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Re: [PATCH v2 2/2] xen: Change parameter of generic_{fls,ffs}() to unsigned int
- To: Michal Orzel <michal.orzel@xxxxxxx>
- From: Henry Wang <Henry.Wang@xxxxxxx>
- Date: Tue, 5 Sep 2023 07:42:18 +0000
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
- Delivery-date: Tue, 05 Sep 2023 07:43:12 +0000
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- Thread-topic: [PATCH v2 2/2] xen: Change parameter of generic_{fls,ffs}() to unsigned int
Hi Michal,
> On Sep 5, 2023, at 15:31, Michal Orzel <michal.orzel@xxxxxxx> wrote:
>
> When running with SMMUv3 and UBSAN enabled on arm64, there are a lot of
> warnings printed related to shifting into sign bit in generic_fls()
> as it takes parameter of type int.
>
> Example:
> (XEN) UBSAN: Undefined behaviour in ./include/xen/bitops.h:69:11
> (XEN) left shift of 134217728 by 4 places cannot be represented in type 'int'
>
> It does not make a lot of sense to ask for the last set bit of a negative
> value. We don't have a direct user of this helper and all the wrappers
> pass value of type unsigned {int,long}.
>
> Linux did the same as part of commit:
> 3fc2579e6f16 ("fls: change parameter to unsigned int")
>
> To keep consistency between the helpers, take the opportunity to:
> - replace __inline__ with inline,
> - modify generic_ffs() to take parameter of type unsigned int as well
> (currently no user and the only wrapper generic_ffsl() passes unsigned
> long).
>
> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
Reviewed-by: Henry Wang <Henry.Wang@xxxxxxx>
Kind regards,
Henry
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