func (dbp *Process) obtainGoSymbols(exe *macho.File, wg *sync.WaitGroup) {
	defer wg.Done()

	var (
		symdat  []byte
		pclndat []byte
		err     error
	)

	if sec := exe.Section("__gosymtab"); sec != nil {
		symdat, err = sec.Data()
		if err != nil {
			fmt.Println("could not get .gosymtab section", err)
			os.Exit(1)
		}
	}

	if sec := exe.Section("__gopclntab"); sec != nil {
		pclndat, err = sec.Data()
		if err != nil {
			fmt.Println("could not get .gopclntab section", err)
			os.Exit(1)
		}
	}

	pcln := gosym.NewLineTable(pclndat, exe.Section("__text").Addr)
	tab, err := gosym.NewTable(symdat, pcln)
	if err != nil {
		fmt.Println("could not get initialize line table", err)
		os.Exit(1)
	}

	dbp.goSymTable = tab
}

func (f *File) PCLineTable() (*gosym.Table, error) {
	textStart, symtab, pclntab, err := f.raw.pcln()
	if err != nil {
		return nil, err
	}
	return gosym.NewTable(symtab, gosym.NewLineTable(pclntab, textStart))
}

func elfGoSyms(f *elf.File) (*gosym.Table, os.Error) {
	text := f.Section(".text")
	symtab := f.Section(".gosymtab")
	pclntab := f.Section(".gopclntab")
	if text == nil || symtab == nil || pclntab == nil {
		return nil, nil
	}

	symdat, err := symtab.Data()
	if err != nil {
		return nil, err
	}
	pclndat, err := pclntab.Data()
	if err != nil {
		return nil, err
	}

	pcln := gosym.NewLineTable(pclndat, text.Addr)
	tab, err := gosym.NewTable(symdat, pcln)
	if err != nil {
		return nil, err
	}

	return tab, nil
}

func symbolTable() *gosym.Table {
	attempts := []func() (uint64, []byte, []byte, error){
		pclnElf,
		pclnMacho,
		pclnPE,
		pclnPlan9,
	}

	var errors []error

	for _, a := range attempts {
		textStart, symtab, pclntab, err := a()
		if err == nil {
			var table *gosym.Table
			table, err = gosym.NewTable(symtab, gosym.NewLineTable(pclntab, textStart))
			if err == nil {
				return table
			}
		}
		errors = append(errors, err)
	}

	for _, err := range errors {
		fmt.Fprintln(os.Stderr, err)
	}
	flagset.Usage()
	os.Exit(1)
	panic("unreachable")
}

func main() {
	log.SetFlags(0)
	log.SetPrefix("addr2line: ")

	// pprof expects this behavior when checking for addr2line
	if len(os.Args) > 1 && os.Args[1] == "--help" {
		printUsage(os.Stdout)
		os.Exit(0)
	}

	flag.Usage = usage
	flag.Parse()
	if flag.NArg() != 1 {
		usage()
	}

	f, err := os.Open(flag.Arg(0))
	if err != nil {
		log.Fatal(err)
	}

	textStart, symtab, pclntab, err := loadTables(f)
	if err != nil {
		log.Fatalf("reading %s: %v", flag.Arg(0), err)
	}

	pcln := gosym.NewLineTable(pclntab, textStart)
	tab, err := gosym.NewTable(symtab, pcln)
	if err != nil {
		log.Fatalf("reading %s: %v", flag.Arg(0), err)
	}

	stdin := bufio.NewScanner(os.Stdin)
	stdout := bufio.NewWriter(os.Stdout)

	for stdin.Scan() {
		p := stdin.Text()
		if strings.Contains(p, ":") {
			// Reverse translate file:line to pc.
			// This was an extension in the old C version of 'go tool addr2line'
			// and is probably not used by anyone, but recognize the syntax.
			// We don't have an implementation.
			fmt.Fprintf(stdout, "!reverse translation not implemented\n")
			continue
		}
		pc, _ := strconv.ParseUint(p, 16, 64)
		file, line, fn := tab.PCToLine(pc)
		name := "?"
		if fn != nil {
			name = fn.Name
		} else {
			file = "?"
			line = 0
		}
		fmt.Fprintf(stdout, "%s\n%s:%d\n", name, file, line)
	}
	stdout.Flush()
}

func (f *File) PCLineTable() (Liner, error) {
	// If the raw file implements Liner directly, use that.
	// Currently, only Go intermediate objects and archives (goobj) use this path.
	if pcln, ok := f.raw.(Liner); ok {
		return pcln, nil
	}
	// Otherwise, read the pcln tables and build a Liner out of that.
	textStart, symtab, pclntab, err := f.raw.pcln()
	if err != nil {
		return nil, err
	}
	return gosym.NewTable(symtab, gosym.NewLineTable(pclntab, textStart))
}

func processGoInformation(f *elf.File) {
	gosymtab := getSectionData(f, ".gosymtab")
	gopclntab := getSectionData(f, ".gopclntab")

	lineTable := gosym.NewLineTable(gopclntab, f.Section(".text").Addr)
	table, err := gosym.NewTable(gosymtab, lineTable)
	if err != nil {
		log.Fatalf("failed making table: %s", err)
	}

	printSyms(table.Syms)
	printFuncs(table.Funcs)
	printFiles(table.Files)
}

// NewExec tries to detect executable type for the given path and returns
// a new executable. It fails if file does not exist, is not a Go executable or
// it's unable to parse the file format.
func NewExec(path string) (*Exec, error) {
	typ, symtab, pclntab, text, err := newtbl(path)
	if err != nil {
		return nil, err
	}
	lntab := gosym.NewLineTable(pclntab, text)
	if lntab == nil {
		return nil, ErrNotGoExec
	}
	tab, err := gosym.NewTable(symtab, lntab)
	if err != nil {
		return nil, ErrNotGoExec
	}
	return &Exec{Path: path, Type: typ, table: tab}, nil
}

