Re: [PATCH] Support Intel USER_MSR

[Jan Beulich <jbeulich@suse.com>]

On 25.10.2023 04:01, Hu, Lin1 wrote:
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@suse.com>
>> Sent: Tuesday, October 24, 2023 8:02 PM
>> To: Hu, Lin1 <lin1.hu@intel.com>
>> Cc: binutils@sourceware.org; Lu, Hongjiu <hongjiu.lu@intel.com>
>> Subject: Re: [PATCH] Support Intel USER_MSR
>>
>> On 24.10.2023 12:01, Hu, Lin1 wrote:
>>>> -----Original Message-----
>>>> From: Jan Beulich <jbeulich@suse.com>
>>>> Sent: Tuesday, October 24, 2023 4:56 PM
>>>>
>>>> On 24.10.2023 10:38, Hu, Lin1 wrote:
>>>>> I've thought of it so far is I can use a Fixup function like
>>>>>
>>>>> static bool
>>>>> uwrmsr_Fixup (instr_info *ins, int bytemode, int sizeflag) {
>>>>>     if (bytemode == d_mode)
>>>>>       {
>>>>>         if (OP_Skip_MODRM (ins, 0, sizeflag))
>>>>>           {
>>>>>             if (OP_I (ins, bytemode, sizeflag))
>>>>>               {
>>>>>                 ins->codep--;
>>>>>               }
>>>>>               return true;
>>>>>           }
>>>>>       }
>>>>>     return false;
>>>>> }
>>>>>
>>>>> Then the uwrmsr's unit will be { "uwrmsr",       {	{ uwrmsr_Fixup,
>> d_mode },
>>>> Rq }, 0 }.
>>>>> What‘s your opinion?
>>>>
>>>> Hmm, not very nice, but I can't exclude it simply won't get any better.
>>>> My desire was for there to not be any new fixup function, and for
>>>> OP_Skip_MODRM to be used directly in the table entry. (In any event,
>>>> if you really need to keep this new function, please combine the
>>>> three if()-s into a single one, helping readability quite a bit.
>>>>
>>>
>>> I have another idea, can I have a new function like
>>>
>>> OP_back_codep(...)
>>> {
>>> 	Ins->codep--;
>>> 	Return true;
>>> }
>>>
>>> So the uwrmsr's unit will be { "uwrmsr", { Skip_MODRM, Id, Back_Codep, Rq },
>> 0 }.
>>
>> Well, the main thing I dislike is the decrementing of codep, no matter where it's
>> put. In case you don't think you can get away without, I guess I'll try afterwards,
>> aiming at an incremental change then.
>>
> 
> I have another one in mind at the moment. Can I have a bool variable in instr_info,
> 
> @@ -221,6 +221,9 @@ struct instr_info
>    /* Record whether EVEX masking is used incorrectly.  */
>    bool illegal_masking;
> 
> +  /* Record whether the modrm byte has been skipped.  */
> +  bool has_skipped_modrm.
> +
>    unsigned char op_ad;
> 
> And the Skip mod/rm byte pattern will be 
> 
> @@ -11668,7 +11658,11 @@ OP_Skip_MODRM (instr_info *ins, int bytemode ATTRIBUTE_UNUSED,
> 
>    /* Skip mod/rm byte.  */
>    MODRM_CHECK;
> -  ins->codep++;
> +  if (!ins->has_skipped_modrm)
> +    {
> +      ins->codep++;
> +      ins->has_skipped_modrm = true;
> +    }
>    return true;
>  }
> .
> This change will be applied to all other similar sections (include OP_E).

Yes, that's along the lines of what I had in mind.

Jan