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MSI SDR device sample code does not compile

I am trying to interface with an MSI SDR dongle, using an android app
This device is a clone of the SDRPlay SDR device, and is compatible with it's software and drivers
I am trying to interface with this using an OTG cable and android phone
The android drivers for this can be downloaded from here https://www.sdrplay.com/downloads/
It is in the Android tab under the API/HW – V2.11 (15TH NOV 2017) link (https://www.sdrplay.com/anddl.php)
A possible sample code for this driver can be found here: https://www.sdrplay.com/docs/AndroidIntegrationNote.pdf
Before making the full android program it says the library (libmir_sdr_api.a) should be built into an .so library file using ndk-build
I currently have Android's hello-jni sample project from here: https://github.com/android/ndk-samples/tree/android-mk/hello-jni
I have replaced the jni folder using the Android.mk file, libmir_sdr_api.a, mir_sdr.h, initialization-jni.cpp, demod-jni.cpp and demod-jni.h files mentioned in section 3 of the AndroidIntegrationNote.pdf file I linked above
When I execute ndk-build from the hello-jni project folder, I get he following error:
Android NDK: Found platform level in ./default.properties. Setting APP_PLATFORM to android-25.
Android NDK: android-25 is an alias for android-24. Adjusting APP_PLATFORM to match.
[arm64-v8a] Gdbserver : [aarch64-linux-android] libs/arm64-v8a/gdbserver
[arm64-v8a] Gdbsetup : libs/arm64-v8a/gdb.setup
[x86_64] Gdbserver : [x86_64-linux-android] libs/x86_64/gdbserver
[x86_64] Gdbsetup : libs/x86_64/gdb.setup
[armeabi-v7a] Gdbserver : [arm-linux-androideabi] libs/armeabi-v7a/gdbserver
[armeabi-v7a] Gdbsetup : libs/armeabi-v7a/gdb.setup
[x86] Gdbserver : [i686-linux-android] libs/x86/gdbserver
[x86] Gdbsetup : libs/x86/gdb.setup
make: *** No rule to make target 'jni/initialisation-jni.cpp', needed by 'obj/local/arm64-v8a/objs-debug/mirics-jni/initialisation-jni.o'. Stop.
I am used to compiling NDK code suing Android Studio and cmake so I am not sure what is going on here. I have not been able to link the .a file through cmake either so I thought of giving the driver manufacturer's sample code a try, but it not working either. Is the Android.mk file in pdf file linked earlier incomplete, or am I not building it correctly? These are the contents of the Android.mk file:
# $(call my-dir) returns the local directory which is the jni directory
LOCAL_PATH := $(call my-dir)
# libmir_sdr_api.a – this section creates a version of the Mirics API to be used below
include $(CLEAR_VARS)
LOCAL_MODULE := mir_sdr_api-prebuilt
LOCAL_SRC_FILES := libmir_sdr_api.a
LOCAL_EXPORT_C_INCLUDES := $(call my-dir)
include $(PREBUILT_STATIC_LIBRARY)
include $(CLEAR_VARS)
# mirics-jni – this section uses the jni C++ source code to build the dynamic library
LOCAL_MODULE := mirics-jni
LOCAL_SRC_FILES := initialisation-jni.cpp demod-jni.cpp
LOCAL_C_INCLUDES := $(call my-dir)
LOCAL_LDLIBS := -L$(SYSROOT)/usr/lib
LOCAL_STATIC_LIBRARIES := mir_sdr_api-prebuilt
include $(BUILD_SHARED_LIBRARY)

Regarding missing jni/initialisation-jni.cpp, you probably have the file jni/initialization-jni.cpp instead.
Also, unfortunately, the document is wrong. You can only use $(call my-dir) easily at the top of the file. Luckily, Android NDK adds the jni directory to includes path for you. Still, to be on the safe side, better write:
# $(call my-dir) returns the local directory which is the jni directory
LOCAL_PATH := $(call my-dir)
# libmir_sdr_api.a – this section creates a version of the Mirics API to be used below
include $(CLEAR_VARS)
LOCAL_MODULE := mir_sdr_api-prebuilt
LOCAL_SRC_FILES := libmir_sdr_api.a
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)
include $(PREBUILT_STATIC_LIBRARY)
include $(CLEAR_VARS)
# mirics-jni – this section uses the jni C++ source code to build the dynamic library
LOCAL_MODULE := mirics-jni
LOCAL_SRC_FILES := initialization-jni.cpp demod-jni.cpp
LOCAL_C_INCLUDES := $(LOCAL_PATH)
LOCAL_LDLIBS := -L$(SYSROOT)/usr/lib
LOCAL_STATIC_LIBRARIES := mir_sdr_api-prebuilt
include $(BUILD_SHARED_LIBRARY)
Finally, pay attention to your build process. You only have one kind of the libmir_sdr_api.a static library, it's built for a 32-bit ARM CPU. Therefore you cannot build your libmirics-jni.so for other architectures. Add
APP_ABIS = armeabi-v7a
to your Application.mk file, or specify
abifilters = armeabi-v7a
in your build.gradle, if you build your library in Android Studio.

Android NDK: Linking x86 shared library

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)

use libcryto.so and libssl.so in an android project?

