[WIP] Get table from Ctx

[tprk77]

Based on some discussion on Spectrum, this change adds a table function to Ctx.

Feedback appreciated!

[lachlansneff]

Looks great! Does it work for the specific issue you had?

[tprk77]

I think there is a bit more to do here, but I'm still figuring it out. For example, Table has a set function, but I think now I need a get function. (Same thing for the AnyfuncTable.)

[lachlansneff]

Yeah, I threw together the Table type pretty quickly without thinking about it too much. If you see a better way of doing it, we can definitely change it! :)

[tprk77]

@lachlansneff I've had some time to look at this again, and I've been able to create and call a DynFunc from a vm::Ctx. But there's a problem. It appears that ProtectedCaller is not designed to work with non-export functions. I found this comment a little too late:

/// The functionality exposed by this trait is expected to be used
/// for calling functions exported by a webassembly module from
/// host code only.
pub trait ProtectedCaller: Send + Sync {

When I try to use DynFunc with a non-exported function, I get, predictably:

thread 'main' panicked at 'assertion failed: self.func_export_set.contains(&func_index)',
/.../wasmer/lib/clif-backend/src/signal/mod.rs:88:9

So I don't think this DynFunc approach is going to work, or anything else using ProtectedCaller::call. It seems like I actually need something like ProtectedCaller but a little more raw. I'm picturing something that takes a function pointer and a context directly. (Then does the trampoline, etc.)

Do you think that's a reasonable idea? Is that something I should try implementing?

[tprk77]

On second thought, this is all very out of date, and I don't think any of it is salvageable.