How to use the Android NDK to build Arm NN

• Introduction
• Download the Android NDK and make a standalone toolchain
• Build the Compute Library
• Build Google's Protobuf library
• Build Arm NN
• Build Standalone Sample Dynamic Backend
• Run the Arm NN unit tests on an Android device

Introduction

These are step by step instructions for using the Android NDK to build Arm NN. They have been tested on a clean install of Ubuntu 16.04 and 18.04, and should also work with other OS versions. The instructions show how to build the Arm NN core library. Building protobuf is optional. We have given steps should the user wish to build it (i.e. as an Onnx dependency). All downloaded or generated files will be saved inside the $HOME/armnn-devenv directory.

Download the Android NDK and make a standalone toolchain

• Download the Android NDK from the official website:

  mkdir -p $HOME/armnn-devenv/
  cd $HOME/armnn-devenv/
  # For Mac OS, change the NDK download link accordingly.
  wget https://dl.google.com/android/repository/android-ndk-r20b-linux-x86_64.zip
  unzip android-ndk-r20b-linux-x86_64.zip
  export NDK=$HOME/armnn-devenv/android-ndk-r20b
  export NDK_TOOLCHAIN_ROOT=$NDK/toolchains/llvm/prebuilt/linux-x86_64
  export PATH=$NDK_TOOLCHAIN_ROOT/bin/:$PATH
  
  # You may want to append the above export variables commands to your `~/.bashrc` (or `~/.bash_profile` in Mac OS).

• With the android ndk-20b, you don't need to use the make_standalone_toolchain script to create a toolchain for a specific version of android. Android's current preference is for you to just specify the architecture and operating system while setting the compiler and just use the ndk directory.

Build the Compute Library

• Clone the Compute Library:

  (Requires Git if not previously installed: sudo apt install git)

  cd $HOME/armnn-devenv
  git clone https://github.com/ARM-software/ComputeLibrary.git

• Checkout ComputeLibrary release tag:

  cd ComputeLibrary
  git checkout <tag_name>

  For example, if you want to checkout release tag of 21.02:

  git checkout v21.02

• Build:

  (Requires SCons if not previously installed: sudo apt install scons)

  scons arch=arm64-v8a neon=1 opencl=1 embed_kernels=1 extra_cxx_flags="-fPIC" \
   benchmark_tests=0 validation_tests=0 os=android -j16

Build Google's Protobuf library (Optional)

• Clone protobuf:

  mkdir $HOME/armnn-devenv/google
  cd $HOME/armnn-devenv/google
  git clone https://github.com/google/protobuf.git
  cd protobuf
  git checkout -b v3.12.0 v3.12.0

• Build a native (x86) version of the protobuf libraries and compiler (protoc):

  (Requires cUrl, autoconf, llibtool, and other build dependencies if not previously installed: sudo apt install curl autoconf libtool build-essential g++)

  ./autogen.sh
  mkdir x86_build
  cd x86_build
  ../configure --prefix=$HOME/armnn-devenv/google/x86_pb_install
  make install -j16
  cd ..

• Build the arm64 version of the protobuf libraries:

  mkdir arm64_build
  cd arm64_build
  CC=aarch64-linux-android<Android_API>-clang \
  CXX=aarch64-linux-android<Android_API>-clang++ \
  CFLAGS="-fPIE -fPIC" \
      LDFLAGS="-llog -lz -lc++_static" \
     ../configure --host=aarch64-linux-android \
     --prefix=$HOME/armnn-devenv/google/arm64_pb_install \
     --enable-cross-compile \
     --with-protoc=$HOME/armnn-devenv/google/x86_pb_install/bin/protoc
  make install -j16
  cd ..

Note: The ANDROID_API variable should be set to the Android API version number you are using. E.g. "30" for Android R.

