Preliminary Computations

Aids for Debugging Assembler, COBOL, and PL/I Programs › COBOL Programs › Preliminary Computations

Preliminary Computations

Before beginning the debugging process, it is recommended that you determine the breakpoints that you want to set and the storage locations that you want to examine.

The first step is to compile the program with appropriate listing options. The following options are recommended:

For VS-COBOL

SOURCE, CLIST or PMAP, DMAP

SOURCE gives a listing of the program source with compiler-assigned line numbers.

CLIST gives a cross reference of the assembler offset of each COBOL statement within the program.

PMAP gives a complete listing of the equivalent assembler code for the entire COBOL program.

CLIST is sufficient for most debugging sessions, but programmers who are familiar with assembler may wish to use the PMAP option.

By examining the register usage in the assembler code, it is sometimes possible to access data fields at a particular breakpoint more efficiently than by using the methods described below using CLIST and DMAP.

Either CLIST or PMAP will also cause the listing of global tables, particularly the TGT which is needed to determine the location of data variables.

DMAP gives a listing of the BL or BLL number and displacement for each field in the WORKING STORAGE and LINKAGE sections.

For COBOL II or LE COBOL

SOURCE, OFFSET or LIST, MAP

SOURCE has the same meaning as for VS-COBOL described above. OFFSET and LIST have the same meanings as CLIST and PMAP, respectively. MAP has the same meaning as the VS-COBOL DMAP option.

Breakpoints

To determine the hexadecimal offset of an executable program instruction at which you want to set a breakpoint, perform the following steps:

Examine the COBOL compiler portion of your listing and record the line number of the statement at which you want to set the breakpoint:

00787 * 00788 * OBTAIN EMPLOYEE DB-KEY IS EMP-DBKEY 00789 * ON ANY-STATUS 00790 MOVE 0 TO DCNUM1 DCNUM2 DCFLG1 DCFLG2 00791 MOVE 0028 TO DML-SEQUENCE 00792 CALL 'IDMSCOBI' USING SUBSCHEMA-CTRL 00793 IDBMSCOM (06) 00794 SR415 00795 EMP-DBKEY 00796 IDBMSCOM (43) 00797 IF NOT ANY-STATUS PERFORM IDMS-STATUS; 00798 ELSE 00799 NEXT SENTENCE. 00800 IF DB-REC-NOT-FOUND 00801 * MAP OUT USING DCTEST01 00802 * MESSAGE IS EMP-NOT-FOUND-MESS 00803 * TO EMP-NOT-FOUND-MESS-END 00804 * DETAIL CURRENT

Examine the condensed listing (CLIST) portion of the COBOL compiler listing, locate the previously recorded COBOL line number, and record its corresponding hexadecimal displacement value:

CONDENSED LISTING . . . . 785 MOVE 001CCC 786 GO 001CD0 790 MOVE 001CD6 791 MOVE 001CEE 792 CALL 001CF4 797 IF 001D3E 797 PERFORM 001D4C 800 IF 001D74 805 MOVE 001D80 806 MOVE 001D98 807 MOVE 001D9E 808 MOVE 001DA4 . . . .

WORKING-STORAGE SECTION variables

To determine the register assignment and offset of WORKING- STORAGE SECTION variables, perform the following steps:

Locate the register assignment portion of the COBOL compiler listing and record the base locator (BL) number that corresponds to each register listed:
```
REGISTER ASSIGNMENT
 REG 6 BL =1
```
Note: For some WORKING-STORAGE or LINKAGE SECTIONfields, there may not be a fixed register which always points to the base locator for linkage (BLL) cell. However, the BL cell is at a given offset from the beginning of the TGT.

For non-LE-compliant compilers, register 13 usually points to the TGT at runtime. For LE-compliant compilers, register 9 usually points to the TGT at runtime.

A copy of the TGT and WORKING STORAGE is allocated in the CA IDMS storage pools for each task at runtime. Therefore, you must not use the TGT or WORKING STORAGE in the program pool.
Locate the data map (DMAP) portion of the COBOL compiler listing and record the displacement value and register assignment for each variable that you want to examine during the debugging process:

DNM=1-364 01 LONGTERM-TEST BL=1 038 DNM=1-364 DS DNM=1-387 01 EMP-DBKEY BL=1 040 DNM=1-387 DS DNM=1-406 01 FIRST-PAGE-SW BL=1 048 DNM=1-406 DS DNM=1-432 88 LESS-THAN-A-PAGE DNM=1-432 . . . DNM=4-276 01 SUBSCHEMA-CTRL BL=1 260 DNM=4-276 DS DNM=4-303 02 PROGRAM-NAME BL=1 260 DNM=4-303 DS DNM=4-325 02 ERROR-STATUS BL=1 268 DNM=4-325 DS DNM=4-350 88 DB-STATUS-OK DNM=4-350 DNM=4-376 88 ANY-STATUS DNM=4-376 DNM=4-399 88 ANY-ERROR-STATUS DNM=4-399 DNM=4-425 88 DB-END-OF-SET DNM=4-425 DNM=4-452 88 DB-REC-NOT-FOUND DNM=4-452 DNM=6-028 02 DBKEY BL=1 26C DNM=6-028 DS DNM=6-043 02 RECORD-NAME BL=1 270 DNM=6-043 DS . .

LINKAGE SECTION variables

To determine the location of LINKAGE SECTION variables, perform the following steps:

Examine the memory map portion of the COBOL compiler listing and locate the hexadecimal displacement values for the TGT and for the base locator for linkage (BLL) cells:

MEMORY MAP TGT 00868 SAVE AREA 00868 SWITCH 008B0 TALLY 008B4 SORT SAVE 008B8 ENTRY-SAVE 008BC . . . TEMP STORAGE-3 00A78 TEMP STORAGE-4 00A78 BLL CELLS 00A78 VLC CELLS 00A8C . .

Perform the following calculation to determine the displacement value for the BLL cells:
```
BLL CELLS - TGT = displacement for BLL cells within TGT

X'A78' - X'868' = X'208'
```
Note: This value will be used later in the runtime phase to locate the actual BLL cells.
Locate the BLL number for the desired LINKAGE SECTION variable from the DMAP portion of the compiler listing:

DNM=14-361     01  PASS-DEPT-INFO          BLL=3    000    DNM=14-361     D
DNM=14-391     02  PASS-DEPT-ID            BLL=3    000    DNM=14-391     D
DNM=14-416     02  PASS-DEPT-INFO-END      BLL=3    004    DNM=14-416     D
DNM=14-444     01  ERROR-DATA              BLL=4    000    DNM=14-444     D
DNM=14-467     02  ERROR-DEPT-ID           BLL=4    000    DNM=14-467     D
DNM=15-000     02  ERROR-MESSAGE-CODE      BLL=4    004    DNM=15-000     D
DNM=15-031     02  ERROR-DATA-END          BLL=4    008    DNM=15-031     D

Save the displacement values of the BLL cells and the BLL numbers of LINKAGE SECTION variables for use during the runtime phase to obtain the absolute address for LINKAGE SECTION values.

You can use the following table to record displacement information before starting a debugger session.