not strictly the FreeBSD kernel but the rather the BSD emulation layer ( which is quite a significant chunk of xnu ) on top of the Mach "microkernel" ( which un

not strictly the FreeBSD kernel but the rather the BSD emulation layer ( which is quite a significant chunk of xnu ) on top of the Mach "microkernel" ( which until Mach 2.5 still ran in the kernel - Mach 3.0 moved the BSD emulation out to userspace). the "BSD emulation" started with 4.3 BSD and kept in sync with its successors but seems to have diverged quite a bit lately.