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>
33 <section xml:id="abi.cxx_interface"><info><title>The C++ Interface</title></info>
37 C++ applications often depend on specific language support
38 routines, say for throwing exceptions, or catching exceptions, and
39 perhaps also depend on features in the C++ Standard Library.
43 The C++ Standard Library has many include files, types defined in
44 those include files, specific named functions, and other
45 behavior. The text of these behaviors, as written in source include
46 files, is called the Application Programing Interface, or API.
50 Furthermore, C++ source that is compiled into object files is
51 transformed by the compiler: it arranges objects with specific
52 alignment and in a particular layout, mangling names according to a
53 well-defined algorithm, has specific arrangements for the support of
54 virtual functions, etc. These details are defined as the compiler
55 Application Binary Interface, or ABI. The GNU C++ compiler uses an
56 industry-standard C++ ABI starting with version 3. Details can be
57 found in the <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://mentorembedded.github.com/cxx-abi/abi.html">ABI
62 The GNU C++ compiler, g++, has a compiler command line option to
63 switch between various different C++ ABIs. This explicit version
64 switch is the flag <code>-fabi-version</code>. In addition, some
65 g++ command line options may change the ABI as a side-effect of
66 use. Such flags include <code>-fpack-struct</code> and
67 <code>-fno-exceptions</code>, but include others: see the complete
68 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
69 for Code Generation Conventions</link>.
73 The configure options used when building a specific libstdc++
74 version may also impact the resulting library ABI. The available
75 configure options, and their impact on the library ABI, are
77 <link linkend="manual.intro.setup.configure">here</link>.
80 <para> Putting all of these ideas together results in the C++ Standard
81 library ABI, which is the compilation of a given library API by a
82 given compiler ABI. In a nutshell:
87 library API + compiler ABI = library ABI
92 The library ABI is mostly of interest for end-users who have
93 unresolved symbols and are linking dynamically to the C++ Standard
94 library, and who thus must be careful to compile their application
95 with a compiler that is compatible with the available C++ Standard
96 library binary. In this case, compatible is defined with the equation
97 above: given an application compiled with a given compiler ABI and
98 library API, it will work correctly with a Standard C++ Library
99 created with the same constraints.
103 To use a specific version of the C++ ABI, one must use a
104 corresponding GNU C++ toolchain (i.e., g++ and libstdc++) that
105 implements the C++ ABI in question.
110 <section xml:id="abi.versioning"><info><title>Versioning</title></info>
113 <para> The C++ interface has evolved throughout the history of the GNU
114 C++ toolchain. With each release, various details have been changed so
115 as to give distinct versions to the C++ interface.
118 <section xml:id="abi.versioning.goals"><info><title>Goals</title></info>
121 <para>Extending existing, stable ABIs. Versioning gives subsequent
122 releases of library binaries the ability to add new symbols and add
123 functionality, all the while retaining compatibility with the previous
124 releases in the series. Thus, program binaries linked with the initial
125 release of a library binary will still run correctly if the library
126 binary is replaced by carefully-managed subsequent library
127 binaries. This is called forward compatibility.
130 The reverse (backwards compatibility) is not true. It is not possible
131 to take program binaries linked with the latest version of a library
132 binary in a release series (with additional symbols added), substitute
133 in the initial release of the library binary, and remain link
137 <para>Allows multiple, incompatible ABIs to coexist at the same time.
141 <section xml:id="abi.versioning.history"><info><title>History</title></info>
145 How can this complexity be managed? What does C++ versioning mean?
146 Because library and compiler changes often make binaries compiled
147 with one version of the GNU tools incompatible with binaries
148 compiled with other (either newer or older) versions of the same GNU
149 tools, specific techniques are used to make managing this complexity
154 The following techniques are used:
159 <listitem><para>Release versioning on the libgcc_s.so binary. </para>
161 <para>This is implemented via file names and the ELF
162 <constant>DT_SONAME</constant> mechanism (at least on ELF
163 systems). It is versioned as follows:
167 <listitem><para>GCC 3.x: libgcc_s.so.1</para></listitem>
168 <listitem><para>GCC 4.x: libgcc_s.so.1</para></listitem>
171 <para>For m68k-linux the versions differ as follows: </para>
174 <listitem><para>GCC 3.4, GCC 4.x: libgcc_s.so.1
175 when configuring <code>--with-sjlj-exceptions</code>, or
176 libgcc_s.so.2 </para> </listitem>
179 <para>For hppa-linux the versions differ as follows: </para>
