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

[Frediano Ziglio <frediano.ziglio@xxxxxxxxx>]

On Wed, Jun 25, 2025 at 9:26 PM Marek Marczykowski-Górecki
<marmarek@xxxxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxx> 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"
- 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
}

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