Wednesday, February 20, 2013

How to compile busybox with Android NDK for both ARM and x86 architectures

I was looking for a way to run busybox on a Motorola RAZRi with an x86 Intel Atom processor but I couldn't find any Android app from the Google play market that was running on the phone (when running any busybox command nothing happened and I was immediately getting the prompt back).
So I decided to cross-compile busybox for Android myself. Now you will find other posts claiming to have done so by downloading an ARM-cross compiler from but I had two problems with that approach:

  1. I needed an x86 cross-compiler and,
  2. I read various complaints of people not being able to run various busybox commands with this method.

Cross-compiling busybox with the Android NDK

My only option was to use the Android NDK itself, since it comes with full support of the ARM, x86, and MIPS architectures. I ended up manually configuring busybox by eliminating any module that would not cross-compile due to missing header files and/or libraries in the Android NDK.
To cut the story short, I managed to cross-compile busybox using the Android NDK compilers for both ARM and x86 architectures (I didn't try MIPS since I don't have a device with a MIPS processor to test the resulting binaries).
To build busybox yourself, download the busybox-android.patch, busybox-android.config, and script and run the latter with the following options:

$ <android NDK dir> <NDK toolchain> <Android ABI> <Toolchain compiler version> <Android Native API Level> <Install prefix>

The script will download the busybox version 1.21.0 source code, apply the busybox-android.patch and configure busybox for the right architecture.
For example if you have your Android NDK installed under /home/android/android-ndk-r8d, to build busybox for the Intel x86 architecture call the script like the following:

$ /home/android/android-ndk-r8d x86-4.7 x86 4.7 android-14 /home/android/busybox-x86

and the cross-compiled busybox binaries will be installed under  the  /home/android/busybox-x86 directory. Similarly if you want to build busybox for the ARM processor, run the following:

$ /home/android/android-ndk-r8d arm-linux-androideabi-4.7 armeabi-v7a  4.7 android-14 /home/android/busybox-arm

Download busybox binaries

The busybox binaries for x86 (compiled using the above procedure), can be found here.

Installing busybox

The above procedure was tested with release r8d of the Android NDK and for both ARM and x86 devices.


  1. Your phone must be rooted (for example check out my blog How to root Motorola RAZRi XT890 running Android 4.0.4)
  2. You must activate USB debugging mode on your device by going to Settings -> Developer Options -> USB Debugging and selecting the corresponding check box.

Installation Procedure

To install busybox on an x86 Android (rooted) device, I run the following commands with the phone connected to the computer via USB:

# logon to the phone and become root to mount the /system file system read/write
$ adb shell
shell@android:/ $ su -
shell@android:/ # mount -o rw,remount -t ext4 /dev/block/system /system
shell@android:/ # chmod 0777 /system/xbin
shell@android:/ # exit
shell@android:/ $ exit

then change directory to the location of the busybox binary file and push it to the phone:

$ adb push busybox /system/xbin/

log back on as root and change permissions appropriately:

$ adb shell
shell@android:/ $ su -
shell@android:/ # chmod 755 /system/xbin/busybox
shell@android:/ # chmod 0755 /system/xbin
shell@android:/ # exit
shell@android:/ $ exit

Installing busybox on an ARM Android device is very similar, only the mounting instruction line changes:

$ adb shell
shell@android:/ $ su -
shell@android:/ # mount -o rw,remount -t yaffs2 /dev/block/mtdblock3 /system
shell@android:/ # chmod 0777 /system/xbin
shell@android:/ # exit
shell@android:/ $ exit
$ adb push busybox /system/xbin/
$ adb shell
shell@android:/ $ su -
shell@android:/ # chmod 755 /system/xbin/busybox
shell@android:/ # chmod 0755 /system/xbin
shell@android:/ # exit
shell@android:/ $ exit

Tuesday, February 12, 2013

How to build the gcc Fortran cross-compiler for Android (ARM and x86)

