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,
80 /// Helper struct for containing some precomputed information on symbols.
81 struct ELFSymbolData {
82 const MCSymbol *Symbol;
83 uint32_t SectionIndex;
86 // Support lexicographic sorting.
87 bool operator<(const ELFSymbolData &RHS) const {
88 unsigned LHSType = MCELF::GetType(*Symbol);
89 unsigned RHSType = MCELF::GetType(*RHS.Symbol);
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;
118 // This holds the symbol table index of the last local symbol.
119 unsigned LastLocalSymbolIndex;
120 // This holds the .strtab section index.
121 unsigned StringTableIndex;
122 // This holds the .symtab section index.
123 unsigned SymbolTableIndex;
124 // This holds the .symtab_shndx section index.
125 unsigned SymtabShndxSectionIndex = 0;
127 // Sections in the order they are to be output in the section table.
128 std::vector<const MCSectionELF *> SectionTable;
129 unsigned addToSectionTable(const MCSectionELF *Sec);
131 // TargetObjectWriter wrappers.
132 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
133 bool hasRelocationAddend() const {
134 return TargetObjectWriter->hasRelocationAddend();
136 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
137 bool IsPCRel) const {
138 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
142 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
144 : MCObjectWriter(OS, IsLittleEndian), TargetObjectWriter(MOTW) {}
146 void reset() override {
148 WeakrefUsedInReloc.clear();
151 StrTabBuilder.clear();
152 SectionTable.clear();
153 MCObjectWriter::reset();
156 ~ELFObjectWriter() override;
158 void WriteWord(uint64_t W) {
165 template <typename T> void write(T Val) {
167 support::endian::Writer<support::little>(OS).write(Val);
169 support::endian::Writer<support::big>(OS).write(Val);
172 void writeHeader(const MCAssembler &Asm);
174 void writeSymbol(SymbolTableWriter &Writer, uint32_t StringIndex,
175 ELFSymbolData &MSD, const MCAsmLayout &Layout);
177 // Start and end offset of each section
178 typedef std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>
181 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
182 const MCSymbolRefExpr *RefA,
183 const MCSymbol *Sym, uint64_t C,
184 unsigned Type) const;
186 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
187 const MCFragment *Fragment, const MCFixup &Fixup,
188 MCValue Target, bool &IsPCRel,
189 uint64_t &FixedValue) override;
191 // Map from a signature symbol to the group section index
192 typedef DenseMap<const MCSymbol *, unsigned> RevGroupMapTy;
194 /// Compute the symbol table data
196 /// \param Asm - The assembler.
197 /// \param SectionIndexMap - Maps a section to its index.
198 /// \param RevGroupMap - Maps a signature symbol to the group section.
199 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
200 const SectionIndexMapTy &SectionIndexMap,
201 const RevGroupMapTy &RevGroupMap,
202 SectionOffsetsTy &SectionOffsets);
204 MCSectionELF *createRelocationSection(MCContext &Ctx,
205 const MCSectionELF &Sec);
207 const MCSectionELF *createStringTable(MCContext &Ctx);
209 void ExecutePostLayoutBinding(MCAssembler &Asm,
210 const MCAsmLayout &Layout) override;
212 void writeSectionHeader(const MCAssembler &Asm, const MCAsmLayout &Layout,
213 const SectionIndexMapTy &SectionIndexMap,
214 const SectionOffsetsTy &SectionOffsets);
216 void writeSectionData(const MCAssembler &Asm, MCSection &Sec,
217 const MCAsmLayout &Layout);
219 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
220 uint64_t Address, uint64_t Offset, uint64_t Size,
221 uint32_t Link, uint32_t Info, uint64_t Alignment,
224 void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
226 bool IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
227 const MCSymbol &SymA,
228 const MCFragment &FB,
230 bool IsPCRel) const override;
232 bool isWeak(const MCSymbol &Sym) const override;
234 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
235 void writeSection(const SectionIndexMapTy &SectionIndexMap,
236 uint32_t GroupSymbolIndex, uint64_t Offset, uint64_t Size,
237 const MCSectionELF &Section);
241 unsigned ELFObjectWriter::addToSectionTable(const MCSectionELF *Sec) {
242 SectionTable.push_back(Sec);
243 StrTabBuilder.add(Sec->getSectionName());
244 return SectionTable.size();
247 void SymbolTableWriter::createSymtabShndx() {
248 if (!ShndxIndexes.empty())
251 ShndxIndexes.resize(NumWritten);
254 template <typename T> void SymbolTableWriter::write(T Value) {
255 EWriter.write(Value);
258 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
259 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
261 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
262 uint64_t size, uint8_t other,
263 uint32_t shndx, bool Reserved) {
264 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
269 if (!ShndxIndexes.empty()) {
271 ShndxIndexes.push_back(shndx);
273 ShndxIndexes.push_back(0);
276 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
279 write(name); // st_name
280 write(info); // st_info
281 write(other); // st_other
282 write(Index); // st_shndx
283 write(value); // st_value
284 write(size); // st_size
286 write(name); // st_name
287 write(uint32_t(value)); // st_value
288 write(uint32_t(size)); // st_size
289 write(info); // st_info
290 write(other); // st_other
291 write(Index); // st_shndx
297 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
298 const MCFixupKindInfo &FKI =
299 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
301 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
304 ELFObjectWriter::~ELFObjectWriter()
307 // Emit the ELF header.