182 <listitem><para>GCC 3.4, GCC 4.[0-1]: either libgcc_s.so.1
183 when configuring <code>--with-sjlj-exceptions</code>, or
184 libgcc_s.so.2 </para> </listitem>
185 <listitem><para>GCC 4.[2-7]: either libgcc_s.so.3 when configuring
186 <code>--with-sjlj-exceptions</code>) or libgcc_s.so.4
192 <listitem><para>Symbol versioning on the libgcc_s.so binary.</para>
194 <para>It is versioned with the following labels and version
195 definitions, where the version definition is the maximum for a
196 particular release. Labels are cumulative. If a particular release
197 is not listed, it has the same version labels as the preceding
200 <para>This corresponds to the mapfile: gcc/libgcc-std.ver</para>
202 <listitem><para>GCC 3.0.0: GCC_3.0</para></listitem>
203 <listitem><para>GCC 3.3.0: GCC_3.3</para></listitem>
204 <listitem><para>GCC 3.3.1: GCC_3.3.1</para></listitem>
205 <listitem><para>GCC 3.3.2: GCC_3.3.2</para></listitem>
206 <listitem><para>GCC 3.3.4: GCC_3.3.4</para></listitem>
207 <listitem><para>GCC 3.4.0: GCC_3.4</para></listitem>
208 <listitem><para>GCC 3.4.2: GCC_3.4.2</para></listitem>
209 <listitem><para>GCC 3.4.4: GCC_3.4.4</para></listitem>
210 <listitem><para>GCC 4.0.0: GCC_4.0.0</para></listitem>
211 <listitem><para>GCC 4.1.0: GCC_4.1.0</para></listitem>
212 <listitem><para>GCC 4.2.0: GCC_4.2.0</para></listitem>
213 <listitem><para>GCC 4.3.0: GCC_4.3.0</para></listitem>
214 <listitem><para>GCC 4.4.0: GCC_4.4.0</para></listitem>
215 <listitem><para>GCC 4.5.0: GCC_4.5.0</para></listitem>
216 <listitem><para>GCC 4.6.0: GCC_4.6.0</para></listitem>
217 <listitem><para>GCC 4.7.0: GCC_4.7.0</para></listitem>
223 Release versioning on the libstdc++.so binary, implemented in
224 the same way as the libgcc_s.so binary above. Listed is the
225 filename: <constant>DT_SONAME</constant> can be deduced from
226 the filename by removing the last two period-delimited numbers. For
227 example, filename <filename>libstdc++.so.5.0.4</filename>
228 corresponds to a <constant>DT_SONAME</constant> of
229 <constant>libstdc++.so.5</constant>. Binaries with equivalent
230 <constant>DT_SONAME</constant>s are forward-compatibile: in
231 the table below, releases incompatible with the previous
232 one are explicitly noted.
233 If a particular release is not listed, its libstdc++.so binary
234 has the same filename and <constant>DT_SONAME</constant> as the
238 <para>It is versioned as follows:
241 <listitem><para>GCC 3.0.0: libstdc++.so.3.0.0</para></listitem>
242 <listitem><para>GCC 3.0.1: libstdc++.so.3.0.1</para></listitem>
243 <listitem><para>GCC 3.0.2: libstdc++.so.3.0.2</para></listitem>
244 <listitem><para>GCC 3.0.3: libstdc++.so.3.0.2 (See Note 1)</para></listitem>
245 <listitem><para>GCC 3.0.4: libstdc++.so.3.0.4</para></listitem>
246 <listitem><para>GCC 3.1.0: libstdc++.so.4.0.0 <emphasis>(Incompatible with previous)</emphasis></para></listitem>
247 <listitem><para>GCC 3.1.1: libstdc++.so.4.0.1</para></listitem>
248 <listitem><para>GCC 3.2.0: libstdc++.so.5.0.0 <emphasis>(Incompatible with previous)</emphasis></para></listitem>
249 <listitem><para>GCC 3.2.1: libstdc++.so.5.0.1</para></listitem>
250 <listitem><para>GCC 3.2.2: libstdc++.so.5.0.2</para></listitem>
251 <listitem><para>GCC 3.2.3: libstdc++.so.5.0.3 (See Note 2)</para></listitem>
252 <listitem><para>GCC 3.3.0: libstdc++.so.5.0.4</para></listitem>
253 <listitem><para>GCC 3.3.1: libstdc++.so.5.0.5</para></listitem>
254 <listitem><para>GCC 3.4.0: libstdc++.so.6.0.0 <emphasis>(Incompatible with previous)</emphasis></para></listitem>
255 <listitem><para>GCC 3.4.1: libstdc++.so.6.0.1</para></listitem>
256 <listitem><para>GCC 3.4.2: libstdc++.so.6.0.2</para></listitem>
257 <listitem><para>GCC 3.4.3: libstdc++.so.6.0.3</para></listitem>
258 <listitem><para>GCC 4.0.0: libstdc++.so.6.0.4</para></listitem>
259 <listitem><para>GCC 4.0.1: libstdc++.so.6.0.5</para></listitem>
260 <listitem><para>GCC 4.0.2: libstdc++.so.6.0.6</para></listitem>
261 <listitem><para>GCC 4.0.3: libstdc++.so.6.0.7</para></listitem>
262 <listitem><para>GCC 4.1.0: libstdc++.so.6.0.7</para></listitem>
263 <listitem><para>GCC 4.1.1: libstdc++.so.6.0.8</para></listitem>
264 <listitem><para>GCC 4.2.0: libstdc++.so.6.0.9</para></listitem>
265 <listitem><para>GCC 4.2.1: libstdc++.so.6.0.9 (See Note 3)</para></listitem>
266 <listitem><para>GCC 4.2.2: libstdc++.so.6.0.9</para></listitem>
267 <listitem><para>GCC 4.3.0: libstdc++.so.6.0.10</para></listitem>
268 <listitem><para>GCC 4.4.0: libstdc++.so.6.0.11</para></listitem>
269 <listitem><para>GCC 4.4.1: libstdc++.so.6.0.12</para></listitem>
270 <listitem><para>GCC 4.4.2: libstdc++.so.6.0.13</para></listitem>
271 <listitem><para>GCC 4.5.0: libstdc++.so.6.0.14</para></listitem>
272 <listitem><para>GCC 4.6.0: libstdc++.so.6.0.15</para></listitem>
273 <listitem><para>GCC 4.6.1: libstdc++.so.6.0.16</para></listitem>
274 <listitem><para>GCC 4.7.0: libstdc++.so.6.0.17</para></listitem>
277 Note 1: Error should be libstdc++.so.3.0.3.
280 Note 2: Not strictly required.
283 Note 3: This release (but not previous or subsequent) has one
284 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>
285 in the GCC bug database.
