Also, WebAssembly can't support most GC runtimes now, because you can't scan the stack for roots. You can keep your own shadow stack on the heap, but that has a bunch of pretty bad performance implications. This actually impacts C/C++/Rust codegen as well, since they can't create references/pointers to anything on the stack, and have to build their own shadow stack (I think this is done in binaryen or LLVM itself?). I understand it's a security thing to disallow direct stack access, but most languages and runtimes expect it.
Anyways, that's why there needs to be support in WebAssembly for GC, because there needs to be a safe way to walk the stack (aside from the obvious JS interop considerations).
Anyways, that's why there needs to be support in WebAssembly for GC, because there needs to be a safe way to walk the stack (aside from the obvious JS interop considerations).