Symbol ambiguities can occur when a symbol (for example, a variable name X) is defined in more than one routine or other program unit.

In most cases, the debugger automatically resolves symbol ambiguities. First, it uses the scope and visibility rules of the currently set language. In addition, because the debugger permits you to specify symbols in arbitrary modules (to set breakpoints and so on), the debugger uses the ordering of routine calls on the call stack to resolve symbol ambiguities.

In some cases, however, the debugger might respond as follows when you specify a symbol that is defined multiple times:

• It might issue a "symbol not unique" message because it is not able to determine the particular declaration of the symbol that you intended.
• It might reference the symbol declaration that is visible in the current scope, not the one you want.

To resolve such problems, you must specify a scope where the debugger should search for the particular declaration of the symbol:

• If the different declarations of the symbol are within routines that are currently active on the call stack, use the Call Stack menu on the main window to reset the current scope (see Section 10.6.2).
• Otherwise, enter the appropriate command at the command prompt (EXAMINE or MONITOR, for example), specifying a path name prefix with the symbol. For example, if the variable X is defined in two modules named COUNTER and SWAP, the following command uses the path name SWAP\X to specify the declaration of X that is in module SWAP:

  DBG> EXAMINE SWAP\X

The register view displays the current contents of all machine registers (see Figure 10-20).

To display the register view, choose Views... from the Options menu on the main window or the optional views window, then click on Registers when the Views dialog box appears.

By default, the register view automatically displays the register values associated with the routine in which execution is currently paused. Any values that change as your program executes are highlighted whenever the debugger regains control from your program.

To display the register values associated with any routine on the call stack, choose its name from the Call Stack menu on the main window (see Section 10.6.2).

To change the value stored in a register:

1. Click on the register value in the register view. A small dialog box is displayed over the current value, which you can now edit.
2. Enter the new value in the dialog box.
3. Click on the check mark (OK) in the dialog box. The debugger removes the dialog box and displays the new value, indicating that the register now contains that value. To dismiss the dialog box without changing the value in the register, click on X (Cancel).

To change the radix used to display register values:

• Choose Change Radix in the Register menu to change the radix in current and subsequent output for a selected register.
• Choose Change All Radix in the Register menu to change the radix in current and subsequent output for all registers.

Figure 10-20 Register View

The instruction view displays the decoded instruction stream of your program: the code that is actually executing (see Figure 10-21). This is useful if the program you are debugging has been optimized by the compiler so that the information in the main window does not exactly reflect the code that is executing (see Section 1.2).

Figure 10-21 Instruction View

To display the instruction view, choose Views... from the Options menu on the main window or the optional views window, then click on Instructions when the Views dialog box appears.

By default, the instruction view automatically displays the decoded instruction stream of the routine in which execution is currently paused. The current-location pointer, to the left of the instructions, marks the instruction that will execute next.

By default, the debugger displays source code line numbers to the left of the instructions with which they are associated. To hide or display line numbers, toggle Display Line Numbers from the File menu in the instruction view.

By default, the debugger displays memory addresses to the left of the instructions. To hide or display addresses, toggle Show Instruction Addresses from the File menu in the instruction view.

After navigating the instruction view, click on the Call Stack menu to redisplay the location at which execution is paused.

To display the instruction stream of any routine on the call stack, choose the routine's name from the Call Stack menu on the main window (see Section 10.6.2).

10.9 Debugging Tasking (Multithread) Programs

Tasking programs, also called multithreaded programs, have multiple threads of execution within a process and include the following:

• Programs in any language that use HP POSIX Threads Library or POSIX 1003.1b services.
• Programs that use language-specific tasking services (services provided directly by the language). Currently, Ada is the only language with built-in tasking services that the debugger supports.

Within the debugger, the term task or thread denotes such a flow of control, regardless of the language or implementation. The debugger's tasking support applies to all such programs.

The debugger enables you to display task information and modify task characteristics to control task execution, priority, state transitions, and so on.

