grub-install crashes installer in 18.04 and 18.10, works in 16.04

[Micah]

Trying to install on an old Mac Pro 1,1 (2006) with upgraded CPUs. This model has 64-bit processors but uses a 32-bit EFI, so i have to add a 32-bit .efi entry to /EFI/BOOT on the installer USB, and with recent kernels must add noefi or noexec=off to the linux line on GRUB to boot.

Once running, the 18.04 and 18.10 installer consistently crashes on grub-install, which fails with an error from efibootmgr. This leaves me with a system I can still manually boot to by building a grub entry at the grub command line.

Oddly enough, 16.04 installs and runs fine. Logs during a distribution upgrade from 16.04 to 18.04 suggests this error occurs during that process too but the upgrade completes successfully, with a working grub install that just needs noefi or noexec=off passed on the linux line of the grub entry.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubiquity 18.04.14.6
ProcVersionSignature: Ubuntu 4.15.0-29.31-generic 4.15.18
Uname: Linux 4.15.0-29-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
CasperVersion: 1.394
Date: Mon Dec 24 07:26:42 2018
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed boot=casper quiet splash noefi ---
LiveMediaBuild: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)