308 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
314 // emitWord method behaves differently for ELF32 and ELF64, writing
315 // 4 bytes in the former and 8 in the latter.
317 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
319 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
322 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
324 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
326 Write8(TargetObjectWriter->getOSABI());
327 Write8(0); // e_ident[EI_ABIVERSION]
329 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
331 Write16(ELF::ET_REL); // e_type
333 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
335 Write32(ELF::EV_CURRENT); // e_version
336 WriteWord(0); // e_entry, no entry point in .o file
337 WriteWord(0); // e_phoff, no program header for .o
338 WriteWord(0); // e_shoff = sec hdr table off in bytes
340 // e_flags = whatever the target wants
341 Write32(Asm.getELFHeaderEFlags());
343 // e_ehsize = ELF header size
344 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
346 Write16(0); // e_phentsize = prog header entry size
347 Write16(0); // e_phnum = # prog header entries = 0
349 // e_shentsize = Section header entry size
350 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
352 // e_shnum = # of section header ents
355 // e_shstrndx = Section # of '.shstrtab'
356 assert(StringTableIndex < ELF::SHN_LORESERVE);
357 Write16(StringTableIndex);
360 uint64_t ELFObjectWriter::SymbolValue(const MCSymbol &Sym,
361 const MCAsmLayout &Layout) {
362 if (Sym.isCommon() && Sym.isExternal())
363 return Sym.getCommonAlignment();
366 if (!Layout.getSymbolOffset(Sym, Res))
369 if (Layout.getAssembler().isThumbFunc(&Sym))
375 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
376 const MCAsmLayout &Layout) {
377 // The presence of symbol versions causes undefined symbols and
378 // versions declared with @@@ to be renamed.
380 for (const MCSymbol &Alias : Asm.symbols()) {
382 if (!Alias.isVariable())
384 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
387 const MCSymbol &Symbol = Ref->getSymbol();
389 StringRef AliasName = Alias.getName();
390 size_t Pos = AliasName.find('@');
391 if (Pos == StringRef::npos)
394 // Aliases defined with .symvar copy the binding from the symbol they alias.
395 // This is the first place we are able to copy this information.
396 Alias.setExternal(Symbol.isExternal());
397 MCELF::SetBinding(Alias, MCELF::GetBinding(Symbol));
399 StringRef Rest = AliasName.substr(Pos);
400 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
403 // FIXME: produce a better error message.
