Phpcompilerinternals 090824022750-phpapp02

(Do not be afraid of)

PHP Compiler Internals
Sebastian Bergmann
August 23rd 2009

Sebastian Bergmann

 Co-Founder and
Principal Consultant
with thePHP.cc
 Creator of PHPUnit
 Involved in the PHP
project since 2000

Under PHP's Hood

Extensions

(date, dom, gd, json, mysql, pcre, pdo, reflection, session, standard, …)

PHP Core Zend Engine

Request Management Compilation and Execution
File and Network Operations Memory and Resource Allocation

Server API (SAPI)

(mod_php, FastCGI, CLI, ...)

This slide contains material by Sara Golemon

How PHP executes code

 Lexical Analysis
Scan the source for sequences of characters
and convert them to a sequence of tokens


 Syntax Analysis
Parse a sequence of tokens to determine
their grammatical structure


 Syntax Analysis
 Bytecode Generation
Generate bytecode based on the information
gathered by analyzing the source


 Syntax Analysis
 Bytecode Generation
 Bytecode Execution

Lexical Analysis
Scan a sequence of characters
1 <?php
2 if (TRUE) {
3 print '*';
4 }
5 ?>

Lexical Analysis
1 <?php T_OPEN_TAG
2 if (TRUE) {
3 print '*';
4 }
5 ?>

Lexical Analysis
1 <?php T_OPEN_TAG
2 if (TRUE) { T_IF
T_WHITESPACE
(
T_STRING
)
T_WHITESPACE
{
T_WHITESPACE
3 print '*';
4 }
5 ?>

Lexical Analysis
1 <?php T_OPEN_TAG
2 if (TRUE) { T_IF
T_WHITESPACE
(
T_STRING
)
T_WHITESPACE
{
T_WHITESPACE
3 print '*'; T_PRINT
T_WHITESPACE
T_CONSTANT_ENCAPSED_STRING
;
4 }
5 ?>

Lexical Analysis
1 <?php T_OPEN_TAG
2 if (TRUE) { T_IF
T_WHITESPACE
(
T_STRING
)
T_WHITESPACE
{
T_WHITESPACE
T_WHITESPACE
;
T_WHITESPACE
4 } }
5 ?>

Lexical Analysis
1 <?php T_OPEN_TAG
2 if (TRUE) { T_IF
T_WHITESPACE
(
T_STRING
)
T_WHITESPACE
{
T_WHITESPACE
T_WHITESPACE
;
T_WHITESPACE
4 } }
T_WHITESPACE
5 ?> T_CLOSE_TAG

Lexical Analysis
T_OPEN_TAG <?php
T_IF if
T_WHITESPACE
(
T_STRING TRUE
)
T_WHITESPACE
{
T_WHITESPACE
T_PRINT print
T_WHITESPACE
T_CONSTANT_ENCAPSE '*'
D_STRING
;
T_WHITESPACE
}
T_WHITESPACE ?>
T_CLOSE_TAG

Lexical Analysis

Lexical Analysis
Scanner Generators
 You do not want to write a scanner by
hand
At least when the code for the scanner should
be efficient and maintainable
 Tools such as flex or re2c generate the
code for a scanner from a set of rules

