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/MCELFSymbolFlags.h"
25 #include "llvm/MC/MCExpr.h"
26 #include "llvm/MC/MCFixupKindInfo.h"
27 #include "llvm/MC/MCObjectWriter.h"
28 #include "llvm/MC/MCSectionELF.h"
29 #include "llvm/MC/MCSymbolELF.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 MCSymbolELF &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 MCSymbolELF *Symbol;
83 uint32_t SectionIndex;
86 // Support lexicographic sorting.
87 bool operator<(const ELFSymbolData &RHS) const {
88 unsigned LHSType = Symbol->getType();
89 unsigned RHSType = RHS.Symbol->getType();
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 MCSymbolELF *, const MCSymbolELF *> 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 &A : Asm.symbols()) {
381 const auto &Alias = cast<MCSymbolELF>(A);
383 if (!Alias.isVariable())
385 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
388 const auto &Symbol = cast<MCSymbolELF>(Ref->getSymbol());
390 StringRef AliasName = Alias.getName();
391 size_t Pos = AliasName.find('@');
392 if (Pos == StringRef::npos)
395 // Aliases defined with .symvar copy the binding from the symbol they alias.
396 // This is the first place we are able to copy this information.
397 Alias.setExternal(Symbol.isExternal());
398 Alias.setBinding(Symbol.getBinding());
400 StringRef Rest = AliasName.substr(Pos);
401 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
404 // FIXME: produce a better error message.
405 if (Symbol.isUndefined() && Rest.startswith("@@") &&
406 !Rest.startswith("@@@"))
407 report_fatal_error("A @@ version cannot be undefined");
409 Renames.insert(std::make_pair(&Symbol, &Alias));
413 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
414 uint8_t Type = newType;
416 // Propagation rules:
417 // IFUNC > FUNC > OBJECT > NOTYPE
418 // TLS_OBJECT > OBJECT > NOTYPE
420 // dont let the new type degrade the old type
424 case ELF::STT_GNU_IFUNC:
425 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
426 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
427 Type = ELF::STT_GNU_IFUNC;
430 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
431 Type == ELF::STT_TLS)
432 Type = ELF::STT_FUNC;
434 case ELF::STT_OBJECT:
435 if (Type == ELF::STT_NOTYPE)
436 Type = ELF::STT_OBJECT;
439 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
440 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
448 void ELFObjectWriter::writeSymbol(SymbolTableWriter &Writer,
449 uint32_t StringIndex, ELFSymbolData &MSD,
450 const MCAsmLayout &Layout) {
451 const auto &Symbol = cast<MCSymbolELF>(*MSD.Symbol);
452 assert((!Symbol.getFragment() ||
453 (Symbol.getFragment()->getParent() == &Symbol.getSection())) &&
454 "The symbol's section doesn't match the fragment's symbol");
455 const MCSymbolELF *Base =
456 cast_or_null<MCSymbolELF>(Layout.getBaseSymbol(Symbol));
458 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
460 bool IsReserved = !Base || Symbol.isCommon();
462 // Binding and Type share the same byte as upper and lower nibbles
463 uint8_t Binding = Symbol.getBinding();
464 uint8_t Type = Symbol.getType();
466 Type = mergeTypeForSet(Type, Base->getType());
468 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
470 // Other and Visibility share the same byte with Visibility using the lower
472 uint8_t Visibility = Symbol.getVisibility();
473 uint8_t Other = Symbol.getOther() << (ELF_STO_Shift - ELF_STV_Shift);
476 uint64_t Value = SymbolValue(*MSD.Symbol, Layout);
479 const MCExpr *ESize = MSD.Symbol->getSize();
481 ESize = Base->getSize();
485 if (!ESize->evaluateKnownAbsolute(Res, Layout))
486 report_fatal_error("Size expression must be absolute.");
490 // Write out the symbol table entry
491 Writer.writeSymbol(StringIndex, Info, Value, Size, Other, MSD.SectionIndex,
495 // It is always valid to create a relocation with a symbol. It is preferable
496 // to use a relocation with a section if that is possible. Using the section
497 // allows us to omit some local symbols from the symbol table.
498 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
499 const MCSymbolRefExpr *RefA,
500 const MCSymbol *S, uint64_t C,
501 unsigned Type) const {
502 const auto *Sym = cast_or_null<MCSymbolELF>(S);
503 // A PCRel relocation to an absolute value has no symbol (or section). We
504 // represent that with a relocation to a null section.
