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);
79 /// Helper struct for containing some precomputed information on symbols.
80 struct ELFSymbolData {
81 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, ELFSymbolData &MSD,
175 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 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
194 // Map from a signature symbol to the group section index
195 typedef DenseMap<const MCSymbol *, unsigned> RevGroupMapTy;
197 /// Compute the symbol table data
199 /// \param Asm - The assembler.
200 /// \param SectionIndexMap - Maps a section to its index.
201 /// \param RevGroupMap - Maps a signature symbol to the group section.
202 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
203 const SectionIndexMapTy &SectionIndexMap,
204 const RevGroupMapTy &RevGroupMap,
205 SectionOffsetsTy &SectionOffsets);
207 MCSectionELF *createRelocationSection(MCContext &Ctx,
208 const MCSectionELF &Sec);
210 const MCSectionELF *createStringTable(MCContext &Ctx);
212 void ExecutePostLayoutBinding(MCAssembler &Asm,
213 const MCAsmLayout &Layout) override;
215 void writeSectionHeader(const MCAssembler &Asm, const MCAsmLayout &Layout,
216 const SectionIndexMapTy &SectionIndexMap,
217 const SectionOffsetsTy &SectionOffsets);
219 void writeSectionData(const MCAssembler &Asm, MCSection &Sec,
220 const MCAsmLayout &Layout);
222 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
223 uint64_t Address, uint64_t Offset, uint64_t Size,
224 uint32_t Link, uint32_t Info, uint64_t Alignment,
227 void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
229 bool IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
230 const MCSymbol &SymA,
231 const MCFragment &FB,
233 bool IsPCRel) const override;
235 bool isWeak(const MCSymbol &Sym) const override;
237 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
238 void writeSection(const SectionIndexMapTy &SectionIndexMap,
239 uint32_t GroupSymbolIndex, uint64_t Offset, uint64_t Size,
240 const MCSectionELF &Section);
244 unsigned ELFObjectWriter::addToSectionTable(const MCSectionELF *Sec) {
245 SectionTable.push_back(Sec);
246 StrTabBuilder.add(Sec->getSectionName());
247 return SectionTable.size();
250 void SymbolTableWriter::createSymtabShndx() {
251 if (!ShndxIndexes.empty())
254 ShndxIndexes.resize(NumWritten);
257 template <typename T> void SymbolTableWriter::write(T Value) {
258 EWriter.write(Value);
261 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
262 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
264 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
265 uint64_t size, uint8_t other,
266 uint32_t shndx, bool Reserved) {
267 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
272 if (!ShndxIndexes.empty()) {
274 ShndxIndexes.push_back(shndx);
276 ShndxIndexes.push_back(0);
279 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
282 write(name); // st_name
283 write(info); // st_info
284 write(other); // st_other
285 write(Index); // st_shndx
286 write(value); // st_value
287 write(size); // st_size
289 write(name); // st_name
290 write(uint32_t(value)); // st_value
291 write(uint32_t(size)); // st_size
292 write(info); // st_info
293 write(other); // st_other
294 write(Index); // st_shndx
300 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
301 const MCFixupKindInfo &FKI =
302 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
304 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
307 ELFObjectWriter::~ELFObjectWriter()
310 // Emit the ELF header.
311 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
317 // emitWord method behaves differently for ELF32 and ELF64, writing
318 // 4 bytes in the former and 8 in the latter.
320 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
322 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
325 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
327 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
329 Write8(TargetObjectWriter->getOSABI());
330 Write8(0); // e_ident[EI_ABIVERSION]
332 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
334 Write16(ELF::ET_REL); // e_type
336 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
338 Write32(ELF::EV_CURRENT); // e_version
339 WriteWord(0); // e_entry, no entry point in .o file
340 WriteWord(0); // e_phoff, no program header for .o
341 WriteWord(0); // e_shoff = sec hdr table off in bytes
343 // e_flags = whatever the target wants
344 Write32(Asm.getELFHeaderEFlags());
346 // e_ehsize = ELF header size
347 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
349 Write16(0); // e_phentsize = prog header entry size
350 Write16(0); // e_phnum = # prog header entries = 0
352 // e_shentsize = Section header entry size
353 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
355 // e_shnum = # of section header ents
358 // e_shstrndx = Section # of '.shstrtab'
359 assert(StringTableIndex < ELF::SHN_LORESERVE);
360 Write16(StringTableIndex);
363 uint64_t ELFObjectWriter::SymbolValue(const MCSymbol &Sym,
364 const MCAsmLayout &Layout) {
365 MCSymbolData &Data = Sym.getData();
366 if (Data.isCommon() && Data.isExternal())
367 return Data.getCommonAlignment();
370 if (!Layout.getSymbolOffset(Sym, Res))
373 if (Layout.getAssembler().isThumbFunc(&Sym))
379 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
380 const MCAsmLayout &Layout) {
381 // The presence of symbol versions causes undefined symbols and
382 // versions declared with @@@ to be renamed.
