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  <div class="section" id="build-paddlepaddle-for-android">
<span id="build-paddlepaddle-for-android"></span><h1>Build PaddlePaddle for Android<a class="headerlink" href="#build-paddlepaddle-for-android" title="Permalink to this headline">¶</a></h1>
<p>There are two approaches to build PaddlePaddle for Android:</p>
<ul class="simple">
<li><a class="reference external" href="#cross-compiling-using-docker">Cross-Compiling Using Docker</a></li>
<li><a class="reference external" href="#cross-compiling-on-linux">Cross-Compiling on Linux</a></li>
</ul>
<div class="section" id="cross-compiling-using-docker">
<span id="cross-compiling-using-docker"></span><h2>Cross-Compiling Using Docker<a class="headerlink" href="#cross-compiling-using-docker" title="Permalink to this headline">¶</a></h2>
<p>Docker-based cross-compiling is the recommended approach because Docker runs on all major operating systems, including Linux, Mac OS X, and Windows.</p>
<div class="section" id="build-the-docker-image">
<span id="build-the-docker-image"></span><h3>Build the Docker Image<a class="headerlink" href="#build-the-docker-image" title="Permalink to this headline">¶</a></h3>
<p>The following steps pack all the tools that we need to build PaddlePaddle into a Docker image.</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>$ git clone https://github.com/PaddlePaddle/Paddle.git
$ <span class="nb">cd</span> Paddle
$ docker build -t paddle:dev-android . -f Dockerfile.android
</pre></div>
</div>
<p>Users can directly use the published Docker image.</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>$ docker pull paddlepaddle/paddle:latest-dev-android
</pre></div>
</div>
<p>For users in China, we provide a faster mirror.</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>$ docker pull docker.paddlepaddlehub.com/paddle:latest-dev-android
</pre></div>
</div>
</div>
<div class="section" id="build-the-inference-library">
<span id="build-the-inference-library"></span><h3>Build the Inference Library<a class="headerlink" href="#build-the-inference-library" title="Permalink to this headline">¶</a></h3>
<p>We can run the Docker image we just created to build the inference library of PaddlePaddle for Android using the command below:</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>$ docker run -it --rm -v <span class="nv">$PWD</span>:/paddle -e <span class="s2">&quot;ANDROID_ABI=armeabi-v7a&quot;</span> -e <span class="s2">&quot;ANDROID_API=21&quot;</span> paddle:dev-android
</pre></div>
</div>
<p>The Docker image accepts two arguments <code class="docutils literal"><span class="pre">ANDROID_ABI</span></code> and <code class="docutils literal"><span class="pre">ANDROID_API</span></code>:</p>
<table class="docutils">
<colgroup>
  <col width="25%" />
  <col width="50%" />
  <col width="25%" />
</colgroup>
<thead valign="bottom">
  <tr class="row-odd">
  <th class="head">Argument</th>
  <th class="head">Optional Values</th>
  <th class="head">Default</th>
</tr>
</thead>
<tbody valign="top">
  <tr class="row-even">
  <td>ANDROID_ABI</td>
  <td>armeabi-v7a, arm64-v8a</td>
  <td>armeabi-v7a</td>
</tr>
<tr class="row-odd">
  <td>ANDROID_API</td>
  <td>>= 16</td>
  <td>21</td>
</tr>
</tbody>
</table><p>The ARM-64 architecture (<code class="docutils literal"><span class="pre">arm64-v8a</span></code>) requires at least level 21 of Android API.</p>
<p>The default entry-point of the Docker image, <a class="reference external" href="https://github.com/PaddlePaddle/Paddle/blob/develop/paddle/scripts/docker/build_android.sh"><code class="docutils literal"><span class="pre">paddle/scripts/docker/build_android.sh</span></code></a> generates the <a class="reference external" href="https://developer.android.com/ndk/guides/standalone_toolchain.html">Android cross-compiling standalone toolchain</a> based on the argument: <code class="docutils literal"><span class="pre">ANDROID_ABI</span></code> or <code class="docutils literal"><span class="pre">ANDROID_API</span></code>.  For information about other configuration arguments, please continue reading.</p>
<p>The above command generates and outputs the inference library in <code class="docutils literal"><span class="pre">$PWD/install_android</span></code> and puts third-party libraries in <code class="docutils literal"><span class="pre">$PWD/install_android/third_party</span></code>.</p>
</div>
</div>
<div class="section" id="cross-compiling-on-linux">
<span id="cross-compiling-on-linux"></span><h2>Cross-Compiling on Linux<a class="headerlink" href="#cross-compiling-on-linux" title="Permalink to this headline">¶</a></h2>
