From: H. Peter Anvin Date: Tue, 25 Aug 2009 23:47:16 +0000 (-0700) Subject: x86: allow "=rm" in native_save_fl() X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=ab94fcf528d127fcb490175512a8910f37e5b346;p=linux-beck.git 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 --- 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");