From: Anton Blanchard <anton@samba•org>
To: Segher Boessenkool <segher@kernel•crashing.org>,
Michael Ellerman <mpe@ellerman•id.au>,
Paul Mackerras <paulus@samba•org>,
Benjamin Herrenschmidt <benh@kernel•crashing.org>,
felix@linux•vnet.ibm.com, Bill Schmidt <wschmidt@us•ibm.com>
Cc: linuxppc-dev@lists•ozlabs.org
Subject: [PATCH] powerpc: create_zero_mask() has bad inline assembly constraint
Date: Sat, 30 Apr 2016 08:29:27 +1000 [thread overview]
Message-ID: <20160430082927.2111f5ae@kryten> (raw)
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.
Signed-off-by: Anton Blanchard <anton@samba•org>
Cc: <stable@vger•kernel.org>
Fixes: d0cebfa650a0 ("powerpc: word-at-a-time optimization for 64-bit Little Endian")
---
diff --git a/arch/powerpc/include/asm/word-at-a-time.h b/arch/powerpc/include/asm/word-at-a-time.h
index e4396a7..4afe66a 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;
}
next reply other threads:[~2016-04-29 22:29 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-29 22:29 Anton Blanchard [this message]
2016-05-03 12:08 ` powerpc: create_zero_mask() has bad inline assembly constraint Michael Ellerman
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