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|
<html devsite>
<head>
<title>Generic System Image (GSI)</title>
<meta name="project_path" value="/_project.yaml" />
<meta name="book_path" value="/_book.yaml" />
</head>
<body>
{% include "_versions.html" %}
<!--
Copyright 2018 The Android Open Source Project
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
-->
<p>
A generic system image (GSI) is a system image with adjusted configurations
for Android devices. It is considered a "pure Android" implementation with
unmodified Android Open Source Project (AOSP) code that any Android device
running Android 8.1 or higher can run successfully.
</p>
<p>
GSI compliance is part of the <a href="/compatibility/overview">Android
Compatibility program</a>. The system image of an Android device is replaced
with a GSI then tested with the <a href="/compatibility/vts/">Vendor Test
Suite (VTS)</a> and the <a href="/compatibility/cts/">Compatibility Test Suite
(CTS)</a> to ensure the device implements vendor inferfaces correctly with the
latest version of Android.
</p>
<aside class="note"><strong>Note:</strong>
This article describes GSI topics for Android OEM and ROM developers; Android
application developers should refer to
<a href="https://developer.android.com/topic/generic-system-image/">developer.android.com</a>
for developer-focused GSI details.
</aside>
<p>
To get started with GSIs, review the following sections for details on
<a href="#gsi-configuration-and-variances">GSI configurations</a> (and allowed
variances), <a href="#gsi-types">types</a> (Android GSI and Legacy GSI), and
<a href="#vendor-binaries-and-vndk-dependencies">vendor binaries and VNDK
dependencies</a>. When you are ready to use a GSI,
<a href="#building-gsis">download and build the GSI</a> for your device
target then <a href="#flashing-gsis">flash the GSI</a> to an Android
device.
</p>
<h2 id="gsi-configuration-and-variances">GSI configuration and variances</h2>
<p>
The current GSI has the following configuration:
</p>
<ul>
<li><strong>Treble</strong>. A GSI includes full support for the
<a href="/devices/architecture/#hidl">HIDL-based architectural changes</a>
(also known as "Treble") introduced in Android 8.0, including support for
<a href="/reference/hidl/">HIDL interfaces</a>. You can use a GSI on any
Android device that uses HIDL vendor interfaces. (For more details, see
<a href="/devices/architecture/#resources">Architecture resources</a>.)</li>
<li><strong>Verify Boot.</strong> A GSI does not include a verify boot
solution (<a href="/security/verifiedboot/">vboot 1.0</a>,
<a href="/security/verifiedboot/avb">AVB</a>, etc.). To flash a GSI to an
Android device, it must have a method for disabling verify boot.</li>
<li><strong>Build variant</strong>. A GSI always uses a <code>userdebug</code>
build variant to enable running VTS and CTS. After replacing the system
image with GSI, you can root the device then test with a
<code>user</code>-build vendor image and a <code>userdebug</code>-build
system image.</li>
<li><strong>File system and image format</strong>. A GSI uses an ext4 file
system with sparse image format.</li>
</ul>
<p>
The current GSI includes following major variances:
</p>
<ul>
<li><strong>Version</strong>. Support for Android 8.0, Android 8.1, and
Android {{ androidPVersionNumber }}.</li>
<li><strong>CPU architecture</strong>. Support for different CPU instructions
(ARM, x86, etc.) and CPU bitness (32-bit or 64-bit).</li>
<li><strong>Partition layout</strong>. Can use
<a href="/devices/bootloader/system-as-root">system-as-root</a> or
non-system-as-root partition layout.</li>
<li>Support for binder interface bitness.</li>
</ul>
<h2 id="gsi-types">GSI types</h2>
<p>
The GSI used for compliance testing is determined by the Android version the
device launches with. Android {{ androidPVersionNumber }} supports the
following GSIs:
</p>
<table>
<tr>
<th>GSI name</th>
<th>Description</th>
<th>Product name</th>
</tr>
<tr>
<td>Android GSI</td>
<td>For devices launching with Android {{ androidPVersionNumber }}</td>
<td><code>aosp_$arch</code></td>
</tr>
<tr>
<td>Legacy GSI</td>
<td>For devices launching with Android 8.0 or Android 8.1</td>
<td><code>aosp_$arch_a(b)</code></td>
</tr>
</table>
<p>
All GSIs are built from the Android {{ androidPVersionNumber }} codebase.
