[PATCH 07/18] x86: add xadd helper macro

[Jeremy Fitzhardinge]

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>

Add a common xadd implementation.

This has the side effect of generating a bad instruction if you try to
use it on a 64-bit value on a 32-bit system - but don't do that.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
 arch/x86/include/asm/cmpxchg.h |   32 ++++++++++++++++++++++++++++++++
 1 files changed, 32 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h
index a460fa0..b771cdb 100644
--- a/arch/x86/include/asm/cmpxchg.h
+++ b/arch/x86/include/asm/cmpxchg.h
@@ -1,5 +1,37 @@
+#ifndef ASM_X86_CMPXCHG_H
+#define ASM_X86_CMPXCHG_H
+
 #ifdef CONFIG_X86_32
 # include "cmpxchg_32.h"
 #else
 # include "cmpxchg_64.h"
 #endif
+
+
+#define xadd(ptr, inc)							\
+	do {								\
+		switch (sizeof(*(ptr))) {				\
+		case 1:							\
+			asm volatile (LOCK_PREFIX "xaddb %b0, %1\n"	\
+				      : "+r" (inc), "+m" (*(ptr))	\
+				      : : "memory", "cc");		\
+			break;						\
+		case 2:							\
+			asm volatile (LOCK_PREFIX "xaddw %w0, %1\n"	\
+				      : "+r" (inc), "+m" (*(ptr))	\
+				      : : "memory", "cc");		\
+			break;						\
+		case 4:							\
+			asm volatile (LOCK_PREFIX "xaddl %0, %1\n"	\
+				      : "+r" (inc), "+m" (*(ptr))	\
+				      : : "memory", "cc");		\
+			break;						\
+		case 8:							\
+			asm volatile (LOCK_PREFIX "xaddq %q0, %1\n"	\
+				      : "+r" (inc), "+m" (*(ptr))	\
+				      : : "memory", "cc");		\
+			break;						\
+		}							\
+	} while(0)
+
+#endif	/* ASM_X86_CMPXCHG_H */
-- 
1.7.6

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