The Source Window

The Source Window is the primary interface between the user and the debugger; it is automatically opened when the debugger starts. The Source Window displays the status of the program, controls execution of the program, and allows visualization of the program execution.

Search Entry

Menus

File Menu

Open: Opens a file selection dialog to select the executable to debug
Close: Closes a previously opened executable file
Source: Reads and executes GDB commands from a text file
Target Settings...: Opens the Target Selection Dialog to edit target settings
Page Setup: (Windows only) Opens the Windows Page Setup dialog to configure printing
Print: Print the contents of the Source Window Display
Exit: Exits the debugger

Run Menu

Connect to target: Connect to the target specified in the Target Selection Dialog. Open the dialog if there are no current settings.
Download: Initiates download of the executable onto the target via the protocol specified in the Target Selection Dialog
Run: Runs or re-runs the program
Disconnect: Close a previously opened connection

View Menu

Stack: Open a Stack Window
Registers: Open a Register Window
Memory: Open a Memory Window
Watch Expressions: Open a Watch Window
Local Variables: Open a Locals Window
Breakpoints: Open a Breakpoint Window
Console: Open a Console Window
Function Browser: Open a window allowing the user to easily search for functions and set breakpoints.
Thread List: Open a window that displays all current threads and allows the user to change active threads

Control Menu

Step: Step program until it reaches a different source line
Next: Step program, proceeding through subroutine calls
Finish: Execute until the current stack frame returns
Continue: Continue program being debugged, after signal or breakpoint
Step Asm Inst: Step one instruction exactly
Next Asm Inst: Step one instruction, but proceed through subroutine calls
Automatic Step: Automatically step the program every two seconds

Preferences Menu

Global: Opens the Global Preferences Dialog and allows editing of global settings
Source: Opens the Source Preferences Dialog and allows editing of Source Window settings

Toolbar

The Source Window toolbar consists of three functional sections: execution control buttons, debugger window buttons, and stack frame control buttons.

Execution Control Buttons

These convenience buttons provide on-screen access to the most important debugger execution control functions:

or Run: The Run Button will start execution of the program, including target selection and downloading, if necessary. If the program is already running, the Run Button will start the program from the beginning (re-run it).
or Stop: The Stop Button will interrupt execution of the program (provided this feature is supported by the underlying debugging protocol and hardware) or cancel downloads. It is also used as an indication that the debugger is busy.
or Step: Step the program until it reaches a different source line
or Next: Step the program, proceeding through subroutine calls
or Finish: Execute until the current stack frame returns
or Continue: Continue the program being debugged, after signal or breakpoint
or Step Asm Inst: Step one instruction exactly. This function is only available when the Source Window is displaying assembler code.
or Next Asm Inst: Step one instruction, but proceed through subroutine calls. This function is only available when the Source Window is displaying assembler code.

Window Buttons

The Debugger Window buttons give instant access to the Debugger's auxiliary windows:

or Registers: Open a Register Window
or Memory: Open a Memory Window
or Stack: Open a Stack Window
or Watch Expressions: Open a Watch Window
or Local Variables: Open a Locals Window
or Breakpoints: Open a Breakpoint Window
or Console: Open a Console Window

Frame Control

The Frame Control area of the toolbar displays information about the PC of the current frame, and the frame control buttons may be used to navigate through the call stack. Whenever any of these buttons are used, both the Source Window Display and the Stack Window will show the selected frame.

Frame Information Display: The left half of the frame information display shows the value of the PC in the current frame. The right half shows the line number of the PC in the source file, if available.
or Up: Select and view the stack frame that called this one
or Down: Select and view the stack frame called by this one
or Bottom: Select and view the bottom-most stack frame

Source Display

The Source Display is used for many things: browsing source code, setting and clearing breakpoints, and a few other special functions. Executable lines (those for which executable code was generated by the compiler) are denoted with a marker (a dash, "-") in the first column of the display.

The debugger highlights the PC in the current frame in either green, indicating that the PC is in the bottom-most frame (i.e., it is being executed) or gold, indicating that the PC is contained in a frame that is not currently executing (because it has called another function). A blue highlight is used by the debugger to indicate a browsing position: the PC is contained in a frame that is not executing or on the call stack. All highlight colors are user selectable in the Source Preferences.

Setting a Breakpoint

Moving the mouse pointer over the "hot spot" of an executable line will change the mouse cursor to a large dot. Clicking the left mouse button will then toggle a breakpoint at this line. If no breakpoint exists, one will be installed and the dash in the left margin will change into a red breakdot. If a breakpoint exists, it will be removed and the red breakdot will revert back to a dash. The executable line marker shows the status of each line: an empty marker (the dash) indicates that no breakpoints are set at the line. A colored breakdot indicates that a breakpoint exists at the line (see Source Pop-up Menus for more information on setting different types of breakpoints and their representations in the Source Display).

Black breakdots in the Source Window display indicate that the breakpoint has been disabled. To re-enable the breakpoint, click the enable/disable checkbox in the Breakpoint Window (see Enabling/Disabling Breakpoints).

Viewing Breakpoints

You can find out more information about a breakpoint by moving the cursor over a breakpoint. A balloon window will pop up with additional information. To get a list of all the active breakpoints, you will need to open a breakpoint window.

