linux-kernel - Re: [PATCH] gpiolib: acpi: use correct format characters

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Message-ID: <CAKwvOdkjb3uR+kqjfdKL5gqA8R+00c5=3E7uGGW+mGZ3QRsjqg@mail.gmail.com>
Date:   Thu, 17 Mar 2022 11:11:21 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Bill Wendling <morbo@...gle.com>
Cc:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Nathan Chancellor <nathan@...nel.org>,
        linux-gpio@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] gpiolib: acpi: use correct format characters

On Thu, Mar 17, 2022 at 2:07 AM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Wed, Mar 16, 2022 at 02:30:55PM -0700, Bill Wendling wrote:
> > When compiling with -Wformat, clang emits the following warning:
> >
> > drivers/gpio/gpiolib-acpi.c:393:4: warning: format specifies type
> > 'unsigned char' but the argument has type 'int' [-Wformat]
> >                         pin);
> >                         ^~~
> >
> > The types of these arguments are unconditionally defined, so this patch
> > updates the format character to the correct ones for ints and unsigned
> > ints.
>
> hhX specifier refers to unsigned char. It's a bug in the compiler.
>
> NAK.

Andy,
Our goal is to enable -Wformat for CC=clang.  Please see also:
commit cbacb5ab0aa0 ("docs: printk-formats: Stop encouraging use of
unnecessary %h[xudi] and %hh[xudi]")
and the lore link it cites.
https://lore.kernel.org/lkml/CAHk-=wgoxnmsj8GEVFJSvTwdnWm8wVJthefNk2n6+4TC=20e0Q@mail.gmail.com/
(I saw your follow up; this patch is one of the less controversial
ones though since the types are not ones that are promoted).

Bill,
I just remembered that we will want to explicitly set
-Wno-format-pedantic when enabling -Wformat. Remember that -Wformat is
a group flag that turns on other flags, such as -Wformat-security
(currently disabled) and -Wformat-pedantic.  See also:
https://reviews.llvm.org/rGcc01d6421f4a896820c02da2ea92b82d973b431e
commit a8735821d198 ("Kbuild: Disable the -Wformat-security gcc flag")

It may be helpful to cite
commit cbacb5ab0aa0 ("docs: printk-formats: Stop encouraging use of
unnecessary %h[xudi] and %hh[xudi]")
in future commits that change the format flags for types that are promoted.
-- 
Thanks,
~Nick Desaulniers