// Copyright 2016 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "src/eh-frame.h"
#include <iomanip>
#include <ostream>
#if !defined(V8_TARGET_ARCH_X64) && !defined(V8_TARGET_ARCH_ARM) && \
!defined(V8_TARGET_ARCH_ARM64)
// Placeholders for unsupported architectures.
namespace v8 {
namespace internal {
const int EhFrameConstants::kCodeAlignmentFactor = 1;
const int EhFrameConstants::kDataAlignmentFactor = 1;
void EhFrameWriter::WriteReturnAddressRegisterCode() { UNIMPLEMENTED(); }
void EhFrameWriter::WriteInitialStateInCie() { UNIMPLEMENTED(); }
int EhFrameWriter::RegisterToDwarfCode(Register) {
UNIMPLEMENTED();
return -1;
}
#ifdef ENABLE_DISASSEMBLER
const char* EhFrameDisassembler::DwarfRegisterCodeToString(int) {
UNIMPLEMENTED();
return nullptr;
}
#endif
} // namespace internal
} // namespace v8
#endif
namespace v8 {
namespace internal {
STATIC_CONST_MEMBER_DEFINITION const int
EhFrameConstants::kEhFrameTerminatorSize;
STATIC_CONST_MEMBER_DEFINITION const int EhFrameConstants::kEhFrameHdrVersion;
STATIC_CONST_MEMBER_DEFINITION const int EhFrameConstants::kEhFrameHdrSize;
STATIC_CONST_MEMBER_DEFINITION const uint32_t EhFrameWriter::kInt32Placeholder;
// static
void EhFrameWriter::WriteEmptyEhFrame(std::ostream& stream) { // NOLINT
stream.put(EhFrameConstants::kEhFrameHdrVersion);
// .eh_frame pointer encoding specifier.
stream.put(EhFrameConstants::kSData4 | EhFrameConstants::kPcRel);
// Lookup table size encoding.
stream.put(EhFrameConstants::kUData4);
// Lookup table entries encoding.
stream.put(EhFrameConstants::kSData4 | EhFrameConstants::kDataRel);
// Dummy pointers and 0 entries in the lookup table.
char dummy_data[EhFrameConstants::kEhFrameHdrSize - 4] = {0};
stream.write(&dummy_data[0], sizeof(dummy_data));
}
EhFrameWriter::EhFrameWriter(Zone* zone)
: cie_size_(0),
last_pc_offset_(0),
writer_state_(InternalState::kUndefined),
base_register_(no_reg),
base_offset_(0),
eh_frame_buffer_(zone) {}
void EhFrameWriter::Initialize() {
DCHECK(writer_state_ == InternalState::kUndefined);
eh_frame_buffer_.reserve(128);
writer_state_ = InternalState::kInitialized;
WriteCie();
WriteFdeHeader();
}
void EhFrameWriter::WriteCie() {
static const int kCIEIdentifier = 0;
static const int kCIEVersion = 3;
static const int kAugmentationDataSize = 2;
static const byte kAugmentationString[] = {'z', 'L', 'R', 0};
// Placeholder for the size of the CIE.
int size_offset = eh_frame_offset();
WriteInt32(kInt32Placeholder);
// CIE identifier and version.
int record_start_offset = eh_frame_offset();
WriteInt32(kCIEIdentifier);
WriteByte(kCIEVersion);
// Augmentation data contents descriptor: LSDA and FDE encoding.
WriteBytes(&kAugmentationString[0], sizeof(kAugmentationString));
// Alignment factors.
WriteSLeb128(EhFrameConstants::kCodeAlignmentFactor);
WriteSLeb128(EhFrameConstants::kDataAlignmentFactor);
WriteReturnAddressRegisterCode();
// Augmentation data.
WriteULeb128(kAugmentationDataSize);
// No language-specific data area (LSDA).
WriteByte(EhFrameConstants::kOmit);
// FDE pointers encoding.
WriteByte(EhFrameConstants::kSData4 | EhFrameConstants::kPcRel);
// Write directives to build the initial state of the unwinding table.
