On Sun, 2 Jun 2024 at 00:06, Brad Spencer <b...@anduin.eldar.org> wrote: > > Chavdar Ivanov <ci4...@gmail.com> writes: > > [snip] > > > But then wouldn't be > > there a chance that the old userland disagrees with the new kernel? > > > > > As a general statement, that should not be a problem as long as the > kernel has the COMPAT_* options set. > > My own personal experience is that since about 1995, I have encountered > exactly two instances where the newer kernel would not run the older > userland completely correctly assuming the new kernel had the COMPAT_* > options. One was very early where some programs from a 0.9 userland had > trouble with a 1.0 kernel. I never understood what was going on, and a > recompile of the programs fixed them. The second was around the 4.x - > 6.x time frame where a system call was removed completely and old > userland had trouble. So if you were going from 4.x to something more > recent, you might have some problems especially with pkgsrc.
Probably the removal of scheduler activation threads around netbsd-5, which were a very efficient (but unfortunately also very complicated) way to implement userland threads. :) David
