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/ADT/ArrayRef.h"
15 #include "llvm/ADT/DenseMap.h"
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/ADT/SmallString.h"
18 #include "llvm/ADT/SmallVector.h"
19 #include "llvm/ADT/StringRef.h"
20 #include "llvm/ADT/Twine.h"
21 #include "llvm/BinaryFormat/ELF.h"
22 #include "llvm/MC/MCAsmInfo.h"
23 #include "llvm/MC/MCAsmLayout.h"
24 #include "llvm/MC/MCAssembler.h"
25 #include "llvm/MC/MCContext.h"
26 #include "llvm/MC/MCELFObjectWriter.h"
27 #include "llvm/MC/MCExpr.h"
28 #include "llvm/MC/MCFixup.h"
29 #include "llvm/MC/MCFragment.h"
30 #include "llvm/MC/MCObjectWriter.h"
31 #include "llvm/MC/MCSection.h"
32 #include "llvm/MC/MCSectionELF.h"
33 #include "llvm/MC/MCSymbol.h"
34 #include "llvm/MC/MCSymbolELF.h"
35 #include "llvm/MC/MCValue.h"
36 #include "llvm/MC/StringTableBuilder.h"
37 #include "llvm/Support/Allocator.h"
38 #include "llvm/Support/Casting.h"
39 #include "llvm/Support/Compression.h"
40 #include "llvm/Support/Endian.h"
41 #include "llvm/Support/Error.h"
42 #include "llvm/Support/ErrorHandling.h"
43 #include "llvm/Support/Host.h"
44 #include "llvm/Support/MathExtras.h"
45 #include "llvm/Support/SMLoc.h"
46 #include "llvm/Support/StringSaver.h"
47 #include "llvm/Support/SwapByteOrder.h"
48 #include "llvm/Support/raw_ostream.h"
62 #define DEBUG_TYPE "reloc-info"
66 using SectionIndexMapTy = DenseMap<const MCSectionELF *, uint32_t>;
68 class ELFObjectWriter;
70 class SymbolTableWriter {
71 ELFObjectWriter &EWriter;
74 // indexes we are going to write to .symtab_shndx.
75 std::vector<uint32_t> ShndxIndexes;
77 // The numbel of symbols written so far.
80 void createSymtabShndx();
82 template <typename T> void write(T Value);
85 SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit);
87 void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
88 uint8_t other, uint32_t shndx, bool Reserved);
90 ArrayRef<uint32_t> getShndxIndexes() const { return ShndxIndexes; }
93 class ELFObjectWriter : public MCObjectWriter {
94 static uint64_t SymbolValue(const MCSymbol &Sym, const MCAsmLayout &Layout);
95 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolELF &Symbol,
96 bool Used, bool Renamed);
98 /// Helper struct for containing some precomputed information on symbols.
99 struct ELFSymbolData {
100 const MCSymbolELF *Symbol;
101 uint32_t SectionIndex;
104 // Support lexicographic sorting.
105 bool operator<(const ELFSymbolData &RHS) const {
106 unsigned LHSType = Symbol->getType();
107 unsigned RHSType = RHS.Symbol->getType();
108 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
110 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
112 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
113 return SectionIndex < RHS.SectionIndex;
114 return Name < RHS.Name;
118 /// The target specific ELF writer instance.
119 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
121 DenseMap<const MCSymbolELF *, const MCSymbolELF *> Renames;
123 DenseMap<const MCSectionELF *, std::vector<ELFRelocationEntry>> Relocations;
126 /// @name Symbol Table Data
129 BumpPtrAllocator Alloc;
130 StringSaver VersionSymSaver{Alloc};
131 StringTableBuilder StrTabBuilder{StringTableBuilder::ELF};
135 // This holds the symbol table index of the last local symbol.
136 unsigned LastLocalSymbolIndex;
137 // This holds the .strtab section index.
138 unsigned StringTableIndex;
139 // This holds the .symtab section index.
140 unsigned SymbolTableIndex;
142 // Sections in the order they are to be output in the section table.
143 std::vector<const MCSectionELF *> SectionTable;
144 unsigned addToSectionTable(const MCSectionELF *Sec);
146 // TargetObjectWriter wrappers.
