src/source/building-kernels.jd

page.title=Building Kernels
@jd:body

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    <h2>In this document</h2>
    <ol id="auto-toc">
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<p>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 <code>git clone</code> steps except the step that downloads the kernel
sources.</p>

<p>All examples in this section use the <code>panda</code> kernel.</p>

<h2 id="figuring-out-which-kernel-to-build">Figuring out which kernel to build</h2>
<p>This table lists the name and locations of the kernel sources and binaries:
<table>
  <tr>
    <th>Device</th>
    <th>Binary location</th>
    <th>Source location</th>
    <th>Build configuration</th>
  </tr>
  <tr>
    <td>shamu</td>
    <td>device/moto/shamu-kernel</td>
    <td>kernel/msm</td>
    <td>shamu_defconfig</td>
  </tr>
  <tr>
    <td>fugu</td>
    <td>device/asus/fugu-kernel</td>
    <td>kernel/x86_64</td>
    <td>fugu_defconfig</td>
  </tr>
  <tr>
    <td>volantis</td>
    <td>device/htc/flounder-kernel</td>
    <td>kernel/tegra</td>
    <td>flounder_defconfig</td>
  </tr>
  <tr>
    <td>hammerhead</td>
    <td>device/lge/hammerhead-kernel</td>
    <td>kernel/msm</td>
    <td>hammerhead_defconfig</td>
  </tr>
  <tr>
    <td>flo</td>
    <td>device/asus/flo-kernel/kernel</td>
    <td>kernel/msm</td>
    <td>flo_defconfig</td>
  </tr>
  <tr>
    <td>deb</td>
    <td>device/asus/flo-kernel/kernel</td>
    <td>kernel/msm</td>
    <td>flo_defconfig</td>
  </tr>
  <tr>
    <td>manta</td>
    <td>device/samsung/manta/kernel</td>
    <td>kernel/exynos</td>
    <td>manta_defconfig</td>
  </tr>
  <tr>
    <td>mako</td>
    <td>device/lge/mako-kernel/kernel</td>
    <td>kernel/msm</td>
    <td>mako_defconfig</td>
  </tr>
  <tr>
    <td>grouper</td>
    <td>device/asus/grouper/kernel</td>
    <td>kernel/tegra</td>
    <td>tegra3_android_defconfig</td>
  </tr>
  <tr>
    <td>tilapia</td>
    <td>device/asus/grouper/kernel</td>
    <td>kernel/tegra</td>
    <td>tegra3_android_defconfig</td>
  </tr>
  <tr>
    <td>maguro</td>
    <td>device/samsung/tuna/kernel</td>
    <td>kernel/omap</td>
    <td>tuna_defconfig</td>
  </tr>
  <tr>
    <td>toro</td>
    <td>device/samsung/tuna/kernel</td>
    <td>kernel/omap</td>
    <td>tuna_defconfig</td>
  </tr>
  <tr>
    <td>panda</td>
    <td>device/ti/panda/kernel</td>
    <td>kernel/omap</td>
    <td>panda_defconfig</td>
  </tr>
  <tr>
    <td>stingray</td>
    <td>device/moto/wingray/kernel</td>
    <td>kernel/tegra</td>
    <td>stingray_defconfig</td>
  </tr>
  <tr>
    <td>wingray</td>
    <td>device/moto/wingray/kernel </td>
    <td>kernel/tegra</td>
    <td>stingray_defconfig</td>
  </tr>
  <tr>
    <td>crespo</td>
    <td>device/samsung/crespo/kernel</td>
    <td>kernel/samsung</td>
    <td>herring_defconfig</td>
  </tr>
  <tr>
    <td>crespo4g</td>
    <td>device/samsung/crespo/kernel</td>
    <td>kernel/samsung</td>
    <td>herring_defconfig</td>
  </tr>
</table>

<p>After determining the device project you want to work with, view the git log
for the kernel binary. Device projects use the form
<code>device/&lt;vendor&gt;/&lt;name&gt;</code>.</p>

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

<p>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.</p>

<h2 id="id-version">Identifying kernel version</h2>

<p>To determine the kernel version used in a system image, run the following
command against the kernel file:</p>

<pre><code>$ 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'
</code></pre>

<p>For Nexus 5 (hammerhead), the command is:</p>
<pre><code>$ 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'
</code></pre>


<h2 id="downloading-sources">Downloading sources</h2>
<p>Download the source for the kernel you want to build using the appropriate
<code>git clone</code> command:</p>

<pre><code>$ 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
</code></pre>

<ul>
<li>The <code>goldfish</code> project contains the kernel sources for the emulated
platforms.</li>
<li>The <code>msm</code> 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.</li>
<li>The <code>omap</code> project is used for PandaBoard and Galaxy Nexus,
and can be used as a starting point for work on TI OMAP chipsets.</li>
<li>The <code>samsung</code> project is used for Nexus S,
and can be used as a starting point for work on Samsung Hummingbird chipsets.</li>
<li>The <code>tegra</code> project is for Xoom, Nexus 7, Nexus 9,
and can be used as a starting point for work on NVIDIA Tegra chipsets.</li>
<li>The <code>exynos</code> project has the kernel sources for Nexus 10,
and can be used as a starting point for work on Samsung Exynos chipsets.</li>
<li>The <code>x86_64</code> project has the kernel sources for Nexus Player,
and can be used as a starting point for work on Intel x86_64 chipsets.</li>
</ul>

<h2 id="downloading-a-prebuilt-gcc">Downloading a prebuilt gcc</h2>
<p>Ensure the prebuilt toolchain is in your path:</p>
<pre>$ export PATH=$(pwd)/prebuilts/gcc/linux-x86/arm/arm-eabi-4.6/bin:$PATH</pre>
<p>or</p>
<pre>$ export PATH=$(pwd)/prebuilts/gcc/darwin-x86/arm/arm-eabi-4.6/bin:$PATH</pre>

<p>On a Linux host, if you don't have an Android source tree, you can download
the prebuilt toolchain from:
<pre>$ git clone https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/arm/arm-eabi-4.6</pre>

<h2 id="building">Building the kernel</h2>
<p>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 panda kernel:</p>
<pre><code>$ export ARCH=arm
$ export SUBARCH=arm
$ export CROSS_COMPILE=arm-eabi-
$ cd omap
$ git checkout &lt;commit_from_first_step&gt;
$ make panda_defconfig
$ make
</code></pre>

<p>To build a different kernel, simply replace <code>panda</code> with the name
of the kernel you want to build.</p>

<p>The kernel binary is output as <code>arch/arm/boot/&lt;kernel_name&gt;</code>
and can be copied into the Android source tree to build the matching boot image.
Alternatively, you can include the <code>TARGET_PREBUILT_KERNEL</code>
variable while using <code>make bootimage</code> (or any other make command line
that builds a boot image). This variable is supported by all devices
as it is set up via <code>device/common/populate-new-device.sh</code>. For
example:</p>

<pre><code>$ export TARGET_PREBUILT_KERNEL=$your_kernel_path/arch/arm/boot/zImage-dtb
</code></pre>

<p class="note"><strong>Note:</strong> Kernel names differ by device. To locate
the correct filename for your kernel, refer to
<code>device/&lt;vendor&gt;/&lt;name&gt;</code> in the kernel source.</p>