The following sections summarize the tasking features of the debugger's HP DECwindows Motif for OpenVMS user interface. For more information about the debugger's tasking support, see Chapter 16.

10.9.1 Displaying Information About Tasks (Threads)

To display information about one or more tasks (threads) of your program, choose Views... from the Options menu on the main window or the optional views window, then click on Threads when the Views dialog box appears.

The Threads view gives information about all currently existing (nonterminated) tasks of your program. The information is updated whenever the debugger regains control from the program, as shown in Figure 10-22.

Figure 10-22 Thread View

The displayed information includes:

• The thread ID. The arrow in the left column marks the active task; i.e., the thread that runs when you click on the Go or STEP button.
• The thread priority.
• Whether the task (thread) has been put on hold as explained in Section 10.9.2.
• The current state of the task (thread). The task in the RUN (running) state is the active task.
• The current substate of the task (thread). The substate helps indicate the possible cause of a task's state.
• A debugger path name for the task (thread) object or the address of the task object if the debugger cannot symbolize the task object.

10.9.2 Changing Task (Threads) Characteristics

The debugger is installed on your system with a default debugger resource file (DECW$SYSTEM_DEFAULTS:VMSDEBUG.DAT) that defines the startup defaults for the following customizable parameters:

• Configuration of windows and views
• Whether to show or hide line numbers in the main window
• Button names and associated debugger commands
• Key sequence to display the dialog box for conditional and action breakpoints
• Key sequence for language-sensitive text selection in the source view and instruction view
• Character fonts for text in the views
• Character font for text displayed in specific windows and views
• Color of the text foreground and background colors in the source view, instruction view, and editor view
• Display of program, module, and routine names in the main window title bar
• Whether or not the debugger requires confirmation before exiting

A copy of the system default debugger resource file with explanatory comments is included in Example 10-1 in Section 10.10.4.

You can modify the first three of these display attributes interactively from the HP DECwindows Motif for OpenVMS user interface, as explained in Section 10.10.1, Section 10.10.2, and Section 10.10.3. In each case, you can save the modified display configuration for future debugging sessions by choosing Save Options from the Options menu.

In addition, you can modify all the listed attributes of the debugger display configuration by editing and saving the debugger resource file, as explained in Section 10.10.4.

When you choose Save Options from the Options menu or you edit and save the local debugger resource file, the debugger creates a new version of the local debugger resource file DECW$USER_DEFAULTS:VMSDEBUG.DAT that contains the definitions of the display configuration attributes. When you next start the debugger, it uses the attributes defined in the most recent local resource file to configure the output display. You can fall back to previous debugger display configurations with appropriate use of the DCL commands DELETE, RENAME, and COPY.

To fall back to the system default display configuration, select Restore Default Options from the OpenVMS Debugger Options menu.

10.10.1 Defining the Startup Configuration of Debugger Views

To define the startup configuration of the debugger views:

1. While using the debugger, set up your preferred configuration of views.
2. Choose Save Options from the Options menu to create a new version of the debugger resource file.

When you next start the debugger, the debugger uses the most recent resource file to create the new display configuration.

You can also define the startup display configuration by editing the definition of these views in the resource file (see Section 10.10.4).

10.10.2 Displaying or Hiding Line Numbers in Source View and Instruction View

The source view and instruction view display source line numbers by default at debugger startup. To hide (or display) line numbers at debugger startup:

1. While using the debugger, choose Display Line Numbers from the File menu on the main window (or the instruction view). Line numbers are displayed when a filled-in button appears next to that menu item.
2. Choose Save Options from the Options menu to create a new version of the debugger's local resource file.

When you next start the debugger, the debugger uses the most recent resource file to create the new display configuration.

You can also set the startup default for line numbers by setting the following resources to either True or False in the resource file (see Section 10.10.4).

