From: Linus Torvalds Date: Thu, 2 Jul 2009 19:05:10 +0000 (-0700) Subject: x86: fix power-of-2 round_up/round_down macros X-Git-Tag: accepted/tizen/common/20141203.182822~15345 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=43644679a1e80f53e6e0155ab75b1093ba3c0365;p=platform%2Fkernel%2Flinux-arm64.git x86: fix power-of-2 round_up/round_down macros These macros had two bugs: - the type of the mask was not correctly expanded to the full size of the argument being expanded, resulting in possible loss of high bits when mixing types. - the alignment argument was evaluated twice, despite the macro looking like a fancy function (but it really does need to be a macro, since it works on arbitrary integer types) Noticed by Peter Anvin, and with a fix that is a modification of his suggestion (bug noticed by Yinghai Lu). Cc: Peter Anvin Cc: Yinghai Lu Signed-off-by: Linus Torvalds --- diff --git a/arch/x86/include/asm/proto.h b/arch/x86/include/asm/proto.h index 49fb3ec..621f56d 100644 --- a/arch/x86/include/asm/proto.h +++ b/arch/x86/include/asm/proto.h @@ -22,7 +22,14 @@ extern int reboot_force; long do_arch_prctl(struct task_struct *task, int code, unsigned long addr); -#define round_up(x, y) (((x) + (y) - 1) & ~((y) - 1)) -#define round_down(x, y) ((x) & ~((y) - 1)) +/* + * This looks more complex than it should be. But we need to + * get the type for the ~ right in round_down (it needs to be + * as wide as the result!), and we want to evaluate the macro + * arguments just once each. + */ +#define __round_mask(x,y) ((__typeof__(x))((y)-1)) +#define round_up(x,y) ((((x)-1) | __round_mask(x,y))+1) +#define round_down(x,y) ((x) & ~__round_mask(x,y)) #endif /* _ASM_X86_PROTO_H */