-===========================
-
-See http://gcc.gnu.org/ml/libstdc++/2002-07/msg00054.html for why this
-document exists, why it's incomplete, and what needs to be done still.
-
-===========================
-
-2002-09-06 Benjamin Kosnik
+2002-10-14 Benjamin Kosnik
Description of the libstdc++ ABI.
The following will cause the library major version number to
increase, say from "libstdc++.so.3.0.4" to "libstdc++.so.4.0.0".
-- any g++ compiler ABI changes
+- (anything) changing in the gcc/g++ compiler ABI
- (anything) changing size of an exported symbol
- (anything) deleting an exported symbol
-Note: adding an exported symbol, if it's in a new linker map name, is ok.
+- (anything) changing the size, alignment, or layout of types
+ specified in the C++ standard. These may not necessarily be
+ instantiated or otherwise exported in the library binary, and
+ include all the required locale facets, as well as things like
+ std::basic_streambuf, et al.
+
+Note: adding an exported symbol, if it's in a new and dependent
+interface name, is ok.
The following will cause the library revision version number to
increase, say from "libstdc++.so.5.0.0" to "libstdc++.so.5.0.1".
are checked to make sure they are the same size as the same object in
the baseline.
-In the future, more tests should be added. In particular, vtable
-information, offsets of data members in class objects, and other
-layout information should be checked.
+This dataset is insufficient, yet a start. Also needed is a
+comprehensive check for all user-visible types part of the standard
+library for sizeof() and alignof() changes.
-It should be possible to use sizeof, alignof, and offset to compute
+Verifying compatible layouts of objects is not even attempted. It
+should be possible to use sizeof, alignof, and offsetof to compute
offsets for each structure and type in the standard library, saving to
-another datafile. Then, compute this for new binaries, and look for
-differences.
+another datafile. Then, compute this in a similar way for new
+binaries, and look for differences.
Another approach might be to use the -fdump-class-hierarchy flag to
-get information.
+get information. However, currently this approach gives insufficient
+data for use in library testing, as class data members, their offsets,
+and other detailed data is not displayed with this flag.
(See g++/7470 on how this was used to find bugs.)
Perhaps there are other C++ ABI checkers. If so, please notify
{
using namespace std;
+ typedef char fake_facet_name[sizeof(char*)]
+ __attribute__ ((aligned(__alignof__(char*))));
+ fake_facet_name facet_name[6 + _GLIBCPP_NUM_CATEGORIES];
+
+ typedef char fake_locale_Impl[sizeof(locale::_Impl)]
+ __attribute__ ((aligned(__alignof__(locale::_Impl))));
+ fake_locale_Impl c_locale_impl;
+
+
// NB: The asm directives renames these non-exported, namespace
// __gnu_cxx symbols into the mistakenly exported, namespace std
// symbols in GLIBCPP_3.2.
fake_locale c_locale;
_GLIBCPP_ASM_SYMVER(_ZN9__gnu_cxx8c_localeE, _ZSt8c_locale, GLIBCPP_3.2)
- typedef char fake_locale_Impl[sizeof(locale::_Impl)]
- __attribute__ ((aligned(__alignof__(locale::_Impl))));
- fake_locale_Impl c_locale_impl;
- _GLIBCPP_ASM_SYMVER(_ZN9__gnu_cxx13c_locale_implE, _ZSt13c_locale_impl, GLIBCPP_3.2)
+ // GLIBCXX_ABI > 5 will not need this symbol at all.
+ // It's here just as a placeholder, as the size of this exported
+ // object changed. The new symbol is not exported.
+ const int o = sizeof(locale::_Impl) - sizeof(char*[_GLIBCPP_NUM_CATEGORIES]);
+ typedef char fake_locale_Impl_compat[o]
+ __attribute__ ((aligned(__alignof__(o))));
+ fake_locale_Impl_compat c_locale_impl_compat;
+ _GLIBCPP_ASM_SYMVER(_ZN9__gnu_cxx20c_locale_impl_compatE, _ZSt13c_locale_impl, GLIBCPP_3.2)
+
typedef char fake_facet_vec[sizeof(locale::facet*)]
__attribute__ ((aligned(__alignof__(locale::facet*))));
fake_facet_vec facet_vec[_GLIBCPP_NUM_FACETS];
_GLIBCPP_ASM_SYMVER(_ZN9__gnu_cxx9facet_vecE, _ZSt9facet_vec, GLIBCPP_3.2)
- typedef char fake_facet_name[sizeof(char*)]
- __attribute__ ((aligned(__alignof__(char*))));
- fake_facet_name facet_name[6 + _GLIBCPP_NUM_CATEGORIES];
-
typedef char fake_ctype_c[sizeof(std::ctype<char>)]
__attribute__ ((aligned(__alignof__(std::ctype<char>))));
fake_ctype_c ctype_c;
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