Detailed explanation of PHP execution cycle

This article mainly introduces the execution cycle of in-depth understanding of PHP principles, and briefly analyzes the relevant principles of the PHP program from editing to lexical analysis, syntax analysis and interpretation and execution. I hope to be helpful.

The details are as follows:

The execution cycle of PHP, from the initial PHP script we wrote-> to the last script being executed-> getting the execution result, this process can actually be divided into the following Several stages:

First, Zend Engine (ZE) calls the lexical analyzer (generated by Lex, the source file is in Zend/zend_language_sanner.l), and removes spaces and comments from the PHP source file we want to execute. , divided into tokens one by one.

Then, ZE will forward the obtained token to the syntax analyzer (generated by yacc, the source file is in Zend/zend_language_parser.y), and generate opcodes one by one. The opcodes generally exist in the form of op array. It is the intermediate language for PHP execution.

Finally, ZE calls zend_executor to execute op array and output the results. (That is, convert the source file into machine language and then run it on a virtual machine.)

ZE is a virtual machine. It is precisely because of its existence that we can write PHP scripts without any need for Consider the type of operating system you are running on, this is why PHP is portable. ZE is a CISC (Complex Instruction Processor), which supports 150 instructions (specific instructions are in Zend/zend_vm_opcodes.h), including the simplest ZEND_ECHO (echo) to the complex ZEND_INCLUDE_OR_EVAL (include, require), All the PHP we write will eventually be processed into a sequence of these 150 instructions (op code), and will eventually be executed.

PHP is a scripting language, that is to say, the PHP code written by the user will eventually be interpreted and executed by the PHP interpreter. All PHP codes written will be translated into the PHP virtual machine ZE virtual instructions (OPCODES) to execute.

So what will our PHP script be "translated" into in the end? In other words, what does the op code look like? Opcode is an intermediate language compiled from PHP scripts.

There is already such a module in PECL, using the VLD (Vulcan Logic Dissassembler) module developed by Derick Rethans. You only need to download this module and load it into PHP, and you can get the result of script translation through simple settings.

Installation and application of VLD module:

[root@localhost software]# tar zxvf vld-0.9.1.tgz.gz
[root@localhost vld-0.9.1]# /usr/local/php/bin/phpize
[root@localhost vld-0.9.1]# ./configure --with-php-config=/usr/local/php/bin/php-config
[root@localhost vld-0.9.1]# make install //不需要make

Edit the php.ini file and activate the vld extension.

Example:

Create a file, such as: hello.php

<?php
  echo &#39;hello, world.&#39;;
?>

Execute:

[root@localhost html]# /usr/local/php/bin/php -dvld.active=1 hello.php
Branch analysis from position: 0
Return found
filename:    /var/www/html/hello.php
function name: (null)
number of ops: 3
compiled vars: none
line   # op              fetch     ext return operands
-------------------------------------------------------------------------------
  2   0 ECHO                           'hello%2C+world.'
  4   1 RETURN                          1
     2* ZEND_HANDLE_EXCEPTION
hello, world.

Look at another one:

[root@localhost html]# vi vld.php
<?php
  $i = "This is a string";
  //I am comments
  echo $i. &#39; that has been echoed on screen&#39;;
?>

Execution:

[root@localhost html]# /usr/local/php/bin/php -dvld.active=1 vld.php
Branch analysis from position: 0
Return found
filename:    /var/www/html/vld.php
function name: (null)
number of ops: 5
compiled vars: !0 = $i
line   # op              fetch     ext return operands
-------------------------------------------------------------------------------
  3   0 ASSIGN                          !0, 'This+is+a+string'
  7   1 CONCAT                      ~1  !0, '+that+has+been+echoed+on+screen'
     2 ECHO                           ~1
 10  3 RETURN                          1
     4* ZEND_HANDLE_EXCEPTION
This is a string that has been echoed on screen

Note: ZEND_HANDLE_EXCEPTION is the 149th instruction in Zend/zend_vm_opcodes.h

compiled vars: !0 = $i Here is to get the variable name" The variable of i" is at !0 (*zval).
#0 Assign the string "this+is+a+string" to !0
#1 String connection
#2 Display

These intermediate codes will be used by Zend VM (Zend Virtual Machine) executes directly. The function actually responsible for execution is: zend_execute (zend_execute.h).

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