Build Arm NN

• Clone Arm NN source code:

  cd $HOME/armnn-devenv/
  git clone https://github.com/ARM-software/armnn.git

• Checkout Arm NN branch:

  cd armnn
  git checkout <branch_name>
  git pull

For example, if you want to checkout release branch of 21.02:

git checkout branches/armnn_21_02
git pull

• Build Arm NN:

  (Requires CMake if not previously installed: sudo apt install cmake)

  mkdir $HOME/armnn-devenv/armnn/build
  cd $HOME/armnn-devenv/armnn/build
  CXX=aarch64-linux-android<Android_API>-clang++ \
  CC=aarch64-linux-android<Android_API>-clang \
  CXX_FLAGS="-fPIE -fPIC" \
  cmake .. \
      -DCMAKE_ANDROID_NDK=$NDK \
      -DCMAKE_SYSTEM_NAME=Android \
      -DCMAKE_SYSTEM_VERSION=<Android_API> \
      -DCMAKE_ANDROID_ARCH_ABI=arm64-v8a \
      -DCMAKE_EXE_LINKER_FLAGS="-pie -llog -lz" \
      -DARMCOMPUTE_ROOT=$HOME/armnn-devenv/ComputeLibrary/ \
      -DARMCOMPUTE_BUILD_DIR=$HOME/armnn-devenv/ComputeLibrary/build \
      -DARMCOMPUTENEON=1 -DARMCOMPUTECL=1 -DARMNNREF=1 \
      -DPROTOBUF_ROOT=$HOME/armnn-devenv/google/arm64_pb_install/

To include standalone sample dynamic backend tests, add the argument to enable the tests and the dynamic backend path to the CMake command:

-DSAMPLE_DYNAMIC_BACKEND=1 \
-DDYNAMIC_BACKEND_PATHS=$SAMPLE_DYNAMIC_BACKEND_PATH
# Where $SAMPLE_DYNAMIC_BACKEND_PATH is the path where libArm_SampleDynamic_backend.so library file is pushed

• Run the build

  make -j16

Build Standalone Sample Dynamic Backend

• The sample dynamic backend is located in armnn/src/dynamic/sample

  mkdir build
  cd build

• Use CMake to configure the build environment, update the following script and run it from the armnn/src/dynamic/sample/build directory to set up the Arm NN build:

  #!/bin/bash
  CXX=aarch64-linux-android<Android_API>-clang++ \
  CC=aarch64-linux-android<Android_API>-clang \
  CXX_FLAGS="-fPIE -fPIC" \
  cmake \
  -DCMAKE_C_COMPILER_WORKS=TRUE \
  -DCMAKE_CXX_COMPILER_WORKS=TRUE \
  -DCMAKE_ANDROID_NDK=$NDK \
  -DCMAKE_SYSTEM_NAME=Android \
  -DCMAKE_SYSTEM_VERSION=$ANDROID_API \
  -DCMAKE_ANDROID_ARCH_ABI=arm64-v8a \
  -DCMAKE_SYSROOT=$HOME/armnn-devenv/android-ndk-r20b/toolchains/llvm/prebuilt/linux-x86_64/sysroot \
  -DCMAKE_CXX_FLAGS=--std=c++14 \
  -DCMAKE_EXE_LINKER_FLAGS="-pie -llog" \
  -DCMAKE_MODULE_LINKER_FLAGS="-llog" \
  -DARMNN_PATH=$HOME/armnn-devenv/armnn/build/libarmnn.so ..

• Run the build

  make

Run the Arm NN unit tests on an Android device

• Push the build results to an Android device and make symbolic links for shared libraries: Currently adb version we have used for testing is 1.0.41.

  adb push libarmnn.so /data/local/tmp/
      adb push libtimelineDecoder.so /data/local/tmp/
  adb push UnitTests /data/local/tmp/
  adb push $NDK/sources/cxx-stl/llvm-libc++/libs/arm64-v8a/libc++_shared.so /data/local/tmp/
  adb push $HOME/armnn-devenv/google/arm64_pb_install/lib/libprotobuf.so /data/local/tmp/libprotobuf.so.23.0.0
  adb shell 'ln -s libprotobuf.so.23.0.0 /data/local/tmp/libprotobuf.so.23'
  adb shell 'ln -s libprotobuf.so.23.0.0 /data/local/tmp/libprotobuf.so'

