[PATCH] compiler: Correct macro parameter expansion problem

[PATCH] compiler: Correct macro parameter expansion problem

[Jeff Kirsher]

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>
---
 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

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

[Josh Triplett]

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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