1 //===- lib/MC/ELFObjectWriter.cpp - ELF File Writer -----------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements ELF object file writer information.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/MC/MCELFObjectWriter.h"
15 #include "llvm/ADT/STLExtras.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/ADT/SmallString.h"
18 #include "llvm/ADT/StringMap.h"
19 #include "llvm/MC/MCAsmBackend.h"
20 #include "llvm/MC/MCAsmInfo.h"
21 #include "llvm/MC/MCAsmLayout.h"
22 #include "llvm/MC/MCAssembler.h"
23 #include "llvm/MC/MCContext.h"
24 #include "llvm/MC/MCELF.h"
25 #include "llvm/MC/MCELFSymbolFlags.h"
26 #include "llvm/MC/MCExpr.h"
27 #include "llvm/MC/MCFixupKindInfo.h"
28 #include "llvm/MC/MCObjectWriter.h"
29 #include "llvm/MC/MCSectionELF.h"
30 #include "llvm/MC/MCValue.h"
31 #include "llvm/MC/StringTableBuilder.h"
32 #include "llvm/Support/Compression.h"
33 #include "llvm/Support/Debug.h"
34 #include "llvm/Support/ELF.h"
35 #include "llvm/Support/Endian.h"
36 #include "llvm/Support/ErrorHandling.h"
41 #define DEBUG_TYPE "reloc-info"
45 typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
47 class ELFObjectWriter;
49 class SymbolTableWriter {
50 ELFObjectWriter &EWriter;
53 // indexes we are going to write to .symtab_shndx.
54 std::vector<uint32_t> ShndxIndexes;
56 // The numbel of symbols written so far.
59 void createSymtabShndx();
61 template <typename T> void write(T Value);
64 SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit);
66 void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
67 uint8_t other, uint32_t shndx, bool Reserved);
69 ArrayRef<uint32_t> getShndxIndexes() const { return ShndxIndexes; }
72 class ELFObjectWriter : public MCObjectWriter {
73 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
74 static uint64_t SymbolValue(const MCSymbol &Sym, const MCAsmLayout &Layout);
75 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbol &Symbol,
76 bool Used, bool Renamed);
77 static bool isLocal(const MCSymbol &Symbol, bool isUsedInReloc);
79 /// Helper struct for containing some precomputed information on symbols.
80 struct ELFSymbolData {
81 const MCSymbol *Symbol;
83 uint32_t SectionIndex;
86 // Support lexicographic sorting.
87 bool operator<(const ELFSymbolData &RHS) const {
88 unsigned LHSType = MCELF::GetType(Symbol->getData());
89 unsigned RHSType = MCELF::GetType(RHS.Symbol->getData());
90 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
92 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
94 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
95 return SectionIndex < RHS.SectionIndex;
96 return Name < RHS.Name;
100 /// The target specific ELF writer instance.
101 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
103 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
104 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
105 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
107 llvm::DenseMap<const MCSectionELF *, std::vector<ELFRelocationEntry>>
111 /// @name Symbol Table Data
114 StringTableBuilder StrTabBuilder;
115 std::vector<ELFSymbolData> LocalSymbolData;
116 std::vector<ELFSymbolData> ExternalSymbolData;
117 std::vector<ELFSymbolData> UndefinedSymbolData;
121 // This holds the symbol table index of the last local symbol.
122 unsigned LastLocalSymbolIndex;
123 // This holds the .strtab section index.
124 unsigned StringTableIndex;
125 // This holds the .symtab section index.
126 unsigned SymbolTableIndex;
127 // This holds the .symtab_shndx section index.
128 unsigned SymtabShndxSectionIndex = 0;
130 // Sections in the order they are to be output in the section table.
131 std::vector<const MCSectionELF *> SectionTable;
132 unsigned addToSectionTable(const MCSectionELF *Sec);
134 // TargetObjectWriter wrappers.
135 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
136 bool hasRelocationAddend() const {
137 return TargetObjectWriter->hasRelocationAddend();
139 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
140 bool IsPCRel) const {
141 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
145 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
147 : MCObjectWriter(OS, IsLittleEndian), TargetObjectWriter(MOTW) {}
149 void reset() override {
151 WeakrefUsedInReloc.clear();
154 StrTabBuilder.clear();
155 LocalSymbolData.clear();
156 ExternalSymbolData.clear();
157 UndefinedSymbolData.clear();
158 SectionTable.clear();
159 MCObjectWriter::reset();
162 ~ELFObjectWriter() override;
164 void WriteWord(uint64_t W) {
171 template <typename T> void write(T Val) {
173 support::endian::Writer<support::little>(OS).write(Val);
175 support::endian::Writer<support::big>(OS).write(Val);
178 void writeHeader(const MCAssembler &Asm);
180 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
181 const MCAsmLayout &Layout);
183 // Start and end offset of each section
184 typedef std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>
187 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
188 const MCSymbolRefExpr *RefA,
189 const MCSymbol *Sym, uint64_t C,
190 unsigned Type) const;
192 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
193 const MCFragment *Fragment, const MCFixup &Fixup,
194 MCValue Target, bool &IsPCRel,
195 uint64_t &FixedValue) override;
197 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
200 // Map from a signature symbol to the group section index
201 typedef DenseMap<const MCSymbol *, unsigned> RevGroupMapTy;
203 /// Compute the symbol table data
205 /// \param Asm - The assembler.