</p>
<h3 id="changes-in-p-gsis">Android {{ androidPVersionNumber }} GSI changes</h3>
<p>
Devices launching with Android {{ androidPVersionNumber }} must use Android
{{ androidPVersionNumber }} GSIs for compliance testing, which includes the
following major changes from earlier GSIs:
</p>
<ul>
<li><strong>Merges GSI and emulator</strong>. GSIs are built from the system
images of emulator products, e.g. <code>aosp_arm64</code>,
<code>aosp_x86</code>, etc.</li>
<li><strong>System-as-root</strong>. In previous versions of Android, devices
that did not support A/B updates could mount the system image under
<code>/system</code> directory. In Android {{ androidPVersionNumber }}, the
root of the system image is mounted as the root of the device.</li>
<li><strong>64-bit binder interface</strong>. In Android 8.x, 32-bit GSIs
used the 32-bit binder interface. Android {{ androidPVersionNumber }} does
not support 32-bit binder interface, so both 32-bit GSIs and 64-bit GSIs
use the 64-bit binder interface.</li>
<li><strong>VNDK enforcement</strong>. In Android 8.1, VNDK was optional. In
Android {{ androidPVersionNumber }}, VNDK is mandatory, meaning the
<code>BOARD_VNDK_RUNTIME_DISABLE</code> must <strong>not</strong> be set
(<code>BOARD_VNDK_RUNTIME_DISABLE := # must not be set</code>).</li>
<li><strong>Compatible system property</strong>. Android
{{ androidPVersionNumber }} enables the access check for compatible system
property (<code>PRODUCT_COMPATIBLE_PROPERTY_OVERRIDE := true</code>).</li>
</ul>
<p>
To test devices launching with Android {{ androidPVersionNumber }} with
cts-on-gsi, use the <a href="#p-gsi-build-targets">build targets for the
Android {{ androidPVersionNumber }} GSI</a>.
</p>
<h3 id="changes-in-legacy-gsis">Android {{ androidPVersionNumber }} Legacy GSI
changes</h3>
<p>
Devices upgrading to Android {{ androidPVersionNumber }} can use Legacy GSI
product named with suffix <code>_ab</code> or <code>_a</code> (e.g.
<code>aosp_arm64_ab</code>, <code>aosp_x86_a</code>) for compliance testing.
This GSI supports the following upgrade use cases:
</p>
<ul>
<li>Devices with an Android 8.1 vendor interface implementation</li>
<li>Devices updated to the Android {{ androidPVersionNumber }} vendor
interface implementation</li>
</ul>
<p>
Legacy GSIs are build from the Android {{ androidPVersionNumber }} source
tree but contain the following backward-compatible configurations for upgraded
devices:
</p>
<ul>
<li><strong>Non system-as-root</strong>. Devices that do not support
system-as-root can continue to use <code>_a</code> products (e.g.,
<code>aosp_arm_a</code>).</li>
<li><strong>32-bit userspace + 32-bit binder interface</strong>. 32-bit GSIs
can continue to use the 32-bit binder interface.</li>
<li><strong>8.1 VNDK</strong>. Devices can use the included 8.1 VNDK.</li>
<li><strong>Mount directories</strong>. Some legacy devices use directories as
mount-pointers (e.g. <code>/bluetooth</code>, <code>/firmware/radio</code>,
<code>/persist</code>, etc.).</li>
</ul>
<p>
To test devices upgrading to Android {{ androidPVersionNumber }} with
cts-on-gsi, use the <a href="#legacy-gsi-build-targets">build targets for
Legacy GSI</a>.
</p>
<aside class="note">
<strong>Note:</strong> If a pre-Android {{ androidPVersionNumber }} device
implements the Android {{ androidPVersionNumber }} vendor interface and meets
all requirements introduced in Android {{ androidPVersionNumber }}, don't use
the Legacy GSIs; instead use Android {{ androidPVersionNumber }} GSIs for VTS
and cts-on-gsi.
</aside>
<h3 id="changes-to-keymaster-behavior">Android {{ androidPVersionNumber }}
Keymaster changes</h3>
<p>
In earlier versions of Android, devices implementing Keymaster 3 or lower were
required to verify the version info (<code>ro.build.version.release</code> and
<code>ro.build.version.security_patch</code>) reported by the running system
matched the version info reported by bootloader. Such information was
typically obtained from the boot image header.
