GNU Make and it's limitations

Yes, you are correct! GNU Make was not specifically targeted for Android. It’s a general-purpose build tool used in a wide variety of software projects, not just Android. Let me explain GNU Make in detail and cover its uses, both historically and in modern applications.

1. What is GNU Make?

GNU Make is a build automation tool that controls the compilation and linking of programs. It’s part of the GNU project, which provides free software components that are compatible with the UNIX operating system. Make helps developers manage dependencies and automate the process of compiling large codebases by reading a file (usually called a Makefile) that contains instructions about how to build the project.

Key Features:

• Dependency Management: It automatically determines which parts of a program need to be recompiled based on changes in the source files or dependencies.

• Automation: It automates the building process, so developers don't need to manually compile each component of a program.

• Cross-Platform: While it was originally created for Unix-like systems, GNU Make is cross-platform and can be used on different operating systems, including Linux, macOS, and Windows (with tools like Cygwin or WSL).

2. How GNU Make Works

At the core of GNU Make is the Makefile, which specifies:

• Targets: These are the outputs that Make should generate, such as executable programs or libraries.

• Dependencies: The files (like source code) that the targets depend on.

• Rules/Recipes: The commands that should be executed to build the target from its dependencies (like compiling or linking).

A typical workflow might look like this:

1. You write a Makefile that defines how the source files in your project should be compiled.

2. When you run make, it reads the Makefile, checks which source files have changed, and only recompiles the necessary parts.

3. make automatically handles the rest, such as invoking the correct compiler commands.

For example, a Makefile for a C project might look like this:

# Define the compiler
CC = gcc

# Define the target executable
TARGET = my_program

# Define the source files
SRC = main.c file1.c file2.c

# Define the object files
OBJ = main.o file1.o file2.o

# Rule for building the final executable
$(TARGET): $(OBJ)
	$(CC) -o $(TARGET) $(OBJ)

# Rule for compiling object files from source files
%.o: %.c
	$(CC) -c $< -o $@

# Clean up generated files
clean:
	rm -f $(TARGET) $(OBJ)

In this example:

• my_program is the target.

• It depends on the object files main.o, file1.o, and file2.o.

• The commands (gcc) specify how to build the object files and the executable.

3. Why was GNU Make Used in AOSP?

When Android was initially developed, GNU Make was already a widely-used and trusted build tool. Many large open-source projects relied on it due to its flexibility, extensibility, and ability to manage dependencies. Since Android had many native C and C++ components, GNU Make was a natural fit for managing the complex builds involved in compiling Android’s system components.

• Compatibility: Android needed to compile many low-level components (like the Linux kernel, system libraries, and native tools), and GNU Make was well-suited for this task.

• Cross-Compilation: Android development involves cross-compiling for ARM or other architectures, and Make provides a straightforward way to handle cross-compiling toolchains.

4. Limitations of GNU Make in AOSP

Although Make was powerful, it had limitations, particularly for large, complex projects like Android:

• Performance: Make was not designed for highly parallel builds across large multi-core machines. As the size of Android grew, the build times became a bottleneck.

• Complexity: Managing dependencies and correctly writing Makefiles for a large project can be difficult and error-prone. This led to complex Makefile hierarchies in AOSP, making the build system harder to maintain.

• Scalability: Make’s ability to handle modern large-scale projects (with tens of thousands of files) was limited, particularly when compared to newer build systems designed for speed and parallelism (such as Ninja).

5. Is GNU Make Still Used?

Yes! Despite its limitations in AOSP, GNU Make is still widely used in many areas of software development.

Current Applications of GNU Make:

• Native Code Projects: It is still widely used in C, C++, and Fortran projects, especially those that require platform-specific compilation steps. Many system-level tools, libraries, and even parts of the Linux kernel still use Makefiles for building.

• Embedded Systems: In embedded systems development, Make remains a popular choice because it is simple, reliable, and works well in environments with constrained resources.

• Open-Source Projects: Many open-source projects, especially those that involve building libraries and tools across multiple platforms (such as the GNU toolchain, compilers, and system utilities), still use GNU Make.

• Scientific Computing: In research, GNU Make is often used to manage the compilation of scientific simulations and models, particularly when different modules need to be compiled based on different configurations.

• Cross-Platform Builds: Projects that need to support different platforms (Linux, macOS, Windows) still use Make because it works well with different compilers and tools.

Example Projects Still Using GNU Make:

• Linux Kernel: The Linux kernel is built using Make, and it has a very complex Makefile system that manages the configuration and compilation of the kernel for different architectures.

• GCC: The GNU Compiler Collection (GCC), a widely-used compiler, uses GNU Make for its build system.

• Other Tools: Many command-line tools and libraries, such as git, Vim, and various parts of the GNU operating system, still use Make for building.

6. Modern Uses of GNU Make and Competition

Even though newer build systems have emerged (like CMake, Ninja, Bazel, and Meson), Make is still widely used because of its simplicity, familiarity, and extensive adoption across many industries.

Comparison with Other Build Systems:

• Make vs. CMake: CMake is often used to generate Makefiles or ninja files. CMake is popular because it provides a higher level of abstraction and is easier to use for cross-platform projects.

• Make vs. Ninja: Ninja is faster than Make, particularly for parallel builds, but Ninja is more minimalistic. Ninja is often generated by other tools like CMake, Soong, or GN, as it lacks the human-readable declarative syntax that Makefiles have.

• Make vs. Bazel: Bazel is used for large, multi-language projects (like TensorFlow or Android’s Soong) and focuses on reproducible builds, making it better suited for highly modular projects. However, Make’s simplicity still makes it a good choice for smaller, more straightforward projects.

7. Summary of GNU Make’s Role Today

In summary, GNU Make remains a versatile and widely-used build automation tool. While AOSP has transitioned to newer build systems like Soong and Ninja due to the complexity and scale of Android, GNU Make still powers many important open-source projects, including the Linux kernel, GCC, and many more. It is particularly valuable for native code projects, cross-platform applications, and embedded systems development.

Feel free to ask for further clarification on any specific part of GNU Make or its applications!