Assembly Language Overview

Introduction

• Definition: Assembly is a low-level programming language designed to simplify CPU instructions.
• Purpose: Acts as a human-readable abstraction of machine code, avoiding manual binary coding.

Historical Context

• Pioneer: Created by Kathleen Booth in 1947 for the All-purpose Electronic Computer.
• Evolution: Evolved over the next decade into various formats for supercomputers.
• Example: IBM 7090, cost $20 million in today's currency.
• Transition: Dominant until the emergence of high-level languages like Fortran.

Modern Use Cases

• Current Applications:
  • Access to bare-metal hardware
  • Addressing low-level performance issues
  • Device drivers
  • Embedded systems
  • Running native software in browsers via WebAssembly

Specifics of Assembly Language

• Architecture Specific: Each assembly language works with specific CPU architectures like ARM or x86.
• Getting Started:
  • Requires an assembler, e.g., Netwide Assembler for x86 chips.

Program Structure

• Main Sections:
  1. Text Section: Contains the program logic and an entry point labeled start.
  2. Block Starting Symbol Section: Contains variables that may change.
  3. Data Section: Contains initialized constants or unchanging data.

Example Code Explanation

• Declaring a Constant:

  • Use a label and DB (Define Byte) to place a string into memory.
  • To print: Convert a symbol into a constant using EQU (Equate).
  • Calculate string length using $ (current position) and subtract the label position.

• Instructions and Operations:

  • Each line includes an instruction and one or more operands.
  • Hundreds of built-in instructions.

• Registers:

  • CPUs have limited numbers of 64-bit memory chunks called registers.
  • Example: Use MOVE instruction to insert data into a register.
  • System Write: Store value in specific registers (e.g., RDI for standard output).

Executing Code

• System Call: Execute code by calling the OS kernel.
• Error Handling: Avoid segmentation faults by updating the RAX register with appropriate system codes (e.g., system exit code).

Compilation and Linking

• Assembler: Compile code into an object file.
• Linker: Convert object file into the final executable.

Conclusion

• Summary: Brief overview of assembly language and its components in under 100 seconds.
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