Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ulowell!apollo!r_miller
From: r_miller@apollo.COM (Roger Miller)
Newsgroups: comp.sys.apollo
Subject: Re: Mystery Error (unable to unwind stack)
Message-ID: <42d82721.8b6c@apollo.COM>
Date: 25 Apr 89 14:23:00 GMT
Organization: Apollo Computer, Chelmsford, MA
Lines: 44

David Krowitz has correctly explained the "unwable to unwind stack"
status as resulting from a trashed stack.  This usually results from
writing outside array bounds or through bogus pointers.  Sooner or
later this will generally cause a program fault, and it is during
the processing of this fault that the trashed stack is noticed and
reported.

Unfortunately the unwinding problem hides the first fault, which is
the one you are really interested in.  But all is not lost.  Try
"tb -full":

    $ tb -f
    Process        672 (parent 450, group 0)
    Time           89/04/24.17:38(EDT)
    Program        /r_miller/tb/test.bin
    Status         0304000B: unable to unwind stack because of invalid stack frame (process manager/process fault manager)
    No traceback available
    
    Proc2 Uid       42D4A42B.B0008B6C
    Parent Process  450 (42D2BF40.80008B6C)
    Process Group   0 (42D2BF40.80008B6C)
    Fault Status    00120011: access violation (OS/fault handler)   <-----
    Access Addr     00000000                                        <-----
    IR              C001
    Acc. Info       B041
    User Fault PC   000081EA                                        <-----
    D0-D3:          FFFFFFFF 00004000 00000000 00000000
    D4-D7:          031CFE00 FFFF0000 00000000 035012CC
    A0-A3:          000081EC 0320001C 031D8C04 03180094
    A4-A7:          031CFDF4 00010000 00000000 031CF600
    Supervisor ECB  00000000
    Supervisor SR   0000
    Supervisor PC   00000000

and, lo and behold, there is the original fault.  It was an access violation
at address 81EA, attempting to access address 0.  Where is 81EA?  Ask dde:

    dde> des -loc `va(81ea)
    statement "\\`image(1)\test\trash\15"
    start address: 000081E8
    end address: 000081EB
    file: "//divali/r_miller/tb/test.pas" (89/04/24.16:59)

Now you're well on your way to debugging the problem.