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

[Takuya Yoshikawa <takuya.yoshikawa@gmail.com>]

On Tue, 15 Mar 2011 11:35:07 +0200
Gleb Natapov <gleb@redhat.com> wrote:

> > > 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.

I see the point!

> > 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.

In my city, electric power supply may become restricted under control
from now, though only a few hours.  So please take the patch series as
is if possible!


> 
> > > > +		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.

I wanted to know whether we should introduce em_cmps() or em_scas() later.

Probably we can eliminate introducing em_scas() because it should be
completely same as em_cmp().

But em_cmps() will be needed for inserting
  c->dst.type = OP_NONE;
before em_cmp().

Anyway, I will submit a patch for CMPS and SCAS conversion separately
if this patch can be applied.

Thanks,
  Takuya

> 
> --
> 			Gleb.