HP OpenVMS systems documentation

Debugger diagnostic messages are displayed in the command view. To display help on a particular message:

1. Choose On Commands from the Help menu of a debugger window.
2. Choose Messages from the list of additional topics.
3. Choose the message identifier from the list of additional topics.

This chapter explains how to:

• Start the debugger ( Section 9.1)
• Continue when your program completes execution ( Section 9.2)
• Rerun the same program from the current debugging session ( Section 9.3)
• Run another program from the current debugging session ( Section 9.4)
• Interrupt program execution and debugger operations ( Section 9.6)
• End a debugging session ( Section 9.7)
• Start the debugger in additional ways for specific purposes ( Section 9.8)
• Debug a program already running in a subprocess or detached process ( Section 9.5)

This section explains the most common way to start the debugger from DCL level ($) and bring your program under debugger control. Section 9.8 explains optional ways to start the debugger.

Starting the kept debugger as explained here enables you to use the Connect (see Section 9.5), Rerun (see Section 9.3), and Run (see Section 9.4) features.

To start the debugger and bring your program under debugger control:

1. Verify that you have compiled and linked the program as explained in Section 1.2.
2. Enter the following command line:

   $ DEBUG/KEEP

   
   By default, the debugger starts up as shown in Figure 9-1. The main window remains empty until you bring a program under debugger control (Step 4). Upon startup, the debugger executes any user-defined initialization file (see Section 13.2).

   Figure 9-1 Debugger at Startup

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3. Bring your program under debugger control using one of the following three techniques:
   • If the program is already running in a subprocess or detached process, use the CONNECT command to bring the program under debugger control. See Section 9.5.
   • Run a specified image (this is the most common technique):
     1. Choose Run Image... from the File menu on the main window. The Run Image dialog lists the executable images in your current directory (see Figure 9-2).
     2. Click on the name of the image to be debugged. The Image: field displays the image name.
     3. If applicable, enter arguments to be passed to the program in the Arguments: field. If you specify a quoted string, you might have to add quotation marks because the debugger strips quotation marks when parsing the string.
     4. Click on OK.

     Figure 9-2 Running a Program by Specifying an Image

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   • Run an image by specifying a DCL command or a symbol for a foreign command:
     1. Choose Run Foreign Command... from the File menu on the main window. The Run Foreign Command dialog is displayed (see Figure 9-3).
     2. Enter the symbol in the Foreign Command: field (such a symbol can provide a shortcut around the directory and file selection process). The foreign command X1, shown in Figure 9-3, has been previously defined:

        $X1 :== RUN MYDISK:[MYDIR.MYSUBDIR]EIGHTQUEENS.EXE

     3. Enter any arguments to be passed with the command in the Arguments: field.
     4. Click on OK.

Figure 9-3 Running a Program by Specifying a Command Symbol

Once the debugger has control of the program, the debugger:

• Displays the program's source code in the main window, as shown in Figure 9-4.
• Suspends execution at the start of the main program. The current-location pointer to the left of the source code shows which line of code will be executed next.

Figure 9-4 Source Display at Startup

The message displayed in the command view indicates that this debugging session is initialized for a C program and that the name of the source module is EIGHTQUEENS.

With certain programs, the debugger sets a temporary breakpoint to suspend program execution at the start of some initialization code, before the main program, and displays the following message:

Type GO to reach MAIN program No source line for address: nnnnnnnn

With some of these programs (for example, Ada programs), the breakpoint enables you to debug the initialization code using full symbolic information. The initialization sets up language-dependent debugger parameters. These parameters control the way the debugger parses names and expressions, formats debugger output, and so on.

You can now debug your program as explained in Chapter 10.

Note the following restrictions about running a program under debugger control:

• You cannot use the procedure in this section to connect the debugger to a running program (see Section 9.8.2).
• To run a program under debugger control over a network link, you must use the debugger client/server interface. See Section 9.9 for more information.

