Provided by: libdevel-gdb-perl_2.02-2_all 
NAME
Devel::GDB - Open and communicate a gdb session
SYNOPSIS
use Devel::GDB;
$gdb = new Devel::GDB();
print $gdb->send_cmd('-environment-path');
print $gdb->get('info functions');
The old "get" syntax (of "Devel::GDB-1.23") has been deprecated and will not be supported
in future versions. See the documentation of the "get" function for an explanation of
why.
If you really want to use the old syntax, set $Devel::GDB::DEPRECATED to true:
use Devel::GDB ;
$Devel::GDB::DEPRECATED = 1;
$gdb = new Devel::GDB();
print $gdb->get('info functions', $timeout, $prompt, $notyet, $alldone);
DESCRIPTION
The "Devel::GDB" package provides an interface for communicating with GDB. Internally, it
uses the GDB/MI interpreter (see
<http://sourceware.org/gdb/current/onlinedocs/gdb_25.html>), which accurately informs the
caller of the program state and, through the use of tokens, guarantees that the results
returned actually correspond to the request sent. By contrast, GDB's console interpreter
returns all responses on "STDOUT", and thus there is no way to ensure that a particular
response corresponds to a particular request.
Therefore, it is obviously preferable to use GDB/MI when programmatically interacting with
GDB. This can be done via the "send_cmd" family of functions ("send_cmd",
"send_cmd_excl", and "send_cmd_async"). There are, however, some cases when there is no
GDB/MI command corresponding to a particular console command, or it has not yet been
implemented (for example, "-symbol-type", corresponding to the console command "ptype", is
not yet implemented as of GDB 6.6). In this case, the "get" function provides a
workaround by capturing all output sent to the console stream.
CONSTRUCTOR
new
$gdb = new Devel::GDB( '-use-threads' => 1 );
'-params' => $extra_gdb_params );
Spawns a new GDB process. In threaded mode, this also spawns a listening thread that
asynchronously processes responses from GDB; in non-threaded mode, the caller is
responsible for handling asynchronous output (that is, output from GDB that is not
directly solicited by a request). See "demux", "get_reader", and the "Non-threaded Usage"
example for further discussion.
The parameters to the constructor are passed in hash form. The following parameters
control how GDB is invoked:
"-execfile"
The GDB binary to execute; defaults to "gdb".
"-params"
Pass additional parameters to GDB. The value can be an array reference (preferred) or
a string.
The following parameters control how to handle interaction with the inferior process, the
program being debugged. The default behavior is to give the inferior process control of
the terminal while it is running, returning control to perl when the program is suspended
or stopped (emulating the behavior of gdb). However, this only works when "STDIN" is
associated with a tty. Two other (mutually exclusive) options are available:
"-use-tty"
Specify the name of the tty that the inferior process should use for its I/O. Note
that this is the path to a tty (e.g. "/dev/pts/123") and not an "IO::Pty" object. See
the example "Debugging Inside an XTerm".
"-create-expect"
If this value is non-zero, create an "Expect" object (which can be subsequently
retrieved by calling "get_expect_obj"); this is useful if you want to programmatically
interact with the inferior process. See the example "Programmatically Interacting
with the Inferior Process".
Miscellaneous parameters:
"-use-threads"
Operate in threaded (1) or non-threaded (0) mode. The default behavior is to enable
threaded mode if the "threads" module has been loaded and disable it otherwise. Note
that if "-use-threads" is enabled, the caller must call "use threads", but
"-use-threads" can be disabled whether or not "threads" has been loaded.
Threaded mode is the easiest to deal with, as it does not require the caller to
interact with the GDB filehandles directly; for a simple non-threaded example, see the
"Non-threaded Usage" example.
"-readline-fn"
Probably only useful in non-threaded mode, this lets the user specify a callback
function $fn to be called when waiting for a response from GDB. It is invoked with
one parameter, the "Devel::GDB" instance, and is expected to return one full line of
output (or "undef" if EOF was reached). The default implementation uses buffered I/O:
$fn = sub { return readline($_[0]->get_reader); }
Typically, in non-threaded mode, the caller will be using "select" to multiplex
multiple file streams (e.g. "STDIN" and "get_reader"); in this case, you will likely
want to specify a value for "-readline-fn" which, at a minimum, uses "sysread" rather
than "readline".
