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Checking out and building Chromium for Android

There are instructions for other platforms linked from the get the code page.

Instructions for Google Employees

Are you a Google employee? See go/building-android-chrome instead.

[TOC]

System requirements

  • An x86-64 machine running Linux with at least 8GB of RAM. More than 16GB is highly recommended.
  • At least 100GB of free disk space.
  • You must have Git and Python installed already.

Most development is done on Ubuntu. Other distros may or may not work; see the Linux instructions for some suggestions.

Building the Android client on Windows or Mac is not supported and doesn't work.

Install depot_tools

Clone the depot_tools repository:

git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git

Add depot_tools to the end of your PATH (you will probably want to put this in your ~/.bashrc or ~/.zshrc). Assuming you cloned depot_tools to /path/to/depot_tools:

export PATH="$PATH:/path/to/depot_tools"

Get the code

Create a chromium directory for the checkout and change to it (you can call this whatever you like and put it wherever you like, as long as the full path has no spaces):

mkdir ~/chromium && cd ~/chromium
fetch --nohooks android

If you don't want the full repo history, you can save a lot of time by adding the --no-history flag to fetch.

Expect the command to take 30 minutes on even a fast connection, and many hours on slower ones.

If you've already installed the build dependencies on the machine (from another checkout, for example), you can omit the --nohooks flag and fetch will automatically execute gclient runhooks at the end.

When fetch completes, it will have created a hidden .gclient file and a directory called src in the working directory. The remaining instructions assume you have switched to the src directory:

cd src

Converting an existing Linux checkout

If you have an existing Linux checkout, you can add Android support by appending target_os = ['linux', 'android'] to your .gclient file (in the directory above src):

echo "target_os = [ 'linux', 'android' ]" >> ../.gclient

Then run gclient sync to pull the new Android dependencies:

gclient sync

(This is the only difference between fetch android and fetch chromium.)

Install additional build dependencies

Once you have checked out the code, run

build/install-build-deps.sh --android

to get all of the dependencies you need to build on Linux, plus all of the Android-specific dependencies (you need some of the regular Linux dependencies because an Android build includes a bunch of the Linux tools and utilities).

Run the hooks

Once you've run install-build-deps at least once, you can now run the Chromium-specific hooks, which will download additional binaries and other things you might need:

gclient runhooks

Optional: You can also install API keys if you want your build to talk to some Google services, but this is not necessary for most development and testing purposes.

Setting up the build

Chromium uses Ninja as its main build tool along with a tool called GN to generate .ninja files. You can create any number of build directories with different configurations. To create a build directory which builds Chrome for Android, run gn args out/Default and edit the file to contain the following arguments:

target_os = "android"
target_cpu = "arm64"  # See "Figuring out target_cpu" below
use_remoteexec = true  # Enables distributed builds. See "Faster Builds".
  • You only have to run this once for each new build directory, Ninja will update the build files as needed.
  • You can replace Default with another name, but it should be a subdirectory of out.
  • For other build arguments, including release settings, see GN build configuration. The default will be a debug component build.
  • For more info on GN, run gn help on the command line or read the quick start guide.

Also be aware that some scripts (e.g. tombstones.py, adb_gdb.py) require you to set CHROMIUM_OUTPUT_DIR=out/Default.

Figuring out target_cpu

The value of target_cpu determines what instruction set to use for native code. Given a device (or emulator), you can determine the correct instruction set with adb shell getprop ro.product.cpu.abi:

getprop ro.product.cpu.abi output target_cpu value
arm64-v8a arm64
armeabi-v7a arm
x86 x86
x86_64 x64

*** promo arm and x86 may optionally be used instead of arm64 and x64 for non-WebView targets. This is also allowed for Monochrome, but only when not set as the WebView provider.

Build Chromium

Build Chromium with Ninja using the command:

autoninja -C out/Default chrome_public_apk

(autoninja is a wrapper that automatically provides optimal values for the arguments passed to ninja.)

You can get a list of all of the other build targets from GN by running gn ls out/Default from the command line. To compile one, pass the GN label to Ninja with no preceding "//" (so, for //chrome/test:unit_tests use autoninja -C out/Default chrome/test:unit_tests).

Multiple Chrome Targets

The Google Play Store allows apps to send customized bundles (.aab files) depending on the version of Android running on a device. Chrome uses this feature to package optimized versions for different OS versions.

