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Re: [XEN PATCH][for-next][for-4.19 v2 1/8] xen/include: add macro LOWEST_BIT
- To: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 16 Oct 2023 17:33:36 +0200
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- Delivery-date: Mon, 16 Oct 2023 15:33:47 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 12.10.2023 17:28, Nicola Vetrini wrote:
> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> @@ -274,6 +274,12 @@ still non-negative."
> -config=MC3R1.R10.1,etypes+={safe,
> "stmt(operator(logical)||node(conditional_operator||binary_conditional_operator))",
> "dst_type(ebool||boolean)"}
> -doc_end
>
> +-doc_begin="The macro LOWEST_BIT encapsulates a well-known pattern to obtain
> the value
> +2^ffs(x) for unsigned integers on two's complement architectures
> +(all the architectures supported by Xen satisfy this requirement)."
> +-config=MC3R1.R10.1,reports+={safe,
> "any_area(any_loc(any_exp(macro(^LOWEST_BIT$))))"}
> +-doc_end
Why is this added here rather than by ...
> --- a/xen/include/xen/macros.h
> +++ b/xen/include/xen/macros.h
> @@ -8,8 +8,10 @@
> #define DIV_ROUND(n, d) (((n) + (d) / 2) / (d))
> #define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
>
> -#define MASK_EXTR(v, m) (((v) & (m)) / ((m) & -(m)))
> -#define MASK_INSR(v, m) (((v) * ((m) & -(m))) & (m))
a SAF-<n>-safe comment here?
> +#define LOWEST_BIT(x) ((x) & -(x))
Personally I consider the name misleading: I'd expect a macro of this
name to return a bit number, not a mask with a single bit set. No
good, reasonably short name comes to mind - ISOLATE_LOW_BIT() is too
long for my taste.
Jan
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