[Bug 1876737] Re: GRUB refuses to boot a 32-bit kernel when in EFI mode

[Dimitri John Ledkov]

Given that 64bit UEFI is there, it means that 64bit kernel can run,
despite using 32bit userspace otherwise.

Why are you using inferior 32bit kernel, with otherwise 32bit userspace?

Please install and use 64bit kernel in such cases, i.e.

sudo dpkg --add-architecture amd64
sudo apt-get update
sudo apt-get install linux-generic:amd64

"works fine" is not true at all, lots of low-level things in Userspace
and kernel are broken when one tries to force booting incompatible
kernel due to different memory layout expectations. If you really want
to fix it, it will need to go upstream to linux kernel to implement
64bit UEFI memory layouts in the 32bit kernel flavour.

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https://bugs.launchpad.net/bugs/1876737

Title:
  GRUB refuses to boot a 32-bit kernel when in EFI mode

Status in grub2 package in Ubuntu:
  Won't Fix

Bug description:
  Also reported at https://savannah.gnu.org/bugs/index.php?58300, but
  doesn't occur in Debian's v2.04 from Bulleye, and only occurred in the
  last few months, so it might be an Ubuntu bug.

  This is grub version 2.02-2ubuntu8.15 as reported by "apt show grub-
  efi"

  GRUB2 fails to boot a 32-bit kernel when started in EFI mode (64-bit
  EFI) on a 64-bit x86 CPU, and gives the message:

  "error: kernel doesn't support 64-bit CPUs"

  However, when a bios grub image made by the same version of grub is
  used, with the same kernel, on the same CPU, everything is normal and
  the kernel boots as expected.

  Hence, I know this kernel will boot on a 64-bit CPU, and with a
  previous version of GRUB 2 (unfortunately I don't know which version),
  it also booted fine in 64-bit mode using GRUB-EFI.

  Running with debug=all doesn't seem to provide any extra useful
  information, as far as I can tell - it just lists sectors being read
  and then freed.

  Any ideas as to what's going on?

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