This is what I get from gdb:
[New process 1]
Core was generated by `httpd'.
Program terminated with signal 11, Segmentation fault.
#0 0xfddf352c in ?? () from /usr/lib/libc.so.12
(gdb) bt
#0 0xfddf352c in ?? () from /usr/lib/libc.so.12
#1 0xfddf345c in ?? () from /usr/lib/libc.so.12
#2 0xfddf5ca4 in free () from /usr/lib/libc.so.12
#3 0xfcb2c160 in zend_hash_destroy () from /usr/local/lib/httpd/mod_php5.so
#4 0xfcb2f45c in zend_destroy_rsrc_list_dtors () from /usr/local/lib/httpd/mod_php5.so
#5 0xfcb1c6c4 in zend_shutdown () from /usr/local/lib/httpd/mod_php5.so
#6 0xfcab22e0 in php_module_shutdown () from /usr/local/lib/httpd/mod_php5.so
#7 0xfcab23b8 in php_module_shutdown_wrapper () from /usr/local/lib/httpd/mod_php5.so
#8 0xfcbe3124 in php_apache_server_shutdown () from /usr/local/lib/httpd/mod_php5.so
#9 0xfdf088d4 in apr_pool_destroy () from /usr/local/lib/libapr-1.so.0
#10 0xfdf088a4 in apr_pool_destroy () from /usr/local/lib/libapr-1.so.0
#11 0x01819a7c in destroy_and_exit_process ()
#12 0x0181ad28 in main ()
(gdb)