  1. monochrome_public_bundle (MonochromePublic.aab)
    • minSdkVersion=24 (Nougat).
    • Contains both Chrome and WebView (to save disk space).
  2. trichrome_chrome_bundle (TrichromeChrome.aab)
    • minSdkVersion=29 (Android 10).
    • Native code shared with WebView through a "Static Shared Library APK": trichrome_library_apk
    • Corresponding WebView target: trichrome_webview_bundle
  3. chrome_public_bundle & chrome_public_apk (ChromePublic.aab, ChromePublic.apk)
    • minSdkVersion=24 (Nougat).
    • Used for local development (to avoid building WebView).
    • WebView packaged independently (system_webview_bundle / system_webview_apk).

*** note Notes:

  • These instructions use chrome_public_apk, but any of the other targets can be substituted.
  • For more about bundles, see android_dynamic feature modules.md.
  • For more about native library packaging & loading, see android_native_libraries.md.
  • There are closed-source equivalents to these targets (for Googlers), which are identical but link in some extra code.

Updating your checkout

To update an existing checkout, you can run

$ git rebase-update
$ gclient sync

The first command updates the primary Chromium source repository and rebases any of your local branches on top of tip-of-tree (aka the Git branch origin/main). If you don't want to use this script, you can also just use git pull or other common Git commands to update the repo.

The second command syncs dependencies to the appropriate versions and re-runs hooks as needed.

Installing and Running Chromium on a device

Plug in your Android device

Make sure your Android device is plugged in via USB, and USB Debugging is enabled.

To enable USB Debugging:

  • Navigate to Settings > About Phone > Build number
  • Click 'Build number' 7 times
  • Now navigate back to Settings > Developer Options
  • Enable 'USB Debugging' and follow the prompts

You may also be prompted to allow access to your PC once your device is plugged in.

You can check if the device is connected by running:

third_party/android_sdk/public/platform-tools/adb devices

Which prints a list of connected devices. If not connected, try unplugging and reattaching your device.

Enable apps from unknown sources

Allow Android to run APKs that haven't been signed through the Play Store:

  • Enable 'Unknown sources' under Settings > Security

In case that setting isn't present, it may be possible to configure it via adb shell instead:

third_party/android_sdk/public/platform-tools/adb shell settings put global verifier_verify_adb_installs 0

Build the full browser

autoninja -C out/Default chrome_public_apk

And deploy it to your Android device:

out/Default/bin/chrome_public_apk install

The app will appear on the device as "Chromium".

Build Content shell

Wraps the content module (but not the /chrome embedder). See https://www.chromium.org/developers/content-module for details on the content module and content shell.

autoninja -C out/Default content_shell_apk
out/Default/bin/content_shell_apk install

this will build and install an Android apk under out/Default/apks/ContentShell.apk.

Build WebView

Android WebView is a system framework component. Since Android KitKat, it is implemented using Chromium code (based off the content module).

If you want to build the complete Android WebView framework component and test the effect of your chromium changes in Android apps using WebView, you should follow the Android AOSP + chromium WebView instructions

Running

For Content shell:

out/Default/bin/content_shell_apk launch [--args='--foo --bar'] http://example.com

For Chrome public:

out/Default/bin/chrome_public_apk launch [--args='--foo --bar'] http://example.com

Logging and debugging

Logging is often the easiest way to understand code flow. In C++ you can print log statements using the LOG macro. In Java, refer to android_logging.md.

You can see these log via adb logcat, or:

out/Default/bin/chrome_public_apk logcat

Logcat supports an additional feature of filtering and highlighting user-defined patterns. To use this mechanism, define a shell variable: CHROMIUM_LOGCAT_HIGHLIGHT and assign your desired pattern. The pattern will be used to search for any substring (ie. no need to prefix or suffix it with .*), eg:

export CHROMIUM_LOGCAT_HIGHLIGHT='(WARNING|cr_Child)'
out/Default/bin/chrome_public_apk logcat
# Highlights messages/tags containing WARNING and cr_Child strings.

Note: both Message and Tag portion of logcat are matched against the pattern.

To debug C++ code, use one of the following commands:

out/Default/bin/content_shell_apk gdb
out/Default/bin/chrome_public_apk gdb

See Android Debugging Instructions for more on debugging, including how to debug Java code.

