I was given a shared library built on Linux x86, let's call it libA.so, and I want to use the function calls provided by this library SDK.
I am having issues building and have a few questions:
1) I will be able to build for x86, but will I be able to build for arm? I believe the answer is no, meaning I cannot run on a Nexus 5 for example.
2) The ndk-build complains of the #include that should be resolved by my LOCAL_SHARED_LIBRARIES. I am not sure why that is. My Android.mk is as follow:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := B
LOCAL_SRC_FILES := B.cpp
LOCAL_SHARED_LIBRARIES := A
LOCAL_LDLIBS := -llog
include $(BUILD_SHARED_LIBRARY)
Can someone please help me resolve my Android.mk? I don't understand why it is complaining about my include statement in B.cpp. Please let me know if I can run B in an arm environment, although the SDK I am relying on was built on x86.
If your shared library libA.so has been compiled for linux-x86, it will certainly not run on android x86 targets (mainly because it needs to be linked to Bionic C library instead of glibc), and absolutely not on android arm devices.
Then, to solve your second issue, if you can get properly compiled android shared libraries for your android targets, you would include your library this way:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := A
LOCAL_SRC_FILES := ../libA/prebuilts/$(TARGET_ARCH_ABI)/libA.so # path to libA .so file, depending on the target ABI.
LOCAL_EXPORT_C_INCLUDES := ../libA/includes # path to libA headers.
include $(PREBUILT_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := B
LOCAL_SRC_FILES := B.cpp
LOCAL_SHARED_LIBRARIES := A
LOCAL_LDLIBS := -llog
include $(BUILD_SHARED_LIBRARY)
Related
I'm trying to compile my application to use tensorflow C++ library after building lintensorflow_core.a into my NDK application. The application has the main java layer, that communicates with the NDK component. In that NDK component, I'm looking to call the tensorflow as such: using namespace ::tensorflow::ops; // NOLINT(build/namespaces)
I've seen bunch of links on how to do it with Android.mk file. But apparently, that does not gets created anymore in the new version of android studio. If it is possible with just Android.mk and ndk-build command, that would be great as well. However, the combination of Android.mk and ndk-build has also failed me. The output basically nothing.
I did have plenty of variation of Android.mk file and here's one of them:
LOCAL_PATH := $(call my-dir)
TENSORFLOW_HOME := $(LOCAL_PATH)/../../../../../tensorflow
TENSORFLOW_CORE := $(LOCAL_PATH)/../../../../../tensorflow/tensorflow/core
TENSORFLOW_OPS := $(LOCAL_PATH)/../../../../../tensorflow/tensorflow/core/ops
include $(CLEAR_VARS)
LOCAL_MODULE := tensorflow
LOCAL_SRC_FILES := $(TENSORFLOW_HOME)/tensorflow/contrib/makefile/gen/lib/android_armeabi-v7a/libtensorflow-core.a
LOCAL_LDLIBS := -static -Wl,--build-id -Wl,--allow-multiple-definition -Wl,--whole-archive
LOCAL_CFLAGS := -std=c++11 -I$(TENSORFLOW_HOME)
LOCAL_C_INCLUDES := $(TENSORFLOW_OPS)
TARGET_ARCH_ABI := armeabi
include $(PREBUILT_STATIC_LIBRARY)
But this has been a total failure. Could someone point me to the right direction?
I got a problem in android.mk.It always show me that cannot find -lsubstrate-dvm and -lsubstrate. I don't know what it is? Could someone tell me how to solve this problem ? Here is the logcat:
Android NDK:non-system libraries in linker flags: -libsubstrate-dvm -libsubstrate
Android NDK: This is likely to result in incorrect builds. Try using LOCAL_STATIC_LIBRARIES
Android NDK: or LOCAL_SHARED_LIBRARIES instead to list the library dependencies of the
Android NDK: current module
cannot find -libsubstrate-dvm
cannot find -libsubstrate
Here is the android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := substrate
LOCAL_SRC_FILES := libsubstrate.so
include $(PREBUILT_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := substrate-dvm
LOCAL_SRC_FILES := libsubstrate-dvm.so
include $(PREBUILT_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := cydiasubstrate.cy
LOCAL_SRC_FILES := cydiasubstrate.cy.cpp
LOCAL_LDLIBS := -llog -L$(LOCAL_PATH) -lsubstrate-dvm -lsubstrate -lz
LOCAL_ARM_MODE := arm
APP_ALLOW_MISSING_DEPS=true
include $(BUILD_SHARED_LIBRARY)
please help me to fix this issue.
