openjdk (openjdk-jdk8u, openjdk-jdk11u, openjdk-jdk17u, openjdk-jdk18u, openjdk-jdk19u, openjdk-jdk20u openjdk-jdk21u)
is a joint venture of FreeBSD & OpenBSD,
that's why it's called bsd-port.
While actually ' wanted to report on (too many) details here, 'just discovering that it will be more profitable for you to pick up the details where they are being processed:
You will get to know a very open-minded and friendly, extremely experienced and very detail-focused team here :
https://github.com/battleblow/jdk17u
the BSD-port is hosted as a GitHub-fork of OpenJDK .
openjdk is not self-contained, which means that you'll always need to create an initial so called bootstrap-jdk if you want to port to a new OS/platform/architecture. the bootstrap-jdk can be from the same jdk-version or from the one before. There are bootstrap-jdks for jdk8, jdk11 and jdk17. To build jdk18 and above, the previous jdk version is required. The makefile will automatically detect an installed compatible (system-linked), bootstrappable jdk. But what is automatic? If not system-linked you can choose your preferred bootstrap-version in the configure-file. First make yourself familiar with openjdk-configuration optional and necessary configure-arguments:
https://github.com/openjdk/jdk/blob/master/doc/building.md
While it is clear, of course, that we all know the java programming language, as a port-developer you will not be surprised that you are usually in the hotspot directory for a jdk-port (which is not a java program) , So don't be surprised if you (please carefully) will get in touch with e.g. asm-code instead of java-code 
if you haven't fallen asleep while reading or maybe already knew that anyway :-), start now boostrapping to your new architecture/platform/OS and add/remove/test/link features in your configure- file..
Please first send general questions / suggestions to:
while you can make a git- PR if you have new features available and while you can send issues/feature-requests described in technical detail of course here :
https://github.com/battleblow/jdk17u/issues
We look forward to getting to know you