I'm beginer to Android NDK. I want to build a RSA example base on openssl libary.
First, I built libssl.so and libcrypto.so librairies with ndk-build in the guardianproject.
Next, I create a new sample project to integrate libary (libss.so & lybcryto.so). I follow the same in this post
My App directory
TrialApp
|
|-->Activity.java (includes System.LoadLibrary calls)
|
|-->jni
|-->TestJNI2.cpp
|
|-->Android.mk
|
|-->includes
| |
| |-->openssl (dir containing *.h files)
|
|-->precompiled
|-->libssl.so
|-->libcrypto.so
My android.mk:
LOCAL_PATH := $(call my-dir)
# Prebuilt libssl
include $(CLEAR_VARS)
LOCAL_MODULE := ssl
LOCAL_SRC_FILES := precompiled/libssl.so
include $(PREBUILT_SHARED_LIBRARY)
# Prebuilt libcrypto
include $(CLEAR_VARS)
LOCAL_MODULE := crypto
LOCAL_SRC_FILES := precompiled/libcrypto.so
include $(PREBUILT_SHARED_LIBRARY)
include $(CLEAR_VARS)
c_includes := $(LOCAL_PATH)
cf_includes := includes/openssl
cf_includes := $(addprefix -Ijni/,$(cf_includes))
export_c_includes := $(c_includes)
LOCAL_MODULE := security
LOCAL_SRC_FILES := TestJNI2.cpp
LOCAL_CFLAGS += $(cf_includes)
LOCAL_EXPORT_C_INCLUDES := $(export_c_includes)
LOCAL_LDLIBS := -llog
LOCAL_LDLIBS += $(LOCAL_PATH)/precompiled/libssl.so
LOCAL_LDLIBS += $(LOCAL_PATH)/precompiled/libcrypto.so
include $(BUILD_SHARED_LIBRARY)
TestJNI2.cpp
/* OpenSSL headers */
#include "openssl/bio.h"
#include "openssl/ssl.h"
#include "openssl/err.h"
/* Initializing OpenSSL */
void init_openssl(void){
SSL_load_error_strings();
ERR_load_BIO_strings();
OpenSSL_add_all_algorithms();
}
Then when i build with ndk-build always have problems like this
/data/workspace/TestJNI2/jni/TestJNI2.cpp:3:25: error: openssl/bio.h: No such file or directory
/data/workspace/TestJNI2/jni/TestJNI2.cpp:4:25: error: openssl/ssl.h: No such file or directory
/data/workspace/TestJNI2/jni/TestJNI2.cpp:5:25: error: openssl/err.h: No such file or directory
/data/workspace/TestJNI2/jni/TestJNI2.cpp: In function 'void init_openssl()':
/data/workspace/TestJNI2/jni/TestJNI2.cpp:10: error: 'SSL_load_error_strings' was not declared in this scope
/data/workspace/TestJNI2/jni/TestJNI2.cpp:11: error: 'ERR_load_BIO_strings' was not declared in this scope
/data/workspace/TestJNI2/jni/TestJNI2.cpp:12: error: 'OpenSSL_add_all_algorithms' was not declared in this scope
make: *** [/data/workspace/TestJNI2/obj/local/armeabi/objs/security/TestJNI2.o] Error 1
Can anyone help me? Or how to build an example RSA algorthim base on openssl lib?

You should build static libraries for libssl and libcrypto in your script. If you can't, rename these libraries (you can do this after build, while copying to your precompiled directory). The reason is that the system comes with its own (probably different) version of these shared libraries, and the loader will use /system/lib/libssl.so and /system/lib/libcrypto.so instead of your private copies.
Regarding the Android.mk file, I slightly cleaned it up for you (note that I did not change the names of prebuilt LOCAL_MODULEs, but changed the name of LOCAL_MODULE you finally build, because security is, well, too generic and could also happen to match a system library on some device):
LOCAL_PATH := $(call my-dir)
# Prebuilt libssl
include $(CLEAR_VARS)
LOCAL_MODULE := ssl
LOCAL_SRC_FILES := precompiled/libPrivateSsl.so
include $(PREBUILT_SHARED_LIBRARY)
# Prebuilt libcrypto
include $(CLEAR_VARS)
LOCAL_MODULE := crypto
LOCAL_SRC_FILES := precompiled/libPrivateCrypto.so
include $(PREBUILT_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := PrivateSecurity
LOCAL_C_INCLUDES := includes
LOCAL_SRC_FILES := TestJNI2.cpp
LOCAL_LDLIBS := -llog
LOCAL_SHARED_LIBRARIES := ssl crypto
include $(BUILD_SHARED_LIBRARY)
Don't forget that your Java should load the dependencies first:
{
System.loadLibrary("PrivateSsl");
System.loadLibrary("PrivateCrypto");
System.loadLibrary("PrivateSecurity");
}

I'm beginer to Android NDK. I want to build a RSA example base on openssl libary.
You can, but you have to be careful. Here's the reason Alex told you to use static libraries for libssl and libcrypto in your script.
The master Android process is zygote. Its like init in Linux. Zygote loads OpenSSL when its start, and it loads version 0.9.8. If you link against OpenSSL 1.0.1, then you will get mysterious runtime crashes. The crashes are due to the Android loader using the 0.9.8 version of the library (already mapped from Zygote), and not your version of OpenSSL.
You can use a shared object, but your shared object must be a wrapper around the static version of libssl and libcrypto.
If you are not using Android's build system, then you can find additional instructions for building purely from the command line at OpenSSL's wiki. The wiki page includes setting the envrionment and cross compiling. See FIPS Library and Android.
Another thing to watch out for: be sure to build with -mfloat-abi=softfp. The stock OpenSSL misses that when cross compiling. You need it to ensure floats are passed on the stack, and not through floating point registers. Otherwise, all your floats will mysteriously have 0.0f value (like the floats used to estimate entropy in RAND_add).

Android NDK/JNI: Building a shared library that depends on other shared libraries

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.

How to link a prebuilt shared Library to an Android NDK project?

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.