Re: [PATCH] compiler: Correct macro parameter expansion problem

[Josh Triplett <josh@joshtriplett.org>]

On Mon, Nov 03, 2014 at 06:34:13AM -0800, Jeff Kirsher wrote:
> From: Mark Rustad <mark.d.rustad@intel.com>
> 
> The macro __compiletime_error_fallback has an error in that it
> lacks parens around the expansion of an expression. It also
> lacks a conversion to a boolean value. The first problem can
> result in a mis-evaluation. The second problem can also result
> in an error if the value comes out negative. That would thwart
> the intended error generation. That is, the error being asserted
> would not in fact generate an error. Fix both problems by adding
> !!() to the expansion.
> 
> Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
> Tested-by: Aaron Brown <aaron.f.brown@intel.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

Good catch.

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

>  include/linux/compiler.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index d5ad7b1..59dc611 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -331,7 +331,7 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
>   */
>  # ifndef __CHECKER__
>  #  define __compiletime_error_fallback(condition) \
> -	do { ((void)sizeof(char[1 - 2 * condition])); } while (0)
> +	do { ((void)sizeof(char[1 - 2 * !!(condition)])); } while (0)
>  # endif
>  #endif
>  #ifndef __compiletime_error_fallback
> -- 
> 1.9.3
> 
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