The definition for syscall NLA_HDRLEN is missing from gccgo in both trunk and the release 5 branch. This is the only one of the NLA_* syscall defines missing from gccgo. All of these syscall are correctly defined in golang master and go 1.5.x branch.

Testcase:

package main

import (
"fmt"
"syscall"
)

func main() {
fmt.Printf("NLA_HDRLEN: %x\n", syscall.NLA_HDRLEN)
fmt.Printf("NLA_F_NESTED: %x\n", syscall.NLA_F_NESTED)
fmt.Printf("NLA_F_NET_BYTEORDER: %x\n", syscall.NLA_F_NET_BYTEORDER)
fmt.Printf("NLA_ALIGNTO: %x\n", syscall.NLA_ALIGNTO)
}

With gccgo this error occurs:

error: reference to undefined identifier 'syscall.NLA_HDRLEN'
fmt.Printf("NLA_HDRLEN: %x\n", syscall.NLA_HDRLEN)

Testcase compiles correctly with golang.
Comment out the line with NLA_HDRLEN and the testcase compiles correctly with gccgo.