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->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;
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 MCSymbolData &Data = Sym.getData();
363 if (Sym.isCommon() && Data.isExternal())
364 return Sym.getCommonAlignment();
367 if (!Layout.getSymbolOffset(Sym, Res))
370 if (Layout.getAssembler().isThumbFunc(&Sym))
376 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
377 const MCAsmLayout &Layout) {
378 // The presence of symbol versions causes undefined symbols and
379 // versions declared with @@@ to be renamed.
381 for (const MCSymbol &Alias : Asm.symbols()) {
382 MCSymbolData &OriginalData = Alias.getData();
385 if (!Alias.isVariable())
387 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
390 const MCSymbol &Symbol = Ref->getSymbol();
391 MCSymbolData &SD = Symbol.getData();
393 StringRef AliasName = Alias.getName();
394 size_t Pos = AliasName.find('@');
395 if (Pos == StringRef::npos)
398 // Aliases defined with .symvar copy the binding from the symbol they alias.
399 // This is the first place we are able to copy this information.
400 OriginalData.setExternal(SD.isExternal());
401 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
403 StringRef Rest = AliasName.substr(Pos);
404 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
407 // FIXME: produce a better error message.
408 if (Symbol.isUndefined() && Rest.startswith("@@") &&
409 !Rest.startswith("@@@"))
410 report_fatal_error("A @@ version cannot be undefined");
412 Renames.insert(std::make_pair(&Symbol, &Alias));
416 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
417 uint8_t Type = newType;
419 // Propagation rules:
420 // IFUNC > FUNC > OBJECT > NOTYPE
421 // TLS_OBJECT > OBJECT > NOTYPE
423 // dont let the new type degrade the old type
427 case ELF::STT_GNU_IFUNC:
428 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
429 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
430 Type = ELF::STT_GNU_IFUNC;
433 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
434 Type == ELF::STT_TLS)
435 Type = ELF::STT_FUNC;
437 case ELF::STT_OBJECT:
438 if (Type == ELF::STT_NOTYPE)
439 Type = ELF::STT_OBJECT;
442 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
443 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
451 void ELFObjectWriter::writeSymbol(SymbolTableWriter &Writer,
452 uint32_t StringIndex, ELFSymbolData &MSD,
453 const MCAsmLayout &Layout) {
454 MCSymbolData &OrigData = MSD.Symbol->getData();
455 assert((!OrigData.getFragment() ||
456 (OrigData.getFragment()->getParent() == &MSD.Symbol->getSection())) &&
457 "The symbol's section doesn't match the fragment's symbol");
458 const MCSymbol *Base = Layout.getBaseSymbol(*MSD.Symbol);
460 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
462 bool IsReserved = !Base || MSD.Symbol->isCommon();
464 // Binding and Type share the same byte as upper and lower nibbles
465 uint8_t Binding = MCELF::GetBinding(OrigData);
466 uint8_t Type = MCELF::GetType(OrigData);
467 MCSymbolData *BaseSD = nullptr;
469 BaseSD = &Base->getData();
470 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
472 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
474 // Other and Visibility share the same byte with Visibility using the lower
476 uint8_t Visibility = MCELF::GetVisibility(OrigData);
477 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
480 uint64_t Value = SymbolValue(*MSD.Symbol, Layout);
483 const MCExpr *ESize = MSD.Symbol->getSize();
485 ESize = Base->getSize();
489 if (!ESize->evaluateKnownAbsolute(Res, Layout))
490 report_fatal_error("Size expression must be absolute.");
494 // Write out the symbol table entry
495 Writer.writeSymbol(StringIndex, Info, Value, Size, Other, MSD.SectionIndex,
499 // It is always valid to create a relocation with a symbol. It is preferable
500 // to use a relocation with a section if that is possible. Using the section
501 // allows us to omit some local symbols from the symbol table.
502 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
503 const MCSymbolRefExpr *RefA,
504 const MCSymbol *Sym, uint64_t C,
505 unsigned Type) const {
506 MCSymbolData *SD = Sym ? &Sym->getData() : nullptr;
508 // A PCRel relocation to an absolute value has no symbol (or section). We
509 // represent that with a relocation to a null section.
