KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q69348: CVP May Generate a Trap B with Large Programs Under OS/2 1.30

Article: Q69348
Product(s): See article
Version(s): 2.20 2.30 3.00 3.10 3.11
Operating System(s): OS/2
Keyword(s): ENDUSER | gp fault protection violation | mspl13_basic
Last Modified: 25-FEB-1991

Debugging a large application with CodeView under OS/2 version 1.30
may result in a Trap B system error. Trap B is a "segment not present"
exception, which results from changes that were made to this version
of the operating system.

In version 1.30 of OS/2, the code for DosPTrace() was made swappable,
while in previous versions it was not. DosPTrace() is part of the OS/2
API that allows a parent process to control the execution of a child
process, and to access the child process's memory directly to insert
breakpoints or change data.

Because CodeView relies heavily on DosPTrace(), problems arise if this
code is swapped from memory. The majority of problems occur when
execution reaches a breakpoint while the DosPTrace() code is not
present; control should then jump to code that is not currently in
RAM.

Because large programs (or heavily loaded systems) tend to result in
more swapping, this problem appears much more readily when debugging
large applications.

The only sure workaround for this problem is to turn off swapping
while debugging, but it also may help to increase or free up available
memory. To disable swapping, modify the MEMMAN switch in CONFIG.SYS as
follows:

   MEMMAN=NOSWAP

To increase available memory, either install more memory in the
computer itself or terminate all other unnecessary processes before
debugging (to remove them from memory).

This problem is the result of a design change with OS/2 1.30 and is
not a problem with CodeView. This change is being reconsidered for
future versions of OS/2. New information will be posted here as it
becomes available.

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.