[PATCH v8 2/2] x86/AT&T: don't default to byte source for ambiguous for MOVSX/MOVZX

[H.J. Lu]

On Mon, Feb 17, 2020 at 9:04 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 17.02.2020 17:55, H.J. Lu wrote:
> > On Mon, Feb 17, 2020 at 7:37 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>
> >> On 17.02.2020 15:14, H.J. Lu wrote:
> >>> On Mon, Feb 17, 2020 at 5:44 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>>>
> >>>> On 14.02.2020 17:51, H.J. Lu wrote:
> >>>>> On Fri, Feb 14, 2020 at 8:35 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>>>>>
> >>>>>> On 14.02.2020 17:26, H.J. Lu wrote:
> >>>>>>> On Fri, Feb 14, 2020 at 7:52 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>>>>>>>
> >>>>>>>> On 14.02.2020 15:37, H.J. Lu wrote:
> >>>>>>>>> On Fri, Feb 14, 2020 at 6:32 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>>>>>>>>>
> >>>>>>>>>> On 14.02.2020 15:25, H.J. Lu wrote:
> >>>>>>>>>>> On Fri, Feb 14, 2020 at 6:23 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>>>>>>>>>>>
> >>>>>>>>>>>> On 14.02.2020 15:16, H.J. Lu wrote:
> >>>>>>>>>>>>> On Fri, Feb 14, 2020 at 5:54 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> On 14.02.2020 13:28, H.J. Lu wrote:
> >>>>>>>>>>>>>>> On Fri, Feb 14, 2020 at 4:26 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>> As pointed out in "x86: replace adhoc (partly wrong) ambiguous operand
> >>>>>>>>>>>>>>>> checking for MOVSX/MOVZX" silently guessing what the programmer may have
> >>>>>>>>>>>>>>>> meant is not helpful, the more that we don't do so elsewhere anymore
> >>>>>>>>>>>>>>>> (except in cases where it is overwhelmingly likely that the other case
> >>>>>>>>>>>>>>>> isn't meant, like here for it meant to be a "sign/zero extension" from
> >>>>>>>>>>>>>>>> 16 bits to 16 bits).
> >>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>> gas/
> >>>>>>>>>>>>>>>> 2020-02-XX  Jan Beulich  <jbeulich@suse.com>
> >>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>         PR gas/25438
> >>>>>>>>>>>>>>>>         * config/tc-i386.c (process_suffix): Default movsx/movzx to byte
> >>>>>>>>>>>>>>>>         suffix only when destination is a word reg.
> >>>>>>>>>>>>>>>>         testsuite/gas/i386/noreg16.l, testsuite/gas/i386/noreg32.l,
> >>>>>>>>>>>>>>>>         testsuite/gas/i386/noreg64.l: Adjust expectations.
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> No need for this since this is documented behavior of AT&T syntax.
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> I've just looked at the documentation again: As said in the
> >>>>>>>>>>>>>> other reply to your doc change, these mnemonics aren't
> >>>>>>>>>>>>>> mentioned as legal in Solaris'es AT&T spec. And I also
> >>>>>>>>>>>>>> can't find gas doc saying so. Would you please point me at
> >>>>>>>>>>>>>> where this is being documented?
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> Solaris spec doesn't mention movsx[bwl] nor movsx.
> >>>>>>>>>>>>
> >>>>>>>>>>>> Right, so where did you take from that "this is documented behavior"?
> >>>>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>> Documented in gas manual.
> >>>>>>>>>>
> >>>>>>>>>> Where? As said, I did look there without finding anything to this effect.
> >>>>>>>>>
> >>>>>>>>> It is there now.
> >>>>>>>>
> >>>>>>>> Hmm, even worse: It's not there. Neither of the two doc changes of
> >>>>>>>> yours today say anything like this. Did you forget to both post a
> >>>>>>>> patch _and_ push it, or am I blind, or are you simply lying to me?
> >>>>>>>> I'm sorry for being blunt, but I'm getting really annoyed.
> >>>>>>>>
> >>>>>>>
> >>>>>>> info as.info on master branch shows
> >>>>>>>
> >>>>>>>
> >>>>>>>  The Intel-syntax extension instructions
> >>>>>>>
> >>>>>>>    * 'movsx' -- sign-extend 'reg8/mem8' to 'reg16'.
> >>>>>>>
> >>>>>>>    * 'movsx' -- sign-extend 'reg8/mem8' to 'reg32'.
> >>>>>>>
> >>>>>>>    * 'movsx' -- sign-extend 'reg8/mem8' to 'reg64' (x86-64 only).
> >>>>>>>
> >>>>>>>    * 'movsx' -- sign-extend 'reg16/mem16' to 'reg32'
> >>>>>>>
> >>>>>>>    * 'movsx' -- sign-extend 'reg16/mem16' to 'reg64' (x86-64 only).
> >>>>>>>
> >>>>>>>    * 'movsxd' -- sign-extend 'reg32/mem32' to 'reg64' (x86-64 only).
> >>>>>>>
> >>>>>>>    * 'movzx' -- zero-extend 'reg8/mem8' to 'reg16'.
> >>>>>>>
> >>>>>>>    * 'movzx' -- zero-extend 'reg8/mem8' to 'reg32'.
> >>>>>>>
> >>>>>>>    * 'movzx' -- zero-extend 'reg8/mem8' to 'reg64' (x86-64 only).
> >>>>>>>
> >>>>>>>    * 'movzx' -- zero-extend 'reg16/mem16' to 'reg32'
> >>>>>>>
> >>>>>>>    * 'movzx' -- zero-extend 'reg16/mem16' to 'reg64' (x86-64 only).
> >>>>>>>
> >>>>>>> are called 'movsbw/movsxb/movsx', 'movsbl/movsxb/movsx',
> >>>>>>> 'movsbq/movsb/movsx', 'movswl/movsxw', 'movswq/movsxw', 'movslq/movsxl',
> >>>>>>> 'movzbw/movzxb/movzx', 'movzbl/movzxb/movzx', 'movzbq/movzxb/movzx',
> >>>>>>> 'movzwl/movzxw' and 'movzwq/movzxw' in AT&T syntax.
> >>>>>>
> >>>>>> Which doesn't say anywhere that with a memory operand but
> >>>>>> without suffix both default to a byte source. Yet that's the
> >>>>>> whole point of the discussion we're having.
> >>>>>>
> >>>>>
> >>>>> Does 'movsbw/movsxb/movsx' cover it?
> >>>>
> >>>> No, it doesn't, because its companion 'movswl/movsxw' is obviously
> >>>> (to me at least) incomplete, as for register operands plain "movsx"
> >>>> is suitable too. It's imo wrong in the first place to formally
> >>>> name any movsx* or movzx* mnemonics to be valid in AT&T syntax. As
> >>>> said, the Solaris spec doesn't mention them. Hence they're at best
> >>>> hybrids, which we mean to permit, but without making them legal AT&T
> >>>> syntax.
> >>>
> >>> Not document movsxX/movsx is fine.  But we should just silently accept
> >>> them since assembly codes are encoded correctly.
> >>
> >> We should accept them, yes, _but not silently_. Even less so without
> >> it being written down anywhere that this is the behavior to expect.
> >
> > Please submit a patch to improve gas manual to document such.
>
> Just like on the other thread - I'm not going to document what I
> believe is wrong behavior. If I am to add documentation here, I'd
> add it such that afterwards the implementation will need bringing
> in sync. Also, let's not forget - you objected to a code change
> mine on the basis that the way you wanted it is documented
> _somewhere_. And now you ask _me_ to add this documentation?

I did add documentation.

-- 
H.J.