Build

Table of contents

Build dependencies

Downloading source code

Since this is syncing the sources for the entire operating system and application layer, it will use a lot of bandwidth and storage space.

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.

Development branch

The pie branch is currently used for all devices other than the Pixel 3a and Pixel 3a XL, and is the correct branch to use for the generic targets or properly specialized ports to new devices:

mkdir grapheneos-pie
cd grapheneos-pie
repo init -u https://github.com/GrapheneOS/platform_manifest.git -b pie
repo sync -j32

The pie-b4s4 branch is currently used for the Pixel 3a and Pixel 3a XL since these were introduced after the current pie maintenance release:

mkdir grapheneos-pie-b4s4
cd grapheneos-pie-b4s4
repo init -u https://github.com/GrapheneOS/platform_manifest.git -b pie-b4s4
repo sync -j32

If your network is unreliable and repo sync fails, you can run the repo sync command again as many times as needed for it to fully succeed.

Stable release

Pick a specific build for a device from the releases page 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.

mkdir grapheneos-TAG_NAME
cd grapheneos-TAG_NAME
repo init -u https://github.com/GrapheneOS/platform_manifest.git -b refs/tags/TAG_NAME

Verify the manifest:

gpg --recv-keys 65EEFE022108E2B708CBFCF7F9E712E59AF5F22A
gpg --recv-keys 4340D13570EF945E83810964E8AD3F819AB10E78
cd .repo/manifests
git verify-tag --raw $(git describe)
cd ../..

Complete the source tree download:

repo sync -j32

Verify the source tree:

repo forall -c 'git verify-tag --raw $(git describe)' || echo Verification failed!

These instructions will be extended in the future to check the verify-tag output.

Note that the repo command itself takes care of updating itself and uses gpg to verify by default.

Updating and switching branches or tags

To update the source tree, run the repo init command again to select the branch or tag and then run repo sync -j32 again. You may need to add --force-sync 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 repo init again to continue down the same branch since GrapheneOS only provides a stable history via tags.

Browser and WebView

Before building GrapheneOS, you need to build Chromium for the WebView and optionally 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 Vanadium patches change. Chromium and the WebView are independent applications built from the Chromium source tree. The GrapheneOS Chromium build is located at external/vanadium and includes the WebView. See Chromium's Android build instructions for details on obtaining the prerequisites.

You can obtain the proper configuration from the GrapheneOS Vanadium repository in args.gn the correct version.

git clone https://github.com/GrapheneOS/Vanadium.git
cd Vanadium

Fetch the Chromium sources:

fetch --nohooks android

Sync to the latest stable release for Android (replace $VERSION with the correct value):

gclient sync -D --with_branch_heads -r $VERSION --jobs 32

Apply the GrapheneOS patches on top of the tagged release:

cd src
git am ../*.patch

Then, configure the build in the src directory:

gn args out/Default

Copy the GrapheneOS configuration from ../args.gn and save/exit the editor.

To build Monochrome, which provides both Chromium and the WebView:

ninja -C out/Default/ monochrome_public_apk

The apk needs to be copied from out/Default/apks/MonochromePublic.apk into the Android source tree at external/vanadium/prebuilt/arm64/MonochromePublic.apk

Standalone builds of Chromium and the WebView can be done via the chrome_modern_public_apk and system_webview_apk 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 frameworks/base/core/res/res/xml/config_webview_packages.

Kernel

The kernel needs to be built in advance, since it uses a separate build system.

List of kernels corresponding to officially supported devices:

As part of the hardening in GrapheneOS, it uses fully monolithic kernel builds with dynamic kernel modules disabled. This improves the effectiveness of mitigations like Control Flow Integrity benefiting from whole program analysis. It also reduces attack surface and complexity somewhat including making the build system simpler. The kernel trees marked as using a split build above need to have the device variant passed to the GrapheneOS kernel build script to select the device.

For the Pixel 3, Pixel 3 XL, Pixel 3a and Pixel 3a XL, the kernel repository uses submodules for building in out-of-tree modules. You need to make sure the submodule sources are updated before building. In the future, this should end up being handled automatically by repo. There's no harm in running the submodule commands for other devices as they will simply not do anything.

For example, to build the kernel for marlin:

For example, to build the kernel for blueline:

cd kernel/google/crosshatch
git submodule sync
git submodule update --init
./build.sh blueline

The kernel/google/marlin repository is for the Pixel and Pixel XL, the kernel/google/wahoo repository is for the Pixel 2 and Pixel 2 XL and the kernel/google/crosshatch repository is for the Pixel 3 and Pixel 3 XL.