substrate-dvm is the name of the module being built, it relies on a prebuild library, not on sources, so you should look for libsubstrate-dvm.so
You could follow the following link for further help:
https://blog.gdssecurity.com/labs/2014/12/16/hooking-non-public-methods-with-the-ndk-using-mobile-substra.html
to include the Substrate libraries. The easiest way to
do this is to navigate to the ‘/sdk/extras/saurikit/cydia_substrate/’
directory and copy ‘substrate.h’ and navigate to the
‘/sdk/extras/saurikit/cydia_substrate/lib//’ directory and copy
‘libsubstrate-dvm.so’ file into the jni folder of the project.
I am writing an android app that wants to make JNI calls into a shared library built in using the NDK. The trick is this shared library calls functions provided by OTHER shared libraries. The other shared libraries are C libraries that have been compiled elsewhere.
Here's what I've tried:
My Environment:
I'm working in Eclipse. I've added native support and have a jni library. In that library I have my code and a \lib directory where I have copied my other .so files.
Attempt #1 Android.mk: Just telling it where the libs are
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := native_lib
LOCAL_SRC_FILES := native_lib.cpp
LOCAL_LDLIBS := -L$(SYSROOT)/../usr/lib -llog
LOCAL_LDLIBS += -L$(LOCAL_PATH)/lib/support_lib1
LOCAL_LDLIBS += -L$(LOCAL_PATH)/lib/support_lib2
include $(BUILD_SHARED_LIBRARY)
This builds just fine, but when I try to run I get errors indicating that dlopen(libnative_lib) failed because it couldn't load libsupport_lib1.
Coming here I found this:
Can shared library call another shared library?
which said that I needed to call load library on all necessary libraries. Great!
Attempt #2 Opening each library first
static {
System.loadLibrary("support_lib1");
System.loadLibrary("support_lib2");
System.loadLibrary("native_lib");
}
Again, this builds just fine, however when I run I get a new error:
couldn't load libsupport_lib1. findLibrary returned null.
Now we're getting somewhere. It must not be loading the libraries over to the target.
Attempt #3 Copying .so files into project/libs/armeabi
Didn't work. When Eclipse builds it deleted the files I dropped in there.
Attempt #4 Creating a new module for each library
So then I found this:
Android NDK: Link using a pre-compiled static library
It's about static libraries, but maybe I am having a similar problem. The gist is that I need to declare a module for each library. So my new Android.mk looks like this:
LOCAL_PATH := $(call my-dir)
#get support_lib1
include $(CLEAR_VARS)
LOCAL_MODULE := support_lib1
LOCAL_SRC_FILES := $(LOCAL_PATH)/lib/support_lib1.so
include $(BUILD_SHARED_LIBRARY)
#get support_lib2
include $(CLEAR_VARS)
LOCAL_MODULE := support_lib2
LOCAL_SRC_FILES := $(LOCAL_PATH)/lib/support_lib2.so
include $(BUILD_SHARED_LIBRARY)
#build native lib
include $(CLEAR_VARS)
LOCAL_MODULE := native_lib
LOCAL_SRC_FILES := native_lib.cpp
LOCAL_LDLIBS := -L$(SYSROOT)/../usr/lib -llog
LOCAL_LDLIBS += -L$(LOCAL_PATH)/lib/support_lib1
LOCAL_LDLIBS += -L$(LOCAL_PATH)/lib/support_lib2
include $(BUILD_SHARED_LIBRARY)
This builds! Even better, armeabi has the sos now! Even BETTER I get the following messages when I try to run it (telling me that support_lib1 and 2 were opened by LoadLibrary:
Trying to load lib /data/app-lib/com.example.tst/libsupport_lib1.so
added shared lib /data/app-lib/com.example.tst/libsupport_lib1.so
no JNI_OnLoad found in /data/app-lib/com.example.tst/libsupport_lib1.so, skipping init
but then...
