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HP OpenVMS Debugger Manual

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1.13.4 Controlling Type Selection and Radix

The following commands control type selection and radix:

(SET,SHOW,CANCEL) RADIX (Establishes, displays, restores) the radix for data entry and display
(SET,SHOW,CANCEL) TYPE (Establishes, displays, restores) the type for program locations that are not associated with a compiler-generated type
SET MODE [NO]G_FLOAT Controls whether double-precision floating-point constants are interpreted as G_FLOAT or D_FLOAT

1.13.5 Controlling Symbol Searches and Symbolization

The following commands control symbol searches and symbolization:

SHOW SYMBOL Displays symbols in your program
(SET,SHOW,CANCEL) MODULE Sets a module by loading its symbol information into the debugger's symbol table, identifies, cancels a set module
(SET,SHOW,CANCEL) IMAGE Sets a shareable image by loading data structures into the debugger's symbol table, identifies, cancels a set image
SET MODE [NO]DYNAMIC Controls whether or not modules and shareable images are set automatically when the debugger interrupts execution
(SET,SHOW,CANCEL) SCOPE (Establishes, displays, restores) the scope for symbol searches
SYMBOLIZE Converts a memory address to a symbolic address expression
SET MODE [NO]LINE Controls whether or not program locations are displayed in terms of line numbers or routine-name + byte offset
SET MODE [NO]SYMBOLIC Controls whether or not program locations are displayed symbolically or in terms of numeric addresses

1.13.6 Displaying Source Code

The following commands control the display of source code:

TYPE Displays lines of source code
EXAMINE/SOURCE Displays the source code at the location specified by the address expression
SEARCH Searches the source code for the specified string
(SET,SHOW) SEARCH (Establishes, displays) the default qualifiers for the SEARCH command
SET STEP [NO]SOURCE Enables/disables the display of source code after a STEP command has been executed or at a breakpoint, tracepoint, or watchpoint
(SET,SHOW) MARGINS (Establishes, displays) the left and right margin settings for displaying source code
(SET,SHOW,CANCEL) SOURCE (Creates, displays, cancels) a source directory search list

1.13.7 Using Screen Mode

The following commands control screen mode and screen displays:

SET MODE [NO]SCREEN Enables/disables screen mode
DISPLAY Creates or modifies a display
SCROLL Scrolls a display
EXPAND Expands or contracts a display
MOVE Moves a display across the screen
(SHOW,CANCEL) DISPLAY (Identifies, deletes) a display
(SET,SHOW,CANCEL) WINDOW (Creates, identifies, deletes) a window definition
SELECT Selects a display for a display attribute
SHOW SELECT Identifies the displays selected for each of the display attributes
SAVE Saves the current contents of a display into another display
EXTRACT Saves a display or the current screen state into a file
(SET,SHOW) TERMINAL (Establishes, displays) the terminal screen height and width that the debugger uses when it formats displays and other output
SET MODE [NO]SCROLL Controls whether an output display is updated line by line or once per command
Refreshes the screen

1.13.8 Editing Source Code

The following commands control source editing from a debugging session:

EDIT Starts an editor during a debugging session
(SET,SHOW) EDITOR (Establishes, identifies) the editor started by the EDIT command

1.13.9 Defining Symbols

The following commands define and delete symbols for addresses, commands, or values:

DEFINE Defines a symbol as an address, command, or value
DELETE Deletes symbol definitions
(SET,SHOW) DEFINE (Establishes, displays) the default qualifier for the DEFINE command
SHOW SYMBOL/DEFINED Identifies symbols that have been defined with the DEFINE command

1.13.10 Using Keypad Mode

The following commands control keypad mode and key definitions:

SET MODE [NO]KEYPAD Enables/disables keypad mode
DEFINE/KEY Creates key definitions
DELETE/KEY Deletes key definitions
SET KEY Establishes the key definition state
SHOW KEY Displays key definitions

1.13.11 Using Command Procedures, Log Files, and Initialization Files

The following commands are used with command procedures and log files:

@ (execute procedure) Executes a command procedure
(SET,SHOW) ATSIGN (Establishes, displays) the default file specification that the debugger uses to search for command procedures
DECLARE Defines parameters to be passed to command procedures
(SET,SHOW) LOG (Specifies, identifies) the debugger log file
SET OUTPUT [NO]LOG Controls whether or not a debugging session is logged
SET OUTPUT [NO]SCREEN_LOG Controls whether or not, in screen mode, the screen contents are logged as the screen is updated
SET OUTPUT [NO]VERIFY Controls whether or not debugger commands are displayed as a command procedure is executed
SHOW OUTPUT Identifies the current output options established by the SET OUTPUT command

1.13.12 Using Control Structures

The following commands establish conditional and looping structures for debugger commands:

FOR Executes a list of commands while incrementing a variable
IF Executes a list of commands conditionally
REPEAT Executes a list of commands a specified number of times
WHILE Executes a list of commands while a condition is true
EXITLOOP Exits an enclosing WHILE, REPEAT, or FOR loop

1.13.13 Debugging Multiprocess Programs

The following commands debug multiprocess programs. Note that these commands are specific to multiprocess programs. Many of the commands listed under other categories have qualifiers or parameters that are specific to multiprocess programs (for example, SET BREAK/ACTIVATING, EXIT process-spec, DISPLAY/PROCESS=).

