func execute(pid int, env *ipc.Env, p *prog.Prog) {
	if *flagExecutor == "" {
		return
	}
	atomic.AddUint64(&statExec, 1)
	if *flagLogProg {
		ticket := gate.Enter()
		defer gate.Leave(ticket)
		outMu.Lock()
		fmt.Printf("executing program %v\n%s\n", pid, p.Serialize())
		outMu.Unlock()
	}

	output, _, _, failed, hanged, err := env.Exec(p)
	if err != nil {
		fmt.Printf("failed to execute executor: %v\n", err)
	}
	paniced := failedRe.Match(output)
	if failed || hanged || paniced || err != nil {
		fmt.Printf("PROGRAM:\n%s\n", p.Serialize())
	}
	if failed || hanged || paniced || err != nil || *flagOutput {
		os.Stdout.Write(output)
	}
}

func execute(env *ipc.Env, p *prog.Prog) {
	if *flagExecutor == "" {
		return
	}
	output, _, _, _, _, err := env.Exec(p)
	if err != nil {
		fmt.Printf("failed to execute executor: %v\n", err)
	}
	failed := failedRe.Match(output)
	if failed {
		fmt.Printf("PROGRAM:\n%s\n", p.Serialize())
	}
	if failed || *flagOutput {
		os.Stdout.Write(output)
	}
}

func execute1(env *ipc.Env, p *prog.Prog, stat *uint64) []cover.Cover {
	if *flagSaveProg {
		f, err := os.Create(fmt.Sprintf("%v.prog", *flagName))
		if err == nil {
			f.Write(p.Serialize())
			f.Close()
		}
	} else {
		// The following output helps to understand what program crashed kernel.
		// It must not be intermixed.
		logMu.Lock()
		log.Printf("executing program:\n%s", p.Serialize())
		logMu.Unlock()
	}

	try := 0
retry:
	*stat++
	output, strace, rawCover, failed, hanged, err := env.Exec(p)
	if err != nil {
		if try > 10 {
			panic(err)
		}
		try++
		debug.FreeOSMemory()
		time.Sleep(time.Second)
		goto retry
	}
	logf(4, "result failed=%v hanged=%v:\n%v\n", failed, hanged, string(output))
	if len(strace) != 0 {
		logf(4, "strace:\n%s\n", strace)
	}
	cov := make([]cover.Cover, len(p.Calls))
	for i, c := range rawCover {
		cov[i] = cover.Cover(c)
	}
	return cov
}

func execute1(pid int, env *ipc.Env, p *prog.Prog, stat *uint64) []cover.Cover {
	if false {
		// For debugging, this function must not be executed with locks held.
		corpusMu.Lock()
		corpusMu.Unlock()
		coverMu.Lock()
		coverMu.Unlock()
		triageMu.Lock()
		triageMu.Unlock()
	}

	// Limit concurrency window and do leak checking once in a while.
	idx := gate.Enter()
	defer gate.Leave(idx, func() {
		if idx == 0 && *flagLeak && atomic.LoadUint32(&allTriaged) != 0 {
			// Scan for leaks once in a while (it is damn slow).
			kmemleakScan(true)
		}
	})

	// The following output helps to understand what program crashed kernel.
	// It must not be intermixed.
	switch *flagOutput {
	case "none":
		// This case intentionally left blank.
	case "stdout":
		data := p.Serialize()
		logMu.Lock()
		log.Printf("executing program %v:\n%s", pid, data)
		logMu.Unlock()
	case "dmesg":
		fd, err := syscall.Open("/dev/kmsg", syscall.O_WRONLY, 0)
		if err == nil {
			buf := new(bytes.Buffer)
			fmt.Fprintf(buf, "syzkaller: executing program %v:\n%s", pid, p.Serialize())
			syscall.Write(fd, buf.Bytes())
			syscall.Close(fd)
		}
	case "file":
		f, err := os.Create(fmt.Sprintf("%v-%v.prog", *flagName, pid))
		if err == nil {
			f.Write(p.Serialize())
			f.Close()
		}
	}

	try := 0
retry:
	atomic.AddUint64(stat, 1)
	output, rawCover, errnos, failed, hanged, err := env.Exec(p)
	_ = errnos
	if failed {
		// BUG in output should be recognized by manager.
		logf(0, "BUG: executor-detected bug:\n%s", output)
		// Don't return any cover so that the input is not added to corpus.
		return make([]cover.Cover, len(p.Calls))
	}
	if err != nil {
		if try > 10 {
			panic(err)
		}
		try++
		debug.FreeOSMemory()
		time.Sleep(time.Second)
		goto retry
	}
	logf(4, "result failed=%v hanged=%v:\n%v\n", failed, hanged, string(output))
	cov := make([]cover.Cover, len(p.Calls))
	for i, c := range rawCover {
		cov[i] = cover.Cover(c)
	}
	return cov
}