</p>
<p>
In Android {{ androidPVersionNumber }}, this requirement has changed to enable
vendors to boot a GSI. Specifically, Keymaster should not perform verification
since the version info reported by the GSI may not match the version info
reported by vendor's bootloader. For devices implementing Keymaster 3 or
lower, vendors must modify the Keymaster implementation to skip verification
(or upgrade to Keymaster 4). For details on Keymaster, refer to
<a href="/security/keystore/">Hardware-backed Keystore</a>.
</p>
<h2 id="vendor-binaries-and-vndk-dependencies">Vendor binaries and VNDK
dependencies</h2>
<p>
Devices upgrading to Android {{ androidPVersionNumber }} have different
upgrade paths depending on the version of vendor binaries in use on the device
and the VNDK-related configurations used to build the device. The following
table summarizes the Legacy GSI support for upgraded devices:
</p>
<table>
<tr>
<th>Use case</th>
<th>Vendor<br>binaries<br>version</th>
<th><code>BOARD_VNDK_VERSION</code></th>
<th><code>BOARD_VNDK_RUNTIME_DISABLE</code></th>
<th>Legacy GSI<br>system binaries version</th>
<th>Legacy GSI support</th>
</tr>
<tr>
<td>0</td>
<td>8.0</td>
<td>(any)</td>
<td>(N/A)</td>
<td>{{ androidPVersionNumber }}</td>
<td>No</td>
</tr>
<tr>
<td>1.a</td>
<td>8.1</td>
<td>(empty)</td>
<td>(any)</td>
<td>{{ androidPVersionNumber }}</td>
<td>No</td>
</tr>
<tr>
<td>1.b</td>
<td>8.1</td>
<td><code>current</code></td>
<td><code>true</code></td>
<td>{{ androidPVersionNumber }}</td>
<td>No</td>
</tr>
<tr>
<td>2</td>
<td>8.1</td>
<td><code>current</code></td>
<td>(empty)</td>
<td>{{ androidPVersionNumber }}</td>
<td>Yes</td>
</tr>
<tr>
<td>3</td>
<td>{{ androidPVersionNumber }}</td>
<td><code>current</code></td>
<td><code>true</code></td>
<td>{{ androidPVersionNumber }}</td>
<td>Yes</td>
</tr>
<tr>
<td>4</td>
<td>{{ androidPVersionNumber }}</td>
<td><code>current</code></td>
<td>(empty)</td>
<td>{{ androidPVersionNumber }}</td>
<td>Yes</td>
</tr>
</table>
<p>
The most common supported use case is #2, where the Legacy GSI supports
devices running Android 8.1 that were built with
<code>BOARD_VNDK_VERSION</code> but built without
<code>BOARD_VNDK_RUNTIME_DISABLE</code> (i.e., runtime enforcement was NOT
disabled).
</p>
<p>
The two unsupported use cases are #1.a and #1.b, where the Legacy GSI does NOT
support devices running Android 8.1 that were not built with
<code>BOARD_VNDK_VERSION</code> or built with
<code>BOARD_VNDK_RUNTIME_DISABLE</code> (i.e. runtime enforcement WAS
disabled). These devices are not supported because their vendor binaries
depend on Android 8.1 non-VNDK shared libraries, which are not included in
Legacy GSIs. To make these devices compatible with the Legacy GSI, vendors
must do one of the following:
</p>
<ul>
<li>Enable <code>BOARD_VNDK_VERSION</code> without
<code>BOARD_VNDK_RUNTIME_DISABLE</code> (use case #2)
<br><br>OR<br><br></li>
<li>Port/upgrade the vendor binaries to depend on the shared libraries from
Android {{ androidPVersionNumber }} (use case #3 and use case #4).</li>
</ul>
<h2 id="building-gsis">Building GSIs</h2>
<p>
Starting with Android {{ androidPVersionNumber }}, each Android version has a
GSI branch named <code><var>DESSERT</var>-gsi</code> on AOSP (for example,
<code>pie-gsi</code> is the GSI branch on Android
{{ androidPVersionNumber }}). GSI branches include the content of Android with
all <a href="/security/bulletin/">security patches</a> and
<a href="#contributing-to-gsis">GSI patches</a> applied.
