x86: allow "=rm" in native_save_fl()
This is a partial revert off1f029c7bf
. "=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 forf1f029c7bf
was apparently using a broken x86 simulator. [ Impact: performance ] Signed-off-by: H. Peter Anvin <hpa@zytor.com> Cc: Gabe Black <spamforgabe@umich.edu>
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@ -13,14 +13,13 @@ static inline unsigned long native_save_fl(void)
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unsigned long flags;
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/*
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* Note: this needs to be "=r" not "=rm", because we have the
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* stack offset from what gcc expects at the time the "pop" is
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* executed, and so a memory reference with respect to the stack
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* would end up using the wrong address.
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* "=rm" is safe here, because "pop" adjusts the stack before
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* it evaluates its effective address -- this is part of the
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* documented behavior of the "pop" instruction.
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*/
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asm volatile("# __raw_save_flags\n\t"
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"pushf ; pop %0"
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: "=r" (flags)
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: "=rm" (flags)
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: /* no input */
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: "memory");
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