DllImport code does not work when compile from Linux

[harry-cpp]

Steps to Reproduce

1. Add the code bellow anywhere
2. Call it

[DllImport("dl")]
public static extern IntPtr dlopen(string path, int flags);

Expected Behavior

No crashing.

Actual Behavior

DllNotFoundException gets called.

Version Information

Last stable Linux build.

Log File

Full logcat: https://gist.github.com/cra0zy/8af965b4f44ec0b954b30f382ca0fdb8

[grendello]

The problem here is this:

06-29 14:21:21.020 3182 3182 E AndroidRuntime: android.runtime.JavaProxyThrowable: System.TypeInitializationException: The type initializer for 'MonoGame.OpenGL.GL' threw an exception. ---> Java.Lang.UnsatisfiedLinkError: dlopen failed: cannot locate symbol "__cxa_finalize" referenced by "/system/lib/libdl.so"...

The __cxa_finalize symbol is a weak symbol reference in any native C++ app/library, used to run C++ destructors registered with atexit and is either resolved to the application native code/dso or to libc (which has the default implementation) which doesn't appear to be the case here. Why? I have no idea - I would need to be able to examine the app code (or a small repro that triggers the issue) in order to start figuring it out.

Here are the symbols in some DSOs involved:

Android/lib/arm64-v8a $ nm -C -D libmono-android.debug.so|grep __cxa_finalize
                 U __cxa_finalize

Android/lib/arm64-v8a $ nm -C -D libmonosgen-2.0.so|grep __cxa_finalize
                 U __cxa_finalize

ndk/platforms/android-21/arch-arm64/usr/lib$ nm -C -D libc.so|grep __cxa_finalize
000000000000c01c T __cxa_finalize

android-21/arch-arm64/usr/lib$ nm -C -D libdl.so|grep __cxa_finalize

Now, considering that libdl.so does not reference libc (in fact, it's dynamically linked but references no DSOs) and does not reference __cxa_finalize itself, the problem isn't in the library (at least for NDK platform 21 reference libraries I'm looking at here):

ndk/platforms/android-21/arch-arm64/usr/lib$ readelf -a libdl.so | grep NEEDED

further on, assuming your app is a Xamarin.Android one and includes Mono and XA runtimes, libdl is already referenced and loaded by the time your code runs (and so the __cxa_finalize symbol should be resolved to the one in libc.so):

Android/lib/arm64-v8a $ readelf -a libmonosgen-2.0.so | grep NEEDED
 0x0000000000000001 (NEEDED)             Shared library: [libz.so]
 0x0000000000000001 (NEEDED)             Shared library: [libdl.so]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so]
 0x0000000000000001 (NEEDED)             Shared library: [libm.so]
 0x0000000000000001 (NEEDED)             Shared library: [liblog.so]

Android/lib/arm64-v8a $ readelf -a libmono-android.debug.so | grep NEEDED
 0x0000000000000001 (NEEDED)             Shared library: [libz.so]
 0x0000000000000001 (NEEDED)             Shared library: [liblog.so]
 0x0000000000000001 (NEEDED)             Shared library: [libxamarin-app.so]
 0x0000000000000001 (NEEDED)             Shared library: [libm.so]
 0x0000000000000001 (NEEDED)             Shared library: [libstdc++.so]
 0x0000000000000001 (NEEDED)             Shared library: [libdl.so]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so]

At this point @cra0zy, I have no slightest clue as to what might be going on. Your device's libdl.so appears to have __cxa_finalize reference which appears to be unresolved, while the reference libraries from NDK I looked at (API levels 16 and 21, which we compile against) include libdl.so without __cxa_finalize reference. Therefore, I'll need more info from you (and, preferably, a repro):

• Android version
• Device architecture
• Platform your app native code is compiled against
• NDK version

Hopefully we can then pin-point the issue (which doesn't seem to be a problem in Xamarin.Android atm, frankly)

[harry-cpp]

So... a quick test later and the only way that this occurs is this specific device and only when compiling the above code from Linux... strange.

Device in question is: https://www.gsmarena.com/alcatel_pixi_4_(7)-7847.php

I can't provide you with more details right now.

[grendello]

@cra0zy __cxa_finalize is a Linux implementation detail possibly? But, since Android is Linux as well... Odd, indeed. Regarding the device - would you be able to pull libc.so and libdl.so off of the device and attach here?

[harry-cpp]

libs.zip

[harry-cpp]

@grendello @dellis1972 So... turns out this issue is not limited to Linux SDK :/