<p>The Linux-base approach to cross-compile is to run steps in <code class="docutils literal"><span class="pre">Dockerfile.android</span></code> manually on a Linux x64 computer.</p>
<div class="section" id="setup-the-environment">
<span id="setup-the-environment"></span><h3>Setup the Environment<a class="headerlink" href="#setup-the-environment" title="Permalink to this headline">¶</a></h3>
<p>To build for Android&#8217;s, we need <a class="reference external" href="https://developer.android.com/ndk/downloads/index.html">Android NDK</a>:</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>wget -q https://dl.google.com/android/repository/android-ndk-r14b-linux-x86_64.zip
unzip -q android-ndk-r14b-linux-x86_64.zip
</pre></div>
</div>
<p>Android NDK includes everything we need to build the <a class="reference external" href="https://developer.android.com/ndk/guides/standalone_toolchain.html"><em>standalone toolchain</em></a>, which in then used to build PaddlePaddle for Android.  (We plan to remove the intermediate stage of building the standalone toolchain in the near future.)</p>
<ul class="simple">
<li>To build the standalone toolchain for <code class="docutils literal"><span class="pre">armeabi-v7a</span></code> and Android API level 21:</li>
</ul>
<div class="highlight-bash"><div class="highlight"><pre><span></span>your/path/to/android-ndk-r14b-linux-x86_64/build/tools/make-standalone-toolchain.sh <span class="se">\</span>
        --arch<span class="o">=</span>arm --platform<span class="o">=</span>android-21 --install-dir<span class="o">=</span>your/path/to/arm_standalone_toolchain
</pre></div>
</div>
<p>The generated standalone toolchain will be in <code class="docutils literal"><span class="pre">your/path/to/arm_standalone_toolchain</span></code>.</p>
<ul class="simple">
<li>To build the standalone toolchain for <code class="docutils literal"><span class="pre">arm64-v8a</span></code> and Android API level 21:</li>
</ul>
<div class="highlight-bash"><div class="highlight"><pre><span></span>your/path/to/android-ndk-r14b-linux-x86_64/build/tools/make-standalone-toolchain.sh <span class="se">\</span>
        --arch<span class="o">=</span>arm64 --platform<span class="o">=</span>android-21 --install-dir<span class="o">=</span>your/path/to/arm64_standalone_toolchain
</pre></div>
</div>
<p>The generated standalone toolchain will be in <code class="docutils literal"><span class="pre">your/path/to/arm64_standalone_toolchain</span></code>.</p>
</div>
<div class="section" id="cross-compiling-arguments">
<span id="cross-compiling-arguments"></span><h3>Cross-Compiling Arguments<a class="headerlink" href="#cross-compiling-arguments" title="Permalink to this headline">¶</a></h3>
<p>CMake supports <a class="reference external" href="https://cmake.org/cmake/help/v3.0/manual/cmake-toolchains.7.html#cross-compiling">choosing the toolchain</a>.  PaddlePaddle provides <a class="reference external" href="https://github.com/PaddlePaddle/Paddle/blob/develop/cmake/cross_compiling/android.cmake"><code class="docutils literal"><span class="pre">android.cmake</span></code></a>, which configures the Android cross-compiling toolchain for CMake.  <code class="docutils literal"><span class="pre">android.cmake</span></code> is not required for CMake &gt;= 3.7, which support Android cross-compiling. PaddlePaddle detects the CMake version, for those newer than 3.7, it uses <a class="reference external" href="https://cmake.org/cmake/help/v3.7/manual/cmake-toolchains.7.html#cross-compiling">the official version</a>.</p>
<p>Some other CMake arguments you need to know:</p>
<ul class="simple">
<li><code class="docutils literal"><span class="pre">CMAKE_SYSTEM_NAME</span></code> must be <code class="docutils literal"><span class="pre">Android</span></code>.  This tells PaddlePaddle&#8217;s CMake system to cross-compile third-party dependencies. This also changes some other CMake arguments like <code class="docutils literal"><span class="pre">WITH_GPU=OFF</span></code>, <code class="docutils literal"><span class="pre">WITH_AVX=OFF</span></code>, <code class="docutils literal"><span class="pre">WITH_PYTHON=OFF</span></code>, <code class="docutils literal"><span class="pre">WITH_RDMA=OFF</span></code>, <code class="docutils literal"><span class="pre">WITH_MKL=OFF</span></code> and <code class="docutils literal"><span class="pre">WITH_GOLANG=OFF</span></code>.</li>
<li><code class="docutils literal"><span class="pre">WITH_C_API</span></code> must be <code class="docutils literal"><span class="pre">ON</span></code>, to build the C-based inference library for Android.</li>
