Android Build System

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Basics of the Android Build system are described at: http://source.android.com/porting/build_system.html

Note that "partner-setup" should be replaced with "choosecombo" or even "lunch" in that description.

(This information seems to be duplicated at: http://pdk.android.com/online-pdk/guide/build_system.html I'm going to assume that the source.android site is the most up-to-date, but I haven't checked.)


More information about the Android build system, and some of the rationale for it, are described at: http://android.git.kernel.org/?p=platform/build.git;a=blob_plain;f=core/build-system.html

You use build/envsetup.sh to set up a "convenience environment" for working on the Android source code. This file should be source'ed into your current shell environment. After doing so you can type 'help' for a list of defined functions which are helpful for interacting with the source.

Overview

The build system uses some pre-set environment variables and a series of 'make' files in order to build an Android system and prepare it for deployment to a platform.

Android make files end in the extension '.mk' by convention.

The build output is placed in 'out/host' and 'out/target' Stuff under 'out/host' are things compiled for your host platform (your desktop machine). Stuff under 'out/target/product/<platform-name>' eventually makes it's way to a target device (or emulator).

The directory 'out/target/product/<platform-name>/obj' is used for staging "object" files, which are intermediate binary images used for building the final programs. Stuff that actually lands in the file system of the target is stored in the directories root, system, and data, under 'out/target/product/<platform-name>'. Usually, these are bundled up into image files called system.img, ramdisk.img, and userdata.img.

This matches the separate file system partitions used on most Android devices.

Build tricks

build helper functions

A whole bunch of build helper functions are defined in the file build/core/definitions.mk

Try grep define build/core/definitions.mk for an exhaustive list.

Here are some possibly interesting functions:

  • print-vars - shall all Makefile variables, for debugging
  • emit-line - output a line during building, to a file
  • dump-words-to-file - output a list of words to a file
  • copy-one-file - copy a file from one place to another (dest on target?)


Add a file directly to the output area

You can copy a file directly to the output area, without building anything, using the add-prebuilt-files function.

The following line, extracted from prebuilt/android-arm/gdbserver/Android.mk copies a list of files to the EXECUTABLES directory in the output area:

$(call add-prebuilt-files, EXECUTABLES, $(prebuilt_files))