On Wed, 6 Dec 2023 at 13:53, Jonathan Wakely <jwak...@redhat.com> wrote:
>
> On Wed, 6 Dec 2023 at 12:30, Thomas Schwinge <tho...@codesourcery.com> wrote:
> >
> > Hi Alexandre!
> >
> > On 2023-12-06T02:28:42-0300, Alexandre Oliva <ol...@adacore.com> wrote:
> > > libsupc++: try cxa_thread_atexit_impl at runtime
> > >
> > > g++.dg/tls/thread_local-order2.C fails when the toolchain is built for
> > > a platform that lacks __cxa_thread_atexit_impl, even if the program is
> > > built and run using that toolchain on a (later) platform that offers
> > > __cxa_thread_atexit_impl.
> > >
> > > This patch adds runtime testing for __cxa_thread_atexit_impl on select
> > > platforms (GNU variants, for starters) that support weak symbols.
> >
> > Need something like:
> >
> > --- libstdc++-v3/libsupc++/atexit_thread.cc
> > +++ libstdc++-v3/libsupc++/atexit_thread.cc
> > @@ -164,2 +164,4 @@ __cxxabiv1::__cxa_thread_atexit (void
> > (_GLIBCXX_CDTOR_CALLABI *dtor)(void *),
> > return __cxa_thread_atexit_impl (dtor, obj, dso_handle);
> > +#else
> > + (void) dso_handle;
> > #endif
>
> I would prefer:
>
> --- a/libstdc++-v3/libsupc++/atexit_thread.cc
> +++ b/libstdc++-v3/libsupc++/atexit_thread.cc
> @@ -148,7 +148,7 @@ __cxa_thread_atexit_impl (void
> (_GLIBCXX_CDTOR_CALLABI *func) (void *),
> // ??? We can't make it an ifunc, can we?
> extern "C" int
> __cxxabiv1::__cxa_thread_atexit (void (_GLIBCXX_CDTOR_CALLABI *dtor)(void *),
> - void *obj, void *dso_handle)
> + void *obj, [[maybe_unused]] void *dso_handle)
> _GLIBCXX_NOTHROW
> {
> #if __GXX_WEAK__
The patch is OK with that change.
>
>
>
>
> >
> > ... to avoid:
> >
> > [...]/source-gcc/libstdc++-v3/libsupc++/atexit_thread.cc: In function
> > ‘int __cxxabiv1::__cxa_thread_atexit(void (*)(void*), void*, void*)’:
> > [...]/source-gcc/libstdc++-v3/libsupc++/atexit_thread.cc:151:51: error:
> > unused parameter ‘dso_handle’ [-Werror=unused-parameter]
> > 151 | void *obj, void *dso_handle)
> > | ~~~~~~^~~~~~~~~~
> > cc1plus: all warnings being treated as errors
> > make[4]: *** [atexit_thread.lo] Error 1
> >
> > With that, GCC/nvptx then is back to:
> >
> > UNSUPPORTED: g++.dg/tls/thread_local6.C -std=c++98
> > PASS: g++.dg/tls/thread_local6.C -std=c++14 (test for excess errors)
> > PASS: g++.dg/tls/thread_local6.C -std=c++14 execution test
> > PASS: g++.dg/tls/thread_local6.C -std=c++17 (test for excess errors)
> > PASS: g++.dg/tls/thread_local6.C -std=c++17 execution test
> > PASS: g++.dg/tls/thread_local6.C -std=c++20 (test for excess errors)
> > PASS: g++.dg/tls/thread_local6.C -std=c++20 execution test
> >
> >
> > Grüße
> > Thomas
> >
> >
> > > for libstdc++-v3/ChangeLog
> > >
> > > * config/os/gnu-linux/os_defines.h
> > > (_GLIBCXX_MAY_HAVE___CXA_THREAD_ATEXIT_IMPL): Define.
