On Wed, Feb 06, 2002 at 12:19:37PM -0800, H. Peter Anvin wrote:
> Followup to: <20020206101231.X21624@devserv.devel.redhat.com>
> By author: Jakub Jelinek <jakub@redhat.com>
> In newsgroup: linux.dev.kernel
> >
> > Most sane architectures reserve a thread pointer register (%g6 resp. %g7 on
> > sparc, tp on ia64, ppc will use %r2, alpha uses a fast pall call as thread
> > "register", s390 uses user access register 0 (and s390x uar 0 and 1), etc.).
> > On register starved ia32 there aren't too many spare registers, so %gs is
> > used instead.
> >
>
> x86-64, interestingly, retains vestigial meaning of the %fs and %gs
> registers (but no others) to use as a base pointer for this reason
> alone.
Well, on x86-64 this is purely x86-64 ABI designers decision, they could
pick one of %r8 - %r15 and use that as thread pointer instead (and were
recommended to do so).
Jakub
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