github.com/goproxy0/go@v0.0.0-20171111080102-49cc0c489d2c/src/debug/dwarf/open.go (about)

     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[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, 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[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.
    94  func (d *Data) AddTypes(name string, types []byte) error {
    95  	return d.parseTypes(name, types)
    96  }