This page details how to build only the kernel. The following instructions assume you have not downloaded all of AOSP; if you have already done so, you can skip the

git clone

steps except the step that downloads the kernel sources.

All examples in this section use the

hikey

kernel.

Selecting a kernel

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

After determining the device project you want to work with, view the git log for the kernel binary. Device projects use the form

device/<vendor>/<name>

.

$ git clone https://android.googlesource.com/kernel/hikey-linaro
$ cd hikey-linaro
$ git log --max-count=1 kernel

The commit message for the kernel binary contains a partial git log of the kernel sources used to build the binary. The first entry in the log is the most recent (the one used to build the kernel). Make a note of the commit message as you will need it in a later step.

Identifying kernel version

To determine the kernel version used in a 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), the command is:

$ dd if=zImage-dtb bs=1 skip=$(LC_ALL=C od -Ad -x -w2 zImage-dtb | grep 8b1f | cut -d ' ' -f1 | head -1) | zgrep -a 'Linux version'

Downloading sources

Download the source for the kernel you want to build using the appropriate

git clone

command:

$ git clone https://android.googlesource.com/kernel/common.git
$ git clone https://android.googlesource.com/kernel/hikey-linaro
$ 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, Nexus 5X, Nexus 6P, Nexus 7 (2013), 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 (2012), 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.
• The
  
hikey-linaro

  project is used for HiKey reference boards, and can be used as a starting point for work on HiSilicon 620 chipsets.

Downloading a prebuilt gcc

Ensure 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 the kernel

When you know the last commit message for a kernel and have successfully downloaded the kernel source and prebuilt gcc, you are ready to build the kernel. The following build commands use the hikey kernel:

$ export ARCH=arm64
$ export CROSS_COMPILE=aarch64-linux-android-
$ cd hikey-linaro
$ git checkout -b android-hikey-linaro-4.1 origin/android-hikey-linaro-4.1
$ make hikey_defconfig
$ make

To build a different kernel, simply replace

hikey-linaro

with the name of the kernel you want to build.

The image outputs to the

arch/arm64/boot/Image

directory; the kernel binary outputs to the

arch/arm64/boot/dts/hisilicon/hi6220-hikey.dtb

fle. Copy the

Image

directory and the

hi6220-hikey.dtb

file to the

hikey-kernel

directory.

Alternatively, you can include the

TARGET_PREBUILT_KERNEL

variable while using

make bootimage

(or any other

make

command line that builds a boot image). This variable is supported by all devices as it is set up via

device/common/populate-new-device.sh

. For example:

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

Note:

Kernel names differ by device. To locate the correct filename for your kernel, refer to

device/<vendor>/<name>

in the kernel source.