Interfacing with external C

[spino17]

Question

I want to know if it is possible that external C can be called inside assemblyscript. Any way to define C function prototype which will be provided by the host code through a WASM runtime like WAMR. Also, it is possible in assemblyscript that some functions can be exported in compiled wasm module.

[dcodeIO]

This is typically accomplished by specifying imports and exports. For example, an external host function can be declared and then called from AssemblyScript code:

@external("myModule", "add")
declare function add(a: i32, b: i32): i32;

add(1,2);

Or a function can be made callable by the host by exporting it from the entry file:

export function add(a: i32, b: i32): i32 {
  return a +b;
}

See also: Concepts / Module imports and exports

[spino17]

Thanks @dcodeIO for the reply. I read the documentation you attached, however I believe assemblyscript is only enabled for js host. I can be completely wrong here. When I am using external decorator for wrapping console.log as consoleLog, and when I am calling it in my wasm module, WAMR gives me linking error. So I think it also expects the runtime to dynamically link certain functions for example console.log. Is there also any restriction of what runtime we are using ?

[spino17]

So @dcodeIO below I am also attaching the code I have in /assembly/index.ts

// The entry file of your WebAssembly module.

@external("env", "console.log")
declare function consoleLog(s: string): void

export function main(): void {
  consoleLog("Hello, world");
}

This successfully compiles to .wasm file. Then when I am trying iwasm release.wasm in the /build dir, I am getting below error:

[05:10:53:628 - 1ED737AC0]: failed to check signature '(i)' and resolve pointer params for import function (env abort)

[05:10:53:717 - 1ED737AC0]: warning: failed to link import function (env, console.log)
[05:10:53:721 - 1ED737AC0]: warning: failed to link import function (env, abort)

#00: 0x0000 - console.log
#01: 0x00c6 - main

Exception: failed to call unlinked import function (env, console.log)

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