x86 Architecture and Instruction Set Overview

Basic Info

• 16-bit (need to clock cycles to transfer alll 32 bits) or 32-bit
• Data types based on size
  • Byte: 8 bits
  • Word: 16 bits
  • Doubleword: 32 bits
  • Quadword: 64 bits
  • Double quadword: 128 bits

Internal Achitecture

Instruction Categories

• Data movement
• Stack manipulation
• Arithmetic and logic
• Conversions
• Control flows
• String and flag manipulation
• Input/Output
• Protected mode

Other instruction categories

• Floating-point instructions
• SIMD instructions
• SSE3 (Streaming SIMD Extension 3)
• AES instructions - for AES encryption
• MPX instructions - for memory protection
• SMX instructions - safer mode
• TSX instructions - for transactional synchronization extensions
• VMX instructions - virtual machine extensions

Common instruction patterns

xor reg, reg ; Set reg to zero
test reg, reg ; Test if reg contains zero
add reg, reg ; Shift reg left by one bit

Instruction formats

• Individual instruction size = 1 to 15 bytes

x86 Assembly Language

Here is an example assembly code that prints a string and exits in Windows console.

.386
.model FLAT,C
.stack 400h
.code
includelib libcmt.lib
includelib legacy_stdio_definitions.lib extern printf:near
extern exit:near
public main
main proc
; Print the message
push offset message
call printf
; Exit the program with status 0
push 0
call exit
main endp
.data
message db "Hello, Computer Architect!",0 end

To run it:

ml /Fl /Zi /Zd hello_x86.asm