panic: runtime error: cgo argument has Go pointer to Go pointer

[mewmew]

Does anyone know more about the new rules for sharing pointers between Go and C? If so, please give us a hand at resolving this issue.

(ref golang/go#12416)

Offending code from cmd/gpsview/gpsview.go:

    onButtonPress := func(ctx *glib.CallbackContext) {
        arg := ctx.Args(0)
        ev := (*gdk.EventButton)(unsafe.Pointer(arg))
        coord := m.ScreenToCoord(int(ev.X), int(ev.Y))

$ go vet ./cmd/gpsview
cmd/gpsview/gpsview.go:172: possible misuse of unsafe.Pointer
exit status 1

$ gpsview
panic: runtime error: cgo argument has Go pointer to Go pointer

goroutine 1 [running]:
panic(0x5b0480, 0xc82000a4f0)
    /home/u/go/src/runtime/panic.go:500 +0x18e
github.com/mattn/go-gtk/gtk._cgoCheckPointer0(0x59d6c0, 0xc820010300, 0xc82000a4e0, 0x1, 0x1, 0xc82000a4c4)
    ??:0 +0x49
github.com/mattn/go-gtk/gtk.Init(0x8fdcc0)
    /home/u/goget/src/github.com/mattn/go-gtk/gtk/gtk.go:228 +0x2cc
main.main()
    /home/u/Desktop/go/src/github.com/mewmew/gtkmap/cmd/gpsview/gpsview.go:116 +0x29e