DCHECK_EQ(eh_frame_offset() - size_offset,
EhFrameConstants::kInitialStateOffsetInCie);
WriteInitialStateInCie();
WritePaddingToAlignedSize(eh_frame_offset() - record_start_offset);
int record_end_offset = eh_frame_offset();
int encoded_cie_size = record_end_offset - record_start_offset;
cie_size_ = record_end_offset - size_offset;
// Patch the size of the CIE now that we know it.
PatchInt32(size_offset, encoded_cie_size);
}
void EhFrameWriter::WriteFdeHeader() {
DCHECK_NE(cie_size_, 0);
// Placeholder for size of the FDE. Will be filled in Finish().
DCHECK_EQ(eh_frame_offset(), fde_offset());
WriteInt32(kInt32Placeholder);
// Backwards offset to the CIE.
WriteInt32(cie_size_ + kInt32Size);
// Placeholder for pointer to procedure. Will be filled in Finish().
DCHECK_EQ(eh_frame_offset(), GetProcedureAddressOffset());
WriteInt32(kInt32Placeholder);
// Placeholder for size of the procedure. Will be filled in Finish().
DCHECK_EQ(eh_frame_offset(), GetProcedureSizeOffset());
WriteInt32(kInt32Placeholder);
// No augmentation data.
WriteByte(0);
}
void EhFrameWriter::WriteEhFrameHdr(int code_size) {
DCHECK(writer_state_ == InternalState::kInitialized);
//
// In order to calculate offsets in the .eh_frame_hdr, we must know the layout
// of the DSO generated by perf inject, which is assumed to be the following:
//
// | ... | |
// +---------------+ <-- (F) --- | Larger offsets in file
// | | ^ |
// | Instructions | | .text v
// | | v
// +---------------+ <-- (E) ---
// |///////////////|
// |////Padding////|
// |///////////////|
// +---------------+ <-- (D) ---
// | | ^
// | CIE | |
// | | |
// +---------------+ <-- (C) |
// | | | .eh_frame
// | FDE | |
// | | |
// +---------------+ |
// | terminator | v
// +---------------+ <-- (B) ---
// | version | ^
// +---------------+ |
// | encoding | |
// | specifiers | |
// +---------------+ <---(A) | .eh_frame_hdr
// | offset to | |
// | .eh_frame | |
// +---------------+ |
// | ... | ...
//
// (F) is aligned to a 16-byte boundary.
// (D) is aligned to a 8-byte boundary.
// (B) is aligned to a 4-byte boundary.
// (C), (E) and (A) have no alignment requirements.
//
// The distance between (A) and (B) is 4 bytes.
//
// The size of the FDE is required to be a multiple of the pointer size, which
// means that (B) will be naturally aligned to a 4-byte boundary on all the
// architectures we support.
//
// Because (E) has no alignment requirements, there is padding between (E) and
// (D). (F) is aligned at a 16-byte boundary, thus to a 8-byte one as well.
//
int eh_frame_size = eh_frame_offset();
WriteByte(EhFrameConstants::kEhFrameHdrVersion);
// .eh_frame pointer encoding specifier.
WriteByte(EhFrameConstants::kSData4 | EhFrameConstants::kPcRel);
// Lookup table size encoding specifier.
WriteByte(EhFrameConstants::kUData4);
// Lookup table entries encoding specifier.
WriteByte(EhFrameConstants::kSData4 | EhFrameConstants::kDataRel);
// Pointer to .eh_frame, relative to this offset (A -> D in the diagram).
WriteInt32(-(eh_frame_size + EhFrameConstants::kFdeVersionSize +
EhFrameConstants::kFdeEncodingSpecifiersSize));
// Number of entries in the LUT, one for the only routine.
WriteInt32(1);
// Pointer to the start of the routine, relative to the beginning of the
// .eh_frame_hdr (B -> F in the diagram).