384 for (const MCSymbol &Alias : Asm.symbols()) {
385 MCSymbolData &OriginalData = Alias.getData();
388 if (!Alias.isVariable())
390 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
393 const MCSymbol &Symbol = Ref->getSymbol();
394 MCSymbolData &SD = Asm.getSymbolData(Symbol);
396 StringRef AliasName = Alias.getName();
397 size_t Pos = AliasName.find('@');
398 if (Pos == StringRef::npos)
401 // Aliases defined with .symvar copy the binding from the symbol they alias.
402 // This is the first place we are able to copy this information.
403 OriginalData.setExternal(SD.isExternal());
404 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
406 StringRef Rest = AliasName.substr(Pos);
407 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
410 // FIXME: produce a better error message.
411 if (Symbol.isUndefined() && Rest.startswith("@@") &&
412 !Rest.startswith("@@@"))
413 report_fatal_error("A @@ version cannot be undefined");
415 Renames.insert(std::make_pair(&Symbol, &Alias));
419 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
420 uint8_t Type = newType;
422 // Propagation rules:
423 // IFUNC > FUNC > OBJECT > NOTYPE
424 // TLS_OBJECT > OBJECT > NOTYPE
426 // dont let the new type degrade the old type
430 case ELF::STT_GNU_IFUNC:
431 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
432 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
433 Type = ELF::STT_GNU_IFUNC;
436 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
437 Type == ELF::STT_TLS)
438 Type = ELF::STT_FUNC;
440 case ELF::STT_OBJECT:
441 if (Type == ELF::STT_NOTYPE)
442 Type = ELF::STT_OBJECT;
445 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
446 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
454 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
455 const MCAsmLayout &Layout) {
456 MCSymbolData &OrigData = MSD.Symbol->getData();
457 assert((!OrigData.getFragment() ||
458 (OrigData.getFragment()->getParent() == &MSD.Symbol->getSection())) &&
459 "The symbol's section doesn't match the fragment's symbol");
460 const MCSymbol *Base = Layout.getBaseSymbol(*MSD.Symbol);
462 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
464 bool IsReserved = !Base || OrigData.isCommon();
466 // Binding and Type share the same byte as upper and lower nibbles
467 uint8_t Binding = MCELF::GetBinding(OrigData);
468 uint8_t Type = MCELF::GetType(OrigData);
469 MCSymbolData *BaseSD = nullptr;
471 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
472 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
474 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
476 // Other and Visibility share the same byte with Visibility using the lower
478 uint8_t Visibility = MCELF::GetVisibility(OrigData);
479 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
482 uint64_t Value = SymbolValue(*MSD.Symbol, Layout);
485 const MCExpr *ESize = OrigData.getSize();
487 ESize = BaseSD->getSize();
491 if (!ESize->evaluateKnownAbsolute(Res, Layout))
492 report_fatal_error("Size expression must be absolute.");
496 // Write out the symbol table entry
497 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
498 MSD.SectionIndex, IsReserved);
501 // It is always valid to create a relocation with a symbol. It is preferable
502 // to use a relocation with a section if that is possible. Using the section
503 // allows us to omit some local symbols from the symbol table.
504 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
505 const MCSymbolRefExpr *RefA,
506 const MCSymbol *Sym, uint64_t C,
507 unsigned Type) const {
508 MCSymbolData *SD = Sym ? &Sym->getData() : nullptr;
510 // A PCRel relocation to an absolute value has no symbol (or section). We
511 // represent that with a relocation to a null section.
515 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
519 // The .odp creation emits a relocation against the symbol ".TOC." which
520 // create a R_PPC64_TOC relocation. However the relocation symbol name
521 // in final object creation should be NULL, since the symbol does not
522 // really exist, it is just the reference to TOC base for the current
523 // object file. Since the symbol is undefined, returning false results
524 // in a relocation with a null section which is the desired result.
