Figure 5.
Debug Procedures for Unexpected Results Unexpected Results in CP --------------------------.., II II • Check that the program is not violating any CP restrictions. Chec* that the f}fogram and {}j)efating system ftmfling on the virtual machine are exactly the same as those
that ran on the real machine.
Use the CP TRACE command to trace CCWs, SIOs, and interrupts.
Look for an error in CCW translation or interrupt reflection . If disk I/O error, use the CP DDR (DASD Dump Restore)
program to print the contents of any disk.
Unexpected results in a virtual machine ----------------------1 l! Check that the program executing on the virtual machine is exactly the same as the one that ran on the real machine.
Make sure that operating system restrictions
are not violated. Use CP TRACE to trace all I/O operations.
Debug Procedures for an ABEND II II Find out why CP abnormally terminated. Examine the PROPSW, INTPR, SVCOPSW, and CPABEND fields in the PSA from the dump. Identify the module that caused the ABEND.
Examine the SAVEAREA, BALRSAVE, and FREESAVE areas of the dump. If I/O operation, examine the real and virtual I/O control blocks. II Determine reason for ABEND from code in ABEND
message DMSABN148T.
Enter debug environment or CP console function mode
to use the commands, to display the PSW, and to examine low storage areas: LASTLMOD and LASTTMOD LASTCMND and PREVCMND LAST EXEC and PREVEXEC and DEVICE Look at the last instruction executed.
Take dump if need be.
Virtual Machine ABEND (other than CMS) ---------------------; II II Examine dump. if there is one.
Use CP commands to examine registers and
control words. Use CP TR,a,CE the '.....j.:; the point where the error occurred.
Debug Procedures for Unexpected Results and an Abend
Part 1. Debugging with Vft/370 17

How to Use VM/370 Facilities to Debug Once the problem and the area where it occurs are identified, you can
gather the information needed to determine the cause of the problem. The
type of information you want to look at varies with the type of problem.
The tools used to gather the information vary depending upon the area in
which the problem occurs. For example, if the problem is a loop
condition, you will want to examine the PSW. For a CP loop, you have to
use the operator's console to display the PSW, but for a virtual machine
loop you can display the PSW via the CP DISPLAY command. The following sections describe specific debugging procedures for the
various error conditions. The procedures will tell you what to do and
what debug tool to use. For example, the procedure may say dump storage
using the CP DUMP command. The procedure will not tell you how to use
the debug tool. Refer to the "CP Commands to Debug the Virtual Machine" and "CMS Debugging Commands" sections for a detailed description of each
debug tool, including how to invoke it.
ABEND
Three types of abnormal terminations (ABEND) can occur on V8/370: CP abends, CMS abends, or virtual machine abends. The following
description provides guidelines for debugging each type of ABEND. When the 'M/370 Control Program abnormally terminates, a dump is taken.
This dump can be directed to tape or printer, cr dynamically allocated
to a direct access storage device. The output device for a CP abend dump is specified by the CP SET command. See the "Abend Dumps" section for a
description of the SET and VMFDUMP commands. Use the dump to determine why the control program terminated and then
determine how to correct the condition. See the "Reading CP Abend Dumps" discussion for detailed information on reading a CP abend dump. REASON FOR THE ABEND: CP will terminate and take an abnormal termIriation dump under-three conditions: 1. Program Check in CP Examine the PROPSi and INTPR fields in the prefix storage area (PSA) to determine the failing module.
2. Module Issuing an SVC 0 Examine the SVC old PSW (SVCOPSW) and abend code (CPABEND) fields
in the Prefix Storage Area to determine the module that issued the SVC 0 and the reason it was issued. CPABEND contains an abnormal termination code. The first three
characters identify the failing module (fer example, abend code TRCOOl indicates DMKTRC is the failing module).
18 IEH iM/37C System Plugrammer=s Guide