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Building CopperheadOS from source

Build dependencies

  • x86_64 Linux build environment (OS X is not supported, unlike AOSP)
  • Android Open Source Project build dependencies
  • Linux kernel build dependencies
  • 16GiB of memory or more
  • 100GiB of free storage space

Supported devices

CopperheadOS currently supports the following devices:

  • Nexus 9 (flounder) - deprecated, only receives bug fixes / security updates
  • Nexus 5X (bullhead)
  • Nexus 6P (angler)
  • Pixel (sailfish)
  • Pixel XL (marlin)

Downloading source code

Android’s source tree is huge, so this will use a lot of bandwidth and disk space.

You likely want to use the most recent stable tag, not the development branch.

Development branch

The nougat-mr2-release branch is used for the Nexus 5X, 6P, Pixel and Pixel XL:

mkdir copperheados-nougat-mr2-release
cd copperheados-nougat-mr2-release
repo init -u https://github.com/CopperheadOS/platform_manifest.git -b nougat-mr2-release
repo sync -j32

The legacy nougat-mr1.1-release branch is used for the Nexus 9:

mkdir copperheados-nougat-mr1.1-release
cd copperheados-nougat-mr1.1-release
repo init -u https://github.com/CopperheadOS/platform_manifest.git -b nougat-mr1.1-release
repo sync -j32

Stable release

Pick a specific build for a device from the downloads page and download the source tree. Note that some devices use different Android Open Source Project branches so they end up with different tags. Make sure to use the correct tag for a device.

mkdir copperheados-N4F26J.2017.01.26.14.27.36
cd copperheados-N4F26J.2017.01.26.14.27.36
repo init -u https://github.com/CopperheadOS/platform_manifest.git -b refs/tags/N4F26J.2017.01.26.14.27.36

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:

cd ../..
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 switches branches/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 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 CopperheadOS only provides a stable history via tags.

Setting up the 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/copperhead.sh

Select the desired build target (aosp_marlin is the Pixel XL):

choosecombo release aosp_marlin 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.

Extracting vendor code from factory images (optional)

CopperheadOS currently makes pre-generated vendor repositories available. However, it’s important to understand how these repositories are generated and we may stop providing the pre-generated repositories in the near future.

Obtain android-prepare-vendor with the set of patches currently used for CopperheadOS:

git clone https://github.com/copperhead/android-prepare-vendor.git

Extract the vendor code corresponding to the matching release. The build id of the Google release doesn’t necessary match the CopperheadOS build id.

cd android-prepare-vendor
./execute-all.sh -d marlin -b NJH47D -o $(pwd)

Replace any previous vendor code:

cd ..
rm -rf vendor/marlin
cp -r android-prepare-vendor/marlin/njh47d/vendor .

Note that android-prepare-vendor is non-deterministic for apk and jar files where Google doesn’t provide them unoptimized / unstripped. This was unintentionally improved by Google for the Pixel and Pixel XL since Google stopped including odex files in the main system image and they are now provided as unstripped apk files.

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. 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.

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.

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

mkdir keys/marlin
cd keys/marlin
../../development/tools/make_key releasekey '/C=CA/ST=Ontario/L=Toronto/O=CopperheadOS/OU=CopperheadOS/CN=CopperheadOS/emailAddress=copperheados@copperhead.co'
../../development/tools/make_key platform '/C=CA/ST=Ontario/L=Toronto/O=CopperheadOS/OU=CopperheadOS/CN=CopperheadOS/emailAddress=copperheados@copperhead.co'
../../development/tools/make_key shared '/C=CA/ST=Ontario/L=Toronto/O=CopperheadOS/OU=CopperheadOS/CN=CopperheadOS/emailAddress=copperheados@copperhead.co'
../../development/tools/make_key media '/C=CA/ST=Ontario/L=Toronto/O=CopperheadOS/OU=CopperheadOS/CN=CopperheadOS/emailAddress=copperheados@copperhead.co'
../../development/tools/make_key verity '/C=CA/ST=Ontario/L=Toronto/O=CopperheadOS/OU=CopperheadOS/CN=CopperheadOS/emailAddress=copperheados@copperhead.co'
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/verity_user.der.x509

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

Building

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 signed factory images and full update packages

For the Pixel and Pixel XL, 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 marlin

The factory images and update package will be in out/release-marlin-$BUILD_NUMBER.

Prebuilt code

Like the Android Open Source Project, CopperheadOS contains some code that’s built separately and then bundled into the source tree as binaries. Ideally, everything would be built-in tree with the AOSP build system but it’s not always practical.

Kernel

Unlike AOSP, CopperheadOS builds the kernel as part of the operating system rather than bundling a pre-built kernel image.

Chromium and WebView

Chromium and the WebView are independent applications built from the Chromium source tree. The CopperheadOS Chromium build is located at external/chromium and includes the WebView.

See Chromium’s Android build instructions for details on obtaining the prerequisites.

mkdir chromium
cd chromium
fetch --nohooks android --target_os_only=true

Sync to the latest stable release for Android:

gclient sync --with_branch_heads -r 59.0.3071.125 --jobs 32

Apply the CopperheadOS patches on top of the tagged release:

git clone https://github.com/CopperheadOS/chromium_patches.git
cd src
git am ../chromium_patches/*.patch

Note that we don’t have our own public repository at the moment because Chromium is too large to host it on GitHub or Bitbucket where we are hosting the other repositories.

Then, configure the build in the src directory:

gn args out/Default

CopperheadOS configuration:

target_os = "android"
target_cpu = "arm64"
is_debug = false

is_official_build = true
is_component_build = false
symbol_level = 0

ffmpeg_branding = "Chrome"
proprietary_codecs = true

android_channel = "stable"
android_default_version_name = "59.0.3071.125"
android_default_version_code = "307112552"

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

ninja -C out/Default/ monochrome_public_apk

The apk is bundled directly into external/chromium and is signed as part of the OS build process.

For development, you can also make standalone builds:

To build Chromium:

ninja -C out/Default/ chrome_modern_public_apk

To build the WebView:

ninja -C out/Default/ system_webview_apk

Note that you’ll need to change org.chromium.chrome to com.android.webview in frameworks/base/core/res/res/xml/config_webview_packages.

F-Droid

F-Droid is built from the CopperheadOS fdroidclient repository and then bundled as an apk in the external/F-Droid repository.

The privileged extension built from source from the packages/apps/F-Droid/privileged-extension repository as part of the normal build process.

Other apps

Etar, Offline Calendar, Net Monitor and Silence are simply built from the latest upstream tag and bundled as apks into external/ repositories. There are no modifications to these apps.