Why is there a "-fm" suffix when getting a function's name in Go?

For the snippet below (runnable via the Go Playground),

package main

import (
  "fmt"
  "net/http"
  "reflect"
  "runtime"
)

type User struct{}

var u = &User{}

func (_ User) DummyHandler(w http.ResponseWriter, r *http.Request) {}

func funcName(i interface{}) {
  p := reflect.ValueOf(i).Pointer()
  n := runtime.FuncForPC(p).Name()
  fmt.Println(n)
}

func main() {
  funcName(u.DummyHandler)
}

The output is main.(User).DummyHandler-fm.

Why is there a -fm at the end of the function name?