DEBUG(2) DEBUG(2)
NAME
debug - process debugging
SYNOPSIS
include "debug.m";
debug := load Debug Debug->PATH;
Pos: adt
{
file: string;
line: int;
pos: int;
};
Src: adt
{
start: Pos; # range within source files
stop: Pos;
};
Sym: adt
{
srctopc: fn(s: self ref Sym, src: ref Src): int;
pctosrc: fn(s: self ref Sym, pc: int): ref Src;
};
Module: adt
{
addsym: fn(m: self ref Module, sym: ref Sym);
stdsym: fn(m: self ref Module);
dis: fn(m: self ref Module): string;
sbl: fn(m: self ref Module): string;
};
Prog: adt
{
cont: fn(p: self ref Prog): string;
delbpt: fn(p: self ref Prog, dis: string, pc: int): string;
event: fn(p: self ref Prog): string;
grab: fn(p: self ref Prog): string;
kill: fn(p: self ref Prog): string;
setbpt: fn(p: self ref Prog, dis: string, pc: int): string;
stack: fn(p: self ref Prog): (array of ref Exp, string);
start: fn(p: self ref Prog): string;
status: fn(p: self ref Prog): (int, string, string, string);
step: fn(p: self ref Prog, how: int): string;
stop: fn(p: self ref Prog): string;
unstop: fn(p: self ref Prog): string;
};
Exp: adt
{
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DEBUG(2) DEBUG(2)
name: string;
m: ref Module;
expand: fn(e: self ref Exp): array of ref Exp;
val: fn(e: self ref Exp): (string, int);
src: fn(e: self ref Exp): ref Src;
findsym:fn(e: self ref Exp): string;
srcstr: fn(e: self ref Exp): string;
};
init: fn(): int;
startprog: fn(dis, dir: string, ctxt: ref Draw->Context,
argv: list of string): (ref Prog, string);
prog: fn(pid: int): (ref Prog, string);
sym: fn(sbl: string): (ref Sym, string);
DESCRIPTION
Debug is the module interface to the debugging facilities
provided by prog(3). It allows facilities for inspection of
a program's data structures, as it is running, and to start
and stop a running program under program control. Init must
be called before any other function to initialise debug's
global state.
Startprog starts up a program under control of the debug
module. Dis is the full pathname of the Dis module to load
(which must be compatible with command(2); dir is the cur-
rent directory in which to put the new process; ctxt and
argv are the arguments given to the new process. Startprog
returns a tuple (prog, err) where prog can be used to inter-
rogate and control the running process, as detailed below,
unless there is an error, in which case prog will be nil,
and err contains a description of the error. Prog is simi-
lar to startprog, except that it attaches to an already run-
ning process identified by pid.
Controlling a process
A Prog adt provides routines for controlling a running pro-
cess. It implements the following routines. Unless other-
wise stated, they return nil on success and a diagnostic
string on error.
prog.cont()
Run the program until a break point is reached.
prog.delbpt(dis, pc)
Delbpt deletes the breakpoint in the Dis module
with filename dis at Dis instruction pc.
prog.event()
Event waits for a state transition in the running
prog and returns the new state, as returned by a
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DEBUG(2) DEBUG(2)
read of the dbgctl file (see prog(3)).
prog.grab()
Grab stops the prog and puts it into a state where
single stepping is possible.
prog.kill()
Kill kills prog.
prog.setbpt(dis, pc)
Setbpt sets a breakpoint in the Dis module with
filename dis at Dis instruction pc.
prog.stack()
Stack returns a tuple (exps, err) where exps is an
array of Exp adts, each representing one frame of
the current execution stack of prog. If an error
occurs, exps will be nil, and err will contain a
description of the error.
prog.start()
Start runs prog until it hits a breakpoint or
exits.
prog.status()
Status returns a tuple (pgrp, user, state, module)
where pgrp is the process group id of prog, user
is the owner of the process, state is the current
state of the process, and module is the module
implementation name of the currently executing
module.
prog.step(how)
Step steps prog forward in a manner specified by
how, which is one of the following constants:
StepExp
Step one expression evaluation.
StepStmt
Step one source statement.
StepOver
Step over one called function.
StepOut
Step until the current function has returned.
prog.stop()
Stop prog from running.
prog.unstop()
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DEBUG(2) DEBUG(2)
Release a program from its stopped state; break-
points will no longer be triggered.
Inspecting data
The Exp adt provides facilities for inspecting the data
structures of a running Dis process. A hierarchical data
structure can be expanded into an array of its component
Exps, as long as the appropriate symbol information has been
located correctly using stdsym or addsym, and findsym.
A Pos represents a position in a Limbo source code file; it
holds the source file name, the line number (origin 1) and
the character within the line (origin 0). The Src adt rep-
resents a range in a Limbo source code file; Src.start and
Src.stop represent the beginning and the end of the range,
respectively.
A Sym represents a .sbl symbol file, and is created by call-
ing sym(p) where p is the pathname of the symbol file; sym
returns a tuple (sym, err), where if sym is nil, err con-
tains an error message. A Sym can map between a Dis PC and
a source file address, and vice versa. For a given Sym sym,
sym.srctopc(src) returns the PC associated with src (or -1
on error); sym.pctosrc converts the other way (and returns
nil on error).
Each element e in the top level stack, as returned by
Prog.stack, has an associated Module e.m which needs to be
associated with a Sym so that debug can glean from it the
type information it needs. Given a module m, m.stdsym()
will try and find a symbol file in a standard place, but
this will fail if the symbol file or the Dis file is in a
non-standard place. M.addsym(s) sets the symbol file for m
to the Sym s. M.dis() and m.sbl() return the paths of the
Dis and symbol files associated with m respectively.
Each top level stack element expands into three elements,
``args'', ``locals'', and ``module'', representing the argu-
ments to the function, the function's local variables, and
the module-global variables of the function's module respec-
tively. Before a top level stack element can be expanded,
it is necessary to call findsym on it to locate the
function's data.
exp.name The name of the symbol.
exp.expand()
Expand a hierarchical structure into an array of
its component elements. A list element expands
into two elements named ``hd'' and ``tl''; a tuple
into elements named ``t0'', ``t1'',..., an array
into elements named ``0'', ``1'',..., etc.
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DEBUG(2) DEBUG(2)
exp.val() Val returns a tuple (s, flag) where s is a string
representation of the value of exp, and if flag is
zero, exp cannot be expanded.
exp.src() Src returns the file range associated with exp.
exp.findsym()
If exp is a top level stack frame (i.e. one of the
members of the array returned by Prog.stack) then
findsym will attempt to locate its type and name.
If it succeeds, it returns the null string, other-
wise it returns an error indicating the problem.
exp.srcstr()
Srcstr returns a string representing the position
in the source file of exp.
FILES
/prog/pid/*
SOURCE
/appl/lib/debug.b
SEE ALSO
wm-deb(1), prog(3)
BUGS
There is no way of looking at the types of the data
extracted.
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