src/porting/build_system.md

# Android Build System #

<p>Android uses a custom build system to generate tools, binaries, and documentation. This document provides an overview of Android's build system and instructions for doing a simple build. </p>
<p>Android's build system is make based and requires a recent version of GNU Make (note that Android uses advanced features of GNU Make that may not yet appear on the GNU Make web site). Before continuing, check your version of make by running <code>% make -v</code>. If you don't have version 3.80 or greater, you need to <a href="http://www.gnu.org/software/make/">upgrade your version of make</a>. </p>




<a name="androidBuildSystemOverview"></a><h4>Understanding the makefile</h4>

<p>A makefile defines how to build a particular application. Makefiles typically include all of the following elements:</p>
<ol>
  <li>Name: Give your build a name (<code>LOCAL_MODULE := &lt;build_name&gt;</code>).</li>
  <li>Local Variables: Clear local variables with CLEAR_VARS  (<code>include $(CLEAR_VARS)</code>).</li>
  <li>Files: Determine which files your application depends upon (<code>LOCAL_SRC_FILES := main.c</code>).</li>
  <li>Tags: Define tags, as necessary (<code>LOCAL_MODULE_TAGS := eng development</code>).</li>
  <li>Libraries: Define whether your application links with other libraries (<code>LOCAL_SHARED_LIBRARIES := cutils</code>).</li>
  <li>Template file: Include a template file to define underlining make tools for a particular target (<code>include $(BUILD_EXECUTABLE)</code>).</li>
</ol>

<p>The following snippet illustrates a typical makefile.</p>
<pre class="prettyprint">
LOCAL_PATH := $(my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := &lt;buil_name&gt;
LOCAL_SRC_FILES := main.c
LOCAL_MODULE_TAGS := eng development
LOCAL_SHARED_LIBRARIES := cutils
include $(BUILD_EXECUTABLE)
(HOST_)EXECUTABLE, (HOST_)JAVA_LIBRARY, (HOST_)PREBUILT, (HOST_)SHARED_LIBRARY,
  (HOST_)STATIC_LIBRARY, PACKAGE, JAVADOC, RAW_EXECUTABLE, RAW_STATIC_LIBRARY,
  COPY_HEADERS, KEY_CHAR_MAP
</pre>
<p>The snippet above includes artificial line breaks to maintain a print-friendly document.</p>


<a name="androidBuildSystemLayers"></a><h4>Layers</h4>

<p>The build hierarchy includes the abstraction layers described in the table below.</p>

<p>Each layer relates to the one above it in a one-to-many relationship. For example, an arch can have more than one board and each board can have more than one device. You may define an element in a given layer as a specialization of an element in the same layer, thus eliminating copying and simplifying maintenance.</p>
 
<table border=1 cellpadding=2 cellspacing=0>
 <tbody><tr>
  <th scope="col">Layer</th>
  <th  scope="col">Example</th>
  <th  scope="col">Description</th>
 </tr>
  <tr>
    <td valign="top">Product</td>
    <td valign="top">myProduct, myProduct_eu, myProduct_eu_fr, j2, sdk</td>
    <td valign="top">The product layer defines a complete specification of a shipping product, defining which modules to build and how to configure them. You might offer a device in several different versions based on locale, for example, or on features such as a camera. </td>
  </tr>
  <tr>
    <td valign="top">Device</td>
    <td valign="top">myDevice, myDevice_eu, myDevice_eu_lite</td>
    <td valign="top">The device layer represents the physical layer of plastic on the device. For example, North American devices probably include QWERTY keyboards whereas devices sold in France probably include AZERTY keyboards. Peripherals typically connect to the device layer. </td>
  </tr>
  <tr>
    <td valign="top">Board</td>
    <td valign="top">sardine, trout, goldfish </td>
    <td valign="top">The board layer represents the bare schematics of a product. You may still connect peripherals to the board layer. </td>
  </tr>
  <tr>
    <td valign="top">Arch</td>
    <td valign="top">arm (arm5te) (arm6), x86, 68k </td>
    <td valign="top">The arch layer describes the processor running on your board. </td>
  </tr>
</table>

<a name="androidSourceSetupBuildingCodeBase"></a><h3>Building the Android Platform</h3>

<p>This section describes how to build the default version of Android. Once you are comfortable with a generic build, then you can begin to modify Android for your own target device.</p>


<a name="androidSourceSetupBuildingDeviceCodeBase"></a><h4>Device Code</h4>

<p>To do a generic build of android, source <code>build/envsetup.sh</code>, which contains necessary variable and function definitions, as described below.</p>
<pre class="prettyprint">
% cd $TOP

% . build/envsetup.sh

# pick a configuration using choosecombo
% choosecombo

% make -j4 PRODUCT-generic-user
</pre>
<p>You can also replace user with eng for a debug engineering build:</p>

<pre class="prettyprint">
% make -j4 PRODUCT-generic-eng
</pre>

<p>These <a href="#androidBuildVariants">Build Variants</a> differ in terms of debug options and packages installed. 
 