525 case MCSymbolRefExpr::VK_PPC_TOCBASE:
528 // These VariantKind cause the relocation to refer to something other than
529 // the symbol itself, like a linker generated table. Since the address of
530 // symbol is not relevant, we cannot replace the symbol with the
531 // section and patch the difference in the addend.
532 case MCSymbolRefExpr::VK_GOT:
533 case MCSymbolRefExpr::VK_PLT:
534 case MCSymbolRefExpr::VK_GOTPCREL:
535 case MCSymbolRefExpr::VK_Mips_GOT:
536 case MCSymbolRefExpr::VK_PPC_GOT_LO:
537 case MCSymbolRefExpr::VK_PPC_GOT_HI:
538 case MCSymbolRefExpr::VK_PPC_GOT_HA:
542 // An undefined symbol is not in any section, so the relocation has to point
543 // to the symbol itself.
544 assert(Sym && "Expected a symbol");
545 if (Sym->isUndefined())
548 unsigned Binding = MCELF::GetBinding(*SD);
551 llvm_unreachable("Invalid Binding");
555 // If the symbol is weak, it might be overridden by a symbol in another
556 // file. The relocation has to point to the symbol so that the linker
559 case ELF::STB_GLOBAL:
560 // Global ELF symbols can be preempted by the dynamic linker. The relocation
561 // has to point to the symbol for a reason analogous to the STB_WEAK case.
565 // If a relocation points to a mergeable section, we have to be careful.
566 // If the offset is zero, a relocation with the section will encode the
567 // same information. With a non-zero offset, the situation is different.
568 // For example, a relocation can point 42 bytes past the end of a string.
569 // If we change such a relocation to use the section, the linker would think
570 // that it pointed to another string and subtracting 42 at runtime will
571 // produce the wrong value.
572 auto &Sec = cast<MCSectionELF>(Sym->getSection());
573 unsigned Flags = Sec.getFlags();
574 if (Flags & ELF::SHF_MERGE) {
578 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
579 // only handle section relocations to mergeable sections if using RELA.
580 if (!hasRelocationAddend())
584 // Most TLS relocations use a got, so they need the symbol. Even those that
585 // are just an offset (@tpoff), require a symbol in gold versions before
586 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
587 // http://sourceware.org/PR16773.
588 if (Flags & ELF::SHF_TLS)
591 // If the symbol is a thumb function the final relocation must set the lowest
592 // bit. With a symbol that is done by just having the symbol have that bit
593 // set, so we would lose the bit if we relocated with the section.
594 // FIXME: We could use the section but add the bit to the relocation value.
595 if (Asm.isThumbFunc(Sym))
598 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
603 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
604 const MCSymbol &Sym = Ref.getSymbol();
606 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
609 if (!Sym.isVariable())
612 const MCExpr *Expr = Sym.getVariableValue();
613 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
617 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
618 return &Inner->getSymbol();
622 // True if the assembler knows nothing about the final value of the symbol.
623 // This doesn't cover the comdat issues, since in those cases the assembler
624 // can at least know that all symbols in the section will move together.
625 static bool isWeak(const MCSymbolData &D) {
626 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
629 switch (MCELF::GetBinding(D)) {
631 llvm_unreachable("Unknown binding");
634 case ELF::STB_GLOBAL:
637 case ELF::STB_GNU_UNIQUE:
642 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
643 const MCAsmLayout &Layout,
644 const MCFragment *Fragment,
645 const MCFixup &Fixup, MCValue Target,
646 bool &IsPCRel, uint64_t &FixedValue) {
647 const MCSectionELF &FixupSection = cast<MCSectionELF>(*Fragment->getParent());
648 uint64_t C = Target.getConstant();
649 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
651 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
652 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
653 "Should not have constructed this");
655 // Let A, B and C being the components of Target and R be the location of
656 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
657 // If it is pcrel, we want to compute (A - B + C - R).
