Swift Runtime for Linux Armv7

Since Linux armv7 is not officially supported by the Swift project (swiftlang), this is an effort to maintain builds of the runtime that can be used for cross-compilation to armv7.

Some main goals:

• Build major versions of Swift (since 5.9) and provide build artifacts for various distributions that support armv7 (Ubuntu, Debian).
• Provide SDKs that can be downloaded and used to cross-compile user applications and libraries to armv7.
• Maintain a CI that can build snapshots/nightly versions of Swift to find and fix issues.

Compilation

There are various options for compiling Swift for armv7 with these scripts.

Build Swift runtime cross compiled from Linux

To build for the default (Debian Bookworm) for armv7, use the build.sh script:

export SWIFT_NATIVE_PATH=/path/to/swift/toolchain
./build.sh

NOTE: The toolchain pointed to by SWIFT_NATIVE_PATH should match the version of Swift being built. If not, failures will occur in the compilation.

Build Swift runtime using custom sysroot

To build a custom sysroot and use it to build, run the build-sysroot.sh script. This requires a working installation of Docker with multi-platform support enabled.

./build-sysroot.sh ubuntu:noble

Then, provide the STAGING_DIR env variable to the build script:

export STAGING_DIR=$(pwd)/sysroot-ubuntu-noble
./build.sh

Extra dependencies can also be installed into the sysroot if desired or needed, which in turn will be installed into the cross-compilation SDK (see Building a Cross Compilation SDK for Linux). To do this, use:

EXTRA_DEPENDENCIES="libsqlite3-dev" ./build-sysroot debian:bookworm.sh

Cross compile Swift package from Linux

export SWIFT_PACKAGE_SRCDIR=/home/user/Developer/MySwiftPackage
./build.sh # Or skip if using cached build
./build-swift-package.sh

Cross compile Swift package from macOS

./generate-xcode-toolchain.sh
export SWIFT_PACKAGE_SRCDIR=/home/user/Developer/MySwiftPackage
export SWIFT_NATIVE_PATH=/tmp/cross-toolchain/debian-bookworm.sdk
./build-swift-package.sh

SWIFT_PACKAGE_SRCDIR can be set to the root of your own packages to cross compile them using build-swift-package.sh.

Building a Cross Compilation SDK for Linux

After building the armv7 runtime using the build.sh script, you can generate a redistributable SDK using the build-linux-cross-sdk.sh script. You must provide the swift tag and distribution name:

./build-linux-cross-sdk.sh swift-6.0.3-RELEASE ubuntu-noble

By default, the SDK will be generated to be installed at a path of /opt/$SWIFT_TAG-$DISTRIBUTION-armv7, but this can be customized by providing a different install prefix to the script:

export SDK_INSTALL_PREFIX=/home/myuser/swift-sdks
./build-linux-cross-sdk.sh swift-6.0.3-RELEASE ubuntu-noble

Continuous Integration & Releases

This repo also contains CI scripts that use GitHub actions to compile different versions of Swift for armv7 for different distributions. Artifacts are generated and published to CI runs that can be downloaded and used locally:

• sysroot-$DISTRIBUTION: Contains sysroot for the given distribution, used to compile Swift and included in SDKs.
• $SWIFT_TAG-$DISTRIBUTION-armv7-install: Swift armv7 runtime built for the given distribution, can be installed to the target.
• $SWIFT_TAG-$DISTRIBUTION-armv7-sdk: The cross-compilation SDK for the given distribution, must be installed to /opt to use.

To use the SDK that is generated by the CI or published to the Releases page, first extract it to /opt:

sudo tar -xf swift-6.0.3-RELEASE-debian-bookworm-armv7-sdk.tar.gz -C /opt

Then, from a Swift package, use the --destination paramter to cross-compile it for the target:

swift build --destination /opt/swift-6.0.3-RELEASE-debian-bookworm-armv7/debian-bookworm.json