<ST_IN_SCRIPTING>"if" {
"if" {
return T_IF;
}

Lexical Analysis
PHP Tokens
 T_ABSTRACT  T_CONCAT_EQUAL  T_ELSE  T_FUNCTION

 T_AND_EQUAL  T_CONST  T_ELSEIF  T_FUNC_C

 T_ARRAY  T_CONSTANT_ENCAPSED_STRING  T_EMPTY  T_GLOBAL

 T_ARRAY_CAST  T_CONTINUE  T_ENCAPSED_AND_WHITESPACE  T_GOTO

 T_AS  T_CURLY_OPEN  T_ENDDECLARE  T_HALT_COMPILER

 T_BAD_CHARACTER  T_DEC  T_ENDFOR  T_IF

 T_BOOLEAN_AND  T_DECLARE  T_ENDFOREACH  T_IMPLEMENTS

 T_BOOLEAN_OR  T_DEFAULT  T_ENDIF  T_INC

 T_BOOL_CAST  T_DIR  T_ENDSWITCH  T_INCLUDE

 T_BREAK  T_DIV_EQUAL  T_ENDWHILE  T_INCLUDE_ONCE

 T_CASE  T_DNUMBER  T_END_HEREDOC  T_INLINE_HTML

 T_CATCH  T_DOC_COMMENT  T_EVAL  T_INSTANCEOF

 T_CHARACTER  T_DO  T_EXIT  T_INT_CAST

 T_CLASS  T_DOLLAR_OPEN_CURLY_BRACES  T_EXTENDS  T_INTERFACE

 T_CLASS_C  T_DOUBLE_ARROW  T_FILE  T_ISSET

 T_CLONE  T_DOUBLE_CAST  T_FINAL  T_IS_EQUAL

 T_CLOSE_TAG  T_DOUBLE_COLON  T_FOR  T_IS_GREATER_OR_EQUAL

 T_COMMENT  T_ECHO  T_FOREACH  T_IS_IDENTICAL

Lexical Analysis
PHP Tokens
 T_IS_NOT_EQUAL  T_OBJECT_CAST  T_SR_EQUAL

 T_IS_NOT_IDENTICAL  T_OBJECT_OPERATOR  T_START_HEREDOC

 T_IS_SMALLER_OR_EQUAL  T_OLD_FUNCTION  T_STATIC

 T_LINE  T_OPEN_TAG  T_STRING

 T_LIST  T_OPEN_TAG_WITH_ECHO  T_STRING_CAST

 T_LNUMBER  T_OR_EQUAL  T_STRING_VARNAME

 T_LOGICAL_AND  T_PAAMAYIM_NEKUDOTAYIM  T_SWITCH

 T_LOGICAL_OR  T_PLUS_EQUAL  T_THROW

 T_LOGICAL_XOR  T_PRINT  T_TRY

 T_METHOD_C  T_PRIVATE  T_UNSET

 T_MINUS_EQUAL  T_PUBLIC  T_UNSET_CAST

 T_ML_COMMENT  T_PROTECTED  T_USE

 T_MOD_EQUAL  T_REQUIRE  T_VAR

 T_MUL_EQUAL  T_REQUIRE_ONCE  T_VARIABLE

 T_NAMESPACE  T_RETURN  T_WHILE

 T_NS_C  T_SL  T_WHITESPACE

 T_NEW  T_SL_EQUAL  T_XOR_EQUAL

 T_NUM_STRING  T_SR

Syntax Analysis
Parse a sequence of tokens

Syntax Analysis
Parse a sequence of tokens
 You do not want to write a parser by hand
At least when the code for the scanner should
be efficient and maintainable
 Tools such as bison or lemon generate
the code for a parser from a set of rules

T_IF '(' expr ')' { ... }
statement { ... }
elseif_list else_single { ... }

PHP Bytecode
Using bytekit-cli to disassemble bytecode
1 <?php
2 if (TRUE) {
3 print '*';
4 }
5 ?>
sb@thinkpad ~ % bytekit if.php
bytekit-cli 1.0.0 by Sebastian Bergmann.

Filename: /home/sb/if.php
Function: main
Number of oplines: 8

line # opcode result operands
-----------------------------------------------------------------------------
2 0 EXT_STMT
1 JMPZ true, ->6

3 2 EXT_STMT
3 PRINT ~0 '*'
4 FREE ~0
4 5 JMP ->6

6 6 EXT_STMT
7 RETURN 1

PHP Bytecode
Using bytekit-cli to visualize bytecode
1 <?php
2 if (TRUE) {
3 print '*';
4 }
5 ?>
sb@thinkpad ~ % bytekit --graph /tmp --format svg if.php

How if is compiled
Zend/zend_compile.c
void zend_do_if_cond
(const znode *cond, znode *closing_bracket_token TSRMLS_DC)
{
typedef struct _znode {
int op_type;
union {
zval constant;

zend_uint var;
zend_uint opline_num;
zend_op_array *op_array;
zend_op *jmp_addr;
struct {
zend_uint var;
zend_uint type;
} EA;
} u;
} } znode;

zend_do_if_cond() is called when an if statement is compiled

How if is compiled
Zend/zend_compile.c
{
int if_cond_op_number =
get_next_op_number(CG(active_op_array));
zend_op *opline =
get_next_op(CG(active_op_array) TSRMLS_CC);

struct _zend_op {
opcode_handler_t handler;
znode result;
znode op1;
znode op2;
ulong extended_value;
uint lineno;
zend_uchar opcode;
} };

Allocate a new opline in the current oparray

How if is compiled
Zend/zend_compile.c
{
zend_op *opline =

opline->opcode = ZEND_JMPZ;

}

Set the opcode of the new opline to JMPZ (jump if zero)

How if is compiled
Zend/zend_compile.c
{
zend_op *opline =

opline->op1 = *cond;

