Re: [PATCH 1/1] Speedfreq-SMI call clobbers ECX

Stephan Diestelhorst
2008-03-06T08:51:24Z

> On, March 5th 2008 16:35:20 Ingo Molnar wrote:
> > * Stephan Diestelhorst <langer_mann@web.de> wrote:
> > > @@ -184,7 +184,7 @@ static void speedstep_set_state (unsigne
> > > __asm__ __volatile__(
> > > "movl $0, %%edi\n"
> > > "out %%al, (%%dx)\n"
> > > - : "=b" (new_state), "=D" (result)
> > > + : "=b" (new_state), "=D" (result), "=c" (ecx_clobber)
> > >
> > > : "a" (command), "b" (function), "c" (state), "d"
> > > : (smi_port), "S" (0)
> > >
> > > );
> >
> > stupid suggestion: why not do a pusha/popa around those
> > instructions, to make sure everything is restored? This isnt a
> > fastpath and being conservative about SMI side-effects cannot
> > hurt

Stephan Diestelhorst wrote:
> That sounds like a sane thing to do to me. Should I provide a
> 'patch'? Or leave that (and the decision about it) to the
> maintainer?

H. Peter Anvin wrote:
> You can't pusha/popa if you expect a result. You can, of course,
> push and pop individual registers.
>
> It's also kind of odd to do "movl $0,%%edi" instead of just setting
> EDI as an input.

Whoops, HPA is correct, of course. Manually pushing / popping the
registers is ugly, how about a larger clobber-list? Let the compiler
figure out what it wants to save/restore. Only thing to worry about
is EBP then.

Again, should I provide these patches? This thing just annoyed me for
a while as I have been patching it in my personal kernels for too
long.

Regards,
Stephan

PS: I'm not on LKML, please CC me at your discretion.