289 <listitem><para>Symbol versioning on the libstdc++.so binary.</para>
291 <para>mapfile: libstdc++-v3/config/abi/pre/gnu.ver</para>
292 <para>It is versioned with the following labels and version
293 definitions, where the version definition is the maximum for a
294 particular release. Note, only symbols which are newly introduced
295 will use the maximum version definition. Thus, for release series
296 with the same label, but incremented version definitions, the later
297 release has both versions. (An example of this would be the
298 GCC 3.2.1 release, which has GLIBCPP_3.2.1 for new symbols and
299 GLIBCPP_3.2 for symbols that were introduced in the GCC 3.2.0
300 release.) If a particular release is not listed, it has the same
301 version labels as the preceding release.
304 <listitem><para>GCC 3.0.0: (Error, not versioned)</para></listitem>
305 <listitem><para>GCC 3.0.1: (Error, not versioned)</para></listitem>
306 <listitem><para>GCC 3.0.2: (Error, not versioned)</para></listitem>
307 <listitem><para>GCC 3.0.3: (Error, not versioned)</para></listitem>
308 <listitem><para>GCC 3.0.4: (Error, not versioned)</para></listitem>
309 <listitem><para>GCC 3.1.0: GLIBCPP_3.1, CXXABI_1</para></listitem>
310 <listitem><para>GCC 3.1.1: GLIBCPP_3.1, CXXABI_1</para></listitem>
311 <listitem><para>GCC 3.2.0: GLIBCPP_3.2, CXXABI_1.2</para></listitem>
312 <listitem><para>GCC 3.2.1: GLIBCPP_3.2.1, CXXABI_1.2</para></listitem>
313 <listitem><para>GCC 3.2.2: GLIBCPP_3.2.2, CXXABI_1.2</para></listitem>
314 <listitem><para>GCC 3.2.3: GLIBCPP_3.2.2, CXXABI_1.2</para></listitem>
315 <listitem><para>GCC 3.3.0: GLIBCPP_3.2.2, CXXABI_1.2.1</para></listitem>
316 <listitem><para>GCC 3.3.1: GLIBCPP_3.2.3, CXXABI_1.2.1</para></listitem>
317 <listitem><para>GCC 3.3.2: GLIBCPP_3.2.3, CXXABI_1.2.1</para></listitem>
318 <listitem><para>GCC 3.3.3: GLIBCPP_3.2.3, CXXABI_1.2.1</para></listitem>
319 <listitem><para>GCC 3.4.0: GLIBCXX_3.4, CXXABI_1.3</para></listitem>
320 <listitem><para>GCC 3.4.1: GLIBCXX_3.4.1, CXXABI_1.3</para></listitem>
321 <listitem><para>GCC 3.4.2: GLIBCXX_3.4.2</para></listitem>
322 <listitem><para>GCC 3.4.3: GLIBCXX_3.4.3</para></listitem>
323 <listitem><para>GCC 4.0.0: GLIBCXX_3.4.4, CXXABI_1.3.1</para></listitem>
324 <listitem><para>GCC 4.0.1: GLIBCXX_3.4.5</para></listitem>
325 <listitem><para>GCC 4.0.2: GLIBCXX_3.4.6</para></listitem>
326 <listitem><para>GCC 4.0.3: GLIBCXX_3.4.7</para></listitem>
327 <listitem><para>GCC 4.1.1: GLIBCXX_3.4.8</para></listitem>
328 <listitem><para>GCC 4.2.0: GLIBCXX_3.4.9</para></listitem>
329 <listitem><para>GCC 4.3.0: GLIBCXX_3.4.10, CXXABI_1.3.2</para></listitem>
330 <listitem><para>GCC 4.4.0: GLIBCXX_3.4.11, CXXABI_1.3.3</para></listitem>
331 <listitem><para>GCC 4.4.1: GLIBCXX_3.4.12, CXXABI_1.3.3</para></listitem>
332 <listitem><para>GCC 4.4.2: GLIBCXX_3.4.13, CXXABI_1.3.3</para></listitem>
333 <listitem><para>GCC 4.5.0: GLIBCXX_3.4.14, CXXABI_1.3.4</para></listitem>
334 <listitem><para>GCC 4.6.0: GLIBCXX_3.4.15, CXXABI_1.3.5</para></listitem>
335 <listitem><para>GCC 4.6.1: GLIBCXX_3.4.16, CXXABI_1.3.5</para></listitem>
336 <listitem><para>GCC 4.7.0: GLIBCXX_3.4.17, CXXABI_1.3.6</para></listitem>
341 <para>Incremental bumping of a compiler pre-defined macro,
342 __GXX_ABI_VERSION. This macro is defined as the version of the
343 compiler v3 ABI, with g++ 3.0 being version 100. This macro will
344 be automatically defined whenever g++ is used (the curious can
345 test this by invoking g++ with the '-v' flag.)
349 This macro was defined in the file "lang-specs.h" in the gcc/cp directory.
350 Later versions defined it in "c-common.c" in the gcc directory, and from
351 G++ 3.4 it is defined in c-cppbuiltin.c and its value determined by the
352 '-fabi-version' command line option.