METHODS
send_cmd
$response = $gdb->send_cmd($command)
Send $command to GDB, and block until a response is received. In threaded mode, this
does not prevent other threads from simultaneously sending requests.
The $command can be a GDB/MI command, prefixed with a hyphen (e.g. "-exec-run") or a
console command ("run"). However, the response returned will always be a GDB/MI
response, so "$gdb->send_cmd("info variables")" will only return "done"; the actual
output you probably wanted will be dumped into the console stream. To execute console
commands and capture the output sent back to the console, use "get".
send_cmd_excl
$gdb->send_cmd_excl($cmd, $before_fn, $after_fn)
Send $cmd to GDB in exclusive mode. In threaded mode, this means that other
"send_cmd" and "send_cmd_excl" calls will not coincide with this call. In non-
threaded mode, this ensures that any pending "send_cmd_async" calls are processed
before proceeding.
If provided, the $before_fn and $after_fn functions will, respectively, be called
before the command is sent (after the exclusive lock is acquired) and after the result
has been received (before the exclusive lock is released).
send_cmd_async
$gdb->send_cmd_excl($cmd, $callback_fn)
Not yet implemented.
Send $cmd to GDB in async mode. This returns immediately, rather than blocking until
a response is received; instead, the $callback_fn callback function is called, with
the response as the first argument.
This will likely only be supported in non-threaded mode.
get
$gdb->get($command)
Issues the $command to GDB, and returns all output sent to the console output stream.
Note that there is no way to ensure that the output "belongs" to a particular command,
so it is possible that spurious output will be included! In particular, if you call
"$gdb->get($command)" immediately after creating the "Devel::GDB" object, and don't
suppress GDB's initialization messages (by passing "-q" to "-params"), some of these
messages may end up in the response to "get".
In list context, returns "($buffer, $error)", with exactly one of the two defined;
$buffer is the text captured from the console stream and $error is the GDB/MI error
message. In scalar context, only $buffer is returned ("undef" if there was an error).
get (DEPRECATED)
$gdb->get($command, $timeout, $prompt, $notyet, $alldone)
This version of "get" is used when $Devel::GDB::DEPRECATED is true, and provides
backwards compatibility with older versions of "Devel::GDB". It is not compatible
with any of the new features (e.g. "send_cmd", threaded mode) and will be removed in
future versions.
This method is flawed in a number of ways: the semantics of when $notyet is called are
unclear, the handling of $timeout is broken, and most importantly, the fact that it
allows execution to be interrupted can put the module into an inconsistent state.
No new code should use this function.
get_expect_obj
Returns the "Expect" object created by "-create-expect".
get_reader
Returns the filehandle from which to read GDB responses.
In non-threaded mode, the caller will need this filehandle in its "-readline-fn"; in
addition, to support asynchronous GDB responses, the caller should pass lines read
from this filehandle to "demux".
demux
$gdb->demux($line)
Process a line read from the GDB stream (see "get_reader"). This should only be
called in non-threaded mode. (See example: "Non-threaded Usage")
interrupt
Send SIGINT to the GDB session, interrupting the inferior process (if any).
end Kills the GDB connection. You must call this to ensure that the GDB process is killed
gracefully.
EXAMPLES
Non-threaded Usage
use Devel::GDB;
use IO::BufferedSelect;
my $gdb = new Devel::GDB( '-use-threads' => 0,
'-readline-fn' => \&message_loop );
my $gdb_fh = $gdb->get_reader;
my $bs = new IO::BufferedSelect(\*STDIN, $gdb_fh);
sub message_loop
{
my @result = $bs->read_line($gdb_fh);
return @result ? $result[0][1] : undef;
}
OUTER:
while(1)
{
my @ready = $bs->read_line();
foreach( @ready )
{
my ($fh, $line) = @$_;
defined($line) or last OUTER;
chomp $line;
if($fh == \*STDIN)
{
print STDERR "RECEIVED: $line\n";
my $result = $gdb->get($line);
last unless defined($result);
print STDERR $result;
}
else
{
$gdb->demux($line);
}
}
}
Programmatically Interacting with the Inferior Process
Here's a simple example that communicates with an inferior process (in this case, "tr")
using the "Expect" module.
