[Bug inline-asm/66631] inability to clobber segment regs makes tls problematic

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66631

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Stas Sergeev from comment #5)
> (In reply to Andrew Pinski from comment #4)
> > (In reply to Stas Sergeev from comment #3)
> > > The signal handler needs to do the following things:
> > > 1. Restore segment registers (init_handler() func)
> > 
> > Why are you doing this, that is the question I am trying to understand here.
> > What signal handler is happening?
> Ah, OK.
> This is a jit compiler.
> It uses segment registers at will, and it uses
> a memory protection too, so the signal is SIGSEGV.

That seems bogus usage really.  And very unportable.  Don't use segment
registers at all.

> 
> > Because you can't do this under Linux at
> > all.
> What exactly do you mean?
> 
> > I am also trying to understand if you are writing a kernel/userspace why you
> > can't write this part in pure assembly function instead of using GCC here to
> > do this work.
> How am I supposed to access TLS in asm?
> init_handler() itself is mostly in asm though, yes.
> But the main sighandler is a huge convoluted func.