dlopen failed: Could not locate symbol func_that_exists_in_libsupport_lib.so referenced by libnative_lib.so
Edit: Attempt 5: Use PREBUILT_SHARED_LIBRARY
So I found this:
How can i Link prebuilt shared Library to Android NDK project?
which seems to be exactly what I'm asking. Their answer seems to be 'don't use 'build_shared_library' but instead 'use PREBUILT_SHARED_LIBRARY
Okay, let's try.
LOCAL_PATH := $(call my-dir)
#get support_lib1
include $(CLEAR_VARS)
LOCAL_MODULE := support_lib1
LOCAL_SRC_FILES := $(LOCAL_PATH)/lib/support_lib1.so
include $(PREBUILT_SHARED_LIBRARY)
#get support_lib2
include $(CLEAR_VARS)
LOCAL_MODULE := support_lib2
LOCAL_SRC_FILES := $(LOCAL_PATH)/lib/support_lib2.so
include $(PREBUILT_SHARED_LIBRARY)
#build native lib
include $(CLEAR_VARS)
LOCAL_MODULE := native_lib
LOCAL_SRC_FILES := native_lib.cpp
LOCAL_LDLIBS := -L$(SYSROOT)/../usr/lib -llog
LOCAL_SHARED_LIBRARIES := support_lib1 support_lib2
include $(BUILD_SHARED_LIBRARY)
Build... fails! The build complains about missing symbols now.
Edit: Attempt 6: Flatten everything
So I went back to the prebuilts documentation in the NDK. It says:
Each prebuilt library must be declared as a single independent module to the build system. Here is a trivial example where we assume that the file "libfoo.so" is located in the same directory than the Android.mk below:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := foo-prebuilt
LOCAL_SRC_FILES := libfoo.so
include $(PREBUILT_SHARED_LIBRARY)
Notice that, to declare such a module, you really only need the following:
Give the module a name (here 'foo-prebuilt'). This does not need to correspond to the name of the prebuilt library itself.
Assign to LOCAL_SRC_FILES the path to the prebuilt library you are providing. As usual, the path is relative to your LOCAL_PATH.
Include PREBUILT_SHARED_LIBRARY, instead of BUILD_SHARED_LIBRARY, if you are providing a shared, library. For static ones, use PREBUILT_STATIC_LIBRARY.
A prebuilt module does not build anything. However, a copy of your prebuilt shared library will be copied into $PROJECT/obj/local, and another will be copied and stripped into $PROJECT/libs/.
So let's try flattening everything out to match the trivial example. I copied my libraries out of their cozy /lib folder and put them in the jni root. I then did this:
LOCAL_PATH := $(call my-dir)
#get support_lib1
include $(CLEAR_VARS)
LOCAL_MODULE := support_lib1
LOCAL_SRC_FILES := support_lib1.so
include $(PREBUILT_SHARED_LIBRARY)
#get support_lib2
include $(CLEAR_VARS)
LOCAL_MODULE := support_lib2
LOCAL_SRC_FILES := support_lib2.so
include $(PREBUILT_SHARED_LIBRARY)
#build native lib
include $(CLEAR_VARS)
LOCAL_MODULE := native_lib
LOCAL_SRC_FILES := native_lib.cpp
LOCAL_LDLIBS := -L$(SYSROOT)/../usr/lib -llog
LOCAL_SHARED_LIBRARIES := support_lib1 support_lib2
include $(BUILD_SHARED_LIBRARY)
and... same error. Moreover I'm most definitely NOT seeing library files getting copied to $PROJECT/obj/local.
sooooo.... now what?
