40x PPC relocation issue during boot

40x PPC relocation issue during boot

[Torben Mathiasen]

Looking at the current 2.6 tree, there's an issue when one tries to boot a
zImage image (with or without an attached initrd). This is present in the -benh
tree as well.

In ~/arch/ppc/boot/simple/relocate.S the following snip is present:

..
	li	r9,0xc
	mtlr	r9
#ifdef CONFIG_PPC_MULTIPLATFORM
	/* tell kernel we're prep, by putting 0xdeadc0de at KERNELLOAD,
	 * and tell the kernel to start on the 4th instruction since we
	 * overwrite the first 3 sometimes (which are 'nop').
	 */
	lis	r10,0xdeadc0de@h
	ori	r10,r10,0xdeadc0de@l
	li	r9,0
	stw	r10,0(r9)
#endif
	blr


We jump to the 4th instruction, but for the 40x class of cpu's this inst being
taken into account anymore. 3 nop's are missing from head_4xx.S:

	.text
_GLOBAL(_stext)
_GLOBAL(_start)

	/* Save parameters we are passed.
	*/
	mr	r31,r3
	mr	r30,r4
	...
	...

The requirements of the 3 nops is silly anyway, but the relocation code needs
to be fixed. I haven't done the patch as I'm not sure if any other code will
overwrite the first 3 instructions. I hit this bug on an IBM 405EP dev
platform.

Torben
- 

Re: 40x PPC relocation issue during boot

[Matt Porter]

On Fri, Apr 02, 2004 at 02:07:12PM +0200, Torben Mathiasen wrote:
> Looking at the current 2.6 tree, there's an issue when one tries to boot a
> zImage image (with or without an attached initrd). This is present in the -benh
> tree as well.
> 
> In ~/arch/ppc/boot/simple/relocate.S the following snip is present:

Tom and I discussed this yesterday since it was breaking ppc44x as
well.  He already has a relocate.S patch in akpm's queue to fix
the issue.

-Matt