Android NDK: build fat binary with BUILD_EXECUTABLE and armeabi-v7a-hard

Question

Short: How does Android NDK system transform "APP_ABI := armeabi-v7a-hard" to final .so files located in "libs/armeabi-v7a"? What is the proper way to do same thing in Android.mk? Currently, to build standalone executable and place it in folders corresponding to different ABIs I use this, which is it looks ugly because of hard coded "ifeq ($(TARGET_ARCH_ABI),armeabi-v7a-hard)":

LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)
SAVED_NDK_APP_DST_DIR := $(NDK_APP_DST_DIR)

ifeq ($(TARGET_ARCH_ABI),armeabi-v7a-hard)
    NDK_APP_DST_DIR := assets/armeabi-v7a
else
    NDK_APP_DST_DIR := assets/$(TARGET_ARCH_ABI)
endif

LOCAL_MODULE := run_pie
LOCAL_SRC_FILES := run_pie.c    
include $(BUILD_EXECUTABLE)
NDK_APP_DST_DIR := $(SAVED_NDK_APP_DST_DIR)

Long: In my Android app I'm using set of standalone binaries. After build they stored in APK resources. On first app launch I copy them to my app private folder, chmod 777, and than use them as system utilities, like "ls" or "cp". I want to produce "fat binary": single APK that has binaries for all ABIs and choose right binary for current device after installation. For .so libraries Android doing all this stuff automatically. And "APP_ABI := armeabi-v7a-hard" is internal to NDK build system, it's stated in docs, and final .so files for "armeabi-v7a-hard" is placed in "armeabi-v7a" folder. I can do same for my binaries and currently I have way that is working, however it looks ugly.

What is the proper way to place output binaries to custom folders named with ABIs and handle "armeabi-v7a-hard" to "armeabi-v7a" conversion?

Dmitry Moskalchuk Dmitry Moskalchuk · Accepted Answer · 2016-01-08T12:35:49

If you look into $NDK/build/core/setup-toolchain.mk, you'll find the following lines there:

# compute NDK_APP_DST_DIR as the destination directory for the generated files
NDK_APP_DST_DIR := $(NDK_APP_LIBS_OUT)/$(TARGET_ARCH_ABI)
# install armeabi-v7a-hard to lib/armeabi-v7a, unless under testing where env. var. _NDK_TESTING_ALL_
# is set to one of yes, all, all32, or all64
ifeq (,$(filter yes all all32 all64,$(_NDK_TESTING_ALL_)))
ifeq ($(TARGET_ARCH_ABI),armeabi-v7a-hard)
NDK_APP_DST_DIR := $(NDK_APP_LIBS_OUT)/armeabi-v7a
endif
endif

So, as you see, it's the same approach as you do in your Android.mk. The only difference is that you don't take into account _NDK_TESTING_ALL_, which is internal to NDK testing system. So just continue use your Android.mk as is and don't worry.

Another approach would be to build your executables as usual, but name them as lib${TOOLNAME}.so. In this case they will be placed into default NDK_APP_DST_DIR as well as real libraries, and when installing on device, Android Package Manager will copy them into proper place. Then, on first run, you could copy them from lib folder (rather than from assets, as you do currently), and rename appropriately.

Android NDK: build fat binary with BUILD_EXECUTABLE and armeabi-v7a-hard

1 Answers