Native function signature

[AlixANNERAUD]

Hello, I was wondering how WAMR determines the signature of native functions since the signature strings of these functions were recently removed from registration. Indeed, I noticed that WAMR is able to determine, for example, whether the function requires an execution environment (wasm_exec_env_t) parameter or not.

[loganek]

Could you clarify what do you mean by signature strings being removed? They're still required: https://github.com/bytecodealliance/wasm-micro-runtime/blob/main/core/iwasm/include/lib_export.h#L23

AFAIK wasm_exec_env_t is always required for the native function; do you have any example of working code that doesn't require it?

[AlixANNERAUD]

This is probably not the best example I've found since this function has no parameters. However, I encountered this behavior and I don't understand how it could have occurred because, without wasm_exec_env_t, the other parameters (if they are passed blindly) are supposed to overlap each other. But that didn't happen.

[lum1n0us]

If there is a string in wasm(not sure will it ends with \0 if the guest language is Rust, But if with C，there is one '\0'), its wasm getter(if it exists) will return its starting index(since the string is saved in linear memory) as an i32.

After host getting the i32, it requires a address space translation for directly accessing or use API(like wasm_memory_data()) as a helper, and a move action from wasm world to host world which isn't because host functions can access linear memory. The real reason is rust using different string encoding with c.

We tend to pack all above details in rust-sdk. So rust-sdk users can have a rust string filled with the content of the string in wasm.

[AlixANNERAUD]

Alright, but my question now is how to pass strings and mutable buffers concretely with rust-sdk?

[lum1n0us]

I am working on sth. about passing strings between host and wasm. If you are interested, please follow bytecodealliance/wamr-rust-sdk#39. It is still in progress but is enough to explain above idea.

[AlixANNERAUD]

This is exactly what I'm looking for. I can't wait for this to be released.