513 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
517 // The .odp creation emits a relocation against the symbol ".TOC." which
518 // create a R_PPC64_TOC relocation. However the relocation symbol name
519 // in final object creation should be NULL, since the symbol does not
520 // really exist, it is just the reference to TOC base for the current
521 // object file. Since the symbol is undefined, returning false results
522 // in a relocation with a null section which is the desired result.
523 case MCSymbolRefExpr::VK_PPC_TOCBASE:
526 // These VariantKind cause the relocation to refer to something other than
527 // the symbol itself, like a linker generated table. Since the address of
528 // symbol is not relevant, we cannot replace the symbol with the
529 // section and patch the difference in the addend.
530 case MCSymbolRefExpr::VK_GOT:
531 case MCSymbolRefExpr::VK_PLT:
532 case MCSymbolRefExpr::VK_GOTPCREL:
533 case MCSymbolRefExpr::VK_Mips_GOT:
534 case MCSymbolRefExpr::VK_PPC_GOT_LO:
535 case MCSymbolRefExpr::VK_PPC_GOT_HI:
536 case MCSymbolRefExpr::VK_PPC_GOT_HA:
540 // An undefined symbol is not in any section, so the relocation has to point
541 // to the symbol itself.
542 assert(Sym && "Expected a symbol");
543 if (Sym->isUndefined())
546 unsigned Binding = MCELF::GetBinding(*SD);
549 llvm_unreachable("Invalid Binding");
553 // If the symbol is weak, it might be overridden by a symbol in another
554 // file. The relocation has to point to the symbol so that the linker
557 case ELF::STB_GLOBAL:
558 // Global ELF symbols can be preempted by the dynamic linker. The relocation
559 // has to point to the symbol for a reason analogous to the STB_WEAK case.
563 // If a relocation points to a mergeable section, we have to be careful.
564 // If the offset is zero, a relocation with the section will encode the
565 // same information. With a non-zero offset, the situation is different.
566 // For example, a relocation can point 42 bytes past the end of a string.
567 // If we change such a relocation to use the section, the linker would think
568 // that it pointed to another string and subtracting 42 at runtime will
569 // produce the wrong value.
570 auto &Sec = cast<MCSectionELF>(Sym->getSection());
571 unsigned Flags = Sec.getFlags();
572 if (Flags & ELF::SHF_MERGE) {
576 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
577 // only handle section relocations to mergeable sections if using RELA.
578 if (!hasRelocationAddend())
582 // Most TLS relocations use a got, so they need the symbol. Even those that
583 // are just an offset (@tpoff), require a symbol in gold versions before
584 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
585 // http://sourceware.org/PR16773.
586 if (Flags & ELF::SHF_TLS)
589 // If the symbol is a thumb function the final relocation must set the lowest
590 // bit. With a symbol that is done by just having the symbol have that bit
591 // set, so we would lose the bit if we relocated with the section.
592 // FIXME: We could use the section but add the bit to the relocation value.
593 if (Asm.isThumbFunc(Sym))
596 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
601 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
602 const MCSymbol &Sym = Ref.getSymbol();
604 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
607 if (!Sym.isVariable())
610 const MCExpr *Expr = Sym.getVariableValue();
611 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
615 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
616 return &Inner->getSymbol();
620 // True if the assembler knows nothing about the final value of the symbol.
621 // This doesn't cover the comdat issues, since in those cases the assembler
622 // can at least know that all symbols in the section will move together.
623 static bool isWeak(const MCSymbolData &D) {
624 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
627 switch (MCELF::GetBinding(D)) {
629 llvm_unreachable("Unknown binding");
632 case ELF::STB_GLOBAL:
635 case ELF::STB_GNU_UNIQUE:
640 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
641 const MCAsmLayout &Layout,
642 const MCFragment *Fragment,
643 const MCFixup &Fixup, MCValue Target,
644 bool &IsPCRel, uint64_t &FixedValue) {
645 const MCSectionELF &FixupSection = cast<MCSectionELF>(*Fragment->getParent());
646 uint64_t C = Target.getConstant();
647 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
649 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
650 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
651 "Should not have constructed this");
653 // Let A, B and C being the components of Target and R be the location of
654 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
655 // If it is pcrel, we want to compute (A - B + C - R).
