Book Image

Learn LLVM 12

By : Kai Nacke
Book Image

Learn LLVM 12

By: Kai Nacke

Overview of this book

LLVM was built to bridge the gap between compiler textbooks and actual compiler development. It provides a modular codebase and advanced tools which help developers to build compilers easily. This book provides a practical introduction to LLVM, gradually helping you navigate through complex scenarios with ease when it comes to building and working with compilers. You’ll start by configuring, building, and installing LLVM libraries, tools, and external projects. Next, the book will introduce you to LLVM design and how it works in practice during each LLVM compiler stage: frontend, optimizer, and backend. Using a subset of a real programming language as an example, you will then learn how to develop a frontend and generate LLVM IR, hand it over to the optimization pipeline, and generate machine code from it. Later chapters will show you how to extend LLVM with a new pass and how instruction selection in LLVM works. You’ll also focus on Just-in-Time compilation issues and the current state of JIT-compilation support that LLVM provides, before finally going on to understand how to develop a new backend for LLVM. By the end of this LLVM book, you will have gained real-world experience in working with the LLVM compiler development framework with the help of hands-on examples and source code snippets.
Table of Contents (17 chapters)
Section 1 – The Basics of Compiler Construction with LLVM
Section 2 – From Source to Machine Code Generation
Section 3 –Taking LLVM to the Next Level

Finding bugs with libFuzzer

To test your application, you'll need to write unit tests. This is a great way to make sure your software behaves correctly. However, due to the exponential number of possible inputs, you'll probably miss certain weird inputs, and a few bugs as well.

Fuzz testing can help here. The idea is to present your application with randomly generated data, or data based on valid input but with random changes. This is done over and over again, and so your application is tested with a large number of inputs. This is a very powerful testing approach. Literally hundreds of bugs in web browsers and other software have been found with fuzz testing.

LLVM comes with its own fuzz testing library. Originally part of the LLVM core libraries, the libFuzzer implementation was finally moved to compiler-rt. The library is designed to test small and fast functions.

Let's run a small example. You'll need to provide the LLVMFuzzerTestOneInput() function...