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;
115 std::vector<uint64_t> FileSymbolData;
116 std::vector<ELFSymbolData> LocalSymbolData;
117 std::vector<ELFSymbolData> ExternalSymbolData;
118 std::vector<ELFSymbolData> UndefinedSymbolData;
122 // This holds the symbol table index of the last local symbol.
123 unsigned LastLocalSymbolIndex;
124 // This holds the .strtab section index.
125 unsigned StringTableIndex;
126 // This holds the .symtab section index.
127 unsigned SymbolTableIndex;
128 // This holds the .symtab_shndx section index.
129 unsigned SymtabShndxSectionIndex = 0;
131 // Sections in the order they are to be output in the section table.
132 std::vector<const MCSectionELF *> SectionTable;
133 unsigned addToSectionTable(const MCSectionELF *Sec);
135 // TargetObjectWriter wrappers.
136 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
137 bool hasRelocationAddend() const {
138 return TargetObjectWriter->hasRelocationAddend();
140 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
141 bool IsPCRel) const {
142 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
146 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
148 : MCObjectWriter(OS, IsLittleEndian), TargetObjectWriter(MOTW) {}
150 void reset() override {
152 WeakrefUsedInReloc.clear();
155 StrTabBuilder.clear();
156 FileSymbolData.clear();
157 LocalSymbolData.clear();
158 ExternalSymbolData.clear();
159 UndefinedSymbolData.clear();
160 SectionTable.clear();
161 MCObjectWriter::reset();
164 ~ELFObjectWriter() override;
166 void WriteWord(uint64_t W) {
173 template <typename T> void write(T Val) {
175 support::endian::Writer<support::little>(OS).write(Val);
177 support::endian::Writer<support::big>(OS).write(Val);
180 void writeHeader(const MCAssembler &Asm);
182 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
183 const MCAsmLayout &Layout);
185 // Start and end offset of each section
186 typedef std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>
189 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
190 const MCSymbolRefExpr *RefA,
191 const MCSymbol *Sym, uint64_t C,
192 unsigned Type) const;
194 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
195 const MCFragment *Fragment, const MCFixup &Fixup,
196 MCValue Target, bool &IsPCRel,
197 uint64_t &FixedValue) override;
199 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
202 // Map from a signature symbol to the group section index
203 typedef DenseMap<const MCSymbol *, unsigned> RevGroupMapTy;
205 /// Compute the symbol table data
207 /// \param Asm - The assembler.
208 /// \param SectionIndexMap - Maps a section to its index.
209 /// \param RevGroupMap - Maps a signature symbol to the group section.
210 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
211 const SectionIndexMapTy &SectionIndexMap,
212 const RevGroupMapTy &RevGroupMap,
213 SectionOffsetsTy &SectionOffsets);
215 MCSectionELF *createRelocationSection(MCContext &Ctx,
216 const MCSectionELF &Sec);
218 const MCSectionELF *createStringTable(MCContext &Ctx);
220 void ExecutePostLayoutBinding(MCAssembler &Asm,
221 const MCAsmLayout &Layout) override;
223 void writeSectionHeader(const MCAssembler &Asm, const MCAsmLayout &Layout,
224 const SectionIndexMapTy &SectionIndexMap,
225 const SectionOffsetsTy &SectionOffsets);
227 void writeSectionData(const MCAssembler &Asm, MCSection &Sec,
228 const MCAsmLayout &Layout);
230 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
231 uint64_t Address, uint64_t Offset, uint64_t Size,
232 uint32_t Link, uint32_t Info, uint64_t Alignment,
235 void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
237 bool IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
238 const MCSymbol &SymA,
239 const MCFragment &FB,
241 bool IsPCRel) const override;
243 bool isWeak(const MCSymbol &Sym) const override;
245 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
246 void writeSection(const SectionIndexMapTy &SectionIndexMap,
247 uint32_t GroupSymbolIndex, uint64_t Offset, uint64_t Size,
248 const MCSectionELF &Section);
252 unsigned ELFObjectWriter::addToSectionTable(const MCSectionELF *Sec) {
253 SectionTable.push_back(Sec);
254 StrTabBuilder.add(Sec->getSectionName());
255 return SectionTable.size();
258 void SymbolTableWriter::createSymtabShndx() {
259 if (!ShndxIndexes.empty())
262 ShndxIndexes.resize(NumWritten);
265 template <typename T> void SymbolTableWriter::write(T Value) {
266 EWriter.write(Value);
269 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
270 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
272 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
273 uint64_t size, uint8_t other,
274 uint32_t shndx, bool Reserved) {
275 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
280 if (!ShndxIndexes.empty()) {
282 ShndxIndexes.push_back(shndx);
284 ShndxIndexes.push_back(0);
287 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
290 write(name); // st_name
291 write(info); // st_info
292 write(other); // st_other
293 write(Index); // st_shndx
294 write(value); // st_value
295 write(size); // st_size
297 write(name); // st_name
298 write(uint32_t(value)); // st_value
299 write(uint32_t(size)); // st_size
300 write(info); // st_info
301 write(other); // st_other
302 write(Index); // st_shndx
308 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
309 const MCFixupKindInfo &FKI =
310 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
312 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
315 ELFObjectWriter::~ELFObjectWriter()
318 // Emit the ELF header.
