CS208 Introduction to Computer Systems
Wednesday, 22 Feb 2023

+ What happens when a function gets called?
- Answer expressed in terms of
    - registers
    - the system stack (i.e., the portion
      of memory pointed to by rsp)

rip -- points to the next instruction to execute
rsp -- points to the top of the stack

- Before: caller puts parameters into registers (rdi, rsi,...)
- Before: rip points to some callq instruction in caller ...
- During callq
    - push rip (address of the instruction immediately after callq)
    - set rip = address of the function
- The function pushes the values of registers that it's going to use
    so the old values can be restored before the function returns
- The function subtracts some offset from rsp to make room on the stack
    for local variables, etc.


+ What happens when a function returns?
- set up rax as the return value
- add that offset back to rsp to deallocate the stack frame space
- pop saved registers
- retq
    - jumps back to the return address
           (pop return address from stack into rip)


+ Buffer overflow assignment walkthrough

To do:
- Read the assignment, take notes
- How can I set a break point where I want it?
    (objdump -d ctarget > ctarget.d)
- What's on the stack when Gets gets called?