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From: derstad@CIM-VAX.HONEYWELL.COM ("DAVE ERSTAD")
Newsgroups: comp.sys.apollo
Subject: Re:  GUARD FAULT ?
Message-ID: <8912141627.AA09068@umix.cc.umich.edu>
Date: 13 Dec 89 14:18:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 25

>    Does anyone know what a GUARD FAULT is ?.  I got it in a deeply recursive
>    routine on an DN-4000, SR 0.1, bsd4.2.  The same program runs ok on a SUN.

Too much junk on the stack, usually.  Another message you might get is

    unable to unwind stack because of invalid stack frame
                                                                                      
Generally, I have found the "guard fault" is issued when procedures have
large local storage, and the "invalid stack frame" when the recursion
is very, very deep (for example, 10,000 deep).

If you can move some data items which are local to the recursive routine into
a global area, or mark them as STATIC that will help.  

The maximum stack size is 262144 bytes.  This means you can call a procedure
with about a quarter meg of local storage, or recurse twice on a procedure
with about 0.12 MB, recurse three times on 0.08 MB, etc.

I have no idea where the limit comes from.  It seems pretty silly to have
64 MB or whatever of address space and limit applications to such a small
stack space.  Maybe someone at Apollo can shed some light?...

Dave Erstad
Honeywell SSEC
DERSTAD@cim-vax.honeywell.com