src/pkg/debug/dwarf/open.go

// Copyright 2009 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This package provides access to DWARF debugging information
// loaded from executable files, as defined in the DWARF 2.0 Standard
// at http://dwarfstd.org/dwarf-2.0.0.pdf.
package dwarf

import (
	"encoding/binary";
	"os";
)

// Data represents the DWARF debugging information
// loaded from an executable file (for example, an ELF or Mach-O executable).
type Data struct {
	// raw data
	abbrev		[]byte;
	aranges		[]byte;
	frame		[]byte;
	info		[]byte;
	line		[]byte;
	pubnames	[]byte;
	ranges		[]byte;
	str		[]byte;

	// parsed data
	abbrevCache	map[uint32]abbrevTable;
	addrsize	int;
	order		binary.ByteOrder;
	typeCache	map[Offset]Type;
	unit		[]unit;
}

// New returns a new Data object initialized from the given parameters.
// Clients should typically use [TODO(rsc): method to be named later] instead of calling
// New directly.
//
// The []byte arguments are the data from the corresponding debug section
// in the object file; for example, for an ELF object, abbrev is the contents of
// the ".debug_abbrev" section.
func New(abbrev, aranges, frame, info, line, pubnames, ranges, str []byte) (*Data, os.Error) {
	d := &Data{
		abbrev: abbrev,
		aranges: aranges,
		frame: frame,
		info: info,
		line: line,
		pubnames: pubnames,
		ranges: ranges,
		str: str,
		abbrevCache: make(map[uint32]abbrevTable),
		typeCache: make(map[Offset]Type),
	};

	// Sniff .debug_info to figure out byte order.
	// bytes 4:6 are the version, a tiny 16-bit number (1, 2, 3).
	if len(d.info) < 6 {
		return nil, DecodeError{"info", Offset(len(d.info)), "too short"}
	}
	x, y := d.info[4], d.info[5];
	switch {
	case x == 0 && y == 0:
		return nil, DecodeError{"info", 4, "unsupported version 0"}
	case x == 0:
		d.order = binary.BigEndian
	case y == 0:
		d.order = binary.LittleEndian
	default:
		return nil, DecodeError{"info", 4, "cannot determine byte order"}
	}

	u, err := d.parseUnits();
	if err != nil {
		return nil, err
	}
	d.unit = u;
	return d, nil;
}