The INSTALL.arm64 instructions <https://ftp.openbsd.org/pub/OpenBSD/6.5/arm64/INSTALL.arm64> mentions writing a miniroot, opening the boot partition and adding board specific DTB files if your board isn't bootable with stock miniroot. As far as I know, the boot partition (/dev/sdXi) is MSDOS/Fat32 and should be mountable and writeable on GNU/Linux.
I don't have an RPi3 so I cannot test my instructions thoroughly but from what I understand, the RPi 3's DTB files are default and already present in ARM64's miniroot65.fs <https://cdn.openbsd.org/pub/OpenBSD/6.5/arm64/miniroot65.fs> so you shouldn't need to do much more than write the miniroot65.fs to an SD card and boot it. If it doesn't boot, make sure you're using ARM64 miniroot65.fs and not AMD64 miniroot65.fs. SHA256 (miniroot65.fs) = 329ab164b6ad1b2fdd7bb596f5b5e68f07445c26e37f169f0dd7c12b4cb50794 <https://openbsd.cs.toronto.edu/pub/OpenBSD/6.5/arm64/SHA256.sig> A quick google search revealed an Undeadly article about booting OpenBSD on RPi 3 and its limitations <https://undeadly.org/cgi?action=article&sid=20170409123528>, it may be of interest to you. Happy Hacking Le 2019-05-05 à 05:59, Luis P. Mendes a écrit :
Hi, I'd like to have OpenBSD on one of my Raspberry Pi 3B+ boards, but, currently, I have no physical x86_64 OpenBSD installations. <SNIP>
