Re: [Qemu-devel] Race condition between signal handler and cpu_exec()

[malc]

On Fri, 6 Mar 2009, Julian Seward wrote:

> On Friday 06 March 2009, Jamie Lokier wrote:
> > Aurelien Jarno wrote:
> > > I am currently too tired to find a proper solution (which should only
> > > use read/write to a variable to keep the operations atomic), I'll look
> > > at that tomorrow, but patches are welcome in the meanwhile.
> >
> > The theoretically right thing in C is read/write a "volatile
> > sig_atomic_t".
> 
> It looks to me like this requires to atomically test that a bit in a
> byte is set, and if so clear it.  That would require a lock;cmpxchg
> sequence on x86 and lwarx/stwcx on ppc.  I wonder if it can be done
> with gcc's __sync_bool_compare_and_swap builtin, in order to make
> it portable.

Just for the record GCCs sync builtins involve full memory barriers which
are unnecessary here.

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