From e5545fb6d0dc5e2c48b2e450d18246d9bc1ae35b Mon Sep 17 00:00:00 2001 From: Ian Campbell Date: Mon, 7 Apr 2014 12:07:04 +0100 Subject: [PATCH] xen: make sure that likely and unlikely convert the expression to a boolean According to http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html __builtin_expect has the prototype: long __builtin_expect (long exp, long c) If sizeof(exp) > sizeof(long) then this will effectively mask off the top bits of exp, meaning that the if in "if (unlikey(x))" will see the masked version, which might be false when true was expected, likely has the same issue. This is mostly likely to affect x86_32 and arm32 builds. x86_32 is not present on 4.3 onwards and a quick grep of current staging shows that all the existing arm32 uses of both likely and unlikely already pass a boolean. I noticed this with an as yet unposted patch which did not have this property. Also the defintion of likely might not have had the expected affect for cases where a true value > 1 might be passed. Signed-off-by: Ian Campbell Reviewed-by: Jan Beulich Cc: Keir Fraser Cc: Tim Deegan --- xen/include/xen/compiler.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h index 6e07990f23..4b3472daee 100644 --- a/xen/include/xen/compiler.h +++ b/xen/include/xen/compiler.h @@ -7,8 +7,8 @@ #define barrier() __asm__ __volatile__("": : :"memory") -#define likely(x) __builtin_expect((x),1) -#define unlikely(x) __builtin_expect((x),0) +#define likely(x) __builtin_expect(!!(x),1) +#define unlikely(x) __builtin_expect(!!(x),0) #define inline __inline__ #define always_inline __inline__ __attribute__ ((always_inline)) -- 2.39.5