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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 util
import (
"debug/dwarf"
"fmt"
)
// Data buffer being decoded.
type buf struct {
dwarf *dwarf.Data
format dataFormat
name string
off dwarf.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 *dwarf.Data, format dataFormat, name string, off dwarf.Offset, data []byte) buf {
return buf{d, format, name, off, data, nil}
}
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
}
// 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 += dwarf.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
}
// 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 = dwarf.DecodeError{Name: b.name, Offset: b.off, Err: s}
}
}
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