Testing

For information on running tests, see Android Test Instructions

Faster Builds

Use Reclient

*** note Warning: If you are a Google employee, do not follow the instructions below. See go/building-android-chrome#initialize-remote-execution-distributed-builds instead.

Chromium's build can be sped up significantly by using a remote execution system compatible with REAPI. This allows you to benefit from remote caching and executing many build actions in parallel on a shared cluster of workers.

To use Reclient, follow the corresponding Linux build instructions.

GN Args

Args that affect build speed:

  • use_remoteexec = true (default=false)
    • What it does: Enables distributed builds via Reclient
  • symbol_level = 0 (default=1)
    • What it does: Disables debug information in native code.
    • Use this when doing primarily Java development.
    • To disable symbols only in Blink / V8: blink_symbol_level = 0, v8_symbol_level = 0
  • is_component_build = true (default=is_debug)
    • What it does: Uses multiple .so files instead of just one (faster links)
  • is_java_debug = true (default=is_debug)
    • What it does: Disables R8 (whole-program Java optimizer)
  • treat_warnings_as_errors = false (default=true)
    • Causes any compiler warnings or lint checks to not fail the build.
    • Allows you to iterate without needing to satisfy static analysis checks.
  • android_static_analysis = "build_server" (default="on")
    • Offloads static analysis steps to the build server. Explained below.
    • Set this to "off" if you want to turn off static analysis altogether.
  • incremental_install = true (default=false)
    • Makes build and install quite a bit faster. Explained in a later section.
  • enable_chrome_android_internal = false (Googlers only)
    • Disables non-public code, which exists even when building public targets.
    • Use this is you do not need to test internal-only things.

Running Static Analysis Asynchronously

Normally analysis build steps like Lint and Error Prone will run as normal build steps. The build will then wait for all analysis steps to complete successfully. By offloading analysis build steps to a separate build server to be run lazily at a low priority when the machine is idle, the actual build can complete much faster.

Note: Since the build completes before the analysis checks finish, the build will not fail if an analysis check fails. Make sure to check the server's output at regular intervals to fix outstanding issues caught by these analysis checks.

First way (by running it manually)

There are two steps to using the build server.

  1. Add the gn arg android_static_analysis = "build_server"
  2. Run the script at //build/android/fast_local_dev_server.py

All your local builds will now forward analysis steps to this server, including android lint, errorprone, bytecode processor.

If you run (2) in a terminal, the output of the checks will be displayed there.

Second way (using systemd)

Alternatively, you can set up the server as a Linux service, so it runs on the background and starts on boot. If you're using systemd:

Save the following as /etc/systemd/user/fast-local-dev-server.service.

[Unit]
Description=Chrome server for android build static analysis

[Service]
Type=simple
ExecStart=<path to fast_local_dev_server.py>
Restart=always

[Install]
WantedBy=default.target

Then

systemctl --user daemon-reload
systemctl --user enable fast-local-dev-server
systemctl --user start fast-local-dev-server

The output can be inspected with

journalctl --user -e -u fast-local-dev-server

Incremental Install

Incremental Install uses reflection and sideloading to speed up the edit & deploy cycle (normally < 10 seconds). The initial launch of the apk will be a lot slower on older Android versions (pre-N) where the OS needs to pre-optimize the side-loaded files, but then be only marginally slower after the first launch.

To enable Incremental Install, add the gn args:

incremental_install = true

Some APKs (e.g. WebView) do not work with incremental install = true and are always built as normal APKs. This behavior is controlled via never_incremental = true.

Installing and Running Chromium on an Emulator

Running on an emulator is the same as on a device. Refer to android_emulator.md for setting up emulators.

Tips, tricks, and troubleshooting

Rebuilding libchrome.so for a particular release

These instructions are only necessary for Chrome 51 and earlier.

In the case where you want to modify the native code for an existing release of Chrome for Android (v25+) you can do the following steps. Note that in order to get your changes into the official release, you'll need to send your change for a codereview using the regular process for committing code to chromium.

  1. Open Chrome on your Android device and visit chrome://version
  2. Copy down the id listed next to "Build ID:"
  3. Go to http://storage.googleapis.com/chrome-browser-components/BUILD_ID_FROM_STEP_2/index.html
  4. Download the listed files and follow the steps in the README.