The exit status is an 8-bit integer; this means that even if the argument for the Go function is an integer, then the status that is returned will be the result of a modulo operation between the passed value and 256.

Let's take a look at the following program:

package main

import (
    "fmt"
    "os"
)

func main() {
    fmt.Println("Hello, playground")
    os.Exit(-1)
}

The full example is available at https://play.golang.org/p/vzwI1kDiGrP. 

This will have an exit status of 255 even if the function argument is -1 because (-1)%256=255. This happens because the exit code is an 8-bit number (0, 255).