README.md

Bazel on ARM

Bazel is an open source build tool from Google, used to build projects such as TensorFlow. Raspberry Pi OS (Raspbian) doesn't have a package for Bazel, and the Bazel project doesn't provide a binary for armhf.

Luckily, Bazel can be compiled from source on the Raspberry Pi with only a small patch. All the pieces were there yet, but Bazel on ARM is a script that streamlines this and builds Bazel for the Raspberry Pi's ARMv7 processor architecture with a single command: make bazel.

System requirements

• Raspberry Pi (tested on Raspberry Pi 4B with 2 GB RAM)
• 16 GB microSD card
• Raspberry Pi OS (previously called Raspbian) Buster (10), 32-bit

If you manage to make this work on another version of Raspbian, another Linux distribution, another model of the Raspberry Pi or even another ARM computer, please let me know so I can generalize the script.

Usage

First make sure to have all build requirements for Bazel. These can be installed with:

sudo make requirements

This installs OpenJDK 11 and makes it your default JDK.

Note: this can take a while, because it installs a whopping 1 GB of JDK files.

Then, if you want to build the latest Bazel version supported by this project (which is stored in the file BAZEL_VERSION), just run:

make bazel

If you want to build a specific Bazel version, run the build script with the version number as an argument:

./scripts/build_bazel.sh 3.3.1

The build script downloads Bazel's distribution file, patches it and builds the Bazel binary. The build itself takes roughly half an hour on a Raspberry Pi 4B with 2 GB RAM. If all goes well, at the end you should see a message like this:

Build successful! Binary is here: /home/pi/bazel-on-arm/bazel/output/bazel

You can install it to /usr/local/bin with:

sudo make install

Now you can use the bazel command to build other projects. Check its version with:

bazel version

This should show something like:

Extracting Bazel installation...
Build label: 3.3.1- (@non-git)
Build target: bazel-out/arm-opt/bin/src/main/java/com/google/devtools/build/lib/bazel/BazelServer_deploy.jar                                                                                                      
Build time: Sat Jul 4 11:04:19 2020 (1593860659)
Build timestamp: 1593860659
Build timestamp as int: 1593860659

The message "Extracting Bazel installation..." is only shown the first time you run Bazel. It takes a couple of seconds to extract the files.

If you want to uninstall Bazel later, run:

sudo make uninstall

Patching other Bazel versions

If you want to build another Bazel version than the ones supported by Bazel on ARM, just copy the unpacked Bazel distribution directory, make your changes, create the patch and put it in the directory patches with the version number in the file name. Then the build script will pick this up. For instance:

wget https://github.com/bazelbuild/bazel/releases/download/3.3.1/bazel-3.3.1-dist.zip
unzip -d bazel bazel-3.3.1-dist.zip
cp -r bazel bazel-2
# Make your changes in the `bazel-2` directory
diff -ruN bazel bazel-2 > patches/bazel-3.3.1-arm.patch
./scripts/build_bazel.sh 3.3.1

If you have successfully built the release, please contribute your patch to this project by a pull request so others can benefit from it too.

Have a look at the existing patches. Chances are that you need one of these to successfully build another recent version of Bazel.

Motivation

I needed Bazel to build TensorFlow Addons, which I needed because I wanted to run Rasa on my Raspberry Pi. This turned out to be a challenge, and building Bazel was the easiest part of it.

Because I don't trust a random person's binary files on a Google Drive, I decided to build Bazel myself.

Pre-built binaries

I recommend you to build Bazel yourself, but if you really don't want to do it, you can download binary releases built by this project.

References

When I was searching for a Bazel build for Raspberry Pi, I encountered the following projects, which I didn't use for various reasons but they gave some helpful background information about building Bazel on ARM:

• ochafik/rpi-raspbian-bazel: Seems to be unmaintained since end-2017.
• PINTO0309/Bazel_bin: Has an impressive list of pre-built binaries for armhf, aarch64 and x86_64 as well as build instructions, but no recent releases when I started this project.
• This fix by @redsigma was the key to solve my initial issue with building Bazel on ARM.

License

This project is provided by Koen Vervloesem as open source software with the MIT license. See the LICENSE file for more information.