11.2. The Linux Kernel Makefile

The Linux kernel makefile is an excellent example of using make in a complex build environment. While it is beyond the scope of this book to explain how the Linux kernel is structured and built, we can examine several interesting uses of make employed by the kernel build system. See http://archive.linuxsymposium.org/ols2003/Proceedings/All-Reprints/Reprint-Germaschewski-OLS2003.pdf for a more complete discussion of the 2.5/2.6 kernel build process and its evolution from the 2.4 approach.

Since the makefile has so many facets, we will discuss just a few features that are applicable to a variety of applications. First, we'll look at how single-letter make variables are used to simulate single-letter command-line options. We'll see how the source and binary trees are separated in a way that allows users to invoke make from the source tree. Next, we'll examine the way the makefile controls the verboseness of the output. Then we'll review the most interesting user-defined functions and see how they reduce code duplication, improve readability, and provide encapsulation. Finally, we'll look at the way the makefile implements a simple help facility.