tools/fuzz/build.go - fuchsia - Git at Google

 // Copyright 2020 The Fuchsia 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 fuzz

 import (
 	"bufio"
 	"encoding/json"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"os"
 	"path/filepath"
 	"regexp"
 	"runtime"
 	"strings"

 	"github.com/golang/glog"
 )

 // A Build represents a Fuchsia build, consisting of all the resources needed
 // to run a fuzzer on an instance (e.g. a Fuchsia image, fuzzer packages and
 // metadata, binary symbols, support utilities, etc.).
 type Build interface {
 	// Ensures all the needed resources are present and fetches any that are
 	// missing. Multiple calls to Prepare should be idempotent for the same
 	// Build.
 	Prepare() error

 	// Returns a fuzzer specified by a `package/binary` name, or an error if it
 	// isn't found.
 	Fuzzer(name string) (*Fuzzer, error)

 	// Returns the absolute host paths for each key.  Each key corresponds to a
 	// specific resource provided by the Build.  This abstraction allows for
 	// different build types to have different structures.
 	Path(keys ...string) ([]string, error)

 	// Reads input from `in`, symbolizes it, and writes it back to `out`.
 	// Returns on error, or when `in` has no more data to read.  Processing
 	// will be streamed, line-by-line.
 	// TODO(fxbug.dev/47482): does this belong elsewhere?
 	Symbolize(in io.ReadCloser, out io.Writer) error

 	// Returns a list of the names of the fuzzers that are available to run
 	ListFuzzers() []string
 }

 // BaseBuild is a simple implementation of the Build interface
 type BaseBuild struct {
 	Fuzzers map[string]*Fuzzer
 	Paths   map[string]string
 	IDs     []string
 }

 // This is stubbed out to allow for test code to replace it
 var NewBuild = NewBuildFromEnvironment

 // This environment variable is set by the ClusterFuzz build manager
 const clusterFuzzBundleDirEnvVar = "FUCHSIA_RESOURCES_DIR"

 // Attempt to auto-detect the correct Build type
 func NewBuildFromEnvironment() (Build, error) {
 	if _, found := os.LookupEnv(clusterFuzzBundleDirEnvVar); found {
 		return NewClusterFuzzLegacyBuild()
 	}
 	return NewLocalFuchsiaBuild()
 }

 // NewClusterFuzzLegacyBuild will create a BaseBuild with path layouts
 // corresponding to the legacy build bundles used by ClusterFuzz's original
 // Python integration. Note that these build bundles only support x64.
 func NewClusterFuzzLegacyBuild() (Build, error) {
 	bundleDir, found := os.LookupEnv(clusterFuzzBundleDirEnvVar)
 	if !found {
 		return nil, fmt.Errorf("%s not set", clusterFuzzBundleDirEnvVar)
 	}

 	buildDir := filepath.Join(bundleDir, "build")
 	targetDir := filepath.Join(bundleDir, "target", "x64")
 	clangDir := filepath.Join(buildDir, "buildtools", "linux-x64", "clang")
 	build := &BaseBuild{
 		Paths: map[string]string{
 			"zbi":             filepath.Join(targetDir, "fuchsia.zbi"),
 			"fvm":             filepath.Join(buildDir, "out", "default.zircon", "tools", "fvm"),
 			"zbitool":         filepath.Join(buildDir, "out", "default.zircon", "tools", "zbi"),
 			"blk":             filepath.Join(targetDir, "fvm.blk"),
 			"qemu":            filepath.Join(bundleDir, "qemu-for-fuchsia", "bin", "qemu-system-x86_64"),
 			"kernel":          filepath.Join(targetDir, "multiboot.bin"),
 			"llvm-symbolizer": filepath.Join(clangDir, "bin", "llvm-symbolizer"),
 			"symbolizer":      filepath.Join(buildDir, "zircon", "prebuilt", "downloads", "symbolize", "linux-x64", "symbolize"),
 			"fuzzers.json":    filepath.Join(buildDir, "out", "default", "fuzzers.json"),
 		},
 		IDs: []string{
 			filepath.Join(clangDir, "lib", "debug", ".build_id"),
 			filepath.Join(buildDir, "out", "default", ".build-id"),
 			filepath.Join(buildDir, "out", "default.zircon", ".build-id"),
 		},
 	}
 	if err := build.LoadFuzzers(); err != nil {
 		return nil, err
 	}

 	return build, nil
 }

 var Platforms = map[string]string{
 	"linux":  "linux",
 	"darwin": "mac",
 }

 var Archs = map[string]struct {
 	Binary string
 	Kernel string
 }{
 	"x64":   {"qemu-system-x86_64", "multiboot.bin"},
 	"arm64": {"qemu-system-aarch64", "qemu-boot-shim.bin"},
 }

 var hostDir = map[string]string{"arm64": "host_arm64", "amd64": "host_x64"}[runtime.GOARCH]

