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authorLinus Torvalds <torvalds@linux-foundation.org>2009-07-02 12:05:10 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-07-02 12:05:10 -0700
commit43644679a1e80f53e6e0155ab75b1093ba3c0365 (patch)
tree8c06f272fe6290c9031adc7f176711af12435902
parent42ca4fb69126dd9d0e25112edca1cacf846aa5c3 (diff)
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 <hpa@zytor.com> Cc: Yinghai Lu <yinghai@kernel.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--arch/x86/include/asm/proto.h11
1 files changed, 9 insertions, 2 deletions
diff --git a/arch/x86/include/asm/proto.h b/arch/x86/include/asm/proto.h
index 49fb3ecf3bb..621f56d7312 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 */