diff options
| author | H. Peter Anvin <hpa@zytor.com> | 2009-08-25 16:47:16 -0700 |
|---|---|---|
| committer | H. Peter Anvin <hpa@zytor.com> | 2009-08-25 16:47:16 -0700 |
| commit | ab94fcf528d127fcb490175512a8910f37e5b346 (patch) | |
| tree | 6649ea39d0b085dbe143da9474870c46a6b78761 /arch/x86 | |
| parent | e8a2eb47e6ca03d4a4f98f0beef73720c5dddc0c (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')
| -rw-r--r-- | arch/x86/include/asm/irqflags.h | 9 |
1 files changed, 4 insertions, 5 deletions
diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h index c6ccbe7e81a..9e2b952f810 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"); |