215 lines
6.6 KiB
C++
215 lines
6.6 KiB
C++
//===- EhFrame.cpp -------------------------------------------------------===//
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//
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// The LLVM Linker
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// .eh_frame section contains information on how to unwind the stack when
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// an exception is thrown. The section consists of sequence of CIE and FDE
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// records. The linker needs to merge CIEs and associate FDEs to CIEs.
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// That means the linker has to understand the format of the section.
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//
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// This file contains a few utility functions to read .eh_frame contents.
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//
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//===----------------------------------------------------------------------===//
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#include "EhFrame.h"
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#include "Error.h"
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#include "InputSection.h"
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#include "Relocations.h"
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#include "Strings.h"
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#include "llvm/Object/ELF.h"
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#include "llvm/Support/Dwarf.h"
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#include "llvm/Support/Endian.h"
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using namespace llvm;
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using namespace llvm::ELF;
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using namespace llvm::dwarf;
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using namespace llvm::object;
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using namespace llvm::support::endian;
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using namespace lld;
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using namespace lld::elf;
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namespace {
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template <class ELFT> class EhReader {
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public:
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EhReader(InputSectionBase<ELFT> *S, ArrayRef<uint8_t> D) : IS(S), D(D) {}
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size_t readEhRecordSize();
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uint8_t getFdeEncoding();
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private:
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template <class P> void failOn(const P *Loc, const Twine &Msg) {
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fatal(IS->getLocation((const uint8_t *)Loc - IS->Data.data()) + ": " + Msg);
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}
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uint8_t readByte();
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void skipBytes(size_t Count);
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StringRef readString();
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void skipLeb128();
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void skipAugP();
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InputSectionBase<ELFT> *IS;
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ArrayRef<uint8_t> D;
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};
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}
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template <class ELFT>
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size_t elf::readEhRecordSize(InputSectionBase<ELFT> *S, size_t Off) {
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return EhReader<ELFT>(S, S->Data.slice(Off)).readEhRecordSize();
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}
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// .eh_frame section is a sequence of records. Each record starts with
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// a 4 byte length field. This function reads the length.
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template <class ELFT> size_t EhReader<ELFT>::readEhRecordSize() {
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const endianness E = ELFT::TargetEndianness;
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if (D.size() < 4)
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failOn(D.data(), "CIE/FDE too small");
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// First 4 bytes of CIE/FDE is the size of the record.
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// If it is 0xFFFFFFFF, the next 8 bytes contain the size instead,
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// but we do not support that format yet.
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uint64_t V = read32<E>(D.data());
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if (V == UINT32_MAX)
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failOn(D.data(), "CIE/FDE too large");
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uint64_t Size = V + 4;
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if (Size > D.size())
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failOn(D.data(), "CIE/FDE ends past the end of the section");
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return Size;
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}
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// Read a byte and advance D by one byte.
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template <class ELFT> uint8_t EhReader<ELFT>::readByte() {
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if (D.empty())
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failOn(D.data(), "unexpected end of CIE");
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uint8_t B = D.front();
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D = D.slice(1);
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return B;
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}
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template <class ELFT> void EhReader<ELFT>::skipBytes(size_t Count) {
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if (D.size() < Count)
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failOn(D.data(), "CIE is too small");
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D = D.slice(Count);
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}
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// Read a null-terminated string.
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template <class ELFT> StringRef EhReader<ELFT>::readString() {
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const uint8_t *End = std::find(D.begin(), D.end(), '\0');
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if (End == D.end())
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failOn(D.data(), "corrupted CIE (failed to read string)");
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StringRef S = toStringRef(D.slice(0, End - D.begin()));
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D = D.slice(S.size() + 1);
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return S;
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}
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// Skip an integer encoded in the LEB128 format.
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// Actual number is not of interest because only the runtime needs it.
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// But we need to be at least able to skip it so that we can read
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// the field that follows a LEB128 number.
