[PATCH] libsupc++: try cxa_thread_atexit_impl at runtime

[PATCH] libsupc++: try cxa_thread_atexit_impl at runtime

[Alexandre Oliva]

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?


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

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

[Jonathan Wakely]

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
>

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

[Alexandre Oliva]

On Nov  9, 2023, Jonathan Wakely <jwakely@redhat.com> wrote:

> 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?

Jason, ping?
https://gcc.gnu.org/pipermail/gcc-patches/2023-November/635750.html

-- 
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

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

[Jason Merrill]

On 12/1/23 15:40, Alexandre Oliva wrote:
> On Nov  9, 2023, Jonathan Wakely <jwakely@redhat.com> wrote:
> 
>> 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?
> 
> Jason, ping?
> https://gcc.gnu.org/pipermail/gcc-patches/2023-November/635750.html

OK by me.

Jason

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

[Thomas Schwinge]

Hi Alexandre!

On 2023-12-06T02:28:42-0300, Alexandre Oliva <oliva@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

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

[Jonathan Wakely]

On Wed, 6 Dec 2023 at 12:30, Thomas Schwinge <thomas@codesourcery.com> wrote:
>
> Hi Alexandre!
>
> On 2023-12-06T02:28:42-0300, Alexandre Oliva <oliva@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__





>
> ... 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 ())
> >      {
> -----------------
> Siemens Electronic Design Automation GmbH; Anschrift: Arnulfstraße 201, 80634 München; Gesellschaft mit beschränkter Haftung; Geschäftsführer: Thomas Heurung, Frank Thürauf; Sitz der Gesellschaft: München; Registergericht München, HRB 106955
>

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

[Jonathan Wakely]

On Wed, 6 Dec 2023 at 13:53, Jonathan Wakely <jwakely@redhat.com> wrote:
>
> On Wed, 6 Dec 2023 at 12:30, Thomas Schwinge <thomas@codesourcery.com> wrote:
> >
> > Hi Alexandre!
> >
> > On 2023-12-06T02:28:42-0300, Alexandre Oliva <oliva@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 ())
> > >      {
> > -----------------
> > Siemens Electronic Design Automation GmbH; Anschrift: Arnulfstraße 201, 80634 München; Gesellschaft mit beschränkter Haftung; Geschäftsführer: Thomas Heurung, Frank Thürauf; Sitz der Gesellschaft: München; Registergericht München, HRB 106955
> >
>

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

[Alexandre Oliva]

On Dec  6, 2023, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:

>> -                                void *obj, void *dso_handle)
>> +                                void *obj, [[maybe_unused]] void *dso_handle)

> The patch is OK with that change.

Thanks, here's what I'm going to install.  Regstrapped on
x86_64-linux-gnu, with and without
ac_cv_func___cxa_thread_atexit_impl=no, on a machine that has
__cxa_thread_atexit_impl (but not __cxa_thread_atexit) in libc.


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.


for  libstdc++-v3/ChangeLog

	PR libstdc++/112858
	* 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..28423344a0f34 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, [[maybe_unused]] 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 ())
     {

-- 
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