Question

I’m having a problem with building an Android ROM (galaxys2att, gingerbread). I decided it was time to get smarter about makefile processing. So I created a simple test project to play with. But it’s not getting compiled. Here’s what I did:

1 I create a directory (“myproject/“) under a buildable module (I used “Mms/” but others had the same problem).
2 I create Android.mk in that directory containing

hello:

   echo "Hello from myproject"

(I have no blank line between hello: and echo: the page editor added these)

3 I ran mm in the “Mms/” directory.

Mms and other subproject compiled but no evidence of myproject.

Android.mk in Mms contained line
include $(call all-makefiles-under, $(LOCAL_PATH))

Of course I ran envsetup.sh originally.
What am I missing here?

Answer 1

In the Android NDK, there’s some documentation in .../docs/ANDROID-MK.html. Unfortunately, there’s not much other documentation to find, beside looking into existing makefiles. A minimal Android.mk for building a shared library, might look like this

# "initialize" Makefile
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)

# setup some variables
LOCAL_MODULE    := hello-jni
LOCAL_SRC_FILES := hello-jni.c

# do the build
include $(BUILD_SHARED_LIBRARY)

An Android.mk is not like a regular Makefile. You have a boilerplate, define some variables needed in sub makefiles and then do the work by including predefined Android makefiles.

BUILD_SHARED_LIBRARY, for example, is defined in build/core/build-all.mk as

BUILD_SHARED_LIBRARY := $(BUILD_SYSTEM)/build-shared-library.mk

which itself defines and checks some make variables and then includes $(BUILD_SYSTEM)/build-module.mk, and so on.

Inside build-all.mk, there are other variables defined as well, like BUILD_HOST_EXECUTABLE, BUILD_STATIC_LIBRARY or BUILD_EXECUTABLE, which are used to build a static library or an executable.