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/MCExpr.h"
25 #include "llvm/MC/MCFixupKindInfo.h"
26 #include "llvm/MC/MCObjectWriter.h"
27 #include "llvm/MC/MCSectionELF.h"
28 #include "llvm/MC/MCSymbolELF.h"
29 #include "llvm/MC/MCValue.h"
30 #include "llvm/MC/StringTableBuilder.h"
31 #include "llvm/Support/Compression.h"
32 #include "llvm/Support/Debug.h"
33 #include "llvm/Support/ELF.h"
34 #include "llvm/Support/Endian.h"
35 #include "llvm/Support/ErrorHandling.h"
40 #define DEBUG_TYPE "reloc-info"
44 typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
46 class ELFObjectWriter;
48 class SymbolTableWriter {
49 ELFObjectWriter &EWriter;
52 // indexes we are going to write to .symtab_shndx.
53 std::vector<uint32_t> ShndxIndexes;
55 // The numbel of symbols written so far.
58 void createSymtabShndx();
60 template <typename T> void write(T Value);
63 SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit);
65 void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
66 uint8_t other, uint32_t shndx, bool Reserved);
68 ArrayRef<uint32_t> getShndxIndexes() const { return ShndxIndexes; }
71 class ELFObjectWriter : public MCObjectWriter {
72 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
73 static uint64_t SymbolValue(const MCSymbol &Sym, const MCAsmLayout &Layout);
74 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolELF &Symbol,
75 bool Used, bool Renamed);
77 /// Helper struct for containing some precomputed information on symbols.
78 struct ELFSymbolData {
79 const MCSymbolELF *Symbol;
80 uint32_t SectionIndex;
83 // Support lexicographic sorting.
84 bool operator<(const ELFSymbolData &RHS) const {
85 unsigned LHSType = Symbol->getType();
86 unsigned RHSType = RHS.Symbol->getType();
87 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
89 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
91 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
92 return SectionIndex < RHS.SectionIndex;
93 return Name < RHS.Name;
97 /// The target specific ELF writer instance.
98 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
100 DenseMap<const MCSymbolELF *, const MCSymbolELF *> Renames;
102 llvm::DenseMap<const MCSectionELF *, std::vector<ELFRelocationEntry>>
106 /// @name Symbol Table Data
109 StringTableBuilder StrTabBuilder;
113 // This holds the symbol table index of the last local symbol.
114 unsigned LastLocalSymbolIndex;
115 // This holds the .strtab section index.
116 unsigned StringTableIndex;
117 // This holds the .symtab section index.
118 unsigned SymbolTableIndex;
119 // This holds the .symtab_shndx section index.
120 unsigned SymtabShndxSectionIndex = 0;
122 // Sections in the order they are to be output in the section table.
123 std::vector<const MCSectionELF *> SectionTable;
124 unsigned addToSectionTable(const MCSectionELF *Sec);
126 // TargetObjectWriter wrappers.
127 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
128 bool hasRelocationAddend() const {
129 return TargetObjectWriter->hasRelocationAddend();
131 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
132 bool IsPCRel) const {
133 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
136 void align(unsigned Alignment);
139 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
141 : MCObjectWriter(OS, IsLittleEndian), TargetObjectWriter(MOTW) {}
143 void reset() override {
146 StrTabBuilder.clear();
147 SymtabShndxSectionIndex = 0;
148 SectionTable.clear();
149 MCObjectWriter::reset();
152 ~ELFObjectWriter() override;
154 void WriteWord(uint64_t W) {
161 template <typename T> void write(T Val) {
163 support::endian::Writer<support::little>(OS).write(Val);
165 support::endian::Writer<support::big>(OS).write(Val);
168 void writeHeader(const MCAssembler &Asm);
170 void writeSymbol(SymbolTableWriter &Writer, uint32_t StringIndex,
171 ELFSymbolData &MSD, const MCAsmLayout &Layout);
173 // Start and end offset of each section
174 typedef std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>
177 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
178 const MCSymbolRefExpr *RefA,
179 const MCSymbol *Sym, uint64_t C,
180 unsigned Type) const;
182 void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
183 const MCFragment *Fragment, const MCFixup &Fixup,
184 MCValue Target, bool &IsPCRel,
185 uint64_t &FixedValue) override;
187 // Map from a signature symbol to the group section index
188 typedef DenseMap<const MCSymbol *, unsigned> RevGroupMapTy;
190 /// Compute the symbol table data
192 /// \param Asm - The assembler.