DebugSource.StartupShowSourceLineno: True DebugInstruction.StartupShowInstLineno: True

10.10.3 Modifying, Adding, Removing, and Resequencing Push Buttons

• Change a button's label or associated command
• Add a new button
• Remove a button
• Resequence a button

To save these modifications for future debugger sessions, choose Save Options from the Options menu.

Section 10.10.3.1, Section 10.10.3.2, and Section 10.10.3.3 explain how to customize push buttons interactively through the HP DECwindows Motif for OpenVMS user interface. You can also customize push buttons by editing the resource file. Button definitions in the resource file begin with:

DebugControl.Button

(See Example 10-1.)

10.10.3.1 Changing a Button's Label or Associated Command

To change a button's label or associated command:

1. Choose Customize Buttons... from the Options menu on the main window or the optional views window. The Customize Buttons dialog box is displayed (see Figure 10-23).
2. Within the dialog box, click on the button you are modifying. This fills the Command and Label fields with the parameters for that button. The example in Figure 10-23 shows that the STEP button was selected.
3. To change the button icon, pull down the Icon menu within the dialog box and select one of the predefined icons. As Figure 10-23 shows, the Label field dims and is filled with the debugger's internal name for the predefined icon. The icon itself appears in the dialog box's push button display.
   To change the button label, select None on the Icon menu and enter a new label in the Label field.
4. To change the command associated with the button, enter the new command in the Command field. For online help about the commands, see Section 8.4.3.
   If the command is to operate on a name or language expression selected in a window, specify %S as the command parameter. For example, the following command displays the current value of the language expression that is currently selected:

   EVALUATE %s

   
   If the command is to operate on a debugger built-in symbol or any other name that has a percent sign (%) as the first character, specify two percent signs. For example:

   EXAMINE %%NEXTLOC

5. Click on Modify. The button's label or associated command is changed within the dialog box push button display.
6. Click on Apply. The button's label or associated command is changed within the debugger's push button view.

To save these modifications for future debugger sessions, choose Save Options from the Options menu.

Figure 10-23 Changing the STEP Button Label to an Icon

To add a new button to the push button view and assign a debugger command to that button:

1. Choose Customize Buttons... from the Options menu. The Customize Buttons dialog box is displayed (see Figure 10-24).
2. Enter the debugger command for the new button in the Command field (see Section 10.10.3.1). Figure 10-24 shows the debugger command run mydisk:[mydirectory]x.exe was entered.
3. Enter a label for that button in the Label field or choose a predefined icon from the Icon menu. Figure 10-24 shows that the Run-X label was chosen.
4. Click on Add. The button is added to the dialog box push button display.
5. Click on Apply. The button is added to the debugger's push button view.

To save these modifications for future debugger sessions, choose Save Options from the Options menu.

Figure 10-24 Adding a Button

To remove a button:

1. Choose Customize Buttons... from the Options menu on the main or optional views window. The Customize Buttons dialog box is displayed.
2. Within the dialog box, click on the button you are removing. This fills the Command and Label fields with the parameters for that button.
3. Click on Remove. The button is removed from the dialog box push button display.
4. Click on Apply. The button is removed from the debugger's push button view.

To save these modifications for future debugger sessions, choose Save Options from the Options menu.

10.10.3.4 Resequencing a Button

To resequence a button:

1. Choose Customize Buttons... from the Options menu on the main or optional views window. The Customize Buttons dialog box is displayed.
2. Within the dialog box, click on the button you are resequencing. This fills the Command and Label fields with the parameters for that button.
3. Click on the left or right arrow to move the button one position to the left or right. Continue to click until the button has moved, one position at a time, to its final position.
4. Click on Apply to transfer this position to the debugger's push button view.

To save these modifications for future debugger sessions, choose Save Options from the Options menu.

10.10.4 Editing the Debugger Resource File

The debugger is installed on your system with a default debugger resource file (DECW$SYSTEM_DEFAULTS:VMSDEBUG.DAT) that defines the default display configuration for the debugger. When you modify the display attributes as described in Section 10.10 and then save the modifications with the Save Options command in the Options menu, the debugger creates a local debugger resource file, DECW$USER_DEFAULTS:VMSDEBUG.DAT. You can edit this file to further modify the debugger display configuration.

