CS208 Introduction to Computer Systems
Friday, 13 February 2026

+ Quick picture of a stack frame

+ The zoo assignment
- The history of this assignment
    (including what's been going on the last couple days)

- What's in your tar file?

- How to approach it
    - breakpoint at the "phase_N" call in main()
    - r passcodes.txt
    - step into phase_N
    - figure out what the function is doing
        - use techniques from the "asm and C" assignment
        - baby steps (si and ni)
        - examine registers ("i r" to see all of them,
            "i r eax ebx" to see just a couple
        - examine the top of the stack
            x/40xw $rsp
            x/40xg $rsp
            x/64xb $rsp
        - examine memory at specific addresses
            x/1ss 0x432124  (if you think that address points to a string)
            x/10wx 0x432124 (if you think it's an array of ints)
        - figure out when trigger_alarm is getting called,
            then repeat, slower, to look at the state of
            registers and memory just before the last conditional
            jump before "call trigger_alarm"
    - go slowly; pay attention; take breaks

+ Tips
- When gdb asm layout gets messed up, Ctrl-L fixes it.