<a name="androidBuildingCleaning"></a><h4>Cleaning Up</h4>

<p>Execute <code>% m clean</code> to clean up the binaries you just created. You can also execute <code>% m clobber</code> to get rid of the binaries of all combos. <code>% m clobber</code> is equivalent to removing the <code>//out/</code> directory where all generated files are stored.</p>


<a name="androidBuildingSpeeding"></a><h4>Speeding Up Rebuilds</h4>

<p> The binaries of each combo are stored as distinct sub-directories of <code>//out/</code>, making it possible to quickly switch between combos without having to recompile all sources each time. </p>
<p> However, performing a clean rebuild is necessary if the build system doesn't catch changes to environment variables or makefiles. If this happens often, you should define the <code>USE_CCACHE</code> environment variable as shown below: </p>
<pre class="prettyprint">
% export USE_CCACHE=1
</pre>
<p>Doing so will force the build system to use the ccache compiler cache tool, which reduces recompiling all sources.</p>

<p><code>ccache</code> binaries are provided in <code>//prebuilt/...</code> and don't need to get installed on your system.</p>


<a name="androidBuildingTroubleshooting"></a><h4>Troubleshooting</h4>

<p>The following error is likely caused by running an outdated version of Java.</p>
<pre class="prettyprint">
device Dex: core  UNEXPECTED TOP-LEVEL ERROR:
java.lang.NoSuchMethodError: method java.util.Arrays.hashCode with
signature ([Ljava.lang.Object;)I was not found.
  at com.google.util.FixedSizeList.hashCode(FixedSizeList.java:66)
  at com.google.rop.code.Rop.hashCode(Rop.java:245)
  at java.util.HashMap.hash(libgcj.so.7)
[...]
</pre>
<p><code>dx</code> is a Java program that uses facilities first made available in Java version 1.5. Check your version of Java by executing <code>% java -version</code> in the shell you use to build. You should see something like:</p>
<pre class="prettyprint">
java version "1.5.0_07"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_07-164)
Java HotSpot(TM) Client VM (build 1.5.0_07-87, mixed mode, sharing)
</pre>
<p>If you do have Java 1.5 or later and your receive this error, verify that you have properly updated your <code>PATH</code> variable.</p>


<a name="androidSourceSetupBuildingKernel"></a><h3>Building the Android Kernel</h3>

<p>This section describes how to build Android's default kernel. Once you are comfortable with a generic build, then you can begin to modify Android drivers for your own target device.</p>


<p>To build the kernel base, switch to the device directory (<code>/home/joe/android/device</code>) in order to establish variables and run:
<pre class="prettyprint">
% . build/envsetup.sh
% partner_setup generic
</pre>
<p>Then switch to the kernel directory <code>/home/joe/android/kernel</code>.


<a name="androidSourceSetupBuildingKernelCheckingBranch"></a><h4>Checking Out a Branch</h4>

<p>The default branch is always <code>android</code>. To check out a different branch, execute the following:</p>

<pre class="prettyprint">
% git checkout --track -b android-mydevice origin/android-mydevice
  //Branch android-mydevice set up to track remote branch
% refs/remotes/origin/android-mydevice.
  //Switched to a new branch "android-mydevice"
</pre>

<p>To simplify code management, give your local branch the same name as the remote branch it is tracking (as illustrated in the snippet above). Switch between branches by executing <code>% git checkout &lt;branchname&gt;</code>.</p>


<a name="androidSourceSetupBuildingKernelBranchLocation"></a><h4>Verifying Location</h4>

<p>Find out which branches exist (both locally and remotely) and which one is active (marked with an asterisk) by executing the following:</p>
<pre class="prettyprint">
% git branch -a
  android
* android-mydevice
  origin/HEAD
  origin/android
  origin/android-mydevice
  origin/android-mychipset
</pre>
<p>To only see local branches, omit the <code>-a</code> flag.</p> 


<a name="androidSourceSetupBuildingKernelBuild"></a><h4>Building the Kernel</h4>

<p>To build the kernel, execute:</p>
<pre class="prettyprint">
% make -j4
</pre>

<a name="androidBuildVariants"></a><h3>Build Variants</h3>

<p> 
When building for a particular product, it's often useful to have minor
variations on what is ultimately the final release build.  These are the
currently-defined build variants:
</p> 
 
<table border=1> 
<tr> 
    <td> 
        <code>eng <code> 
    </td> 
    <td> 
        This is the default flavor. A plain <code>make</code> is the
        same as <code>make eng</code>.
        <ul> 
        <li>Installs modules tagged with: <code>eng</code>, <code>debug</code>,
            <code>user</code>, and/or <code>development</code>.
        <li>Installs non-APK modules that have no tags specified.
        <li>Installs APKs according to the product definition files, in
            addition to tagged APKs.
        <li><code>ro.secure=0</code> 
        <li><code>ro.debuggable=1</code> 
        <li><code>ro.kernel.android.checkjni=1</code> 
        <li><code>adb</code> is enabled by default.
    </td> 
</tr> 
<tr> 
    <td> 
        <code>user <code> 
    </td> 
    <td> 
        <code>make user</code>
        <p> 
        This is the flavor intended to be the final release bits.
        <ul> 
        <li>Installs modules tagged with <code>user</code>.</li>
        <li>Installs non-APK modules that have no tags specified.</li>
        <li>Installs APKs according to the product definition files; tags
            are ignored for APK modules.</li>
        <li><code>ro.secure=1</code> </li>
        <li><code>ro.debuggable=0</code> </li>
        <li><code>adb</code> is disabled by default.</li>
    </td> 
</tr> 
<tr> 
    <td> 
        <code>userdebug <code> 
    </td> 
    <td> 
        <code>make userdebug</code>
        <p> 
        The same as <code>user</code>, except:
        <ul> 
        <li>Also installs modules tagged with <code>debug</code>.
        <li><code>ro.debuggable=1</code> 
        <li><code>adb</code> is enabled by default.
    </td> 
</tr> 
</table> 
 
<p> 
If you build one flavor and then want to build another, you should run
<code>make installclean</code> between the two makes to guarantee that
you don't pick up files installed by the previous flavor.  <code>make
clean</code> will also suffice, but it takes a lot longer.
</p>