linux-kernel - Re: [PATCH: 1/1] sh4: avoid spurious gcc warning

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Message-ID: <2085aec3-796b-71c3-7cb2-d4103d3b6175@infradead.org>
Date:   Sat, 21 Jan 2023 23:00:38 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     "Michael.Karcher" <Michael.Karcher@...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>
Cc:     jakub@....gnu.org
Subject: Re: [PATCH: 1/1] sh4: avoid spurious gcc warning

Hi--

It's just sh: AFAICT. The patch fixes the build error for me on sh2,
using gcc 12.1.0 from the kernel.org crosstool builds.

On 1/21/23 16:15, Michael.Karcher wrote:
> Prevent sizeof-pointer-div warning in SH4 intc macros
> 
> 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>
> ---
> 
> diff --git a/include/linux/sh_intc.h b/include/linux/sh_intc.h
> index c255273b0281..d7a7ffb60a34 100644
> --- a/include/linux/sh_intc.h
> +++ b/include/linux/sh_intc.h
> @@ -97,7 +97,7 @@ struct intc_hw_desc {
>      unsigned int nr_subgroups;
>  };
> 
> -#define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a)
> +#define _INTC_ARRAY(a) a, sizeof(a)/(_Generic((a), typeof(NULL): 0xFFFFFFFFU, default: sizeof(*a)))

s/: / : / in 2 places.

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

How far back in gcc versions does this work?

Thanks.

> 
>  #define INTC_HW_DESC(vectors, groups, mask_regs,    \
>               prio_regs,    sense_regs, ack_regs)    \
> 

-- 
~Randy