Handling run-time errors for C
Code Debug TSO intercepts program abends and prevents the system from producing a dump.
When an abend occurs in a program for which the source is available, execution automatically pauses, the execution arrow points to the offending statement, and a message indicating the action to take is displayed.
The following figure is an example of Code Debug TSO responding to an abend.
Intercepting an Abend
COMMAND ===> SCROLL ===> CSR
S0C4 ABEND ENCOUNTERED, USE "AA SNAP" COMMAND FOR ADDITIONAL INFORMATION
000134 triangle_type > +0 FULLWORD
000041 tarray[triangle_type-1].tricnt > NO ADDR
** END **
------ ------------------------------ SOC4 Abend at TRIMAINC:142/AMODE 31 <>
000139 if (bytesread == 80) /* fread success */
000140 {
000141 triangle_type = tritstc(&work_rec);
000142 tarray??(triangle_type-1??).tricnt++;
=====> tarray[triangle_type-1].tricnt++;
000143 return('n');
000144 }
000145 else /* fread() failed */
000146 {
000147 if ( feof(stream)) /* possibility 2 */
000148 {
000149 return('Y');
000150 }
000151 else
000152 {
To assist you in determining the cause of the abend and how to correct the problem, Code Debug TSO provides the following:
- Enter AA SNAP to display an Abend-AID Snapshot report.
- Use the LOG command to display the diagnostic summary contained in the session log.
- Use the HELP command to display help information about the abend.
- Use debugging commands to investigate the cause of the abend.
Viewing the session log
Code Debug TSO records the cause of the abend, the exact location, and a diagnostic summary in the session log. To look at the session log, enter LOG on the command line of the Source display screen.
An example of the diagnostic summary in the session log is shown in the following figure.
Diagnostic Summary in the Session Log
COMMAND ===> SCROLL ===> CSR
PROGRAM: TRIMAINC MODULE: TRIMAINC COMP DATE: 08/31/2000 COMP TIME:14:31:30
--------------------------------------- SOC4 Abend at TRIMAINC:142/AMODE 31 ->
go
XPD0439 RA105 S0C4 ABEND AT 105C694E REASON CODE 00000004
PSW AT TIME OF ERROR 078D1400 - 905C694E
DATA AT PSW - 06204C20 30E25802 10184A00
GP REGISTERS AT ABEND 0 00000004 1 00142280 2 1BFFFFC8 3 105C68D2
4 801118F4 5 105C69E8 6 001349C8 7 105C6BC8
8 00000001 9 80000000 10 90949A22 11 80111810
12 00135A38 13 001422F8 14 905C693A 15 00000004
AR REGISTERS AT ABEND 0 00F46600 1 00000000 2 00000000 3 00000000
4 00000000 5 00000000 6 00000000 7 00000000
8 00000000 9 00000000 10 00000000 11 00000000
12 00000000 13 00000000 14 00000000 15 00000000
INTERRUPT ADDRESS AT OFFSET 0004F6 IN LOAD MODULE TRIMAINC
*** S0C4 ABEND IN USER MODULE TRIMAINC AT STATE 000142 AT OFFSET 000468
*** ACTIVE APPLICATION MODULE AT TIME OF ABNORMAL TERMINATION IS TRIMAINC ***
*** LAST INTERCEPTED CALL BY MODULE TRIMAINC PRIOR TO TERMINATION WAS MADE TO
MODULE TRITSTC BEFORE STATE 000141 IN PROC analyze_next_rec
*** APPLICATION MODULE CONTROL HIERARCHY AT TIME OF ABNORMAL TERMINATION ***
LVL MODULE ENTRY MEMBER RETURN LOCATION FOR MOST RECENT CALL
1 CODEDEBG
2 CEESTART CEESTART TRIMAINC OFFSET 70080
3 X TRIMAINC MAIN TRIMAINC STATE 000141 analyze_next_rec
4 $PRIVATE TRITSTC TRIMAINC OFFSET 00448
5 ATOI ATOI TRIMAINC
The first part of the diagnostic summary identifies the error message, PSW, data at PSW, general-purpose registers, offset, and the module in which the error occurred.
The last part shows the abend type, module name, statement number, offset, paragraph name, and the failing verb. This information is followed by the module stack that identifies the last call that took place.
If desired, the load modules can also be displayed by entering SHOW MODULES.
Displaying the Abend-AID snapshot report
When an abend occurs in your program during a Code Debug TSO test session, you can display an Abend-AID Snapshot report. This report contains context sensitive diagnostic information. (The report will not contain source support.)
In a non-abending situation, you can request the Snapshot report to display environment specific run-time characteristics and subsystem-related debugging information for VSAM, IDMS, IMS, and Db2 (if you have these Abend-AID options). See the Displaying Environmental Data for more information.
To display the Snapshot report, enter AA SNAP on the command line of any run-time screen. The Snapshot report is formatted according to your terminal size (80 or 133) and written to a temporary data set DD called ABENDAID.
