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Re: [PATCH v7] x86: replace adhoc (partly wrong) ambiguous operand checking for MOVSX/MOVZX
On Thu, Feb 13, 2020 at 8:49 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 13.02.2020 17:39, H.J. Lu wrote:
> > On Thu, Feb 13, 2020 at 8:26 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>
> >> On 13.02.2020 17:18, H.J. Lu wrote:
> >>> On Thu, Feb 13, 2020 at 7:02 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>>>
> >>>> On 13.02.2020 15:34, H.J. Lu wrote:
> >>>>> On Thu, Feb 13, 2020 at 1:21 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>>>>> @@ -6551,6 +6558,32 @@ process_suffix (void)
> >>>>>> }
> >>>>>> }
> >>>>>>
> >>>>>> + if ((i.tm.base_opcode | 8) == 0xfbe
> >>>>>> + || (i.tm.base_opcode == 0x63 && i.tm.cpu_flags.bitfield.cpu64))
> >>>>>> + {
> >>>>>> + /* In Intel syntax, movsx/movzx must have a "suffix" (checked above).
> >>>>>> + In AT&T syntax, if there is no suffix (warned about above), the default
> >>>>>> + will be byte extension. */
> >>>>>
> >>>>> Please drop the warning for AT&T syntax and document it instead.
> >>>>
> >>>> But it is wrong to make a choice silently. When there are multiple
> >>>> options, we ought to inform the user, i.e. it needs to be at least
> >>>
> >>> I have seen
> >>>
> >>> movzx 7(%eax), %ecx
> >>>
> >>> from 2010. We need to live with this oddity of movsx/movzx.
> >>
> >> Right, hence not an error, but just a warning. Not giving a warning
> >
> > If a project checks assembler warnings, it will fail to build with
> > the new assembler. We don't want it.
>
> That's the case for all other new warnings, too. H.J., come on - there
> shouldn't be arbitrary / random differences in behavior. Things should
> be predictable for people.
That is one reason I'd like to see new errors, not new warnings.
--
H.J.