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Re: [XEN PATCH] xen/types: address Rule 10.1 for macro BITS_TO_LONGS
- To: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 5 Sep 2023 09:46:41 +0200
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- Cc: sstabellini@xxxxxxxxxx, michal.orzel@xxxxxxx, xenia.ragiadakou@xxxxxxx, ayan.kumar.halder@xxxxxxx, consulting@xxxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 05 Sep 2023 07:46:55 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 05.09.2023 09:31, Nicola Vetrini wrote:
> Given its use in the declaration
> 'DECLARE_BITMAP(features, IOMMU_FEAT_count)' the argument
> 'bits' has essential type 'enum iommu_feature', which is not
> allowed by the Rule as an operand to the addition operator.
> Given that its value can be represented by a signed integer,
> the explicit cast resolves the violation.
Wait - why would this lead to a change to BITS_TO_LONGS()? And if that
was to be changed, why plain int? I don't think negative input makes
sense there, and in principle I'd expect values beyond 4 billion to
also be permissible (even if likely no such use will ever appear in a
DECLARE_BITMAP(), but elsewhere it may make sense). Even going to
"unsigned long" may be too limiting ...
> --- a/xen/include/xen/types.h
> +++ b/xen/include/xen/types.h
> @@ -23,7 +23,7 @@ typedef signed long ssize_t;
> typedef __PTRDIFF_TYPE__ ptrdiff_t;
>
> #define BITS_TO_LONGS(bits) \
> - (((bits)+BITS_PER_LONG-1)/BITS_PER_LONG)
> + (((int)(bits)+BITS_PER_LONG-1)/BITS_PER_LONG)
> #define DECLARE_BITMAP(name,bits) \
> unsigned long name[BITS_TO_LONGS(bits)]
>
Furthermore, as always - if this was to be touched, please take care
of style violations (numerous missing blanks) at this occasion.
Jan
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