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Re: [Xen-users] ARM: Xen on Vexpress

On 06/04/2014 10:43 AM, Ian Campbell wrote:
> CCing Julien and Stefano who I think have both run Xen on vexpress

Woah, I haven't boot Xen on the vexpress since a while :).

> On Tue, 2014-06-03 at 18:11 +0100, Jeenu Viswambharan wrote:
>> Hi,
>> I've built necessary files and setup uboot and board to boot Xen on
>> Vexpress following the Wiki page. But what I see is u-boot going silent,
>> presumably after it jumps to Xen. My logs are attached.
> Jeenu, Which version of Xen are you building?
> Skimming that wiki page it seems to be describing how to use an older
> version of Xen (like 4.3 or early 4.4 development era) and not a modern
> 4.4 or 4.5 development hypervisor.

The wiki page is based on a Xen 4.4 with a proper multiboot support. I
don't think there was many change in Xen since the page were written
(back in september 2013).

> In particular I'm not sure it is referencing a u-boot which boots the
> kernel in HYP mode (Xen used to carry a hacky workaround for thus, but
> doesn't now) and the stuff about KERNEL_FLASH_ADDRESS (another
> workaround for lack of a boot protocol which is no longer present) isn't
> true any more either.

The wiki page for the Vexpress is referencing a valid u-boot:

I was using it with Xen 4.4 a while ago.

> Julien/Stefano can you confirm and/or deny? I think Linaro tests on
> vexpress so I suppose there are more modern steps somewhere?

We don't have any Linaro tests on the vexpress for Xen. IIRC, it was too
difficult to use U-boot with the validation loop so we chose to only
test Xen on the Arndale & Midway.

>> I've a couple of questions:
>>   - I've noticed from the Vexpress Wiki that the u-boot variable
>>     xen_addr_r is set to 0x80400000, but the xen-uImage is built with
>>     both load and entry addresses as 0x80200000. I also checked the
>>     xen/xen.axf file (from which xen/xen is built), and its entry too is
>>     0x80200000. I'm afraid to ask if this a typo/bit rot in the Wiki?
> I'm not sure, but I think in general it is OK for these to differ,
> u-boot will relocate from the load address to the address requested by
> the header as part of booting. So long as it is in RAM and 2MB aligned I
> don't think the actual address matters too much.

the xen-uImage will be loaded at the xen_addr_r, then U-boot will
extract the image and load at 0x802000000.

We don't care about the ELF entry. It's a hack for the model to be able
to directly run Xen. Now we require to boot with either bootwrapper or
U-boot, so I think we can get a rid of it. See:

"# XXX: VE model loads by VMA so instead of
 # making a proper ELF we link with LMA == VMA and adjust crudely


Julien Grall

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