Subject: GCOV_PROFILE_ALL breaks BUILD_BUG_ON(!is_power_of_2(8))

From: Johannes Berg <[email-masked]>
Date: Fri, 14 Aug 2015 10:29:04 +0200

+linux-kernel

> +#define DECLARE_EWMA(name, _factor, _weight)> 	> 	> 	> 	> \
> +> 	> struct ewma_##name {> 	> 	> 	> 	> 	> 	> \
> +> 	> 	> unsigned long internal;> 	> 	> 	> 	> 	> \
> +> 	> };> 	> 	> 	> 	> 	> 	> 	> 	> \
> +> 	> static inline void ewma_##name##_init(struct ewma_##name *e)> 	> \
> +> 	> {> 	> 	> 	> 	> 	> 	> 	> 	> \
> +> 	> 	> BUILD_BUG_ON(!__builtin_constant_p(_factor));> 	> 	> \
> +> 	> 	> BUILD_BUG_ON(!__builtin_constant_p(_weight));> 	> 	> \
> +> 	> 	> BUILD_BUG_ON(!is_power_of_2(_factor));> 	> 	> 	> \
> +> 	> 	> BUILD_BUG_ON(!is_power_of_2(_weight));> 	> 	> 	> \
> 

So this seemed fine to me, but for some reason the compiler is saying
the BUILD_BUG_ON(!is_power_of_2(x)) fails, if and only if (!)
CONFIG_GCOV_PROFILE_ALL is enabled, which seems to boil down to the
compiler option -fprofile-arcs.

I'm going to replace this with just the code itself, i.e.

                /* both must be a power of 2 */
                BUILD_BUG_ON(_factor & (_factor - 1));
                BUILD_BUG_ON(_weight & (_weight - 1));

but should I have expected this?

johannes