func main() {
	fmt.Println("task 1: verify version")
	fmt.Println("   program compiled with", runtime.Version())

	fmt.Println("task 2: check for presence of variable and function")
	// inspect ELF symbol table
	f, err := elf.Open(os.Args[0])
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()
	symSection := f.Section(".gosymtab")
	lineSection := f.Section(".gopclntab")
	textSection := f.Section(".text")
	if symSection == nil || lineSection == nil || textSection == nil {
		log.Fatal("symbolic information not found")
	}
	symData, err := symSection.Data()
	if err != nil {
		log.Fatal(err)
	}
	lineData, err := lineSection.Data()
	if err != nil {
		log.Fatal(err)
	}
	table, err := gosym.NewTable(symData,
		gosym.NewLineTable(lineData, textSection.Addr))
	if err != nil {
		log.Fatal("  ", err)
	}
	var foundBloop, foundFabs bool
	for _, s := range table.Syms {
		if s.Name == "main.bloop" {
			foundBloop = true
			fmt.Println("   bloop symbol table entry:", s)
		} else if s.Name == "math.Abs" {
			foundFabs = true
			fmt.Println("   abs symbol table entry:", s)
		}
	}
	if foundBloop && foundFabs {
		fmt.Println("   bloop:     ", bloop)
		fmt.Println("   abs(bloop): ", math.Abs(bloop))
	}
}

func (dbp *Process) obtainGoSymbols(exe *pe.File, wg *sync.WaitGroup) {
	defer wg.Done()

	_, symdat, pclndat, err := pcln(exe)
	if err != nil {
		fmt.Println("could not get Go symbols", err)
		os.Exit(1)
	}

	pcln := gosym.NewLineTable(pclndat, uint64(exe.Section(".text").Offset))
	tab, err := gosym.NewTable(symdat, pcln)
	if err != nil {
		fmt.Println("could not get initialize line table", err)
		os.Exit(1)
	}

	dbp.goSymTable = tab
}

func makeTable(f debugFile) (*gosym.Table, error) {
	symdat, err := f.Symtab()
	if err != nil {
		return nil, err
	}
	pclndat, err := f.Pclntab()
	if err != nil {
		return nil, err
	}
	pcln := gosym.NewLineTable(pclndat, f.TextAddr())
	tab, err := gosym.NewTable(symdat, pcln)
	if err != nil {
		return nil, err
	}

	return tab, nil

}

func findAddr(r io.ReaderAt, sym string) (uintptr, error) {
	file, err := elf.NewFile(r)
	if err != nil {
		return 0, err
	}
	defer file.Close()

	var (
		textStart       uint64
		symtab, pclntab []byte
	)

	if sect := file.Section(".text"); sect != nil {
		textStart = sect.Addr
	}
	if sect := file.Section(".gosymtab"); sect != nil {
		if symtab, err = sect.Data(); err != nil {
			return 0, err
		}
	}
	if sect := file.Section(".gopclntab"); sect != nil {
		if pclntab, err = sect.Data(); err != nil {
			return 0, err
		}
	}

	tab, err := gosym.NewTable(symtab, gosym.NewLineTable(pclntab, textStart))
	if err != nil {
		return 0, err
	}

	fn := tab.LookupFunc(sym)
	if fn == nil {
		return 0, fmt.Errorf("could not find symbol %q", sym)
	}
	return uintptr(fn.Entry), nil
}

func main() {
	log.SetFlags(0)
	log.SetPrefix("objdump: ")

	flag.Usage = usage
	flag.Parse()
	if flag.NArg() != 1 && flag.NArg() != 3 {
		usage()
	}

	if *symregexp != "" {
		re, err := regexp.Compile(*symregexp)
		if err != nil {
			log.Fatalf("invalid -s regexp: %v", err)
		}
		symRE = re
	}

	f, err := os.Open(flag.Arg(0))
	if err != nil {
		log.Fatal(err)
	}

	textStart, textData, symtab, pclntab, err := loadTables(f)
	if err != nil {
		log.Fatalf("reading %s: %v", flag.Arg(0), err)
	}

	syms, goarch, err := loadSymbols(f)
	if err != nil {
		log.Fatalf("reading %s: %v", flag.Arg(0), err)
	}

	// Filter out section symbols, overwriting syms in place.
	keep := syms[:0]
	for _, sym := range syms {
		switch sym.Name {
		case "text", "_text", "etext", "_etext":
			// drop
		default:
			keep = append(keep, sym)
		}
	}
	syms = keep

	disasm := disasms[goarch]
	if disasm == nil {
		log.Fatalf("reading %s: unknown architecture", flag.Arg(0))
	}

	lookup := func(addr uint64) (string, uint64) {
		i := sort.Search(len(syms), func(i int) bool { return syms[i].Addr > addr })
		if i > 0 {
			s := syms[i-1]
			if s.Addr <= addr && addr < s.Addr+uint64(s.Size) && s.Name != "etext" && s.Name != "_etext" {
				return s.Name, s.Addr
			}
		}
		return "", 0
	}

	pcln := gosym.NewLineTable(pclntab, textStart)
	tab, err := gosym.NewTable(symtab, pcln)
	if err != nil {
		log.Fatalf("reading %s: %v", flag.Arg(0), err)
	}

	if flag.NArg() == 1 {
		// disassembly of entire object - our format
		dump(tab, lookup, disasm, syms, textData, textStart)
		os.Exit(exitCode)
	}

	// disassembly of specific piece of object - gnu objdump format for pprof
	gnuDump(tab, lookup, disasm, textData, textStart)
	os.Exit(exitCode)
}