[PATCH 1/3] x86: extend LEA's segment override warning

[H.J. Lu]

On Thu, Feb 13, 2020 at 8:00 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 13.02.2020 16:51, H.J. Lu wrote:
> > On Thu, Feb 13, 2020 at 6:48 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>
> >> On 13.02.2020 15:11, H.J. Lu wrote:
> >>> On Thu, Feb 13, 2020 at 6:05 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>>>
> >>>> For one both possible forms should be warned about. And then there are
> >>>> a couple of MPX insns behaving LEA-like, which should be warned about in
> >>>> the same way. Finally, to guard against future surprises, qualify the
> >>>> original opcode check by excluding VEX/EVEX-like templates.
> >>>>
> >>>> gas/
> >>>> 2020-02-XX  Jan Beulich  <jbeulich@suse.com>
> >>>>
> >>>>         * config/tc-i386.c (process_operands): Also check insn prefix
> >>>>         for ineffectual segment override warning. Also cover BNDC* and
> >>>>         BNDMK there. Don't cover possible VEX/EVEX encoded insns there.
> >>>>         * testsuite/gas/i386/lea.s, testsuite/gas/i386/lea.d,
> >>>>         testsuite/gas/i386/lea.e: New.
> >>>>         * testsuite/gas/i386/i386.exp: Run new test.
> >>>>
> >>>
> >>> Why should it be warning, not error?
> >>
> >> Because the code isn't wrong, just inefficient. I also don't think
> >> converting from warning to error should be done in the same patch
> >> as extending the coverage of what gets a diagnostic emitted.
> >
> > What do we gain to allow it?
>
> It has always been allowed, and in one of the two cases even silently.
> We're liable to break people's working code if we changed this.
>

Given that MPX has been deprecated, MPX codes are very unlikely to
change.  Assembler shouldn't bother with this.

-- 
H.J.