ref: 948870cffe2572efb68ef0b3873b36238fb53263
dir: /man/2/debug/
.TH DEBUG 2
.SH NAME
debug \- process debugging
.SH SYNOPSIS
.EX
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
{
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);
.EE
.SH DESCRIPTION
.B Debug
is the module interface to the debugging facilities provided by
.IR 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.
.B Init
must be called before any other function to initialise
.IR debug 's
global state.
.PP
.B Startprog
starts up a program under control of the debug module.
.I Dis
is the full pathname of the Dis module to load (which must
be compatible with
.IR command (2);
.I dir
is the current directory in which to put the new process;
.I ctxt
and
.I argv
are the arguments given to the new process.
.B Startprog
returns a tuple
.RI ( prog ,\ err )
where
.I prog
can be used to interrogate and control the running process,
as detailed below, unless there is an error, in which case
.I prog
will be nil, and
.I err
contains a description of the error.
.B Prog
is similar to startprog, except that it attaches to an
already running process identified by
.IR pid .
.SS Controlling a process
A
.B Prog
adt provides routines for controlling a running process.
It implements the following routines.
Unless otherwise stated, they return
.B nil
on success and a diagnostic string on error.
.TP 10
.IB prog .cont()
Run the program until a break point is reached.
.TP
.IB prog .delbpt(\fIdis\fP,\ \fIpc\fP)
.B Delbpt
deletes the breakpoint in the Dis module with filename
.I dis
at Dis instruction
.IR pc .
.TP
.IB prog .event()
.B Event
waits for a state transition in the running
.I prog
and returns the new state, as returned by a read
of the
.B dbgctl
file (see
.IR prog (3)).
.TP
.IB prog .grab()
.B Grab
stops the
.I prog
and puts it into a state where single stepping
is possible.
.TP
.IB prog .kill()
.B Kill
kills
.IR prog .
.TP
.IB prog .setbpt(\fIdis\fP,\ \fIpc\fP)
.B Setbpt
sets a breakpoint in the Dis module with filename
.I dis
at Dis instruction
.IR pc .
.TP
.IB prog .stack()
.B Stack
returns a tuple
.RI ( exps ,\ err )
where
.I exps
is an array of
.B Exp
adts, each representing one frame of the current
execution stack of
.IR prog .
If an error occurs,
.I exps
will be nil, and
.I err
will contain a description of the error.
.TP
.IB prog .start()
.B Start
runs
.I prog
until it hits a breakpoint or exits.
.TP
.IB prog .status()
.B Status
returns a tuple
(\fIpgrp\fP, \fPuser\fP, \fPstate\fP, \fPmodule\fP)
where
.I pgrp
is the process group id of
.IR prog ,
.I user
is the owner of the process,
.I state
is the current state of the process, and
.I module
is the module implementation name of the currently
executing module.
.TP
.IB prog .step(\fIhow\fP)
.B Step
steps
.I prog
forward in a manner specified by
.IR how ,
which is one of the following constants:
.RS
.TP
.B StepExp
Step one expression evaluation.
.TP
.B StepStmt
Step one source statement.
.TP
.B StepOver
Step over one called function.
.TP
.B StepOut
Step until the current function has returned.
.RE
.TP
.IB prog .stop()
Stop
.IR prog
from running.
.TP
.IB prog .unstop()
Release a program from its stopped state;
breakpoints will no longer be triggered.
.SS "Inspecting data"
The
.B 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
.BR Exp s,
as long as the appropriate symbol information has
been located correctly using
.B stdsym
or
.BR addsym ,
and
.BR findsym .
.PP
A
.B 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
.B Src
adt represents a range in a Limbo source code file;
.B Src.start
and
.B Src.stop
represent the beginning and the end of the
range, respectively.
.PP
A
.B Sym
represents a
.B .sbl
symbol file, and is created by calling
.BI sym( p )
where
.I p
is the pathname of the symbol file;
.B sym
returns a tuple
.RI ( sym ,\ err ),
where if
.I sym
is nil,
.I err
contains an error message.
A
.B Sym
can map between a Dis PC and a source file address,
and vice versa.
For a given
.B Sym
.IR sym ,
.IB sym .srctopc( src )
returns the PC associated with
.IR src
(or -1 on error);
.IB sym .pctosrc
converts the other way (and returns
.B nil
on error).
.PP
Each element
.I e
in the top level stack, as returned by
.BR Prog.stack ,
has an associated
.B Module
.IB e .m
which needs to be associated with a
.B Sym
so that
.I debug
can glean from it the type information it needs.
Given a module
.IR m ,
.IB 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.
.IB M .addsym( s )
sets the symbol file for
.I m
to the
.B Sym
.IR s .
.IB M .dis()
and
.IB m .sbl()
return the paths of the Dis and symbol files associated
with
.I m
respectively.
.PP
Each top level stack element
expands into three elements, ``args'', ``locals'',
and ``module'', representing the arguments to the function,
the function's local variables, and the module-global
variables of the function's module respectively.
Before a top level stack element can be expanded,
it is necessary to call
.B findsym
on it to locate the function's data.
.TP 10
.IB exp .name
The name of the symbol.
.TP
.IB 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.
.TP
.IB exp .val()
.B Val
returns a tuple
.RI ( s ,\ flag )
where
.I s
is a string representation of the value of
.IR exp ,
and if
.I flag
is zero,
.I exp
cannot be expanded.
.TP
.IB exp .src()
.B Src
returns the file range associated with
.IR exp.
.TP
.IB exp .findsym()
If
.I exp
is a top level stack frame (i.e. one of the members of the array
returned by
.BR Prog.stack )
then
.B findsym
will attempt to locate its type and name. If it succeeds,
it returns the null string, otherwise it returns
an error indicating the problem.
.TP
.IB exp .srcstr()
.B Srcstr
returns a string representing the position in the source file
of
.IR exp .
.SH FILES
.BI /prog/ pid /*
.SH SOURCE
.B /appl/lib/debug.b
.SH SEE ALSO
.IR wm-deb (1),
.IR prog (3)
.SH BUGS
There is no way of looking at the types of the data extracted.