193 /// \param SectionIndexMap - Maps a section to its index.
194 /// \param RevGroupMap - Maps a signature symbol to the group section.
195 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
196 const SectionIndexMapTy &SectionIndexMap,
197 const RevGroupMapTy &RevGroupMap,
198 SectionOffsetsTy &SectionOffsets);
200 MCSectionELF *createRelocationSection(MCContext &Ctx,
201 const MCSectionELF &Sec);
203 const MCSectionELF *createStringTable(MCContext &Ctx);
205 void executePostLayoutBinding(MCAssembler &Asm,
206 const MCAsmLayout &Layout) override;
208 void writeSectionHeader(const MCAsmLayout &Layout,
209 const SectionIndexMapTy &SectionIndexMap,
210 const SectionOffsetsTy &SectionOffsets);
212 void writeSectionData(const MCAssembler &Asm, MCSection &Sec,
213 const MCAsmLayout &Layout);
215 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
216 uint64_t Address, uint64_t Offset, uint64_t Size,
217 uint32_t Link, uint32_t Info, uint64_t Alignment,
220 void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
222 bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
223 const MCSymbol &SymA,
224 const MCFragment &FB,
226 bool IsPCRel) const override;
228 bool isWeak(const MCSymbol &Sym) const override;
230 void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
231 void writeSection(const SectionIndexMapTy &SectionIndexMap,
232 uint32_t GroupSymbolIndex, uint64_t Offset, uint64_t Size,
233 const MCSectionELF &Section);
237 void ELFObjectWriter::align(unsigned Alignment) {
238 uint64_t Padding = OffsetToAlignment(OS.tell(), Alignment);
242 unsigned ELFObjectWriter::addToSectionTable(const MCSectionELF *Sec) {
243 SectionTable.push_back(Sec);
244 StrTabBuilder.add(Sec->getSectionName());
245 return SectionTable.size();
248 void SymbolTableWriter::createSymtabShndx() {
249 if (!ShndxIndexes.empty())
252 ShndxIndexes.resize(NumWritten);
255 template <typename T> void SymbolTableWriter::write(T Value) {
256 EWriter.write(Value);
259 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
260 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
262 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
263 uint64_t size, uint8_t other,
264 uint32_t shndx, bool Reserved) {
265 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
270 if (!ShndxIndexes.empty()) {
272 ShndxIndexes.push_back(shndx);
274 ShndxIndexes.push_back(0);
277 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
280 write(name); // st_name
281 write(info); // st_info
282 write(other); // st_other
283 write(Index); // st_shndx
284 write(value); // st_value
285 write(size); // st_size
287 write(name); // st_name
288 write(uint32_t(value)); // st_value
289 write(uint32_t(size)); // st_size
290 write(info); // st_info
291 write(other); // st_other
292 write(Index); // st_shndx
298 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
299 const MCFixupKindInfo &FKI =
300 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
302 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
305 ELFObjectWriter::~ELFObjectWriter()
308 // Emit the ELF header.
309 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
315 // emitWord method behaves differently for ELF32 and ELF64, writing
316 // 4 bytes in the former and 8 in the latter.
318 writeBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
320 write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
323 write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
325 write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
327 write8(TargetObjectWriter->getOSABI());
328 write8(0); // e_ident[EI_ABIVERSION]
330 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
332 write16(ELF::ET_REL); // e_type
334 write16(TargetObjectWriter->getEMachine()); // e_machine = target
336 write32(ELF::EV_CURRENT); // e_version
337 WriteWord(0); // e_entry, no entry point in .o file
338 WriteWord(0); // e_phoff, no program header for .o
339 WriteWord(0); // e_shoff = sec hdr table off in bytes
341 // e_flags = whatever the target wants
342 write32(Asm.getELFHeaderEFlags());
344 // e_ehsize = ELF header size
345 write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
347 write16(0); // e_phentsize = prog header entry size
348 write16(0); // e_phnum = # prog header entries = 0
350 // e_shentsize = Section header entry size
351 write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
353 // e_shnum = # of section header ents
356 // e_shstrndx = Section # of '.shstrtab'
357 assert(StringTableIndex < ELF::SHN_LORESERVE);
358 write16(StringTableIndex);
361 uint64_t ELFObjectWriter::SymbolValue(const MCSymbol &Sym,
362 const MCAsmLayout &Layout) {
363 if (Sym.isCommon() && Sym.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 &A : Asm.symbols()) {
382 const auto &Alias = cast<MCSymbolELF>(A);
384 if (!Alias.isVariable())
386 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
389 const auto &Symbol = cast<MCSymbolELF>(Ref->getSymbol());
391 StringRef AliasName = Alias.getName();
392 size_t Pos = AliasName.find('@');
393 if (Pos == StringRef::npos)
396 // Aliases defined with .symvar copy the binding from the symbol they alias.