If you need to cross-compile for Android a program written in Fortran, you know already that the official Android NDK does not come with the gfortran compiler, and if like me you need to port to Android code that depends on Fortran (such as the lapack libraries), you are out of luck.
Fortunately I managed to compile the gcc Fortran cross-compiler with the help of  Mike Long's blog. As an added bonus, I managed to build gfortran 4.8.0 not only for the ARM but also for the x86 toolchain, as well as update the script to the latest Android NDK (currently r8d).
What you need to do is the following:
  1. download the fortran4android shell script.
  2. download the ndk-r8d fortran patch.
  3. run the script in your directory:

    $ fortran4android
  4. wait, wait, wait, ... and you will see in the android-ndk-r8d/toolchains directory two new toolchains called arm-linux-androideabi-4.8.0 and x86-4.8.0
  5. Enjoy your new gfortran compiler.

Note that I've successfully tested the script only on Ubuntu 12.04.

Addendum of August 30, 2013

I now have available a patch for the newer android-ndk-r9. To use this instead of the patch above:
  1. download the ndk-r9-fortran-patch
  2. change the fortran4android script by replacing "r8d" with "r9" everywhere
  3. run the fortran4android script in your directory.
 Note that r9 of the NDK already comes with a 4.8 gcc toolchain and to keep it separated, the fortran4android script will still generate in output a "4.8.0" toolchain.

Monday, February 11, 2013

How to root Motorola RAZRi XT890 running Android 4.0.4

This procedure is only valid for Motorola RAZRi model XT890 (Intel inside) running Android 4.0.4 (system version 81.5.39001.XT890.Retail.en.GB). The following instructions refer to rooting the RAZRi from a Windows 7 PC.

You need to download the Android SDK 

Go to the Android Developer web site and download the Android SDK for Windows.
Make sure you then set the PATH environment variable to the <sdk>\platform-tools directory where all the tools can be found from the command line.

Install the latest Motorola USB drivers for you phone

Install the latest Motorola USB Drivers. Get them here.

Your phone should be factory unlocked

This is a must or else rooting the device will fail with the phone stuck on the bootloader. Go to the Motorola Web site and follow the step by step instructions. Basically open a Command Prompt window and get your Device ID by running the fastboot command. The instructions from Motorola are the following:

  1. Put your device in fastboot mode (press the power button and volume down button at the same time and connect your device to your computer with a USB cable).
  2. On your computer, open a command prompt or Terminal session.
  3. Go to the Directory where you installed the Android SDK tools, and type:$ fastboot oem get_unlock_data
  4. This fastboot command will return a character string. This is the Device ID which you will be using to generate your unique unlock key.

    Example Device ID (PC User)$ fastboot oem get_unlock_data
    (bootloader) 0A40040192024205#4C4D3556313230
    (bootloader) 30373731363031303332323239#BD00
    (bootloader) 8A672BA4746C2CE02328A2AC0C39F95
    (bootloader) 1A3E5#1F53280002000000000000000
    (bootloader) 0000000

At this point if you submit the device ID to the web form, Motorola will send you the unlock code via e-mail (after warning you that the warranty will be void if you do so).
To unlock the device:

  1. Turn off your device.
  2. Start your device in fastboot mode. To do this on most Motorola devices, push and hold the power and volume down at the same time, release the power button then release volume down. The device will power up in fastboot mode
  3. Connect the device to the computer with a USB cable. You'll get a confirmation message on the device will indicate that it's connected.
  4. Open a command window or terminal on your computer.
  5. Change field to show the path to the tools folder within the Android SDK folder.
  6. Verify that the desktop and device are connected by entering the following in the command field:$ fastboot devicesYou should see that your device is connected.
  7. Now you will unlock the bootloader. Simply enter the following in the command line:$ fastboot oem unlock UNIQUE_KEYThe UNIQUE_KEY is the code you received in the email. It is case-sensitive.
  8. If the line was entered correctly, your device's screen will confirm that your device is unlocked. You have just unlocked your device's bootloader.

Root the device

Get the RAZRi rooting utility for Windows. Get it here.
Extract the zipped files and from a Command Prompt or terminal window, change directory to the location of the utility. Make sure your RAZRi is connected to your Windows PC via the USB cable. Finally run the Root.bat command, follow the instructions, and cross your fingers.
After rebooting at least three times the phone should be rooted.