659 // In general, ELF has no relocations for -B. It can only represent (A + C)
660 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
661 // replace B to implement it: (A - R - K + C)
663 Asm.getContext().reportFatalError(
665 "No relocation available to represent this relative expression");
667 const MCSymbol &SymB = RefB->getSymbol();
669 if (SymB.isUndefined())
670 Asm.getContext().reportFatalError(
672 Twine("symbol '") + SymB.getName() +
673 "' can not be undefined in a subtraction expression");
675 assert(!SymB.isAbsolute() && "Should have been folded");
676 const MCSection &SecB = SymB.getSection();
677 if (&SecB != &FixupSection)
678 Asm.getContext().reportFatalError(
679 Fixup.getLoc(), "Cannot represent a difference across sections");
681 if (::isWeak(SymB.getData()))
682 Asm.getContext().reportFatalError(
683 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
685 uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
686 uint64_t K = SymBOffset - FixupOffset;
691 // We either rejected the fixup or folded B into C at this point.
692 const MCSymbolRefExpr *RefA = Target.getSymA();
693 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
695 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
696 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymA, C, Type);
697 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
698 C += Layout.getSymbolOffset(*SymA);
701 if (hasRelocationAddend()) {
708 if (!RelocateWithSymbol) {
709 const MCSection *SecA =
710 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
711 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
712 const MCSymbol *SectionSymbol = ELFSec ? ELFSec->getBeginSymbol() : nullptr;
713 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
714 Relocations[&FixupSection].push_back(Rec);
719 if (const MCSymbol *R = Renames.lookup(SymA))
722 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
723 WeakrefUsedInReloc.insert(WeakRef);
725 UsedInReloc.insert(SymA);
727 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
728 Relocations[&FixupSection].push_back(Rec);
734 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
736 assert(S->hasData());
737 return S->getIndex();
740 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
741 const MCSymbol &Symbol, bool Used,
743 const MCSymbolData &Data = Symbol.getData();
744 if (Symbol.isVariable()) {
745 const MCExpr *Expr = Symbol.getVariableValue();
746 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
747 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
758 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
761 if (Symbol.isVariable()) {
762 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
763 if (Base && Base->isUndefined())
767 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
768 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
771 if (MCELF::GetType(Data) == ELF::STT_SECTION)
774 if (Symbol.isTemporary())
780 bool ELFObjectWriter::isLocal(const MCSymbol &Symbol, bool isUsedInReloc) {
781 const MCSymbolData &Data = Symbol.getData();
782 if (Data.isExternal())
785 if (Symbol.isDefined())
794 void ELFObjectWriter::computeSymbolTable(
795 MCAssembler &Asm, const MCAsmLayout &Layout,
796 const SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap,
797 SectionOffsetsTy &SectionOffsets) {
798 MCContext &Ctx = Asm.getContext();
799 SymbolTableWriter Writer(*this, is64Bit());
802 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
803 MCSectionELF *SymtabSection =
804 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
805 SymtabSection->setAlignment(is64Bit() ? 8 : 4);
806 SymbolTableIndex = addToSectionTable(SymtabSection);
809 OffsetToAlignment(OS.tell(), SymtabSection->getAlignment());
812 uint64_t SecStart = OS.tell();
814 // The first entry is the undefined symbol entry.
815 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
817 std::vector<ELFSymbolData> LocalSymbolData;
818 std::vector<ELFSymbolData> ExternalSymbolData;
819 std::vector<ELFSymbolData> UndefinedSymbolData;
821 // Add the data for the symbols.
822 bool HasLargeSectionIndex = false;
823 for (const MCSymbol &Symbol : Asm.symbols()) {
824 MCSymbolData &SD = Symbol.getData();
826 bool Used = UsedInReloc.count(&Symbol);
827 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
828 bool isSignature = RevGroupMap.count(&Symbol);
830 if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
831 Renames.count(&Symbol)))
835 MSD.Symbol = &Symbol;
836 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
838 // Undefined symbols are global, but this is the first place we
839 // are able to set it.
