linux-kernel - [PATCH 3.12 090/100] metag: Fix __cmpxchg

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Message-Id: <fd07c45cd9bf8c1e9e54c272d7a12690aba306b6.1471589700.git.jslaby@suse.cz>
Date:   Fri, 19 Aug 2016 09:11:29 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, James Hogan <james.hogan@...tec.com>,
        linux-metag@...r.kernel.org, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 090/100] metag: Fix __cmpxchg_u32 asm constraint for CMP

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

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

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
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 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 0154e2807ebb..2369ad394876 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"
 		      );
-- 
2.9.3