Monday, December 31, 2012

Building LLVM 3.2 from source

A short guide on how to compile LLVM 3.2 a low level compiler infrastructure with Clang on Ubuntu 12.04 (64bit).

1. Create a directory for LLVM
$mkdir ~/llvm
$cd ~/llvm
Install required dependencies (Note : my system is already setup for development so I cannot find out the exact packages required, if you know them post them as comments)
$sudo apt-get install build-essential
2. Download the latest version of LLVM sources including clang (C frontend) and compiler RT from
3. Extract the downloaded sources
$tar zxvf ./llvm-3.2.src.tar.gz
$tar zxvf ./clang-3.2.src.tar.gz
$tar zxvf ./compiler-rt-3.2.src.tar.gz
4. Move folders to correct location. We start by renaming 'llvm-3.2.src' to 'llvm-3.2' and moving 'clang' inside the LLVM 'tools' folder and compiler-rt under the LLVM 'projects' folder. This is where LLVM expects them to be.
$mv ./llvm-3.2.src ./llvm-3.2
$mv ./clang-3.2.src ./clang
$mv ./clang ./llvm-3.2/tools/
$mv ./compiler-rt-3.2.src ./compiler-rt
$mv ./compiler-rt ./llvm-3.2/projects/
5. Once everything is in place we create a separate folder for the build process
$mkdir ./build
$cd ./build
This is how the folder structure looks like
|-- build (currently we are here)
|-- llvm-3.2
|   |-- projects
|   |   |-- compiler-rt
|   |-- tools
|   |   |-- clang
|-- clang-3.2.src.tar.gz
|-- compiler-rt-3.2.src.tar.gz
|-- llvm-3.2.src.tar.gz
6. Now we start the actual configuration and compilation of LLVM inside the 'build' folder outside of the main source directory so as to keep the main source tree clean
$../llvm-3.2/configure --enable-shared
Note : There are various configuration flags for CPU architecture, optimize builds, threads, etc. Check them with the '--help' option.
$../llvm-3.2/configure --help
If there are any missing packages required to compile LLVM it will ask you here.
7. If everything is good we can go ahead and compile it and also keep track of the time taken. After compilation all binaries are available in the 'build/Release+Asserts/bin' folder and libraries are available in the 'build/Release+Asserts/lib' folder.
$time make -j 3
llvm[0]: ***** Completed Release+Asserts Build
real 31m58.051s
user 52m50.842s
sys 2m37.610s
Great job so far, few more steps to go :)

8. Its good to run some test suites that comes along with LLVM to verify everything is working.
$make check-all
9. To start using LLVM we have to include the LLVM binaries and libraries in our path.
To add the LLVM binaries
$gedit ~/.bashrc
Add this line to the end of the file
export PATH=$PATH:~/llvm/build/Release+Asserts/bin
To add the LLVM libraries
sudo gedit /etc/
Add this line to the file (replace <your_user_name> with your current username)
To apply the new settings do
$source ~/.bashrc
$sudo ldconfig
10. To check whether the LLVM binaries and libraries are correctly set
$which clang
$sudo ldconfig -p | grep LLVM (libc6,x86-64) => ~/llvm/build/Release+Asserts/lib/
11. Test a sample program
$cd ..
$mkdir test
$cd test
$gedit test.c
Add the following lines of a simple C program and save it
#include <stdio.h>
int main(void)
 printf("Hello World from LLVM!\n");
 return 0;
Compile it using clang the C frontend to LLVM
$clang test.c -o test
Run it
Hello World from LLVM!


  1. I followed these instructions, as well as running `sudo make install` at the end to have the binaries copied into `/usr/local`. I don't seem to have the BlocksRuntime available (when I run clang with the `-lBlocksRuntime` flag I get a message saying its missing). Is there more to the procedure to get compiler-rt working?

    1. I ended up using this library as a solution:

  2. Nice walkthrough! Got me on the right track.

    Anyone who gets a missing bits/c++config.h, run 'locate c++config.h', copy an apropriate path to the bits/ dir and do 'export CPLUS_INCLUDE_PATH=thatpath'. Still wont pass the check-all test, but it will find it when you compile your stuff.

    I installed clang++ to update-alternatives, and I'd recommend doing that rather than setting PATH envs.
    ln -s ~/llvm/build/Release+Asserts/bin/clang++ /usr/bin/clang++-3.2
    update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-3.2 20
    update-alternatives --install /usr/bin/c++ c++ /usr/bin/clang++ 20
    update-alternatives --config c++

    and do the same for 'clang' towards 'cc'
    Makes it easy to switch between compilers if need be. Just use c++/cc in build scripts

  3. Thanks for the guidance!

    Stupid question: should there be an actual difference if i dont do the build and installation on home/llvm directory but rather in /usr/local/llvm ? If yes, can I copy them from /usr/local to home, once the building is done?


  4. you can do the build / copy anywhere you want as long as you do the step 9 correctly.

  5. Thanx for the post.. Helped a lot!!!!

  6. I am Korean Student.

    I appreciate your instruction for installing LLVM.

    As I am beginner, this video is so useful.

    I think that a lot of people have received help from this instruction.

    Once again, Thank you so much ~

  7. after step number 10 path for clang was shown as /usr/bin/clang is it normal??
    also, I got (libc6,x86-64) => /usr/lib/x86_64-linux-gnu/ (libc6,x86-64) => /usr/lib/x86_64-linux-gnu/ (libc6,x86-64) => /home/ayesha/llvm/build/Release+Asserts/lib/

    Is this normal??

    1. > after step number 10 path for clang was shown as /usr/bin/clang is it normal??

      no. you already have a installed version of llvm on your system.

    2. @ a clean install of linux bcz purge coomands wont wor...and follow the updated need to cross-compile for ARM...normally all targets are supported in simple compile

  8. Hello Sir I don't know whether its Right to request here but can u please help me in building vellvm ?what might be the necessary step actually i m completely unaware about it

  9. hello sir
    please can u tell me
    how to uninstall total llvm+clang from the system