cmd/trace: add new command

Trace command allows to visualize and analyze traces.
Run as:
$ go tool trace binary trace.file
The commands opens web browser with the main page,
which contains links for trace visualization,
blocking profiler, network IO profiler and per-goroutine
traces.

Also move trace parser from runtime/pprof/trace_parser_test.go
to internal/trace/parser.go, so that it can be shared between
tests and the command.

Change-Id: Ic97ed59ad6e4c7e1dc9eca5e979701a2b4aed7cf
Reviewed-on: https://go-review.googlesource.com/3601
Reviewed-by: Andrew Gerrand <adg@golang.org>

9 files changed, 1894 insertions, 666 deletions

diff --git a/src/cmd/go/pkg.go b/src/cmd/go/pkg.go
index f9fbe9c452..fd6b056fc1 100644
--- a/src/cmd/go/pkg.go
+++ b/src/cmd/go/pkg.go
@@ -400,6 +400,7 @@ var goTools = map[string]targetDir{
 	"cmd/objdump":                          toTool,
 	"cmd/pack":                             toTool,
 	"cmd/pprof":                            toTool,
+	"cmd/trace":                            toTool,
 	"cmd/yacc":                             toTool,
 	"golang.org/x/tools/cmd/cover":         toTool,
 	"golang.org/x/tools/cmd/godoc":         toBin,
diff --git a/src/cmd/trace/goroutines.go b/src/cmd/trace/goroutines.go
new file mode 100644
index 0000000000..f8d1289c29
--- /dev/null
+++ b/src/cmd/trace/goroutines.go
@@ -0,0 +1,328 @@
+// 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.
+
+// Goroutine-related profiles.
+
+package main
+
+import (
+	"fmt"
+	"html/template"
+	"internal/trace"
+	"net/http"
+	"sort"
+	"strconv"
+)
+
+func init() {
+	http.HandleFunc("/goroutines", httpGoroutines)
+	http.HandleFunc("/goroutine", httpGoroutine)
+}
+
+// gtype describes a group of goroutines grouped by start PC.
+type gtype struct {
+	ID       uint64 // Unique identifier (PC).
+	Name     string // Start function.
+	N        int    // Total number of goroutines in this group.
+	ExecTime int64  // Total execution time of all goroutines in this group.
+}
+
+type gtypeList []gtype
+
+func (l gtypeList) Len() int {
+	return len(l)
+}
+
+func (l gtypeList) Less(i, j int) bool {
+	return l[i].ExecTime > l[j].ExecTime
+}
+
+func (l gtypeList) Swap(i, j int) {
+	l[i], l[j] = l[j], l[i]
+}
+
+// gdesc desribes a single goroutine.
+type gdesc struct {
+	ID         uint64
+	Name       string
+	PC         uint64
+	CreateTime int64
+	StartTime  int64
+	EndTime    int64
+	LastStart  int64
+
+	ExecTime      int64
+	SchedWaitTime int64
+	IOTime        int64
+	BlockTime     int64
+	SyscallTime   int64
+	GCTime        int64
+	SweepTime     int64
+	TotalTime     int64
+
+	blockNetTime     int64
+	blockSyncTime    int64
+	blockSyscallTime int64
+	blockSweepTime   int64
+	blockGCTime      int64
+	blockSchedTime   int64
+}
+
+type gdescList []*gdesc
+
+func (l gdescList) Len() int {
+	return len(l)
+}
+
+func (l gdescList) Less(i, j int) bool {
+	return l[i].TotalTime > l[j].TotalTime
+}
+
+func (l gdescList) Swap(i, j int) {
+	l[i], l[j] = l[j], l[i]
+}
+
+var gs = make(map[uint64]*gdesc)
+
+// analyzeGoroutines generates list gdesc's from the trace and stores it in gs.
+func analyzeGoroutines(events []*trace.Event) {
+	if len(gs) > 0 { //!!! racy
+		return
+	}
+	var lastTs int64
+	var gcStartTime int64
+	for _, ev := range events {
+		lastTs = ev.Ts
+		switch ev.Type {
+		case trace.EvGoCreate:
+			g := &gdesc{CreateTime: ev.Ts}
+			g.blockSchedTime = ev.Ts
+			gs[ev.Args[0]] = g
+		case trace.EvGoStart:
+			g := gs[ev.G]
+			if g.PC == 0 {
+				g.PC = ev.Stk[0].PC
+				g.Name = ev.Stk[0].Fn
+			}
+			g.LastStart = ev.Ts
+			if g.StartTime == 0 {
+				g.StartTime = ev.Ts
+			}
+			if g.blockSchedTime != 0 {
+				g.SchedWaitTime += ev.Ts - g.blockSchedTime
+				g.blockSchedTime = 0
+			}
+		case trace.EvGoEnd, trace.EvGoStop:
+			g := gs[ev.G]
+			g.ExecTime += ev.Ts - g.LastStart
+			g.TotalTime = ev.Ts - g.CreateTime
+			g.EndTime = ev.Ts
+		case trace.EvGoBlockSend, trace.EvGoBlockRecv, trace.EvGoBlockSelect,
+			trace.EvGoBlockSync, trace.EvGoBlockCond:
+			g := gs[ev.G]
+			g.ExecTime += ev.Ts - g.LastStart
+			g.blockSyncTime = ev.Ts
+		case trace.EvGoSched, trace.EvGoPreempt:
+			g := gs[ev.G]
+			g.ExecTime += ev.Ts - g.LastStart
+			g.blockSchedTime = ev.Ts
+		case trace.EvGoSleep, trace.EvGoBlock:
+			g := gs[ev.G]
+			g.ExecTime += ev.Ts - g.LastStart
+		case trace.EvGoBlockNet:
+			g := gs[ev.G]
+			g.ExecTime += ev.Ts - g.LastStart
+			g.blockNetTime = ev.Ts
+		case trace.EvGoUnblock:
+			g := gs[ev.Args[0]]
+			if g.blockNetTime != 0 {
+				g.IOTime += ev.Ts - g.blockNetTime
+				g.blockNetTime = 0
+			}
+			if g.blockSyncTime != 0 {
+				g.BlockTime += ev.Ts - g.blockSyncTime
+				g.blockSyncTime = 0
+			}
+			g.blockSchedTime = ev.Ts
+		case trace.EvGoSysBlock:
+			g := gs[ev.G]
+			g.ExecTime += ev.Ts - g.LastStart
+			g.blockSyscallTime = ev.Ts
+		case trace.EvGoSysExit:
+			g := gs[ev.G]
+			if g.blockSyscallTime != 0 {
+				g.SyscallTime += ev.Ts - g.blockSyscallTime
+				g.blockSyscallTime = 0
+			}
+			g.blockSchedTime = ev.Ts
+		case trace.EvGCSweepStart:
+			g := gs[ev.G]
+			if g != nil {
+				// Sweep can happen during GC on system goroutine.
+				g.blockSweepTime = ev.Ts
+			}
+		case trace.EvGCSweepDone:
+			g := gs[ev.G]
+			if g != nil && g.blockSweepTime != 0 {
+				g.SweepTime += ev.Ts - g.blockSweepTime
+				g.blockSweepTime = 0
+			}
+		case trace.EvGCStart:
+			gcStartTime = ev.Ts
+		case trace.EvGCDone:
+			for _, g := range gs {
+				if g.EndTime == 0 {
+					g.GCTime += ev.Ts - gcStartTime
+				}
+			}
+		}
+	}
+
+	for _, g := range gs {
+		if g.TotalTime == 0 {
+			g.TotalTime = lastTs - g.CreateTime
+		}
+		if g.EndTime == 0 {
+			g.EndTime = lastTs
+		}
+		if g.blockNetTime != 0 {
+			g.IOTime += lastTs - g.blockNetTime
+			g.blockNetTime = 0
+		}
+		if g.blockSyncTime != 0 {
+			g.BlockTime += lastTs - g.blockSyncTime
+			g.blockSyncTime = 0
+		}
+		if g.blockSyscallTime != 0 {
+			g.SyscallTime += lastTs - g.blockSyscallTime
+			g.blockSyscallTime = 0
+		}
+		if g.blockSchedTime != 0 {
+			g.SchedWaitTime += lastTs - g.blockSchedTime
+			g.blockSchedTime = 0
+		}
+	}
+}
+
+// httpGoroutines serves list of goroutine groups.
+func httpGoroutines(w http.ResponseWriter, r *http.Request) {
+	events, err := parseEvents()
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	analyzeGoroutines(events)
+	gss := make(map[uint64]gtype)
+	for _, g := range gs {
+		gs1 := gss[g.PC]
+		gs1.ID = g.PC
+		gs1.Name = g.Name
+		gs1.N++
+		gs1.ExecTime += g.ExecTime
+		gss[g.PC] = gs1
+	}
+	var glist gtypeList
+	for k, v := range gss {
+		v.ID = k
+		glist = append(glist, v)
+	}
+	sort.Sort(glist)
+	templGoroutines.Execute(w, glist)
+}
+
+var templGoroutines = template.Must(template.New("").Parse(`
+<html>
+<body>
+Goroutines: <br>
+{{range $}}
+  <a href="/goroutine?id={{.ID}}">{{.Name}}</a> N={{.N}} <br>
+{{end}}
+</body>
+</html>
+`))
+
+// httpGoroutine serves list of goroutines in a particular group.
+func httpGoroutine(w http.ResponseWriter, r *http.Request) {
+	events, err := parseEvents()
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	pc, err := strconv.ParseUint(r.FormValue("id"), 10, 64)
+	if err != nil {
+		http.Error(w, fmt.Sprintf("failed to parse id parameter '%v': %v", r.FormValue("id"), err), http.StatusInternalServerError)
+		return
+	}
+	analyzeGoroutines(events)
+	var glist gdescList
+	for gid, g := range gs {
+		if g.PC != pc || g.ExecTime == 0 {
+			continue
+		}
+		g.ID = gid
+		glist = append(glist, g)
+	}
+	sort.Sort(glist)
+	err = templGoroutine.Execute(w, glist)
+	if err != nil {
+		http.Error(w, fmt.Sprintf("failed to execute template: %v", err), http.StatusInternalServerError)
+		return
+	}
+}
+
+var templGoroutine = template.Must(template.New("").Parse(`
+<html>
+<body>
+<table border="1" sortable="1">
+<tr>
+<th> Goroutine </th>
+<th> Total time, ns </th>
+<th> Execution time, ns </th>
+<th> Network wait time, ns </th>
+<th> Sync block time, ns </th>
+<th> Blocking syscall time, ns </th>
+<th> Scheduler wait time, ns </th>
+<th> GC sweeping time, ns </th>
+<th> GC pause time, ns </th>
+</tr>
+{{range $}}
+  <tr>
+    <td> <a href="/trace?goid={{.ID}}">{{.ID}}</a> </td>
+    <td> {{.TotalTime}} </td>
+    <td> {{.ExecTime}} </td>
+    <td> {{.IOTime}} </td>
+    <td> {{.BlockTime}} </td>
+    <td> {{.SyscallTime}} </td>
+    <td> {{.SchedWaitTime}} </td>
+    <td> {{.SweepTime}} </td>
+    <td> {{.GCTime}} </td>
+  </tr>
+{{end}}
+</table>
+</body>
+</html>
+`))
+
+// relatedGoroutines finds set of related goroutines that we need to include
+// into trace for goroutine goid.
+func relatedGoroutines(events []*trace.Event, goid uint64) map[uint64]bool {
+	// BFS of depth 2 over "unblock" edges
+	// (what goroutines unblock goroutine goid?).
+	gmap := make(map[uint64]bool)
+	gmap[goid] = true
+	for i := 0; i < 2; i++ {
+		gmap1 := make(map[uint64]bool)
+		for g := range gmap {
+			gmap1[g] = true
+		}
+		for _, ev := range events {
+			if ev.Type == trace.EvGoUnblock && gmap[ev.Args[0]] {
+				gmap1[ev.G] = true
+			}
+		}
+		gmap = gmap1
+	}
+	gmap[0] = true // for GC events
+	return gmap
+}
diff --git a/src/cmd/trace/main.go b/src/cmd/trace/main.go
new file mode 100644
index 0000000000..ea6eef353f
--- /dev/null
+++ b/src/cmd/trace/main.go
@@ -0,0 +1,156 @@
+// 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.
