if !ok || failed {
		t.Errorf("asm: %s assembly failed", goarch)
		return
	}
	output := strings.Split(testOut.String(), "\n")

	// Reconstruct expected output by independently "parsing" the input.
	data, err := os.ReadFile(input)
	if err != nil {
		t.Error(err)
		return
	}
	lineno := 0
	seq := 0
	hexByLine := map[string]string{}
	lines := strings.SplitAfter(string(data), "\n")
Diff:
	for _, line := range lines {

			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)
		}
		wanted := strings.Split(string(bs), "\n")
		slices.Sort(wanted)
		for _, feature := range wanted {

	"os.FileInfo", "fs.FileInfo",
	"os.FileMode", "fs.FileMode",
	"os.PathError", "fs.PathError",
)

func fileFeatures(filename string, needApproval bool) []string {
	bs, err := os.ReadFile(filename)
	if err != nil {
		log.Fatal(err)
	}
	s := string(bs)

	// Diagnose common mistakes people make,
	// since there is no apifmt to format these files.