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


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.

Jan


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