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

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Date:   Sat, 25 Feb 2017 04:35:04 +0900
From:   Stafford Horne <shorne@...il.com>
To:     Jonas Bonn <jonas@...thpole.se>
Cc:     Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        linux@...ck-us.net, openrisc@...ts.librecores.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 24/24] openrisc: head: Init r0 to 0 on start

On Fri, Feb 24, 2017 at 10:21:50AM +0100, Jonas Bonn wrote:
> On 02/24/2017 05:32 AM, Stafford Horne wrote:
> > 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.
> 
> Use the Reported-by: tag here since you are taking the time to mention him
> in the summary mail.

Right, added.

Thanks.

> Reported-by:  Jakob...
> > 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 */
> 
>