Your problem is with the naming convention. NDK and Android insist on the shared library names to always begin with lib. Otherwise, the libraries will not be linked properly, and not copied to the libs/armeabi folder properly, and not installed on the device (copied to /data/data/package/lib directory properly.
If you rename support_lib1.so to libsupport_1.so and support_lib2.so to libsupport_2.so, and put these two files in jni/lib directory, then your Attempt #5 will work with minor change:
LOCAL_PATH := $(call my-dir)
#get support_lib1
include $(CLEAR_VARS)
LOCAL_MODULE := support_lib1
LOCAL_SRC_FILES := lib/libsupport_1.so
include $(PREBUILT_SHARED_LIBRARY)
#get support_lib2
include $(CLEAR_VARS)
LOCAL_MODULE := support_lib2
LOCAL_SRC_FILES := lib/libsupport_2.so
include $(PREBUILT_SHARED_LIBRARY)
#build native lib
include $(CLEAR_VARS)
LOCAL_MODULE := native_lib
LOCAL_SRC_FILES := native_lib.cpp
LOCAL_LDLIBS := -L$(SYSROOT)/../usr/lib -llog
LOCAL_SHARED_LIBRARIES := support_lib1 support_lib2
include $(BUILD_SHARED_LIBRARY)
BTW, I don't think you need this -L$(SYSROOT)/../usr/lib.
PS Don't forget to update the Java side, too:
static {
System.loadLibrary("support_lib1");
System.loadLibrary("support_lib2");
System.loadLibrary("native_lib");
}
Not sure if this is exactly where you are at, but here's what I know about these sorts of things.
Make each prebuilt libary its own separate Makefile. Multiple targets in Android.mk tends to get wonky. Sad.
Include each make file using $(call import-add-path) and $(call import-module)
Export as much as you can from the prebuilt's make files, using the LOCAL_EXPORT_ family of variables.
Prebuilt Shared Library Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := my_module_name
MY_LIBRARY_NAME := shared_library_name
### export include path
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/include
### path to library
LOCAL_SRC_FILES := libs/$(TARGET_ARCH_ABI)/lib$(MY_LIBRARY_NAME).so
### export dependency on the library
LOCAL_EXPORT_LDLIBS := -L$(LOCAL_PATH)/libs/$(TARGET_ARCH_ABI)/
LOCAL_EXPORT_LDLIBS += -l$(MY_LIBRARY_NAME)
include $(PREBUILT_SHARED_LIBRARY)
This is assuming that the prebuilt libaries live in a dir structure like this
+ SharedProjectFolderName
+--- Android.mk
+--- include/
+-+- libs/$(TARGET_ARCH_ABI)/
|- libshared_library_name.so
If you are not building for multiple ABI, I guess you can leave that bit out
The Project's Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := my_jni_module
## source files here, etc...
### define dependency on the other library
LOCAL_SHARED_LIBRARIES := my_module_name
include $(BUILD_SHARED_LIBRARY)
$(call import-add-path,$(LOCAL_PATH)/path/to/myLibraries/)
$(call import-module,SharedProjectFolderName)
$(call import-module,AnotherSharedProject)
I recommend you put all shared libraries in one folder. When you say $(call import-module,SharedProjectFolderName) it looks for a folder containing an Android.mk along the search path you told it (import-add-path)
By the way, you probably shouldn't specify LOCAL_LDLIBS := -L$(SYSROOT)/../usr/lib. It should be finding the proper libs from NDK by itself. Adding more linker paths will probably confuse it. The proper way is to export the linker paths as flags from the sub-modules.
ALSO, you can use ndk-build V=1 to get a ton of info on why it can't find paths, etc
The -L option gives the linker a directory path in which to look for libraries. The -l option gives the linker a library file name to link in. Library file names must begin with "lib". Your libraries should be named libsupport_lib1.so and libsupport_lib2.so. If you do that, then this is probably what you should do (replacing attempt #1):
LOCAL_LDLIBS := -L$(SYSROOT)/../usr/lib -llog -lsupport_lib1 -lsupport_lib2
LOCAL_LDLIBS += -L$(LOCAL_PATH)/lib
The linker will prefix the library name you specify using -l with "lib" and suffix it with ".so". (Why do you have -L$(SYSROOT)/../usr/lib?)
