Re: black screen troubles trying to boot with Xen Hypervisor grub option

[zithro <slack@xxxxxxxxx>]

On 10 Jul 2023 19:02, Jamie Campbell wrote:
> I tried load_video, serial disable, and diverting I still got black 
> screen but then I tried your suggestion of going into BIOS and just 
> totally suppressing EFI and forcing the system to do strictly legacy 
> stuff and now it actually boots!  I'm curious as to whether the EFI 
> approach could still get to a bootable system, but not curious enough to 
> re-break it and be stuck again.  Thanks for getting me to bootability!
> -Jamie
(Please bottom-post (; )

I had the same problem booting Xen+Debian on UEFI, found a solution, 
maybe it applies to you ?
The problem started when I updated dom0 from Stretch to Buster (at the 
time Buster became stable). With the new version of 
"/etc/grub.d/20_linux_xen", no more boot.
If you compare the old (stretch) and the actual files (from buster on), 
some changes are about multiboot/module to multiboot2/module2 and in the 
check you pointed ($grub_platform isn't "pc").
But as you may have eliminated the $grub_platform problem, maybe it's 
the use of multiboot versus multiboot2 ?
What I would do is move or rename "/etc/grub.d/20_linux_xen", and then 
try with the Stretch version of the file.
(If just renaming, I recommend you to edit the "title" stanzas to better 
identify the menus : you'd have identical lines).
If you want to rambo edit "20_linux_xen" in place, below you will find 
the concerning differences between two versions.
Basically replace ${xen_loader} and ${module_loader} by respectively 
multiboot and module.
I'm still booting a bookworm dom0 with multiboot/module, YMMV !

---
WORKING VERSION
[...]
if [ "\$grub_platform" = "pc" -o "\$grub_platform" = "efi" -o 
"\$grub_platform" = "" ]; then
            xen_rm_opts=
        else
            xen_rm_opts="no-real-mode edd=off"
        fi
	multiboot	${rel_xen_dirname}/${xen_basename} placeholder ${xen_args} 
\${xen_rm_opts}
        echo    '$(echo "$lmessage" | grub_quote)'
	module	${rel_dirname}/${basename} placeholder 
root=${linux_root_device_thisversion} ro ${args}
[...]
        module  --nounzip   ${rel_dirname}/${initrd}
[...]

---
NON-WORKING VERSION
[...]
if [ "\$grub_platform" = "pc" -o "\$grub_platform" = "" ]; then
            xen_rm_opts=
        else
            xen_rm_opts="no-real-mode edd=off"
        fi
	${xen_loader}	${rel_xen_dirname}/${xen_basename} placeholder 
${xen_args} \${xen_rm_opts}
        echo    '$(echo "$lmessage" | grub_quote)'
	${module_loader}	${rel_dirname}/${basename} placeholder 
root=${linux_root_device_thisversion} ro ${args}
[...]
        ${module_loader}        --nounzip   ${rel_dirname}/${initrd}
[...]
if ($grub_file --is-x86-multiboot2 $current_xen); then
        xen_loader="multiboot2"
        module_loader="module2"
    else
        xen_loader="multiboot"
        module_loader="module"
    fi
[...]