Introduction to Machine And Assembly Language

1
Introduction to Machine And Assembly Language

• IA-32 Processor Architecture
• Dr. Richard Ford

2
Understanding the Processor

• How is the IA-32 processor structured?
• How is the computer structured?
• Fundamental items
• Registers
• Heap
• Stack

3
Why the IA-32 Arch?

• Probably most common architecture out there
• The host for Windows
• Probably one of the worst assembly languages to
  learn!
• Why?

4
The Structure of the Computer

• Processor (CPU)
• Memory Storage Unit
• I/O Devices
• Driven by the clock

5
The Processor Itself

• Attached to the rest of the hardware via the data
  bus, control bus and address bus
• Is responsible for all(?) calculations and logic
  for the machine
• Is the location that the real program runs
  broken down into very simple instructions
• Has access to limited storage locations called
  registers

6
Multitasking?

• The CPU can, in general, execute one full
  instruction at a time
• So how does Windows run five different things at
  once?

7
Processor Modes of Operation

• Protected Mode
• All instructions and features available programs
  work in their own protected memory segment
• Virtual 8086 Mode
• Execution of old MSDOS programs in a safe
  multitasking environment
• Real Address Mode
• Looks like an 8086 processor
• System Management Mode
• Functions for power management etc.

8
Address Space

• Protected mode Direct memory addressing of up to
  4GB
• Real mode 1MB of memory can be accessed
• How? Wait and see, its a little messy

9
Registers

• High speed storage locations no lag compared to
  regular memory
• Note Much quicker to access registers than
  system memory
• Basic Program Execution Registers
• 8 General Purpose Registers
• 8 Segment Registers
• 1 Flags Register
• 1 Instruction Pointer

10
General Purpose Registers

• Primarily arithmetic and data movement
• 8 bit, 16 bit and 32 bit
• 32-bit
• EAX, EBX, ECX, EDX, EBP, ESP, ESI, EDI
• 16-bit
• AX, BX, CX etc.
• 8-bit
• AH, AL, BH, BL etc.

11
Specialized Uses?

• Not necessarily, but some are more apropos for
  some things than others
• EAX Multiplication and division instructions
• ECX Loop counter
• ESP Stack pointer (more on this later)
• ESI, EDI High speed memory transfer (indexes
  remember this as Source Index and Destination
  Index)
• EBP Frame pointer, pointing to a particular
  stack frame
• CAVEAT Dont assume that a register is for
  something. This is especially important when
  reverse engineering code!

12
Segment Registers

• Used to address particular segments of memory
  (code segment, various data segments etc.)

13
Instruction Pointer

• The address of the next instruction to be
  executed by the processor. Jumps and Calls work
  by manipulating this value.

14
EFLAGS

• Bit-field of states
• Each bit means something different
• Control flags which effect the CPU operation
  (more later as needed)
• Status Flags
• Carry (CF) set when an unsigned arithmetic
  operation overflows
• Overflow (OF) set when a signed arithmetic
  operation overflows
• Sign (SF) set when a negative result is
  generated logically or arithmetically
• Zero (ZF) set when the result of a comparison
  or arithmetical operation is Zero
• Auxiliary Carry Set when an 8-bit operation
  causes a carry from bit 3 to bit 4
• Parity sums the number of set bits in a number
  and indicates whether the result is odd or even

15
Other Registers

• Not really going to use them in an introductory
  class, but
• FPU Registers
• ST(0), ST(1) ST(7)
• 64-bit registers for MMX instruction set
• 128-bit XMM registers