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

[Bart Van Assche]

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@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Martin Uecker <Martin.Uecker@xxxxxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
 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@xxxxxxxxxxxxxxxxxxxxx>
+ * Glory to Martin Uecker <Martin.Uecker@xxxxxxxxxxxxxxxxxxxxx>. 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