Bug#1112063: ITP: stubble -- UEFI kernel stub with device-tree loading capability
Hi Johannes,
On Tue, 26 Aug 2025 at 11:13, Johannes Schauer Marin Rodrigues
<josch@debian.org> wrote:
>
> Hi,
>
> Quoting Christopher Obbard (2025-08-25 21:13:23)
> > Package: wnpp
> > Severity: wishlist
> > Owner: Christopher Obbard <obbardc@debian.org>
> > X-Debbugs-Cc: debian-devel@lists.debian.org, Christopher Obbard <obbardc@debian.org>, Tobias Heider <tobias.heider@canonical.com>
> >
> > Package name : stubble
> > Version : v3
> > Upstream Contact: Tobias Heider <tobias.heider@canonical.com>
> > URL : https://github.com/canonical/stubble
> > License : LGPL2.1
> > Programming Lang: C
> > Description : UEFI kernel stub with device-tree loading capability
> >
> > Small Linux kernel EFI boot stub bundling device trees, a CHID database
> > and the kernel. The stub finds a matching device tree based on CHIDs
> > generated from SMBIOS and loads it before executing the embedded
> > kernel.
> >
> > Booting generic Distro images on ARM64 laptops is quite hard due to
> > (currently) no way to tell what hardware the image is running on, or to
> > load the correct device tree from the kernel.
> >
> > Stubble aims to mitigate against this by loading the correct device tree
> > for the laptop at runtime.
> >
> > This package will be useful to build ARM64 Debian images which
> > "just-work" on ARM laptops, specifically Qualcomm X-Elite laptops.
>
> I'm very interested in this as I maintain the Debian integration for the MNT
> Reform and MNT Pocket Reform open hardware laptop. They usually boot via u-boot
> and then either /boot/boot.scr or /boot/extlinux/extlinux.conf which are
> populated by flash-kernel and u-boot-menu with the correct device tree for the
> platform, respectively. We can create images that work on all platforms
> supported by MNT by using u-boots $fdtfile option which allows the
> platform-specific u-boot binary to select the right device tree from an
> otherwise device-agnostic system image.
>
> I already have a POC for EFI booting with EDK2 but one big downside is, that
> using the facilities provided by systemd-ukify, systemd-boot and
> systemd-boot-efi creates a binary which has a device-specific dtb baked into
> the binary making it device specific.
>
> If stubble would allow us to create efi stubs which are identical independent
> of the platform because they select the dtb "at runtime" then I am extremely
> interested in using stubble for the MNT Reform.
>
> Can you confirm that stubble might be providing the functionality we are
> looking for?
Yes, it looks like it will also work perfectly for this use case :-).
The idea is to generate a UKI image in the standard systemd-boot way,
but with the generic "stubble" stub instead of systemd-boot's stub,
kernel, initrd, as well as a list of DTBs to choose from.
This UKI image could then be signed with MOK (or signed upstream...
but that's a little further down the road I guess).
When stubble loads, it detects which DTB to load (currently by
matching CHIDs in stubble to what is running on the hardware).
Thanks!
Chris
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