657 // In general, ELF has no relocations for -B. It can only represent (A + C)
658 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
659 // replace B to implement it: (A - R - K + C)
661 Asm.getContext().reportFatalError(
663 "No relocation available to represent this relative expression");
665 const MCSymbol &SymB = RefB->getSymbol();
667 if (SymB.isUndefined())
668 Asm.getContext().reportFatalError(
670 Twine("symbol '") + SymB.getName() +
671 "' can not be undefined in a subtraction expression");
673 assert(!SymB.isAbsolute() && "Should have been folded");
674 const MCSection &SecB = SymB.getSection();
675 if (&SecB != &FixupSection)
676 Asm.getContext().reportFatalError(
677 Fixup.getLoc(), "Cannot represent a difference across sections");
679 if (::isWeak(SymB.getData()))
680 Asm.getContext().reportFatalError(
681 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
683 uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
684 uint64_t K = SymBOffset - FixupOffset;
689 // We either rejected the fixup or folded B into C at this point.
690 const MCSymbolRefExpr *RefA = Target.getSymA();
691 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
693 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
694 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymA, C, Type);
695 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
696 C += Layout.getSymbolOffset(*SymA);
699 if (hasRelocationAddend()) {
706 if (!RelocateWithSymbol) {
707 const MCSection *SecA =
708 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
709 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
710 const MCSymbol *SectionSymbol = ELFSec ? ELFSec->getBeginSymbol() : nullptr;
711 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
712 Relocations[&FixupSection].push_back(Rec);
717 if (const MCSymbol *R = Renames.lookup(SymA))
720 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
721 WeakrefUsedInReloc.insert(WeakRef);
723 UsedInReloc.insert(SymA);
725 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
726 Relocations[&FixupSection].push_back(Rec);
730 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
731 const MCSymbol &Symbol, bool Used,
733 const MCSymbolData &Data = Symbol.getData();
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.getName() == "_GLOBAL_OFFSET_TABLE_")
751 if (Symbol.isVariable()) {
752 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
753 if (Base && Base->isUndefined())
757 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
758 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
761 if (MCELF::GetType(Data) == ELF::STT_SECTION)
764 if (Symbol.isTemporary())
770 bool ELFObjectWriter::isLocal(const MCSymbol &Symbol, bool IsUsedInReloc,
772 const MCSymbolData &Data = Symbol.getData();
773 if (Data.isExternal())
776 if (Symbol.isDefined())
785 void ELFObjectWriter::computeSymbolTable(
786 MCAssembler &Asm, const MCAsmLayout &Layout,
787 const SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap,
788 SectionOffsetsTy &SectionOffsets) {
789 MCContext &Ctx = Asm.getContext();
790 SymbolTableWriter Writer(*this, is64Bit());
793 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
794 MCSectionELF *SymtabSection =
795 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
796 SymtabSection->setAlignment(is64Bit() ? 8 : 4);
797 SymbolTableIndex = addToSectionTable(SymtabSection);
800 OffsetToAlignment(OS.tell(), SymtabSection->getAlignment());
803 uint64_t SecStart = OS.tell();
805 // The first entry is the undefined symbol entry.
806 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
808 std::vector<ELFSymbolData> LocalSymbolData;
809 std::vector<ELFSymbolData> ExternalSymbolData;
811 // Add the data for the symbols.
812 bool HasLargeSectionIndex = false;
813 for (const MCSymbol &Symbol : Asm.symbols()) {
814 MCSymbolData &SD = Symbol.getData();
816 bool Used = UsedInReloc.count(&Symbol);
817 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
818 bool isSignature = RevGroupMap.count(&Symbol);
820 if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
821 Renames.count(&Symbol)))
825 MSD.Symbol = &Symbol;
827 // Undefined symbols are global, but this is the first place we
828 // are able to set it.
