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://www.codesourcery.com/public/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>
276 Note 1: Error should be libstdc++.so.3.0.3.
279 Note 2: Not strictly required.
282 Note 3: This release (but not previous or subsequent) has one
283 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>
284 in the GCC bug database.
288 <listitem><para>Symbol versioning on the libstdc++.so binary.</para>
290 <para>mapfile: libstdc++-v3/config/abi/pre/gnu.ver</para>
291 <para>It is versioned with the following labels and version
292 definitions, where the version definition is the maximum for a
293 particular release. Note, only symbols which are newly introduced
294 will use the maximum version definition. Thus, for release series
295 with the same label, but incremented version definitions, the later
296 release has both versions. (An example of this would be the
297 GCC 3.2.1 release, which has GLIBCPP_3.2.1 for new symbols and
298 GLIBCPP_3.2 for symbols that were introduced in the GCC 3.2.0
299 release.) If a particular release is not listed, it has the same
300 version labels as the preceding release.
303 <listitem><para>GCC 3.0.0: (Error, not versioned)</para></listitem>
304 <listitem><para>GCC 3.0.1: (Error, not versioned)</para></listitem>
305 <listitem><para>GCC 3.0.2: (Error, not versioned)</para></listitem>
306 <listitem><para>GCC 3.0.3: (Error, not versioned)</para></listitem>
307 <listitem><para>GCC 3.0.4: (Error, not versioned)</para></listitem>
308 <listitem><para>GCC 3.1.0: GLIBCPP_3.1, CXXABI_1</para></listitem>
309 <listitem><para>GCC 3.1.1: GLIBCPP_3.1, CXXABI_1</para></listitem>
310 <listitem><para>GCC 3.2.0: GLIBCPP_3.2, CXXABI_1.2</para></listitem>
311 <listitem><para>GCC 3.2.1: GLIBCPP_3.2.1, CXXABI_1.2</para></listitem>
312 <listitem><para>GCC 3.2.2: GLIBCPP_3.2.2, CXXABI_1.2</para></listitem>
313 <listitem><para>GCC 3.2.3: GLIBCPP_3.2.2, CXXABI_1.2</para></listitem>
314 <listitem><para>GCC 3.3.0: GLIBCPP_3.2.2, CXXABI_1.2.1</para></listitem>
315 <listitem><para>GCC 3.3.1: GLIBCPP_3.2.3, CXXABI_1.2.1</para></listitem>
316 <listitem><para>GCC 3.3.2: GLIBCPP_3.2.3, CXXABI_1.2.1</para></listitem>
317 <listitem><para>GCC 3.3.3: GLIBCPP_3.2.3, CXXABI_1.2.1</para></listitem>
318 <listitem><para>GCC 3.4.0: GLIBCXX_3.4, CXXABI_1.3</para></listitem>
319 <listitem><para>GCC 3.4.1: GLIBCXX_3.4.1, CXXABI_1.3</para></listitem>
320 <listitem><para>GCC 3.4.2: GLIBCXX_3.4.2</para></listitem>
321 <listitem><para>GCC 3.4.3: GLIBCXX_3.4.3</para></listitem>
322 <listitem><para>GCC 4.0.0: GLIBCXX_3.4.4, CXXABI_1.3.1</para></listitem>
323 <listitem><para>GCC 4.0.1: GLIBCXX_3.4.5</para></listitem>
324 <listitem><para>GCC 4.0.2: GLIBCXX_3.4.6</para></listitem>
325 <listitem><para>GCC 4.0.3: GLIBCXX_3.4.7</para></listitem>
326 <listitem><para>GCC 4.1.1: GLIBCXX_3.4.8</para></listitem>
327 <listitem><para>GCC 4.2.0: GLIBCXX_3.4.9</para></listitem>
328 <listitem><para>GCC 4.3.0: GLIBCXX_3.4.10, CXXABI_1.3.2</para></listitem>
329 <listitem><para>GCC 4.4.0: GLIBCXX_3.4.11, CXXABI_1.3.3</para></listitem>
330 <listitem><para>GCC 4.4.1: GLIBCXX_3.4.12, CXXABI_1.3.3</para></listitem>
331 <listitem><para>GCC 4.4.2: GLIBCXX_3.4.13, CXXABI_1.3.3</para></listitem>
332 <listitem><para>GCC 4.5.0: GLIBCXX_3.4.14, CXXABI_1.3.4</para></listitem>
333 <listitem><para>GCC 4.6.0: GLIBCXX_3.4.15, CXXABI_1.3.5</para></listitem>
334 <listitem><para>GCC 4.6.1: GLIBCXX_3.4.16, CXXABI_1.3.5</para></listitem>
339 <para>Incremental bumping of a compiler pre-defined macro,
340 __GXX_ABI_VERSION. This macro is defined as the version of the
341 compiler v3 ABI, with g++ 3.0 being version 100. This macro will
342 be automatically defined whenever g++ is used (the curious can
343 test this by invoking g++ with the '-v' flag.)
