Problems with recent Debian GNU/Hurd ISO GRUB menu graphics

[Thomas Schmitt]

Hi,

i am discussing with Samuel Thibault two riddling issues of the new
Debian GNU/Hurd ISOs, e.g. this one of about 160 MB:

  
http://ftp.ports.debian.org/debian-ports-cd/hurd-i386/debian-hurd-2017/debian-hurd-2017-i386-NETINST-1.iso

Those ISOs are among the very few which use GRUB for booting via BIOS.
So i think the problems are worth to be discussed here.
I assume that Debian maintainers of GRUB are around, too.

My discussion with Samuel begins at:
  https://lists.debian.org/debian-hurd/2017/06/msg00019.html

----------------------------------------------------------------------
Issue 1:

There is an MBR with probably x86 code after byte 446 where normally
the partition table is located. This yields of course weird results with
partition editors and would expose the code for being damaged by editors.

The MBR is a 1:1 copy of what my Debian 8 amd64 has as
  /usr/lib/grub/i386-pc/boot.img

It gets appended a grub-mkimage result in line 53 of
  
https://anonscm.debian.org/cgit/d-i/debian-installer.git/tree/build/util/x86-image

The concatenated result is then submitted to xorrisofs by option -G without
any options to write a partition table.

Questions:

- Is the state of i386-pc/boot.img intentional ?
  If yes:
  - With what use case is it useful to have an MBR with garbled partition
    table ?
  - Are the bytes 446 to 509 indeed intended to be executed as x86 code ?
    If yes:
    - Are there other MBR templates which do not have code in bytes 446 to
      509 but would nevertheless be suitable for getting appended a result
      from grub-mkimage ?
  If no:
  - What might have went wrong with the production of i386-pc/boot.img ?


----------------------------------------------------------------------
Issue 2:

The GRUB menu of the ISOs when started on Debian 8 amd64 by

  qemu-system-i386 -enable-kvm -m 1024 -hda debian-hurd-2017-i386-NETINST-1.iso

appears with wrong color, pushed up by about 30 percent of image size,
and rolled over horizontally by about 45 percent. Same effect with qemu
option -cdrom rather than -hda.

I can post an image if this cannot be reproduced easily.

The first arrow key press repairs the graphics, but the second arrow key
press brings it back into wrong state. So every second menu choice is
visible and every other item has to be chosen blindly.
(A nice trick is to navigate to the last item and to press arrow once
 in vain. When moving up, the previously bad screens become good and the
 good ones go bad.)


The problem with qemu + SeaBIOS seems well reproducible.
But only some versions of OVMF seem not to work well with the GRUB software
of the Debian 9.0.0 amd64 netinst ISO.
Samuel posted a PNG of a garbled menu which he gets from his local OVMF,
which the debian-hurd mailing list seems to have rejected. It's not to see
in the archives, i fear.
My local OVMF shows the menu ok.

Questions:
- Is it known that GRUB graphics and SeaBIOS or OVMF do not go well
  together ?
- Any ideas how to give the GNU/Hurd ISO a flawlessly working menu
  on SeaBIOS ? (VMs are the main installation target of GNU/Hurd.)


----------------------------------------------------------------------

Have a nice day :)

Thomas