Re: [Xen-devel] [PATCH 5/5] x86/emulate: add support for {, v}movd {, x}mm, r/m32 and {, v}movq {, x}mm, r/m64

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.09.16 at 13:59, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 08/09/16 14:46, Jan Beulich wrote:
>> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
>> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
>> @@ -223,7 +223,7 @@ static const opcode_desc_t twobyte_table
>>      /* 0x70 - 0x7F */
>>      SrcImmByte|ModRM, SrcImmByte|ModRM, SrcImmByte|ModRM, SrcImmByte|ModRM,
>>      ModRM, ModRM, ModRM, ImplicitOps,
>> -    ModRM, ModRM, 0, 0, ModRM, ModRM, ModRM, ImplicitOps|ModRM,
>> +    ModRM, ModRM, 0, 0, ModRM, ModRM, ImplicitOps|ModRM, ImplicitOps|ModRM,
>>      /* 0x80 - 0x87 */
>>      DstImplicit|SrcImm, DstImplicit|SrcImm,
>>      DstImplicit|SrcImm, DstImplicit|SrcImm,
>> @@ -2291,6 +2291,10 @@ x86_decode(
>>          return X86EMUL_UNHANDLEABLE;
>>      }
>>  
>> +    if ( op_bytes == 2 &&
>> +         (ctxt->opcode & X86EMUL_OPC_PFX_MASK) == X86EMUL_OPC_66(0, 0) )
>> +        op_bytes = 4;
> 
> What is this change for?  I presume it is to undo the effect of the
> operand size override prefix when we have decided that the prefix
> actually had an alternate meaning?

Yes.

> If so, can we have a comment to this effect?

+    /*
+     * Undo the operand-size override effect of prefix 66 when it was
+     * determined to have another meaning.
+     */

> Everything else looks ok.

Can I take this as R-b then with the comment added?

Jan


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