 // NewLocalFuchsiaBuild will create a BaseBuild with path layouts corresponding
 // to a local Fuchsia checkout
 func NewLocalFuchsiaBuild() (Build, error) {
 	fuchsiaDir := os.Getenv("FUCHSIA_DIR")
 	if fuchsiaDir == "" {
 		// Fall back to relative path from this file
 		fuchsiaDir = filepath.Join("..", "..")
 	}

 	fxBuildDir := filepath.Join(fuchsiaDir, ".fx-build-dir")
 	contents, err := ioutil.ReadFile(fxBuildDir)
 	if err != nil {
 		return nil, fmt.Errorf("failed to read %q: %s", fxBuildDir, err)
 	}

 	buildDir := strings.TrimSpace(string(contents))
 	if !filepath.IsAbs(buildDir) {
 		buildDir = filepath.Join(fuchsiaDir, buildDir)
 	}
 	prebuiltDir := filepath.Join(fuchsiaDir, "prebuilt")

 	platform, ok := Platforms[runtime.GOOS]
 	if !ok {
 		return nil, fmt.Errorf("unsupported os: %s", runtime.GOOS)
 	}

 	fxConfig := filepath.Join(buildDir, "fx.config")
 	file, err := os.Open(fxConfig)
 	if err != nil {
 		return nil, fmt.Errorf("failed to open %q: %s", fxConfig, err)
 	}
 	defer file.Close()

 	properties := map[string]string{}
 	re := regexp.MustCompile(`^([^=]+)=(?:'([^']+)'|(.+))?$`)
 	scanner := bufio.NewScanner(file)
 	for scanner.Scan() {
 		m := re.FindStringSubmatch(scanner.Text())
 		if m != nil {
 			properties[m[1]] = m[2]
 		}
 	}

 	arch, found := properties["FUCHSIA_ARCH"]
 	if !found {
 		return nil, fmt.Errorf("no arch in %s", fxConfig)
 	}

 	archInfo, ok := Archs[arch]
 	if !ok {
 		supported := make([]string, 0, len(Archs))
 		for k := range Archs {
 			supported = append(supported, k)
 		}
 		return nil, fmt.Errorf("unsupported arch: %s (supported: %v)", arch, supported)
 	}

 	binary := archInfo.Binary
 	kernel := archInfo.Kernel
 	platform += "-" + arch

 	clangDir := filepath.Join(prebuiltDir, "third_party/clang", platform)
 	qemuDir := filepath.Join(prebuiltDir, "third_party/qemu", platform)
 	imgDir := filepath.Join(buildDir, "obj", "build", "images", "fuchsia", "fuchsia")

 	build := &BaseBuild{
 		Paths: map[string]string{
 			"zbi":             filepath.Join(imgDir, "fuchsia.zbi"),
 			"fvm":             filepath.Join(buildDir, hostDir, "fvm"),
 			"zbitool":         filepath.Join(buildDir, hostDir, "zbi"),
 			"blk":             filepath.Join(imgDir, "fvm.blk"),
 			"qemu":            filepath.Join(qemuDir, "bin", binary),
 			"kernel":          filepath.Join(buildDir, kernel),
 			"llvm-symbolizer": filepath.Join(clangDir, "bin", "llvm-symbolizer"),
 			"symbolizer":      filepath.Join(buildDir, hostDir, "symbolize"),
 			"fuzzers.json":    filepath.Join(buildDir, "fuzzers.json"),
 		},
 		IDs: []string{
 			filepath.Join(clangDir, "lib", "debug", ".build-id"),
 			filepath.Join(buildDir, ".build-id"),
 		},
 	}
 	if err := build.LoadFuzzers(); err != nil {
 		return nil, err
 	}

 	return build, nil
 }

 // Convenience type alias for heterogenous metadata objects in fuzzers.json
 type fuzzerMetadata map[string]string

