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//===-- DWARFDebugFrame.h - Parsing of .debug_frame -------------*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
#include "DWARFDebugFrame.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Support/DataTypes.h"
#include "llvm/Support/Dwarf.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/raw_ostream.h"
#include <string>
#include <vector>
using namespace llvm;
using namespace dwarf;
/// \brief Abstract frame entry defining the common interface concrete
/// entries implement.
class llvm::FrameEntry {
enum FrameKind {FK_CIE, FK_FDE};
FrameEntry(FrameKind K, uint64_t Offset, uint64_t Length)
: Kind(K), Offset(Offset), Length(Length) {}
virtual ~FrameEntry() {
FrameKind getKind() const { return Kind; }
virtual uint64_t getOffset() const { return Offset; }
/// \brief Parse and store a sequence of CFI instructions from Data,
/// starting at *Offset and ending at EndOffset. If everything
/// goes well, *Offset should be equal to EndOffset when this method
/// returns. Otherwise, an error occurred.
virtual void parseInstructions(DataExtractor Data, uint32_t *Offset,
uint32_t EndOffset);
/// \brief Dump the entry header to the given output stream.
virtual void dumpHeader(raw_ostream &OS) const = 0;
/// \brief Dump the entry's instructions to the given output stream.
virtual void dumpInstructions(raw_ostream &OS) const;
const FrameKind Kind;
/// \brief Offset of this entry in the section.
uint64_t Offset;
/// \brief Entry length as specified in DWARF.
uint64_t Length;
/// An entry may contain CFI instructions. An instruction consists of an
/// opcode and an optional sequence of operands.
typedef std::vector<uint64_t> Operands;
struct Instruction {
Instruction(uint8_t Opcode)
: Opcode(Opcode)
uint8_t Opcode;
Operands Ops;
std::vector<Instruction> Instructions;
/// Convenience methods to add a new instruction with the given opcode and
/// operands to the Instructions vector.
void addInstruction(uint8_t Opcode) {
void addInstruction(uint8_t Opcode, uint64_t Operand1) {
void addInstruction(uint8_t Opcode, uint64_t Operand1, uint64_t Operand2) {
// See DWARF standard v3, section 7.23
const uint8_t DWARF_CFI_PRIMARY_OPCODE_MASK = 0xc0;
const uint8_t DWARF_CFI_PRIMARY_OPERAND_MASK = 0x3f;
void FrameEntry::parseInstructions(DataExtractor Data, uint32_t *Offset,
uint32_t EndOffset) {
while (*Offset < EndOffset) {
uint8_t Opcode = Data.getU8(Offset);
// Some instructions have a primary opcode encoded in the top bits.
uint8_t Primary = Opcode & DWARF_CFI_PRIMARY_OPCODE_MASK;
if (Primary) {
// If it's a primary opcode, the first operand is encoded in the bottom
// bits of the opcode itself.
switch (Primary) {
default: llvm_unreachable("Impossible primary CFI opcode");
case DW_CFA_advance_loc:
case DW_CFA_restore:
addInstruction(Primary, Op1);
case DW_CFA_offset:
addInstruction(Primary, Op1, Data.getULEB128(Offset));
} else {
// Extended opcode - its value is Opcode itself.
switch (Opcode) {
default: llvm_unreachable("Invalid extended CFI opcode");
case DW_CFA_nop:
case DW_CFA_remember_state:
case DW_CFA_restore_state:
case DW_CFA_GNU_window_save:
// No operands
case DW_CFA_set_loc:
// Operands: Address
addInstruction(Opcode, Data.getAddress(Offset));
case DW_CFA_advance_loc1:
// Operands: 1-byte delta
addInstruction(Opcode, Data.getU8(Offset));
case DW_CFA_advance_loc2:
// Operands: 2-byte delta
addInstruction(Opcode, Data.getU16(Offset));
case DW_CFA_advance_loc4:
// Operands: 4-byte delta
addInstruction(Opcode, Data.getU32(Offset));
case DW_CFA_restore_extended:
case DW_CFA_undefined:
case DW_CFA_same_value:
case DW_CFA_def_cfa_register:
case DW_CFA_def_cfa_offset:
// Operands: ULEB128
addInstruction(Opcode, Data.getULEB128(Offset));
case DW_CFA_def_cfa_offset_sf:
// Operands: SLEB128
addInstruction(Opcode, Data.getSLEB128(Offset));
case DW_CFA_offset_extended:
case DW_CFA_register:
case DW_CFA_def_cfa:
case DW_CFA_val_offset:
// Operands: ULEB128, ULEB128
addInstruction(Opcode, Data.getULEB128(Offset),
case DW_CFA_offset_extended_sf:
case DW_CFA_def_cfa_sf:
case DW_CFA_val_offset_sf:
// Operands: ULEB128, SLEB128
addInstruction(Opcode, Data.getULEB128(Offset),
case DW_CFA_def_cfa_expression:
case DW_CFA_expression:
case DW_CFA_val_expression:
// TODO: implement this
report_fatal_error("Values with expressions not implemented yet!");
void FrameEntry::dumpInstructions(raw_ostream &OS) const {
// TODO: at the moment only instruction names are dumped. Expand this to
// dump operands as well.
for (const auto &Instr : Instructions) {
uint8_t Opcode = Instr.Opcode;
OS << " " << CallFrameString(Opcode) << ":\n";
namespace {
/// \brief DWARF Common Information Entry (CIE)
class CIE : public FrameEntry {
// CIEs (and FDEs) are simply container classes, so the only sensible way to
// create them is by providing the full parsed contents in the constructor.