+
+/*
+Trace is a tool for viewing trace files.
+
+Trace files can be generated with:
+	- runtime/pprof.StartTrace
+	- net/http/pprof package
+	- go test -trace
+
+Example usage:
+Generate a trace file with 'go test':
+	go test -trace trace.out pkg
+View the trace in a web browser:
+	go tool trace pkg.test trace.out
+*/
+package main
+
+import (
+	"bufio"
+	"flag"
+	"fmt"
+	"internal/trace"
+	"net"
+	"net/http"
+	"os"
+	"os/exec"
+	"runtime"
+	"sync"
+)
+
+const usageMessage = "" +
+	`Usage of 'go tool trace':
+Given a trace file produced by 'go test':
+	go test -trace=trace.out pkg
+
+Open a web browser displaying trace:
+	go tool trace [flags] pkg.test trace.out
+
+Flags:
+	-http=addr: HTTP service address (e.g., ':6060')
+`
+
+var (
+	httpFlag = flag.String("http", "localhost:0", "HTTP service address (e.g., ':6060')")
+
+	// The binary file name, left here for serveSVGProfile.
+	programBinary string
+	traceFile     string
+)
+
+func main() {
+	flag.Usage = func() {
+		fmt.Fprintln(os.Stderr, usageMessage)
+		os.Exit(2)
+	}
+	flag.Parse()
+
+	// Usage information when no arguments.
+	if flag.NArg() != 2 {
+		flag.Usage()
+	}
+	programBinary = flag.Arg(0)
+	traceFile = flag.Arg(1)
+
+	ln, err := net.Listen("tcp", *httpFlag)
+	if err != nil {
+		dief("failed to create server socket: %v\n", err)
+	}
+	// Open browser.
+	if !startBrowser("http://" + ln.Addr().String()) {
+		dief("failed to start browser\n")
+	}
+
+	// Parse and symbolize trace asynchronously while browser opens.
+	go parseEvents()
+
+	// Start http server.
+	http.HandleFunc("/", httpMain)
+	err = http.Serve(ln, nil)
+	dief("failed to start http server: %v\n", err)
+}
+
+var loader struct {
+	once   sync.Once
+	events []*trace.Event
+	err    error
+}
+
+func parseEvents() ([]*trace.Event, error) {
+	loader.once.Do(func() {
+		tracef, err := os.Open(flag.Arg(1))
+		if err != nil {
+			loader.err = fmt.Errorf("failed to open trace file: %v", err)
+			return
+		}
+		defer tracef.Close()
+
+		// Parse and symbolize.
+		events, err := trace.Parse(bufio.NewReader(tracef))
+		if err != nil {
+			loader.err = fmt.Errorf("failed to parse trace: %v", err)
+			return
+		}
+		err = trace.Symbolize(events, programBinary)
+		if err != nil {
+			loader.err = fmt.Errorf("failed to symbolize trace: %v", err)
+			return
+		}
+		loader.events = events
+	})
+	return loader.events, loader.err
+}
+
+// httpMain serves the starting page.
+func httpMain(w http.ResponseWriter, r *http.Request) {
+	w.Write(templMain)
+}
+
+var templMain = []byte(`
+<html>
+<body>
+<a href="/trace">View trace</a><br>
+<a href="/goroutines">Goroutine analysis</a><br>
+<a href="/io">IO blocking profile</a><br>
+<a href="/block">Synchronization blocking profile</a><br>
+<a href="/syscall">Syscall blocking profile</a><br>
+<a href="/sched">Scheduler latency profile</a><br>
+</body>
+</html>
+`)
+
+// startBrowser tries to open the URL in a browser
+// and reports whether it succeeds.
+// Note: copied from x/tools/cmd/cover/html.go
+func startBrowser(url string) bool {
+	// try to start the browser
+	var args []string
+	switch runtime.GOOS {
+	case "darwin":
+		args = []string{"open"}
+	case "windows":
+		args = []string{"cmd", "/c", "start"}
+	default:
+		args = []string{"xdg-open"}
+	}
+	cmd := exec.Command(args[0], append(args[1:], url)...)
+	return cmd.Start() == nil
+}
+
+func dief(msg string, args ...interface{}) {
+	fmt.Fprintf(os.Stderr, msg, args...)
+	os.Exit(1)
+}
diff --git a/src/cmd/trace/pprof.go b/src/cmd/trace/pprof.go
new file mode 100644
index 0000000000..9e6f277978
--- /dev/null
+++ b/src/cmd/trace/pprof.go
@@ -0,0 +1,162 @@
+// 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.
+
+// Serving of pprof-like profiles.
+
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"internal/trace"
+	"io/ioutil"
+	"net/http"
+	"os"
+	"os/exec"
+)
+
+func init() {
+	http.HandleFunc("/io", httpIO)
+	http.HandleFunc("/block", httpBlock)
+	http.HandleFunc("/syscall", httpSyscall)
+	http.HandleFunc("/sched", httpSched)
+}
+
+// Record represents one entry in pprof-like profiles.
+type Record struct {
+	stk  []*trace.Frame
+	n    uint64
+	time int64
+}
+
+// httpIO serves IO pprof-like profile (time spent in IO wait).
+func httpIO(w http.ResponseWriter, r *http.Request) {
+	events, err := parseEvents()
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	prof := make(map[uint64]Record)
+	for _, ev := range events {
+		if ev.Type != trace.EvGoBlockNet || ev.Link == nil || ev.StkID == 0 || len(ev.Stk) == 0 {
+			continue
+		}
+		rec := prof[ev.StkID]
+		rec.stk = ev.Stk
+		rec.n++
+		rec.time += ev.Link.Ts - ev.Ts
+		prof[ev.StkID] = rec
+	}
+	serveSVGProfile(w, r, prof)
+}
+
+// httpBlock serves blocking pprof-like profile (time spent blocked on synchronization primitives).
+func httpBlock(w http.ResponseWriter, r *http.Request) {
+	events, err := parseEvents()
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	prof := make(map[uint64]Record)
+	for _, ev := range events {
+		switch ev.Type {
+		case trace.EvGoBlockSend, trace.EvGoBlockRecv, trace.EvGoBlockSelect,
+			trace.EvGoBlockSync, trace.EvGoBlockCond:
+		default:
+			continue
+		}
+		if ev.Link == nil || ev.StkID == 0 || len(ev.Stk) == 0 {
+			continue
+		}
+		rec := prof[ev.StkID]
+		rec.stk = ev.Stk
+		rec.n++
+		rec.time += ev.Link.Ts - ev.Ts
+		prof[ev.StkID] = rec
+	}
+	serveSVGProfile(w, r, prof)
+}
+
+// httpSyscall serves syscall pprof-like profile (time spent blocked in syscalls).
+func httpSyscall(w http.ResponseWriter, r *http.Request) {
+	events, err := parseEvents()
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	prof := make(map[uint64]Record)
+	for _, ev := range events {
+		if ev.Type != trace.EvGoSysCall || ev.Link == nil || ev.StkID == 0 || len(ev.Stk) == 0 {
+			continue
+		}
+		rec := prof[ev.StkID]
+		rec.stk = ev.Stk
+		rec.n++
+		rec.time += ev.Link.Ts - ev.Ts
+		prof[ev.StkID] = rec
+	}
+	serveSVGProfile(w, r, prof)
+}
+
+// httpSched serves scheduler latency pprof-like profile
+// (time between a goroutine become runnable and actually scheduled for execution).
+func httpSched(w http.ResponseWriter, r *http.Request) {
+	events, err := parseEvents()
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	prof := make(map[uint64]Record)
+	for _, ev := range events {
+		if (ev.Type != trace.EvGoUnblock && ev.Type != trace.EvGoCreate) ||
+			ev.Link == nil || ev.StkID == 0 || len(ev.Stk) == 0 {
+			continue
+		}
+		rec := prof[ev.StkID]
+		rec.stk = ev.Stk
+		rec.n++
+		rec.time += ev.Link.Ts - ev.Ts
+		prof[ev.StkID] = rec
+	}
+	serveSVGProfile(w, r, prof)
+}
+
+// generateSVGProfile generates pprof-like profile stored in prof and writes in to w.
+func serveSVGProfile(w http.ResponseWriter, r *http.Request, prof map[uint64]Record) {
+	blockf, err := ioutil.TempFile("", "block")
+	if err != nil {
+		http.Error(w, fmt.Sprintf("failed to create temp file: %v", err), http.StatusInternalServerError)
+		return
+	}
+	defer os.Remove(blockf.Name())
+	blockb := bufio.NewWriter(blockf)
+	fmt.Fprintf(blockb, "--- contention:\ncycles/second=1000000000\n")
+	for _, rec := range prof {
+		fmt.Fprintf(blockb, "%v %v @", rec.time, rec.n)
+		for _, f := range rec.stk {
+			fmt.Fprintf(blockb, " 0x%x", f.PC)
+		}
+		fmt.Fprintf(blockb, "\n")
+	}
+	err = blockb.Flush()
+	if err != nil {
+		http.Error(w, fmt.Sprintf("failed to flush temp file: %v", err), http.StatusInternalServerError)
+		return
+	}
+	err = blockf.Close()
+	if err != nil {
+		http.Error(w, fmt.Sprintf("failed to close temp file: %v", err), http.StatusInternalServerError)
+		return
+	}
+
+	svgFilename := blockf.Name() + ".svg"
+	_, err = exec.Command("go", "tool", "pprof", "-svg", "-output", svgFilename, programBinary, blockf.Name()).CombinedOutput()
+	if err != nil {
+		http.Error(w, fmt.Sprintf("failed to execute go tool pprof: %v", err), http.StatusInternalServerError)
+		return
+	}
+	defer os.Remove(svgFilename)
+	w.Header().Set("Content-Type", "image/svg+xml")
+	http.ServeFile(w, r, svgFilename)
+}
diff --git a/src/cmd/trace/trace.go b/src/cmd/trace/trace.go
new file mode 100644
index 0000000000..8f8ef14687
--- /dev/null
+++ b/src/cmd/trace/trace.go
@@ -0,0 +1,434 @@
+// 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/json"
+	"fmt"
+	"internal/trace"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+func init() {
+	http.HandleFunc("/trace", httpTrace)
+	http.HandleFunc("/jsontrace", httpJsonTrace)
+	http.HandleFunc("/trace_viewer_html", httpTraceViewerHTML)
+}
+
+// httpTrace serves either whole trace (goid==0) or trace for goid goroutine.
+func httpTrace(w http.ResponseWriter, r *http.Request) {
+	_, err := parseEvents()
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	params := ""
+	if goids := r.FormValue("goid"); goids != "" {
+		goid, err := strconv.ParseUint(goids, 10, 64)
+		if err != nil {
+			http.Error(w, fmt.Sprintf("failed to parse goid parameter '%v': %v", goids, err), http.StatusInternalServerError)
+			return
+		}
+		params = fmt.Sprintf("?goid=%v", goid)
+	}
+	html := strings.Replace(templTrace, "{{PARAMS}}", params, -1)
+	w.Write([]byte(html))
+
+}
+
+var templTrace = `
+<html>
+	<head>
+		<link href="/trace_viewer_html" rel="import">
+		<script>
+			document.addEventListener("DOMContentLoaded", function(event) {
+				var viewer = new tv.TraceViewer('/jsontrace{{PARAMS}}');
+				document.body.appendChild(viewer);
+			});
+		</script>
+	</head>
+	<body>
+	</body>
+</html>
+`
+
+// httpTraceViewerHTML serves static part of trace-viewer.
+// This URL is queried from templTrace HTML.
+func httpTraceViewerHTML(w http.ResponseWriter, r *http.Request) {
+	http.ServeFile(w, r, filepath.Join(os.Getenv("GOROOT"), "misc", "trace", "trace_viewer_lean.html"))
+}
+
+// httpJsonTrace serves json trace, requested from within templTrace HTML.
