linux-kernel - [PATCH v4 24/24] openrisc: head: Init r0 to 0 on start

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Message-Id: <77f7a25e10627b60b2553817f05b20ec2ec25a28.1487910170.git.shorne@gmail.com>
Date:   Fri, 24 Feb 2017 13:32:44 +0900
From:   Stafford Horne <shorne@...il.com>
To:     Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>
Cc:     linux@...ck-us.net, openrisc@...ts.librecores.org,
        linux-kernel@...r.kernel.org, Stafford Horne <shorne@...il.com>
Subject: [PATCH v4 24/24] openrisc: head: Init r0 to 0 on start

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.

Signed-off-by: Stafford Horne <shorne@...il.com>
---
 arch/openrisc/kernel/head.S | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/openrisc/kernel/head.S b/arch/openrisc/kernel/head.S
index 573e131..e8a1784 100644
--- 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 */
 
-- 
2.9.3