356 It is versioned as follows, where 'n' is given by '-fabi-version=n':
359 <listitem><para>GCC 3.0: 100</para></listitem>
360 <listitem><para>GCC 3.1: 100 (Error, should be 101)</para></listitem>
361 <listitem><para>GCC 3.2: 102</para></listitem>
362 <listitem><para>GCC 3.3: 102</para></listitem>
363 <listitem><para>GCC 3.4, GCC 4.x: 102 (when n=1)</para></listitem>
364 <listitem><para>GCC 3.4, GCC 4.x: 1000 + n (when n>1) </para></listitem>
365 <listitem><para>GCC 3.4, GCC 4.x: 999999 (when n=0)</para></listitem>
371 <para>Changes to the default compiler option for
372 <code>-fabi-version</code>.
375 It is versioned as follows:
378 <listitem><para>GCC 3.0: (Error, not versioned) </para></listitem>
379 <listitem><para>GCC 3.1: (Error, not versioned) </para></listitem>
380 <listitem><para>GCC 3.2: <code>-fabi-version=1</code></para></listitem>
381 <listitem><para>GCC 3.3: <code>-fabi-version=1</code></para></listitem>
382 <listitem><para>GCC 3.4, GCC 4.x: <code>-fabi-version=2</code> <emphasis>(Incompatible with previous)</emphasis></para></listitem>
388 <para>Incremental bumping of a library pre-defined macro. For releases
389 before 3.4.0, the macro is __GLIBCPP__. For later releases, it's
390 __GLIBCXX__. (The libstdc++ project generously changed from CPP to
391 CXX throughout its source to allow the "C" pre-processor the CPP
392 macro namespace.) These macros are defined as the date the library
393 was released, in compressed ISO date format, as an unsigned long.
397 This macro is defined in the file "c++config" in the
398 "libstdc++-v3/include/bits" directory. (Up to GCC 4.1.0, it was
399 changed every night by an automated script. Since GCC 4.1.0, it is
400 the same value as gcc/DATESTAMP.)
403 It is versioned as follows:
406 <listitem><para>GCC 3.0.0: 20010615</para></listitem>
407 <listitem><para>GCC 3.0.1: 20010819</para></listitem>
408 <listitem><para>GCC 3.0.2: 20011023</para></listitem>
409 <listitem><para>GCC 3.0.3: 20011220</para></listitem>
410 <listitem><para>GCC 3.0.4: 20020220</para></listitem>
411 <listitem><para>GCC 3.1.0: 20020514</para></listitem>
412 <listitem><para>GCC 3.1.1: 20020725</para></listitem>
413 <listitem><para>GCC 3.2.0: 20020814</para></listitem>
414 <listitem><para>GCC 3.2.1: 20021119</para></listitem>
415 <listitem><para>GCC 3.2.2: 20030205</para></listitem>
416 <listitem><para>GCC 3.2.3: 20030422</para></listitem>
417 <listitem><para>GCC 3.3.0: 20030513</para></listitem>
418 <listitem><para>GCC 3.3.1: 20030804</para></listitem>
419 <listitem><para>GCC 3.3.2: 20031016</para></listitem>
420 <listitem><para>GCC 3.3.3: 20040214</para></listitem>
421 <listitem><para>GCC 3.4.0: 20040419</para></listitem>
422 <listitem><para>GCC 3.4.1: 20040701</para></listitem>
423 <listitem><para>GCC 3.4.2: 20040906</para></listitem>
424 <listitem><para>GCC 3.4.3: 20041105</para></listitem>
425 <listitem><para>GCC 3.4.4: 20050519</para></listitem>
426 <listitem><para>GCC 3.4.5: 20051201</para></listitem>
427 <listitem><para>GCC 3.4.6: 20060306</para></listitem>
428 <listitem><para>GCC 4.0.0: 20050421</para></listitem>
429 <listitem><para>GCC 4.0.1: 20050707</para></listitem>
430 <listitem><para>GCC 4.0.2: 20050921</para></listitem>
431 <listitem><para>GCC 4.0.3: 20060309</para></listitem>
432 <listitem><para>GCC 4.1.0: 20060228</para></listitem>
433 <listitem><para>GCC 4.1.1: 20060524</para></listitem>
434 <listitem><para>GCC 4.1.2: 20070214</para></listitem>
435 <listitem><para>GCC 4.2.0: 20070514</para></listitem>
436 <listitem><para>GCC 4.2.1: 20070719</para></listitem>
437 <listitem><para>GCC 4.2.2: 20071007</para></listitem>
438 <listitem><para>GCC 4.2.3: 20080201</para></listitem>
439 <listitem><para>GCC 4.2.4: 20080519</para></listitem>
440 <listitem><para>GCC 4.3.0: 20080306</para></listitem>
441 <listitem><para>GCC 4.3.1: 20080606</para></listitem>
442 <listitem><para>GCC 4.3.2: 20080827</para></listitem>
443 <listitem><para>GCC 4.3.3: 20090124</para></listitem>
444 <listitem><para>GCC 4.3.4: 20090804</para></listitem>
445 <listitem><para>GCC 4.3.5: 20100522</para></listitem>
446 <listitem><para>GCC 4.3.6: 20110627</para></listitem>
447 <listitem><para>GCC 4.4.0: 20090421</para></listitem>
448 <listitem><para>GCC 4.4.1: 20090722</para></listitem>
449 <listitem><para>GCC 4.4.2: 20091015</para></listitem>
450 <listitem><para>GCC 4.4.3: 20100121</para></listitem>
451 <listitem><para>GCC 4.4.4: 20100429</para></listitem>
