ARM: Add ARMv6 or older __sync_synchronize built-in

* On ARMv6 or older, we do a simulated dsb.
* Move __sync_synchronize into thread.c in libroot
  and use the new arch_atomic.h dsb/dmb defines.
* Gets arm @bootstrap-raw to end of bootstrap.

headers/private/kernel/arch/arm/arch_atomic.h

@@ -9,24 +9,35 @@
 #define _KERNEL_ARCH_ARM_ATOMIC_H
 
 
+#if __ARM_ARCH__ <= 6
+#define dsb() __asm__ __volatile__("mcr p15, 0, %0, c7, c10, 4" \
+    : : "r" (0) : "memory")
+#define dmb() __asm__ __volatile__("mcr p15, 0, %0, c7, c10, 4" \
+    : : "r" (0) : "memory")
+#else
+#define dsb() __asm__ __volatile__("dsb" : : : "memory")
+#define dmb() __asm__ __volatile__("dmb" : : : "memory")
+#endif
+
+
 static inline void
 memory_read_barrier_inline(void)
 {
-	asm volatile ("":::"memory");
+	dmb();
 }
 
 
 static inline void
 memory_write_barrier_inline(void)
 {
-	asm volatile ("":::"memory");
+	dmb();
 }
 
 
 static inline void
 memory_full_barrier_inline(void)
 {
-	asm volatile ("":::"memory");
+	dmb();
 }
 
 
@@ -34,4 +45,5 @@ memory_full_barrier_inline(void)
 #define memory_write_barrier memory_write_barrier_inline
 #define memory_full_barrier memory_full_barrier_inline
 
+
 #endif	// _KERNEL_ARCH_ARM_ATOMIC_H

src/system/libroot/os/arch/arm/atomic.S

@@ -6,6 +6,7 @@
 #include <asm_defs.h>
 #include <arch_config.h>
 
+
 .text
 
 #ifndef ATOMIC_FUNCS_ARE_SYSCALLS
@@ -22,9 +23,6 @@ miss1:	       	ldrex       r12, [r0]
 	        bx          lr
 FUNCTION_END(atomic_add)
 
-
-
-
 /* int atomic_and(int *value, int andValue)
  */
 FUNCTION(atomic_and):
@@ -88,13 +86,6 @@ FUNCTION(atomic_get):
         bx	lr
 FUNCTION_END(atomic_get)
 
-/* void __sync_synchronize(void)
- */
-FUNCTION(__sync_synchronize):
-	dmb
-	bx lr
-FUNCTION_END(__sync_synchronize)
-
 #endif /* ATOMIC_FUNCS_ARE_SYSCALLS */
 
 #ifndef ATOMIC64_FUNCS_ARE_SYSCALLS

src/system/libroot/os/arch/arm/thread.c

@@ -1,4 +1,16 @@
+/*
+ * Copyright 2012-2014, Haiku, Inc. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *		Jerome Duval <[email protected]>
+ *		Alexander von Gluck IV <[email protected]>
+ */
+
+
 #include <OS.h>
+
+#include <arch_atomic.h>
 #include "syscalls.h"
 
 
@@ -7,3 +19,13 @@ find_thread(const char *name)
 {
 	return _kern_find_thread(name);
 }
+
+
+/*
+ * Fill out gcc __sync_synchronize built-in for ARM
+ */
+void
+__sync_synchronize(void)
+{
+	dsb();
+}