On Fri, Aug 14, 2015 at 10:29:04AM +0200, Johannes Berg wrote:
> +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?
It might have something to do with the fact that is_power_of_2() being
an inline function, perhaps with this compiler option it translates to
something that can't be used in the context BUILD_BUG_ON() uses it in.
There is a BUILD_BUG_ON_NOT_POWER_OF_2() macro you could use.
Michal Kubecek
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