How the Soong/Android.bp Build Works
Introduction
The Soong build system, based on the Android.bp language, is the core of Android’s build process. It replaces the traditional Make-based system, offering numerous advantages in terms of modularity, scalability, and performance. This article explores how Soong/Android.bp works, focusing on the key concepts and components involved.
Android.bp Language
Soong uses the Android.bp language to define the build targets and their dependencies. This language is declarative and provides a structured way to describe the build process. Here’s a simple example:
“`
cc_library {
name: “my_library”,
srcs: [“my_library.cpp”],
includes: [“my_includes”],
static_libs: [“libbase”],
}
“`
This snippet defines a C++ library named “my_library” built from the “my_library.cpp” source file, using the “my_includes” directory for header files and linking against the “libbase” static library.
Build Process
The Soong build process can be broken down into these major stages:
* **Parsing**: The `soong` command parses the Android.bp files and generates a build graph representing the dependencies between build targets.
* **Configuration**: Soong analyzes the build graph, determines the required configurations, and creates build rules for each target.
* **Compilation**: Based on the build rules, Soong executes the appropriate build commands (compilers, linkers, etc.) to generate output files.
* **Installation**: Once compiled, output files are installed to the appropriate locations (e.g., system partitions, APK files).
Key Components
* **Module**: A module is a building block in Soong. It represents a specific target (e.g., library, executable, APK).
* **Rule**: A rule defines the steps involved in building a module. It specifies commands, input files, and output files.
* **Dependency**: Modules can depend on other modules. This relationship is captured by the build graph, ensuring that dependent modules are built before their consumers.
* **Variant**: A variant represents a specific configuration of a module. Examples include debug/release builds, target architectures (ARM, x86), or specific device configurations.
Advantages of Soong
* **Modularity**: Soong promotes a modular build system, allowing projects to be organized into reusable modules.
* **Scalability**: Soong can efficiently handle large codebases and complex dependencies, making it suitable for Android’s extensive codebase.
* **Performance**: Soong leverages parallel execution and caching mechanisms to optimize build times.
* **Flexibility**: Soong is flexible and allows for customization through custom rules and modules.
Comparison with Make
| Feature | Make | Soong |
|—————-|—————————————–|————————————–|
| Language | Imperative (procedural) | Declarative |
| Modularity | Less modular | Highly modular |
| Scalability | Can struggle with large projects | Designed for large-scale projects |
| Performance | Slower for complex builds | Faster due to parallel execution |
| Flexibility | Limited customization options | Highly customizable |
Conclusion
The Soong/Android.bp build system is a powerful and efficient tool for building Android. Its modular design, declarative language, and optimization features contribute to a streamlined and scalable build process. Understanding the concepts and components discussed in this article provides a solid foundation for working with and leveraging the Soong build system.