347 This macro was defined in the file "lang-specs.h" in the gcc/cp directory.
348 Later versions defined it in "c-common.c" in the gcc directory, and from
349 G++ 3.4 it is defined in c-cppbuiltin.c and its value determined by the
350 '-fabi-version' command line option.
354 It is versioned as follows, where 'n' is given by '-fabi-version=n':
357 <listitem><para>GCC 3.0: 100</para></listitem>
358 <listitem><para>GCC 3.1: 100 (Error, should be 101)</para></listitem>
359 <listitem><para>GCC 3.2: 102</para></listitem>
360 <listitem><para>GCC 3.3: 102</para></listitem>
361 <listitem><para>GCC 3.4, GCC 4.x: 102 (when n=1)</para></listitem>
362 <listitem><para>GCC 3.4, GCC 4.x: 1000 + n (when n>1) </para></listitem>
363 <listitem><para>GCC 3.4, GCC 4.x: 999999 (when n=0)</para></listitem>
369 <para>Changes to the default compiler option for
370 <code>-fabi-version</code>.
373 It is versioned as follows:
376 <listitem><para>GCC 3.0: (Error, not versioned) </para></listitem>
377 <listitem><para>GCC 3.1: (Error, not versioned) </para></listitem>
378 <listitem><para>GCC 3.2: <code>-fabi-version=1</code></para></listitem>
379 <listitem><para>GCC 3.3: <code>-fabi-version=1</code></para></listitem>
380 <listitem><para>GCC 3.4, GCC 4.x: <code>-fabi-version=2</code> <emphasis>(Incompatible with previous)</emphasis></para></listitem>
386 <para>Incremental bumping of a library pre-defined macro. For releases
387 before 3.4.0, the macro is __GLIBCPP__. For later releases, it's
388 __GLIBCXX__. (The libstdc++ project generously changed from CPP to
389 CXX throughout its source to allow the "C" pre-processor the CPP
390 macro namespace.) These macros are defined as the date the library
391 was released, in compressed ISO date format, as an unsigned long.
395 This macro is defined in the file "c++config" in the
396 "libstdc++-v3/include/bits" directory. (Up to GCC 4.1.0, it was
397 changed every night by an automated script. Since GCC 4.1.0, it is
398 the same value as gcc/DATESTAMP.)
