23 Jun
2021
23 Jun
'21
8:08 p.m.
On 23/06/21, silas poulson wrote:
I’m aware line 2238’s famous “You are not expected to
understand
this.” Comment is due to odd PDP-11/45 behaviour.
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.
Do you know if other sections of the C show remnants
of B or the PDP?
Or is it just those spots?
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