linux-kernel - Re: [PATCH 06/12] tools: sync small_const

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Date:   Mon, 22 Mar 2021 09:34:47 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Yury Norov <yury.norov@...il.com>, linux-kernel@...r.kernel.org
Cc:     linux-m68k@...ts.linux-m68k.org, linux-arch@...r.kernel.org,
        linux-sh@...r.kernel.org, Alexey Klimov <aklimov@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>, David Sterba <dsterba@...e.com>,
        Dennis Zhou <dennis@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Jianpeng Ma <jianpeng.ma@...el.com>,
        Joe Perches <joe@...ches.com>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Rich Felker <dalias@...c.org>,
        Stefano Brivio <sbrivio@...hat.com>,
        Wei Yang <richard.weiyang@...ux.alibaba.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>
Subject: Re: [PATCH 06/12] tools: sync small_const_nbits() macro with the
 kernel

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@...il.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@...musvillemoes.dk>