Unity: DllNotFoundException (Unity 2018.2; Android)

Question

I have an Android native library (C++ code base) called:

libserverapp.so

And I cannot get the Android build to find it:

"DllNotFoundException: serverapp"

I am using an internal build system, but when I parse the output of the build process, I can see many calls of the form:

android-ndk/toolchains/arm-linux-androideabi-4.6/prebuilt/windows/bin/arm-linux-androideabi-g++.exe -march=armv7-a

After building my Android app, I inspect the resulting APK (renaming to .zip and extracting), and can see my library file here:

lib/armeabi-v7a/libserverapp.so

I can confirm that "ARMv7" is the target architecture in the Android Player settings, and I access the library, in C#, via:

[DllImport("serverapp", CallingConvention = CallingConvention.Cdecl)]
private static extern void run_sim(StringBuilder matchInput, StringBuilder results, int randomSeed);

I have built a Windows DLL of the C++ code, to use in the Editor, and everything works great. However, when I move to Android, the .so cannot be found. The import settings for libserverapp.so are:

Platform: Android; CPU: ARMv7; Path: Assets/Plugins/Android/libserverapp.so; Type: Native

Given that the final APK includes the .so where I expect it to be (lib/armeabi-v7a/), I assume my Unity settings are correct? Also, I am not using IL2CPP for the Android build.

Finally, when I do an object dump of the library file (using arm-linux-androideabi-objdump.exe), the file format of the library file is "elf32-littlearm".

I feel that the issue here is simply finding the .so, not the functionality within it. Any ideas on what's going on here?

Thanks!

Answer 1

I ended up solving the problem. I mentioned that was using an internal build system. Well, there seems to be a bug in it. I ported things over to official Android NDK makefiles, and then it "just worked". So in this case, the library could be found, but its contents weren't valid.