401 It is versioned as follows:
404 <listitem><para>GCC 3.0.0: 20010615</para></listitem>
405 <listitem><para>GCC 3.0.1: 20010819</para></listitem>
406 <listitem><para>GCC 3.0.2: 20011023</para></listitem>
407 <listitem><para>GCC 3.0.3: 20011220</para></listitem>
408 <listitem><para>GCC 3.0.4: 20020220</para></listitem>
409 <listitem><para>GCC 3.1.0: 20020514</para></listitem>
410 <listitem><para>GCC 3.1.1: 20020725</para></listitem>
411 <listitem><para>GCC 3.2.0: 20020814</para></listitem>
412 <listitem><para>GCC 3.2.1: 20021119</para></listitem>
413 <listitem><para>GCC 3.2.2: 20030205</para></listitem>
414 <listitem><para>GCC 3.2.3: 20030422</para></listitem>
415 <listitem><para>GCC 3.3.0: 20030513</para></listitem>
416 <listitem><para>GCC 3.3.1: 20030804</para></listitem>
417 <listitem><para>GCC 3.3.2: 20031016</para></listitem>
418 <listitem><para>GCC 3.3.3: 20040214</para></listitem>
419 <listitem><para>GCC 3.4.0: 20040419</para></listitem>
420 <listitem><para>GCC 3.4.1: 20040701</para></listitem>
421 <listitem><para>GCC 3.4.2: 20040906</para></listitem>
422 <listitem><para>GCC 3.4.3: 20041105</para></listitem>
423 <listitem><para>GCC 3.4.4: 20050519</para></listitem>
424 <listitem><para>GCC 3.4.5: 20051201</para></listitem>
425 <listitem><para>GCC 3.4.6: 20060306</para></listitem>
426 <listitem><para>GCC 4.0.0: 20050421</para></listitem>
427 <listitem><para>GCC 4.0.1: 20050707</para></listitem>
428 <listitem><para>GCC 4.0.2: 20050921</para></listitem>
429 <listitem><para>GCC 4.0.3: 20060309</para></listitem>
430 <listitem><para>GCC 4.1.0: 20060228</para></listitem>
431 <listitem><para>GCC 4.1.1: 20060524</para></listitem>
432 <listitem><para>GCC 4.1.2: 20070214</para></listitem>
433 <listitem><para>GCC 4.2.0: 20070514</para></listitem>
434 <listitem><para>GCC 4.2.1: 20070719</para></listitem>
435 <listitem><para>GCC 4.2.2: 20071007</para></listitem>
436 <listitem><para>GCC 4.2.3: 20080201</para></listitem>
437 <listitem><para>GCC 4.2.4: 20080519</para></listitem>
438 <listitem><para>GCC 4.3.0: 20080306</para></listitem>
439 <listitem><para>GCC 4.3.1: 20080606</para></listitem>
440 <listitem><para>GCC 4.3.2: 20080827</para></listitem>
441 <listitem><para>GCC 4.3.3: 20090124</para></listitem>
442 <listitem><para>GCC 4.3.4: 20090804</para></listitem>
443 <listitem><para>GCC 4.3.5: 20100522</para></listitem>
444 <listitem><para>GCC 4.3.6: 20110627</para></listitem>
445 <listitem><para>GCC 4.4.0: 20090421</para></listitem>
446 <listitem><para>GCC 4.4.1: 20090722</para></listitem>
447 <listitem><para>GCC 4.4.2: 20091015</para></listitem>
448 <listitem><para>GCC 4.4.3: 20100121</para></listitem>
449 <listitem><para>GCC 4.4.4: 20100429</para></listitem>
450 <listitem><para>GCC 4.4.5: 20101001</para></listitem>
451 <listitem><para>GCC 4.4.6: 20110416</para></listitem>
452 <listitem><para>GCC 4.5.0: 20100414</para></listitem>
453 <listitem><para>GCC 4.5.1: 20100731</para></listitem>
454 <listitem><para>GCC 4.5.2: 20101216</para></listitem>
455 <listitem><para>GCC 4.5.3: 20110428</para></listitem>
456 <listitem><para>GCC 4.6.0: 20110325</para></listitem>
457 <listitem><para>GCC 4.6.1: 20110627</para></listitem>
458 <listitem><para>GCC 4.6.2: 20111026</para></listitem>
465 Incremental bumping of a library pre-defined macro,
466 _GLIBCPP_VERSION. This macro is defined as the released version of
467 the library, as a string literal. This is only implemented in
468 GCC 3.1.0 releases and higher, and is deprecated in 3.4 (where it
469 is called _GLIBCXX_VERSION).
