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

["Jan Beulich" <JBeulich at suse dot com>]

>>> On 04.07.16 at 18:07, <hjl.tools@gmail.com> wrote:
> On Mon, Jul 4, 2016 at 1:07 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>>> On 01.07.16 at 17:20, <jonas-devlists@watlock.be> wrote:
>>
>>> Jan Beulich wrote on Fri, 01 Jul 2016:
>>>
>>>>>>> On 01.07.16 at 16:24, <jonas-devlists@watlock.be> wrote:
>>>>> Referring again to the above document, it says about movsb/movsw:
>>>>> "movsb is not movsb{wlq}" and "movsw
>>>>> is not movsw{lq}" (on p. 37). Those are the only mnemonics that are
>>>>> singled out in this way.
>>>>
>>>> Well, the document referenced is a random one; it's way too new
>>>> to be a canonical reference.
>>>
>>> I disagree that (originally) Sun documentation is a random reference
>>> in the context of AT&T/System V UNIX. Yes, SVR4.2 i386 documentation
>>> would be even better (if it mentions this issue), but I guess that
>>> only exists as hard copy in someone's basement.
>>>
>>>> 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.
>>>
>>> It is not consistent that all base mnemonics (i.e., without size
>>> suffix) refer to individual opcodes (or groups of opcodes) as defined
>>> in Intel's architecture manuals, except for movsb/w/l.
>>
>> I don't see what's wrong with this, when it's okay for the assembler
>> to accept all kinds on non-AT&T syntax instructions in AT&T mode.
>> Note how, for example, both movsx and movzx have specific AT&T
>> entries despite these being Intel syntax mnemonics.
> 
> Those are for historical reasons.  We shouldn't add new ones when
> they buy nothing for programmers.

Well, in the case here the addition does buy something for
programmers, or else I wouldn't have stumbled into this mess. So
I guess you only mean certain programmers, and I'm not one of
them...

Jan