<li><code class="docutils literal"><span class="pre">WITH_SWIG_PY</span></code> must be <code class="docutils literal"><span class="pre">OFF</span></code> because the Android platform doesn&#8217;t support SWIG-based API.</li>
</ul>
<p>Some Android-specific arguments:</p>
<ul class="simple">
<li><code class="docutils literal"><span class="pre">ANDROID_STANDALONE_TOOLCHAIN</span></code>: the absolute path of the Android standalone toolchain, or the path relative to the CMake build directory.  PaddlePaddle&#8217;s CMake extensions would derive the cross-compiler, sysroot and Android API level from this argument.</li>
<li><code class="docutils literal"><span class="pre">ANDROID_TOOLCHAIN</span></code>: could be <code class="docutils literal"><span class="pre">gcc</span></code> or <code class="docutils literal"><span class="pre">clang</span></code>.  The default value is <code class="docutils literal"><span class="pre">clang</span></code>.<ul>
<li>For CMake &gt;= 3.7, it should anyway be <code class="docutils literal"><span class="pre">clang</span></code>.  For older versions, it could be <code class="docutils literal"><span class="pre">gcc</span></code>.</li>
<li>Android&#8217;s official <code class="docutils literal"><span class="pre">clang</span></code> requires <code class="docutils literal"><span class="pre">glibc</span></code> &gt;= 2.15.</li>
</ul>
</li>
<li><code class="docutils literal"><span class="pre">ANDROID_ABI</span></code>: could be <code class="docutils literal"><span class="pre">armeabi-v7a</span></code> or <code class="docutils literal"><span class="pre">arm64-v8a</span></code>.  The default value is <code class="docutils literal"><span class="pre">armeabi-v7a</span></code>.</li>
<li><code class="docutils literal"><span class="pre">ANDROID_NATIVE_API_LEVEL</span></code>: could be derived from the value of <code class="docutils literal"><span class="pre">ANDROID_STANDALONE_TOOLCHAIN</span></code>.</li>
<li><code class="docutils literal"><span class="pre">ANROID_ARM_MODE</span></code>:<ul>
<li>could be <code class="docutils literal"><span class="pre">ON</span></code> or <code class="docutils literal"><span class="pre">OFF</span></code>, and defaults to <code class="docutils literal"><span class="pre">ON</span></code>, when <code class="docutils literal"><span class="pre">ANDROID_ABI=armeabi-v7a</span></code>;</li>
<li>no need to specify when <code class="docutils literal"><span class="pre">ANDROID_ABI=arm64-v8a</span></code>.</li>
</ul>
</li>
<li><code class="docutils literal"><span class="pre">ANDROID_ARM_NEON</span></code>: indicates if to use NEON instructions.<ul>
<li>could be <code class="docutils literal"><span class="pre">ON</span></code> or <code class="docutils literal"><span class="pre">OFF</span></code>, and defaults to <code class="docutils literal"><span class="pre">ON</span></code>, when <code class="docutils literal"><span class="pre">ANDROID_ABI=armeabi-v7a</span></code>;</li>
<li>no need to specify when <code class="docutils literal"><span class="pre">ANDROID_ABI=arm64-v8a</span></code>.</li>
</ul>
</li>
</ul>
<p>Other useful arguments:</p>
<ul class="simple">
<li><code class="docutils literal"><span class="pre">USE_EIGEN_FOR_BLAS</span></code>: indicates if using Eigen.  Could be <code class="docutils literal"><span class="pre">ON</span></code> or <code class="docutils literal"><span class="pre">OFF</span></code>, defaults to <code class="docutils literal"><span class="pre">OFF</span></code>.</li>
<li><code class="docutils literal"><span class="pre">HOST_C/CXX_COMPILER</span></code>: specifies the host compiler, which is used to build the host-specific protoc and target-specific OpenBLAS.  It defaults to the value of the environment variable <code class="docutils literal"><span class="pre">CC/C++</span></code>, or <code class="docutils literal"><span class="pre">cc/c++</span></code>.</li>
</ul>
<p>Some frequent configurations for your reference:</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>cmake -DCMAKE_SYSTEM_NAME<span class="o">=</span>Android <span class="se">\</span>
      -DANDROID_STANDALONE_TOOLCHAIN<span class="o">=</span>your/path/to/arm_standalone_toolchain <span class="se">\</span>
      -DANDROID_ABI<span class="o">=</span>armeabi-v7a <span class="se">\</span>
      -DANDROID_ARM_NEON<span class="o">=</span>ON <span class="se">\</span>
      -DANDROID_ARM_MODE<span class="o">=</span>ON <span class="se">\</span>
      -DUSE_EIGEN_FOR_BLAS<span class="o">=</span>ON <span class="se">\</span>
      -DCMAKE_INSTALL_PREFIX<span class="o">=</span>your/path/to/install <span class="se">\</span>
      -DWITH_C_API<span class="o">=</span>ON <span class="se">\</span>
      -DWITH_SWIG_PY<span class="o">=</span>OFF <span class="se">\</span>
      ..
