Re: [RFC] LKMM: Add volatile_if()

Segher Boessenkool
2021-06-04T15:51:50Z

On Fri, Jun 04, 2021 at 01:31:48PM +0200, Peter Zijlstra wrote:
> On Fri, Jun 04, 2021 at 11:44:00AM +0100, Will Deacon wrote:
> > > +{
> > > + asm_volatile_goto("cbnz %0, %l[l_yes]"
> > > + : : "r" (cond) : "cc", "memory" : l_yes);
> > > + return 0;
> > > +l_yes:
> > > + return 1;
> > > +}
> >
> > nit: you don't need the "cc" clobber here.
>
> Yeah I know, "cc" is implied.

It isn't needed at all here. cbnz does not write to the condition
register. Neither does it change or access memory, but the "memory"
clobber is to force a false dependency. Writing "cc" as well looks a
bit confusing, given that.

Segher