 // LoadFuzzers reads and parses fuzzers.json to populate the build's map of Fuzzers.
 // Unless an error is returned, any previously loaded fuzzers will be discarded.
 func (b *BaseBuild) LoadFuzzers() error {
 	paths, err := b.Path("fuzzers.json")
 	if err != nil {
 		return err
 	}

 	jsonPath := paths[0]

 	glog.Infof("Loading fuzzers from %q", jsonPath)

 	jsonBlob, err := ioutil.ReadFile(jsonPath)
 	if err != nil {
 		return fmt.Errorf("failed to read %q: %s", jsonPath, err)
 	}

 	var metadataList []fuzzerMetadata
 	if err := json.Unmarshal(jsonBlob, &metadataList); err != nil {
 		return fmt.Errorf("failed to parse %q: %s", jsonPath, err)
 	}

 	// Condense metadata entries by label
 	metadataByLabel := make(map[string]fuzzerMetadata)
 	for _, metadata := range metadataList {
 		label, found := metadata["label"]
 		if !found {
 			return fmt.Errorf("failed to parse %q: entry missing label", jsonPath)
 		}

 		if _, found := metadataByLabel[label]; !found {
 			metadataByLabel[label] = make(fuzzerMetadata)
 		}

 		for k, v := range metadata {
 			if v != "" {
 				metadataByLabel[label][k] = v
 			}
 		}
 	}

 	b.Fuzzers = make(map[string]*Fuzzer)
 	for label, metadata := range metadataByLabel {
 		pkg, found := metadata["package"]
 		if !found {
 			return fmt.Errorf("failed to parse %q: no package for %q", jsonPath, label)
 		}

 		fuzzer, found := metadata["fuzzer"]
 		if !found {
 			return fmt.Errorf("failed to parse %q: no fuzzer for %q", jsonPath, label)
 		}

 		f := NewFuzzer(b, pkg, fuzzer)
 		b.Fuzzers[f.Name] = f
 	}

 	return nil
 }

 // ListFuzzers lists the names of fuzzers present in the build, excluding any
 // that we don't want ClusterFuzz to actually pick up. We can't just omit the
 // example fuzzers from the build entirely because they are used in integration
 // testing.
 func (b *BaseBuild) ListFuzzers() []string {
 	var names []string
 	for _, fuzzer := range b.Fuzzers {
 		if !fuzzer.IsExample() {
 			names = append(names, fuzzer.Name)
 		}
 	}
 	return names
 }

 // Fuzzer finds the Fuzzer with the given name, if available
 func (b *BaseBuild) Fuzzer(name string) (*Fuzzer, error) {
 	fuzzer, found := b.Fuzzers[name]
 	if !found {
 		return nil, fmt.Errorf("no such fuzzer: %s", name)
 	}
 	return fuzzer, nil
 }

 // Prepare is a no-op for simple builds
 func (b *BaseBuild) Prepare() error {
 	return nil
 }

 // Path returns the absolute paths to the list of files indicated by keys. This
 // allows callers to abstract away the detail of where specific file resources
 // are.
 func (b *BaseBuild) Path(keys ...string) ([]string, error) {
 	paths := make([]string, len(keys))
 	for i, key := range keys {
 		if path, found := b.Paths[key]; found {
 			paths[i] = path
 		} else {
 			return nil, fmt.Errorf("no path for %q", key)
 		}
 	}
 	return paths, nil
 }

 var logPrefixRegex = regexp.MustCompile(`[0-9\[\]\.]*\[klog\] INFO: `)

 // Remove timestamps, etc.
 func stripLogPrefix(line string) string {
 	return logPrefixRegex.ReplaceAllString(line, "")
 }

 // Symbolize reads from in and replaces symbolizer markup with debug
 // information before writing the result to out.  This is blocking, and does
 // not propagate EOFs from in to out.
 func (b *BaseBuild) Symbolize(in io.ReadCloser, out io.Writer) error {
 	// Close `in` on return so that the fuzzer doesn't block on a write if an
 	// early exit occurs later in the output-processing chain.
 	defer in.Close()

 	paths, err := b.Path("symbolizer", "llvm-symbolizer")
 	if err != nil {
 		return err
 	}

 	symbolizer, llvmSymbolizer := paths[0], paths[1]

 	args := []string{"-llvm-symbolizer", llvmSymbolizer}
 	for _, dir := range b.IDs {
 		args = append(args, "-build-id-dir", dir)
 	}
 	cmd := NewCommand(symbolizer, args...)
 	cmd.Stdin = in
 	pipe, err := cmd.StdoutPipe()
 	if err != nil {
 		return err
 	}
 	if err := cmd.Start(); err != nil {
 		return err
 	}
 	scanner := bufio.NewScanner(pipe)

 	for scanner.Scan() {
 		io.WriteString(out, stripLogPrefix(scanner.Text())+"\n")
 	}

 	if err := scanner.Err(); err != nil {
 		return fmt.Errorf("failed during scan: %s", err)
 	}

 	return cmd.Wait()
 }
	// Copyright 2020 The Fuchsia 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 fuzz

	import (
	"bufio"
	"encoding/json"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path/filepath"
	"regexp"
	"runtime"
	"strings"