+func httpJsonTrace(w http.ResponseWriter, r *http.Request) {
+	events, err := parseEvents()
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	params := &traceParams{
+		events:  events,
+		endTime: int64(1<<63 - 1),
+	}
+
+	if goids := r.FormValue("goid"); goids != "" {
+		goid, err := strconv.ParseUint(goids, 10, 64)
+		if err != nil {
+			http.Error(w, fmt.Sprintf("failed to parse goid parameter '%v': %v", goids, err), http.StatusInternalServerError)
+			return
+		}
+		analyzeGoroutines(events)
+		g := gs[goid]
+		params.gtrace = true
+		params.startTime = g.StartTime
+		params.endTime = g.EndTime
+		params.maing = goid
+		params.gs = relatedGoroutines(events, goid)
+	}
+
+	err = json.NewEncoder(w).Encode(generateTrace(params))
+	if err != nil {
+		http.Error(w, fmt.Sprintf("failed to serialize trace: %v", err), http.StatusInternalServerError)
+		return
+	}
+}
+
+type traceParams struct {
+	events    []*trace.Event
+	gtrace    bool
+	startTime int64
+	endTime   int64
+	maing     uint64
+	gs        map[uint64]bool
+}
+
+type traceContext struct {
+	*traceParams
+	data      ViewerData
+	frameTree frameNode
+	frameSeq  int
+	arrowSeq  uint64
+	heapAlloc uint64
+	nextGC    uint64
+	gcount    uint64
+	grunnable uint64
+	grunning  uint64
+	insyscall uint64
+	prunning  uint64
+}
+
+type frameNode struct {
+	id       int
+	children map[uint64]frameNode
+}
+
+type ViewerData struct {
+	Events []*ViewerEvent         `json:"traceEvents"`
+	Frames map[string]ViewerFrame `json:"stackFrames"`
+}
+
+type ViewerEvent struct {
+	Name     string      `json:"name,omitempty"`
+	Phase    string      `json:"ph"`
+	Scope    string      `json:"s,omitempty"`
+	Time     int64       `json:"ts"`
+	Dur      int64       `json:"dur,omitempty"`
+	Pid      uint64      `json:"pid"`
+	Tid      uint64      `json:"tid"`
+	ID       uint64      `json:"id,omitempty"`
+	Stack    int         `json:"sf,omitempty"`
+	EndStack int         `json:"esf,omitempty"`
+	Arg      interface{} `json:"args,omitempty"`
+}
+
+type ViewerFrame struct {
+	Name   string `json:"name"`
+	Parent int    `json:"parent,omitempty"`
+}
+
+type NameArg struct {
+	Name string `json:"name"`
+}
+
+type SortIndexArg struct {
+	Index int `json:"sort_index"`
+}
+
+// generateTrace generates json trace for trace-viewer:
+// https://github.com/google/trace-viewer
+// Trace format is described at:
+// https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/view
+// If gtrace=true, generate trace for goroutine goid, otherwise whole trace.
+// startTime, endTime determine part of the trace that we are interested in.
+// gset restricts goroutines that are included in the resulting trace.
+func generateTrace(params *traceParams) ViewerData {
+	ctx := &traceContext{traceParams: params}
+	ctx.frameTree.children = make(map[uint64]frameNode)
+	ctx.data.Frames = make(map[string]ViewerFrame)
+	maxProc := 0
+	gnames := make(map[uint64]string)
+	for _, ev := range ctx.events {
+		// Handle trace.EvGoStart separately, because we need the goroutine name
+		// even if ignore the event otherwise.
+		if ev.Type == trace.EvGoStart {
+			if _, ok := gnames[ev.G]; !ok {
+				if len(ev.Stk) > 0 {
+					gnames[ev.G] = fmt.Sprintf("G%v %s", ev.G, ev.Stk[0].Fn)
+				} else {
+					gnames[ev.G] = fmt.Sprintf("G%v", ev.G)
+				}
+			}
+		}
+
+		// Ignore events that are from uninteresting goroutines
+		// or outside of the interesting timeframe.
+		if ctx.gs != nil && ev.P < trace.FakeP && !ctx.gs[ev.G] {
+			continue
+		}
+		if ev.Ts < ctx.startTime || ev.Ts > ctx.endTime {
+			continue
+		}
+
+		if ev.P < trace.FakeP && ev.P > maxProc {
+			maxProc = ev.P
+		}
+
+		switch ev.Type {
+		case trace.EvProcStart:
+			if ctx.gtrace {
+				continue
+			}
+			ctx.prunning++
+			ctx.emitThreadCounters(ev)
+			ctx.emitInstant(ev, "proc start")
+		case trace.EvProcStop:
+			if ctx.gtrace {
+				continue
+			}
+			ctx.prunning--
+			ctx.emitThreadCounters(ev)
+			ctx.emitInstant(ev, "proc stop")
+		case trace.EvGCStart:
+			ctx.emitSlice(ev, "GC")
+		case trace.EvGCDone:
+		case trace.EvGCScanStart:
+			if ctx.gtrace {
+				continue
+			}
+			ctx.emitSlice(ev, "MARK")
+		case trace.EvGCScanDone:
+		case trace.EvGCSweepStart:
+			ctx.emitSlice(ev, "SWEEP")
+		case trace.EvGCSweepDone:
+		case trace.EvGoStart:
+			ctx.grunnable--
+			ctx.grunning++
+			ctx.emitGoroutineCounters(ev)
+			ctx.emitSlice(ev, gnames[ev.G])
+		case trace.EvGoCreate:
+			ctx.gcount++
+			ctx.grunnable++
+			ctx.emitGoroutineCounters(ev)
+			ctx.emitArrow(ev, "go")
+		case trace.EvGoEnd:
+			ctx.gcount--
+			ctx.grunning--
+			ctx.emitGoroutineCounters(ev)
+		case trace.EvGoUnblock:
+			ctx.grunnable++
+			ctx.emitGoroutineCounters(ev)
+			ctx.emitArrow(ev, "unblock")
+		case trace.EvGoSysCall:
+			ctx.emitInstant(ev, "syscall")
+		case trace.EvGoSysExit:
+			ctx.grunnable++
+			ctx.emitGoroutineCounters(ev)
+			ctx.insyscall--
+			ctx.emitThreadCounters(ev)
+			ctx.emitArrow(ev, "sysexit")
+		case trace.EvGoSysBlock:
+			ctx.grunning--
+			ctx.emitGoroutineCounters(ev)
+			ctx.insyscall++
+			ctx.emitThreadCounters(ev)
+		case trace.EvGoSched, trace.EvGoPreempt:
+			ctx.grunnable++
+			ctx.grunning--
+			ctx.emitGoroutineCounters(ev)
+		case trace.EvGoStop,
+			trace.EvGoSleep, trace.EvGoBlock, trace.EvGoBlockSend, trace.EvGoBlockRecv,
+			trace.EvGoBlockSelect, trace.EvGoBlockSync, trace.EvGoBlockCond, trace.EvGoBlockNet:
+			ctx.grunning--
+			ctx.emitGoroutineCounters(ev)
+		case trace.EvGoWaiting:
+			ctx.grunnable--
+			ctx.emitGoroutineCounters(ev)
+		case trace.EvGoInSyscall:
+			ctx.insyscall++
+			ctx.emitThreadCounters(ev)
+		case trace.EvHeapAlloc:
+			ctx.heapAlloc = ev.Args[0]
+			ctx.emitHeapCounters(ev)
+		case trace.EvNextGC:
+			ctx.nextGC = ev.Args[0]
+			ctx.emitHeapCounters(ev)
+		}
+	}
+
+	ctx.emit(&ViewerEvent{Name: "process_name", Phase: "M", Pid: 0, Arg: &NameArg{"PROCS"}})
+	ctx.emit(&ViewerEvent{Name: "process_sort_index", Phase: "M", Pid: 0, Arg: &SortIndexArg{1}})
+
+	ctx.emit(&ViewerEvent{Name: "process_name", Phase: "M", Pid: 1, Arg: &NameArg{"STATS"}})
+	ctx.emit(&ViewerEvent{Name: "process_sort_index", Phase: "M", Pid: 1, Arg: &SortIndexArg{0}})
+
+	ctx.emit(&ViewerEvent{Name: "thread_name", Phase: "M", Pid: 0, Tid: trace.NetpollP, Arg: &NameArg{"Network"}})
+	ctx.emit(&ViewerEvent{Name: "thread_sort_index", Phase: "M", Pid: 0, Tid: trace.NetpollP, Arg: &SortIndexArg{-5}})
+
+	ctx.emit(&ViewerEvent{Name: "thread_name", Phase: "M", Pid: 0, Tid: trace.TimerP, Arg: &NameArg{"Timers"}})
+	ctx.emit(&ViewerEvent{Name: "thread_sort_index", Phase: "M", Pid: 0, Tid: trace.TimerP, Arg: &SortIndexArg{-4}})
+
+	ctx.emit(&ViewerEvent{Name: "thread_name", Phase: "M", Pid: 0, Tid: trace.SyscallP, Arg: &NameArg{"Syscalls"}})
+	ctx.emit(&ViewerEvent{Name: "thread_sort_index", Phase: "M", Pid: 0, Tid: trace.SyscallP, Arg: &SortIndexArg{-3}})
+
+	if !ctx.gtrace {
+		for i := 0; i <= maxProc; i++ {
+			ctx.emit(&ViewerEvent{Name: "thread_name", Phase: "M", Pid: 0, Tid: uint64(i), Arg: &NameArg{fmt.Sprintf("Proc %v", i)}})
+		}
+	}
+
+	if ctx.gtrace && ctx.gs != nil {
+		for k, v := range gnames {
+			if !ctx.gs[k] {
+				continue
+			}
+			ctx.emit(&ViewerEvent{Name: "thread_name", Phase: "M", Pid: 0, Tid: k, Arg: &NameArg{v}})
+		}
+		ctx.emit(&ViewerEvent{Name: "thread_sort_index", Phase: "M", Pid: 0, Tid: ctx.maing, Arg: &SortIndexArg{-2}})
+		ctx.emit(&ViewerEvent{Name: "thread_sort_index", Phase: "M", Pid: 0, Tid: 0, Arg: &SortIndexArg{-1}})
+	}
+
+	return ctx.data
+}
+
+func (ctx *traceContext) emit(e *ViewerEvent) {
+	ctx.data.Events = append(ctx.data.Events, e)
+}
+
+func (ctx *traceContext) time(ev *trace.Event) int64 {
+	if ev.Ts < ctx.startTime || ev.Ts > ctx.endTime {
+		fmt.Printf("ts=%v startTime=%v endTime\n", ev.Ts, ctx.startTime, ctx.endTime)
+		panic("timestamp is outside of trace range")
+	}
+	// NOTE: trace viewer wants timestamps in microseconds and it does not
+	// handle fractional timestamps (rounds them). We give it timestamps
+	// in nanoseconds to avoid rounding. See:
+	// https://github.com/google/trace-viewer/issues/624
+	return ev.Ts - ctx.startTime
+}
+
+func (ctx *traceContext) proc(ev *trace.Event) uint64 {
+	if ctx.gtrace && ev.P < trace.FakeP {
+		return ev.G
+	} else {
+		return uint64(ev.P)
+	}
+}
+
+func (ctx *traceContext) emitSlice(ev *trace.Event, name string) {
+	ctx.emit(&ViewerEvent{
+		Name:  name,
+		Phase: "X",
+		Time:  ctx.time(ev),
+		Dur:   ctx.time(ev.Link) - ctx.time(ev),
+		Tid:   ctx.proc(ev),
+		//Stack: ctx.stack(ev.Stk),
+		EndStack: ctx.stack(ev.Link.Stk),
+	})
+}
+
+func (ctx *traceContext) emitHeapCounters(ev *trace.Event) {
+	type Arg struct {
+		Allocated uint64
+		NextGC    uint64
+	}
+	if ctx.gtrace {
+		return
+	}
+	diff := uint64(0)
+	if ctx.nextGC > ctx.heapAlloc {
+		diff = ctx.nextGC - ctx.heapAlloc
+	}
+	ctx.emit(&ViewerEvent{Name: "Heap", Phase: "C", Time: ctx.time(ev), Pid: 1, Arg: &Arg{ctx.heapAlloc, diff}})
+}
+
+func (ctx *traceContext) emitGoroutineCounters(ev *trace.Event) {
+	type Arg struct {
+		Running  uint64
+		Runnable uint64
+	}
+	if ctx.gtrace {
+		return
+	}
+	ctx.emit(&ViewerEvent{Name: "Goroutines", Phase: "C", Time: ctx.time(ev), Pid: 1, Arg: &Arg{ctx.grunning, ctx.grunnable}})
+}
+
+func (ctx *traceContext) emitThreadCounters(ev *trace.Event) {
+	type Arg struct {
+		Running   uint64
+		InSyscall uint64
+	}
+	if ctx.gtrace {
+		return
+	}
+	ctx.emit(&ViewerEvent{Name: "Threads", Phase: "C", Time: ctx.time(ev), Pid: 1, Arg: &Arg{ctx.prunning, ctx.insyscall}})
+}
+
+func (ctx *traceContext) emitInstant(ev *trace.Event, name string) {
+	ctx.emit(&ViewerEvent{Name: name, Phase: "I", Scope: "t", Time: ctx.time(ev), Tid: ctx.proc(ev), Stack: ctx.stack(ev.Stk)})
+}
+
+func (ctx *traceContext) emitArrow(ev *trace.Event, name string) {
+	if ev.Link == nil {
+		// The other end of the arrow is not captured in the trace.
