TOC
1. Introduction
2. Installing and setting up the Android environment
3. Getting the source code
4. Installing the required Ubuntu packages
5. How to compile
6. Installing XBMC in an Android system
7. Running and debugging XBMC in an Android system
8. Architecture
9. Useful Commands

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1. Introduction
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We currently recommend Ubuntu Natty (11.04) or later. Current work has been
done here. Additionally, building from OSX Snow Leopard is working.

NOTE TO NEW USERS: All lines that are prefixed with the '#'
character are commands that need to be typed into a terminal window /
console (similar to the command prompt for Windows). Note that the '#'
character itself should NOT be typed as part of the command.

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2. Installing the required Ubuntu packages
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These are the minimum packages necessary for building XBMC. Non-Ubuntu
users will need to get the equivalents.

   # sudo apt-get install build-essential default-jdk git curl autoconf \
       unzip zip zlib1g-dev gawk gperf cmake

If you run a 64bit operating system you will also need to get ia32-libs

   # sudo apt-get install ia32-libs


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3. Installing and setting up the Android environment
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To develop XBMC for Android the Android SDK and NDK are required.
Because the Android NDK is lacking support for wide characters (wchar_t)
which XBMC relies on for Unicode implementation, a third-party NDK
from Crystax is being used.

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3.1. Getting the Android SDK and NDK
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To get the Android SDK, go to http://developer.android.com/sdk and
download the latest version for your operating system. The Crystax NDK
can be downloaded from http://www.crystax.net/en/android/ndk

[NOTICE] Compiling XBMC for Android requires at least Crystax Android NDK
         Revision 7b. Crystax Android NDK Revision 7 and earlier do not work
         properly for our cause. The corresponding Crystax NDK version
         is android-ndk-r7-crystax-5.beta3 Do not use the standard Android NDK.

[NOTICE] We previously used android-ndk-r7-crystax-5.beta2, but it produced
         binaries that would NOT run on Jellybean 4.2. At this time,
         android-ndk-r7-crystax-5.beta3 is required.
         
After downloading the SDK and NDK extract the files contained in the
archives to your harddisk.

Make sure you have a recent JRE and JDK installed otherwise the
Android SDK will not work.

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3.2. Installing Android SDK packages
--------------------------------------------------------------------

After having extracted the Android SDK to <android-sdk> you need to
install some android packages using the Android SDK Manager:

   # cd <android-sdk>/tools
   # ./android update sdk -u -t platform,platform-tool

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3.3. Setup the Android toolchain
--------------------------------------------------------------------

To be able to compile XBMC and the libraries it depends on for the
Android platform you first need to setup an Android toolchain using
the Android NDK which you earlier extracted to <android-ndk>. The
following commands will create a toolchain suitable for the most
common scenario.
The --install-dir option (and therefore the <android-toolchain> value)
specifies where the resulting toolchain should be installed (your choice).

   # cd <android-ndk>
   # ls platforms
   # cd build/tools
   # ./make-standalone-toolchain.sh --ndk-dir=../../ \
     --install-dir=<android-toolchain>/android-9 --platform=android-9

ATTENTION FOR X86 BUILDS - THIS DOES NOT APPLY TO 99% OF BUILDS:
If you want to build for the x86 platform there is a flaw in the mentioned
NDK. See http://code.google.com/p/android/issues/detail?id=19851 which results
in linker errors mentioning "sigsetjmp and siglongjmp".
In that case you have to download the libc.tar.bz2 from that google issue
entry:

http://android.googlecode.com/issues/attachment?aid=198510003000&name=libc.tar.bz2&token=6uNpHc1v8ixmVOTq3y6-ohUfb0o%3A1341156659947

And extract it to <android-toolchain>/android-<x>/sysroot/usr/lib/ and overwrite
the libc.so there. (where <android-toolchain>/android-<x>/ is the path you have given on the
--install-dir option above)

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3.4. Create a (new) debug key to sign debug APKs
--------------------------------------------------------------------

  All packages must be signed. The following command will generate a
  self-signed debug key. If the result is a cryptic error, it
  probably just means a debug key already existed, no cause for alarm.

  # keytool -genkey -keystore ~/.android/debug.keystore -v -alias \
      androiddebugkey -dname "CN=Android Debug,O=Android,C=US" -keypass \
      android -storepass android -keyalg RSA -keysize 2048 -validity 10000

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4. Getting the source code
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   # cd $HOME
   # git clone git://github.com/xbmc/xbmc.git xbmc-android
   # cd xbmc-android
   # git submodule update --init addons/skin.touched

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5. How to compile
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Compiling XBMC for Android consists of compiling the libraries XBMC depends
on with the Android toolchain and creating an Android Application Package
(APK) which can be installed in an Android system.

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5.1. Building dependencies
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   # cd $HOME/xbmc-android/tools/android/depends
   # ./bootstrap
   # ./configure --help

   Run configure with the correct settings for you local configuration.

   Anyone working on the dependencies themselves will want to set the
   environment variables specified in ~/.bashrc or similar, to avoid
   having to input these with each configure. 

