Add cross-compilation to Aarch64 logic and investigate CI testing

[hug-dev]

Currently all tests in our CI execute on x86.
We need to make sure that compiling the service is as easy as cargo build --target aarch64-unknown-linux-gnu. It will be currently except for the compilation of Mbed Crypto which needs extra logic in build.rs scripts.
We also need to investigate CI testing on this target and what are our options.
We can look at cross and at native testing using Travis.

[hug-dev]

To cross-compile before, it used to be as easy as changing the Mbed Crypto library compiler in the build-conf.toml file and do the command: cargo build --target aarch64-unknown-linux-gnu
But with that now the compilation fails with the following issue:

          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: Relocations in generic ELF (EM: 183)
          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: Relocations in generic ELF (EM: 183)
          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: Relocations in generic ELF (EM: 183)
          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: Relocations in generic ELF (EM: 183)
          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: Relocations in generic ELF (EM: 183)
          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: Relocations in generic ELF (EM: 183)
          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: Relocations in generic ELF (EM: 183)
          /usr/bin/ld: /home/hugdev01/dev/parsec/parsec/target/aarch64-unknown-linux-gnu/debug/deps/parsec-b832778a0064e80a.103gqkamrymphzyu.rcgu.o: error adding symbols: file in wrong format
          collect2: error: ld returned 1 exit status

It might be because the linker used is the system linker and not an Aarch64-toolchain linker?

[adamparco]

You could also leverage buildx to do emulated builds, or to point to a remote armv8 builder instance (AWS A1).

[hug-dev]

Part of this issue is being addressed in #61: cargo build --target aarch64-unknown-linux-gnu will now cross-compile everything to this target.
To fix the issue above, the linker is precised in .cargo/config. I thought that the linker shipped with Rust installation could be used as well for cross-compiling but I think it does not support this target (or is not included?).

The remaining parts of this issue are related with testing:

• adding a CI job that cross-compile PARSEC for the Arm64 target (maybe buildx or cross could be used here)
• adding CI system where some of the tests are compiled and executed natively on Arm64 (Travis CI, AWS A1, Codefresh can be looked at)

[hug-dev]

#64 completed the first point above

[hug-dev]

We are going to set up a GitHub Actions self-hosted runner on an Arm Machine! That way we will only need little modification to our GH Actions workflows to make them run on Arm as well.

cf WorksOnArm/cluster#190

[hug-dev]

Due to security problems about using GitHub Actions self-hosted runners, we decided to switch to Travis CI which has been enabled in #90