829 bool Local = isLocal(Symbol, Used, isSignature);
830 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL)
831 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
833 if (Symbol.isAbsolute()) {
834 MSD.SectionIndex = ELF::SHN_ABS;
835 } else if (Symbol.isCommon()) {
837 MSD.SectionIndex = ELF::SHN_COMMON;
838 } else if (Symbol.isUndefined()) {
839 if (isSignature && !Used) {
840 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
841 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
842 HasLargeSectionIndex = true;
844 MSD.SectionIndex = ELF::SHN_UNDEF;
846 if (!Used && WeakrefUsed)
847 MCELF::SetBinding(SD, ELF::STB_WEAK);
849 const MCSectionELF &Section =
850 static_cast<const MCSectionELF &>(Symbol.getSection());
851 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
852 assert(MSD.SectionIndex && "Invalid section index!");
853 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
854 HasLargeSectionIndex = true;
857 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
860 // FIXME: All name handling should be done before we get to the writer,
861 // including dealing with GNU-style version suffixes. Fixing this isn't
864 // We thus have to be careful to not perform the symbol version replacement
867 // The ELF format is used on Windows by the MCJIT engine. Thus, on
868 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
869 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
870 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
871 // the EFLObjectWriter should not interpret the "@@@" sub-string as
872 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
873 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
874 // "__imp_?" or "__imp_@?".
876 // It would have been interesting to perform the MS mangling prefix check
877 // only when the target triple is of the form *-pc-windows-elf. But, it
878 // seems that this information is not easily accessible from the
880 StringRef Name = Symbol.getName();
881 if (!Name.startswith("?") && !Name.startswith("@?") &&
882 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
883 // This symbol isn't following the MSVC C++ name mangling convention. We
884 // can thus safely interpret the @@@ in symbol names as specifying symbol
887 size_t Pos = Name.find("@@@");
888 if (Pos != StringRef::npos) {
889 Buf += Name.substr(0, Pos);
890 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
891 Buf += Name.substr(Pos + Skip);
896 // Sections have their own string table
897 if (MCELF::GetType(SD) != ELF::STT_SECTION)
898 MSD.Name = StrTabBuilder.add(Name);
901 LocalSymbolData.push_back(MSD);
903 ExternalSymbolData.push_back(MSD);
906 if (HasLargeSectionIndex) {
907 MCSectionELF *SymtabShndxSection =
908 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
909 SymtabShndxSectionIndex = addToSectionTable(SymtabShndxSection);
910 SymtabShndxSection->setAlignment(4);
913 ArrayRef<std::string> FileNames = Asm.getFileNames();
914 for (const std::string &Name : FileNames)
915 StrTabBuilder.add(Name);
917 StrTabBuilder.finalize(StringTableBuilder::ELF);
919 for (const std::string &Name : FileNames)
920 Writer.writeSymbol(StrTabBuilder.getOffset(Name),
921 ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, ELF::STV_DEFAULT,
924 // Symbols are required to be in lexicographic order.
925 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
926 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
928 // Set the symbol indices. Local symbols must come before all other
929 // symbols with non-local bindings.
930 unsigned Index = FileNames.size() + 1;
932 for (ELFSymbolData &MSD : LocalSymbolData) {
933 unsigned StringIndex =
934 MCELF::GetType(MSD.Symbol->getData()) == ELF::STT_SECTION
936 : StrTabBuilder.getOffset(MSD.Name);
937 MSD.Symbol->setIndex(Index++);
938 writeSymbol(Writer, StringIndex, MSD, Layout);
941 // Write the symbol table entries.