If you try to run a program that does not exist, or misspell the name of a program that does exist, the following error messages are displayed in the DECterm window, rather than in the command view:

%DCL-W-ACTIMAGE, error activating image -CLI-E-IMAGEFNF, image file not found

9.2 When Your Program Completes Execution

When your program completes execution normally during a debugging session, the debugger issues the following message:

'Normal successful completion'

You then have the following options:

• You can rerun your program from the same debugging session (see Section 9.3).
• You can run another program from the same debugging session (see Section 9.4).
• You can end the debugging session (see Section 9.7).

When running the kept debugger (see Section 9.1), you can rerun the program currently under debugger control at any time during a debugging session.

To rerun the program:

1. Choose Rerun Same... from the File menu on the main window. The Rerun dialog is displayed (see Figure 9-5).
2. Enter any arguments to be passed to the program, if required, in the Arguments: field. If you specify a quoted string, you might have to add quotation marks because the debugger strips quotation marks when parsing the string.
3. Choose whether or not to keep the current state of any breakpoints, tracepoints, or static watchpoints that you previously set, activated, or deactivated (see Section 10.4 and Section 10.5.5). Nonstatic watchpoints might or might not be saved, depending on the scope of the variable being watched relative to the main program unit (where execution restarts).
4. Click on OK.

Figure 9-5 Rerunning the Same Program

When you rerun a program, it is in the same initial state as a program that is brought under debugger control as explained in Section 9.1, except for any saved breakpoints, tracepoints, or static watchpoints. The source display and current location pointer are updated accordingly.

When you rerun a program, the debugger uses the same version of the image that is currently under debugger control. To debug a different version of that program (or a different program) from the same debugging session, choose Run Image... or Run Foreign Command.. from the File menu on the main window (see Section 9.1).

9.4 Running Another Program from the Current Debugging Session

You can bring another program under debugger control at any time during a debugging session, if you started the debugger as explained in Section 9.1. Follow the procedure in that section for bringing a program under debugger control (also note the restrictions about using that procedure).

9.5 Debugging an Already Running Program

This section describes how to debug a program that is already running in a subprocess or in a detached process. Perform the following steps:

1. Start the Kept debugger configuration using the DCL command:

   $ DEBUG/KEEP

2. At the DBG> prompt, use the CONNECT command to interrupt the program and bring it under debug control. CONNECT can be used to attach to a program running in a subprocess or attach to a program running in a detached process. Detached processes must meet both of the following requirements:
   • The detached process UIC must be in the same group as your process
   • The detached process must have a CLI mapped
   
   The second requirement effectively means that the program must have been started with a command similar to this:

   $ RUN/DETACH/INPUT=xxx.com SYS$SYSTEM:LOGINOUT

   
   where xxx.com is a command procedure that starts the program with /NODEBUG.
   Once you have connected to the program, the rest of the debugging session is the same as a normal debugger session.

3. When you have finished debugging the program, do either of the following:
   • Use the DISCONNECT command to release debugger control of the program. The program continues execution.
   • Exit the debugger. The program will terminate.

To interrupt program execution during a debugging session, click on the Stop button on the push button view (see Figure 8-3). This is useful if, for example, the program is in an infinite loop.

To abort a debugger operation in progress, click on Stop. This is useful if, for example, the debugger is displaying a long stream of data.

Clicking on Stop does not end the debugging session. Clicking on Stop has no effect when the program is not running or when the debugger is not executing a command.

9.7 Ending a Debugging Session

To end a debugging session and terminate the debugger, choose Exit Debugger from the File menu on the main window, or enter EXIT at the prompt (to avoid confirmation dialogue). This returns control to system level.

To rerun your program from the current debugging session, see Section 9.3.

To run another program from the current debugging session, see Section 9.4.

