PHP Opcodes

First, what is an Opcode? It's a compiled form of a PHP script, similar to Java bytecode. Or, more precisely, from php.net

"When parsing PHP files, Zend Engine 2 generates a series of operation codes, commonly known as "opcodes", representing the function of the code."

<?php
  $a = "Hello ";
  $b = "World\n";
  echo $a . $b;

For a script like this, the opcodes look like that:

number of ops:  5
compiled vars:  !0 = $a, !1 = $b
line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
   2     0  >   ASSIGN                                                   !0, 'Hello+'
   3     1      ASSIGN                                                   !1, 'World%0A'
   4     2      CONCAT                                           ~2      !0, !1
         3      ECHO                                                     ~2
   5     4    > RETURN                                                   1

branch: #  0; line:     2-    5; sop:     0; eop:     4
path #1: 0,

Translate Sourcecode to op_array

Whoa. Now, how do you get the opcodes, i.e., op_array? You need a PHP extensions, like VLD (Vulcan Logic Disasembler). If you have pecl installed, you can download, build, and install it in one step by running

> sudo pecl install vld 

If you get an error message about a stable version, try running

> sudo pecl install vld-0.12.0

Now that you have installed it, you need to load it. In your php.ini, add the following, best if you put it close to extension=modulename.extension.

;  for op code
extension=vld.so

You find your php.ini by running

> php --ini
Configuration File (php.ini) Path: /usr/local/zend/etc

To generate the opcodes, all you need to do now is run the script with the following parameters (-d for ini entries)

> php -d vld.active=1 -d vld.execute=0 -f helloWorld.php