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">cmake</span> <span class="o">-</span><span class="n">DCMAKE_SYSTEM_NAME</span><span class="o">=</span><span class="n">Android</span> \
      <span class="o">-</span><span class="n">DANDROID_STANDALONE_TOOLCHAIN</span><span class="o">=</span><span class="n">your</span><span class="o">/</span><span class="n">path</span><span class="o">/</span><span class="n">to</span><span class="o">/</span><span class="n">arm64_standalone_toolchain</span> \
      <span class="o">-</span><span class="n">DANDROID_ABI</span><span class="o">=</span><span class="n">arm64</span><span class="o">-</span><span class="n">v8a</span> \
      <span class="o">-</span><span class="n">DUSE_EIGEN_FOR_BLAS</span><span class="o">=</span><span class="n">OFF</span> \
      <span class="o">-</span><span class="n">DCMAKE_INSTALL_PREFIX</span><span class="o">=</span><span class="n">your</span><span class="o">/</span><span class="n">path</span><span class="o">/</span><span class="n">to</span><span class="o">/</span><span class="n">install</span> \
      <span class="o">-</span><span class="n">DWITH_C_API</span><span class="o">=</span><span class="n">ON</span> \
      <span class="o">-</span><span class="n">DWITH_SWIG_PY</span><span class="o">=</span><span class="n">OFF</span> \
      <span class="o">..</span>
</pre></div>
</div>
<p>There are some other arguments you might want to configure.</p>
<ul class="simple">
<li><code class="docutils literal"><span class="pre">CMAKE_BUILD_TYPE=MinSizeRel</span></code> minimizes the size of library.</li>
<li><code class="docutils literal"><span class="pre">CMAKE_BUILD_TYPE-Release</span></code> optimizes the runtime performance.</li>
</ul>
<p>Our own tip for performance optimization to use clang and Eigen or OpenBLAS:</p>
<ul class="simple">
<li><code class="docutils literal"><span class="pre">CMAKE_BUILD_TYPE=Release</span></code></li>
<li><code class="docutils literal"><span class="pre">ANDROID_TOOLCHAIN=clang</span></code></li>
<li><code class="docutils literal"><span class="pre">USE_EIGEN_BLAS=ON</span></code> for <code class="docutils literal"><span class="pre">armeabi-v7a</span></code>, or <code class="docutils literal"><span class="pre">USE_EIGEN_FOR_BLAS=OFF</span></code> for <code class="docutils literal"><span class="pre">arm64-v8a</span></code>.</li>
</ul>
</div>
<div class="section" id="build-and-install">
<span id="build-and-install"></span><h3>Build and Install<a class="headerlink" href="#build-and-install" title="Permalink to this headline">¶</a></h3>
<p>After running <code class="docutils literal"><span class="pre">cmake</span></code>, we can run <code class="docutils literal"><span class="pre">make;</span> <span class="pre">make</span> <span class="pre">install</span></code> to build and install.</p>
<p>Before building, you might want to remove the <code class="docutils literal"><span class="pre">third_party</span></code> and <code class="docutils literal"><span class="pre">build</span></code> directories including pre-built libraries for other architectures.</p>
<p>After building，in the directory <code class="docutils literal"><span class="pre">CMAKE_INSTALL_PREFIX</span></code>, you will find three sub-directories:</p>
<ul class="simple">
<li><code class="docutils literal"><span class="pre">include</span></code>: the header file of the inference library,</li>
<li><code class="docutils literal"><span class="pre">lib</span></code>: the inference library built for various Android ABIs,</li>
<li><code class="docutils literal"><span class="pre">third_party</span></code>: dependent third-party libraries built for Android.</li>
</ul>
</div>
</div>
</div>


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