Straightforward Android Native Executables

출처 : http://vilimpoc.org/blog/2010/09/26/straightforward-android-native-executables/

I spent some time trying to figure out how to build a native code "Hello, world!" program for Android and noticed that prior to the r4b release of the Android NDK, there is a lot of bad info out there on how to do this. Usually, it involves using some kind of unofficial cross-compiler, plus the entire source tree of the Android OS, and/or whatever other kludgy hacks like linking the executable statically to some kind of ARM libc. This seems bad. With the newest version of the NDK generating a proper gdbserver executable and gdb setup stubs, why anyone would want to do this by hand is beyond me.

There was a script that made sense at one point: agcc.pl (here), which essentially takes all of the Makefile fragments and command-line switches and wraps them for you, letting you treat the NDK's cross-compilers almost like a normal gcc, but this is probably still more work than it's worth.

The Easy Way

The easiest way to get the NDK to build a native executable for you is just to use

include $(BUILD_EXECUTABLE)

at the end of your Android.mk, and then build like normal.

Anything else will just cause premature baldness.

Read on to see a fully-worked example...

hello-exe.c

1

#include

2	int main(int argc, char ** argv)

3

{

4	printf("Hello, world!\n");

5

return 0;

6

}

Android.mk

1	LOCAL_PATH := $(call my-dir)

2

3	include $(CLEAR_VARS)

4

5	LOCAL_MODULE    := hello-exe

6	LOCAL_SRC_FILES := hello-exe.c

7

8	include $(BUILD_EXECUTABLE)

Example build + install output (it really is that easy)

01	vilimpoc@funky ~

02	$ cd ~/android-ndk-r4b/samples/hello-exe

03

04	vilimpoc@funky ~/android-ndk-r4b/samples/hello-exe

05

$ ls

06

jni

07

08	vilimpoc@funky ~/android-ndk-r4b/samples/hello-exe

09	$ ~/android-ndk-r4b/ndk-build -B

10	Compile thumb  : hello-exe <= /home/vilimpoc/android-ndk-r4b/samples/hello-exe/jni/hello-exe.c

11	Executable     : hello-exe

12	Install        : hello-exe => /home/vilimpoc/android-ndk-r4b/samples/hello-exe/libs/armeabi

13

14	vilimpoc@funky ~/android-ndk-r4b/samples/hello-exe

15

$ ls

16	jni  libs  obj

17

18	vilimpoc@funky ~/android-ndk-r4b/samples/hello-exe

19	$ cd libs/armeabi

20

21	vilimpoc@funky ~/android-ndk-r4b/samples/hello-exe/libs/armeabi

22

$ ls

23

hello-exe

24

25	vilimpoc@funky ~/android-ndk-r4b/samples/hello-exe/libs/armeabi

26	$ adb devices

27	List of devices attached

28	emulator-5554   device

29

30	vilimpoc@funky ~/android-ndk-r4b/samples/hello-exe/libs/armeabi

31	$ adb -e shell

32	# mkdir /data/data/hello-exe

33	# ls /data/data/hello-exe

34

# exit

35

36	vilimpoc@funky ~/android-ndk-r4b/samples/hello-exe/libs/armeabi

37	$ adb -e push hello-exe /data/data/hello-exe/hello-exe

38	427 KB/s (0 bytes in 13670.000s)

39

40	vilimpoc@funky ~/android-ndk-r4b/samples/hello-exe/libs/armeabi

41	$ adb -e shell

42	# cd /data/data/hello-exe

43

# ls -l

44	-rw-rw-rw- root     root        13670 2010-09-23 12:37 hello-exe

45	# chmod 777 ./hello-exe

46

# ls -l

47	-rwxrwxrwx root     root        13670 2010-09-23 12:37 hello-exe

48	# ./hello-exe

49	Hello, world!

50

#

51

# exit

52

53	vilimpoc@funky ~/android-ndk-r4b/samples/hello-exe/libs/armeabi

54

$