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