Re: [Xen-devel] [PATCH v8 41/50] x86emul: support AVX512_4FMAPS insns

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.06.19 at 16:58, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 15/03/2019 11:04, Jan Beulich wrote:
>> @@ -3205,6 +3206,18 @@ x86_decode(
>>                                                     state);
>>                      state->simd_size = simd_other;
>>                  }
>> +
>> +                switch ( b )
>> +                {
>> +                /* v4f{,n}madd{p,s}s need special casing */
> 
> Why?  Given that this isn't boilerplate addition of new instructions, it
> needs a discussion in the commit message.

I've added

A decoder adjustment is needed here because of the current sharing of
table entries between different (implied) opcode prefixes: The same
major opcodes are used for vfmsub{132,213}{p,s}{s,d}, which have a
different memory operand size and different Disp8 scaling.

Jan



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