404 if (Symbol.isUndefined() && Rest.startswith("@@") &&
405 !Rest.startswith("@@@"))
406 report_fatal_error("A @@ version cannot be undefined");
408 Renames.insert(std::make_pair(&Symbol, &Alias));
412 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
413 uint8_t Type = newType;
415 // Propagation rules:
416 // IFUNC > FUNC > OBJECT > NOTYPE
417 // TLS_OBJECT > OBJECT > NOTYPE
419 // dont let the new type degrade the old type
423 case ELF::STT_GNU_IFUNC:
424 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
425 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
426 Type = ELF::STT_GNU_IFUNC;
429 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
430 Type == ELF::STT_TLS)
431 Type = ELF::STT_FUNC;
433 case ELF::STT_OBJECT:
434 if (Type == ELF::STT_NOTYPE)
435 Type = ELF::STT_OBJECT;
438 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
439 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
447 void ELFObjectWriter::writeSymbol(SymbolTableWriter &Writer,
448 uint32_t StringIndex, ELFSymbolData &MSD,
449 const MCAsmLayout &Layout) {
450 const MCSymbol &Symbol = *MSD.Symbol;
451 assert((!Symbol.getFragment() ||
452 (Symbol.getFragment()->getParent() == &Symbol.getSection())) &&
453 "The symbol's section doesn't match the fragment's symbol");
454 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
456 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
458 bool IsReserved = !Base || Symbol.isCommon();
460 // Binding and Type share the same byte as upper and lower nibbles
461 uint8_t Binding = MCELF::GetBinding(Symbol);
462 uint8_t Type = MCELF::GetType(Symbol);
464 Type = mergeTypeForSet(Type, MCELF::GetType(*Base));
466 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
468 // Other and Visibility share the same byte with Visibility using the lower
470 uint8_t Visibility = MCELF::GetVisibility(Symbol);
471 uint8_t Other = MCELF::getOther(Symbol) << (ELF_STO_Shift - ELF_STV_Shift);
474 uint64_t Value = SymbolValue(*MSD.Symbol, Layout);
477 const MCExpr *ESize = MSD.Symbol->getSize();
479 ESize = Base->getSize();
483 if (!ESize->evaluateKnownAbsolute(Res, Layout))
484 report_fatal_error("Size expression must be absolute.");
488 // Write out the symbol table entry
489 Writer.writeSymbol(StringIndex, Info, Value, Size, Other, MSD.SectionIndex,
493 // It is always valid to create a relocation with a symbol. It is preferable
494 // to use a relocation with a section if that is possible. Using the section
495 // allows us to omit some local symbols from the symbol table.
496 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
497 const MCSymbolRefExpr *RefA,
498 const MCSymbol *Sym, uint64_t C,
499 unsigned Type) const {
500 // A PCRel relocation to an absolute value has no symbol (or section). We
501 // represent that with a relocation to a null section.
505 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
509 // The .odp creation emits a relocation against the symbol ".TOC." which
510 // create a R_PPC64_TOC relocation. However the relocation symbol name
511 // in final object creation should be NULL, since the symbol does not
512 // really exist, it is just the reference to TOC base for the current
513 // object file. Since the symbol is undefined, returning false results
514 // in a relocation with a null section which is the desired result.
515 case MCSymbolRefExpr::VK_PPC_TOCBASE:
518 // These VariantKind cause the relocation to refer to something other than
519 // the symbol itself, like a linker generated table. Since the address of
520 // symbol is not relevant, we cannot replace the symbol with the
521 // section and patch the difference in the addend.
522 case MCSymbolRefExpr::VK_GOT:
523 case MCSymbolRefExpr::VK_PLT:
524 case MCSymbolRefExpr::VK_GOTPCREL:
525 case MCSymbolRefExpr::VK_Mips_GOT:
526 case MCSymbolRefExpr::VK_PPC_GOT_LO:
527 case MCSymbolRefExpr::VK_PPC_GOT_HI:
528 case MCSymbolRefExpr::VK_PPC_GOT_HA:
532 // An undefined symbol is not in any section, so the relocation has to point
533 // to the symbol itself.
534 assert(Sym && "Expected a symbol");
535 if (Sym->isUndefined())
538 unsigned Binding = MCELF::GetBinding(*Sym);
541 llvm_unreachable("Invalid Binding");
545 // If the symbol is weak, it might be overridden by a symbol in another
546 // file. The relocation has to point to the symbol so that the linker
549 case ELF::STB_GLOBAL:
550 // Global ELF symbols can be preempted by the dynamic linker. The relocation
551 // has to point to the symbol for a reason analogous to the STB_WEAK case.
555 // If a relocation points to a mergeable section, we have to be careful.
556 // If the offset is zero, a relocation with the section will encode the
557 // same information. With a non-zero offset, the situation is different.
558 // For example, a relocation can point 42 bytes past the end of a string.
559 // If we change such a relocation to use the section, the linker would think
560 // that it pointed to another string and subtracting 42 at runtime will
561 // produce the wrong value.
562 auto &Sec = cast<MCSectionELF>(Sym->getSection());
563 unsigned Flags = Sec.getFlags();
564 if (Flags & ELF::SHF_MERGE) {
568 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
569 // only handle section relocations to mergeable sections if using RELA.
570 if (!hasRelocationAddend())
574 // Most TLS relocations use a got, so they need the symbol. Even those that
575 // are just an offset (@tpoff), require a symbol in gold versions before
576 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
577 // http://sourceware.org/PR16773.
578 if (Flags & ELF::SHF_TLS)
581 // If the symbol is a thumb function the final relocation must set the lowest
582 // bit. With a symbol that is done by just having the symbol have that bit
583 // set, so we would lose the bit if we relocated with the section.
584 // FIXME: We could use the section but add the bit to the relocation value.
