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 <[email protected]>
Signed-off-by: H. Peter Anvin <[email protected]>
Cc: Glauber Costa <[email protected]>
Cc: Avi Kivity <[email protected]>
Cc: Peter Palfrader <[email protected]>
Cc: Greg KH <[email protected]>
Cc: Alan Cox <[email protected]>
Cc: Zachary Amsden <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: <[email protected]>
LKML-Reference: <[email protected]>

2 files changed, 54 insertions, 54 deletions

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;
 }
diff --git a/arch/x86/include/asm/cmpxchg_64.h b/arch/x86/include/asm/cmpxchg_64.h
index 485ae415faec..b92f147339f3 100644
--- a/arch/x86/include/asm/cmpxchg_64.h
+++ b/arch/x86/include/asm/cmpxchg_64.h
@@ -26,26 +26,26 @@ extern void __cmpxchg_wrong_size(void);
 	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 %k0,%1"				\
-			     : "=r" (__x)				\
-			     : "m" (*__xg(ptr)), "0" (__x)		\
+			     : "=r" (__x), "+m" (*__xg(ptr))		\
+			     : "0" (__x)				\
 			     : "memory");				\
 		break;							\
 	case 8:								\
 		asm volatile("xchgq %0,%1"				\
-			     : "=r" (__x)				\
-			     : "m" (*__xg(ptr)), "0" (__x)		\
+			     : "=r" (__x), "+m" (*__xg(ptr))		\
+			     : "0" (__x)				\
 			     : "memory");				\
 		break;							\
 	default:							\
@@ -71,27 +71,27 @@ 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 %k1,%2"			\
-			     : "=a"(__ret)				\
-			     : "r"(__new), "m"(*__xg(ptr)), "0"(__old)	\
+		asm volatile(lock "cmpxchgl %k2,%1"			\
+			     : "=a" (__ret), "+m" (*__xg(ptr))		\
+			     : "r" (__new), "0" (__old)			\
 			     : "memory");				\
 		break;							\
 	case 8:								\
-		asm volatile(lock "cmpxchgq %1,%2"			\
-			     : "=a"(__ret)				\
-			     : "r"(__new), "m"(*__xg(ptr)), "0"(__old)	\
+		asm volatile(lock "cmpxchgq %2,%1"			\
+			     : "=a" (__ret), "+m" (*__xg(ptr))		\
+			     : "r" (__new), "0" (__old)			\
 			     : "memory");				\
 		break;							\
 	default:							\