DEB(1)DEB(1)NAMEdeb - graphical Limbo debugger
SYNOPSIS
wm/deb [-f file] [-p pid]
DESCRIPTION
Wm/deb displays two windows, the main debugging window and a stack win‐
dow for browsing the data values of the thread currently being
debugged.
Debugging is performed using the facilities of the prog device bound to
the local /prog directory (see prog(3)). Debugging of code running on
a remote machine can be performed by binding the remote /prog directory
in place of the local one. (See bind(1)).
In order to display source code and set breakpoints accurately, an up
to date symbol file (.sbl) must be available as well as the limbo
source file (.b).
Main window
The main window is comprised of a menu bar, an icon bar and three text
panels. One panel, labelled Threads, lists the process IDs (PIDs) of
the threads being debugged. Another panel, labelled Break, lists the
set of breakpoints, each given a unique number. The third and largest
panel displays the source code of the thread being debugged.
Breakpoint positions are shown by red text in the source code display.
Clicking on a breakpoint number in the Break panel results in the
source code panel being scrolled or updated to show the breakpoint.
Breakpoints are toggled by clicking on the statement or sub-expression
in the source code window and clicking the breakpoint button on the
icon bar. A breakpoint can be hit by any of the threads being debugged
- breakpoints are set on source code, not on individual threads.
Clicking on a PID in the Threads panel results in the source code panel
being scrolled or updated to highlight where in the code the thread is
blocked, broken or halted on a breakpoint.
A running thread can be halted by clicking the stop button on the icon
bar. A thread will also halt when it hits a breakpoint. Once a thread
is halted (not blocked or broken) its execution can be advanced a step
at a time by means of the buttons on the icon bar. The thread can be
stepped one operation at a time or a statement at a time. Normally
when single stepping, function calls are stepped into. Stepping com‐
mands allow for stepping over function calls, whereby the function is
still called but its whole execution is treated as a single step.
Stepping out of a function is also provided, whereby execution contin‐
ues unabated until returning from the function. Execution of the
halted thread can be continued, running until it terminates, breaks or
hits another breakpoint.
Any of the threads being debugged can be killed or detached from the
debugger using buttons on the icon bar. Detaching a halted thread
resumes its execution.
The main window provides a set of menus for viewing source files,
attaching to other threads, setting debugger options and searching for
text in the source code window.
Stack Window
The stack window is used to inspect the values of local and global
variables and function arguments. Items are displayed in a hierarchi‐
cal manner. Any item that contains other items, such as a variable of
an ADT type, can be expanded to show the values of the sub-items. The
sub-items are displayed by clicking on the expand button on the left of
the containing item, they can be hidden by pressing the button again.
The sub-item list is displayed indented from its container as a visual
cue to their association.
The stack window shows the full stack trace of the current thread. The
stack trace is displayed as a list of frames, the current frame dis‐
played at the top of the window. Each frame is given by the function
name and source location of the code being executed in the frame. Each
frame has the following sub-items:
locals Local variables declared in the function of the frame.
args The arguments passed to the frame function.
module The module global variables in the implementation module of
the frame function.
Clicking on the name of a variable or function argument highlights the
declaration of that name in the source panel of the main debug window.
Clicking on the function name of a stack frame causes the main window
source panel to display the current statement of the frame.
The debugger has a stack button which simply brings that window to the
front of the display.
The options menu has a layout configuration which allows the user to
have a horizontal scroll bar or to wrap long lines (the default); and
an option to strip carriage return characters that precede newlines
(for the benefit of those using Windows' editors). The state of the
options is saved in the file /usr/username/lib/deb if that file can be
created. The debugger attempts to read this file on startup to set the
user's preferred options.
OPTIONS-f file Specifies a source file (.b) to load. The associated exe‐
cutable file (.dis) is not launched until the continue (run
to breakpoint) button is pressed. This option takes prece‐
dence over the -p option.
-p pid Attach to the already running thread given by pid.
PLUMBING
wm/deb plumbs the address of text selected using button 3 in the source
display panel, as text of the form
file-name:line-number
FILES
/prog/n/*
/usr/username/lib/deb
SOURCE
/appl/wm/deb.b
/appl/wm/debdata.b
/appl/wm/debsrc.b
SEE ALSOlimbo(1), prog(3)BUGS
Displaying large arrays in the Stack window can use excessive amounts
of memory.
When setting breakpoints there is no visual cue for the selected state‐
ment or operation until the breakpoint is actually set.
It is only possible to debug modules executed by the interpreter. Code
that has been JITed, the compilation execution method, yields stack
information that does not correspond to information in the symbol
(.sbl) file.
DEB(1)
