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Date: Thu, 25 Feb 2010 15:04:28 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: [Qemu-devel] Re: [PATCH v2 2/2] get rid of hostregs_helper.h
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Blue Swirl <blauwirbel@gmail.com>, qemu-devel@nongnu.org

On Thu, Feb 25, 2010 at 01:50:56PM +0100, Paolo Bonzini wrote:
> On 02/25/2010 12:40 PM, Michael S. Tsirkin wrote:
>> On Thu, Feb 18, 2010 at 11:28:14PM +0200, Blue Swirl wrote:
>>>>      /* restore global registers */
>>>> -#include "hostregs_helper.h"
>>>> +    asm("");
>>>> +    env = (void *) saved_env_reg;
>>>>
>>
>> Is this sufficient?
>> I see __asm__ __volatile__("": : :"memory") in virtio.
>> Is memory clobber implied? What about volatile?
>
> All asms without colons ("old-style") are volatile.  Clobbering memory  
> is not necessary since we are only caring about blocking assignments of  
> "env", which is by definition in a register

Then I think you should add that as a clobber. Otherwise what prevents the
compiler from reordering this asm wrt assignments?

> (hostregs_helper.h wasn't  
> clobbering memory either).


Maybe it was buggy :)

> Paolo