I have been trying for the last few weeks to get the Android Kernel source and then build a kernel of my own and then load it into the emulator to try to test out the modules. I spent numerous hours in trying to understand about how to go about it. So here’s a post so I can log all that I did in an effort from going from nothing to having my kernel loaded in the Android Emulator.

There are posts such as the one on eeknay32’s blog and the Stackoverflow post that really helped me in getting started. Also there is a HOWTO in the qemu documentation located at external/qemu/docs/KERNEL.TXT

I first started to follow the directions from here but this is only to get the source code of the Android SDK and other tools and to compile those. That was not initially my goal because getting the source of the tools and SDK was not my goal. Don’t bother downloading this (you could get the tools pre-compiled) unless you really want to compile the tools on your own.

The following steps will help you compile the code for the Android emulator and other tools:
sudo apt-get install git-core gnupg flex bison gperf build-essential \
zip curl zlib1g-dev libc6-dev lib32ncurses5-dev ia32-libs \
x11proto-core-dev libx11-dev lib32readline5-dev lib32z-dev \
libgl1-mesa-dev g++-multilib mingw32 tofrodos python-markdown \
libxml2-utils xsltproc
mkdir ~/bin
export PATH=~/bin:$PATH
curl https://dl-ssl.google.com/dl/googlesource/git-repo/repo > ~/bin/repo
chmod a+x ~/bin/repo
cd src
repo init -u https://android.googlesource.com/platform/manifest -b android-2.3_r1
repo sync
. build/envsetup.sh
lunch full-eng

Now going to our main goal.

Get the Android source
git clone https://android.googlesource.com/kernel/goldfish.git goldfish
cd goldfish
Put the cross compilation toolchain into your path and also put the tools (emulator, android tools etc) in your path:
export PATH=$PATH:~/bin:~/bin/src/prebuilt/linux-x86/toolchain/arm-eabi-4.4.3/bin:/root/bin/src/out/host/linux-x86/bin
make ARCH=arm goldfish_defconfig
make ARCH=arm SUBARCH=arm CROSS_COMPILE=arm-eabi- -j4
This is a good resource on different errors you could encounter. If you get a message “zImage is ready” you are good to load this image into the emulator to have a running emulator.
Before you run the android tool you need to first set an environment variable otherwise the tool will complain that ANDROID_SWT is not set.
export ANDROID_SWT=/root/bin/src/prebuilt/linux-x86_64/swt

Now you have to download some of the SDK Framework from the Google website so that you can create your own Android Virtual Device (AVD). Without downloading the SDK platform you will get no output when you issue the following command:
android list targets
After you get the right ANDROID platform you can issue the following commands:
android create avd -n my_android1.5 -t 1
emulator -kernel ~/bin/kern/kernel-common/goldfish/arch/arm/boot/zImage -show-kernel -verbose @my_android1.5
Now you should have a running emulator with your shiny new kernel.
Now if you want to compile your own kernel module and load it into the emulator at runtime then you need to use Android Debug Bridge (ADB) tool. See this post, where the author creates a kernel module. For me I had to modify the Makefile a little as shown below:
VERSION = 2
PATCHLEVEL = 6
SUBLEVEL = 29
EXTRAVERSION = -00054-g5f01537
obj-m += hello.o
KDIR=/root/bin/kern/kernel-common/goldfish
PWD := $(shell pwd)
all:
make -C $(KDIR) ARCH=arm CROSS_COMPILE=/root/bin/src1/prebuilt/linux-x86/toolchain/arm-eabi-4.4.0/bin/arm-eabi- SUBDIRS=$(PWD) modules

clean:
make -C $(KDIR) ARCH=arm CROSS_COMPILE=/root/bin/src1/prebuilt/linux-x86/toolchain/arm-eabi-4.4.0/bin/arm-eabi- SUBDIRS=$(PWD) clean

Issue the make command from the directory where you have your makefile and the sources to get hello.ko.
See the partition not mounted as read only by searching for “rw” mount mode by issuing the following command:
/root/bin/src/out/host/linux-x86/bin/adb shell mount
/root/bin/src/out/host/linux-x86/bin/adb push hello.ko /data
/root/bin/src/out/host/linux-x86/bin/adb insmod /data/hello.ko