.
1008 <para> As above, libone is constructed as follows: </para>
1010 %$bld/H-x86-gcc-3.4.0/bin/g++ -fPIC -DPIC -c a.cc
1012 %$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
1014 %ln -s libone.so.1.0.0 libone.so
1016 %$bld/H-x86-gcc-3.4.0/bin/g++ -c a.cc
1018 %ar cru libone.a a.o
1021 <para> And, libtwo is constructed as follows: </para>
1024 %$bld/H-x86-gcc-3.3.3/bin/g++ -fPIC -DPIC -c b.cc
1026 %$bld/H-x86-gcc-3.3.3/bin/g++ -shared -Wl,-soname -Wl,libtwo.so.1 -Wl,-O1 -Wl,-z,defs b.o -o libtwo.so.1.0.0
1028 %ln -s libtwo.so.1.0.0 libtwo.so
1030 %$bld/H-x86-gcc-3.3.3/bin/g++ -c b.cc
1032 %ar cru libtwo.a b.o
1035 <para> ...with the resulting libraries looking like </para>
1039 %ldd libone.so.1.0.0
1040 libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x40016000)
1041 libm.so.6 => /lib/tls/libm.so.6 (0x400fa000)
1042 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x4011c000)
1043 libc.so.6 => /lib/tls/libc.so.6 (0x40125000)
1044 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
1046 %ldd libtwo.so.1.0.0
1047 libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x40027000)
1048 libm.so.6 => /lib/tls/libm.so.6 (0x400e1000)
1049 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x40103000)
1050 libc.so.6 => /lib/tls/libc.so.6 (0x4010c000)
1051 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
1056 Then, the "C" compiler is used to compile a source file that uses
1057 functions from each library.
1060 gcc test.c -g -O2 -L. -lone -ltwo /usr/lib/libstdc++.so.5 /usr/lib/libstdc++.so.6
1064 Which gives the expected:
1070 libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x00764000)
1071 libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x40015000)
1072 libc.so.6 => /lib/tls/libc.so.6 (0x0036d000)
1073 libm.so.6 => /lib/tls/libm.so.6 (0x004a8000)
1074 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x400e5000)
1075 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
1080 This resulting binary, when executed, will be able to safely use
1081 code from both liba, and the dependent libstdc++.so.6, and libb,
1082 with the dependent libstdc++.so.5.
1087 <section xml:id="abi.issues"><info><title>Outstanding Issues</title></info>
1091 Some features in the C++ language make versioning especially
1092 difficult. In particular, compiler generated constructs such as
1093 implicit instantiations for templates, typeinfo information, and
1094 virtual tables all may cause ABI leakage across shared library
1095 boundaries. Because of this, mixing C++ ABIs is not recommended at
1100 For more background on this issue, see these bugzilla entries:
1104 <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/PR24660">24660: versioning weak symbols in libstdc++</link>
1108 <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/PR19664">19664: libstdc++ headers should have pop/push of the visibility around the declarations</link>
1113 <bibliography xml:id="abi.biblio"><info><title>Bibliography</title></info>
1115 <biblioentry xml:id="biblio.abicheck">
1117 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1118 xlink:href="http://abicheck.sourceforge.net">
1124 <biblioentry xml:id="biblio.cxxabi">
1126 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1127 xlink:href="https://itanium-cxx-abi.github.io/cxx-abi/">
1136 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1137 xlink:href="https://software.intel.com/en-us/articles/intel-compilers-for-linux-compatibility-with-gnu-compilers">
1138 Intel Compilers for Linux: Compatibility with GNU Compilers
1145 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1146 xlink:href="https://docs.oracle.com/cd/E23824_01/html/819-0690/index.html">
1147 Linker and Libraries Guide (document 819-0690)
1155 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1156 xlink:href="https://docs.oracle.com/cd/E19422-01/819-3689/">
1157 Sun Studio 11: C++ Migration Guide (document 819-3689)
1164 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1165 xlink:href="https://www.akkadia.org/drepper/dsohowto.pdf">
1166 How to Write Shared Libraries
1172 <firstname>Ulrich</firstname><surname>Drepper</surname>
1179 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1180 xlink:href="http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ihi0036b/index.html">
1181 C++ ABI for the ARM Architecture
1188 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1189 xlink:href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1976.html">
1190 Dynamic Shared Objects: Survey and Issues
1197 <author><personname><firstname>Benjamin</firstname><surname>Kosnik</surname></personname></author>
1202 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1203 xlink:href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2013.html">
1204 Versioning With Namespaces
1210 <author><personname><firstname>Benjamin</firstname><surname>Kosnik</surname></personname></author>
1215 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1216 xlink:href="http://syrcose.ispras.ru/2009/files/02_paper.pdf">
1217 Binary Compatibility of Shared Libraries Implemented in C++
1218 on GNU/Linux Systems
1225 <author><personname><firstname>Pavel</firstname><surname>Shved</surname></personname></author>
1226 <author><personname><firstname>Denis</firstname><surname>Silakov</surname></personname></author>