How to create your own Android OS? A complete roadmap for building a custom Android OS from AOSP

How to create your own Android OS? A complete roadmap for building a custom Android OS from AOSP

You have likely used Samsung’s One UI, seen Xiaomi’s HyperOS, or operated OnePlus’s OxygenOS. When these companies launch new operating systems every year, it often feels like creating an Android OS is beyond the reach of an ordinary person. We tend to think it requires a trillion-dollar company like Google and secret labs staffed by thousands of scientists.

But what is the reality

The truth is, it isn’t impossible rocket science. Every Android OS in the world is built upon the foundation of AOSP—the Android Open Source Project. It is a recipe comprising the Linux Kernel, Device Tree, Framework, and code; once you understand this, you can move forward with creating your own custom Android OS on your computer. Today, we will explore a master roadmap covering what you need to learn, why you need to learn it, and which tools to use. If you want to understand the inner workings of Android and become a core operating system developer, let’s dive into how to build your own Android OS.

What do you need first to build an Android OS

If you want to build a sturdy house, you don’t start by painting the walls; you first dig the ground and lay a strong foundation. Similarly, to create your own Android OS, the first step is setting up your workspace and the necessary tools.

1. Ubuntu Linux

The first thing you need is the Ubuntu Linux operating system. You might ask, “Why not Windows?” Android’s entire source code is designed for the Linux environment; therefore, a Linux environment is essential for Android OS development. You will need to use the LTS (Long-Term Support) version of Ubuntu Linux on your PC. For this, you need at least an 8-core processor, 32GB of RAM, and fast SSD storage, as a vast number of files are processed simultaneously during compilation.

2. Repo Tool

Next on the list is a crucial tool from Google called “Repo.” Think of it this way: if hundreds of freight trains from different cities were lined up in front of you, how would you manage them all by yourself? The entire AOSP code isn’t stored in a single folder; instead, it is distributed across various Git repositories. ‘Repo’ acts as a master controller, enabling you to download and synchronize these disparate repositories onto your computer with a single command.

3. Clang and LLVM Compilers

Next come the Clang and LLVM compilers. Computers do not directly understand the C and C++ code we write. The Clang compiler helps convert our code into the binary language required by the phone’s processor. We also need OpenJDK (Open Java Development Kit), which assists in compiling Android’s system apps and other Java-based components.

4. Android Emulator

You might be wondering: what if I don’t have an extra phone for testing? The Android Emulator is a useful solution here. You don’t need to risk using a real phone; your computer can create a virtual phone on the screen where you can test your Android OS. This is how we set up our workshop and essential tools. Now, let’s understand how Android’s internal system works.

Key Pillars of Android OS

Android consists of several important layers and components. Understanding them is crucial for building a custom Android OS.

1. Linux Kernel

You can think of the Linux Kernel as the actual engine and heart of the phone. The kernel interacts with the phone’s hardware, battery, RAM, and processor, facilitating essential communication between the system and the hardware.

2. HAL (Hardware Abstraction Layer)

The second crucial component is the HAL, or Hardware Abstraction Layer. Let’s understand this with an example. Suppose you visit a restaurant; you only speak Hindi, but the chef in the kitchen understands only Japanese. The waiter standing between you conveys your message to the chef. Similarly, the HAL acts as a layer between the hardware and the Android system. Since the Android components operating at the higher level do not directly understand the hardware’s language, the HAL assists in communicating with the hardware.

3. Android Framework and System Server

The third important component is the Android Framework and System Server. You can think of this as the phone’s traffic control tower. Several vital system services operate within it. For instance, the Activity Manager Service (AMS) determines which app opens and manages app activities. Meanwhile, the Window Manager Service (WMS) handles elements related to windows and graphics on the screen.

4. System UI

Next comes the System UI. This is the part visible on your phone’s screen, such as the status bar, notification panel, and interface elements associated with the home screen. Thus, these various Android layers work together to run the entire system.

Why doesn’t AOSP contain device-specific code

Here is a crucial point: when you download AOSP code from Google, it does not include the complete device-specific code for your specific phone’s camera, fingerprint sensor, or display. AOSP provides a base system; device-specific components are required to operate the hardware of a particular phone. Let us now move forward and understand how the device tree and vendor components are prepared for a phone.

What is a Device Tree

First, you need to prepare your device tree. You can think of it as the architectural blueprint—or floor plan—of a house. The Device Tree contains various configuration and device-specific files that provide the Android build system with information about the phone’s hardware and configuration. Files such as Product Configuration and Board Configuration are crucial among these. Product configuration files, like `AndroidProducts.mk`, help define the product, while files related to board configuration help specify the hardware configuration.

What are vendor blobs

Now, let’s look at a crucial component: Vendor Blobs. Companies like Qualcomm and MediaTek do not release the full source code for internal components associated with their hardware—such as cameras and GPUs—to the public. Think of it like a company that doesn’t reveal its product’s secret formula but instead provides a ready-to-use product. Similarly, vendor blobs are pre-built binary files extracted from a device’s original software that can be utilized in a custom Android build. Accompanying these are Device Tree Source (DTS) files, which help inform the kernel about hardware components and their interconnections.

SELinux and Android Security

Imagine you have compiled your code and booted the phone for the first time, but it fails to boot and gets stuck in a boot loop.
This can happen for various reasons. SELinux is a vital part of Android security; think of it as a strict security guard. If you create a new service or feature in your OS but lack the necessary security policy, SELinux might block that service’s access. Tools like `audit2allow` can help interpret security logs, allowing you to configure SELinux policies as needed.

Android Compilation Pipeline

Now comes the actual task of creating the Android OS: compilation. Android utilizes its own build system along with build tools like Ninja. After setting up the necessary build environment in the terminal, you select the target and execute the build command. Picture a massive automated factory springing into action: the compiler and build system process millions of source files and components to generate the final Android images. Once the build is complete, various Android images are produced, ready for use on the specific device.

Dynamic Partitions and Super Image

Many modern Android phones utilize dynamic partitions. You can visualize this as a “smart suitcase” where the internal space expands or contracts based on requirements. Various components related to the Android system and the vendor can be managed within a single logical “Super Partition,” and a “Super Image” is generated during the build process. Flashing the Android OS onto the Phone

Once your Android build is ready, the next step is to flash it onto the phone. The phone is put into Fastboot mode and connected to the computer via a USB cable. Subsequently, the necessary images are flashed using Fastboot commands, tailored to the specific device and build. Upon rebooting the phone, the logo and interface of your custom Android OS may appear on the screen. This completes the entire process, spanning from the AOSP source code to device configuration, vendor components, the build itself, and the final flashing.

Conclusion

Creating your own Android OS is no easy task, but one can begin by understanding AOSP and the internal architecture of Android. Understanding components such as the Linux environment, Repo, compiler, emulator, Linux kernel, HAL, Android framework, system services, device tree, vendor blobs, SELinux, the build system, and Fastboot is a crucial part of this entire process.
If you grasp this entire roadmap, you move beyond being merely an Android app user and can progress toward understanding Android at the system level and the intricacies of operating system development.