# Re: \[PATCH 06/12\] tools: sync small\_const\_nbits() macro with the kernel

- From: Rasmus Villemoes \<linux@rasmusvillemoes.dk\>
- Date: 2021-03-22 08:35:52 
- List: linux-arch
- Page: https://ratatoskr.run/linux-arch/2021/03/6309765
- Thread: https://ratatoskr.run/linux-arch/2021/03/6309335/t.md

```text
On 21/03/2021 22.54, Yury Norov wrote:
> Move the macro from tools/include/asm-generic/bitsperlong.h
> to tools/include/linux/bitmap.h

The patch does it the other way around :)

> Signed-off-by: Yury Norov <yury.norov@gmail.com>
> ---
>  tools/include/asm-generic/bitsperlong.h | 3 +++
>  tools/include/linux/bitmap.h            | 3 ---
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/include/asm-generic/bitsperlong.h b/tools/include/asm-generic/bitsperlong.h
> index 8f2283052333..f530da2506cc 100644
> --- a/tools/include/asm-generic/bitsperlong.h
> +++ b/tools/include/asm-generic/bitsperlong.h
> @@ -18,4 +18,7 @@
>  #define BITS_PER_LONG_LONG 64
>  #endif
>  
> +#define small_const_nbits(nbits) \
> +	(__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG)
> +

Well, the movement is consistent with the kernel, but shouldn't the
definition also be updated to exclude constant-zero-size? It's not that
they exist or ever have, in tools/ or kernel proper, but just if some
day some oddball CONFIG_ combination ends up creating such a beast, I'd
rather not have code like

+	if (small_const_nbits(size)) {
+		unsigned long val = *addr & GENMASK(size - 1, 0);

blow up at run-time.

Other than that (and the above commit log typo), consider the series

Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
```