Ack: [PATCH Trusty SRU 1/3] bitops: Fix signedness of compile-time hweight implementations

[Brad Figg]

On 06/12/2014 12:24 PM, Tim Gardner wrote:
> From: Paul Walmsley <pwalmsley at nvidia.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/1321791
> 
> Enabling '-Wsign-compare' compiler warnings on code that includes
> include/linux/bitops.h can generate the following warning:
> 
>   In file included from include/linux/kernel.h:10:0,
>                     from <random filename>:48:
>   include/linux/bitops.h: In function 'hweight_long':
>   include/linux/bitops.h:77:26: error: signed and unsigned type in conditional expression [-Werror=sign-compare]
> 
> (converted to an error with -Werror)
> 
> This is due to the use of the logical negation operator '!' in the
> __const_hweight8 macro in include/asm-generic/bitops/const_hweight.h.
> The use of that operator here results in a signed value.
> 
> Fix by explicitly casting the __const_hweight8 macro expansion to
> 'unsigned int'.  While here, clean up several checkpatch.pl warnings.
> 
> Signed-off-by: Paul Walmsley <pwalmsley at nvidia.com>
> Cc: Arnd Bergmann <arnd at arndb.de>
> Cc: H. Peter Anvin <hpa at zytor.com>
> Cc: Linus Torvalds <torvalds at linux-foundation.org>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Signed-off-by: Peter Zijlstra <peterz at infradead.org>
> Link: http://lkml.kernel.org/r/alpine.DEB.2.02.1312180459580.30198@tamien
> Signed-off-by: Ingo Molnar <mingo at kernel.org>
> (cherry picked from commit c32fa99f0b4252633aa464e28d1cb925bd2a79df)
> Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
> ---
>  include/asm-generic/bitops/const_hweight.h | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/include/asm-generic/bitops/const_hweight.h b/include/asm-generic/bitops/const_hweight.h
> index fa2a50b..0a7e066 100644
> --- a/include/asm-generic/bitops/const_hweight.h
> +++ b/include/asm-generic/bitops/const_hweight.h
> @@ -5,14 +5,15 @@
>   * Compile time versions of __arch_hweightN()
>   */
>  #define __const_hweight8(w)		\
> -      (	(!!((w) & (1ULL << 0))) +	\
> -	(!!((w) & (1ULL << 1))) +	\
> -	(!!((w) & (1ULL << 2))) +	\
> -	(!!((w) & (1ULL << 3))) +	\
> -	(!!((w) & (1ULL << 4))) +	\
> -	(!!((w) & (1ULL << 5))) +	\
> -	(!!((w) & (1ULL << 6))) +	\
> -	(!!((w) & (1ULL << 7)))	)
> +	((unsigned int)			\
> +	 ((!!((w) & (1ULL << 0))) +	\
> +	  (!!((w) & (1ULL << 1))) +	\
> +	  (!!((w) & (1ULL << 2))) +	\
> +	  (!!((w) & (1ULL << 3))) +	\
> +	  (!!((w) & (1ULL << 4))) +	\
> +	  (!!((w) & (1ULL << 5))) +	\
> +	  (!!((w) & (1ULL << 6))) +	\
> +	  (!!((w) & (1ULL << 7)))))
>  
>  #define __const_hweight16(w) (__const_hweight8(w)  + __const_hweight8((w)  >> 8 ))
>  #define __const_hweight32(w) (__const_hweight16(w) + __const_hweight16((w) >> 16))
> 


-- 
Brad Figg brad.figg at canonical.com http://www.canonical.com