[PATCH] x86_64: add systemd-boot images

[Jonas Lochmann]

Am Tue, Dec 30, 2025 at 01:43:15PM -0800, schrieb Elliott Mitchell:
> I'm well-aware x86 bootsector booting is being killed.  UEFI is better in
> several ways, but rather higher overhead.  Yet it was still possible to
> purchase current-generation hardware with bootsector support.  I also
> note that is *Intel*, not every company which has ever produced an
> x86-compatible processor.
> 
> Not a strong argument, merely a comment bootsector will be around a long
> time.  OpenWRT x86 images in theory support hardware manufactured in
> 1995, so bootsector support will need to stick around a long time.

I don't have the goal to remove grub based booting - so legacy booting
will continue working.

> > I know the theoretical option of loading grub as first stage in
> > hypervisors and early in physical hardware. I never saw this beeing used
> > in practice.
> 
> I guess this shows we're in different circles.  GRUB-PV is recommended
> for booting Linux images on Xen, most Linux distributions document this
> and have packages available.

I found a description from Debian and it does not sound like a
recommendation but like one possible solution [1]. I am working
with KVM for virtualization.

> Such is quite stable.  Unlike Python, GRUBv2's configuration file syntax
> has been quite stable.  Since 2.0 most changes have been bugfixes and
> module additions.  There was talk of chainloading the VM's version of
> GRUB to ensure compatibility, but to my knowledge that has merely been
> proposed.

The grub version and the provided modules and the modules included by
the grub.cfg differ between distributions. I remember beeing able to
boot Fedora from a f2fs partition using Debians grub, but not using
Fedoras grub. If you load a kernel from a efi partition, then all
distributions should be able to handle it - but then you don't need
grub at all.

> > basic things like efi files the best possible entry point. The linux
> > kernel itself can be executed by the uefi, but then I can not specify
> > the command line parameters while still using the default path.
> > systemd-boot is just used as a helper to fill this gap - read a config
> > file and tell the uefi to load the actual kernel. It is possible to
> > develop an own solution for this step - but it's not worth it.
> 
> There is one key thing which GRUB allows, but this doesn't claim to.
> GRUB allows having multiple kernels installed and choosing between them.
> Not too urgent for most OpenWRT targets, but critical kernel bugs do
> show up.  Being able to keep an older known working kernel around has
> been extremely helpful.

systemd-boot allows that too. With boot counting [2], it can automatically
fall back to an older kernel if the new one has problems.

[1] https://wiki.debian.org/PvGrub
[2] https://uapi-group.org/specifications/specs/boot_loader_specification/#boot-counting