From ab94fcf528d127fcb490175512a8910f37e5b346 Mon Sep 17 00:00:00 2001 From: "H. Peter Anvin" Date: Tue, 25 Aug 2009 16:47:16 -0700 Subject: [PATCH] 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 Cc: Gabe Black --- arch/x86/include/asm/irqflags.h | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h index c6ccbe7..9e2b952 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"); -- 2.7.4