HP OpenVMS systems documentation

The SET MARGINS command enables you to specify the leftmost and rightmost source-line character positions at which to begin and end the display of a source line (respectively, the left and right margins). This is useful for controlling the display of source code when, for example, the code is deeply indented or long lines wrap at the right margin. In such cases, you can set the left margin to eliminate indented space in the source display, and you can decrease the right margin setting to truncate lines and prevent them from wrapping.

For example, the following command line sets the left margin to column 20 and the right margin to column 35.

DBG> SET MARGINS 20:35

Subsequently, only that portion of the source code that is between columns 20 and 35 is displayed when you enter commands that display source lines (for example, TYPE, SEARCH, STEP). Use the SHOW MARGINS command to identify the current margin settings for the display of source lines.

Note that the SET MARGINS command affects only the display of source lines. It does not affect the display of other debugger output (for example, output from an EXAMINE command).

The SET MARGINS command is useful mostly in line (noscreen) mode. In screen mode, the SET MARGINS command has no effect on the display of source lines in a source display, such as the predefined display SRC.

Screen mode is an enhancement to the command line interface of the OpenVMS debugger that enables you to simultaneously display separate groups of data about the debugging session, in a manner similar to that available with the HP DECwindows Motif for OpenVMS user interface (see Part 3). For example, you can display source code in one portion of the screen, register contents in a different portion, debugger output in another portion, and so on.

To invoke screen mode, press PF3 on the keypad (or enter the SET MODE SCREEN command). To return to line-oriented debugging, press PF1 PF3 (or enter the SET MODE NOSCREEN command).

Screen mode output is best displayed on VT-series terminals with higher numbers than VT52, and on workstations running VWS. The larger screen of workstations is particularly suitable to using a number of displays for different purposes.

This chapter covers the following topics:

• Screen mode concepts and terminology used throughout the chapter
• Using different kinds of displays
• Directing debugger output to different displays by assigning display attributes
• Using predefined displays SRC, OUT, PROMPT, INST, REG, IREG, and FREG (Alpha only), which are automatically available when you enter screen mode
• Scrolling, hiding, deleting, moving, and resizing a display
• Creating a new display
• Specifying a display window
• Creating a display configuration
• Saving the current state of screen displays
• Changing your terminal screen's height and width during a debugging session and the effect on display windows
• Using screen-related debugger built-in symbols
• Using predefined windows
• Enabling country-specific features for screen mode

Many screen mode commands are bound to keypad keys. For key definitions, see Appendix A.

A display is a group of text lines. The text can be lines from a source file, assembly-language instructions, the values contained in registers, your input to the debugger, debugger output, or program input and output.

You view a display through its display window, which can occupy any rectangular area of the screen. Because a display window is typically smaller than the associated display, you can scroll the display window up, down, right, and left across the display text to view any part of the display.

Figure 7-1 is an example of screen mode that shows three display windows. The name of each display (SRC, OUT, and PROMPT) appears at the top left corner of its display window. The display name serves both as a tag on the display itself and as a name for future reference in commands.

Figure 7-1 Default Screen Mode Display Configuration

Figure 7-1 is the default display configuration established when you first invoke screen mode. SRC, OUT, and PROMPT are three of the predefined displays that the debugger provides when you enter screen mode (see Section 7.4). You can modify the configuration of these displays as well as create additional displays.

Displays SRC, OUT, and PROMPT have the following basic characteristics:

• SRC is a source-code display that occupies the upper half of the screen (it displays Fortran code in Figure 7-1). The name of the source module displayed, SQUARES$MAIN, is to the right of the display name.
• OUT, located in a window directly below SRC, shows the output of debugger commands.
• PROMPT, at the bottom of the screen, shows the debugger prompt and debugger input.

Conceptually, displays are placed on the screen as on a pasteboard. The display most recently referenced by a command is put on top of the pasteboard by default. Therefore, depending on their screen locations, display windows that you have referenced recently might overlay or hide other display windows.

The debugger maintains a display list, which is the pasting order of displays. Several keypad key definitions use the display list to cycle through the displays currently on the pasteboard.

