Re: [PATCH] libsupc++: try cxa_thread_atexit_impl at runtime

[Jonathan Wakely <jwakely@redhat.com>]

On Thu, 9 Nov 2023 at 01:56, Alexandre Oliva <oliva@adacore.com> wrote:
>
>
> 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
> platforms that support weak symbols.
>
> Regstrapped on x86_64-linux-gnu, also tested with gcc-13 on i686- and
> x86_64-, and with ac_cv_func___cxa_thread_atexit_impl=no, that, on a
> distro that lacks __cxa_thread_atexit in libc, forces the newly-added
> code to be exercised, and that enabled thread_local-order2.C to pass
> where the runtime libc has __cxa_thread_atexit_impl.  Ok to install?

Seems fine to me. Any objections, Jason?


>
>
> for  libstdc++-v3/ChangeLog
>
>         * libsupc++/atexit_thread.cc [__GXX_WEAK__]: Add dynamic
>         detection of __cxa_thread_atexit_impl.
> ---
>  libstdc++-v3/libsupc++/atexit_thread.cc |   15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/libstdc++-v3/libsupc++/atexit_thread.cc b/libstdc++-v3/libsupc++/atexit_thread.cc
> index 9346d50f5dafe..cabd7c0a4a057 100644
> --- a/libstdc++-v3/libsupc++/atexit_thread.cc
> +++ b/libstdc++-v3/libsupc++/atexit_thread.cc
> @@ -138,11 +138,24 @@ namespace {
>    }
>  }
>
> +#if __GXX_WEAK__
> +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__
> +  if (__cxa_thread_atexit_impl)
> +    return __cxa_thread_atexit_impl (dtor, obj, dso_handle);
> +#endif
> +
>    // Do this initialization once.
>    if (__gthread_active_p ())
>      {
>
> --
> Alexandre Oliva, happy hacker            https://FSFLA.org/blogs/lxo/
>    Free Software Activist                   GNU Toolchain Engineer
> More tolerance and less prejudice are key for inclusion and diversity
> Excluding neuro-others for not behaving ""normal"" is *not* inclusive
>