Example how to cross-compile C++ program with Bazel and various toolchains.

These targets are supported:

1. Local x86_64 using system GCC
2. External Linaro/aarch64 toolchain in /opt (see below)
3. embedded Linux (elinux) aarch64 target from TensorFlow (TF)
4. embedded Linux (elinux) amrhf (32 bit ARM with Hardware Float) target from TensorFlow (TF)

Tested OS: openSUSE LEAP 15.3/x86_64

You need to install at least packages:

sudo zypper in curl git-core gcc-c++ gcc

To run aarch64 and armhf targets in QEMU emulator, install this package:

sudo zypper in qemu-linux-user

Now install Bazelisk:

mkdir -p ~/bin
curl -fL -o ~/bin/bazel https://github.com/bazelbuild/bazelisk/releases/download/v1.11.0/bazelisk-linux-amd64
chmod +x ~/bin/bazel

Ensure that you are using your Bazelisk (named as bazel):

which bazel

/home/$USER/bin/bazel

Now checkout this source:

mkdir -p ~/projects
cd ~/projects
git clone https://github.com/hpaluch-pil/bazel-cross-example.git
cd bazel-cross-example

Now verify Bazel version - must be 4.2.2 to match .bazelversion in this project:

$ bazel --version

bazel 4.2.2

It is useful to verify that Bazel is working as expected:

Just run:

# to see available targets
bazel query ...
# build target...
bazel build '//:hello'

You can run this program invoking:

bazel run '//:hello'

Example output:

INFO: Analyzed target //:hello (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
Target //:hello up-to-date:
  bazel-bin/hello
INFO: Elapsed time: 1.056s, Critical Path: 0.80s
INFO: 3 processes: 1 internal, 2 linux-sandbox.
INFO: Build completed successfully, 3 total actions
INFO: Build completed successfully, 3 total actions
Hello, x86_64 world!

At first install Linaro aarch64 cross-compiler:

• download:
  • https://releases.linaro.org/components/toolchain/binaries/7.2-2017.11/aarch64-linux-gnu/gcc-linaro-7.2.1-2017.11-x86_64_aarch64-linux-gnu.tar.xz
• unpack it under /opt
• rename unpacked directory - WARNING! Symlink will not work with Bazel (it will use canonical path)

  sudo mv /opt/gcc-linaro-7.2.1-2017.11-x86_64_aarch64-linux-gnu \
    /opt/aarch64-linux-gnu

• so verify that you have path like:

  /opt/aarch64-linux-gnu/bin/aarch64-linux-gnu-gcc
  

And run:

bazel build --config=aarch64 '//:hello'

It should build aarch64 binary - you can verify it with command:

$ readelf -h bazel-bin/hello | fgrep Machine:

 Machine:                           AArch64

To run aarch64 binary under QEMU emulation you can try this:

• and run binary user QEMU USER:

  qemu-aarch64 -L /opt/aarch64-linux-gnu/aarch64-linux-gnu/libc \
     bazel-bin/hello

• shoud produce output:

  Hello, aarch64 world!
  

Uses embedded Linux (elinux) aarch64 target from TF. To build this target run script:

./build_elinux_aarch64.sh

To verify target architecture try:

$ readelf -h bazel-bin/hello | fgrep Machine:

  Machine:                           AArch64

$ readelf -d bazel-bin/hello | fgrep NEEDED

 0x0000000000000001 (NEEDED)             Shared library: [libstdc++.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [ld-linux-aarch64.so.1]

To run elinux_aarch64 binary under QEMU AArch64 emulator try:

./run_qemu_elinux_aarch64.sh

Uses embedded Linux (elinux) 32-bit ARM HF (hardware float) target from TF. To build this target run script:

./build_elinux_armhf.sh

To verify target architecture try:

$ readelf -h bazel-bin/hello | fgrep Machine:

  Machine:                           ARM

$ readelf -d bazel-bin/hello | fgrep NEEDED

 0x00000001 (NEEDED)                     Shared library: [libstdc++.so.6]
 0x00000001 (NEEDED)                     Shared library: [libgcc_s.so.1]
 0x00000001 (NEEDED)                     Shared library: [libc.so.6]
 0x00000001 (NEEDED)                     Shared library: [ld-linux-armhf.so.3]

To run elinux_armhf binary under QEMU ARM try:

./run_qemu_elinux_armhf.sh

• TensorFlow - elinux toolchains come from this project:
  • https://github.com/tensorflow/tensorflow
• https://docs.bazel.build/versions/main/tutorial/cc-toolchain-config.html
• https://docs.bazel.build/versions/2.2.0/tutorial/cc-toolchain-config.html