callbackMutex.Lock()
	callbackToken++
	i := callbackToken
	callbackFuncs[i] = f
	callbackMutex.Unlock()

	// Pass the address of i because the C function was written to
	// take a pointer.  We could pass an int if we felt like
	// rewriting the C code.
	C.callback(unsafe.Pointer(&i))

	callbackMutex.Lock()
	delete(callbackFuncs, i)
	callbackMutex.Unlock()
}

//export goCallback
func goCallback(p unsafe.Pointer) {

		pkg, _ := w.import_(fi.Name())
		w.export(pkg)

		if *updateGolden {
			os.Remove(goldenFile)
			f, err := os.Create(goldenFile)
			if err != nil {
				t.Fatal(err)
			}
			for _, feat := range w.Features() {
				fmt.Fprintf(f, "%s\n", feat)
			}
			f.Close()
		}

		bs, err := os.ReadFile(goldenFile)
		if err != nil {
			t.Fatalf("opening golden.txt for package %q: %v", fi.Name(), err)
		}

		// this is created by code in this file.
		if t.Name == "unsafe.Pointer" {
			return ast.NewIdent("_cgo_unsafe.Pointer")
		}
	case *ast.ArrayType:
		t1 := p.rewriteUnsafe(t.Elt)
		if t1 != t.Elt {
			r := *t
			r.Elt = t1
			return &r
		}
	case *ast.StructType:
		changed := false
		fields := *t.Fields
		fields.List = nil
		for _, f := range t.Fields.List {