585 if (Asm.isThumbFunc(Sym))
588 if (TargetObjectWriter->needsRelocateWithSymbol(*Sym, Type))
593 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
594 const MCSymbol &Sym = Ref.getSymbol();
596 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
599 if (!Sym.isVariable())
602 const MCExpr *Expr = Sym.getVariableValue();
603 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
607 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
608 return &Inner->getSymbol();
612 // True if the assembler knows nothing about the final value of the symbol.
613 // This doesn't cover the comdat issues, since in those cases the assembler
614 // can at least know that all symbols in the section will move together.
615 static bool isWeak(const MCSymbol &Sym) {
616 if (MCELF::GetType(Sym) == ELF::STT_GNU_IFUNC)
619 switch (MCELF::GetBinding(Sym)) {
621 llvm_unreachable("Unknown binding");
624 case ELF::STB_GLOBAL:
627 case ELF::STB_GNU_UNIQUE:
632 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
633 const MCAsmLayout &Layout,
634 const MCFragment *Fragment,
635 const MCFixup &Fixup, MCValue Target,
636 bool &IsPCRel, uint64_t &FixedValue) {
637 const MCSectionELF &FixupSection = cast<MCSectionELF>(*Fragment->getParent());
638 uint64_t C = Target.getConstant();
639 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
641 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
642 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
643 "Should not have constructed this");
645 // Let A, B and C being the components of Target and R be the location of
646 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
647 // If it is pcrel, we want to compute (A - B + C - R).
649 // In general, ELF has no relocations for -B. It can only represent (A + C)
650 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
651 // replace B to implement it: (A - R - K + C)
653 Asm.getContext().reportFatalError(
655 "No relocation available to represent this relative expression");
657 const MCSymbol &SymB = RefB->getSymbol();
659 if (SymB.isUndefined())
660 Asm.getContext().reportFatalError(
662 Twine("symbol '") + SymB.getName() +
663 "' can not be undefined in a subtraction expression");
665 assert(!SymB.isAbsolute() && "Should have been folded");
666 const MCSection &SecB = SymB.getSection();
667 if (&SecB != &FixupSection)
668 Asm.getContext().reportFatalError(
669 Fixup.getLoc(), "Cannot represent a difference across sections");
672 Asm.getContext().reportFatalError(
673 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
675 uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
676 uint64_t K = SymBOffset - FixupOffset;
681 // We either rejected the fixup or folded B into C at this point.
682 const MCSymbolRefExpr *RefA = Target.getSymA();
683 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
685 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
686 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymA, C, Type);
687 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
688 C += Layout.getSymbolOffset(*SymA);
691 if (hasRelocationAddend()) {
698 if (!RelocateWithSymbol) {
699 const MCSection *SecA =
700 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
701 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
702 const MCSymbol *SectionSymbol = ELFSec ? ELFSec->getBeginSymbol() : nullptr;
703 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
704 Relocations[&FixupSection].push_back(Rec);
709 if (const MCSymbol *R = Renames.lookup(SymA))
712 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
713 WeakrefUsedInReloc.insert(WeakRef);
715 UsedInReloc.insert(SymA);
717 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
718 Relocations[&FixupSection].push_back(Rec);
722 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
723 const MCSymbol &Symbol, bool Used,
725 if (Symbol.isVariable()) {
726 const MCExpr *Expr = Symbol.getVariableValue();
727 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
728 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
739 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
742 if (Symbol.isVariable()) {
743 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
744 if (Base && Base->isUndefined())
748 bool IsGlobal = MCELF::GetBinding(Symbol) == ELF::STB_GLOBAL;
749 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
752 if (MCELF::GetType(Symbol) == ELF::STT_SECTION)
755 if (Symbol.isTemporary())
761 bool ELFObjectWriter::isLocal(const MCSymbol &Symbol, bool IsUsedInReloc,
763 if (Symbol.isExternal())
766 if (Symbol.isDefined())
775 void ELFObjectWriter::computeSymbolTable(
776 MCAssembler &Asm, const MCAsmLayout &Layout,
777 const SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap,
778 SectionOffsetsTy &SectionOffsets) {
779 MCContext &Ctx = Asm.getContext();
780 SymbolTableWriter Writer(*this, is64Bit());
783 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
784 MCSectionELF *SymtabSection =
785 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
786 SymtabSection->setAlignment(is64Bit() ? 8 : 4);
787 SymbolTableIndex = addToSectionTable(SymtabSection);
790 OffsetToAlignment(OS.tell(), SymtabSection->getAlignment());
793 uint64_t SecStart = OS.tell();
795 // The first entry is the undefined symbol entry.
