blob: 90be30a5f0f91b7477afcdfd1cf59b7afb72e30a [file] [log] [blame]
//===- EhFrame.cpp -------------------------------------------------------===//
// The LLVM Linker
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// .eh_frame section contains information on how to unwind the stack when
// an exception is thrown. The section consists of sequence of CIE and FDE
// records. The linker needs to merge CIEs and associate FDEs to CIEs.
// That means the linker has to understand the format of the section.
// This file contains a few utility functions to read .eh_frame contents.
#include "EhFrame.h"
#include "Error.h"
#include "InputSection.h"
#include "Relocations.h"
#include "Strings.h"
#include "llvm/Object/ELF.h"
#include "llvm/Support/Dwarf.h"
#include "llvm/Support/Endian.h"
using namespace llvm;
using namespace llvm::ELF;
using namespace llvm::dwarf;
using namespace llvm::object;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::elf;
namespace {
template <class ELFT> class EhReader {
EhReader(InputSectionBase *S, ArrayRef<uint8_t> D) : IS(S), D(D) {}
size_t readEhRecordSize();
uint8_t getFdeEncoding();
template <class P> void failOn(const P *Loc, const Twine &Msg) {
fatal("corrupted .eh_frame: " + Msg + "\n>>> defined in " +
IS->getObjMsg<ELFT>((const uint8_t *)Loc - IS->;
uint8_t readByte();
void skipBytes(size_t Count);
StringRef readString();
void skipLeb128();
void skipAugP();
InputSectionBase *IS;
ArrayRef<uint8_t> D;
template <class ELFT>
size_t elf::readEhRecordSize(InputSectionBase *S, size_t Off) {
return EhReader<ELFT>(S, S->Data.slice(Off)).readEhRecordSize();
// .eh_frame section is a sequence of records. Each record starts with
// a 4 byte length field. This function reads the length.
template <class ELFT> size_t EhReader<ELFT>::readEhRecordSize() {
const endianness E = ELFT::TargetEndianness;
if (D.size() < 4)
failOn(, "CIE/FDE too small");
// First 4 bytes of CIE/FDE is the size of the record.
// If it is 0xFFFFFFFF, the next 8 bytes contain the size instead,
// but we do not support that format yet.
uint64_t V = read32<E>(;
if (V == UINT32_MAX)
failOn(, "CIE/FDE too large");
uint64_t Size = V + 4;
if (Size > D.size())
failOn(, "CIE/FDE ends past the end of the section");
return Size;
// Read a byte and advance D by one byte.
template <class ELFT> uint8_t EhReader<ELFT>::readByte() {
if (D.empty())
failOn(, "unexpected end of CIE");
uint8_t B = D.front();
D = D.slice(1);
return B;
template <class ELFT> void EhReader<ELFT>::skipBytes(size_t Count) {
if (D.size() < Count)
failOn(, "CIE is too small");
D = D.slice(Count);
// Read a null-terminated string.
template <class ELFT> StringRef EhReader<ELFT>::readString() {
const uint8_t *End = std::find(D.begin(), D.end(), '\0');
if (End == D.end())
failOn(, "corrupted CIE (failed to read string)");
StringRef S = toStringRef(D.slice(0, End - D.begin()));
D = D.slice(S.size() + 1);
return S;
// Skip an integer encoded in the LEB128 format.
// Actual number is not of interest because only the runtime needs it.
// But we need to be at least able to skip it so that we can read
// the field that follows a LEB128 number.
template <class ELFT> void EhReader<ELFT>::skipLeb128() {
const uint8_t *ErrPos =;
while (!D.empty()) {
uint8_t Val = D.front();
D = D.slice(1);
if ((Val & 0x80) == 0)
failOn(ErrPos, "corrupted CIE (failed to read LEB128)");
static size_t getAugPSize(unsigned Enc) {
switch (Enc & 0x0f) {
case DW_EH_PE_absptr:
case DW_EH_PE_signed:
return Config->Wordsize;
case DW_EH_PE_udata2:
case DW_EH_PE_sdata2:
return 2;
case DW_EH_PE_udata4:
case DW_EH_PE_sdata4:
return 4;
case DW_EH_PE_udata8:
case DW_EH_PE_sdata8:
return 8;
return 0;
template <class ELFT> void EhReader<ELFT>::skipAugP() {
uint8_t Enc = readByte();
if ((Enc & 0xf0) == DW_EH_PE_aligned)
failOn( - 1, "DW_EH_PE_aligned encoding is not supported");
size_t Size = getAugPSize(Enc);
if (Size == 0)
failOn( - 1, "unknown FDE encoding");
if (Size >= D.size())
failOn( - 1, "corrupted CIE");
D = D.slice(Size);
template <class ELFT> uint8_t elf::getFdeEncoding(EhSectionPiece *P) {
auto *IS = static_cast<InputSectionBase *>(P->ID);
return EhReader<ELFT>(IS, P->data()).getFdeEncoding();
template <class ELFT> uint8_t EhReader<ELFT>::getFdeEncoding() {
int Version = readByte();
if (Version != 1 && Version != 3)
failOn( - 1,
"FDE version 1 or 3 expected, but got " + Twine(Version));
StringRef Aug = readString();
// Skip code and data alignment factors.
// Skip the return address register. In CIE version 1 this is a single
// byte. In CIE version 3 this is an unsigned LEB128.
if (Version == 1)
// We only care about an 'R' value, but other records may precede an 'R'
// record. Unfortunately records are not in TLV (type-length-value) format,
// so we need to teach the linker how to skip records for each type.
for (char C : Aug) {
if (C == 'R')
return readByte();
if (C == 'z') {
if (C == 'P') {
if (C == 'L') {
failOn(, "unknown .eh_frame augmentation string: " + Aug);
return DW_EH_PE_absptr;
template size_t elf::readEhRecordSize<ELF32LE>(InputSectionBase *S, size_t Off);
template size_t elf::readEhRecordSize<ELF32BE>(InputSectionBase *S, size_t Off);
template size_t elf::readEhRecordSize<ELF64LE>(InputSectionBase *S, size_t Off);
template size_t elf::readEhRecordSize<ELF64BE>(InputSectionBase *S, size_t Off);
template uint8_t elf::getFdeEncoding<ELF32LE>(EhSectionPiece *P);
template uint8_t elf::getFdeEncoding<ELF32BE>(EhSectionPiece *P);
template uint8_t elf::getFdeEncoding<ELF64LE>(EhSectionPiece *P);
template uint8_t elf::getFdeEncoding<ELF64BE>(EhSectionPiece *P);