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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 (
"debug/binary";
"os";
"strconv";
)
// Data buffer being decoded.
type buf struct {
dwarf *Data;
order binary.ByteOrder;
name string;
off Offset;
data []byte;
addrsize int;
err os.Error;
}
func makeBuf(d *Data, name string, off Offset, data []byte, addrsize int) buf {
return buf{d, d.order, name, off, data, addrsize, 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 : len(b.data)];
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 : len(b.data)];
b.off += Offset(n);
return data;
}
func (b *buf) skip(n int) {
b.bytes(n);
}
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 : len(b.data)];
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 : len(b.data)];
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.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;
}
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;
Error string;
}
func (e DecodeError) String() string {
return "decoding dwarf section " + e.Name + " at offset 0x" + strconv.Itob64(int64(e.Offset), 16) + ": " + e.Error;
}
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