Every display belongs to a display kind (see Section 7.2). The display kind determines what type of information the display can capture and display, such as source code, or debugger output. The display kind defines whether displayed data is paged into the memory buffer or discarded when the memory buffer overflows. The display kind also determines how the contents of the display are generated.

The contents of a display are generated in two ways:

• Some displays are automatically updated. Their definition includes a command list that is executed whenever the debugger gains control from the program. The output of the command list forms the contents of those displays. Display SRC belongs to that category: it is automatically updated so that an arrow points to the source line at which execution is currently paused.
• Other displays, for example, display OUT, are updated in response to commands you enter interactively. For a display of this type to be updated, it must first be assigned an appropriate display attribute (with the SELECT command). The display attribute identifies the display as the target display for one or more types of output (see Section 7.3).

The names of any attributes assigned to a display appear to the right of the display name, in lowercase letters. In Figure 7-1, SRC has the source and scroll attributes (SRC is the current source display and the current scrolling display), OUT has the output attribute (it is the current output display), and so on. Note that, although SRC is automatically updated by its own built-in command, it can also receive the output of certain interactive commands (such as EXAMINE/SOURCE) because it has the source attribute.

The concepts introduced in this section are developed in more detail in the rest of this chapter.

7.2 Display Kinds

Every display has a display kind. The display kind determines the type of information a display contains, how that information is generated, and whether the memory buffer associated with the display is paged.

Typically, you specify a display kind when you use the DISPLAY command to create a new display (if you do not specify a display kind, an output display is created). You can also use the DISPLAY command to change the display kind of an existing display with the following keywords:

DO (command[,...])
INSTRUCTION
INSTRUCTION (command)
OUTPUT
REGISTER
SOURCE
SOURCE (command)

The contents of a register display are generated and updated automatically by the debugger. The contents of other kinds of displays are generated by commands, and these display kinds fall into two general groups.

A display that belongs to one of the following display kinds has its contents updated automatically according to the command or command list you supply when defining that display:

DO (command[,...])
INSTRUCTION (command)
REGISTER
SOURCE (command)

The command list specified is executed each time the debugger gains control from your program, if the display is not marked as removed. The output of the commands forms the new contents of the display. If the display is marked as removed, the debugger does not execute the command list until you view that display (marking that display as unremoved).

A display that belongs to one of the following display kinds derives its contents from commands that you enter interactively:

INSTRUCTION
OUTPUT
SOURCE

To direct debugger output to a specific display in this group, you must first select it with the SELECT command. The technique is explained in the following sections and in Section 7.3. After a display is selected for a certain type of output, the output from your commands forms the contents of the display.

7.2.1 DO (Command[;...]) Display Kind

A DO display is an automatically-updated display. The commands in the command list are executed in the order listed each time the debugger gains control from your program. Their output forms the contents of the display and erases any previous contents.

For example, the following command creates the DO display CALLS at window Q3. (Window Q3 refers to screen dimensions of the window. For information about screen dimensions and predefined windows, see Section 7.12.) Each time the debugger gains control from the program, the SHOW CALLS command is executed and the output is displayed in CALLS, replacing any previous contents.

DBG> DISPLAY CALLS AT Q3 DO (SHOW CALLS)

The following command creates a DO display named V2_DISP that shows the contents of elements 4 to 7 of the vector register V2 (using Fortran array syntax). The display is automatically updated whenever the debugger gains control from the program:

DBG> DISPLAY V2_DISP AT RQ2 DO (EXAMINE %V2(4:7))

The default size of the memory buffer associated with any DO display is 64 lines. When the memory buffer is full, the oldest lines are discarded to make room for new text. You can use the DISPLAY/SIZE command to change the buffer size.

7.2.2 INSTRUCTION Display Kind

An instruction display shows the output of an EXAMINE/INSTRUCTION command within the instruction stream of a routine. Because the instructions displayed are decoded from the image being debugged and show the exact code that is executing, this kind of display is particularly useful in helping you debug optimized code (see Section 14.1).

In the display, one line is devoted to each instruction. Source-line numbers corresponding to the instructions are displayed in the left column. The instruction at the location being examined is centered in the display and is marked by an arrow in the left column.

Before anything can be written to an instruction display, you must select it as the current instruction display with the SELECT/INSTRUCTION command.

