[Qemu-devel] Re: Regression: segfault on ARM host

[Aurelien Jarno <aurelien@aurel32.net>]

On Mon, Mar 01, 2010 at 11:33:23PM +0100, Paolo Bonzini wrote:
> On 03/01/2010 10:33 PM, Aurelien Jarno wrote:
>> While trying to implement setcond on TCG ARM, I have discovered it does
>> not work anymore. I have bisected this regression to:
>>
>> commit 6113d6d3169393c323ac4c82d756a850145a5e7a
>> Author: Paolo Bonzini<pbonzini@redhat.com>
>> Date:   Fri Jan 15 09:42:09 2010 +0100
>>
>>      change while to if
>>
>>      The while loop will be executed exactly 0 or 1 times, depending on
>>      env->exit_request.
>>
>>      Signed-off-by: Paolo Bonzini<pbonzini@redhat.com>
>>      Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
>>
>> The assertion is actually triggered. When the next patch removing the
>> assertion is also applied it segfaults instead.
>
> Looks like a race.  The only piece of logic that is changed by that  
> commit is reverted in the attached patch, can you try it?  If it passes,  
> I can resubmit with S-o-b.

Unfortunately it doesn't work.

> If it doesn't pass, I wonder whether the while loop was there to trick  
> the compiler into not optimizing something.  Seems a bit too clever 
> though.
>

It looks like it is the case. Just replacing the if by a while in your
patch make it working again. But I do wonder what this trick is actually
preventing, as there is probably a better way to prevent that.

-- 
Aurelien Jarno	                        GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net