508 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
512 // The .odp creation emits a relocation against the symbol ".TOC." which
513 // create a R_PPC64_TOC relocation. However the relocation symbol name
514 // in final object creation should be NULL, since the symbol does not
515 // really exist, it is just the reference to TOC base for the current
516 // object file. Since the symbol is undefined, returning false results
517 // in a relocation with a null section which is the desired result.
518 case MCSymbolRefExpr::VK_PPC_TOCBASE:
521 // These VariantKind cause the relocation to refer to something other than
522 // the symbol itself, like a linker generated table. Since the address of
523 // symbol is not relevant, we cannot replace the symbol with the
524 // section and patch the difference in the addend.
525 case MCSymbolRefExpr::VK_GOT:
526 case MCSymbolRefExpr::VK_PLT:
527 case MCSymbolRefExpr::VK_GOTPCREL:
528 case MCSymbolRefExpr::VK_Mips_GOT:
529 case MCSymbolRefExpr::VK_PPC_GOT_LO:
530 case MCSymbolRefExpr::VK_PPC_GOT_HI:
531 case MCSymbolRefExpr::VK_PPC_GOT_HA:
535 // An undefined symbol is not in any section, so the relocation has to point
536 // to the symbol itself.
537 assert(Sym && "Expected a symbol");
538 if (Sym->isUndefined())
541 unsigned Binding = Sym->getBinding();
544 llvm_unreachable("Invalid Binding");
548 // If the symbol is weak, it might be overridden by a symbol in another
549 // file. The relocation has to point to the symbol so that the linker
552 case ELF::STB_GLOBAL:
553 // Global ELF symbols can be preempted by the dynamic linker. The relocation
554 // has to point to the symbol for a reason analogous to the STB_WEAK case.
558 // If a relocation points to a mergeable section, we have to be careful.
559 // If the offset is zero, a relocation with the section will encode the
560 // same information. With a non-zero offset, the situation is different.
561 // For example, a relocation can point 42 bytes past the end of a string.
562 // If we change such a relocation to use the section, the linker would think
563 // that it pointed to another string and subtracting 42 at runtime will
564 // produce the wrong value.
565 auto &Sec = cast<MCSectionELF>(Sym->getSection());
566 unsigned Flags = Sec.getFlags();
567 if (Flags & ELF::SHF_MERGE) {
571 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
572 // only handle section relocations to mergeable sections if using RELA.
573 if (!hasRelocationAddend())
577 // Most TLS relocations use a got, so they need the symbol. Even those that
578 // are just an offset (@tpoff), require a symbol in gold versions before
579 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
580 // http://sourceware.org/PR16773.
581 if (Flags & ELF::SHF_TLS)
584 // If the symbol is a thumb function the final relocation must set the lowest
585 // bit. With a symbol that is done by just having the symbol have that bit
586 // set, so we would lose the bit if we relocated with the section.
587 // FIXME: We could use the section but add the bit to the relocation value.
588 if (Asm.isThumbFunc(Sym))
591 if (TargetObjectWriter->needsRelocateWithSymbol(*Sym, Type))
596 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
597 const MCSymbol &Sym = Ref.getSymbol();
599 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
602 if (!Sym.isVariable())
605 const MCExpr *Expr = Sym.getVariableValue();
606 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
610 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
611 return &Inner->getSymbol();
615 // True if the assembler knows nothing about the final value of the symbol.
616 // This doesn't cover the comdat issues, since in those cases the assembler
617 // can at least know that all symbols in the section will move together.
618 static bool isWeak(const MCSymbolELF &Sym) {
619 if (Sym.getType() == ELF::STT_GNU_IFUNC)
622 switch (Sym.getBinding()) {
624 llvm_unreachable("Unknown binding");
627 case ELF::STB_GLOBAL:
630 case ELF::STB_GNU_UNIQUE:
635 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
636 const MCAsmLayout &Layout,
637 const MCFragment *Fragment,
638 const MCFixup &Fixup, MCValue Target,
639 bool &IsPCRel, uint64_t &FixedValue) {
640 const MCSectionELF &FixupSection = cast<MCSectionELF>(*Fragment->getParent());
641 uint64_t C = Target.getConstant();
642 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
644 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
645 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
646 "Should not have constructed this");
648 // Let A, B and C being the components of Target and R be the location of
649 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
650 // If it is pcrel, we want to compute (A - B + C - R).
