Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!RICHTER.MIT.EDU!krowitz
From: krowitz@RICHTER.MIT.EDU (David Krowitz)
Newsgroups: comp.sys.apollo
Subject: Re:  Mystery Error
Message-ID: <8904211343.AA07537@richter.mit.edu>
Date: 21 Apr 89 13:43:32 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 32

yup! "unable to unwind stack" means that somehow your program has
trashed its stack, gotten a fatal error, and then been unable to 
decipher the stack (because you trashed it) in order to give you
a traceback of where the error occurred. Normally, when a program
gets an error you get a traceback that looks something like:

process quit (OS/fault handler)
In routine "VFMT_$FORMAT_NUMBER" line 171
Called from "VFMT_$MAIN" line 552
Called from "VFMT_$S" line 67
Called from "VFMT_STREAMS_ASM:PROCEDURE$"
Called from "LIST_DIR" line 1871
Called from "LIST_DIRECTORY" line 1946
Called from "PM_$CALL"

which tells you where the error occurred. The system gets this by
examining the stack and finding all of the subroutine calls that
were stored on it. The stack also contains local variables (ie.
variables which are not passed in the subroutine call and which
are not in global memory (ie. not in a COMMON block for you
Fortran programmers)). If your program accidentatlly overflows an
array you can wind up clobbering your list of subroutine calls in
addition to your local variables.


 -- David Krowitz

krowitz@richter.mit.edu   (18.83.0.109)
krowitz%richter@eddie.mit.edu
krowitz%richter@athena.mit.edu
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