This is an old revision of the document!

This page contains bits and pieces of the Zend Engine documentation:

Op-array structure

  • each op_array has an array of literals (constant values)
  • opocde operands don't contain zval directly any more but points to thistable instead
  • during compilation they are accessible by index e.g:
  • the pass_two() changes indexes into pointers so during execution they are accessible by:


See here.


These are questions, often times with answers, for the PHP Internals. This document is temporary until it's polished and finds a home within the PHP Manual sources. Feel free to add questions with or without answers.

Note: This is rough, feel free to clean it up.


Extensions can be written in C++, you have to add PHP_REQUIRE_CXX to the config.m4 file to make the build system C++-aware though.

To allow static builds of the extension one has to mind this:

09:20:43 <johannes_> and ext/extname/php_extname.h has to be a valid C header, not C++, as it's included in internal_functions.c ...
09:22:06 <dsp_> hmm, that's the point..
09:23:01 <johannes_> you can have your own additional header for C++ suff, but that one has to be C compatible

Memory Management

[12:00pm] scoates: ok.. last question for now, I think: should I explicitly destroy on RSHUTDOWN, or let the non-persistent flag take care of that?
[12:00pm] johannes_: always cleanup yourself

Note here: while MM shutdown will take care of all allocated memory, it won't run any dtors etc., that's why it is important to clean up the resources properly - otherwise external dependencies can be messed up. And of course you'd get leaks reported in the debug mode.

Causes for crashes

Throwing Exceptions

If throwing exceptions results in a segmentation fault on 64bit systems only, then be sure that you have:

#include "zend_exceptions.h" 

(Remark: This header is always needed. The segfault might be caused by the fact, that C defaults the return value and parameters of undefined parameters to int. In cases where pointers and/or long data types are needed this might be wrong so a wrong function call is being made. A good compiler should give a warning. --johannes)


[11:58am] scoates: what's the difference between zend_hash_[add] and zend_hash_quick_[add] ?
[11:58am] scoates: removal of gofaster loops? (-:
[11:58am] Derick: with the 2nd one you can provide an already calculated hash-list index
[11:59am] scoates: and the hashtable will automatically grow on _add, right? the length passed to init is just a hint?
[11:59am] johannes_: right


Add your random stuff here. I'll move it/update it/fix it (Derick)

Extension Globals

To use extension globals (which are either true globals or thread local globals, depending on whether ZTS is enabled), follow these steps:

- In php_extname.h, declare which global variables you need with:

	int	var1;
	char	*var2;

This will declare a structure (typedef'd to zend_extname_globals) that will hold all your globals.

- In php_extname.h, add


. This will produce an allusion that will allow you to access the globals from every compile unit that includes php_extname.h In particular, this produces an allusion to an integer named extname_globals_id in ZTS builds or directly to a zend_extname_globals named extname_globals in non-ZTS builds.

- In php_extname.h, define a macro named EXTNAME_G, like this:

#ifdef ZTS
# define EXTNAME_G(v) TSRMG(extname_globals_id, zend_extname_globals *, v)
# define EXTNAME_G(v) (extname_globals.v)

This will allow you to access the globals in a consistent manner in both ZTS and non-ZTS builds, like this:


- Now that you have declared the type that aggregates the globals and the variable that holds the globals, you must define the globals. In extname.c, add


This produces a tentative definition of extname_globals_id or extname_globals (depending on whether it's a ZTS or non-ZTS build).

- If you needn't do any startup operations on your variables, you would already have function extension globals in non-ZTS builds. Tipically, you will also want to initialize some extension globals (for instance, to allocate some memory for the var2 extension global above) -- this is done with globals constructors and destructors. To make it work in ZTS builds and allow such operations, add the following to your zend_module_entry:

zend_module_entry extname_module_entry = {

Note: do not use ZEND_INIT_MODULE_GLOBALS/ts_allocate_id. If used a shared extension, they will provoke an attempt to call the destructor after the module has been unloaded!

- Now define the constructor and destructor functions:

	extname_globals->arg2 = pemalloc(1024, 1);

	pefree(extname_globals->arg2, 1);

Note: ZEND_MODULE_GLOBALS_CTOR_D will declare a function as receiving a zend_extname_globals*, not void* and zend_module_entry is supposed to contain a function pointer type that receives void*. I think this violates the C standard (the declarations are incompatible), but should however by safe since the arguments have the same size.

internals/engine.1273748194.txt.gz · Last modified: 2017/09/22 13:28 (external edit)