	"github.com/golang/glog"
	)

	// A Build represents a Fuchsia build, consisting of all the resources needed
	// to run a fuzzer on an instance (e.g. a Fuchsia image, fuzzer packages and
	// metadata, binary symbols, support utilities, etc.).
	type Build interface {
	// Ensures all the needed resources are present and fetches any that are
	// missing. Multiple calls to Prepare should be idempotent for the same
	// Build.
	Prepare() error

	// Returns a fuzzer specified by a `package/binary` name, or an error if it
	// isn't found.
	Fuzzer(name string) (*Fuzzer, error)

	// Returns the absolute host paths for each key. Each key corresponds to a
	// specific resource provided by the Build. This abstraction allows for
	// different build types to have different structures.
	Path(keys ...string) ([]string, error)

	// Reads input from `in`, symbolizes it, and writes it back to `out`.
	// Returns on error, or when `in` has no more data to read. Processing
	// will be streamed, line-by-line.
	// TODO(fxbug.dev/47482): does this belong elsewhere?
	Symbolize(in io.ReadCloser, out io.Writer) error

	// Returns a list of the names of the fuzzers that are available to run
	ListFuzzers() []string
	}

	// BaseBuild is a simple implementation of the Build interface
	type BaseBuild struct {
	Fuzzers map[string]*Fuzzer
	Paths map[string]string
	IDs []string
	}

	// This is stubbed out to allow for test code to replace it
	var NewBuild = NewBuildFromEnvironment

	// This environment variable is set by the ClusterFuzz build manager
	const clusterFuzzBundleDirEnvVar = "FUCHSIA_RESOURCES_DIR"

	// Attempt to auto-detect the correct Build type
	func NewBuildFromEnvironment() (Build, error) {
	if _, found := os.LookupEnv(clusterFuzzBundleDirEnvVar); found {
	return NewClusterFuzzLegacyBuild()
	}
	return NewLocalFuchsiaBuild()
	}

	// NewClusterFuzzLegacyBuild will create a BaseBuild with path layouts
	// corresponding to the legacy build bundles used by ClusterFuzz's original
	// Python integration. Note that these build bundles only support x64.
	func NewClusterFuzzLegacyBuild() (Build, error) {
	bundleDir, found := os.LookupEnv(clusterFuzzBundleDirEnvVar)
	if !found {
	return nil, fmt.Errorf("%s not set", clusterFuzzBundleDirEnvVar)
	}

	buildDir := filepath.Join(bundleDir, "build")
	targetDir := filepath.Join(bundleDir, "target", "x64")
	clangDir := filepath.Join(buildDir, "buildtools", "linux-x64", "clang")
	build := &BaseBuild{
	Paths: map[string]string{
	"zbi": filepath.Join(targetDir, "fuchsia.zbi"),
	"fvm": filepath.Join(buildDir, "out", "default.zircon", "tools", "fvm"),
	"zbitool": filepath.Join(buildDir, "out", "default.zircon", "tools", "zbi"),
	"blk": filepath.Join(targetDir, "fvm.blk"),
	"qemu": filepath.Join(bundleDir, "qemu-for-fuchsia", "bin", "qemu-system-x86_64"),
	"kernel": filepath.Join(targetDir, "multiboot.bin"),
	"llvm-symbolizer": filepath.Join(clangDir, "bin", "llvm-symbolizer"),
	"symbolizer": filepath.Join(buildDir, "zircon", "prebuilt", "downloads", "symbolize", "linux-x64", "symbolize"),
	"fuzzers.json": filepath.Join(buildDir, "out", "default", "fuzzers.json"),
	},
	IDs: []string{
	filepath.Join(clangDir, "lib", "debug", ".build_id"),
	filepath.Join(buildDir, "out", "default", ".build-id"),
	filepath.Join(buildDir, "out", "default.zircon", ".build-id"),
	},
	}
	if err := build.LoadFuzzers(); err != nil {
	return nil, err
	}

	return build, nil
	}

	var Platforms = map[string]string{
	"linux": "linux",
	"darwin": "mac",
	}

	var Archs = map[string]struct {
	Binary string
	Kernel string
	}{
	"x64": {"qemu-system-x86_64", "multiboot.bin"},
	"arm64": {"qemu-system-aarch64", "qemu-boot-shim.bin"},
	}

	var hostDir = map[string]string{"arm64": "host_arm64", "amd64": "host_x64"}[runtime.GOARCH]

