added aosp tree source
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PROPGSP
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aosp-source-tree.md
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aosp-source-tree.md
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###### AOSP Source tree
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Let’s take our first confident step into the world of Android’s internals.
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#### Understanding the AOSP Source Tree Structure
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Im going explain the things first and then put you hands on the source so slow down you curiosity and stabilize you brain to learn.
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Once when you download the Android source code using Google’s `repo` tool, you’ll see a massive directory. But it’s not as overwhelming as it looks — most of it’s are precisely organized by its functions and some may not. Dont worry about it i will explain everything you need to know.
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Here’s a list of the directories that you will see when you sucessfully pulled the source to your local machine or you remote machine.
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| Directory | Description |
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|-----------------------|-----------------------------------------------------------------------------|
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| `art/` | Android Runtime (ART) source code |
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| `bionic/` | Android’s custom C library (`libc`, `libm`, etc.) |
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| `bootable/` | Bootloader and recovery-related code |
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| `build/` | Build system files (Make, Soong, config scripts) |
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| `compatibility/` | Compatibility Test Suite (CTS) and related tools |
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| `cts/` | Compatibility Test Suite source code |
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| `dalvik/` | Legacy Dalvik VM (mostly deprecated) |
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| `developers/` | Developer tools and documentation |
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| `development/` | Tools and sample code for platform development |
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| `device/` | Device-specific configuration and files |
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| `external/` | Third-party open-source libraries (e.g., OpenSSL, SQLite) |
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| `frameworks/` | Android framework code (Java APIs, system services) |
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| `hardware/` | HALs and hardware interface implementations |
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| `kernel/` | Kernel source trees (if included; often managed separately) |
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| `libcore/` | Core Java libraries (`java.*`, `javax.*`) |
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| `packages/` | System apps like Settings, SystemUI, etc. |
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| `pdk/` | Platform Development Kit |
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| `platform_testing/` | Infrastructure for platform-level testing |
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| `prebuilts/` | Precompiled binaries and tools used during build |
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| `sdk/` | Android SDK components |
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| `system/` | Core system components (init, sepolicy, etc.) |
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| `test/` | Unit and integration tests |
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| `toolchain/` | Toolchain sources (e.g., GCC, Clang) |
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| `tools/` | Build tools and utilities |
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| `vendor/` | Vendor-specific blobs and configuration |
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Depending on the branch or target (like Pixel or emulator), you might also see:
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- `product/` – Product partition overlays
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- `vndk/` – Vendor Native Development Kit
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- `common/` – Shared components across devices
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- `soong/` – Soong build system internals (sometimes under `build/`)
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- Some more if you have you choose some specific branch but for 99% of the times you dont probably have more than this.
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### 1. `art/` – Android Runtime
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- **Purpose:** Contains the source code for ART, which replaced the Dalvik VM.
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- **Key Components:**
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- `runtime/`: Core of the ART virtual machine.
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- `compiler/`: ART’s optimizing compiler for converting DEX to native code.
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- `oat/`, `dex2oat/`: Tools and formats for ahead-of-time compilation.
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- **Why it matters:** ART is what executes your Android apps. Just an runtime program to be simple.
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### 2. `bionic/` – C Runtime (libc)
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- **Purpose:** Android’s custom implementation of the C standard library (`libc`, `libm`, `libdl`).
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- **Key Components:**
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- `libc/`: The lightweight libc optimized for embedded use.
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- `tests/`: Unit tests ensuring standard behavior.
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- **Why it matters:** Every native app and system service relies on this for basic memory, string, and math operations.
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### 3. `bootable/` – Bootloader & Recovery
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- **Purpose:** Contains source for Android bootloader parts and the recovery mode.
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- **Key Components:**
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- `bootloader/`: Minimal code to boot up the system on some devices.
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- `recovery/`: Source code for stock recovery image.
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- **Why it matters:** The first line of code that runs after powering on, before the kernel.
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### 4. `build/` – Build System
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- **Purpose:** Core build scripts using Make, Soong, and other tools.
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- **Key Components:**
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- `build/make/`: Classic Makefiles and product configs.
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- `build/soong/`: The new build system in Go.
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- **Why it matters:** You can’t compile Android without this—defines how everything is put together.
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### 5. `compatibility/` and `cts/` – Compatibility Testing
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- **Purpose:** Enforce Android ecosystem standards across OEMs.
