On 23/06/21, silas poulson wrote: Actually there are two different takes on what it is exactly that you're not expected to understand. The "obvious" one in Lions' book, (i.e. saved stack being overwritten when swapping so you have to restore from the special swap-saved stack), but dmr had a different take on it, that it had to do with functions really not being happy if you switch the stack underneath them. You can find dummy variables in the interdata port that make sure the stack frames of some functions (newproc and swtch?) match. So not really a hardware thing but a consequence of the compiler. For the kernel I'm just aware of this one. printf was copied over a number of times (the c compiler also includes a version) but the kernel was never written in B, so i wouldn't expect any B-ness in there otherwise. aap