Add builtin_memcpy helper

We will need it in parasite code where we can't use libc functions.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/memcpy_64.h

+#ifndef __MEMCPY_64_H__
+#define __MEMCPY_64_H__
+
+#include "compiler.h"
+#include "types.h"
+
+static always_inline void *builtin_memcpy(void *to, const void *from, unsigned int n)
+{
+	int d0, d1, d2;
+	asm volatile("rep ; movsl		\n"
+		     "movl %4,%%ecx		\n"
+		     "andl $3,%%ecx		\n"
+		     "jz 1f			\n"
+		     "rep ; movsb		\n"
+		     "1:"
+		     : "=&c" (d0), "=&D" (d1), "=&S" (d2)
+		     : "0" (n / 4), "g" (n), "1" ((long)to), "2" ((long)from)
+		     : "memory");
+	return to;
+}
+
+#endif /* __MEMCPY_64_H__ */