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frame.go
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frame.go
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package main
import (
"bytes"
"encoding/binary"
"fmt"
"go.uber.org/zap"
"io"
)
// http://dwarfstd.org/doc/Dwarf3.pdf
type CommonInformationEntry struct {
length uint32
cie_id uint64
version byte
augmentation string
code_alignment_factor uint64
data_alignment_factor int64
return_address_register uint64
initial_instructions []byte
// `padding`, Enough DW_CFA_nop instructions to make the size of this entry match the length value above.
}
func (cie *CommonInformationEntry) String() string {
if cie == nil {
return "`cie == nil` is true, please check cie"
}
return fmt.Sprintf("len=%d, cie_id=0x%x, "+
"versiont=%v, augmentation=%s, code_alignment_factor=%d, "+
"data_alignment_factor=%d, return_address_register=0x%x, "+
"initial_instructions=%v",
cie.length,
cie.cie_id, cie.version, cie.augmentation,
cie.code_alignment_factor, cie.data_alignment_factor, cie.return_address_register,
cie.initial_instructions)
}
type FrameDescriptionEntry struct {
length uint32
CIE *CommonInformationEntry
instructions []byte
begin, size uint64
}
func (fde *FrameDescriptionEntry) String() string {
if fde == nil {
return "`fde == nil` is true, please check fde"
}
return fmt.Sprintf("len=%d, instructions=%v, begin=0x%x, size=%d",
fde.length, fde.instructions, fde.begin, fde.size)
}
type VirtualUnwindFrameInformation struct {
len uint32
CIE *CommonInformationEntry
FDE *FrameDescriptionEntry
}
type Frame struct {
instructions []byte
address uint64
cie *CommonInformationEntry
Offset int64
cfa *DWRule
regsRule map[uint64]DWRule
regs []uint64
framebase uint64
loc uint64
}
func parseFrameInformation(buffer *bytes.Buffer) (*VirtualUnwindFrameInformation, error) {
if buffer.Len() == 0 {
return nil, io.EOF
}
var (
cieEntry *CommonInformationEntry
fdeEntry *FrameDescriptionEntry
err error
info *VirtualUnwindFrameInformation
)
info = &VirtualUnwindFrameInformation{}
binary.Read(buffer, binary.LittleEndian, &info.len)
tbytes := buffer.Next(4)
info.len -= 4
input := buffer.Next(int(info.len))
if bytes.Equal(tbytes, []byte{0xff, 0xff, 0xff, 0xff}) {
// cie
if cieEntry, err = parseCommonInformationEntryByte(info.len, input); err != nil {
return nil, err
}
info.CIE = cieEntry
} else {
// fde
if fdeEntry, err = parseFrameDescriptionEntryByte(info.len, input); err != nil {
return nil, err
}
info.FDE = fdeEntry
}
return info, nil
}
// https://en.wikipedia.org/wiki/LEB128
// result = 0;
// shift = 0;
// while(true) {
// byte = next byte in input;
// result |= (low order 7 bits of byte) << shift;
// if (high order bit of byte == 0)
// break;
// shift += 7;
// }
func DecodeULEB128(buf *bytes.Buffer) (uint64, uint32, error) {
var (
res uint64
len uint32
err error
b byte
shift uint64
)
for {
if b, err = buf.ReadByte(); err != nil {
return 0, 0, err
}
len++
res |= uint64((uint(b) & 0x7f) << shift)
// If high order bit is 1.
if b&0x80 == 0 {
break
}
shift += 7
}
return res, len, nil
}
// https://en.wikipedia.org/wiki/LEB128
// result = 0;
// shift = 0;
// size = number of bits in signed integer;
// do{
// byte = next byte in input;
// result |= (low order 7 bits of byte << shift);
// shift += 7;
// } while (high order bit of byte != 0);
//
// /* sign bit of byte is second high order bit (0x40) */
// if ((shift <size) && (sign bit of byte is set))
// /* sign extend */
// result |= (~0 << shift);
func DecodeSLEB128(buf *bytes.Buffer) (int64, uint32, error) {
var (
res int64
len uint32
err error
b byte
shift uint64
)
for {
b, err = buf.ReadByte()
if err != nil {
return 0, 0, err
}
len++
res |= int64((int64(b) & 0x7f) << shift)
shift += 7
if b&0x80 == 0 {
break
}
}
if (shift < 8*uint64(len)) && (b&0x40 > 0) {
res |= -(1 << shift)
}
return res, len, nil
}
func parseCommonInformationEntryByte(len uint32, data []byte) (*CommonInformationEntry, error) {
var (
err error
str string
)
cie := &CommonInformationEntry{}
buf := bytes.NewBuffer(data)
cie.length = len
cie.cie_id = 0xffffffff
cie.version = buf.Next(1)[0]
// A null-terminated UTF-8 string that identifies the augmentation to this CIE or to the FDEs that use it.
if str, err = buf.ReadString(0x0); err != nil {
return nil, err
}
cie.augmentation = str
// code_alignment_factor (unsigned LEB128)
if cie.code_alignment_factor, _, err = DecodeULEB128(buf); err != nil {
return nil, err
}
// data_alignment_factor (signed LEB128)
if cie.data_alignment_factor, _, err = DecodeSLEB128(buf); err != nil {
return nil, err
}
// return_address_register (unsigned LEB128)
if cie.return_address_register, _, err = DecodeULEB128(buf); err != nil {
return nil, err
}
// A sequence of rules that are interpreted to create the initial setting of each column in the table.
cie.initial_instructions = buf.Bytes()
// padding (array of ubyte)
// Enough DW_CFA_nop instructions to make the size of this entry match the length value above.
return cie, nil
}
// ???
func parseFrameDescriptionEntryByte(len uint32, data []byte) (*FrameDescriptionEntry, error) {
fde := &FrameDescriptionEntry{}
fde.length = len
fde.begin = binary.LittleEndian.Uint64(data[:8]) // + ctx.staticBase
fde.size = binary.LittleEndian.Uint64(data[8:16])
fde.instructions = data[16:]
logger.Debug("parseFrameDescriptionEntryByte",
zap.Uint32("len", len),
zap.Uint64("begin", fde.begin),
zap.Uint64("size", fde.size))
return fde, nil
}