I believe that attempts #1 and #2 failed because you did not link your libraries into your executable - they are not mentioned in a -l option. By the way, you can verify this yourself. Unzip the .apk file and look in the lib directory and subdirectories. Are your .so files in there?
Looking at the error:
but then... dlopen failed: Could not locate symbol func_that_exists_in_libsupport_lib.so referenced by libnative_lib.so
Can you supply the entire message? dlopen() loads and links libraries into the running process.
Now I am making an application using on MacOSx with Tessaract and Android NDK.
I use Eclipse as an IDE to develop the program.
I have two questions to ask:
1). I set up tessaract using the most famous example "tess-two" and modified a bit to fit with my existing code. I copied folder "com_googlecode_leptonica_android" and "com_googlecode_tessaract_android" to /jni folder. Then edit Android.mk for setting path to those library folder. Everything works fine! Except one thing.. Every time that I build the project, I need to build both "leptonica" and "tessaract" library again and again..in order to get libtess and liblept.. It takes soooo long. How can I edit android makefile (Android.mk) not to build those libraries.. just compile my code only... thats all.. Here is my Android.mk
LOCAL_PATH := $(call my-dir)
MY_PATH := $(LOCAL_PATH)
TESSERACT_PATH := $(call my-dir)/com_googlecode_tesseract_android
LEPTONICA_PATH := $(call my-dir)/com_googlecode_leptonica_android
include $(call all-subdir-makefiles)
include $(CLEAR_VARS)
include /Applications/eclipse-android/OpenCV-2.4.3-android-sdk/sdk/native/jni/OpenCV.mk
LOCAL_PATH := $(MY_PATH)
LOCAL_MODULE := my_project
LOCAL_SRC_FILES := cppmain.cpp
LOCAL_LDLIBS += -llog -ldl
include $(BUILD_SHARED_LIBRARY)
)
2). I found a lot of examples about using tessaract with Android. However most of them using tessaract with Java (call via JNI) and call JNI from java code (Java -> Tessaract C++ JNI -> Tessaract C++). I cannot find any example that call tessaract from c++ NDK (Java -> my JNI -> my C++ -> Tessract C++). The reason that I want to call tessaract directly from c++ is portability.
Use PREBUILT_STATIC_LIBRARY, something like
LOCAL_PATH = $(MY_PATH)/com_googlecode_tesseract_android/lib
include $(CLEAR_VARS)
LOCAL_MODULE := tesseract
LOCAL_SRC_FILES := libtesseract.a
include $(PREBUILT_STATIC_LIBRARY)
LOCAL_PATH = $(MY_PATH)/com_googlecode_leptonica_android/lib
include $(CLEAR_VARS)
LOCAL_MODULE := leptonica
LOCAL_SRC_FILES := libleptonica.a
include $(PREBUILT_STATIC_LIBRARY)
LOCAL_PATH := $(MY_PATH)
LOCAL_MODULE := my_project
LOCAL_SRC_FILES := cppmain.cpp
LOCAL_LDLIBS += -llog -ldl
LOCAL_LDFLAGS += -ltesseract -lleptonica
include $(BUILD_SHARED_LIBRARY)
The tesseract project does not contain prebuilt libraries, but if you follow the official instructions, these libraries will be built. Using PREBUILT_STATIC_LIBRARY only helps you to avoid unnecessary rebuilds of these libraries all the time. Same approach is recommended for libjpeg and libpng, as long as you don't change these libraries yourself.
Here I used this Android.mk file in jni/ folder.
