[Bug c/65083] New: Can not indirectly call some C11 atomic library functions

["bin.x.fan at oracle dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65083

            Bug ID: 65083
           Summary: Can not indirectly call some C11 atomic library
                    functions
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bin.x.fan at oracle dot com

C11 defines these as actual functions, not generic functions or macros:

  atomic_thread_fence
  atomic_signal_fence
  atomic_flag_test_and_set
  atomic_flag_test_and_set_explicit
  atomic_flag_clear
  atomic_flag_clear_explicit

User should be able to take their address and call them indirectly. However,
GCC does not provide definitions of these functions in libatomic.so, so GCC
does not allow the user to take the address of these functions.

Here is an example:

-bash-4.1$ gcc -v
Using built-in specs.
COLLECT_GCC=/net/dv104/export/tools/gcc/4.9.2/sparc-S2/bin/gcc.bin
COLLECT_LTO_WRAPPER=/net/dv104/export/tools/gcc/4.9.2/sparc-S2/libexec/gcc/sparc-sun-solaris2.10/4.9.2/lto-wrapper
Target: sparc-sun-solaris2.10
Configured with: ../gcc-4.9.2/configure
--prefix=/net/dv104/export/tools/gcc/4.9.2/sparc-S2
--enable-languages=c,c++,fortran
--with-gmp=/net/dv104/export/tools/gcc/4.9.2/sparc-S2
--with-mpfr=/net/dv104/export/tools/gcc/4.9.2/sparc-S2
--with-mpc=/net/dv104/export/tools/gcc/4.9.2/sparc-S2
Thread model: posix
gcc version 4.9.2 (GCC) 

-bash-4.1$ cat t.c
#include <stdatomic.h>
void (*func_ptr) (memory_order order);
int main()
{
 func_ptr = &atomic_thread_fence;
 (*func_ptr)(memory_order_seq_cst);
 return 0;
}
-bash-4.1$ gcc t.c -latomic
t.c: In function 'main':
t.c:5:15: error: 'atomic_thread_fence' undeclared (first use in this function)
  func_ptr = &atomic_thread_fence;
              ^
t.c:5:15: note: each undeclared identifier is reported only once for each
function it appears in