linux-kernel - Re: [PATCH v4 1/1] arch/sh: avoid spurious sizeof-pointer-div warning

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Message-ID: <f540c26e-baa8-5c18-9502-622a4091b675@infradead.org>
Date:   Mon, 23 Jan 2023 11:37:31 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     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>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Subject: Re: [PATCH v4 1/1] arch/sh: avoid spurious sizeof-pointer-div warning

Hi,

I'm curious how you generated this patch.
'patch' complains:

patch: **** malformed patch at line 53:                prio_regs,    sense_regs, ack_regs)    \

(more below)

On 1/23/23 10:48, 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
> in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108483 by Jakub Jelinek
> 
> Signed-off-by: Michael Karcher <kernel@...rcher.dialup.fu-berlin.de>
> ---
> This edition of the mail has the correct "v4" designation in the subject.
> 
> History:
> 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..98d1da0d8e36 100644
> --- a/include/linux/sh_intc.h
> +++ b/include/linux/sh_intc.h
> @@ -97,7 +97,9 @@ struct intc_hw_desc {

That ,9 should be ,10.

With that change:

Acked-by: Randy Dunlap <rdunlap@...radead.org> # build-tested

Thanks.

>      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)    \
> 
> 

-- 
~Randy