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template <class ELFT> void EhReader<ELFT>::skipLeb128() {
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const uint8_t *ErrPos = D.data();
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while (!D.empty()) {
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uint8_t Val = D.front();
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D = D.slice(1);
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if ((Val & 0x80) == 0)
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return;
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}
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failOn(ErrPos, "corrupted CIE (failed to read LEB128)");
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}
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template <class ELFT> static size_t getAugPSize(unsigned Enc) {
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switch (Enc & 0x0f) {
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case DW_EH_PE_absptr:
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case DW_EH_PE_signed:
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return ELFT::Is64Bits ? 8 : 4;
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case DW_EH_PE_udata2:
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case DW_EH_PE_sdata2:
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return 2;
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case DW_EH_PE_udata4:
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case DW_EH_PE_sdata4:
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return 4;
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case DW_EH_PE_udata8:
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case DW_EH_PE_sdata8:
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return 8;
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}
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return 0;
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}
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template <class ELFT> void EhReader<ELFT>::skipAugP() {
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uint8_t Enc = readByte();
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if ((Enc & 0xf0) == DW_EH_PE_aligned)
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failOn(D.data() - 1, "DW_EH_PE_aligned encoding is not supported");
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size_t Size = getAugPSize<ELFT>(Enc);
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if (Size == 0)
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failOn(D.data() - 1, "unknown FDE encoding");
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if (Size >= D.size())
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failOn(D.data() - 1, "corrupted CIE");
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D = D.slice(Size);
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}
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template <class ELFT> uint8_t elf::getFdeEncoding(EhSectionPiece *P) {
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auto *IS = static_cast<InputSectionBase<ELFT> *>(P->ID);
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return EhReader<ELFT>(IS, P->data()).getFdeEncoding();
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}
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template <class ELFT> uint8_t EhReader<ELFT>::getFdeEncoding() {
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skipBytes(8);
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int Version = readByte();
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if (Version != 1 && Version != 3)
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failOn(D.data() - 1,
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"FDE version 1 or 3 expected, but got " + Twine(Version));
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StringRef Aug = readString();
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// Skip code and data alignment factors.
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skipLeb128();
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skipLeb128();
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// Skip the return address register. In CIE version 1 this is a single
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// byte. In CIE version 3 this is an unsigned LEB128.
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if (Version == 1)
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readByte();
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else
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skipLeb128();
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// We only care about an 'R' value, but other records may precede an 'R'
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// record. Unfortunately records are not in TLV (type-length-value) format,
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// so we need to teach the linker how to skip records for each type.
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for (char C : Aug) {
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if (C == 'R')
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return readByte();
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if (C == 'z') {
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skipLeb128();
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continue;
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}
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if (C == 'P') {
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skipAugP();
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continue;
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}
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if (C == 'L') {
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readByte();
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continue;
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}
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failOn(Aug.data(), "unknown .eh_frame augmentation string: " + Aug);
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}
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return DW_EH_PE_absptr;
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}
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template size_t elf::readEhRecordSize<ELF32LE>(InputSectionBase<ELF32LE> *S,
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size_t Off);
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template size_t elf::readEhRecordSize<ELF32BE>(InputSectionBase<ELF32BE> *S,
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size_t Off);
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template size_t elf::readEhRecordSize<ELF64LE>(InputSectionBase<ELF64LE> *S,
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size_t Off);
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template size_t elf::readEhRecordSize<ELF64BE>(InputSectionBase<ELF64BE> *S,
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size_t Off);
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template uint8_t elf::getFdeEncoding<ELF32LE>(EhSectionPiece *P);
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template uint8_t elf::getFdeEncoding<ELF32BE>(EhSectionPiece *P);
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template uint8_t elf::getFdeEncoding<ELF64LE>(EhSectionPiece *P);
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template uint8_t elf::getFdeEncoding<ELF64BE>(EhSectionPiece *P);
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