   # make -j <jobs>

   This build was designed to be massively parallel. Don't be afraid to
   give it a 'make -j20' or so.

   Verify that all deps built correctly (it will tell you so) before
   continuing. You will get crazy build errors otherwise.

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5.2. Building XBMC
--------------------------------------------------------------------

   # cd $HOME/xbmc-android
   # make -C tools/android/depends/xbmc

   After the first build (assuming bootstrap and configure are successful),
   subsequent builds can be run with a simple 'make' and 'make apk'.

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6. Installing XBMC in an Android system
-----------------------------------------------------------------------------

To install XBMC through the previously built APK in an Android system you can
either install it on a real device (smartphone/tablet/...) running Android
 >= 2.3.x.

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6.1. Installing XBMC on the Android device
--------------------------------------------------------------------

Make sure your Android device is connected to your computer through
USB. Furthermore you have to enable the following option in your
device's Android settings:

  - Applications
    [X] Unknown sources

   # cd $HOME/xbmc-android/tools/android/packaging
   # adb devices
   # adb -s <device-id> install -r images/xbmcapp-debug.apk
      
The <device-id> can be retrieved from the list returned by the
"adb devices" command and is the first value in the row representing
your device.

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7. Running and debugging XBMC in an Android system
-----------------------------------------------------------------------------

After installing XBMC's APK in an Android system you can start it using its
Launcher icon in Android's Application Launcher.

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7.1. Debugging XBMC
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To be able to see what is happening while running XBMC you first need
to enable USB debugging in your Android settings (this is already done
when using the emulator):

  - Applications
    [X] Unknown sources
     -  Development
      [X] USB debugging

To access the log output of your Android system run (the -s parameter
and the <device-id> may not be needed when using the Android emulator)

  # adb -s <device-id> logcat


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7.2. GDB
--------------------------------------------------------------------

GDB can be used to debug, though the support is rather primitive. Rather than
using gdb directly, you will need to use ndk-gdb which wraps it. Do NOT trust
the -p/--project switches, as of ndk7b they do not work. Instead you will need
to cd to tools/android/packaging/xbmc and execute it from there.

  # ndk-gdb --start --delay=0

This will open the installed version of XBMC and break. The warnings can be
ignored as we have setup the appropriate paths already.

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8. Architecture
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During the early days of the android port, xbmc was launched via a stub lib
that then dlopen'd libxbmc. This was done to get around bionic's poor handling
of shared libs. We now compile everything into libxbmc itself so that it has
no runtime dependencies beyond system libs. Done this way, we're able to launch
into libxbmc directly.

But we still hit Bionic's loader's deficiencies when we dlopen a lib. There are
two main issues to overcome for loading:

1. Bionic imports all symbols for a lib as soon as it is loaded, and it will
refuse to open a lib if it has a single unresolved symbol

2. It does not search recursively during the resolve. So if liba depends on
libb, dlopen'ing liba will _not_ pull in missing symbols from libb. This is
particularly nasty considering #1.

To work-around these problems we use our own recursive loader in place of
dlopen. This loader mimics expected behavior. Using the example above, loading
libb before liba will mean that everything will resolve correctly.

Additionally, Android does not use versioned solibs. libfoo.so.1 which is
typical on linux would not be found by the loader. This means that we must
strip the SONAME and NEEDED values out of the libs as well as changing the
filenames themselves. The cleaner solution would be to patch libtool/cmake/etc
to not add versioning in the first place. For now, we use the brute-force
approach of modifying the binary and blanking out the versions.

See here for more info:
http://www.bernawebdesign.ch/byteblog/2011/11/23/creating-non-versioned-shared-libraries-for-android/

As a final gotcha, all libs must be in the form of ^lib.*so$ with no
exceptions (they won't even install otherwise), and the soname must match.
So we have to do some renaming to get some of our self-built libs loaded.

Development:
Typical android native activities are built with ndk-build which is a wrapper
around Make. It would be a nightmare to port our entire buildsystem over, so
instead we build as usual then package ourselves. It may be beneficial to use
ndk-build to do the actual packaging, but for now its behavior is emulated.

ABI:
Presently we are targeting armv7a+neon for arm, and i686 for x86. Note that x86
builds successfully but has not been tested.

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9. Useful Commands
--------------------------------------------------------------------

Below are a few helpful commands when building/debugging. These assume that pwd
is 'tools/android/packaging' and that the proper sdk/ndk paths are set.

-Install a new build over the existing one
  # adb -e install -r images/xbmcapp-debug.apk

-Launch XBMC on the emulator without the GUI
  # adb shell am start -a android.intent.action.MAIN -n org.xbmc.xbmc/android.app.NativeActivity

-Kill a misbehaving XBMC
  # adb shell ps | grep org.xbmc | awk '{print $2}' | xargs adb shell kill

-Filter logcat messages by a specific tag (e.g. "XBMC")
  # adb logcat -s XBMC:V
  
-Enable CheckJNI (BEFORE starting the application)
  # adb shell setprop debug.checkjni 1
  