CIE(uint64_t Offset, uint64_t Length, uint8_t Version,
SmallString<8> Augmentation, uint64_t CodeAlignmentFactor,
int64_t DataAlignmentFactor, uint64_t ReturnAddressRegister)
: FrameEntry(FK_CIE, Offset, Length), Version(Version),
Augmentation(Augmentation), CodeAlignmentFactor(CodeAlignmentFactor),
ReturnAddressRegister(ReturnAddressRegister) {}
~CIE() {
void dumpHeader(raw_ostream &OS) const override {
OS << format("%08x %08x %08x CIE",
(uint32_t)Offset, (uint32_t)Length, DW_CIE_ID)
<< "\n";
OS << format(" Version: %d\n", Version);
OS << " Augmentation: \"" << Augmentation << "\"\n";
OS << format(" Code alignment factor: %u\n",
OS << format(" Data alignment factor: %d\n",
OS << format(" Return address column: %d\n",
OS << "\n";
static bool classof(const FrameEntry *FE) {
return FE->getKind() == FK_CIE;
/// The following fields are defined in section 6.4.1 of the DWARF standard v3
uint8_t Version;
SmallString<8> Augmentation;
uint64_t CodeAlignmentFactor;
int64_t DataAlignmentFactor;
uint64_t ReturnAddressRegister;
/// \brief DWARF Frame Description Entry (FDE)
class FDE : public FrameEntry {
// Each FDE has a CIE it's "linked to". Our FDE contains is constructed with
// an offset to the CIE (provided by parsing the FDE header). The CIE itself
// is obtained lazily once it's actually required.
FDE(uint64_t Offset, uint64_t Length, int64_t LinkedCIEOffset,
uint64_t InitialLocation, uint64_t AddressRange)
: FrameEntry(FK_FDE, Offset, Length), LinkedCIEOffset(LinkedCIEOffset),
InitialLocation(InitialLocation), AddressRange(AddressRange),
LinkedCIE(nullptr) {}
~FDE() {
void dumpHeader(raw_ostream &OS) const override {
OS << format("%08x %08x %08x FDE ",
(uint32_t)Offset, (uint32_t)Length, (int32_t)LinkedCIEOffset);
OS << format("cie=%08x pc=%08x...%08x\n",
(uint32_t)InitialLocation + (uint32_t)AddressRange);
if (LinkedCIE) {
OS << format("%p\n", LinkedCIE);
static bool classof(const FrameEntry *FE) {
return FE->getKind() == FK_FDE;
/// The following fields are defined in section 6.4.1 of the DWARF standard v3
uint64_t LinkedCIEOffset;
uint64_t InitialLocation;
uint64_t AddressRange;
CIE *LinkedCIE;
} // end anonymous namespace
DWARFDebugFrame::DWARFDebugFrame() {
DWARFDebugFrame::~DWARFDebugFrame() {
static void LLVM_ATTRIBUTE_UNUSED dumpDataAux(DataExtractor Data,
uint32_t Offset, int Length) {
errs() << "DUMP: ";
for (int i = 0; i < Length; ++i) {
uint8_t c = Data.getU8(&Offset);
errs().write_hex(c); errs() << " ";
errs() << "\n";
void DWARFDebugFrame::parse(DataExtractor Data) {
uint32_t Offset = 0;
while (Data.isValidOffset(Offset)) {
uint32_t StartOffset = Offset;
bool IsDWARF64 = false;
uint64_t Length = Data.getU32(&Offset);
uint64_t Id;
if (Length == UINT32_MAX) {
// DWARF-64 is distinguished by the first 32 bits of the initial length
// field being 0xffffffff. Then, the next 64 bits are the actual entry
// length.
IsDWARF64 = true;
Length = Data.getU64(&Offset);
// At this point, Offset points to the next field after Length.
// Length is the structure size excluding itself. Compute an offset one
// past the end of the structure (needed to know how many instructions to
// read).
// TODO: For honest DWARF64 support, DataExtractor will have to treat
// offset_ptr as uint64_t*
uint32_t EndStructureOffset = Offset + static_cast<uint32_t>(Length);
// The Id field's size depends on the DWARF format
Id = Data.getUnsigned(&Offset, IsDWARF64 ? 8 : 4);
bool IsCIE = ((IsDWARF64 && Id == DW64_CIE_ID) || Id == DW_CIE_ID);
if (IsCIE) {
// Note: this is specifically DWARFv3 CIE header structure. It was
// changed in DWARFv4. We currently don't support reading DWARFv4
// here because LLVM itself does not emit it (and LLDB doesn't
// support it either).
uint8_t Version = Data.getU8(&Offset);
const char *Augmentation = Data.getCStr(&Offset);
uint64_t CodeAlignmentFactor = Data.getULEB128(&Offset);
int64_t DataAlignmentFactor = Data.getSLEB128(&Offset);
uint64_t ReturnAddressRegister = Data.getULEB128(&Offset);
Entries.emplace_back(new CIE(StartOffset, Length, Version,
StringRef(Augmentation), CodeAlignmentFactor,
DataAlignmentFactor, ReturnAddressRegister));
} else {
// FDE
uint64_t CIEPointer = Id;
uint64_t InitialLocation = Data.getAddress(&Offset);
uint64_t AddressRange = Data.getAddress(&Offset);
Entries.emplace_back(new FDE(StartOffset, Length, CIEPointer,
InitialLocation, AddressRange));
Entries.back()->parseInstructions(Data, &Offset, EndStructureOffset);
if (Offset != EndStructureOffset) {
std::string Str;
raw_string_ostream OS(Str);
OS << format("Parsing entry instructions at %lx failed", StartOffset);
void DWARFDebugFrame::dump(raw_ostream &OS) const {
OS << "\n";
for (const auto &Entry : Entries) {
OS << "\n";