147 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
148 bool hasRelocationAddend() const {
149 return TargetObjectWriter->hasRelocationAddend();
151 unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
152 const MCFixup &Fixup, bool IsPCRel) const {
153 return TargetObjectWriter->getRelocType(Ctx, Target, Fixup, IsPCRel);
156 void align(unsigned Alignment);
158 bool maybeWriteCompression(uint64_t Size,
159 SmallVectorImpl<char> &CompressedContents,
160 bool ZLibStyle, unsigned Alignment);
163 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
165 : MCObjectWriter(OS, IsLittleEndian), TargetObjectWriter(MOTW) {}
167 ~ELFObjectWriter() override = default;
169 void reset() override {
172 StrTabBuilder.clear();
173 SectionTable.clear();
174 MCObjectWriter::reset();
177 void WriteWord(uint64_t W) {
184 template <typename T> void write(T Val) {
186 support::endian::Writer<support::little>(getStream()).write(Val);
188 support::endian::Writer<support::big>(getStream()).write(Val);
191 void writeHeader(const MCAssembler &Asm);
193 void writeSymbol(SymbolTableWriter &Writer, uint32_t StringIndex,
194 ELFSymbolData &MSD, const MCAsmLayout &Layout);
196 // Start and end offset of each section
197 using SectionOffsetsTy =
198 std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>;
200 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
201 const MCSymbolRefExpr *RefA,
202 const MCSymbol *Sym, uint64_t C,
203 unsigned Type) const;
205 void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
206 const MCFragment *Fragment, const MCFixup &Fixup,
207 MCValue Target, bool &IsPCRel,
208 uint64_t &FixedValue) override;
210 // Map from a signature symbol to the group section index
211 using RevGroupMapTy = DenseMap<const MCSymbol *, unsigned>;
213 /// Compute the symbol table data
215 /// \param Asm - The assembler.
216 /// \param SectionIndexMap - Maps a section to its index.
217 /// \param RevGroupMap - Maps a signature symbol to the group section.
218 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
219 const SectionIndexMapTy &SectionIndexMap,
220 const RevGroupMapTy &RevGroupMap,
221 SectionOffsetsTy &SectionOffsets);
223 MCSectionELF *createRelocationSection(MCContext &Ctx,
224 const MCSectionELF &Sec);
226 const MCSectionELF *createStringTable(MCContext &Ctx);
228 void executePostLayoutBinding(MCAssembler &Asm,
229 const MCAsmLayout &Layout) override;
231 void writeSectionHeader(const MCAsmLayout &Layout,
232 const SectionIndexMapTy &SectionIndexMap,
233 const SectionOffsetsTy &SectionOffsets);
235 void writeSectionData(const MCAssembler &Asm, MCSection &Sec,
236 const MCAsmLayout &Layout);
238 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
239 uint64_t Address, uint64_t Offset, uint64_t Size,
240 uint32_t Link, uint32_t Info, uint64_t Alignment,
243 void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
245 using MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl;
246 bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
247 const MCSymbol &SymA,
248 const MCFragment &FB, bool InSet,
249 bool IsPCRel) const override;
251 void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
252 void writeSection(const SectionIndexMapTy &SectionIndexMap,
253 uint32_t GroupSymbolIndex, uint64_t Offset, uint64_t Size,
254 const MCSectionELF &Section);
257 } // end anonymous namespace
259 void ELFObjectWriter::align(unsigned Alignment) {
260 uint64_t Padding = OffsetToAlignment(getStream().tell(), Alignment);
264 unsigned ELFObjectWriter::addToSectionTable(const MCSectionELF *Sec) {
265 SectionTable.push_back(Sec);
266 StrTabBuilder.add(Sec->getSectionName());
267 return SectionTable.size();
270 void SymbolTableWriter::createSymtabShndx() {
271 if (!ShndxIndexes.empty())
274 ShndxIndexes.resize(NumWritten);
277 template <typename T> void SymbolTableWriter::write(T Value) {
278 EWriter.write(Value);
281 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
282 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
284 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
285 uint64_t size, uint8_t other,
286 uint32_t shndx, bool Reserved) {
287 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
292 if (!ShndxIndexes.empty()) {
294 ShndxIndexes.push_back(shndx);
296 ShndxIndexes.push_back(0);
299 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
302 write(name); // st_name
303 write(info); // st_info
304 write(other); // st_other
305 write(Index); // st_shndx
306 write(value); // st_value
307 write(size); // st_size
309 write(name); // st_name
310 write(uint32_t(value)); // st_value
311 write(uint32_t(size)); // st_size
312 write(info); // st_info
313 write(other); // st_other
314 write(Index); // st_shndx
320 // Emit the ELF header.
321 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
327 // emitWord method behaves differently for ELF32 and ELF64, writing
328 // 4 bytes in the former and 8 in the latter.
330 writeBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
332 write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
335 write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
337 write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
339 write8(TargetObjectWriter->getOSABI());
340 write8(0); // e_ident[EI_ABIVERSION]
342 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
344 write16(ELF::ET_REL); // e_type
346 write16(TargetObjectWriter->getEMachine()); // e_machine = target
348 write32(ELF::EV_CURRENT); // e_version
349 WriteWord(0); // e_entry, no entry point in .o file
350 WriteWord(0); // e_phoff, no program header for .o
351 WriteWord(0); // e_shoff = sec hdr table off in bytes
353 // e_flags = whatever the target wants
354 write32(Asm.getELFHeaderEFlags());
356 // e_ehsize = ELF header size
357 write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
359 write16(0); // e_phentsize = prog header entry size
360 write16(0); // e_phnum = # prog header entries = 0
362 // e_shentsize = Section header entry size
363 write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
365 // e_shnum = # of section header ents
368 // e_shstrndx = Section # of '.shstrtab'
369 assert(StringTableIndex < ELF::SHN_LORESERVE);
370 write16(StringTableIndex);
373 uint64_t ELFObjectWriter::SymbolValue(const MCSymbol &Sym,
374 const MCAsmLayout &Layout) {
375 if (Sym.isCommon() && Sym.isExternal())
376 return Sym.getCommonAlignment();
379 if (!Layout.getSymbolOffset(Sym, Res))
382 if (Layout.getAssembler().isThumbFunc(&Sym))
388 void ELFObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
389 const MCAsmLayout &Layout) {
390 // The presence of symbol versions causes undefined symbols and
391 // versions declared with @@@ to be renamed.
