Undefined symbol: _new_tunnel

Good morning everyone.

I am hoping this is a simple issue and someone can help me out. I have spent a lot of time searching for a solution without any luck.

## **Summary**
I have created a static library using the [instructions in the repository](https://github.com/cloudflare/boringtun/blob/master/README.md) for the target triple aarch64-apple-ios. The library built without issues. However, when I try to compile the project using the library, I get this error: "*Undefined symbol: _new_tunnel*". As the library is properly added to my project and the required "bridging header" is correct, I used **nm** to look at the library and discovered that, in fact, the symbol is not in the library.

What can cause this issue and how can I produce a library which contains the necessary exports to use the library?

## **Details**

Although I have built a version of the library for more than one target triple, let's focus on the aarch64-apple-ios case for the moment. I have installed rustup and have the following versions installed.

```
rustup 1.27.0 (2024-03-08)
info: This is the version for the rustup toolchain manager, not the rustc compiler.
info: The currently active rustc version is rustc 1.77.1 (7cf61ebde 2024-03-27)
```
```
Apple clang version 15.0.0 (clang-1500.3.9.4)
Target: x86_64-apple-darwin23.4.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
```

I have also installed the target using rustup.

```
rustup target add aarch64-apple-ios
```
Then, I built the library using the command from the README.md, which was:

```
cargo build --lib --release --no-default-features --target aarch64-apple-ios
```

This builds and produces the static and dynamic libraries as expected. Using the **nm** command on the resulting library, I see the following information (excerpt, but includes the only reference to boringtun as the rest are the many dependencies of the project).

```
cd targets/aarch64-apple-ios/release
nm libboringtun.a > t.txt

First part of t.txt

boringtun.oltf1cth477n37t.rcgu.o:
U ___rdl_alloc
U ___rdl_alloc_zeroed
U ___rdl_dealloc
U ___rdl_realloc
U ___rg_oom
---------------- T ___rust_alloc
---------------- T ___rust_alloc_error_handler
---------------- D ___rust_alloc_error_handler_should_panic
---------------- T ___rust_alloc_zeroed
---------------- T ___rust_dealloc
---------------- D ___rust_no_alloc_shim_is_unstable
---------------- T ___rust_realloc

hmac-96c14486fb5f355e.hmac.f89c15fd2c601d84-cgu.0.rcgu.o:

pin_project_lite-3d50fbfca7744f31.pin_project_lite.3f539c677dac0c66-cgu.0.rcgu.o:

lock_api-d5f5fcd6e14ec8d4.lock_api.8554128397852c1-cgu.0.rcgu.o:

```

I am unclear why none of the symbols I expected are present. To ensure there was not an issue with my setup, I installed a sample project that generates a simple static library and verified that after building it, the symbols that I expected to be present were in fact in the library.

Start with the README.md build instructions and reproduce the aarch64-apple-ios build using the reported cargo command. Inspect targets/aarch64-apple-ios/release/libboringtun.a with nm and trace how the expected new_tunnel export is defined or exposed. Done means identifying the cause and documenting a build that contains the required exports.

Written by the indexing model from the issue text.