$ dtrace -n 'php*:::zval-addref { printf("zval: %x, refcount: %i, is_ref: %i\n", arg0, arg1, arg2); ustack(); }' 
dtrace: description 'php*:::zval-addref ' matched 1 probe
CPU     ID                    FUNCTION:NAME
  3  95562 zend_dtrace_zval_addref:zval-addref zval: 88f5e84, refcount: 3, is_ref: 0

              0x8496412
              0x84dc297
              0x859b9f7
              0x84ded53
              0x84962fb
              0x84aa4ba
              0x842ffa4
              0x85ca89a
              0x85cb7c9
              0x80d2103

  3  95562 zend_dtrace_zval_addref:zval-addref zval: 88f5e84, refcount: 3, is_ref: 0

              0x8496412
              0x84dc297
              0x85c680f
              0x84ded53
              0x84962fb
              0x84aa4ba
              0x842ffa4
              0x85ca89a
              0x85cb7c9
              0x80d2103

  3  95562 zend_dtrace_zval_addref:zval-addref zval: 89197e0, refcount: 2, is_ref: 1

              0x8496412
              0x84dc4c6
              0x85c6834
              0x84ded53
              0x84962fb
              0x84aa4ba
              0x842ffa4
              0x85ca89a
              0x85cb7c9
              0x80d2103

  3  95562 zend_dtrace_zval_addref:zval-addref zval: 89197e0, refcount: 3, is_ref: 1

              0x8496412
              0x8592217
              0x85923b5
              0x84ded53
              0x84962fb
              0x84aa4ba
              0x842ffa4
              0x85ca89a
              0x85cb7c9
              0x80d2103

  3  95562 zend_dtrace_zval_addref:zval-addref zval: 88f5e84, refcount: 3, is_ref: 0

              0x8496412
              0x84dc1ec
              0x84e14e5
              0x84ded53
              0x84962fb
              0x84e0508
              0x84e12e9
              0x84ded53
              0x84962fb
              0x84aa4ba
              0x842ffa4
              0x85ca89a
              0x85cb7c9
              0x80d2103

  3  95562 zend_dtrace_zval_addref:zval-addref zval: 89197e0, refcount: 4, is_ref: 1

              0x8496412
              0x84e1547
              0x84ded53
              0x84962fb
              0x84e0508
              0x84e12e9
              0x84ded53
              0x84962fb
              0x84aa4ba
              0x842ffa4
              0x85ca89a
              0x85cb7c9
              0x80d2103