On Mon, 2013-04-22 at 14:16 -0700, Andrew Morton wrote:
> On Mon, 22 Apr 2013 16:58:21 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> > When looking into this, we found the only two users of the index_of()
> > static function that has this issue, passes in size_of(), which will
> > always be a constant, making the check redundant.
>
> Looking at the current callers is cheating. What happens if someone
> adds another caller which doesn't use sizeof?
Well, as it required a size of something, if it was dynamic then what
would the size be of?
>
> > Note, this is a bug in Clang that will hopefully be fixed soon. But for
> > now, this strange redundant compile time check is preventing Clang from
> > even testing the Linux kernel build.
> > </little birdie voice>
> >
> > And I still think the original change log has rational for the change,
> > as it does make it rather confusing to what is happening there.
>
> The patch made index_of() weaker!
>
> It's probably all a bit academic, given that linux-next does
>
> -/*
> - * This function must be completely optimized away if a constant is passed to
> - * it. Mostly the same as what is in linux/slab.h except it returns an index.
> - */
> -static __always_inline int index_of(const size_t size)
> -{
> - extern void __bad_size(void);
> -
> - if (__builtin_constant_p(size)) {
> - int i = 0;
> -
> -#define CACHE(x) \
> - if (size <=x) \
> - return i; \
> - else \
> - i++;
> -#include <linux/kmalloc_sizes.h>
> -#undef CACHE
> - __bad_size();
> - } else
> - __bad_size();
> - return 0;
> -}
> -
Looks like someone just ate the bird.
-- Steve
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