linux-kernel - Re: [PATCH 01/13] tools: disable -Wno-type-limits

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Date:   Tue, 16 Mar 2021 09:17:24 +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 01/13] tools: disable -Wno-type-limits

On 16/03/2021 02.54, Yury Norov wrote:
> GENMASK(h, l) may be passed with unsigned types. In such case, type-limits
> warning is generated for example in case of GENMASK(h, 0).
> 
> Signed-off-by: Yury Norov <yury.norov@...il.com>
> ---
>  tools/scripts/Makefile.include | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
> index 84dbf61a7eca..15e99905cb7d 100644
> --- a/tools/scripts/Makefile.include
> +++ b/tools/scripts/Makefile.include
> @@ -38,6 +38,7 @@ EXTRA_WARNINGS += -Wswitch-enum
>  EXTRA_WARNINGS += -Wundef
>  EXTRA_WARNINGS += -Wwrite-strings
>  EXTRA_WARNINGS += -Wformat
> +EXTRA_WARNINGS += -Wno-type-limits
>

I don't like that kind of collateral damage. I seem to recall another
instance where a macro was instead rewritten to avoid triggering the
type-limits warning (with a comment explaining the uglyness). Something like

foo > bar      is the same as
!(foo <= bar)  which is the same as
!(foo == bar || foo < bar)

Dunno if that would work here, but if it did, it would have the bonus
that when somebody builds the kernel proper with Wtype-limits enabled
(maybe W=1 or W=2) there would be no false positives from GENMASK to
wade through.

Alternatively, we really should consider making use of _Pragma to
locally disable/re-enable certain warnings.

Rasmus