add initial build documentation

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Daniel Micay 2019-04-27 08:45:16 -04:00
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<h1>Build</h1> <h1>Build</h1>
<p>This is temporarily a stub since the old building instructions need to be ported <h2>Build dependencies</h2>
over to this web format.</p> <ul>
<li>x86_64 Linux build environment (macOS is not supported, unlike AOSP which
partially supports it)</li>
<li>Android Open Source Project build dependencies</li>
<li>Linux kernel build dependencies</li>
<li>16GiB of memory or more</li>
<li>200GiB of free storage space</li>
</ul>
<h2>Downloading source code</h2>
<p>Since this is syncing the sources for the entire operating system and application
layer, it will use a lot of bandwidth and storage space.</p>
<p>You likely want to use the most recent stable tag, not the development branch, even
for developing a feature. It's easier to port between stable tags that are known to
work properly than dealing with a moving target.</p>
<h2>Development branch</h2>
<p>The pie branch is currently used for all supported devices:</p>
<pre>mkdir grapheneos-pie
cd grapheneos-pie
repo init -u https://github.com/GrapheneOS/platform_manifest.git -b pie
repo sync -j32</pre>
</p>If your network is unreliable and <code>repo sync</code> fails, you can run the
<code>repo sync</code> command again as many times as needed for it to fully
succeed.</p>
<h2>Stable release</h2>
<p>Pick a specific build for a device from the <a href="/releases">releases page</a>
and download the source tree. Note that some devices use different Android Open Source
Project branches so they can end up with different tags. Make sure to use the correct
tag for a device. For devices without official support, use the latest tag for the
Pixel 3.</p>
<pre>mkdir grapheneos-TAG_NAME
cd grapheneos-TAG_NAME
repo init -u https://github.com/GrapheneOS/platform_manifest.git -b refs/tags/TAG_NAME</pre>
<p>Verify the manifest:</p>
<pre>gpg --recv-keys 65EEFE022108E2B708CBFCF7F9E712E59AF5F22A
gpg --recv-keys 4340D13570EF945E83810964E8AD3F819AB10E78
cd .repo/manifests
git verify-tag --raw $(git describe)
cd ../..</pre>
<p>Complete the source tree download:</p>
<pre>repo sync -j32</pre>
<p>Verify the source tree:</p>
<pre>repo forall -c 'git verify-tag --raw $(git describe)' || echo Verification failed!</pre>
<p>These instructions will be extended in the future to check the verify-tag
output.</p>
<p>Note that the repo command itself takes care of updating itself and uses gpg to
verify by default.</p>
<h2>Updating and switching branches/tags</h2>
<p>To update the source tree, run the <code>repo init</code> command again to select
the branch or tag and then run <code>repo sync -j32</code> again. You may need to add
<code>--force-sync</code> if a repository from switched from one source to another,
such as when GrapheneOS forks an additional Android Open Source Project repository.
You don't need to start over to switch between different branches or tags. You may
need to run <code>repo init</code> again to continue down the same branch since
GrapheneOS only provides a stable history via tags.</p>
<h2>Chromium and WebView</h2>
Before building GrapheneOS, you need to build Chromium for the WebView and
<em>optionally</em> the standalone browser app. GrapheneOS uses a hardened fork of
Chromium for these. It needs to be rebuilt when Chromium is updated or the GrapheneOS
<code>chromium_patches</code> repository changes.
Chromium and the WebView are independent applications built from the Chromium source tree. The
GrapheneOS Chromium build is located at external/chromium and includes the WebView.
See <a href="https://www.chromium.org/developers/how-tos/android-build-instructions">
Chromium's Android build instructions</a> for details on obtaining the prerequisites.
<pre>mkdir chromium
cd chromium
fetch --nohooks android</pre>
<p>Sync to the latest stable release for Android (replace $VERSION with the correct
value):</p>
<pre>gclient sync --with_branch_heads -r $VERSION --jobs 32</pre>
<p>Apply the GrapheneOS patches on top of the tagged release:</p>
<pre>git clone https://github.com/GrapheneOS/chromium_patches.git
cd src
git am ../chromium_patches/*.patch</pre>
<p>Then, configure the build in the <code>src</code> directory:</p>
<pre>gn args out/Default</pre>
<p>You can obtain the proper configuration from the
<a href="https://github.com/GrapheneOS/chromium_build">
GrapheneOS chromium_build repository</a>.</p>
<p>To build Monochrome, which provides both Chromium and the WebView:</p>
<pre>ninja -C out/Default/ monochrome_public_apk</pre>
<p>The apk needs to be copied from <code>out/Default/apks/MonochromePublic.apk</code>
into the Android source tree at
<code>external/chromium/prebuilt/arm64/MonochromePublic.apk</code></p>
<p>Standalone builds of Chromium and the WebView can be done via the
<code>chrome_modern_public_apk</code> and <code>system_webview_apk</code> targets but
those aren't used by GrapheneOS. The build system isn't set up for including them and
the standalone WebView isn't whitelisted in
<code>frameworks/base/core/res/res/xml/config_webview_packages</code>.</p>
<h2>Kernel</h2>
<p>The kernel needs to be built in advance, since it uses a separate build system.</p>
<p>For example, to build the kernel for blueline:</p>
<pre>cd kernel/google/crosshatch
./build.sh blueline</pre>
<p>The <code>kernel/google/wahoo</code> repository is for the Pixel 2 and Pixel 2 XL
and the <code>kernel/google/crosshatch</code> repository is for the Pixel 3 and Pixel
3 XL.</p>
<h2>Setting up the OS build environment</h2>
<p>The build has to be done from bash as envsetup.sh is not compatible with other
shells like zsh.</p>
<p>Set up the build environment:</p>
<pre>source script/envsetup.sh</pre>
<p>Select the desired build target (<code>aosp_crosshatch</code> is the Pixel 3 XL):
<pre>choosecombo release aosp_marlin user</pre>
<p>For a development build, you may want to replace <code>user</code> with
<code>userdebug</code> in order to have better debugging support. Production builds
