linux-kernel - Re: [jic23-iio:testing 124/129] drivers/iio/accel/msa311.c:993:24: warning: format specifies type 'unsigned char' but the argument has type 'unsigned int'

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Message-ID: <CAHp75VfA=w+Q2ccdTiQXeWRw0wSjbkUf6J3+tp-kE50mxdkTNg@mail.gmail.com>
Date:   Tue, 30 Aug 2022 15:45:12 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     kernel test robot <lkp@...el.com>,
        Dmitry Rokosov <DDRokosov@...rdevices.ru>,
        llvm@...ts.linux.dev, kbuild-all@...ts.01.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [jic23-iio:testing 124/129] drivers/iio/accel/msa311.c:993:24:
 warning: format specifies type 'unsigned char' but the argument has type
 'unsigned int'

On Tue, Aug 30, 2022 at 1:03 PM Jonathan Cameron
<Jonathan.Cameron@...wei.com> wrote:
> On Mon, 29 Aug 2022 06:25:53 +0800
> kernel test robot <lkp@...el.com> wrote:

...

> > >> drivers/iio/accel/msa311.c:993:24: warning: format specifies type 'unsigned char' but the argument has type 'unsigned int' [-Wformat]
> >                                               "msa311-%hhx", partid);
> >                                                       ~~~~   ^~~~~~
> >                                                       %x
> >    1 warning generated.

> >    992                msa311->chip_name = devm_kasprintf(dev, GFP_KERNEL,
> >  > 993                                                   "msa311-%hhx", partid);

> I'm thinking intent here was to limit range of what was printed. Maybe better to use
> local u8 variable or cast?
>
> I can fix it up if that's fine with you - or even better send me a patch that fixes
> it however you prefer!

Looking back at what Linus said about those specifiers, I would rather
go with simple %x or %02x.

P.S. Surprisingly many C developers don't know the difference between
%hhx and %02x, which is easy to check by

  char a = -1;
  printf("%hhx <==> %02x\n", a, a);
  a = 217;
  printf("%hhx <==> %02x\n", a, a);

-- 
With Best Regards,
Andy Shevchenko