Debugging an IBM High Level Assembler (HLASM) program involves systematically identifying and correcting errors in your code. Here’s a step-by-step method and instructions you can follow to debug an assembler program:

Step 1: Prepare the Environment

1. Ensure that you have access to an IBM mainframe or emulator that supports HLASM.
2. Set up the necessary tools for editing, assembling, and debugging the program. Popular tools include TSO/ISPF, TSO/E, or an integrated development environment (IDE) like Compuware’s Xpediter.

Step 2: Review the Source Code

1. Open the source code of your HLASM program using your preferred editor.
2. Carefully review the code to understand its logic and purpose.

Step 3: Assemble the Code

1. Submit the HLASM source code for assembly using a JCL (Job Control Language) script.
2. Check the assembly output for any error messages or warnings. Address them before proceeding.

Step 4: Set Up Debugging

1. Determine the location of the program in memory (load address) after assembly.
2. Open the debugger (e.g., Xpediter) and specify the program load address.

Step 5: Start Debugging

1. Set breakpoints at the desired locations in your program using the debugger’s commands. This will pause execution at those points for analysis.
2. Start the debugging session and let the program run until a breakpoint is hit.

Step 6: Analyze Variables and Registers

1. At each breakpoint, inspect the contents of registers and memory locations. This can help identify incorrect values or data inconsistencies.
2. Compare the expected values with the actual values to pinpoint errors.

Step 7: Single-Step Execution

1. Use the debugger’s single-step or step-into command to execute the program one instruction at a time.
2. Observe the changes in registers, memory, and variables to track how the program is progressing.

Step 8: Monitor Program Flow

1. Continuously track the program’s flow to ensure it follows the expected logic.
2. Identify any unexpected branches, loops, or conditional statements that may lead to errors.

Step 9: Investigate Abnormal Terminations

1. If the program terminates abnormally (e.g., abend), review the error messages and codes provided by the debugger.
2. Use these error messages to diagnose and rectify the issue.

Step 10: Modify and Reassemble

1. Make necessary code corrections based on your analysis during debugging.
2. Assemble the corrected code again and repeat the debugging process if needed.

Step 11: Test Corner Cases

1. Test your program with various input data to ensure it handles different scenarios correctly.
2. Debug any issues that arise during these tests.

Step 12: Document and Verify Fixes

1. Keep detailed records of the debugging process, including identified issues, corrections, and test results.
2. Verify that your program now executes as expected without errors.

Remember, debugging is an iterative process. You might need to go back and forth through these steps until your program is error-free and functions correctly. Patience, thoroughness, and systematic analysis are key to successful debugging.

Step 1: Review the Source Code

1. Open the HLASM source code using your preferred text editor.
2. Understand the logic and purpose of the program.

Step 2: Assemble the Code

1. Submit the HLASM source code for assembly using JCL or the appropriate command.
2. Check the assembler listing output for any error messages or warnings. Address them before proceeding.

Step 3: Set Up Debugging

1. Determine the load address of the program after assembly.
2. Identify key points in your code where you want to inspect registers, memory, or variables.

Step 4: Insert Debugging Code

1. Insert instructions to display or output relevant information during program execution. Common instructions include PRINT or DISPLAY macros to output data to the system log or terminal.
2. Modify your program to include breakpoints or temporary stops to allow you to observe the program’s state.

Step 5: Start Debugging

1. Execute the program with the debugging instructions in place.
2. Monitor the output or logs to observe the behavior of the program.

Step 6: Analyze Variables and Registers

1. Inspect the output logs or terminal messages to view the contents of registers, memory locations, and variables at different points in the program.
2. Compare expected values with actual values to identify discrepancies.

Step 7: Single-Step Execution

1. Manually execute the program one instruction at a time, using the relevant debugger commands available on the mainframe.
2. Keep track of changes in registers, memory, and variables as you step through the code.

Step 8: Monitor Program Flow

1. Continuously track the program’s flow to ensure it follows the expected logic.
2. Identify any unexpected branches, loops, or conditional statements that may lead to errors.

Step 9: Investigate Abnormal Terminations

1. If the program terminates abnormally (e.g., abend), review the error messages and codes provided by the mainframe.
2. Use these error messages to diagnose and rectify the issue.

Step 10: Modify and Reassemble

1. Make necessary code corrections based on your analysis during debugging.
2. Assemble the corrected code again and repeat the debugging process if needed.

Step 11: Test Corner Cases

1. Test your program with various input data to ensure it handles different scenarios correctly.
2. Debug any issues that arise during these tests.

Step 12: Document and Verify Fixes

1. Keep detailed records of the debugging process, including identified issues, corrections, and test results.
2. Verify that your program now executes as expected without errors.

While debugging without a specialized tool like Xpediter may require more manual effort, it’s still a feasible approach to identify and fix issues in your HLASM program.

Here’s an example of how you might use the DC macro to achieve a similar effect to printing or displaying information:

In this example, the DC macro is used to define a character constant (C) named PRINTMSG with the text “This is a debug message”. You can then include this instruction in your program at the desired location to output the message when the program is executed.

However, keep in mind that using DC macros for debugging purposes might not provide as detailed or interactive information as a specialized debugging tool like Xpediter. You would need to strategically place these DC macros in your code to observe the program’s behavior and state at specific points.

If you’re working on a mainframe environment, you might also have access to system commands or utilities that allow you to display information interactively during program execution.

Remember that IBM HLASM has its own unique syntax and set of macros, so it’s important to refer to the IBM HLASM documentation or manuals for a comprehensive list of available macros and their usage.