https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96200
--- Comment #7 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Florian Weimer from comment #6)
> (In reply to H.J. Lu from comment #4)
> > On Linux/i386 and Linux/x86-64, thread pointer access is done via syscall.
> > On Linux/x86-64, __builtin_thread_pointer and __builtin_set_thread_pointer
> > may be implemented with FSGSBASE ISA. Is it possible to implement these
> > builtins on Linux/i386 and Linux/x86-64 for all processors?
>
> It's effectively part of the x86-64 ABI, but I think it's currently
> undocumented. On x86-64, it looks like this:
>
> static inline void *
> thread_pointer (void)
> {
> void *result;
> asm ("mov %%fs:0, %0" : "=r" (result));
> return result;
> }
>
> i386 is similar, but with %gs, I think.
>
> This is ABI since the early NPTL days, and GCC knows about this very
> explicitly, to implement the -mno-tls-direct-seg-refs option.
Give that the tcb field is setup by the C run-time on Linux/x86, should
it be provided by a run-time header file?
