[PATCH] Add an optional size limit to debug_backtrace

Hi:

Attached is a patch that adds an optional 'limit' parameter to
debug_backtrace, which limits the size of the returned array. In cases
where a script wants debug information only for the current function, or
for the function <n> levels above that, we can save a lot of unnecessary
call-stack traversal and zval allocation by bailing out early. For a
sufficiently large call depth and a small <n>, I'd expect this to
improve performance quite a bit.

The patch adds a total of six lines to the function, and one test in the
main loop for the zero-argument case. Should apply cleanly to both PHP_4_3
and HEAD.

Is there any chance this could be applied? :)

Thanks in advance,

• Dave
  dave@codewhore.org

--- Zend/zend_builtin_functions.c~ 2003-05-20 11:33:36.000000000 -0400
+++ Zend/zend_builtin_functions.c 2003-05-20 13:34:40.000000000 -0400
@@ -1173,7 +1173,7 @@
return arg_array;
}

-/* {{{ proto void debug_backtrace(void)
+/* {{{ proto void debug_backtrace([int limit])
Prints out a backtrace */
ZEND_FUNCTION(debug_backtrace)
{
@@ -1189,11 +1189,18 @@
void **args = cur_arg_pos;
int arg_stack_consistent = 0;
int frames_on_stack = 0;

• zval **limit_zval = NULL;
• long limit;

• if (ZEND_NUM_ARGS()) {

• if (ZEND_NUM_ARGS() > 1) {
  ZEND_WRONG_PARAM_COUNT();
  }

• if (ZEND_NUM_ARGS() == 1 && zend_get_parameters_ex(1, &limit_zval) == SUCCESS) {

•   convert_to_long_ex(limit_zval);
  

•   limit = (*limit_zval)->value.lval;
  

• }

• while (--args >= EG(argument_stack).elements) {
  if (*args--) {
  break;
  @@ -1217,6 +1224,9 @@
  array_init(return_value);

  while (ptr) {

•   if (limit_zval && --limit < 0)
  

•   	break;
  

•   MAKE_STD_ZVAL(stack_frame);
    array_init(stack_frame);