04. machine-basics

'Computer Systems: A Programmer's Perspective 3rd (Randal E. Bryant)'를 주교재로 한 시스템 소프트웨어 강의 수업자료를 복습하며 정리한 것

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C, assembly, machine code

• Architecture
  • also ISA : instruction set architecture
  • machine, assembly code를 쓰기 위해 이해해야 하는 프로세서 설계 부분
  • e.g.) instruction set specification, registers
  • Machine code : byte-level programs that a processor executes
  • Assembly code : machine code를 text로 표현한 것
• Microarchitecture
  • architecture의 구현
  • e.g.) cache sizes and core frequency
• Assembly/Machine Code View

 

• Turning C into Object Code
  • command : gcc -Og p1.c p2.c -o p
  • -Og : Optimization level
  • -o p : 생성될 binary file의 이름을 p로 하겠다.
  • 

• Assembly Characteristics : Data Types
  • Integer data of 1, 2, 4, or 8 bytes
  • Data values, Addresses
  • Floating point data of 4(float), 8(double), or 10(long double) bytes
  • Code : Byte sequences encoding series of instructions
  • array나 별도의 자료구조와 같은 aggregate type은 지원하지 않음(just contiguously allocated bytes in memory)
• Assembly Characteristics : Operations
  • arithmetic function(산술적 연산)은 register나 memory를 대상으로 수행됨
  • Transfer data between memory and register
  • Transfer control
  • call, jump, conditional branches
• Assembler
  • Translates .s into .o
  • Binary encoding of each instruction
  • Missing linkages between code in different files
• Linker
  • Resolves references between files
  • Combines with static run-time libraries
  • e.g.) code for malloc, printf
  • some libaries are dynamically linked (Linking occurs when program begins execution)
• Machine Instruction Example

C Code	Assembly	Object code
*dest = t;	movq %rax, (%rbx)	0x40059e: 48 89 03
	t : register %rax dest : register %rbx *dest : Memory M[%rbx]

• Disassemble
  • Object code를 assembly code로 변환

 

Assembly Basics : Registers, operands, move

• x86-64 Integer registers

16개의 register

• • 32bit에서 사용하던 8개 레지스터(%eax ~ %ebp)에 64bit로 변경되며 추가된 것들로 이루어짐
  • %rsp(%esp)는 다른 레지스터들과 달리 스택 메모리 영역을 가리키는 용도로만 사용
  • %rax의 하위 32bit를 사용하고싶다면 %eax를 사용
• Moving Data
  • movq Source, Dest : 어떠한 데이터를 source로부터 destination으로 이동시켜라
  • Operand Types
    • Immediate : Constant integer data  e.g.) $0x400, $-533
    • Register : e.g.) %rax
    • Memory : e.g.) (%rax)

movq Operand Combinations (memory - memory transfer는 single instruction으로 불가능하다)

 

Arithmetic & logical operations

• Address Computation Instruction
  • leaq Src, Dst
    • Src : address mode를 사용한 표현식
    • Dst를 src에 표현된 address로 set
    • e.g.) p = &x[i]; k = 1, 2, 4, or 8
• Some Arithmetic Operations
  • Two Operand Instructions
    • addq : +
    • subq : -
    • imulq : *
    • salq : <<
    • sarq : >> (arithmetic right shift)
    • shrq : >> (logical right shift)
    • xorq : ^
    • andq : &
    • orq : |
  • One Operand Instructions
    • incq : Dest + 1
    • decq : Dest - 1
    • negq : -Dest
    • notq : ~Dest