#include <stdio.h>

/*
 Simple program demonstrating function calls and stack updates
 Use gdb to walk through the assembly code and see how the stack is updated.

 Useful commands for exploring the stack are:
 "info registers" - lists register contents (pay attention to eip, esp, ebp)
 "x /32xw $esp" - displays last 32 words added to the stack

 The last command is especially useful when stepping through the code
 line by line, and seeing how arguments are added and removed from the
 stack.

 For a review of how the stack should update, review the
 "Procedures and Stacks" lecture slides.

 */

int func(int a, int b) {
  return a+b;
}

int main(void) {
  int d = func(22,33);
  printf("%d\n", d);
  return 0;
} 

/*
You should see something like the following in gbd

    Dump of assembler code for function func:
    0x00001faa <func+0> push %ebp
    0x00001fab <func+1>> mov %esp,%ebp
    0x00001fad <func+3>> sub $0x8,%esp
    0x00001fb0 <func+6>> mov 0xc(%ebp),%eax
    0x00001fb3 <func+9>> add 0x8(%ebp),%eax
    0x00001fb6 <func+12>> leave 
    0x00001fb7 <func+13>> ret 
    End of assembler dump.

This is what the call stack looks like by line func+3.
%ebp+12a = 22
%ebp+8b = 33
%ebp+4return address = 0x00001fd9
%ebpold %ebp = 0xbffff338
%ebp-4 
%ebp-8== %esp, from the instruction at func+3 above

The return value a+b is placed into the %eax register. 
*/