linux-kernel - [PATCH] kernel.h: Avoid that sparse complains about using sizeof(void)

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Message-Id: <20180705161709.17028-1-bart.vanassche@wdc.com>
Date:   Thu,  5 Jul 2018 09:17:09 -0700
From:   Bart Van Assche <bart.vanassche@....com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Bart Van Assche <bart.vanassche@....com>,
        Martin Uecker <Martin.Uecker@....uni-goettingen.de>,
        Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...nel.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        stable@...r.kernel.org
Subject: [PATCH] kernel.h: Avoid that sparse complains about using sizeof(void)

The macro __is_constexpr() causes sparse to report the following:

    warning: expression using sizeof(void)

Avoid this by using __builtin_constant_p() instead.

Fixes: 3c8ba0d61d04 ("kernel.h: Retain constant expression output for max()/min()")
Signed-off-by: Bart Van Assche <bart.vanassche@....com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Martin Uecker <Martin.Uecker@....uni-goettingen.de>
Cc: Kees Cook <keescook@...omium.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: <stable@...r.kernel.org>
---
 include/linux/kernel.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index d23123238534..a9f0d0d48971 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -811,13 +811,19 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
 #define __typecheck(x, y) \
 		(!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
 
+#ifndef __CHECKER__
 /*
  * This returns a constant expression while determining if an argument is
  * a constant expression, most importantly without evaluating the argument.
- * Glory to Martin Uecker <Martin.Uecker@....uni-goettingen.de>
+ * Glory to Martin Uecker <Martin.Uecker@....uni-goettingen.de>. However, this
+ * macro causes sparse to report the warning "expression using sizeof(void)".
+ * Hence use __builtin_constant_p() instead when using sparse.
  */
 #define __is_constexpr(x) \
 	(sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
+#else
+#define __is_constexpr(x) __builtin_constant_p((x))
+#endif
 
 #define __no_side_effects(x, y) \
 		(__is_constexpr(x) && __is_constexpr(y))
-- 
2.18.0