In the following example, the DISPLAY command creates the instruction display INST2 at RH1. The SELECT/INSTRUCTION command then selects INST2 as the current instruction display. When the EXAMINE/INSTRUCTION X command is executed, window RH1 fills with the instruction stream surrounding the location denoted by X. The arrow points to the instruction at location X, which is centered in the display.

DBG> DISPLAY INST2 AT RH1 INSTRUCTION DBG> SELECT/INSTRUCTION INST2 DBG> EXAMINE/INSTRUCTION X

Each subsequent EXAMINE/INSTRUCTION command updates the display.

The default size of the memory buffer associated with any instruction display is 64 lines; however, you can scroll back and forth to view all the instructions within the routine. You can use the DISPLAY/SIZE command to change the buffer size and improve performance.

7.2.3 INSTRUCTION (Command) Display Kind

This is an instruction display that is automatically updated with the output of the command specified. That command, which must be an
EXAMINE/INSTRUCTION command, is executed each time the debugger gains control from your program.

For example, the following command creates the instruction display INST3 at window RS45. Each time the debugger gains control, the built-in command EXAMINE/INSTRUCTION .%INST_SCOPE\%PC is executed, updating the display.

DBG> DISPLAY INST3 AT RS45 INSTRUCT (EX/INST .%INST_SCOPE\%PC)

This command creates a display that functions like the predefined display INST. The built-in EXAMINE/INSTRUCTION command displays the instruction at the current PC value in the current scope (see Section 7.4.4).

If an automatically updated instruction display is selected as the current instruction display, it is updated like a simple instruction display by an interactive EXAMINE/INSTRUCTION command (in addition to being updated by its built-in command).

The default size of the memory buffer associated with any instruction display is 64 lines; however, you can scroll back and forth to view all the instructions within the routine. You can use the DISPLAY/SIZE command to change the buffer size and improve performance.

7.2.4 OUTPUT Display Kind

An output display shows any debugger output that is not directed to another display. New output is appended to the previous contents of the display.

Before anything can be written to an output display, it must be selected as the current output display with the SELECT/OUTPUT command, or as the current error display with the SELECT/ERROR command, or as the current input display with the SELECT/INPUT command. See Section 7.3 for more information about using the SELECT command with output displays.

In the following example, the DISPLAY command creates the output display OUT2 at window T2 (the display kind OUTPUT can be omitted from this example, because it is the default kind). The SELECT/OUTPUT command then selects OUT2 as the current output display. These two commands create a display that functions like the predefined display OUT:

DBG> DISPLAY OUT2 AT T2 OUTPUT DBG> SELECT/OUTPUT OUT2

OUT2 now collects any debugger output that is not directed to another display. For example:

• The output of a SHOW CALLS command goes to OUT2.
• If no instruction display has been selected as the current instruction display, the output of an EXAMINE/INSTRUCTION command goes to OUT2.
• By default, debugger diagnostic messages are directed to the PROMPT display. They can be directed to OUT2 with the SELECT/ERROR command.

The default size of the memory buffer associated with any output display is 64 lines. When the memory buffer is full, the oldest lines are discarded to make room for new text. You can use the DISPLAY/SIZE command to change the buffer size.

7.2.5 REGISTER Display Kind

A register display is an automatically updated display that shows the current values, in hexadecimal format, of the processor registers and as many of the top call-stack values as will fit in the display.

The register values displayed are for the routine in which execution is currently paused. The values are updated whenever the debugger takes control. Any changed values are highlighted.

There are up to three predefined register displays. The REG and IREG displays are predefined on VAX, Alpha, and Itanium® processors. The FREG display is predefined on Alpha and Itanium® processors. The contents of the predefined displays is shown in Table 7-1.

