Notes taken during php source exploration to identify weird error message

php-source-exploration-process.md

• when using github, ./configure is not present and didn't know how to start

• download from http://php.net/downloads.php

• downloading specific version http://php.net/get/php-5.6.30.tar.gz/from/a/mirror

• I want to build minimal version only for testing

• following http://www.phpinternalsbook.com/build_system/building_php.html#obtaining-the-source-code

• Run ./configure --disable-all

• Run time make

• OR run both at the same time time ./configure --disable-all && time make

• check version at sapi/cli/php -v

• Run sapi/cli/php -m should give minimal number of modules only

  [PHP Modules]
  Core
  date
  ereg
  pcre
  Reflection
  SPL
  standard
  

• random looking for main function, just looking at file names

• found php_execute_script in php_main.h

• found definition in main.c

• Added printf("Running php_execute_script"); in that function And i can see that in cli

• Run /Users/anjesh/Dev/source/php-5.6.30/sapi/cli/php test.php

• It appears that i don't have to run ./configure everytime after making changes in the source. This makes the build quick.

• found http://php.find-info.ru/php/016/ch23lev1sec2.html

• http://jpauli.github.io/2015/01/22/on-php-function-calls.html

• https://www.slideshare.net/jpauli/quick-tour-of-php-from-inside

Running VLD for opcodes

• got info from https://ctors.net/2015/09/11/php_opcodes
• clone https://github.com/derickr/vld
• compiled and copy to local folder when test.php is present
• Run php -dextension=./vld.so -dvld.active=1 test.php and got the op_codes or
• Run /Users/anjesh/Dev/source/php-5.6.30/sapi/cli/php -dextension=./vld.so -dvld.active=1 test.php and got the op_codes

Looking for specific function call

• http://php.find-info.ru/php/016/ch20lev1sec3.html
• https://stackoverflow.com/questions/8340991/how-does-php-opcode-relate-to-the-actually-executed-binary-code
• http://jpauli.github.io/2015/01/22/on-php-function-calls.html has details on func calls

Searching

• searched for Call to undefined function from http://jpauli.github.io/2015/01/22/on-php-function-calls.html

• found zend_vm_execute.c file

• just scanning the file and found execute_ex which appears to be loop

• put some printf command there

• Run /Users/anjesh/Dev/source/php-5.6.30/sapi/cli/php test.php and got that printf msg

• Read README.ZEND_VM file and it talks about zend_vm_def.h, which is mentioned in zend_vm_gen.php and that file has some comments that it generates files This script creates zend_vm_execute.h and zend_vm_opcodes.h from existing zend_vm_def.h and zend_vm_execute.skl

• Run /Users/anjesh/Dev/source/php-5.6.30/sapi/cli/php Zend/zend_vm_gen.php and comment in zend_vm_def.h is reflected in zend_vm_execute.c

• http://jpauli.github.io/2015/01/22/on-php-function-calls.html content is present in zend_vm_def.h

• php under the hoods https://www.youtube.com/watch?v=tyEFF7brU-I

• message is coming from zend_verify_arg_class_kind in zend_execute.c, when searched for instance of text of the error message.

• found where the message is coming from in zend_execute.c

    else if (Z_TYPE_P(arg) != IS_NULL || !(cur_arg_info->allow_null || (default_value && is_null_constant(default_value TSRMLS_CC)))) {
			need_msg = zend_verify_arg_class_kind(cur_arg_info, fetch_type, &class_name, &ce TSRMLS_CC);
			return zend_verify_arg_error(E_RECOVERABLE_ERROR, zf, arg_num, need_msg, class_name, zend_zval_type_name(arg), "" TSRMLS_CC);
		}

• i can replace need_msg = zend_verify_arg_class_kind(cur_arg_info, fetch_type, &class_name, &ce TSRMLS_CC); with class_name = " myclass "; need_msg = " hello "; and the output message is changed.
• if i comment above line, the output appears, infact it doesn't check for the typehint in the function param