796 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
798 std::vector<ELFSymbolData> LocalSymbolData;
799 std::vector<ELFSymbolData> ExternalSymbolData;
801 // Add the data for the symbols.
802 bool HasLargeSectionIndex = false;
803 for (const MCSymbol &Symbol : Asm.symbols()) {
804 bool Used = UsedInReloc.count(&Symbol);
805 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
806 bool isSignature = RevGroupMap.count(&Symbol);
808 if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
809 Renames.count(&Symbol)))
813 MSD.Symbol = &Symbol;
815 // Undefined symbols are global, but this is the first place we
816 // are able to set it.
817 bool Local = isLocal(Symbol, Used, isSignature);
818 if (!Local && MCELF::GetBinding(Symbol) == ELF::STB_LOCAL)
819 MCELF::SetBinding(Symbol, ELF::STB_GLOBAL);
821 if (Symbol.isAbsolute()) {
822 MSD.SectionIndex = ELF::SHN_ABS;
823 } else if (Symbol.isCommon()) {
825 MSD.SectionIndex = ELF::SHN_COMMON;
826 } else if (Symbol.isUndefined()) {
827 if (isSignature && !Used) {
828 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
829 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
830 HasLargeSectionIndex = true;
832 MSD.SectionIndex = ELF::SHN_UNDEF;
834 if (!Used && WeakrefUsed)
835 MCELF::SetBinding(Symbol, ELF::STB_WEAK);
837 const MCSectionELF &Section =
838 static_cast<const MCSectionELF &>(Symbol.getSection());
839 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
840 assert(MSD.SectionIndex && "Invalid section index!");
841 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
842 HasLargeSectionIndex = true;
845 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
848 // FIXME: All name handling should be done before we get to the writer,
849 // including dealing with GNU-style version suffixes. Fixing this isn't
852 // We thus have to be careful to not perform the symbol version replacement
855 // The ELF format is used on Windows by the MCJIT engine. Thus, on
856 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
857 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
858 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
859 // the EFLObjectWriter should not interpret the "@@@" sub-string as
860 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
861 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
862 // "__imp_?" or "__imp_@?".
864 // It would have been interesting to perform the MS mangling prefix check
865 // only when the target triple is of the form *-pc-windows-elf. But, it
866 // seems that this information is not easily accessible from the
868 StringRef Name = Symbol.getName();
869 if (!Name.startswith("?") && !Name.startswith("@?") &&
870 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
871 // This symbol isn't following the MSVC C++ name mangling convention. We
872 // can thus safely interpret the @@@ in symbol names as specifying symbol
875 size_t Pos = Name.find("@@@");
876 if (Pos != StringRef::npos) {
877 Buf += Name.substr(0, Pos);
878 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
879 Buf += Name.substr(Pos + Skip);
884 // Sections have their own string table
885 if (MCELF::GetType(Symbol) != ELF::STT_SECTION)
886 MSD.Name = StrTabBuilder.add(Name);
889 LocalSymbolData.push_back(MSD);
891 ExternalSymbolData.push_back(MSD);
894 if (HasLargeSectionIndex) {
895 MCSectionELF *SymtabShndxSection =
896 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
897 SymtabShndxSectionIndex = addToSectionTable(SymtabShndxSection);
898 SymtabShndxSection->setAlignment(4);
901 ArrayRef<std::string> FileNames = Asm.getFileNames();
902 for (const std::string &Name : FileNames)
903 StrTabBuilder.add(Name);
905 StrTabBuilder.finalize(StringTableBuilder::ELF);
907 for (const std::string &Name : FileNames)
908 Writer.writeSymbol(StrTabBuilder.getOffset(Name),
909 ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, ELF::STV_DEFAULT,
912 // Symbols are required to be in lexicographic order.
913 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
914 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
916 // Set the symbol indices. Local symbols must come before all other
917 // symbols with non-local bindings.
918 unsigned Index = FileNames.size() + 1;
920 for (ELFSymbolData &MSD : LocalSymbolData) {
921 unsigned StringIndex = MCELF::GetType(*MSD.Symbol) == ELF::STT_SECTION
923 : StrTabBuilder.getOffset(MSD.Name);
924 MSD.Symbol->setIndex(Index++);
925 writeSymbol(Writer, StringIndex, MSD, Layout);
928 // Write the symbol table entries.
