cmd/link: replace golden binary files with hex dumps

The hex dumps will diff better, and I hope they will avoid
a repeat of http://bugs.debian.org/716853.

The CL will probably show the testdata diffs as "binary",
but in fact the binary versions are being replaced by
textual hex dumps (output of hexdump -C).

R=iant
CC=golang-codereviews
https://golang.org/cl/51000044

src/cmd/link/hex_test.go

+// Copyright 2014 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"encoding/hex"
+	"fmt"
+	"io/ioutil"
+	"regexp"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+// mustParseHexdumpFile returns a block of data generated by
+// parsing the hex dump in the named file.
+// If the file cannot be read or does not contain a valid hex dump,
+// mustParseHexdumpFile calls t.Fatal.
+func mustParseHexdumpFile(t *testing.T, file string) []byte {
+	hex, err := ioutil.ReadFile(file)
+	if err != nil {
+		t.Fatal(err)
+	}
+	data, err := parseHexdump(string(hex))
+	if err != nil {
+		t.Fatal(err)
+	}
+	return data
+}
+
+// parseHexdump parses the hex dump in text, which should be the
+// output of "hexdump -C" or Plan 9's "xd -b",
+// and returns the original data used to produce the dump.
+// It is meant to enable storing golden binary files as text, so that
+// changes to the golden files can be seen during code reviews.
+func parseHexdump(text string) ([]byte, error) {
+	var out []byte
+	for _, line := range strings.Split(text, "\n") {
+		if i := strings.Index(line, "|"); i >= 0 { // remove text dump
+			line = line[:i]
+		}
+		f := strings.Fields(line)
+		if len(f) > 1+16 {
+			return nil, fmt.Errorf("parsing hex dump: too many fields on line %q", line)
+		}
+		if len(f) == 0 || len(f) == 1 && f[0] == "*" { // all zeros block omitted
+			continue
+		}
+		addr64, err := strconv.ParseUint(f[0], 16, 0)
+		if err != nil {
+			return nil, fmt.Errorf("parsing hex dump: invalid address %q", f[0])
+		}
+		addr := int(addr64)
+		if len(out) < addr {
+			out = append(out, make([]byte, addr-len(out))...)
+		}
+		for _, x := range f[1:] {
+			val, err := strconv.ParseUint(x, 16, 8)
+			if err != nil {
+				return nil, fmt.Errorf("parsing hexdump: invalid hex byte %q", x)
+			}
+			out = append(out, byte(val))
+		}
+	}
+	return out, nil
+}
+
+func hexdump(data []byte) string {
+	text := hex.Dump(data) + fmt.Sprintf("%08x\n", len(data))
+	text = regexp.MustCompile(`\n([0-9a-f]+(\s+00){16}.*\n)+`).ReplaceAllString(text, "\n*\n")
+	return text
+}

src/cmd/link/prog_test.go

@@ -136,15 +136,17 @@ func cloneSection(sect *Section) *Section {
 	return t
 }
 
+const saveMismatch = true
+
 // checkGolden checks that data matches the named file.
 // If not, it reports the error to the test.
 func checkGolden(t *testing.T, data []byte, name string) {
-	golden, err := ioutil.ReadFile(name)
-	if err != nil {
-		t.Errorf("%s: %v", name, err)
-		return
-	}
+	golden := mustParseHexdumpFile(t, name)
 	if !bytes.Equal(data, golden) {
+		if saveMismatch {
+			ioutil.WriteFile(name+".raw", data, 0666)
+			ioutil.WriteFile(name+".hex", []byte(hexdump(data)), 0666)
+		}
 		// TODO(rsc): A better diff would be nice, as needed.
 		i := 0
 		for i < len(data) && i < len(golden) && data[i] == golden[i] {