</p>
<p>
To build a GSI, set up the Android source tree by
<a href="/setup/build/downloading">downloading</a> from a GSI branch and
<a href="/setup/build/building#choose-a-target">choosing a GSI build
target</a>. Use the build target tables below to determine the correct GSI
version for your device. After the build completes, the GSI is the system
image (e.g. <code>system.img</code>) and appears in the output folder
<code>out/target/product/<strong>generic_arm64_ab</strong></code>. The build
also outputs <code>vbmeta.img</code> , which you can use to disable verify
boot on the devices using <a href="/security/verifiedboot/avb">Android
Verified Boot</a>.
<p>
<p>
For example, to build the Legacy GSI build target
<code>aosp_arm64_ab-userdebug</code> on GSI branch <code>pie-gsi</code>, run
the following commands:
</p>
<pre class="prettyprint">
$ repo init -u https://android.googlesource.com/platform/manifest -b pie-gsi
$ repo sync -cq
$ source build/envsetup.sh
$ lunch aosp_arm64_ab-userdebug
$ make -j4
</pre>
<h3 id="p-gsi-build-targets">Android {{ androidPVersionNumber }} GSI build
targets</h3>
<p>
The following GSI build targets are for devices launching with Android
{{ androidPVersionNumber }}. Due to a reduction in variances between
architectures, Android {{ androidPVersionNumber }} includes only four GSI
products.
</p>
<table>
<tr>
<th>GSI name</th>
<th>CPU arch</th>
<th>Binder interface bitness</th>
<th>System-as-root</th>
<th>Product name</th>
</tr>
<tr>
<td><code>aosp_arm</code></td>
<td><code>ARM</code></td>
<td><code>64</code></td>
<td><code>Y</code></td>
<td><code>aosp_arm-userdebug</code></td>
</tr>
<tr>
<td><code>aosp_arm64</code></td>
<td><code>ARM64</code></td>
<td><code>64</code></td>
<td><code>Y</code></td>
<td><code>aosp_arm64-userdebug</code></td>
</tr>
<tr>
<td><code>aosp_x86</code></td>
<td><code>x86</code></td>
<td><code>64</code></td>
<td><code>Y</code></td>
<td><code>aosp_x86-userdebug</code></td>
</tr>
<tr>
<td><code>aosp_x86_64</code></td>
<td><code>x86-64</code></td>
<td><code>64</code></td>
<td><code>Y</code></td>
<td><code>aosp_x86_64-userdebug</code></td>
</tr>
</table>
<h3 id="legacy-gsi-build-targets">Android {{ androidPVersionNumber }} Legacy
GSI build targets</h3>
<p>
The following Legacy GSI build targets are for devices upgrading to Android
{{ androidPVersionNumber }}. Legacy GSI names include the suffix
<code>_ab</code> or <code>_a</code> to distinguish them from Android
{{ androidPVersionNumber }} GSI names.
</p>
<table>
<tr>
<th>GSI name</th>
<th>CPU arch</th>
<th>Binder interface bitness</th>
<th>System-as-root</th>
<th>Product name</th>
</tr>
<tr>
<td><code>aosp_arm_a</code></td>
<td><code>ARM</code></td>
<td><code>32</code></td>
<td><code>N</code></td>
<td><code>aosp_arm_a-userdebug</code></td>
</tr>
<tr>
<td><code>aosp_arm_ab</code></td>
<td><code>ARM</code></td>
<td><code>32</code></td>
<td><code>Y</code></td>
<td><code>aosp_arm_ab-userdebug</code></td>
</tr>
<tr>
<td><code>**NA</code></td>
<td><code>ARM</code></td>
<td><code>64</code></td>
<td><code>N</code></td>
<td></td>
</tr>
<tr>
<td><code>aosp_arm_64b_ab</code></td>
<td><code>ARM</code></td>
<td><code>64</code></td>
<td><code>Y</code></td>
<td><code>aosp_arm_64b_ab-userdebug</code></td>
</tr>
<tr>
<td><code>aosp_arm64_a</code></td>
<td><code>ARM64</code></td>
<td><code>64</code></td>
<td><code>N</code></td>
<td><code>aosp_arm64_a-userdebug</code></td>
</tr>
<tr>
<td><code>aosp_arm64_ab</code></td>
<td><code>ARM64</code></td>
<td><code>64</code></td>
<td><code>Y</code></td>
<td><code>aosp_arm64_ab-userdebug</code></td>
</tr>
<tr>
<td><code>aosp_x86_a</code></td>
<td><code>x86</code></td>
<td><code>32</code></td>
<td><code>N</code></td>
<td><code>aosp_x86_a-userdebug</code></td>
