Assembly Language and Computer Architecture Lecture Notes

Overview

• Discussion on assembly language and computer architecture.
• Importance of understanding performance considerations for writing fast code.

Stages of Compilation

1. Pre-Processing
   • Use clang -E to run pre-processor and view macro expansions.
2. Compilation
   • Use clang -S to produce assembly code.
3. Assembly
   • Convert assembly code to binary machine code.
4. Linking
   • Use LD to produce the final executable.

Purpose of Assembly Language

• Helps understand what the compiler does and identify optimizations.
• Useful for debugging and reverse engineering.
• Allows for manual coding when necessary.

Expectations for Students

• Understand how compilers implement constructs with x86 instructions.
• Read and understand x86 assembly with architecture manual aid.
• Comprehend performance implications of assembly patterns.
• Be able to write assembly code if needed.

x86-64 Instruction Set Architecture (ISA)

• Focus on registers, instructions, data types, and memory addressing modes.
• Important registers:
  • General Purpose Registers (64-bit)
  • Flags Register (status flags)
  • Instruction Pointer (IP)
  • Vector Registers (SSE/AVX)

x86 Instructions

• Format: Opcode followed by operand list.
• Common opcodes and their operations:
  • MOV: Moves data between registers.
  • ADD: Adds contents of registers.
  • SUB, MUL, DIV: Arithmetic operations.
  • JMP, CALL, RET: Control flow.

Conditional Jumps

• Conditional operations rely on status flags in the Flags Register.
• Examples: JE (Jump if Equal), JNE (Jump if Not Equal).

Memory Addressing Modes

• Direct Addressing: Accessing specific memory locations.
• Indirect Addressing: Using registers to determine memory addresses.
• Complex addressing modes (e.g., base index scale) for advanced data structures.

Idioms in Assembly

• Common assembly idioms (e.g., using XOR to zero registers).
• Use of NOP for alignment optimization.

Floating-Point and Vector Hardware

• Overview of scalar and vector instructions.
• Importance of vector units for performance.

Computer Architecture

• Overview of modern processor structures (5-stage pipeline vs. superscalar processors).
• Discussion of instruction-level parallelism (ILP) and hazards (structural, data, control).
• Techniques for minimizing stalls, including bypassing and out-of-order execution.

Branch Prediction

• Importance of predicting branch outcomes for performance.
• Speculative execution as a technique to enhance throughput.

Conclusion

• Understanding assembly language provides insights into performance and optimization in software development.
• Preparation for future project work and applications in real-world scenarios.