Dynamically loading a Swift `shared object` / `dylib`

Using Swift
1

Hello,

I have a Swift code, that loads a Swift .dylib (or .so) at runtime and uses a function of of a known name type as an interface. The loading process then uses dlopen and dlsym to execute the function. (I do not )

The source code of .dylib

@_cdecl("mySymbol")
public func mySymbol() -> Any {
    return "Hello world!"
}

The source code of the application

typealias FunctionPrototype = @convention(c) () -> Any

let handle = dlopen(libraryPath, RTLD_NOW)!
let symbol = dlsym(handle, "mySymbol")
let callable = unsafeBitCast(symbol, to: FunctionPrototype.self)
print(callable() as! String)

Everything works fine and I have never had an issue.

However, I was wondering, whether there might be an issue with calling conventions, since I'm using the @convention(c) annotation. I've used it "to make the FunctionPrototype type 1 pointer wide", but are there any other effects caused by the annotation, that I'm not taking into consideration? Is there any standard type, that might just break the program?

2

Marking the function as @_cdecl forces it to use the c calling convention, so what you're doing looks fine to me.

Types that aren't compatible with the c calling convention should be diagnosed by the compiler on both/either the actual function definition because it's marked @_cdecl or the function type.

1 Like