452 <listitem><para>GCC 4.4.5: 20101001</para></listitem>
453 <listitem><para>GCC 4.4.6: 20110416</para></listitem>
454 <listitem><para>GCC 4.4.7: 20120313</para></listitem>
455 <listitem><para>GCC 4.5.0: 20100414</para></listitem>
456 <listitem><para>GCC 4.5.1: 20100731</para></listitem>
457 <listitem><para>GCC 4.5.2: 20101216</para></listitem>
458 <listitem><para>GCC 4.5.3: 20110428</para></listitem>
459 <listitem><para>GCC 4.5.4: 20120702</para></listitem>
460 <listitem><para>GCC 4.6.0: 20110325</para></listitem>
461 <listitem><para>GCC 4.6.1: 20110627</para></listitem>
462 <listitem><para>GCC 4.6.2: 20111026</para></listitem>
463 <listitem><para>GCC 4.6.3: 20120301</para></listitem>
464 <listitem><para>GCC 4.7.0: 20120322</para></listitem>
465 <listitem><para>GCC 4.7.1: 20120614</para></listitem>
466 <listitem><para>GCC 4.7.2: 20120920</para></listitem>
473 Incremental bumping of a library pre-defined macro,
474 _GLIBCPP_VERSION. This macro is defined as the released version of
475 the library, as a string literal. This is only implemented in
476 GCC 3.1.0 releases and higher, and is deprecated in 3.4 (where it
477 is called _GLIBCXX_VERSION).
481 This macro is defined in the file "c++config" in the
482 "libstdc++-v3/include/bits" directory and is generated
483 automatically by autoconf as part of the configure-time generation
488 It is versioned as follows:
491 <listitem><para>GCC 3.0.0: "3.0.0"</para></listitem>
492 <listitem><para>GCC 3.0.1: "3.0.0" (Error, should be "3.0.1")</para></listitem>
493 <listitem><para>GCC 3.0.2: "3.0.0" (Error, should be "3.0.2")</para></listitem>
494 <listitem><para>GCC 3.0.3: "3.0.0" (Error, should be "3.0.3")</para></listitem>
495 <listitem><para>GCC 3.0.4: "3.0.0" (Error, should be "3.0.4")</para></listitem>
496 <listitem><para>GCC 3.1.0: "3.1.0"</para></listitem>
497 <listitem><para>GCC 3.1.1: "3.1.1"</para></listitem>
498 <listitem><para>GCC 3.2.0: "3.2"</para></listitem>
499 <listitem><para>GCC 3.2.1: "3.2.1"</para></listitem>
500 <listitem><para>GCC 3.2.2: "3.2.2"</para></listitem>
501 <listitem><para>GCC 3.2.3: "3.2.3"</para></listitem>
502 <listitem><para>GCC 3.3.0: "3.3"</para></listitem>
503 <listitem><para>GCC 3.3.1: "3.3.1"</para></listitem>
504 <listitem><para>GCC 3.3.2: "3.3.2"</para></listitem>
505 <listitem><para>GCC 3.3.3: "3.3.3"</para></listitem>
506 <listitem><para>GCC 3.4: "version-unused"</para></listitem>
507 <listitem><para>GCC 4.x: "version-unused"</para></listitem>
514 Matching each specific C++ compiler release to a specific set of
515 C++ include files. This is only implemented in GCC 3.1.1 releases
519 All C++ includes are installed in
520 <filename class="directory">include/c++</filename>, then nest in a
521 directory hierarchy corresponding to the C++ compiler's released
522 version. This version corresponds to the variable "gcc_version" in
523 "libstdc++-v3/acinclude.m4," and more details can be found in that
524 file's macro GLIBCXX_CONFIGURE (GLIBCPP_CONFIGURE before GCC 3.4.0).
527 C++ includes are versioned as follows:
530 <listitem><para>GCC 3.0.0: include/g++-v3</para></listitem>
531 <listitem><para>GCC 3.0.1: include/g++-v3</para></listitem>
532 <listitem><para>GCC 3.0.2: include/g++-v3</para></listitem>
533 <listitem><para>GCC 3.0.3: include/g++-v3</para></listitem>
534 <listitem><para>GCC 3.0.4: include/g++-v3</para></listitem>
535 <listitem><para>GCC 3.1.0: include/g++-v3</para></listitem>
536 <listitem><para>GCC 3.1.1: include/c++/3.1.1</para></listitem>
537 <listitem><para>GCC 3.2.0: include/c++/3.2</para></listitem>
538 <listitem><para>GCC 3.2.1: include/c++/3.2.1</para></listitem>
539 <listitem><para>GCC 3.2.2: include/c++/3.2.2</para></listitem>
540 <listitem><para>GCC 3.2.3: include/c++/3.2.3</para></listitem>
541 <listitem><para>GCC 3.3.0: include/c++/3.3</para></listitem>
542 <listitem><para>GCC 3.3.1: include/c++/3.3.1</para></listitem>
543 <listitem><para>GCC 3.3.2: include/c++/3.3.2</para></listitem>
544 <listitem><para>GCC 3.3.3: include/c++/3.3.3</para></listitem>
545 <listitem><para>GCC 3.4.x: include/c++/3.4.x</para></listitem>
546 <listitem><para>GCC 4.x.y: include/c++/4.x.y</para></listitem>
553 Taken together, these techniques can accurately specify interface
554 and implementation changes in the GNU C++ tools themselves. Used
555 properly, they allow both the GNU C++ tools implementation, and
556 programs using them, an evolving yet controlled development that
557 maintains backward compatibility.
