Dylink NPM | npm.io

dylink - WebAssembly dynamic loader for the Zig libc runtime

This is a WebAssembly dynamic loader for the ABI used by emscripten and the llvm backend when targeting emscripten. It runs both on node.js and in the browser. It supports the libc provided by Zig, not emscripten.

How to use this:

When you build your code, you have to link in the static archive file dist/wasm/libdylink.a, and provide some flags:

zig cc -target wasm32-wasi app.c -o build/wasm/app.wasm \
    -L path/to/dist/wasm/ -ldylink \
    -rdynamic -shared -fvisibility=default \
    -Xlinker --import-memory -Xlinker --import-table

Then the following functions will be available to use from app.c:

extern void* dlopen(const char* filename, int flags);
extern void* dlsym(void* handle, const char* symbol);

There are examples in the tests/ subdirectories.

Scope

I care about implementing enough of the linker spec to support loading Python extension modules. In particular, I'm probably not worried about dependencies, i.e., automatically loading all the dynamic libraries that dynamic library depends on.

Why?

There is already code in emscripten itself that fully implements the dynamic loader spec. However, I would like to build and run WebAssembly modules using a lightweight modern toolchain built around Zig instead. It is thus necessary to implement a self-contained dynamic loader.

PR's welcome to implement more!

References

There doesn't seem to be an actual write up of how dynamic linking actually works with WebAssembly, and I think the official WebAssembly project gave up on it in favor of other things that don't exist yet. it got implemented for emscripten (mainly here).