All patches used to build these SDKs are open source and listed below. I maintain a daily CI on github Actions that cross-compiles the SDK from the three main source branches of the Swift toolchain for AArch64, armv7, and x86_64, builds several Swift packages against those SDKs, and then runs their tests in the Android x86_64 emulator.
To build with a Swift 5.6 SDK, first download the latest Android LTS NDK 23c and Swift 5.6.2 compiler (make sure to install the Swift compiler's dependencies listed there). Unpack these archives and the SDK.
I will write up a Swift script to do this SDK configuration, but you will need to do it manually for now. You can see how I do it on the CI for a concrete example.
The SDK will need to be modified with the path to some clang headers bundled with the Swift compiler (I'll show aarch64 below, the same will need to be done for the armv7 or x86_64 SDKs).
Change the symbolic link at swift-5.6-android-aarch64-24-sdk/usr/lib/swift/clang
to point to the clang headers that come with your swift compiler, eg
ln -sf /home/yourname/swift-5.6.2-RELEASE-ubuntu20.04/usr/lib/clang/13.0.0
swift-5.6-android-aarch64-24-sdk/usr/lib/swift/clang
Next, modify the cross-compilation JSON file android-aarch64.json in this repo
similarly:
-
All paths to the NDK should change from
/home/butta/android-ndk-r23cto the path to your NDK,/home/yourname/android-ndk-r23c. -
The path to the compiler should change from
/home/butta/swift-5.6.2-RELEASE-ubuntu20.04to the path to your Swift compiler,/home/yourname/swift-5.6.2-RELEASE-centos8. -
The path to the Android SDK should change from
/home/butta/swift-5.6-android-aarch64-24-sdkto the path where you unpacked the Android SDK,/home/yourname/swift-5.6-android-aarch64-24-sdk.
Now you're ready to cross-compile a Swift package with the cross-compilation
configuration JSON file, android-aarch64.json, and run its tests on Android.
I'll demonstrate with the swift-argument-parser package:
git clone --depth 1 https://github.com/apple/swift-argument-parser.git
cd swift-argument-parser/
/home/yourname/swift-5.6.2-RELEASE-ubuntu20.04/usr/bin/swift build --build-tests
--enable-test-discovery --destination ~/swift-android-sdk/android-aarch64.json
-Xlinker -rpath -Xlinker \$ORIGIN/swift-5.6-android-aarch64-24-sdk/usr/lib/swift/android
This will cross-compile the package for Android aarch64 and produce a test
runner executable with the .xctest extension, in this case at
.build/aarch64-unknown-linux-android24/debug/swift-argument-parserPackageTests.xctest.
It adds a rpath for where it expects the SDK libraries to be relative to the
test runner when run on Android.
Sometimes the test runner will depend on additional files or executables: this
one depends on the example executables math, repeat, and roll in the
same build directory. Other packages use #file to point at test data in the
repo: I've had success moving this data with the test runner, after modifying
the test source so it has the path to this test data in the Android test
environment. See the example of swift-crypto on the
CI.
You can copy these executables and the SDK to an emulator or a USB debugging-enabled device with adb, or put them on an Android device with a terminal emulator app like Termux. I test aarch64 with Termux so I'll show how to run the test runner there, but the process is similar with adb, as can be seen on the CI.
Copy the test executables to the same directory as the SDK:
cp .build/aarch64-unknown-linux-android24/debug/{swift-argument-parserPackageTests.xctest,math,repeat,roll} ..
You can copy the SDK and test executables to Termux using scp from OpenSSH, run these commands in Termux on the Android device:
uname -m # check if you're running on the right architecture, should say `aarch64`
cd # move to the Termux app's home directory
pkg install openssh
scp [email protected]:{swift-5.6-android-aarch64-24-sdk.tar.xz,
swift-argument-parserPackageTests.xctest,math,repeat,roll} .
tar xf swift-5.6-android-aarch64-24-sdk.tar.xz
./swift-argument-parserPackageTests.xctest
I tried a handful of Swift packages, including some mostly written in C or C++, and all the cross-compiled tests passed.
You can even run armv7 tests on an aarch64 device, though Termux may require
running unset LD_PRELOAD before invoking an armv7 test runner on aarch64.
Revert that with export LD_PRELOAD=/data/data/com.termux/files/usr/lib/libtermux-exec.so
when you're done running armv7 tests and want to go back to the normal aarch64
mode.
Since Android 11, many AArch64 devices have started enabling memory tagging, which collides with Swift's own tags in strings and other allocations. I have submitted a pull upstream to move the Swift tags but since it requires patching the Swift compiler, simply patching this SDK won't be enough. Once that pull is in, this AArch64 SDK will be updated with that fix too.
Download the Swift 5.6.2 compiler and Android NDK 23c as above. Check out this
repo and run
SWIFT_TAG=swift-5.6.2-RELEASE ANDROID_ARCH=aarch64 swift get-packages-and-swift-source.swift
to get some prebuilt Android libraries and the Swift source to build the SDK. If
you pass in a different tag like swift-DEVELOPMENT-SNAPSHOT-2022-03-13-a
for the latest Swift trunk snapshot and pass in the path to the corresponding
official prebuilt Swift toolchain to build-script below, you can build a Swift
trunk SDK too, as seen on the CI.
