RE: [PATCH] Support Intel USER_MSR

["Hu, Lin1" <lin1.hu@intel.com>]

> -----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).

So the uwrmsr's unit will be { "uwrmsr", { Skip_MODRM, Id, Rq }, 0 }, because the codep won't increasing in Rq, I don't need the decrementing of codep.

> Jan