Executable memory

main.swift

import Foundation

typealias TwoIntsOneInt = @convention(c) (Int, Int) -> Int

let code = [
  0x55,                     // push rbp
  0x48, 0x89, 0xE5,         // mov rbp, rsp
  0x48, 0x8D, 0x04, 0x37,   // lea rax, [rdi + rsi]
  0x5D,                     // pop rbp
  0xC3                      // ret
] as [UInt8]

func fudge(x: Int, y: Int) -> Int {
  let buf = mmap(nil, code.count, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_ANON, -1, 0)

  memcpy(buf, code, code.count)

  let fun = unsafeBitCast(buf, to: TwoIntsOneInt.self)
  let ret = fun(x, y)

  munmap(buf, code.count)

  return ret
}

print(fudge(x: 7, y: 12))