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authorH. Peter Anvin <hpa@zytor.com>2009-08-25 16:47:16 -0700
committerH. Peter Anvin <hpa@zytor.com>2009-08-25 16:47:16 -0700
commitab94fcf528d127fcb490175512a8910f37e5b346 (patch)
tree6649ea39d0b085dbe143da9474870c46a6b78761 /arch/x86/include/asm/irqflags.h
parente8a2eb47e6ca03d4a4f98f0beef73720c5dddc0c (diff)
x86: allow "=rm" in native_save_fl()
This is a partial revert of f1f029c7bfbf4ee1918b90a431ab823bed812504. "=rm" is allowed in this context, because "pop" is explicitly defined to adjust the stack pointer *before* it evaluates its effective address, if it has one. Thus, we do end up writing to the correct address even if we use an on-stack memory argument. The original reporter for f1f029c7bfbf4ee1918b90a431ab823bed812504 was apparently using a broken x86 simulator. [ Impact: performance ] Signed-off-by: H. Peter Anvin <hpa@zytor.com> Cc: Gabe Black <spamforgabe@umich.edu>
Diffstat (limited to 'arch/x86/include/asm/irqflags.h')
-rw-r--r--arch/x86/include/asm/irqflags.h9
1 files changed, 4 insertions, 5 deletions
diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
index c6ccbe7e81ad..9e2b952f810a 100644
--- a/arch/x86/include/asm/irqflags.h
+++ b/arch/x86/include/asm/irqflags.h
@@ -13,14 +13,13 @@ static inline unsigned long native_save_fl(void)
unsigned long flags;
/*
- * Note: this needs to be "=r" not "=rm", because we have the
- * stack offset from what gcc expects at the time the "pop" is
- * executed, and so a memory reference with respect to the stack
- * would end up using the wrong address.
+ * "=rm" is safe here, because "pop" adjusts the stack before
+ * it evaluates its effective address -- this is part of the
+ * documented behavior of the "pop" instruction.
*/
asm volatile("# __raw_save_flags\n\t"
"pushf ; pop %0"
- : "=r" (flags)
+ : "=rm" (flags)
: /* no input */
: "memory");