Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!ICAEN.UIOWA.EDU!dbfunk
From: dbfunk@ICAEN.UIOWA.EDU (David B. Funk)
Newsgroups: comp.sys.apollo
Subject: Re: Problems with invalid stack frame
Message-ID: <8812100358.AA05936@umaxc.weeg.uiowa.edu>
Date: 10 Dec 88 03:22:27 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: Iowa Computer Aided Engineering Network, University of Iowa
Lines: 45

WRT posting <914@nic.MR.NET> from pabong@gonzo.eta.com (Paul A. Bong):

>	Occasionally, a program will die with the following error:
>
>?(sh) "./fs_dump" - unable to unwind stack because of invalid stack frame
>  (process manager/process fault manager)

When a process faults (access violation, odd address trap, divide by zero, etc)
the process manager tries to walk back thru the process' stack so as to be
able to store a trace-back, look for resources that need to be released, and
do general cleaning up. It does this by looking for various land-marks that are
stored on the stack, return addresses, stack base pointers, etc. If the program
was very badly behaved and wiped out the information stored on its stack
before dieing, then this information can be lost. When this happens, the fault
manager gives you the above error message.
    So when you see that error message, it indicates a process that was writing
values in memory in places that it shouldn't have. There are many ways this can
happen, here are some of the more common:

1)  The number of arguments in a procedure call don't match the number
        of arguments in the procedure's parameter list. IE calling a subroutine
        with 3 arguments when it expects 4.

2)  The type of arguments in a procedure call don't match the type of
        arguments in the procedure's parameter list. IE calling a subroutine
        with simple variables when it expects arrays.

3)  Indexing outside the bounds of an array. IE trying to store 20 values in
        an array that was dimensioned with 10 elements. Using a negative index
        in an array.

4)  Using an uninitialized or corrupted pointer. Usually caused by a coding
        error in pointer usage, but good pointer code can go wrong when a
        pointer is damaged. Pointer corruption can be caused by one of the
        preceeding problems or by using a pointer returned by a system call
        without first checking the returned status to see if the call worked.

5)  The stack frame was already messed up by the previous running of a
        miscreant program. This is very rare but possible. Try running the
        offending program in a fresh shell.

These kinds of problems can be very hard to catch because they destroy
the incriminating evidence.

Dave Funk
University of Iowa