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BUILDING_LLVM.md

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Building Apple LLVM for Kotlin/Native

This document describes how to compile LLVM distribution and use it to build Kotlin/Native on macOS.
Usually, you don't need to compile LLVM by yourself:

  • If you use Kotlin/Native compiler it will download LLVM on the first run.
  • If you contribute to kotlin-native repository then use :dependencies:update Gradle task.

But if you don't want to download prebuilt LLVM or want to experiment with your own distribution, you came to the right place.

Part 1. Building the right LLVM version for macOS.

For macOS host we use LLVM from Apple downstream. Branch is apple/stable/20190104 because it is similar (or even the same) to what Apple ships with Xcode 11.*. After cloning the repo and changing the branch we perform the following steps to build LLVM toolchain:

mkdir build

cd build

cmake -DLLVM_ENABLE_PROJECTS="clang;lld;libcxx;libcxxabi" \
 -DCMAKE_BUILD_TYPE=Release \
 -DLLVM_ENABLE_ASSERTIONS=Off \
 -G Ninja \
 -DCMAKE_INSTALL_PREFIX=clang-llvm-apple-8.0.0-darwin-macos \
 ../llvm

ninja install

After these steps clang-llvm-apple-8.0.0-darwin-macos directory will contain LLVM distribution that is suitable for building Kotlin/Native.

Part 2. Building Kotlin/Native against given LLVM distribution.

By default, Kotlin/Native will try to download LLVM distribution from CDN if it is not present in $HOME/.konan/dependencies folder. There are two ways to bypass this behaviour.

Option A. Substitute prebuilt distribution.

This option doesn't require you to edit compiler sources, but a bit harder.

The compiler checks dependency presence by reading contents of $HOME/.konan/dependencies/.extracted file. So to avoid LLVM downloading, we should manually add a record to the .extracted file:

  1. Create $HOME/.konan/dependencies/.extracted file if it is not created.
  2. Add clang-llvm-apple-8.0.0-darwin-macos line.

and put clang-llvm-apple-8.0.0-darwin-macos directory from the Part 1 to $HOME/.konan/dependencies/.

Option B. Provide an absolute path to the distribution.

This option requires user to edit konan.properties file. Set llvmHome.<HOST_NAME> to an absolute path to your LLVM distribution and set llvmVersion.<HOST_NAME> to its version. For example, provide a path to clang-llvm-apple-8.0.0-darwin-macos from the Part 1 and set version to 8.0.0.

Now we are ready to build Kotlin/Native itself. The process is described in README.md. Please note that we still need to run ./gradlew dependencies:update to download other dependencies (e.g. libffi).

Q&A

— Can I override .konan location?
— Yes, by setting $KONAN_DATA_DIR environment variable. See HACKING.md.

  • Can I use another LLVM distribution without rebuilding Kotlin/Native?
  • Yes, see HACKING.md.