From 113fc5a6e8c2288619ff7e8187a6f556b7e0d372 Mon Sep 17 00:00:00 2001
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Tue, 27 Jul 2010 17:01:49 -0700
Subject: x86: Add memory modify constraints to xchg() and cmpxchg()

xchg() and cmpxchg() modify their memory operands, not merely read
them.  For some versions of gcc the "memory" clobber has apparently
dealt with the situation, but not for all.

Originally-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Glauber Costa <glommer@redhat.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Peter Palfrader <peter@palfrader.org>
Cc: Greg KH <gregkh@suse.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Zachary Amsden <zamsden@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: <stable@kernel.org>
LKML-Reference: <4C4F7277.8050306@zytor.com>
---
 arch/x86/include/asm/cmpxchg_32.h | 68 +++++++++++++++++++--------------------
 1 file changed, 34 insertions(+), 34 deletions(-)

(limited to 'arch/x86/include/asm/cmpxchg_32.h')

diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h
index 8859e12dd3cf..c1cf59d72f09 100644
--- a/arch/x86/include/asm/cmpxchg_32.h
+++ b/arch/x86/include/asm/cmpxchg_32.h
@@ -27,20 +27,20 @@ struct __xchg_dummy {
 	switch (size) {							\
 	case 1:								\
 		asm volatile("xchgb %b0,%1"				\
-			     : "=q" (__x)				\
-			     : "m" (*__xg(ptr)), "0" (__x)		\
+			     : "=q" (__x), "+m" (*__xg(ptr))		\
+			     : "0" (__x)				\
 			     : "memory");				\
 		break;							\
 	case 2:								\
 		asm volatile("xchgw %w0,%1"				\
-			     : "=r" (__x)				\
-			     : "m" (*__xg(ptr)), "0" (__x)		\
+			     : "=r" (__x), "+m" (*__xg(ptr))		\
+			     : "0" (__x)				\
 			     : "memory");				\
 		break;							\
 	case 4:								\
 		asm volatile("xchgl %0,%1"				\
-			     : "=r" (__x)				\
-			     : "m" (*__xg(ptr)), "0" (__x)		\
+			     : "=r" (__x), "+m" (*__xg(ptr))		\
+			     : "0" (__x)				\
 			     : "memory");				\
 		break;							\
 	default:							\
@@ -70,14 +70,14 @@ static inline void __set_64bit(unsigned long long *ptr,
 			       unsigned int low, unsigned int high)
 {
 	asm volatile("\n1:\t"
-		     "movl (%0), %%eax\n\t"
-		     "movl 4(%0), %%edx\n\t"
-		     LOCK_PREFIX "cmpxchg8b (%0)\n\t"
+		     "movl (%1), %%eax\n\t"
+		     "movl 4(%1), %%edx\n\t"
+		     LOCK_PREFIX "cmpxchg8b (%1)\n\t"
 		     "jnz 1b"
-		     : /* no outputs */
-		     : "D"(ptr),
-		       "b"(low),
-		       "c"(high)
+		     : "=m" (*ptr)
+		     : "D" (ptr),
+		       "b" (low),
+		       "c" (high)
 		     : "ax", "dx", "memory");
 }
 
@@ -121,21 +121,21 @@ extern void __cmpxchg_wrong_size(void);
 	__typeof__(*(ptr)) __new = (new);				\
 	switch (size) {							\
 	case 1:								\
-		asm volatile(lock "cmpxchgb %b1,%2"			\
-			     : "=a"(__ret)				\
-			     : "q"(__new), "m"(*__xg(ptr)), "0"(__old)	\
+		asm volatile(lock "cmpxchgb %b2,%1"			\
+			     : "=a" (__ret), "+m" (*__xg(ptr))		\
+			     : "q" (__new), "0" (__old)			\
 			     : "memory");				\
 		break;							\
 	case 2:								\
-		asm volatile(lock "cmpxchgw %w1,%2"			\
-			     : "=a"(__ret)				\
-			     : "r"(__new), "m"(*__xg(ptr)), "0"(__old)	\
+		asm volatile(lock "cmpxchgw %w2,%1"			\
+			     : "=a" (__ret), "+m" (*__xg(ptr))		\
+			     : "r" (__new), "0" (__old)			\
 			     : "memory");				\
 		break;							\
 	case 4:								\
-		asm volatile(lock "cmpxchgl %1,%2"			\
-			     : "=a"(__ret)				\
-			     : "r"(__new), "m"(*__xg(ptr)), "0"(__old)	\
+		asm volatile(lock "cmpxchgl %2,%1"			\
+			     : "=a" (__ret), "+m" (*__xg(ptr))		\
+			     : "r" (__new), "0" (__old)			\
 			     : "memory");				\
 		break;							\
 	default:							\
@@ -180,12 +180,12 @@ static inline unsigned long long __cmpxchg64(volatile void *ptr,
 					     unsigned long long new)
 {
 	unsigned long long prev;
-	asm volatile(LOCK_PREFIX "cmpxchg8b %3"
-		     : "=A"(prev)
-		     : "b"((unsigned long)new),
-		       "c"((unsigned long)(new >> 32)),
-		       "m"(*__xg(ptr)),
-		       "0"(old)
+	asm volatile(LOCK_PREFIX "cmpxchg8b %1"
+		     : "=A" (prev),
+		       "+m" (*__xg(ptr))
+		     : "b" ((unsigned long)new),
+		       "c" ((unsigned long)(new >> 32)),
+		       "0" (old)
 		     : "memory");
 	return prev;
 }
@@ -195,12 +195,12 @@ static inline unsigned long long __cmpxchg64_local(volatile void *ptr,
 						   unsigned long long new)
 {
 	unsigned long long prev;
-	asm volatile("cmpxchg8b %3"
-		     : "=A"(prev)
-		     : "b"((unsigned long)new),
-		       "c"((unsigned long)(new >> 32)),
-		       "m"(*__xg(ptr)),
-		       "0"(old)
+	asm volatile("cmpxchg8b %1"
+		     : "=A" (prev),
+		       "+m" (*__xg(ptr))
+		     : "b" ((unsigned long)new),
+		       "c" ((unsigned long)(new >> 32)),
+		       "0" (old)
 		     : "memory");
 	return prev;
 }
-- 
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