Re: [Xen-devel] [for-4.7 1/2] xen/bitops: Introduce macros to generate mask

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 13/04/16 16:55, Julien Grall wrote:
> The code has been imported from the header include/linux/bitops.h in
> Linux v4.6-rc3.
>
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
>
> ---
> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Keir Fraser <keir@xxxxxxx>
> Cc: Tim Deegan <tim@xxxxxxx>
> ---
>  xen/include/xen/bitops.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/xen/include/xen/bitops.h b/xen/include/xen/bitops.h
> index cb56f24..e1a4d93 100644
> --- a/xen/include/xen/bitops.h
> +++ b/xen/include/xen/bitops.h
> @@ -3,6 +3,17 @@
>  #include <asm/types.h>
>  
>  /*
> + * Create a contiguous bitmask starting at bit position @l and ending at
> + * position @h. For example
> + * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.
> + */
> +#define GENMASK(h, l) \
> +     (((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h))))
> +
> +#define GENMASK_ULL(h, l) \
> +     (((~0ULL) << (l)) & (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h))))

You should have just a single GENMASK() which works in terms of LL.

Masks must be signed to work correctly when implicitly extended.

~Andrew

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