+		// For example, a goroutine was unblocked but was not scheduled before trace stop.
+		return
+	}
+	if ctx.gtrace && (!ctx.gs[ev.Link.G] || ev.Link.Ts < ctx.startTime || ev.Link.Ts > ctx.endTime) {
+		return
+	}
+
+	ctx.arrowSeq++
+	ctx.emit(&ViewerEvent{Name: name, Phase: "s", Tid: ctx.proc(ev), ID: ctx.arrowSeq, Time: ctx.time(ev), Stack: ctx.stack(ev.Stk)})
+	ctx.emit(&ViewerEvent{Name: name, Phase: "t", Tid: ctx.proc(ev.Link), ID: ctx.arrowSeq, Time: ctx.time(ev.Link)})
+}
+
+func (ctx *traceContext) stack(stk []*trace.Frame) int {
+	return ctx.buildBranch(ctx.frameTree, stk)
+}
+
+// buildBranch builds one branch in the prefix tree rooted at ctx.frameTree.
+func (ctx *traceContext) buildBranch(parent frameNode, stk []*trace.Frame) int {
+	if len(stk) == 0 {
+		return parent.id
+	}
+	last := len(stk) - 1
+	frame := stk[last]
+	stk = stk[:last]
+
+	node, ok := parent.children[frame.PC]
+	if !ok {
+		ctx.frameSeq++
+		node.id = ctx.frameSeq
+		node.children = make(map[uint64]frameNode)
+		parent.children[frame.PC] = node
+		ctx.data.Frames[strconv.Itoa(node.id)] = ViewerFrame{fmt.Sprintf("%v:%v", frame.Fn, frame.Line), parent.id}
+	}
+	return ctx.buildBranch(node, stk)
+}
diff --git a/src/internal/trace/parser.go b/src/internal/trace/parser.go
new file mode 100644
index 0000000000..62d063c5d8
--- /dev/null
+++ b/src/internal/trace/parser.go
@@ -0,0 +1,662 @@
+// 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 trace
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+// Event describes one event in the trace.
+type Event struct {
+	Off   int       // offset in input file (for debugging and error reporting)
+	Type  byte      // one of Ev*
+	Ts    int64     // timestamp in nanoseconds
+	P     int       // P on which the event happened (can be one of TimerP, NetpollP, SyscallP)
+	G     uint64    // G on which the event happened
+	StkID uint64    // unique stack ID
+	Stk   []*Frame  // stack trace (can be empty)
+	Args  [2]uint64 // event-type-specific arguments
+	// linked event (can be nil), depends on event type:
+	// for GCStart: the GCStop
+	// for GCScanStart: the GCScanDone
+	// for GCSweepStart: the GCSweepDone
+	// for GoCreate: first GoStart of the created goroutine
+	// for GoStart: the associated GoEnd, GoBlock or other blocking event
+	// for GoSched/GoPreempt: the next GoStart
+	// for GoBlock and other blocking events: the unblock event
+	// for GoUnblock: the associated GoStart
+	// for blocking GoSysCall: the associated GoSysExit
+	// for GoSysExit: the next GoStart
+	Link *Event
+}
+
+// Frame is a frame in stack traces.
+type Frame struct {
+	PC   uint64
+	Fn   string
+	File string
+	Line int
+}
+
+const (
+	// Special P identifiers:
+	FakeP    = 1000000 + iota
+	TimerP   // depicts timer unblocks
+	NetpollP // depicts network unblocks
+	SyscallP // depicts returns from syscalls
+)
+
+// parseTrace parses, post-processes and verifies the trace.
+func Parse(r io.Reader) ([]*Event, error) {
+	rawEvents, err := readTrace(r)
+	if err != nil {
+		return nil, err
+	}
+	events, err := parseEvents(rawEvents)
+	if err != nil {
+		return nil, err
+	}
+	err = postProcessTrace(events)
+	if err != nil {
+		return nil, err
+	}
+	return events, nil
+}
+
+// rawEvent is a helper type used during parsing.
+type rawEvent struct {
+	off  int
+	typ  byte
+	args []uint64
+}
+
+// readTrace does wire-format parsing and verification.
+// It does not care about specific event types and argument meaning.
+func readTrace(r io.Reader) ([]rawEvent, error) {
+	// Read and validate trace header.
+	var buf [8]byte
+	off, err := r.Read(buf[:])
+	if off != 8 || err != nil {
+		return nil, fmt.Errorf("failed to read header: read %v, err %v", off, err)
+	}
+	if bytes.Compare(buf[:], []byte("gotrace\x00")) != 0 {
+		return nil, fmt.Errorf("not a trace file")
+	}
+
+	// Read events.
+	var events []rawEvent
+	for {
+		// Read event type and number of arguments (1 byte).
+		off0 := off
+		n, err := r.Read(buf[:1])
+		if err == io.EOF {
+			break
+		}
+		if err != nil || n != 1 {
+			return nil, fmt.Errorf("failed to read trace at offset 0x%x: n=%v err=%v", off0, n, err)
+		}
+		off += n
+		typ := buf[0] << 2 >> 2
+		narg := buf[0]>>6 + 1
+		ev := rawEvent{typ: typ, off: off0}
+		if narg <= 3 {
+			for i := 0; i < int(narg); i++ {
+				var v uint64
+				v, off, err = readVal(r, off)
+				if err != nil {
+					return nil, err
+				}
+				ev.args = append(ev.args, v)
+			}
+		} else {
+			// If narg == 4, the first value is length of the event in bytes.
+			var v uint64
+			v, off, err = readVal(r, off)
+			if err != nil {
+				return nil, err
+			}
+			evLen := v
+			off1 := off
+			for evLen > uint64(off-off1) {
+				v, off, err = readVal(r, off)
+				if err != nil {
+					return nil, err
+				}
+				ev.args = append(ev.args, v)
+			}
+			if evLen != uint64(off-off1) {
+				return nil, fmt.Errorf("event has wrong length at offset 0x%x: want %v, got %v", off0, evLen, off-off1)
+			}
+		}
+		events = append(events, ev)
+	}
+	return events, nil
+}
+
+// Parse events transforms raw events into events.
+// It does analyze and verify per-event-type arguments.
+func parseEvents(rawEvents []rawEvent) (events []*Event, err error) {
+	var ticksPerSec, lastTs int64
+	var lastG, timerGoid uint64
+	var lastP int
+	lastGs := make(map[int]uint64) // last goroutine running on P
+	stacks := make(map[uint64][]*Frame)
+	for _, raw := range rawEvents {
+		if raw.typ == EvNone || raw.typ >= EvCount {
+			err = fmt.Errorf("unknown event type %v at offset 0x%x", raw.typ, raw.off)
+			return
+		}
+		desc := EventDescriptions[raw.typ]
+		if desc.Name == "" {
+			err = fmt.Errorf("missing description for event type %v", raw.typ)
+			return
+		}
+		if raw.typ != EvStack {
+			narg := len(desc.Args)
+			if desc.Stack {
+				narg++
+			}
+			if raw.typ != EvBatch && raw.typ != EvFrequency && raw.typ != EvTimerGoroutine {
+				narg++ // timestamp
+			}
+			if len(raw.args) != narg {
+				err = fmt.Errorf("%v has wrong number of arguments at offset 0x%x: want %v, got %v",
+					desc.Name, raw.off, narg, len(raw.args))
+				return
+			}
+		}
+		switch raw.typ {
+		case EvBatch:
+			lastGs[lastP] = lastG
+			lastP = int(raw.args[0])
+			lastG = lastGs[lastP]
+			lastTs = int64(raw.args[1])
+		case EvFrequency:
+			ticksPerSec = int64(raw.args[0])
+			if ticksPerSec <= 0 {
+				err = fmt.Errorf("EvFrequency contains invalid frequency %v at offset 0x%x",
+					ticksPerSec, raw.off)
+				return
+			}
+		case EvTimerGoroutine:
+			timerGoid = raw.args[0]
+		case EvStack:
+			if len(raw.args) < 2 {
+				err = fmt.Errorf("EvStack has wrong number of arguments at offset 0x%x: want at least 2, got %v",
+					raw.off, len(raw.args))
+				return
+			}
+			size := raw.args[1]
+			if size > 1000 {
+				err = fmt.Errorf("EvStack has bad number of frames at offset 0x%x: %v",
+					raw.off, size)
+				return
+			}
+			id := raw.args[0]
+			if id != 0 && size > 0 {
+				stk := make([]*Frame, size)
+				for i := 0; i < int(size); i++ {
+					stk[i] = &Frame{PC: raw.args[i+2]}
+				}
+				stacks[id] = stk
+			}
+		default:
+			e := &Event{Off: raw.off, Type: raw.typ, P: lastP, G: lastG}
+			e.Ts = lastTs + int64(raw.args[0])
+			lastTs = e.Ts
+			for i := range desc.Args {
+				e.Args[i] = raw.args[i+1]
+			}
+			if desc.Stack {
+				e.StkID = raw.args[len(desc.Args)+1]
+			}
+			switch raw.typ {
+			case EvGoStart:
+				lastG = e.Args[0]
+				e.G = lastG
+			case EvGCStart, EvGCDone, EvGCScanStart, EvGCScanDone:
+				e.G = 0
+			case EvGoEnd, EvGoStop, EvGoSched, EvGoPreempt,
+				EvGoSleep, EvGoBlock, EvGoBlockSend, EvGoBlockRecv,
+				EvGoBlockSelect, EvGoBlockSync, EvGoBlockCond, EvGoBlockNet,
+				EvGoSysBlock:
+				lastG = 0
+			}
+			events = append(events, e)
+		}
+	}
+
+	// Attach stack traces.
+	for _, ev := range events {
+		if ev.StkID != 0 {
+			ev.Stk = stacks[ev.StkID]
+		}
+	}
+
+	// Sort by time and translate cpu ticks to real time.
+	sort.Sort(eventList(events))
+	if ticksPerSec == 0 {
+		err = fmt.Errorf("no EvFrequency event")
+		return
+	}
+	minTs := events[0].Ts
+	for _, ev := range events {
+		ev.Ts = (ev.Ts - minTs) * 1e9 / ticksPerSec
+		// Move timers and syscalls to separate fake Ps.
+		if timerGoid != 0 && ev.G == timerGoid && ev.Type == EvGoUnblock {
+			ev.P = TimerP
+		}
+		if ev.Type == EvGoSysExit {
+			ev.P = SyscallP
+			ev.G = ev.Args[0]
+		}
+	}
+
+	return
+}
+
+// postProcessTrace does inter-event verification and information restoration.
+// The resulting trace is guaranteed to be consistent
+// (for example, a P does not run two Gs at the same time, or a G is indeed
+// blocked before an unblock event).