473 This macro is defined in the file "c++config" in the
474 "libstdc++-v3/include/bits" directory and is generated
475 automatically by autoconf as part of the configure-time generation
480 It is versioned as follows:
483 <listitem><para>GCC 3.0.0: "3.0.0"</para></listitem>
484 <listitem><para>GCC 3.0.1: "3.0.0" (Error, should be "3.0.1")</para></listitem>
485 <listitem><para>GCC 3.0.2: "3.0.0" (Error, should be "3.0.2")</para></listitem>
486 <listitem><para>GCC 3.0.3: "3.0.0" (Error, should be "3.0.3")</para></listitem>
487 <listitem><para>GCC 3.0.4: "3.0.0" (Error, should be "3.0.4")</para></listitem>
488 <listitem><para>GCC 3.1.0: "3.1.0"</para></listitem>
489 <listitem><para>GCC 3.1.1: "3.1.1"</para></listitem>
490 <listitem><para>GCC 3.2.0: "3.2"</para></listitem>
491 <listitem><para>GCC 3.2.1: "3.2.1"</para></listitem>
492 <listitem><para>GCC 3.2.2: "3.2.2"</para></listitem>
493 <listitem><para>GCC 3.2.3: "3.2.3"</para></listitem>
494 <listitem><para>GCC 3.3.0: "3.3"</para></listitem>
495 <listitem><para>GCC 3.3.1: "3.3.1"</para></listitem>
496 <listitem><para>GCC 3.3.2: "3.3.2"</para></listitem>
497 <listitem><para>GCC 3.3.3: "3.3.3"</para></listitem>
498 <listitem><para>GCC 3.4: "version-unused"</para></listitem>
499 <listitem><para>GCC 4.x: "version-unused"</para></listitem>
506 Matching each specific C++ compiler release to a specific set of
507 C++ include files. This is only implemented in GCC 3.1.1 releases
511 All C++ includes are installed in
512 <filename class="directory">include/c++</filename>, then nest in a
513 directory hierarchy corresponding to the C++ compiler's released
514 version. This version corresponds to the variable "gcc_version" in
515 "libstdc++-v3/acinclude.m4," and more details can be found in that
516 file's macro GLIBCXX_CONFIGURE (GLIBCPP_CONFIGURE before GCC 3.4.0).
519 C++ includes are versioned as follows:
522 <listitem><para>GCC 3.0.0: include/g++-v3</para></listitem>
523 <listitem><para>GCC 3.0.1: include/g++-v3</para></listitem>
524 <listitem><para>GCC 3.0.2: include/g++-v3</para></listitem>
525 <listitem><para>GCC 3.0.3: include/g++-v3</para></listitem>
526 <listitem><para>GCC 3.0.4: include/g++-v3</para></listitem>
527 <listitem><para>GCC 3.1.0: include/g++-v3</para></listitem>
528 <listitem><para>GCC 3.1.1: include/c++/3.1.1</para></listitem>
529 <listitem><para>GCC 3.2.0: include/c++/3.2</para></listitem>
530 <listitem><para>GCC 3.2.1: include/c++/3.2.1</para></listitem>
531 <listitem><para>GCC 3.2.2: include/c++/3.2.2</para></listitem>
532 <listitem><para>GCC 3.2.3: include/c++/3.2.3</para></listitem>
533 <listitem><para>GCC 3.3.0: include/c++/3.3</para></listitem>
534 <listitem><para>GCC 3.3.1: include/c++/3.3.1</para></listitem>
535 <listitem><para>GCC 3.3.2: include/c++/3.3.2</para></listitem>
536 <listitem><para>GCC 3.3.3: include/c++/3.3.3</para></listitem>
537 <listitem><para>GCC 3.4.x: include/c++/3.4.x</para></listitem>
538 <listitem><para>GCC 4.x.y: include/c++/4.x.y</para></listitem>
545 Taken together, these techniques can accurately specify interface
546 and implementation changes in the GNU C++ tools themselves. Used
547 properly, they allow both the GNU C++ tools implementation, and
548 programs using them, an evolving yet controlled development that
549 maintains backward compatibility.