840 bool Local = isLocal(Symbol, Used);
841 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
843 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
844 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
845 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
849 MSD.SectionIndex = ELF::SHN_ABS;
850 } else if (SD.isCommon()) {
852 MSD.SectionIndex = ELF::SHN_COMMON;
853 } else if (BaseSymbol->isUndefined()) {
854 if (isSignature && !Used) {
855 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
856 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
857 HasLargeSectionIndex = true;
859 MSD.SectionIndex = ELF::SHN_UNDEF;
861 if (!Used && WeakrefUsed)
862 MCELF::SetBinding(SD, ELF::STB_WEAK);
864 const MCSectionELF &Section =
865 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
866 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
867 assert(MSD.SectionIndex && "Invalid section index!");
868 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
869 HasLargeSectionIndex = true;
872 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
875 // FIXME: All name handling should be done before we get to the writer,
876 // including dealing with GNU-style version suffixes. Fixing this isn't
879 // We thus have to be careful to not perform the symbol version replacement
882 // The ELF format is used on Windows by the MCJIT engine. Thus, on
883 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
884 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
885 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
886 // the EFLObjectWriter should not interpret the "@@@" sub-string as
887 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
888 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
889 // "__imp_?" or "__imp_@?".
891 // It would have been interesting to perform the MS mangling prefix check
892 // only when the target triple is of the form *-pc-windows-elf. But, it
893 // seems that this information is not easily accessible from the
895 StringRef Name = Symbol.getName();
896 if (!Name.startswith("?") && !Name.startswith("@?") &&
897 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
898 // This symbol isn't following the MSVC C++ name mangling convention. We
899 // can thus safely interpret the @@@ in symbol names as specifying symbol
902 size_t Pos = Name.find("@@@");
903 if (Pos != StringRef::npos) {
904 Buf += Name.substr(0, Pos);
905 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
906 Buf += Name.substr(Pos + Skip);
911 // Sections have their own string table
912 if (MCELF::GetType(SD) != ELF::STT_SECTION)
913 MSD.Name = StrTabBuilder.add(Name);
915 if (MSD.SectionIndex == ELF::SHN_UNDEF)
916 UndefinedSymbolData.push_back(MSD);
918 LocalSymbolData.push_back(MSD);
920 ExternalSymbolData.push_back(MSD);
923 if (HasLargeSectionIndex) {
924 MCSectionELF *SymtabShndxSection =
925 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
926 SymtabShndxSectionIndex = addToSectionTable(SymtabShndxSection);
927 SymtabShndxSection->setAlignment(4);
930 ArrayRef<std::string> FileNames = Asm.getFileNames();
931 for (const std::string &Name : FileNames)
932 StrTabBuilder.add(Name);
934 StrTabBuilder.finalize(StringTableBuilder::ELF);
936 for (const std::string &Name : FileNames)
937 Writer.writeSymbol(StrTabBuilder.getOffset(Name),
938 ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, ELF::STV_DEFAULT,
941 // Symbols are required to be in lexicographic order.
942 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
943 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
944 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
946 // Set the symbol indices. Local symbols must come before all other
947 // symbols with non-local bindings.
948 unsigned Index = FileNames.size() + 1;
950 for (ELFSymbolData &MSD : LocalSymbolData) {
951 MSD.StringIndex = MCELF::GetType(MSD.Symbol->getData()) == ELF::STT_SECTION
953 : StrTabBuilder.getOffset(MSD.Name);
954 MSD.Symbol->setIndex(Index++);
955 WriteSymbol(Writer, MSD, Layout);
958 // Write the symbol table entries.
959 LastLocalSymbolIndex = Index;
961 for (ELFSymbolData &MSD : ExternalSymbolData) {
962 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
963 MSD.Symbol->setIndex(Index++);
964 MCSymbolData &Data = MSD.Symbol->getData();
965 assert(((Data.getFlags() & ELF_STB_Global) ||
966 (Data.getFlags() & ELF_STB_Weak)) &&
967 "External symbol requires STB_GLOBAL or STB_WEAK flag");
968 WriteSymbol(Writer, MSD, Layout);
969 assert(MCELF::GetBinding(Data) != ELF::STB_LOCAL);
971 for (ELFSymbolData &MSD : UndefinedSymbolData) {
972 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
973 MSD.Symbol->setIndex(Index++);
974 MCSymbolData &Data = MSD.Symbol->getData();
975 WriteSymbol(Writer, MSD, Layout);
976 assert(MCELF::GetBinding(Data) != ELF::STB_LOCAL);
979 uint64_t SecEnd = OS.tell();
980 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
982 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
983 if (ShndxIndexes.empty()) {
984 assert(SymtabShndxSectionIndex == 0);
987 assert(SymtabShndxSectionIndex != 0);
989 SecStart = OS.tell();
990 const MCSectionELF *SymtabShndxSection =
991 SectionTable[SymtabShndxSectionIndex - 1];
992 for (uint32_t Index : ShndxIndexes)
995 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
999 ELFObjectWriter::createRelocationSection(MCContext &Ctx,
1000 const MCSectionELF &Sec) {
1001 if (Relocations[&Sec].empty())
1004 const StringRef SectionName = Sec.getSectionName();
1005 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1006 RelaSectionName += SectionName;
1009 if (hasRelocationAddend())
1010 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1012 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1015 if (Sec.getFlags() & ELF::SHF_GROUP)
1016 Flags = ELF::SHF_GROUP;
1018 MCSectionELF *RelaSection = Ctx.createELFRelSection(
1019 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1020 Flags, EntrySize, Sec.getGroup(), &Sec);
1021 RelaSection->setAlignment(is64Bit() ? 8 : 4);
1025 static SmallVector<char, 128>
1026 getUncompressedData(const MCAsmLayout &Layout,
1027 const MCSection::FragmentListType &Fragments) {
1028 SmallVector<char, 128> UncompressedData;
1029 for (const MCFragment &F : Fragments) {
1030 const SmallVectorImpl<char> *Contents;
1031 switch (F.getKind()) {
1032 case MCFragment::FT_Data:
1033 Contents = &cast<MCDataFragment>(F).getContents();
1035 case MCFragment::FT_Dwarf:
1036 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1038 case MCFragment::FT_DwarfFrame:
1039 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1043 "Not expecting any other fragment types in a debug_* section");
1045 UncompressedData.append(Contents->begin(), Contents->end());
1047 return UncompressedData;
1050 // Include the debug info compression header:
1051 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1052 // useful for consumers to preallocate a buffer to decompress into.
1054 prependCompressionHeader(uint64_t Size,
1055 SmallVectorImpl<char> &CompressedContents) {
1056 const StringRef Magic = "ZLIB";
1057 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1059 if (sys::IsLittleEndianHost)
1060 sys::swapByteOrder(Size);
1061 CompressedContents.insert(CompressedContents.begin(),
1062 Magic.size() + sizeof(Size), 0);
1063 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1064 std::copy(reinterpret_cast<char *>(&Size),
1065 reinterpret_cast<char *>(&Size + 1),
1066 CompressedContents.begin() + Magic.size());
1070 void ELFObjectWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
1071 const MCAsmLayout &Layout) {
1072 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1073 StringRef SectionName = Section.getSectionName();
1075 // Compressing debug_frame requires handling alignment fragments which is
1076 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1077 // for writing to arbitrary buffers) for little benefit.
1078 if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
1079 !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
1080 Asm.writeSectionData(&Section, Layout);
1084 // Gather the uncompressed data from all the fragments.
1085 const MCSection::FragmentListType &Fragments = Section.getFragmentList();
1086 SmallVector<char, 128> UncompressedData =
1087 getUncompressedData(Layout, Fragments);
1089 SmallVector<char, 128> CompressedContents;
1090 zlib::Status Success = zlib::compress(
1091 StringRef(UncompressedData.data(), UncompressedData.size()),
1092 CompressedContents);
1093 if (Success != zlib::StatusOK) {
1094 Asm.writeSectionData(&Section, Layout);
1098 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
1099 Asm.writeSectionData(&Section, Layout);
1102 Asm.getContext().renameELFSection(&Section,
1103 (".z" + SectionName.drop_front(1)).str());
1104 OS << CompressedContents;
1107 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1108 uint64_t Flags, uint64_t Address,
1109 uint64_t Offset, uint64_t Size,
1110 uint32_t Link, uint32_t Info,
1112 uint64_t EntrySize) {
1113 Write32(Name); // sh_name: index into string table
1114 Write32(Type); // sh_type
1115 WriteWord(Flags); // sh_flags
1116 WriteWord(Address); // sh_addr
1117 WriteWord(Offset); // sh_offset
1118 WriteWord(Size); // sh_size
1119 Write32(Link); // sh_link
1120 Write32(Info); // sh_info
1121 WriteWord(Alignment); // sh_addralign
1122 WriteWord(EntrySize); // sh_entsize
1125 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1126 const MCSectionELF &Sec) {
1127 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1129 // Sort the relocation entries. Most targets just sort by Offset, but some
1130 // (e.g., MIPS) have additional constraints.
