main.go

package main

import (
	"fmt"
	"plugin"
)

func main() {
	p, _ := plugin.Open("./myplugin.so")
	add, _ := p.Lookup("Add")
	sum := add.(func(int, int) int)(1, 2)
	fmt.Println(sum)
}

myplugin.go

package main

func Add(x, y int) int {
    return x+y
}

func panicOnError(err error) {
  if err != nil {
    panic(err)
  }
}

You should handle errors.