Android Porting Book--Android Build System

AndroidBuild System

In thisdocument

• Understandingthe makefile

• Layers

• Buildingthe Android Platform

• Buildingthe Android Kernel

• BuildVariants

Androiduses a custom build system to generate tools, binaries, anddocumentation. This document provides an overview of Android's buildsystem and instructions for doing a simple build.

 

Android'sbuild system is make based and requires a recent version of GNU Make(note that Android uses advanced features of GNU Make that may notyet appear on the GNU Make web site). Before continuing, check yourversion of make by running %make -v.If you don't have version 3.80 or greater, you need to upgradeyour version of make.

Understandingthe makefile

Amakefile defines how to build a particular application. Makefilestypically include all of the following elements:

1. Name:Give your build a name (LOCAL_MODULE:= <build_name>).

2. LocalVariables: 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. Templatefile: Include a template file to define underlining make tools fora particular target (include$(BUILD_EXECUTABLE)).

Thefollowing snippet illustrates a typical makefile.

LOCAL_PATH := $(my-dir)include $(CLEAR_VARS)LOCAL_MODULE := <buil_name>LOCAL_SRC_FILES := main.cLOCAL_MODULE_TAGS := eng developmentLOCAL_SHARED_LIBRARIES := cutilsinclude $(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

Thesnippet above includes artificial line breaks to maintain aprint-friendly document.

Layers

Thebuild hierarchy includes the abstraction layers described in thetable below.

Eachlayer relates to the one above it in a one-to-many relationship. Forexample, an arch can have more than one board and each board canhave more than one device. You may define an element in a givenlayer as a specialization of an element in the same layer, thuseliminating copying and simplifying maintenance.

Layer

Example

Description

Product

myProduct,myProduct_eu, myProduct_eu_fr, j2, sdk

Theproduct layer defines a complete specification of a shippingproduct, defining which modules to build and how to configurethem. You might offer a device in several different versionsbased on locale, for example, or on features such as a camera.

Device

myDevice,myDevice_eu, myDevice_eu_lite

Thedevice layer represents the physical layer of plastic on thedevice. For example, North American devices probably includeQWERTY keyboards whereas devices sold in France probably includeAZERTY keyboards. Peripherals typically connect to the devicelayer.

Board

sardine,trout, goldfish

Theboard layer represents the bare schematics of a product. You maystill connect peripherals to the board layer.

Arch

arm(arm5te) (arm6), x86, 68k

Thearch layer describes the processor running on your board.

Buildingthe Android Platform

Thissection describes how to build the default version of Android. Onceyou are comfortable with a generic build, then you can begin tomodify Android for your own target device.

DeviceCode

Todo a generic build of android, source build/envsetup.sh,which contains necessary variable and function definitions, asdescribed below.

% cd $TOP% . build/envsetup.sh# pick a configuration using choosecombo% choosecombo% make -j4 PRODUCT-generic-user

Youcan also replace user with eng for a debug engineering build:

% make -j4 PRODUCT-generic-eng

These BuildVariants differin terms of debug options and packages installed.

CleaningUp

Execute %m clean toclean up the binaries you just created. You can also execute %m clobber toget rid of the binaries of all combos. %m clobber isequivalent to removing the//out/ directorywhere all generated files are stored.

SpeedingUp Rebuilds

Thebinaries of each combo are stored as distinct sub-directoriesof //out/,making it possible to quickly switch between combos without havingto recompile all sources each time.

However,performing a clean rebuild is necessary if the build system doesn'tcatch changes to environment variables or makefiles. If this happensoften, you should define theUSE_CCACHE environmentvariable as shown below:

% export USE_CCACHE=1

Doingso will force the build system to use the ccache compiler cachetool, which reduces recompiling all sources.

ccache binariesare provided in //prebuilt/... anddon't need to get installed on your system.

Troubleshooting

Thefollowing error is likely caused by running an outdated version ofJava.

device Dex: core  UNEXPECTED TOP-LEVEL ERROR:java.lang.NoSuchMethodError: method java.util.Arrays.hashCode withsignature ([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 isa Java program that uses facilities first made available in Javaversion 1.5. Check your version of Java by executing %java -version inthe 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)

Ifyou do have Java 1.5 or later and your receive this error, verifythat you have properly updated your PATH variable.

Buildingthe Android Kernel

Thissection describes how to build Android's default kernel. Once youare comfortable with a generic build, then you can begin to modifyAndroid drivers for your own target device.

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

% . build/envsetup.sh% partner_setup generic

Thenswitch to the kernel directory /home/joe/android/kernel.

CheckingOut a Branch

Thedefault 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"

Tosimplify code management, give your local branch the same name asthe remote branch it is tracking (as illustrated in the snippetabove). Switch between branches by executing %git checkout <branchname>.

VerifyingLocation

Findout which branches exist (both locally and remotely) and which oneis 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

Toonly see local branches, omit the -a flag.

Buildingthe Kernel

Tobuild the kernel, execute:

% make -j4

BuildVariants

Whenbuilding for a particular product, it's often useful to have minorvariations on what is ultimately the final release build. These arethe currently-defined build variants:

eng

Thisis the default flavor. A plain make isthe same as makeeng.

• Installsmodules tagged with: eng, debug, user,and/or development.

• Installsnon-APK modules that have no tags specified.

• InstallsAPKs according to the product definition files, in addition totagged APKs.

• ro.secure=0

• ro.debuggable=1

• ro.kernel.android.checkjni=1

• adb isenabled by default.

user

makeuser

Thisis the flavor intended to be the final release bits.

• Installsmodules tagged with user.

• Installsnon-APK modules that have no tags specified.

• InstallsAPKs according to the product definition files; tags are ignoredfor APK modules.

• ro.secure=1

• ro.debuggable=0

• adb isdisabled by default.

userdebug

makeuserdebug

Thesame as user,except:

• Alsoinstalls modules tagged with debug.

• ro.debuggable=1

• adb isenabled by default.

Ifyou build one flavor and then want to build another, you shouldrun makeinstallclean betweenthe two makes to guarantee that you don't pick up files installed bythe previous flavor. makeclean willalso suffice, but it takes a lot longer.