message: Fix co_bt in gdb script.
diff: @@ -105,7 +105,7 @@ define __co_bt
  if $co
  set $task = (php_coro_task *)$co->task
  if $task
  - dump_bt $eg.current_execute_data
  + dump_bt $task->execute_data
  end
  else
  printf "coroutines %d not found\n", $cid
  