Develop Reference

Symbol from C file is not being added even though the MakeFile includes its object file

I'm trying to build libavformat with this MAKEFILE. Although the makefile includes avio.o file in its build instruction but it doesn't add any symbol for the functions that are declared on the header file url.h. Source folder which includes the avio.c, avio.h and url.h files can be found HERE.
The nm command for avio.o returns
nm: avio.o: File format not recognized
file command on avio.o shows the following output
avio.o: LLVM IR bitcode
I have checked the nm command on the generated libavformat.so and did not find any symbols for the functions declared on the url.h file
I have been stuck on this for two days. Could not figure out how to solve this problem!
Calling the ff_check_interrupt method and results in
undefined reference to 'ff_check_interrupt'
Configurations and flags.
FFmpeg Configuration File: Config.h
FFmpeg Root MakeFile: Root MakeFile
CC, CXX, CFLAGS, LDFLAGS: FLAGS

First off, a function declared by url.h should be defined in url.c, not in avio.c.
Second the only use of the ff_check_interrupt in avoi.c is within a static inline function, so indeed the toolchain is likely optimizing this symbol away.
I think what's occurring for you is that the toolchain making the decision that this is only used in this compilation unit.
Moving the definition of ff_check_interrupt to 'url.c' should resolve the issue. This is a library though, so out of your control.
However, this doesn't answer why thousands of users on Github have this same library in their code. I'd suggest comparing your Makefile against those (e.g. first search return is this one.

Cannot compile tensorflowlite C++ API on android

I think the problem is I'm not including the shared library in the right away, but I'm not sure.
The error I get is
error: undefined reference to 'tflite::InterpreterBuilder::operator()(std::__ndk1::unique_ptr<tflite::Interpreter, std::__ndk1::default_delete<tflite::Interpreter> >*)
Which points at the last line of:
std::unique_ptr<tflite::FlatBufferModel> model = tflite::FlatBufferModel::BuildFromFile(casemodel_path.c_str());
tflite::ops::builtin::BuiltinOpResolver resolver;
tflite::InterpreterBuilder builder(*model.get(), resolver);
std::unique_ptr<tflite::Interpreter> interpreter;
builder(&interpreter);
I took this from here, as the documentation seems to be out of date.
I compiled tensorflow from source using NDK16b. I followed this to compile it.
The relevant portion of my cmake file looks like:
[...]
# Flatbuffer
set(FLATB_DIR <path-to>/git/flatbuffers)
include_directories(${FLATB_DIR}/include)
include_directories(${FLATB_DIR}/grpc)
file(GLOB flatb_src "${FLATB_DIR}/src/*.cpp")
add_library(flatbuffer ${flatb_src})
add_library(libtensorflowlite SHARED IMPORTED)
set_target_properties(libtensorflowlite PROPERTIES IMPORTED_LOCATION
<path-to>/app/src/main/jniLibs/armeabi-v7a/libtensorflowlite.so)
include_directories(<path-to>/git/tensorflow-android)
[...]
target_link_libraries(flatbuffer libtensorflowlite <tons-of-other-libraries>)
As I mentioned already I think the problem is I'm not including the shared library in the right way. All I've done is created the folder(s) jniLibs/armeabi-v7a/ under src/main, where I put the libtensorflowlite.so. Googling around that seems to be one way to do it? I've tried some other ways (with sourceSets and implementation fileTree but nothing worked).
I've got some other precompiled libraries that I'm using just fine, but they are static (in target_link_libraries I point directly to their path). Is it a problem mixing static/shared libraries like that?
edit: Following this, I also tried using ndk15c and editing ANDROID_NDK_API_LEVEL, but that did not help.

Is it necessary to follow same package name as it was for so file while using .so file in new Android project

I had created one project using native c++ support. In this project I am passing int value from activity to c++ code and native code returns whether this is prime number or not. This works perfectly, Now I want to create .so file to use in another project. I had google many post but not got answer how to get different .so file for all devices. So I had rename .apk file to .zip and extract it. After that I got one .so file.
Now I want to use this .so file in another project. therefore I had created new project with different name but package name is same. I had created one directory inside src/main and named it as jniLib in this lib I had copied my .so file directory. In my MainActivity I load so file as static {
System.loadLibrary("native-lib");
}
and call my native method private native String isPrimeNumber(int number);. Here everything is perfect. Now I can get result without having actual c++ code.
Now Again I created new project and follow above steps which was followed by creating second project, but difference is that now I had changed package name of my application. when I run application my application got crashed with error as
FATAL EXCEPTION: main
Process: com.app.androidkt.differentpackage, PID: 16970
java.lang.UnsatisfiedLinkError: No implementation found for java.lang.String com.app.androidkt.differentpackage.MainActivity.isPrimeNumber(int) (tried Java_com_app_androidkt_differentpackage_MainActivity_isPrimeNumber and Java_com_app_androidkt_differentpackage_MainActivity_isPrimeNumber__I)
at com.app.androidkt.differentpackage.MainActivity.isPrimeNumber(Native Method)
at com.app.androidkt.differentpackage.MainActivity.access$000(MainActivity.java:10)
at com.app.androidkt.differentpackage.MainActivity$1.onClick(MainActivity.java:38)
at android.view.View.performClick(View.java:5268)
at android.view.View$PerformClick.run(View.java:21550)
at android.os.Handler.handleCallback(Handler.java:822)
at android.os.Handler.dispatchMessage(Handler.java:104)
at android.os.Looper.loop(Looper.java:207)
at android.app.ActivityThread.main(ActivityThread.java:5811)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:681)
So my question are - 1) Is it necessary to use same package name to use .so file in our application as that of .so file.
2) How I can get different .so file directory - currently for time being I had extracted it from apk.
3) To use of .so file is to hide the native code only or there is any other purpose also there?
Thanks in advance.

