linux-kernel - Re: drivers/net/wireless/ralink/rt2x00/rt2800lib.c:9439:15: warning: result of comparison of constant -7 with expression of type 'char' is always false

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Message-ID: <CAHmME9qFKMLJiZa=pg9bnBWHSfbgP-+yimteL_t4sxuepQ6bAg@mail.gmail.com>
Date:   Wed, 19 Oct 2022 01:59:58 -0600
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Kalle Valo <kvalo@...nel.org>
Cc:     kernel test robot <lkp@...el.com>,
        Tomislav Požega <pozega.tomislav@...il.com>,
        llvm@...ts.linux.dev, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, Daniel Golle <daniel@...rotopia.org>,
        linux-wireless@...r.kernel.org
Subject: Re: drivers/net/wireless/ralink/rt2x00/rt2800lib.c:9439:15: warning:
 result of comparison of constant -7 with expression of type 'char' is always false

On Wed, Oct 19, 2022 at 1:55 AM Kalle Valo <kvalo@...nel.org> wrote:
>
> + jason, linux-wireless
>
> kernel test robot <lkp@...el.com> writes:
>
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > head:   aae703b02f92bde9264366c545e87cec451de471
> > commit: dab902fe1d29dc0fa1dccc8d13dc89ffbf633881 wifi: rt2x00: add TX
> > LOFT calibration for MT7620
> > date:   4 weeks ago
> > config: arm64-allmodconfig
> > compiler: clang version 16.0.0 (https://github.com/llvm/llvm-project
> > 791a7ae1ba3efd6bca96338e10ffde557ba83920)
> > reproduce (this is a W=1 build):
> >         wget
> > https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross
> > -O ~/bin/make.cross
> >         chmod +x ~/bin/make.cross
> >         # install arm64 cross compiling tool for clang build
> >         # apt-get install binutils-aarch64-linux-gnu
> >         #
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=dab902fe1d29dc0fa1dccc8d13dc89ffbf633881
> >         git remote add linus
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> >         git fetch --no-tags linus master
> >         git checkout dab902fe1d29dc0fa1dccc8d13dc89ffbf633881
> >         # save the config file
> >         mkdir build_dir && cp config build_dir/.config
> >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1
> > O=build_dir ARCH=arm64 SHELL=/bin/bash drivers/gpu/drm/amd/amdgpu/
> > drivers/net/wireless/ralink/rt2x00/ drivers/staging/media/
> >
> > If you fix the issue, kindly add following tag where applicable
> > | Reported-by: kernel test robot <lkp@...el.com>
> >
> > All warnings (new ones prefixed by >>):
> >
> >>> drivers/net/wireless/ralink/rt2x00/rt2800lib.c:9439:15: warning:
> >> result of comparison of constant -7 with expression of type 'char'
> >> is always false [-Wtautological-constant-out-of-range-compare]
> >            gerr = (gerr < -0x07) ? -0x07 : (gerr > 0x05) ? 0x05 : gerr;
> >                    ~~~~ ^ ~~~~~
> >    drivers/net/wireless/ralink/rt2x00/rt2800lib.c:9443:15: warning: result of comparison of constant -31 with expression of type 'char' is always false [-Wtautological-constant-out-of-range-compare]
> >            perr = (perr < -0x1f) ? -0x1f : (perr > 0x1d) ? 0x1d : perr;
> >                    ~~~~ ^ ~~~~~
> >    2 warnings generated.
>
> I believe this patch should fix it:
>
> https://patchwork.kernel.org/project/linux-wireless/patch/20221018202734.140489-1-Jason@zx2c4.com/
>
> Jason, is my understanding correct?

That's a different bug caused by the same pitfall: assuming char is
signed. I'll send a patch for that function too.

Jason