CONNECT Brings a process under debugger control
DEFINE/PROCESS_SET Assigns a symbolic name to a list of process specifications
SET MODE [NO]INTERRUPT Controls whether execution is interrupted in other processes when it is paused in some process
(SET,SHOW) PROCESS Modifies the multiprocess debugging environment, displays process information
WAIT When debugging a multiprocess program, controls whether the debugger waits until all processes have stopped before prompting for another command

1.13.14 Additional Commands

The following commands are used for miscellaneous purposes:

HELP Displays online help on debugger commands and selected topics
ANALYZE/CRASH_DUMP Opens a process dump for analysis with the System Dump Debugger (SDD)
ANALYZE/PROCESS_DUMP Opens a process dump for analysis with the System Code Debugger (SCD)
(DISABLE,ENABLE,SHOW) AST (Disables, enables) the delivery of ASTs in the program, identifies whether delivery is enabled or disabled
PTHREAD Passes a command to the POSIX Threads Debugger
(SET,SHOW) EVENT_FACILITY (Establishes, identifies) the current run-time facility for Ada, POSIX Threads, and SCAN events
(SET,SHOW) LANGUAGE (Establishes, identifies) the current language
SET OUTPUT [NO]TERMINAL Controls whether debugger output, except for diagnostic messages, is displayed or suppressed
SET PROMPT Specifies the debugger prompt
(SET,SHOW) TASK|THREAD Modifies the tasking environment, displays task information
SHOW EXIT_HANDLERS Identifies the exit handlers declared in the program
SHOW MODE Identifies the current debugger modes established by the SET MODE command (for example, screen mode, step mode)
SHOW OUTPUT Identifies the current output options established by the SET OUTPUT command

Part II
Command Interface

This part describes the debugger's command interface.

For information about the debugger's DECwindows Motif user interface, see Part 3.

Chapter 2
Getting Started with the Debugger

This chapter gives a tutorial introduction to the debugger's command interface.

The way you use the debugger depends on several factors: the kind of program you are working on, the kinds of errors you are looking for, and your own personal style and experience with the debugger. This chapter explains the following basic tasks that apply to most situations:

  • Entering debugger commands and getting online help
  • Viewing your source code with the TYPE command and in screen mode
  • Controlling program execution with the GO, STEP, and SET BREAK commands, and monitoring execution with the SHOW CALLS, SET TRACE, and SET WATCH commands
  • Examining and manipulating data with the EXAMINE, DEPOSIT, and EVALUATE commands
  • Controlling symbol references with path names and the SET MODULE and SET SCOPE commands

Several examples are language specific. However, the general concepts are readily adaptable to all supported languages.

The sample debugging session in Section 2.6 shows how to use some of this information to locate an error and correct it.

For information about starting and ending a debugging session, see Section 1.3.

2.1 Entering Debugger Commands and Accessing Online Help

After you start the debugger as explained in Section 1.3, you can enter debugger commands whenever the debugger prompt (DBG>) is displayed. To enter a command, type it at the keyboard and press Return. For example, the following command sets a watchpoint on the variable COUNT:


Detailed reference information about debugger commands is available in Part 6 and through the debugger's online help:

  • To list the help topics, type HELP at the prompt.
  • For an explanation of the help system, type HELP HELP.
  • For complete rules on entering commands, type HELP Command_Format.
  • To display help on a particular command, type HELP command. For example, to display HELP on the SET WATCH command, type HELP SET WATCH.
  • To list commands grouped by function, type HELP Command_Summary.

Online help is also available on the following topics:

Messages (diagnostic messages)
Path_Names (to qualify symbolic names)
SS$_DEBUG condition (to start debugger from program)

To display help about any of these topics, type HELP topic. For example, to display information about diagnostic messages, type HELP Messages.

When you start the debugger, a few commonly used command sequences are automatically assigned to the keys on the numeric keypad (to the right of the main keyboard). Thus, you can perform certain functions either by entering a command or by pressing a keypad key.

The predefined key functions are identified in Figure 2-1.

Figure 2-1 Keypad Key Functions Predefined by the Debugger---Command Interface

Most keypad keys have three predefined functions---DEFAULT, GOLD, and BLUE.

  • To enter a key's DEFAULT function, press the key.
  • To enter its GOLD function, first press and release the PF1 (GOLD) key, and then press the key.
  • To enter its BLUE function, first press and release the PF4 (BLUE) key, and then press the key.