942 LastLocalSymbolIndex = Index;
944 for (ELFSymbolData &MSD : ExternalSymbolData) {
945 unsigned StringIndex = StrTabBuilder.getOffset(MSD.Name);
946 MSD.Symbol->setIndex(Index++);
947 writeSymbol(Writer, StringIndex, MSD, Layout);
948 assert(MCELF::GetBinding(MSD.Symbol->getData()) != ELF::STB_LOCAL);
951 uint64_t SecEnd = OS.tell();
952 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
954 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
955 if (ShndxIndexes.empty()) {
956 assert(SymtabShndxSectionIndex == 0);
959 assert(SymtabShndxSectionIndex != 0);
961 SecStart = OS.tell();
962 const MCSectionELF *SymtabShndxSection =
963 SectionTable[SymtabShndxSectionIndex - 1];
964 for (uint32_t Index : ShndxIndexes)
967 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
971 ELFObjectWriter::createRelocationSection(MCContext &Ctx,
972 const MCSectionELF &Sec) {
973 if (Relocations[&Sec].empty())
976 const StringRef SectionName = Sec.getSectionName();
977 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
978 RelaSectionName += SectionName;
981 if (hasRelocationAddend())
982 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
984 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
987 if (Sec.getFlags() & ELF::SHF_GROUP)
988 Flags = ELF::SHF_GROUP;
990 MCSectionELF *RelaSection = Ctx.createELFRelSection(
991 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
992 Flags, EntrySize, Sec.getGroup(), &Sec);
993 RelaSection->setAlignment(is64Bit() ? 8 : 4);
997 static SmallVector<char, 128>
998 getUncompressedData(const MCAsmLayout &Layout,
999 const MCSection::FragmentListType &Fragments) {
1000 SmallVector<char, 128> UncompressedData;
1001 for (const MCFragment &F : Fragments) {
1002 const SmallVectorImpl<char> *Contents;
1003 switch (F.getKind()) {
1004 case MCFragment::FT_Data:
1005 Contents = &cast<MCDataFragment>(F).getContents();
1007 case MCFragment::FT_Dwarf:
1008 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1010 case MCFragment::FT_DwarfFrame:
1011 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1015 "Not expecting any other fragment types in a debug_* section");
1017 UncompressedData.append(Contents->begin(), Contents->end());
1019 return UncompressedData;
1022 // Include the debug info compression header:
1023 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1024 // useful for consumers to preallocate a buffer to decompress into.
1026 prependCompressionHeader(uint64_t Size,
1027 SmallVectorImpl<char> &CompressedContents) {
1028 const StringRef Magic = "ZLIB";
1029 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1031 if (sys::IsLittleEndianHost)
1032 sys::swapByteOrder(Size);
1033 CompressedContents.insert(CompressedContents.begin(),
1034 Magic.size() + sizeof(Size), 0);
1035 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1036 std::copy(reinterpret_cast<char *>(&Size),
1037 reinterpret_cast<char *>(&Size + 1),
1038 CompressedContents.begin() + Magic.size());
1042 void ELFObjectWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
1043 const MCAsmLayout &Layout) {
1044 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1045 StringRef SectionName = Section.getSectionName();
1047 // Compressing debug_frame requires handling alignment fragments which is
1048 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1049 // for writing to arbitrary buffers) for little benefit.
1050 if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
1051 !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
1052 Asm.writeSectionData(&Section, Layout);
1056 // Gather the uncompressed data from all the fragments.
1057 const MCSection::FragmentListType &Fragments = Section.getFragmentList();
1058 SmallVector<char, 128> UncompressedData =
1059 getUncompressedData(Layout, Fragments);
1061 SmallVector<char, 128> CompressedContents;
1062 zlib::Status Success = zlib::compress(
1063 StringRef(UncompressedData.data(), UncompressedData.size()),
1064 CompressedContents);
1065 if (Success != zlib::StatusOK) {
1066 Asm.writeSectionData(&Section, Layout);
1070 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
1071 Asm.writeSectionData(&Section, Layout);
1074 Asm.getContext().renameELFSection(&Section,
1075 (".z" + SectionName.drop_front(1)).str());
1076 OS << CompressedContents;
1079 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1080 uint64_t Flags, uint64_t Address,
1081 uint64_t Offset, uint64_t Size,
1082 uint32_t Link, uint32_t Info,
1084 uint64_t EntrySize) {
1085 Write32(Name); // sh_name: index into string table
1086 Write32(Type); // sh_type
1087 WriteWord(Flags); // sh_flags
1088 WriteWord(Address); // sh_addr
1089 WriteWord(Offset); // sh_offset
1090 WriteWord(Size); // sh_size
1091 Write32(Link); // sh_link
1092 Write32(Info); // sh_info
1093 WriteWord(Alignment); // sh_addralign
1094 WriteWord(EntrySize); // sh_entsize
1097 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1098 const MCSectionELF &Sec) {
1099 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1101 // Sort the relocation entries. Most targets just sort by Offset, but some
1102 // (e.g., MIPS) have additional constraints.