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- **Key Components:**
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- `cts/`: Compatibility Test Suite sources.
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- `vts/`, `gts/`: Vendor and Google test suites.
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- **Why it matters:** Ensures your device behaves like any other Android-compliant one.
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### 6. `dalvik/` – Legacy Runtime
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- **Purpose:** Original Android runtime, replaced by ART but still kept around for historical reasons or backward compatibility testing.
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- **Key Components:**
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- `vm/`: Dalvik Virtual Machine internals.
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- **Why it matters:** It was Android’s first runtime environment. Studying it can give you context for ART’s improvements.
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### 7. `development/` – Platform Dev Tools
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- **Purpose:** Houses sample projects, SDK tools, and various utilities.
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- **Key Components:**
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- `apps/`: Test apps like Dev Tools and spare launchers.
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- `scripts/`: Helper scripts for developers (e.g., systrace, profiling).
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- **Why it matters:** Great for exploring how developers debug and experiment with Android features.
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### 8. `device/` – Device-Specific Configs
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- **Purpose:** Contains configuration files for supported devices (like Pixel, emulator, etc.).
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- **Key Components:**
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- `device/google/`: Pixel configuration examples.
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- `BoardConfig.mk`, `device.mk`: Setup how the build system understands the hardware.
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- **Why it matters:** This is where you customize for new hardware — essential for custom ROMs. Also where you put those configurations of your motherborad, camera,... like devices info to make the AOSP to build for it.
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### 9. `external/` – Third-Party Libraries
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- **Purpose:** Bundles open-source software Android depends on.
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- **Examples:**
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- `openssl/`, `zlib/`, `libpng/`, `clang/`
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- **Why it matters:** Keeps all upstream dependencies organized and versioned in sync with AOSP. Like the tolls used to dig a hole. here these are to build and streamline our experience while developing.
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### 10. `frameworks/` – The Android Framework
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- **Purpose:** Java-based layer that provides high-level services used by apps.
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- **Key Components:**
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- `base/`: Core framework — ActivityManager, WindowManager, ContentProviders, etc.
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- `av/`: Media framework.
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- `native/`: Native services and JNI bindings.
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- **Why it matters:** If you want to modify system behavior, this is *the* place. You can optimize the performance by using your cutting edge skills by modifying things inside it.
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### 11. `hardware/` – Hardware Abstraction Layer (HAL)
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- **Purpose:** Interface between Android and device hardware.
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- **Key Components:**
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- Subfolders like `interfaces/`, `libhardware/`, `google/`
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- Contains HIDL/AIDL definitions and implementations.
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- **Why it matters:** Lets Android talk to device-specific hardware without hardcoding vendor logic into the OS.
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### 12. `kernel/` – Linux Kernel (if present)
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- **Purpose:** Kernel source trees for devices (optional — some are pulled externally).
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- **Key Components:**
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- Typically named `kernel/google/msm/` or similar.
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- **Why it matters:** It’s the base of Android. You can modify schedulers, drivers, or build your own kernel.
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### 13. `libcore/` – Java Core Libraries
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- **Purpose:** Provides foundational Java packages (`java.util`, `java.io`, etc.).
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- **Key Components:**
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- `luni/`: Core libraries (`java.lang`, etc.)
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- `ojluni/`: Merged OpenJDK libraries.
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- **Why it matters:** Every Java app on Android relies on this — it’s the bedrock of the language APIs.
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### 14. `packages/` – System Apps
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- **Purpose:** Hosts the source code for system apps and UI components.
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- **Key Examples:**
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- `Settings/`, `SystemUI/`, `Launcher3/`
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- **Why it matters:** This is where things like the lock screen, Quick Settings, and launcher behavior live.
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### 15. `platform_testing/` – Testing Infrastructure
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- **Purpose:** Platform-wide test runners, benchmarking, and test coordination scripts.
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- **Why it matters:** Ensures platform stability with continuous testing across modules.
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### 16. `prebuilts/` – Precompiled Tools
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- **Purpose:** Tools and binaries that don’t need to be built from source (e.g., clang, aapt).
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- **Structure:**
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- `clang/`, `gcc/`, `sdk/`, `tools/`
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- **Why it matters:** These speed up builds and ensure consistent toolchains.
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