Re: [PATCH] i386: Check invalid (%dx) usage

["H.J. Lu" <hjl.tools@gmail.com>]

On Tue, Nov 8, 2022 at 11:21 PM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 08.11.2022 22:06, H.J. Lu wrote:
> > On Mon, Nov 7, 2022 at 11:34 PM Jan Beulich <jbeulich@suse.com> wrote:
> >> On 07.11.2022 20:58, H.J. Lu wrote:
> >>> On Mon, Nov 7, 2022 at 3:44 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>>> x86: restrict use of (%dx)
> >>>>
> >>>> PR gas/29751
> >>>> The AT&T mode special case operand (%dx) is valid to use only with
> >>>> instructions nominally expecting %dx to specify an I/O port address.
> >>>> Prefix the respective checking with an opcode check. Keep that as
> >>>> simple as possible by recognizing that opcodes 0x64 and 0x66 (which
> >>>
> >>> Since current_templates doesn't point to the matched instruction,
> >>> checking current_templates looks like abuse.  I don't think error
> >>> messages should be a concern here.
> >>
> >> We use current_templates in similar ways in quite a number of places,
> >> when match_templates() hasn't run yet.
> >
> > Since the first template isn't the selected one, your check allows
> > the invalid opcodes.
>
> I guess I don't understand, but I guess I'll also give up. Which

Your proposed change does

current_templates->start->base_opcode | 0x8a) == 0xee

to allow opcode 0xe4 and (%dx) is allowed for non-I/O opcodes.

> template the check is done against doesn't really matter here, as
> long as it's one with the correct mnemonic. We could of course
> also re-order templates to have ones allowing for %dx first, but
> I view any such ordering dependencies as fragile.
>

That is true.

I posted the v2 patch to add inw tests.

-- 
H.J.