LLVM Intro Function Pass

It is an LLVM-based project which warns developers if they have any method in their C/C++ code that has more than three parameters. It is an introductory project which utilizes LLVM compiler infrastructure.

Environment Setup for the First Time

Here is my first-time environment setup which I have used for this project:

• Operating system: Ubuntu 18.04 LTS

• Commands to setup LLVM: To setup LLVM on my Ubuntu machine, I have used the following commands:

  • To update and upgrade repositories:

    sudo apt-get update
    sudo apt-get upgrade

  • To install LLVM and Clang:

    sudo apt-get install clang-6.0 lldb-6.0 lld-6.0
    sudo apt-get install llvm
    sudo apt-get install clang
    sudo apt-get install clang-tools

  • To install CMake and other build tools:

    sudo apt-get install build-essential
    sudo apt-get install cmake

• Test whether the setup done correctly: I have used the following commands to test whether the environment setup has been done correctly:

  username@PC-NAME:~$ llvm-config --version
  6.0.0
  username@PC-NAME:~$ llvm-config --prefix
  /usr/lib/llvm-6.0
  username@PC-NAME:~$ clang
  clang: error: no input files
  username@PC-NAME:~$ 

  Notice the output of each command.

Build LLVM Function Pass

• Commands to build LLVM Function Pass: Notice that there is an LLVM function pass defined in /skeleton/Skeleton.cpp file. I have opened a terminal window outside of /skeleton directory. Then I have run the following commands:

  mkdir build
  cd build/
  cmake ..
  make

  Notice that /build/skeleton/libSkeletonPass.so file has been generated.

• Commands to use the LLVM Function Pass to compile code:

  • If you open /skeleton/Skeleton.cpp file, then you will see that SkeletonPass function pass actually warns developers if they have any function in their code that has more than three parameters.
  • Now notice that /HelloWorld.c file has a function called void concatCharArray(char *result, const char *a, const char *b, const char *c). So concatCharArray function has more than three arguments (four arguments).
  • I have used the following command to compile /HelloWorld.c file with SkeletonPass function pass:

    username@PC-NAME:~/Desktop/LLVM Intro Function Pass/build$ clang -Xclang -load -Xclang skeleton/libSkeletonPass.so ../HelloWorld.c
    Warning: 'concatCharArray' function has 4 arguments!
    username@PC-NAME:~/Desktop/LLVM Intro Function Pass/build$ 

    Notice that the above console output shows a warning generated by SkeletonPass function pass.

• Commands to run the compiled executable code: Since the compiled executable code of /HelloWorld.c has been created, I can use the following command to run it:

  username@PC-NAME:~/Desktop/LLVM Intro Function Pass/build$ ./a.out 
  Hello World!
  I am testing llvm!
  username@PC-NAME:~/Desktop/LLVM Intro Function Pass/build$ 

Additional Resource

• Here is an extremely helpful LLVM learning resource for absolute beginners:

  Adrian Sampson: LLVM for Grad Students