If you do not have a local debugger resource file, you can create one with the Restore Default Options item in the Options menu. Whenever you start the debugger, it creates the debugger display configuration as defined in the most recent version of the local debugger resource file if there is one; otherwise, the debugger uses the definitions in the system debugger resource file, DECW$SYSTEM_DEFAULTS:VMSDEBUG.DAT.

You cannot edit the system resource file. You can modify the debugger display configuration either by following the procedures in Section 10.10.1, Section 10.10.2, and Section 10.10.3, or by editing and saving your local debugger resource file.

Example 10-1 contains a copy of the system default debugger resource file. Most entries are annotated within the file or are self-explanatory. Section 10.10.4.1, Section 10.10.4.2, Section 10.10.4.3, and Section 10.10.4.4 contain additional information about modifying certain key sequences. For complete information about specifying key sequences, see the translation table syntax in the X Toolkit Intrinsics documentation.

Example 10-1 System Default Debugger Resource File (DECW$SYSTEM_DEFAULTS:VMSDEBUG.DAT)

! ! OpenVMS Debug32/64 Debugger Resource File ! DebugVersion: 71 ! ! GEOMETRY RESOURCES: ! ! Written when you execute "SAVE OPTIONS" from the Options Menu. ! DebugSource.x: 11 DebugSource.y: 30 DebugSource.width: 620 DebugSource.height: 700 ! DebugControl.x: 650 DebugControl.y: 30 DebugControl.width: 600 DebugControl.height: 700 ! DebugEditor.x: 650 DebugEditor.y: 30 DebugEditor.width: 600 DebugEditor.height: 700 ! DebugInstruction.x: 11 DebugInstruction.y: 769 DebugInstruction.width: 620 DebugInstruction.height: 243 ! *DebugBrowser.x: 650 *DebugBrowser.y: 30 *DebugBrowser.width: 335 *DebugBrowser.height: 300 ! ! LINE NUMBER DISPLAY RESOURCES: ! ! Create the line or address number display in views at startup? ! DebugSource.StartupShowSourceLineno: True DebugInstruction.StartupShowInstLineno: True DebugInstruction.StartupShowInstAddrno: False ! ! WINDOW PANE RESOURCES: ! ! Relative size of panes in main window. ! Main window height is derived from sum of panes. ! DebugSource*SrcView.height: 460 DebugSource*PushbuttonPanel.height: 36 DebugSource*MessageOutputPanel.height: 145 ! DebugControl.BreakpointView.height: 175 DebugControl.MonitorView.height: 150 DebugControl.TaskView.height: 130 DebugControl.RegisterView.height: 250 ! ! CUSTOM BUTTON RESOURCES: ! ! The following resources determine which buttons to put in the button panel. ! Buttons will show in the order they are listed here. ! For each button there MUST be a set of associated resources. ! EXAMPLE: ! ButtonCommand - Associates a command with the button. ! ButtonLegend - Button Label or pixmap name if pixmap flag is True. ! ButtonPixmapFlag - If True uses ButtonLegend as predefined pixmap name. ! DebugControl.ButtonList: \ GoButton, StepButton, StepInButton, ... ! DebugControl.ButtonCommand.GoButton: go DebugControl.ButtonLegend.GoButton: go_pixmap DebugControl.ButtonPixmapFlag.GoButton: True ! DebugControl.ButtonCommand.StepButton: step DebugControl.ButtonLegend.StepButton: STEP DebugControl.ButtonPixmapFlag.StepButton: False ! DebugControl.ButtonCommand.StepInButton: step/in DebugControl.ButtonLegend.StepInButton: S/in DebugControl.ButtonPixmapFlag.StepInButton: False ! DebugControl.ButtonCommand.StepReturnButton: step/return DebugControl.ButtonLegend.StepReturnButton: S/ret DebugControl.ButtonPixmapFlag.StepReturnButton: False ! DebugControl.ButtonCommand.StepCallButton: step/call DebugControl.ButtonLegend.StepCallButton: S/call DebugControl.ButtonPixmapFlag.StepCallButton: False ! DebugControl.ButtonCommand.ExamineButton: examine %s DebugControl.ButtonLegend.ExamineButton: EX DebugControl.ButtonPixmapFlag.ExamineButton: False ! DebugControl.ButtonCommand.ExamineASCIZButton: examine/asciz %s DebugControl.ButtonLegend.ExamineASCIZButton: E/az DebugControl.ButtonPixmapFlag.ExamineASCIZButton: False ! DebugControl.ButtonCommand.ExamineASCICButton: examine/ascic %s DebugControl.ButtonLegend.ExamineASCICButton: E/ac DebugControl.ButtonPixmapFlag.ExamineASCICButton: False ! DebugControl.ButtonCommand.EvalButton: evaluate %s DebugControl.ButtonLegend.EvalButton: EVAL DebugControl.ButtonPixmapFlag.EvalButton: False ! DebugControl.ButtonCommand.MonitorButton: monitor %s DebugControl.ButtonLegend.MonitorButton: MON DebugControl.ButtonPixmapFlag.MonitorButton: False ! ! THE FOLLOWING RESOURCES CAN ONLY BE CHANGED BY EDITING THIS FILE. ! ----------------------------------------------------------------- ! Be sure to trim off any trailing white-spaces. ! ! FONT RESOURCES: ! ! If a font is specified for a view, and the font is available on the ! system, it will be used for that view. ! ! For any views which do not explicitly specify a font, the font specified ! by the resource "DebugDefault.Font" will be used if it is available on the ! system. ! ! If no font resources are specified at all, the debugger will use the ! systems own default font specification. ! ! The "DebugOptions.Font" applies to all optional views. We suggest that ! you select a font with a point size no larger than 14 in the option views ! in order to preserve label alignment. ! ! Using 132 column sources? Try this narrow font: ! -dec-terminal-medium-r-narrow--14-100-100-100-c-60-iso8859-1 ! ! FORMAT: -*-FONTNAM-FACE-T-*--*-PTS-*-*-*-*-CHARSET ! DebugDefault.Font: -*-COURIER-BOLD-R-*--*-120-*-*-*-*-ISO8859-1 DebugSource.Font: -*-COURIER-BOLD-R-*--*-120-*-*-*-*-ISO8859-1 DebugInstruction.Font: -*-COURIER-BOLD-R-*--*-140-*-*-*-*-ISO8859-1 DebugMessage.Font: -*-COURIER-BOLD-R-*--*-120-*-*-*-*-ISO8859-1 DebugOptions.Font: -*-COURIER-BOLD-R-*--*-120-*-*-*-*-ISO8859-1 ! ! STARTUP RESOURCES: 3=Iconified, 0=Visible ! DebugSource.initialState: 0 DebugControl.initialState: 0 DebugEditor.initialState: 0 DebugInstruction.initialState: 0 ! ! COLOR RESOURCES: ! ! Use any of the OSF Motif Named Colors. ! ! Foreground = Text Color, Background = Window Color ! ! Try: Gainsboro, MintCream, Linen, SeaShell, MistyRose, Honeydew ! Cornsilk, Lavender ! ! To use your system default color scheme, comment out all lines ! pertaining to color. ! ! Common color scheme (unless overridden for a specific view) ! *background: Gainsboro *borderColor: Red ! ! Source View Colors ! !DebugSource*background: Gainsboro DebugSource*topShadowColor: WindowTopshadow DebugSource*bottomShadowColor: WindowBottomshadow DebugSource*src_txt.foreground: blue DebugSource*src_txt.background: white DebugSource*src_lineno_txtw.foreground: red DebugSource*cnt_msg_txt.foreground: black DebugSource*cnt_msg_txt.background: white ! ! Control View Colors ! !DebugControl*background: Gainsboro DebugControl*topShadowColor: WindowTopshadow DebugControl*bottomShadowColor: WindowBottomshadow ! ! Instruction View Colors ! !DebugInstruction*background: Gainsboro DebugInstruction*topShadowColor: WindowTopshadow DebugInstruction*bottomShadowColor: WindowBottomshadow DebugInstruction*inst_txt.foreground: blue DebugInstruction*inst_txt.background: white DebugInstruction*inst_addrno_txtw.foreground: red ! ! Editor Colors ! !DebugEditor*background: Gainsboro DebugEditor*topShadowColor: WindowTopshadow DebugEditor*bottomShadowColor: WindowBottomshadow DebugEditor*edit_textw.foreground: black DebugEditor*edit_textw.background: white ! ! REGISTER VIEW RESOURCES: ! ! Which Registers to display by default in the Register View? ! CF = Call Frame, GP = General Purpose, FP = Floating Point (Integrity server and Alpha Only) ! *Show_CF_Registers.set: True *Show_GP_Registers.set: False *Show_FP_Registers.set: False ! ! SHOW MESSAGE/COMMAND SEPARATOR LINES? ! *Show_Message_Separators.set: True ! ! TRACK LANGUAGE CHANGES? (parser follows module language) ! *Track_Language_Changes.set: False ! ! KEY SEQUENCE RESOURCES: ! ! Key sequence used to activate the dialog box for conditional and action ! breakpoints. ! DebugSource.ModifyBreakpointToggleSequence: Ctrl <Btn1Down>, Ctrl <Btn1Up> ! ! GENERAL KEYPAD FUNCTIONS: ! !<Key>0xFFB0=KP0, <Key>0xFF91,<Key>0xFFB0=GOLD-KP0, !<Key>0xFF94,<Key>0xFFB0=BLUE-KP0, <Key>0xFFB1=KP1, !<Key>0xFF91,<Key>0xFFB1=GOLD-KP1, <Key>0xFFAC=KP, DebugSource.*XmText.translations:#override\n\ <Key>0xFFB0: EnterCmdOnCmdLine("step/line") \n\ <Key>0xFFB1: EnterCmdOnCmdLine("examine") \n\ <Key>0xFFAC: EnterCmdOnCmdLine("go") \n\ <Key>0xFF91,<Key>0xFFB0: EnterCmdOnCmdLine("step/into") \n\ <Key>0xFF94,<Key>0xFFB0: EnterCmdOnCmdLine("step/over") \n\ <Key>0xFF91,<Key>0xFFB1: EnterCmdOnCmdLine("examine^") \n\ <Key>0xFFB5: EnterCmdOnCmdLine("show calls") \n\ <Key>0xFF91,<Key>0xFFB5: EnterCmdOnCmdLine("show calls 3") \n\ <Key>0xFF8D: activate()\n ! ! IDENTIFIER WORD SELECTION: (language-based delimiters) ! NOTE: DO NOT use any double click combination for the following resource ! otherwise normal text selection in the source window will not work. ! DebugSource.IdentifierSelectionSequence: Ctrl<Btn1Down> ! ! EXIT CONFIRMATION: ! DebugDisplayExitConfirmDB: True ! ! COMMAND ECHO: ! DebugEchoCommands: True ! ! TITLE FORMAT: Main window and optional view window. ! ! The following title format directives are supported: ! ! %t - The title of the debugger application. ! %p - The name of the user program being debugged. ! %f - The name of the current file displayed in the source window. ! DebugControl.TitleFormat: %t - %p: %f ! ! DRAG AND DROP MESSAGE SUPRESSION: (Dont mess with these) ! *.dragInitiatorProtocolStyle: DRAG_NONE *.dragReceiverProtocolStyle: DRAG_NONE