206 /// \param SectionIndexMap - Maps a section to its index.
207 /// \param RevGroupMap - Maps a signature symbol to the group section.
208 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
209 const SectionIndexMapTy &SectionIndexMap,
210 const RevGroupMapTy &RevGroupMap,
211 SectionOffsetsTy &SectionOffsets);
213 MCSectionELF *createRelocationSection(MCContext &Ctx,
214 const MCSectionELF &Sec);
216 const MCSectionELF *createStringTable(MCContext &Ctx);
218 void ExecutePostLayoutBinding(MCAssembler &Asm,
219 const MCAsmLayout &Layout) override;
221 void writeSectionHeader(const MCAssembler &Asm, const MCAsmLayout &Layout,
222 const SectionIndexMapTy &SectionIndexMap,
223 const SectionOffsetsTy &SectionOffsets);
225 void writeSectionData(const MCAssembler &Asm, MCSection &Sec,
226 const MCAsmLayout &Layout);
228 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
229 uint64_t Address, uint64_t Offset, uint64_t Size,
230 uint32_t Link, uint32_t Info, uint64_t Alignment,
233 void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
235 bool IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
236 const MCSymbol &SymA,
237 const MCFragment &FB,
239 bool IsPCRel) const override;
241 bool isWeak(const MCSymbol &Sym) const override;
243 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
244 void writeSection(const SectionIndexMapTy &SectionIndexMap,
245 uint32_t GroupSymbolIndex, uint64_t Offset, uint64_t Size,
246 const MCSectionELF &Section);
250 unsigned ELFObjectWriter::addToSectionTable(const MCSectionELF *Sec) {
251 SectionTable.push_back(Sec);
252 StrTabBuilder.add(Sec->getSectionName());
253 return SectionTable.size();
256 void SymbolTableWriter::createSymtabShndx() {
257 if (!ShndxIndexes.empty())
260 ShndxIndexes.resize(NumWritten);
263 template <typename T> void SymbolTableWriter::write(T Value) {
264 EWriter.write(Value);
267 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
268 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
270 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
271 uint64_t size, uint8_t other,
272 uint32_t shndx, bool Reserved) {
273 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
278 if (!ShndxIndexes.empty()) {
280 ShndxIndexes.push_back(shndx);
282 ShndxIndexes.push_back(0);
285 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
288 write(name); // st_name
289 write(info); // st_info
290 write(other); // st_other
291 write(Index); // st_shndx
292 write(value); // st_value
293 write(size); // st_size
295 write(name); // st_name
296 write(uint32_t(value)); // st_value
297 write(uint32_t(size)); // st_size
298 write(info); // st_info
299 write(other); // st_other
300 write(Index); // st_shndx
306 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
307 const MCFixupKindInfo &FKI =
308 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
310 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
313 ELFObjectWriter::~ELFObjectWriter()
316 // Emit the ELF header.
317 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
323 // emitWord method behaves differently for ELF32 and ELF64, writing
324 // 4 bytes in the former and 8 in the latter.
326 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
328 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
331 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
333 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
335 Write8(TargetObjectWriter->getOSABI());
336 Write8(0); // e_ident[EI_ABIVERSION]
338 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
340 Write16(ELF::ET_REL); // e_type
342 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
344 Write32(ELF::EV_CURRENT); // e_version
345 WriteWord(0); // e_entry, no entry point in .o file
346 WriteWord(0); // e_phoff, no program header for .o
347 WriteWord(0); // e_shoff = sec hdr table off in bytes
349 // e_flags = whatever the target wants
350 Write32(Asm.getELFHeaderEFlags());
352 // e_ehsize = ELF header size
353 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
355 Write16(0); // e_phentsize = prog header entry size
356 Write16(0); // e_phnum = # prog header entries = 0
358 // e_shentsize = Section header entry size
359 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
361 // e_shnum = # of section header ents
364 // e_shstrndx = Section # of '.shstrtab'
365 assert(StringTableIndex < ELF::SHN_LORESERVE);
366 Write16(StringTableIndex);
369 uint64_t ELFObjectWriter::SymbolValue(const MCSymbol &Sym,
370 const MCAsmLayout &Layout) {
371 MCSymbolData &Data = Sym.getData();
372 if (Data.isCommon() && Data.isExternal())
373 return Data.getCommonAlignment();
376 if (!Layout.getSymbolOffset(Sym, Res))
379 if (Layout.getAssembler().isThumbFunc(&Sym))
385 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
386 const MCAsmLayout &Layout) {
387 // The presence of symbol versions causes undefined symbols and
388 // versions declared with @@@ to be renamed.
390 for (const MCSymbol &Alias : Asm.symbols()) {
391 MCSymbolData &OriginalData = Alias.getData();
394 if (!Alias.isVariable())
396 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
399 const MCSymbol &Symbol = Ref->getSymbol();
400 MCSymbolData &SD = Asm.getSymbolData(Symbol);
402 StringRef AliasName = Alias.getName();
403 size_t Pos = AliasName.find('@');
404 if (Pos == StringRef::npos)
407 // Aliases defined with .symvar copy the binding from the symbol they alias.
408 // This is the first place we are able to copy this information.
409 OriginalData.setExternal(SD.isExternal());
410 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
412 StringRef Rest = AliasName.substr(Pos);
413 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
416 // FIXME: produce a better error message.
417 if (Symbol.isUndefined() && Rest.startswith("@@") &&
418 !Rest.startswith("@@@"))
419 report_fatal_error("A @@ version cannot be undefined");
421 Renames.insert(std::make_pair(&Symbol, &Alias));
425 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
426 uint8_t Type = newType;
428 // Propagation rules:
429 // IFUNC > FUNC > OBJECT > NOTYPE
430 // TLS_OBJECT > OBJECT > NOTYPE
432 // dont let the new type degrade the old type
436 case ELF::STT_GNU_IFUNC:
437 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
438 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
439 Type = ELF::STT_GNU_IFUNC;
442 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
443 Type == ELF::STT_TLS)
444 Type = ELF::STT_FUNC;
446 case ELF::STT_OBJECT:
447 if (Type == ELF::STT_NOTYPE)
448 Type = ELF::STT_OBJECT;
451 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
452 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
460 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
461 const MCAsmLayout &Layout) {
462 MCSymbolData &OrigData = MSD.Symbol->getData();
463 assert((!OrigData.getFragment() ||
464 (OrigData.getFragment()->getParent() == &MSD.Symbol->getSection())) &&
465 "The symbol's section doesn't match the fragment's symbol");
466 const MCSymbol *Base = Layout.getBaseSymbol(*MSD.Symbol);
468 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
470 bool IsReserved = !Base || OrigData.isCommon();
472 // Binding and Type share the same byte as upper and lower nibbles
473 uint8_t Binding = MCELF::GetBinding(OrigData);
474 uint8_t Type = MCELF::GetType(OrigData);
475 MCSymbolData *BaseSD = nullptr;
477 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
478 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
480 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
482 // Other and Visibility share the same byte with Visibility using the lower
484 uint8_t Visibility = MCELF::GetVisibility(OrigData);
485 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
488 uint64_t Value = SymbolValue(*MSD.Symbol, Layout);
491 const MCExpr *ESize = OrigData.getSize();
493 ESize = BaseSD->getSize();
497 if (!ESize->evaluateKnownAbsolute(Res, Layout))
498 report_fatal_error("Size expression must be absolute.");
502 // Write out the symbol table entry
503 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
504 MSD.SectionIndex, IsReserved);
507 // It is always valid to create a relocation with a symbol. It is preferable
508 // to use a relocation with a section if that is possible. Using the section
509 // allows us to omit some local symbols from the symbol table.
510 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
511 const MCSymbolRefExpr *RefA,
512 const MCSymbol *Sym, uint64_t C,
513 unsigned Type) const {
514 MCSymbolData *SD = Sym ? &Sym->getData() : nullptr;
516 // A PCRel relocation to an absolute value has no symbol (or section). We
517 // represent that with a relocation to a null section.
521 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
525 // The .odp creation emits a relocation against the symbol ".TOC." which
526 // create a R_PPC64_TOC relocation. However the relocation symbol name
527 // in final object creation should be NULL, since the symbol does not
528 // really exist, it is just the reference to TOC base for the current
529 // object file. Since the symbol is undefined, returning false results
530 // in a relocation with a null section which is the desired result.
531 case MCSymbolRefExpr::VK_PPC_TOCBASE:
534 // These VariantKind cause the relocation to refer to something other than
535 // the symbol itself, like a linker generated table. Since the address of
536 // symbol is not relevant, we cannot replace the symbol with the
537 // section and patch the difference in the addend.
538 case MCSymbolRefExpr::VK_GOT:
539 case MCSymbolRefExpr::VK_PLT:
540 case MCSymbolRefExpr::VK_GOTPCREL:
541 case MCSymbolRefExpr::VK_Mips_GOT:
542 case MCSymbolRefExpr::VK_PPC_GOT_LO:
543 case MCSymbolRefExpr::VK_PPC_GOT_HI:
544 case MCSymbolRefExpr::VK_PPC_GOT_HA:
548 // An undefined symbol is not in any section, so the relocation has to point
549 // to the symbol itself.
550 assert(Sym && "Expected a symbol");
551 if (Sym->isUndefined())
554 unsigned Binding = MCELF::GetBinding(*SD);
557 llvm_unreachable("Invalid Binding");
561 // If the symbol is weak, it might be overridden by a symbol in another
562 // file. The relocation has to point to the symbol so that the linker
565 case ELF::STB_GLOBAL:
566 // Global ELF symbols can be preempted by the dynamic linker. The relocation
567 // has to point to the symbol for a reason analogous to the STB_WEAK case.
571 // If a relocation points to a mergeable section, we have to be careful.
572 // If the offset is zero, a relocation with the section will encode the
573 // same information. With a non-zero offset, the situation is different.
574 // For example, a relocation can point 42 bytes past the end of a string.
575 // If we change such a relocation to use the section, the linker would think
576 // that it pointed to another string and subtracting 42 at runtime will
577 // produce the wrong value.
578 auto &Sec = cast<MCSectionELF>(Sym->getSection());
579 unsigned Flags = Sec.getFlags();
580 if (Flags & ELF::SHF_MERGE) {
584 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
585 // only handle section relocations to mergeable sections if using RELA.
586 if (!hasRelocationAddend())
590 // Most TLS relocations use a got, so they need the symbol. Even those that
591 // are just an offset (@tpoff), require a symbol in gold versions before
592 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
593 // http://sourceware.org/PR16773.
594 if (Flags & ELF::SHF_TLS)
597 // If the symbol is a thumb function the final relocation must set the lowest
598 // bit. With a symbol that is done by just having the symbol have that bit
599 // set, so we would lose the bit if we relocated with the section.
600 // FIXME: We could use the section but add the bit to the relocation value.
601 if (Asm.isThumbFunc(Sym))
604 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
609 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
610 const MCSymbol &Sym = Ref.getSymbol();
612 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
615 if (!Sym.isVariable())
618 const MCExpr *Expr = Sym.getVariableValue();
619 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
623 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
624 return &Inner->getSymbol();
628 // True if the assembler knows nothing about the final value of the symbol.
629 // This doesn't cover the comdat issues, since in those cases the assembler
630 // can at least know that all symbols in the section will move together.
631 static bool isWeak(const MCSymbolData &D) {
632 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
635 switch (MCELF::GetBinding(D)) {
637 llvm_unreachable("Unknown binding");
640 case ELF::STB_GLOBAL:
643 case ELF::STB_GNU_UNIQUE:
648 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
649 const MCAsmLayout &Layout,
650 const MCFragment *Fragment,
651 const MCFixup &Fixup, MCValue Target,
652 bool &IsPCRel, uint64_t &FixedValue) {
653 const MCSectionELF &FixupSection = cast<MCSectionELF>(*Fragment->getParent());
654 uint64_t C = Target.getConstant();
655 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
657 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
658 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
659 "Should not have constructed this");
661 // Let A, B and C being the components of Target and R be the location of
662 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
663 // If it is pcrel, we want to compute (A - B + C - R).
665 // In general, ELF has no relocations for -B. It can only represent (A + C)
666 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
667 // replace B to implement it: (A - R - K + C)
669 Asm.getContext().reportFatalError(
671 "No relocation available to represent this relative expression");
673 const MCSymbol &SymB = RefB->getSymbol();
675 if (SymB.isUndefined())
676 Asm.getContext().reportFatalError(
678 Twine("symbol '") + SymB.getName() +
679 "' can not be undefined in a subtraction expression");
681 assert(!SymB.isAbsolute() && "Should have been folded");
682 const MCSection &SecB = SymB.getSection();
683 if (&SecB != &FixupSection)
684 Asm.getContext().reportFatalError(
685 Fixup.getLoc(), "Cannot represent a difference across sections");
687 if (::isWeak(SymB.getData()))
688 Asm.getContext().reportFatalError(
689 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
691 uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
692 uint64_t K = SymBOffset - FixupOffset;
697 // We either rejected the fixup or folded B into C at this point.
698 const MCSymbolRefExpr *RefA = Target.getSymA();
699 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
701 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
702 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymA, C, Type);
703 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
704 C += Layout.getSymbolOffset(*SymA);
707 if (hasRelocationAddend()) {
714 if (!RelocateWithSymbol) {
715 const MCSection *SecA =
716 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
717 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
718 const MCSymbol *SectionSymbol = ELFSec ? ELFSec->getBeginSymbol() : nullptr;
719 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
720 Relocations[&FixupSection].push_back(Rec);
725 if (const MCSymbol *R = Renames.lookup(SymA))
728 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
729 WeakrefUsedInReloc.insert(WeakRef);
731 UsedInReloc.insert(SymA);
733 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
734 Relocations[&FixupSection].push_back(Rec);
740 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
742 assert(S->hasData());
743 return S->getIndex();
746 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
747 const MCSymbol &Symbol, bool Used,
749 const MCSymbolData &Data = Symbol.getData();
750 if (Symbol.isVariable()) {
751 const MCExpr *Expr = Symbol.getVariableValue();
752 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
753 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
764 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
767 if (Symbol.isVariable()) {
768 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
769 if (Base && Base->isUndefined())
773 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
774 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
777 if (MCELF::GetType(Data) == ELF::STT_SECTION)
780 if (Symbol.isTemporary())
786 bool ELFObjectWriter::isLocal(const MCSymbol &Symbol, bool isUsedInReloc) {
787 const MCSymbolData &Data = Symbol.getData();
788 if (Data.isExternal())
791 if (Symbol.isDefined())
800 void ELFObjectWriter::computeSymbolTable(
801 MCAssembler &Asm, const MCAsmLayout &Layout,
802 const SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap,
803 SectionOffsetsTy &SectionOffsets) {
804 MCContext &Ctx = Asm.getContext();
805 SymbolTableWriter Writer(*this, is64Bit());
808 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
809 MCSectionELF *SymtabSection =
810 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
811 SymtabSection->setAlignment(is64Bit() ? 8 : 4);
812 SymbolTableIndex = addToSectionTable(SymtabSection);
815 OffsetToAlignment(OS.tell(), SymtabSection->getAlignment());
818 uint64_t SecStart = OS.tell();
820 // The first entry is the undefined symbol entry.
821 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
823 // Add the data for the symbols.
824 bool HasLargeSectionIndex = false;
825 for (const MCSymbol &Symbol : Asm.symbols()) {
826 MCSymbolData &SD = Symbol.getData();
828 bool Used = UsedInReloc.count(&Symbol);
829 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
830 bool isSignature = RevGroupMap.count(&Symbol);
832 if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
833 Renames.count(&Symbol)))
837 MSD.Symbol = &Symbol;
838 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
840 // Undefined symbols are global, but this is the first place we
841 // are able to set it.
842 bool Local = isLocal(Symbol, Used);
843 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
845 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
846 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
847 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
851 MSD.SectionIndex = ELF::SHN_ABS;
852 } else if (SD.isCommon()) {
854 MSD.SectionIndex = ELF::SHN_COMMON;
855 } else if (BaseSymbol->isUndefined()) {
856 if (isSignature && !Used) {
857 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
858 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
859 HasLargeSectionIndex = true;
861 MSD.SectionIndex = ELF::SHN_UNDEF;
863 if (!Used && WeakrefUsed)
864 MCELF::SetBinding(SD, ELF::STB_WEAK);
866 const MCSectionELF &Section =
867 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
868 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
869 assert(MSD.SectionIndex && "Invalid section index!");
870 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
871 HasLargeSectionIndex = true;
874 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
877 // FIXME: All name handling should be done before we get to the writer,
878 // including dealing with GNU-style version suffixes. Fixing this isn't
881 // We thus have to be careful to not perform the symbol version replacement
884 // The ELF format is used on Windows by the MCJIT engine. Thus, on
885 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
886 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
887 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
888 // the EFLObjectWriter should not interpret the "@@@" sub-string as
889 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
890 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
891 // "__imp_?" or "__imp_@?".
893 // It would have been interesting to perform the MS mangling prefix check
894 // only when the target triple is of the form *-pc-windows-elf. But, it
895 // seems that this information is not easily accessible from the
897 StringRef Name = Symbol.getName();
898 if (!Name.startswith("?") && !Name.startswith("@?") &&
899 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
900 // This symbol isn't following the MSVC C++ name mangling convention. We
901 // can thus safely interpret the @@@ in symbol names as specifying symbol
904 size_t Pos = Name.find("@@@");
905 if (Pos != StringRef::npos) {
906 Buf += Name.substr(0, Pos);
907 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
908 Buf += Name.substr(Pos + Skip);
913 // Sections have their own string table
914 if (MCELF::GetType(SD) != ELF::STT_SECTION)
915 MSD.Name = StrTabBuilder.add(Name);
917 if (MSD.SectionIndex == ELF::SHN_UNDEF)
918 UndefinedSymbolData.push_back(MSD);
920 LocalSymbolData.push_back(MSD);
922 ExternalSymbolData.push_back(MSD);
925 if (HasLargeSectionIndex) {
926 MCSectionELF *SymtabShndxSection =
927 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
928 SymtabShndxSectionIndex = addToSectionTable(SymtabShndxSection);
929 SymtabShndxSection->setAlignment(4);
932 ArrayRef<std::string> FileNames = Asm.getFileNames();
933 for (const std::string &Name : FileNames)
934 StrTabBuilder.add(Name);
936 StrTabBuilder.finalize(StringTableBuilder::ELF);
938 // Symbols are required to be in lexicographic order.
939 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
940 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
941 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
943 // Set the symbol indices. Local symbols must come before all other
944 // symbols with non-local bindings.
945 unsigned Index = FileNames.size() + 1;
947 for (ELFSymbolData &MSD : LocalSymbolData) {
948 MSD.StringIndex = MCELF::GetType(MSD.Symbol->getData()) == ELF::STT_SECTION
950 : StrTabBuilder.getOffset(MSD.Name);
951 MSD.Symbol->setIndex(Index++);
953 for (ELFSymbolData &MSD : ExternalSymbolData) {
954 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
955 MSD.Symbol->setIndex(Index++);
957 for (ELFSymbolData &MSD : UndefinedSymbolData) {
958 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
959 MSD.Symbol->setIndex(Index++);
962 for (const std::string &Name : FileNames)
963 Writer.writeSymbol(StrTabBuilder.getOffset(Name),
964 ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, ELF::STV_DEFAULT,
967 // Write the symbol table entries.
968 LastLocalSymbolIndex = FileNames.size() + LocalSymbolData.size() + 1;
970 for (ELFSymbolData &MSD : LocalSymbolData)
971 WriteSymbol(Writer, MSD, Layout);
973 for (ELFSymbolData &MSD : ExternalSymbolData) {
974 MCSymbolData &Data = MSD.Symbol->getData();
975 assert(((Data.getFlags() & ELF_STB_Global) ||
976 (Data.getFlags() & ELF_STB_Weak)) &&
977 "External symbol requires STB_GLOBAL or STB_WEAK flag");
978 WriteSymbol(Writer, MSD, Layout);
979 assert(MCELF::GetBinding(Data) != ELF::STB_LOCAL);
982 for (ELFSymbolData &MSD : UndefinedSymbolData) {
983 MCSymbolData &Data = MSD.Symbol->getData();
984 WriteSymbol(Writer, MSD, Layout);
985 assert(MCELF::GetBinding(Data) != ELF::STB_LOCAL);
988 uint64_t SecEnd = OS.tell();
989 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
991 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
992 if (ShndxIndexes.empty()) {
993 assert(SymtabShndxSectionIndex == 0);
996 assert(SymtabShndxSectionIndex != 0);
998 SecStart = OS.tell();
999 const MCSectionELF *SymtabShndxSection =
1000 SectionTable[SymtabShndxSectionIndex - 1];
1001 for (uint32_t Index : ShndxIndexes)
1004 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
1008 ELFObjectWriter::createRelocationSection(MCContext &Ctx,
1009 const MCSectionELF &Sec) {
1010 if (Relocations[&Sec].empty())
1013 const StringRef SectionName = Sec.getSectionName();
1014 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1015 RelaSectionName += SectionName;
1018 if (hasRelocationAddend())
1019 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1021 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1024 if (Sec.getFlags() & ELF::SHF_GROUP)
1025 Flags = ELF::SHF_GROUP;
1027 MCSectionELF *RelaSection = Ctx.createELFRelSection(
1028 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1029 Flags, EntrySize, Sec.getGroup(), &Sec);
1030 RelaSection->setAlignment(is64Bit() ? 8 : 4);
1034 static SmallVector<char, 128>
1035 getUncompressedData(const MCAsmLayout &Layout,
1036 const MCSection::FragmentListType &Fragments) {
1037 SmallVector<char, 128> UncompressedData;
1038 for (const MCFragment &F : Fragments) {
1039 const SmallVectorImpl<char> *Contents;
1040 switch (F.getKind()) {
1041 case MCFragment::FT_Data:
1042 Contents = &cast<MCDataFragment>(F).getContents();
1044 case MCFragment::FT_Dwarf:
1045 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1047 case MCFragment::FT_DwarfFrame:
1048 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1052 "Not expecting any other fragment types in a debug_* section");
1054 UncompressedData.append(Contents->begin(), Contents->end());
1056 return UncompressedData;
1059 // Include the debug info compression header:
1060 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1061 // useful for consumers to preallocate a buffer to decompress into.
1063 prependCompressionHeader(uint64_t Size,
1064 SmallVectorImpl<char> &CompressedContents) {
1065 const StringRef Magic = "ZLIB";
1066 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1068 if (sys::IsLittleEndianHost)
1069 sys::swapByteOrder(Size);
1070 CompressedContents.insert(CompressedContents.begin(),
1071 Magic.size() + sizeof(Size), 0);
1072 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1073 std::copy(reinterpret_cast<char *>(&Size),
1074 reinterpret_cast<char *>(&Size + 1),
1075 CompressedContents.begin() + Magic.size());
1079 void ELFObjectWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
1080 const MCAsmLayout &Layout) {
1081 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1082 StringRef SectionName = Section.getSectionName();
1084 // Compressing debug_frame requires handling alignment fragments which is
1085 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1086 // for writing to arbitrary buffers) for little benefit.
1087 if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
1088 !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
1089 Asm.writeSectionData(&Section, Layout);
1093 // Gather the uncompressed data from all the fragments.
1094 const MCSection::FragmentListType &Fragments = Section.getFragmentList();
1095 SmallVector<char, 128> UncompressedData =
1096 getUncompressedData(Layout, Fragments);
1098 SmallVector<char, 128> CompressedContents;
1099 zlib::Status Success = zlib::compress(
1100 StringRef(UncompressedData.data(), UncompressedData.size()),
1101 CompressedContents);
1102 if (Success != zlib::StatusOK) {
1103 Asm.writeSectionData(&Section, Layout);
1107 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
1108 Asm.writeSectionData(&Section, Layout);
1111 Asm.getContext().renameELFSection(&Section,
1112 (".z" + SectionName.drop_front(1)).str());
1113 OS << CompressedContents;
1116 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1117 uint64_t Flags, uint64_t Address,
1118 uint64_t Offset, uint64_t Size,
1119 uint32_t Link, uint32_t Info,
1121 uint64_t EntrySize) {
1122 Write32(Name); // sh_name: index into string table
1123 Write32(Type); // sh_type
1124 WriteWord(Flags); // sh_flags
1125 WriteWord(Address); // sh_addr
1126 WriteWord(Offset); // sh_offset
1127 WriteWord(Size); // sh_size
1128 Write32(Link); // sh_link
1129 Write32(Info); // sh_info
1130 WriteWord(Alignment); // sh_addralign
1131 WriteWord(EntrySize); // sh_entsize
1134 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1135 const MCSectionELF &Sec) {
1136 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1138 // Sort the relocation entries. Most targets just sort by Offset, but some
1139 // (e.g., MIPS) have additional constraints.
1140 TargetObjectWriter->sortRelocs(Asm, Relocs);
1142 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1143 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1145 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1148 write(Entry.Offset);
1149 if (TargetObjectWriter->isN64()) {
1150 write(uint32_t(Index));
1152 write(TargetObjectWriter->getRSsym(Entry.Type));
1153 write(TargetObjectWriter->getRType3(Entry.Type));
1154 write(TargetObjectWriter->getRType2(Entry.Type));
1155 write(TargetObjectWriter->getRType(Entry.Type));
1157 struct ELF::Elf64_Rela ERE64;
1158 ERE64.setSymbolAndType(Index, Entry.Type);
1159 write(ERE64.r_info);
1161 if (hasRelocationAddend())
1162 write(Entry.Addend);
1164 write(uint32_t(Entry.Offset));
1166 struct ELF::Elf32_Rela ERE32;
1167 ERE32.setSymbolAndType(Index, Entry.Type);
1168 write(ERE32.r_info);
1170 if (hasRelocationAddend())
1171 write(uint32_t(Entry.Addend));
1176 const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
1177 const MCSectionELF *StrtabSection = SectionTable[StringTableIndex - 1];
1178 OS << StrTabBuilder.data();
1179 return StrtabSection;
1182 void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
1183 uint32_t GroupSymbolIndex, uint64_t Offset,
1184 uint64_t Size, const MCSectionELF &Section) {
1185 uint64_t sh_link = 0;
1186 uint64_t sh_info = 0;
1188 switch(Section.getType()) {
1193 case ELF::SHT_DYNAMIC:
1194 llvm_unreachable("SHT_DYNAMIC in a relocatable object");
1197 case ELF::SHT_RELA: {
1198 sh_link = SymbolTableIndex;
1199 assert(sh_link && ".symtab not found");
1200 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1201 sh_info = SectionIndexMap.lookup(InfoSection);
1205 case ELF::SHT_SYMTAB:
1206 case ELF::SHT_DYNSYM:
1207 sh_link = StringTableIndex;
1208 sh_info = LastLocalSymbolIndex;
1211 case ELF::SHT_SYMTAB_SHNDX:
1212 sh_link = SymbolTableIndex;
1215 case ELF::SHT_GROUP:
1216 sh_link = SymbolTableIndex;
1217 sh_info = GroupSymbolIndex;
1221 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1222 Section.getType() == ELF::SHT_ARM_EXIDX)
1223 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1225 WriteSecHdrEntry(StrTabBuilder.getOffset(Section.getSectionName()),
1226 Section.getType(), Section.getFlags(), 0, Offset, Size,
1227 sh_link, sh_info, Section.getAlignment(),
1228 Section.getEntrySize());
1231 void ELFObjectWriter::writeSectionHeader(
1232 const MCAssembler &Asm, const MCAsmLayout &Layout,
1233 const SectionIndexMapTy &SectionIndexMap,
1234 const SectionOffsetsTy &SectionOffsets) {
1235 const unsigned NumSections = SectionTable.size();
1237 // Null section first.
1238 uint64_t FirstSectionSize =
1239 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1240 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1242 for (const MCSectionELF *Section : SectionTable) {
1243 uint32_t GroupSymbolIndex;
1244 unsigned Type = Section->getType();
1245 if (Type != ELF::SHT_GROUP)
1246 GroupSymbolIndex = 0;
1248 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section->getGroup());
1250 const std::pair<uint64_t, uint64_t> &Offsets =
1251 SectionOffsets.find(Section)->second;
1253 if (Type == ELF::SHT_NOBITS)
1254 Size = Layout.getSectionAddressSize(Section);
1256 Size = Offsets.second - Offsets.first;
1258 writeSection(SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1263 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1264 const MCAsmLayout &Layout) {
1265 MCContext &Ctx = Asm.getContext();
1266 MCSectionELF *StrtabSection =
1267 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1268 StringTableIndex = addToSectionTable(StrtabSection);
1270 RevGroupMapTy RevGroupMap;
1271 SectionIndexMapTy SectionIndexMap;
1273 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1275 // Write out the ELF header ...
1278 // ... then the sections ...
1279 SectionOffsetsTy SectionOffsets;
1280 std::vector<MCSectionELF *> Groups;
1281 std::vector<MCSectionELF *> Relocations;
1282 for (MCSection &Sec : Asm) {
1283 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1285 uint64_t Padding = OffsetToAlignment(OS.tell(), Section.getAlignment());
1286 WriteZeros(Padding);
1288 // Remember the offset into the file for this section.
1289 uint64_t SecStart = OS.tell();
1291 const MCSymbol *SignatureSymbol = Section.getGroup();
1292 writeSectionData(Asm, Section, Layout);
1294 uint64_t SecEnd = OS.tell();
1295 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1297 MCSectionELF *RelSection = createRelocationSection(Ctx, Section);
1299 if (SignatureSymbol) {
1300 Asm.getOrCreateSymbolData(*SignatureSymbol);
1301 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1303 MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1304 GroupIdx = addToSectionTable(Group);
1305 Group->setAlignment(4);
1306 Groups.push_back(Group);
1308 GroupMembers[SignatureSymbol].push_back(&Section);
1310 GroupMembers[SignatureSymbol].push_back(RelSection);
1313 SectionIndexMap[&Section] = addToSectionTable(&Section);
1315 SectionIndexMap[RelSection] = addToSectionTable(RelSection);
1316 Relocations.push_back(RelSection);
1320 for (MCSectionELF *Group : Groups) {
1321 uint64_t Padding = OffsetToAlignment(OS.tell(), Group->getAlignment());
1322 WriteZeros(Padding);
1324 // Remember the offset into the file for this section.
1325 uint64_t SecStart = OS.tell();
1327 const MCSymbol *SignatureSymbol = Group->getGroup();
1328 assert(SignatureSymbol);
1329 write(uint32_t(ELF::GRP_COMDAT));
1330 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1331 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1335 uint64_t SecEnd = OS.tell();
1336 SectionOffsets[Group] = std::make_pair(SecStart, SecEnd);
1339 // Compute symbol table information.
1340 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, SectionOffsets);
1342 for (MCSectionELF *RelSection : Relocations) {
1343 uint64_t Padding = OffsetToAlignment(OS.tell(), RelSection->getAlignment());
1344 WriteZeros(Padding);
1346 // Remember the offset into the file for this section.
1347 uint64_t SecStart = OS.tell();
1349 writeRelocations(Asm, *RelSection->getAssociatedSection());
1351 uint64_t SecEnd = OS.tell();
1352 SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
1356 uint64_t SecStart = OS.tell();
1357 const MCSectionELF *Sec = createStringTable(Ctx);
1358 uint64_t SecEnd = OS.tell();
1359 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1362 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1363 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1364 WriteZeros(Padding);
1366 const unsigned SectionHeaderOffset = OS.tell();
1368 // ... then the section header table ...
1369 writeSectionHeader(Asm, Layout, SectionIndexMap, SectionOffsets);
1371 uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
1372 ? (uint16_t)ELF::SHN_UNDEF
1373 : SectionTable.size() + 1;
1374 if (sys::IsLittleEndianHost != IsLittleEndian)
1375 sys::swapByteOrder(NumSections);
1376 unsigned NumSectionsOffset;
1379 uint64_t Val = SectionHeaderOffset;
1380 if (sys::IsLittleEndianHost != IsLittleEndian)
1381 sys::swapByteOrder(Val);
1382 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1383 offsetof(ELF::Elf64_Ehdr, e_shoff));
1384 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1386 uint32_t Val = SectionHeaderOffset;
1387 if (sys::IsLittleEndianHost != IsLittleEndian)
1388 sys::swapByteOrder(Val);
1389 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1390 offsetof(ELF::Elf32_Ehdr, e_shoff));
1391 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1393 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1397 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1398 const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
1399 bool InSet, bool IsPCRel) const {
1402 if (::isWeak(SymA.getData()))
1405 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
1409 bool ELFObjectWriter::isWeak(const MCSymbol &Sym) const {
1410 const MCSymbolData &SD = Sym.getData();
1414 // It is invalid to replace a reference to a global in a comdat
1415 // with a reference to a local since out of comdat references
1416 // to a local are forbidden.
1417 // We could try to return false for more cases, like the reference
1418 // being in the same comdat or Sym being an alias to another global,
1419 // but it is not clear if it is worth the effort.
1420 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1423 if (!Sym.isInSection())
1426 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1427 return Sec.getGroup();
1430 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1431 raw_pwrite_stream &OS,
1432 bool IsLittleEndian) {
1433 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);