Re: [PATCH v5 6/9] bug.h: Prevent double evaulation of in BUILD_BUG_ON

Borislav Petkov
2012-11-15T15:07:12Z

On Tue, Nov 13, 2012 at 04:13:38PM -0600, danielfsantos@att.net wrote:
> When calling BUILD_BUG_ON in an optimized build using gcc 4.3 and later,
> the condition will be evaulated twice, possibily with side-effects.
> This patch eliminates that error.
>
> Signed-off-by: Daniel Santos <daniel.santos@pobox.com>
> ---
> include/linux/bug.h | 5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/bug.h b/include/linux/bug.h
> index 1b2465d..ccd44ce 100644
> --- a/include/linux/bug.h
> +++ b/include/linux/bug.h
> @@ -58,8 +58,9 @@ struct pt_regs;
> extern int __build_bug_on_failed;
> #define BUILD_BUG_ON(condition) \
> do { \
> - ((void)sizeof(char[1 - 2*!!(condition)])); \
> - if (condition) __build_bug_on_failed = 1; \
> + bool __cond = !!(condition); \
> + ((void)sizeof(char[1 - 2*!!(__cond)])); \

No need for the !!(__cond) here because you've done it in the line
above. IOW,

bool __cond = !!(condition);
((void)sizeof(char[1 - 2 * __cond]));

which is even a bit more readable, as a matter of fact.

> + if (__cond) __build_bug_on_failed = 1; \
> } while(0)
> #endif

Thanks.

--
Regards/Gruss,
Boris.