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Re: [PATCH] x86: allow suffix-less sign-extending movsb, movsw, and movsl


>>> On 01.07.16 at 18:14, <hjl.tools@gmail.com> wrote:
> On Fri, Jul 1, 2016 at 9:12 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>>> On 01.07.16 at 18:07, <hjl.tools@gmail.com> wrote:
>>> On Fri, Jul 1, 2016 at 8:32 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>>>>> On 01.07.16 at 17:23, <hjl.tools@gmail.com> wrote:
>>>>> On Fri, Jul 1, 2016 at 8:19 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>>>>>>> On 01.07.16 at 17:12, <hjl.tools@gmail.com> wrote:
>>>>>>> On Fri, Jul 1, 2016 at 7:55 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>>>>>>>>> On 01.07.16 at 16:24, <jonas-devlists@watlock.be> wrote:
>>>>>>>>> So in the end, I guess the movzb/movzw change is fine, but this one is
>>>>>>>>> not. It's in inherent inconsistency related to the ability of leaving
>>>>>>>>> away the size suffixes in combination with the chosen mnemonics, it
>>>>>>>>> seems.
>>>>>>>>
>>>>>>>> I do not understand what inconsistency you refer to here. The
>>>>>>>> only inconsistency I can see is that one can't omit the suffixes
>>>>>>>> from these three instructions, unlike any others with GPR
>>>>>>>> operands.
>>>>>>>
>>>>>>> This mnemonic inconsistency comes from ISA and AT&T syntax.
>>>>>>> But there are no issues now.
>>>>>>
>>>>>> There is - as said, I fell into the trap seeing "movzb" in source code
>>>>>> and assuming I then could also use "movzw" or "movsb" (etc). I
>>>>>> can certainly open a bug if that helps you re-consider.
>>>>>
>>>>> It is unfortunate.  But it won't lead to wrong instructions being used.
>>>>
>>>> So since I see that rational arguments won't lead anywhere here
>>>> - would you at least allow in the fix for the bug that this change
>>>> uncovered (the one hunk changing tc-i386.c), even if that also
>>>> doesn't seem to cause any issues right now?
>>>
>>> Please open a bug report with a testcase.
>>
>> You're kidding? As said, the issue got uncovered only with the
>> other adjustments here; I'm not aware of a case where this
>> would cause a problem without the other changes, and I'm not
>> going to spend a whole lot of time trying to figure a broken case.
> 
> So there is no issue with the current code base?

I'm not aware of one (other than the source looking wrong), but
I can't say there is none.

Jan


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