Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!olivea!mintaka!bloom-beacon!eru!hagbard!sunic!compuram!pgd
From: pgd@bbt.se
Newsgroups: comp.lang.c
Subject: Re: Ambiguity in definition of setjmp/longjmp makes them much less useful
Message-ID: <1990Oct15.174203.21441@bbt.se>
Date: 15 Oct 90 17:42:03 GMT
References: <1597@redsox.bsw.com> <1990Oct09.143521.24019@unx.sas.com> <1990Oct10.152659.6334@zoo.toronto.edu>
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Lines: 15

In article <1990Oct10.152659.6334@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes:
>In article <1990Oct09.143521.24019@unx.sas.com> sasrer@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.)