I've been building OpenJDK on Solaris and illumos for a while.
This has been moderately successful; illumos distributions now have access to up to date LTS releases, most of which work well. (At least 11 and 17 are fine; 21 isn't quite right.)
There are even some third-party collections of my patches, primarily for Solaris (as opposed to illumos) builds.
I've added another tool. The SunOS jdk builder.
The aim here is to be able to build every single jdk tag, rather than going to one of the existing repos which only have the current builds. And, yes, you could grope through the git history to get to older builds, but one problem with that is that you can't actually fix problems with past builds.
Most of the content is in the jdk-sunos-patches repository. Here there are patches for both illumos and Solaris (they're ever so slightly different) for every tag I've built.
(That's almost every jdk tag since the Solaris/SPARC/Studio removal, and a few before that. Every so often I find I missed one. And there's been the odd bad patch along the way.)
The idea here is to make it easy to build every tag, and to do so on a current system. I've had to add new patches to get some of the older builds to work. The world has changed, we have newer compilers and other tools, and the OS we're building on has evolved. So if someone wanted to start building the jdk from scratch (and remember that you have to build all the versions in sequence) then this would be useful.
I'm using it for a couple of other things.
One is to put back SPARC support on illumos and Solaris. The initial port I did was on x86 only, so I'm walking through older builds and getting them to work on SPARC. We'll almost certainly not get to jdk21, but 17 seems a reasonable target.
The other thing is to enable the test suites, and then run them, and hopefully get them clean. At the moment they aren't, but a lot of that is because many tests are OS-specific and they don't know what Solaris is so get confused. With all the tags, I can bisect on failures and (hopefully) fix them.