Your application package name may be anything, but the Java class that consumes native methods implemented in libnative-lib.so must be exactly the same as intended by the authors of this libnative-lib.so file.
The easiest workaround for your setup is to move your com.app.androidkt.differentpackage.MainActivity class to the com.app.androidkt.samplendk package. Android Studio will help you with this refactoring. Note that now you must declare the full path for MainActivity in your AndroidManifest.xml.
Alternatively, you can create a small com.app.androidkt.samplendk.MainActivity
class:
package com.app.androidkt.oldpackage;
public class MainActivity {
static {
System.loadLibrary("native-lib");
}
public native String isPrimeNumber(int number);
}
and add few lines to your MainActivity.java:
package com.app.androidkt.differentpackage;
public class MainActivity extends AppCompatActivity {
private com.app.androidkt.oldpackage.MainActivity pmSolver;
private String isPrimeNumber(int number) {
return pmSolver.isPrimeNumber(number);
}
…
}
If you don't know the exact package name used for this libnative-lib.so, you can find it by parsing its ELF headers: you will see an exported function named similar to Java_com_app_androidkt_ samplendk_MainActivity_isPrimeNumber.
Nitpicker's corner: it is possible to build a JNI library that will hide its designated class name(s), but it is hard to reliably prevent reverse engineering these names; it is also possible to build a JNI library that will seamlessly connect to different packages.

1) Is it necessary to use same package name to use .so file in our
application as that of .so file
No, you can use any package name you desire
2) How I can get different .so file directory - currently for time
being I had extracted it from apk
Copy all .so files to your new project folder: src/main/jniLibs/armeabi
3) To use of .so file is to hide the native code only or there is any
other purpose also there?
.so file is a library. Hence the purpose is to be convenient in reusing implemented features in multiple projects.

arm-linux-androideabi-g++ can not find header cstdarg

Trying to cross-compile an android app from linux using arm-linux-androideabi-g++, I get an error that the header file cstdarg can not be found.
common.h:27:19: fatal error: cstdarg: No such file or directory
compilation terminated.
If I look into the /usr/arm-linux-androideabi/include/, the header is not there but other c++ header files are present. How can I fix this problem ?

<cstdarg> is not a system header, in sense that it comes from C++ standard library. Looks like you've missed to add C++ headers to command line. They are placed under $ANDROID_NDK/sources/cxx-stl/. Of course ensure that you're using header for appropriate library implementation.
Also you may need to include complier-specific C-headers (at least <stdarg.h> as it is used by <cstdarg>).
Some of standard headers are compiler-specific because they use some compiler-specific extensions, intrinsics, so on. <stdarg.h> is one of them. Because of their nature there is no much sense to put them to generic sysroot include directory. Look under $ANDROID_NDK/toolchains/ directory.

Android : merging static libraries into single one

I use Android NDK r8 to generate multiple static libraries with include $(BUILD_STATIC_LIBRARY) and I successfully get : lib1.a, lib2.a, lib3.a, etc.
Now I would like to merge these static libraries into single one.
I try do it with ar.exe from Android NDK :
android-ndk-r8\toolchains\arm-linux-androideabi-4.4.3\prebuilt\windows\arm-linux-androideabi\bin\ar.exe r libALL.a lib1.a lib2.a lib3.a
But when I use libAll.a into Android NDK makefile, it fails saying there is no index.
How can I add this index ?
Other question :
When I display contents of archive libAll.a, I see lib1.a, lib2.a, lib3.a instead of .o symbols from these libraries.
How can I change that (= extract .o from static libraries to merge it in libAll.a) ?
Thanks

ar is simply an archiving tool like zip. It takes the given input files and produces an .aarchive. If you want to include all .ofiles in a single archive, you have to specify each individual file. I don't know how to do this on WIndows, but on Linux you can use somthing like ar rs $(find . -name *.o).