Whole Program Analysis (using WLLVM)

Analyzing a complex project

Within PhASAR, analyses are done on LLVM IR that comes either as human-readable .ll files or binary .bc files. In order to produce LLVM IR, firstly the project should be compiled. For more complex C/C++ projects, you may want to use WLLVM, which provides tools for building whole-program LLVM bitcode files. You can use the wllvm compiler wrapper as drop-in replacement for clang or clang++. After compiling, you can use the WLLVM tool extract-bc to produce a LLVM bitcode file for each object file, executable, or library. WLLVM takes care that all bitcode parts of the individual object files are correctly linked together.

Install WLLVM

WLLVM is a pip package. You can just install it by either of these commands:

$ pip install wllvm
$ sudo pip install wllvm

Then set LLVM_COMPILER environment variable to clang by the following command:

export LLVM_COMPILER=clang

Two following examples show how WLLVM can be used to produce bitcode file for C++ projects:

First, download two example projects from PhASAR website. Then, do the following.

In the Makefile of simple_makefile_project, change:

$ CXX = clang++

into

$ CXX = wllvm++

In CMakeLists.txt file of simple_cmake_project, change:

$ set(CMAKE_C_COMPILER clang)
$ set(CMAKE_CXX_COMPILER clang++)

into

$ set(CMAKE_C_COMPILER wllvm)
$ set(CMAKE_CXX_COMPILER wllvm++)

or set these variables when configuring the project with the cmake command.

After compiling each project, run the extract-bc command on each .exe file:

extract-bc main for simple_makefile_project and extract-bc myprogram for simple_cmakefile_project.

Above commands produce LLVM bitcode files of the whole project. To create human readable .ll file of the produced .bc file, run the llvm-dis main.bc and llvm-dis mypogram.bc for simple_makefile_project and simple_cmakefile_project respectively.

You can read more about WLLM on WLLVM git and WLLVM Project description.