Android Kernel Development - Kernel compilation and Hello World

Introduction

Due to the lack of the material that clearly kick off the  android kernel development , hopefully it will gives the clearer  guide to develop your own android driver and debugging it.

p.s. Due to the version differential, this article  is not ensure all of the Android Version , SDK version,  source  code , and   Emulator is compatible , however,  the door of   research is always opened,   just   feel   free   to contact me  and play together :P

All the materials   are also  saved   in   the VM  ,   you can just directly leverage  the  existing VM Image for  development or  alternatively, as a research and studying, follow the following guide  to create your own workplace. 

Android kernel didn't have dynamically insmod like the other linux, so this tutorial is trying to build a new Android Kernel and make test our kernel driver as well.

Material

Ubuntu 18.04.2 LTS 
Android studio
Android ndk-r10
Android SDK
Goldfish v3.10
VMWare 15  

Prepare the environment

- Install a  Ubuntu  VM
- Install a Android Studio in your Ubuntu
- Install a latest android SDK
- Install a emulator by Android studio as following:

- Download the R10(suggested version) Android NDK  for compiling your Android Kernel

Compile the goldfish kernel

- Goldfish is a kernel that opensource by Google, and it is packed with INSMOD and RMMOD for dynamically installing the driver and removing as well.

- First of all, open your terminal, and execute the following command:

 cd ~  
 mkdir kernel  
 cd kernel  
 git clone http://android.googlesource.com/kernel/goldfish.git  
 git branch -a   

Afterward, check all the branch it has

p.s. I have test with 3.10 pure version. 

- We could check out by the following command:

 git checkout remotes/origin/android-goldfish-3.10  

- We set the compile path and emulator path into the environment variable

- The NDK is used for compile the Goldfish

- The emulator is used for testing

After the variable set, we could enter the command 

 make goldfish_armv7_defconfig  
 make menuconfig  

So that you're able to custom your kernel configuration right now

In this tutorial we want to create a kernel with Loadable kernel module capability

so we enable the option that 'Enable loadable module support'

press 'esc' twice for quiting and saving the config 

Enter the following command in current directory  

 gedit Makefile  

After that, just simple enter 'make' command for building the kernel, mostly it usually compile perfectly. As the following output, mean the kernel compile success

Next, we could use that newer kernel for launching the emulator! such an exciting moment!

Compile our hello driver 

Just create a directory and change to there.

Create the Makefile in the directory, as following

ARCH and CROSS_COMPILE have to be as same as the kernel config (arm and arm-linux-androidebi-)

Just check it out,  is there a hello.ko comes out , after compilation

Testing

With the emulator, we connect the adb to the device (adb should be installed along with android studio, so we could just simply enter 'adb' command on the terminal.

First of all , we check the existence of device

Second, we have to push (moving) the system drier file , to the disk of android emulator.

Thirdly, we connect to the shell of emulator, by using gdb shell command

and change directory to our destination (/data/local/tmp/) and install it on the the system

So, In the example, we just print out that, says, hello Tencent

  

Reference:
https://developer.android.com/ndk/