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debug - process debugging


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);


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 current directory in which to put the new process; ctxt and argv are the arguments given to the new process. Startprog returns a tuple (progerr) where prog can be used to interrogate 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 similar to startprog, except that it attaches to an already running process identified by pid.

Controlling a process
A Prog adt provides routines for controlling a running process. It implements the following routines. Unless otherwise stated, they return nil on success and a diagnostic string on error.

Run the program until a break point is reached.
Delbpt deletes the breakpoint in the Dis module with filename dis at Dis instruction pc.
Event waits for a state transition in the running prog and returns the new state, as returned by a read of the dbgctl file (see prog(3)).
Grab stops the prog and puts it into a state where single stepping is possible.
Kill kills prog.
Setbpt sets a breakpoint in the Dis module with filename dis at Dis instruction pc.
Stack returns a tuple (expserr) 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.
Start runs prog until it hits a breakpoint or exits.
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.
Step steps prog forward in a manner specified by how, which is one of the following constants:
Step one expression evaluation.
Step one source statement.
Step over one called function.
Step until the current function has returned.
Stop prog from running.
Release a program from its stopped state; breakpoints 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 represents 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 calling sym(p) where p is the pathname of the symbol file; sym returns a tuple (symerr), where if sym is nil, err contains 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 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 findsym on it to locate the function's data.

The name of the symbol.
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.
Val returns a tuple (sflag) where s is a string representation of the value of exp, and if flag is zero, exp cannot be expanded.
Src returns the file range associated with exp.
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, otherwise it returns an error indicating the problem.
Srcstr returns a string representing the position in the source file of exp.






wm-deb(1), prog(3)


There is no way of looking at the types of the data extracted.

DEBUG(2 ) Rev:  Tue Mar 31 02:42:39 GMT 2015