> > > * libsupc++/atexit_thread.cc [__GXX_WEAK__ &&
> > > _GLIBCXX_MAY_HAVE___CXA_THREAD_ATEXIT_IMPL]
> > > (__cxa_thread_atexit): Add dynamic detection of
> > > __cxa_thread_atexit_impl.
> > > ---
> > > libstdc++-v3/config/os/gnu-linux/os_defines.h | 5 +++++
> > > libstdc++-v3/libsupc++/atexit_thread.cc | 23
> > > ++++++++++++++++++++++-
> > > 2 files changed, 27 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/libstdc++-v3/config/os/gnu-linux/os_defines.h
> > > b/libstdc++-v3/config/os/gnu-linux/os_defines.h
> > > index 87317031fcd71..a2e4baec069d5 100644
> > > --- a/libstdc++-v3/config/os/gnu-linux/os_defines.h
> > > +++ b/libstdc++-v3/config/os/gnu-linux/os_defines.h
> > > @@ -60,6 +60,11 @@
> > > # define _GLIBCXX_HAVE_FLOAT128_MATH 1
> > > #endif
> > >
> > > +// Enable __cxa_thread_atexit to rely on a (presumably libc-provided)
> > > +// __cxa_thread_atexit_impl, if it happens to be defined, even if
> > > +// configure couldn't find it during the build.
> > > +#define _GLIBCXX_MAY_HAVE___CXA_THREAD_ATEXIT_IMPL 1
> > > +
> > > #ifdef __linux__
> > > // The following libpthread properties only apply to Linux, not GNU/Hurd.
> > >
> > > diff --git a/libstdc++-v3/libsupc++/atexit_thread.cc
> > > b/libstdc++-v3/libsupc++/atexit_thread.cc
> > > index 9346d50f5dafe..aa4ed5312bfe3 100644
> > > --- a/libstdc++-v3/libsupc++/atexit_thread.cc
> > > +++ b/libstdc++-v3/libsupc++/atexit_thread.cc
> > > @@ -138,11 +138,32 @@ namespace {
> > > }
> > > }
> > >
> > > +#if __GXX_WEAK__ && _GLIBCXX_MAY_HAVE___CXA_THREAD_ATEXIT_IMPL
> > > +extern "C"
> > > +int __attribute__ ((__weak__))
> > > +__cxa_thread_atexit_impl (void (_GLIBCXX_CDTOR_CALLABI *func) (void *),
> > > + void *arg, void *d);
> > > +#endif
> > > +
> > > +// ??? We can't make it an ifunc, can we?
> > > extern "C" int
> > > __cxxabiv1::__cxa_thread_atexit (void (_GLIBCXX_CDTOR_CALLABI
> > > *dtor)(void *),
> > > - void *obj, void */*dso_handle*/)
> > > + void *obj, void *dso_handle)
> > > _GLIBCXX_NOTHROW
> > > {
> > > +#if __GXX_WEAK__ && _GLIBCXX_MAY_HAVE___CXA_THREAD_ATEXIT_IMPL
> > > + if (__cxa_thread_atexit_impl)
> > > + // Rely on a (presumably libc-provided) __cxa_thread_atexit_impl,
> > > + // if it happens to be defined, even if configure couldn't find it
> > > + // during the build. _GLIBCXX_MAY_HAVE___CXA_THREAD_ATEXIT_IMPL
> > > + // may be defined e.g. in os_defines.h on platforms where some
> > > + // versions of libc have a __cxa_thread_atexit_impl definition,
> > > + // but whose earlier versions didn't. This enables programs build
> > > + // by toolchains compatible with earlier libc versions to still
> > > + // benefit from a libc-provided __cxa_thread_atexit_impl.
> > > + return __cxa_thread_atexit_impl (dtor, obj, dso_handle);
> > > +#endif
> > > +
> > > // Do this initialization once.
> > > if (__gthread_active_p ())
> > > {
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