Missing: How to configure Android project for GNUstep use about tools-android

[mehlkelm]

The good news: I got it working!
The bad news: I still have to find out how…
Will analyze a bit more and then post step by step how it works reproducibly for me.

[triplef]

Thanks for your feedback! One step that’s missing is setting the NDK path in the app settings > SDK Location. If you’re on a Mac you should set it to the custom NDK that is installed by the toolchain in:
~/Library/Android/android-ndk-r20-clang-r353983c1

Can you check if that helps with the linker error?

[mehlkelm]

I can't find "App settings".
Do you mean "Android NDK location" in File > Project Structure… > SDK Location?
Setting it there doesn't help.

[triplef]

Yeah that’s the right setting.

I found that for me, if I understand it correctly _ZNSt6__ndk111__call_onceERVmPvPFvS2_E is defined in (not referenced by) libgnustep-base.so. Can you run the following and see if you get the same result?

$ nm ~/Library/Android/GNUstep/x86/lib/libgnustep-base.so | grep _ZNSt6__ndk111__call_onceERVmPvPFvS2_E
00758380 T _ZNSt6__ndk111__call_onceERVmPvPFvS2_E

[triplef]

Also, does the hello-objectivec example work for you?

[mehlkelm]

The hello-objectivec example works perfectly, and that without any "Android NDK location" setting!

My result:

$ nm ~/Library/Android/GNUstep/x86/lib/libgnustep-base.so | grep _ZNSt6__ndk111__call_onceERVmPvPFvS2_E
         U _ZNSt6__ndk111__call_onceERVmPvPFvS2_E

[triplef]

Hmm interesting. Looks like your libgnustep-base.so (unlike mine) doesn’t define the function. Could you attach your (zipped) ~/Library/Android/GNUstep/build.log?

That being said, question is why the example still works... I noticed in step 6 above you wrote that you call System.loadLibrary() in an init method. Can you try putting it in a static initializer as in the example?

static {
    System.loadLibrary("native-lib");
}

[mehlkelm]

I'm on Kotlin, so static won't work here. I tried to do it according to the "Native C++" Android Studio template (like below) which also doesn't work:

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {

        initializeGNUstep(this);

        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val navView: BottomNavigationView = findViewById(R.id.nav_view)

        val navController = findNavController(R.id.nav_host_fragment)
        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        val appBarConfiguration = AppBarConfiguration(
            setOf(
                R.id.navigation_home, R.id.navigation_dashboard, R.id.navigation_notifications, R.id.navigation_temperatures
            )
        )
        setupActionBarWithNavController(navController, appBarConfiguration)
        navView.setupWithNavController(navController)
    }

    external fun initializeGNUstep(context: Context?)

    companion object {

        // Used to load the 'native-lib' library on application startup.
        init {
            System.loadLibrary("native-lib")
        }
    }
}

[triplef]

I’ve never used Kotlin – could you try it with a Java project just to narrow it down further?

[mehlkelm]

Kotlin can't be the issue:
a) I get the same problem with a brand new Java Project (no Kotlin, no AndroidX)
b) I can convert your hello-objectivec and its MainActivity to Kotlin while still being able to load native-lib

[triplef]

I see. I have no idea why the example project works and a new project doesn’t, and I cannot reproduce the issue. But the core issue seems to be that your GNUstep library file doesn’t define some symbols that mine does. If you could send me your build.log I can see if I can spot some differences in your build process that might be specific to your machine/setup.

[mehlkelm]

This pull request would document what worked for me: #8.

[triplef]

Thanks for the PR! Can you tell what the missing bit was to get it working in the end?

[mehlkelm]

In the end I tried so much stuff that I'm not sure what exactly worked but I suspect step 6: "Link to C++" was missing.

[triplef]

I fixed the underlying issue causing the linker error with _ZNSt6__ndk111__call_onceERVmPvPFvS2_E: the toolchain libraries were not correctly linking against the shared C++ runtime library.

Please try rebuilding the toolchain with the latest changes, and also update your Gradle setup to use the shared C++ runtime library like this:
gnustep/android-examples@d3f5aba

Regarding instructions to integrate this in your own project I hope to be able to create a standalone CMake toolchain file that can simply be included in Android Studio (that’s why I haven’t merged your PR yet).