+func postProcessTrace(events []*Event) error {
+	const (
+		gDead = iota
+		gRunnable
+		gRunning
+		gWaiting
+	)
+	type gdesc struct {
+		state   int
+		ev      *Event
+		evStart *Event
+	}
+	type pdesc struct {
+		running bool
+		g       uint64
+		evGC    *Event
+		evScan  *Event
+		evSweep *Event
+	}
+
+	gs := make(map[uint64]gdesc)
+	ps := make(map[int]pdesc)
+	gs[0] = gdesc{state: gRunning}
+
+	checkRunning := func(p pdesc, g gdesc, ev *Event) error {
+		name := EventDescriptions[ev.Type].Name
+		if g.state != gRunning {
+			return fmt.Errorf("g %v is not running while %v (offset %v, time %v)", ev.G, name, ev.Off, ev.Ts)
+		}
+		if p.g != ev.G {
+			return fmt.Errorf("p %v is not running g %v while %v (offset %v, time %v)", ev.P, ev.G, name, ev.Off, ev.Ts)
+		}
+		return nil
+	}
+
+	for _, ev := range events {
+		g := gs[ev.G]
+		p := ps[ev.P]
+
+		switch ev.Type {
+		case EvProcStart:
+			if p.running {
+				return fmt.Errorf("p %v is running before start (offset %v, time %v)", ev.P, ev.Off, ev.Ts)
+			}
+			p.running = true
+		case EvProcStop:
+			if !p.running {
+				return fmt.Errorf("p %v is not running before stop (offset %v, time %v)", ev.P, ev.Off, ev.Ts)
+			}
+			if p.g != 0 {
+				return fmt.Errorf("p %v is running a goroutine %v during stop (offset %v, time %v)", ev.P, p.g, ev.Off, ev.Ts)
+			}
+			p.running = false
+		case EvGCStart:
+			if p.evGC != nil {
+				return fmt.Errorf("previous GC is not ended before a new one (offset %v, time %v)", ev.Off, ev.Ts)
+			}
+			p.evGC = ev
+		case EvGCDone:
+			if p.evGC == nil {
+				return fmt.Errorf("bogus GC end (offset %v, time %v)", ev.Off, ev.Ts)
+			}
+			p.evGC.Link = ev
+			p.evGC = nil
+		case EvGCScanStart:
+			if p.evScan != nil {
+				return fmt.Errorf("previous scanning is not ended before a new one (offset %v, time %v)", ev.Off, ev.Ts)
+			}
+			p.evScan = ev
+		case EvGCScanDone:
+			if p.evScan == nil {
+				return fmt.Errorf("bogus scanning end (offset %v, time %v)", ev.Off, ev.Ts)
+			}
+			p.evScan.Link = ev
+			p.evScan = nil
+		case EvGCSweepStart:
+			if p.evSweep != nil {
+				return fmt.Errorf("previous sweeping is not ended before a new one (offset %v, time %v)", ev.Off, ev.Ts)
+			}
+			p.evSweep = ev
+		case EvGCSweepDone:
+			if p.evSweep == nil {
+				return fmt.Errorf("bogus sweeping end (offset %v, time %v)", ev.Off, ev.Ts)
+			}
+			p.evSweep.Link = ev
+			p.evSweep = nil
+		case EvGoWaiting:
+			g1 := gs[ev.Args[0]]
+			if g1.state != gRunnable {
+				return fmt.Errorf("g %v is not runnable before EvGoWaiting (offset %v, time %v)", ev.Args[0], ev.Off, ev.Ts)
+			}
+			g1.state = gWaiting
+			gs[ev.Args[0]] = g1
+		case EvGoInSyscall:
+			// this case is intentionally left blank
+		case EvGoCreate:
+			if err := checkRunning(p, g, ev); err != nil {
+				return err
+			}
+			if _, ok := gs[ev.Args[0]]; ok {
+				return fmt.Errorf("g %v already exists (offset %v, time %v)", ev.Args[0], ev.Off, ev.Ts)
+			}
+			gs[ev.Args[0]] = gdesc{state: gRunnable, ev: ev}
+		case EvGoStart:
+			if g.state != gRunnable {
+				return fmt.Errorf("g %v is not runnable before start (offset %v, time %v)", ev.G, ev.Off, ev.Ts)
+			}
+			if p.g != 0 {
+				return fmt.Errorf("p %v is already running g %v while start g %v (offset %v, time %v)", ev.P, p.g, ev.G, ev.Off, ev.Ts)
+			}
+			g.state = gRunning
+			g.evStart = ev
+			p.g = ev.G
+			if g.ev != nil {
+				if g.ev.Type == EvGoCreate {
+					// +1 because symblizer expects return pc.
+					ev.Stk = []*Frame{&Frame{PC: g.ev.Args[1] + 1}}
+				}
+				g.ev.Link = ev
+				g.ev = nil
+			}
+		case EvGoEnd, EvGoStop:
+			if err := checkRunning(p, g, ev); err != nil {
+				return err
+			}
+			g.evStart.Link = ev
+			g.evStart = nil
+			g.state = gDead
+			p.g = 0
+		case EvGoSched, EvGoPreempt:
+			if err := checkRunning(p, g, ev); err != nil {
+				return err
+			}
+			g.state = gRunnable
+			g.evStart.Link = ev
+			g.evStart = nil
+			p.g = 0
+			g.ev = ev
+		case EvGoUnblock:
+			if g.state != gRunning {
+				return fmt.Errorf("g %v is not running while unpark (offset %v, time %v)", ev.G, ev.Off, ev.Ts)
+			}
+			if ev.P != TimerP && p.g != ev.G {
+				return fmt.Errorf("p %v is not running g %v while unpark (offset %v, time %v)", ev.P, ev.G, ev.Off, ev.Ts)
+			}
+			g1 := gs[ev.Args[0]]
+			if g1.state != gWaiting {
+				return fmt.Errorf("g %v is not waiting before unpark (offset %v, time %v)", ev.Args[0], ev.Off, ev.Ts)
+			}
+			if g1.ev != nil && g1.ev.Type == EvGoBlockNet && ev.P != TimerP {
+				ev.P = NetpollP
+			}
+			if g1.ev != nil {
+				g1.ev.Link = ev
+			}
+			g1.state = gRunnable
+			g1.ev = ev
+			gs[ev.Args[0]] = g1
+		case EvGoSysCall:
+			if err := checkRunning(p, g, ev); err != nil {
+				return err
+			}
+			g.ev = ev
+		case EvGoSysBlock:
+			if err := checkRunning(p, g, ev); err != nil {
+				return err
+			}
+			g.state = gRunnable
+			g.evStart.Link = ev
+			g.evStart = nil
+			p.g = 0
+		case EvGoSysExit:
+			if g.state != gRunnable {
+				return fmt.Errorf("g %v is not runnable during syscall exit (offset %v, time %v)", ev.G, ev.Off, ev.Ts)
+			}
+			if g.ev != nil && g.ev.Type == EvGoSysCall {
+				g.ev.Link = ev
+			}
+			g.ev = ev
+		case EvGoSleep, EvGoBlock, EvGoBlockSend, EvGoBlockRecv,
+			EvGoBlockSelect, EvGoBlockSync, EvGoBlockCond, EvGoBlockNet:
+			if err := checkRunning(p, g, ev); err != nil {
+				return err
+			}
+			g.state = gWaiting
+			g.ev = ev
+			g.evStart.Link = ev
+			g.evStart = nil
+			p.g = 0
+		}
+
+		gs[ev.G] = g
+		ps[ev.P] = p
+	}
+
+	// TODO(dvyukov): restore stacks for EvGoStart events.
+	// TODO(dvyukov): test that all EvGoStart events has non-nil Link.
+
+	return nil
+}
+
+// symbolizeTrace attaches func/file/line info to stack traces.
+func Symbolize(events []*Event, bin string) error {
+	// First, collect and dedup all pcs.
+	pcs := make(map[uint64]*Frame)
+	for _, ev := range events {
+		for _, f := range ev.Stk {
+			pcs[f.PC] = nil
+		}
+	}
+
+	// Start addr2line.
+	cmd := exec.Command("go", "tool", "addr2line", bin)
+	in, err := cmd.StdinPipe()
+	if err != nil {
+		return fmt.Errorf("failed to pipe addr2line stdin: %v", err)
+	}
+	cmd.Stderr = os.Stderr
+	out, err := cmd.StdoutPipe()
+	if err != nil {
+		return fmt.Errorf("failed to pipe addr2line stdout: %v", err)
+	}
+	err = cmd.Start()
+	if err != nil {
+		return fmt.Errorf("failed to start addr2line: %v", err)
+	}
+	outb := bufio.NewReader(out)
+
+	// Write all pcs to addr2line.
+	// Need to copy pcs to an array, because map iteration order is non-deterministic.
+	var pcArray []uint64
+	for pc := range pcs {
+		pcArray = append(pcArray, pc)
+		_, err := fmt.Fprintf(in, "0x%x\n", pc-1)
+		if err != nil {
+			return fmt.Errorf("failed to write to addr2line: %v", err)
+		}
+	}
+	in.Close()
+
+	// Read in answers.
+	for _, pc := range pcArray {
+		fn, err := outb.ReadString('\n')
+		if err != nil {
+			return fmt.Errorf("failed to read from addr2line: %v", err)
+		}
+		file, err := outb.ReadString('\n')
+		if err != nil {
+			return fmt.Errorf("failed to read from addr2line: %v", err)
+		}
+		f := &Frame{PC: pc}
+		f.Fn = fn[:len(fn)-1]
+		f.File = file[:len(file)-1]
+		if colon := strings.LastIndex(f.File, ":"); colon != -1 {
+			ln, err := strconv.Atoi(f.File[colon+1:])
+			if err == nil {
+				f.File = f.File[:colon]
+				f.Line = ln
+			}
+		}
+		pcs[pc] = f
+	}
+	cmd.Wait()
+
+	// Replace frames in events array.
+	for _, ev := range events {
+		for i, f := range ev.Stk {
+			ev.Stk[i] = pcs[f.PC]
+		}
+	}
+
+	return nil
+}
+
+// readVal reads unsigned base-128 value from r.
+func readVal(r io.Reader, off0 int) (v uint64, off int, err error) {
+	off = off0
+	for i := 0; i < 10; i++ {
+		var buf [1]byte
+		var n int
+		n, err = r.Read(buf[:])
+		if err != nil || n != 1 {
+			return 0, 0, fmt.Errorf("failed to read trace at offset: read %v, error %v", off0, n, err)
+		}
+		off++
+		v |= uint64(buf[0]&0x7f) << (uint(i) * 7)
+		if buf[0]&0x80 == 0 {
+			return
+		}
+	}
+	return 0, 0, fmt.Errorf("bad value at offset 0x%x", off0)
+}
+
+type eventList []*Event
+
+func (l eventList) Len() int {
+	return len(l)
+}
+
+func (l eventList) Less(i, j int) bool {
+	return l[i].Ts < l[j].Ts
+}
+
+func (l eventList) Swap(i, j int) {
+	l[i], l[j] = l[j], l[i]
+}
+
+// Event types in the trace.
+// Verbatim copy from src/runtime/trace.go.
