Changes to INI file handling
Migrating from PHP 5.3.x to PHP 5.4.x
Migrating from PHP 5.4.x to PHP 5.5.x
PHP Manual

## Changes to PHP Internals

- Extensions cannot override zend_execute() any more and should override zend_execute_ex() instead. EG(current_execute_data) is already initialized in zend_execute_ex(), so for compatibility extensions may need to use EG(current_execute_data)->prev_execute_data instead.
- Removed EG(arg_types_stack), EX(fbc), EX(called_scope) and EX(current_object).
- Added op_array->nested_calls, which is calculated at compile time.
- Added EX(call_slots), which is an array to store information about syntaticaly nested calls (e.g. foo(bar())) and is preallocated together with execute_data.
- Added EX(call), which is a pointer to a current calling function, and is an element of EX(call_slots).
- Opcodes INIT_METHOD_CALL, ZEND_INIT_STATIC_METHOD_CALL, ZEND_INIT_FCALL_BY_NAME and ZEND_INIT_NS_FCALL_BY_NAME use result.num as an index in EX(call_slots).
- Opcode ZEND_NEW uses extended_value as an index in EX(call_slots).
- Opcodes ZEND_DO_FCALL and ZEND_DO_FCALL_BY_NAME use op2.num as an index in EX(call_slots).
- Added op_array->used_stack, which is calculated at compile time; the corresponding stack space is preallocated together with execute_data. As a result, the ZEND_SEND* and ZEND_DO_FCALL* opcodes no longer need to check for stack overflow.
- Removed execute_data->Ts field. The VM temporary variables are always allocated immediately before the execute_data structure, and are now accessed by their offset from the execute_data base pointer instead of via execute_data->Ts. The compiler stores new offsets in op_array->opcodes[*].op?.num. The EX_TMP_VAR() and EX_TMP_VAR_NUM() macros can be used to access temporary variables by offset or number. You can convert the number to an offset using EX_TMP_VAR_NUM(0, num) or offset to number using (EX_TMP_VAR_NUM(0,0)-EX_TMP_VAR(0,offset)).
- Removed the execute_data->CVs field. The VM compiled variables are always allocated immediately after the execute_data structure, and are now accessed by the offset from the execute_data base pointer instead of via execute_data->CVs. You can use the EX_CV_NUM() macro to access compiled variables by number.