1 //===- EhFrame.cpp -------------------------------------------------------===//
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // .eh_frame section contains information on how to unwind the stack when
11 // an exception is thrown. The section consists of sequence of CIE and FDE
12 // records. The linker needs to merge CIEs and associate FDEs to CIEs.
13 // That means the linker has to understand the format of the section.
15 // This file contains a few utility functions to read .eh_frame contents.
17 //===----------------------------------------------------------------------===//
21 #include "InputSection.h"
22 #include "Relocations.h"
25 #include "llvm/BinaryFormat/Dwarf.h"
26 #include "llvm/Object/ELF.h"
27 #include "llvm/Support/Endian.h"
30 using namespace llvm::ELF;
31 using namespace llvm::dwarf;
32 using namespace llvm::object;
33 using namespace llvm::support::endian;
36 using namespace lld::elf;
39 template <class ELFT> class EhReader {
41 EhReader(InputSectionBase *S, ArrayRef<uint8_t> D) : IS(S), D(D) {}
42 size_t readEhRecordSize();
43 uint8_t getFdeEncoding();
46 template <class P> void failOn(const P *Loc, const Twine &Msg) {
47 fatal("corrupted .eh_frame: " + Msg + "\n>>> defined in " +
48 IS->getObjMsg<ELFT>((const uint8_t *)Loc - IS->Data.data()));
52 void skipBytes(size_t Count);
53 StringRef readString();
63 size_t elf::readEhRecordSize(InputSectionBase *S, size_t Off) {
64 return EhReader<ELFT>(S, S->Data.slice(Off)).readEhRecordSize();
67 // .eh_frame section is a sequence of records. Each record starts with
68 // a 4 byte length field. This function reads the length.
69 template <class ELFT> size_t EhReader<ELFT>::readEhRecordSize() {
70 const endianness E = ELFT::TargetEndianness;
72 failOn(D.data(), "CIE/FDE too small");
74 // First 4 bytes of CIE/FDE is the size of the record.
75 // If it is 0xFFFFFFFF, the next 8 bytes contain the size instead,
76 // but we do not support that format yet.
77 uint64_t V = read32<E>(D.data());
79 failOn(D.data(), "CIE/FDE too large");
80 uint64_t Size = V + 4;
82 failOn(D.data(), "CIE/FDE ends past the end of the section");
86 // Read a byte and advance D by one byte.
87 template <class ELFT> uint8_t EhReader<ELFT>::readByte() {
89 failOn(D.data(), "unexpected end of CIE");
90 uint8_t B = D.front();
95 template <class ELFT> void EhReader<ELFT>::skipBytes(size_t Count) {
97 failOn(D.data(), "CIE is too small");
101 // Read a null-terminated string.
102 template <class ELFT> StringRef EhReader<ELFT>::readString() {
103 const uint8_t *End = std::find(D.begin(), D.end(), '\0');
105 failOn(D.data(), "corrupted CIE (failed to read string)");
106 StringRef S = toStringRef(D.slice(0, End - D.begin()));
107 D = D.slice(S.size() + 1);
111 // Skip an integer encoded in the LEB128 format.
112 // Actual number is not of interest because only the runtime needs it.
113 // But we need to be at least able to skip it so that we can read
114 // the field that follows a LEB128 number.
115 template <class ELFT> void EhReader<ELFT>::skipLeb128() {
116 const uint8_t *ErrPos = D.data();
118 uint8_t Val = D.front();
120 if ((Val & 0x80) == 0)
123 failOn(ErrPos, "corrupted CIE (failed to read LEB128)");
126 static size_t getAugPSize(unsigned Enc) {
127 switch (Enc & 0x0f) {
128 case DW_EH_PE_absptr:
129 case DW_EH_PE_signed:
130 return Config->Wordsize;
131 case DW_EH_PE_udata2:
132 case DW_EH_PE_sdata2:
134 case DW_EH_PE_udata4:
135 case DW_EH_PE_sdata4:
137 case DW_EH_PE_udata8:
138 case DW_EH_PE_sdata8:
144 template <class ELFT> void EhReader<ELFT>::skipAugP() {
145 uint8_t Enc = readByte();
146 if ((Enc & 0xf0) == DW_EH_PE_aligned)
147 failOn(D.data() - 1, "DW_EH_PE_aligned encoding is not supported");
148 size_t Size = getAugPSize(Enc);
150 failOn(D.data() - 1, "unknown FDE encoding");
151 if (Size >= D.size())
152 failOn(D.data() - 1, "corrupted CIE");
156 template <class ELFT> uint8_t elf::getFdeEncoding(EhSectionPiece *P) {
157 auto *IS = static_cast<InputSectionBase *>(P->ID);
158 return EhReader<ELFT>(IS, P->data()).getFdeEncoding();
161 template <class ELFT> uint8_t EhReader<ELFT>::getFdeEncoding() {
163 int Version = readByte();
164 if (Version != 1 && Version != 3)
166 "FDE version 1 or 3 expected, but got " + Twine(Version));
168 StringRef Aug = readString();
170 // Skip code and data alignment factors.
174 // Skip the return address register. In CIE version 1 this is a single
175 // byte. In CIE version 3 this is an unsigned LEB128.
181 // We only care about an 'R' value, but other records may precede an 'R'
182 // record. Unfortunately records are not in TLV (type-length-value) format,
183 // so we need to teach the linker how to skip records for each type.
199 failOn(Aug.data(), "unknown .eh_frame augmentation string: " + Aug);
201 return DW_EH_PE_absptr;
204 template size_t elf::readEhRecordSize<ELF32LE>(InputSectionBase *S, size_t Off);
205 template size_t elf::readEhRecordSize<ELF32BE>(InputSectionBase *S, size_t Off);
206 template size_t elf::readEhRecordSize<ELF64LE>(InputSectionBase *S, size_t Off);
207 template size_t elf::readEhRecordSize<ELF64BE>(InputSectionBase *S, size_t Off);
209 template uint8_t elf::getFdeEncoding<ELF32LE>(EhSectionPiece *P);
210 template uint8_t elf::getFdeEncoding<ELF32BE>(EhSectionPiece *P);
211 template uint8_t elf::getFdeEncoding<ELF64LE>(EhSectionPiece *P);
212 template uint8_t elf::getFdeEncoding<ELF64BE>(EhSectionPiece *P);