397 // This is the first place we are able to copy this information.
398 Alias.setExternal(Symbol.isExternal());
399 Alias.setBinding(Symbol.getBinding());
401 StringRef Rest = AliasName.substr(Pos);
402 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
405 // FIXME: produce a better error message.
406 if (Symbol.isUndefined() && Rest.startswith("@@") &&
407 !Rest.startswith("@@@"))
408 report_fatal_error("A @@ version cannot be undefined");
410 Renames.insert(std::make_pair(&Symbol, &Alias));
414 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
415 uint8_t Type = newType;
417 // Propagation rules:
418 // IFUNC > FUNC > OBJECT > NOTYPE
419 // TLS_OBJECT > OBJECT > NOTYPE
421 // dont let the new type degrade the old type
425 case ELF::STT_GNU_IFUNC:
426 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
427 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
428 Type = ELF::STT_GNU_IFUNC;
431 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
432 Type == ELF::STT_TLS)
433 Type = ELF::STT_FUNC;
435 case ELF::STT_OBJECT:
436 if (Type == ELF::STT_NOTYPE)
437 Type = ELF::STT_OBJECT;
440 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
441 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
449 void ELFObjectWriter::writeSymbol(SymbolTableWriter &Writer,
450 uint32_t StringIndex, ELFSymbolData &MSD,
451 const MCAsmLayout &Layout) {
452 const auto &Symbol = cast<MCSymbolELF>(*MSD.Symbol);
453 assert((!Symbol.getFragment() ||
454 (Symbol.getFragment()->getParent() == &Symbol.getSection())) &&
455 "The symbol's section doesn't match the fragment's symbol");
456 const MCSymbolELF *Base =
457 cast_or_null<MCSymbolELF>(Layout.getBaseSymbol(Symbol));
459 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
461 bool IsReserved = !Base || Symbol.isCommon();
463 // Binding and Type share the same byte as upper and lower nibbles
464 uint8_t Binding = Symbol.getBinding();
465 uint8_t Type = Symbol.getType();
467 Type = mergeTypeForSet(Type, Base->getType());
469 uint8_t Info = (Binding << 4) | Type;
471 // Other and Visibility share the same byte with Visibility using the lower
473 uint8_t Visibility = Symbol.getVisibility();
474 uint8_t Other = Symbol.getOther() | Visibility;
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 // True if the assembler knows nothing about the final value of the symbol.
597 // This doesn't cover the comdat issues, since in those cases the assembler
598 // can at least know that all symbols in the section will move together.
599 static bool isWeak(const MCSymbolELF &Sym) {
600 if (Sym.getType() == ELF::STT_GNU_IFUNC)
603 switch (Sym.getBinding()) {
605 llvm_unreachable("Unknown binding");
608 case ELF::STB_GLOBAL:
611 case ELF::STB_GNU_UNIQUE:
616 void ELFObjectWriter::recordRelocation(MCAssembler &Asm,
617 const MCAsmLayout &Layout,
618 const MCFragment *Fragment,
619 const MCFixup &Fixup, MCValue Target,
620 bool &IsPCRel, uint64_t &FixedValue) {
621 const MCSectionELF &FixupSection = cast<MCSectionELF>(*Fragment->getParent());
622 uint64_t C = Target.getConstant();
623 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
625 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
626 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
627 "Should not have constructed this");
629 // Let A, B and C being the components of Target and R be the location of
630 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
631 // If it is pcrel, we want to compute (A - B + C - R).
