From: utzoo!decvax!decwrl!sun!megatest!fortune!hpda!hplabs!hao!seismo!rocheste!ritcv!mjl
Newsgroups: net.unix-wizards
Title: Re: Questions about nil-pointer dereferences (the "plague")
Article-I.D.: ritcv.255
Posted: Tue Apr  5 09:42:42 1983
Received: Thu Apr  7 04:14:59 1983
References: watcgl.300

The C compiler on V7 had (has?) an interesting problem due to referencing thru
a NIL pointer.  Somewhere in the parsing routines there is a check of a bit in
a structure that maintains parser state information.  Under some weird condi-
tions that I can't remember exactly (I saw this over 2 years ago) a NIL
pointer gets passed to the checking routine.  As it so happens, the bit being
checked is in the correct state because of the particular instructions in
crt0.o.  However, we changed the runtime startoff routines, the bit changed,
and a syntax error was generated where none in fact existed.  Needless to say,
this was an EXTREMELY hard bug to find (and correct).  In fact, we considered
relinking the compiler as a separate I+D program with the standard runtime
startoff in data space just to get around this problem (desperation can lead
you to do strange things).

Mike Lutz (ucbvax!allegra!rochester!ritcv!mjl)