Part 3. Debugging with VM/SP Part 3, the debugging section, contains the following information:
Introductory Information
How to start debugging
How to use VM/SP facilities to debug abends, unexpected results, loops,
and waits Summary of VM/SP debugging tools
Comparison of CP and eMS debugging tools
Program Product Information
Debugging CP on a virtual machine
Commands useful in de bugging
Internal trace table
Restrictions
Abend dumps
Reading CP abend dumps
Control block summary
Conversational Monitor System Information
Debugging commands
Nucleus load map
Reading CMS abend dumps
Control block summary
Part 3. Debugging with VM/SP 465

Introduction to Debugging
How To Start Debugging
Does a Problem Exist?
466 VM/SP System Programmer's Guide
The VM/SP Program Product manages the resources of a single computer such
that multiple computing systems appear to exist. Each "virtual computing
system&ocq., or virtual machine, is the functional equivalent of an IBM
System/370. Therefore, the person trying to determine the cause of a VM/SP
software problem must consider three separate areas:
1. The Control Program (CP), which controls the resources of the real
machine.
2. The virtual machine operating system running under the control of CP,
such as CMS, RSCS, OS, or DOS. 3. The problem program, which executes under the control of a virtual
machine operating system.
Information explaining how to debug CP or CMS is contained in this book;
information explaining how to debug applications programs is in the VM / SP CMS User's Guide. For information that explains how to use the VM/370 Interactive Problem Control System (IPCS) for debugging, refer to the VM /370 Interactive Problem Control System (IPCS) User's Guide.
If an IPCS problem is caused by a virtual machine operating system (other than
CMS and RSCS), refer to the publications pertaining to that operating system
for specific information. However, use the CP debugging facilities, such as the
CP commands, to perform the recommended debugging procedures discussed
in the other publication.
If it becomes necessary to apply a PTF (Program Temporary Fix) to a compo­
nent of VM/370 or VM/SP, refer to the VM/SP Installation Guide for
detailed information on applying PTFs.
Before you can correct any problem, you must recognize that one exists. Next,
you must identify the problem, collect information, and determine the cause so
that the problem can be fixed. When running VM/SP, you must also decide
whether the problem is in CP, the virtual machine, or the problem program.
A good approach to debugging is:
1. Recognize that a problem exists.
2. Identify the problem type and the area affected.
3. Analyze the data you have available, collect more data if you need it, then
isolate the data that pertains to your problem.
4. Finally, determine the cause of the problem and correct it.
There are four types of problems: