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140 lines
4.5 KiB
Markdown
140 lines
4.5 KiB
Markdown
# Zend Engine
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## Zend memory manager
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### General
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The goal of the new memory manager (available since PHP 5.2) is to reduce memory
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allocation overhead and speedup memory management.
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### Debugging
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Normal:
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```bash
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sapi/cli/php -r 'leak();'
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```
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Zend MM disabled:
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```bash
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USE_ZEND_ALLOC=0 valgrind --leak-check=full sapi/cli/php -r 'leak();'
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```
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### Shared extensions
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Since PHP 5.3.11 it is possible to prevent shared extensions from unloading so
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that valgrind can correctly track the memory leaks in shared extensions. For
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this there is the `ZEND_DONT_UNLOAD_MODULES` environment variable. If set, then
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`DL_UNLOAD()` is skipped during the shutdown of shared extensions.
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## ZEND_VM
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`ZEND_VM` architecture allows specializing opcode handlers according to
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`op_type` fields and using different execution methods (call threading, switch
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threading and direct threading). As a result ZE2 got more than 20% speedup on
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raw PHP code execution (with specialized executor and direct threading execution
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method). As in most PHP applications raw execution speed isn't the limiting
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factor but system calls and database calls are, your mileage with this patch
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will vary.
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Most parts of the old zend_execute.c go into `zend_vm_def.h`. Here you can find
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opcode handlers and helpers. The typical opcode handler template looks like
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this:
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```c
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ZEND_VM_HANDLER(<OPCODE-NUMBER>, <OPCODE>, <OP1_TYPES>, <OP2_TYPES>)
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{
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<HANDLER'S CODE>
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}
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```
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`<OPCODE-NUMBER>` is a opcode number (0, 1, ...)
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`<OPCODE>` is an opcode name (ZEN_NOP, ZEND_ADD, :)
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`<OP1_TYPES>` and `<OP2_TYPES>` are masks for allowed operand op_types.
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Specializer will generate code only for defined combination of types. You can
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use any combination of the following op_types UNUSED, CONST, VAR, TMP and CV
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also you can use ANY mask to disable specialization according operand's op_type.
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`<HANDLER'S CODE>` is a handler's code itself. For most handlers it stills the
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same as in old `zend_execute.c`, but now it uses macros to access opcode
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operands and some internal executor data.
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You can see the conformity of new macros to old code in the following list:
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```c
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EXECUTE_DATA
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execute_data
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ZEND_VM_DISPATCH_TO_HANDLER(<OP>)
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return <OP>_helper(ZEND_OPCODE_HANDLER_ARGS_PASSTHRU)
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ZEND_VM_DISPATCH_TO_HELPER(<NAME>)
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return <NAME>(ZEND_OPCODE_HANDLER_ARGS_PASSTHRU)
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ZEND_VM_DISPATCH_TO_HELPER_EX(<NAME>,<PARAM>,<VAL>)
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return <NAME>(<VAL>, ZEND_OPCODE_HANDLER_ARGS_PASSTHRU)
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ZEND_VM_CONTINUE()
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return 0
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ZEND_VM_NEXT_OPCODE()
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NEXT_OPCODE()
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ZEND_VM_SET_OPCODE(<TARGET>
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SET_OPCODE(<TARGET>
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ZEND_VM_INC_OPCODE()
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INC_OPCOD()
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ZEND_VM_RETURN_FROM_EXECUTE_LOOP()
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RETURN_FROM_EXECUTE_LOOP()
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ZEND_VM_C_LABEL(<LABEL>):
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<LABEL>:
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ZEND_VM_C_GOTO(<LABEL>)
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goto <LABEL>
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OP<X>_TYPE
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opline->op<X>.op_type
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GET_OP<X>_ZVAL_PTR(<TYPE>)
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get_zval_ptr(&opline->op<X>, EX(Ts), &free_op<X>, <TYPE>)
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GET_OP<X>_ZVAL_PTR_PTR(<TYPE>)
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get_zval_ptr_ptr(&opline->op<X>, EX(Ts), &free_op<X>, <TYPE>)
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GET_OP<X>_OBJ_ZVAL_PTR(<TYPE>)
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get_obj_zval_ptr(&opline->op<X>, EX(Ts), &free_op<X>, <TYPE>)
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GET_OP<X>_OBJ_ZVAL_PTR_PTR(<TYPE>)
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get_obj_zval_ptr_ptr(&opline->op<X>, EX(Ts), &free_op<X>, <TYPE>)
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IS_OP<X>_TMP_FREE()
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IS_TMP_FREE(free_op<X>)
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FREE_OP<X>()
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FREE_OP(free_op<X>)
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FREE_OP<X>_IF_VAR()
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FREE_VAR(free_op<X>)
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FREE_OP<X>_VAR_PTR()
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FREE_VAR_PTR(free_op<X>)
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```
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Executor's helpers can be defined without parameters or with one parameter. This
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is done with the following constructs:
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```c
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ZEND_VM_HELPER(<HELPER-NAME>, <OP1_TYPES>, <OP2_TYPES>)
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{
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<HELPER'S CODE>
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}
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ZEND_VM_HELPER_EX(<HELPER-NAME>, <OP1_TYPES>, <OP2_TYPES>, <PARAM_SPEC>)
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{
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<HELPER'S CODE>
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}
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```
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Executor's code is generated by PHP script zend_vm_gen.php it uses
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`zend_vm_def.h` and `zend_vm_execute.skl` as input and produces
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`zend_vm_opcodes.h` and `zend_vm_execute.h`. The first file is a list of opcode
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definitions. It is included from `zend_compile.h`. The second one is an executor
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code itself. It is included from `zend_execute.c`.
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`zend_vm_gen.php` can produce different kind of executors. You can select
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different opcode threading model using `--with-vm-kind=CALL|SWITCH|GOTO`. You
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can disable opcode specialization using `--without-specializer`. You can include
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or exclude old executor together with specialized one using
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`--without-old-executor`. At last you can debug executor using original
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`zend_vm_def.h` or generated file `zend_vm_execute.h`. Debugging with original
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file requires `--with-lines` option. By default ZE2 uses the following command
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to generate executor:
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```bash
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php zend_vm_gen.php --with-vm-kind=CALL
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```
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