linux-kernel - Re: [PATCH 1/1] signal: use BUILD_BUG() instead of _NSIG_WORDS_is_unsupported

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Date:	Mon, 22 Sep 2014 10:26:05 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Richard Weinberger <richard@....at>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>, sparse@...isli.org,
	Mark Rustad <mark.d.rustad@...el.com>,
	linux-sparse@...r.kernel.org, linux-kernel@...r.kernel.org,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Brian Norris <computersforpeace@...il.com>
Subject: Re: [PATCH 1/1] signal: use BUILD_BUG() instead of
 _NSIG_WORDS_is_unsupported_size()

On Sun, Sep 21, 2014 at 06:43:06PM +0200, Oleg Nesterov wrote:
> Kill _NSIG_WORDS_is_unsupported_size(), use BUILD_BUG() instead.
> This simplifies the code, avoids the nested-externs warnings, and
> this way we do not defer the problem to linker.
> 
> Also, fix the indentation in _SIG_SET_BINOP() and _SIG_SET_OP().
> 
> Note: this patch assumes that the code like "if (0) BUILD_BUG();"
> is valid. If not (say __compiletime_error() is not defined and thus
> __compiletime_error_fallback() uses a negative array) we should fix
> BUILD_BUG() and/or BUILD_BUG_ON_MSG(). This code should be fine by
> definition, this is the documented purpose of BUILD_BUG().
> 
> Reported-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Thanks for posting this.

Reviewed-by: Josh Triplett <josh@...htriplett.org>

>  include/linux/signal.h |   28 ++++++++++++----------------
>  1 files changed, 12 insertions(+), 16 deletions(-)
> 
> diff --git a/include/linux/signal.h b/include/linux/signal.h
> index 750196f..14acfd5 100644
> --- a/include/linux/signal.h
> +++ b/include/linux/signal.h
> @@ -67,7 +67,6 @@ static inline int sigismember(sigset_t *set, int _sig)
>  
>  static inline int sigisemptyset(sigset_t *set)
>  {
> -	extern void _NSIG_WORDS_is_unsupported_size(void);
>  	switch (_NSIG_WORDS) {
>  	case 4:
>  		return (set->sig[3] | set->sig[2] |
> @@ -77,7 +76,7 @@ static inline int sigisemptyset(sigset_t *set)
>  	case 1:
>  		return set->sig[0] == 0;
>  	default:
> -		_NSIG_WORDS_is_unsupported_size();
> +		BUILD_BUG();
>  		return 0;
>  	}
>  }
> @@ -90,24 +89,23 @@ static inline int sigisemptyset(sigset_t *set)
>  #define _SIG_SET_BINOP(name, op)					\
>  static inline void name(sigset_t *r, const sigset_t *a, const sigset_t *b) \
>  {									\
> -	extern void _NSIG_WORDS_is_unsupported_size(void);		\
>  	unsigned long a0, a1, a2, a3, b0, b1, b2, b3;			\
>  									\
>  	switch (_NSIG_WORDS) {						\
> -	    case 4:							\
> +	case 4:								\
>  		a3 = a->sig[3]; a2 = a->sig[2];				\
>  		b3 = b->sig[3]; b2 = b->sig[2];				\
>  		r->sig[3] = op(a3, b3);					\
>  		r->sig[2] = op(a2, b2);					\
> -	    case 2:							\
> +	case 2:								\
>  		a1 = a->sig[1]; b1 = b->sig[1];				\
>  		r->sig[1] = op(a1, b1);					\
> -	    case 1:							\
> +	case 1:								\
>  		a0 = a->sig[0]; b0 = b->sig[0];				\
>  		r->sig[0] = op(a0, b0);					\
>  		break;							\
> -	    default:							\
> -		_NSIG_WORDS_is_unsupported_size();			\
> +	default:							\
> +		BUILD_BUG();						\
>  	}								\
>  }
>  
> @@ -128,16 +126,14 @@ _SIG_SET_BINOP(sigandnsets, _sig_andn)
>  #define _SIG_SET_OP(name, op)						\
>  static inline void name(sigset_t *set)					\
>  {									\
> -	extern void _NSIG_WORDS_is_unsupported_size(void);		\
> -									\
>  	switch (_NSIG_WORDS) {						\
> -	    case 4: set->sig[3] = op(set->sig[3]);			\
> -		    set->sig[2] = op(set->sig[2]);			\
> -	    case 2: set->sig[1] = op(set->sig[1]);			\
> -	    case 1: set->sig[0] = op(set->sig[0]);			\
> +	case 4:	set->sig[3] = op(set->sig[3]);				\
> +		set->sig[2] = op(set->sig[2]);				\
> +	case 2:	set->sig[1] = op(set->sig[1]);				\
> +	case 1:	set->sig[0] = op(set->sig[0]);				\
>  		    break;						\
> -	    default:							\
> -		_NSIG_WORDS_is_unsupported_size();			\
> +	default:							\
> +		BUILD_BUG();						\
>  	}								\
>  }
>  
> -- 
> 1.5.5.1
> 
> 
> --
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