This is the mail archive of the
java@gcc.gnu.org
mailing list for the Java project.
Re: Using __kuser_cmpxchg
On Fri, 16 Nov 2007, Paul Brook wrote:
> > > > On a pre-ARMv6 processor
> > >
> > > Similar "spurious" failures can happen on ARMv6 processors.
> > >
> > > ARMv6 cpus don't have atomic operations either. They have ldrex/strex,
> > > where the latter will fail if another CPU modifies the memory *or* a
> > > context switch occurs.
> >
> > Due to the current implementation this is indeed true.
> >
> > ARMv6 is more trivial to fix though, since the operation can be
> > reattempted whenever the strex fails.
>
> I'm confused. Why is this any different to ARMv5? AFAICS the two kuser_cmpxchg
> implementations are functionally equivalent.
Yes they are. My point is that fixing the ARMv6 one to eliminate the
false negative is almost trivial. The pre-ARMv6 is not so trivial
though. And I don't want to change the interface of course.
I implemented a fix here but I still want to think it through so not to
miss some implications wrt page faults for example.
Nicolas