The RISC-V [1] and ARM64 [2] ports have been submitted to Phabricator for review. I've also committed various changes and fixes to DTrace in the meantime, such as adding register bindings for ARM64 [3].
Christos [1] https://reviews.freebsd.org/D39884 [2] https://reviews.freebsd.org/D40337 [3] https://cgit.freebsd.org/src/commit/?id=21a16d55cc15b12809b982c2026a26bcf97fe79b
