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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 24 Jan 2023 14:07:54 +0100
Message-ID: <CAMuHMdUUq0FLmsRPw122My7tOUyRLJxsEKOSFgtfG3ec5OiyKQ@mail.gmail.com>
Subject: Re: [PATCH v4 1/1] arch/sh: avoid spurious sizeof-pointer-div warning
To:     Randy Dunlap <rdunlap@infradead.org>
Cc:     Michael Karcher <kernel@mkarcher.dialup.fu-berlin.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-sh list <linux-sh@vger.kernel.org>,
        Segher Boessenkool <segher@kernel.crashing.org>,
        Rich Felker <dalias@libc.org>,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
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On Mon, Jan 23, 2023 at 8:40 PM Randy Dunlap <rdunlap@infradead.org> wrote:
> 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@mkarcher.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.

Indeed.

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

Note that I didn't receive v5 (neither did lore), only Adrian's reply.

> > -#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)))

_INTC_SIZEOF_OR_ZERO() might be useful in general.

> > +#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)    \

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds