Android is a bit awkward in that users are expected to load transitive dependencies before the main library. For example, if A depends on B, users must loadLibrary("B") before loadLibrary("A"), otherwise the latter will fail.

Instead of leaking platform-specific behavior into application code, we could load the transitive dependencies automatically.

lo_dlopen(), found at http://cgit.freedesktop.org/libreoffice/core/tree/sal/android/lo-bootstrap.c#n821 claims to do exactly that. According to https://groups.google.com/d/msg/android-ndk/J3lzK4X--bM/mjnj5P9UcIkJ this code:

- Searches where the shared object in question is. It searches a set of directories passed to it by the Java code. The Java code looks at LD_LIBRARY_PATH and adds the app's lib directory to that.
- Opens the found shared object file and reads the ELF structures in it . Not all, but just enough to find out what shared objects it needs (the DT_NEEDED ones as displayed by arm-linux-androideabi-readelf -d). It calls itself recursively on the needed shared objects.
- Only after that, i.e. after making sure that all needed other shared objects have been loaded, it calls the real dlopen() on the found full pathname to the shared object.

A few gotchas that the code handles:

- You should not call dlopen() unless you are sure it will succeed. The Bionic dynamic linker "helpfully" remembers if a dlopen() call has failed and refuses to even try again dlopening the same library a second time, even if you after the first attempt have loaded the required dependencies that caused the failure the first time. I.e. it is not a good idea to just try dlopen() first and if it fails, parse the dlerror() message...

- The wrapper needs to remember what libraries it already has loaded to avoid infinitely looping when libraries have circular dependencies (which they do have).

Benefit: Improved portability for application or library code (versus having to add Android-specific workarounds for System.loadLibrary()).

Issue 36950617

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