linux-kernel - [PATCH 3.10 168/180] metag: Fix __cmpxchg

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Message-Id: <1471793510-13022-169-git-send-email-w@1wt.eu>
Date:   Sun, 21 Aug 2016 17:31:38 +0200
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     James Hogan <james.hogan@...tec.com>, linux-metag@...r.kernel.org,
        stable@...r.kernel.org#3.9.x-, Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 168/180] metag: Fix __cmpxchg_u32 asm constraint for CMP

From: James Hogan <james.hogan@...tec.com>

commit 6154c187b97ee7513046bb4eb317a89f738f13ef upstream.

The LNKGET based atomic sequence in __cmpxchg_u32 has slightly incorrect
constraints for the return value which under certain circumstances can
allow an address unit register to be used as the first operand of a CMP
instruction. This isn't a valid instruction however as the encodings
only allow a data unit to be specified. This would result in an
assembler error like the following:

  Error: failed to assemble instruction: "CMP A0.2,D0Ar6"

Fix by changing the constraint from "=&da" (assigned, early clobbered,
data or address unit register) to "=&d" (data unit register only).

The constraint for the second operand, "bd" (an op2 register where op1
is a data unit register and the instruction supports O2R) is already
correct assuming the first operand is a data unit register.

Other cases of CMP in inline asm have had their constraints checked, and
appear to all be fine.

Fixes: 6006c0d8ce94 ("metag: Atomics, locks and bitops")
Signed-off-by: James Hogan <james.hogan@...tec.com>
Cc: linux-metag@...r.kernel.org
Cc: <stable@...r.kernel.org> # 3.9.x-
Signed-off-by: Willy Tarreau <w@....eu>
---
 arch/metag/include/asm/cmpxchg_lnkget.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/metag/include/asm/cmpxchg_lnkget.h b/arch/metag/include/asm/cmpxchg_lnkget.h
index 0154e28..2369ad3 100644
--- a/arch/metag/include/asm/cmpxchg_lnkget.h
+++ b/arch/metag/include/asm/cmpxchg_lnkget.h
@@ -73,7 +73,7 @@ static inline unsigned long __cmpxchg_u32(volatile int *m, unsigned long old,
 		      "	DCACHE	[%2], %0\n"
 #endif
 		      "2:\n"
-		      : "=&d" (temp), "=&da" (retval)
+		      : "=&d" (temp), "=&d" (retval)
 		      : "da" (m), "bd" (old), "da" (new)
 		      : "cc"
 		      );
-- 
2.8.0.rc2.1.gbe9624a