[PATCH] x86/APX: correct disassembly for EVEX.B4

[Jan Beulich]

On 06.09.2024 04:04, Cui, Lili wrote:
> 
> 
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@suse.com>
>> Sent: Thursday, September 5, 2024 7:31 PM
>> To: Binutils <binutils@sourceware.org>
>> Cc: Cui, Lili <lili.cui@intel.com>; H.J. Lu <hjl.tools@gmail.com>
>> Subject: [PATCH] x86/APX: correct disassembly for EVEX.B4
>>
>> EVEX.B4 is used only for GPR (or addressing of memory) operands. SIMD
>> registers encoded via ModR/M.rm (when ModR/M.mod == 3) have their top bit
>> in EVEX.X3. Supposedly (doc version 004) EVEX.B4 is ignored when unused,
>> hence also don't flag such encodings as invalid.
>>
>> --- a/opcodes/i386-dis.c
>> +++ b/opcodes/i386-dis.c
>> @@ -13001,14 +13001,15 @@ OP_EX (instr_info *ins, int bytemode, in
>>    USED_REX (REX_B);
>>    if (ins->rex & REX_B)
>>      reg += 8;
>> -  if (ins->rex2 & REX_B)
>> -    reg += 16;
>>    if (ins->vex.evex)
>>      {
>>        USED_REX (REX_X);
>>        if ((ins->rex & REX_X))
>>  	reg += 16;
>> +      ins->rex2_used &= ~REX_B;
>>      }
>> +  else if (ins->rex2 & REX_B)
>> +    reg += 16;
>>
>>    if ((sizeflag & SUFFIX_ALWAYS)
>>        && (bytemode == x_swap_mode
> 
> when setting ins->vex.evex , we use EVEX.X to decode SIMD, then ins->rex also needs to be put into the else branch since it uses REX_B right?
> 
> If (ins->vex.evex)
>   {
>      Use REX_X.
>   }
> else
>   {
>     Use REX_B.
>   }

Except that at that point we don't know yet whether it's a GPR, a memory
operand, or a SIMD register.

Jan