652 // In general, ELF has no relocations for -B. It can only represent (A + C)
653 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
654 // replace B to implement it: (A - R - K + C)
656 Asm.getContext().reportFatalError(
658 "No relocation available to represent this relative expression");
660 const auto &SymB = cast<MCSymbolELF>(RefB->getSymbol());
662 if (SymB.isUndefined())
663 Asm.getContext().reportFatalError(
665 Twine("symbol '") + SymB.getName() +
666 "' can not be undefined in a subtraction expression");
668 assert(!SymB.isAbsolute() && "Should have been folded");
669 const MCSection &SecB = SymB.getSection();
670 if (&SecB != &FixupSection)
671 Asm.getContext().reportFatalError(
672 Fixup.getLoc(), "Cannot represent a difference across sections");
675 Asm.getContext().reportFatalError(
676 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
678 uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
679 uint64_t K = SymBOffset - FixupOffset;
684 // We either rejected the fixup or folded B into C at this point.
685 const MCSymbolRefExpr *RefA = Target.getSymA();
686 const auto *SymA = RefA ? cast<MCSymbolELF>(&RefA->getSymbol()) : nullptr;
688 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
689 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymA, C, Type);
690 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
691 C += Layout.getSymbolOffset(*SymA);
694 if (hasRelocationAddend()) {
701 if (!RelocateWithSymbol) {
702 const MCSection *SecA =
703 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
704 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
705 const auto *SectionSymbol =
706 ELFSec ? cast<MCSymbolELF>(ELFSec->getBeginSymbol()) : nullptr;
707 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
708 Relocations[&FixupSection].push_back(Rec);
713 if (const MCSymbolELF *R = Renames.lookup(SymA))
716 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
717 WeakrefUsedInReloc.insert(WeakRef);
719 UsedInReloc.insert(SymA);
721 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
722 Relocations[&FixupSection].push_back(Rec);
726 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
727 const MCSymbolELF &Symbol, bool Used,
729 if (Symbol.isVariable()) {
730 const MCExpr *Expr = Symbol.getVariableValue();
731 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
732 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
743 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
746 if (Symbol.isVariable()) {
747 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
748 if (Base && Base->isUndefined())
752 bool IsGlobal = Symbol.getBinding() == ELF::STB_GLOBAL;
753 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
756 if (Symbol.getType() == ELF::STT_SECTION)
759 if (Symbol.isTemporary())
765 bool ELFObjectWriter::isLocal(const MCSymbol &Symbol, bool IsUsedInReloc,
767 if (Symbol.isExternal())
770 if (Symbol.isDefined())
779 void ELFObjectWriter::computeSymbolTable(
780 MCAssembler &Asm, const MCAsmLayout &Layout,
781 const SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap,
782 SectionOffsetsTy &SectionOffsets) {
783 MCContext &Ctx = Asm.getContext();
784 SymbolTableWriter Writer(*this, is64Bit());
787 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
788 MCSectionELF *SymtabSection =
789 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
790 SymtabSection->setAlignment(is64Bit() ? 8 : 4);
791 SymbolTableIndex = addToSectionTable(SymtabSection);
794 OffsetToAlignment(OS.tell(), SymtabSection->getAlignment());
797 uint64_t SecStart = OS.tell();
799 // The first entry is the undefined symbol entry.
800 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
802 std::vector<ELFSymbolData> LocalSymbolData;
803 std::vector<ELFSymbolData> ExternalSymbolData;
805 // Add the data for the symbols.
806 bool HasLargeSectionIndex = false;
807 for (const MCSymbol &S : Asm.symbols()) {
808 const auto &Symbol = cast<MCSymbolELF>(S);
809 bool Used = UsedInReloc.count(&Symbol);
810 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
811 bool isSignature = RevGroupMap.count(&Symbol);
813 if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
814 Renames.count(&Symbol)))
818 MSD.Symbol = cast<MCSymbolELF>(&Symbol);
820 // Undefined symbols are global, but this is the first place we
821 // are able to set it.
822 bool Local = isLocal(Symbol, Used, isSignature);
823 if (!Local && Symbol.getBinding() == ELF::STB_LOCAL)
824 Symbol.setBinding(ELF::STB_GLOBAL);
826 if (Symbol.isAbsolute()) {
827 MSD.SectionIndex = ELF::SHN_ABS;
828 } else if (Symbol.isCommon()) {
830 MSD.SectionIndex = ELF::SHN_COMMON;
831 } else if (Symbol.isUndefined()) {
832 if (isSignature && !Used) {
833 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
834 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
835 HasLargeSectionIndex = true;
837 MSD.SectionIndex = ELF::SHN_UNDEF;
839 if (!Used && WeakrefUsed)
840 Symbol.setBinding(ELF::STB_WEAK);
842 const MCSectionELF &Section =
843 static_cast<const MCSectionELF &>(Symbol.getSection());
844 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
845 assert(MSD.SectionIndex && "Invalid section index!");
846 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
847 HasLargeSectionIndex = true;
850 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
853 // FIXME: All name handling should be done before we get to the writer,
854 // including dealing with GNU-style version suffixes. Fixing this isn't
857 // We thus have to be careful to not perform the symbol version replacement
860 // The ELF format is used on Windows by the MCJIT engine. Thus, on
861 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
862 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
863 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
864 // the EFLObjectWriter should not interpret the "@@@" sub-string as
865 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
866 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
867 // "__imp_?" or "__imp_@?".
869 // It would have been interesting to perform the MS mangling prefix check
870 // only when the target triple is of the form *-pc-windows-elf. But, it
871 // seems that this information is not easily accessible from the
873 StringRef Name = Symbol.getName();
874 if (!Name.startswith("?") && !Name.startswith("@?") &&
875 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
876 // This symbol isn't following the MSVC C++ name mangling convention. We
877 // can thus safely interpret the @@@ in symbol names as specifying symbol
880 size_t Pos = Name.find("@@@");
881 if (Pos != StringRef::npos) {
882 Buf += Name.substr(0, Pos);
883 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
884 Buf += Name.substr(Pos + Skip);
889 // Sections have their own string table
890 if (Symbol.getType() != ELF::STT_SECTION)
891 MSD.Name = StrTabBuilder.add(Name);
894 LocalSymbolData.push_back(MSD);
896 ExternalSymbolData.push_back(MSD);
899 if (HasLargeSectionIndex) {
900 MCSectionELF *SymtabShndxSection =
901 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
902 SymtabShndxSectionIndex = addToSectionTable(SymtabShndxSection);
903 SymtabShndxSection->setAlignment(4);
906 ArrayRef<std::string> FileNames = Asm.getFileNames();
907 for (const std::string &Name : FileNames)
908 StrTabBuilder.add(Name);
910 StrTabBuilder.finalize(StringTableBuilder::ELF);
912 for (const std::string &Name : FileNames)
913 Writer.writeSymbol(StrTabBuilder.getOffset(Name),
914 ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, ELF::STV_DEFAULT,
917 // Symbols are required to be in lexicographic order.
918 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
919 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
921 // Set the symbol indices. Local symbols must come before all other
922 // symbols with non-local bindings.
923 unsigned Index = FileNames.size() + 1;
925 for (ELFSymbolData &MSD : LocalSymbolData) {
926 unsigned StringIndex = MSD.Symbol->getType() == ELF::STT_SECTION
928 : StrTabBuilder.getOffset(MSD.Name);
929 MSD.Symbol->setIndex(Index++);
930 writeSymbol(Writer, StringIndex, MSD, Layout);
933 // Write the symbol table entries.
