Dynamic code generation in Perl

Dynamic Code Generation

Marian HackMan Marinov

22.Nov.2014

Marian HackMan Marinov Dynamic Code Generation

Why would you need that?



Faster Development time




Easier interfaces




Easier interfaces

Abstraction




Easier interfaces

Abstraction

Obfuscation




Easier interfaces

Abstraction

Obfuscation/crypto

Performance


I will focus mainly on PERFORMANCE


Let’s start with a basic script

#!/usr/bin/perl

use warnings;

use strict;

sub DEBUG { 0; };

use constant ADEBUG => 0;


The following would be optimised out

if (DEBUG) {

print "Debuging\n";

}

if (ADEBUG) {

print "Debuging A\n";

}


What if we need to have something like this

if (defined($ARGV[0]) && $ARGV[0] eq ’ok’) {

sub DEBUG { 1; };

}


What if we need to have something like this


sub DEBUG { 1; };

}

$ perl f.pl ok

Subroutine DEBUG redefined at f.pl line 9.

$


Or something like this


ADEBUG => 1;

}


Or something like this


ADEBUG => 1;

}

$ perl f.pl ok

Useless use of a constant ("ADEBUG") in void context at f.pl line 9.


What if we start playing dirty :)


undef &ADEBUG;

use constant ADEBUG => 1;

}

$ perl f.pl ok

Constant subroutine main::ADEBUG redefined at /usr/share/perl5/constant.pm line 140.

Constant subroutine (anonymous) undefined at f.pl line 9.

Debuging

$


Let’s declare this as futile

Figure : Resistance is futile


So why did I tried to redifine a constant ?

What if we have a script which does:

while (my $line = <$fd>) {

if ($line =~ /RE/) { };

if ($line =~ /RE/) { };

....

....

if ($line =~ /RE/) { };

}


So why did I tried to redifine a constant ?

We can update it to:

while (my $line = <$fd>) {

if ($config{’type1’} && $line =~ /RE/) { };

if ($config{’type2’} && $line =~ /RE/) { };

....

....

if ($config{’typeN’} && $line =~ /RE/) { };

}


Hook::Filter

First looked at this

use Hook::Filter::RulePool qw(get_rule_pool);

get_rule_pool->add_rule("subname eq ’mydebug’ &&

from =~ /^My::Filthy::Attempt/");

->add_rule("from =~ /^My::Filthy::Attempt::func$/");

->add_rule("args(1) =~ /bob/");


Welcome to perlfilter

Preprocessor like directives for Perl


perlfilter

Filter::Util::Call - the main filter module


perlfilter


Filter::Simple - simplified version of the Util::Call


perlfilter



Filter::sh - filter the source trough cmd with shell


perlfilter




Filter::exec - filter the source trough cmd


perlfilter





Filter::tee - copies all text from the line after the use


perlfilter





Filter::tee - copies all text from the line after the use

Filter::cpp - pipes all souce trough the cpp pre-processor


Crypto filters

Filter::decrypt - example documentation for enc/decrypting


Crypto filters


Filter::Rijndael - decrypting source filter based on Rijndaelencryption


Crypto filters



Filter::CBC - Source filter for Cipher Block Chaining


Crypto filters



Filter::CBC - Source filter for Cipher Block Chaining

Filter::Crypto::CryptFile & Filter::Crypto::Decrypt


Filter::Util::Call part I

package Debug;

use strict;

use warnings;

use Filter::Util::Call;

use constant TRUE => 1;

use constant FALSE => 0;

sub import {

my ($type) = @_;

my (%context) = (

Enabled => defined $ENV{DEBUG},

InTraceBlock => FALSE,

Filename => (caller)[1],

LineNo => 0,

LastBegin => 0,

);

filter_add(bless \%context);

}Marian HackMan Marinov Dynamic Code Generation

Filter::Util::Call part II

sub filter {

my ($self) = @_;

my ($status);

$status = filter_read();

++ $self->{LineNo};

if ($self->{InTraceBlock}) {

if (/^\s*##\s*DEBUG_END/) {

$self->{InTraceBlock} = FALSE;

}

s/^/#/ if ! $self->{Enabled};

} elsif ( /^\s*##\s*DEBUG_BEGIN/ ) {

$self->{InTraceBlock} = TRUE;

$self->{LastBegin} = $self->{LineNo};

}

return $status;

}

1;Marian HackMan Marinov Dynamic Code Generation

Filter::Simple

package BANG;

use Filter::Simple;

FILTER {

s/BANG\s+BANG/die ’BANG’ if \$BANG/g;

};

1;


Filter::cpp

use Filter::cpp;

#define FRED 1

$a = 2 + FRED;

print "a = $a\n";

#ifdef FRED

print "Hello FRED\n";

#else

print "Where is FRED\n";

#endif


Thank you

Questions ?

Additional readinghttp://www.bytelabs.org/pub/papers/hburg07.pdf

Contact me:

Marian HackMan Marinov

mm [maybe at] 1h.com

icq: 7556201

irc: irc.freenode.net HackMan

jabber: [email protected]


http://www.bytelabs.org/pub/papers/hburg07.pdf

Education

Dynamic code generation in Perl