929 LastLocalSymbolIndex = Index;
931 for (ELFSymbolData &MSD : ExternalSymbolData) {
932 unsigned StringIndex = StrTabBuilder.getOffset(MSD.Name);
933 MSD.Symbol->setIndex(Index++);
934 writeSymbol(Writer, StringIndex, MSD, Layout);
935 assert(MCELF::GetBinding(*MSD.Symbol) != ELF::STB_LOCAL);
938 uint64_t SecEnd = OS.tell();
939 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
941 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
942 if (ShndxIndexes.empty()) {
943 assert(SymtabShndxSectionIndex == 0);
946 assert(SymtabShndxSectionIndex != 0);
948 SecStart = OS.tell();
949 const MCSectionELF *SymtabShndxSection =
950 SectionTable[SymtabShndxSectionIndex - 1];
951 for (uint32_t Index : ShndxIndexes)
954 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
958 ELFObjectWriter::createRelocationSection(MCContext &Ctx,
959 const MCSectionELF &Sec) {
960 if (Relocations[&Sec].empty())
963 const StringRef SectionName = Sec.getSectionName();
964 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
965 RelaSectionName += SectionName;
968 if (hasRelocationAddend())
969 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
971 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
974 if (Sec.getFlags() & ELF::SHF_GROUP)
975 Flags = ELF::SHF_GROUP;
977 MCSectionELF *RelaSection = Ctx.createELFRelSection(
978 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
979 Flags, EntrySize, Sec.getGroup(), &Sec);
980 RelaSection->setAlignment(is64Bit() ? 8 : 4);
984 static SmallVector<char, 128>
985 getUncompressedData(const MCAsmLayout &Layout,
986 const MCSection::FragmentListType &Fragments) {
987 SmallVector<char, 128> UncompressedData;
988 for (const MCFragment &F : Fragments) {
989 const SmallVectorImpl<char> *Contents;
990 switch (F.getKind()) {
991 case MCFragment::FT_Data:
992 Contents = &cast<MCDataFragment>(F).getContents();
994 case MCFragment::FT_Dwarf:
995 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
997 case MCFragment::FT_DwarfFrame:
998 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1002 "Not expecting any other fragment types in a debug_* section");
1004 UncompressedData.append(Contents->begin(), Contents->end());
1006 return UncompressedData;
1009 // Include the debug info compression header:
1010 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1011 // useful for consumers to preallocate a buffer to decompress into.
1013 prependCompressionHeader(uint64_t Size,
1014 SmallVectorImpl<char> &CompressedContents) {
1015 const StringRef Magic = "ZLIB";
1016 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1018 if (sys::IsLittleEndianHost)
1019 sys::swapByteOrder(Size);
1020 CompressedContents.insert(CompressedContents.begin(),
1021 Magic.size() + sizeof(Size), 0);
1022 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1023 std::copy(reinterpret_cast<char *>(&Size),
1024 reinterpret_cast<char *>(&Size + 1),
1025 CompressedContents.begin() + Magic.size());
1029 void ELFObjectWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
1030 const MCAsmLayout &Layout) {
1031 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1032 StringRef SectionName = Section.getSectionName();
1034 // Compressing debug_frame requires handling alignment fragments which is
1035 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1036 // for writing to arbitrary buffers) for little benefit.
1037 if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
1038 !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
1039 Asm.writeSectionData(&Section, Layout);
1043 // Gather the uncompressed data from all the fragments.
1044 const MCSection::FragmentListType &Fragments = Section.getFragmentList();
1045 SmallVector<char, 128> UncompressedData =
1046 getUncompressedData(Layout, Fragments);
1048 SmallVector<char, 128> CompressedContents;
1049 zlib::Status Success = zlib::compress(
1050 StringRef(UncompressedData.data(), UncompressedData.size()),
1051 CompressedContents);
1052 if (Success != zlib::StatusOK) {
1053 Asm.writeSectionData(&Section, Layout);
1057 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
1058 Asm.writeSectionData(&Section, Layout);
1061 Asm.getContext().renameELFSection(&Section,
1062 (".z" + SectionName.drop_front(1)).str());
1063 OS << CompressedContents;
1066 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1067 uint64_t Flags, uint64_t Address,
1068 uint64_t Offset, uint64_t Size,
1069 uint32_t Link, uint32_t Info,
1071 uint64_t EntrySize) {
1072 Write32(Name); // sh_name: index into string table
1073 Write32(Type); // sh_type
1074 WriteWord(Flags); // sh_flags
1075 WriteWord(Address); // sh_addr
1076 WriteWord(Offset); // sh_offset
1077 WriteWord(Size); // sh_size
1078 Write32(Link); // sh_link
1079 Write32(Info); // sh_info
1080 WriteWord(Alignment); // sh_addralign
1081 WriteWord(EntrySize); // sh_entsize
1084 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1085 const MCSectionELF &Sec) {
1086 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1088 // Sort the relocation entries. Most targets just sort by Offset, but some
1089 // (e.g., MIPS) have additional constraints.
1090 TargetObjectWriter->sortRelocs(Asm, Relocs);
1092 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1093 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1094 unsigned Index = Entry.Symbol ? Entry.Symbol->getIndex() : 0;
1097 write(Entry.Offset);
1098 if (TargetObjectWriter->isN64()) {
1099 write(uint32_t(Index));
1101 write(TargetObjectWriter->getRSsym(Entry.Type));
1102 write(TargetObjectWriter->getRType3(Entry.Type));
1103 write(TargetObjectWriter->getRType2(Entry.Type));
1104 write(TargetObjectWriter->getRType(Entry.Type));
1106 struct ELF::Elf64_Rela ERE64;
1107 ERE64.setSymbolAndType(Index, Entry.Type);
1108 write(ERE64.r_info);
1110 if (hasRelocationAddend())
1111 write(Entry.Addend);
1113 write(uint32_t(Entry.Offset));
1115 struct ELF::Elf32_Rela ERE32;
1116 ERE32.setSymbolAndType(Index, Entry.Type);
1117 write(ERE32.r_info);
1119 if (hasRelocationAddend())
1120 write(uint32_t(Entry.Addend));
1125 const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
1126 const MCSectionELF *StrtabSection = SectionTable[StringTableIndex - 1];
1127 OS << StrTabBuilder.data();
1128 return StrtabSection;
1131 void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
1132 uint32_t GroupSymbolIndex, uint64_t Offset,
1133 uint64_t Size, const MCSectionELF &Section) {
1134 uint64_t sh_link = 0;
1135 uint64_t sh_info = 0;
1137 switch(Section.getType()) {
1142 case ELF::SHT_DYNAMIC:
1143 llvm_unreachable("SHT_DYNAMIC in a relocatable object");
1146 case ELF::SHT_RELA: {
1147 sh_link = SymbolTableIndex;
1148 assert(sh_link && ".symtab not found");
1149 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1150 sh_info = SectionIndexMap.lookup(InfoSection);
1154 case ELF::SHT_SYMTAB:
1155 case ELF::SHT_DYNSYM:
1156 sh_link = StringTableIndex;
1157 sh_info = LastLocalSymbolIndex;
1160 case ELF::SHT_SYMTAB_SHNDX:
1161 sh_link = SymbolTableIndex;
1164 case ELF::SHT_GROUP:
1165 sh_link = SymbolTableIndex;
1166 sh_info = GroupSymbolIndex;
1170 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1171 Section.getType() == ELF::SHT_ARM_EXIDX)
1172 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1174 WriteSecHdrEntry(StrTabBuilder.getOffset(Section.getSectionName()),
1175 Section.getType(), Section.getFlags(), 0, Offset, Size,
1176 sh_link, sh_info, Section.getAlignment(),
1177 Section.getEntrySize());
1180 void ELFObjectWriter::writeSectionHeader(
1181 const MCAssembler &Asm, const MCAsmLayout &Layout,
1182 const SectionIndexMapTy &SectionIndexMap,
1183 const SectionOffsetsTy &SectionOffsets) {
1184 const unsigned NumSections = SectionTable.size();
1186 // Null section first.
1187 uint64_t FirstSectionSize =
1188 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1189 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1191 for (const MCSectionELF *Section : SectionTable) {
1192 uint32_t GroupSymbolIndex;
1193 unsigned Type = Section->getType();
1194 if (Type != ELF::SHT_GROUP)
1195 GroupSymbolIndex = 0;
1197 GroupSymbolIndex = Section->getGroup()->getIndex();
1199 const std::pair<uint64_t, uint64_t> &Offsets =
1200 SectionOffsets.find(Section)->second;
1202 if (Type == ELF::SHT_NOBITS)
1203 Size = Layout.getSectionAddressSize(Section);
1205 Size = Offsets.second - Offsets.first;
1207 writeSection(SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1212 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1213 const MCAsmLayout &Layout) {
1214 MCContext &Ctx = Asm.getContext();
1215 MCSectionELF *StrtabSection =
1216 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1217 StringTableIndex = addToSectionTable(StrtabSection);
1219 RevGroupMapTy RevGroupMap;
1220 SectionIndexMapTy SectionIndexMap;
1222 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1224 // Write out the ELF header ...
