I had the same impression but them I went and read the Intel documentation
and xchg is one of these exceptions where the lock is implicit.
George.
On Wed, Mar 25, 2015 at 4:59 PM, Dave Goodell (dgoodell) <dgood...@cisco.com
> wrote:
> On Mar 25, 2015, at 3:02 PM, git...@crest.iu.edu wrote:
>
> > +static inline int32_t opal_atomic_swap_32( volatile int32_t *addr,
> > + int32_t newval)
> > +{
> > + int32_t oldval;
> > +
> > + __asm__ __volatile__("xchg %1, %0" :
>
> This code *looks* buggy because it lacks the "SMPLOCK" prefix, but can be
> safely omitted because "xchg" is always locked. A comment to this effect
> should be added.
>
> Also, this should probably be "xchgl" instead of "xchg".
>
> > + "=r" (oldval), "=m" (*addr) :
>
> Shouldn't the modifier on the second constraint above be "+" for the same
> reasons as the rest of this commit? In that case I also think you can omit
> the second constraint below altogether, though I'm less sure about that.
>
> > + "0" (newval), "m" (*addr) :
> > + "memory");
> > + return oldval;
> > +}
>
> -Dave
>
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