clarification about parameters ' wasi functions · wasmtime

I got confused about parameters of wasi functions.
fd_write function has imported in my wasm module. Its signature shows that it has 5 integers parameters (like below):

(import "wasi_snapshot_preview1" "fd_write" (func $__imported_wasi_snapshot_preview1_fd_write (type 5)))
(type (;5;) (func (param i32 i32 i32 i32) (result i32))

But fd_write signature in witx (and preview_1.rs) shows that it has been implemented with two paramteres:

(@interface func (export "fd_write")
    (param $fd $fd)
    ;;; List of scatter/gather vectors from which to retrieve data.
    (param $iovs $ciovec_array)
    (result $error (expected $size (error $errno)))
  )

I couldn't understand which part of wasmtime is responsible for this parameter transformation and what happen in wasmtime.
Can you please help me with that? Thanks.

Alphyr (Sep 12 2022 at 15:07):

julia (Sep 12 2022 at 15:47):

julia (Sep 16 2022 at 07:59):

@Alphyr I found that some types that use in wasi functions, such as Ciovec type, are defined in WITX specification and generates during compilation of wasmtime. But I need to use these types outside of wasi-common crate. Can you please tell me if it is possible and how?

Alphyr (Sep 19 2022 at 07:32):

I don't know a lot about WITX, but maybe you can re-generate WASI structs from the witx files and start from there.

Another solution is to define them yourself, (you can look at code from wasi to help), eg :

#[repr(C)]
struct Ciovec {
    pub buf: i32,
    pub buf_len: i32,
}

julia (Sep 19 2022 at 23:02):

Thanks for your reply. I could use the types with adding wasi-common crate to dependencies. And then I imported types using the below line:
wasi_common::snapshots::preview_1::types::*;

Also for my first question, I found out the call_interface function in the below file is responsible to do the job.
wasi-common/WASI/tools/witx/src/abi.rs

Jesús González (Sep 20 2022 at 19:43):

Pat Hickey (Sep 22 2022 at 00:15):

@julia for places where wiggle is generating types in wasi-common and you can’t read their source, you can use cargo doc

Stream: wasmtime

Topic: clarification about parameters ' wasi functions

julia (Sep 12 2022 at 03:29):