+const (
+	EvNone           = 0  // unused
+	EvBatch          = 1  // start of per-P batch of events [pid, timestamp]
+	EvFrequency      = 2  // contains tracer timer frequency [frequency (ticks per second)]
+	EvStack          = 3  // stack [stack id, number of PCs, array of PCs]
+	EvGomaxprocs     = 4  // current value of GOMAXPROCS [timestamp, GOMAXPROCS, stack id]
+	EvProcStart      = 5  // start of P [timestamp]
+	EvProcStop       = 6  // stop of P [timestamp]
+	EvGCStart        = 7  // GC start [timestamp, stack id]
+	EvGCDone         = 8  // GC done [timestamp]
+	EvGCScanStart    = 9  // GC scan start [timestamp]
+	EvGCScanDone     = 10 // GC scan done [timestamp]
+	EvGCSweepStart   = 11 // GC sweep start [timestamp, stack id]
+	EvGCSweepDone    = 12 // GC sweep done [timestamp]
+	EvGoCreate       = 13 // goroutine creation [timestamp, new goroutine id, start PC, stack id]
+	EvGoStart        = 14 // goroutine starts running [timestamp, goroutine id]
+	EvGoEnd          = 15 // goroutine ends [timestamp]
+	EvGoStop         = 16 // goroutine stops (like in select{}) [timestamp, stack]
+	EvGoSched        = 17 // goroutine calls Gosched [timestamp, stack]
+	EvGoPreempt      = 18 // goroutine is preempted [timestamp, stack]
+	EvGoSleep        = 19 // goroutine calls Sleep [timestamp, stack]
+	EvGoBlock        = 20 // goroutine blocks [timestamp, stack]
+	EvGoUnblock      = 21 // goroutine is unblocked [timestamp, goroutine id, stack]
+	EvGoBlockSend    = 22 // goroutine blocks on chan send [timestamp, stack]
+	EvGoBlockRecv    = 23 // goroutine blocks on chan recv [timestamp, stack]
+	EvGoBlockSelect  = 24 // goroutine blocks on select [timestamp, stack]
+	EvGoBlockSync    = 25 // goroutine blocks on Mutex/RWMutex [timestamp, stack]
+	EvGoBlockCond    = 26 // goroutine blocks on Cond [timestamp, stack]
+	EvGoBlockNet     = 27 // goroutine blocks on network [timestamp, stack]
+	EvGoSysCall      = 28 // syscall enter [timestamp, stack]
+	EvGoSysExit      = 29 // syscall exit [timestamp, goroutine id]
+	EvGoSysBlock     = 30 // syscall blocks [timestamp, stack]
+	EvGoWaiting      = 31 // denotes that goroutine is blocked when tracing starts [goroutine id]
+	EvGoInSyscall    = 32 // denotes that goroutine is in syscall when tracing starts [goroutine id]
+	EvHeapAlloc      = 33 // memstats.heap_alloc change [timestamp, heap_alloc]
+	EvNextGC         = 34 // memstats.next_gc change [timestamp, next_gc]
+	EvTimerGoroutine = 35 // denotes timer goroutine [timer goroutine id]
+	EvCount          = 36
+)
+
+var EventDescriptions = [EvCount]struct {
+	Name  string
+	Stack bool
+	Args  []string
+}{
+	EvNone:           {"None", false, []string{}},
+	EvBatch:          {"Batch", false, []string{"p", "ticks"}},
+	EvFrequency:      {"Frequency", false, []string{"freq"}},
+	EvStack:          {"Stack", false, []string{"id", "siz"}},
+	EvGomaxprocs:     {"Gomaxprocs", true, []string{"procs"}},
+	EvProcStart:      {"ProcStart", false, []string{}},
+	EvProcStop:       {"ProcStop", false, []string{}},
+	EvGCStart:        {"GCStart", true, []string{}},
+	EvGCDone:         {"GCDone", false, []string{}},
+	EvGCScanStart:    {"GCScanStart", false, []string{}},
+	EvGCScanDone:     {"GCScanDone", false, []string{}},
+	EvGCSweepStart:   {"GCSweepStart", true, []string{}},
+	EvGCSweepDone:    {"GCSweepDone", false, []string{}},
+	EvGoCreate:       {"GoCreate", true, []string{"g", "pc"}},
+	EvGoStart:        {"GoStart", false, []string{"g"}},
+	EvGoEnd:          {"GoEnd", false, []string{}},
+	EvGoStop:         {"GoStop", true, []string{}},
+	EvGoSched:        {"GoSched", true, []string{}},
+	EvGoPreempt:      {"GoPreempt", true, []string{}},
+	EvGoSleep:        {"GoSleep", true, []string{}},
+	EvGoBlock:        {"GoBlock", true, []string{}},
+	EvGoUnblock:      {"GoUnblock", true, []string{"g"}},
+	EvGoBlockSend:    {"GoBlockSend", true, []string{}},
+	EvGoBlockRecv:    {"GoBlockRecv", true, []string{}},
+	EvGoBlockSelect:  {"GoBlockSelect", true, []string{}},
+	EvGoBlockSync:    {"GoBlockSync", true, []string{}},
+	EvGoBlockCond:    {"GoBlockCond", true, []string{}},
+	EvGoBlockNet:     {"GoBlockNet", true, []string{}},
+	EvGoSysCall:      {"GoSysCall", true, []string{}},
+	EvGoSysExit:      {"GoSysExit", false, []string{"g"}},
+	EvGoSysBlock:     {"GoSysBlock", true, []string{}},
+	EvGoWaiting:      {"GoWaiting", false, []string{"g"}},
+	EvGoInSyscall:    {"GoInSyscall", false, []string{"g"}},
+	EvHeapAlloc:      {"HeapAlloc", false, []string{"mem"}},
+	EvNextGC:         {"NextGC", false, []string{"mem"}},
+	EvTimerGoroutine: {"TimerGoroutine", false, []string{"g"}},
+}
diff --git a/src/runtime/pprof/trace_parser_test.go b/src/runtime/pprof/trace_parser_test.go
deleted file mode 100644
index c1c43245ef..0000000000
--- a/src/runtime/pprof/trace_parser_test.go
+++ /dev/null
@@ -1,656 +0,0 @@
-// 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 pprof_test
-
-import (
-	"bufio"
-	"bytes"
-	"fmt"
-	"io"
-	"os/exec"
-	"sort"
-	"strconv"
-	"strings"
-)
-
-// Event describes one event in the trace.
-type Event struct {
-	off   int       // offset in input file (for debugging and error reporting)
-	typ   byte      // one of traceEv*
-	ts    int64     // timestamp in nanoseconds
-	p     int       // P on which the event happened (can be one of timerP, netpollP, syscallP)
-	g     uint64    // G on which the event happened
-	stkID uint64    // unique stack ID
-	stk   []*Frame  // stack trace (can be empty)
-	args  [2]uint64 // event-type-specific arguments
-	// linked event (can be nil), depends on event type:
-	// for GCStart: the GCStop
-	// for GCScanStart: the GCScanDone
-	// for GCSweepStart: the GCSweepDone
-	// for GoCreate: first GoStart of the created goroutine
-	// for GoStart: the associated GoEnd, GoBlock or other blocking event
-	// for GoSched/GoPreempt: the next GoStart
-	// for GoBlock and other blocking events: the unblock event
-	// for GoUnblock: the associated GoStart
-	// for blocking GoSysCall: the associated GoSysExit
-	// for GoSysExit: the next GoStart
-	link *Event
-}
-
-// Frame is a frame in stack traces.
-type Frame struct {
-	pc   uint64
-	fn   string
-	file string
-	line int
-}
-
-const (
-	// Special P identifiers:
-	timerP   = 1000000 + iota // depicts timer unblocks
-	netpollP                  // depicts network unblocks
-	syscallP                  // depicts returns from syscalls
-)
-
-// parseTrace parses, post-processes and verifies the trace.
-func parseTrace(r io.Reader) ([]*Event, error) {
-	rawEvents, err := readTrace(r)
-	if err != nil {
-		return nil, err
-	}
-	events, err := parseEvents(rawEvents)
-	if err != nil {
-		return nil, err
-	}
-	err = postProcessTrace(events)
-	if err != nil {
-		return nil, err
-	}
-	return events, nil
-}
-
-// RawEvent is a helper type used during parsing.
-type RawEvent struct {
-	off  int
-	typ  byte
-	args []uint64
-}
-
-// readTrace does wire-format parsing and verification.
-// It does not care about specific event types and argument meaning.
-func readTrace(r io.Reader) ([]RawEvent, error) {
-	// Read and validate trace header.
-	var buf [8]byte
-	off, err := r.Read(buf[:])
-	if off != 8 || err != nil {
-		return nil, fmt.Errorf("failed to read header: read %v, err %v", off, err)
-	}
-	if bytes.Compare(buf[:], []byte("gotrace\x00")) != 0 {
-		return nil, fmt.Errorf("not a trace file")
-	}
-
-	// Read events.
-	var events []RawEvent
-	for {
-		// Read event type and number of arguments (1 byte).
-		off0 := off
-		n, err := r.Read(buf[:1])
-		if err == io.EOF {
-			break
-		}
-		if err != nil || n != 1 {
-			return nil, fmt.Errorf("failed to read trace at offset 0x%x: n=%v err=%v", off0, n, err)
-		}
-		off += n
-		typ := buf[0] << 2 >> 2
-		narg := buf[0]>>6 + 1
-		ev := RawEvent{typ: typ, off: off0}
-		if narg <= 3 {
-			for i := 0; i < int(narg); i++ {
-				var v uint64
-				v, off, err = readVal(r, off)
-				if err != nil {
-					return nil, err
-				}
-				ev.args = append(ev.args, v)
-			}
-		} else {
-			// If narg == 4, the first value is length of the event in bytes.
-			var v uint64
-			v, off, err = readVal(r, off)
-			if err != nil {
-				return nil, err
-			}
-			evLen := v
-			off1 := off
-			for evLen > uint64(off-off1) {
-				v, off, err = readVal(r, off)
-				if err != nil {
-					return nil, err
-				}
-				ev.args = append(ev.args, v)
-			}
-			if evLen != uint64(off-off1) {
-				return nil, fmt.Errorf("event has wrong length at offset 0x%x: want %v, got %v", off0, evLen, off-off1)
-			}
-		}
-		events = append(events, ev)
-	}
-	return events, nil
-}
-
-// Parse events transforms raw events into events.
-// It does analyze and verify per-event-type arguments.
-func parseEvents(rawEvents []RawEvent) (events []*Event, err error) {
-	var ticksPerSec, lastTs int64
-	var lastG, timerGoid uint64
-	var lastP int
-	lastGs := make(map[int]uint64) // last goroutine running on P
-	stacks := make(map[uint64][]*Frame)
-	for _, raw := range rawEvents {
-		if raw.typ == traceEvNone || raw.typ >= traceEvCount {
-			err = fmt.Errorf("unknown event type %v at offset 0x%x", raw.typ, raw.off)
-			return
-		}
-		desc := evDescriptions[raw.typ]
-		if desc.name == "" {
-			err = fmt.Errorf("missing description for event type %v", raw.typ)
-			return
-		}
-		if raw.typ != traceEvStack {
-			narg := len(desc.args)
-			if desc.stack {
-				narg++
-			}
-			if raw.typ != traceEvBatch && raw.typ != traceEvFrequency && raw.typ != traceEvTimerGoroutine {
-				narg++ // timestamp
-			}
-			if len(raw.args) != narg {
-				err = fmt.Errorf("%v has wrong number of arguments at offset 0x%x: want %v, got %v",
-					desc.name, raw.off, narg, len(raw.args))
-				return
-			}
-		}
-		switch raw.typ {
-		case traceEvBatch:
-			lastGs[lastP] = lastG
-			lastP = int(raw.args[0])
-			lastG = lastGs[lastP]
-			lastTs = int64(raw.args[1])
-		case traceEvFrequency:
-			ticksPerSec = int64(raw.args[0])
-			if ticksPerSec <= 0 {
-				err = fmt.Errorf("traceEvFrequency contains invalid frequency %v at offset 0x%x",
-					ticksPerSec, raw.off)
-				return
-			}
-		case traceEvTimerGoroutine:
-			timerGoid = raw.args[0]
-		case traceEvStack:
-			if len(raw.args) < 2 {
-				err = fmt.Errorf("traceEvStack has wrong number of arguments at offset 0x%x: want at least 2, got %v",
-					raw.off, len(raw.args))
-				return
-			}
-			size := raw.args[1]
-			if size > 1000 {
-				err = fmt.Errorf("traceEvStack has bad number of frames at offset 0x%x: %v",
-					raw.off, size)
-				return
-			}
-			id := raw.args[0]
-			if id != 0 && size > 0 {
-				stk := make([]*Frame, size)
-				for i := 0; i < int(size); i++ {
-					stk[i] = &Frame{pc: raw.args[i+2]}
-				}
-				stacks[id] = stk
-			}
-		default:
-			e := &Event{off: raw.off, typ: raw.typ, p: lastP, g: lastG}
-			e.ts = lastTs + int64(raw.args[0])
-			lastTs = e.ts
-			for i := range desc.args {
-				e.args[i] = raw.args[i+1]
-			}
-			if desc.stack {
-				e.stkID = raw.args[len(desc.args)+1]
-			}
-			switch raw.typ {
-			case traceEvGoStart:
-				lastG = e.args[0]
-				e.g = lastG
-			case traceEvGCStart, traceEvGCDone, traceEvGCScanStart, traceEvGCScanDone:
-				e.g = 0
-			case traceEvGoEnd, traceEvGoStop, traceEvGoSched, traceEvGoPreempt,
-				traceEvGoSleep, traceEvGoBlock, traceEvGoBlockSend, traceEvGoBlockRecv,
-				traceEvGoBlockSelect, traceEvGoBlockSync, traceEvGoBlockCond, traceEvGoBlockNet,
-				traceEvGoSysBlock:
-				lastG = 0
-			}
-			events = append(events, e)
-		}
-	}
-
-	// Attach stack traces.
