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

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Message-ID: <b41ea008-d9c4-fd76-a5ce-00fe435deed5@mkarcher.dialup.fu-berlin.de>
Date:   Mon, 23 Jan 2023 19:48:58 +0100
From:   Michael Karcher <kernel@...rcher.dialup.fu-berlin.de>
To:     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: [PATCH v4 1/1] arch/sh: avoid spurious sizeof-pointer-div warning

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 {
      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)    \