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
# Here we give our module name and source file(s)
LOCAL_MODULE := offlineDownload
LOCAL_SRC_FILES := offline_download.c
LOCAL_SHARED_LIBRARIES :=../lib/libpackext.so.1.0
LOCAL_LDLIBS := -L$(SYSROOT)/usr/lib -llog
include $(BUILD_SHARED_LIBRARY)
And make one lib folder in project directory and put my prebuilt .so library and make one Android.mk file which contains following
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := packext
LOCAL_SRC_FILES := libpackext.so.1.0
LOCAL_C_INCLUDES := $(LOCAL_PATH)/../include
include $(PREBUILT_SHARED_LIBRARY)
And when i use ndk-build -B command than i got undefined reference to packageExtraction. Here I use my prebuilt library functions means I can't link my prebuilt shared library to my offlinedownload library.
So any body please help me to solved out this issue.
Here is a complete Android.mk file for using a 3rd party shared library.
The library (libffmpeg.so) is placed in the jni folder.
Its "LOCAL_EXPORT_C_INCLUDES" specifies where the header files are kept for the library.
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := ffmpeg
LOCAL_SRC_FILES := libffmpeg.so
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/../../ffmpeg/libs/arm-linux-androideabi4.7_1/include
include $(PREBUILT_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := ffmpegandroid
LOCAL_SRC_FILES := ffmpegandroid.c
LOCAL_SHARED_LIBRARIES := ffmpeg
include $(BUILD_SHARED_LIBRARY)
If you wanted to support multiple architectures then you could specify:
APP_ABI := armeabi armeabi-v7a x86 mips
in your jni/Application.mk and change the LOCAL_SRC_FILES to something like:
LOCAL_SRC_FILES := $(TARGET_ARCH_ABI)/libffmpeg.so
and place a libffmpeg.so at jni/armeabi/libffmpeg.so, jni/armeabi-v7a/libffmpeg.so etc ..
Android NDK official hello-libs CMake example
https://github.com/googlesamples/android-ndk/tree/840858984e1bb8a7fab37c1b7c571efbe7d6eb75/hello-libs
Just worked for me on Ubuntu 17.10 host, Android Studio 3, Android SDK 26, NDK 15.2. so I strongly recommend that you base your project on it.
The shared library is called libgperf, the key code parts are:
hello-libs/app/src/main/cpp/CMakeLists.txt:
// -L
add_library(lib_gperf SHARED IMPORTED)
set_target_properties(lib_gperf PROPERTIES IMPORTED_LOCATION
${distribution_DIR}/gperf/lib/${ANDROID_ABI}/libgperf.so)
// -I
target_include_directories(hello-libs PRIVATE
${distribution_DIR}/gperf/include)
// -lgperf
target_link_libraries(hello-libs
lib_gperf)
on C++ code, use: #include <gperf.h>
header location: hello-libs/distribution/gperf/include/gperf.h
lib location: distribution/gperf/lib/arm64-v8a/libgperf.so
app/build.gradle:
android {
sourceSets {
main {
// let gradle pack the shared library into apk
jniLibs.srcDirs = ['../distribution/gperf/lib']
Then, if you look under /data/app on the device, libgperf.so will be there as well.
If you only support some architectures, see: Gradle Build NDK target only ARM
The example git tracks the prebuilt shared libraries, but it also contains the build system to actually build them as well: https://github.com/googlesamples/android-ndk/tree/840858984e1bb8a7fab37c1b7c571efbe7d6eb75/hello-libs/gen-libs
You have to do either one of the following:
Cut and paste everything except LOCAL_PATH := $(call my-dir) from your second Android.mk into your first.
Put the following in the end of your first Android.mk:
$(call import-module,packext)
Also make sure that you set your NDK_MODULE_PATH environment variable to a path where the Android.mk-file defining the module packext can be found.
You also have to change the LOCAL_SHARED_LIBRARIES in the same way mgiza said in the first answer. I suppose the packageExtraction that you got undefined reference to is in your prebuilt library so unless you have other linking problems this should solve the issue.
Have a look at the ndk documentation for prebuilts:
android-ndk/docs/PREBUILTS.html
You have to change
LOCAL_SHARED_LIBRARIES :=../lib/libpackext.so.1.0
to
LOCAL_SHARED_LIBRARIES := packext
Be sure that your folder containing the Android.mk for the packext module is named packext and can be found in in your NDK_MODULE_PATH.