Re: [PATCH] ARM: Fix relocation if image end past uncompressed kernel end

[Tony Lindgren <tony@atomide.com>]

* Nicolas Pitre <nicolas.pitre@linaro.org> [110428 01:12]:
> On Wed, 27 Apr 2011, Tony Lindgren wrote:
> 
> > * Tony Lindgren <tony@atomide.com> [110427 05:44]:
> > > We can't overwrite the running code when relocating only a small amount,
> > > say 0x100 or so.
> > > 
> > > There's no need to relocate all the way past the compressed kernel,
> > > we just need to relocate past the size of the code in head.o.
> > > 
> > > Updated patch below using the GOT end instead of the compressed
> > > image end.
> > 
> > Oops, the mov should be movle of course. Updated patch below.
> 
> This is wrong.  You're using r12 before it is fixed up with the 
> proper offset.

Hmm I see. I guess I was thinking it only needs to be fixed up after
the relocation.
 
> And this could simply be fixed with a big enough constant like this:
> 
> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> index 8dab5e3..71fc1d9 100644
> --- a/arch/arm/boot/compressed/head.S
> +++ b/arch/arm/boot/compressed/head.S
> @@ -250,8 +250,11 @@ restart:	adr	r0, LC0
>   * Because we always copy ahead, we need to do it from the end and go
>   * backward in case the source and destination overlap.
>   */
> -		/* Round up to next 256-byte boundary. */
> -		add	r10, r10, #256
> +		/*
> +		 * Round to a 256-byte boundary on the next page. This
> +		 * avoids overwriting ourself if the offset is small.
> +		 */
> +		add	r10, r10, #4096
>  		bic	r10, r10, #255
>  
>  		sub	r9, r6, r5		@ size to copy

Yeah that's what I had originally, but then we'll be potentially
hitting the same bug again once more cache flushing code etc gets
added.

Regards,

Tony