Re: [Qemu-devel] [RFC PATCH V3] Use atomic cmpxchg to atomically check the exclusive value in a STREX

[Mark Burton]

> On 19 Jun 2015, at 09:31, Paolo Bonzini <address@hidden> wrote:
> 
> 
> 
> On 19/06/2015 09:29, Mark Burton wrote:
>> Does anybody know if the current atomic_cmpxchg will support 64 bit
>> on a (normal) 32 bit x86, or do we need to special case that with
>> cmpxchg8b ? (I get the impression that it will automatically use
>> cmpxchg8b, but not cmpxchg16b - but I’m by no means sure).
> 
> Both cmpxchg8b and cmpxchg16b are used, respectively on 32-bit and
> 64-bit x86.
> 

Thanks Paolo, so  we are OK for x86, but we would need to disable multi-thread 
for other 32 bit hosts, and provide a correct implementation for non 
multi-thread…
You dont happen to know of a convenient macro we can use to test for ’32 bit 
hosts that dont support 64bit cmpxchg ….’

Cheers

Mark.



> Paolo



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