[Bug libstdc++/95989] Segmentation fault compiling with static libraries and using jthread::request_stop

["redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95989

--- Comment #14 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #13)
> I'm testing this:
> 
> diff --git a/libgcc/gthr-posix.h b/libgcc/gthr-posix.h
> index 965247602ac..0af84a781e5 100644
> --- a/libgcc/gthr-posix.h
> +++ b/libgcc/gthr-posix.h
> @@ -684,7 +684,12 @@ __gthread_equal (__gthread_t __t1, __gthread_t __t2)
>  static inline __gthread_t
>  __gthread_self (void)
>  {
> +#if __GLIBC_PREREQ(2, 27)

Hmm, maybe we should just check #ifdef __GLIBC__ here, since it's available in
libc even before glibc 2.27 (it returns 0 rather than a real tid before 2.27,
but that's OK).

> +  /* See PR libstdc++/95989  */
> +  return pthread_self ();
> +#else
>    return __gthrw_(pthread_self) ();
> +#endif
>  }
>  
>  static inline int
> diff --git a/libstdc++-v3/include/std/thread
> b/libstdc++-v3/include/std/thread
> index 0445ab1e319..2772dd3950e 100644
> --- a/libstdc++-v3/include/std/thread
> +++ b/libstdc++-v3/include/std/thread
> @@ -364,13 +364,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>      inline thread::id
>      get_id() noexcept
>      {
> -#ifdef __GLIBC__
> +#if defined __GLIBC__ && ! __GLIBC_PREREQ(2, 27)

And maybe we shouldn't change this check either.

If we make it depend on the glibc version then because this function is inline
a program could have two different definitions inlined if different objects
were compiled by different versions of gcc, or against different versions of
glibc. One object could inline the version returning thread::id(1) and another
could inline the version returning thread::id(__gthread_self()). This could
result in two different IDs for the main thread of a single-threaded program.
So maybe we should just stick to returning thread::id(1) for all glibc
versions.