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Date: Thu, 23 Jul 2009 14:47:38 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Joe Perches <joe@perches.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] kernel.h: Verify that arguments to swap() are the same
 type
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On Wed, 15 Jul 2009 18:34:21 -0700
Joe Perches <joe@perches.com> wrote:

> Signed-off-by: Joe Perches <joe@perches.com>
> 
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index d6320a3..72878a5 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -637,8 +637,13 @@ static inline void ftrace_dump(void) { }
>  /*
>   * swap - swap value of @a and @b
>   */
> -#define swap(a, b) \
> -	do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
> +#define swap(a, b)				\
> +do {						\
> +	typeof(a) __tmp = (a);			\
> +	BUILD_BUG_ON(!__same_type(__tmp, (b)));	\
> +	(a) = (b);				\
> +	(b) = __tmp;				\
> +} while (0)
>  

I wonder if we can do

	typecheck(a, typeof(b));