1 //===- SyntheticSections.cpp ----------------------------------------------===//
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file contains linker-synthesized sections. Currently,
11 // synthetic sections are created either output sections or input sections,
12 // but we are rewriting code so that all synthetic sections are created as
15 //===----------------------------------------------------------------------===//
17 #include "SyntheticSections.h"
20 #include "InputFiles.h"
21 #include "LinkerScript.h"
23 #include "OutputSections.h"
25 #include "SymbolTable.h"
29 #include "lld/Config/Version.h"
30 #include "llvm/BinaryFormat/Dwarf.h"
31 #include "llvm/DebugInfo/DWARF/DWARFDebugPubTable.h"
32 #include "llvm/Object/Decompressor.h"
33 #include "llvm/Object/ELFObjectFile.h"
34 #include "llvm/Support/Endian.h"
35 #include "llvm/Support/MD5.h"
36 #include "llvm/Support/RandomNumberGenerator.h"
37 #include "llvm/Support/SHA1.h"
38 #include "llvm/Support/xxhash.h"
42 using namespace llvm::dwarf;
43 using namespace llvm::ELF;
44 using namespace llvm::object;
45 using namespace llvm::support;
46 using namespace llvm::support::endian;
49 using namespace lld::elf;
51 uint64_t SyntheticSection::getVA() const {
52 if (OutputSection *Sec = getParent())
53 return Sec->Addr + OutSecOff;
57 template <class ELFT> static std::vector<DefinedCommon *> getCommonSymbols() {
58 std::vector<DefinedCommon *> V;
59 for (Symbol *S : Symtab<ELFT>::X->getSymbols())
60 if (auto *B = dyn_cast<DefinedCommon>(S->body()))
65 // Find all common symbols and allocate space for them.
66 template <class ELFT> InputSection *elf::createCommonSection() {
67 if (!Config->DefineCommon)
70 // Sort the common symbols by alignment as an heuristic to pack them better.
71 std::vector<DefinedCommon *> Syms = getCommonSymbols<ELFT>();
75 std::stable_sort(Syms.begin(), Syms.end(),
76 [](const DefinedCommon *A, const DefinedCommon *B) {
77 return A->Alignment > B->Alignment;
80 BssSection *Sec = make<BssSection>("COMMON");
81 for (DefinedCommon *Sym : Syms)
82 Sym->Offset = Sec->reserveSpace(Sym->Size, Sym->Alignment);
86 // Returns an LLD version string.
87 static ArrayRef<uint8_t> getVersion() {
88 // Check LLD_VERSION first for ease of testing.
89 // You can get consitent output by using the environment variable.
90 // This is only for testing.
91 StringRef S = getenv("LLD_VERSION");
93 S = Saver.save(Twine("Linker: ") + getLLDVersion());
95 // +1 to include the terminating '\0'.
96 return {(const uint8_t *)S.data(), S.size() + 1};
99 // Creates a .comment section containing LLD version info.
100 // With this feature, you can identify LLD-generated binaries easily
101 // by "readelf --string-dump .comment <file>".
102 // The returned object is a mergeable string section.
103 template <class ELFT> MergeInputSection *elf::createCommentSection() {
104 typename ELFT::Shdr Hdr = {};
105 Hdr.sh_flags = SHF_MERGE | SHF_STRINGS;
106 Hdr.sh_type = SHT_PROGBITS;
108 Hdr.sh_addralign = 1;
111 make<MergeInputSection>((ObjectFile<ELFT> *)nullptr, &Hdr, ".comment");
112 Ret->Data = getVersion();
113 Ret->splitIntoPieces();
117 // .MIPS.abiflags section.
118 template <class ELFT>
119 MipsAbiFlagsSection<ELFT>::MipsAbiFlagsSection(Elf_Mips_ABIFlags Flags)
120 : SyntheticSection(SHF_ALLOC, SHT_MIPS_ABIFLAGS, 8, ".MIPS.abiflags"),
122 this->Entsize = sizeof(Elf_Mips_ABIFlags);
125 template <class ELFT> void MipsAbiFlagsSection<ELFT>::writeTo(uint8_t *Buf) {
126 memcpy(Buf, &Flags, sizeof(Flags));
129 template <class ELFT>
130 MipsAbiFlagsSection<ELFT> *MipsAbiFlagsSection<ELFT>::create() {
131 Elf_Mips_ABIFlags Flags = {};
134 for (InputSectionBase *Sec : InputSections) {
135 if (Sec->Type != SHT_MIPS_ABIFLAGS)
140 std::string Filename = toString(Sec->getFile<ELFT>());
141 const size_t Size = Sec->Data.size();
142 // Older version of BFD (such as the default FreeBSD linker) concatenate
143 // .MIPS.abiflags instead of merging. To allow for this case (or potential
144 // zero padding) we ignore everything after the first Elf_Mips_ABIFlags
145 if (Size < sizeof(Elf_Mips_ABIFlags)) {
146 error(Filename + ": invalid size of .MIPS.abiflags section: got " +
147 Twine(Size) + " instead of " + Twine(sizeof(Elf_Mips_ABIFlags)));
150 auto *S = reinterpret_cast<const Elf_Mips_ABIFlags *>(Sec->Data.data());
151 if (S->version != 0) {
152 error(Filename + ": unexpected .MIPS.abiflags version " +
157 // LLD checks ISA compatibility in getMipsEFlags(). Here we just
158 // select the highest number of ISA/Rev/Ext.
159 Flags.isa_level = std::max(Flags.isa_level, S->isa_level);
160 Flags.isa_rev = std::max(Flags.isa_rev, S->isa_rev);
161 Flags.isa_ext = std::max(Flags.isa_ext, S->isa_ext);
162 Flags.gpr_size = std::max(Flags.gpr_size, S->gpr_size);
163 Flags.cpr1_size = std::max(Flags.cpr1_size, S->cpr1_size);
164 Flags.cpr2_size = std::max(Flags.cpr2_size, S->cpr2_size);
165 Flags.ases |= S->ases;
166 Flags.flags1 |= S->flags1;
167 Flags.flags2 |= S->flags2;
168 Flags.fp_abi = elf::getMipsFpAbiFlag(Flags.fp_abi, S->fp_abi, Filename);
172 return make<MipsAbiFlagsSection<ELFT>>(Flags);
176 // .MIPS.options section.
177 template <class ELFT>
178 MipsOptionsSection<ELFT>::MipsOptionsSection(Elf_Mips_RegInfo Reginfo)
179 : SyntheticSection(SHF_ALLOC, SHT_MIPS_OPTIONS, 8, ".MIPS.options"),
181 this->Entsize = sizeof(Elf_Mips_Options) + sizeof(Elf_Mips_RegInfo);
184 template <class ELFT> void MipsOptionsSection<ELFT>::writeTo(uint8_t *Buf) {
185 auto *Options = reinterpret_cast<Elf_Mips_Options *>(Buf);
186 Options->kind = ODK_REGINFO;
187 Options->size = getSize();
189 if (!Config->Relocatable)
190 Reginfo.ri_gp_value = InX::MipsGot->getGp();
191 memcpy(Buf + sizeof(Elf_Mips_Options), &Reginfo, sizeof(Reginfo));
194 template <class ELFT>
195 MipsOptionsSection<ELFT> *MipsOptionsSection<ELFT>::create() {
200 Elf_Mips_RegInfo Reginfo = {};
203 for (InputSectionBase *Sec : InputSections) {
204 if (Sec->Type != SHT_MIPS_OPTIONS)
209 std::string Filename = toString(Sec->getFile<ELFT>());
210 ArrayRef<uint8_t> D = Sec->Data;
213 if (D.size() < sizeof(Elf_Mips_Options)) {
214 error(Filename + ": invalid size of .MIPS.options section");
218 auto *Opt = reinterpret_cast<const Elf_Mips_Options *>(D.data());
219 if (Opt->kind == ODK_REGINFO) {
220 if (Config->Relocatable && Opt->getRegInfo().ri_gp_value)
221 error(Filename + ": unsupported non-zero ri_gp_value");
222 Reginfo.ri_gprmask |= Opt->getRegInfo().ri_gprmask;
223 Sec->getFile<ELFT>()->MipsGp0 = Opt->getRegInfo().ri_gp_value;
228 fatal(Filename + ": zero option descriptor size");
229 D = D.slice(Opt->size);
234 return make<MipsOptionsSection<ELFT>>(Reginfo);
238 // MIPS .reginfo section.
239 template <class ELFT>
240 MipsReginfoSection<ELFT>::MipsReginfoSection(Elf_Mips_RegInfo Reginfo)
241 : SyntheticSection(SHF_ALLOC, SHT_MIPS_REGINFO, 4, ".reginfo"),
243 this->Entsize = sizeof(Elf_Mips_RegInfo);
246 template <class ELFT> void MipsReginfoSection<ELFT>::writeTo(uint8_t *Buf) {
247 if (!Config->Relocatable)
248 Reginfo.ri_gp_value = InX::MipsGot->getGp();
249 memcpy(Buf, &Reginfo, sizeof(Reginfo));
252 template <class ELFT>
253 MipsReginfoSection<ELFT> *MipsReginfoSection<ELFT>::create() {
254 // Section should be alive for O32 and N32 ABIs only.
258 Elf_Mips_RegInfo Reginfo = {};
261 for (InputSectionBase *Sec : InputSections) {
262 if (Sec->Type != SHT_MIPS_REGINFO)
267 if (Sec->Data.size() != sizeof(Elf_Mips_RegInfo)) {
268 error(toString(Sec->getFile<ELFT>()) +
269 ": invalid size of .reginfo section");
272 auto *R = reinterpret_cast<const Elf_Mips_RegInfo *>(Sec->Data.data());
273 if (Config->Relocatable && R->ri_gp_value)
274 error(toString(Sec->getFile<ELFT>()) +
275 ": unsupported non-zero ri_gp_value");
277 Reginfo.ri_gprmask |= R->ri_gprmask;
278 Sec->getFile<ELFT>()->MipsGp0 = R->ri_gp_value;
282 return make<MipsReginfoSection<ELFT>>(Reginfo);
286 InputSection *elf::createInterpSection() {
287 // StringSaver guarantees that the returned string ends with '\0'.
288 StringRef S = Saver.save(Config->DynamicLinker);
289 ArrayRef<uint8_t> Contents = {(const uint8_t *)S.data(), S.size() + 1};
292 make<InputSection>(SHF_ALLOC, SHT_PROGBITS, 1, Contents, ".interp");
297 SymbolBody *elf::addSyntheticLocal(StringRef Name, uint8_t Type, uint64_t Value,
298 uint64_t Size, InputSectionBase *Section) {
299 auto *S = make<DefinedRegular>(Name, /*IsLocal*/ true, STV_DEFAULT, Type,
300 Value, Size, Section, nullptr);
302 InX::SymTab->addSymbol(S);
306 static size_t getHashSize() {
307 switch (Config->BuildId) {
308 case BuildIdKind::Fast:
310 case BuildIdKind::Md5:
311 case BuildIdKind::Uuid:
313 case BuildIdKind::Sha1:
315 case BuildIdKind::Hexstring:
316 return Config->BuildIdVector.size();
318 llvm_unreachable("unknown BuildIdKind");
322 BuildIdSection::BuildIdSection()
323 : SyntheticSection(SHF_ALLOC, SHT_NOTE, 1, ".note.gnu.build-id"),
324 HashSize(getHashSize()) {}
326 void BuildIdSection::writeTo(uint8_t *Buf) {
327 endianness E = Config->Endianness;
328 write32(Buf, 4, E); // Name size
329 write32(Buf + 4, HashSize, E); // Content size
330 write32(Buf + 8, NT_GNU_BUILD_ID, E); // Type
331 memcpy(Buf + 12, "GNU", 4); // Name string
335 // Split one uint8 array into small pieces of uint8 arrays.
336 static std::vector<ArrayRef<uint8_t>> split(ArrayRef<uint8_t> Arr,
338 std::vector<ArrayRef<uint8_t>> Ret;
339 while (Arr.size() > ChunkSize) {
340 Ret.push_back(Arr.take_front(ChunkSize));
341 Arr = Arr.drop_front(ChunkSize);
348 // Computes a hash value of Data using a given hash function.
349 // In order to utilize multiple cores, we first split data into 1MB
350 // chunks, compute a hash for each chunk, and then compute a hash value
351 // of the hash values.