9.8 Additional Options for Starting the Debugger

In addition to the startup procedure described in Section 9.1, the following options are available for starting the debugger from DCL level ($):

• Start the debugger by running the program to be debugged with the DCL command RUN (see Section 9.8.1).
• Interrupt a running program by pressing Ctrl/Y and then start the debugger using the DCL command DEBUG (see Section 9.8.2).
• Override the debugger's default (HP DECwindows Motif for OpenVMS user interface (see Section 9.8.3) to achieve the following:
  • Display the HP DECwindows Motif for OpenVMS user interface on another workstation
  • Display the command interface in a DECterm window along with any program input/output (I/O)
  • Display the command interface and program I/O in separate DECterm windows

In all cases, before starting the debugger, verify that you have compiled and linked the modules of your program (as explained in Section 1.2).

9.8.1 Starting the Debugger by Running a Program

You can start the debugger and also bring your program under debugger control in one step by entering the DCL command RUN filespec (assuming the program was compiled and linked with the /DEBUG qualifier).

However, you cannot then use the Rerun or Run features explained in Section 9.3 and Section 9.4, respectively. To rerun the same program or run a new program under debugger control, you must first exit the debugger and start it again.

To start the debugger by running a program, enter the DCL command RUN filespec to start the debugger. For example:

$ RUN EIGHTQUEENS

By default, the debugger starts up as shown in Figure 9-4, executing any user-defined initialization file and displaying the program's source code in the main window. The current-location pointer shows that execution is paused at the start of the main program. The debugger sets the language-dependent parameters to the source language of the main program unit.

For more information about debugger startup, see Section 9.1.

9.8.2 Starting the Debugger After Interrupting a Running Program

To bring your program under debugger control:

1. Enter the DCL command RUN/NODEBUG filespec to execute the program without debugger control.
2. Press Ctrl/Y to interrupt the executing program. Control passes to the DCL command interpreter.
3. Enter the DCL command DEBUG to start the debugger.

For example:

$ RUN/NODEBUG EIGHTQUEENS . . . [Ctrl/Y] Interrupt $ DEBUG [starts debugger]

At startup, the debugger displays the main window and executes any user-defined initialization file, and sets the language-dependent parameters to the source language of the module in which execution was interrupted.

To help you determine where execution was interrupted:

1. Look at the main window.
2. Enter the SET MODULES/CALLS command at the command-entry prompt.
3. Display the Call Stack menu on that window to identify the sequence of routine calls on the call stack. The routine at level 0 is the routine in which execution is currently paused (see Section 10.3.1).

When you start the debugger in this manner, you cannot then use the Rerun or Run features explained in Section 9.3 and Section 9.4, respectively. To rerun the same program or run a new program under debugger control, you must first exit the debugger and start it again.

For more information about debugger startup, see Section 9.1.

9.8.3 Overriding the Debugger's Default Interface

By default, if your workstation is running HP DECwindows Motif for OpenVMS, the debugger starts up in the HP DECwindows Motif for OpenVMS user interface, which is displayed on the workstation specified by the HP DECwindows Motif for OpenVMS applicationwide logical name DECW$DISPLAY.

This section explains how to override the debugger's default DECwindows Motif user interface to achieve the following:

• Display the debugger's HP DECwindows Motif for OpenVMS user interface on another workstation
• Display the debugger's command interface in a DECterm window along with any program I/O
• Display the debugger's command interface and program I/O in separate DECterm windows

The logical name DBG$DECW$DISPLAY enables you to override the default interface of the debugger. In most cases, there is no need to define DBG$DECW$DISPLAY because the default is appropriate.

Section 9.8.3.4 provides more information about the logical names DBG$DECW$DISPLAY and DECW$DISPLAY.

9.8.3.1 Displaying the Debugger's HP DECwindows Motif for OpenVMS User Interface on Another Workstation

If you are debugging a HP DECwindows Motif for OpenVMS application that uses most of the screen (or if you are debugging pop-ups in a Motif application), you might find it useful to run the program on one workstation and display the debugger's HP DECwindows Motif for OpenVMS user interface on another. To do so:

1. Enter a logical definition with the following syntax in the DECterm window from which you plan to run the program:

   DEFINE/JOB DBG$DECW$DISPLAY workstation_pathname

   
   The path name for the workstation where the debugger's HP DECwindows Motif for OpenVMS user interface is to be displayed is workstation_pathname. See the description of the SET DISPLAY command in the HP OpenVMS DCL Dictionary for the syntax of this path name.
   It is recommended that you use a job definition. If you use a process definition, it must not have the CONFINE attribute.