In Figure 2-1, the DEFAULT, GOLD, and BLUE functions are listed within each key's outline, from top to bottom, respectively. For example:

  • Pressing KP0 (keypad key 0) enters the STEP command.
  • Pressing PF1 KP0 enters the STEP/INTO command.
  • Pressing PF4 KP0 enters the STEP/OVER command.

Normally, keys KP2, KP4, KP6, and KP8 scroll screen displays down, left, right, or up, respectively. By putting the keypad in the MOVE, EXPAND, or CONTRACT state, indicated in Figure 2-1, you can also use these keys to move, expand, or contract displays in four directions. Enter the command HELP Keypad_Definitions to display the keypad key definitions.

You can redefine keypad key functions with the DEFINE/KEY command.

2.2 Displaying Source Code

The debugger provides two modes for displaying information: noscreen mode and screen mode. By default, when you start the debugger, you are in noscreen mode, but you might find that it is easier to view source code in screen mode. The following sections briefly describe both modes.

2.2.1 Noscreen Mode

Noscreen mode is the default, line-oriented mode of displaying input and output. The interactive examples throughout this chapter, excluding Section 2.2.2, show noscreen mode.

In noscreen mode, use the TYPE command to display one or more source lines. For example, the following command displays line 7 of the module in which execution is currently paused:

     7:        TEMP := A;

The display of source lines is independent of program execution. To display source code from a module (compilation unit) other than the one in which execution is currently paused, use the TYPE command with a path name to specify the module. For example, the following command displays lines 16 to 21 of module TEST:


Path names are discussed in more detail in Section 2.3.2, with the STEP command.

You can also use the EXAMINE/SOURCE command to display the source line for a routine or any other program location that is associated with an instruction.

The debugger also displays source lines automatically when it suspends execution at a breakpoint or watchpoint, after a STEP command, or when a tracepoint is triggered (see Section 2.3).

After displaying source lines at various locations in your program, you can redisplay the location at which execution is currently paused by pressing KP5.

If the debugger cannot locate source lines for display, it issues a diagnostic message. Source lines might not be available for a variety of reasons. For example:

  • Execution is paused within a module that was compiled or linked without the /DEBUG qualifier.
  • Execution is paused within a system or shareable image routine for which no source code is available.
  • The source file was moved to a different directory after it was compiled (the location of source files is embedded in the object modules). In this case, use the SET SOURCE command to specify the new location.
  • The module might need to be set with the SET MODULE command. Module setting is explained in Section 2.5.1.

To switch to noscreen mode from screen mode, press PF1 PF3 (or type SET MODE NOSCREEN). You can use the TYPE and EXAMINE/SOURCE commands in screen mode as well as noscreen mode.

2.2.2 Screen Mode

Screen mode provides the easiest way to view your source code. To switch to screen mode, press PF3 (or type SET MODE SCREEN). In screen mode, by default the debugger splits the screen into three displays named SRC, OUT, and PROMPT, as shown in Figure 2-2.

Figure 2-2 Default Screen Mode Display Configuration

The SRC display shows the source code of the module in which execution is currently paused. An arrow in the left column points to the source line corresponding to the current value of the program counter (PC). The PC is a register that contains the memory address of the instruction to be executed next. The line numbers, which are assigned by the compiler, match those in a listing file. As you execute the program, the arrow moves down and the source code is scrolled vertically to center the arrow in the display.

The OUT display captures the debugger's output in response to the commands that you enter. The PROMPT display shows the debugger prompt, your input (the commands that you enter), debugger diagnostic messages, and program output.

You can scroll both SRC and OUT to see whatever information might scroll beyond the display window's edge. Press KP3 repeatedly as needed to select the display to be scrolled (by default, SRC is scrolled). Press KP8 to scroll up and KP2 to scroll down. Scrolling a display does not affect program execution.

In screen mode, if the debugger cannot locate source lines for the routine in which execution is currently paused, it tries to display source lines in the next routine down on the call stack for which source lines are available. If the debugger can display source lines for such a routine, it issues the following message:

%DEBUG-I-SOURCESCOPE, Source lines not available for .0\%PC.
Displaying source in a caller of the current routine.

In such cases, the arrow in the SRC display identifies the line that contains code following the call statement in the calling routine.

2.3 Controlling and Monitoring Program Execution

This section explains how to perform the following tasks:

  • Start and resume program execution
  • Execute the program to the next source line, instruction, or other step unit
  • Determine where execution is currently paused
  • Use breakpoints to suspend program execution at points of interest
  • Use tracepoints to trace the execution path of your program through specified locations
  • Use watchpoints to monitor changes in the values of variables

With this information you can pick program locations where you can then test and manipulate the contents of variables as described in Section 2.4.

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