Variable Balloons

If the program to be debugged has started and is stopped, the display will show the value of variables in variable balloons. To activate a variable balloon, simply hold the mouse cursor over the name of a variable in the Source Display for a second or two: the debugger displays the name of the variable, its type, and its value in a pop-up balloon.

Source Pop-up Menus

The Source Display has two pop-up menus. One is activated by clicking the right mouse button when the mouse cursor is over an executable line marker's hot spot. This pop-up menu looks like this:

Continue to Here: Continue program execution until it reaches this point. All breakpoints will be ignored. Be aware that if the program never executes the line you selected, it will run until completion.
Set Breakpoint: Set a breakpoint at this line. This has the same effect as left clicking on this line. Breakpoints are shown as red breakdots in the Source Window Display.
Set Temporary Breakpoint: Set a temporary breakpoint at this line. Temporary breakpoints are shown as orange breakdots in the Source Window Display. The remove themselves automatically the first time they are hit.
Set Breakpoint on Thread(s)...: GDB allows the user to set a breakpoint on a particular thread or threads. This menu item will display a dialog with a list of threads. The user can select a list of threads that will have breakpoints set at the selected line number. A warning will be displayed if there are no active threads.

The other pop-up menu is activated by clicking the right mouse button anywhere else in the Source Display. It is only available when a variable or number in the display lies below the mouse cursor or is selected (by clicking the left mouse button and dragging the mouse to highlight the variable/number). The pop-up menu looks like this:

Add expr to Watch: Adds the selected expression to the Watch Window, opening it, if necessary.
Dump Memory at expr: Opens a new Memory Window at the selected expression. If the expression is a variable, then the Memory Window is opened with memory addresses starting at the value of the variable.
Open Another SOurce Window: GDB allows multiple source windows to co-exist. You can, for example, have one window in source mode and one in assembly mode. Or you can use one window to browse the stack or other files.

Source Window Status Bars

The Source Window has two status bars which inform the user of the status of the program (the "status bar") and the status of the Source Window.

The Program Status Bar (or simply "Status Bar") displays the status of the program. Common messages seen here include:

No program loaded.: No program has been loaded into target memory.
Program is ready to run.: A program has been loaded into target memory and may be executed. Start the program by hitting Run.
Program stopped at line/address: The program stopped at line line or address address. Execution may continue by hitting any of the execution control buttons on the toolbar.
Program terminated. 'Run' will restart.: The program exited. Pressing Run will restart it.

The Status Bar also displays some help information. For instance, the Status Bar will show the function of a button on the toolbar or the Source Display Status Bar as well as any keyboard shortcut for any button in the Source Window.

Source Display Status Bar

The Source Display Status Bar shows the current state of the Source Window: the name of the file displayed in the Display, the name of the function in the Display which contains the PC for the current frame (if any), and the display mode.

The Source File Selector is a dropdown menu which contains the names of all the files that were compiled into the program being debugged.

Normally, the File Selector displays the name of the file currently being viewed, but any file from the dropdown menu may be selected for browsing. Simply select the file to view from the available choices (or type it directly into the File Selector) and the Source Window will load that file into the Display. To return to the PC of the program, simply press the Bottom Frame Control Button.

The Source Function Selector displays the name of the function containing the Source Window's PC, if one exists, but it may be used to browse any function in the current file. Simply type the name of the desired function into the Function Selector or select it from the dropdown menu. The Source Window's PC is updated to point at this function. To return to the PC of the program, simply press the Bottom Frame Control Button.

The Source Display Mode Selector displays the viewing mode of the current file/function shown in the Source Window Display.

The function of the "step" keyboard shortcut will differ depending on the mode the Source Window Display. "Stepping" in Source Mode (or in the Source Pane of SRC+ASM Mode) will cause a source-level step. "Stepping" in Assembly or Mixed Mode (or in the Assembly Pane of the SRC+ASM Mode) will cause the debugger to step exactly one machine instruction. This also applies to the shortcut for "next".

The Display Mode Selector may be used to change the view of the current source file. The available display modes are

SOURCE: The contents of the Display are shown as source code. If source code is not available (either because no debugging information is available or the source file is not found), the Source Window will temporarily set the Display Mode to "ASSEMBLY".
ASSEMBLY: A disassembly of the target's memory is shown in the Display. Even assembly source files show a disassembly of target memory; to see the assembly source code, use the SOURCE mode. Note that the debugger can only display assembly code on a function-by-function basis. It cannot display all the instructions generated from a single source file.
MIXED: The Display shows source code mixed with the assembler instructions which were generated for those lines by the compiler for the current function. Note that the addresses of the assembly lines is not necessarily monotonically increasing. If the source file associated with the function cannot be found, the Source Window will revert to ASSEMBLY mode.
SRC+ASM: The Source Window Display is divided into two panes: an assembly pane and a source pane. Breakpoints may be set/cleared in either pane.

Search Entry

The Search Entry facilitates searching for text in the Source Window Display. Simply enter the text to be found into the Search Entry and press the Enter key on the keyboard to search forwards in the Source Window Display (hold down the Shift key to search backwards). If a match is found, it is highlighted in the Source Window and the Program Status Bar displays information about where the match was found.

The Search Entry can also jump the Source Window to a specific line. Enter the line number preceded by an "at" sign (@) into the Search Entry and press enter. If entered line number is greater than the total number of lines in the Source Window Display, the Display will jump to the end of the current file.