Project 3: Relocation and the PLT/GOT

Another lab-based project. You’ll write simple C code that calls a shared library function (like printf). You will then disassemble the executable and trace its execution in a debugger to see the Procedure Linkage Table (PLT) and Global Offset Table (GOT) in action.

Quick Reference

Attribute Value
Primary Language C
Alternative Languages N/A
Difficulty Level 3: Advanced
Time Estimate 1-2 weeks
Knowledge Area Assembly / Dynamic Linking
Tooling A debugger (GDB/LLDB) and a disassembler (objdump).
Prerequisites Project 1, basic GDB skills (setting breakpoints, stepping instructions (si), examining memory (x)).

What You Will Build

Another lab-based project. You’ll write simple C code that calls a shared library function (like printf). You will then disassemble the executable and trace its execution in a debugger to see the Procedure Linkage Table (PLT) and Global Offset Table (GOT) in action.

Why It Matters

This project builds core skills that appear repeatedly in real-world systems and tooling.

Core Challenges

  • Generating readable assembly → maps to using objdump -d or GDB’s disassemble command
  • Finding the PLT and GOT sections → maps to using your inspector or readelf -S
  • Stepping through the PLT indirection in a debugger → maps to seeing the lazy binding process happen live
  • Understanding how the GOT entry is patched on the first call → maps to witnessing the dynamic loader’s work

Key Concepts

  • Procedure Linkage Table: Excellent explanation at technovelty.org
  • Lazy Binding: “Computer Systems: A Programmer’s Perspective” Ch. 7.9
  • x86 Assembly: A basic understanding of call, jmp, and memory addressing is needed.

Real-World Outcome

Deliver a working demo with observable output that proves the feature is correct.

Implementation Guide

  1. Reproduce the simplest happy-path scenario.
  2. Build the smallest working version of the core feature.
  3. Add input validation and error handling.
  4. Add instrumentation/logging to confirm behavior.
  5. Refactor into clean modules with tests.

Milestones

  • Milestone 1: Minimal working program that runs end-to-end.
  • Milestone 2: Correct outputs for typical inputs.
  • Milestone 3: Robust handling of edge cases.
  • Milestone 4: Clean structure and documented usage.

Validation Checklist

  • Output matches the real-world outcome example
  • Handles invalid inputs safely
  • Provides clear errors and exit codes
  • Repeatable results across runs

References

  • Main guide: LEARN_C_LINKING_DEEP_DIVE.md
  • “Linkers and Loaders” by John R. Levine