1131 TargetObjectWriter->sortRelocs(Asm, Relocs);
1133 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1134 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1136 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1139 write(Entry.Offset);
1140 if (TargetObjectWriter->isN64()) {
1141 write(uint32_t(Index));
1143 write(TargetObjectWriter->getRSsym(Entry.Type));
1144 write(TargetObjectWriter->getRType3(Entry.Type));
1145 write(TargetObjectWriter->getRType2(Entry.Type));
1146 write(TargetObjectWriter->getRType(Entry.Type));
1148 struct ELF::Elf64_Rela ERE64;
1149 ERE64.setSymbolAndType(Index, Entry.Type);
1150 write(ERE64.r_info);
1152 if (hasRelocationAddend())
1153 write(Entry.Addend);
1155 write(uint32_t(Entry.Offset));
1157 struct ELF::Elf32_Rela ERE32;
1158 ERE32.setSymbolAndType(Index, Entry.Type);
1159 write(ERE32.r_info);
1161 if (hasRelocationAddend())
1162 write(uint32_t(Entry.Addend));
1167 const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
1168 const MCSectionELF *StrtabSection = SectionTable[StringTableIndex - 1];
1169 OS << StrTabBuilder.data();
1170 return StrtabSection;
1173 void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
1174 uint32_t GroupSymbolIndex, uint64_t Offset,
1175 uint64_t Size, const MCSectionELF &Section) {
1176 uint64_t sh_link = 0;
1177 uint64_t sh_info = 0;
1179 switch(Section.getType()) {
1184 case ELF::SHT_DYNAMIC:
1185 llvm_unreachable("SHT_DYNAMIC in a relocatable object");
1188 case ELF::SHT_RELA: {
1189 sh_link = SymbolTableIndex;
1190 assert(sh_link && ".symtab not found");
1191 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1192 sh_info = SectionIndexMap.lookup(InfoSection);
1196 case ELF::SHT_SYMTAB:
1197 case ELF::SHT_DYNSYM:
1198 sh_link = StringTableIndex;
1199 sh_info = LastLocalSymbolIndex;
1202 case ELF::SHT_SYMTAB_SHNDX:
1203 sh_link = SymbolTableIndex;
1206 case ELF::SHT_GROUP:
1207 sh_link = SymbolTableIndex;
1208 sh_info = GroupSymbolIndex;
1212 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1213 Section.getType() == ELF::SHT_ARM_EXIDX)
1214 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1216 WriteSecHdrEntry(StrTabBuilder.getOffset(Section.getSectionName()),
1217 Section.getType(), Section.getFlags(), 0, Offset, Size,
1218 sh_link, sh_info, Section.getAlignment(),
1219 Section.getEntrySize());
1222 void ELFObjectWriter::writeSectionHeader(
1223 const MCAssembler &Asm, const MCAsmLayout &Layout,
1224 const SectionIndexMapTy &SectionIndexMap,
1225 const SectionOffsetsTy &SectionOffsets) {
1226 const unsigned NumSections = SectionTable.size();
1228 // Null section first.
1229 uint64_t FirstSectionSize =
1230 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1231 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1233 for (const MCSectionELF *Section : SectionTable) {
1234 uint32_t GroupSymbolIndex;
1235 unsigned Type = Section->getType();
1236 if (Type != ELF::SHT_GROUP)
1237 GroupSymbolIndex = 0;
1239 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section->getGroup());
1241 const std::pair<uint64_t, uint64_t> &Offsets =
1242 SectionOffsets.find(Section)->second;
1244 if (Type == ELF::SHT_NOBITS)
1245 Size = Layout.getSectionAddressSize(Section);
1247 Size = Offsets.second - Offsets.first;
1249 writeSection(SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1254 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1255 const MCAsmLayout &Layout) {
1256 MCContext &Ctx = Asm.getContext();
1257 MCSectionELF *StrtabSection =
1258 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1259 StringTableIndex = addToSectionTable(StrtabSection);
1261 RevGroupMapTy RevGroupMap;
1262 SectionIndexMapTy SectionIndexMap;
1264 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1266 // Write out the ELF header ...
1269 // ... then the sections ...
1270 SectionOffsetsTy SectionOffsets;
1271 std::vector<MCSectionELF *> Groups;
1272 std::vector<MCSectionELF *> Relocations;
1273 for (MCSection &Sec : Asm) {
1274 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1276 uint64_t Padding = OffsetToAlignment(OS.tell(), Section.getAlignment());
1277 WriteZeros(Padding);
1279 // Remember the offset into the file for this section.