use strict;
use warnings;
use threads;
use Devel::GDB;
my $gdb = new Devel::GDB( '-create-expect' => 1 );
my $e = $gdb->get_expect_obj;
$gdb->send_cmd("file tr");
$gdb->send_cmd("set args a-zA-Z A-Za-z");
$gdb->send_cmd("-exec-run");
$e->send("one TWO\n");
$e->send("ONE two\n");
$e->expect(undef, '-re', '^.+$')
and $e->match =~ /^ONE two/
and print "ok 1\n"
or die;
$e->expect(undef, '-re', '^.+$')
and $e->match =~ /^one TWO/
and print "ok 2\n"
or die;
$gdb->end;
$e->slave->close;
$e->expect(undef);
printf "EXPECT(EOF): %s\n", $e->before;
Debugging Inside an XTerm
Here's an example that spawns an xterm and runs the inferior process inside it. Commands
are read from STDIN, and responses written to STDERR.
use strict;
use warnings;
use threads;
use Devel::GDB;
use IO::Pty;
use POSIX;
sub set_termios_lflag($$$)
{
my($fd, $flag, $value) = @_;
my $termios = new POSIX::Termios;
$termios->getattr($fd);
$termios->setlflag($value ? ($termios->getlflag | $flag) : ($termios->getlflag & ~$flag));
$termios->setattr($fd);
undef $termios;
}
my $pty = new IO::Pty;
# Disable echo temporarily
set_termios_lflag(fileno($pty), &POSIX::ECHO, 0);
# Fork an xterm
unless(my $xterm_pid = fork)
{
die "Fork failed" unless defined($xterm_pid);
# Reopen $fd with close-on-exec disabled
my $fd = fileno($pty);
$^F = $fd > $^F ? $fd : $^F;
local *MASTER;
open(MASTER, "<&=$fd") and $fd == fileno(\*MASTER)
or die "Failed reopening pty handle";
my $cmd = "xterm -Sxx$fd";
print "calling exec($cmd)\n";
exec($cmd);
die "exec() failed: $!";
}
# xterm likes to write its window id to the pty; eat it up
# (echo is disabled so the inferior process doesn't see this output)
my $window_id = readline($pty->slave);
# Now turn echo back on
set_termios_lflag(fileno($pty), &POSIX::ECHO, 1);
# No longer need the master (but don't close the slave!)
close $pty;
# Create the GDB object, telling the inferior process to use the new xterm's pty
my $gdb = new Devel::GDB( '-use-tty' => $pty->ttyname );
while(<STDIN>)
{
chomp;
if(/^Z/)
{
$gdb->interrupt;
next;
}
my $result = $gdb->send_cmd($_);
last unless defined($result);
print STDERR "[GDB] $result\n";
}
$gdb->end;
TODO
There are a number of features that will be made available in future versions of
"Devel::GDB". Among them:
• Finish implementing "send_cmd_async".
• Add an interface for redirecting GDB/MI output. Currently, all "out-of-band-records"
(see <http://sourceware.org/gdb/current/onlinedocs/gdb_25.html#SEC246>) are redirected
to "STDERR"; there should be a facility for callers to specify what to do with each
stream.
• In order to allow full-fledged GDB front-ends to be implemented with this module, we
need a more "intelligent" layer above "Devel::GDB": rather than simply sending
commands and receiving their results, the hypothetical "Devel::GDB::HighLevel" module
would be aware of the program state; it would know whether or not the inferior process
is running, what breakpoints are set, and so forth.
SEE ALSO
Devel::GDB::LowLevel
AUTHORS
Antal Novak <afn@cpan.org>, Josef Ezra <jezra@cpan.org>
COPYRIGHT AND LICENSE
Copyright (C) 2007 by Antal Novak & Josef Ezra
This library is free software; you can redistribute it and/or modify it under the same
terms as Perl itself, either Perl version 5.8.8 or, at your option, any later version of
Perl 5 you may have available.