3.16.36-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Anton Blanchard <anton@xxxxxxxxx>
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@xxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
[bwh: Backported to 3.16: same issue exists with a different variable in
find_zero()]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
arch/powerpc/include/asm/word-at-a-time.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/powerpc/include/asm/word-at-a-time.h
+++ b/arch/powerpc/include/asm/word-at-a-time.h
@@ -62,7 +62,7 @@ static inline unsigned long find_zero(un
"andc %1,%1,%2\n\t"
"popcntd %0,%1"
: "=r" (leading_zero_bits), "=&r" (trailing_zero_bit_mask)
- : "r" (mask));
+ : "b" (mask));
return leading_zero_bits >> 3;
}
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