WriteInt32(-(RoundUp(code_size, 8) + eh_frame_size));
// Pointer to the start of the associated FDE, relative to the start of the
// .eh_frame_hdr (B -> C in the diagram).
WriteInt32(-(eh_frame_size - cie_size_));
DCHECK_EQ(eh_frame_offset() - eh_frame_size,
EhFrameConstants::kEhFrameHdrSize);
}
void EhFrameWriter::WritePaddingToAlignedSize(int unpadded_size) {
DCHECK(writer_state_ == InternalState::kInitialized);
DCHECK_GE(unpadded_size, 0);
int padding_size = RoundUp(unpadded_size, kPointerSize) - unpadded_size;
byte nop = static_cast<byte>(EhFrameConstants::DwarfOpcodes::kNop);
static const byte kPadding[] = {nop, nop, nop, nop, nop, nop, nop, nop};
DCHECK_LE(padding_size, static_cast<int>(sizeof(kPadding)));
WriteBytes(&kPadding[0], padding_size);
}
void EhFrameWriter::AdvanceLocation(int pc_offset) {
DCHECK(writer_state_ == InternalState::kInitialized);
DCHECK_GE(pc_offset, last_pc_offset_);
uint32_t delta = pc_offset - last_pc_offset_;
DCHECK_EQ(delta % EhFrameConstants::kCodeAlignmentFactor, 0u);
uint32_t factored_delta = delta / EhFrameConstants::kCodeAlignmentFactor;
if (factored_delta <= EhFrameConstants::kLocationMask) {
WriteByte((EhFrameConstants::kLocationTag
<< EhFrameConstants::kLocationMaskSize) |
(factored_delta & EhFrameConstants::kLocationMask));
} else if (factored_delta <= kMaxUInt8) {
WriteOpcode(EhFrameConstants::DwarfOpcodes::kAdvanceLoc1);
WriteByte(factored_delta);
} else if (factored_delta <= kMaxUInt16) {
WriteOpcode(EhFrameConstants::DwarfOpcodes::kAdvanceLoc2);
WriteInt16(factored_delta);
} else {
WriteOpcode(EhFrameConstants::DwarfOpcodes::kAdvanceLoc4);
WriteInt32(factored_delta);
}
last_pc_offset_ = pc_offset;
}
void EhFrameWriter::SetBaseAddressOffset(int base_offset) {
DCHECK(writer_state_ == InternalState::kInitialized);
DCHECK_GE(base_offset, 0);
WriteOpcode(EhFrameConstants::DwarfOpcodes::kDefCfaOffset);
WriteULeb128(base_offset);
base_offset_ = base_offset;
}
void EhFrameWriter::SetBaseAddressRegister(Register base_register) {
DCHECK(writer_state_ == InternalState::kInitialized);
int code = RegisterToDwarfCode(base_register);
WriteOpcode(EhFrameConstants::DwarfOpcodes::kDefCfaRegister);
WriteULeb128(code);
base_register_ = base_register;
}
void EhFrameWriter::SetBaseAddressRegisterAndOffset(Register base_register,
int base_offset) {
DCHECK(writer_state_ == InternalState::kInitialized);
DCHECK_GE(base_offset, 0);
int code = RegisterToDwarfCode(base_register);
WriteOpcode(EhFrameConstants::DwarfOpcodes::kDefCfa);
WriteULeb128(code);
WriteULeb128(base_offset);
base_offset_ = base_offset;
base_register_ = base_register;
}
void EhFrameWriter::RecordRegisterSavedToStack(int register_code, int offset) {
DCHECK(writer_state_ == InternalState::kInitialized);
DCHECK_EQ(offset % EhFrameConstants::kDataAlignmentFactor, 0);
int factored_offset = offset / EhFrameConstants::kDataAlignmentFactor;
if (factored_offset >= 0) {
DCHECK_LE(register_code, EhFrameConstants::kSavedRegisterMask);
WriteByte((EhFrameConstants::kSavedRegisterTag
<< EhFrameConstants::kSavedRegisterMaskSize) |
(register_code & EhFrameConstants::kSavedRegisterMask));
WriteULeb128(factored_offset);
} else {
WriteOpcode(EhFrameConstants::DwarfOpcodes::kOffsetExtendedSf);
WriteULeb128(register_code);
WriteSLeb128(factored_offset);
}
}
void EhFrameWriter::RecordRegisterNotModified(Register name) {
