Re: [PATCH] x86: Add .nop directive to assembler

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, Feb 19, 2018 at 6:17 AM, Michael Matz <matz@suse.de> wrote:
> Hi,
>
> On Mon, 19 Feb 2018, Maciej W. Rozycki wrote:
>
>> > OK, except for one quibble with the default md_generate_nops.  I think
>> > that should error rather than filling with zeros (which is likely to
>> > be an illegal instruction or trap).
>>
>>  I have a feeling the default should wire in HANDLE_ALIGN somehow.  For
>> many targets, such as fixed instruction width RISC processors, there is
>> only going to be one way of filling a given amount of space with no-op
>> instructions, so I think there's no point in having code duplication
>> here.  And even if there are more ways possible for a given target, then
>> the `.align' way is still right even if suboptimal.
>
> How would you propose to express "I need three nop
> instructions aka 12 bytes from here" with just .align?  (Note: no matter
> how "here" is currently aligned!)
>

.align isn't the same as .nop.   However, HANDLE_ALIGN can be updated
to shared the same code with md_generate_nops, like what I did for x86.


H.J.