• Push the files needed for the unit tests (they are a mix of files, directories and symbolic links):

  adb shell mkdir -p /data/local/tmp/src/backends/backendsCommon/test/testSharedObject
  adb push -p $HOME/armnn-devenv/armnn/build/src/backends/backendsCommon/test/testSharedObject/* /data/local/tmp/src/backends/backendsCommon/test/testSharedObject/
  
  adb shell mkdir -p /data/local/tmp/src/backends/backendsCommon/test/testDynamicBackend
  adb push -p $HOME/armnn-devenv/armnn/build/src/backends/backendsCommon/test/testDynamicBackend/* /data/local/tmp/src/backends/backendsCommon/test/testDynamicBackend/
  
  adb shell mkdir -p /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath1
  adb push -p $HOME/armnn-devenv/armnn/build/src/backends/backendsCommon/test/backendsTestPath1/* /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath1/
  
  adb shell mkdir -p /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath2
  adb push -p $HOME/armnn-devenv/armnn/build/src/backends/backendsCommon/test/backendsTestPath2/Arm_CpuAcc_backend.so /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath2/
  adb shell ln -s Arm_CpuAcc_backend.so /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath2/Arm_CpuAcc_backend.so.1
  adb shell ln -s Arm_CpuAcc_backend.so.1 /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath2/Arm_CpuAcc_backend.so.1.2
  adb shell ln -s Arm_CpuAcc_backend.so.1.2 /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath2/Arm_CpuAcc_backend.so.1.2.3
  adb push -p $HOME/armnn-devenv/armnn/build/src/backends/backendsCommon/test/backendsTestPath2/Arm_GpuAcc_backend.so /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath2/
  adb shell ln -s nothing /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath2/Arm_no_backend.so
  
  adb shell mkdir -p /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath3
  
  adb shell mkdir -p /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath5
  adb push -p $HOME/armnn-devenv/armnn/build/src/backends/backendsCommon/test/backendsTestPath5/* /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath5/
  
  adb shell mkdir -p /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath6
  adb push -p $HOME/armnn-devenv/armnn/build/src/backends/backendsCommon/test/backendsTestPath6/* /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath6/
  
  adb shell mkdir -p /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath7
  
  adb shell mkdir -p /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath9
  adb push -p $HOME/armnn-devenv/armnn/build/src/backends/backendsCommon/test/backendsTestPath9/* /data/local/tmp/src/backends/backendsCommon/test/backendsTestPath9/
  
  adb shell mkdir -p /data/local/tmp/src/backends/dynamic/reference
  adb push -p $HOME/armnn-devenv/armnn/build/src/backends/dynamic/reference/Arm_CpuRef_backend.so /data/local/tmp/src/backends/dynamic/reference/
  
  # If the standalone sample dynamic tests are enabled, also push libArm_SampleDynamic_backend.so library file to the folder specified as $SAMPLE_DYNAMIC_BACKEND_PATH when Arm NN is built.
  # This is the example when $SAMPLE_DYNAMIC_BACKEND_PATH is specified as /data/local/tmp/dynamic/sample/:
  
  adb shell mkdir -p /data/local/tmp/dynamic/sample/
  adb push -p $HOME/armnn-devenv/armnn/src/dynamic/sample/build/libArm_SampleDynamic_backend.so /data/local/tmp/dynamic/sample/

• Run Arm NN unit tests:

  adb shell 'LD_LIBRARY_PATH=/data/local/tmp:/vendor/lib64:/vendor/lib64/egl /data/local/tmp/UnitTests'

  If libarmnnUtils.a is present in $HOME/armnn-devenv/armnn/build/ and the unit tests run without failure then the build was successful.