563 <section xml:id="abi.versioning.prereq"><info><title>Prerequisites</title></info>
566 Minimum environment that supports a versioned ABI: A supported
567 dynamic linker, a GNU linker of sufficient vintage to understand
568 demangled C++ name globbing (ld) or the Sun linker, a shared
570 with g++, and shared libraries (libgcc_s, libstdc++) compiled by
571 a compiler (g++) with a compatible ABI. Phew.
575 On top of all that, an additional constraint: libstdc++ did not
576 attempt to version symbols (or age gracefully, really) until
581 Most modern GNU/Linux and BSD versions, particularly ones using
582 GCC 3.1 and later, will meet the
583 requirements above, as does Solaris 2.5 and up.
587 <section xml:id="abi.versioning.config"><info><title>Configuring</title></info>
591 It turns out that most of the configure options that change
592 default behavior will impact the mangled names of exported
593 symbols, and thus impact versioning and compatibility.
597 For more information on configure options, including ABI
599 <link linkend="manual.intro.setup.configure">here</link>
603 There is one flag that explicitly deals with symbol versioning:
608 In particular, libstdc++-v3/acinclude.m4 has a macro called
609 GLIBCXX_ENABLE_SYMVERS that defaults to yes (or the argument
610 passed in via --enable-symvers=foo). At that point, the macro
611 attempts to make sure that all the requirement for symbol
612 versioning are in place. For more information, please consult
617 <section xml:id="abi.versioning.active"><info><title>Checking Active</title></info>
621 When the GNU C++ library is being built with symbol versioning
622 on, you should see the following at configure time for
628 checking versioning on shared library symbols... gnu
633 or another of the supported styles.
634 If you don't see this line in the configure output, or if this line
635 appears but the last word is 'no', then you are out of luck.
639 If the compiler is pre-installed, a quick way to test is to compile
640 the following (or any) simple C++ file and link it to the shared
645 #include <iostream>
648 { std::cout << "hello" << std::endl; return 0; }
650 %g++ hello.cc -o hello.out
653 libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x00764000)
654 libm.so.6 => /lib/tls/libm.so.6 (0x004a8000)
655 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x40016000)
656 libc.so.6 => /lib/tls/libc.so.6 (0x0036d000)
657 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
663 If you see symbols in the resulting output with "GLIBCXX_3" as part
664 of the name, then the executable is versioned. Here's an example:
668 <code>U _ZNSt8ios_base4InitC1Ev@@GLIBCXX_3.4</code>
672 On Solaris 2, you can use <code>pvs -r</code> instead:
676 %g++ hello.cc -o hello.out
679 libstdc++.so.6 (GLIBCXX_3.4, GLIBCXX_3.4.12);
680 libgcc_s.so.1 (GCC_3.0);
681 libc.so.1 (SUNWprivate_1.1, SYSVABI_1.3);
685 <code>ldd -v</code> works too, but is very verbose.
691 <section xml:id="abi.changes_allowed"><info><title>Allowed Changes</title></info>
695 The following will cause the library minor version number to
696 increase, say from "libstdc++.so.3.0.4" to "libstdc++.so.3.0.5".
699 <listitem><para>Adding an exported global or static data member</para></listitem>
700 <listitem><para>Adding an exported function, static or non-virtual member function</para></listitem>
701 <listitem><para>Adding an exported symbol or symbols by additional instantiations</para></listitem>
704 Other allowed changes are possible.
709 <section xml:id="abi.changes_no"><info><title>Prohibited Changes</title></info>
713 The following non-exhaustive list will cause the library major version
714 number to increase, say from "libstdc++.so.3.0.4" to
715 "libstdc++.so.4.0.0".
719 <listitem><para>Changes in the gcc/g++ compiler ABI</para></listitem>
720 <listitem><para>Changing size of an exported symbol</para></listitem>
721 <listitem><para>Changing alignment of an exported symbol</para></listitem>
722 <listitem><para>Changing the layout of an exported symbol</para></listitem>
723 <listitem><para>Changing mangling on an exported symbol</para></listitem>
724 <listitem><para>Deleting an exported symbol</para></listitem>
725 <listitem><para>Changing the inheritance properties of a type by adding or removing
726 base classes</para></listitem>
728 Changing the size, alignment, or layout of types
729 specified in the C++ standard. These may not necessarily be
730 instantiated or otherwise exported in the library binary, and
731 include all the required locale facets, as well as things like
732 std::basic_streambuf, et al.
735 <listitem><para> Adding an explicit copy constructor or destructor to a
736 class that would otherwise have implicit versions. This will change
737 the way the compiler deals with this class in by-value return
738 statements or parameters: instead of passing instances of this
739 class in registers, the compiler will be forced to use memory. See the
740 section on <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://mentorembedded.github.com/cxx-abi/abi.html#calls">Function
741 Calling Conventions and APIs</link>
742 of the C++ ABI documentation for further details.