-	for _, ev := range events {
-		if ev.stkID != 0 {
-			ev.stk = stacks[ev.stkID]
-		}
-	}
-
-	// Sort by time and translate cpu ticks to real time.
-	sort.Sort(EventList(events))
-	if ticksPerSec == 0 {
-		err = fmt.Errorf("no traceEvFrequency event")
-		return
-	}
-	minTs := events[0].ts
-	for _, ev := range events {
-		ev.ts = (ev.ts - minTs) * 1e9 / ticksPerSec
-		// Move timers and syscalls to separate fake Ps.
-		if timerGoid != 0 && ev.g == timerGoid && ev.typ == traceEvGoUnblock {
-			ev.p = timerP
-		}
-		if ev.typ == traceEvGoSysExit {
-			ev.p = syscallP
-			ev.g = ev.args[0]
-		}
-	}
-
-	return
-}
-
-// postProcessTrace does inter-event verification and information restoration.
-// The resulting trace is guaranteed to be consistent
-// (for example, a P does not run two Gs at the same time, or a G is indeed
-// blocked before an unblock event).
-func postProcessTrace(events []*Event) error {
-	const (
-		gDead = iota
-		gRunnable
-		gRunning
-		gWaiting
-	)
-	type gdesc struct {
-		state   int
-		ev      *Event
-		evStart *Event
-	}
-	type pdesc struct {
-		running bool
-		g       uint64
-		evGC    *Event
-		evScan  *Event
-		evSweep *Event
-	}
-
-	gs := make(map[uint64]gdesc)
-	ps := make(map[int]pdesc)
-	gs[0] = gdesc{state: gRunning}
-
-	checkRunning := func(p pdesc, g gdesc, ev *Event) error {
-		name := evDescriptions[ev.typ].name
-		if g.state != gRunning {
-			return fmt.Errorf("g %v is not running while %v (offset %v, time %v)", ev.g, name, ev.off, ev.ts)
-		}
-		if p.g != ev.g {
-			return fmt.Errorf("p %v is not running g %v while %v (offset %v, time %v)", ev.p, ev.g, name, ev.off, ev.ts)
-		}
-		return nil
-	}
-
-	for _, ev := range events {
-		g := gs[ev.g]
-		p := ps[ev.p]
-
-		switch ev.typ {
-		case traceEvProcStart:
-			if p.running {
-				return fmt.Errorf("p %v is running before start (offset %v, time %v)", ev.p, ev.off, ev.ts)
-			}
-			p.running = true
-		case traceEvProcStop:
-			if !p.running {
-				return fmt.Errorf("p %v is not running before stop (offset %v, time %v)", ev.p, ev.off, ev.ts)
-			}
-			if p.g != 0 {
-				return fmt.Errorf("p %v is running a goroutine %v during stop (offset %v, time %v)", ev.p, p.g, ev.off, ev.ts)
-			}
-			p.running = false
-		case traceEvGCStart:
-			if p.evGC != nil {
-				return fmt.Errorf("previous GC is not ended before a new one (offset %v, time %v)", ev.off, ev.ts)
-			}
-			p.evGC = ev
-		case traceEvGCDone:
-			if p.evGC == nil {
-				return fmt.Errorf("bogus GC end (offset %v, time %v)", ev.off, ev.ts)
-			}
-			p.evGC.link = ev
-			p.evGC = nil
-		case traceEvGCScanStart:
-			if p.evScan != nil {
-				return fmt.Errorf("previous scanning is not ended before a new one (offset %v, time %v)", ev.off, ev.ts)
-			}
-			p.evScan = ev
-		case traceEvGCScanDone:
-			if p.evScan == nil {
-				return fmt.Errorf("bogus scanning end (offset %v, time %v)", ev.off, ev.ts)
-			}
-			p.evScan.link = ev
-			p.evScan = nil
-		case traceEvGCSweepStart:
-			if p.evSweep != nil {
-				return fmt.Errorf("previous sweeping is not ended before a new one (offset %v, time %v)", ev.off, ev.ts)
-			}
-			p.evSweep = ev
-		case traceEvGCSweepDone:
-			if p.evSweep == nil {
-				return fmt.Errorf("bogus sweeping end (offset %v, time %v)", ev.off, ev.ts)
-			}
-			p.evSweep.link = ev
-			p.evSweep = nil
-		case traceEvGoWaiting:
-			g1 := gs[ev.args[0]]
-			if g1.state != gRunnable {
-				return fmt.Errorf("g %v is not runnable before traceEvGoWaiting (offset %v, time %v)", ev.args[0], ev.off, ev.ts)
-			}
-			g1.state = gWaiting
-			gs[ev.args[0]] = g1
-		case traceEvGoInSyscall:
-			// this case is intentionally left blank
-		case traceEvGoCreate:
-			if err := checkRunning(p, g, ev); err != nil {
-				return err
-			}
-			if _, ok := gs[ev.args[0]]; ok {
-				return fmt.Errorf("g %v already exists (offset %v, time %v)", ev.args[0], ev.off, ev.ts)
-			}
-			gs[ev.args[0]] = gdesc{state: gRunnable, ev: ev}
-		case traceEvGoStart:
-			if g.state != gRunnable {
-				return fmt.Errorf("g %v is not runnable before start (offset %v, time %v)", ev.g, ev.off, ev.ts)
-			}
-			if p.g != 0 {
-				return fmt.Errorf("p %v is already running g %v while start g %v (offset %v, time %v)", ev.p, p.g, ev.g, ev.off, ev.ts)
-			}
-			g.state = gRunning
-			g.evStart = ev
-			p.g = ev.g
-			if g.ev != nil {
-				if g.ev.typ == traceEvGoCreate {
-					// +1 because symblizer expects return pc.
-					ev.stk = []*Frame{&Frame{pc: g.ev.args[1] + 1}}
-				}
-				g.ev.link = ev
-				g.ev = nil
-			}
-		case traceEvGoEnd, traceEvGoStop:
-			if err := checkRunning(p, g, ev); err != nil {
-				return err
-			}
-			g.evStart.link = ev
-			g.evStart = nil
-			g.state = gDead
-			p.g = 0
-		case traceEvGoSched, traceEvGoPreempt:
-			if err := checkRunning(p, g, ev); err != nil {
-				return err
-			}
-			g.state = gRunnable
-			g.evStart.link = ev
-			g.evStart = nil
-			p.g = 0
-			g.ev = ev
-		case traceEvGoUnblock:
-			if g.state != gRunning {
-				return fmt.Errorf("g %v is not running while unpark (offset %v, time %v)", ev.g, ev.off, ev.ts)
-			}
-			if ev.p != timerP && p.g != ev.g {
-				return fmt.Errorf("p %v is not running g %v while unpark (offset %v, time %v)", ev.p, ev.g, ev.off, ev.ts)
-			}
-			g1 := gs[ev.args[0]]
-			if g1.state != gWaiting {
-				return fmt.Errorf("g %v is not waiting before unpark (offset %v, time %v)", ev.args[0], ev.off, ev.ts)
-			}
-			if g1.ev != nil && g1.ev.typ == traceEvGoBlockNet && ev.p != timerP {
-				ev.p = netpollP
-			}
-			if g1.ev != nil {
-				g1.ev.link = ev
-			}
-			g1.state = gRunnable
-			g1.ev = ev
-			gs[ev.args[0]] = g1
-		case traceEvGoSysCall:
-			if err := checkRunning(p, g, ev); err != nil {
-				return err
-			}
-			g.ev = ev
-		case traceEvGoSysBlock:
-			if err := checkRunning(p, g, ev); err != nil {
-				return err
-			}
-			g.state = gRunnable
-			g.evStart.link = ev
-			g.evStart = nil
-			p.g = 0
-		case traceEvGoSysExit:
-			if g.state != gRunnable {
-				return fmt.Errorf("g %v is not runnable during syscall exit (offset %v, time %v)", ev.g, ev.off, ev.ts)
-			}
-			if g.ev != nil && g.ev.typ == traceEvGoSysCall {
-				g.ev.link = ev
-			}
-			g.ev = ev
-		case traceEvGoSleep, traceEvGoBlock, traceEvGoBlockSend, traceEvGoBlockRecv,
-			traceEvGoBlockSelect, traceEvGoBlockSync, traceEvGoBlockCond, traceEvGoBlockNet:
-			if err := checkRunning(p, g, ev); err != nil {
-				return err
-			}
-			g.state = gWaiting
-			g.ev = ev
-			g.evStart.link = ev
-			g.evStart = nil
-			p.g = 0
-		}
-
-		gs[ev.g] = g
-		ps[ev.p] = p
-	}
-
-	return nil
-}
-
-// symbolizeTrace attaches func/file/line info to stack traces.
-func symbolizeTrace(events []*Event, bin string) error {
-	// First, collect and dedup all pcs.
-	pcs := make(map[uint64]*Frame)
-	for _, ev := range events {
-		for _, f := range ev.stk {
-			pcs[f.pc] = nil
-		}
-	}
-
-	// Start addr2line.
-	cmd := exec.Command("go", "tool", "addr2line", bin)
-	in, err := cmd.StdinPipe()
-	if err != nil {
-		return fmt.Errorf("failed to pipe addr2line stdin: %v", err)
-	}
-	out, err := cmd.StdoutPipe()
-	if err != nil {
-		return fmt.Errorf("failed to pipe addr2line stdout: %v", err)
-	}
-	err = cmd.Start()
-	if err != nil {
-		return fmt.Errorf("failed to start addr2line: %v", err)
-	}
-	outb := bufio.NewReader(out)
-
-	// Write all pcs to addr2line.
-	// Need to copy pcs to an array, because map iteration order is non-deterministic.
-	var pcArray []uint64
-	for pc := range pcs {
-		pcArray = append(pcArray, pc)
-		_, err := fmt.Fprintf(in, "0x%x\n", pc-1)
-		if err != nil {
-			return fmt.Errorf("failed to write to addr2line: %v", err)
-		}
-	}
-	in.Close()
-
-	// Read in answers.
-	for _, pc := range pcArray {
-		fn, err := outb.ReadString('\n')
-		if err != nil {
-			return fmt.Errorf("failed to read from addr2line: %v", err)
-		}
-		file, err := outb.ReadString('\n')
-		if err != nil {
-			return fmt.Errorf("failed to read from addr2line: %v", err)
-		}
-		f := &Frame{pc: pc}
-		f.fn = fn[:len(fn)-1]
-		f.file = file[:len(file)-1]
-		if colon := strings.LastIndex(f.file, ":"); colon != -1 {
-			ln, err := strconv.Atoi(f.file[colon+1:])
-			if err == nil {
-				f.file = f.file[:colon]
-				f.line = ln
-			}
-		}
-		pcs[pc] = f
-	}
-	cmd.Wait()
-
-	// Replace frames in events array.
-	for _, ev := range events {
-		for i, f := range ev.stk {
-			ev.stk[i] = pcs[f.pc]
-		}
-	}
-
-	return nil
-}
-
-// readVal reads unsigned base-128 value from r.
-func readVal(r io.Reader, off0 int) (v uint64, off int, err error) {
-	off = off0
-	for i := 0; i < 10; i++ {
-		var buf [1]byte
-		var n int
-		n, err = r.Read(buf[:])
-		if err != nil || n != 1 {
-			return 0, 0, fmt.Errorf("failed to read trace at offset: read %v, error %v", off0, n, err)
-		}
-		off++
-		v |= uint64(buf[0]&0x7f) << (uint(i) * 7)
-		if buf[0]&0x80 == 0 {
-			return
-		}
-	}
-	return 0, 0, fmt.Errorf("bad value at offset 0x%x", off0)
-}
-
-type EventList []*Event
-
-func (l EventList) Len() int {
-	return len(l)
-}
-
-func (l EventList) Less(i, j int) bool {
-	return l[i].ts < l[j].ts
-}
-
-func (l EventList) Swap(i, j int) {
-	l[i], l[j] = l[j], l[i]
-}
-
-// Event types in the trace.
-// Verbatim copy from src/runtime/trace.go.
