Re: [Xen-devel] [PATCH 2/4] x86emul: drop RIP-relative special case for TEST

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.08.16 at 16:25, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 15/08/16 09:34, Jan Beulich wrote:
>> @@ -1851,11 +1911,6 @@ x86_emulate(
>>                          ((op_bytes == 8) ? 4 : op_bytes);
>>                  else if ( (d & SrcMask) == SrcImmByte )
>>                      ea.mem.off += 1;
>> -                else if ( !ext && ((b & 0xfe) == 0xf6) &&
>> -                          ((modrm_reg & 7) <= 1) )
> 
> Do we actually handle these cases correctly?  0xf6 /0 (imm8) and 0xf7 /0
> (imm) look to work as expected

I think we do; what makes you think we might not?

> However, 0xf6 /1, 0xf7 /1 are harder to pin down.  We have an
> implementation of it, but the only other reference I can find to them
> are in the AMD grp3 opcode map, where they appear equal to their /0
> variants.  The /1 variants do not appear in the AMD description of the
> TEST instruction, and do not appear anywhere in the Intel manuals.
> 
> Suravee: Can you confirm whether the /1 variants are expected to be
> implemented and copies of the /0 variants?

I've check on Intel systems that they are aliases (Intel doesn't
document them), and AMD halfway documenting them as aliases
makes me assume they indeed are. Other than opcode 82 they're
also aliases regardless of whether in 64-bit mode (on Intel again,
that is, I can't get to my AMD boxes right now).

Jan


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