	// NewLocalFuchsiaBuild will create a BaseBuild with path layouts corresponding
	// to a local Fuchsia checkout
	func NewLocalFuchsiaBuild() (Build, error) {
	fuchsiaDir := os.Getenv("FUCHSIA_DIR")
	if fuchsiaDir == "" {
	// Fall back to relative path from this file
	fuchsiaDir = filepath.Join("..", "..")
	}

	fxBuildDir := filepath.Join(fuchsiaDir, ".fx-build-dir")
	contents, err := ioutil.ReadFile(fxBuildDir)
	if err != nil {
	return nil, fmt.Errorf("failed to read %q: %s", fxBuildDir, err)
	}

	buildDir := strings.TrimSpace(string(contents))
	if !filepath.IsAbs(buildDir) {
	buildDir = filepath.Join(fuchsiaDir, buildDir)
	}
	prebuiltDir := filepath.Join(fuchsiaDir, "prebuilt")

	platform, ok := Platforms[runtime.GOOS]
	if !ok {
	return nil, fmt.Errorf("unsupported os: %s", runtime.GOOS)
	}

	fxConfig := filepath.Join(buildDir, "fx.config")
	file, err := os.Open(fxConfig)
	if err != nil {
	return nil, fmt.Errorf("failed to open %q: %s", fxConfig, err)
	}
	defer file.Close()

	properties := map[string]string{}
	re := regexp.MustCompile(`^([^=]+)=(?:'([^']+)'\|(.+))?$`)
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
	m := re.FindStringSubmatch(scanner.Text())
	if m != nil {
	properties[m[1]] = m[2]
	}
	}

	arch, found := properties["FUCHSIA_ARCH"]
	if !found {
	return nil, fmt.Errorf("no arch in %s", fxConfig)
	}

	archInfo, ok := Archs[arch]
	if !ok {
	supported := make([]string, 0, len(Archs))
	for k := range Archs {
	supported = append(supported, k)
	}
	return nil, fmt.Errorf("unsupported arch: %s (supported: %v)", arch, supported)
	}

	binary := archInfo.Binary
	kernel := archInfo.Kernel
	platform += "-" + arch

	clangDir := filepath.Join(prebuiltDir, "third_party/clang", platform)
	qemuDir := filepath.Join(prebuiltDir, "third_party/qemu", platform)
	imgDir := filepath.Join(buildDir, "obj", "build", "images", "fuchsia", "fuchsia")

	build := &BaseBuild{
	Paths: map[string]string{
	"zbi": filepath.Join(imgDir, "fuchsia.zbi"),
	"fvm": filepath.Join(buildDir, hostDir, "fvm"),
	"zbitool": filepath.Join(buildDir, hostDir, "zbi"),
	"blk": filepath.Join(imgDir, "fvm.blk"),
	"qemu": filepath.Join(qemuDir, "bin", binary),
	"kernel": filepath.Join(buildDir, kernel),
	"llvm-symbolizer": filepath.Join(clangDir, "bin", "llvm-symbolizer"),
	"symbolizer": filepath.Join(buildDir, hostDir, "symbolize"),
	"fuzzers.json": filepath.Join(buildDir, "fuzzers.json"),
	},
	IDs: []string{
	filepath.Join(clangDir, "lib", "debug", ".build-id"),
	filepath.Join(buildDir, ".build-id"),
	},
	}
	if err := build.LoadFuzzers(); err != nil {
	return nil, err
	}

	return build, nil
	}

	// Convenience type alias for heterogenous metadata objects in fuzzers.json
	type fuzzerMetadata map[string]string

