On 18/01/16 17:30 +0100, Torvald Riegel wrote:
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.
Builds OK on AIX, OK for trunk, thanks.