Table 7-1 Predefined Register Displays

Display	VAX	Alpha	Intel® Itanium®
REG	- R0 to R15 - PSL Does not contain vector registers. To display vector registers in screen mode, use a DO display (see Section 7.2.1).	- R0 to R31 - PC - PS - F0 to F31 - FPCR - SFPCR - top of call-stack values	- PC - CFM - R1 to R31 - R32 to R127 ( as many as are used) - F2 to F127 - top-of-stack values
IREG	Same information as in the REG display, shown in a different order. This display is provided to allow debugger .COM and .INI files to be ported and shared.	- R0 to R31 - PC - PS - top of call-stack values The data are shown in hexadecimal format.	- PC - CFM - R1 to R31 - top of call-stack values The data are shown in hexadecimal format.
FREG	Not Defined.	- F0 to F31 - FPCR - SFPCR - top of call-stack values The data are shown in floating-point format.	- F2 to F127 - top-of-stack values The register data are shown in the format consistent with the data value (integer or floating-point); the stack values are shown in floating-point format.

On VAX processors, the predefined display REG contains, in hexadecimal format, general-purpose registers R0 to R15 and the PSL, but does not contain the vector registers. To display data contained in vector registers or vector control registers in screen mode, use a DO display (see Section 7.2.1).

On VAX processors, the predefined display IREG contains the same information as the predefined display REG, but the display window is configured differently. Display IREG is included in the VAX implementation to allow debugger .COM and .INI files to be ported more easily between VAX and Alpha debugging applications.

On Alpha processors, the predefined display REG contains, in hexadecimal format, general-purpose registers R0 to R28, FP (R29), SP (R30), R31, PC, PS floating-point registers F0 to F31, FPCR, SFPCR, and as many of the top call-stack values as will fit in the display.

On Alpha processors, the predefined display IREG contains, in hexadecimal format, general-purpose registers R0 to R28, FP, and as many of the top call-stack values as can be displayed in the window.

On Alpha processors, the predefined display FREG contains floating-point registers F0 to F31, FPCR, SFPCR, displayed in floating-point format and as many of the top call-stack values (in hexadecimal format) as can be displayed in the window.

The default size of the memory buffer associated with any register display is 64 lines. When the memory buffer is full, the oldest lines are discarded to make room for new text. You can use the DISPLAY/SIZE command to change the buffer size.

7.2.6 SOURCE Display Kind

A source display shows the output of a TYPE or EXAMINE/SOURCE command within the source code of a module, if that source code is available. Source line numbers are displayed in the left column. The source line that is the output of the command is centered in the display and is marked by an arrow in the left column. If a range of lines is specified with the TYPE command, the lines are centered in the display, but no arrow is shown.

Before anything can be written to a source display, you must select it as the current source display with the SELECT/SOURCE command.

In the following example, the DISPLAY command creates source display SRC2 at Q2. The SELECT/SOURCE command then selects SRC2 as the current source display. When the TYPE 34 command is executed, window RH1 fills with the source code surrounding line 34 of the module being debugged. The arrow points to line 34, centered in the display.

DBG> DISPLAY SRC2 AT Q2 SOURCE DBG> SELECT/SOURCE SRC2 DBG> TYPE 34

Each subsequent TYPE or EXAMINE/SOURCE command updates the display.

The default size of the memory buffer of a source display is 64 lines. The memory buffer of a source display is paged, enabling you to scroll back and forth through the entire source module or routine. You can use the DISPLAY/SIZE command to change the buffer size to improve performance.

7.2.7 SOURCE (Command) Display Kind

This is a source display that is automatically updated with the output of the command specified. That command, which must be an EXAMINE/SOURCE or TYPE command, is executed each time the debugger gains control from your program.

For example, the following command creates source display SRC3 at window RS45. Each time the debugger gains control, it executes the built-in command EXAMINE/SOURCE .%SOURCE_SCOPE\%PC and updates the display.

DBG> DISPLAY SRC3 AT RS45 SOURCE (EX/SOURCE .%SOURCE_SCOPE\%PC)

This command creates a display that functions like the predefined display SRC. The built-in EXAMINE/SOURCE command displays the source line for the current PC value in the current scope (see Section 7.4.1).

If you select an automatically updated source display as the current source display, it displays the output generated by an interactive
EXAMINE/SOURCE or TYPE command in addition to the output generated by its built-in command.

The default size of the memory buffer of a source display is 64 lines. The memory buffer of an automatically updated source display is paged, enabling you to scroll back and forth through the entire source module or routine. You can use the DISPLAY/SIZE command to change the buffer size to improve performance.