multi boot - Booting a BIOS bootloader from UEFI mode

I have a Linux setup that I boot in UEFI mode with GRUB. I want to try out OpenBSD, which unfortunately doesn't support GPT or UEFI yet, so I partitioned a drive with a traditional MBR table and installed OpenBSD to that disk using their install CD.

I then attempt to chainload the OpenBSD bootloader in typical GRUB fashion:

menuentry "OpenBSD" {
    insmod part_msdos
    insmod chain
    set root=(hd1,4)
    chainloader +1
}

but I am met with "Invalid EFI File Path".

Is it possible to chainload a BIOS bootloader once you have first booted in EFI mode? I can fall back to selecting the drive to boot from in my motherboard's boot menu, but a GRUB menu entry would obviously be preferable.

Answer

As far as I know, no. While you can use MBR-partitioned disks within UEFI, you cannot use BIOS (MBR) format bootloaders, as they expect to run in a mostly "fresh" system, not inside the UEFI-prepared environment. So GRUB.efi doesn't even attempt to start one; it expects you to give an .efi path only.