This repo has three crates in it, one root crate and two dependent crates. All three have some #[no_mangle] pub extern "C" fns in them, and the root would like to contain all of these when compiled as a cdylib.

Unfortunately, some targets (not all) seem to break this. This repo demonstrates the issue (and also a somewhat tedious workaround, which is enabled when building with --features='export_fns').

One target that reliably produces the issue is i686-linux-android, so you will probably have to set it up.

1. Download the NDK from https://developer.android.com/ndk/downloads, it doesn't matter what version, and unzip it.
2. Run /path/to/downloaded/ndk/build/tools/make_standalone_toolchain.py --arch=x86 --api=28 --install-dir="/tmp/ndk-x86-28". The api version doesn't matter, nor does where you install it, although you'll need to refer to where you install it later.
3. Run rustup target add i686-linux-android.

Once that's done, it's just a matter of running the following (assuming you installed the ndk toolchain to /tmp/ndk-x86-28 as described above):

RUSTFLAGS="-C linker=/tmp/ndk-x86-28/bin/i686-linux-android-clang" cargo build --target i686-linux-android

This will produce target/i686-linux-android/debug/libmegazord.so. If you inspect it with nm -g (if you don't have it installed, /tmp/ndk-x86-28/bin/i686-linux-android-nm is available as part of the NDK you installed), you can see that foo_fn and bar_fn are not present.

This can be worked around, and if you build with --features='export_fns', it will enable our fairly tedious and somewhat hacky workaround, and you can see that the symbols in question are present.