Building Kernels

In this document

If you are only interested in the kernel, you may use this guide to download and build the appropriate kernel.

The following instructions assume that you have not downloaded all of AOSP. If you have downloaded all of AOSP, you may skip the git clone steps other than the step to download the actual kernel sources.

We will use the Pandaboard kernel in all the following examples.

Figuring out which kernel to build

This table lists the name and locations of the kernel sources and binaries:

Device Binary location Source location Build configuration
shamu device/moto/shamu-kernel kernel/msm shamu_defconfig
fugu device/asus/fugu-kernel kernel/x86_64 fugu_defconfig
volantis device/htc/flounder-kernel kernel/tegra flounder_defconfig
hammerhead device/lge/hammerhead-kernel kernel/msm hammerhead_defconfig
flo device/asus/flo-kernel/kernel kernel/msm flo_defconfig
deb device/asus/flo-kernel/kernel kernel/msm flo_defconfig
manta device/samsung/manta/kernel kernel/exynos manta_defconfig
mako device/lge/mako-kernel/kernel kernel/msm mako_defconfig
grouper device/asus/grouper/kernel kernel/tegra tegra3_android_defconfig
tilapia device/asus/grouper/kernel kernel/tegra tegra3_android_defconfig
maguro device/samsung/tuna/kernel kernel/omap tuna_defconfig
toro device/samsung/tuna/kernel kernel/omap tuna_defconfig
panda device/ti/panda/kernel kernel/omap panda_defconfig
stingray device/moto/wingray/kernel kernel/tegra stingray_defconfig
wingray device/moto/wingray/kernel kernel/tegra stingray_defconfig
crespo device/samsung/crespo/kernel kernel/samsung herring_defconfig
crespo4g device/samsung/crespo/kernel kernel/samsung herring_defconfig

You will want to look at the git log for the kernel binary in the device project that you are interested in.

Device projects are of the form device/<vendor>/<name>.

$ git clone https://android.googlesource.com/device/ti/panda
$ cd panda
$ git log --max-count=1 kernel

The commit message for the kernel binary contains a partial git log of the kernel sources that were used to build the binary in question. The first entry in the log is the most recent, i.e. the one used to build that kernel. You will need it at a later step.

Identifying kernel version

To determine the kernel version used in a particular system image, run the following command against the kernel file:


$ dd if=kernel bs=1 skip=$(LC_ALL=C grep -a -b -o $'\x1f\x8b\x08\x00\x00\x00\x00\x00' kernel | cut -d ':' -f 1) | zgrep -a 'Linux version'

For Nexus 5 (hammerhead), this can be accomplished with:


$ bzgrep -a 'Linux version' vmlinux.bz2

Downloading sources

Depending on which kernel you want,

$ git clone https://android.googlesource.com/kernel/common.git
$ git clone https://android.googlesource.com/kernel/x86_64.git
$ git clone https://android.googlesource.com/kernel/exynos.git
$ git clone https://android.googlesource.com/kernel/goldfish.git
$ git clone https://android.googlesource.com/kernel/msm.git
$ git clone https://android.googlesource.com/kernel/omap.git
$ git clone https://android.googlesource.com/kernel/samsung.git
$ git clone https://android.googlesource.com/kernel/tegra.git
  • The goldfish project contains the kernel sources for the emulated platforms.
  • The msm project has the sources for ADP1, ADP2, Nexus One, Nexus 4, Nexus 5, Nexus 6, and can be used as a starting point for work on Qualcomm MSM chipsets.
  • The omap project is used for PandaBoard and Galaxy Nexus, and can be used as a starting point for work on TI OMAP chipsets.
  • The samsung project is used for Nexus S, and can be used as a starting point for work on Samsung Hummingbird chipsets.
  • The tegra project is for Xoom, Nexus 7, Nexus 9, and can be used as a starting point for work on NVIDIA Tegra chipsets.
  • The exynos project has the kernel sources for Nexus 10, and can be used as a starting point for work on Samsung Exynos chipsets.
  • The x86_64 project has the kernel sources for Nexus Player, and can be used as a starting point for work on Intel x86_64 chipsets.

Downloading a prebuilt gcc

Ensure that the prebuilt toolchain is in your path.

$ export PATH=$(pwd)/prebuilts/gcc/linux-x86/arm/arm-eabi-4.6/bin:$PATH
or
$ export PATH=$(pwd)/prebuilts/gcc/darwin-x86/arm/arm-eabi-4.6/bin:$PATH

On a linux host, if you don't have an Android source tree, you can download the prebuilt toolchain from:

$ git clone https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/arm/arm-eabi-4.6

Building

As an example, we would build the panda kernel using the following commands:

$ export ARCH=arm
$ export SUBARCH=arm
$ export CROSS_COMPILE=arm-eabi-
$ cd omap
$ git checkout <commit_from_first_step>
$ make panda_defconfig
$ make

To build the tuna kernel, you may run the previous commands replacing all instances of "panda" with "tuna".

The kernel binary is output as: `arch/arm/boot/zImage` It can be copied into the Android source tree in order to build the matching boot image.

Or you can include the TARGET_PREBUILT_KERNEL variable while using make bootimage or any other make command line that builds a boot image.


$ export TARGET_PREBUILT_KERNEL=$your_kernel_path/arch/arm/boot/zImage

That variable is supported by all devices as it is set up via device/common/populate-new-device.sh