Index: sys/arch/sparc/include/openfirm.h
===================================================================
RCS file: /cvsroot/src/sys/arch/sparc/include/openfirm.h,v
retrieving revision 1.9
diff -u -r1.9 openfirm.h
--- sys/arch/sparc/include/openfirm.h	6 Oct 2015 20:03:05 -0000	1.9
+++ sys/arch/sparc/include/openfirm.h	31 Mar 2016 19:31:48 -0000
@@ -61,6 +61,7 @@
 #define HDQ2CELL_LO(x)	(cell_t)(x)
 #endif /* __sparc_v9__ */
 
+void	OF_init(void);
 int	OF_test(const char *);
 int	OF_test_method(int, const char *);
 void	OF_set_symbol_lookup(void (*)(void *), void (*)(void *));
Index: sys/arch/sparc/sparc/openfirm.c
===================================================================
RCS file: /cvsroot/src/sys/arch/sparc/sparc/openfirm.c,v
retrieving revision 1.20
diff -u -r1.20 openfirm.c
--- sys/arch/sparc/sparc/openfirm.c	27 Mar 2015 06:10:25 -0000	1.20
+++ sys/arch/sparc/sparc/openfirm.c	31 Mar 2016 19:31:48 -0000
@@ -44,6 +44,34 @@
 #include <sys/stdarg.h>
 #endif
 
+#ifdef SUN4V
+#ifdef __arch64__
+#define OFBOUNCE_MAXSIZE 1024
+/* 
+ * Sun4v OpenBoot is not always happy with 64-bit addresses - an example is the
+ * addr parameter in the OF_write() call which can be truncated to a 32-bit
+ * value.
+ * Avoid this behaviour by using a local buffer which is assumed to be mapped
+ * in on a 32-bit address.
+ * Use a mutext to protect access to the buffer from multiple threads.
+ * 
+ */
+kmutex_t ofcall_mtx;
+static char ofbounce[OFBOUNCE_MAXSIZE];
+#endif
+#endif
+
+void
+OF_init(void)
+{
+#ifdef SUN4V
+#ifdef __arch64__
+  KASSERT(((uint64_t)&ofbounce & 0xffffffffUL)==(uint64_t)&ofbounce);
+  mutex_init(&ofcall_mtx, MUTEX_DEFAULT, IPL_NONE);
+#endif	
+#endif
+}
+
 int
 OF_peer(int phandle)
 {
@@ -512,6 +540,15 @@
 	if (len > 1024) {
 		panic("OF_write(len = %d)\n", len);
 	}
+#ifdef SUN4V
+#if __arch64__
+	mutex_enter(&ofcall_mtx);
+	if (len > OFBOUNCE_MAXSIZE) 
+		panic("OF_write(len = %d) exceedes bounce buffer\n", len);
+	memcpy(ofbounce, addr, len);
+	addr = ofbounce;
+#endif	
+#endif
 	args.name = ADR2CELL("write");
 	args.nargs = 3;
 	args.nreturns = 1;
@@ -525,6 +562,11 @@
 		l = args.actual;
 		act += l;
 	}
+#ifdef SUN4V
+#if __arch64__
+	mutex_exit(&ofcall_mtx);
+#endif
+#endif
 	return act;
 }
 
Index: sys/arch/sparc/sparc/promlib.c
===================================================================
RCS file: /cvsroot/src/sys/arch/sparc/sparc/promlib.c,v
retrieving revision 1.44
diff -u -r1.44 promlib.c
--- sys/arch/sparc/sparc/promlib.c	26 Mar 2014 15:55:43 -0000	1.44
+++ sys/arch/sparc/sparc/promlib.c	31 Mar 2016 19:31:48 -0000
@@ -1276,6 +1276,8 @@
 	node = findchosen();
 	OF_getprop(node, "stdin", &promops.po_stdin, sizeof(int));
 	OF_getprop(node, "stdout", &promops.po_stdout, sizeof(int));
+
+	OF_init();
 }
 
 /*