x86汇编语言基础1

为什么要学习机器码？

• Many years ago, people write programs with machine code
• Nowadays, people write programs with high-level languages mainly for productivity and portability reasons
• To write a program that runs is easy
• To write a program that runs well (reliable and efficient), you need to understand how the machine execute programs

相关定义

• Architecture (instruction set architecture - ISA)「体系结构（指令集体系结构-ISA）」: The parts of a processor design that one needs to understand to write assembly code

• • Examples: instruction set specification, registers「指令集规范，寄存器」
  • We will mainly focus on the x86-64 architecture there

• Microarchitecture「微体系结构」: Implementation of the architecture

• • Examples: cache sizes and core frequency「体系结构的实现」

• Code Forms

• • Machine Code「机器码」: The byte-level programs that a processor executes「处理器执行的字节级程序」
  • Assembly Code「汇编语言」: A text representation of machine code「机器代码的文本表示」

From high-level language to assembly

Assembly programmer’s view

Programmer-Visible State

• PC: Program counter

  • Address of next instruction

    • Called “EIP” (IA32) or “RIP” (x86-64)

  • Register file

    • Memory inside the CPU
    • Used for instruction execution「用于指令执行」

  • Condition codes

    • Store status information about most recent arithmetic operation「存储有关最新算术运算的状态信息」
    • Used for conditional branching「Used for conditional branching」

Memory

• Byte addressable array
• Code, user data, (some) OS data
• Includes stack used to support procedures

Machine instruction example

Data types

“word” in x86-64 ISA

• Word: 16 bits, 2 bytes

• Double words: 32 bits, 4 bytes

• Quad words: 64 bits, 8 bytes

  C declaration	Intel data type	Assembly code suffix	Size (bytes)
  char	Byte	b	1
  short	Word	w	2
  int	Double word	l	4
  long	Quad word	q	8
  char *	Quad word	q	8
  float	Single precision	s	4
  double	Double precision	l	8

注明：在不同的ISA架构中，word的长度不同

“word” in MiPS-x64 ISA

• Word: 32 bits, 4 bytes
• Double words: 64 bits, 8 bytes

X86-64 registers

寄存器图示

寄存器的兼容实现

64位系统向下兼容的原因

Instruction

Moving data

movq,Source, Dest

• Source values can be constants, from registers or from memory「源值可以是常量，可以是寄存器中的值，也可以是存储器中的值」
• Results can be stored in either registers or memory「结果可以存储在寄存器或存储器中「结果可以存储在寄存器或存储器中」
• Moving different data sizes: movq, movl, movw, movb（依照来源和目的地的最大长度，使用相应的指令」

Operand Types

Operand Types (basically, where data are stored)

• Immediate: Constant integer data

  • Example: $ 0x400，$-533
  • Like C constant, prefixed with $ in the assembly code
    像C常量一样，在汇编代码中以$开头

• Register: One of 16 integer registers

  • Example: %rax, %r13

  • But %rsp reserved for special use

    • Others have special uses for particular instructions

  • Memory: 8 consecutive bytes of memory at address given by register

  • Simplest example: (%rax)
    - Various other “address modes”
    - 实现原理：指针

Cannot do memory-memory transfer with a single instruction!

Some arithmetic operations

Two Operand Instructions

Format Computation
addq Src,Dest Dest = Dest + Src
subq Src,Dest Dest = Dest − Src
imulq Src,Dest Dest = Dest * Src
salq Src,Dest Dest = Dest << Src Also called shlq
sarq Src,Dest Dest = Dest >> Src Arithmetic
shrq Src,Dest Dest = Dest >> Src Logical
xorq Src,Dest Dest = Dest ^ Src
andq Src,Dest Dest = Dest & Src
orq Src,Dest Dest = Dest | Src

Watch out for argument order!
No distinction between signed and unsigned int

Leaq

Memory addressing

simple modes

Complete memory addressing modes

引用

• COMP1411@Polyu PowerPoint