1280 uint64_t SecStart = OS.tell();
1282 const MCSymbol *SignatureSymbol = Section.getGroup();
1283 writeSectionData(Asm, Section, Layout);
1285 uint64_t SecEnd = OS.tell();
1286 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1288 MCSectionELF *RelSection = createRelocationSection(Ctx, Section);
1290 if (SignatureSymbol) {
1291 Asm.getOrCreateSymbolData(*SignatureSymbol);
1292 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1294 MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1295 GroupIdx = addToSectionTable(Group);
1296 Group->setAlignment(4);
1297 Groups.push_back(Group);
1299 GroupMembers[SignatureSymbol].push_back(&Section);
1301 GroupMembers[SignatureSymbol].push_back(RelSection);
1304 SectionIndexMap[&Section] = addToSectionTable(&Section);
1306 SectionIndexMap[RelSection] = addToSectionTable(RelSection);
1307 Relocations.push_back(RelSection);
1311 for (MCSectionELF *Group : Groups) {
1312 uint64_t Padding = OffsetToAlignment(OS.tell(), Group->getAlignment());
1313 WriteZeros(Padding);
1315 // Remember the offset into the file for this section.
1316 uint64_t SecStart = OS.tell();
1318 const MCSymbol *SignatureSymbol = Group->getGroup();
1319 assert(SignatureSymbol);
1320 write(uint32_t(ELF::GRP_COMDAT));
1321 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1322 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1326 uint64_t SecEnd = OS.tell();
1327 SectionOffsets[Group] = std::make_pair(SecStart, SecEnd);
1330 // Compute symbol table information.
1331 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, SectionOffsets);
1333 for (MCSectionELF *RelSection : Relocations) {
1334 uint64_t Padding = OffsetToAlignment(OS.tell(), RelSection->getAlignment());
1335 WriteZeros(Padding);
1337 // Remember the offset into the file for this section.
1338 uint64_t SecStart = OS.tell();
1340 writeRelocations(Asm, *RelSection->getAssociatedSection());
1342 uint64_t SecEnd = OS.tell();
1343 SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
1347 uint64_t SecStart = OS.tell();
1348 const MCSectionELF *Sec = createStringTable(Ctx);
1349 uint64_t SecEnd = OS.tell();
1350 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1353 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1354 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1355 WriteZeros(Padding);
1357 const unsigned SectionHeaderOffset = OS.tell();
1359 // ... then the section header table ...
1360 writeSectionHeader(Asm, Layout, SectionIndexMap, SectionOffsets);
1362 uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
1363 ? (uint16_t)ELF::SHN_UNDEF
1364 : SectionTable.size() + 1;
1365 if (sys::IsLittleEndianHost != IsLittleEndian)
1366 sys::swapByteOrder(NumSections);
1367 unsigned NumSectionsOffset;
1370 uint64_t Val = SectionHeaderOffset;
1371 if (sys::IsLittleEndianHost != IsLittleEndian)
1372 sys::swapByteOrder(Val);
1373 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1374 offsetof(ELF::Elf64_Ehdr, e_shoff));
1375 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1377 uint32_t Val = SectionHeaderOffset;
1378 if (sys::IsLittleEndianHost != IsLittleEndian)
1379 sys::swapByteOrder(Val);
1380 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1381 offsetof(ELF::Elf32_Ehdr, e_shoff));
1382 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1384 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1388 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1389 const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
1390 bool InSet, bool IsPCRel) const {
1393 if (::isWeak(SymA.getData()))
1396 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
1400 bool ELFObjectWriter::isWeak(const MCSymbol &Sym) const {
1401 const MCSymbolData &SD = Sym.getData();
1405 // It is invalid to replace a reference to a global in a comdat
1406 // with a reference to a local since out of comdat references
1407 // to a local are forbidden.
1408 // We could try to return false for more cases, like the reference
1409 // being in the same comdat or Sym being an alias to another global,
1410 // but it is not clear if it is worth the effort.
1411 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1414 if (!Sym.isInSection())
1417 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1418 return Sec.getGroup();
1421 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1422 raw_pwrite_stream &OS,
1423 bool IsLittleEndian) {
1424 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);