x/net/{ipv4,ipv6}: PacketConn.SetControlMessage panics in reflect

[danderson]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version devel +a7e2556 Tue Feb 21 01:05:55 2017 +0000 linux/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/travis/gopath"
GORACE=""
GOROOT="/home/travis/.gimme/versions/go"
GOTOOLDIR="/home/travis/.gimme/versions/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build669925158=/tmp/go-build"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"

What did you do?

go get go.universe.tf/netboot/dhcp4
go test go.universe.tf/netboot/dhcp4

The above test passes in 1.6, 1.7 and 1.8, but crashes at tip.

What did you expect to see?

Test passing.

What did you see instead?

panic: reflect: call of reflect.Value.Int on zero Value [recovered]
panic: reflect: call of reflect.Value.Int on zero Value
goroutine 5 [running]:
testing.tRunner.func1(0xc42006c680)
/home/travis/.gimme/versions/go/src/testing/testing.go:624 +0x264
panic(0x57f8a0, 0xc42000cee0)
/home/travis/.gimme/versions/go/src/runtime/panic.go:489 +0x25a
reflect.Value.Int(0x0, 0x0, 0x0, 0x5b3ca6)
/home/travis/.gimme/versions/go/src/reflect/value.go:902 +0xb5
go.universe.tf/netboot/vendor/golang.org/x/net/internal/netreflect.socketOf(0x671920, 0xc42000e0a0, 0xc42000e0a0, 0x671920, 0xc42000e0a0)
/home/travis/gopath/src/go.universe.tf/netboot/vendor/golang.org/x/net/internal/netreflect/socket_posix.go:26 +0x196
go.universe.tf/netboot/vendor/golang.org/x/net/internal/netreflect.PacketSocketOf(0x671680, 0xc42000e0a0, 0xc42000e0a0, 0xc42001e780, 0xc42000e0a0)
/home/travis/gopath/src/go.universe.tf/netboot/vendor/golang.org/x/net/internal/netreflect/socket.go:33 +0x7d
go.universe.tf/netboot/vendor/golang.org/x/net/ipv4.(*PacketConn).SetControlMessage(0xc42001e780, 0x8, 0xc42001e701, 0x6, 0x671680)
/home/travis/gopath/src/go.universe.tf/netboot/vendor/golang.org/x/net/ipv4/endpoint.go:62 +0x5d
go.universe.tf/netboot/dhcp4.newPortableConn(0xbe7d, 0x0, 0x0, 0xb, 0x671680)
/home/travis/gopath/src/go.universe.tf/netboot/dhcp4/conn.go:221 +0x11f
go.universe.tf/netboot/dhcp4.TestPortableConn(0xc42006c680)
/home/travis/gopath/src/go.universe.tf/netboot/dhcp4/conn_test.go:128 +0x175
testing.tRunner(0xc42006c680, 0x5be468)
/home/travis/.gimme/versions/go/src/testing/testing.go:659 +0x98
created by testing.(*T).Run
/home/travis/.gimme/versions/go/src/testing/testing.go:701 +0x2da
FAIL go.universe.tf/netboot/dhcp4 0.006s

I'm working on a smaller reproduction recipe, I'll update the bug when I have one.

[mikioh]

Yup, dup of #19051.