555 <section xml:id="abi.versioning.prereq"><info><title>Prerequisites</title></info>
558 Minimum environment that supports a versioned ABI: A supported
559 dynamic linker, a GNU linker of sufficient vintage to understand
560 demangled C++ name globbing (ld) or the Sun linker, a shared
562 with g++, and shared libraries (libgcc_s, libstdc++) compiled by
563 a compiler (g++) with a compatible ABI. Phew.
567 On top of all that, an additional constraint: libstdc++ did not
568 attempt to version symbols (or age gracefully, really) until
573 Most modern GNU/Linux and BSD versions, particularly ones using
574 GCC 3.1 and later, will meet the
575 requirements above, as does Solaris 2.5 and up.
579 <section xml:id="abi.versioning.config"><info><title>Configuring</title></info>
583 It turns out that most of the configure options that change
584 default behavior will impact the mangled names of exported
585 symbols, and thus impact versioning and compatibility.
589 For more information on configure options, including ABI
591 <link linkend="manual.intro.setup.configure">here</link>
595 There is one flag that explicitly deals with symbol versioning:
600 In particular, libstdc++-v3/acinclude.m4 has a macro called
601 GLIBCXX_ENABLE_SYMVERS that defaults to yes (or the argument
602 passed in via --enable-symvers=foo). At that point, the macro
603 attempts to make sure that all the requirement for symbol
604 versioning are in place. For more information, please consult
609 <section xml:id="abi.versioning.active"><info><title>Checking Active</title></info>
613 When the GNU C++ library is being built with symbol versioning
614 on, you should see the following at configure time for
620 checking versioning on shared library symbols... gnu
625 or another of the supported styles.
626 If you don't see this line in the configure output, or if this line
627 appears but the last word is 'no', then you are out of luck.
631 If the compiler is pre-installed, a quick way to test is to compile
632 the following (or any) simple C++ file and link it to the shared
637 #include <iostream>
640 { std::cout << "hello" << std::endl; return 0; }
642 %g++ hello.cc -o hello.out
645 libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x00764000)
646 libm.so.6 => /lib/tls/libm.so.6 (0x004a8000)
647 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x40016000)
648 libc.so.6 => /lib/tls/libc.so.6 (0x0036d000)
649 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
655 If you see symbols in the resulting output with "GLIBCXX_3" as part
656 of the name, then the executable is versioned. Here's an example:
660 <code>U _ZNSt8ios_base4InitC1Ev@@GLIBCXX_3.4</code>
664 On Solaris 2, you can use <code>pvs -r</code> instead:
668 %g++ hello.cc -o hello.out
671 libstdc++.so.6 (GLIBCXX_3.4, GLIBCXX_3.4.12);
672 libgcc_s.so.1 (GCC_3.0);
673 libc.so.1 (SUNWprivate_1.1, SYSVABI_1.3);
677 <code>ldd -v</code> works too, but is very verbose.
683 <section xml:id="abi.changes_allowed"><info><title>Allowed Changes</title></info>
687 The following will cause the library minor version number to
688 increase, say from "libstdc++.so.3.0.4" to "libstdc++.so.3.0.5".
691 <listitem><para>Adding an exported global or static data member</para></listitem>
692 <listitem><para>Adding an exported function, static or non-virtual member function</para></listitem>
693 <listitem><para>Adding an exported symbol or symbols by additional instantiations</para></listitem>
696 Other allowed changes are possible.
701 <section xml:id="abi.changes_no"><info><title>Prohibited Changes</title></info>
705 The following non-exhaustive list will cause the library major version
706 number to increase, say from "libstdc++.so.3.0.4" to
707 "libstdc++.so.4.0.0".
