From b4c112114aab9aff5ed4568ca5e662bb02cdfe74 Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Sat, 30 Apr 2016 08:29:27 +1000 Subject: [PATCH] powerpc: Fix bad inline asm constraint in create_zero_mask() In create_zero_mask() we have: addi %1,%2,-1 andc %1,%1,%2 popcntd %0,%1 using the "r" constraint for %2. r0 is a valid register in the "r" set, but addi X,r0,X turns it into an li: li r7,-1 andc r7,r7,r0 popcntd r4,r7 Fix this by using the "b" constraint, for which r0 is not a valid register. This was found with a kernel build using gcc trunk, narrowed down to when -frename-registers was enabled at -O2. It is just luck however that we aren't seeing this on older toolchains. Thanks to Segher for working with me to find this issue. Cc: stable@vger.kernel.org Fixes: d0cebfa650a0 ("powerpc: word-at-a-time optimization for 64-bit Little Endian") Signed-off-by: Anton Blanchard Signed-off-by: Michael Ellerman --- arch/powerpc/include/asm/word-at-a-time.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/powerpc/include/asm/word-at-a-time.h b/arch/powerpc/include/asm/word-at-a-time.h index e4396a7d0f7c..4afe66aa1400 100644 --- a/arch/powerpc/include/asm/word-at-a-time.h +++ b/arch/powerpc/include/asm/word-at-a-time.h @@ -82,7 +82,7 @@ static inline unsigned long create_zero_mask(unsigned long bits) "andc %1,%1,%2\n\t" "popcntd %0,%1" : "=r" (leading_zero_bits), "=&r" (trailing_zero_bit_mask) - : "r" (bits)); + : "b" (bits)); return leading_zero_bits; } -- 2.20.1