powerpc: Fix bad inline asm constraint in create_zero_mask()
authorAnton Blanchard <anton@samba.org>
Fri, 29 Apr 2016 22:29:27 +0000 (08:29 +1000)
committerMichael Ellerman <mpe@ellerman.id.au>
Mon, 2 May 2016 01:10:25 +0000 (11:10 +1000)
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 <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
arch/powerpc/include/asm/word-at-a-time.h

index e4396a7d0f7cf5627a92ea8c07756aba6bc52c7a..4afe66aa1400d5d7e3783e696a0a1de12d3a316c 100644 (file)
@@ -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;
 }