Re: [PATCH Xen 4.20] x86/apic: Fix asm() constraints in TMICT calculation

[Jan Beulich <jbeulich@suse.com>]

On 21.04.2026 12:22, Andrew Cooper wrote:
> On 21/04/2026 7:39 am, Jan Beulich wrote:
>> On 20.04.2026 19:46, Andrew Cooper wrote:
>>> The encoded MUL is 64 bits, so writes %rdx too.  At a minimum, this needs
>>> expressing as a clobber.
>> I'm embarrassed of missing this.
>>
>>> Also fix a logical disconnect between 'overflow' being the carry flag not the
>>> overflow flag.  CF and OF are always the same for MUL instructions, so use the
>>> flag which matches the variable name.
>> I don't mind this too much, but the use of CF was deliberate: Imo OF is
>> relevant to signed arithmetic only, whereas CF is the flag to use with
>> unsigned operations.
>>
>>> Fixes: d5c70a51bfbe ("x86/APIC: handle overflow in TMICT calculation")
>>> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
>> Reviewed-by: Jan Beulich <jbeulich@suse.com>
> 
> Thanks.  I could rename the variable to carry instead then?  Either works.

I'd slightly prefer that alternative, yes.

Thanks, Jan