392 for (const MCSymbol &A : Asm.symbols()) {
393 const auto &Alias = cast<MCSymbolELF>(A);
395 if (!Alias.isVariable())
397 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
400 const auto &Symbol = cast<MCSymbolELF>(Ref->getSymbol());
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 Alias.setExternal(Symbol.isExternal());
410 Alias.setBinding(Symbol.getBinding());
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,
461 uint32_t StringIndex, ELFSymbolData &MSD,
462 const MCAsmLayout &Layout) {
463 const auto &Symbol = cast<MCSymbolELF>(*MSD.Symbol);
464 const MCSymbolELF *Base =
465 cast_or_null<MCSymbolELF>(Layout.getBaseSymbol(Symbol));
467 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
469 bool IsReserved = !Base || Symbol.isCommon();
471 // Binding and Type share the same byte as upper and lower nibbles
472 uint8_t Binding = Symbol.getBinding();
473 uint8_t Type = Symbol.getType();
475 Type = mergeTypeForSet(Type, Base->getType());
477 uint8_t Info = (Binding << 4) | Type;
479 // Other and Visibility share the same byte with Visibility using the lower
481 uint8_t Visibility = Symbol.getVisibility();
482 uint8_t Other = Symbol.getOther() | Visibility;
484 uint64_t Value = SymbolValue(*MSD.Symbol, Layout);
487 const MCExpr *ESize = MSD.Symbol->getSize();
489 ESize = Base->getSize();
493 if (!ESize->evaluateKnownAbsolute(Res, Layout))
494 report_fatal_error("Size expression must be absolute.");
498 // Write out the symbol table entry
499 Writer.writeSymbol(StringIndex, Info, Value, Size, Other, MSD.SectionIndex,
503 // It is always valid to create a relocation with a symbol. It is preferable
504 // to use a relocation with a section if that is possible. Using the section
505 // allows us to omit some local symbols from the symbol table.
506 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
507 const MCSymbolRefExpr *RefA,
508 const MCSymbol *S, uint64_t C,
509 unsigned Type) const {
510 const auto *Sym = cast_or_null<MCSymbolELF>(S);
511 // A PCRel relocation to an absolute value has no symbol (or section). We
512 // represent that with a relocation to a null section.
516 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
520 // The .odp creation emits a relocation against the symbol ".TOC." which
521 // create a R_PPC64_TOC relocation. However the relocation symbol name
522 // in final object creation should be NULL, since the symbol does not
523 // really exist, it is just the reference to TOC base for the current
524 // object file. Since the symbol is undefined, returning false results
525 // in a relocation with a null section which is the desired result.
526 case MCSymbolRefExpr::VK_PPC_TOCBASE:
529 // These VariantKind cause the relocation to refer to something other than
530 // the symbol itself, like a linker generated table. Since the address of
531 // symbol is not relevant, we cannot replace the symbol with the
532 // section and patch the difference in the addend.
533 case MCSymbolRefExpr::VK_GOT:
534 case MCSymbolRefExpr::VK_PLT:
535 case MCSymbolRefExpr::VK_GOTPCREL:
536 case MCSymbolRefExpr::VK_PPC_GOT_LO:
537 case MCSymbolRefExpr::VK_PPC_GOT_HI:
538 case MCSymbolRefExpr::VK_PPC_GOT_HA:
542 // An undefined symbol is not in any section, so the relocation has to point
543 // to the symbol itself.
544 assert(Sym && "Expected a symbol");
545 if (Sym->isUndefined())
548 unsigned Binding = Sym->getBinding();
551 llvm_unreachable("Invalid Binding");
555 // If the symbol is weak, it might be overridden by a symbol in another
556 // file. The relocation has to point to the symbol so that the linker
559 case ELF::STB_GLOBAL:
560 // Global ELF symbols can be preempted by the dynamic linker. The relocation
561 // has to point to the symbol for a reason analogous to the STB_WEAK case.
565 // If a relocation points to a mergeable section, we have to be careful.
566 // If the offset is zero, a relocation with the section will encode the
567 // same information. With a non-zero offset, the situation is different.
568 // For example, a relocation can point 42 bytes past the end of a string.
569 // If we change such a relocation to use the section, the linker would think
570 // that it pointed to another string and subtracting 42 at runtime will
571 // produce the wrong value.
