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      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
      8 package dwarf
      9 
     10 import "encoding/binary"
     11 
     12 // Data represents the DWARF debugging information
     13 // loaded from an executable file (for example, an ELF or Mach-O executable).
     14 type 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[uint32]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, or debug/pe.
     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.
     41 func 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[uint32]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 	// bytes 4:6 are the version, a tiny 16-bit number (1, 2, 3).
     58 	if len(d.info) < 6 {
     59 		return nil, DecodeError{"info", Offset(len(d.info)), "too short"}
     60 	}
     61 	x, y := d.info[4], d.info[5]
     62 	switch {
     63 	case x == 0 && y == 0:
     64 		return nil, DecodeError{"info", 4, "unsupported version 0"}
     65 	case x == 0:
     66 		d.order = binary.BigEndian
     67 	case y == 0:
     68 		d.order = binary.LittleEndian
     69 	default:
     70 		return nil, DecodeError{"info", 4, "cannot determine byte order"}
     71 	}
     72 
     73 	u, err := d.parseUnits()
     74 	if err != nil {
     75 		return nil, err
     76 	}
     77 	d.unit = u
     78 	return d, nil
     79 }
     80 
     81 // AddTypes will add one .debug_types section to the DWARF data.  A
     82 // typical object with DWARF version 4 debug info will have multiple
     83 // .debug_types sections.  The name is used for error reporting only,
     84 // and serves to distinguish one .debug_types section from another.
     85 func (d *Data) AddTypes(name string, types []byte) error {
     86 	return d.parseTypes(name, types)
     87 }
     88