Ambiguity in definition of setjmp/longjmp makes them much less useful

[pgd at bbt.se]

In article <1990Oct10.152659.6334 at zoo.toronto.edu> henry at zoo.toronto.edu (Henry Spencer) writes:
>In article <1990Oct09.143521.24019 at unx.sas.com> sasrer at unx.sas.com (Rodney Radford) writes:
>>I believe (just guessing really) that the original C used 'builtins' for the
>>setjmp/longjmp functions, ie: they special cased them.
>
>Nope.  The original pdp11 C compiler had a predictable stack-frame format
>and could do stack unravelling right.

I am not 100% sure of this, but I think that the original C library
just restored some registers without any fancy unravelling. (r5,sp,pc).
It also kept all variables, except for register variables, in memory.

The original c-library also had nargs(), but that one was a horrible
kludge. (It was looking at the machine instructions to check out how
many bytes were popped from the stack after return from the call instruction.)