Mastering module Makefiles

Android Makefiles are an essential piece of the NDK building process. Thus, to build and manage a project properly, it is important to understand the way they work.

Makefile variables

Compilation settings are defined through a set of predefined NDK variables. We have already seen the three most important ones: LOCAL_PATH, LOCAL_MODULE, and LOCAL_SRC_FILES, but many others exist. We can differentiate the following four types of variables, each with a different prefix:

• LOCAL_ variables: These are dedicated to individual module compilation and are defined in Android.mk files.
• APP_ variables: These refer to application-wide options and are set in Application.mk.
• NDK_ variables: These are mainly internal variables that usually refer to environment variables (for example, NDK_ROOT, NDK_APP_CFLAGS, or NDK_APP_CPPFLAGS). There are two notable exceptions: NDK_TOOLCHAIN_VERSION and NDK_APPLICATION_MK. The latter can be passed to the NDK-Build in parameter to define a different...