[PATCH] x86: Disable XCHG to MOV optimization

[Jan Beulich]

On 15.07.2026 10:17, H.J. Lu wrote:
> On Wed, Jul 15, 2026 at 3:46 PM Jan Beulich <jbeulich@suse.com> wrote:
>> On 15.07.2026 09:37, H.J. Lu wrote:
>>> The only rule for me is that -O can be used safely on any applications.
>>
>> In which case we need to rip out all optimizations (assuming you mean all
>> forms of -O, which I think you do, since elsewhere you said the same more
>> explicitly also for e.g. -Os).
> 
> Please show me a binutils bug report for the broken application because
> of using -O with today's binutils master branch.
> 
>> You did notice though that I'm not the only one who isn't sharing this
>> position of yours. Optimization _can_ break code using trickery. That's
>> to be expected, and people playing tricks need to stay away from enabling
>> optimization. We simply can't make that "safe".
> 
> GNU assembler is used by GCC to generate binaries.  GCC may not
> always generate the optimal encoding.   That is why I added -O to
> assembler in the first place.  There is no point in adding it if it isn't safe.
> We can't break applications because of some assembler optimizations.

As said - I will, once time permits (later this week hopefully).

Jan