1103 TargetObjectWriter->sortRelocs(Asm, Relocs);
1105 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1106 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1107 unsigned Index = Entry.Symbol ? Entry.Symbol->getIndex() : 0;
1110 write(Entry.Offset);
1111 if (TargetObjectWriter->isN64()) {
1112 write(uint32_t(Index));
1114 write(TargetObjectWriter->getRSsym(Entry.Type));
1115 write(TargetObjectWriter->getRType3(Entry.Type));
1116 write(TargetObjectWriter->getRType2(Entry.Type));
1117 write(TargetObjectWriter->getRType(Entry.Type));
1119 struct ELF::Elf64_Rela ERE64;
1120 ERE64.setSymbolAndType(Index, Entry.Type);
1121 write(ERE64.r_info);
1123 if (hasRelocationAddend())
1124 write(Entry.Addend);
1126 write(uint32_t(Entry.Offset));
1128 struct ELF::Elf32_Rela ERE32;
1129 ERE32.setSymbolAndType(Index, Entry.Type);
1130 write(ERE32.r_info);
1132 if (hasRelocationAddend())
1133 write(uint32_t(Entry.Addend));
1138 const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
1139 const MCSectionELF *StrtabSection = SectionTable[StringTableIndex - 1];
1140 OS << StrTabBuilder.data();
1141 return StrtabSection;
1144 void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
1145 uint32_t GroupSymbolIndex, uint64_t Offset,
1146 uint64_t Size, const MCSectionELF &Section) {
1147 uint64_t sh_link = 0;
1148 uint64_t sh_info = 0;
1150 switch(Section.getType()) {
1155 case ELF::SHT_DYNAMIC:
1156 llvm_unreachable("SHT_DYNAMIC in a relocatable object");
1159 case ELF::SHT_RELA: {
1160 sh_link = SymbolTableIndex;
1161 assert(sh_link && ".symtab not found");
1162 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1163 sh_info = SectionIndexMap.lookup(InfoSection);
1167 case ELF::SHT_SYMTAB:
1168 case ELF::SHT_DYNSYM:
1169 sh_link = StringTableIndex;
1170 sh_info = LastLocalSymbolIndex;
1173 case ELF::SHT_SYMTAB_SHNDX:
1174 sh_link = SymbolTableIndex;
1177 case ELF::SHT_GROUP:
1178 sh_link = SymbolTableIndex;
1179 sh_info = GroupSymbolIndex;
1183 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1184 Section.getType() == ELF::SHT_ARM_EXIDX)
1185 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1187 WriteSecHdrEntry(StrTabBuilder.getOffset(Section.getSectionName()),
1188 Section.getType(), Section.getFlags(), 0, Offset, Size,
1189 sh_link, sh_info, Section.getAlignment(),
1190 Section.getEntrySize());
1193 void ELFObjectWriter::writeSectionHeader(
1194 const MCAssembler &Asm, const MCAsmLayout &Layout,
1195 const SectionIndexMapTy &SectionIndexMap,
1196 const SectionOffsetsTy &SectionOffsets) {
1197 const unsigned NumSections = SectionTable.size();
1199 // Null section first.
1200 uint64_t FirstSectionSize =
1201 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1202 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1204 for (const MCSectionELF *Section : SectionTable) {
1205 uint32_t GroupSymbolIndex;
1206 unsigned Type = Section->getType();
1207 if (Type != ELF::SHT_GROUP)
1208 GroupSymbolIndex = 0;
1210 GroupSymbolIndex = Section->getGroup()->getIndex();
1212 const std::pair<uint64_t, uint64_t> &Offsets =
1213 SectionOffsets.find(Section)->second;
1215 if (Type == ELF::SHT_NOBITS)
1216 Size = Layout.getSectionAddressSize(Section);
1218 Size = Offsets.second - Offsets.first;
1220 writeSection(SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1225 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1226 const MCAsmLayout &Layout) {
1227 MCContext &Ctx = Asm.getContext();
1228 MCSectionELF *StrtabSection =
1229 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1230 StringTableIndex = addToSectionTable(StrtabSection);
1232 RevGroupMapTy RevGroupMap;
1233 SectionIndexMapTy SectionIndexMap;
1235 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1237 // Write out the ELF header ...
1240 // ... then the sections ...
1241 SectionOffsetsTy SectionOffsets;
1242 std::vector<MCSectionELF *> Groups;
1243 std::vector<MCSectionELF *> Relocations;
1244 for (MCSection &Sec : Asm) {
1245 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1247 uint64_t Padding = OffsetToAlignment(OS.tell(), Section.getAlignment());
1248 WriteZeros(Padding);
1250 // Remember the offset into the file for this section.