352 void BuildIdSection::computeHash(
353 llvm::ArrayRef<uint8_t> Data,
354 std::function<void(uint8_t *Dest, ArrayRef<uint8_t> Arr)> HashFn) {
355 std::vector<ArrayRef<uint8_t>> Chunks = split(Data, 1024 * 1024);
356 std::vector<uint8_t> Hashes(Chunks.size() * HashSize);
358 // Compute hash values.
359 parallelForEachN(0, Chunks.size(), [&](size_t I) {
360 HashFn(Hashes.data() + I * HashSize, Chunks[I]);
363 // Write to the final output buffer.
364 HashFn(HashBuf, Hashes);
367 BssSection::BssSection(StringRef Name)
368 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_NOBITS, 0, Name) {}
370 size_t BssSection::reserveSpace(uint64_t Size, uint32_t Alignment) {
371 if (OutputSection *Sec = getParent())
372 Sec->updateAlignment(Alignment);
373 this->Size = alignTo(this->Size, Alignment) + Size;
374 this->Alignment = std::max(this->Alignment, Alignment);
375 return this->Size - Size;
378 void BuildIdSection::writeBuildId(ArrayRef<uint8_t> Buf) {
379 switch (Config->BuildId) {
380 case BuildIdKind::Fast:
381 computeHash(Buf, [](uint8_t *Dest, ArrayRef<uint8_t> Arr) {
382 write64le(Dest, xxHash64(toStringRef(Arr)));
385 case BuildIdKind::Md5:
386 computeHash(Buf, [](uint8_t *Dest, ArrayRef<uint8_t> Arr) {
387 memcpy(Dest, MD5::hash(Arr).data(), 16);
390 case BuildIdKind::Sha1:
391 computeHash(Buf, [](uint8_t *Dest, ArrayRef<uint8_t> Arr) {
392 memcpy(Dest, SHA1::hash(Arr).data(), 20);
395 case BuildIdKind::Uuid:
396 if (getRandomBytes(HashBuf, HashSize))
397 error("entropy source failure");
399 case BuildIdKind::Hexstring:
400 memcpy(HashBuf, Config->BuildIdVector.data(), Config->BuildIdVector.size());
403 llvm_unreachable("unknown BuildIdKind");
407 template <class ELFT>
408 EhFrameSection<ELFT>::EhFrameSection()
409 : SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 1, ".eh_frame") {}
411 // Search for an existing CIE record or create a new one.
412 // CIE records from input object files are uniquified by their contents
413 // and where their relocations point to.
414 template <class ELFT>
415 template <class RelTy>
416 CieRecord *EhFrameSection<ELFT>::addCie(EhSectionPiece &Piece,
417 ArrayRef<RelTy> Rels) {
418 auto *Sec = cast<EhInputSection>(Piece.ID);
419 const endianness E = ELFT::TargetEndianness;
420 if (read32<E>(Piece.data().data() + 4) != 0)
421 fatal(toString(Sec) + ": CIE expected at beginning of .eh_frame");
423 SymbolBody *Personality = nullptr;
424 unsigned FirstRelI = Piece.FirstRelocation;
425 if (FirstRelI != (unsigned)-1)
427 &Sec->template getFile<ELFT>()->getRelocTargetSym(Rels[FirstRelI]);
429 // Search for an existing CIE by CIE contents/relocation target pair.
430 CieRecord *Cie = &CieMap[{Piece.data(), Personality}];
432 // If not found, create a new one.
433 if (Cie->Piece == nullptr) {
440 // There is one FDE per function. Returns true if a given FDE
441 // points to a live function.
442 template <class ELFT>
443 template <class RelTy>
444 bool EhFrameSection<ELFT>::isFdeLive(EhSectionPiece &Piece,
445 ArrayRef<RelTy> Rels) {
446 auto *Sec = cast<EhInputSection>(Piece.ID);
447 unsigned FirstRelI = Piece.FirstRelocation;
448 if (FirstRelI == (unsigned)-1)
450 const RelTy &Rel = Rels[FirstRelI];
451 SymbolBody &B = Sec->template getFile<ELFT>()->getRelocTargetSym(Rel);
452 auto *D = dyn_cast<DefinedRegular>(&B);
453 if (!D || !D->Section)
456 cast<InputSectionBase>(cast<InputSectionBase>(D->Section)->Repl);
457 return Target && Target->Live;
460 // .eh_frame is a sequence of CIE or FDE records. In general, there
461 // is one CIE record per input object file which is followed by
462 // a list of FDEs. This function searches an existing CIE or create a new
463 // one and associates FDEs to the CIE.
464 template <class ELFT>
465 template <class RelTy>
466 void EhFrameSection<ELFT>::addSectionAux(EhInputSection *Sec,
467 ArrayRef<RelTy> Rels) {
468 const endianness E = ELFT::TargetEndianness;
470 DenseMap<size_t, CieRecord *> OffsetToCie;
471 for (EhSectionPiece &Piece : Sec->Pieces) {
472 // The empty record is the end marker.
473 if (Piece.size() == 4)
476 size_t Offset = Piece.InputOff;
477 uint32_t ID = read32<E>(Piece.data().data() + 4);
479 OffsetToCie[Offset] = addCie(Piece, Rels);
483 uint32_t CieOffset = Offset + 4 - ID;
484 CieRecord *Cie = OffsetToCie[CieOffset];
486 fatal(toString(Sec) + ": invalid CIE reference");
488 if (!isFdeLive(Piece, Rels))
490 Cie->FdePieces.push_back(&Piece);
495 template <class ELFT>
496 void EhFrameSection<ELFT>::addSection(InputSectionBase *C) {
497 auto *Sec = cast<EhInputSection>(C);
499 updateAlignment(Sec->Alignment);
500 Sections.push_back(Sec);
501 for (auto *DS : Sec->DependentSections)
502 DependentSections.push_back(DS);
504 // .eh_frame is a sequence of CIE or FDE records. This function
505 // splits it into pieces so that we can call
506 // SplitInputSection::getSectionPiece on the section.
508 if (Sec->Pieces.empty())
511 if (Sec->NumRelocations) {
512 if (Sec->AreRelocsRela)
513 addSectionAux(Sec, Sec->template relas<ELFT>());
515 addSectionAux(Sec, Sec->template rels<ELFT>());
518 addSectionAux(Sec, makeArrayRef<Elf_Rela>(nullptr, nullptr));
521 template <class ELFT>
522 static void writeCieFde(uint8_t *Buf, ArrayRef<uint8_t> D) {
523 memcpy(Buf, D.data(), D.size());
525 // Fix the size field. -4 since size does not include the size field itself.
526 const endianness E = ELFT::TargetEndianness;
527 write32<E>(Buf, alignTo(D.size(), sizeof(typename ELFT::uint)) - 4);
530 template <class ELFT> void EhFrameSection<ELFT>::finalizeContents() {
532 return; // Already finalized.
535 for (CieRecord *Cie : Cies) {
536 Cie->Piece->OutputOff = Off;
537 Off += alignTo(Cie->Piece->size(), Config->Wordsize);
539 for (EhSectionPiece *Fde : Cie->FdePieces) {
540 Fde->OutputOff = Off;
541 Off += alignTo(Fde->size(), Config->Wordsize);
545 // The LSB standard does not allow a .eh_frame section with zero
546 // Call Frame Information records. Therefore add a CIE record length
547 // 0 as a terminator if this .eh_frame section is empty.
554 template <class ELFT> static uint64_t readFdeAddr(uint8_t *Buf, int Size) {
555 const endianness E = ELFT::TargetEndianness;
557 case DW_EH_PE_udata2:
558 return read16<E>(Buf);
559 case DW_EH_PE_udata4:
560 return read32<E>(Buf);
561 case DW_EH_PE_udata8:
562 return read64<E>(Buf);
563 case DW_EH_PE_absptr:
565 return read64<E>(Buf);
566 return read32<E>(Buf);
568 fatal("unknown FDE size encoding");
571 // Returns the VA to which a given FDE (on a mmap'ed buffer) is applied to.
572 // We need it to create .eh_frame_hdr section.
573 template <class ELFT>
574 uint64_t EhFrameSection<ELFT>::getFdePc(uint8_t *Buf, size_t FdeOff,
576 // The starting address to which this FDE applies is
577 // stored at FDE + 8 byte.
578 size_t Off = FdeOff + 8;
579 uint64_t Addr = readFdeAddr<ELFT>(Buf + Off, Enc & 0x7);
580 if ((Enc & 0x70) == DW_EH_PE_absptr)
582 if ((Enc & 0x70) == DW_EH_PE_pcrel)
583 return Addr + getParent()->Addr + Off;
584 fatal("unknown FDE size relative encoding");
587 template <class ELFT> void EhFrameSection<ELFT>::writeTo(uint8_t *Buf) {
588 const endianness E = ELFT::TargetEndianness;
589 for (CieRecord *Cie : Cies) {
590 size_t CieOffset = Cie->Piece->OutputOff;
591 writeCieFde<ELFT>(Buf + CieOffset, Cie->Piece->data());
593 for (EhSectionPiece *Fde : Cie->FdePieces) {
594 size_t Off = Fde->OutputOff;
595 writeCieFde<ELFT>(Buf + Off, Fde->data());
597 // FDE's second word should have the offset to an associated CIE.
599 write32<E>(Buf + Off + 4, Off + 4 - CieOffset);
603 for (EhInputSection *S : Sections)
604 S->relocateAlloc(Buf, nullptr);
606 // Construct .eh_frame_hdr. .eh_frame_hdr is a binary search table
607 // to get a FDE from an address to which FDE is applied. So here
608 // we obtain two addresses and pass them to EhFrameHdr object.
609 if (In<ELFT>::EhFrameHdr) {
610 for (CieRecord *Cie : Cies) {
611 uint8_t Enc = getFdeEncoding<ELFT>(Cie->Piece);
612 for (SectionPiece *Fde : Cie->FdePieces) {
613 uint64_t Pc = getFdePc(Buf, Fde->OutputOff, Enc);
614 uint64_t FdeVA = getParent()->Addr + Fde->OutputOff;
615 In<ELFT>::EhFrameHdr->addFde(Pc, FdeVA);
621 GotSection::GotSection()
622 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
623 Target->GotEntrySize, ".got") {}
625 void GotSection::addEntry(SymbolBody &Sym) {
626 Sym.GotIndex = NumEntries;
630 bool GotSection::addDynTlsEntry(SymbolBody &Sym) {
631 if (Sym.GlobalDynIndex != -1U)
633 Sym.GlobalDynIndex = NumEntries;
634 // Global Dynamic TLS entries take two GOT slots.
639 // Reserves TLS entries for a TLS module ID and a TLS block offset.
640 // In total it takes two GOT slots.
641 bool GotSection::addTlsIndex() {
642 if (TlsIndexOff != uint32_t(-1))
644 TlsIndexOff = NumEntries * Config->Wordsize;
649 uint64_t GotSection::getGlobalDynAddr(const SymbolBody &B) const {
650 return this->getVA() + B.GlobalDynIndex * Config->Wordsize;
653 uint64_t GotSection::getGlobalDynOffset(const SymbolBody &B) const {
654 return B.GlobalDynIndex * Config->Wordsize;
657 void GotSection::finalizeContents() { Size = NumEntries * Config->Wordsize; }
659 bool GotSection::empty() const {
660 // If we have a relocation that is relative to GOT (such as GOTOFFREL),
661 // we need to emit a GOT even if it's empty.
662 return NumEntries == 0 && !HasGotOffRel;
665 void GotSection::writeTo(uint8_t *Buf) {
666 // Buf points to the start of this section's buffer,
667 // whereas InputSectionBase::relocateAlloc() expects its argument
668 // to point to the start of the output section.
669 relocateAlloc(Buf - OutSecOff, Buf - OutSecOff + Size);
672 MipsGotSection::MipsGotSection()
673 : SyntheticSection(SHF_ALLOC | SHF_WRITE | SHF_MIPS_GPREL, SHT_PROGBITS, 16,
676 void MipsGotSection::addEntry(SymbolBody &Sym, int64_t Addend, RelExpr Expr) {
677 // For "true" local symbols which can be referenced from the same module
678 // only compiler creates two instructions for address loading:
680 // lw $8, 0($gp) # R_MIPS_GOT16
681 // addi $8, $8, 0 # R_MIPS_LO16
683 // The first instruction loads high 16 bits of the symbol address while
684 // the second adds an offset. That allows to reduce number of required
685 // GOT entries because only one global offset table entry is necessary
686 // for every 64 KBytes of local data. So for local symbols we need to
687 // allocate number of GOT entries to hold all required "page" addresses.