572 if (Sym->isInSection()) {
573 auto &Sec = cast<MCSectionELF>(Sym->getSection());
574 unsigned Flags = Sec.getFlags();
575 if (Flags & ELF::SHF_MERGE) {
579 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
580 // only handle section relocations to mergeable sections if using RELA.
581 if (!hasRelocationAddend())
585 // Most TLS relocations use a got, so they need the symbol. Even those that
586 // are just an offset (@tpoff), require a symbol in gold versions before
587 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
588 // http://sourceware.org/PR16773.
589 if (Flags & ELF::SHF_TLS)
593 // If the symbol is a thumb function the final relocation must set the lowest
594 // bit. With a symbol that is done by just having the symbol have that bit
595 // set, so we would lose the bit if we relocated with the section.
596 // FIXME: We could use the section but add the bit to the relocation value.
597 if (Asm.isThumbFunc(Sym))
600 if (TargetObjectWriter->needsRelocateWithSymbol(*Sym, Type))
605 // True if the assembler knows nothing about the final value of the symbol.
606 // This doesn't cover the comdat issues, since in those cases the assembler
607 // can at least know that all symbols in the section will move together.
608 static bool isWeak(const MCSymbolELF &Sym) {
609 if (Sym.getType() == ELF::STT_GNU_IFUNC)
612 switch (Sym.getBinding()) {
614 llvm_unreachable("Unknown binding");
617 case ELF::STB_GLOBAL:
620 case ELF::STB_GNU_UNIQUE:
625 void ELFObjectWriter::recordRelocation(MCAssembler &Asm,
626 const MCAsmLayout &Layout,
627 const MCFragment *Fragment,
628 const MCFixup &Fixup, MCValue Target,
629 bool &IsPCRel, uint64_t &FixedValue) {
630 const MCSectionELF &FixupSection = cast<MCSectionELF>(*Fragment->getParent());
631 uint64_t C = Target.getConstant();
632 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
633 MCContext &Ctx = Asm.getContext();
635 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
636 // Let A, B and C being the components of Target and R be the location of
637 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
638 // If it is pcrel, we want to compute (A - B + C - R).
640 // In general, ELF has no relocations for -B. It can only represent (A + C)
641 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
642 // replace B to implement it: (A - R - K + C)
646 "No relocation available to represent this relative expression");
650 const auto &SymB = cast<MCSymbolELF>(RefB->getSymbol());
652 if (SymB.isUndefined()) {
653 Ctx.reportError(Fixup.getLoc(),
654 Twine("symbol '") + SymB.getName() +
655 "' can not be undefined in a subtraction expression");
659 assert(!SymB.isAbsolute() && "Should have been folded");
660 const MCSection &SecB = SymB.getSection();
661 if (&SecB != &FixupSection) {
662 Ctx.reportError(Fixup.getLoc(),
663 "Cannot represent a difference across sections");
667 uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
668 uint64_t K = SymBOffset - FixupOffset;
673 // We either rejected the fixup or folded B into C at this point.
674 const MCSymbolRefExpr *RefA = Target.getSymA();
675 const auto *SymA = RefA ? cast<MCSymbolELF>(&RefA->getSymbol()) : nullptr;
677 bool ViaWeakRef = false;
678 if (SymA && SymA->isVariable()) {
679 const MCExpr *Expr = SymA->getVariableValue();
680 if (const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr)) {
681 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF) {
682 SymA = cast<MCSymbolELF>(&Inner->getSymbol());
688 unsigned Type = getRelocType(Ctx, Target, Fixup, IsPCRel);
689 uint64_t OriginalC = C;
690 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymA, C, Type);
691 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
692 C += Layout.getSymbolOffset(*SymA);
695 if (hasRelocationAddend()) {
702 if (!RelocateWithSymbol) {
703 const MCSection *SecA =
704 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
705 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
706 const auto *SectionSymbol =
707 ELFSec ? cast<MCSymbolELF>(ELFSec->getBeginSymbol()) : nullptr;
709 SectionSymbol->setUsedInReloc();
710 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend, SymA,
712 Relocations[&FixupSection].push_back(Rec);
716 const auto *RenamedSymA = SymA;
718 if (const MCSymbolELF *R = Renames.lookup(SymA))
722 RenamedSymA->setIsWeakrefUsedInReloc();
724 RenamedSymA->setUsedInReloc();
726 ELFRelocationEntry Rec(FixupOffset, RenamedSymA, Type, Addend, SymA,
728 Relocations[&FixupSection].push_back(Rec);
731 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
732 const MCSymbolELF &Symbol, bool Used,
734 if (Symbol.isVariable()) {
735 const MCExpr *Expr = Symbol.getVariableValue();
736 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
737 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
748 if (Symbol.isVariable() && Symbol.isUndefined()) {
749 // FIXME: this is here just to diagnose the case of a var = commmon_sym.
