Description:
------------
If a constant in a define() call is already defined, Zend engine issues a warning with E_NOTICE set. This warning code might use memory after it's freed. This can cause interpreter crash, especially under threaded Apache 2.x.

Following fixes the problem (this patch is in NetBSD pkgsrc ATM):

--- Zend/zend_constants.c.orig  2004-07-13 14:01:27.000000000 +0200
+++ Zend/zend_constants.c       2004-07-13 14:01:54.000000000 +0200
@@ -265,11 +265,11 @@
        }

        if (zend_hash_add(EG(zend_constants), name, c->name_len, (void *) c, sizeof(zend_constant), NULL)==FAILURE) {
+               zend_error(E_NOTICE,"Constant %s already defined", name);
                free(c->name);
                if (!(c->flags & CONST_PERSISTENT)) {
                        zval_dtor(&c->value);
                }
-               zend_error(E_NOTICE,"Constant %s already defined", name);
                ret = FAILURE;
        }
        if (lowercase_name) {


Reproduce code:
---------------
Under NetBSD, switch on extended malloc() debugging, by telling malloc to fill free()d values with junk:

ln -s J /etc/malloc.conf

then, run:

php -r 'error_reporting(E_ALL); define("foo", "j"); define("foo", "j");'

see something along:

PHP Notice:  Constant ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ in Command line code on line 1