Break the false dependency on the uninitialized value of 'mask' in array_index_mask_nospec(). This potentially allows the CPU to rename the register, avoids reports from tools that can detect uninitialized inline asm arguments, and makes it explicit that this sequence wants the result of (0 - 0 - CARRY).
Reported-by: Andi Kleen <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: "H. Peter Anvin" <[email protected]> Cc: [email protected] Signed-off-by: Dan Williams <[email protected]> --- arch/x86/include/asm/barrier.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h index e1259f043ae9..b572b6a77e12 100644 --- a/arch/x86/include/asm/barrier.h +++ b/arch/x86/include/asm/barrier.h @@ -36,10 +36,10 @@ static inline unsigned long array_index_mask_nospec(unsigned long index, unsigned long size) { - unsigned long mask; + unsigned long mask = 0; - asm ("cmp %1,%2; sbb %0,%0;" - :"=r" (mask) + asm ("cmp %1,%2; sbb $0,%0;" + :"+r" (mask) :"g"(size),"r" (index) :"cc"); return mask;
