https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63731
--- Comment #12 from Yohei Ueda <yohei at jp dot ibm.com> --- "pure-Go goLookupIP" means that goLookupIP is written in Go as usual. https://code.google.com/p/go/source/browse/src/net/dnsclient_unix.go#364 cgoLookupIP uses getaddrinfo via CGO unless the netgo tag is set. https://code.google.com/p/go/source/browse/src/net/cgo_unix.go#147 Fallback means that goLookupIP is called when cgoLookup fails with ok == false in this code. https://code.google.com/p/go/source/browse/src/net/lookup_unix.go#63 func lookupIP(host string) (addrs []IP, err error) { addrs, err, ok := cgoLookupIP(host) if !ok { addrs, err = goLookupIP(host) } return } When code that uses LookupHost is compiled with "go build -ldflags '-linkmode external -extldflags -static' -a -tags netgo", the Go standard library including cgoLookupIP is rebuilt. In this case, cgoLookupIP always returns ok == false as defined here. https://code.google.com/p/go/source/browse/src/net/cgo_stub.go#19 func cgoLookupIP(name string) (addrs []IP, err error, completed bool) { return nil, nil, false } This leads to calling goLookupIP from lookupIP. I called this mechanism "fallback".
