Android Build System

Introduction

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.

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 % make -v. If you don't have version 3.80 or greater, you need to .

Understanding Android's Build System

Understanding the makefile

A makefile defines how to build a particular application. Makefiles typically include all of the following elements:

1. Name: Give your build a name (LOCAL_MODULE := ).
2. Local Variables: Clear local variables with CLEAR_VARS (include $(CLEAR_VARS)).
3. Files: Determine which files your application depends upon (LOCAL_SRC_FILES := main.c).
4. Tags: Define tags, as necessary (LOCAL_MODULE_TAGS := eng development).
5. Libraries: Define whether your application links with other libraries (LOCAL_SHARED_LIBRARIES := cutils).
6. Template file: Include a template file to define underlining make tools for a particular target (include $(BUILD_EXECUTABLE)).

The following snippet illustrates a typical makefile.

LOCAL_PATH := $(my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := 
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

The snippet above includes artificial line breaks to maintain a print-friendly document.

Layers

The build hierarchy includes the abstraction layers described in the table below.

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.

Layer	Example	Description
Product	myProduct, myProduct_eu, myProduct_eu_fr, j2, sdk	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.
Device	myDevice, myDevice_eu, myDevice_eu_lite	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.
Board	sardine, trout, goldfish	The board layer represents the bare schematics of a product. You may still connect peripherals to the board layer.
Arch	arm (arm5te) (arm6), x86, 68k	The arch layer describes the processor running on your board.

Product Definition Files

Product-specific variables are defined in product definition files. A product definition file can inherit from other product definition files, thus reducing the need to copy and simplifying maintenance.

Variables maintained in a product definition files include:

• PRODUCT_DEVICE
• LOCALES
• BRANDING_PARTNER
• PROPERTY_OVERRIDES

The snippet below illustrates a typical product definition file.

//device/target/product/core.mk
PRODUCT_PACKAGES := Home SettingsProvider ...
//device/target/product/generic.mk
PRODUCT_PACKAGES := Calendar Camera SyncProvider ...
$(call inherit-product, target/product/core.mk)
PRODUCT_NAME := generic
//device/partner/google/products/core.mk
PRODUCT_PACKAGES := Maps GoogleAppsProvider ...
$(call inherit-product, target/product/core.mk)
//device/partner/google/products/generic.mk
PRODUCT_PACKAGES := Gmail GmailProvider ...
$(call inherit-product, partner/google/products/core.mk)
$(call inherit-product, target/product/generic.mk)
PRODUCT_NAME := google_generic

Building the Android Platform

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.

Device Code

Of the two options below, the first tends to yield more consistent results.

Option 1

Create a local version of buildspec.mk. The easiest way to do so is to change to your device directory and execute the following:

% cp buildspec.mk.default buildspec.mk ; chmod u=rw buildspec.mk

The default buildspec.mk. file is written so that all options appear commented. In order to establish a personal configuration environment, edit buildspec.mk as desired.

Once you have established your configuration environment, you can build the device code base by executing make in order to build the Android binaries. This may take a long time the first time you issue this command. On a dual-core machine, consider using '-j2' (or even '-j4') to speed up the build.

% make -j2

Option 2

To do a generic build of android, source //device/envsetup.sh, which contains necessary variable and function definitions, as described below.

% cd $TOP

% . envsetup.sh

% partner_setup generic
   //select generic as the product

% make -j4 PRODUCT-generic-user

You can also replace user with eng for a debug engineering build:

% make -j4 PRODUCT-generic-eng

Cleaning Up

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

Speeding Up Rebuilds

The binaries of each combo are stored as distinct sub-directories of //device/out/, making it possible to quickly switch between combos without having to recompile all sources each time.

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 USE_CCACHE environment variable as shown below:

% export USE_CCACHE=1

Doing so will force the build system to use the ccache compiler cache tool, which reduces recompiling all sources.

ccache binaries are provided in //device/prebuilt/... and don't need to get installed on your system.

Troubleshooting

The following error is likely caused by running an outdated version of Java.

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)
[...]

dx is a Java program that uses facilities first made available in Java version 1.5. Check your version of Java by executing % java -version in the shell you use to build. You should see something like:

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)

If you do have Java 1.5 or later and your receive this error, verify that you have properly updated your PATH variable.

Building the Android Kernel

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.

To build the kernel base, switch to the device directory (/home/joe/android/device) in order to establish variables and run:

% . envsetup.sh
% partner_setup generic

Then switch to the kernel directory /home/joe/android/kernel.

Checking Out a Branch

The default branch is always android. To check out a different branch, execute the following:

% 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"

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 % git checkout .

Verifying Location

Find out which branches exist (both locally and remotely) and which one is active (marked with an asterisk) by executing the following:

% git branch -a
  android
* android-mydevice
  origin/HEAD
  origin/android
  origin/android-mydevice
  origin/android-mychipset

To only see local branches, omit the -a flag.

Building the Kernel

To build the kernel, execute:

% make -j4