689 // All global symbols (hidden and regular) considered by compiler uniformly.
690 // It always generates a single `lw` instruction and R_MIPS_GOT16 relocation
691 // to load address of the symbol. So for each such symbol we need to
692 // allocate dedicated GOT entry to store its address.
694 // If a symbol is preemptible we need help of dynamic linker to get its
695 // final address. The corresponding GOT entries are allocated in the
696 // "global" part of GOT. Entries for non preemptible global symbol allocated
697 // in the "local" part of GOT.
699 // See "Global Offset Table" in Chapter 5:
700 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
701 if (Expr == R_MIPS_GOT_LOCAL_PAGE) {
702 // At this point we do not know final symbol value so to reduce number
703 // of allocated GOT entries do the following trick. Save all output
704 // sections referenced by GOT relocations. Then later in the `finalize`
705 // method calculate number of "pages" required to cover all saved output
706 // section and allocate appropriate number of GOT entries.
707 PageIndexMap.insert({Sym.getOutputSection(), 0});
711 // GOT entries created for MIPS TLS relocations behave like
712 // almost GOT entries from other ABIs. They go to the end
713 // of the global offset table.
714 Sym.GotIndex = TlsEntries.size();
715 TlsEntries.push_back(&Sym);
718 auto AddEntry = [&](SymbolBody &S, uint64_t A, GotEntries &Items) {
719 if (S.isInGot() && !A)
721 size_t NewIndex = Items.size();
722 if (!EntryIndexMap.insert({{&S, A}, NewIndex}).second)
724 Items.emplace_back(&S, A);
726 S.GotIndex = NewIndex;
728 if (Sym.isPreemptible()) {
729 // Ignore addends for preemptible symbols. They got single GOT entry anyway.
730 AddEntry(Sym, 0, GlobalEntries);
731 Sym.IsInGlobalMipsGot = true;
732 } else if (Expr == R_MIPS_GOT_OFF32) {
733 AddEntry(Sym, Addend, LocalEntries32);
734 Sym.Is32BitMipsGot = true;
736 // Hold local GOT entries accessed via a 16-bit index separately.
737 // That allows to write them in the beginning of the GOT and keep
738 // their indexes as less as possible to escape relocation's overflow.
739 AddEntry(Sym, Addend, LocalEntries);
743 bool MipsGotSection::addDynTlsEntry(SymbolBody &Sym) {
744 if (Sym.GlobalDynIndex != -1U)
746 Sym.GlobalDynIndex = TlsEntries.size();
747 // Global Dynamic TLS entries take two GOT slots.
748 TlsEntries.push_back(nullptr);
749 TlsEntries.push_back(&Sym);
753 // Reserves TLS entries for a TLS module ID and a TLS block offset.
754 // In total it takes two GOT slots.
755 bool MipsGotSection::addTlsIndex() {
756 if (TlsIndexOff != uint32_t(-1))
758 TlsIndexOff = TlsEntries.size() * Config->Wordsize;
759 TlsEntries.push_back(nullptr);
760 TlsEntries.push_back(nullptr);
764 static uint64_t getMipsPageAddr(uint64_t Addr) {
765 return (Addr + 0x8000) & ~0xffff;
768 static uint64_t getMipsPageCount(uint64_t Size) {
769 return (Size + 0xfffe) / 0xffff + 1;
772 uint64_t MipsGotSection::getPageEntryOffset(const SymbolBody &B,
773 int64_t Addend) const {
774 const OutputSection *OutSec = B.getOutputSection();
775 uint64_t SecAddr = getMipsPageAddr(OutSec->Addr);
776 uint64_t SymAddr = getMipsPageAddr(B.getVA(Addend));
777 uint64_t Index = PageIndexMap.lookup(OutSec) + (SymAddr - SecAddr) / 0xffff;
778 assert(Index < PageEntriesNum);
779 return (HeaderEntriesNum + Index) * Config->Wordsize;
782 uint64_t MipsGotSection::getBodyEntryOffset(const SymbolBody &B,
783 int64_t Addend) const {
784 // Calculate offset of the GOT entries block: TLS, global, local.
785 uint64_t Index = HeaderEntriesNum + PageEntriesNum;
787 Index += LocalEntries.size() + LocalEntries32.size() + GlobalEntries.size();
788 else if (B.IsInGlobalMipsGot)
789 Index += LocalEntries.size() + LocalEntries32.size();
790 else if (B.Is32BitMipsGot)
791 Index += LocalEntries.size();
792 // Calculate offset of the GOT entry in the block.
796 auto It = EntryIndexMap.find({&B, Addend});
797 assert(It != EntryIndexMap.end());
800 return Index * Config->Wordsize;
803 uint64_t MipsGotSection::getTlsOffset() const {
804 return (getLocalEntriesNum() + GlobalEntries.size()) * Config->Wordsize;
807 uint64_t MipsGotSection::getGlobalDynOffset(const SymbolBody &B) const {
808 return B.GlobalDynIndex * Config->Wordsize;
811 const SymbolBody *MipsGotSection::getFirstGlobalEntry() const {
812 return GlobalEntries.empty() ? nullptr : GlobalEntries.front().first;
815 unsigned MipsGotSection::getLocalEntriesNum() const {
816 return HeaderEntriesNum + PageEntriesNum + LocalEntries.size() +
817 LocalEntries32.size();
820 void MipsGotSection::finalizeContents() { updateAllocSize(); }
822 void MipsGotSection::updateAllocSize() {
824 for (std::pair<const OutputSection *, size_t> &P : PageIndexMap) {
825 // For each output section referenced by GOT page relocations calculate
826 // and save into PageIndexMap an upper bound of MIPS GOT entries required
827 // to store page addresses of local symbols. We assume the worst case -
828 // each 64kb page of the output section has at least one GOT relocation
829 // against it. And take in account the case when the section intersects
831 P.second = PageEntriesNum;
832 PageEntriesNum += getMipsPageCount(P.first->Size);
834 Size = (getLocalEntriesNum() + GlobalEntries.size() + TlsEntries.size()) *
838 bool MipsGotSection::empty() const {
839 // We add the .got section to the result for dynamic MIPS target because
840 // its address and properties are mentioned in the .dynamic section.
841 return Config->Relocatable;
844 uint64_t MipsGotSection::getGp() const { return ElfSym::MipsGp->getVA(0); }
846 static uint64_t readUint(uint8_t *Buf) {
848 return read64(Buf, Config->Endianness);
849 return read32(Buf, Config->Endianness);
852 static void writeUint(uint8_t *Buf, uint64_t Val) {
854 write64(Buf, Val, Config->Endianness);
856 write32(Buf, Val, Config->Endianness);
859 void MipsGotSection::writeTo(uint8_t *Buf) {
860 // Set the MSB of the second GOT slot. This is not required by any
861 // MIPS ABI documentation, though.
863 // There is a comment in glibc saying that "The MSB of got[1] of a
864 // gnu object is set to identify gnu objects," and in GNU gold it
865 // says "the second entry will be used by some runtime loaders".
866 // But how this field is being used is unclear.
868 // We are not really willing to mimic other linkers behaviors
869 // without understanding why they do that, but because all files
870 // generated by GNU tools have this special GOT value, and because
871 // we've been doing this for years, it is probably a safe bet to
872 // keep doing this for now. We really need to revisit this to see
873 // if we had to do this.
874 writeUint(Buf + Config->Wordsize, (uint64_t)1 << (Config->Wordsize * 8 - 1));
875 Buf += HeaderEntriesNum * Config->Wordsize;
876 // Write 'page address' entries to the local part of the GOT.
877 for (std::pair<const OutputSection *, size_t> &L : PageIndexMap) {
878 size_t PageCount = getMipsPageCount(L.first->Size);
879 uint64_t FirstPageAddr = getMipsPageAddr(L.first->Addr);
880 for (size_t PI = 0; PI < PageCount; ++PI) {
881 uint8_t *Entry = Buf + (L.second + PI) * Config->Wordsize;
882 writeUint(Entry, FirstPageAddr + PI * 0x10000);
885 Buf += PageEntriesNum * Config->Wordsize;
886 auto AddEntry = [&](const GotEntry &SA) {
887 uint8_t *Entry = Buf;
888 Buf += Config->Wordsize;
889 const SymbolBody *Body = SA.first;
890 uint64_t VA = Body->getVA(SA.second);
891 writeUint(Entry, VA);
893 std::for_each(std::begin(LocalEntries), std::end(LocalEntries), AddEntry);
894 std::for_each(std::begin(LocalEntries32), std::end(LocalEntries32), AddEntry);
895 std::for_each(std::begin(GlobalEntries), std::end(GlobalEntries), AddEntry);
896 // Initialize TLS-related GOT entries. If the entry has a corresponding
897 // dynamic relocations, leave it initialized by zero. Write down adjusted
898 // TLS symbol's values otherwise. To calculate the adjustments use offsets
899 // for thread-local storage.
900 // https://www.linux-mips.org/wiki/NPTL
901 if (TlsIndexOff != -1U && !Config->Pic)
902 writeUint(Buf + TlsIndexOff, 1);
903 for (const SymbolBody *B : TlsEntries) {
904 if (!B || B->isPreemptible())
906 uint64_t VA = B->getVA();
907 if (B->GotIndex != -1U) {
908 uint8_t *Entry = Buf + B->GotIndex * Config->Wordsize;
909 writeUint(Entry, VA - 0x7000);
911 if (B->GlobalDynIndex != -1U) {
912 uint8_t *Entry = Buf + B->GlobalDynIndex * Config->Wordsize;
914 Entry += Config->Wordsize;
915 writeUint(Entry, VA - 0x8000);
920 GotPltSection::GotPltSection()
921 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
922 Target->GotPltEntrySize, ".got.plt") {}
924 void GotPltSection::addEntry(SymbolBody &Sym) {
925 Sym.GotPltIndex = Target->GotPltHeaderEntriesNum + Entries.size();
926 Entries.push_back(&Sym);
929 size_t GotPltSection::getSize() const {
930 return (Target->GotPltHeaderEntriesNum + Entries.size()) *
931 Target->GotPltEntrySize;
934 void GotPltSection::writeTo(uint8_t *Buf) {
935 Target->writeGotPltHeader(Buf);
936 Buf += Target->GotPltHeaderEntriesNum * Target->GotPltEntrySize;
937 for (const SymbolBody *B : Entries) {
938 Target->writeGotPlt(Buf, *B);
939 Buf += Config->Wordsize;
943 // On ARM the IgotPltSection is part of the GotSection, on other Targets it is
944 // part of the .got.plt
945 IgotPltSection::IgotPltSection()
946 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
947 Target->GotPltEntrySize,
948 Config->EMachine == EM_ARM ? ".got" : ".got.plt") {}
950 void IgotPltSection::addEntry(SymbolBody &Sym) {
952 Sym.GotPltIndex = Entries.size();
953 Entries.push_back(&Sym);
956 size_t IgotPltSection::getSize() const {
957 return Entries.size() * Target->GotPltEntrySize;
960 void IgotPltSection::writeTo(uint8_t *Buf) {
961 for (const SymbolBody *B : Entries) {
962 Target->writeIgotPlt(Buf, *B);
963 Buf += Config->Wordsize;
967 StringTableSection::StringTableSection(StringRef Name, bool Dynamic)
968 : SyntheticSection(Dynamic ? (uint64_t)SHF_ALLOC : 0, SHT_STRTAB, 1, Name),
970 // ELF string tables start with a NUL byte.
974 // Adds a string to the string table. If HashIt is true we hash and check for
975 // duplicates. It is optional because the name of global symbols are already
976 // uniqued and hashing them again has a big cost for a small value: uniquing
977 // them with some other string that happens to be the same.
978 unsigned StringTableSection::addString(StringRef S, bool HashIt) {
980 auto R = StringMap.insert(std::make_pair(S, this->Size));
982 return R.first->second;
984 unsigned Ret = this->Size;
985 this->Size = this->Size + S.size() + 1;
986 Strings.push_back(S);
990 void StringTableSection::writeTo(uint8_t *Buf) {
991 for (StringRef S : Strings) {
992 memcpy(Buf, S.data(), S.size());
997 // Returns the number of version definition entries. Because the first entry
998 // is for the version definition itself, it is the number of versioned symbols
999 // plus one. Note that we don't support multiple versions yet.
1000 static unsigned getVerDefNum() { return Config->VersionDefinitions.size() + 1; }
1002 template <class ELFT>
1003 DynamicSection<ELFT>::DynamicSection()
1004 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_DYNAMIC, Config->Wordsize,
1006 this->Entsize = ELFT::Is64Bits ? 16 : 8;
1008 // .dynamic section is not writable on MIPS and on Fuchsia OS
1009 // which passes -z rodynamic.
1010 // See "Special Section" in Chapter 4 in the following document:
1011 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
1012 if (Config->EMachine == EM_MIPS || Config->ZRodynamic)
1013 this->Flags = SHF_ALLOC;
1018 // There are some dynamic entries that don't depend on other sections.
1019 // Such entries can be set early.
1020 template <class ELFT> void DynamicSection<ELFT>::addEntries() {
1021 // Add strings to .dynstr early so that .dynstr's size will be
1023 for (StringRef S : Config->FilterList)
1024 add({DT_FILTER, InX::DynStrTab->addString(S)});
1025 for (StringRef S : Config->AuxiliaryList)
1026 add({DT_AUXILIARY, InX::DynStrTab->addString(S)});
1027 if (!Config->Rpath.empty())
1028 add({Config->EnableNewDtags ? DT_RUNPATH : DT_RPATH,
1029 InX::DynStrTab->addString(Config->Rpath)});
1030 for (SharedFile<ELFT> *F : Symtab<ELFT>::X->getSharedFiles())
1032 add({DT_NEEDED, InX::DynStrTab->addString(F->SoName)});
1033 if (!Config->SoName.empty())
1034 add({DT_SONAME, InX::DynStrTab->addString(Config->SoName)});
1036 // Set DT_FLAGS and DT_FLAGS_1.
1037 uint32_t DtFlags = 0;
1038 uint32_t DtFlags1 = 0;
1039 if (Config->Bsymbolic)
1040 DtFlags |= DF_SYMBOLIC;
1041 if (Config->ZNodelete)
1042 DtFlags1 |= DF_1_NODELETE;
1043 if (Config->ZNodlopen)
1044 DtFlags1 |= DF_1_NOOPEN;
1046 DtFlags |= DF_BIND_NOW;
1047 DtFlags1 |= DF_1_NOW;
1049 if (Config->ZOrigin) {
1050 DtFlags |= DF_ORIGIN;
1051 DtFlags1 |= DF_1_ORIGIN;
1055 add({DT_FLAGS, DtFlags});
1057 add({DT_FLAGS_1, DtFlags1});
1059 // DT_DEBUG is a pointer to debug informaion used by debuggers at runtime. We
1060 // need it for each process, so we don't write it for DSOs. The loader writes
1061 // the pointer into this entry.
1063 // DT_DEBUG is the only .dynamic entry that needs to be written to. Some
1064 // systems (currently only Fuchsia OS) provide other means to give the
1065 // debugger this information. Such systems may choose make .dynamic read-only.
1066 // If the target is such a system (used -z rodynamic) don't write DT_DEBUG.
1067 if (!Config->Shared && !Config->Relocatable && !Config->ZRodynamic)
1068 add({DT_DEBUG, (uint64_t)0});
1071 // Add remaining entries to complete .dynamic contents.
1072 template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
1074 return; // Already finalized.
1076 this->Link = InX::DynStrTab->getParent()->SectionIndex;
1077 if (In<ELFT>::RelaDyn->getParent() && !In<ELFT>::RelaDyn->empty()) {
1078 bool IsRela = Config->IsRela;
1079 add({IsRela ? DT_RELA : DT_REL, In<ELFT>::RelaDyn});
1080 add({IsRela ? DT_RELASZ : DT_RELSZ, In<ELFT>::RelaDyn->getParent(),
1082 add({IsRela ? DT_RELAENT : DT_RELENT,
1083 uint64_t(IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel))});
1085 // MIPS dynamic loader does not support RELCOUNT tag.
1086 // The problem is in the tight relation between dynamic
1087 // relocations and GOT. So do not emit this tag on MIPS.
1088 if (Config->EMachine != EM_MIPS) {
1089 size_t NumRelativeRels = In<ELFT>::RelaDyn->getRelativeRelocCount();
1090 if (Config->ZCombreloc && NumRelativeRels)
1091 add({IsRela ? DT_RELACOUNT : DT_RELCOUNT, NumRelativeRels});
1094 if (In<ELFT>::RelaPlt->getParent() && !In<ELFT>::RelaPlt->empty()) {
1095 add({DT_JMPREL, In<ELFT>::RelaPlt});
1096 add({DT_PLTRELSZ, In<ELFT>::RelaPlt->getParent(), Entry::SecSize});
1097 switch (Config->EMachine) {
1099 add({DT_MIPS_PLTGOT, In<ELFT>::GotPlt});
1102 add({DT_PLTGOT, In<ELFT>::Plt});
1105 add({DT_PLTGOT, In<ELFT>::GotPlt});
1108 add({DT_PLTREL, uint64_t(Config->IsRela ? DT_RELA : DT_REL)});
1111 add({DT_SYMTAB, InX::DynSymTab});
1112 add({DT_SYMENT, sizeof(Elf_Sym)});
1113 add({DT_STRTAB, InX::DynStrTab});
1114 add({DT_STRSZ, InX::DynStrTab->getSize()});
1116 add({DT_TEXTREL, (uint64_t)0});
1117 if (InX::GnuHashTab)
1118 add({DT_GNU_HASH, InX::GnuHashTab});
1119 if (In<ELFT>::HashTab)
1120 add({DT_HASH, In<ELFT>::HashTab});
1122 if (Out::PreinitArray) {
1123 add({DT_PREINIT_ARRAY, Out::PreinitArray});
1124 add({DT_PREINIT_ARRAYSZ, Out::PreinitArray, Entry::SecSize});
1126 if (Out::InitArray) {
1127 add({DT_INIT_ARRAY, Out::InitArray});
1128 add({DT_INIT_ARRAYSZ, Out::InitArray, Entry::SecSize});
1130 if (Out::FiniArray) {
1131 add({DT_FINI_ARRAY, Out::FiniArray});
1132 add({DT_FINI_ARRAYSZ, Out::FiniArray, Entry::SecSize});
1135 if (SymbolBody *B = Symtab<ELFT>::X->findInCurrentDSO(Config->Init))
1137 if (SymbolBody *B = Symtab<ELFT>::X->findInCurrentDSO(Config->Fini))
1140 bool HasVerNeed = In<ELFT>::VerNeed->getNeedNum() != 0;
1141 if (HasVerNeed || In<ELFT>::VerDef)
1142 add({DT_VERSYM, In<ELFT>::VerSym});
1143 if (In<ELFT>::VerDef) {
1144 add({DT_VERDEF, In<ELFT>::VerDef});
1145 add({DT_VERDEFNUM, getVerDefNum()});
1148 add({DT_VERNEED, In<ELFT>::VerNeed});
1149 add({DT_VERNEEDNUM, In<ELFT>::VerNeed->getNeedNum()});
1152 if (Config->EMachine == EM_MIPS) {
1153 add({DT_MIPS_RLD_VERSION, 1});
1154 add({DT_MIPS_FLAGS, RHF_NOTPOT});
1155 add({DT_MIPS_BASE_ADDRESS, Config->ImageBase});
1156 add({DT_MIPS_SYMTABNO, InX::DynSymTab->getNumSymbols()});
1157 add({DT_MIPS_LOCAL_GOTNO, InX::MipsGot->getLocalEntriesNum()});
1158 if (const SymbolBody *B = InX::MipsGot->getFirstGlobalEntry())
1159 add({DT_MIPS_GOTSYM, B->DynsymIndex});
1161 add({DT_MIPS_GOTSYM, InX::DynSymTab->getNumSymbols()});
1162 add({DT_PLTGOT, InX::MipsGot});
1163 if (InX::MipsRldMap)
1164 add({DT_MIPS_RLD_MAP, InX::MipsRldMap});
1167 getParent()->Link = this->Link;
1170 this->Size = (Entries.size() + 1) * this->Entsize;
1173 template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *Buf) {
1174 auto *P = reinterpret_cast<Elf_Dyn *>(Buf);
1176 for (const Entry &E : Entries) {
1179 case Entry::SecAddr:
1180 P->d_un.d_ptr = E.OutSec->Addr;
1182 case Entry::InSecAddr:
1183 P->d_un.d_ptr = E.InSec->getParent()->Addr + E.InSec->OutSecOff;
1185 case Entry::SecSize:
1186 P->d_un.d_val = E.OutSec->Size;
1188 case Entry::SymAddr:
1189 P->d_un.d_ptr = E.Sym->getVA();
1191 case Entry::PlainInt:
1192 P->d_un.d_val = E.Val;
1199 uint64_t DynamicReloc::getOffset() const {
1200 return InputSec->getOutputSection()->Addr + InputSec->getOffset(OffsetInSec);
1203 int64_t DynamicReloc::getAddend() const {
1205 return Sym->getVA(Addend);
1209 uint32_t DynamicReloc::getSymIndex() const {
1210 if (Sym && !UseSymVA)
1211 return Sym->DynsymIndex;
1215 template <class ELFT>
1216 RelocationSection<ELFT>::RelocationSection(StringRef Name, bool Sort)
1217 : SyntheticSection(SHF_ALLOC, Config->IsRela ? SHT_RELA : SHT_REL,
1218 Config->Wordsize, Name),
1220 this->Entsize = Config->IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
1223 template <class ELFT>
1224 void RelocationSection<ELFT>::addReloc(const DynamicReloc &Reloc) {
1225 if (Reloc.Type == Target->RelativeRel)
1226 ++NumRelativeRelocs;
1227 Relocs.push_back(Reloc);
1230 template <class ELFT, class RelTy>
1231 static bool compRelocations(const RelTy &A, const RelTy &B) {
1232 bool AIsRel = A.getType(Config->IsMips64EL) == Target->RelativeRel;
1233 bool BIsRel = B.getType(Config->IsMips64EL) == Target->RelativeRel;
1234 if (AIsRel != BIsRel)
1237 return A.getSymbol(Config->IsMips64EL) < B.getSymbol(Config->IsMips64EL);
1240 template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *Buf) {
1241 uint8_t *BufBegin = Buf;
1242 for (const DynamicReloc &Rel : Relocs) {
1243 auto *P = reinterpret_cast<Elf_Rela *>(Buf);
1244 Buf += Config->IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
1247 P->r_addend = Rel.getAddend();
1248 P->r_offset = Rel.getOffset();
1249 if (Config->EMachine == EM_MIPS && Rel.getInputSec() == InX::MipsGot)
1250 // Dynamic relocation against MIPS GOT section make deal TLS entries
1251 // allocated in the end of the GOT. We need to adjust the offset to take
1252 // in account 'local' and 'global' GOT entries.
1253 P->r_offset += InX::MipsGot->getTlsOffset();
1254 P->setSymbolAndType(Rel.getSymIndex(), Rel.Type, Config->IsMips64EL);
1259 std::stable_sort((Elf_Rela *)BufBegin,
1260 (Elf_Rela *)BufBegin + Relocs.size(),
1261 compRelocations<ELFT, Elf_Rela>);
1263 std::stable_sort((Elf_Rel *)BufBegin, (Elf_Rel *)BufBegin + Relocs.size(),
1264 compRelocations<ELFT, Elf_Rel>);
1268 template <class ELFT> unsigned RelocationSection<ELFT>::getRelocOffset() {
1269 return this->Entsize * Relocs.size();
1272 template <class ELFT> void RelocationSection<ELFT>::finalizeContents() {
1273 this->Link = InX::DynSymTab ? InX::DynSymTab->getParent()->SectionIndex
1274 : InX::SymTab->getParent()->SectionIndex;
1276 // Set required output section properties.
