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Re: [PATCH v2] x86: fix handling of 64-bit operand size VPCMPESTR{I,M}


>>> On 23.02.17 at 16:58, <hjl.tools@gmail.com> wrote:
> On Thu, Feb 23, 2017 at 4:40 AM, Jan Beulich <JBeulich@suse.com> wrote:
>> Just like REX.W affects operand size of the implicit rAX/rDX inputs to
>> PCMPESTR{I,M}, VEX.W does for VPCMPESTR{I,M}. Allow Q or L suffixes on
>> the instructions for AT&T mode.
>>
>> For Intel mode, however, suffixes aren't the preferred choice, so
>> build_vex_prefix() needs to not only honor internally specified REX
>> flags (converting them to their VEX equivalents), but also such
>> resulting from explicit REX* prefix uses. Also adjust
>> build_evex_prefix() for consistency.
> 
> Please don't use EXISTING REX prefixes for this purpose.  A new
> prefix to control encoding is better, but it probably belongs to another
> patch.

I'm sorry, but I don't follow. If you want to go that route, we'll need
more than just one new prefix, and it would be far from clear where
to draw the boundary. Granted this would allow to address the
32-/16-bit side of things at once, but no, I don't think I have the
time or energy to go that route (or else I would have done so right
away, instead of adding a remark to the description in this regard).

Jan


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