For the first generation Pixel (sailfish) and Pixel XL (marlin), signed releases require building the verity public key into the kernel so the keys need to be generated per the instructions below before building the kernel.

Setting up the OS build environment

The build has to be done from bash as envsetup.sh is not compatible with other shells like zsh.

Set up the build environment:

source script/envsetup.sh

Select the desired build target (aosp_crosshatch is the Pixel 3 XL): 

choosecombo release aosp_crosshatch user

For a development build, you may want to replace user with userdebug in order to have better debugging support. Production builds should be user builds as they are significantly more secure and don't make additional performance sacrifices to improve debugging.

Reproducible builds

To reproduce a past build, you need to export BUILD_DATETIME and BUILD_NUMBER to the values set for the past build. These can be obtained from out/build_date.txt and out/build_number.txt in a build output directory and the ro.build.date.utc and ro.build.version.incremental properties which are also included in the over-the-air zip metadata rather than just the OS itself.

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.

Extracting vendor files for Pixel devices

This section does not apply to devices where no extra vendor files are required (HiKey, HiKey 960, emulator, generic targets).

Many of these components are already open source, but not everything is set up to be built by the Android Open Source Project build system. Switching to building these components from source will be an incremental effort. In many cases, the vendor files simply need to be ignored and AOSP will already provide them instead. Firmware cannot generally be built from source even when sources are available, other than to verify that the official builds match the sources, since it has signature verification (which is an important part of the verified boot and attestation security model).

Extract the vendor files corresponding to the matching release:

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/

Note that android-prepare-vendor is non-deterministic unless a timestamp parameter is passed with --timestamp (seconds since Epoch).

Building

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:

rm -r out

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:

make target-files-package -j20

Faster builds for development use only

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:

make -j20

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.

Generating release signing keys

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.

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.

The Pixel and Pixel XL use Android Verified Boot 1.0. The Pixel 2, Pixel 2 XL, Pixel 3 and Pixel 3 XL use Android Verified Boot 2.0 (AVB). Follow the appropriate instructions below.

For the first generation Pixel (sailfish) and Pixel XL (marlin), signed releases require building the verity public key into the kernel, so this needs to be done before building the kernel

Android Verified Boot 1.0

To generate keys for marlin (you should use unique keys per device variant):

mkdir -p keys/marlin
cd keys/marlin
../../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/'
../../development/tools/make_key verity '/CN=GrapheneOS/'
cd ../..

Generate the verity public key:

make -j20 generate_verity_key
out/host/linux-x86/bin/generate_verity_key -convert keys/marlin/verity.x509.pem keys/marlin/verity_key

Generate verity keys in the format used by the kernel for the Pixel and Pixel XL:

openssl x509 -outform der -in keys/marlin/verity.x509.pem -out kernel/google/marlin/verifiedboot_marlin_relkeys.der.x509

The same kernel and device repository is used for the Pixel and Pixel XL. There's no separate sailfish kernel.

Android Verified Boot 2.0 (AVB)

To generate keys for crosshatch (you should use unique keys per device variant):

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 ../..

The avb_pkmd.bin file isn't needed for generating a signed release but rather to set the public key used by the device to enforce verified boot.

Generating signed factory images and full update packages

Build the tool needed to generate A/B updates:

make -j20 brillo_update_payload

Generate a signed release build with the release.sh script:

script/release.sh crosshatch

The factory images and update package will be in out/release-crosshatch-$BUILD_NUMBER. 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 target_files zips and generating incremental updates from those to the most recent signed target_files zip.

Prebuilt code

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.

Prebuilt apps

The official releases of the Auditor and PdfViewer apps are bundled as an apk into external/ repositories. There are no modifications to these for GrapheneOS.

Testing

This section will be expanded to cover various test suites and testing procedures rather than only the current very minimal coverage of the Compatibility Test Suite (CTS).

Compatibility Test Suite

Download

Testing with the Compatibility Test Suite (CTS) can be done by either building the test suite from source or using the official releases.

Official releases of the CTS can be downloaded from the Compatibility Suite Downloads page. You should download the CTS for the relevant release (Android 9) and architecture (ARM). There's a separate zip for the main CTS, the manual portion (CTS Verifier) and the CTS for Instant Apps. The latest release of the CTS Media Files also needs to be downloaded from that section.