934 LastLocalSymbolIndex = Index;
936 for (ELFSymbolData &MSD : ExternalSymbolData) {
937 unsigned StringIndex = StrTabBuilder.getOffset(MSD.Name);
938 MSD.Symbol->setIndex(Index++);
939 writeSymbol(Writer, StringIndex, MSD, Layout);
940 assert(MSD.Symbol->getBinding() != ELF::STB_LOCAL);
943 uint64_t SecEnd = OS.tell();
944 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
946 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
947 if (ShndxIndexes.empty()) {
948 assert(SymtabShndxSectionIndex == 0);
951 assert(SymtabShndxSectionIndex != 0);
953 SecStart = OS.tell();
954 const MCSectionELF *SymtabShndxSection =
955 SectionTable[SymtabShndxSectionIndex - 1];
956 for (uint32_t Index : ShndxIndexes)
959 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
963 ELFObjectWriter::createRelocationSection(MCContext &Ctx,
964 const MCSectionELF &Sec) {
965 if (Relocations[&Sec].empty())
968 const StringRef SectionName = Sec.getSectionName();
969 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
970 RelaSectionName += SectionName;
973 if (hasRelocationAddend())
974 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
976 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
979 if (Sec.getFlags() & ELF::SHF_GROUP)
980 Flags = ELF::SHF_GROUP;
982 MCSectionELF *RelaSection = Ctx.createELFRelSection(
983 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
984 Flags, EntrySize, Sec.getGroup(), &Sec);
985 RelaSection->setAlignment(is64Bit() ? 8 : 4);
989 static SmallVector<char, 128>
990 getUncompressedData(const MCAsmLayout &Layout,
991 const MCSection::FragmentListType &Fragments) {
992 SmallVector<char, 128> UncompressedData;
993 for (const MCFragment &F : Fragments) {
994 const SmallVectorImpl<char> *Contents;
995 switch (F.getKind()) {
996 case MCFragment::FT_Data:
997 Contents = &cast<MCDataFragment>(F).getContents();
999 case MCFragment::FT_Dwarf:
1000 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1002 case MCFragment::FT_DwarfFrame:
1003 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1007 "Not expecting any other fragment types in a debug_* section");
1009 UncompressedData.append(Contents->begin(), Contents->end());
1011 return UncompressedData;
1014 // Include the debug info compression header:
1015 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1016 // useful for consumers to preallocate a buffer to decompress into.
1018 prependCompressionHeader(uint64_t Size,
1019 SmallVectorImpl<char> &CompressedContents) {
1020 const StringRef Magic = "ZLIB";
1021 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1023 if (sys::IsLittleEndianHost)
1024 sys::swapByteOrder(Size);
1025 CompressedContents.insert(CompressedContents.begin(),
1026 Magic.size() + sizeof(Size), 0);
1027 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1028 std::copy(reinterpret_cast<char *>(&Size),
1029 reinterpret_cast<char *>(&Size + 1),
1030 CompressedContents.begin() + Magic.size());
1034 void ELFObjectWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
1035 const MCAsmLayout &Layout) {
1036 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1037 StringRef SectionName = Section.getSectionName();
1039 // Compressing debug_frame requires handling alignment fragments which is
1040 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1041 // for writing to arbitrary buffers) for little benefit.
1042 if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
1043 !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
1044 Asm.writeSectionData(&Section, Layout);
1048 // Gather the uncompressed data from all the fragments.
1049 const MCSection::FragmentListType &Fragments = Section.getFragmentList();
1050 SmallVector<char, 128> UncompressedData =
1051 getUncompressedData(Layout, Fragments);
1053 SmallVector<char, 128> CompressedContents;
1054 zlib::Status Success = zlib::compress(
1055 StringRef(UncompressedData.data(), UncompressedData.size()),
1056 CompressedContents);
1057 if (Success != zlib::StatusOK) {
1058 Asm.writeSectionData(&Section, Layout);
1062 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
1063 Asm.writeSectionData(&Section, Layout);
1066 Asm.getContext().renameELFSection(&Section,
1067 (".z" + SectionName.drop_front(1)).str());
1068 OS << CompressedContents;
1071 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1072 uint64_t Flags, uint64_t Address,
1073 uint64_t Offset, uint64_t Size,
1074 uint32_t Link, uint32_t Info,
1076 uint64_t EntrySize) {
1077 Write32(Name); // sh_name: index into string table
1078 Write32(Type); // sh_type
1079 WriteWord(Flags); // sh_flags
1080 WriteWord(Address); // sh_addr
1081 WriteWord(Offset); // sh_offset
1082 WriteWord(Size); // sh_size
1083 Write32(Link); // sh_link
1084 Write32(Info); // sh_info
1085 WriteWord(Alignment); // sh_addralign
1086 WriteWord(EntrySize); // sh_entsize
1089 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1090 const MCSectionELF &Sec) {
1091 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1093 // Sort the relocation entries. Most targets just sort by Offset, but some
1094 // (e.g., MIPS) have additional constraints.
