Re: [Xen-devel] [PATCH 1/6] x86emul: extend / amend supported FPU opcodes

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.12.16 at 15:35, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 06/12/16 14:11, Jan Beulich wrote:
>> First of all there are a number of secondary encodings both Intel and
>> AMD support, but which aren't formally documented.
> 
> Where did you get them from then?
> 
> (I'm fine with introducing these if they exist, but it would be good to
> provide references if possible.)

From memory, plus re-validation of that memory. I have my own
disassembler library, where years ago I did put all of that in. I can't
tell what - if any - source I may have had back then, other than
having tried them all out on hardware.

>> @@ -3798,7 +3801,7 @@ x86_emulate(
>>                  emulate_fpu_insn_memdst("fnstcw", dst.val);
>>                  break;
>>              default:
>> -                goto cannot_emulate;
>> +                generate_exception_if(true, EXC_UD);
> 
> You can use generate_exception(EXC_UD); here, and several places below.

Oh, yes, I meant to check for those during re-base but then forgot
to do so here.

>> @@ -4090,13 +4100,19 @@ x86_emulate(
>>              dst.reg = (unsigned long *)&_regs.eax;
>>              emulate_fpu_insn_memdst("fnstsw", dst.val);
>>              break;
>> +        case 0xc0 ... 0xc7: /* ffreep %stN */
> 
> This positioning looks wrong.  ffreep doesn't appear to interact with
> FEATURE_CMOV, or eflags.  Did you mean to have it part of the lower
> introduced block?

Yes indeed. Thanks for spotting.

Jan


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