1251 uint64_t SecStart = OS.tell();
1253 const MCSymbol *SignatureSymbol = Section.getGroup();
1254 writeSectionData(Asm, Section, Layout);
1256 uint64_t SecEnd = OS.tell();
1257 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1259 MCSectionELF *RelSection = createRelocationSection(Ctx, Section);
1261 if (SignatureSymbol) {
1262 Asm.getOrCreateSymbolData(*SignatureSymbol);
1263 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1265 MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1266 GroupIdx = addToSectionTable(Group);
1267 Group->setAlignment(4);
1268 Groups.push_back(Group);
1270 GroupMembers[SignatureSymbol].push_back(&Section);
1272 GroupMembers[SignatureSymbol].push_back(RelSection);
1275 SectionIndexMap[&Section] = addToSectionTable(&Section);
1277 SectionIndexMap[RelSection] = addToSectionTable(RelSection);
1278 Relocations.push_back(RelSection);
1282 for (MCSectionELF *Group : Groups) {
1283 uint64_t Padding = OffsetToAlignment(OS.tell(), Group->getAlignment());
1284 WriteZeros(Padding);
1286 // Remember the offset into the file for this section.
1287 uint64_t SecStart = OS.tell();
1289 const MCSymbol *SignatureSymbol = Group->getGroup();
1290 assert(SignatureSymbol);
1291 write(uint32_t(ELF::GRP_COMDAT));
1292 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1293 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1297 uint64_t SecEnd = OS.tell();
1298 SectionOffsets[Group] = std::make_pair(SecStart, SecEnd);
1301 // Compute symbol table information.
1302 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, SectionOffsets);
1304 for (MCSectionELF *RelSection : Relocations) {
1305 uint64_t Padding = OffsetToAlignment(OS.tell(), RelSection->getAlignment());
1306 WriteZeros(Padding);
1308 // Remember the offset into the file for this section.
1309 uint64_t SecStart = OS.tell();
1311 writeRelocations(Asm, *RelSection->getAssociatedSection());
1313 uint64_t SecEnd = OS.tell();
1314 SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
1318 uint64_t SecStart = OS.tell();
1319 const MCSectionELF *Sec = createStringTable(Ctx);
1320 uint64_t SecEnd = OS.tell();
1321 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1324 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1325 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1326 WriteZeros(Padding);
1328 const unsigned SectionHeaderOffset = OS.tell();
1330 // ... then the section header table ...
1331 writeSectionHeader(Asm, Layout, SectionIndexMap, SectionOffsets);
1333 uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
1334 ? (uint16_t)ELF::SHN_UNDEF
1335 : SectionTable.size() + 1;
1336 if (sys::IsLittleEndianHost != IsLittleEndian)
1337 sys::swapByteOrder(NumSections);
1338 unsigned NumSectionsOffset;
1341 uint64_t Val = SectionHeaderOffset;
1342 if (sys::IsLittleEndianHost != IsLittleEndian)
1343 sys::swapByteOrder(Val);
1344 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1345 offsetof(ELF::Elf64_Ehdr, e_shoff));
1346 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1348 uint32_t Val = SectionHeaderOffset;
1349 if (sys::IsLittleEndianHost != IsLittleEndian)
1350 sys::swapByteOrder(Val);
1351 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1352 offsetof(ELF::Elf32_Ehdr, e_shoff));
1353 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1355 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1359 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1360 const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
1361 bool InSet, bool IsPCRel) const {
1364 if (::isWeak(SymA.getData()))
1367 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
1371 bool ELFObjectWriter::isWeak(const MCSymbol &Sym) const {
1372 const MCSymbolData &SD = Sym.getData();
1376 // It is invalid to replace a reference to a global in a comdat
1377 // with a reference to a local since out of comdat references
1378 // to a local are forbidden.
1379 // We could try to return false for more cases, like the reference
1380 // being in the same comdat or Sym being an alias to another global,
1381 // but it is not clear if it is worth the effort.
1382 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1385 if (!Sym.isInSection())
1388 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1389 return Sec.getGroup();
1392 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1393 raw_pwrite_stream &OS,
1394 bool IsLittleEndian) {
1395 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);