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
> 
> 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.

And btw., your questions are kind of orthogonal to the purpose of
this patch, which doesn't change which opcodes we do or do not
emulate. It solely slightly re-orders how we do so.

Jan


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