1// Copyright 2009 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// Package dwarf provides access to DWARF debugging information loaded from
6// executable files, as defined in the DWARF 2.0 Standard at
7// http://dwarfstd.org/doc/dwarf-2.0.0.pdf
8package dwarf
9
10import "encoding/binary"
11
12// Data represents the DWARF debugging information
13// loaded from an executable file (for example, an ELF or Mach-O executable).
14type Data struct {
15	// raw data
16	abbrev   []byte
17	aranges  []byte
18	frame    []byte
19	info     []byte
20	line     []byte
21	pubnames []byte
22	ranges   []byte
23	str      []byte
24
25	// parsed data
26	abbrevCache map[uint64]abbrevTable
27	order       binary.ByteOrder
28	typeCache   map[Offset]Type
29	typeSigs    map[uint64]*typeUnit
30	unit        []unit
31}
32
33// New returns a new Data object initialized from the given parameters.
34// Rather than calling this function directly, clients should typically use
35// the DWARF method of the File type of the appropriate package debug/elf,
36// debug/macho, debug/pe, or debug/xcoff.
37//
38// The []byte arguments are the data from the corresponding debug section
39// in the object file; for example, for an ELF object, abbrev is the contents of
40// the ".debug_abbrev" section.
41func New(abbrev, aranges, frame, info, line, pubnames, ranges, str []byte) (*Data, error) {
42	d := &Data{
43		abbrev:      abbrev,
44		aranges:     aranges,
45		frame:       frame,
46		info:        info,
47		line:        line,
48		pubnames:    pubnames,
49		ranges:      ranges,
50		str:         str,
51		abbrevCache: make(map[uint64]abbrevTable),
52		typeCache:   make(map[Offset]Type),
53		typeSigs:    make(map[uint64]*typeUnit),
54	}
55
56	// Sniff .debug_info to figure out byte order.
57	// 32-bit DWARF: 4 byte length, 2 byte version.
58	// 64-bit DWARf: 4 bytes of 0xff, 8 byte length, 2 byte version.
59	if len(d.info) < 6 {
60		return nil, DecodeError{"info", Offset(len(d.info)), "too short"}
61	}
62	offset := 4
63	if d.info[0] == 0xff && d.info[1] == 0xff && d.info[2] == 0xff && d.info[3] == 0xff {
64		if len(d.info) < 14 {
65			return nil, DecodeError{"info", Offset(len(d.info)), "too short"}
66		}
67		offset = 12
68	}
69	// Fetch the version, a tiny 16-bit number (1, 2, 3, 4, 5).
70	x, y := d.info[offset], d.info[offset+1]
71	switch {
72	case x == 0 && y == 0:
73		return nil, DecodeError{"info", 4, "unsupported version 0"}
74	case x == 0:
75		d.order = binary.BigEndian
76	case y == 0:
77		d.order = binary.LittleEndian
78	default:
79		return nil, DecodeError{"info", 4, "cannot determine byte order"}
80	}
81
82	u, err := d.parseUnits()
83	if err != nil {
84		return nil, err
85	}
86	d.unit = u
87	return d, nil
88}
89
90// AddTypes will add one .debug_types section to the DWARF data. A
91// typical object with DWARF version 4 debug info will have multiple
92// .debug_types sections. The name is used for error reporting only,
93// and serves to distinguish one .debug_types section from another.
94func (d *Data) AddTypes(name string, types []byte) error {
95	return d.parseTypes(name, types)
96}
97