Following on from OpenBSD/arm64 on QEMU, it’s not always practical to compile userland software or a new kernel on some systems, particularly small SoCs with limited space and memory – or indeed QEMU, in fear of melting your CPU.
There are two scenarios here – the first, if you are looking for a standard cross-compiler for Aarch64, and the second if you want an OpenBSD-specific environment.
↫ Daniel Nechtan
Exactly what it says on the tin.
Meanwhile, NetBSD just always cross-compiles (even when building e.g. NetBSD/amd64 on NetBSD/amd64) and nothing is unpredictable – NetBSD/amd64 can even be built reproducibly (and the ISO actually is!). It’s OK to say that it’s a choice not to cross-compile, but saying it is not supported because it is unpredictable is not really accurate – it’s just that OpenBSD doesn’t want to.