Re: [Xen-devel] [PATCH 3/8] x86emul: support BMI1 insns

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.01.17 at 15:17, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 16/01/17 13:58, Jan Beulich wrote:
>>>>> On 16.01.17 at 14:51, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> Right.  What happens in reality is this:
>>>
>>> --- Xen Test Framework ---
>>> Environment: HVM 32bit (No paging)
>>> Test VEX.W matching mode:
>>>   andn cccca5a5, ff00ff00 = 00cc00a5
>>> Test VEX.W opposite to mode:
>>>   andn cccca5a5, ff00ff00 = 00cc00a5
>>> Test result: SUCCESS
>>>
>>> --- Xen Test Framework ---
>>> Environment: HVM 64bit (Long mode 4 levels)
>>> Test VEX.W matching mode:
>>>   andn cccca5a5cccca5a5, ff00ff00ff00ff00 = 00cc00a500cc00a5
>>> Test VEX.W opposite to mode:
>>>   andn cccca5a5cccca5a5, ff00ff00ff00ff00 = 0000000000cc00a5
>>> Test result: SUCCESS
>>>
>>> So VEX.W is ignored in 32bit (i.e. doesn't raise #UD), and *does* cause
>>> 64bit mode to operate on 32bit operands, contrary to the manual.
>> Doesn't look so to me: The first result is a 64-bit one, and I'd expect
>> VEX.W=1 to be "matching mode".
> 
> "matching mode" means "what the assembler generated when using the
> mnemonic".  I didn't try hand-coding andn it to start with.
> 
> Here it is spelt out more clearly.
> 
> --- Xen Test Framework ---
> Environment: HVM 32bit (No paging)
> Test andn
> Test VEX.W=0:
>   andn cccca5a5, ff00ff00 = 00cc00a5
> Test VEX.W=1:
>   andn cccca5a5, ff00ff00 = 00cc00a5
> Test result: SUCCESS
> 
> --- Xen Test Framework ---
> Environment: HVM 64bit (Long mode 4 levels)
> Test andn
> Test VEX.W=1:
>   andn cccca5a5cccca5a5, ff00ff00ff00ff00 = 00cc00a500cc00a5
> Test VEX.W=0:
>   andn cccca5a5cccca5a5, ff00ff00ff00ff00 = 0000000000cc00a5
> Test result: SUCCESS
> 
> My conclusions still stand.

I don't follow; are we talking of different things? VEX.W=1 very
clearly produces a 64-bit operation above, as expected, and as
written in the SDM.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel