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) { relocateAlloc(Buf, Buf + Size); }
667 MipsGotSection::MipsGotSection()
668 : SyntheticSection(SHF_ALLOC | SHF_WRITE | SHF_MIPS_GPREL, SHT_PROGBITS, 16,
671 void MipsGotSection::addEntry(SymbolBody &Sym, int64_t Addend, RelExpr Expr) {
672 // For "true" local symbols which can be referenced from the same module
673 // only compiler creates two instructions for address loading:
675 // lw $8, 0($gp) # R_MIPS_GOT16
676 // addi $8, $8, 0 # R_MIPS_LO16
678 // The first instruction loads high 16 bits of the symbol address while
679 // the second adds an offset. That allows to reduce number of required
680 // GOT entries because only one global offset table entry is necessary
681 // for every 64 KBytes of local data. So for local symbols we need to
682 // allocate number of GOT entries to hold all required "page" addresses.
684 // All global symbols (hidden and regular) considered by compiler uniformly.
685 // It always generates a single `lw` instruction and R_MIPS_GOT16 relocation
686 // to load address of the symbol. So for each such symbol we need to
687 // allocate dedicated GOT entry to store its address.
689 // If a symbol is preemptible we need help of dynamic linker to get its
690 // final address. The corresponding GOT entries are allocated in the
691 // "global" part of GOT. Entries for non preemptible global symbol allocated
692 // in the "local" part of GOT.
694 // See "Global Offset Table" in Chapter 5:
695 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
696 if (Expr == R_MIPS_GOT_LOCAL_PAGE) {
697 // At this point we do not know final symbol value so to reduce number
698 // of allocated GOT entries do the following trick. Save all output
699 // sections referenced by GOT relocations. Then later in the `finalize`
700 // method calculate number of "pages" required to cover all saved output
701 // section and allocate appropriate number of GOT entries.
702 PageIndexMap.insert({Sym.getOutputSection(), 0});
706 // GOT entries created for MIPS TLS relocations behave like
707 // almost GOT entries from other ABIs. They go to the end
708 // of the global offset table.
709 Sym.GotIndex = TlsEntries.size();
710 TlsEntries.push_back(&Sym);
713 auto AddEntry = [&](SymbolBody &S, uint64_t A, GotEntries &Items) {
714 if (S.isInGot() && !A)
716 size_t NewIndex = Items.size();
717 if (!EntryIndexMap.insert({{&S, A}, NewIndex}).second)
719 Items.emplace_back(&S, A);
721 S.GotIndex = NewIndex;
723 if (Sym.isPreemptible()) {
724 // Ignore addends for preemptible symbols. They got single GOT entry anyway.
725 AddEntry(Sym, 0, GlobalEntries);
726 Sym.IsInGlobalMipsGot = true;
727 } else if (Expr == R_MIPS_GOT_OFF32) {
728 AddEntry(Sym, Addend, LocalEntries32);
729 Sym.Is32BitMipsGot = true;
731 // Hold local GOT entries accessed via a 16-bit index separately.
732 // That allows to write them in the beginning of the GOT and keep
733 // their indexes as less as possible to escape relocation's overflow.
734 AddEntry(Sym, Addend, LocalEntries);
738 bool MipsGotSection::addDynTlsEntry(SymbolBody &Sym) {
739 if (Sym.GlobalDynIndex != -1U)
741 Sym.GlobalDynIndex = TlsEntries.size();
742 // Global Dynamic TLS entries take two GOT slots.
743 TlsEntries.push_back(nullptr);
744 TlsEntries.push_back(&Sym);
748 // Reserves TLS entries for a TLS module ID and a TLS block offset.
749 // In total it takes two GOT slots.
750 bool MipsGotSection::addTlsIndex() {
751 if (TlsIndexOff != uint32_t(-1))
753 TlsIndexOff = TlsEntries.size() * Config->Wordsize;
754 TlsEntries.push_back(nullptr);
755 TlsEntries.push_back(nullptr);
759 static uint64_t getMipsPageAddr(uint64_t Addr) {
760 return (Addr + 0x8000) & ~0xffff;
763 static uint64_t getMipsPageCount(uint64_t Size) {
764 return (Size + 0xfffe) / 0xffff + 1;
767 uint64_t MipsGotSection::getPageEntryOffset(const SymbolBody &B,
768 int64_t Addend) const {
769 const OutputSection *OutSec = B.getOutputSection();
770 uint64_t SecAddr = getMipsPageAddr(OutSec->Addr);
771 uint64_t SymAddr = getMipsPageAddr(B.getVA(Addend));
772 uint64_t Index = PageIndexMap.lookup(OutSec) + (SymAddr - SecAddr) / 0xffff;
773 assert(Index < PageEntriesNum);
774 return (HeaderEntriesNum + Index) * Config->Wordsize;
777 uint64_t MipsGotSection::getBodyEntryOffset(const SymbolBody &B,
778 int64_t Addend) const {
779 // Calculate offset of the GOT entries block: TLS, global, local.
780 uint64_t Index = HeaderEntriesNum + PageEntriesNum;
782 Index += LocalEntries.size() + LocalEntries32.size() + GlobalEntries.size();
783 else if (B.IsInGlobalMipsGot)
784 Index += LocalEntries.size() + LocalEntries32.size();
785 else if (B.Is32BitMipsGot)
786 Index += LocalEntries.size();
787 // Calculate offset of the GOT entry in the block.
791 auto It = EntryIndexMap.find({&B, Addend});
792 assert(It != EntryIndexMap.end());
795 return Index * Config->Wordsize;
798 uint64_t MipsGotSection::getTlsOffset() const {
799 return (getLocalEntriesNum() + GlobalEntries.size()) * Config->Wordsize;
802 uint64_t MipsGotSection::getGlobalDynOffset(const SymbolBody &B) const {
803 return B.GlobalDynIndex * Config->Wordsize;
806 const SymbolBody *MipsGotSection::getFirstGlobalEntry() const {
807 return GlobalEntries.empty() ? nullptr : GlobalEntries.front().first;
810 unsigned MipsGotSection::getLocalEntriesNum() const {
811 return HeaderEntriesNum + PageEntriesNum + LocalEntries.size() +
812 LocalEntries32.size();
815 void MipsGotSection::finalizeContents() {
819 void MipsGotSection::updateAllocSize() {
821 for (std::pair<const OutputSection *, size_t> &P : PageIndexMap) {
822 // For each output section referenced by GOT page relocations calculate
823 // and save into PageIndexMap an upper bound of MIPS GOT entries required
824 // to store page addresses of local symbols. We assume the worst case -
825 // each 64kb page of the output section has at least one GOT relocation
826 // against it. And take in account the case when the section intersects
828 P.second = PageEntriesNum;
829 PageEntriesNum += getMipsPageCount(P.first->Size);
831 Size = (getLocalEntriesNum() + GlobalEntries.size() + TlsEntries.size()) *
835 bool MipsGotSection::empty() const {
836 // We add the .got section to the result for dynamic MIPS target because
837 // its address and properties are mentioned in the .dynamic section.
838 return Config->Relocatable;
841 uint64_t MipsGotSection::getGp() const {
842 return ElfSym::MipsGp->getVA(0);
845 static uint64_t readUint(uint8_t *Buf) {
847 return read64(Buf, Config->Endianness);
848 return read32(Buf, Config->Endianness);
851 static void writeUint(uint8_t *Buf, uint64_t Val) {
853 write64(Buf, Val, Config->Endianness);
855 write32(Buf, Val, Config->Endianness);
858 void MipsGotSection::writeTo(uint8_t *Buf) {
859 // Set the MSB of the second GOT slot. This is not required by any
860 // MIPS ABI documentation, though.
862 // There is a comment in glibc saying that "The MSB of got[1] of a
863 // gnu object is set to identify gnu objects," and in GNU gold it
864 // says "the second entry will be used by some runtime loaders".
865 // But how this field is being used is unclear.
867 // We are not really willing to mimic other linkers behaviors
868 // without understanding why they do that, but because all files
869 // generated by GNU tools have this special GOT value, and because
870 // we've been doing this for years, it is probably a safe bet to
871 // keep doing this for now. We really need to revisit this to see
872 // if we had to do this.
873 writeUint(Buf + Config->Wordsize, (uint64_t)1 << (Config->Wordsize * 8 - 1));
874 Buf += HeaderEntriesNum * Config->Wordsize;
875 // Write 'page address' entries to the local part of the GOT.
876 for (std::pair<const OutputSection *, size_t> &L : PageIndexMap) {
877 size_t PageCount = getMipsPageCount(L.first->Size);
878 uint64_t FirstPageAddr = getMipsPageAddr(L.first->Addr);
879 for (size_t PI = 0; PI < PageCount; ++PI) {
880 uint8_t *Entry = Buf + (L.second + PI) * Config->Wordsize;
881 writeUint(Entry, FirstPageAddr + PI * 0x10000);
884 Buf += PageEntriesNum * Config->Wordsize;
885 auto AddEntry = [&](const GotEntry &SA) {
886 uint8_t *Entry = Buf;
887 Buf += Config->Wordsize;
888 const SymbolBody *Body = SA.first;
889 uint64_t VA = Body->getVA(SA.second);
890 writeUint(Entry, VA);
892 std::for_each(std::begin(LocalEntries), std::end(LocalEntries), AddEntry);
893 std::for_each(std::begin(LocalEntries32), std::end(LocalEntries32), AddEntry);
894 std::for_each(std::begin(GlobalEntries), std::end(GlobalEntries), AddEntry);
895 // Initialize TLS-related GOT entries. If the entry has a corresponding
896 // dynamic relocations, leave it initialized by zero. Write down adjusted
897 // TLS symbol's values otherwise. To calculate the adjustments use offsets
898 // for thread-local storage.
899 // https://www.linux-mips.org/wiki/NPTL
900 if (TlsIndexOff != -1U && !Config->Pic)
901 writeUint(Buf + TlsIndexOff, 1);
902 for (const SymbolBody *B : TlsEntries) {
903 if (!B || B->isPreemptible())
905 uint64_t VA = B->getVA();
906 if (B->GotIndex != -1U) {
907 uint8_t *Entry = Buf + B->GotIndex * Config->Wordsize;
908 writeUint(Entry, VA - 0x7000);
910 if (B->GlobalDynIndex != -1U) {
911 uint8_t *Entry = Buf + B->GlobalDynIndex * Config->Wordsize;
913 Entry += Config->Wordsize;
914 writeUint(Entry, VA - 0x8000);
919 GotPltSection::GotPltSection()
920 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
921 Target->GotPltEntrySize, ".got.plt") {}
923 void GotPltSection::addEntry(SymbolBody &Sym) {
924 Sym.GotPltIndex = Target->GotPltHeaderEntriesNum + Entries.size();
925 Entries.push_back(&Sym);
928 size_t GotPltSection::getSize() const {
929 return (Target->GotPltHeaderEntriesNum + Entries.size()) *
930 Target->GotPltEntrySize;
933 void GotPltSection::writeTo(uint8_t *Buf) {
934 Target->writeGotPltHeader(Buf);
935 Buf += Target->GotPltHeaderEntriesNum * Target->GotPltEntrySize;
936 for (const SymbolBody *B : Entries) {
937 Target->writeGotPlt(Buf, *B);
938 Buf += Config->Wordsize;
942 // On ARM the IgotPltSection is part of the GotSection, on other Targets it is
943 // part of the .got.plt
944 IgotPltSection::IgotPltSection()
945 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
946 Target->GotPltEntrySize,
947 Config->EMachine == EM_ARM ? ".got" : ".got.plt") {}
949 void IgotPltSection::addEntry(SymbolBody &Sym) {
951 Sym.GotPltIndex = Entries.size();
952 Entries.push_back(&Sym);
955 size_t IgotPltSection::getSize() const {
956 return Entries.size() * Target->GotPltEntrySize;
959 void IgotPltSection::writeTo(uint8_t *Buf) {
960 for (const SymbolBody *B : Entries) {
961 Target->writeIgotPlt(Buf, *B);
962 Buf += Config->Wordsize;
966 StringTableSection::StringTableSection(StringRef Name, bool Dynamic)
967 : SyntheticSection(Dynamic ? (uint64_t)SHF_ALLOC : 0, SHT_STRTAB, 1, Name),
969 // ELF string tables start with a NUL byte.
973 // Adds a string to the string table. If HashIt is true we hash and check for
974 // duplicates. It is optional because the name of global symbols are already
975 // uniqued and hashing them again has a big cost for a small value: uniquing
976 // them with some other string that happens to be the same.
977 unsigned StringTableSection::addString(StringRef S, bool HashIt) {
979 auto R = StringMap.insert(std::make_pair(S, this->Size));
981 return R.first->second;
983 unsigned Ret = this->Size;
984 this->Size = this->Size + S.size() + 1;
985 Strings.push_back(S);
989 void StringTableSection::writeTo(uint8_t *Buf) {
990 for (StringRef S : Strings) {
991 memcpy(Buf, S.data(), S.size());
996 // Returns the number of version definition entries. Because the first entry
997 // is for the version definition itself, it is the number of versioned symbols
998 // plus one. Note that we don't support multiple versions yet.
999 static unsigned getVerDefNum() { return Config->VersionDefinitions.size() + 1; }
1001 template <class ELFT>
1002 DynamicSection<ELFT>::DynamicSection()
1003 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_DYNAMIC, Config->Wordsize,
1005 this->Entsize = ELFT::Is64Bits ? 16 : 8;
1007 // .dynamic section is not writable on MIPS and on Fuchsia OS
1008 // which passes -z rodynamic.
1009 // See "Special Section" in Chapter 4 in the following document:
1010 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
1011 if (Config->EMachine == EM_MIPS || Config->ZRodynamic)
1012 this->Flags = SHF_ALLOC;
1017 // There are some dynamic entries that don't depend on other sections.
1018 // Such entries can be set early.
1019 template <class ELFT> void DynamicSection<ELFT>::addEntries() {
1020 // Add strings to .dynstr early so that .dynstr's size will be
1022 for (StringRef S : Config->AuxiliaryList)
1023 add({DT_AUXILIARY, InX::DynStrTab->addString(S)});
1024 if (!Config->Rpath.empty())
1025 add({Config->EnableNewDtags ? DT_RUNPATH : DT_RPATH,
1026 InX::DynStrTab->addString(Config->Rpath)});
1027 for (SharedFile<ELFT> *F : Symtab<ELFT>::X->getSharedFiles())
1029 add({DT_NEEDED, InX::DynStrTab->addString(F->SoName)});
1030 if (!Config->SoName.empty())
1031 add({DT_SONAME, InX::DynStrTab->addString(Config->SoName)});
1033 // Set DT_FLAGS and DT_FLAGS_1.
1034 uint32_t DtFlags = 0;
1035 uint32_t DtFlags1 = 0;
1036 if (Config->Bsymbolic)
1037 DtFlags |= DF_SYMBOLIC;
1038 if (Config->ZNodelete)
1039 DtFlags1 |= DF_1_NODELETE;
1040 if (Config->ZNodlopen)
1041 DtFlags1 |= DF_1_NOOPEN;
1043 DtFlags |= DF_BIND_NOW;
1044 DtFlags1 |= DF_1_NOW;
1046 if (Config->ZOrigin) {
1047 DtFlags |= DF_ORIGIN;
1048 DtFlags1 |= DF_1_ORIGIN;
1052 add({DT_FLAGS, DtFlags});
1054 add({DT_FLAGS_1, DtFlags1});
1056 // DT_DEBUG is a pointer to debug informaion used by debuggers at runtime. We
1057 // need it for each process, so we don't write it for DSOs. The loader writes
1058 // the pointer into this entry.
1060 // DT_DEBUG is the only .dynamic entry that needs to be written to. Some
1061 // systems (currently only Fuchsia OS) provide other means to give the
1062 // debugger this information. Such systems may choose make .dynamic read-only.
1063 // If the target is such a system (used -z rodynamic) don't write DT_DEBUG.
1064 if (!Config->Shared && !Config->Relocatable && !Config->ZRodynamic)
1065 add({DT_DEBUG, (uint64_t)0});
1068 // Add remaining entries to complete .dynamic contents.
1069 template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
1071 return; // Already finalized.
1073 this->Link = InX::DynStrTab->getParent()->SectionIndex;
1074 if (In<ELFT>::RelaDyn->getParent()->Size > 0) {
1075 bool IsRela = Config->IsRela;
1076 add({IsRela ? DT_RELA : DT_REL, In<ELFT>::RelaDyn});
1077 add({IsRela ? DT_RELASZ : DT_RELSZ, In<ELFT>::RelaDyn->getParent()->Size});
1078 add({IsRela ? DT_RELAENT : DT_RELENT,
1079 uint64_t(IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel))});
1081 // MIPS dynamic loader does not support RELCOUNT tag.
1082 // The problem is in the tight relation between dynamic
1083 // relocations and GOT. So do not emit this tag on MIPS.
1084 if (Config->EMachine != EM_MIPS) {
1085 size_t NumRelativeRels = In<ELFT>::RelaDyn->getRelativeRelocCount();
1086 if (Config->ZCombreloc && NumRelativeRels)
1087 add({IsRela ? DT_RELACOUNT : DT_RELCOUNT, NumRelativeRels});
1090 if (In<ELFT>::RelaPlt->getParent()->Size > 0) {
1091 add({DT_JMPREL, In<ELFT>::RelaPlt});
1092 add({DT_PLTRELSZ, In<ELFT>::RelaPlt->getParent()->Size});
1093 add({Config->EMachine == EM_MIPS ? DT_MIPS_PLTGOT : DT_PLTGOT,
1095 add({DT_PLTREL, uint64_t(Config->IsRela ? DT_RELA : DT_REL)});
1098 add({DT_SYMTAB, InX::DynSymTab});
1099 add({DT_SYMENT, sizeof(Elf_Sym)});
1100 add({DT_STRTAB, InX::DynStrTab});
1101 add({DT_STRSZ, InX::DynStrTab->getSize()});
1103 add({DT_TEXTREL, (uint64_t)0});
1104 if (InX::GnuHashTab)
1105 add({DT_GNU_HASH, InX::GnuHashTab});
1106 if (In<ELFT>::HashTab)
1107 add({DT_HASH, In<ELFT>::HashTab});
1109 if (Out::PreinitArray) {
1110 add({DT_PREINIT_ARRAY, Out::PreinitArray});
1111 add({DT_PREINIT_ARRAYSZ, Out::PreinitArray, Entry::SecSize});
1113 if (Out::InitArray) {
1114 add({DT_INIT_ARRAY, Out::InitArray});
1115 add({DT_INIT_ARRAYSZ, Out::InitArray, Entry::SecSize});
1117 if (Out::FiniArray) {
1118 add({DT_FINI_ARRAY, Out::FiniArray});
1119 add({DT_FINI_ARRAYSZ, Out::FiniArray, Entry::SecSize});
1122 if (SymbolBody *B = Symtab<ELFT>::X->findInCurrentDSO(Config->Init))
1124 if (SymbolBody *B = Symtab<ELFT>::X->findInCurrentDSO(Config->Fini))
1127 bool HasVerNeed = In<ELFT>::VerNeed->getNeedNum() != 0;
1128 if (HasVerNeed || In<ELFT>::VerDef)
1129 add({DT_VERSYM, In<ELFT>::VerSym});
1130 if (In<ELFT>::VerDef) {
1131 add({DT_VERDEF, In<ELFT>::VerDef});
1132 add({DT_VERDEFNUM, getVerDefNum()});
1135 add({DT_VERNEED, In<ELFT>::VerNeed});
1136 add({DT_VERNEEDNUM, In<ELFT>::VerNeed->getNeedNum()});
1139 if (Config->EMachine == EM_MIPS) {
1140 add({DT_MIPS_RLD_VERSION, 1});
1141 add({DT_MIPS_FLAGS, RHF_NOTPOT});
1142 add({DT_MIPS_BASE_ADDRESS, Config->ImageBase});
1143 add({DT_MIPS_SYMTABNO, InX::DynSymTab->getNumSymbols()});
1144 add({DT_MIPS_LOCAL_GOTNO, InX::MipsGot->getLocalEntriesNum()});
1145 if (const SymbolBody *B = InX::MipsGot->getFirstGlobalEntry())
1146 add({DT_MIPS_GOTSYM, B->DynsymIndex});
1148 add({DT_MIPS_GOTSYM, InX::DynSymTab->getNumSymbols()});
1149 add({DT_PLTGOT, InX::MipsGot});
1150 if (InX::MipsRldMap)
1151 add({DT_MIPS_RLD_MAP, InX::MipsRldMap});
1154 getParent()->Link = this->Link;
1157 this->Size = (Entries.size() + 1) * this->Entsize;
1160 template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *Buf) {
1161 auto *P = reinterpret_cast<Elf_Dyn *>(Buf);
1163 for (const Entry &E : Entries) {
1166 case Entry::SecAddr:
1167 P->d_un.d_ptr = E.OutSec->Addr;
1169 case Entry::InSecAddr:
1170 P->d_un.d_ptr = E.InSec->getParent()->Addr + E.InSec->OutSecOff;
1172 case Entry::SecSize:
1173 P->d_un.d_val = E.OutSec->Size;
1175 case Entry::SymAddr:
1176 P->d_un.d_ptr = E.Sym->getVA();
1178 case Entry::PlainInt:
1179 P->d_un.d_val = E.Val;
1186 uint64_t DynamicReloc::getOffset() const {
1187 return InputSec->getOutputSection()->Addr + InputSec->getOffset(OffsetInSec);
1190 int64_t DynamicReloc::getAddend() const {
1192 return Sym->getVA(Addend);
1196 uint32_t DynamicReloc::getSymIndex() const {
1197 if (Sym && !UseSymVA)
1198 return Sym->DynsymIndex;
1202 template <class ELFT>
1203 RelocationSection<ELFT>::RelocationSection(StringRef Name, bool Sort)
1204 : SyntheticSection(SHF_ALLOC, Config->IsRela ? SHT_RELA : SHT_REL,
1205 Config->Wordsize, Name),
1207 this->Entsize = Config->IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
1210 template <class ELFT>
1211 void RelocationSection<ELFT>::addReloc(const DynamicReloc &Reloc) {
1212 if (Reloc.Type == Target->RelativeRel)
1213 ++NumRelativeRelocs;
1214 Relocs.push_back(Reloc);
1217 template <class ELFT, class RelTy>
1218 static bool compRelocations(const RelTy &A, const RelTy &B) {
1219 bool AIsRel = A.getType(Config->IsMips64EL) == Target->RelativeRel;
1220 bool BIsRel = B.getType(Config->IsMips64EL) == Target->RelativeRel;
1221 if (AIsRel != BIsRel)
1224 return A.getSymbol(Config->IsMips64EL) < B.getSymbol(Config->IsMips64EL);
1227 template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *Buf) {
1228 uint8_t *BufBegin = Buf;
1229 for (const DynamicReloc &Rel : Relocs) {
1230 auto *P = reinterpret_cast<Elf_Rela *>(Buf);
1231 Buf += Config->IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
1234 P->r_addend = Rel.getAddend();
1235 P->r_offset = Rel.getOffset();
1236 if (Config->EMachine == EM_MIPS && Rel.getInputSec() == InX::MipsGot)
1237 // Dynamic relocation against MIPS GOT section make deal TLS entries
1238 // allocated in the end of the GOT. We need to adjust the offset to take
1239 // in account 'local' and 'global' GOT entries.
1240 P->r_offset += InX::MipsGot->getTlsOffset();
1241 P->setSymbolAndType(Rel.getSymIndex(), Rel.Type, Config->IsMips64EL);
1246 std::stable_sort((Elf_Rela *)BufBegin,
1247 (Elf_Rela *)BufBegin + Relocs.size(),
1248 compRelocations<ELFT, Elf_Rela>);
1250 std::stable_sort((Elf_Rel *)BufBegin, (Elf_Rel *)BufBegin + Relocs.size(),
1251 compRelocations<ELFT, Elf_Rel>);
1255 template <class ELFT> unsigned RelocationSection<ELFT>::getRelocOffset() {
1256 return this->Entsize * Relocs.size();
1259 template <class ELFT> void RelocationSection<ELFT>::finalizeContents() {
1260 this->Link = InX::DynSymTab ? InX::DynSymTab->getParent()->SectionIndex
1261 : InX::SymTab->getParent()->SectionIndex;
1263 // Set required output section properties.
1264 getParent()->Link = this->Link;
1267 SymbolTableBaseSection::SymbolTableBaseSection(StringTableSection &StrTabSec)
1268 : SyntheticSection(StrTabSec.isDynamic() ? (uint64_t)SHF_ALLOC : 0,
1269 StrTabSec.isDynamic() ? SHT_DYNSYM : SHT_SYMTAB,
1271 StrTabSec.isDynamic() ? ".dynsym" : ".symtab"),
1272 StrTabSec(StrTabSec) {}
1274 // Orders symbols according to their positions in the GOT,
1275 // in compliance with MIPS ABI rules.
1276 // See "Global Offset Table" in Chapter 5 in the following document
1277 // for detailed description:
1278 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
1279 static bool sortMipsSymbols(const SymbolTableEntry &L,
1280 const SymbolTableEntry &R) {
1281 // Sort entries related to non-local preemptible symbols by GOT indexes.
1282 // All other entries go to the first part of GOT in arbitrary order.
1283 bool LIsInLocalGot = !L.Symbol->IsInGlobalMipsGot;
1284 bool RIsInLocalGot = !R.Symbol->IsInGlobalMipsGot;
1285 if (LIsInLocalGot || RIsInLocalGot)
1286 return !RIsInLocalGot;
1287 return L.Symbol->GotIndex < R.Symbol->GotIndex;
1290 // Finalize a symbol table. The ELF spec requires that all local
1291 // symbols precede global symbols, so we sort symbol entries in this
1292 // function. (For .dynsym, we don't do that because symbols for
1293 // dynamic linking are inherently all globals.)
1294 void SymbolTableBaseSection::finalizeContents() {
1295 getParent()->Link = StrTabSec.getParent()->SectionIndex;
1297 // If it is a .dynsym, there should be no local symbols, but we need
1298 // to do a few things for the dynamic linker.
1299 if (this->Type == SHT_DYNSYM) {
1300 // Section's Info field has the index of the first non-local symbol.
1301 // Because the first symbol entry is a null entry, 1 is the first.
1302 getParent()->Info = 1;
1304 if (InX::GnuHashTab) {
1305 // NB: It also sorts Symbols to meet the GNU hash table requirements.
1306 InX::GnuHashTab->addSymbols(Symbols);
1307 } else if (Config->EMachine == EM_MIPS) {
1308 std::stable_sort(Symbols.begin(), Symbols.end(), sortMipsSymbols);
1312 for (const SymbolTableEntry &S : Symbols)
1313 S.Symbol->DynsymIndex = ++I;
1318 void SymbolTableBaseSection::postThunkContents() {
1319 if (this->Type == SHT_DYNSYM)
1321 // move all local symbols before global symbols.
1322 auto It = std::stable_partition(
1323 Symbols.begin(), Symbols.end(), [](const SymbolTableEntry &S) {
1324 return S.Symbol->isLocal() ||
1325 S.Symbol->symbol()->computeBinding() == STB_LOCAL;
1327 size_t NumLocals = It - Symbols.begin();
1328 getParent()->Info = NumLocals + 1;
1331 void SymbolTableBaseSection::addSymbol(SymbolBody *B) {
1332 // Adding a local symbol to a .dynsym is a bug.
1333 assert(this->Type != SHT_DYNSYM || !B->isLocal());
1335 bool HashIt = B->isLocal();
1336 Symbols.push_back({B, StrTabSec.addString(B->getName(), HashIt)});
1339 size_t SymbolTableBaseSection::getSymbolIndex(SymbolBody *Body) {
1340 auto I = llvm::find_if(Symbols, [&](const SymbolTableEntry &E) {
1341 if (E.Symbol == Body)
1343 // This is used for -r, so we have to handle multiple section
1344 // symbols being combined.
1345 if (Body->Type == STT_SECTION && E.Symbol->Type == STT_SECTION)
1346 return Body->getOutputSection() == E.Symbol->getOutputSection();
1349 if (I == Symbols.end())
1351 return I - Symbols.begin() + 1;
1354 template <class ELFT>
1355 SymbolTableSection<ELFT>::SymbolTableSection(StringTableSection &StrTabSec)
1356 : SymbolTableBaseSection(StrTabSec) {
1357 this->Entsize = sizeof(Elf_Sym);
1360 // Write the internal symbol table contents to the output symbol table.
1361 template <class ELFT> void SymbolTableSection<ELFT>::writeTo(uint8_t *Buf) {
1362 // The first entry is a null entry as per the ELF spec.
1363 Buf += sizeof(Elf_Sym);
1365 auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
1367 for (SymbolTableEntry &Ent : Symbols) {
1368 SymbolBody *Body = Ent.Symbol;
1370 // Set st_info and st_other.
1371 if (Body->isLocal()) {
1372 ESym->setBindingAndType(STB_LOCAL, Body->Type);
1374 ESym->setBindingAndType(Body->symbol()->computeBinding(), Body->Type);
1375 ESym->setVisibility(Body->symbol()->Visibility);
1378 ESym->st_name = Ent.StrTabOffset;
1379 ESym->st_size = Body->getSize<ELFT>();
1381 // Set a section index.
1382 if (const OutputSection *OutSec = Body->getOutputSection())
1383 ESym->st_shndx = OutSec->SectionIndex;
1384 else if (isa<DefinedRegular>(Body))
1385 ESym->st_shndx = SHN_ABS;
1386 else if (isa<DefinedCommon>(Body))
1387 ESym->st_shndx = SHN_COMMON;
1389 // st_value is usually an address of a symbol, but that has a
1390 // special meaining for uninstantiated common symbols (this can
1391 // occur if -r is given).
1392 if (!Config->DefineCommon && isa<DefinedCommon>(Body))
1393 ESym->st_value = cast<DefinedCommon>(Body)->Alignment;
1395 ESym->st_value = Body->getVA();
1400 // On MIPS we need to mark symbol which has a PLT entry and requires
1401 // pointer equality by STO_MIPS_PLT flag. That is necessary to help
1402 // dynamic linker distinguish such symbols and MIPS lazy-binding stubs.
1403 // https://sourceware.org/ml/binutils/2008-07/txt00000.txt
1404 if (Config->EMachine == EM_MIPS) {
1405 auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
1407 for (SymbolTableEntry &Ent : Symbols) {
1408 SymbolBody *Body = Ent.Symbol;
1409 if (Body->isInPlt() && Body->NeedsPltAddr)
1410 ESym->st_other |= STO_MIPS_PLT;
1412 if (Config->Relocatable)
1413 if (auto *D = dyn_cast<DefinedRegular>(Body))
1414 if (D->isMipsPIC<ELFT>())
1415 ESym->st_other |= STO_MIPS_PIC;
1421 // .hash and .gnu.hash sections contain on-disk hash tables that map
1422 // symbol names to their dynamic symbol table indices. Their purpose
1423 // is to help the dynamic linker resolve symbols quickly. If ELF files
1424 // don't have them, the dynamic linker has to do linear search on all
1425 // dynamic symbols, which makes programs slower. Therefore, a .hash
1426 // section is added to a DSO by default. A .gnu.hash is added if you
1427 // give the -hash-style=gnu or -hash-style=both option.
1429 // The Unix semantics of resolving dynamic symbols is somewhat expensive.
1430 // Each ELF file has a list of DSOs that the ELF file depends on and a
1431 // list of dynamic symbols that need to be resolved from any of the
1432 // DSOs. That means resolving all dynamic symbols takes O(m)*O(n)
1433 // where m is the number of DSOs and n is the number of dynamic
1434 // symbols. For modern large programs, both m and n are large. So
1435 // making each step faster by using hash tables substiantially
1436 // improves time to load programs.
1438 // (Note that this is not the only way to design the shared library.
1439 // For instance, the Windows DLL takes a different approach. On
1440 // Windows, each dynamic symbol has a name of DLL from which the symbol
1441 // has to be resolved. That makes the cost of symbol resolution O(n).
1442 // This disables some hacky techniques you can use on Unix such as
1443 // LD_PRELOAD, but this is arguably better semantics than the Unix ones.)
1445 // Due to historical reasons, we have two different hash tables, .hash
1446 // and .gnu.hash. They are for the same purpose, and .gnu.hash is a new
1447 // and better version of .hash. .hash is just an on-disk hash table, but
1448 // .gnu.hash has a bloom filter in addition to a hash table to skip
1449 // DSOs very quickly. If you are sure that your dynamic linker knows
1450 // about .gnu.hash, you want to specify -hash-style=gnu. Otherwise, a
1451 // safe bet is to specify -hash-style=both for backward compatibilty.
1452 GnuHashTableSection::GnuHashTableSection()
1453 : SyntheticSection(SHF_ALLOC, SHT_GNU_HASH, Config->Wordsize, ".gnu.hash") {
1456 void GnuHashTableSection::finalizeContents() {
1457 getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
1459 // Computes bloom filter size in word size. We want to allocate 8
1460 // bits for each symbol. It must be a power of two.
1461 if (Symbols.empty())
1464 MaskWords = NextPowerOf2((Symbols.size() - 1) / Config->Wordsize);
1466 Size = 16; // Header
1467 Size += Config->Wordsize * MaskWords; // Bloom filter
1468 Size += NBuckets * 4; // Hash buckets
1469 Size += Symbols.size() * 4; // Hash values
1472 void GnuHashTableSection::writeTo(uint8_t *Buf) {
1474 write32(Buf, NBuckets, Config->Endianness);
1475 write32(Buf + 4, InX::DynSymTab->getNumSymbols() - Symbols.size(),
1476 Config->Endianness);
1477 write32(Buf + 8, MaskWords, Config->Endianness);
1478 write32(Buf + 12, getShift2(), Config->Endianness);
1481 // Write a bloom filter and a hash table.
1482 writeBloomFilter(Buf);
1483 Buf += Config->Wordsize * MaskWords;
1484 writeHashTable(Buf);
1487 // This function writes a 2-bit bloom filter. This bloom filter alone
1488 // usually filters out 80% or more of all symbol lookups [1].
1489 // The dynamic linker uses the hash table only when a symbol is not
1490 // filtered out by a bloom filter.
1492 // [1] Ulrich Drepper (2011), "How To Write Shared Libraries" (Ver. 4.1.2),
1493 // p.9, https://www.akkadia.org/drepper/dsohowto.pdf
1494 void GnuHashTableSection::writeBloomFilter(uint8_t *Buf) {
1495 const unsigned C = Config->Wordsize * 8;
1496 for (const Entry &Sym : Symbols) {
1497 size_t I = (Sym.Hash / C) & (MaskWords - 1);
1498 uint64_t Val = readUint(Buf + I * Config->Wordsize);
1499 Val |= uint64_t(1) << (Sym.Hash % C);
1500 Val |= uint64_t(1) << ((Sym.Hash >> getShift2()) % C);
1501 writeUint(Buf + I * Config->Wordsize, Val);
1505 void GnuHashTableSection::writeHashTable(uint8_t *Buf) {
1506 // Group symbols by hash value.
1507 std::vector<std::vector<Entry>> Syms(NBuckets);
1508 for (const Entry &Ent : Symbols)
1509 Syms[Ent.Hash % NBuckets].push_back(Ent);
1511 // Write hash buckets. Hash buckets contain indices in the following
1512 // hash value table.
1513 uint32_t *Buckets = reinterpret_cast<uint32_t *>(Buf);
1514 for (size_t I = 0; I < NBuckets; ++I)
1515 if (!Syms[I].empty())
1516 write32(Buckets + I, Syms[I][0].Body->DynsymIndex, Config->Endianness);
1518 // Write a hash value table. It represents a sequence of chains that
1519 // share the same hash modulo value. The last element of each chain
1520 // is terminated by LSB 1.
1521 uint32_t *Values = Buckets + NBuckets;
1523 for (std::vector<Entry> &Vec : Syms) {
1526 for (const Entry &Ent : makeArrayRef(Vec).drop_back())
1527 write32(Values + I++, Ent.Hash & ~1, Config->Endianness);
1528 write32(Values + I++, Vec.back().Hash | 1, Config->Endianness);
1532 static uint32_t hashGnu(StringRef Name) {
1534 for (uint8_t C : Name)
1535 H = (H << 5) + H + C;
1539 // Returns a number of hash buckets to accomodate given number of elements.
1540 // We want to choose a moderate number that is not too small (which
1541 // causes too many hash collisions) and not too large (which wastes
1544 // We return a prime number because it (is believed to) achieve good
1545 // hash distribution.
1546 static size_t getBucketSize(size_t NumSymbols) {
1547 // List of largest prime numbers that are not greater than 2^n + 1.
1548 for (size_t N : {131071, 65521, 32749, 16381, 8191, 4093, 2039, 1021, 509,
1549 251, 127, 61, 31, 13, 7, 3, 1})
1550 if (N <= NumSymbols)
1555 // Add symbols to this symbol hash table. Note that this function
1556 // destructively sort a given vector -- which is needed because
1557 // GNU-style hash table places some sorting requirements.
1558 void GnuHashTableSection::addSymbols(std::vector<SymbolTableEntry> &V) {
1559 // We cannot use 'auto' for Mid because GCC 6.1 cannot deduce
1560 // its type correctly.
1561 std::vector<SymbolTableEntry>::iterator Mid =
1562 std::stable_partition(V.begin(), V.end(), [](const SymbolTableEntry &S) {
1563 return S.Symbol->isUndefined();
1568 for (SymbolTableEntry &Ent : llvm::make_range(Mid, V.end())) {
1569 SymbolBody *B = Ent.Symbol;
1570 Symbols.push_back({B, Ent.StrTabOffset, hashGnu(B->getName())});
1573 NBuckets = getBucketSize(Symbols.size());
1574 std::stable_sort(Symbols.begin(), Symbols.end(),
1575 [&](const Entry &L, const Entry &R) {
1576 return L.Hash % NBuckets < R.Hash % NBuckets;
1579 V.erase(Mid, V.end());
1580 for (const Entry &Ent : Symbols)
1581 V.push_back({Ent.Body, Ent.StrTabOffset});
1584 template <class ELFT>
1585 HashTableSection<ELFT>::HashTableSection()
1586 : SyntheticSection(SHF_ALLOC, SHT_HASH, 4, ".hash") {
1590 template <class ELFT> void HashTableSection<ELFT>::finalizeContents() {
1591 getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
1593 unsigned NumEntries = 2; // nbucket and nchain.
1594 NumEntries += InX::DynSymTab->getNumSymbols(); // The chain entries.
1596 // Create as many buckets as there are symbols.
1597 // FIXME: This is simplistic. We can try to optimize it, but implementing
1598 // support for SHT_GNU_HASH is probably even more profitable.
1599 NumEntries += InX::DynSymTab->getNumSymbols();
1600 this->Size = NumEntries * 4;
1603 template <class ELFT> void HashTableSection<ELFT>::writeTo(uint8_t *Buf) {
1604 // A 32-bit integer type in the target endianness.
1605 typedef typename ELFT::Word Elf_Word;
1607 unsigned NumSymbols = InX::DynSymTab->getNumSymbols();
1609 auto *P = reinterpret_cast<Elf_Word *>(Buf);
1610 *P++ = NumSymbols; // nbucket
1611 *P++ = NumSymbols; // nchain
1613 Elf_Word *Buckets = P;
1614 Elf_Word *Chains = P + NumSymbols;
1616 for (const SymbolTableEntry &S : InX::DynSymTab->getSymbols()) {
1617 SymbolBody *Body = S.Symbol;
1618 StringRef Name = Body->getName();
1619 unsigned I = Body->DynsymIndex;
1620 uint32_t Hash = hashSysV(Name) % NumSymbols;
1621 Chains[I] = Buckets[Hash];
1626 PltSection::PltSection(size_t S)
1627 : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16, ".plt"),
1630 void PltSection::writeTo(uint8_t *Buf) {
1631 // At beginning of PLT but not the IPLT, we have code to call the dynamic
1632 // linker to resolve dynsyms at runtime. Write such code.
1633 if (HeaderSize != 0)
1634 Target->writePltHeader(Buf);
1635 size_t Off = HeaderSize;
1636 // The IPlt is immediately after the Plt, account for this in RelOff
1637 unsigned PltOff = getPltRelocOff();
1639 for (auto &I : Entries) {
1640 const SymbolBody *B = I.first;
1641 unsigned RelOff = I.second + PltOff;
1642 uint64_t Got = B->getGotPltVA();
1643 uint64_t Plt = this->getVA() + Off;
1644 Target->writePlt(Buf + Off, Got, Plt, B->PltIndex, RelOff);
1645 Off += Target->PltEntrySize;
1649 template <class ELFT> void PltSection::addEntry(SymbolBody &Sym) {
1650 Sym.PltIndex = Entries.size();
1651 RelocationSection<ELFT> *PltRelocSection = In<ELFT>::RelaPlt;
1652 if (HeaderSize == 0) {
1653 PltRelocSection = In<ELFT>::RelaIplt;
1654 Sym.IsInIplt = true;
1656 unsigned RelOff = PltRelocSection->getRelocOffset();
1657 Entries.push_back(std::make_pair(&Sym, RelOff));
1660 size_t PltSection::getSize() const {
1661 return HeaderSize + Entries.size() * Target->PltEntrySize;
1664 // Some architectures such as additional symbols in the PLT section. For
1665 // example ARM uses mapping symbols to aid disassembly
1666 void PltSection::addSymbols() {
1667 // The PLT may have symbols defined for the Header, the IPLT has no header
1668 if (HeaderSize != 0)
1669 Target->addPltHeaderSymbols(this);
1670 size_t Off = HeaderSize;
1671 for (size_t I = 0; I < Entries.size(); ++I) {
1672 Target->addPltSymbols(this, Off);
1673 Off += Target->PltEntrySize;
1677 unsigned PltSection::getPltRelocOff() const {
1678 return (HeaderSize == 0) ? InX::Plt->getSize() : 0;
1681 GdbIndexSection::GdbIndexSection()
1682 : SyntheticSection(0, SHT_PROGBITS, 1, ".gdb_index"),
1683 StringPool(llvm::StringTableBuilder::ELF) {}
1685 // Iterative hash function for symbol's name is described in .gdb_index format
1686 // specification. Note that we use one for version 5 to 7 here, it is different
1688 static uint32_t hash(StringRef Str) {
1690 for (uint8_t C : Str)
1691 R = R * 67 + tolower(C) - 113;
1695 static std::vector<CompilationUnitEntry> readCuList(DWARFContext &Dwarf,
1696 InputSection *Sec) {
1697 std::vector<CompilationUnitEntry> Ret;
1698 for (std::unique_ptr<DWARFCompileUnit> &CU : Dwarf.compile_units())
1699 Ret.push_back({Sec->OutSecOff + CU->getOffset(), CU->getLength() + 4});
1703 static std::vector<AddressEntry> readAddressArea(DWARFContext &Dwarf,
1704 InputSection *Sec) {
1705 std::vector<AddressEntry> Ret;
1707 uint32_t CurrentCu = 0;
1708 for (std::unique_ptr<DWARFCompileUnit> &CU : Dwarf.compile_units()) {
1709 DWARFAddressRangesVector Ranges;
1710 CU->collectAddressRanges(Ranges);
1712 ArrayRef<InputSectionBase *> Sections = Sec->File->getSections();
1713 for (DWARFAddressRange &R : Ranges) {
1714 InputSectionBase *S = Sections[R.SectionIndex];
1715 if (!S || S == &InputSection::Discarded || !S->Live)
1717 // Range list with zero size has no effect.
1718 if (R.LowPC == R.HighPC)
1720 Ret.push_back({cast<InputSection>(S), R.LowPC, R.HighPC, CurrentCu});
1727 static std::vector<NameTypeEntry> readPubNamesAndTypes(DWARFContext &Dwarf,
1729 StringRef Data[] = {Dwarf.getGnuPubNamesSection(),
1730 Dwarf.getGnuPubTypesSection()};
1732 std::vector<NameTypeEntry> Ret;
1733 for (StringRef D : Data) {
1734 DWARFDebugPubTable PubTable(D, IsLE, true);
1735 for (const DWARFDebugPubTable::Set &Set : PubTable.getData())
1736 for (const DWARFDebugPubTable::Entry &Ent : Set.Entries)
1737 Ret.push_back({Ent.Name, Ent.Descriptor.toBits()});
1742 static std::vector<InputSection *> getDebugInfoSections() {
1743 std::vector<InputSection *> Ret;
1744 for (InputSectionBase *S : InputSections)
1745 if (InputSection *IS = dyn_cast<InputSection>(S))
1746 if (IS->getParent() && IS->Name == ".debug_info")
1751 void GdbIndexSection::buildIndex() {
1752 std::vector<InputSection *> V = getDebugInfoSections();
1756 for (InputSection *Sec : V)
1757 Chunks.push_back(readDwarf(Sec));
1760 for (GdbIndexChunk &D : Chunks) {
1761 for (AddressEntry &E : D.AddressArea)
1764 // Populate constant pool area.
1765 for (NameTypeEntry &NameType : D.NamesAndTypes) {
1766 uint32_t Hash = hash(NameType.Name);
1767 size_t Offset = StringPool.add(NameType.Name);
1771 std::tie(IsNew, Sym) = SymbolTable.add(Hash, Offset);
1773 Sym->CuVectorIndex = CuVectors.size();
1774 CuVectors.resize(CuVectors.size() + 1);
1777 CuVectors[Sym->CuVectorIndex].insert(CuId | (NameType.Type << 24));
1780 CuId += D.CompilationUnits.size();
1784 GdbIndexChunk GdbIndexSection::readDwarf(InputSection *Sec) {
1785 Expected<std::unique_ptr<object::ObjectFile>> Obj =
1786 object::ObjectFile::createObjectFile(Sec->File->MB);
1788 error(toString(Sec->File) + ": error creating DWARF context");
1792 DWARFContextInMemory Dwarf(*Obj.get());
1795 Ret.CompilationUnits = readCuList(Dwarf, Sec);
1796 Ret.AddressArea = readAddressArea(Dwarf, Sec);
1797 Ret.NamesAndTypes = readPubNamesAndTypes(Dwarf, Config->IsLE);
1801 static size_t getCuSize(std::vector<GdbIndexChunk> &C) {
1803 for (GdbIndexChunk &D : C)
1804 Ret += D.CompilationUnits.size();
1808 static size_t getAddressAreaSize(std::vector<GdbIndexChunk> &C) {
1810 for (GdbIndexChunk &D : C)
1811 Ret += D.AddressArea.size();
1815 void GdbIndexSection::finalizeContents() {
1822 SymbolTable.finalizeContents();
1824 // GdbIndex header consist from version fields
1825 // and 5 more fields with different kinds of offsets.
1826 CuTypesOffset = CuListOffset + getCuSize(Chunks) * CompilationUnitSize;
1827 SymTabOffset = CuTypesOffset + getAddressAreaSize(Chunks) * AddressEntrySize;
1829 ConstantPoolOffset =
1830 SymTabOffset + SymbolTable.getCapacity() * SymTabEntrySize;
1832 for (std::set<uint32_t> &CuVec : CuVectors) {
1833 CuVectorsOffset.push_back(CuVectorsSize);
1834 CuVectorsSize += OffsetTypeSize * (CuVec.size() + 1);
1836 StringPoolOffset = ConstantPoolOffset + CuVectorsSize;
1838 StringPool.finalizeInOrder();
1841 size_t GdbIndexSection::getSize() const {
1842 const_cast<GdbIndexSection *>(this)->finalizeContents();
1843 return StringPoolOffset + StringPool.getSize();
1846 void GdbIndexSection::writeTo(uint8_t *Buf) {
1847 write32le(Buf, 7); // Write version.
1848 write32le(Buf + 4, CuListOffset); // CU list offset.
1849 write32le(Buf + 8, CuTypesOffset); // Types CU list offset.
1850 write32le(Buf + 12, CuTypesOffset); // Address area offset.
1851 write32le(Buf + 16, SymTabOffset); // Symbol table offset.
1852 write32le(Buf + 20, ConstantPoolOffset); // Constant pool offset.
1855 // Write the CU list.
1856 for (GdbIndexChunk &D : Chunks) {
1857 for (CompilationUnitEntry &Cu : D.CompilationUnits) {
1858 write64le(Buf, Cu.CuOffset);
1859 write64le(Buf + 8, Cu.CuLength);
1864 // Write the address area.
1865 for (GdbIndexChunk &D : Chunks) {
1866 for (AddressEntry &E : D.AddressArea) {
1868 E.Section->getParent()->Addr + E.Section->getOffset(0);
1869 write64le(Buf, BaseAddr + E.LowAddress);
1870 write64le(Buf + 8, BaseAddr + E.HighAddress);
1871 write32le(Buf + 16, E.CuIndex);
1876 // Write the symbol table.
1877 for (size_t I = 0; I < SymbolTable.getCapacity(); ++I) {
1878 GdbSymbol *Sym = SymbolTable.getSymbol(I);
1881 Sym->NameOffset + StringPoolOffset - ConstantPoolOffset;
1882 size_t CuVectorOffset = CuVectorsOffset[Sym->CuVectorIndex];
1883 write32le(Buf, NameOffset);
1884 write32le(Buf + 4, CuVectorOffset);
1889 // Write the CU vectors into the constant pool.
1890 for (std::set<uint32_t> &CuVec : CuVectors) {
1891 write32le(Buf, CuVec.size());
1893 for (uint32_t Val : CuVec) {
1894 write32le(Buf, Val);
1899 StringPool.write(Buf);
1902 bool GdbIndexSection::empty() const {
1903 return !Out::DebugInfo;
1906 template <class ELFT>
1907 EhFrameHeader<ELFT>::EhFrameHeader()
1908 : SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 1, ".eh_frame_hdr") {}
1910 // .eh_frame_hdr contains a binary search table of pointers to FDEs.
1911 // Each entry of the search table consists of two values,
1912 // the starting PC from where FDEs covers, and the FDE's address.
1913 // It is sorted by PC.
1914 template <class ELFT> void EhFrameHeader<ELFT>::writeTo(uint8_t *Buf) {
1915 const endianness E = ELFT::TargetEndianness;
1917 // Sort the FDE list by their PC and uniqueify. Usually there is only
1918 // one FDE for a PC (i.e. function), but if ICF merges two functions
1919 // into one, there can be more than one FDEs pointing to the address.
1920 auto Less = [](const FdeData &A, const FdeData &B) { return A.Pc < B.Pc; };
1921 std::stable_sort(Fdes.begin(), Fdes.end(), Less);
1922 auto Eq = [](const FdeData &A, const FdeData &B) { return A.Pc == B.Pc; };
1923 Fdes.erase(std::unique(Fdes.begin(), Fdes.end(), Eq), Fdes.end());
1926 Buf[1] = DW_EH_PE_pcrel | DW_EH_PE_sdata4;
1927 Buf[2] = DW_EH_PE_udata4;
1928 Buf[3] = DW_EH_PE_datarel | DW_EH_PE_sdata4;
1929 write32<E>(Buf + 4, In<ELFT>::EhFrame->getParent()->Addr - this->getVA() - 4);
1930 write32<E>(Buf + 8, Fdes.size());
1933 uint64_t VA = this->getVA();
1934 for (FdeData &Fde : Fdes) {
1935 write32<E>(Buf, Fde.Pc - VA);
1936 write32<E>(Buf + 4, Fde.FdeVA - VA);
1941 template <class ELFT> size_t EhFrameHeader<ELFT>::getSize() const {
1942 // .eh_frame_hdr has a 12 bytes header followed by an array of FDEs.
1943 return 12 + In<ELFT>::EhFrame->NumFdes * 8;
1946 template <class ELFT>
1947 void EhFrameHeader<ELFT>::addFde(uint32_t Pc, uint32_t FdeVA) {
1948 Fdes.push_back({Pc, FdeVA});
1951 template <class ELFT> bool EhFrameHeader<ELFT>::empty() const {
1952 return In<ELFT>::EhFrame->empty();
1955 template <class ELFT>
1956 VersionDefinitionSection<ELFT>::VersionDefinitionSection()
1957 : SyntheticSection(SHF_ALLOC, SHT_GNU_verdef, sizeof(uint32_t),
1958 ".gnu.version_d") {}
1960 static StringRef getFileDefName() {
1961 if (!Config->SoName.empty())
1962 return Config->SoName;
1963 return Config->OutputFile;
1966 template <class ELFT> void VersionDefinitionSection<ELFT>::finalizeContents() {
1967 FileDefNameOff = InX::DynStrTab->addString(getFileDefName());
1968 for (VersionDefinition &V : Config->VersionDefinitions)
1969 V.NameOff = InX::DynStrTab->addString(V.Name);
1971 getParent()->Link = InX::DynStrTab->getParent()->SectionIndex;
1973 // sh_info should be set to the number of definitions. This fact is missed in
1974 // documentation, but confirmed by binutils community:
1975 // https://sourceware.org/ml/binutils/2014-11/msg00355.html
1976 getParent()->Info = getVerDefNum();
1979 template <class ELFT>
1980 void VersionDefinitionSection<ELFT>::writeOne(uint8_t *Buf, uint32_t Index,
1981 StringRef Name, size_t NameOff) {
1982 auto *Verdef = reinterpret_cast<Elf_Verdef *>(Buf);
1983 Verdef->vd_version = 1;
1985 Verdef->vd_aux = sizeof(Elf_Verdef);
1986 Verdef->vd_next = sizeof(Elf_Verdef) + sizeof(Elf_Verdaux);
1987 Verdef->vd_flags = (Index == 1 ? VER_FLG_BASE : 0);
1988 Verdef->vd_ndx = Index;
1989 Verdef->vd_hash = hashSysV(Name);
1991 auto *Verdaux = reinterpret_cast<Elf_Verdaux *>(Buf + sizeof(Elf_Verdef));
1992 Verdaux->vda_name = NameOff;
1993 Verdaux->vda_next = 0;
1996 template <class ELFT>
1997 void VersionDefinitionSection<ELFT>::writeTo(uint8_t *Buf) {
1998 writeOne(Buf, 1, getFileDefName(), FileDefNameOff);
2000 for (VersionDefinition &V : Config->VersionDefinitions) {
2001 Buf += sizeof(Elf_Verdef) + sizeof(Elf_Verdaux);
2002 writeOne(Buf, V.Id, V.Name, V.NameOff);
2005 // Need to terminate the last version definition.
2006 Elf_Verdef *Verdef = reinterpret_cast<Elf_Verdef *>(Buf);
2007 Verdef->vd_next = 0;
2010 template <class ELFT> size_t VersionDefinitionSection<ELFT>::getSize() const {
2011 return (sizeof(Elf_Verdef) + sizeof(Elf_Verdaux)) * getVerDefNum();
2014 template <class ELFT>
2015 VersionTableSection<ELFT>::VersionTableSection()
2016 : SyntheticSection(SHF_ALLOC, SHT_GNU_versym, sizeof(uint16_t),
2018 this->Entsize = sizeof(Elf_Versym);
2021 template <class ELFT> void VersionTableSection<ELFT>::finalizeContents() {
2022 // At the moment of june 2016 GNU docs does not mention that sh_link field
2023 // should be set, but Sun docs do. Also readelf relies on this field.
2024 getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
2027 template <class ELFT> size_t VersionTableSection<ELFT>::getSize() const {
2028 return sizeof(Elf_Versym) * (InX::DynSymTab->getSymbols().size() + 1);
2031 template <class ELFT> void VersionTableSection<ELFT>::writeTo(uint8_t *Buf) {
2032 auto *OutVersym = reinterpret_cast<Elf_Versym *>(Buf) + 1;
2033 for (const SymbolTableEntry &S : InX::DynSymTab->getSymbols()) {
2034 OutVersym->vs_index = S.Symbol->symbol()->VersionId;
2039 template <class ELFT> bool VersionTableSection<ELFT>::empty() const {
2040 return !In<ELFT>::VerDef && In<ELFT>::VerNeed->empty();
2043 template <class ELFT>
2044 VersionNeedSection<ELFT>::VersionNeedSection()
2045 : SyntheticSection(SHF_ALLOC, SHT_GNU_verneed, sizeof(uint32_t),
2047 // Identifiers in verneed section start at 2 because 0 and 1 are reserved
2048 // for VER_NDX_LOCAL and VER_NDX_GLOBAL.
2049 // First identifiers are reserved by verdef section if it exist.
2050 NextIndex = getVerDefNum() + 1;
2053 template <class ELFT>
2054 void VersionNeedSection<ELFT>::addSymbol(SharedSymbol *SS) {
2055 auto *Ver = reinterpret_cast<const typename ELFT::Verdef *>(SS->Verdef);
2057 SS->symbol()->VersionId = VER_NDX_GLOBAL;
2061 auto *File = cast<SharedFile<ELFT>>(SS->File);
2063 // If we don't already know that we need an Elf_Verneed for this DSO, prepare
2064 // to create one by adding it to our needed list and creating a dynstr entry
2066 if (File->VerdefMap.empty())
2067 Needed.push_back({File, InX::DynStrTab->addString(File->SoName)});
2068 typename SharedFile<ELFT>::NeededVer &NV = File->VerdefMap[Ver];
2069 // If we don't already know that we need an Elf_Vernaux for this Elf_Verdef,
2070 // prepare to create one by allocating a version identifier and creating a
2071 // dynstr entry for the version name.
2072 if (NV.Index == 0) {
2073 NV.StrTab = InX::DynStrTab->addString(File->getStringTable().data() +
2074 Ver->getAux()->vda_name);
2075 NV.Index = NextIndex++;
2077 SS->symbol()->VersionId = NV.Index;
2080 template <class ELFT> void VersionNeedSection<ELFT>::writeTo(uint8_t *Buf) {
2081 // The Elf_Verneeds need to appear first, followed by the Elf_Vernauxs.
2082 auto *Verneed = reinterpret_cast<Elf_Verneed *>(Buf);
2083 auto *Vernaux = reinterpret_cast<Elf_Vernaux *>(Verneed + Needed.size());
2085 for (std::pair<SharedFile<ELFT> *, size_t> &P : Needed) {
2086 // Create an Elf_Verneed for this DSO.
2087 Verneed->vn_version = 1;
2088 Verneed->vn_cnt = P.first->VerdefMap.size();
2089 Verneed->vn_file = P.second;
2091 reinterpret_cast<char *>(Vernaux) - reinterpret_cast<char *>(Verneed);
2092 Verneed->vn_next = sizeof(Elf_Verneed);
2095 // Create the Elf_Vernauxs for this Elf_Verneed. The loop iterates over
2096 // VerdefMap, which will only contain references to needed version
2097 // definitions. Each Elf_Vernaux is based on the information contained in
2098 // the Elf_Verdef in the source DSO. This loop iterates over a std::map of
2099 // pointers, but is deterministic because the pointers refer to Elf_Verdef
2100 // data structures within a single input file.
2101 for (auto &NV : P.first->VerdefMap) {
2102 Vernaux->vna_hash = NV.first->vd_hash;
2103 Vernaux->vna_flags = 0;
2104 Vernaux->vna_other = NV.second.Index;
2105 Vernaux->vna_name = NV.second.StrTab;
2106 Vernaux->vna_next = sizeof(Elf_Vernaux);
2110 Vernaux[-1].vna_next = 0;
2112 Verneed[-1].vn_next = 0;
2115 template <class ELFT> void VersionNeedSection<ELFT>::finalizeContents() {
2116 getParent()->Link = InX::DynStrTab->getParent()->SectionIndex;
2117 getParent()->Info = Needed.size();
2120 template <class ELFT> size_t VersionNeedSection<ELFT>::getSize() const {
2121 unsigned Size = Needed.size() * sizeof(Elf_Verneed);
2122 for (const std::pair<SharedFile<ELFT> *, size_t> &P : Needed)
2123 Size += P.first->VerdefMap.size() * sizeof(Elf_Vernaux);
2127 template <class ELFT> bool VersionNeedSection<ELFT>::empty() const {
2128 return getNeedNum() == 0;
2131 MergeSyntheticSection::MergeSyntheticSection(StringRef Name, uint32_t Type,
2132 uint64_t Flags, uint32_t Alignment)
2133 : SyntheticSection(Flags, Type, Alignment, Name),
2134 Builder(StringTableBuilder::RAW, Alignment) {}
2136 void MergeSyntheticSection::addSection(MergeInputSection *MS) {
2138 Sections.push_back(MS);
2141 void MergeSyntheticSection::writeTo(uint8_t *Buf) { Builder.write(Buf); }
2143 bool MergeSyntheticSection::shouldTailMerge() const {
2144 return (this->Flags & SHF_STRINGS) && Config->Optimize >= 2;
2147 void MergeSyntheticSection::finalizeTailMerge() {
2148 // Add all string pieces to the string table builder to create section
2150 for (MergeInputSection *Sec : Sections)
2151 for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
2152 if (Sec->Pieces[I].Live)
2153 Builder.add(Sec->getData(I));
2155 // Fix the string table content. After this, the contents will never change.
2158 // finalize() fixed tail-optimized strings, so we can now get
2159 // offsets of strings. Get an offset for each string and save it
2160 // to a corresponding StringPiece for easy access.
2161 for (MergeInputSection *Sec : Sections)
2162 for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
2163 if (Sec->Pieces[I].Live)
2164 Sec->Pieces[I].OutputOff = Builder.getOffset(Sec->getData(I));
2167 void MergeSyntheticSection::finalizeNoTailMerge() {
2168 // Add all string pieces to the string table builder to create section
2169 // contents. Because we are not tail-optimizing, offsets of strings are
2170 // fixed when they are added to the builder (string table builder contains
2171 // a hash table from strings to offsets).
2172 for (MergeInputSection *Sec : Sections)
2173 for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
2174 if (Sec->Pieces[I].Live)
2175 Sec->Pieces[I].OutputOff = Builder.add(Sec->getData(I));
2177 Builder.finalizeInOrder();
2180 void MergeSyntheticSection::finalizeContents() {
2181 if (shouldTailMerge())
2182 finalizeTailMerge();
2184 finalizeNoTailMerge();
2187 size_t MergeSyntheticSection::getSize() const {
2188 return Builder.getSize();
2191 // This function decompresses compressed sections and scans over the input
2192 // sections to create mergeable synthetic sections. It removes
2193 // MergeInputSections from the input section array and adds new synthetic
2194 // sections at the location of the first input section that it replaces. It then
2195 // finalizes each synthetic section in order to compute an output offset for
2196 // each piece of each input section.
2197 void elf::decompressAndMergeSections() {
2198 // splitIntoPieces needs to be called on each MergeInputSection before calling
2199 // finalizeContents(). Do that first.
2200 parallelForEach(InputSections.begin(), InputSections.end(),
2201 [](InputSectionBase *S) {
2204 if (Decompressor::isCompressedELFSection(S->Flags, S->Name))
2206 if (auto *MS = dyn_cast<MergeInputSection>(S))
2207 MS->splitIntoPieces();
2210 std::vector<MergeSyntheticSection *> MergeSections;
2211 for (InputSectionBase *&S : InputSections) {
2212 MergeInputSection *MS = dyn_cast<MergeInputSection>(S);
2216 // We do not want to handle sections that are not alive, so just remove
2217 // them instead of trying to merge.
2221 StringRef OutsecName = getOutputSectionName(MS->Name);
2222 uint64_t Flags = MS->Flags & ~(uint64_t)SHF_GROUP;
2223 uint32_t Alignment = std::max<uint32_t>(MS->Alignment, MS->Entsize);
2225 auto I = llvm::find_if(MergeSections, [=](MergeSyntheticSection *Sec) {
2226 return Sec->Name == OutsecName && Sec->Flags == Flags &&
2227 Sec->Alignment == Alignment;
2229 if (I == MergeSections.end()) {
2230 MergeSyntheticSection *Syn =
2231 make<MergeSyntheticSection>(OutsecName, MS->Type, Flags, Alignment);
2232 MergeSections.push_back(Syn);
2233 I = std::prev(MergeSections.end());
2238 (*I)->addSection(MS);
2240 for (auto *MS : MergeSections)
2241 MS->finalizeContents();
2243 std::vector<InputSectionBase *> &V = InputSections;
2244 V.erase(std::remove(V.begin(), V.end(), nullptr), V.end());
2247 MipsRldMapSection::MipsRldMapSection()
2248 : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, Config->Wordsize,
2251 ARMExidxSentinelSection::ARMExidxSentinelSection()
2252 : SyntheticSection(SHF_ALLOC | SHF_LINK_ORDER, SHT_ARM_EXIDX,
2253 Config->Wordsize, ".ARM.exidx") {}
2255 // Write a terminating sentinel entry to the end of the .ARM.exidx table.
2256 // This section will have been sorted last in the .ARM.exidx table.
2257 // This table entry will have the form:
2258 // | PREL31 upper bound of code that has exception tables | EXIDX_CANTUNWIND |
2259 // The sentinel must have the PREL31 value of an address higher than any
2260 // address described by any other table entry.
2261 void ARMExidxSentinelSection::writeTo(uint8_t *Buf) {
2262 // The Sections are sorted in order of ascending PREL31 address with the
2263 // sentinel last. We need to find the InputSection that precedes the
2264 // sentinel. By construction the Sentinel is in the last
2265 // InputSectionDescription as the InputSection that precedes it.
2266 OutputSectionCommand *C = Script->getCmd(getParent());
2267 auto ISD = std::find_if(C->Commands.rbegin(), C->Commands.rend(),
2268 [](const BaseCommand *Base) {
2269 return isa<InputSectionDescription>(Base);
2271 auto L = cast<InputSectionDescription>(*ISD);
2272 InputSection *Highest = L->Sections[L->Sections.size() - 2];
2273 InputSection *LS = Highest->getLinkOrderDep();
2274 uint64_t S = LS->getParent()->Addr + LS->getOffset(LS->getSize());
2275 uint64_t P = getVA();
2276 Target->relocateOne(Buf, R_ARM_PREL31, S - P);
2277 write32le(Buf + 4, 0x1);
2280 ThunkSection::ThunkSection(OutputSection *OS, uint64_t Off)
2281 : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS,
2282 Config->Wordsize, ".text.thunk") {
2284 this->OutSecOff = Off;
2287 void ThunkSection::addThunk(Thunk *T) {
2288 uint64_t Off = alignTo(Size, T->alignment);
2290 Thunks.push_back(T);
2291 T->addSymbols(*this);
2292 Size = Off + T->size();
2295 void ThunkSection::writeTo(uint8_t *Buf) {
2296 for (const Thunk *T : Thunks)
2297 T->writeTo(Buf + T->Offset, *this);
2300 InputSection *ThunkSection::getTargetInputSection() const {
2301 const Thunk *T = Thunks.front();
2302 return T->getTargetInputSection();
2305 InputSection *InX::ARMAttributes;
2306 BssSection *InX::Bss;
2307 BssSection *InX::BssRelRo;
2308 BuildIdSection *InX::BuildId;
2309 InputSection *InX::Common;
2310 SyntheticSection *InX::Dynamic;
2311 StringTableSection *InX::DynStrTab;
2312 SymbolTableBaseSection *InX::DynSymTab;
2313 InputSection *InX::Interp;
2314 GdbIndexSection *InX::GdbIndex;
2315 GotSection *InX::Got;
2316 GotPltSection *InX::GotPlt;
2317 GnuHashTableSection *InX::GnuHashTab;
2318 IgotPltSection *InX::IgotPlt;
2319 MipsGotSection *InX::MipsGot;
2320 MipsRldMapSection *InX::MipsRldMap;
2321 PltSection *InX::Plt;
2322 PltSection *InX::Iplt;
2323 StringTableSection *InX::ShStrTab;
2324 StringTableSection *InX::StrTab;
2325 SymbolTableBaseSection *InX::SymTab;
2327 template void PltSection::addEntry<ELF32LE>(SymbolBody &Sym);
2328 template void PltSection::addEntry<ELF32BE>(SymbolBody &Sym);
2329 template void PltSection::addEntry<ELF64LE>(SymbolBody &Sym);
2330 template void PltSection::addEntry<ELF64BE>(SymbolBody &Sym);
2332 template InputSection *elf::createCommonSection<ELF32LE>();
2333 template InputSection *elf::createCommonSection<ELF32BE>();
2334 template InputSection *elf::createCommonSection<ELF64LE>();
2335 template InputSection *elf::createCommonSection<ELF64BE>();
2337 template MergeInputSection *elf::createCommentSection<ELF32LE>();
2338 template MergeInputSection *elf::createCommentSection<ELF32BE>();
2339 template MergeInputSection *elf::createCommentSection<ELF64LE>();
2340 template MergeInputSection *elf::createCommentSection<ELF64BE>();
2342 template class elf::MipsAbiFlagsSection<ELF32LE>;
2343 template class elf::MipsAbiFlagsSection<ELF32BE>;
2344 template class elf::MipsAbiFlagsSection<ELF64LE>;
2345 template class elf::MipsAbiFlagsSection<ELF64BE>;
2347 template class elf::MipsOptionsSection<ELF32LE>;
2348 template class elf::MipsOptionsSection<ELF32BE>;
2349 template class elf::MipsOptionsSection<ELF64LE>;
2350 template class elf::MipsOptionsSection<ELF64BE>;
2352 template class elf::MipsReginfoSection<ELF32LE>;
2353 template class elf::MipsReginfoSection<ELF32BE>;
2354 template class elf::MipsReginfoSection<ELF64LE>;
2355 template class elf::MipsReginfoSection<ELF64BE>;
2357 template class elf::DynamicSection<ELF32LE>;
2358 template class elf::DynamicSection<ELF32BE>;
2359 template class elf::DynamicSection<ELF64LE>;
2360 template class elf::DynamicSection<ELF64BE>;
2362 template class elf::RelocationSection<ELF32LE>;
2363 template class elf::RelocationSection<ELF32BE>;
2364 template class elf::RelocationSection<ELF64LE>;
2365 template class elf::RelocationSection<ELF64BE>;
2367 template class elf::SymbolTableSection<ELF32LE>;
2368 template class elf::SymbolTableSection<ELF32BE>;
2369 template class elf::SymbolTableSection<ELF64LE>;
2370 template class elf::SymbolTableSection<ELF64BE>;
2372 template class elf::HashTableSection<ELF32LE>;
2373 template class elf::HashTableSection<ELF32BE>;
2374 template class elf::HashTableSection<ELF64LE>;
2375 template class elf::HashTableSection<ELF64BE>;
2377 template class elf::EhFrameHeader<ELF32LE>;
2378 template class elf::EhFrameHeader<ELF32BE>;
2379 template class elf::EhFrameHeader<ELF64LE>;
2380 template class elf::EhFrameHeader<ELF64BE>;
2382 template class elf::VersionTableSection<ELF32LE>;
2383 template class elf::VersionTableSection<ELF32BE>;
2384 template class elf::VersionTableSection<ELF64LE>;
2385 template class elf::VersionTableSection<ELF64BE>;
2387 template class elf::VersionNeedSection<ELF32LE>;
2388 template class elf::VersionNeedSection<ELF32BE>;
2389 template class elf::VersionNeedSection<ELF64LE>;
2390 template class elf::VersionNeedSection<ELF64BE>;
2392 template class elf::VersionDefinitionSection<ELF32LE>;
2393 template class elf::VersionDefinitionSection<ELF32BE>;
2394 template class elf::VersionDefinitionSection<ELF64LE>;
2395 template class elf::VersionDefinitionSection<ELF64BE>;
2397 template class elf::EhFrameSection<ELF32LE>;
2398 template class elf::EhFrameSection<ELF32BE>;
2399 template class elf::EhFrameSection<ELF64LE>;
2400 template class elf::EhFrameSection<ELF64BE>;