[PATCH] ARM:boot:device tree: Allow the device tree binary to be appended to zImage
John Bonesio
bones at secretlab.ca
Tue Mar 22 05:36:56 EST 2011
Comments below.
- John
On 03/21/2011 11:22 AM, Nicolas Pitre wrote:
> On Mon, 21 Mar 2011, John Bonesio wrote:
>
>> Hi Nicolas,
>>
>> Thanks for the comments. I have a question (below).
>>
> [...]
[snip]
>>>
>>> Now if no dtb was found, or if that code is not configured, then lr
>>> contains garbage and that may have random consequences with the code
>>> that follows, which would explain the reported bad behaviors with this
>>> patch applied even if not configured in the kernel.
>>
>> I'm probably not understanding something here. When I look at the code
>> prior to my patch, it looks like lr is not initialized by head.S.
>
> Exact.
>
>> It also looks like this code makes use of lr when it relocates the
>> code and leaves it uninitialized when it jumps back to 'restart'.
>
> Exact.
>
>> Is this a bug in the previous code too?
>
> No.
>
>> What should lr be initialized to, or should we just be preserving it's
>> value?
>
> No. The problem is that you do use lr further down in your patch when
> adjusting GOT entries, assuming it contains the size of the dtb. If no
> DTB is found then lr contains random stuff that will mess up the GOT for
> .bss references.
Oh! Good catch. Thanks.
>
>> I saw the comment about the performance is different with this patch -
>> something about a pause between 'Uncompressing Linux...' and the kernel
>> boot output. I'm not sure what's going on here. By the time
>> 'Uncompressing Linux...' comes out all relocations and dtb discovery is
>> complete. Do you really think having lr uninitialized would cause this?
>
> Certainly. See above.
>
>
> Nicolas
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