machine level code

• eip: address in memory of next instruction
• registers: some hold important addresses other used for temporary data
  • on 32-bit architecture 8 registers are used
  • 2 have special meaning:
    • Stack pointer: esp
    • frame pointer: ebp
  • others are general purpose for most part: eax,ebx,ecx,edx,edi,esi
  • either 32bit pointers (e??) or 16bit version (??)
  • e?x can also be accessed as 8bit pointer: ?h, ?l
  • example: eax, ax, ah, al
• different notations: GAS (gnu assembly) is used here
• instructions can have arguments(operands)
  • immediate/const
    • using $ notation: $0x1F
  • register
    • using value stored within an register
    • notation: %eax: use eax as value
  • memory
    • get value within some memory block
    • different notations:
      • (%eax): get value stored in memory refernced from eax
      • 0x123: get value from address 0x123
• data movement:
  • move:
    • movl src, dst
    • movl $eax,$ebx:
  • push/pop from stack:
    • push src
    • pop dst
• stack
  • grows downward: top element has lowest addr
  • convention: draw stack upside-down
  • esp: holds addr of top elem in stack
  • pushing dword:
    • decrementing esp by 4
    • push val into addr of esp

program  memory used for: object code, OS info, run-time stack for managing procedure calls and returns, and blocks of memory allocated by the user. addressed using virtual addresses.