Yep, it looks like they have a kernel module for handling the Mach subset of syscalls.
> Emulating XNU system calls directly in Linux would have a few benefits, but isn't really workable. Unlike BSD kernels, Linux has no support for foreign system call emulation and having such an extensive and intrusive patchset merged into Linux would be too difficult. Requiring Darling's users to patch their kernels is out of question as well.
The module is amazing and actually kinda terrifying: it grafts in a decent bit of xnu, rather than re-implementing all xnu's features from scratch. This is made a bit more sane because Mach was designed to be extremely portable and has a good abstraction layer for manipulating very low-level stuff like page tables and contexts. But it's still kinda incredible. Part of me wonders if it wouldn't have been easier to graft Linux into xnu instead.
> Emulating XNU system calls directly in Linux would have a few benefits, but isn't really workable. Unlike BSD kernels, Linux has no support for foreign system call emulation and having such an extensive and intrusive patchset merged into Linux would be too difficult. Requiring Darling's users to patch their kernels is out of question as well.
I wonder what such a patch set might look like.