}

Set the first operand of the new opline to the if condition

How if is compiled
Zend/zend_compile.c
{
zend_op *opline =

closing_bracket_token->u.opline_num =
if_cond_op_number;
SET_UNUSED(opline->op2);
INC_BPC(CG(active_op_array));
}

Perform book keeping tasks such as marking the second operand of the
new opline as unused or incrementing the backpatching counter for the
current oparray

PHP Bytecode
PHP Opcodes
 NOP  IS_NOT_EQUAL  POST_INC  ADD_VAR  UNSET_DIM

 ADD  IS_SMALLER  POST_DEC  BEGIN_SILENCE  UNSET_OBJ

 SUB  IS_SMALLER_OR_EQUAL  ASSIGN  END_SILENCE  FE_RESET

 MUL  CAST  ASSIGN_REF  INIT_FCALL_BY_NAME  FE_FETCH

 DIV  QM_ASSIGN  ECHO  DO_FCALL  EXIT

 MOD  ASSIGN_ADD  PRINT  DO_FCALL_BY_NAME  FETCH_R

 SL  ASSIGN_SUB  JMPZ  RETURN  FETCH_DIM_R

 SR  ASSIGN_MUL  JMPNZ  RECV  FETCH_OBJ_R

 CONCAT  ASSIGN_DIV  JMPZNZ  RECV_INIT  FETCH_W

 BW_OR  ASSIGN_MOD  JMPZ_EX  SEND_VAL  FETCH_DIM_W

 BW_AND  ASSIGN_SL  JMPNZ_EX  SEND_VAR  FETCH_OBJ_W

 BW_XOR  ASSIGN_SR  CASE  SEND_REF  FETCH_RW

 BW_NOT  ASSIGN_CONCAT  SWITCH_FREE  NEW  FETCH_DIM_RW

 BOOL_NOT  ASSIGN_BW_OR  BRK  FREE  FETCH_OBJ_RW

 BOOL_XOR  ASSIGN_BW_AND  BOOL  INIT_ARRAY  FETCH_IS

 IS_IDENTICAL  ASSIGN_BW_XOR  INIT_STRING  ADD_ARRAY_ELEMENT  FETCH_DIM_IS

 IS_NOT_IDENTICAL  PRE_INC  ADD_CHAR  INCLUDE_OR_EVAL  FETCH_OBJ_IS

 IS_EQUAL  PRE_DEC  ADD_STRING  UNSET_VAR  FETCH_FUNC_ARG

PHP Bytecode
PHP Opcodes
 FETCH_DIM_FUNC_ARG  INIT_STATIC_METHOD_CALL

 FETCH_OBJ_FUNC_ARG  ISSET_ISEMPTY_VAR

 FETCH_UNSET  ISSET_ISEMPTY_DIM_OBJ

 FETCH_DIM_UNSET  PRE_INC_OBJ

 FETCH_OBJ_UNSET  PRE_DEC_OBJ

 FETCH_DIM_TMP_VAR  POST_INC_OBJ

 FETCH_CONSTANT  POST_DEC_OBJ

 EXT_STMT  ASSIGN_OBJ

 EXT_FCALL_BEGIN  INSTANCEOF

 EXT_FCALL_END  DECLARE_CLASS

 EXT_NOP  DECLARE_INHERITED_CLASS

 TICKS  DECLARE_FUNCTION

 SEND_VAR_NO_REF  RAISE_ABSTRACT_ERROR

 CATCH  ADD_INTERFACE

 THROW  VERIFY_ABSTRACT_CLASS

 FETCH_CLASS  ASSIGN_DIM

 CLONE  ISSET_ISEMPTY_PROP_OBJ

 INIT_METHOD_CALL  HANDLE_EXCEPTION

Extending the PHP Compiler
Test First!
--TEST--
unless statement
--FILE--
<?php
unless (FALSE) {
print 'unless FALSE is TRUE, this is printed';
}

unless (TRUE) {
print 'unless TRUE is TRUE, this is printed';
}
?>
--EXPECT--
unless FALSE is TRUE, this is printed

Extending the PHP Compiler

 Add token for unless to the scanner
 Add rule for unless to the parser
 Implement bytecode generation for
unless in the compiler
 Add token for unless to ext/tokenizer

Add unless scanner token
Zend/zend_language_parser.y
%token T_NAMESPACE
%token T_NS_C
%token T_DIR
%token T_NS_SEPARATOR
%token T_UNLESS

Add unless scanner token
Zend/zend_language_scanner.l
<ST_IN_SCRIPTING>"if" {
return T_IF;
}