</tr>
<tr>
<td><code>aosp_x86_ab</code></td>
<td><code>x86</code></td>
<td><code>32</code></td>
<td><code>Y</code></td>
<td><code>aosp_x86_ab-userdebug</code></td>
</tr>
<tr>
<td><code>**NA</code></td>
<td><code>x86</code></td>
<td><code>64</code></td>
<td><code>N</code></td>
<td></td>
</tr>
<tr>
<td><code>**NA</code></td>
<td><code>x86</code></td>
<td><code>64</code></td>
<td><code>Y</code></td>
<td></td>
</tr>
<tr>
<td><code>aosp_x86_64_a</code></td>
<td><code>x86-64</code></td>
<td><code>64</code></td>
<td><code>N</code></td>
<td><code>aosp_x86_64_a-userdebug</code></td>
</tr>
<tr>
<td><code>aosp_x86_64_ab</code></td>
<td><code>x86-64</code></td>
<td><code>64</code></td>
<td><code>Y</code></td>
<td><code>aosp_x86_64_ab-userdebug</code></td>
</tr>
</table>
<em>** Could be added by request</em>
<aside class="aside">
<strong>Note:</strong> These build targets will likely be removed in a
future version of Android.
</aside>
<h2 id="flashing-gsis">Flashing GSIs Requirements</h2>
<p>
Android devices can have different designs, so no single command or set of
instructions for flashing a GSI to a specific device is possible. You can
check with the manufacturer of the Android device for explicit flashing
instructions or use the following general steps as guidelines:
</p>
<ol>
<li>Ensure the device has the following:
<ul>
<li>Support for HIDL-HAL interfaces.</li>
<li>A method for unlocking devices (so they can be flashed using
<code>fastboot</code>).</li>
<li>A method for disabling verify boot (e.g.
<a href="/security/verifiedboot/">vboot 1.0</a>,
<a href="/security/verifiedboot/avb">AVB</a>, etc.).</li>
<li>Unlock the device to make it flashable via <code>fastboot</code>. (To
ensure you have the latest version of <code>fastboot</code>, build it
from Android source tree.)</li>
</ul>
</li>
<li>Disable verify boot.</li>
<li>Erase the current system partition, then flash the GSI to system
partition.</li>
<li>Wipe userdata and clear data from other necessary partitions (e.g.
metadata).</li>
<li>Reboot the device.</li>
</ol>
<p>
For example, to flash a GSI to any Pixel device:
</p>
<ol>
<li><a href="/setup/build/running#booting-into-fastboot-mode">Boot to
bootloader mode</a> and
<a href="/setup/build/running#unlocking-the-bootloader">unlock the
bootloader</a>.</li>
<li>Disable verify boot (AVB) by flashing <code>vbmeta.img</code>:
<pre class="prettyprint">$ fastboot flash vbmeta vbmeta.img</pre></li>
<li>Erase and flash the GSI to system partition:
<pre class="prettyprint">
$ fastboot erase system
$ fastboot flash system system.img
</pre></li>
<li>Wipe userdata and clear other necessary partitions:
<pre class="prettyprint">$ fastboot -w</pre></li>
<li>Reboot:
<pre class="prettyprint">$ fastboot reboot</pre></li>
</ol>
<h2 id="contributing-to-gsis">Contributing to GSIs</h2>
<p>
Android welcomes your contributions to GSI development. You can get involved
and help improve the GSI by:
</p>
<ul>
<li><strong>Creating a GSI patch</strong>. Because
<code><var>DESSERT</var>-gsi</code> is <strong>not</strong> a development
branch and accepts only cherrypicks from the AOSP master branch, to submit a
GSI patch, you must:
<ol>
<li>Submit the patch to the
<a href="https://android-review.googlesource.com" class="external">AOSP</a>
master branch.</li>
<li>Cherrypick the patch to <code><var>DESSERT</var>-gsi</code>.</li>
<li>File a bug to get the cherrypick reviewed.</li>
</ol>
</li>
<li><strong>Reporting GSI bugs</strong> or making other suggestions. Review
the instructions in
<a href="/setup/contribute/report-bugs#platform">Reporting Bugs</a>, then
browse or file GSI bugs (look for "Generic System Image" in the Platform
table).</li>
</ul>
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