linux-kernel - Re: [PATCH v5 1/1] arch/sh: avoid spurious sizeof-pointer-div warning

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Date:   Tue, 24 Jan 2023 08:41:21 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Michael Karcher <kernel@...rcher.dialup.fu-berlin.de>,
        linux-kernel@...r.kernel.org, linux-sh@...r.kernel.org,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Rich Felker <dalias@...c.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>
Subject: Re: [PATCH v5 1/1] arch/sh: avoid spurious sizeof-pointer-div warning



On 1/24/23 00:11, John Paul Adrian Glaubitz wrote:
> Hello!
> 
> On 1/23/23 21:05, Michael Karcher wrote:
>> Gcc warns about the pattern sizeof(void*)/sizeof(void), as it looks like
>> the abuse of a pattern to calculate the array size. This pattern appears
>> in the unevaluated part of the ternary operator in _INTC_ARRAY if the
>> parameter is NULL.
>>
>> The replacement uses an alternate approach to return 0 in case of NULL
>> which does not generate the pattern sizeof(void*)/sizeof(void), but still
>> emits the warning if _INTC_ARRAY is called with a nonarray parameter.
>>
>> This patch is required for successful compilation with -Werror enabled.
>>
>> The idea to use _Generic for type distinction is taken from Comment #7
>> inhttps://gcc.gnu.org/bugzilla/show_bug.cgi?id=108483  by Jakub Jelinek
>>
>> Signed-off-by: Michael Karcher<kernel@...rcher.dialup.fu-berlin.de>
>> ---
>> History:
>> v5:
>>    - Cleanly generated the patch
>> v4:
>>    - Put the case distinction into the numerator instead of the denominator
>>    - Refactor the case disctinction into a second macro
>> v3:
>>    - I had a stern discussion with Thunderbird about not mangling the
>>      space characters in my email, and I hope spaces get sent as standard
>>      spaces now
>> v2:
>>    - improve title and remove mostly redundant first sentence of the
>>      description
>>    - adjust formatting of the _Generic construction
>>
>> diff --git a/include/linux/sh_intc.h b/include/linux/sh_intc.h
>> index c255273b0281..37ad81058d6a 100644
>> --- a/include/linux/sh_intc.h
>> +++ b/include/linux/sh_intc.h
>> @@ -97,7 +97,10 @@ struct intc_hw_desc {
>>          unsigned int nr_subgroups;
>>   };
>>
>> -#define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a)
>> +#define _INTC_SIZEOF_OR_ZERO(a) (_Generic(a,                 \
>> +                                 typeof(NULL):  0,           \
>> +                                 default:       sizeof(a)))
>> +#define _INTC_ARRAY(a) a, _INTC_SIZEOF_OR_ZERO(a)/sizeof(*a)
>>
>>   #define INTC_HW_DESC(vectors, groups, mask_regs,       \
>>                       prio_regs, sense_regs, ack_regs)   \
> 
> Can anyone suggest which tree to pick this up through until we have established a
> new linux-sh tree?
> 
> Shall this go through Andrew's tree?

I think Andrew or Arnd could merge it.

-- 
~Randy