Re: [PATCH 1/5] KVM: x86 emulator: Use single stage decoding for Group 1 instructions

[Gleb Natapov <gleb@redhat.com>]

On Tue, Mar 15, 2011 at 06:32:32AM +0900, Takuya Yoshikawa wrote:
> On Mon, 14 Mar 2011 17:11:40 +0200
> Gleb Natapov <gleb@redhat.com> wrote:
> 
> > > @@ -3212,11 +3235,13 @@ special_insn:
> > >  		break;
> > >  	case 0xa6 ... 0xa7:	/* cmps */
> > >  		c->dst.type = OP_NONE; /* Disable writeback. */
> > > -		goto cmp;
> > > +		emulate_2op_SrcV("cmp", c->src, c->dst, ctxt->eflags);
> > Why not call em_cmp() here?
> 
> I thought that I needed to check of
> 	c->dst.type = OP_NONE; /* Disable writeback. */
> later.
> 
I mean call em_cmp() after c->dst.type = OP_NONE line, not replacing it.
> So I just decided to treat CMPS and SCAS in another patch.
> I mean I may introduce em_cmps or em_scas later if needed.
> 
scas will likely just call em_cmp.

> You prefer to treat these in this patch?
> 
If there will be other patch for those instruction then it may be left
as is.

> > > +		break;
> > >  	case 0xa8 ... 0xa9:	/* test ax, imm */
> > >  		goto test;
> > >  	case 0xae ... 0xaf:	/* scas */
> > > -		goto cmp;
> > > +		emulate_2op_SrcV("cmp", c->src, c->dst, ctxt->eflags);
> > And here?
> 
> What is the difference of CMPS and SCAS?
> 
> 
One compares to memory locations and another memory with AX register.

--
			Gleb.