Creating pseudo-assembler source for COBOL

Code Debug TSO allows you to interactively debug programs for which source is not available (no source listing in the DDIO), such as old modules which were compiled before Code Debug was acquired. By entering the PSEUDOSOURCE command (commonly abbreviated as PSEUDOSO, PSEUDO, or PS), you can display pseudo-assembler source on the Code Debug TSO Source screen.

This feature enables you to debug main programs and subprograms in much the same way as with Code Debug’s interactive source level debugging. Test session setup and startup is the same as for interactive debugging at the source level. Only minor differences occur during the debugging session.

Pseudo-Source Creation for a Main Program

When program execution begins and the main program does not have source, the session log is automatically displayed with the message NO SOURCE LISTING DATA SET MEMBER FOR procedure-name as shown in the following figure.

No Source Message

You can enter the PSEUDOSOURCE command on the Log screen to request a pseudo-assembler view of the object module. For more information on using the PSEUDOSOURCE command, see the Command-and-syntax-reference. In this example, you would enter the command with the name of the target program as a parameter:

Code Debug TSO would create a pseudo-assembler view of the program and display it on the Source screen as shown in the following figure.

Pseudo-Assembler on Source Screen 

Each line of the pseudo-assembler source view is composed of a hex representation of the instruction on the left, the assembler equivalent in the center, and a character representation on the right. The screen is formatted the same as the standard view presented when a DDIO source listing is available. From this screen, breakpoints can be set and stepping initiated in the same way as when debugging an Assembler application with source.

Pseudo-Source Creation for a Subprogram

When your debugging session begins and your main program does have source, the Source screen is displayed. You can set breakpoints in the regular way on this screen.

Normally, you would set breakpoints in a subprogram by entering a fully qualified breakpoint command or by using the SOURCE or INTERCEPT commands to access the subprogram from this screen. However, if the subprogram did not have source, the message NO SOURCE LISTING INFORMATION FOUND FOR MODULE would be displayed at the top of the source display.

You can use the PSEUDO command at this point (or before entering the SOURCE or INTERCEPT command, if you know no source listing member exists) to bring up the pseudo-assembler view. For example, if the subroutine TRISUB was linked into a multi-CSECT object TRIPAK, the command would be entered as follows:

Debugging a Pseudo-Source Program

The PSEUDO command is used to generate a pseudo-assembler source view of a program. Even if the original source used to create the program was a high-level language such as COBOL or C, the pseudo-source view will be displayed as assembler.

Code Debug TSO analyzes the object code to construct an assembler interpretation. Because this source view is an approximation of the assembler code corresponding to the machine code, you should have assembler knowledge in order to verify and step through the displayed image.

A DDIO source listing and a pseudo-assembler view cannot co-exist for a single program during an Code Debug test session. You can either use the DDIO source listing for a program (with a TEST, INTERCEPT, or initial SOURCE command, for example), or create a pseudo-assembler view for the program by entering the PSEUDO command. The command that is entered first will determine which source is used for the rest of the session.

Unlike when using the INTERCEPT command, when the pseudo-assembler view is first displayed using the PSEUDO command, no breakpoints are set. You must set a breakpoint in order to have execution pause in the desired module.

Before setting a breakpoint, you should verify that the assembler code is accurate. It is possible for Code Debug to have misinterpreted some data elements as instructions. This may cause errors when setting breakpoints or stepping through the code, because Code Debug sometimes needs to place breakpoints on every instruction. To avoid this problem, you need to make Code Debug treat as data the code it previously identified as being an instruction. This is done by entering the SET DATA command for the applicable line. If you need to change the data line back to an instruction, enter the SET INSTR command.

If data is misinterpreted as an instruction, it is possible for Code Debug to lose track of the program’s instruction boundaries. In this situation, you should enter the PSEUDO command with the appropriate OFFSET parameter to indicate where Code Debug should restart its construction of a new assembler view. In the example shown in Pseudo-Assembler on Source Screen(above figure), you need to prevent Code Debug from treating the spaces after the literal TRITAD as a STORE HALFWORD instruction. To do this, make Code Debug analyze the code again, beginning at offset 24, by entering the following command:

The new pseudo-assembler source generated by Code Debug is shown in the following figure.

Regenerated Pseudo-Assembler Source

When you are sure the pseudo-assembler view is accurate, you can start debugging using all the commands you would normally use for a program with a matching DDIO source listing. Primary and line commands can both be used, including BEFORE, AFTER, COUNT, ONETIME, and TRACE. Only limited output will be displayed for data-related commands such as PEEK and KEEP, because Code Debug has no information about a data element’s starting location, size, or data-type. The VERIFY and MEMORY commands can be used to view the underlying storage, and you can enter the GPREGS command to display the current contents of the general purpose registers in a modifiable window at the bottom of your screen. The SHOW ACTIVE command can also be entered to display a summary of register contents, the PSW, and some control block information.

You may still want to use the AT command instead of the PSEUDO command in certain situations, such as when you want to set a breakpoint in a memory location not contained in a loaded module.