751 <section xml:id="abi.impl"><info><title>Implementation</title></info>
757 Separation of interface and implementation
760 This is accomplished by two techniques that separate the API from
761 the ABI: forcing undefined references to link against a library
762 binary for definitions.
767 <term>Include files have declarations, source files have defines</term>
771 For non-templatized types, such as much of <code>class
772 locale</code>, the appropriate standard C++ include, say
773 <code>locale</code>, can contain full declarations, while
774 various source files (say <code> locale.cc, locale_init.cc,
775 localename.cc</code>) contain definitions.
781 <term>Extern template on required types</term>
785 For parts of the standard that have an explicit list of
786 required instantiations, the GNU extension syntax <code> extern
787 template </code> can be used to control where template
788 definitions reside. By marking required instantiations as
789 <code> extern template </code> in include files, and providing
790 explicit instantiations in the appropriate instantiation files,
791 non-inlined template functions can be versioned. This technique
792 is mostly used on parts of the standard that require <code>
793 char</code> and <code> wchar_t</code> instantiations, and
794 includes <code> basic_string</code>, the locale facets, and the
795 types in <code> iostreams</code>.
803 In addition, these techniques have the additional benefit that they
804 reduce binary size, which can increase runtime performance.
810 Namespaces linking symbol definitions to export mapfiles
813 All symbols in the shared library binary are processed by a
814 linker script at build time that either allows or disallows
815 external linkage. Because of this, some symbols, regardless of
816 normal C/C++ linkage, are not visible. Symbols that are internal
817 have several appealing characteristics: by not exporting the
818 symbols, there are no relocations when the shared library is
819 started and thus this makes for faster runtime loading
820 performance by the underlying dynamic loading mechanism. In
821 addition, they have the possibility of changing without impacting
825 <para>The following namespaces are transformed by the mapfile:</para>
830 <term><code>namespace std</code></term>
831 <listitem><para> Defaults to exporting all symbols in label
832 <code>GLIBCXX</code> that do not begin with an underscore, i.e.,
833 <code>__test_func</code> would not be exported by default. Select
834 exceptional symbols are allowed to be visible.</para></listitem>
838 <term><code>namespace __gnu_cxx</code></term>
839 <listitem><para> Defaults to not exporting any symbols in label
840 <code>GLIBCXX</code>, select items are allowed to be visible.</para></listitem>
844 <term><code>namespace __gnu_internal</code></term>
845 <listitem><para> Defaults to not exported, no items are allowed to be visible.</para></listitem>
849 <term><code>namespace __cxxabiv1</code>, aliased to <code> namespace abi</code></term>
850 <listitem><para> Defaults to not exporting any symbols in label
851 <code>CXXABI</code>, select items are allowed to be visible.</para></listitem>
859 <listitem><para>Freezing the API</para>
860 <para>Disallowed changes, as above, are not made on a stable release
861 branch. Enforcement tends to be less strict with GNU extensions that
862 standard includes.</para>
868 <section xml:id="abi.testing"><info><title>Testing</title></info>
871 <section xml:id="abi.testing.single"><info><title>Single ABI Testing</title></info>
875 Testing for GNU C++ ABI changes is composed of two distinct
876 areas: testing the C++ compiler (g++) for compiler changes, and
877 testing the C++ library (libstdc++) for library changes.
881 Testing the C++ compiler ABI can be done various ways.
885 One. Intel ABI checker.
890 The second is yet unreleased, but has been announced on the gcc
891 mailing list. It is yet unspecified if these tools will be freely
892 available, and able to be included in a GNU project. Please contact
893 Mark Mitchell (mark@codesourcery.com) for more details, and current
899 Involves using the vlad.consistency test framework. This has also been
900 discussed on the gcc mailing lists.
904 Testing the C++ library ABI can also be done various ways.
909 (Brendan Kehoe, Jeff Law suggestion to run 'make check-c++' two ways,
910 one with a new compiler and an old library, and the other with an old
911 compiler and a new library, and look for testsuite regressions)
915 Details on how to set this kind of test up can be found here:
916 http://gcc.gnu.org/ml/gcc/2002-08/msg00142.html
921 Use the 'make check-abi' rule in the libstdc++ Makefile.
925 This is a proactive check of the library ABI. Currently, exported symbol
926 names that are either weak or defined are checked against a last known
927 good baseline. Currently, this baseline is keyed off of 3.4.0
928 binaries, as this was the last time the .so number was incremented. In
929 addition, all exported names are demangled, and the exported objects
930 are checked to make sure they are the same size as the same object in
933 Notice that each baseline is relative to a <emphasis>default</emphasis>
934 configured library and compiler: in particular, if options such as
935 --enable-clocale, or --with-cpu, in case of multilibs, are used at
936 configure time, the check may fail, either because of substantive
937 differences or because of limitations of the current checking
942 This dataset is insufficient, yet a start. Also needed is a
943 comprehensive check for all user-visible types part of the standard
944 library for sizeof() and alignof() changes.
948 Verifying compatible layouts of objects is not even attempted. It
949 should be possible to use sizeof, alignof, and offsetof to compute
950 offsets for each structure and type in the standard library, saving to
951 another datafile. Then, compute this in a similar way for new
952 binaries, and look for differences.
956 Another approach might be to use the -fdump-class-hierarchy flag to
957 get information. However, currently this approach gives insufficient
958 data for use in library testing, as class data members, their offsets,
959 and other detailed data is not displayed with this flag.
960 (See PR g++/7470 on how this was used to find bugs.)
