From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir@xen.org>
Subject: Re: [PATCH] use C11's _Static_assert() for BUILD_BUG_ON
 etc when available
Date: Thu, 26 Jul 2012 16:32:59 +0100
Message-ID: <CC3721BB.46B61%keir@xen.org>
References: <501179DA0200007800090A8C@nat28.tlf.novell.com>
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To: Jan Beulich <JBeulich@suse.com>, xen-devel <xen-devel@lists.xen.org>
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On 26/07/2012 16:09, "Jan Beulich" <JBeulich@suse.com> wrote:

> This produces a more meaningful compiler diagnostic in case it happens
> to trigger.
> 
> As a minor piece of cleanup, at once also use BUILD_BUG_ON_ZERO() to
> actually define BUILD_BUG_ON() in the legacy case, slightly reducing
> redundancy.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Acked-by: Keir Fraser <keir@xen.org>

> --- a/xen/include/xen/lib.h
> +++ b/xen/include/xen/lib.h
> @@ -14,14 +14,20 @@ void __warn(char *file, int line);
>  #define BUG_ON(p)  do { if (unlikely(p)) BUG();  } while (0)
>  #define WARN_ON(p) do { if (unlikely(p)) WARN(); } while (0)
>  
> +#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
>  /* Force a compilation error if condition is true */
> -#define BUILD_BUG_ON(condition) ((void)sizeof(struct { int:-!!(condition);
> }))
> +#define BUILD_BUG_ON(cond) ({ _Static_assert(!(cond), "!(" #cond ")"); })
>  
>  /* Force a compilation error if condition is true, but also produce a
>     result (of value 0 and type size_t), so the expression can be used
>     e.g. in a structure initializer (or where-ever else comma expressions
>     aren't permitted). */
> -#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
> +#define BUILD_BUG_ON_ZERO(cond) \
> +    sizeof(struct { _Static_assert(!(cond), "!(" #cond ")"); })
> +#else
> +#define BUILD_BUG_ON_ZERO(cond) sizeof(struct { int:-!!(cond); })
> +#define BUILD_BUG_ON(cond) ((void)BUILD_BUG_ON_ZERO(cond))
> +#endif
>  
>  #ifndef assert_failed
>  #define assert_failed(p)                                        \
> 
> 
> 
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