understanding-clang-llvm

Repository for understanding and writing LLVM passes.

Building and installing Clang/LLVM

This needs ~40GB disk space and compilation time of ~90min.

1. Download LLVM-8.0.0, clang-8.0.0

2. Unzip the LLVM and Clang source files

   tar xf llvm-8.0.0.src.tar.xz
   tar xf cfe-8.0.0.src.tar.xz
   mv cfe-8.0.0.src llvm-8.0.0.src/tools/clang
   

3. Create your target build folder and make

   mkdir llvm-8.0.0.obj
   cd llvm-8.0.0.obj
   cmake -DCMAKE_BUILD_TYPE=Debug ../llvm-8.0.0.src (or add "-DCMAKE_BUILD_TYPE:STRING=Release" for releae version)
   make -j8  
   

4. Add paths for LLVM and Clang

   export LLVM_SRC=your_path_to_llvm-8.0.0.src
   export LLVM_OBJ=your_path_to_llvm-8.0.0.obj
   export LLVM_DIR=your_path_to_llvm-8.0.0.obj
   export PATH=$LLVM_DIR/bin:$PATH
   

Converting .c file to bitcode file

The folder examples contains a couple of example .c files which you can play with.

LLVM passes run on bitcode file. Here, we explain how to convert a C file to bitcode file.

clang -c -emit-llvm <path_to_c_file> -o <path_to_output_bitcode_file>

Example:

cd examples
clang -c -emit-llvm simple.c -o simple.bc

LLVM Passes

The folder llvm_passes contains various sample LLVM passes.