Re: [Xen-devel] [PATCH 1/9] Xen Share: Simplified I/O Mechanism

[Rusty Russell <rusty@xxxxxxxxxxxxxxx>]

On Tue, 2006-06-06 at 15:31 +0100, Harry Butterworth wrote:
> On Tue, 2006-06-06 at 15:35 +1000, Rusty Russell wrote:
> > +        __asm__ __volatile__(
> > +            LOCK_PREFIX "cmpxchg8b %3"
> > +            : "=d" (nd), "=a" (y), "=c" (d),
> > +              "=m" (*(volatile u64 *)(&page->count_info))
> > +            : "0" (d), "1" (x), "c" (d), "b" (nx) );
> > +    }
> > +    while ( unlikely(nd != d) || unlikely(y != x) );
> > +
> > +    return 1;
> > +}
> 
> What is the "=c" (d) there for?  And doesn't cmpxchg8b modify the zero
> flag---is it necessary to clobber the condition code register?

Good questions.  I copied this code from below, though, so I can
conveniently punt on this one...

> > diff -r d5f98d23427a xen/include/public/xen.h
> > --- a/xen/include/public/xen.h      Tue May 30 10:44:23 2006
> > +++ b/xen/include/public/xen.h      Wed May 31 17:39:54 2006
> > @@ -64,6 +64,7 @@
> >  #define __HYPERVISOR_xenoprof_op          31
> >  #define __HYPERVISOR_event_channel_op     32
> >  #define __HYPERVISOR_physdev_op           33
> > +#define __HYPERVISOR_share_op             33
> 
> Sharing no 33?

Oops.  Good catch, this must have been my sloppy merging.  I've fixed
this locally.

Thanks!
Rusty.
-- 
 ccontrol: http://ccontrol.ozlabs.org


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