711 <listitem><para>Changes in the gcc/g++ compiler ABI</para></listitem>
712 <listitem><para>Changing size of an exported symbol</para></listitem>
713 <listitem><para>Changing alignment of an exported symbol</para></listitem>
714 <listitem><para>Changing the layout of an exported symbol</para></listitem>
715 <listitem><para>Changing mangling on an exported symbol</para></listitem>
716 <listitem><para>Deleting an exported symbol</para></listitem>
717 <listitem><para>Changing the inheritance properties of a type by adding or removing
718 base classes</para></listitem>
720 Changing the size, alignment, or layout of types
721 specified in the C++ standard. These may not necessarily be
722 instantiated or otherwise exported in the library binary, and
723 include all the required locale facets, as well as things like
724 std::basic_streambuf, et al.
727 <listitem><para> Adding an explicit copy constructor or destructor to a
728 class that would otherwise have implicit versions. This will change
729 the way the compiler deals with this class in by-value return
730 statements or parameters: instead of passing instances of this
731 class in registers, the compiler will be forced to use memory. See the
732 section on <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.codesourcery.com/public/cxx-abi/abi.html#calls">Function
733 Calling Conventions and APIs</link>
734 of the C++ ABI documentation for further details.
743 <section xml:id="abi.impl"><info><title>Implementation</title></info>
749 Separation of interface and implementation
752 This is accomplished by two techniques that separate the API from
753 the ABI: forcing undefined references to link against a library
754 binary for definitions.
759 <term>Include files have declarations, source files have defines</term>
763 For non-templatized types, such as much of <code>class
764 locale</code>, the appropriate standard C++ include, say
765 <code>locale</code>, can contain full declarations, while
766 various source files (say <code> locale.cc, locale_init.cc,
767 localename.cc</code>) contain definitions.
773 <term>Extern template on required types</term>
777 For parts of the standard that have an explicit list of
778 required instantiations, the GNU extension syntax <code> extern
779 template </code> can be used to control where template
780 definitions reside. By marking required instantiations as
781 <code> extern template </code> in include files, and providing
782 explicit instantiations in the appropriate instantiation files,
783 non-inlined template functions can be versioned. This technique
784 is mostly used on parts of the standard that require <code>
785 char</code> and <code> wchar_t</code> instantiations, and
786 includes <code> basic_string</code>, the locale facets, and the
787 types in <code> iostreams</code>.
795 In addition, these techniques have the additional benefit that they
796 reduce binary size, which can increase runtime performance.
802 Namespaces linking symbol definitions to export mapfiles
805 All symbols in the shared library binary are processed by a
806 linker script at build time that either allows or disallows
807 external linkage. Because of this, some symbols, regardless of
808 normal C/C++ linkage, are not visible. Symbols that are internal
809 have several appealing characteristics: by not exporting the
810 symbols, there are no relocations when the shared library is
811 started and thus this makes for faster runtime loading
812 performance by the underlying dynamic loading mechanism. In
813 addition, they have the possibility of changing without impacting
817 <para>The following namespaces are transformed by the mapfile:</para>
822 <term><code>namespace std</code></term>
823 <listitem><para> Defaults to exporting all symbols in label
824 <code>GLIBCXX</code> that do not begin with an underscore, i.e.,
825 <code>__test_func</code> would not be exported by default. Select
826 exceptional symbols are allowed to be visible.</para></listitem>
830 <term><code>namespace __gnu_cxx</code></term>
831 <listitem><para> Defaults to not exporting any symbols in label
832 <code>GLIBCXX</code>, select items are allowed to be visible.</para></listitem>
836 <term><code>namespace __gnu_internal</code></term>
837 <listitem><para> Defaults to not exported, no items are allowed to be visible.</para></listitem>
841 <term><code>namespace __cxxabiv1</code>, aliased to <code> namespace abi</code></term>
842 <listitem><para> Defaults to not exporting any symbols in label
843 <code>CXXABI</code>, select items are allowed to be visible.</para></listitem>
851 <listitem><para>Freezing the API</para>
852 <para>Disallowed changes, as above, are not made on a stable release
853 branch. Enforcement tends to be less strict with GNU extensions that
854 standard includes.</para>
860 <section xml:id="abi.testing"><info><title>Testing</title></info>
863 <section xml:id="abi.testing.single"><info><title>Single ABI Testing</title></info>
867 Testing for GNU C++ ABI changes is composed of two distinct
868 areas: testing the C++ compiler (g++) for compiler changes, and
869 testing the C++ library (libstdc++) for library changes.