DCHECK(writer_state_ == InternalState::kInitialized);
WriteOpcode(EhFrameConstants::DwarfOpcodes::kSameValue);
WriteULeb128(RegisterToDwarfCode(name));
}
void EhFrameWriter::RecordRegisterFollowsInitialRule(Register name) {
DCHECK(writer_state_ == InternalState::kInitialized);
int code = RegisterToDwarfCode(name);
DCHECK_LE(code, EhFrameConstants::kFollowInitialRuleMask);
WriteByte((EhFrameConstants::kFollowInitialRuleTag
<< EhFrameConstants::kFollowInitialRuleMaskSize) |
(code & EhFrameConstants::kFollowInitialRuleMask));
}
void EhFrameWriter::Finish(int code_size) {
DCHECK(writer_state_ == InternalState::kInitialized);
DCHECK_GE(eh_frame_offset(), cie_size_);
DCHECK_GE(eh_frame_offset(), fde_offset() + kInt32Size);
WritePaddingToAlignedSize(eh_frame_offset() - fde_offset() - kInt32Size);
// Write the size of the FDE now that we know it.
// The encoded size does not include the size field itself.
int encoded_fde_size = eh_frame_offset() - fde_offset() - kInt32Size;
PatchInt32(fde_offset(), encoded_fde_size);
// Write size and offset to procedure.
PatchInt32(GetProcedureAddressOffset(),
-(RoundUp(code_size, 8) + GetProcedureAddressOffset()));
PatchInt32(GetProcedureSizeOffset(), code_size);
// Terminate the .eh_frame.
static const byte kTerminator[EhFrameConstants::kEhFrameTerminatorSize] = {0};
WriteBytes(&kTerminator[0], EhFrameConstants::kEhFrameTerminatorSize);
WriteEhFrameHdr(code_size);
writer_state_ = InternalState::kFinalized;
}
void EhFrameWriter::GetEhFrame(CodeDesc* desc) {
DCHECK(writer_state_ == InternalState::kFinalized);
desc->unwinding_info_size = static_cast<int>(eh_frame_buffer_.size());
desc->unwinding_info = eh_frame_buffer_.data();
}
void EhFrameWriter::WriteULeb128(uint32_t value) {
do {
byte chunk = value & 0x7f;
value >>= 7;
if (value != 0) chunk |= 0x80;
WriteByte(chunk);
} while (value != 0);
}
void EhFrameWriter::WriteSLeb128(int32_t value) {
static const int kSignBitMask = 0x40;
bool done;
do {
byte chunk = value & 0x7f;
value >>= 7;
done = ((value == 0) && ((chunk & kSignBitMask) == 0)) ||
((value == -1) && ((chunk & kSignBitMask) != 0));
if (!done) chunk |= 0x80;
WriteByte(chunk);
} while (!done);
}
uint32_t EhFrameIterator::GetNextULeb128() {
int size = 0;
uint32_t result = DecodeULeb128(next_, &size);
DCHECK_LE(next_ + size, end_);
next_ += size;
return result;
}
int32_t EhFrameIterator::GetNextSLeb128() {
int size = 0;
int32_t result = DecodeSLeb128(next_, &size);
DCHECK_LE(next_ + size, end_);
next_ += size;
return result;
}
// static
uint32_t EhFrameIterator::DecodeULeb128(const byte* encoded,
int* encoded_size) {
const byte* current = encoded;
uint32_t result = 0;
int shift = 0;
do {
DCHECK_LT(shift, 8 * static_cast<int>(sizeof(result)));
result |= (*current & 0x7f) << shift;
shift += 7;
} while (*current++ >= 128);
DCHECK_NOT_NULL(encoded_size);
*encoded_size = static_cast<int>(current - encoded);
return result;
}
// static
int32_t EhFrameIterator::DecodeSLeb128(const byte* encoded, int* encoded_size) {
static const byte kSignBitMask = 0x40;
const byte* current = encoded;
int32_t result = 0;
int shift = 0;
byte chunk;
do {
chunk = *current++;
DCHECK_LT(shift, 8 * static_cast<int>(sizeof(result)));
result |= (chunk & 0x7f) << shift;
shift += 7;
} while (chunk >= 128);
// Sign extend the result if the last chunk has the sign bit set.
