Update: Actually, you might be able to install 64bit Linux on a Mac with 32bit EFI by including the “fakebios” GRUB2 option. I’ve updated the grub-efi tarball to include this and it works on my Mac Pro. Thanks to Martijn Broeders for this.
To install 64bit Linux onto a Mac using only EFI (and not MBR emulation) then your Mac must have a 64bit EFI. Run the following under OS X to discover whether you have 64bit or only 32bit:
ioreg -l -p IODeviceTree | grep firmware-abi
This should return something like:
| | "firmware-abi" = <"EFI32">
If you see “EFI32” like I do, then it means your machine can’t execute 64bit EFI loaders, so you’re stuck with 32bit, d’oh!. If you see “EFI64” then you should be able to install native 64bit Linux using EFI only, yay!
I discovered this while trying to load 64bit only my Mac Pro at work as an alternative to running Linux with multiple drives and MBR (which doesn’t really work)
This is why the 64bit Fedora efidisk.img never worked on my Mac, but the 32bit one does.