1095 TargetObjectWriter->sortRelocs(Asm, Relocs);
1097 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1098 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1099 unsigned Index = Entry.Symbol ? Entry.Symbol->getIndex() : 0;
1102 write(Entry.Offset);
1103 if (TargetObjectWriter->isN64()) {
1104 write(uint32_t(Index));
1106 write(TargetObjectWriter->getRSsym(Entry.Type));
1107 write(TargetObjectWriter->getRType3(Entry.Type));
1108 write(TargetObjectWriter->getRType2(Entry.Type));
1109 write(TargetObjectWriter->getRType(Entry.Type));
1111 struct ELF::Elf64_Rela ERE64;
1112 ERE64.setSymbolAndType(Index, Entry.Type);
1113 write(ERE64.r_info);
1115 if (hasRelocationAddend())
1116 write(Entry.Addend);
1118 write(uint32_t(Entry.Offset));
1120 struct ELF::Elf32_Rela ERE32;
1121 ERE32.setSymbolAndType(Index, Entry.Type);
1122 write(ERE32.r_info);
1124 if (hasRelocationAddend())
1125 write(uint32_t(Entry.Addend));
1130 const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
1131 const MCSectionELF *StrtabSection = SectionTable[StringTableIndex - 1];
1132 OS << StrTabBuilder.data();
1133 return StrtabSection;
1136 void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
1137 uint32_t GroupSymbolIndex, uint64_t Offset,
1138 uint64_t Size, const MCSectionELF &Section) {
1139 uint64_t sh_link = 0;
1140 uint64_t sh_info = 0;
1142 switch(Section.getType()) {
1147 case ELF::SHT_DYNAMIC:
1148 llvm_unreachable("SHT_DYNAMIC in a relocatable object");
1151 case ELF::SHT_RELA: {
1152 sh_link = SymbolTableIndex;
1153 assert(sh_link && ".symtab not found");
1154 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1155 sh_info = SectionIndexMap.lookup(InfoSection);
1159 case ELF::SHT_SYMTAB:
1160 case ELF::SHT_DYNSYM:
1161 sh_link = StringTableIndex;
1162 sh_info = LastLocalSymbolIndex;
1165 case ELF::SHT_SYMTAB_SHNDX:
1166 sh_link = SymbolTableIndex;
1169 case ELF::SHT_GROUP:
1170 sh_link = SymbolTableIndex;
1171 sh_info = GroupSymbolIndex;
1175 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1176 Section.getType() == ELF::SHT_ARM_EXIDX)
1177 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1179 WriteSecHdrEntry(StrTabBuilder.getOffset(Section.getSectionName()),
1180 Section.getType(), Section.getFlags(), 0, Offset, Size,
1181 sh_link, sh_info, Section.getAlignment(),
1182 Section.getEntrySize());
1185 void ELFObjectWriter::writeSectionHeader(
1186 const MCAssembler &Asm, const MCAsmLayout &Layout,
1187 const SectionIndexMapTy &SectionIndexMap,
1188 const SectionOffsetsTy &SectionOffsets) {
1189 const unsigned NumSections = SectionTable.size();
1191 // Null section first.
1192 uint64_t FirstSectionSize =
1193 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1194 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1196 for (const MCSectionELF *Section : SectionTable) {
1197 uint32_t GroupSymbolIndex;
1198 unsigned Type = Section->getType();
1199 if (Type != ELF::SHT_GROUP)
1200 GroupSymbolIndex = 0;
1202 GroupSymbolIndex = Section->getGroup()->getIndex();
1204 const std::pair<uint64_t, uint64_t> &Offsets =
1205 SectionOffsets.find(Section)->second;
1207 if (Type == ELF::SHT_NOBITS)
1208 Size = Layout.getSectionAddressSize(Section);
1210 Size = Offsets.second - Offsets.first;
1212 writeSection(SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1217 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1218 const MCAsmLayout &Layout) {
1219 MCContext &Ctx = Asm.getContext();
1220 MCSectionELF *StrtabSection =
1221 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1222 StringTableIndex = addToSectionTable(StrtabSection);
1224 RevGroupMapTy RevGroupMap;
1225 SectionIndexMapTy SectionIndexMap;
1227 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1229 // Write out the ELF header ...
1232 // ... then the sections ...
1233 SectionOffsetsTy SectionOffsets;
1234 std::vector<MCSectionELF *> Groups;
1235 std::vector<MCSectionELF *> Relocations;
1236 for (MCSection &Sec : Asm) {
1237 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1239 uint64_t Padding = OffsetToAlignment(OS.tell(), Section.getAlignment());
1240 WriteZeros(Padding);
1242 // Remember the offset into the file for this section.