633 // In general, ELF has no relocations for -B. It can only represent (A + C)
634 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
635 // replace B to implement it: (A - R - K + C)
637 Asm.getContext().reportFatalError(
639 "No relocation available to represent this relative expression");
641 const auto &SymB = cast<MCSymbolELF>(RefB->getSymbol());
643 if (SymB.isUndefined())
644 Asm.getContext().reportFatalError(
646 Twine("symbol '") + SymB.getName() +
647 "' can not be undefined in a subtraction expression");
649 assert(!SymB.isAbsolute() && "Should have been folded");
650 const MCSection &SecB = SymB.getSection();
651 if (&SecB != &FixupSection)
652 Asm.getContext().reportFatalError(
653 Fixup.getLoc(), "Cannot represent a difference across sections");
656 Asm.getContext().reportFatalError(
657 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
659 uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
660 uint64_t K = SymBOffset - FixupOffset;
665 // We either rejected the fixup or folded B into C at this point.
666 const MCSymbolRefExpr *RefA = Target.getSymA();
667 const auto *SymA = RefA ? cast<MCSymbolELF>(&RefA->getSymbol()) : nullptr;
669 bool ViaWeakRef = false;
670 if (SymA && SymA->isVariable()) {
671 const MCExpr *Expr = SymA->getVariableValue();
672 if (const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr)) {
673 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF) {
674 SymA = cast<MCSymbolELF>(&Inner->getSymbol());
680 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
681 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymA, C, Type);
682 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
683 C += Layout.getSymbolOffset(*SymA);
686 if (hasRelocationAddend()) {
693 if (!RelocateWithSymbol) {
694 const MCSection *SecA =
695 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
696 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
697 const auto *SectionSymbol =
698 ELFSec ? cast<MCSymbolELF>(ELFSec->getBeginSymbol()) : nullptr;
700 SectionSymbol->setUsedInReloc();
701 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
702 Relocations[&FixupSection].push_back(Rec);
707 if (const MCSymbolELF *R = Renames.lookup(SymA))
711 SymA->setIsWeakrefUsedInReloc();
713 SymA->setUsedInReloc();
715 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
716 Relocations[&FixupSection].push_back(Rec);
720 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
721 const MCSymbolELF &Symbol, bool Used,
723 if (Symbol.isVariable()) {
724 const MCExpr *Expr = Symbol.getVariableValue();
725 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
726 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
737 if (Symbol.isVariable() && Symbol.isUndefined()) {
738 // FIXME: this is here just to diagnose the case of a var = commmon_sym.
739 Layout.getBaseSymbol(Symbol);
743 if (Symbol.isUndefined() && !Symbol.isBindingSet())
746 if (Symbol.isTemporary())
749 if (Symbol.getType() == ELF::STT_SECTION)
755 void ELFObjectWriter::computeSymbolTable(
756 MCAssembler &Asm, const MCAsmLayout &Layout,
757 const SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap,
758 SectionOffsetsTy &SectionOffsets) {
759 MCContext &Ctx = Asm.getContext();
760 SymbolTableWriter Writer(*this, is64Bit());
763 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
764 MCSectionELF *SymtabSection =
765 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
766 SymtabSection->setAlignment(is64Bit() ? 8 : 4);
767 SymbolTableIndex = addToSectionTable(SymtabSection);
769 align(SymtabSection->getAlignment());
770 uint64_t SecStart = OS.tell();
772 // The first entry is the undefined symbol entry.
773 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
775 std::vector<ELFSymbolData> LocalSymbolData;
776 std::vector<ELFSymbolData> ExternalSymbolData;
778 // Add the data for the symbols.
779 bool HasLargeSectionIndex = false;
780 for (const MCSymbol &S : Asm.symbols()) {
781 const auto &Symbol = cast<MCSymbolELF>(S);
782 bool Used = Symbol.isUsedInReloc();
783 bool WeakrefUsed = Symbol.isWeakrefUsedInReloc();
784 bool isSignature = Symbol.isSignature();
786 if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
787 Renames.count(&Symbol)))
790 if (Symbol.isTemporary() && Symbol.isUndefined())
791 Ctx.reportFatalError(SMLoc(), "Undefined temporary");
794 MSD.Symbol = cast<MCSymbolELF>(&Symbol);
796 bool Local = Symbol.getBinding() == ELF::STB_LOCAL;
797 assert(Local || !Symbol.isTemporary());
799 if (Symbol.isAbsolute()) {
800 MSD.SectionIndex = ELF::SHN_ABS;
801 } else if (Symbol.isCommon()) {
803 MSD.SectionIndex = ELF::SHN_COMMON;
804 } else if (Symbol.isUndefined()) {
805 if (isSignature && !Used) {
806 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
807 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
808 HasLargeSectionIndex = true;
810 MSD.SectionIndex = ELF::SHN_UNDEF;
813 const MCSectionELF &Section =
814 static_cast<const MCSectionELF &>(Symbol.getSection());
815 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
816 assert(MSD.SectionIndex && "Invalid section index!");
817 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
818 HasLargeSectionIndex = true;
821 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
824 // FIXME: All name handling should be done before we get to the writer,
825 // including dealing with GNU-style version suffixes. Fixing this isn't
828 // We thus have to be careful to not perform the symbol version replacement
831 // The ELF format is used on Windows by the MCJIT engine. Thus, on
832 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
833 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
834 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
835 // the EFLObjectWriter should not interpret the "@@@" sub-string as
836 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
837 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
838 // "__imp_?" or "__imp_@?".
840 // It would have been interesting to perform the MS mangling prefix check
841 // only when the target triple is of the form *-pc-windows-elf. But, it
842 // seems that this information is not easily accessible from the
844 StringRef Name = Symbol.getName();
845 if (!Name.startswith("?") && !Name.startswith("@?") &&
846 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
847 // This symbol isn't following the MSVC C++ name mangling convention. We
848 // can thus safely interpret the @@@ in symbol names as specifying symbol
851 size_t Pos = Name.find("@@@");
852 if (Pos != StringRef::npos) {
853 Buf += Name.substr(0, Pos);
854 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
855 Buf += Name.substr(Pos + Skip);
860 // Sections have their own string table
861 if (Symbol.getType() != ELF::STT_SECTION)
862 MSD.Name = StrTabBuilder.add(Name);
865 LocalSymbolData.push_back(MSD);
867 ExternalSymbolData.push_back(MSD);
870 if (HasLargeSectionIndex) {
871 MCSectionELF *SymtabShndxSection =
872 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
873 SymtabShndxSectionIndex = addToSectionTable(SymtabShndxSection);
874 SymtabShndxSection->setAlignment(4);
877 ArrayRef<std::string> FileNames = Asm.getFileNames();
878 for (const std::string &Name : FileNames)
879 StrTabBuilder.add(Name);
881 StrTabBuilder.finalize(StringTableBuilder::ELF);
883 for (const std::string &Name : FileNames)
884 Writer.writeSymbol(StrTabBuilder.getOffset(Name),
885 ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, ELF::STV_DEFAULT,
888 // Symbols are required to be in lexicographic order.
889 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
890 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
892 // Set the symbol indices. Local symbols must come before all other
893 // symbols with non-local bindings.
894 unsigned Index = FileNames.size() + 1;
896 for (ELFSymbolData &MSD : LocalSymbolData) {
897 unsigned StringIndex;
898 if (MSD.Symbol->getType() == ELF::STT_SECTION || MSD.Name.empty())
901 StringIndex = StrTabBuilder.getOffset(MSD.Name);
902 MSD.Symbol->setIndex(Index++);
903 writeSymbol(Writer, StringIndex, MSD, Layout);
906 // Write the symbol table entries.
907 LastLocalSymbolIndex = Index;
909 for (ELFSymbolData &MSD : ExternalSymbolData) {
910 unsigned StringIndex = StrTabBuilder.getOffset(MSD.Name);
911 MSD.Symbol->setIndex(Index++);
912 writeSymbol(Writer, StringIndex, MSD, Layout);
913 assert(MSD.Symbol->getBinding() != ELF::STB_LOCAL);
916 uint64_t SecEnd = OS.tell();
917 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
919 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
920 if (ShndxIndexes.empty()) {
921 assert(SymtabShndxSectionIndex == 0);
924 assert(SymtabShndxSectionIndex != 0);
926 SecStart = OS.tell();
927 const MCSectionELF *SymtabShndxSection =
928 SectionTable[SymtabShndxSectionIndex - 1];
929 for (uint32_t Index : ShndxIndexes)
932 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
936 ELFObjectWriter::createRelocationSection(MCContext &Ctx,
937 const MCSectionELF &Sec) {
938 if (Relocations[&Sec].empty())
941 const StringRef SectionName = Sec.getSectionName();
942 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
943 RelaSectionName += SectionName;
946 if (hasRelocationAddend())
947 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
949 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
952 if (Sec.getFlags() & ELF::SHF_GROUP)
953 Flags = ELF::SHF_GROUP;
955 MCSectionELF *RelaSection = Ctx.createELFRelSection(
956 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
957 Flags, EntrySize, Sec.getGroup(), &Sec);
958 RelaSection->setAlignment(is64Bit() ? 8 : 4);
962 static SmallVector<char, 128>
963 getUncompressedData(const MCAsmLayout &Layout,
964 const MCSection::FragmentListType &Fragments) {
965 SmallVector<char, 128> UncompressedData;
966 for (const MCFragment &F : Fragments) {
967 const SmallVectorImpl<char> *Contents;
968 switch (F.getKind()) {
969 case MCFragment::FT_Data:
970 Contents = &cast<MCDataFragment>(F).getContents();
972 case MCFragment::FT_Dwarf:
973 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
975 case MCFragment::FT_DwarfFrame:
976 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
980 "Not expecting any other fragment types in a debug_* section");
982 UncompressedData.append(Contents->begin(), Contents->end());
984 return UncompressedData;
987 // Include the debug info compression header:
988 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
989 // useful for consumers to preallocate a buffer to decompress into.
991 prependCompressionHeader(uint64_t Size,
992 SmallVectorImpl<char> &CompressedContents) {
993 const StringRef Magic = "ZLIB";
994 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
996 if (sys::IsLittleEndianHost)
997 sys::swapByteOrder(Size);
998 CompressedContents.insert(CompressedContents.begin(),
999 Magic.size() + sizeof(Size), 0);
1000 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1001 std::copy(reinterpret_cast<char *>(&Size),
1002 reinterpret_cast<char *>(&Size + 1),
1003 CompressedContents.begin() + Magic.size());
1007 void ELFObjectWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
1008 const MCAsmLayout &Layout) {
1009 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1010 StringRef SectionName = Section.getSectionName();
1012 // Compressing debug_frame requires handling alignment fragments which is
1013 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1014 // for writing to arbitrary buffers) for little benefit.
1015 if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
1016 !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
1017 Asm.writeSectionData(&Section, Layout);
1021 // Gather the uncompressed data from all the fragments.
1022 const MCSection::FragmentListType &Fragments = Section.getFragmentList();
1023 SmallVector<char, 128> UncompressedData =
1024 getUncompressedData(Layout, Fragments);
1026 SmallVector<char, 128> CompressedContents;
1027 zlib::Status Success = zlib::compress(
1028 StringRef(UncompressedData.data(), UncompressedData.size()),
1029 CompressedContents);
1030 if (Success != zlib::StatusOK) {
1031 Asm.writeSectionData(&Section, Layout);
1035 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
1036 Asm.writeSectionData(&Section, Layout);
1039 Asm.getContext().renameELFSection(&Section,
1040 (".z" + SectionName.drop_front(1)).str());
1041 OS << CompressedContents;
1044 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1045 uint64_t Flags, uint64_t Address,
1046 uint64_t Offset, uint64_t Size,
1047 uint32_t Link, uint32_t Info,
1049 uint64_t EntrySize) {
1050 write32(Name); // sh_name: index into string table
1051 write32(Type); // sh_type
1052 WriteWord(Flags); // sh_flags
1053 WriteWord(Address); // sh_addr
1054 WriteWord(Offset); // sh_offset
1055 WriteWord(Size); // sh_size
1056 write32(Link); // sh_link
1057 write32(Info); // sh_info
1058 WriteWord(Alignment); // sh_addralign
1059 WriteWord(EntrySize); // sh_entsize
1062 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1063 const MCSectionELF &Sec) {
1064 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1066 // Sort the relocation entries. Most targets just sort by Offset, but some
1067 // (e.g., MIPS) have additional constraints.
