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Building Clang from source on Linux involves several steps, including downloading the source code, resolving dependencies, configuring the build options, and compiling the toolchain. Here’s a detailed guide to help you build Clang on a Linux system:

Prerequisites

  1. Operating System: Ensure you have a Linux distribution installed. Ubuntu, Fedora, or CentOS are commonly used for building Clang.

  2. Required Tools and Libraries: You need to have cmake, make, gcc, g++, and python installed to build Clang. You might also need additional development libraries depending on your Linux distribution.

Step-by-Step Guide

Step 1: Install Required Packages

For Ubuntu, Update the Package List:

sudo apt update

You can install the required packages and dependencies using the following command:

sudo apt-get install -y build-essential cmake git python3 libtool libssl-dev

For Fedora/CentOS, the command might look like:

sudo dnf install gcc gcc-c++ cmake3 make git python3

Step 2: Download and Clone the LLVM Source Code You can download the source code using git. It’s recommended to get the sources from the official LLVM monorepo.

  • The LLVM project includes Clang as one of its sub-projects. Change directory to where you want the llvm directory placed.
git clone https://github.com/llvm/llvm-project.git
cd llvm-project

The above command is very slow. It can be made faster by creating a shallow clone. Shallow clone saves storage and speeds up the checkout time. This is done by using the command:

git clone --depth=1 https://github.com/llvm/llvm-project.git
cd llvm-project

(using this only the latest version of llvm can be built)

Step 3: Configure, Build LLVM and Clang Create a directory for building, It’s good practice to build LLVM/Clang in a separate directory:

mkdir build  # (in-tree build is not supported)
cd build

This builds both LLVM and Clang in release mode.

Configure the build using cmake. Here, you can customize build options like installation directory or build type:

cmake -G "Unix Makefiles" -DLLVM_ENABLE_PROJECTS="clang" -DCMAKE_BUILD_TYPE=Release ../llvm
  • -G "Unix Makefiles" specifies the generator, which is Makefiles in this case.
  • -DLLVM_ENABLE_PROJECTS="clang" includes the Clang project.
  • -DCMAKE_BUILD_TYPE=Release builds the compiler in release mode (you can choose Debug for a debug build).

Step 4: Build Clang Compile Clang using:

make -j$(nproc)
  • make -j$(nproc) uses all available processors to speed up the build process.

Step 5: Install Clang (Optional) To install Clang, use:

sudo make install

This step is optional. If you prefer, you can use Clang directly from the build directory.

Verify Installation

After installation, you can verify that Clang is correctly installed by checking its version:

clang --version

Troubleshooting

  • Missing Dependencies: Ensure all necessary development libraries are installed. Some specific libraries may be required depending on your Linux distribution.

  • Build Errors: Look at the error messages carefully. They often provide hints about what’s missing or what went wrong.

  • Insufficient Resources: Building LLVM/Clang can be resource-intensive. Ensure your machine has enough RAM and disk space.

This process compiles Clang from the source, giving you the flexibility to customize your build according to your needs. Remember that compiling LLVM and Clang from source can be time-consuming and resource-intensive, depending on your system's specifications.