873 Testing the C++ compiler ABI can be done various ways.
877 One. Intel ABI checker.
882 The second is yet unreleased, but has been announced on the gcc
883 mailing list. It is yet unspecified if these tools will be freely
884 available, and able to be included in a GNU project. Please contact
885 Mark Mitchell (mark@codesourcery.com) for more details, and current
891 Involves using the vlad.consistency test framework. This has also been
892 discussed on the gcc mailing lists.
896 Testing the C++ library ABI can also be done various ways.
901 (Brendan Kehoe, Jeff Law suggestion to run 'make check-c++' two ways,
902 one with a new compiler and an old library, and the other with an old
903 compiler and a new library, and look for testsuite regressions)
907 Details on how to set this kind of test up can be found here:
908 http://gcc.gnu.org/ml/gcc/2002-08/msg00142.html
913 Use the 'make check-abi' rule in the libstdc++ Makefile.
917 This is a proactive check of the library ABI. Currently, exported symbol
918 names that are either weak or defined are checked against a last known
919 good baseline. Currently, this baseline is keyed off of 3.4.0
920 binaries, as this was the last time the .so number was incremented. In
921 addition, all exported names are demangled, and the exported objects
922 are checked to make sure they are the same size as the same object in
925 Notice that each baseline is relative to a <emphasis>default</emphasis>
926 configured library and compiler: in particular, if options such as
927 --enable-clocale, or --with-cpu, in case of multilibs, are used at
928 configure time, the check may fail, either because of substantive
929 differences or because of limitations of the current checking
934 This dataset is insufficient, yet a start. Also needed is a
935 comprehensive check for all user-visible types part of the standard
936 library for sizeof() and alignof() changes.
940 Verifying compatible layouts of objects is not even attempted. It
941 should be possible to use sizeof, alignof, and offsetof to compute
942 offsets for each structure and type in the standard library, saving to
943 another datafile. Then, compute this in a similar way for new
944 binaries, and look for differences.
948 Another approach might be to use the -fdump-class-hierarchy flag to
949 get information. However, currently this approach gives insufficient
950 data for use in library testing, as class data members, their offsets,
951 and other detailed data is not displayed with this flag.
952 (See PR g++/7470 on how this was used to find bugs.)
956 Perhaps there are other C++ ABI checkers. If so, please notify
957 us. We'd like to know about them!
961 <section xml:id="abi.testing.multi"><info><title>Multiple ABI Testing</title></info>
964 A "C" application, dynamically linked to two shared libraries, liba,
965 libb. The dependent library liba is a C++ shared library compiled with
966 GCC 3.3, and uses io, exceptions, locale, etc. The dependent library
967 libb is a C++ shared library compiled with GCC 3.4, and also uses io,
968 exceptions, locale, etc.
971 <para> As above, libone is constructed as follows: </para>
973 %$bld/H-x86-gcc-3.4.0/bin/g++ -fPIC -DPIC -c a.cc
975 %$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
977 %ln -s libone.so.1.0.0 libone.so
979 %$bld/H-x86-gcc-3.4.0/bin/g++ -c a.cc
984 <para> And, libtwo is constructed as follows: </para>
987 %$bld/H-x86-gcc-3.3.3/bin/g++ -fPIC -DPIC -c b.cc
989 %$bld/H-x86-gcc-3.3.3/bin/g++ -shared -Wl,-soname -Wl,libtwo.so.1 -Wl,-O1 -Wl,-z,defs b.o -o libtwo.so.1.0.0
991 %ln -s libtwo.so.1.0.0 libtwo.so
993 %$bld/H-x86-gcc-3.3.3/bin/g++ -c b.cc
998 <para> ...with the resulting libraries looking like </para>
1002 %ldd libone.so.1.0.0
1003 libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x40016000)
1004 libm.so.6 => /lib/tls/libm.so.6 (0x400fa000)
1005 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x4011c000)
1006 libc.so.6 => /lib/tls/libc.so.6 (0x40125000)
1007 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
1009 %ldd libtwo.so.1.0.0
1010 libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x40027000)
1011 libm.so.6 => /lib/tls/libm.so.6 (0x400e1000)
1012 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x40103000)
1013 libc.so.6 => /lib/tls/libc.so.6 (0x4010c000)
1014 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
1019 Then, the "C" compiler is used to compile a source file that uses
1020 functions from each library.
