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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.
// Buffered reading and decoding of DWARF data streams.
package dwarf
import (
"encoding/binary"
"fmt"
"strconv"
)
// Data buffer being decoded.
type buf struct {
dwarf *Data
order binary.ByteOrder
format dataFormat
name string
off Offset
data []byte
err error
}
// Data format, other than byte order. This affects the handling of
// certain field formats.
type dataFormat interface {
// DWARF version number. Zero means unknown.
version() int
// 64-bit DWARF format?
dwarf64() (dwarf64 bool, isKnown bool)
// Size of an address, in bytes. Zero means unknown.
addrsize() int
}
// Some parts of DWARF have no data format, e.g., abbrevs.
type unknownFormat struct{}
func (u unknownFormat) version() int {
return 0
}
func (u unknownFormat) dwarf64() (bool, bool) {
return false, false
}
func (u unknownFormat) addrsize() int {
return 0
}
func makeBuf(d *Data, format dataFormat, name string, off Offset, data []byte) buf {
return buf{d, d.order, format, name, off, data, nil}
}
func (b *buf) slice(length int) buf {
n := *b
data := b.data
b.skip(length) // Will validate length.
n.data = data[:length]
return n
}
func (b *buf) uint8() uint8 {
if len(b.data) < 1 {
b.error("underflow")
return 0
}
val := b.data[0]
b.data = b.data[1:]
b.off++
return val
}
func (b *buf) bytes(n int) []byte {
if len(b.data) < n {
b.error("underflow")
return nil
}
data := b.data[0:n]
b.data = b.data[n:]
b.off += Offset(n)
return data
}
func (b *buf) skip(n int) { b.bytes(n) }
// string returns the NUL-terminated (C-like) string at the start of the buffer.
// The terminal NUL is discarded.
func (b *buf) string() string {
for i := 0; i < len(b.data); i++ {
if b.data[i] == 0 {
s := string(b.data[0:i])
b.data = b.data[i+1:]
b.off += Offset(i + 1)
return s
}
}
b.error("underflow")
return ""
}
func (b *buf) uint16() uint16 {
a := b.bytes(2)
if a == nil {
return 0
}
return b.order.Uint16(a)
}
func (b *buf) uint32() uint32 {
a := b.bytes(4)
if a == nil {
return 0
}
return b.order.Uint32(a)
}
func (b *buf) uint64() uint64 {
a := b.bytes(8)
if a == nil {
return 0
}
return b.order.Uint64(a)
}
// Read a varint, which is 7 bits per byte, little endian.
// the 0x80 bit means read another byte.
func (b *buf) varint() (c uint64, bits uint) {
for i := 0; i < len(b.data); i++ {
byte := b.data[i]
c |= uint64(byte&0x7F) << bits
bits += 7
if byte&0x80 == 0 {
b.off += Offset(i + 1)
b.data = b.data[i+1:]
return c, bits
}
}
return 0, 0
}
// Unsigned int is just a varint.
func (b *buf) uint() uint64 {
x, _ := b.varint()
return x
}
// Signed int is a sign-extended varint.
func (b *buf) int() int64 {
ux, bits := b.varint()
x := int64(ux)
if x&(1<<(bits-1)) != 0 {
x |= -1 << bits
}
return x
}
// Address-sized uint.
func (b *buf) addr() uint64 {
switch b.format.addrsize() {
case 1:
return uint64(b.uint8())
case 2:
return uint64(b.uint16())
case 4:
return uint64(b.uint32())
case 8:
return uint64(b.uint64())
}
b.error("unknown address size")
return 0
}
// assertEmpty checks that everything has been read from b.
func (b *buf) assertEmpty() {
if len(b.data) == 0 {
return
}
if len(b.data) > 5 {
b.error(fmt.Sprintf("unexpected extra data: %x...", b.data[0:5]))
}
b.error(fmt.Sprintf("unexpected extra data: %x", b.data))
}
func (b *buf) error(s string) {
if b.err == nil {
b.data = nil
b.err = DecodeError{b.name, b.off, s}
}
}
type DecodeError struct {
Name string
Offset Offset
Err string
}
func (e DecodeError) Error() string {
return "decoding dwarf section " + e.Name + " at offset 0x" + strconv.FormatInt(int64(e.Offset), 16) + ": " + e.Err
}
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