should be <code>user</code> builds as they are significantly more secure and don't
make additional performance sacrifices to improve debugging.</pre>
<h2>Reproducible builds</h2>
<p>To reproduce a past build, you need to export <code>BUILD_DATETIME</code> and
<code>BUILD_NUMBER</code> to the values set for the past build. These can be obtained
from <code>out/build_date.txt</code> and <code>out/build_number.txt</code> in a build
output directory and the <code>ro.build.date.utc</code> and
<code>ro.build.version.incremental</code> properties which are also included in the
over-the-air zip metadata rather than just the OS itself.</p>
<p>The signing process for release builds is done after completing builds and replaces
the dm-verity trees, apk signatures, etc. and can only be reproduced with access to
the same private keys. If you want to compare to production builds signed with
different keys you need to stick to comparing everything other than the
signatures.</p>
<h2>Extracting vendor files for Pixel devices</h2>
<p>This section does not apply to devices with no extra vendor files are required.</p>
<p>Extract the vendor files corresponding to the matching release:</p>
<pre>vendor/android-prepare-vendor/execute-all.sh -d DEVICE -b BUILD_ID -o vendor/android-prepare-vendor
mkdir -p vendor/google_devices
rm -rf vendor/google_devices/DEVICE
mv vendor/android-prepare-vendor/DEVICE/BUILD_ID/vendor/google_devices/* vendor/google_devices/</pre>
<p>Note that android-prepare-vendor is non-deterministic unless a timestamp parameter is
passed.</p>
<h2>Generating release signing keys</h2>
<p>Keys need to be generated for resigning completed builds from the publicly available test keys.
The keys must then be reused for subsequent builds and cannot be changed without flashing the
generated factory images again which will perform a factory reset. Note that the keys are used for
a lot more than simply verifying updates and verified boot. Keys must be generated before building
for the Pixel and Pixel XL due to needing to provide the keys to the kernel build system, but this
step can be done after building for Nexus devices.</p>
<p>The keys should not be given passwords due to limitations in the upstream scripts. If you want to
secure them at rest, you should take a different approach where they can still be available to the
signing scripts as a directory of unencrypted keys. The sample certificate subject can be replaced
with your own information or simply left as-is.</p>
<p>To generate keys for crosshatch (you should use unique keys per device
variant):</p>
<pre>mkdir -p keys/crosshatch
cd keys/crosshatch
../../development/tools/make_key releasekey '/CN=GrapheneOS/'
../../development/tools/make_key platform '/CN=GrapheneOS/'
../../development/tools/make_key shared '/CN=GrapheneOS/'
../../development/tools/make_key media '/CN=GrapheneOS/'
openssl genrsa -out avb.pem 2048
../../external/avb/avbtool extract_public_key --key avb.pem --output avb_pkmd.bin
cd ../..</pre>
<p>The <code>avb_pkmd.bin</code> file isn't needed for generating a signed release but
rather to set the public key used by the device to enforce verified boot.</p>
<h2>Building</h2>
<p>Incremental builds (i.e. starting from the old build) usually work for development and are the
normal way to develop changes. However, there are cases where changes are not properly picked up
by the build system. For production builds, you should remove the remnants of any past builds
before starting, particularly if there were non-trivial changes:</p>
<pre>rm -r out</pre>
<p>Start the build process, with -j# used to set the number of parallel jobs to the number of CPU
threads. You also need 2-4GiB of memory per job, so reduce it based on available memory if
necessary:</p>
<pre>make target-files-package -j20</pre>
<h2>Faster builds for development use only</h2>
<p>The normal production build process involves building a target files package to be resigned with
secure release keys and then converted into factory images and/or an update zip via the sections
below. If you have a dedicated development device with no security requirements, you can save time
by using the default make target, leaving the bootloader unlocked and flashing the raw images that
are signed with the default public test keys:</p>
<pre>make -j20</pre>
<p>Technically, you could generate test key signed update packages. However, there's no point of
sideloading update packages when the bootloader is unlocked and there's no value in a locked
bootloader without signing the build using release keys, since verified boot will be meaningless
and the keys used to verify sideloaded updates are also public. The only reason to use update
packages or a locked bootloader without signing the build with release keys would be testing that
functionality and it makes a lot more sense to test it with proper signing keys rather than the
default public test keys.</p>
<h2>Generating signed factory images and full update packages</h2>
<p>Generate a signed release build with the release.sh script:</p>
<pre>script/release.sh crosshatch</pre>
<p>The factory images and update package will be in
<code>out/release-crosshatch-$BUILD_NUMBER</code>. The update zip performs a full OS
installation so it can be used to update from any previous version. More efficient
incremental updates are used for official over-the-air GrapheneOS updates and can be
generated by keeping around past signed <code>target_files</code> zips and generating
incremental updates from those to the most recent signed <code>target_files</code>
zip.</p>
<h2>Prebuilt code</h2>
Like the Android Open Source Project, GrapheneOS contains some code that's built
separately and then bundled into the source tree as binaries. This section will be
gradually expanded to cover building all of it.
<h3>Prebuilt apps</h3>
<p>The Auditor app is simply built from the latest upstream tag and bundled as an apk into
external/ repositories. There are no modifications to it for GrapheneOS.</p>
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