Re-entrancy

[kshpytsya]

Is it supposed to be possible to have the following call chain:

HOST -> WASM -> HOST -> WASM

?

In my case both host and wasm parts are implemented in Rust. The HOST -> WASM -> HOST works perfectly. However, once the extra nesting level is introduced, I get a panic from tinywasm saying "Stack index out of bounds, this is a bug" on transition from level 3 (host) to level 2 (wasm).

If this use case is supposed to be supported, I will try to come up with an MRE.

Context: level 2 to level 3 is wasm calling some host function, and level 3 to level 4 is host calling wasm to allocate a buffer for result (which cannot be pre-allocated since result size is not known beforehand).

Not sure if the is relevant: bytecodealliance/wasmtime#9600

If re-entrancy is not supported by spec, the at least a clearer error would be useful.