Installing a 64 bit system with a 32 bit bootloader

Help
1

Hello,

I’m currently trying to install NixOS on a T100TAF, it has a 64 bit CPU but only supports 32 bit bootloaders.

I would use (and managed to install) an i686 image but Hydra doesn’t build i686 packages anymore, meaning that installing anything would take ages.

  • I tried using nixos-rebuild --build-host with my fast x86_64 machine but it sent me back 64-bit binaries, even though I forced nixpkgs.system = 'i686-linux';
  • I tried installing an x86_64 image but the USB refuses to boot altogether, following this guide’s step 4 also led to failures during stage 1 (however it booted).
  • I’m currently tring to migrate from my i686 installation to x86_64 using this guide. I managed to build a generation with an x86_64 kernel but it will refuse to boot (Failed to execute NixOS (\efi\nixos\$HASH-linux-4.14-bzImage.efi): Unsupported)
  • I installed NixOS with UEFI support, I think this means systemd-boot will match my installed architecture and this may cause issues if I manage to migrate to x86_64.

I think multiple choices are available to me:

  • Keep my i686 install and figure out a way to build from my main x86_64 PC. This is most likely the easiest solution but I could not find any relevant help in manuals.
  • Attempt to install from an x86_64 USB again using a bootia32.efi from an i686 USB rather than a random one from the internet
  • Keep attempting to migrate to x86_64
  • Last two options probably still mean incompatibilities in bootloader architecture

What do you think ? What glaring issues can you notice?

Thanks

2

Completely untested, but maybe you could try something like this within your configuration.nix for systemd-boot:

{ pkgs, lib, config, ... }:

{
  system.build.installBootLoader = let
    cfg = config.boot.loader.systemd-boot;
    inherit (config.boot.loader) efi;
  in pkgs.substituteAll {
    src = <nixpkgs/nixos/modules/system/boot/loader/systemd-boot/systemd-boot-builder.py>;
    isExecutable = true;
    inherit (pkgs) python3;
    systemd = pkgs.pkgsi686Linux.systemd.package;
    nix = config.nix.package.out;
    timeout = lib.optionalString (config.boot.loader.timeout != null) config.boot.loader.timeout;
    editor = if cfg.editor then "True" else "False";
    inherit (cfg) consoleMode;
    inherit (efi) efiSysMountPoint canTouchEfiVariables;
  };
}

Eg. you can add this to systemd-boot32.nix or something like that and use imports = [ /path/to/systemd-boot32.nix ]; in your configuration.nix.

This should in theory get you a i686 bootloader while the rest of your system stays at whatever builtins.currentSystem is (or what you specified explicitly).

3

Wow, thanks for taking the time to write that, I’ll attempt to make it work shortly

EDIT:
It seems like that worked out fine but it turns out that systemd-boot in i686 just can’t load the 64 bit kernel “botoload stub”(?), giving me the error message I had previously (Failed to execute NixOS (\efi\nixos\$HASH-linux-4.14-bzImage.efi): Unsupported)
EDIT 2: Yup, just found a random reddit thread mentioning systemd-boot only supports booting stubs from its own architecture. Thanks for helping me pinpoint the issue!

4

The weird and wonderful systems you find nowadays… GRUB might be worth a try as well, since it aims to support a lot more things than systemd-boot. Using a 32-bit grub ought to be a bit simpler as well, since it’s its own package (not tested though):

{
  nixpkgs.overlays = [(self: super: { inherit (super.pkgsi686Linux) grub2_efi; })]
  boot.loader.grub = {
    enable = true;
    efiSupport = true;
    device = "nodev";
  };
}
1 Like
5

That’s exactly where I’m headed, haha
Is the grub.device mean to be nodev?
I still have my 512mb /boot partition, should I keep that ? It doesn’t exactly seem like grub is using it but I’ve booted with EFI support :man_shrugging:
I booted with an x86_64 kernel, woo!
EDIT: And I migrated to a complete x86_64 system, thanks to you two for helping me.

6

Ah, yeah forgot about that, systemd-boot actually is quite minimal and just starts EFI executables, so mixing 32/64 bit doesn’t work here.

7

For EFI boot, yes. It should only be set to something else for legacy (MBR) boot.

Yes, do keep it! That’s where GRUB and its config live.

Yay, congratulations! Glad I could help.

8

This doesn’t work for me sadly on a similar machine with 64 bit Atom CPU and 32 bit UEFI bootloader. If I do as recommended by @lheckemann nixpkgs.overlays = [(self: super: { inherit (super.pkgsi686Linux) grub2_efi; })], it hangs the machine for a bit after “building the system configuration” message, then runs out of memory. I tried to do --build-host root@build-machine.lan, but then it runs out of 16 gigs of memory + 16 gigs of swap on the build machine. --verbose doesn’t give any hints, as all the messages stop after evaluating NixOS. strace just gives neverending amount of reads (if I do strace nix-build <nixpkgs/nixos> -A system). I guess it might cause infinite recursion or just evaluate whole pkgsi686Linux for some reason. BTW, I can totally do nix-shell -p pkgsi686Linux.grub2 on the same machine, and it works.
If I instead do nixpkgs.overlays = [(self: super: { inherit (import <nixpkgs> {system = "i686-linux";}) grub2_efi; })] it builds, but then it fails on GRUB installation, saying that blkid for /boot failed. When I took a closer look on exact perl script, it seems that util-linux that is used doesn’t work (ELF headers of libblkid are incorrect). Yet just doing $ blkid on the system works. How can I force usage of system blkid as opposed to the broken one?
EDIT: actually, it seems that no matter what I try to do, the new util-linux is always broken (invalid ELF header is the error message). (I am on x86_64 kernel but i686 nixpkgs).