Build LDC for Android

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Revision as of 13:50, 26 August 2017 by Joakim (talk | contribs) (Small tweaks to prerequisites)
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This page will show you how to build an ldc cross-compiler for Android/ARM on linux or Windows 10 (by using the new bash on linux subsystem), along with how to build and run the standard library's tests using the cross-compiler, both as a command-line binary and as a GUI Android app. Prebuilt native and cross-compilers are available here.

All of the standard library's unit tests and the full compiler testsuite passes on Android/ARM. Remaining work to be done is listed last.


  • linux/x64 shell, where you'll build and run ldc
    • You can use a virtual machine like VirtualBox/VMware, with at least 512 MB of memory and 1 GB of swap, particularly if building the phobos unit tests, and 10 GB of disk space.
    • Windows 10: You can alternately use Bash on Windows (the Windows Subsystem for Linux), see full steps below
  • C++ compiler and toolchain, to build a slightly patched llvm and parts of ldc
  • A pre-built D compiler for linux, as the ldc frontend is written in D.
  • Common development tools, such as CMake, Make, and git
  • ldc/druntime/phobos source
    • Get the source using git, as these Android patches were tested on the release-1.3.x branch
  • llvm 4.0.1 source, lightly tweaked for ldc
  • Android native toolchain, the NDK and optionally the SDK
    • The SDK is only needed if you want to package a GUI app; the NDK is enough if you just want to build a command-line binary, such as a test runner.
  • Android/ARM, whether a device or emulator
    • The SDK comes with an emulator. I use actual hardware, so that's what I'll discuss.

Notes for Bash on Ubuntu on Windows

  • Necessary packages
sudo apt-get install build-essential
sudo apt-get install git
sudo apt-get install cmake
sudo apt-get install unzip
sudo apt-get install libconfig-dev
  • DMD Compiler
cd ~
curl -L -O
sudo dpkg -i dmd_2.075.1-0_amd64.deb
  • Android Native Development Kit
sudo mkdir -p /opt/android-sdk/ndk-bundle
curl -L -O
sudo unzip 'android-ndk-r15c/*' -d /opt/android-sdk/ndk-bundle
export NDK=/opt/android-sdk/ndk-bundle/android-ndk-r15c

As Windows Subsystem for Linux does not support USB, you have to install Android SDK and Ant on your Windows system and execute the commands "android" and "ant" from your DOS console.

Compile llvm

Get the source for llvm, either this lightly tweaked llvm 4.0.1 source tarfile or the git repository for that tweaked branch. Build llvm as you would normally, with the ARM, AArch64, and X86 targets, for Android/ARM as the default target, and leaving out tools and utilities you don't need:

curl -L -O
tar xvf llvm-4.0.1.src.tar.xz
cd llvm-4.0.1.src/

mkdir build
cd build/
make all llvm-config -j5

Build ldc for Android/ARM

Clone the ldc repository, apply the Android patch, set the DMD and NDK environment variables to the paths of your pre-built D compiler and NDK install, and build ldc as usual:

cd ../../
git clone --recursive
cd ldc/
git checkout -b ldc13 origin/release-1.3.x
git submodule update
curl -O
git apply ldc_1.3_android_arm

mkdir build
cd build/
export DMD=/path/to/your/dmd2/linux/bin64/dmd
export NDK=/path/to/your/android-ndk-r15b
cmake .. -DLLVM_CONFIG=../../llvm-4.0.1.src/build/bin/llvm-config
make ldc2 -j5

Download and apply a small patch for the standard library, phobos, before building the D runtime and stdlib:

cd ../runtime/phobos/
curl -O
git apply phobos_1.3_ldc_arm

cd ../../build/
make druntime-ldc phobos2-ldc -j5

More info about the Android/ARM patches can be found with their release.

You can now try cross-compiling a sample program as shown here. You will need a terminal emulator Android app and to set the path to the LDC cross-compiler and libraries you just built:

export LDC=/path/to/your/ldc/build

Run the druntime and phobos unit tests

You can build the druntime and phobos unit tests and run the command-line test runner binaries on Android (don't add the -j5 flag to build in parallel unless you have gigabytes of memory available, as compiling some of the phobos modules' tests takes a fair amount of RAM):

make druntime-test-runner phobos2-test-runner

Copy the test runners to your device and run them. Assuming you have an SSH server set up on the computer where you're building with the linux shell and its IP address is, you can scp the binaries into the Termux Android app with these commands and run the tests:

apt install openssh
scp jo@"/path/to/your/ldc/build/runtime/{druntime,phobos2}-test-runner" .

The tests take about 25 seconds to run on my quad-core tablet: all should pass. One module, core.sync.semaphore, will fail for any Android older than 6.0, because sem_destroy used to work differently in bionic. You can also run the tests for specified modules by passing their names to the test runner:

./druntime-test-runner core.thread core.sync.semaphore
./phobos2-testrunner std.datetime std.random

Run the druntime and phobos unit tests in an apk

You can also run the tests as part of a GUI app, ie an apk, which is a slightly different runtime environment. First, you can try cross-compiling a sample GUI app from the NDK that has been translated from C to D, as shown here. That simple OpenGLES 1.0 GUI app can be modified to run all the tests, which is what we'll do next. Clone my Android repo, if you haven't already, go to the native-activity sample app, and create the output directory the SDK expects:

cd ../../
git clone

cd android/samples/native-activity/
mkdir -p libs/armeabi-v7a/

Download and apply a small patch to have the sample app invoke the test runner and a patch for the test runner in druntime, then build the tests into a shared library this time:

curl -O
git apply native_ldc_arm

cd ../../../ldc/runtime/druntime/
curl -O
git apply druntime_1.3_ldc_arm

cd ../../build/
make test-runner-apk

This assumes that the ldc and android repositories are in the same directory, as shown in these instructions. If not, modify ANDROID_DIR in the CMake build script to use the path you want.

Finally, package the test runner apk:

cd ../../android/samples/native-activity/
export SDK=/path/to/your/android-sdk-linux
$SDK/tools/android update project -p . -s --target 1
ant debug

Transfer the resulting bin/NativeActivity-debug.apk to your device and install it. Also, copy the list of modules to test to the /sdcard/ directory. The app will append its results to /sdcard/test.log, so if you happen to have a file with that name, move it.

The app should show a black screen for about a minute, while all the tests run. A touch after that and it should start flashing a bunch of colors. If not, look at the output in /sdcard/test.log and check if the app hung after any particular tested module. You can remove that module from test.list and try running again.

Directions for future work

  • You may notice that I added an empty main function in the D translation of the C sample app: that's a hack to build a shared library. The linux shared library support in druntime's rt.sections_elf_shared may eventually be integrated with Android to get rid of that.
  • Now that we can write D code for Android, it'll make building easier if the D cross-compilers are integrated with a build tool, like dub, reggae, or Button.