The following figure shows the header page of the Snapshot report:
Abend-AID Snapshot Report Header
|----------------------- CODE DEBUG TSO - BROWSE -----------------------------
| COMMAND ===> SCROLL ===> C
| PROGRAM: TRITST MODULE: TRIMAIN COMP DATE: 08/23/95 COMP TIME: 18:05
| ---------------------------------------------------S0C7 Abend at TRITST:18
| SYS95054.T181542.RA000.FLGDAA1.R0134656 dd ABENDAID line 00
| ********************************* TOP OF DATA ******************************
|1 A B E N D - A I D PAGE 1
|
| MONDAY 16 APR 2023 H17.02.00 R17.02.00
| ***********************************************************************
| * A b e n d - A I D D i a g n o s t i c s *
| ***********************************************************************
| Copyright (C) 1976, 2023, BMC Corporation. Unpublished.
| Rights Reserved Under The Copyright Laws Of The United States.
|
| Licensed for use at: XXXXXX
| YOUR COMPANY NAME
|
| Online Technical Support available at: https://support.bmc.com
|
| JESID - T0883121 OPSYS - z/OS 2.4.0 Model - 8562
| Job - FLGDAA1 DFSMS/MVS - V2R4M0 CP FMID - HBB77C0
| Step - TSOPROC JES2 - z/OS 2.4 System - LPAR
| Time - 09.02.27
+-----------------------------------------------------------------------------
Optionally, you can display a column template at the top of the report by using SET COLS ON. The column template can be useful when viewing records or data. Enter SET COLS OFF (the default) to turn off the column template.
Browsing the snapshot report
The Snapshot report can be browsed using the PF8 (DOWN) and PF7 (UP) keys. You can also bypass the header page and go directly to a specific section of the Snapshot report from the source display. For example, to go directly to the Diagnostic Section, you can enter the following: AA SNAP; FIND 'DIAGNOSTIC'
The Diagnostic Section of the Snapshot report is displayed on the following page, as shown in the following figure.
Snapshot Report Diagnostic Section
COMMAND ===> SCROLL ===> CSR
CHARS 'DIAGNOSTIC' FOUND.
--------------------------------------- SOC4 Abend at TRIMAINC:142/AMODE 31 ->
SYS00251.T091929.RA000.USERID1.R0112882 dd ABENDAID line 000024
**********************
* Diagnostic Section *
**********************
The system completion code of 0C4 is issued when the
program attempts to use storage that is not accessible.
*** List of Probable 0C4 Causes ***
1. Missing or incorrect DD statement -
Check system messages from abending step.
2. Tried to read or write an unopened file.
3. Tried to reference record area before file opened.
4. Indexing or subscripting outside defined limits.
When you have finished viewing the Snapshot report, press PF3 (END) to return to the source display.
If you inadvertently press PF3 (END) while viewing the Snapshot report, you can enter BROWSE ABENDAID on the command line of the source or session log display to redisplay the Snapshot report.
Displaying HELP information
The HELP command can be used to obtain further information to determine the cause and possible resolution of the abend. Any of the most commonly occurring abends (listed as follows) can be entered as a keyword with the HELP command.
SB37 S0C4 S001 S106
SD37 S0C5 S013 S213
The following figure displays HELP information for a S0C7 abend.
HELP Information on S0C7
COMMAND ===> SCROLL ===> CSR
PROGRAM: TRIMAINC MODULE: TRIMAINC COMP DATE: 08/31/2000 COMP TIME:14:31:30
--------------------------------------- SOC4 Abend at TRIMAINC:142/AMODE 31 --
********************************* TOP OF DATA **********************************
S0C4
An invalid main storage address was generated.
POSSIBLE CAUSES
1. Uninitialized index or a runaway index due to a program loop. (This
could also cause a S0C7).
2. An attempt to reference an output area before the data set was opened or
after it was closed.
3. An attempt to execute a module with unresolved link-edit references.
4. The items specified in the USING lists of the calling and called pro-
grams are assumed by the compiler to be identical in order, data type,
and field length. Any discrepancy in this correspondence may result in
a S0C4.
Analyzing the problem
When an abend occurs, you can use Code Debug TSOdebugging commands to investigate the cause of the abend. For example, you can view the contents of the data referenced on the statement causing the abend, analyze the data flow and control structure, and optionally, review the path and data values that lead to the error.
Applying fixes
Even when Code Debug TSOintercepts an abend, you have the opportunity to temporarily apply fixes to the problem and resume execution as if the abend had never occurred. The GO (PF12) command resumes execution. However, there may be times that you will not be able to continue normal program execution until the abend is resolved.
Using all of the information provided by the Abend-AID Snapshot report, you can experiment with possible solutions and test the fixes.
Obtaining a memory dump
If a dump is necessary, the SET DUMP ON command can be issued immediately to direct Code Debug TSOto allow the dump to be written if one of the standard dump DD files (SYSUDUMP, SYSMDUMP, or SYSABEND) is allocated to the test session. The dump file can be dynamically allocated just prior to the issuance of the SET DUMP ON command or could have been preallocated through various methods such as the File Allocation Utility (FAU), the TSO ALLOCATE command, JCL if in Batch Connect, etc. (See Using the File Allocation Utility.)