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- // Copyright 2018 Google Inc. All Rights Reserved.
- //
- // Licensed under the Apache License, Version 2.0 (the "License");
- // you may not use this file except in compliance with the License.
- // You may obtain a copy of the License at
- //
- // http://www.apache.org/licenses/LICENSE-2.0
- //
- // Unless required by applicable law or agreed to in writing, software
- // distributed under the License is distributed on an "AS IS" BASIS,
- // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- // See the License for the specific language governing permissions and
- // limitations under the License.
-
- // 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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