Re: [Xen-devel] [PATCH v4 5/9] arm/mem_access: Extend BIT-operations to unsigned long long

[Julien Grall <julien.grall@xxxxxxx>]

Hi Sergej,

On 20/06/17 21:33, Sergej Proskurin wrote:
> We extend the BIT macro to using values of unsigned long long as to
> enable setting bits of 64-bit registers on AArch32.  In addition, this
> commit adds a define holding the register width of 64 bit double-word
> registers. This define simplifies using the associated constants in the
> following commits.
>
> Signed-off-by: Sergej Proskurin <proskurin@xxxxxxxxxxxxx>
> ---
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>
> ---
> v4: We reused the previous commit with the msg "arm/mem_access: Add
>     defines holding the width of 32/64bit regs" from v3, as we can reuse
>     the already existing define BITS_PER_WORD.
> ---
>  xen/include/asm-arm/bitops.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/xen/include/asm-arm/bitops.h b/xen/include/asm-arm/bitops.h
> index bda889841b..c3486d497c 100644
> --- a/xen/include/asm-arm/bitops.h
> +++ b/xen/include/asm-arm/bitops.h
> @@ -21,7 +21,8 @@
>  #define __clear_bit(n,p)          clear_bit(n,p)
>
>  #define BITS_PER_WORD           32
> -#define BIT(nr)                 (1UL << (nr))
> +#define BITS_PER_DOUBLE_WORD    64
> +#define BIT(nr)                 (1ULL << (nr))
This macro is part of a set (BIT, BIT_MASK, BIT_WORD) that work on 
unsigned long. Now you are suggesting to upgrade BIT to support unsigned 
long long. This will confuse more than one user and break this set.
I would much prefer if you introduce BIT_ULL as Linux does. At the same 
time BITS_PER_DOUBLE_WORD should be renamed BITS_PER_LONG_LONG.
>  #define BIT_MASK(nr)            (1UL << ((nr) % BITS_PER_WORD))
>  #define BIT_WORD(nr)            ((nr) / BITS_PER_WORD)
>  #define BITS_PER_BYTE           8
Cheers,

--
Julien Grall

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