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Re: [PATCH Xen 4.20] x86/apic: Fix asm() constraints in TMICT calculation
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 21 Apr 2026 12:26:04 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 21 Apr 2026 10:26:09 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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@xxxxxxxxxx>
>> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> Thanks. I could rename the variable to carry instead then? Either works.
I'd slightly prefer that alternative, yes.
Thanks, Jan
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