1068 TargetObjectWriter->sortRelocs(Asm, Relocs);
1070 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1071 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1072 unsigned Index = Entry.Symbol ? Entry.Symbol->getIndex() : 0;
1075 write(Entry.Offset);
1076 if (TargetObjectWriter->isN64()) {
1077 write(uint32_t(Index));
1079 write(TargetObjectWriter->getRSsym(Entry.Type));
1080 write(TargetObjectWriter->getRType3(Entry.Type));
1081 write(TargetObjectWriter->getRType2(Entry.Type));
1082 write(TargetObjectWriter->getRType(Entry.Type));
1084 struct ELF::Elf64_Rela ERE64;
1085 ERE64.setSymbolAndType(Index, Entry.Type);
1086 write(ERE64.r_info);
1088 if (hasRelocationAddend())
1089 write(Entry.Addend);
1091 write(uint32_t(Entry.Offset));
1093 struct ELF::Elf32_Rela ERE32;
1094 ERE32.setSymbolAndType(Index, Entry.Type);
1095 write(ERE32.r_info);
1097 if (hasRelocationAddend())
1098 write(uint32_t(Entry.Addend));
1103 const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
1104 const MCSectionELF *StrtabSection = SectionTable[StringTableIndex - 1];
1105 OS << StrTabBuilder.data();
1106 return StrtabSection;
1109 void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
1110 uint32_t GroupSymbolIndex, uint64_t Offset,
1111 uint64_t Size, const MCSectionELF &Section) {
1112 uint64_t sh_link = 0;
1113 uint64_t sh_info = 0;
1115 switch(Section.getType()) {
1120 case ELF::SHT_DYNAMIC:
1121 llvm_unreachable("SHT_DYNAMIC in a relocatable object");
1124 case ELF::SHT_RELA: {
1125 sh_link = SymbolTableIndex;
1126 assert(sh_link && ".symtab not found");
1127 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1128 sh_info = SectionIndexMap.lookup(InfoSection);
1132 case ELF::SHT_SYMTAB:
1133 case ELF::SHT_DYNSYM:
1134 sh_link = StringTableIndex;
1135 sh_info = LastLocalSymbolIndex;
1138 case ELF::SHT_SYMTAB_SHNDX:
1139 sh_link = SymbolTableIndex;
1142 case ELF::SHT_GROUP:
1143 sh_link = SymbolTableIndex;
1144 sh_info = GroupSymbolIndex;
1148 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1149 Section.getType() == ELF::SHT_ARM_EXIDX)
1150 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1152 WriteSecHdrEntry(StrTabBuilder.getOffset(Section.getSectionName()),
1153 Section.getType(), Section.getFlags(), 0, Offset, Size,
1154 sh_link, sh_info, Section.getAlignment(),
1155 Section.getEntrySize());
1158 void ELFObjectWriter::writeSectionHeader(
1159 const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap,
1160 const SectionOffsetsTy &SectionOffsets) {
1161 const unsigned NumSections = SectionTable.size();
1163 // Null section first.
1164 uint64_t FirstSectionSize =
1165 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1166 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1168 for (const MCSectionELF *Section : SectionTable) {
1169 uint32_t GroupSymbolIndex;
1170 unsigned Type = Section->getType();
1171 if (Type != ELF::SHT_GROUP)
1172 GroupSymbolIndex = 0;
1174 GroupSymbolIndex = Section->getGroup()->getIndex();
1176 const std::pair<uint64_t, uint64_t> &Offsets =
1177 SectionOffsets.find(Section)->second;
1179 if (Type == ELF::SHT_NOBITS)
1180 Size = Layout.getSectionAddressSize(Section);
1182 Size = Offsets.second - Offsets.first;
1184 writeSection(SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1189 void ELFObjectWriter::writeObject(MCAssembler &Asm,
1190 const MCAsmLayout &Layout) {
1191 MCContext &Ctx = Asm.getContext();
1192 MCSectionELF *StrtabSection =
1193 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1194 StringTableIndex = addToSectionTable(StrtabSection);
1196 RevGroupMapTy RevGroupMap;
1197 SectionIndexMapTy SectionIndexMap;
1199 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1201 // Write out the ELF header ...
1204 // ... then the sections ...
1205 SectionOffsetsTy SectionOffsets;
1206 std::vector<MCSectionELF *> Groups;
1207 std::vector<MCSectionELF *> Relocations;
1208 for (MCSection &Sec : Asm) {
1209 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1211 align(Section.getAlignment());
1213 // Remember the offset into the file for this section.