1277 getParent()->Link = this->Link;
1280 SymbolTableBaseSection::SymbolTableBaseSection(StringTableSection &StrTabSec)
1281 : SyntheticSection(StrTabSec.isDynamic() ? (uint64_t)SHF_ALLOC : 0,
1282 StrTabSec.isDynamic() ? SHT_DYNSYM : SHT_SYMTAB,
1284 StrTabSec.isDynamic() ? ".dynsym" : ".symtab"),
1285 StrTabSec(StrTabSec) {}
1287 // Orders symbols according to their positions in the GOT,
1288 // in compliance with MIPS ABI rules.
1289 // See "Global Offset Table" in Chapter 5 in the following document
1290 // for detailed description:
1291 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
1292 static bool sortMipsSymbols(const SymbolTableEntry &L,
1293 const SymbolTableEntry &R) {
1294 // Sort entries related to non-local preemptible symbols by GOT indexes.
1295 // All other entries go to the first part of GOT in arbitrary order.
1296 bool LIsInLocalGot = !L.Symbol->IsInGlobalMipsGot;
1297 bool RIsInLocalGot = !R.Symbol->IsInGlobalMipsGot;
1298 if (LIsInLocalGot || RIsInLocalGot)
1299 return !RIsInLocalGot;
1300 return L.Symbol->GotIndex < R.Symbol->GotIndex;
1303 // Finalize a symbol table. The ELF spec requires that all local
1304 // symbols precede global symbols, so we sort symbol entries in this
1305 // function. (For .dynsym, we don't do that because symbols for
1306 // dynamic linking are inherently all globals.)
1307 void SymbolTableBaseSection::finalizeContents() {
1308 getParent()->Link = StrTabSec.getParent()->SectionIndex;
1310 // If it is a .dynsym, there should be no local symbols, but we need
1311 // to do a few things for the dynamic linker.
1312 if (this->Type == SHT_DYNSYM) {
1313 // Section's Info field has the index of the first non-local symbol.
1314 // Because the first symbol entry is a null entry, 1 is the first.
1315 getParent()->Info = 1;
1317 if (InX::GnuHashTab) {
1318 // NB: It also sorts Symbols to meet the GNU hash table requirements.
1319 InX::GnuHashTab->addSymbols(Symbols);
1320 } else if (Config->EMachine == EM_MIPS) {
1321 std::stable_sort(Symbols.begin(), Symbols.end(), sortMipsSymbols);
1325 for (const SymbolTableEntry &S : Symbols)
1326 S.Symbol->DynsymIndex = ++I;
1331 void SymbolTableBaseSection::postThunkContents() {
1332 if (this->Type == SHT_DYNSYM)
1334 // move all local symbols before global symbols.
1335 auto It = std::stable_partition(
1336 Symbols.begin(), Symbols.end(), [](const SymbolTableEntry &S) {
1337 return S.Symbol->isLocal() ||
1338 S.Symbol->symbol()->computeBinding() == STB_LOCAL;
1340 size_t NumLocals = It - Symbols.begin();
1341 getParent()->Info = NumLocals + 1;
1344 void SymbolTableBaseSection::addSymbol(SymbolBody *B) {
1345 // Adding a local symbol to a .dynsym is a bug.
1346 assert(this->Type != SHT_DYNSYM || !B->isLocal());
1348 bool HashIt = B->isLocal();
1349 Symbols.push_back({B, StrTabSec.addString(B->getName(), HashIt)});
1352 size_t SymbolTableBaseSection::getSymbolIndex(SymbolBody *Body) {
1353 auto I = llvm::find_if(Symbols, [&](const SymbolTableEntry &E) {
1354 if (E.Symbol == Body)
1356 // This is used for -r, so we have to handle multiple section
1357 // symbols being combined.
1358 if (Body->Type == STT_SECTION && E.Symbol->Type == STT_SECTION)
1359 return Body->getOutputSection() == E.Symbol->getOutputSection();
1362 if (I == Symbols.end())
1364 return I - Symbols.begin() + 1;
1367 template <class ELFT>
1368 SymbolTableSection<ELFT>::SymbolTableSection(StringTableSection &StrTabSec)
1369 : SymbolTableBaseSection(StrTabSec) {
1370 this->Entsize = sizeof(Elf_Sym);
1373 // Write the internal symbol table contents to the output symbol table.
1374 template <class ELFT> void SymbolTableSection<ELFT>::writeTo(uint8_t *Buf) {
1375 // The first entry is a null entry as per the ELF spec.
1376 Buf += sizeof(Elf_Sym);
1378 auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
1380 for (SymbolTableEntry &Ent : Symbols) {
1381 SymbolBody *Body = Ent.Symbol;
1383 // Set st_info and st_other.
1384 if (Body->isLocal()) {
1385 ESym->setBindingAndType(STB_LOCAL, Body->Type);
1387 ESym->setBindingAndType(Body->symbol()->computeBinding(), Body->Type);
1388 ESym->setVisibility(Body->symbol()->Visibility);
1391 ESym->st_name = Ent.StrTabOffset;
1393 // Set a section index.
1394 if (const OutputSection *OutSec = Body->getOutputSection())
1395 ESym->st_shndx = OutSec->SectionIndex;
1396 else if (isa<DefinedRegular>(Body))
1397 ESym->st_shndx = SHN_ABS;
1398 else if (isa<DefinedCommon>(Body))
1399 ESym->st_shndx = SHN_COMMON;
1401 // Copy symbol size if it is a defined symbol. st_size is not significant
1402 // for undefined symbols, so whether copying it or not is up to us if that's
1403 // the case. We'll leave it as zero because by not setting a value, we can
1404 // get the exact same outputs for two sets of input files that differ only
1405 // in undefined symbol size in DSOs.
1406 if (ESym->st_shndx != SHN_UNDEF)
1407 ESym->st_size = Body->getSize<ELFT>();
1409 // st_value is usually an address of a symbol, but that has a
1410 // special meaining for uninstantiated common symbols (this can
1411 // occur if -r is given).
1412 if (!Config->DefineCommon && isa<DefinedCommon>(Body))
1413 ESym->st_value = cast<DefinedCommon>(Body)->Alignment;
1415 ESym->st_value = Body->getVA();
1420 // On MIPS we need to mark symbol which has a PLT entry and requires
1421 // pointer equality by STO_MIPS_PLT flag. That is necessary to help
1422 // dynamic linker distinguish such symbols and MIPS lazy-binding stubs.
1423 // https://sourceware.org/ml/binutils/2008-07/txt00000.txt
1424 if (Config->EMachine == EM_MIPS) {
1425 auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
1427 for (SymbolTableEntry &Ent : Symbols) {
1428 SymbolBody *Body = Ent.Symbol;
1429 if (Body->isInPlt() && Body->NeedsPltAddr)
1430 ESym->st_other |= STO_MIPS_PLT;
1432 if (Config->Relocatable)
1433 if (auto *D = dyn_cast<DefinedRegular>(Body))
1434 if (D->isMipsPIC<ELFT>())
1435 ESym->st_other |= STO_MIPS_PIC;
1441 // .hash and .gnu.hash sections contain on-disk hash tables that map
1442 // symbol names to their dynamic symbol table indices. Their purpose
1443 // is to help the dynamic linker resolve symbols quickly. If ELF files
1444 // don't have them, the dynamic linker has to do linear search on all
1445 // dynamic symbols, which makes programs slower. Therefore, a .hash
1446 // section is added to a DSO by default. A .gnu.hash is added if you
1447 // give the -hash-style=gnu or -hash-style=both option.
1449 // The Unix semantics of resolving dynamic symbols is somewhat expensive.
1450 // Each ELF file has a list of DSOs that the ELF file depends on and a
1451 // list of dynamic symbols that need to be resolved from any of the
1452 // DSOs. That means resolving all dynamic symbols takes O(m)*O(n)
1453 // where m is the number of DSOs and n is the number of dynamic
1454 // symbols. For modern large programs, both m and n are large. So
1455 // making each step faster by using hash tables substiantially
1456 // improves time to load programs.
1458 // (Note that this is not the only way to design the shared library.
1459 // For instance, the Windows DLL takes a different approach. On
1460 // Windows, each dynamic symbol has a name of DLL from which the symbol
1461 // has to be resolved. That makes the cost of symbol resolution O(n).
1462 // This disables some hacky techniques you can use on Unix such as
1463 // LD_PRELOAD, but this is arguably better semantics than the Unix ones.)
1465 // Due to historical reasons, we have two different hash tables, .hash
1466 // and .gnu.hash. They are for the same purpose, and .gnu.hash is a new
1467 // and better version of .hash. .hash is just an on-disk hash table, but
1468 // .gnu.hash has a bloom filter in addition to a hash table to skip
1469 // DSOs very quickly. If you are sure that your dynamic linker knows
1470 // about .gnu.hash, you want to specify -hash-style=gnu. Otherwise, a
1471 // safe bet is to specify -hash-style=both for backward compatibilty.
1472 GnuHashTableSection::GnuHashTableSection()
1473 : SyntheticSection(SHF_ALLOC, SHT_GNU_HASH, Config->Wordsize, ".gnu.hash") {
1476 void GnuHashTableSection::finalizeContents() {
1477 getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
1479 // Computes bloom filter size in word size. We want to allocate 8
1480 // bits for each symbol. It must be a power of two.
1481 if (Symbols.empty())
1484 MaskWords = NextPowerOf2((Symbols.size() - 1) / Config->Wordsize);
1486 Size = 16; // Header
1487 Size += Config->Wordsize * MaskWords; // Bloom filter
1488 Size += NBuckets * 4; // Hash buckets
1489 Size += Symbols.size() * 4; // Hash values
1492 void GnuHashTableSection::writeTo(uint8_t *Buf) {
1494 write32(Buf, NBuckets, Config->Endianness);
1495 write32(Buf + 4, InX::DynSymTab->getNumSymbols() - Symbols.size(),
1496 Config->Endianness);
1497 write32(Buf + 8, MaskWords, Config->Endianness);
1498 write32(Buf + 12, getShift2(), Config->Endianness);
1501 // Write a bloom filter and a hash table.
1502 writeBloomFilter(Buf);
1503 Buf += Config->Wordsize * MaskWords;
1504 writeHashTable(Buf);
1507 // This function writes a 2-bit bloom filter. This bloom filter alone
1508 // usually filters out 80% or more of all symbol lookups [1].
1509 // The dynamic linker uses the hash table only when a symbol is not
1510 // filtered out by a bloom filter.
1512 // [1] Ulrich Drepper (2011), "How To Write Shared Libraries" (Ver. 4.1.2),
1513 // p.9, https://www.akkadia.org/drepper/dsohowto.pdf
1514 void GnuHashTableSection::writeBloomFilter(uint8_t *Buf) {
1515 const unsigned C = Config->Wordsize * 8;
1516 for (const Entry &Sym : Symbols) {
1517 size_t I = (Sym.Hash / C) & (MaskWords - 1);
1518 uint64_t Val = readUint(Buf + I * Config->Wordsize);
1519 Val |= uint64_t(1) << (Sym.Hash % C);
1520 Val |= uint64_t(1) << ((Sym.Hash >> getShift2()) % C);
1521 writeUint(Buf + I * Config->Wordsize, Val);
1525 void GnuHashTableSection::writeHashTable(uint8_t *Buf) {
1526 // Group symbols by hash value.
1527 std::vector<std::vector<Entry>> Syms(NBuckets);
1528 for (const Entry &Ent : Symbols)
1529 Syms[Ent.Hash % NBuckets].push_back(Ent);
1531 // Write hash buckets. Hash buckets contain indices in the following
1532 // hash value table.
1533 uint32_t *Buckets = reinterpret_cast<uint32_t *>(Buf);
1534 for (size_t I = 0; I < NBuckets; ++I)
1535 if (!Syms[I].empty())
1536 write32(Buckets + I, Syms[I][0].Body->DynsymIndex, Config->Endianness);
1538 // Write a hash value table. It represents a sequence of chains that
1539 // share the same hash modulo value. The last element of each chain
1540 // is terminated by LSB 1.
1541 uint32_t *Values = Buckets + NBuckets;
1543 for (std::vector<Entry> &Vec : Syms) {
1546 for (const Entry &Ent : makeArrayRef(Vec).drop_back())
1547 write32(Values + I++, Ent.Hash & ~1, Config->Endianness);
1548 write32(Values + I++, Vec.back().Hash | 1, Config->Endianness);
1552 static uint32_t hashGnu(StringRef Name) {
1554 for (uint8_t C : Name)
1555 H = (H << 5) + H + C;
1559 // Returns a number of hash buckets to accomodate given number of elements.