964 Perhaps there are other C++ ABI checkers. If so, please notify
965 us. We'd like to know about them!
969 <section xml:id="abi.testing.multi"><info><title>Multiple ABI Testing</title></info>
972 A "C" application, dynamically linked to two shared libraries, liba,
973 libb. The dependent library liba is a C++ shared library compiled with
974 GCC 3.3, and uses io, exceptions, locale, etc. The dependent library
975 libb is a C++ shared library compiled with GCC 3.4, and also uses io,
976 exceptions, locale, etc.
979 <para> As above, libone is constructed as follows: </para>
981 %$bld/H-x86-gcc-3.4.0/bin/g++ -fPIC -DPIC -c a.cc
983 %$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
985 %ln -s libone.so.1.0.0 libone.so
987 %$bld/H-x86-gcc-3.4.0/bin/g++ -c a.cc
992 <para> And, libtwo is constructed as follows: </para>
995 %$bld/H-x86-gcc-3.3.3/bin/g++ -fPIC -DPIC -c b.cc
997 %$bld/H-x86-gcc-3.3.3/bin/g++ -shared -Wl,-soname -Wl,libtwo.so.1 -Wl,-O1 -Wl,-z,defs b.o -o libtwo.so.1.0.0
999 %ln -s libtwo.so.1.0.0 libtwo.so
1001 %$bld/H-x86-gcc-3.3.3/bin/g++ -c b.cc
1003 %ar cru libtwo.a b.o
1006 <para> ...with the resulting libraries looking like </para>
1010 %ldd libone.so.1.0.0
1011 libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x40016000)
1012 libm.so.6 => /lib/tls/libm.so.6 (0x400fa000)
1013 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x4011c000)
1014 libc.so.6 => /lib/tls/libc.so.6 (0x40125000)
1015 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
1017 %ldd libtwo.so.1.0.0
1018 libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x40027000)
1019 libm.so.6 => /lib/tls/libm.so.6 (0x400e1000)
1020 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x40103000)
1021 libc.so.6 => /lib/tls/libc.so.6 (0x4010c000)
1022 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
1027 Then, the "C" compiler is used to compile a source file that uses
1028 functions from each library.
1031 gcc test.c -g -O2 -L. -lone -ltwo /usr/lib/libstdc++.so.5 /usr/lib/libstdc++.so.6
1035 Which gives the expected:
1041 libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x00764000)
1042 libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x40015000)
1043 libc.so.6 => /lib/tls/libc.so.6 (0x0036d000)
1044 libm.so.6 => /lib/tls/libm.so.6 (0x004a8000)
1045 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x400e5000)
1046 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
1051 This resulting binary, when executed, will be able to safely use
1052 code from both liba, and the dependent libstdc++.so.6, and libb,
1053 with the dependent libstdc++.so.5.
1058 <section xml:id="abi.issues"><info><title>Outstanding Issues</title></info>
1062 Some features in the C++ language make versioning especially
1063 difficult. In particular, compiler generated constructs such as
1064 implicit instantiations for templates, typeinfo information, and
1065 virtual tables all may cause ABI leakage across shared library
1066 boundaries. Because of this, mixing C++ ABIs is not recommended at
1071 For more background on this issue, see these bugzilla entries:
1075 <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/PR24660">24660: versioning weak symbols in libstdc++</link>
1079 <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>
1084 <bibliography xml:id="abi.biblio"><info><title>Bibliography</title></info>
1086 <biblioentry xml:id="biblio.abicheck">
1088 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1089 xlink:href="http://abicheck.sourceforge.net">
1095 <biblioentry xml:id="biblio.cxxabi">
1097 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1098 xlink:href="http://www.codesourcery.com/cxx-abi/">
1107 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1108 xlink:href="http://www.intel.com/cd/software/products/asmo-na/eng/284736.htm">
1109 Intel Compilers for Linux Compatibility with the GNU Compilers
1116 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1117 xlink:href="http://download.oracle.com/docs/cd/E19963-01/html/819-0690/index.html">
1118 Linker and Libraries Guide (document 819-0690)
1126 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1127 xlink:href="http://download.oracle.com/docs/cd/E19422-01/819-3689/index.html">
1128 Sun Studio 11: C++ Migration Guide (document 819-3689)
1135 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1136 xlink:href="http://www.akkadia.org/drepper/dsohowto.pdf">
1137 How to Write Shared Libraries
1143 <firstname>Ulrich</firstname><surname>Drepper</surname>
1150 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1151 xlink:href="http://www.arm.com/miscPDFs/8033.pdf">
1152 C++ ABI for the ARM Architecture
1159 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1160 xlink:href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1976.html">
1161 Dynamic Shared Objects: Survey and Issues
1168 <author><personname><firstname>Benjamin</firstname><surname>Kosnik</surname></personname></author>
1173 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1174 xlink:href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2013.html">
1175 Versioning With Namespaces
1181 <author><personname><firstname>Benjamin</firstname><surname>Kosnik</surname></personname></author>
1186 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1187 xlink:href="http://syrcose.ispras.ru/2009/files/SYRCoSE2009-CfP.pdf">
1188 Binary Compatibility of Shared Libraries Implemented in C++
1189 on GNU/Linux Systems
1196 <author><personname><firstname>Pavel</firstname><surname>Shved</surname></personname></author>
1197 <author><personname><firstname>Denis</firstname><surname>Silakov</surname></personname></author>