[gcc r14-6082] libsupc++: try cxa_thread_atexit_impl at runtime

[Alexandre Oliva]

https://gcc.gnu.org/g:f4dd9416843308d4ae519983415fe62212662536

commit r14-6082-gf4dd9416843308d4ae519983415fe62212662536
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Sat Dec 2 14:14:02 2023 -0300

    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
    platforms that support weak symbols.
    
    
    for  libstdc++-v3/ChangeLog
    
            * libsupc++/atexit_thread.cc [__GXX_WEAK__]: Add dynamic
            detection of __cxa_thread_atexit_impl.

Diff:
---
 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 9346d50f5da..cabd7c0a4a0 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 ())
     {