Messages in this thread Patch in this message | | | From | Kamal Mostafa <> | Subject | [PATCH 3.19.y-ckt 36/54] powerpc: Fix bad inline asm constraint in create_zero_mask() | Date | Mon, 9 May 2016 17:04:55 -0700 |
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3.19.8-ckt21 -stable review patch. If anyone has any objections, please let me know.
---8<------------------------------------------------------------
From: Anton Blanchard <anton@samba.org>
commit b4c112114aab9aff5ed4568ca5e662bb02cdfe74 upstream.
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.
Fixes: d0cebfa650a0 ("powerpc: word-at-a-time optimization for 64-bit Little Endian") Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- 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 5b3a903..7043539 100644 --- a/arch/powerpc/include/asm/word-at-a-time.h +++ b/arch/powerpc/include/asm/word-at-a-time.h @@ -77,7 +77,7 @@ 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; } -- 2.7.4
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