<ST_IN_SCRIPTING>"unless" {
return T_UNLESS;
}

<ST_IN_SCRIPTING>"elseif" {
return T_ELSEIF;
}

<ST_IN_SCRIPTING>"endif" {
return T_ENDIF;
}

<ST_IN_SCRIPTING>"else" {
return T_ELSE;
}

Add unless parser rule
Zend/zend_language_parser.y
unticked_statement:
'{' inner_statement_list '}'
| T_IF '(' expr ')' {
.
.
| T_UNLESS '(' expr ')' {
zend_do_unless_cond(&$3, &$4 TSRMLS_CC);
} statement {
zend_do_if_after_statement(&$4, 1 TSRMLS_CC);
} {
zend_do_if_end(TSRMLS_C);
}

Add unless to the compiler
Zend/zend_compile.c
{
int unless_cond_op_number =
zend_op *opline =

opline->opcode = ZEND_JMPNZ;
closing_bracket_token->u.opline_num =
unless_cond_op_number;
SET_UNUSED(opline->op2);
INC_BPC(CG(active_op_array));
}

All we have to do to generate code for the unless statement,
as compared to generate code for the if statement, is to emit
JMPNZ (jump if not zero) instead of JMPZ (jump if zero)

Add unless to the compiler
The generated bytecode
1 <?php
2 unless (FALSE) {
3 print '*';
4 }
5 ?>
sb@thinkpad ~ % bytekit unless.php
bytekit-cli 1.0.0 by Sebastian Bergmann.

Filename: /home/sb/unless.php
Function: main
Number of oplines: 8

line # opcode result operands
-----------------------------------------------------------------------------
2 0 EXT_STMT
1 JMPNZ true, ->6

3 2 EXT_STMT
3 PRINT ~0 '*'
4 FREE ~0
4 5 JMP ->6

6 6 EXT_STMT
7 RETURN 1

Running the test
sb@thinkpad php-5.3-unless % make test TESTS=Zend/tests/unless.phpt

Build complete.
Don't forget to run 'make test'.

=====================================================================
PHP : /usr/local/src/php/php-5.3-unless/sapi/cli/php
PHP_SAPI : cli
PHP_VERSION : 5.3.1-dev
ZEND_VERSION: 2.3.0
PHP_OS : Linux 2.6.28-14-generic #47-Ubuntu SMP Sat Jul 25 01:19:55 UTC 2009 i686 GNU/Linux
INI actual : /usr/local/src/php/php-5.3-unless/tmp-php.ini
More .INIs :
CWD : /usr/local/src/php/php-5.3-unless
Extra dirs :
VALGRIND : Not used
=====================================================================
Running selected tests.
PASS unless statement [Zend/tests/unless.phpt]
=====================================================================
Number of tests : 1 1
Tests skipped : 0 ( 0.0%) --------
Tests warned : 0 ( 0.0%) ( 0.0%)
Tests failed : 0 ( 0.0%) ( 0.0%)
Expected fail : 0 ( 0.0%) ( 0.0%)
Tests passed : 1 (100.0%) (100.0%)
---------------------------------------------------------------------
Time taken : 0 seconds
=====================================================================

Add unless to ext/tokenizer

sb@thinkpad tokenizer % ./tokenizer_data_gen.sh
Wrote tokenizer_data.c

The End

Thank you for your interest!

These slides will be posted on
http://slideshare.net/sebastian_bergmann

Acknowledgements

 Thomas Lee, whose Python Language
Internals presentation at OSDC 2008
inspired this presentation
 Stefan Esser for creating the Bytekit
extension that provides PHP bytecode
access and analysis features
 Derick Rethans, David Soria Parra, and
Scott MacVicar for reviewing these slides

References
 http://www.php.net/manual/en/tokens.php
 http://www.zapt.info/opcodes.html
 ”Extending and Embedding PHP”,
Sara Golemon
 http://bytekit.org/
 http://github.com/sebastianbergmann/bytekit-cli/

License
This presentation material is published under the Attribution-Share Alike 3.0 Unported
license.
You are free:
✔ to Share – to copy, distribute and transmit the work.
✔ to Remix – to adapt the work.
Under the following conditions:
● Attribution. You must attribute the work in the manner specified by the author or
licensor (but not in any way that suggests that they endorse you or your use of the
work).
● Share Alike. If you alter, transform, or build upon this work, you may distribute the
resulting work only under the same, similar or a compatible license.
For any reuse or distribution, you must make clear to others the license terms of this
work.
Any of the above conditions can be waived if you get permission from the copyright
holder.
Nothing in this license impairs or restricts the author's moral rights.

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