WM-DEB(1) WM-DEB(1)
NAME
deb - graphical Limbo debugger
SYNOPSIS
wm/deb [-f file] [-p pid]
DESCRIPTION
Wm/deb displays two windows, the main debugging window and a
stack window for browsing the data values of the thread cur-
rently 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 per-
formed by binding the remote /prog directory in place of the
local one. (See bind(1)).
In order to display source code and set breakpoints accu-
rately, 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 indi-
vidual 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 break-
point.
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
Page 1 Plan 9 (printed 11/17/24)
WM-DEB(1) WM-DEB(1)
single stepping, function calls are stepped into. Stepping
commands 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 pro-
vided, whereby execution continues 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 dis-
played in a hierarchical 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 displayed 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.
Page 2 Plan 9 (printed 11/17/24)
WM-DEB(1) WM-DEB(1)
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 char-
acters 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 associ-
ated executable file (.dis) is not launched until
the continue (run to breakpoint) button is
pressed. This option takes precedence 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 ALSO
limbo(1), prog(3)
BUGS
Displaying large arrays in the Stack window can use exces-
sive amounts of memory.
When setting breakpoints there is no visual cue for the
selected statement or operation until the breakpoint is
actually set.
It is only possible to debug modules executed by the inter-
preter. Code that has been JITed, the compilation execution
method, yields stack information that does not correspond to
information in the symbol (.sbl) file.
Page 3 Plan 9 (printed 11/17/24)