if (chunk & kSignBitMask) result |= (~0ull) << shift;
DCHECK_NOT_NULL(encoded_size);
*encoded_size = static_cast<int>(current - encoded);
return result;
}
#ifdef ENABLE_DISASSEMBLER
namespace {
class StreamModifiersScope final {
public:
explicit StreamModifiersScope(std::ostream* stream)
: stream_(stream), flags_(stream->flags()) {}
~StreamModifiersScope() { stream_->flags(flags_); }
private:
std::ostream* stream_;
std::ios::fmtflags flags_;
};
} // namespace
// static
void EhFrameDisassembler::DumpDwarfDirectives(std::ostream& stream, // NOLINT
const byte* start,
const byte* end) {
StreamModifiersScope modifiers_scope(&stream);
EhFrameIterator eh_frame_iterator(start, end);
uint32_t offset_in_procedure = 0;
while (!eh_frame_iterator.Done()) {
stream << eh_frame_iterator.current_address() << " ";
byte bytecode = eh_frame_iterator.GetNextByte();
if (((bytecode >> EhFrameConstants::kLocationMaskSize) & 0xff) ==
EhFrameConstants::kLocationTag) {
int value = (bytecode & EhFrameConstants::kLocationMask) *
EhFrameConstants::kCodeAlignmentFactor;
offset_in_procedure += value;
stream << "| pc_offset=" << offset_in_procedure << " (delta=" << value
<< ")\n";
continue;
}
if (((bytecode >> EhFrameConstants::kSavedRegisterMaskSize) & 0xff) ==
EhFrameConstants::kSavedRegisterTag) {
int32_t decoded_offset = eh_frame_iterator.GetNextULeb128();
stream << "| " << DwarfRegisterCodeToString(
bytecode & EhFrameConstants::kLocationMask)
<< " saved at base" << std::showpos
<< decoded_offset * EhFrameConstants::kDataAlignmentFactor
<< std::noshowpos << '\n';
continue;
}
if (((bytecode >> EhFrameConstants::kFollowInitialRuleMaskSize) & 0xff) ==
EhFrameConstants::kFollowInitialRuleTag) {
stream << "| " << DwarfRegisterCodeToString(
bytecode & EhFrameConstants::kLocationMask)
<< " follows rule in CIE\n";
continue;
}
switch (static_cast<EhFrameConstants::DwarfOpcodes>(bytecode)) {
case EhFrameConstants::DwarfOpcodes::kOffsetExtendedSf: {
stream << "| "
<< DwarfRegisterCodeToString(eh_frame_iterator.GetNextULeb128());
int32_t decoded_offset = eh_frame_iterator.GetNextSLeb128();
stream << " saved at base" << std::showpos
<< decoded_offset * EhFrameConstants::kDataAlignmentFactor
<< std::noshowpos << '\n';
break;
}
case EhFrameConstants::DwarfOpcodes::kAdvanceLoc1: {
int value = eh_frame_iterator.GetNextByte() *
EhFrameConstants::kCodeAlignmentFactor;
offset_in_procedure += value;
stream << "| pc_offset=" << offset_in_procedure << " (delta=" << value
<< ")\n";
break;
}
case EhFrameConstants::DwarfOpcodes::kAdvanceLoc2: {
int value = eh_frame_iterator.GetNextUInt16() *
EhFrameConstants::kCodeAlignmentFactor;
offset_in_procedure += value;
stream << "| pc_offset=" << offset_in_procedure << " (delta=" << value
<< ")\n";
break;
}
case EhFrameConstants::DwarfOpcodes::kAdvanceLoc4: {
int value = eh_frame_iterator.GetNextUInt32() *
EhFrameConstants::kCodeAlignmentFactor;
offset_in_procedure += value;
stream << "| pc_offset=" << offset_in_procedure << " (delta=" << value
