On Mon, 2016-01-18 at 14:54 +0100, Torvald Riegel wrote: > On Sun, 2016-01-17 at 18:30 -0500, David Edelsohn wrote: > > On Sun, Jan 17, 2016 at 3:21 PM, Torvald Riegel <trie...@redhat.com> wrote: > > > On Sat, 2016-01-16 at 15:38 -0500, David Edelsohn wrote: > > >> On Sat, Jan 16, 2016 at 8:35 AM, Jakub Jelinek <ja...@redhat.com> wrote: > > >> > On Sat, Jan 16, 2016 at 07:47:33AM -0500, David Edelsohn wrote: > > >> >> stage1 libstdc++ builds just fine. the problem is stage2 configure > > >> >> fails due to missing ITM_xxx symbols when configure tries to compile > > >> >> and run conftest programs. > > >> > > > >> > On x86_64-linux, the _ITM_xxx symbols are undef weak ones and thus it > > >> > is > > >> > fine to load libstdc++ without libitm and libstdc++ doesn't depend on > > >> > libitm. > > >> > > > >> > So, is AIX defining __GXX_WEAK__ or not? Perhaps some other macro or > > >> > configure check needs to be used to determine if undefined weak symbols > > >> > work the way libstdc++ needs them to. > > >> > > >> __GXX_WEAK__ appears to be defined by gcc/c-family/c-cppbuiltin.c > > >> based on SUPPORTS_ONE_ONLY. gcc/defaults.h defines SUPPORTS_ONE_ONLY > > >> if the target supports MAKE_DECL_ONE_ONLY and link-once semantics. > > >> AIX weak correctly supports link-once semantics. AIX also supports > > >> the definition of __GXX_WEAK__ in gcc/doc/cpp.texi, namely collapsing > > >> symbols with vague linkage in multiple translation units. > > >> > > >> libstdc++/src/c++11/cow-stdexcept.cc appears to be using __GXX_WEAK__ > > >> and __attribute__ ((weak)) for references to symbols that may not be > > >> defined at link time or run time. AIX does not allow undefined symbol > > >> errors by default. And the libstdc++ inference about the semantics of > > >> __GXX_WEAK__ are different than the documentation. > > >> > > >> AIX supports MAKE_DECL_ONE_ONLY and the documented meaning of > > >> __GXX_WEAK__. AIX does not support extension of the meaning to > > >> additional SVR4 semantics not specified in the documentation. > > > > > > I see, so we might be assuming that __GXX_WEAK__ means more than it > > > actually does (I'm saying "might" because personally, I don't know; your > > > information supports this is the case, but the initial info I got was > > > that __GXX_WEAK__ would mean we could have weak decls without > > > definitions). > > > > I believe that libstdc++ must continue with the weak undefined > > references to the symbols as designed, but protect them with a > > different macro. For example, __GXX_WEAK_REF__ or __GXX_WEAK_UNDEF__ > > defined in defaults.h based on configure test or simply overridden in > > config/rs6000/aix.h. Or the macro could be local to libstdc++ and > > overridden in config/os/aix/os_defines.h. > > OK. I'm currently testing the attached patch on x86_64-linux.
No regressions in the libstdc++ and libitm tests on x86_64-linux.