-const (
-	traceEvNone           = 0  // unused
-	traceEvBatch          = 1  // start of per-P batch of events [pid, timestamp]
-	traceEvFrequency      = 2  // contains tracer timer frequency [frequency (ticks per second)]
-	traceEvStack          = 3  // stack [stack id, number of PCs, array of PCs]
-	traceEvGomaxprocs     = 4  // current value of GOMAXPROCS [timestamp, GOMAXPROCS, stack id]
-	traceEvProcStart      = 5  // start of P [timestamp]
-	traceEvProcStop       = 6  // stop of P [timestamp]
-	traceEvGCStart        = 7  // GC start [timestamp, stack id]
-	traceEvGCDone         = 8  // GC done [timestamp]
-	traceEvGCScanStart    = 9  // GC scan start [timestamp]
-	traceEvGCScanDone     = 10 // GC scan done [timestamp]
-	traceEvGCSweepStart   = 11 // GC sweep start [timestamp, stack id]
-	traceEvGCSweepDone    = 12 // GC sweep done [timestamp]
-	traceEvGoCreate       = 13 // goroutine creation [timestamp, new goroutine id, start PC, stack id]
-	traceEvGoStart        = 14 // goroutine starts running [timestamp, goroutine id]
-	traceEvGoEnd          = 15 // goroutine ends [timestamp]
-	traceEvGoStop         = 16 // goroutine stops (like in select{}) [timestamp, stack]
-	traceEvGoSched        = 17 // goroutine calls Gosched [timestamp, stack]
-	traceEvGoPreempt      = 18 // goroutine is preempted [timestamp, stack]
-	traceEvGoSleep        = 19 // goroutine calls Sleep [timestamp, stack]
-	traceEvGoBlock        = 20 // goroutine blocks [timestamp, stack]
-	traceEvGoUnblock      = 21 // goroutine is unblocked [timestamp, goroutine id, stack]
-	traceEvGoBlockSend    = 22 // goroutine blocks on chan send [timestamp, stack]
-	traceEvGoBlockRecv    = 23 // goroutine blocks on chan recv [timestamp, stack]
-	traceEvGoBlockSelect  = 24 // goroutine blocks on select [timestamp, stack]
-	traceEvGoBlockSync    = 25 // goroutine blocks on Mutex/RWMutex [timestamp, stack]
-	traceEvGoBlockCond    = 26 // goroutine blocks on Cond [timestamp, stack]
-	traceEvGoBlockNet     = 27 // goroutine blocks on network [timestamp, stack]
-	traceEvGoSysCall      = 28 // syscall enter [timestamp, stack]
-	traceEvGoSysExit      = 29 // syscall exit [timestamp, goroutine id]
-	traceEvGoSysBlock     = 30 // syscall blocks [timestamp, stack]
-	traceEvGoWaiting      = 31 // denotes that goroutine is blocked when tracing starts [goroutine id]
-	traceEvGoInSyscall    = 32 // denotes that goroutine is in syscall when tracing starts [goroutine id]
-	traceEvHeapAlloc      = 33 // memstats.heap_alloc change [timestamp, heap_alloc]
-	traceEvNextGC         = 34 // memstats.next_gc change [timestamp, next_gc]
-	traceEvTimerGoroutine = 35 // denotes timer goroutine [timer goroutine id]
-	traceEvCount          = 36
-)
-
-var evDescriptions = [traceEvCount]struct {
-	name  string
-	stack bool
-	args  []string
-}{
-	traceEvNone:           {"None", false, []string{}},
-	traceEvBatch:          {"Batch", false, []string{"p", "ticks"}},
-	traceEvFrequency:      {"Frequency", false, []string{"freq"}},
-	traceEvStack:          {"Stack", false, []string{"id", "siz"}},
-	traceEvGomaxprocs:     {"Gomaxprocs", true, []string{"procs"}},
-	traceEvProcStart:      {"ProcStart", false, []string{}},
-	traceEvProcStop:       {"ProcStop", false, []string{}},
-	traceEvGCStart:        {"GCStart", true, []string{}},
-	traceEvGCDone:         {"GCDone", false, []string{}},
-	traceEvGCScanStart:    {"GCScanStart", false, []string{}},
-	traceEvGCScanDone:     {"GCScanDone", false, []string{}},
-	traceEvGCSweepStart:   {"GCSweepStart", true, []string{}},
-	traceEvGCSweepDone:    {"GCSweepDone", false, []string{}},
-	traceEvGoCreate:       {"GoCreate", true, []string{"g", "pc"}},
-	traceEvGoStart:        {"GoStart", false, []string{"g"}},
-	traceEvGoEnd:          {"GoEnd", false, []string{}},
-	traceEvGoStop:         {"GoStop", true, []string{}},
-	traceEvGoSched:        {"GoSched", true, []string{}},
-	traceEvGoPreempt:      {"GoPreempt", true, []string{}},
-	traceEvGoSleep:        {"GoSleep", true, []string{}},
-	traceEvGoBlock:        {"GoBlock", true, []string{}},
-	traceEvGoUnblock:      {"GoUnblock", true, []string{"g"}},
-	traceEvGoBlockSend:    {"GoBlockSend", true, []string{}},
-	traceEvGoBlockRecv:    {"GoBlockRecv", true, []string{}},
-	traceEvGoBlockSelect:  {"GoBlockSelect", true, []string{}},
-	traceEvGoBlockSync:    {"GoBlockSync", true, []string{}},
-	traceEvGoBlockCond:    {"GoBlockCond", true, []string{}},
-	traceEvGoBlockNet:     {"GoBlockNet", true, []string{}},
-	traceEvGoSysCall:      {"GoSysCall", true, []string{}},
-	traceEvGoSysExit:      {"GoSysExit", false, []string{"g"}},
-	traceEvGoSysBlock:     {"GoSysBlock", true, []string{}},
-	traceEvGoWaiting:      {"GoWaiting", false, []string{"g"}},
-	traceEvGoInSyscall:    {"GoInSyscall", false, []string{"g"}},
-	traceEvHeapAlloc:      {"HeapAlloc", false, []string{"mem"}},
-	traceEvNextGC:         {"NextGC", false, []string{"mem"}},
-	traceEvTimerGoroutine: {"TimerGoroutine", false, []string{"g"}},
-}
diff --git a/src/runtime/pprof/trace_test.go b/src/runtime/pprof/trace_test.go
index 1b99830bfa..e19e695e50 100644
--- a/src/runtime/pprof/trace_test.go
+++ b/src/runtime/pprof/trace_test.go
@@ -6,6 +6,7 @@ package pprof_test
 
 import (
 	"bytes"
+	"internal/trace"
 	"net"
 	"os"
 	"runtime"
@@ -66,7 +67,7 @@ func TestTrace(t *testing.T) {
 		t.Fatalf("failed to start tracing: %v", err)
 	}
 	StopTrace()
-	_, err := parseTrace(buf)
+	_, err := trace.Parse(buf)
 	if err != nil {
 		t.Fatalf("failed to parse trace: %v", err)
 	}
@@ -198,12 +199,153 @@ func TestTraceStress(t *testing.T) {
 	runtime.GOMAXPROCS(procs)
 
 	StopTrace()
-	_, err = parseTrace(buf)
+	_, err = trace.Parse(buf)
 	if err != nil {
 		t.Fatalf("failed to parse trace: %v", err)
 	}
 }
 
+// Do a bunch of various stuff (timers, GC, network, etc) in a separate goroutine.
+// And concurrently with all that start/stop trace 3 times.
+func TestTraceStressStartStop(t *testing.T) {
+	skipTraceTestsIfNeeded(t)
+
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(8))
+	outerDone := make(chan bool)
+
+	go func() {
+		defer func() {
+			outerDone <- true
+		}()
+
+		var wg sync.WaitGroup
+		done := make(chan bool)
+
+		wg.Add(1)
+		go func() {
+			<-done
+			wg.Done()
+		}()
+
+		rp, wp, err := os.Pipe()
+		if err != nil {
+			t.Fatalf("failed to create pipe: %v", err)
+		}
+		defer func() {
+			rp.Close()
+			wp.Close()
+		}()
+		wg.Add(1)
+		go func() {
+			var tmp [1]byte
+			rp.Read(tmp[:])
+			<-done
+			wg.Done()
+		}()
+		time.Sleep(time.Millisecond)
+
+		go func() {
+			runtime.LockOSThread()
+			for {
+				select {
+				case <-done:
+					return
+				default:
+					runtime.Gosched()
+				}
+			}
+		}()
+
+		runtime.GC()
+		// Trigger GC from malloc.
+		for i := 0; i < 1e3; i++ {
+			_ = make([]byte, 1<<20)
+		}
+
+		// Create a bunch of busy goroutines to load all Ps.
+		for p := 0; p < 10; p++ {
+			wg.Add(1)
+			go func() {
+				// Do something useful.
+				tmp := make([]byte, 1<<16)
+				for i := range tmp {
+					tmp[i]++
+				}
+				_ = tmp
+				<-done
+				wg.Done()
+			}()
+		}
+
+		// Block in syscall.
+		wg.Add(1)
+		go func() {
+			var tmp [1]byte
+			rp.Read(tmp[:])
+			<-done
+			wg.Done()
+		}()
+
+		runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))
+
+		// Test timers.
+		timerDone := make(chan bool)
+		go func() {
+			time.Sleep(time.Millisecond)
+			timerDone <- true
+		}()
+		<-timerDone
+
+		// A bit of network.
+		ln, err := net.Listen("tcp", "127.0.0.1:0")
+		if err != nil {
+			t.Fatalf("listen failed: %v", err)
+		}
+		defer ln.Close()
+		go func() {
+			c, err := ln.Accept()
+			if err != nil {
+				return
+			}
+			time.Sleep(time.Millisecond)
+			var buf [1]byte
+			c.Write(buf[:])
+			c.Close()
+		}()
+		c, err := net.Dial("tcp", ln.Addr().String())
+		if err != nil {
+			t.Fatalf("dial failed: %v", err)
+		}
+		var tmp [1]byte
+		c.Read(tmp[:])
+		c.Close()
+
+		go func() {
+			runtime.Gosched()
+			select {}
+		}()
+
+		// Unblock helper goroutines and wait them to finish.
+		wp.Write(tmp[:])
+		wp.Write(tmp[:])
+		close(done)
+		wg.Wait()
+	}()
+
+	for i := 0; i < 3; i++ {
+		buf := new(bytes.Buffer)
+		if err := StartTrace(buf); err != nil {
+			t.Fatalf("failed to start tracing: %v", err)
+		}
+		time.Sleep(time.Millisecond)
+		StopTrace()
+		if _, err := trace.Parse(buf); err != nil {
+			t.Fatalf("failed to parse trace: %v", err)
+		}
+	}
+	<-outerDone
+}
+
 func TestTraceSymbolize(t *testing.T) {
 	skipTraceTestsIfNeeded(t)
 	if runtime.GOOS == "nacl" {
@@ -215,24 +357,24 @@ func TestTraceSymbolize(t *testing.T) {
 	}
 	runtime.GC()
 	StopTrace()
-	events, err := parseTrace(buf)
+	events, err := trace.Parse(buf)
 	if err != nil {
 		t.Fatalf("failed to parse trace: %v", err)
 	}
-	err = symbolizeTrace(events, os.Args[0])
+	err = trace.Symbolize(events, os.Args[0])
 	if err != nil {
 		t.Fatalf("failed to symbolize trace: %v", err)
 	}
 	found := false
 eventLoop:
 	for _, ev := range events {
-		if ev.typ != traceEvGCStart {
+		if ev.Type != trace.EvGCStart {
 			continue
 		}
-		for _, f := range ev.stk {
-			if strings.HasSuffix(f.file, "trace_test.go") &&
-				strings.HasSuffix(f.fn, "pprof_test.TestTraceSymbolize") &&
-				f.line == 216 {
+		for _, f := range ev.Stk {
+			if strings.HasSuffix(f.File, "trace_test.go") &&
+				strings.HasSuffix(f.Fn, "pprof_test.TestTraceSymbolize") &&
+				f.Line == 358 {
 				found = true
 				break eventLoop
 			}
diff --git a/src/runtime/trace.go b/src/runtime/trace.go
index e7937b3d17..9804092da3 100644
--- a/src/runtime/trace.go
+++ b/src/runtime/trace.go
@@ -190,7 +190,6 @@ func StopTrace() {
 	}
 
 	traceGoSched()
-	traceGoStart()
 
 	for _, p := range &allp {
 		if p == nil {