Re: [Qemu-devel] [PATCH v2] bitmap: fix BITMAP_LAST_WORD_MASK

[Peter Xu <peterx@redhat.com>]

On Tue, Jul 31, 2018 at 06:01:18PM +0800, Wei Wang wrote:
> When "nbits = 0", which means no bits to mask, this macro is expected to
> return 0, instead of 0xffffffff. This patch changes the macro to return
> 0 when there is no bit needs to be masked.
> 
> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> CC: Juan Quintela <quintela@redhat.com>
> CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
> CC: Peter Xu <peterx@redhat.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

Is there any existing path that can trigger this nbits==0?

> ---
>  include/qemu/bitmap.h | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> v1->v2 ChangeLog:
> - fix the macro directly, instead of fixing the callers one by one.
> 
> diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h
> index 509eedd..9372423 100644
> --- a/include/qemu/bitmap.h
> +++ b/include/qemu/bitmap.h
> @@ -60,7 +60,10 @@
>   */
>  
>  #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1)))
> -#define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))
> +#define BITMAP_LAST_WORD_MASK(nbits)                       \
> +(                                                          \
> +    nbits ? (~0UL >> (-(nbits) & (BITS_PER_LONG - 1))) : 0 \
> +)
>  
>  #define DECLARE_BITMAP(name,bits)                  \
>          unsigned long name[BITS_TO_LONGS(bits)]
> -- 
> 2.7.4
> 

Regards,

-- 
Peter Xu