<< ")\n";
break;
}
case EhFrameConstants::DwarfOpcodes::kDefCfa: {
uint32_t base_register = eh_frame_iterator.GetNextULeb128();
uint32_t base_offset = eh_frame_iterator.GetNextULeb128();
stream << "| base_register=" << DwarfRegisterCodeToString(base_register)
<< ", base_offset=" << base_offset << '\n';
break;
}
case EhFrameConstants::DwarfOpcodes::kDefCfaOffset: {
stream << "| base_offset=" << eh_frame_iterator.GetNextULeb128()
<< '\n';
break;
}
case EhFrameConstants::DwarfOpcodes::kDefCfaRegister: {
stream << "| base_register="
<< DwarfRegisterCodeToString(eh_frame_iterator.GetNextULeb128())
<< '\n';
break;
}
case EhFrameConstants::DwarfOpcodes::kSameValue: {
stream << "| "
<< DwarfRegisterCodeToString(eh_frame_iterator.GetNextULeb128())
<< " not modified from previous frame\n";
break;
}
case EhFrameConstants::DwarfOpcodes::kNop:
stream << "| nop\n";
break;
default:
UNREACHABLE();
return;
}
}
}
void EhFrameDisassembler::DisassembleToStream(std::ostream& stream) { // NOLINT
// The encoded CIE size does not include the size field itself.
const int cie_size = ReadUnalignedUInt32(start_) + kInt32Size;
const int fde_offset = cie_size;
const byte* cie_directives_start =
start_ + EhFrameConstants::kInitialStateOffsetInCie;
const byte* cie_directives_end = start_ + cie_size;
DCHECK_LE(cie_directives_start, cie_directives_end);
stream << reinterpret_cast<const void*>(start_) << " .eh_frame: CIE\n";
DumpDwarfDirectives(stream, cie_directives_start, cie_directives_end);
const byte* procedure_offset_address =
start_ + fde_offset + EhFrameConstants::kProcedureAddressOffsetInFde;
int32_t procedure_offset =
ReadUnalignedValue<int32_t>(procedure_offset_address);
const byte* procedure_size_address =
start_ + fde_offset + EhFrameConstants::kProcedureSizeOffsetInFde;
uint32_t procedure_size = ReadUnalignedUInt32(procedure_size_address);
const byte* fde_start = start_ + fde_offset;
stream << reinterpret_cast<const void*>(fde_start) << " .eh_frame: FDE\n"
<< reinterpret_cast<const void*>(procedure_offset_address)
<< " | procedure_offset=" << procedure_offset << '\n'
<< reinterpret_cast<const void*>(procedure_size_address)
<< " | procedure_size=" << procedure_size << '\n';
const int fde_directives_offset = fde_offset + 4 * kInt32Size + 1;
const byte* fde_directives_start = start_ + fde_directives_offset;
const byte* fde_directives_end = end_ - EhFrameConstants::kEhFrameHdrSize -
EhFrameConstants::kEhFrameTerminatorSize;
DCHECK_LE(fde_directives_start, fde_directives_end);
DumpDwarfDirectives(stream, fde_directives_start, fde_directives_end);
const byte* fde_terminator_start = fde_directives_end;
stream << reinterpret_cast<const void*>(fde_terminator_start)
<< " .eh_frame: terminator\n";
const byte* eh_frame_hdr_start =
fde_terminator_start + EhFrameConstants::kEhFrameTerminatorSize;
stream << reinterpret_cast<const void*>(eh_frame_hdr_start)
<< " .eh_frame_hdr\n";
}
#endif
} // namespace internal
} // namespace v8