linux-kernel - Re: [PATCH 01/21] powerpc: Remove warning on array size when empty

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Date:   Tue, 27 Feb 2018 18:25:31 +0100
From:   Mathieu Malaterre <malat@...ian.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Christophe LEROY <christophe.leroy@....fr>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Paul Mackerras <paulus@...ba.org>,
        Jiri Slaby <jslaby@...e.com>,
        "open list:LINUX FOR POWERPC PA SEMI PWRFICIENT" 
        <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 01/21] powerpc: Remove warning on array size when empty

On Tue, Feb 27, 2018 at 4:52 PM, Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> On Tue, Feb 27, 2018 at 9:44 AM, Mathieu Malaterre <malat@...ian.org> wrote:
>> On Tue, Feb 27, 2018 at 8:33 AM, Christophe LEROY
>> <christophe.leroy@....fr> wrote:
>
>>>>>> Much simpler is just add
>>>>>>
>>>>>> if (ARRAY_SIZE() == 0)
>>>>>>   return;
>
>>> Or add in front:
>>> if (!ARRAY_SIZE(feature_properties))
>>>         return;
>>
>> (not tested) I believe the compiler still go over the for() loop and
>> will complain about the original unsigned comparison.
>
> Did you run tests? Did you look into object file?

The goal of this series is simply to remove warning treated as error.

I tried from home and I can still see the error using gcc 6.3.0, so
the original for() loop needs to be rewritten.

  CC      arch/powerpc/kernel/prom.o
arch/powerpc/kernel/prom.c: In function ‘check_cpu_feature_properties’:
arch/powerpc/kernel/prom.c:301:16: error: comparison of unsigned
expression < 0 is always false [-Werror=type-limits]
  for (i = 0; i < ARRAY_SIZE(feature_properties); ++i, ++fp) {
                ^
cc1: all warnings being treated as errors


> In kernel we much rely on the compiling away the code which is
> deterministically not in use.
> Here I'm pretty sure it will compile away entire function.
>
> --
> With Best Regards,
> Andy Shevchenko