openrisc: head: Init r0 to 0 on start

stffrdhrn · stffrdhrn · commit a4d442663580 · 2017-02-25T05:08:47.000+09:00
Originally openrisc spec 0 specified that r0 would be wired to ground.
This is no longer the case.  r0 is not guaranteed to be 0 at init, so we
need to initialize it to 0 before using it.

Also, if we are clearing r0 we cant use r0 to clear itself. Change the
the CLEAR_GPR macro to use movhi for clearing.

Reported-by: Jakob Viketoft &lt;jakob.viketoft@aacmicrotec.com&gt;
Signed-off-by: Stafford Horne &lt;shorne@gmail.com&gt;
diff --git a/arch/openrisc/kernel/head.S b/arch/openrisc/kernel/head.S
@@ -35,7 +35,7 @@
 	l.add	rd,rd,rs
 
 #define CLEAR_GPR(gpr)				\
-	l.or    gpr,r0,r0
+	l.movhi	gpr,0x0
 
 #define LOAD_SYMBOL_2_GPR(gpr,symbol)		\
 	l.movhi gpr,hi(symbol)			;\
@@ -443,6 +443,9 @@ _dispatch_do_ipage_fault:
 	__HEAD
 	.global _start
 _start:
+	/* Init r0 to zero as per spec */
+	CLEAR_GPR(r0)
+
 	/* save kernel parameters */
 	l.or	r25,r0,r3	/* pointer to fdt */
 
