Re: How to boot FreeBSD for arm 32 bit as DomU with u-boot on my ARM Chromebook

[Julien Grall <julien@xxxxxxx>]

Hi,

On 30/12/2023 12:44, Mario Marietto wrote:
> > https://src.fedoraproject.org/repo/pkgs/uboot-tools/u-boot-2017.05.tar.bz2/sha512/be270f9242a72b05463092a022bbabd54996762de1ff23bf7575124ac02e62f49572a4e2f6f571a5019047d40027e56e35593b5cc373c4a5a39b100c3377ba93/
> > This source code has no support for Xen guests. This was only added in 2020. 
> > Can you clarify why you can't use the latest upstream U-boot?
> It's true. I've got the source code of that custom u-boot
> implementation in the wrong place. This is the right place :
>
> https://forum.doozan.com/read.php?3,49039
>
> an u-boot / xen developer suggested to me to explore that site because
> there is the one and only u-boot customized and off the tree version
> that can chainload the freebsd bootloader "ubldr". Unfortunately to
> work the FreeBSD rootfs should be compiled with armV5,but my ARM
> Chromebook works with armV7. I don't know if armV7 is retrocompatible
> with armV5.
> In addition,armV5 has been removed from FreeBSD starting from version
> 12. Infact Balanga used FreeBSD 11.2. FreeBSD 11 has gone EOL for
> several years and it's very hard to make it in a usable state today.
I am not entirely sure. The Arm Arm implies that there are some sort of 
compatibility between Armv5 and Armv7, but they also removed some features.
That said, I don't understand why it would matter that binaries are 
built with Armv5. U-boot should only care about the filesystem type 
(e.g. ZFS). So you should be able to build your own filesystem.
> ---> In fact, there are some missing low-level layers (e.g.
> hypercalls) in order to properly use it for 32-bit domU. I don't know
> if there is support out-of-tree.
>
> @Elliott Mitchell some time ago concerning that point,said :
>
> I've only ever tried arm64, but since arm32 didn't appear to need much
> to be operational I tried to make it possible.  In theory it
> /should/work on arm32, but I've never tried it.  What was missing was
> I had never added it to the configuration and one link was needed.
> Updated "submit" branch has a tiny adjustment. (the only difference is
> the hypercall wrappers, register naming and where the op code goes,
> very simple compatibility)
>
> I'm not experienced,but it seems to me that only a few patches are
> needed to make the job done.
It is it not clear to me whether the last sentence is from you or 
Elliott. Regardless that, I think we are talking about two different 
things. Elliott seems to refer to FreeBSD whereas I was referring to U-boot.
If you plan to use U-boot, then I recommend to first focus on U-boot. 
Then you could look at FreeBSD.
> ---> Do you have a tree with FreeBSD + your patches? I would like to
> check the zImage code.
>
> my patches ? Are you talking about the patches that should have been
> used on the @Elliott Mitchell github ?
I am referring to what ever you are trying.

> https://gitlab.com/ehem/freebsd-src.git
>
> yes,I tried to use his code but I've got the same error "invalid kernel"
[...]

> He said that it should work,but I get the error "invalid kernel".
[...]

> It appears FreeBSD-CURRENT removed the last step converting the kernel
> file to kernel.bin.The patch can be readily rebased, but without
> kernel.bin that doesn't do too much. So,without a rebase of that patch
> the first option is not applicable.
This is likely the culprit. I haven't used FreeBSD for a while, so I 
can't advise on how to fix it. If it were me, I would try to revert the 
commiting removing the step to create kernel.bin.
Cheers,

--
Julien Grall