750 Layout.getBaseSymbol(Symbol);
754 if (Symbol.isUndefined() && !Symbol.isBindingSet())
757 if (Symbol.isTemporary())
760 if (Symbol.getType() == ELF::STT_SECTION)
766 void ELFObjectWriter::computeSymbolTable(
767 MCAssembler &Asm, const MCAsmLayout &Layout,
768 const SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap,
769 SectionOffsetsTy &SectionOffsets) {
770 MCContext &Ctx = Asm.getContext();
771 SymbolTableWriter Writer(*this, is64Bit());
774 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
775 MCSectionELF *SymtabSection =
776 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
777 SymtabSection->setAlignment(is64Bit() ? 8 : 4);
778 SymbolTableIndex = addToSectionTable(SymtabSection);
780 align(SymtabSection->getAlignment());
781 uint64_t SecStart = getStream().tell();
783 // The first entry is the undefined symbol entry.
784 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
786 std::vector<ELFSymbolData> LocalSymbolData;
787 std::vector<ELFSymbolData> ExternalSymbolData;
789 // Add the data for the symbols.
790 bool HasLargeSectionIndex = false;
791 for (const MCSymbol &S : Asm.symbols()) {
792 const auto &Symbol = cast<MCSymbolELF>(S);
793 bool Used = Symbol.isUsedInReloc();
794 bool WeakrefUsed = Symbol.isWeakrefUsedInReloc();
795 bool isSignature = Symbol.isSignature();
797 if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
798 Renames.count(&Symbol)))
801 if (Symbol.isTemporary() && Symbol.isUndefined()) {
802 Ctx.reportError(SMLoc(), "Undefined temporary symbol");
807 MSD.Symbol = cast<MCSymbolELF>(&Symbol);
809 bool Local = Symbol.getBinding() == ELF::STB_LOCAL;
810 assert(Local || !Symbol.isTemporary());
812 if (Symbol.isAbsolute()) {
813 MSD.SectionIndex = ELF::SHN_ABS;
814 } else if (Symbol.isCommon()) {
816 MSD.SectionIndex = ELF::SHN_COMMON;
817 } else if (Symbol.isUndefined()) {
818 if (isSignature && !Used) {
819 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
820 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
821 HasLargeSectionIndex = true;
823 MSD.SectionIndex = ELF::SHN_UNDEF;
826 const MCSectionELF &Section =
827 static_cast<const MCSectionELF &>(Symbol.getSection());
828 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
829 assert(MSD.SectionIndex && "Invalid section index!");
830 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
831 HasLargeSectionIndex = true;
834 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
837 // FIXME: All name handling should be done before we get to the writer,
838 // including dealing with GNU-style version suffixes. Fixing this isn't
841 // We thus have to be careful to not perform the symbol version replacement
844 // The ELF format is used on Windows by the MCJIT engine. Thus, on
845 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
846 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
847 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
848 // the EFLObjectWriter should not interpret the "@@@" sub-string as
849 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
850 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
851 // "__imp_?" or "__imp_@?".
853 // It would have been interesting to perform the MS mangling prefix check
854 // only when the target triple is of the form *-pc-windows-elf. But, it
855 // seems that this information is not easily accessible from the
857 StringRef Name = Symbol.getName();
859 if (!Name.startswith("?") && !Name.startswith("@?") &&
860 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
861 // This symbol isn't following the MSVC C++ name mangling convention. We
862 // can thus safely interpret the @@@ in symbol names as specifying symbol
864 size_t Pos = Name.find("@@@");
865 if (Pos != StringRef::npos) {
866 Buf += Name.substr(0, Pos);
867 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
868 Buf += Name.substr(Pos + Skip);
869 Name = VersionSymSaver.save(Buf.c_str());
873 // Sections have their own string table
874 if (Symbol.getType() != ELF::STT_SECTION) {
876 StrTabBuilder.add(Name);
880 LocalSymbolData.push_back(MSD);
882 ExternalSymbolData.push_back(MSD);
885 // This holds the .symtab_shndx section index.
886 unsigned SymtabShndxSectionIndex = 0;
888 if (HasLargeSectionIndex) {
889 MCSectionELF *SymtabShndxSection =
890 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
891 SymtabShndxSectionIndex = addToSectionTable(SymtabShndxSection);
892 SymtabShndxSection->setAlignment(4);
895 ArrayRef<std::string> FileNames = Asm.getFileNames();
896 for (const std::string &Name : FileNames)
897 StrTabBuilder.add(Name);
899 StrTabBuilder.finalize();
901 // File symbols are emitted first and handled separately from normal symbols,
902 // i.e. a non-STT_FILE symbol with the same name may appear.
903 for (const std::string &Name : FileNames)
904 Writer.writeSymbol(StrTabBuilder.getOffset(Name),
905 ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, ELF::STV_DEFAULT,
908 // Symbols are required to be in lexicographic order.
909 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
910 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
912 // Set the symbol indices. Local symbols must come before all other
913 // symbols with non-local bindings.
