Re: [Qemu-devel] [RISU RFC PATCH v2 06/14] x86.risu: add MMX instructions

[Alex Bennée]

Richard Henderson <address@hidden> writes:

> On 7/10/19 8:32 PM, Jan Bobek wrote:
>> On 7/3/19 5:49 PM, Richard Henderson wrote:
>>> On 7/1/19 6:35 AM, Jan Bobek wrote:
>>>> +MOVQ            MMX     00001111 011 d 1110 !emit { rex(w => 1); 
>>>> modrm(mod => MOD_DIRECT, rm => ~REG_ESP); }
>>>> +MOVQ_mem        MMX     00001111 011 d 1110 !emit { rex(w => 1); 
>>>> modrm(mod => ~MOD_DIRECT); mem(size => 8); }
>>>
>>> Oh, note that there are only 8 mmx registers, so the respective rex.{r,b} 
>>> bit
>>> can't be set.
>>
>> Actually, my CPU chewed it without choking even when the bits were
>> set, but it will taken care of in v3.
>
> That's interesting data.
>
> I wonder if it's worth retaining this as a feature in order to check qemu's
> implementation?

We could be some time, c.f. BlackHat 2017

  https://www.youtube.com/watch?v=KrksBdWcZgQ

I suspect if we set https://github.com/xoreaxeaxeax/sandsifter on QEMU
we might find a few breakages.

>
>
> r~


--
Alex Bennée