Implementation of xchg primitives derived from MIT license

[urcu.git] / arch_atomic_x86.h

diff --git a/arch_atomic_x86.h b/arch_atomic_x86.h
new file mode 100644 (file)
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+++ b/arch_atomic_x86.h
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+#ifndef _ARCH_ATOMIC_X86_H
+#define _ARCH_ATOMIC_X86_H
+
+/* 
+ * Copyright (c) 1991-1994 by Xerox Corporation.  All rights reserved.
+ * Copyright (c) 1996-1999 by Silicon Graphics.  All rights reserved.
+ * Copyright (c) 1999-2004 Hewlett-Packard Development Company, L.P.
+ * Copyright (c) 2009      Mathieu Desnoyers
+ *
+ * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
+ * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
+ *
+ * Permission is hereby granted to use or copy this program
+ * for any purpose,  provided the above notices are retained on all copies.
+ * Permission to modify the code and to distribute modified code is granted,
+ * provided the above notices are retained, and a notice that the code was
+ * modified is included with the above copyright notice.
+ *
+ * Code inspired from libatomic_ops-1.2, inherited in part from the
+ * Boehm-Demers-Weiser conservative garbage collector.
+ */
+
+#ifndef BITS_PER_LONG
+#define BITS_PER_LONG  (__SIZEOF_LONG__ * 8)
+#endif
+
+#ifndef _INCLUDE_API_H
+
+/*
+ * Using a isync as second barrier for exchange to provide acquire semantic.
+ * According to atomic_ops/sysdeps/gcc/powerpc.h, the documentation is "fairly
+ * explicit that this also has acquire semantics."
+ * Derived from AO_compare_and_swap() and AO_test_and_set_full().
+ */
+
+static __attribute__((always_inline))
+unsigned int atomic_exchange_32(volatile unsigned int *addr, unsigned int val)
+{
+       unsigned int result;
+
+       __asm__ __volatile__(
+               /* Note: the "xchg" instruction does not need a "lock" prefix */
+               "xchgl %0, %1"
+                       : "=&r"(result), "=m"(*addr)
+                       : "0" (val), "m"(*addr)
+                       : "memory");
+
+       return result;
+}
+
+#if (BITS_PER_LONG == 64)
+
+static __attribute__((always_inline))
+unsigned long atomic_exchange_64(volatile unsigned long *addr,
+                                unsigned long val)
+{
+       unsigned long result;
+
+       __asm__ __volatile__(
+               /* Note: the "xchg" instruction does not need a "lock" prefix */
+               "xchgq %0, %1"
+                       : "=&r"(result), "=m"(*addr)
+                       : "0" (val), "m"(*addr)
+                       : "memory");
+
+       return result;
+}
+
+#endif
+
+static __attribute__((always_inline))
+unsigned long _atomic_exchange(volatile void *addr, unsigned long val, int len)
+{
+       switch (len) {
+       case 4: return atomic_exchange_32(addr, val);
+#if (BITS_PER_LONG == 64)
+       case 8: return atomic_exchange_64(addr, val);
+#endif
+       }
+       /* generate an illegal instruction. Cannot catch this with linker tricks
+        * when optimizations are disabled. */
+       __asm__ __volatile__("ud2");
+       return 0;
+}
+
+#define xchg(addr, v)                                                      \
+       ((__typeof__(*(addr))) _atomic_exchange((addr), (unsigned long)(v), \
+                                               sizeof(*(addr))))
+
+#endif /* #ifndef _INCLUDE_API_H */
+
+#endif /* ARCH_ATOMIC_X86_H */