Segmented argument_stack

Hi Nuno,

Thank you for your notes.

Nuno Lopes wrote:

Hi Dmitry,

The patch looks fine. Although it wastes a bit more memory than the
current implementation, I think it's ok.

I think the patch uses exactly the same amount of memory, except that
the current implementation uses CPU stack and the patch uses ZE heap.

It also has some memory
fragmentation, which shouldn't be an issue (we don't have functions with
100 arguments :P).

Functions with 100 (or 10000 :) arguments might work slower, but anyway
it's an unusual case.

As a side note, I think the following code could be optimized:

Probably it could, but note that the code not just moves the stack
pointer, but also destroys arguments there (zval_ptr_dtor).

• while (zend_vm_stack_top(TSRMLS_C) != stack_frame) {
• zval *stack_zval_p = zend_vm_stack_pop(TSRMLS_C);
• zval_ptr_dtor(&stack_zval_p);
  }

I think you can simply discard the last n ptrs on the stack. A
zend_vm_stack_pop(num_elements) would do the trick (or a
zend_vm_stack_pop_until(stack_frame)). That way the function call
cleanup would be a little faster.

May be I misunderstood you. Lets commit unmodified patch and then you'll
show me a way to optimize it.

Thanks. Dmitry.

Thanks,
Nuno

----- Original Message ----- From: "Dmitry Stogov" dmitry@zend.com
To: "PHP Internals List" internals@lists.php.net
Sent: Monday, January 21, 2008 7:47 PM
Subject: [PHP-DEV] Segmented argument_stack

Hi,

The attached patch (for PHP_5_3) implements the segmented argument_stack
that has the following advantages:

1. It fixes #43426 and other crashes which occur because of stack
   reallocation.

2. The whole stack is never reallocated. So we don't have penalties
   because of the while stack copying (it may be 1MB and more).

3. CPU stack usage reduced, because execute_data, Ts and CVs now are
   stored in the same argument_stack. As result the probability of CPU
   stack overflow is reduced.

4. func_num_args(), func_get_agr(), func_get_args(),
   debug_print_backtrace() and exception's backtrace now always able to get
   arguments. They didn't work before in case of incomplete "arguments
   frame". For example: "foo(1, func_num_args());".

5. bench.php got about 1% speedup

I'm going to commit the patch into HEAD and PHP_5_3 on Thursday.
Any objections?

Thanks. Dmitry.