1 #00 pc 00000685 waiter (call_level3+53) 2 #01 pc 000006b7 waiter (call_level2+23) 3 #02 pc 000006d7 waiter (call_level1+23) 4 #03 pc 000006f7 waiter (main+23) 5 #04 pc 00018275 libc.so 6