914 unsigned Index = FileNames.size() + 1;
916 for (ELFSymbolData &MSD : LocalSymbolData) {
917 unsigned StringIndex = MSD.Symbol->getType() == ELF::STT_SECTION
919 : StrTabBuilder.getOffset(MSD.Name);
920 MSD.Symbol->setIndex(Index++);
921 writeSymbol(Writer, StringIndex, MSD, Layout);
924 // Write the symbol table entries.
925 LastLocalSymbolIndex = Index;
927 for (ELFSymbolData &MSD : ExternalSymbolData) {
928 unsigned StringIndex = StrTabBuilder.getOffset(MSD.Name);
929 MSD.Symbol->setIndex(Index++);
930 writeSymbol(Writer, StringIndex, MSD, Layout);
931 assert(MSD.Symbol->getBinding() != ELF::STB_LOCAL);
934 uint64_t SecEnd = getStream().tell();
935 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
937 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
938 if (ShndxIndexes.empty()) {
939 assert(SymtabShndxSectionIndex == 0);
942 assert(SymtabShndxSectionIndex != 0);
944 SecStart = getStream().tell();
945 const MCSectionELF *SymtabShndxSection =
946 SectionTable[SymtabShndxSectionIndex - 1];
947 for (uint32_t Index : ShndxIndexes)
949 SecEnd = getStream().tell();
950 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
954 ELFObjectWriter::createRelocationSection(MCContext &Ctx,
955 const MCSectionELF &Sec) {
956 if (Relocations[&Sec].empty())
959 const StringRef SectionName = Sec.getSectionName();
960 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
961 RelaSectionName += SectionName;
964 if (hasRelocationAddend())
965 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
967 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
970 if (Sec.getFlags() & ELF::SHF_GROUP)
971 Flags = ELF::SHF_GROUP;
973 MCSectionELF *RelaSection = Ctx.createELFRelSection(
974 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
975 Flags, EntrySize, Sec.getGroup(), &Sec);
976 RelaSection->setAlignment(is64Bit() ? 8 : 4);
980 // Include the debug info compression header.
981 bool ELFObjectWriter::maybeWriteCompression(
982 uint64_t Size, SmallVectorImpl<char> &CompressedContents, bool ZLibStyle,
983 unsigned Alignment) {
986 is64Bit() ? sizeof(ELF::Elf32_Chdr) : sizeof(ELF::Elf64_Chdr);
987 if (Size <= HdrSize + CompressedContents.size())
989 // Platform specific header is followed by compressed data.
991 // Write Elf64_Chdr header.
992 write(static_cast<ELF::Elf64_Word>(ELF::ELFCOMPRESS_ZLIB));
993 write(static_cast<ELF::Elf64_Word>(0)); // ch_reserved field.
994 write(static_cast<ELF::Elf64_Xword>(Size));
995 write(static_cast<ELF::Elf64_Xword>(Alignment));
997 // Write Elf32_Chdr header otherwise.
998 write(static_cast<ELF::Elf32_Word>(ELF::ELFCOMPRESS_ZLIB));
999 write(static_cast<ELF::Elf32_Word>(Size));
1000 write(static_cast<ELF::Elf32_Word>(Alignment));
1005 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1006 // useful for consumers to preallocate a buffer to decompress into.
1007 const StringRef Magic = "ZLIB";
1008 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1010 write(ArrayRef<char>(Magic.begin(), Magic.size()));
1015 void ELFObjectWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
1016 const MCAsmLayout &Layout) {
1017 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1018 StringRef SectionName = Section.getSectionName();
1020 auto &MC = Asm.getContext();
1021 const auto &MAI = MC.getAsmInfo();
1023 // Compressing debug_frame requires handling alignment fragments which is
1024 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1025 // for writing to arbitrary buffers) for little benefit.
1026 bool CompressionEnabled =
1027 MAI->compressDebugSections() != DebugCompressionType::None;
1028 if (!CompressionEnabled || !SectionName.startswith(".debug_") ||
1029 SectionName == ".debug_frame") {
1030 Asm.writeSectionData(&Section, Layout);
1034 assert((MAI->compressDebugSections() == DebugCompressionType::Z ||
1035 MAI->compressDebugSections() == DebugCompressionType::GNU) &&
1036 "expected zlib or zlib-gnu style compression");
1038 SmallVector<char, 128> UncompressedData;
1039 raw_svector_ostream VecOS(UncompressedData);
1040 raw_pwrite_stream &OldStream = getStream();
1042 Asm.writeSectionData(&Section, Layout);
1043 setStream(OldStream);
1045 SmallVector<char, 128> CompressedContents;
1046 if (Error E = zlib::compress(
1047 StringRef(UncompressedData.data(), UncompressedData.size()),
1048 CompressedContents)) {
1049 consumeError(std::move(E));
1050 getStream() << UncompressedData;
1054 bool ZlibStyle = MAI->compressDebugSections() == DebugCompressionType::Z;
1055 if (!maybeWriteCompression(UncompressedData.size(), CompressedContents,
1056 ZlibStyle, Sec.getAlignment())) {
1057 getStream() << UncompressedData;
1062 // Set the compressed flag. That is zlib style.