1243 uint64_t SecStart = OS.tell();
1245 const MCSymbolELF *SignatureSymbol = Section.getGroup();
1246 writeSectionData(Asm, Section, Layout);
1248 uint64_t SecEnd = OS.tell();
1249 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1251 MCSectionELF *RelSection = createRelocationSection(Ctx, Section);
1253 if (SignatureSymbol) {
1254 Asm.registerSymbol(*SignatureSymbol);
1255 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1257 MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1258 GroupIdx = addToSectionTable(Group);
1259 Group->setAlignment(4);
1260 Groups.push_back(Group);
1262 GroupMembers[SignatureSymbol].push_back(&Section);
1264 GroupMembers[SignatureSymbol].push_back(RelSection);
1267 SectionIndexMap[&Section] = addToSectionTable(&Section);
1269 SectionIndexMap[RelSection] = addToSectionTable(RelSection);
1270 Relocations.push_back(RelSection);
1274 for (MCSectionELF *Group : Groups) {
1275 uint64_t Padding = OffsetToAlignment(OS.tell(), Group->getAlignment());
1276 WriteZeros(Padding);
1278 // Remember the offset into the file for this section.
1279 uint64_t SecStart = OS.tell();
1281 const MCSymbol *SignatureSymbol = Group->getGroup();
1282 assert(SignatureSymbol);
1283 write(uint32_t(ELF::GRP_COMDAT));
1284 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1285 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1289 uint64_t SecEnd = OS.tell();
1290 SectionOffsets[Group] = std::make_pair(SecStart, SecEnd);
1293 // Compute symbol table information.
1294 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, SectionOffsets);
1296 for (MCSectionELF *RelSection : Relocations) {
1297 uint64_t Padding = OffsetToAlignment(OS.tell(), RelSection->getAlignment());
1298 WriteZeros(Padding);
1300 // Remember the offset into the file for this section.
1301 uint64_t SecStart = OS.tell();
1303 writeRelocations(Asm, *RelSection->getAssociatedSection());
1305 uint64_t SecEnd = OS.tell();
1306 SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
1310 uint64_t SecStart = OS.tell();
1311 const MCSectionELF *Sec = createStringTable(Ctx);
1312 uint64_t SecEnd = OS.tell();
1313 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1316 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1317 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1318 WriteZeros(Padding);
1320 const unsigned SectionHeaderOffset = OS.tell();
1322 // ... then the section header table ...
1323 writeSectionHeader(Asm, Layout, SectionIndexMap, SectionOffsets);
1325 uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
1326 ? (uint16_t)ELF::SHN_UNDEF
1327 : SectionTable.size() + 1;
1328 if (sys::IsLittleEndianHost != IsLittleEndian)
1329 sys::swapByteOrder(NumSections);
1330 unsigned NumSectionsOffset;
1333 uint64_t Val = SectionHeaderOffset;
1334 if (sys::IsLittleEndianHost != IsLittleEndian)
1335 sys::swapByteOrder(Val);
1336 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1337 offsetof(ELF::Elf64_Ehdr, e_shoff));
1338 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1340 uint32_t Val = SectionHeaderOffset;
1341 if (sys::IsLittleEndianHost != IsLittleEndian)
1342 sys::swapByteOrder(Val);
1343 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1344 offsetof(ELF::Elf32_Ehdr, e_shoff));
1345 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1347 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1351 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1352 const MCAssembler &Asm, const MCSymbol &SA, const MCFragment &FB,
1353 bool InSet, bool IsPCRel) const {
1354 const auto &SymA = cast<MCSymbolELF>(SA);
1360 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
1364 bool ELFObjectWriter::isWeak(const MCSymbol &S) const {
1365 const auto &Sym = cast<MCSymbolELF>(S);
1369 // It is invalid to replace a reference to a global in a comdat
1370 // with a reference to a local since out of comdat references
1371 // to a local are forbidden.
1372 // We could try to return false for more cases, like the reference
1373 // being in the same comdat or Sym being an alias to another global,
1374 // but it is not clear if it is worth the effort.
1375 if (Sym.getBinding() != ELF::STB_GLOBAL)
1378 if (!Sym.isInSection())
1381 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1382 return Sec.getGroup();
1385 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1386 raw_pwrite_stream &OS,
1387 bool IsLittleEndian) {
1388 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);