1560 // We want to choose a moderate number that is not too small (which
1561 // causes too many hash collisions) and not too large (which wastes
1564 // We return a prime number because it (is believed to) achieve good
1565 // hash distribution.
1566 static size_t getBucketSize(size_t NumSymbols) {
1567 // List of largest prime numbers that are not greater than 2^n + 1.
1568 for (size_t N : {131071, 65521, 32749, 16381, 8191, 4093, 2039, 1021, 509,
1569 251, 127, 61, 31, 13, 7, 3, 1})
1570 if (N <= NumSymbols)
1575 // Add symbols to this symbol hash table. Note that this function
1576 // destructively sort a given vector -- which is needed because
1577 // GNU-style hash table places some sorting requirements.
1578 void GnuHashTableSection::addSymbols(std::vector<SymbolTableEntry> &V) {
1579 // We cannot use 'auto' for Mid because GCC 6.1 cannot deduce
1580 // its type correctly.
1581 std::vector<SymbolTableEntry>::iterator Mid =
1582 std::stable_partition(V.begin(), V.end(), [](const SymbolTableEntry &S) {
1583 return S.Symbol->isUndefined();
1588 for (SymbolTableEntry &Ent : llvm::make_range(Mid, V.end())) {
1589 SymbolBody *B = Ent.Symbol;
1590 Symbols.push_back({B, Ent.StrTabOffset, hashGnu(B->getName())});
1593 NBuckets = getBucketSize(Symbols.size());
1594 std::stable_sort(Symbols.begin(), Symbols.end(),
1595 [&](const Entry &L, const Entry &R) {
1596 return L.Hash % NBuckets < R.Hash % NBuckets;
1599 V.erase(Mid, V.end());
1600 for (const Entry &Ent : Symbols)
1601 V.push_back({Ent.Body, Ent.StrTabOffset});
1604 template <class ELFT>
1605 HashTableSection<ELFT>::HashTableSection()
1606 : SyntheticSection(SHF_ALLOC, SHT_HASH, 4, ".hash") {
1610 template <class ELFT> void HashTableSection<ELFT>::finalizeContents() {
1611 getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
1613 unsigned NumEntries = 2; // nbucket and nchain.
1614 NumEntries += InX::DynSymTab->getNumSymbols(); // The chain entries.
1616 // Create as many buckets as there are symbols.
1617 // FIXME: This is simplistic. We can try to optimize it, but implementing
1618 // support for SHT_GNU_HASH is probably even more profitable.
1619 NumEntries += InX::DynSymTab->getNumSymbols();
1620 this->Size = NumEntries * 4;
1623 template <class ELFT> void HashTableSection<ELFT>::writeTo(uint8_t *Buf) {
1624 // A 32-bit integer type in the target endianness.
1625 typedef typename ELFT::Word Elf_Word;
1627 unsigned NumSymbols = InX::DynSymTab->getNumSymbols();
1629 auto *P = reinterpret_cast<Elf_Word *>(Buf);
1630 *P++ = NumSymbols; // nbucket
1631 *P++ = NumSymbols; // nchain
1633 Elf_Word *Buckets = P;
1634 Elf_Word *Chains = P + NumSymbols;
1636 for (const SymbolTableEntry &S : InX::DynSymTab->getSymbols()) {
1637 SymbolBody *Body = S.Symbol;
1638 StringRef Name = Body->getName();
1639 unsigned I = Body->DynsymIndex;
1640 uint32_t Hash = hashSysV(Name) % NumSymbols;
1641 Chains[I] = Buckets[Hash];
1646 PltSection::PltSection(size_t S)
1647 : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16, ".plt"),
1649 // The PLT needs to be writable on SPARC as the dynamic linker will
1650 // modify the instructions in the PLT entries.
1651 if (Config->EMachine == EM_SPARCV9)
1652 this->Flags |= SHF_WRITE;
1655 void PltSection::writeTo(uint8_t *Buf) {
1656 // At beginning of PLT but not the IPLT, we have code to call the dynamic
1657 // linker to resolve dynsyms at runtime. Write such code.
1658 if (HeaderSize != 0)
1659 Target->writePltHeader(Buf);
1660 size_t Off = HeaderSize;
1661 // The IPlt is immediately after the Plt, account for this in RelOff
1662 unsigned PltOff = getPltRelocOff();
1664 for (auto &I : Entries) {
1665 const SymbolBody *B = I.first;
1666 unsigned RelOff = I.second + PltOff;
1667 uint64_t Got = B->getGotPltVA();
1668 uint64_t Plt = this->getVA() + Off;
1669 Target->writePlt(Buf + Off, Got, Plt, B->PltIndex, RelOff);
1670 Off += Target->PltEntrySize;
1674 template <class ELFT> void PltSection::addEntry(SymbolBody &Sym) {
1675 Sym.PltIndex = Entries.size();
1676 RelocationSection<ELFT> *PltRelocSection = In<ELFT>::RelaPlt;
1677 if (HeaderSize == 0) {
1678 PltRelocSection = In<ELFT>::RelaIplt;
1679 Sym.IsInIplt = true;
1681 unsigned RelOff = PltRelocSection->getRelocOffset();
1682 Entries.push_back(std::make_pair(&Sym, RelOff));
1685 size_t PltSection::getSize() const {
1686 return HeaderSize + Entries.size() * Target->PltEntrySize;
1689 // Some architectures such as additional symbols in the PLT section. For
1690 // example ARM uses mapping symbols to aid disassembly
1691 void PltSection::addSymbols() {
1692 // The PLT may have symbols defined for the Header, the IPLT has no header
1693 if (HeaderSize != 0)
1694 Target->addPltHeaderSymbols(this);
1695 size_t Off = HeaderSize;
1696 for (size_t I = 0; I < Entries.size(); ++I) {
1697 Target->addPltSymbols(this, Off);
1698 Off += Target->PltEntrySize;
1702 unsigned PltSection::getPltRelocOff() const {
1703 return (HeaderSize == 0) ? InX::Plt->getSize() : 0;
1706 GdbIndexSection::GdbIndexSection(std::vector<GdbIndexChunk> &&Chunks)
1707 : SyntheticSection(0, SHT_PROGBITS, 1, ".gdb_index"),
1708 StringPool(llvm::StringTableBuilder::ELF), Chunks(std::move(Chunks)) {}
1710 // Iterative hash function for symbol's name is described in .gdb_index format
1711 // specification. Note that we use one for version 5 to 7 here, it is different
1713 static uint32_t hash(StringRef Str) {
1715 for (uint8_t C : Str)
1716 R = R * 67 + tolower(C) - 113;
1720 static std::vector<CompilationUnitEntry> readCuList(DWARFContext &Dwarf) {
1721 std::vector<CompilationUnitEntry> Ret;
1722 for (std::unique_ptr<DWARFCompileUnit> &CU : Dwarf.compile_units())
1723 Ret.push_back({CU->getOffset(), CU->getLength() + 4});
1727 static std::vector<AddressEntry> readAddressArea(DWARFContext &Dwarf,
1728 InputSection *Sec) {
1729 std::vector<AddressEntry> Ret;
1731 uint32_t CurrentCu = 0;
1732 for (std::unique_ptr<DWARFCompileUnit> &CU : Dwarf.compile_units()) {
1733 DWARFAddressRangesVector Ranges;
1734 CU->collectAddressRanges(Ranges);
1736 ArrayRef<InputSectionBase *> Sections = Sec->File->getSections();
1737 for (DWARFAddressRange &R : Ranges) {
1738 InputSectionBase *S = Sections[R.SectionIndex];
1739 if (!S || S == &InputSection::Discarded || !S->Live)
1741 // Range list with zero size has no effect.
1742 if (R.LowPC == R.HighPC)
1744 Ret.push_back({cast<InputSection>(S), R.LowPC, R.HighPC, CurrentCu});
1751 static std::vector<NameTypeEntry> readPubNamesAndTypes(DWARFContext &Dwarf,
1753 StringRef Data[] = {Dwarf.getGnuPubNamesSection(),
1754 Dwarf.getGnuPubTypesSection()};
1756 std::vector<NameTypeEntry> Ret;
1757 for (StringRef D : Data) {
1758 DWARFDebugPubTable PubTable(D, IsLE, true);
1759 for (const DWARFDebugPubTable::Set &Set : PubTable.getData())
1760 for (const DWARFDebugPubTable::Entry &Ent : Set.Entries)
1761 Ret.push_back({Ent.Name, Ent.Descriptor.toBits()});
1766 static std::vector<InputSection *> getDebugInfoSections() {
1767 std::vector<InputSection *> Ret;
1768 for (InputSectionBase *S : InputSections)
1769 if (InputSection *IS = dyn_cast<InputSection>(S))
1770 if (IS->Name == ".debug_info")
1775 void GdbIndexSection::buildIndex() {
1780 for (GdbIndexChunk &D : Chunks) {
1781 for (AddressEntry &E : D.AddressArea)
1784 // Populate constant pool area.
1785 for (NameTypeEntry &NameType : D.NamesAndTypes) {
1786 uint32_t Hash = hash(NameType.Name);
1787 size_t Offset = StringPool.add(NameType.Name);
1791 std::tie(IsNew, Sym) = SymbolTable.add(Hash, Offset);
1793 Sym->CuVectorIndex = CuVectors.size();
1794 CuVectors.resize(CuVectors.size() + 1);
1797 CuVectors[Sym->CuVectorIndex].insert(CuId | (NameType.Type << 24));
1800 CuId += D.CompilationUnits.size();
1804 static GdbIndexChunk readDwarf(DWARFContextInMemory &Dwarf, InputSection *Sec) {
1806 Ret.DebugInfoSec = Sec;
1807 Ret.CompilationUnits = readCuList(Dwarf);
1808 Ret.AddressArea = readAddressArea(Dwarf, Sec);
1809 Ret.NamesAndTypes = readPubNamesAndTypes(Dwarf, Config->IsLE);
1813 template <class ELFT> GdbIndexSection *elf::createGdbIndex() {
1814 std::vector<GdbIndexChunk> Chunks;
1815 for (InputSection *Sec : getDebugInfoSections()) {
1816 InputFile *F = Sec->File;
1818 ELFObjectFile<ELFT> Obj(F->MB, EC);
1820 fatal(EC.message());
1821 DWARFContextInMemory Dwarf(Obj, nullptr, [&](Error E) {
1822 error(toString(F) + ": error parsing DWARF data:\n>>> " +
1823 toString(std::move(E)));
1824 return ErrorPolicy::Continue;
1826 Chunks.push_back(readDwarf(Dwarf, Sec));
1828 return make<GdbIndexSection>(std::move(Chunks));
1831 static size_t getCuSize(std::vector<GdbIndexChunk> &C) {
1833 for (GdbIndexChunk &D : C)
1834 Ret += D.CompilationUnits.size();
1838 static size_t getAddressAreaSize(std::vector<GdbIndexChunk> &C) {
1840 for (GdbIndexChunk &D : C)
1841 Ret += D.AddressArea.size();
1845 void GdbIndexSection::finalizeContents() {
1852 SymbolTable.finalizeContents();
1854 // GdbIndex header consist from version fields
1855 // and 5 more fields with different kinds of offsets.
1856 CuTypesOffset = CuListOffset + getCuSize(Chunks) * CompilationUnitSize;
1857 SymTabOffset = CuTypesOffset + getAddressAreaSize(Chunks) * AddressEntrySize;
1859 ConstantPoolOffset =
1860 SymTabOffset + SymbolTable.getCapacity() * SymTabEntrySize;
1862 for (std::set<uint32_t> &CuVec : CuVectors) {
1863 CuVectorsOffset.push_back(CuVectorsSize);
1864 CuVectorsSize += OffsetTypeSize * (CuVec.size() + 1);
1866 StringPoolOffset = ConstantPoolOffset + CuVectorsSize;
1868 StringPool.finalizeInOrder();
1871 size_t GdbIndexSection::getSize() const {
1872 const_cast<GdbIndexSection *>(this)->finalizeContents();
1873 return StringPoolOffset + StringPool.getSize();
1876 void GdbIndexSection::writeTo(uint8_t *Buf) {
1877 write32le(Buf, 7); // Write version.
1878 write32le(Buf + 4, CuListOffset); // CU list offset.
