linux-kernel - Re: [PATCH] linux/bits.h: fix -Wtype-limits warnings in GENMASK_INPUT

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Date:   Mon, 7 Mar 2022 15:40:33 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Alexander Lobakin <alexandr.lobakin@...el.com>
Cc:     Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        Rikard Falkeborn <rikard.falkeborn@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] linux/bits.h: fix -Wtype-limits warnings in GENMASK_INPUT_CHECK()

On Mon, Mar 7, 2022 at 1:00 PM Alexander Lobakin
<alexandr.lobakin@...el.com> wrote:
> From: Andy Shevchenko <andy.shevchenko@...il.com>
> Date: Fri, 4 Mar 2022 20:46:08 +0200
> > On Fri, Mar 4, 2022 at 7:36 PM Vincent Mailhol
> > <mailhol.vincent@...adoo.fr> wrote:
> >
> > > This pattern is harmless but because it occurs in header files
> > > (example find_first_bit() from linux/find.h [1]) and because of the
> > > include hell, the macro GENMASK_INPUT_CHECK() is accountable for 31%
> > > (164714/532484) of all warnings when compiling all modules at W=2
> > > level.
>
> Nice catch, thanks! I wanted to submit the very same fix, but
> postponed it for some reason, and now here we are.
>
> > Have you fixed W=1 warnings?
> > Without fixing W=1 (which makes much more sense, when used with
> > WERROR=y && COMPILE_TEST=y) this has no value.
>
> How is this connected?

By priorities.
I don't see much value in fixing W=2 per se if the code doesn't compile for W=1.

> When I do `make W=2 path/to/my/code`, I want to see the actual code
> problems, not something that comes from the include files.
> When I do `make W=2 path/to/new/code/from/lkml`, I want to see the
> actual new warnings, not something coming from the includes.
> It's much easier to overlook or miss some real warnings when the
> stderr is being flooded by the warnings from the include files.
> I'm aware there are some scripts to compare before/after, but I
> don't want to use them just because "this has to value".

I rephrased above.

> I don't want to do `make W=2 KCFLAGS='-Wno-shadow -Wno-type-limits'`
> because then I'm not able to spot the actual shadow or type limit
> problems in my/new code.
> I fixed several `-Wshadow` warnings previously in the include files
> related to networking, and *nobody* said "this has no value" or
> NAKed it. And `-Wshadow` has always been in W=2.

Yes, because people rarely enable COMPILE_TEST + WERROR.
To be clear, my comment is given in that scope.

-- 
With Best Regards,
Andy Shevchenko