On Tue, Mar 20, 2018 at 4:23 PM, Linus Torvalds
<[email protected]> wrote:
>
> Hmm. So thanks to the diseased mind of Martin Uecker, there's a better
> test for "__is_constant()":
>
> /* Glory to Martin Uecker <[email protected]> */
> #define __is_constant(a) \
> (sizeof(int) == sizeof(*(1 ? ((void*)((a) * 0l)) : (int*)1)))
>
> that is actually *specified* by the C standard to work, and doesn't
> even depend on any gcc extensions.
Well, it does depend on 'sizeof(*(void *)X)' being 1 and the compiler
not complaining about it, and that sizeof(int) is not 1.
But since we depend on those things in the kernel anyway, that's fine.
Linus
