Re: [PATCH 0/2] xen/efi: Make boot more flexible, especially with GRUB2

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

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On Thu, Jun 26, 2025 at 09:12:53AM +0100, Frediano Ziglio wrote:
> On Wed, Jun 25, 2025 at 9:26 PM Marek Marczykowski-Górecki
> <marmarek@invisiblethingslab.com> wrote:
> >
> > On Tue, Jun 24, 2025 at 09:38:42AM +0100, Frediano Ziglio wrote:
> > > On Tue, Jun 24, 2025 at 9:32 AM Frediano Ziglio
> > > <frediano.ziglio@cloud.com> wrote:
> > > >
> > > > The combination of GRUB2, EFI and UKI allows potentially more flexibility.
> > > > For instance is possible to load xen.efi from a no ESP partition leaving
> > > > a boot loader like GRUB2 taking care of the file loading.
> > > > This however requires some changes in Xen to be less restrictive.
> > > > Specifically for GRUB2 these changes allows the usage of "chainloader"
> > > > command with UKI and reading xen.efi from no ESP (so no DeviceHandle
> > > > set) and usage of "linux" and "initrd" commands to load separately
> > > > the kernel (embedding using UKI) and initrd (using LoadFile2 protocol).
> > >
> > > I was forgetting. If somebody wants to test "linux" and "initrd"
> > > command with these changes be aware that GRUB currently has a problem
> > > passing arguments, I posted a patch, see
> > > https://lists.gnu.org/archive/html/grub-devel/2025-06/msg00156.html.
> > > I also have a workaround for this issue in xen but it would be better
> > > to have a fix in GRUB.
> >
> > Can you tell more how to test this, especially the second variant? When
> > trying to use GRUB linux or linuxefi commands on xen.efi, I get "invalid
> > magic number" error.
> >
> 
> That's weird.
> 
> Be the way. As usual I have a super complicated script that does everything.
> 
> But to simplify:
> - I compile xen (plain upstream plus my patches) with "make -C
> ~/work/xen/xen -j O=normal MAP"

Is there any that would be related to the "invalid magic" error? IIUC
without your patches options will be mangled, but I don't think I get
this far.

> - output xen.efi in "~/work/xen/xen/normal/xen.efi"
> - add configuration and kernel with "./add_sections xen.efi
> xen.unified.efi .config xen.cfg .kernel vmlinuz-xen"
> - boot using patched Grub (or patched Xen, to handle command line, if
> you don't care about command line you can use a stock one), the menu
> entry is
> 
> menuentry 'XenServer (Serial)' {
>         search --label --set root EFI-BOOT
>         linux /boot/xen.unified.efi -- com1=115200,8n1
> console=com1,vga dom0_mem=1232M,max:1232M watchdog dom0_max_vcpus=1-4
> crashkernel=256M,below=4G -- root=LABEL=root-qjhppe ro nolvm
> hpet=disable console=tty0 console=hvc0
>         initrd /boot/initrd.img
> }

All looks quite similar. FWIW my setup is:
https://gitlab.com/xen-project/people/marmarek/xen/-/blob/test-uki/automation/scripts/qemu-smoke-x86-64-efi-uki.sh?ref_type=heads

Booting such UKI from OVMF directly works, as well as with
"chainloader" grub command:

https://gitlab.com/xen-project/people/marmarek/xen/-/pipelines/1891308263

CI uses Grub 2.06 from Debian, but I get the same result with 2.12 from
Fedora too.

> 
> xen.cfg file:
> ----------
> [global]
> default=xen
> 
> [xen]
> ----------
> 
> add_sections file:
> ----------
> #!/usr/bin/env perl
> use strict;
> 
> die if $#ARGV < 1;
> my $in = shift @ARGV;
> my $out = shift @ARGV;
> 
> my $max = 0;
> open(IN, "objdump -h $in |") or die;
> while (<IN>) {
>         next if !/^\s*\d+\s+\S+\s+([0-9a-f]+)\s+([0-9a-f]+)\s+/;
>         my $val = hex($1) + hex($2);
>         $max = $val if $val > $max;
> }
> close(IN);
> 
> sub up($) {
>         my $n = shift;
>         return ($n + 4095) & -4096;
> }
> 
> my @args = ('objcopy');
> 
> my $start = up($max);
> while ($#ARGV >= 1) {
>         my $name = shift;
>         my $fn = shift;
>         push @args, '--add-section', "$name=$fn";
>         push @args, '--change-section-vma', sprintf("%s=%#x", $name, $start);
>         $start += -s $fn;
>         $start = up($start);
> }
> push @args, $in, $out;
> print "Executing @args\n";
> system(@args) == 0 || die "Error!";
> ----------
> 
> My script creates the initrd, builds a full disk for Qemu and launches
> Qemu too with specific options.
> 
> Frediano

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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