1879 write32le(Buf + 8, CuTypesOffset); // Types CU list offset.
1880 write32le(Buf + 12, CuTypesOffset); // Address area offset.
1881 write32le(Buf + 16, SymTabOffset); // Symbol table offset.
1882 write32le(Buf + 20, ConstantPoolOffset); // Constant pool offset.
1885 // Write the CU list.
1886 for (GdbIndexChunk &D : Chunks) {
1887 for (CompilationUnitEntry &Cu : D.CompilationUnits) {
1888 write64le(Buf, D.DebugInfoSec->OutSecOff + Cu.CuOffset);
1889 write64le(Buf + 8, Cu.CuLength);
1894 // Write the address area.
1895 for (GdbIndexChunk &D : Chunks) {
1896 for (AddressEntry &E : D.AddressArea) {
1898 E.Section->getParent()->Addr + E.Section->getOffset(0);
1899 write64le(Buf, BaseAddr + E.LowAddress);
1900 write64le(Buf + 8, BaseAddr + E.HighAddress);
1901 write32le(Buf + 16, E.CuIndex);
1906 // Write the symbol table.
1907 for (size_t I = 0; I < SymbolTable.getCapacity(); ++I) {
1908 GdbSymbol *Sym = SymbolTable.getSymbol(I);
1911 Sym->NameOffset + StringPoolOffset - ConstantPoolOffset;
1912 size_t CuVectorOffset = CuVectorsOffset[Sym->CuVectorIndex];
1913 write32le(Buf, NameOffset);
1914 write32le(Buf + 4, CuVectorOffset);
1919 // Write the CU vectors into the constant pool.
1920 for (std::set<uint32_t> &CuVec : CuVectors) {
1921 write32le(Buf, CuVec.size());
1923 for (uint32_t Val : CuVec) {
1924 write32le(Buf, Val);
1929 StringPool.write(Buf);
1932 bool GdbIndexSection::empty() const { return !Out::DebugInfo; }
1934 template <class ELFT>
1935 EhFrameHeader<ELFT>::EhFrameHeader()
1936 : SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 1, ".eh_frame_hdr") {}
1938 // .eh_frame_hdr contains a binary search table of pointers to FDEs.
1939 // Each entry of the search table consists of two values,
1940 // the starting PC from where FDEs covers, and the FDE's address.
1941 // It is sorted by PC.
1942 template <class ELFT> void EhFrameHeader<ELFT>::writeTo(uint8_t *Buf) {
1943 const endianness E = ELFT::TargetEndianness;
1945 // Sort the FDE list by their PC and uniqueify. Usually there is only
1946 // one FDE for a PC (i.e. function), but if ICF merges two functions
1947 // into one, there can be more than one FDEs pointing to the address.
1948 auto Less = [](const FdeData &A, const FdeData &B) { return A.Pc < B.Pc; };
1949 std::stable_sort(Fdes.begin(), Fdes.end(), Less);
1950 auto Eq = [](const FdeData &A, const FdeData &B) { return A.Pc == B.Pc; };
1951 Fdes.erase(std::unique(Fdes.begin(), Fdes.end(), Eq), Fdes.end());
1954 Buf[1] = DW_EH_PE_pcrel | DW_EH_PE_sdata4;
1955 Buf[2] = DW_EH_PE_udata4;
1956 Buf[3] = DW_EH_PE_datarel | DW_EH_PE_sdata4;
1957 write32<E>(Buf + 4, In<ELFT>::EhFrame->getParent()->Addr - this->getVA() - 4);
1958 write32<E>(Buf + 8, Fdes.size());
1961 uint64_t VA = this->getVA();
1962 for (FdeData &Fde : Fdes) {
1963 write32<E>(Buf, Fde.Pc - VA);
1964 write32<E>(Buf + 4, Fde.FdeVA - VA);
1969 template <class ELFT> size_t EhFrameHeader<ELFT>::getSize() const {
1970 // .eh_frame_hdr has a 12 bytes header followed by an array of FDEs.
1971 return 12 + In<ELFT>::EhFrame->NumFdes * 8;
1974 template <class ELFT>
1975 void EhFrameHeader<ELFT>::addFde(uint32_t Pc, uint32_t FdeVA) {
1976 Fdes.push_back({Pc, FdeVA});
1979 template <class ELFT> bool EhFrameHeader<ELFT>::empty() const {
1980 return In<ELFT>::EhFrame->empty();
1983 template <class ELFT>
1984 VersionDefinitionSection<ELFT>::VersionDefinitionSection()
1985 : SyntheticSection(SHF_ALLOC, SHT_GNU_verdef, sizeof(uint32_t),
1986 ".gnu.version_d") {}
1988 static StringRef getFileDefName() {
1989 if (!Config->SoName.empty())
1990 return Config->SoName;
1991 return Config->OutputFile;
1994 template <class ELFT> void VersionDefinitionSection<ELFT>::finalizeContents() {
1995 FileDefNameOff = InX::DynStrTab->addString(getFileDefName());
1996 for (VersionDefinition &V : Config->VersionDefinitions)
1997 V.NameOff = InX::DynStrTab->addString(V.Name);
1999 getParent()->Link = InX::DynStrTab->getParent()->SectionIndex;
2001 // sh_info should be set to the number of definitions. This fact is missed in
2002 // documentation, but confirmed by binutils community:
2003 // https://sourceware.org/ml/binutils/2014-11/msg00355.html
2004 getParent()->Info = getVerDefNum();
2007 template <class ELFT>
2008 void VersionDefinitionSection<ELFT>::writeOne(uint8_t *Buf, uint32_t Index,
2009 StringRef Name, size_t NameOff) {
2010 auto *Verdef = reinterpret_cast<Elf_Verdef *>(Buf);
2011 Verdef->vd_version = 1;
2013 Verdef->vd_aux = sizeof(Elf_Verdef);
2014 Verdef->vd_next = sizeof(Elf_Verdef) + sizeof(Elf_Verdaux);
2015 Verdef->vd_flags = (Index == 1 ? VER_FLG_BASE : 0);
2016 Verdef->vd_ndx = Index;
2017 Verdef->vd_hash = hashSysV(Name);
2019 auto *Verdaux = reinterpret_cast<Elf_Verdaux *>(Buf + sizeof(Elf_Verdef));
2020 Verdaux->vda_name = NameOff;
2021 Verdaux->vda_next = 0;
2024 template <class ELFT>
2025 void VersionDefinitionSection<ELFT>::writeTo(uint8_t *Buf) {
2026 writeOne(Buf, 1, getFileDefName(), FileDefNameOff);
2028 for (VersionDefinition &V : Config->VersionDefinitions) {
2029 Buf += sizeof(Elf_Verdef) + sizeof(Elf_Verdaux);
2030 writeOne(Buf, V.Id, V.Name, V.NameOff);
2033 // Need to terminate the last version definition.
2034 Elf_Verdef *Verdef = reinterpret_cast<Elf_Verdef *>(Buf);
2035 Verdef->vd_next = 0;
2038 template <class ELFT> size_t VersionDefinitionSection<ELFT>::getSize() const {
2039 return (sizeof(Elf_Verdef) + sizeof(Elf_Verdaux)) * getVerDefNum();
2042 template <class ELFT>
2043 VersionTableSection<ELFT>::VersionTableSection()
2044 : SyntheticSection(SHF_ALLOC, SHT_GNU_versym, sizeof(uint16_t),
2046 this->Entsize = sizeof(Elf_Versym);
2049 template <class ELFT> void VersionTableSection<ELFT>::finalizeContents() {
2050 // At the moment of june 2016 GNU docs does not mention that sh_link field
2051 // should be set, but Sun docs do. Also readelf relies on this field.
2052 getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
2055 template <class ELFT> size_t VersionTableSection<ELFT>::getSize() const {
2056 return sizeof(Elf_Versym) * (InX::DynSymTab->getSymbols().size() + 1);
2059 template <class ELFT> void VersionTableSection<ELFT>::writeTo(uint8_t *Buf) {
2060 auto *OutVersym = reinterpret_cast<Elf_Versym *>(Buf) + 1;
2061 for (const SymbolTableEntry &S : InX::DynSymTab->getSymbols()) {
2062 OutVersym->vs_index = S.Symbol->symbol()->VersionId;
2067 template <class ELFT> bool VersionTableSection<ELFT>::empty() const {
2068 return !In<ELFT>::VerDef && In<ELFT>::VerNeed->empty();
2071 template <class ELFT>
2072 VersionNeedSection<ELFT>::VersionNeedSection()
2073 : SyntheticSection(SHF_ALLOC, SHT_GNU_verneed, sizeof(uint32_t),
2075 // Identifiers in verneed section start at 2 because 0 and 1 are reserved
2076 // for VER_NDX_LOCAL and VER_NDX_GLOBAL.
2077 // First identifiers are reserved by verdef section if it exist.
2078 NextIndex = getVerDefNum() + 1;
2081 template <class ELFT>
2082 void VersionNeedSection<ELFT>::addSymbol(SharedSymbol *SS) {
2083 auto *Ver = reinterpret_cast<const typename ELFT::Verdef *>(SS->Verdef);
2085 SS->symbol()->VersionId = VER_NDX_GLOBAL;
2089 auto *File = cast<SharedFile<ELFT>>(SS->File);
2091 // If we don't already know that we need an Elf_Verneed for this DSO, prepare
2092 // to create one by adding it to our needed list and creating a dynstr entry
2094 if (File->VerdefMap.empty())
2095 Needed.push_back({File, InX::DynStrTab->addString(File->SoName)});
2096 typename SharedFile<ELFT>::NeededVer &NV = File->VerdefMap[Ver];
2097 // If we don't already know that we need an Elf_Vernaux for this Elf_Verdef,
2098 // prepare to create one by allocating a version identifier and creating a
2099 // dynstr entry for the version name.
2100 if (NV.Index == 0) {
2101 NV.StrTab = InX::DynStrTab->addString(File->getStringTable().data() +
2102 Ver->getAux()->vda_name);
2103 NV.Index = NextIndex++;
2105 SS->symbol()->VersionId = NV.Index;
2108 template <class ELFT> void VersionNeedSection<ELFT>::writeTo(uint8_t *Buf) {
2109 // The Elf_Verneeds need to appear first, followed by the Elf_Vernauxs.
2110 auto *Verneed = reinterpret_cast<Elf_Verneed *>(Buf);
2111 auto *Vernaux = reinterpret_cast<Elf_Vernaux *>(Verneed + Needed.size());
2113 for (std::pair<SharedFile<ELFT> *, size_t> &P : Needed) {
2114 // Create an Elf_Verneed for this DSO.
2115 Verneed->vn_version = 1;
2116 Verneed->vn_cnt = P.first->VerdefMap.size();
2117 Verneed->vn_file = P.second;
2119 reinterpret_cast<char *>(Vernaux) - reinterpret_cast<char *>(Verneed);
2120 Verneed->vn_next = sizeof(Elf_Verneed);
2123 // Create the Elf_Vernauxs for this Elf_Verneed. The loop iterates over
2124 // VerdefMap, which will only contain references to needed version
2125 // definitions. Each Elf_Vernaux is based on the information contained in
2126 // the Elf_Verdef in the source DSO. This loop iterates over a std::map of
2127 // pointers, but is deterministic because the pointers refer to Elf_Verdef
2128 // data structures within a single input file.
