Re: [PATCH] gpiolib: acpi: use correct format characters

From: Nick Desaulniers <ndesaulniers@google.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Bill Wendling <morbo@google.com>
Cc: Mika Westerberg <mika.westerberg@linux.intel.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Bartosz Golaszewski <brgl@bgdev.pl>,
	Nathan Chancellor <nathan@kernel.org>,
	linux-gpio@vger.kernel.org, linux-acpi@vger.kernel.org,
	linux-kernel@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH] gpiolib: acpi: use correct format characters
Date: Thu, 17 Mar 2022 11:11:21 -0700	[thread overview]
Message-ID: <CAKwvOdkjb3uR+kqjfdKL5gqA8R+00c5=3E7uGGW+mGZ3QRsjqg@mail.gmail.com> (raw)
In-Reply-To: <YjL6K49CkH+YC4FQ@smile.fi.intel.com>

On Thu, Mar 17, 2022 at 2:07 AM Andy Shevchenko
<andriy.shevchenko@linux.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