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// 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.

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

import "encoding/binary"

// 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, 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
}