Final Report - GSoC 2020

Its almost 3 months since I have been officially working with the SharkBait team at Gentoo. A lot of ground has been covered, a lot is still left. In this blog, I will explain the scope of SharkBait right now and how I plan its future.

Work Covered

Porting SharkBaitOS

When KireinaHoro started working on SharkBait, the latest Android version of that time was 8 or Android Oreo. Sharkbait at that time, supported all the Android devices because it targeted only a specific boot order, which was common till Android 8. Then came Android 9, with its System-As-Root configuration, which rendered SharkBait's original boot order non functional for all devices shipping with Android 9.
The first month of my work revolved around porting SharkBait to SAR based devices. I succeeded in doing so, and wrote blogs about it:

• Android Boot High Jinks
  In this blog we discuss the different approaches at booting Android, Google has experimented with.
• Booting Gentoo from SAR-Preinit
  This blog showcases how I patched my phone's kernel in order to boot Gentoo on my phone.
• Starting System-as-Root Android in a LXC container
  This blog is the first class guide for launching SharkBait in System-As-Root devices.

The projects made in efforts to port SharkBait for SAR were:

• SAR-Preinit
  This repository acts as the setup which patches your custom kernel and makes it boot a GNU/Linux distro, instead of Android on your phone.
• Bootstrap-init
  This repository hosts the source of the init binary executed inside the LXC container which launches System-As-Root Android on top of Gentoo.

Introducing Android builds on AArch64 Hosts

As simple as it sounds, this part of my GSoC tenure turned out to be the exact opposite.
My first task was to provide a AArch64 native port of the LLVM toolchain AOSP uses. I was stuck on compiling and testing my modified scripts till the second month, when my mentor generously set up a beefy AArch64 server for me. I succeeded in delivering that toolchain. Related sources are:

• Building Android: BTS
  In this blog, I look what events get triggered under the hood when we build Android, as to seek insight on breaking down Android later.
• Toolchain_LLVM_Android
  This repository hosts the build scripts and instructions on building AOSP's LLVM distribution on AArch64 Host, which targets AArch64 and Arm platforms

Once I dealt with the toolchains, I could focus on building Android. Unfortunately this part is still unfinished due to the massive scale of thought-process and work it requires. Still, I will report on whatever I have been doing:

• Manifest
  This is the (yet-to-be) SharkBait Manifest. It houses the different AOSP components SharkBait pulls in order to build Android. Some of which I have been working on:
  • android_build_blueprint
  • android_build_soong
  • android_build

Future Work

There are many things to be concerned with such as the flow of project development to follow, how exactly we should aim introducing arm64 as an host.
Plus the final goal of SharkBait is the ability to upgrade its Android container with the use of Portage, thus providing granular, GNU like updates to Android, quite possibly the first time ever. Keeping all this in mind we needed a proper roadmap on how to achieve this. My vision for it resembles somewhat like the following:

1. Build Android as an whole separate entity on AArch64.
2. Then compose a monolithic ebuild for the exact same thing.
3. Start breaking parts from Android:
   • Ship the toolchains used by AOSP separately using Portage and possibly integrate it with crossdev.
   • Ship the necessary prebuilt build-tools AOSP bundles as packages with Portage on arm64.
4. Capitalizing on the fact that AOSP code is highly modular, separate those modules into different packages under a common overlay.

And since I consider myself apt in bringing this for SharkBait, I would love to work on it even after GSoC finishes.

Acknowledgements

I immensely appreciate the patience of my mentor, Benda Xu. He has always given me the helm when it comes to SharkBait, while still actively monitoring my work and helping me out. Without his generous efforts of providing me with an industry-standard arm64 server, I dont think I could consider this GSoC a success.

My co-mentors - Pengcheng Xu, Lucas Ramage and Stephen Christie helped me whenever I got stuck in my work. Pengcheng offered me assistance in getting UART work for my Phone, Lucas actively kept a lookout on my work and Stephen would offer me assistance in getting better hardware without two thoughts.

All of them offered crucial personal help whenever I was stuck, be it my work, understanding the project or even my proposal writing, something which I can never overlook.

The least I can do to return their favours is to bring SharkBait to all its glory, which I eagerly wait for.