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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Date:   Tue, 30 Aug 2022 15:51:04 +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 3:45 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> 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);

And additional part

    unsigned int b = 7, c = 1027;
    printf("%02x(b) %02x(c)\n", b, c);


-- 
With Best Regards,
Andy Shevchenko