2129 for (auto &NV : P.first->VerdefMap) {
2130 Vernaux->vna_hash = NV.first->vd_hash;
2131 Vernaux->vna_flags = 0;
2132 Vernaux->vna_other = NV.second.Index;
2133 Vernaux->vna_name = NV.second.StrTab;
2134 Vernaux->vna_next = sizeof(Elf_Vernaux);
2138 Vernaux[-1].vna_next = 0;
2140 Verneed[-1].vn_next = 0;
2143 template <class ELFT> void VersionNeedSection<ELFT>::finalizeContents() {
2144 getParent()->Link = InX::DynStrTab->getParent()->SectionIndex;
2145 getParent()->Info = Needed.size();
2148 template <class ELFT> size_t VersionNeedSection<ELFT>::getSize() const {
2149 unsigned Size = Needed.size() * sizeof(Elf_Verneed);
2150 for (const std::pair<SharedFile<ELFT> *, size_t> &P : Needed)
2151 Size += P.first->VerdefMap.size() * sizeof(Elf_Vernaux);
2155 template <class ELFT> bool VersionNeedSection<ELFT>::empty() const {
2156 return getNeedNum() == 0;
2159 MergeSyntheticSection::MergeSyntheticSection(StringRef Name, uint32_t Type,
2160 uint64_t Flags, uint32_t Alignment)
2161 : SyntheticSection(Flags, Type, Alignment, Name),
2162 Builder(StringTableBuilder::RAW, Alignment) {}
2164 void MergeSyntheticSection::addSection(MergeInputSection *MS) {
2166 Sections.push_back(MS);
2169 void MergeSyntheticSection::writeTo(uint8_t *Buf) { Builder.write(Buf); }
2171 bool MergeSyntheticSection::shouldTailMerge() const {
2172 return (this->Flags & SHF_STRINGS) && Config->Optimize >= 2;
2175 void MergeSyntheticSection::finalizeTailMerge() {
2176 // Add all string pieces to the string table builder to create section
2178 for (MergeInputSection *Sec : Sections)
2179 for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
2180 if (Sec->Pieces[I].Live)
2181 Builder.add(Sec->getData(I));
2183 // Fix the string table content. After this, the contents will never change.
2186 // finalize() fixed tail-optimized strings, so we can now get
2187 // offsets of strings. Get an offset for each string and save it
2188 // to a corresponding StringPiece for easy access.
2189 for (MergeInputSection *Sec : Sections)
2190 for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
2191 if (Sec->Pieces[I].Live)
2192 Sec->Pieces[I].OutputOff = Builder.getOffset(Sec->getData(I));
2195 void MergeSyntheticSection::finalizeNoTailMerge() {
2196 // Add all string pieces to the string table builder to create section
2197 // contents. Because we are not tail-optimizing, offsets of strings are
2198 // fixed when they are added to the builder (string table builder contains
2199 // a hash table from strings to offsets).
2200 for (MergeInputSection *Sec : Sections)
2201 for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
2202 if (Sec->Pieces[I].Live)
2203 Sec->Pieces[I].OutputOff = Builder.add(Sec->getData(I));
2205 Builder.finalizeInOrder();
2208 void MergeSyntheticSection::finalizeContents() {
2209 if (shouldTailMerge())
2210 finalizeTailMerge();
2212 finalizeNoTailMerge();
2215 size_t MergeSyntheticSection::getSize() const { return Builder.getSize(); }
2217 // This function decompresses compressed sections and scans over the input
2218 // sections to create mergeable synthetic sections. It removes
2219 // MergeInputSections from the input section array and adds new synthetic
2220 // sections at the location of the first input section that it replaces. It then
2221 // finalizes each synthetic section in order to compute an output offset for
2222 // each piece of each input section.
2223 void elf::decompressAndMergeSections() {
2224 // splitIntoPieces needs to be called on each MergeInputSection before calling
2225 // finalizeContents(). Do that first.
2226 parallelForEach(InputSections.begin(), InputSections.end(),
2227 [](InputSectionBase *S) {
2230 if (Decompressor::isCompressedELFSection(S->Flags, S->Name))
2232 if (auto *MS = dyn_cast<MergeInputSection>(S))
2233 MS->splitIntoPieces();
2236 std::vector<MergeSyntheticSection *> MergeSections;
2237 for (InputSectionBase *&S : InputSections) {
2238 MergeInputSection *MS = dyn_cast<MergeInputSection>(S);
2242 // We do not want to handle sections that are not alive, so just remove
2243 // them instead of trying to merge.
2247 StringRef OutsecName = getOutputSectionName(MS->Name);
2248 uint64_t Flags = MS->Flags & ~(uint64_t)SHF_GROUP;
2249 uint32_t Alignment = std::max<uint32_t>(MS->Alignment, MS->Entsize);
2251 auto I = llvm::find_if(MergeSections, [=](MergeSyntheticSection *Sec) {
2252 return Sec->Name == OutsecName && Sec->Flags == Flags &&
2253 Sec->Alignment == Alignment;
2255 if (I == MergeSections.end()) {
2256 MergeSyntheticSection *Syn =
2257 make<MergeSyntheticSection>(OutsecName, MS->Type, Flags, Alignment);
2258 MergeSections.push_back(Syn);
2259 I = std::prev(MergeSections.end());
2264 (*I)->addSection(MS);
2266 for (auto *MS : MergeSections)
2267 MS->finalizeContents();
2269 std::vector<InputSectionBase *> &V = InputSections;
2270 V.erase(std::remove(V.begin(), V.end(), nullptr), V.end());
2273 MipsRldMapSection::MipsRldMapSection()
2274 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, Config->Wordsize,
2277 ARMExidxSentinelSection::ARMExidxSentinelSection()
2278 : SyntheticSection(SHF_ALLOC | SHF_LINK_ORDER, SHT_ARM_EXIDX,
2279 Config->Wordsize, ".ARM.exidx") {}
2281 // Write a terminating sentinel entry to the end of the .ARM.exidx table.
2282 // This section will have been sorted last in the .ARM.exidx table.
2283 // This table entry will have the form:
2284 // | PREL31 upper bound of code that has exception tables | EXIDX_CANTUNWIND |
2285 // The sentinel must have the PREL31 value of an address higher than any
2286 // address described by any other table entry.
2287 void ARMExidxSentinelSection::writeTo(uint8_t *Buf) {
2288 // The Sections are sorted in order of ascending PREL31 address with the
2289 // sentinel last. We need to find the InputSection that precedes the
2290 // sentinel. By construction the Sentinel is in the last
2291 // InputSectionDescription as the InputSection that precedes it.
2292 OutputSectionCommand *C = Script->getCmd(getParent());
2293 auto ISD = std::find_if(C->Commands.rbegin(), C->Commands.rend(),
2294 [](const BaseCommand *Base) {
2295 return isa<InputSectionDescription>(Base);
2297 auto L = cast<InputSectionDescription>(*ISD);
2298 InputSection *Highest = L->Sections[L->Sections.size() - 2];
2299 InputSection *LS = Highest->getLinkOrderDep();
2300 uint64_t S = LS->getParent()->Addr + LS->getOffset(LS->getSize());
2301 uint64_t P = getVA();
2302 Target->relocateOne(Buf, R_ARM_PREL31, S - P);
2303 write32le(Buf + 4, 0x1);
2306 ThunkSection::ThunkSection(OutputSection *OS, uint64_t Off)
2307 : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS,
2308 Config->Wordsize, ".text.thunk") {
2310 this->OutSecOff = Off;
2313 void ThunkSection::addThunk(Thunk *T) {
2314 uint64_t Off = alignTo(Size, T->Alignment);
2316 Thunks.push_back(T);
2317 T->addSymbols(*this);
2318 Size = Off + T->size();
2321 void ThunkSection::writeTo(uint8_t *Buf) {
2322 for (const Thunk *T : Thunks)
2323 T->writeTo(Buf + T->Offset, *this);
2326 InputSection *ThunkSection::getTargetInputSection() const {
2327 const Thunk *T = Thunks.front();
2328 return T->getTargetInputSection();
2331 InputSection *InX::ARMAttributes;
2332 BssSection *InX::Bss;
2333 BssSection *InX::BssRelRo;
2334 BuildIdSection *InX::BuildId;
2335 InputSection *InX::Common;
2336 SyntheticSection *InX::Dynamic;
2337 StringTableSection *InX::DynStrTab;
2338 SymbolTableBaseSection *InX::DynSymTab;
2339 InputSection *InX::Interp;
2340 GdbIndexSection *InX::GdbIndex;
2341 GotSection *InX::Got;
2342 GotPltSection *InX::GotPlt;
2343 GnuHashTableSection *InX::GnuHashTab;
2344 IgotPltSection *InX::IgotPlt;
2345 MipsGotSection *InX::MipsGot;
2346 MipsRldMapSection *InX::MipsRldMap;
2347 PltSection *InX::Plt;
2348 PltSection *InX::Iplt;
2349 StringTableSection *InX::ShStrTab;
2350 StringTableSection *InX::StrTab;
2351 SymbolTableBaseSection *InX::SymTab;
2353 template GdbIndexSection *elf::createGdbIndex<ELF32LE>();
2354 template GdbIndexSection *elf::createGdbIndex<ELF32BE>();
2355 template GdbIndexSection *elf::createGdbIndex<ELF64LE>();
2356 template GdbIndexSection *elf::createGdbIndex<ELF64BE>();
2358 template void PltSection::addEntry<ELF32LE>(SymbolBody &Sym);
2359 template void PltSection::addEntry<ELF32BE>(SymbolBody &Sym);
2360 template void PltSection::addEntry<ELF64LE>(SymbolBody &Sym);
2361 template void PltSection::addEntry<ELF64BE>(SymbolBody &Sym);
2363 template InputSection *elf::createCommonSection<ELF32LE>();
2364 template InputSection *elf::createCommonSection<ELF32BE>();
2365 template InputSection *elf::createCommonSection<ELF64LE>();
2366 template InputSection *elf::createCommonSection<ELF64BE>();
2368 template MergeInputSection *elf::createCommentSection<ELF32LE>();
2369 template MergeInputSection *elf::createCommentSection<ELF32BE>();
2370 template MergeInputSection *elf::createCommentSection<ELF64LE>();
2371 template MergeInputSection *elf::createCommentSection<ELF64BE>();
2373 template class elf::MipsAbiFlagsSection<ELF32LE>;
2374 template class elf::MipsAbiFlagsSection<ELF32BE>;
2375 template class elf::MipsAbiFlagsSection<ELF64LE>;
2376 template class elf::MipsAbiFlagsSection<ELF64BE>;
2378 template class elf::MipsOptionsSection<ELF32LE>;
2379 template class elf::MipsOptionsSection<ELF32BE>;
2380 template class elf::MipsOptionsSection<ELF64LE>;
2381 template class elf::MipsOptionsSection<ELF64BE>;
2383 template class elf::MipsReginfoSection<ELF32LE>;
2384 template class elf::MipsReginfoSection<ELF32BE>;
2385 template class elf::MipsReginfoSection<ELF64LE>;
2386 template class elf::MipsReginfoSection<ELF64BE>;
2388 template class elf::DynamicSection<ELF32LE>;
2389 template class elf::DynamicSection<ELF32BE>;
2390 template class elf::DynamicSection<ELF64LE>;
2391 template class elf::DynamicSection<ELF64BE>;
2393 template class elf::RelocationSection<ELF32LE>;
2394 template class elf::RelocationSection<ELF32BE>;
2395 template class elf::RelocationSection<ELF64LE>;
2396 template class elf::RelocationSection<ELF64BE>;
2398 template class elf::SymbolTableSection<ELF32LE>;
2399 template class elf::SymbolTableSection<ELF32BE>;
2400 template class elf::SymbolTableSection<ELF64LE>;
2401 template class elf::SymbolTableSection<ELF64BE>;
2403 template class elf::HashTableSection<ELF32LE>;
2404 template class elf::HashTableSection<ELF32BE>;
2405 template class elf::HashTableSection<ELF64LE>;
2406 template class elf::HashTableSection<ELF64BE>;
2408 template class elf::EhFrameHeader<ELF32LE>;
2409 template class elf::EhFrameHeader<ELF32BE>;
2410 template class elf::EhFrameHeader<ELF64LE>;
2411 template class elf::EhFrameHeader<ELF64BE>;
2413 template class elf::VersionTableSection<ELF32LE>;
2414 template class elf::VersionTableSection<ELF32BE>;
2415 template class elf::VersionTableSection<ELF64LE>;
2416 template class elf::VersionTableSection<ELF64BE>;
2418 template class elf::VersionNeedSection<ELF32LE>;
2419 template class elf::VersionNeedSection<ELF32BE>;
2420 template class elf::VersionNeedSection<ELF64LE>;
2421 template class elf::VersionNeedSection<ELF64BE>;
2423 template class elf::VersionDefinitionSection<ELF32LE>;
2424 template class elf::VersionDefinitionSection<ELF32BE>;
2425 template class elf::VersionDefinitionSection<ELF64LE>;
2426 template class elf::VersionDefinitionSection<ELF64BE>;
2428 template class elf::EhFrameSection<ELF32LE>;
2429 template class elf::EhFrameSection<ELF32BE>;
2430 template class elf::EhFrameSection<ELF64LE>;
2431 template class elf::EhFrameSection<ELF64BE>;