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Re: [XEN v1] xen/Arm: Probe the entry point address of an uImage correctly
- To: Ayan Kumar Halder <ayankuma@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- Date: Thu, 8 Dec 2022 23:57:08 +0000
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- Thread-topic: [XEN v1] xen/Arm: Probe the entry point address of an uImage correctly
On 08/12/2022 18:42, Ayan Kumar Halder wrote:
> On 08/12/2022 16:53, Julien Grall wrote:
>> On 08/12/2022 15:24, Michal Orzel wrote:
>>> So the first issue with Zephyr is that it does not support zImage
>>> protocol for arm32.
>>> Volodymyr added support only for Image header for arm64 Zephyr.
>>> I guess this is why Ayan, willing to boot it on Xen (arm32), decided
>>> to add u-boot header.
>>
>> If that's the only reason, then I would rather prefer if we go with
>> zImage for a few reasons:
>> - The zImage protocol has at least some documentation (not perfect)
>> of the expected state of the memory/registers when jumping to the image.
>> - AFAICT libxl is not (yet) supporting uImage. So this means zephyr
>> cannot be loaded on older Xen releases (not great).
>
> I am exploring for a similar option as Volodymyr ie support zimage
> protocol for arm32.
>
> But for that I need some public documentation that explains the zimage
> header format for arm32.
>
> Refer xen/arch/arm/kernel.c
>
> #define ZIMAGE32_MAGIC_OFFSET 0x24
> #define ZIMAGE32_START_OFFSET 0x28
> #define ZIMAGE32_END_OFFSET 0x2c
> #define ZIMAGE32_HEADER_LEN 0x30
>
> #define ZIMAGE32_MAGIC 0x016f2818
>
> Is this documented anywhere ?
zImage (32) is entirely undocumented. What exists is from reverse
engineering. I found this while doing some XTF work, and went right
back to the source - the Linux maintainers.
There are things which Xen does wrong with zImage handling. But I
haven't had time to transcribe my notes into something more coherent and
submit fixes.
~Andrew
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