I manually installed the 64-bit Raspberry Pi 3 image onto two partitions (boot: /dev/mmdblk0p16 root:/dev/mmcblk0p17) to my sdcard in a on a NOOBS disk. I made an entry for it in the installed_os.json file on the config partition. I updated the /etc/fstab to reflect these changes.
I noticed there wasn't a /boot/overlays directory on the boot partition. There was also no cmdline.txt. I simply copied these over from my 64-bit gentoo installation (changing root=/dev/mmcblk0p17 in cmdline.txt), in the hopes they might auto-magically work.
Sadly, while the NOOBS setup worked great for me on ALARM-32-bit, and Gentoo 64, when I try to boot it just sticks at u-boot. Is there some command I can give to u-boot to get it to start, or do I need to set up the kernel differently?
How can I get the RPi to boot the kernel properly under these conditions? Do I need to build a custom kernel?