1023 gcc test.c -g -O2 -L. -lone -ltwo /usr/lib/libstdc++.so.5 /usr/lib/libstdc++.so.6
1027 Which gives the expected:
1033 libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x00764000)
1034 libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x40015000)
1035 libc.so.6 => /lib/tls/libc.so.6 (0x0036d000)
1036 libm.so.6 => /lib/tls/libm.so.6 (0x004a8000)
1037 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x400e5000)
1038 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
1043 This resulting binary, when executed, will be able to safely use
1044 code from both liba, and the dependent libstdc++.so.6, and libb,
1045 with the dependent libstdc++.so.5.
1050 <section xml:id="abi.issues"><info><title>Outstanding Issues</title></info>
1054 Some features in the C++ language make versioning especially
1055 difficult. In particular, compiler generated constructs such as
1056 implicit instantiations for templates, typeinfo information, and
1057 virtual tables all may cause ABI leakage across shared library
1058 boundaries. Because of this, mixing C++ ABIs is not recommended at
1063 For more background on this issue, see these bugzilla entries:
1067 <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/PR24660">24660: versioning weak symbols in libstdc++</link>
1071 <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>
1076 <bibliography xml:id="abi.biblio"><info><title>Bibliography</title></info>
1078 <biblioentry xml:id="biblio.abicheck">
1080 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1081 xlink:href="http://abicheck.sourceforge.net">
1087 <biblioentry xml:id="biblio.cxxabi">
1089 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1090 xlink:href="http://www.codesourcery.com/public/cxx-abi">
1099 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1100 xlink:href="http://www.intel.com/cd/software/products/asmo-na/eng/284736.htm">
1101 Intel Compilers for Linux Compatibility with the GNU Compilers
1108 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1109 xlink:href="http://download.oracle.com/docs/cd/E19963-01/html/819-0690/index.html">
1110 Linker and Libraries Guide (document 819-0690)
1118 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1119 xlink:href="http://download.oracle.com/docs/cd/E19422-01/819-3689/index.html">
1120 Sun Studio 11: C++ Migration Guide (document 819-3689)
1127 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1128 xlink:href="http://www.akkadia.org/drepper/dsohowto.pdf">
1129 How to Write Shared Libraries
1135 <firstname>Ulrich</firstname><surname>Drepper</surname>
1142 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1143 xlink:href="http://www.arm.com/miscPDFs/8033.pdf">
1144 C++ ABI for the ARM Architecture
1151 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1152 xlink:href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1976.html">
1153 Dynamic Shared Objects: Survey and Issues
1160 <author><personname><firstname>Benjamin</firstname><surname>Kosnik</surname></personname></author>
1165 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1166 xlink:href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2013.html">
1167 Versioning With Namespaces
1173 <author><personname><firstname>Benjamin</firstname><surname>Kosnik</surname></personname></author>
1178 <link xmlns:xlink="http://www.w3.org/1999/xlink"
1179 xlink:href="http://syrcose.ispras.ru/2009/files/SYRCoSE2009-CfP.pdf">
1180 Binary Compatibility of Shared Libraries Implemented in C++
1181 on GNU/Linux Systems
1188 <author><personname><firstname>Pavel</firstname><surname>Shved</surname></personname></author>
1189 <author><personname><firstname>Denis</firstname><surname>Silakov</surname></personname></author>