	// LoadFuzzers reads and parses fuzzers.json to populate the build's map of Fuzzers.
	// Unless an error is returned, any previously loaded fuzzers will be discarded.
	func (b *BaseBuild) LoadFuzzers() error {
	paths, err := b.Path("fuzzers.json")
	if err != nil {
	return err
	}

	jsonPath := paths[0]

	glog.Infof("Loading fuzzers from %q", jsonPath)

	jsonBlob, err := ioutil.ReadFile(jsonPath)
	if err != nil {
	return fmt.Errorf("failed to read %q: %s", jsonPath, err)
	}

	var metadataList []fuzzerMetadata
	if err := json.Unmarshal(jsonBlob, &metadataList); err != nil {
	return fmt.Errorf("failed to parse %q: %s", jsonPath, err)
	}

	// Condense metadata entries by label
	metadataByLabel := make(map[string]fuzzerMetadata)
	for _, metadata := range metadataList {
	label, found := metadata["label"]
	if !found {
	return fmt.Errorf("failed to parse %q: entry missing label", jsonPath)
	}

	if _, found := metadataByLabel[label]; !found {
	metadataByLabel[label] = make(fuzzerMetadata)
	}

	for k, v := range metadata {
	if v != "" {
	metadataByLabel[label][k] = v
	}
	}
	}

	b.Fuzzers = make(map[string]*Fuzzer)
	for label, metadata := range metadataByLabel {
	pkg, found := metadata["package"]
	if !found {
	return fmt.Errorf("failed to parse %q: no package for %q", jsonPath, label)
	}

	fuzzer, found := metadata["fuzzer"]
	if !found {
	return fmt.Errorf("failed to parse %q: no fuzzer for %q", jsonPath, label)
	}

	f := NewFuzzer(b, pkg, fuzzer)
	b.Fuzzers[f.Name] = f
	}

	return nil
	}

	// ListFuzzers lists the names of fuzzers present in the build, excluding any
	// that we don't want ClusterFuzz to actually pick up. We can't just omit the
	// example fuzzers from the build entirely because they are used in integration
	// testing.
	func (b *BaseBuild) ListFuzzers() []string {
	var names []string
	for _, fuzzer := range b.Fuzzers {
	if !fuzzer.IsExample() {
	names = append(names, fuzzer.Name)
	}
	}
	return names
	}

	// Fuzzer finds the Fuzzer with the given name, if available
	func (b BaseBuild) Fuzzer(name string) (Fuzzer, error) {
	fuzzer, found := b.Fuzzers[name]
	if !found {
	return nil, fmt.Errorf("no such fuzzer: %s", name)
	}
	return fuzzer, nil
	}

	// Prepare is a no-op for simple builds
	func (b *BaseBuild) Prepare() error {
	return nil
	}

	// Path returns the absolute paths to the list of files indicated by keys. This
	// allows callers to abstract away the detail of where specific file resources
	// are.
	func (b *BaseBuild) Path(keys ...string) ([]string, error) {
	paths := make([]string, len(keys))
	for i, key := range keys {
	if path, found := b.Paths[key]; found {
	paths[i] = path
	} else {
	return nil, fmt.Errorf("no path for %q", key)
	}
	}
	return paths, nil
	}

	var logPrefixRegex = regexp.MustCompile(`[0-9\[\]\.]*\[klog\] INFO: `)

	// Remove timestamps, etc.
	func stripLogPrefix(line string) string {
	return logPrefixRegex.ReplaceAllString(line, "")
	}

	// Symbolize reads from in and replaces symbolizer markup with debug
	// information before writing the result to out. This is blocking, and does
	// not propagate EOFs from in to out.
	func (b *BaseBuild) Symbolize(in io.ReadCloser, out io.Writer) error {
	// Close `in` on return so that the fuzzer doesn't block on a write if an
	// early exit occurs later in the output-processing chain.
	defer in.Close()

	paths, err := b.Path("symbolizer", "llvm-symbolizer")
	if err != nil {
	return err
	}

	symbolizer, llvmSymbolizer := paths[0], paths[1]

	args := []string{"-llvm-symbolizer", llvmSymbolizer}
	for _, dir := range b.IDs {
	args = append(args, "-build-id-dir", dir)
	}
	cmd := NewCommand(symbolizer, args...)
	cmd.Stdin = in
	pipe, err := cmd.StdoutPipe()
	if err != nil {
	return err
	}
	if err := cmd.Start(); err != nil {
	return err
	}
	scanner := bufio.NewScanner(pipe)

	for scanner.Scan() {
	io.WriteString(out, stripLogPrefix(scanner.Text())+"\n")
	}

	if err := scanner.Err(); err != nil {
	return fmt.Errorf("failed during scan: %s", err)
	}

	return cmd.Wait()
	}