Next, apply some patches to the Swift source, swift-android.patch from
this repo, which adds a dependency for the Foundation core library in this
Android SDK, and three patches that have been merged into trunk upstream:
git apply swift-android.patch swift-android-ndk-version.patch
cd swift
wget -q https://patch-diff.githubusercontent.com/raw/apple/swift/pull/40976.diff
wget -q https://patch-diff.githubusercontent.com/raw/apple/swift/pull/41510.diff
patch -p1 < 40976.diff
patch -p1 < 41510.diff
cd ..
After making sure needed build tools like python 3, CMake, and ninja
are installed, run the following build-script command with your local paths
substituted instead:
./swift/utils/build-script -RA --skip-build-cmark --build-llvm=0 --android
--android-ndk /home/butta/android-ndk-r23c/ --android-arch aarch64 --android-api-level 24
--build-swift-tools=0 --native-swift-tools-path=/home/butta/swift-5.6.2-RELEASE-ubuntu20.04/usr/bin/
--native-clang-tools-path=/home/butta/swift-5.6.2-RELEASE-ubuntu20.04/usr/bin/
--host-cc=/usr/bin/clang-13 --host-cxx=/usr/bin/clang++-13
--cross-compile-hosts=android-aarch64 --cross-compile-deps-path=/home/butta/swift-release-android-aarch64-24-sdk
--skip-local-build --xctest --swift-install-components='clang-resource-dir-symlink;license;stdlib;sdk-overlay'
--install-swift --install-libdispatch --install-foundation --install-xctest
--install-destdir=/home/butta/swift-release-android-aarch64-24-sdk
--cross-compile-append-host-target-to-destdir=False -j9
Make sure you have an up-to-date CMake and not something old like 3.16. The
--host-cc and --host-cxx flags are not needed if you have a clang and
clang++ in your PATH already, but I don't and they're unused for this build
anyway but required by build-script. Substitute armv7 or x86_64 for aarch64
into these commands to build for those architectures instead.
Finally, copy libc++_shared.so from the NDK and modify the cross-compiled
libdispatch.so and Swift corelibs to include $ORIGIN and other relative
directories in their rpaths:
cp /home/yourname/android-ndk-r23c/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib/aarch64-linux-android/libc++_shared.so swift-release-android-aarch64-24-sdk/usr/lib
patchelf --set-rpath \$ORIGIN/../..:\$ORIGIN swift-release-android-aarch64-24-sdk/usr/lib/swift/android/lib*.so
Here is a description of what the above Swift script is doing:
These prebuilt SDKs were compiled against Android API 24, because the Swift stdlib and corelibs require some libraries like libicu, that are pulled from the prebuilt library packages used by the Termux app which are built against Android API 24. Specifically, it downloads the libicu, libicu-static, libandroid-spawn, libcurl, and libxml2 packages from the Termux package repository.
Each one is unpacked with ar x libicu_70.1_aarch64.deb; tar xf data.tar.xz and
the resulting files moved to a newly-created Swift release SDK directory:
mkdir swift-release-android-aarch64-24-sdk
mv data/data/com.termux/files/usr swift-release-android-aarch64-24-sdk
It removes two config scripts in usr/bin, runs patchelf to remove the
Termux rpath from all Termux shared libraries, and modifies the ICU libraries
to get rid of the versioning and symlinks (three libicu libraries are removed
since they're unused by Swift):
rm swift-release-android-aarch64-24-sdk/usr/bin/*-config
cd swift-release-android-aarch64-24-sdk/usr/lib
rm libicu{io,test,tu}*
patchelf --set-rpath \$ORIGIN libandroid-spawn.so libcurl.so libicu*so.70.1 libxml2.so
# repeat the following for libicui18n.so and libicudata.so, as needed
rm libicuuc.so libicuuc.so.70
readelf -d libicuuc.so.70.1
mv libicuuc.so.70.1 libicuuc.so
patchelf --set-soname libicuuc.so libicuuc.so
patchelf --replace-needed libicudata.so.70 libicudata.so libicuuc.so
The libcurl and libxml2 packages are only needed for the FoundationNetworking and FoundationXML libraries respectively, so you don't have to deploy them on the Android device if you don't use those extra Foundation libraries.
I simply include all four libraries since there's currently no way to disable building them in the CMake configuration, but they won't actually run on Android with this SDK, as libcurl and libxml2 have other library dependencies that aren't included. If you want to use either of these separate Foundation libraries, you will have to track down those other libcurl/xml2 dependencies and include them yourself.
The libicu dependency can be cross-compiled for Android from scratch using these instructions instead, so this Swift SDK for Android could be built without using any prebuilt Termux packages, if you're willing to put in the effort to cross-compile them yourself, for example, against a different Android API.
Finally, it gets the 5.6.2 source
tarballs for five Swift repos and renames them to llvm-project/, swift/,
swift-corelibs-libdispatch, swift-corelibs-foundation, and
swift-corelibs-xctest, as required by the Swift build-script, and creates
an empty directory, mkdir cmark.