Sourceless Debugging with Breakpoint_Assembler user guide

Unlike most examples in this guide, this section does not follow a scenario tied to a particular program and is not designed to correct any specific problem. Instead, it demonstrates how you can use sourceless debugging in your environment. With that in mind, you can either use a program of your own, or continue to use the demonstration program CWDEMASM.

In the previous example, Code Debug CICS trapped the program when it encountered an abend, allowing you to fix the problem. This example demonstrates how to set breakpoints to stop the program to gain access to code and data.

With Code Debug CICS, you can set breakpoints at any instruction in any program, regardless of whether you have source code.

1. From a cleared screen, type XPED CWDEMASM or XPED followed by your program name. Press Enter.

Since you had previously used the PSEUDOSOURCE command in your debugging session, the Source Listing screen (2.L) ( following figure) is displayed. The program is not running, but you can still set breakpoints.

Setting Breakpoints on the Memory Display Screen (2.L)

2. Position the cursor at the COMMAND field, type BEFORE 0, and press Enter. This sets a breakpoint at the first instruction of the program. You can also set other breakpoints from here, but one will be sufficient.

3. Press Clear to return to CICS.

4. Enter XASM or your own transaction ID to execute the test.

As in the last test, Code Debug CICS displays the following Source Listing Screen (2.L). This time, the program is stopped due to your breakpoint. The first instruction in this program, at offset 000000, is a store multiple (STM). Your program may begin with a different command, but it should still be paused at the beginning.

First Breakpoint on the Source Listing Screen (2.L)

While paused, you can set additional breakpoints.

5. If using CWDEMASM, type BEFORE +6A, or check a paper listing to find a valid, executable offset/statement to set a breakpoint in your own application. Press Enter.

6. Once the breakpoint is set, press PF12, or type GO in the COMMAND field and press Enter, to return control to the program. The program will execute until it hits your breakpoint as shown in Source Listing Screen (2.L).

Slow-Motion Execution through Code

While the program is paused at the new breakpoint, you can put the program in slow-motion execution mode to watch as each instruction processes.

1. Type GO 10 1 in the COMMAND field and press Enter to execute the next ten instructions. Since you coded a one second delay, each instruction briefly pauses on the screen.

As shown in the following figure, the CWDEMASM program finally comes to a stop at line 43 (offset +98) after executing the ten instructions.

Line 43 (Offset +98) on the Source Listing Screen (2.L)

Viewing Traced Statements

During your test, Code Debug’s trace facility has been active.

1. To view what has been traced, press PF17, or enter =2.4 in the COMMAND field and press Enter. If multiple facilities have been traced, the Program Trace Directory screen appears. Select your terminal on that screen.

Since a pseudo-listing appears like a real source listing, the lines executed are displayed on the following Program Trace screen (2.4). With the pseudo-listing lines shown, you can see exactly what was executed. You can scroll through the Program Trace screen (2.4).

Program Trace Screen (2.4)

2. Press PF6, or type =2.L in the COMMAND field and press Enter, to return to the Source Listing screen (2.L).

Source Listing Screen (2.L)

Modifying the Logic Path

You can change a sourceless program’s logic path using the offset option of the GOTO command to branch to another location. This is an excellent method to test code that has not been tested or to which other programs are rarely branched.

1. Type GOTO +92, or another offset, in the COMMAND field to change your execution pointer. Press Enter.

As shown in the following figure, the program branched to the new location. If you were to begin single-step execution with the GO command, that instruction would execute.

New Location on the Source Listing Screen (2.L)

Single-Stepping through Code

1. Press PF9, or type GO 1 in the COMMAND field and press Enter, to execute the current instruction.

The following figure shows the instruction was executed. The offset was incremented, and a new instruction is shown.

Instruction Executed on the Source Listing Screen (2.L)

Modifying Registers

Sometimes in testing, you need a different value or address in a register to achieve the desired results. Code Debug CICS gives you this capability.

1. Type SET FOOT REGS in the Command Line and press Enter.

This will turn on the Register Footing. The registers you see on your screen are dynamic; as your program manipulates them, you can see them change. You also have the option of changing them yourself.

2. To change the value of register 0, overtype the current value with 001C0000.

3. To change R5 and R14 to high-values and low-values, overtype the contents of the registers with FFFFFFFF and 00000000 respectively. Press Enter.

The following resulting screen shows the changed values in registers R0, R5, and R14.

Remember to end your session as described in Exiting Code Debug CICS and Ending a Debugging Session. Also, if you renamed CWDEMASM at the start of this section, remember to first undo this change on the List of CSECTs screen (2.6.1).

This concludes sourceless debugging using the PSEUDOSOURCE command to create a pseudo-listing. Remember, by using the PSEUDOSOURCE command to create a pseudo-listing, it is the same as any other testing and debugging session in Code Debug CICS.

Modifying Registers on the Source Listing Screen (2.L0 with Foot Regs.