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Re: [PATCH v6 05/20] xen/bitops: implement fls{l}() in common logic


  • To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Wed, 20 Mar 2024 16:39:06 +0100
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  • Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Wed, 20 Mar 2024 15:39:16 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 15.03.2024 19:06, Oleksii Kurochko wrote:
> Return type was left 'int' because of the following compilation error:
> 
> ./include/xen/kernel.h:18:21: error: comparison of distinct pointer types 
> lacks a cast [-Werror]
>        18 |         (void) (&_x == &_y);            \
>           |                     ^~
>     common/page_alloc.c:1843:34: note: in expansion of macro 'min'
>      1843 |         unsigned int inc_order = min(MAX_ORDER, flsl(e - s) - 1);
> 
> generic_fls{l} was used instead of __builtin_clz{l}(x) as if x is 0,
> the result in undefined.
> 
> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

Assuming Andrew's pending change goes in as posted, I'm okay with this to
(as simply following suit). Without that having happened, I can't very
well offer an ack here. Just one nit:

> --- a/xen/include/xen/bitops.h
> +++ b/xen/include/xen/bitops.h
> @@ -69,6 +69,30 @@ static inline int generic_flsl(unsigned long x)
>  
>  #include <asm/bitops.h>
>  
> +static always_inline __pure int fls(unsigned int x)
> +{
> +    if (__builtin_constant_p(x))

Style (missing blanks immediately inside the parentheses), also again ...

> +        return generic_fls(x);
> +
> +#ifndef arch_fls
> +#define arch_fls generic_fls
> +#endif
> +
> +    return arch_fls(x);
> +}
> +
> +static always_inline __pure int flsl(unsigned long x)
> +{
> +    if (__builtin_constant_p(x))

... here.

Jan



 


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