2. Run the program from that DECterm window. The debugger's HP DECwindows Motif for OpenVMS user interface is now displayed on the workstation specified by DBG$DECW$DISPLAY. The application's windowing interface is displayed on the workstation where it is normally displayed.
3. Use client/server mode (see Section 9.9.2).

To display the debugger's command interface in a DECterm window, along with any program I/O:

1. Enter the following definition in the DECterm window from which you plan to start the debugger:

   $ DEFINE/JOB DBG$DECW$DISPLAY " "

   
   You can specify one or more spaces between the quotation marks. You should use a job definition for the logical name. If you use a process definition, it must not have the CONFINE attribute.

2. Start the debugger from that DECterm window (see Section 9.1). The debugger's command interface is displayed in the same window.

For example:

$ DEFINE/JOB DBG$DECW$DISPLAY " " $ DEBUG/KEEP Debugger Banner and Version Number DBG>

You can now bring your program under debugger control as explained in Section 9.1.

9.8.3.3 Displaying the Command Interface and Program Input/Output in Separate DECterm Windows

This section describes how to display the debugger's command interface in a DECterm window other than the DECterm window in which you start the debugger. This separate window is useful when using the command interface to debug a screen-oriented program as follows:

• The program's input/output (I/O) is displayed in the window from which you start the debugger.
• The debugger's I/O, including any screen-mode display, is displayed in the separate window.

The effect is the same as entering the SET MODE SEPARATE command at the DBG> prompt on a workstation running VWS rather than HP DECwindows Motif for OpenVMS. (The SET MODE SEPARATE command is not valid when used in a DECterm window.)

The following example shows how to display the debugger's command interface in a separate debugger window titled Debugger.

1. Create the command procedure SEPARATE_WINDOW.COM shown in Example 9-1.

   Example 9-1 Command Procedure SEPARATE_WINDOW.COM

   $ ! Simulates effect of SET MODE SEPARATE from a DECterm window $ ! $ CREATE/TERMINAL/NOPROCESS - /WINDOW_ATTRIBUTES=(TITLE="Debugger",- ICON_NAME="Debugger",ROWS=40)- /DEFINE_LOGICAL=(TABLE=LNM$JOB,DBG$INPUT,DBG$OUTPUT) $ ALLOCATE DBG$OUTPUT $ EXIT $ ! $ ! The command CREATE/TERMINAL/NOPROCESS creates a DECterm $ ! window without a process. $ ! $ ! The /WINDOW_ATTRIBUTES qualifier specifies the window's $ ! title (Debugger), icon name (Debugger), and the number $ ! of rows in the window (40). $ ! $ ! The /DEFINE_LOGICAL qualifier assigns the logical names $ ! DBG$INPUT and DBG$OUTPUT to the window, so that it becomes $ ! the debugger input and output device. $ ! $ ! The command ALLOCATE DBG$OUTPUT causes the separate window $ ! to remain open when you end the debugging session.

2. Execute the command procedure as follows:

   $ @SEPARATE_WINDOW %DCL-I-ALLOC, _MYNODE$TWA8: allocated

   
   A new DECterm window is created with the attributes specified in SEPARATE_WINDOW.COM.

3. Follow the steps in Section 9.8.3.2 to display the debugger's command interface. The interface is displayed in the new window.
4. You can now enter debugger commands in the debugger window. Program I/O is displayed in the DECterm window from which you started the debugger.
5. When you end the debugging session with the EXIT command, control returns to the DCL prompt in the program I/O window but the debugger window remains open.
6. To display the debugger's command interface in the same window as the program's I/O (as in Section 9.8.3.2), enter the following commands:

   $ DEASSIGN/JOB DBG$INPUT $ DEASSIGN/JOB DBG$OUTPUT

   
   The debugger window remains open until you close it explicitly.