1214 uint64_t SecStart = OS.tell();
1216 const MCSymbolELF *SignatureSymbol = Section.getGroup();
1217 writeSectionData(Asm, Section, Layout);
1219 uint64_t SecEnd = OS.tell();
1220 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1222 MCSectionELF *RelSection = createRelocationSection(Ctx, Section);
1224 if (SignatureSymbol) {
1225 Asm.registerSymbol(*SignatureSymbol);
1226 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1228 MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1229 GroupIdx = addToSectionTable(Group);
1230 Group->setAlignment(4);
1231 Groups.push_back(Group);
1233 std::vector<const MCSectionELF *> &Members =
1234 GroupMembers[SignatureSymbol];
1235 Members.push_back(&Section);
1237 Members.push_back(RelSection);
1240 SectionIndexMap[&Section] = addToSectionTable(&Section);
1242 SectionIndexMap[RelSection] = addToSectionTable(RelSection);
1243 Relocations.push_back(RelSection);
1247 for (MCSectionELF *Group : Groups) {
1248 align(Group->getAlignment());
1250 // Remember the offset into the file for this section.
1251 uint64_t SecStart = OS.tell();
1253 const MCSymbol *SignatureSymbol = Group->getGroup();
1254 assert(SignatureSymbol);
1255 write(uint32_t(ELF::GRP_COMDAT));
1256 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1257 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1261 uint64_t SecEnd = OS.tell();
1262 SectionOffsets[Group] = std::make_pair(SecStart, SecEnd);
1265 // Compute symbol table information.
1266 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, SectionOffsets);
1268 for (MCSectionELF *RelSection : Relocations) {
1269 align(RelSection->getAlignment());
1271 // Remember the offset into the file for this section.
1272 uint64_t SecStart = OS.tell();
1274 writeRelocations(Asm, *RelSection->getAssociatedSection());
1276 uint64_t SecEnd = OS.tell();
1277 SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
1281 uint64_t SecStart = OS.tell();
1282 const MCSectionELF *Sec = createStringTable(Ctx);
1283 uint64_t SecEnd = OS.tell();
1284 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1287 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1288 align(NaturalAlignment);
1290 const unsigned SectionHeaderOffset = OS.tell();
1292 // ... then the section header table ...
1293 writeSectionHeader(Layout, SectionIndexMap, SectionOffsets);
1295 uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
1296 ? (uint16_t)ELF::SHN_UNDEF
1297 : SectionTable.size() + 1;
1298 if (sys::IsLittleEndianHost != IsLittleEndian)
1299 sys::swapByteOrder(NumSections);
1300 unsigned NumSectionsOffset;
1303 uint64_t Val = SectionHeaderOffset;
1304 if (sys::IsLittleEndianHost != IsLittleEndian)
1305 sys::swapByteOrder(Val);
1306 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1307 offsetof(ELF::Elf64_Ehdr, e_shoff));
1308 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1310 uint32_t Val = SectionHeaderOffset;
1311 if (sys::IsLittleEndianHost != IsLittleEndian)
1312 sys::swapByteOrder(Val);
1313 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1314 offsetof(ELF::Elf32_Ehdr, e_shoff));
1315 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1317 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1321 bool ELFObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
1322 const MCAssembler &Asm, const MCSymbol &SA, const MCFragment &FB,
1323 bool InSet, bool IsPCRel) const {
1324 const auto &SymA = cast<MCSymbolELF>(SA);
1330 return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
1334 bool ELFObjectWriter::isWeak(const MCSymbol &S) const {
1335 const auto &Sym = cast<MCSymbolELF>(S);
1339 // It is invalid to replace a reference to a global in a comdat
1340 // with a reference to a local since out of comdat references
1341 // to a local are forbidden.
1342 // We could try to return false for more cases, like the reference
1343 // being in the same comdat or Sym being an alias to another global,
1344 // but it is not clear if it is worth the effort.
1345 if (Sym.getBinding() != ELF::STB_GLOBAL)
1348 if (!Sym.isInSection())
1351 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1352 return Sec.getGroup();
1355 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1356 raw_pwrite_stream &OS,
1357 bool IsLittleEndian) {
1358 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);