1227 // ... then the sections ...
1228 SectionOffsetsTy SectionOffsets;
1229 std::vector<MCSectionELF *> Groups;
1230 std::vector<MCSectionELF *> Relocations;
1231 for (MCSection &Sec : Asm) {
1232 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1234 uint64_t Padding = OffsetToAlignment(OS.tell(), Section.getAlignment());
1235 WriteZeros(Padding);
1237 // Remember the offset into the file for this section.
1238 uint64_t SecStart = OS.tell();
1240 const MCSymbol *SignatureSymbol = Section.getGroup();
1241 writeSectionData(Asm, Section, Layout);
1243 uint64_t SecEnd = OS.tell();
1244 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1246 MCSectionELF *RelSection = createRelocationSection(Ctx, Section);
1248 if (SignatureSymbol) {
1249 Asm.registerSymbol(*SignatureSymbol);
1250 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1252 MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1253 GroupIdx = addToSectionTable(Group);
1254 Group->setAlignment(4);
1255 Groups.push_back(Group);
1257 GroupMembers[SignatureSymbol].push_back(&Section);
1259 GroupMembers[SignatureSymbol].push_back(RelSection);
1262 SectionIndexMap[&Section] = addToSectionTable(&Section);
1264 SectionIndexMap[RelSection] = addToSectionTable(RelSection);
1265 Relocations.push_back(RelSection);
1269 for (MCSectionELF *Group : Groups) {
1270 uint64_t Padding = OffsetToAlignment(OS.tell(), Group->getAlignment());
1271 WriteZeros(Padding);
1273 // Remember the offset into the file for this section.
1274 uint64_t SecStart = OS.tell();
1276 const MCSymbol *SignatureSymbol = Group->getGroup();
1277 assert(SignatureSymbol);
1278 write(uint32_t(ELF::GRP_COMDAT));
1279 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1280 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1284 uint64_t SecEnd = OS.tell();
1285 SectionOffsets[Group] = std::make_pair(SecStart, SecEnd);
1288 // Compute symbol table information.
1289 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, SectionOffsets);
1291 for (MCSectionELF *RelSection : Relocations) {
1292 uint64_t Padding = OffsetToAlignment(OS.tell(), RelSection->getAlignment());
1293 WriteZeros(Padding);
1295 // Remember the offset into the file for this section.
1296 uint64_t SecStart = OS.tell();
1298 writeRelocations(Asm, *RelSection->getAssociatedSection());
1300 uint64_t SecEnd = OS.tell();
1301 SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
1305 uint64_t SecStart = OS.tell();
1306 const MCSectionELF *Sec = createStringTable(Ctx);
1307 uint64_t SecEnd = OS.tell();
1308 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1311 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1312 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1313 WriteZeros(Padding);
1315 const unsigned SectionHeaderOffset = OS.tell();
1317 // ... then the section header table ...
1318 writeSectionHeader(Asm, Layout, SectionIndexMap, SectionOffsets);
1320 uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
1321 ? (uint16_t)ELF::SHN_UNDEF
1322 : SectionTable.size() + 1;
1323 if (sys::IsLittleEndianHost != IsLittleEndian)
1324 sys::swapByteOrder(NumSections);
1325 unsigned NumSectionsOffset;
1328 uint64_t Val = SectionHeaderOffset;
1329 if (sys::IsLittleEndianHost != IsLittleEndian)
1330 sys::swapByteOrder(Val);
1331 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1332 offsetof(ELF::Elf64_Ehdr, e_shoff));
1333 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1335 uint32_t Val = SectionHeaderOffset;
1336 if (sys::IsLittleEndianHost != IsLittleEndian)
1337 sys::swapByteOrder(Val);
1338 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1339 offsetof(ELF::Elf32_Ehdr, e_shoff));
1340 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1342 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1346 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1347 const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
1348 bool InSet, bool IsPCRel) const {
1354 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
1358 bool ELFObjectWriter::isWeak(const MCSymbol &Sym) const {
1362 // It is invalid to replace a reference to a global in a comdat
1363 // with a reference to a local since out of comdat references
1364 // to a local are forbidden.
1365 // We could try to return false for more cases, like the reference
1366 // being in the same comdat or Sym being an alias to another global,
1367 // but it is not clear if it is worth the effort.
1368 if (MCELF::GetBinding(Sym) != ELF::STB_GLOBAL)
1371 if (!Sym.isInSection())
1374 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1375 return Sec.getGroup();
1378 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1379 raw_pwrite_stream &OS,
1380 bool IsLittleEndian) {
1381 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);