1063 Section.setFlags(Section.getFlags() | ELF::SHF_COMPRESSED);
1065 // Add "z" prefix to section name. This is zlib-gnu style.
1066 MC.renameELFSection(&Section, (".z" + SectionName.drop_front(1)).str());
1067 getStream() << CompressedContents;
1070 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1071 uint64_t Flags, uint64_t Address,
1072 uint64_t Offset, uint64_t Size,
1073 uint32_t Link, uint32_t Info,
1075 uint64_t EntrySize) {
1076 write32(Name); // sh_name: index into string table
1077 write32(Type); // sh_type
1078 WriteWord(Flags); // sh_flags
1079 WriteWord(Address); // sh_addr
1080 WriteWord(Offset); // sh_offset
1081 WriteWord(Size); // sh_size
1082 write32(Link); // sh_link
1083 write32(Info); // sh_info
1084 WriteWord(Alignment); // sh_addralign
1085 WriteWord(EntrySize); // sh_entsize
1088 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1089 const MCSectionELF &Sec) {
1090 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1092 // We record relocations by pushing to the end of a vector. Reverse the vector
1093 // to get the relocations in the order they were created.
1094 // In most cases that is not important, but it can be for special sections
1095 // (.eh_frame) or specific relocations (TLS optimizations on SystemZ).
1096 std::reverse(Relocs.begin(), Relocs.end());
1098 // Sort the relocation entries. MIPS needs this.
1099 TargetObjectWriter->sortRelocs(Asm, Relocs);
1101 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1102 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1103 unsigned Index = Entry.Symbol ? Entry.Symbol->getIndex() : 0;
1106 write(Entry.Offset);
1107 if (TargetObjectWriter->isN64()) {
1108 write(uint32_t(Index));
1110 write(TargetObjectWriter->getRSsym(Entry.Type));
1111 write(TargetObjectWriter->getRType3(Entry.Type));
1112 write(TargetObjectWriter->getRType2(Entry.Type));
1113 write(TargetObjectWriter->getRType(Entry.Type));
1115 struct ELF::Elf64_Rela ERE64;
1116 ERE64.setSymbolAndType(Index, Entry.Type);
1117 write(ERE64.r_info);
1119 if (hasRelocationAddend())
1120 write(Entry.Addend);
1122 write(uint32_t(Entry.Offset));
1124 struct ELF::Elf32_Rela ERE32;
1125 ERE32.setSymbolAndType(Index, Entry.Type);
1126 write(ERE32.r_info);
1128 if (hasRelocationAddend())
1129 write(uint32_t(Entry.Addend));
1134 const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
1135 const MCSectionELF *StrtabSection = SectionTable[StringTableIndex - 1];
1136 StrTabBuilder.write(getStream());
1137 return StrtabSection;
1140 void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
1141 uint32_t GroupSymbolIndex, uint64_t Offset,
1142 uint64_t Size, const MCSectionELF &Section) {
1143 uint64_t sh_link = 0;
1144 uint64_t sh_info = 0;
1146 switch(Section.getType()) {
1151 case ELF::SHT_DYNAMIC:
1152 llvm_unreachable("SHT_DYNAMIC in a relocatable object");
1155 case ELF::SHT_RELA: {
1156 sh_link = SymbolTableIndex;
1157 assert(sh_link && ".symtab not found");
1158 const MCSection *InfoSection = Section.getAssociatedSection();
1159 sh_info = SectionIndexMap.lookup(cast<MCSectionELF>(InfoSection));
1163 case ELF::SHT_SYMTAB:
1164 case ELF::SHT_DYNSYM:
1165 sh_link = StringTableIndex;
1166 sh_info = LastLocalSymbolIndex;
1169 case ELF::SHT_SYMTAB_SHNDX:
1170 sh_link = SymbolTableIndex;
1173 case ELF::SHT_GROUP:
1174 sh_link = SymbolTableIndex;
1175 sh_info = GroupSymbolIndex;
1179 if (Section.getFlags() & ELF::SHF_LINK_ORDER) {
1180 const MCSymbol *Sym = Section.getAssociatedSymbol();
1181 const MCSectionELF *Sec = cast<MCSectionELF>(&Sym->getSection());
1182 sh_link = SectionIndexMap.lookup(Sec);
1185 WriteSecHdrEntry(StrTabBuilder.getOffset(Section.getSectionName()),
1186 Section.getType(), Section.getFlags(), 0, Offset, Size,
1187 sh_link, sh_info, Section.getAlignment(),
1188 Section.getEntrySize());
1191 void ELFObjectWriter::writeSectionHeader(
1192 const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap,
1193 const SectionOffsetsTy &SectionOffsets) {
1194 const unsigned NumSections = SectionTable.size();
1196 // Null section first.
1197 uint64_t FirstSectionSize =
1198 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1199 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1201 for (const MCSectionELF *Section : SectionTable) {
1202 uint32_t GroupSymbolIndex;
1203 unsigned Type = Section->getType();
1204 if (Type != ELF::SHT_GROUP)
1205 GroupSymbolIndex = 0;
1207 GroupSymbolIndex = Section->getGroup()->getIndex();
1209 const std::pair<uint64_t, uint64_t> &Offsets =
1210 SectionOffsets.find(Section)->second;
1212 if (Type == ELF::SHT_NOBITS)
1213 Size = Layout.getSectionAddressSize(Section);
1215 Size = Offsets.second - Offsets.first;
1217 writeSection(SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1222 void ELFObjectWriter::writeObject(MCAssembler &Asm,
1223 const MCAsmLayout &Layout) {
1224 MCContext &Ctx = Asm.getContext();
1225 MCSectionELF *StrtabSection =
1226 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1227 StringTableIndex = addToSectionTable(StrtabSection);
1229 RevGroupMapTy RevGroupMap;
1230 SectionIndexMapTy SectionIndexMap;
1232 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1234 // Write out the ELF header ...
1237 // ... then the sections ...
1238 SectionOffsetsTy SectionOffsets;
1239 std::vector<MCSectionELF *> Groups;
1240 std::vector<MCSectionELF *> Relocations;
1241 for (MCSection &Sec : Asm) {
1242 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1244 align(Section.getAlignment());
1246 // Remember the offset into the file for this section.
1247 uint64_t SecStart = getStream().tell();
1249 const MCSymbolELF *SignatureSymbol = Section.getGroup();
1250 writeSectionData(Asm, Section, Layout);
1252 uint64_t SecEnd = getStream().tell();
1253 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1255 MCSectionELF *RelSection = createRelocationSection(Ctx, Section);
1257 if (SignatureSymbol) {
1258 Asm.registerSymbol(*SignatureSymbol);
1259 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1261 MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1262 GroupIdx = addToSectionTable(Group);
1263 Group->setAlignment(4);
1264 Groups.push_back(Group);
1266 std::vector<const MCSectionELF *> &Members =
1267 GroupMembers[SignatureSymbol];
1268 Members.push_back(&Section);
1270 Members.push_back(RelSection);
1273 SectionIndexMap[&Section] = addToSectionTable(&Section);
1275 SectionIndexMap[RelSection] = addToSectionTable(RelSection);
1276 Relocations.push_back(RelSection);
1280 for (MCSectionELF *Group : Groups) {
1281 align(Group->getAlignment());
1283 // Remember the offset into the file for this section.
1284 uint64_t SecStart = getStream().tell();
1286 const MCSymbol *SignatureSymbol = Group->getGroup();
1287 assert(SignatureSymbol);
1288 write(uint32_t(ELF::GRP_COMDAT));
1289 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1290 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1294 uint64_t SecEnd = getStream().tell();
1295 SectionOffsets[Group] = std::make_pair(SecStart, SecEnd);
1298 // Compute symbol table information.
1299 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, SectionOffsets);
1301 for (MCSectionELF *RelSection : Relocations) {
1302 align(RelSection->getAlignment());
1304 // Remember the offset into the file for this section.
1305 uint64_t SecStart = getStream().tell();
1307 writeRelocations(Asm,
1308 cast<MCSectionELF>(*RelSection->getAssociatedSection()));
1310 uint64_t SecEnd = getStream().tell();
1311 SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
1315 uint64_t SecStart = getStream().tell();
1316 const MCSectionELF *Sec = createStringTable(Ctx);
1317 uint64_t SecEnd = getStream().tell();
1318 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1321 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1322 align(NaturalAlignment);
1324 const uint64_t SectionHeaderOffset = getStream().tell();
1326 // ... then the section header table ...
1327 writeSectionHeader(Layout, SectionIndexMap, SectionOffsets);
1329 uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
1330 ? (uint16_t)ELF::SHN_UNDEF
1331 : SectionTable.size() + 1;
1332 if (sys::IsLittleEndianHost != IsLittleEndian)
1333 sys::swapByteOrder(NumSections);
1334 unsigned NumSectionsOffset;
1337 uint64_t Val = SectionHeaderOffset;
1338 if (sys::IsLittleEndianHost != IsLittleEndian)
1339 sys::swapByteOrder(Val);
1340 getStream().pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1341 offsetof(ELF::Elf64_Ehdr, e_shoff));
1342 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1344 uint32_t Val = SectionHeaderOffset;
1345 if (sys::IsLittleEndianHost != IsLittleEndian)
1346 sys::swapByteOrder(Val);
1347 getStream().pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1348 offsetof(ELF::Elf32_Ehdr, e_shoff));
1349 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1351 getStream().pwrite(reinterpret_cast<char *>(&NumSections),
1352 sizeof(NumSections), NumSectionsOffset);
1355 bool ELFObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
1356 const MCAssembler &Asm, const MCSymbol &SA, const MCFragment &FB,
1357 bool InSet, bool IsPCRel) const {
1358 const auto &SymA = cast<MCSymbolELF>(SA);
1364 return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
1368 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1369 raw_pwrite_stream &OS,
1370 bool IsLittleEndian) {
1371 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);