PHP is one of the most popular open source programming languages in the world. It powers some of the highest traffic sites in the world, and at the same time it powers some of the lowest traffic sites in the world. But have you ever wondered how it works under the hood? Have you been overwelmed by the thought of looking at the C code that runs PHP? Well, this talk is for you! We're going to explore how PHP works under the hood, by looking at a PHP implementation of it: PHPPHP! Have you ever wondered what an OPCODE Cache is really doing? Have you ever wondered what a T_PAAMAYIM_NEKUDOTAYIM is? Have you ever wondered why an interpreted languages has a compiler? We'll explore all of these topics, and more! And the best part of it all? You don't need to know C to understand the details! Using PHPPHP, we can explore the language details in a high level language, where things like memory management don't get in the way of the real content. If you've ever wanted to know how PHP works, this is the talk for you!

1. PHP
Under The Hood

2. What Is PHP?
● An Easy To Learn Language?
○ Sure!
● A Simple Language?
○ Usually
● A Well Designed Language?
○ HA!
● An Effective Language!
○ Absolutely!

4. PHP Is...
Dynamically
Typed

5. $a = 1;
$b = "a";

6. PHP Is...
Weak Typed

7. 1 + "1b" == 2

8. PHP Is...
Implementation
Defined

9. Implementations
Main:
C-PHP: www.php.net
Alt:
HipHop - Facebook
Roadsend - Compiler
Phalanger - .NET
PHP Compiler - Compiler
PHPPHP - PHP

11. Interesting Note:
C-PHP Requires
PHP To Compile!

12. PHP Is...
Compiled

14. PHP Is...
Dynamically
Compiled
On-Demand

16. It All Starts With The
SAPI

17. SAPI
● Server API
● "Starts" PHP and issues request(s)
● Common SAPIs:
○ CLI
○ CGI (and FastCGI)
○ mod_php
○ FPM
○ etc...

18. Execution Pipeline

19. Execution Pipeline
Start Up
Request
Shut Down
SAPI

20. Execution Pipeline
Start Up
Request
Shut Down
SAPI
Config Init
Engine Init
Module Init

21. Zend/zend.c

22. PHPPHP/PHP.php

23. Execution Pipeline
Start Up
Request
Shut Down
SAPI
Module
Shutdown
Engine
Shutdown

24. Zend/zend.c

25. Execution Pipeline
Start Up
Request
Shut Down
SAPI
Request Init
Compile Code
Execute Code
Request
Shutdown

27. Compiler Pipeline
Lexer

28. Lexer Step
● C-PHP
○ Tokenizes using RE2C
○ Produces Array of Tokens
● PHPPHP
○ Uses core tokenizer (or emulative)
○ PHPParser Powered

29. Zend/zend_language_scanner.l

30. PHPParser/Lexer/Emulative.php

31. Compiler Pipeline
Lexer
Parser

32. Parse Step
● C-PHP
○ Directly Generates OPCode Array
○ BISON Powered
● PHPPHP
○ Generates AST Structure
○ PHPParser Powered

33. Zend/zend_language_parser.y

34. Compiler Pipeline
Lexer
Parser
Compiler

35. Compile Step
● C-PHP
○ Compiled Directly During Parse
○ Single Pass Compilation
● PHPPHP
○ Recurses Over AST
○ Single Pass (for now)
○

36. PHPPHP/Engine/Compiler.php

37. Compiler Pipeline
Lexer
Parser
Compiler
OpCode

38. OpCodes
● A Series of Operations
○ Just like Assembler Opcodes
○ Represent "units of functionality"
● Designed to run on Virtual Machine
○ Zend Engine
○ Or PHPPHP!

39. $a = 1;
$b = 2;
echo $a + $b;

41. Notice Anything?

44. What If We
Cached The
OpCodes?

45. We Can Cache!
● Given the compiler is Idempodent
○ (has no side-effects)
○ (hint: it's not)
● OpCodes are really Pointers
○ Swizzling!!!

46. In Other Words

47. OpCode Caching
Is Hard!

49. Time To Execute!

50. Zend/zend_vm_execute.h

51. PHPPHP/Engine/Executor.php

52. Executor Pipeline
OpCode
Is
Return?No Yes
Return

54. But What Are We
Executing?

55. Zend/zend_vm_execute.h

56. Interesting Note:
vm_execute.h
Is Generated By
PHP

57. PHPPHP/Engine/OpLines/Add.php

58. Variables!

59. Zend/zend.h

60. PHPPHP/Engine/Zval/Value.php

62. Ref-Counting
● RefCount + References
○ Allows Copy-On-Write
● Variable Is "Deleted" When
RefCount = 0
● Enables Primitive Garbage
Collection
○ Circular GC is also implemented

63. That's All There Is
To It!

65. Let's Look At An
Example

66. $a = 1;
$b = 2;
var_dump(
$a + $b
);

67. line # op return operands
-----------------------------------
2 0 ASSIGN !0, 1
3 1 ASSIGN !1, 2
6 2 ADD ~2 !0, !1
3 SEND_VAL ~2
4 DO_FCALL 'var_dump'
5 RETURN 1

68. [0] => PHPPHPEngineOpLinesAssign
[1] => PHPPHPEngineOpLinesAssign
[2] => PHPPHPEngineOpLinesAdd
[3] => PHPPHPEngineOpLinesInitFCallByName
[4] => PHPPHPEngineOpLinesSend
[5] => PHPPHPEngineOpLinesFunctionCall
[6] => PHPPHPEngineOpLinesReturnOp

69. [0] => PHPPHPEngineOpLinesAssign Object (
[op1] => PHPPHPEngineZvalPtr Object (
[zval:protected] => PHPPHPEngineZvalVariable Object (
[name:protected] => PHPPHPEngineZvalPtr Object (
[zval:protected] => PHPPHPEngineZvalValue Object (
[value:protected] => a
[refcount:protected] => 1
[isRef:protected] =>
[dtorFunc:protected] =>
)
)
[class:protected] =>
[zval:protected] =>
[executor:protected] =>
[scope] => 1
)
)
[op2] => PHPPHPEngineZvalPtr Object (
[zval:protected] => PHPPHPEngineZvalValue Object (
[value:protected] => 1
[refcount:protected] => 1
[isRef:protected] =>
[dtorFunc:protected] =>
)
)
[result] =>
[lineno] => 2
)

70. PHPPHP/Engine/OpLines/Assign.php

71. PHPPHP/Engine/OpLines/Add.php

72. PHPPHP/Engine/OpLines/InitFCallByName.php

73. PHPPHP/Engine/OpLines/Send.php

74. PHPPHP/Engine/OpLines/FunctionCall.php

75. There's A Ton
More

78. Get Involved!

80. More Info
● github.com/php/php-src
● lxr.php.net
● github.com/ircmaxell/PHPPHP
● Reference Series
○ wiki.php.net
○ blog.ircmaxell.com
■ PHP Internals Series

81. Anthony Ferrara
Joind.in/8443
@ircmaxell
blog.ircmaxell.com
ircmaxell@php.net
youtube.com/ircmaxell