Setup

You'll need a device attached to your computer with ADB enabled along with the Android SDK installed. The build-tools and platform-tools packages need to be installed and the binaries need to be added to your PATH. For example, with the SDK located at /home/username:

export ANDROID_HOME="$HOME/sdk"
export PATH="$PATH:$HOME/sdk/tools:$HOME/sdk/tools/bin:$HOME/sdk/platform-tools:$HOME/sdk/build-tools/27.0.3:$HOME/sdk/ndk-bundle"

Copy media onto the device:

cd android-cts-media-1.4
./copy_images.sh
./copy_media.sh

You also need to do some basic setup for the device. It's possible for changes from a baseline install to cause interference, so it can be a good idea to factory reset the device if assorted changes have been made. The device needs to be running a user build for the security model to be fully intact in order to pass all the security tests. A userdebug build is expected to fail some of the tests. GrapheneOS also makes various changes intentionally deviating from the requirements expected by the CTS, so there will always be some expected failures. A few of the tests are also known to be quite flaky or broken even with the stock OS and/or AOSP. These will be documented here at some point.

Run modules

Run the test harness:

./android-cts/tools/cts-tradefed

Note that _JAVA_OPTIONS being set will break the version detection.

To obtain a list of CTS modules:

list modules

To run a specific module and avoid wasting time capturing device information:

run cts --skip-device-info --module CtsModuleName

To speed up initialization after running some initial tests:

run cts --skip-device-info --skip-preconditions --module CtsModuleName

It's possible to run the whole standard CTS plan with a single command, but running specific modules is recommended, especially if you don't have everything set up for the entire test suite.

Development guidelines

Programming languages

The following programming languages are acceptable for completely new GrapheneOS projects:

Much of the work is done on existing projects, and the existing languages should be used unless there are already clear stable API boundaries where a different language could be used without causing a substantial maintenance burden. The following languages are typical from most to least common: Java, C++, C, JavaScript, arm64 assembly, POSIX shell, Bash.

Code style

For existing projects, use the official upstream code style. Avoid using legacy conventions that they're moving away from themselves. Follow the code style they use for new additions. Some projects have different code styles for different directories or files depending on their sources, in which case respect the per-file style.

For new projects, follow the official code style for the language. Treat the standard library APIs as defining the naming style for usage of the language, i.e. C uses variable_or_function_name, type_name, MACRO_NAME while JavaScript uses variable_or_function_name, ClassName and CONSTANT_NAME. For Python, follow PEP8 and the same goes for other languages with official styles whether defined in a document or by the default mode for the official formatting tool like rustfmt.

For cases where there isn't an official or prevailing code style for other things, avoid tabs, use 4-space indents, function_name, variable_name, TypeName and CONSTANT_NAME. Prefer single-line comment syntax other than rare cases where it makes sense to add a tiny comment within a line of code. In languages with the optional braces misfeature (C, C++, Java), always use them. Open braces on the same line as function definitions / statements. Wrap lines at 100 columns except in rare cases where it would be far uglier to wrap the line.

For JavaScript, put "use strict"; at the top of every file, end lines with semicolons (since automatic insertion is poorly designed) and always use const to declare variables, unless they are reassigned in which case they should be declared with let but never use var as it is effectively broken. Try to prefer loops with for..of.

Avoid designing around class inheritance unless it's a rare case where it's an extremely good fit or the language sucks (Java) and it's the least bad approach, but still try to avoid it.

Use concise but self-explanatory variable names. Prefer communicating information via naming rather than using comments whenever possible. Don't name variables i, j, k, etc. like C programmers. It's okay to use things like x and y for parameters if the function is genuinely that generic and operates on arbitrary values. In general, try to scope variables into the most limited scope (in C or C++, be careful about this when references are taken).

Write code that's clean and self-explanatory. Use comments to explain or justify non-obvious things, but try to avoid needing them in the first place. In most cases, they should just be communicating non-local information such as explaining why an invariant is true based on the code elsewhere (consider a runtime check to make sure it's true, or an assertion if performance would be an issue). Docstrings at the top of top-level functions, modules, etc. are a different story and shouldn't be avoided.

Library usage

Make extensive usage of well designed standard library modules. For apps, treat Jetpack (androidx) as part of the standard library and make good use of it. For Java, Guava can also be treated as part of the standard library.

Libraries outside of the standard library should be used very cautiously. They should be well maintained, stable, well tested and widely used. Libraries implemented with memory unsafe languages should generally be avoided (one exception: SQLite).

Generally, frameworks and libraries existing solely to provide different paradigms and coding patterns are to be avoided. They increase barrier to entry for developers, generally only increase complexity unless used at very large scales (and may not even make things simpler in those cases) and come and go as fads. This is only okay when it's part of the standard libraries or libraries that are considered standard (androidx, Guava) by GrapheneOS and should still be approached cautiously. Only use it if it truly makes the correct approach simpler. Ignore fads and figure out if it actually makes sense to use, otherwise just stick to the old fashioned way if the fancy alternatives aren't genuinely better.