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