Re: [PATCH v2] Support Intel FRED LKGS

[Jan Beulich <jbeulich@suse.com>]

On 25.05.2023 09:57, Jiang, Haochen wrote:
>>> Well, there are two ways of approaching this, but imo in either case
>>> via a prereq change to the other insns that use this operand
>>> descriptor in a questionable manner. We could split decode at the
>>> ModR/M.mod level, but perhaps better is to follow MOV to/from sreg,
>>> SLDT, and STR in using a D suffix and an Sv operand.
>>
>> I suppose the latter is better since Sv will go back to OP_E then split decode
>> ad ModR/M.mod level.
>>
>> I will go through that to make the change.
>>
>> Thx,
>> Haochen
> 
> I just take a look at the whole thing.
> 
> From my perspective, if we are going to use the same pattern like
> SLDT and STR. Does that mean for the instruction below:
> 
> lldt %ax
> 
> We will need to add a 66 prefix for gas to make it happen or it will drop to %eax?
> 
> It will change the current assembler behavior. Is my understanding correct?

No. The assembler was changed already. The disassembler simply wants
to follow suit. IOW the assembler already avoids emitting any unnecessary
prefixes. The disassembler, otoh, should correctly represent redundant
prefixes (and preferably not as raw ones, e.g. not "data16" but a 16-bit
sized register or an insn suffix for AT&T memory operands).

Jan