319 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
325 // emitWord method behaves differently for ELF32 and ELF64, writing
326 // 4 bytes in the former and 8 in the latter.
328 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
330 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
333 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
335 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
337 Write8(TargetObjectWriter->getOSABI());
338 Write8(0); // e_ident[EI_ABIVERSION]
340 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
342 Write16(ELF::ET_REL); // e_type
344 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
346 Write32(ELF::EV_CURRENT); // e_version
347 WriteWord(0); // e_entry, no entry point in .o file
348 WriteWord(0); // e_phoff, no program header for .o
349 WriteWord(0); // e_shoff = sec hdr table off in bytes
351 // e_flags = whatever the target wants
352 Write32(Asm.getELFHeaderEFlags());
354 // e_ehsize = ELF header size
355 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
357 Write16(0); // e_phentsize = prog header entry size
358 Write16(0); // e_phnum = # prog header entries = 0
360 // e_shentsize = Section header entry size
361 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
363 // e_shnum = # of section header ents
366 // e_shstrndx = Section # of '.shstrtab'
367 assert(StringTableIndex < ELF::SHN_LORESERVE);
368 Write16(StringTableIndex);
371 uint64_t ELFObjectWriter::SymbolValue(const MCSymbol &Sym,
372 const MCAsmLayout &Layout) {
373 MCSymbolData &Data = Sym.getData();
374 if (Data.isCommon() && Data.isExternal())
375 return Data.getCommonAlignment();
378 if (!Layout.getSymbolOffset(Sym, Res))
381 if (Layout.getAssembler().isThumbFunc(&Sym))
387 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
388 const MCAsmLayout &Layout) {
389 // The presence of symbol versions causes undefined symbols and
390 // versions declared with @@@ to be renamed.
392 for (const MCSymbol &Alias : Asm.symbols()) {
393 MCSymbolData &OriginalData = Alias.getData();
396 if (!Alias.isVariable())
398 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
401 const MCSymbol &Symbol = Ref->getSymbol();
402 MCSymbolData &SD = Asm.getSymbolData(Symbol);
404 StringRef AliasName = Alias.getName();
405 size_t Pos = AliasName.find('@');
406 if (Pos == StringRef::npos)
409 // Aliases defined with .symvar copy the binding from the symbol they alias.
410 // This is the first place we are able to copy this information.
411 OriginalData.setExternal(SD.isExternal());
412 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
414 StringRef Rest = AliasName.substr(Pos);
415 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
418 // FIXME: produce a better error message.
419 if (Symbol.isUndefined() && Rest.startswith("@@") &&
420 !Rest.startswith("@@@"))
421 report_fatal_error("A @@ version cannot be undefined");
423 Renames.insert(std::make_pair(&Symbol, &Alias));
427 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
428 uint8_t Type = newType;
430 // Propagation rules:
431 // IFUNC > FUNC > OBJECT > NOTYPE
432 // TLS_OBJECT > OBJECT > NOTYPE
434 // dont let the new type degrade the old type
438 case ELF::STT_GNU_IFUNC:
439 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
440 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
441 Type = ELF::STT_GNU_IFUNC;
444 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
445 Type == ELF::STT_TLS)
446 Type = ELF::STT_FUNC;
448 case ELF::STT_OBJECT:
449 if (Type == ELF::STT_NOTYPE)
450 Type = ELF::STT_OBJECT;
453 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
454 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
462 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
463 const MCAsmLayout &Layout) {
464 MCSymbolData &OrigData = MSD.Symbol->getData();
465 assert((!OrigData.getFragment() ||
466 (OrigData.getFragment()->getParent() == &MSD.Symbol->getSection())) &&
467 "The symbol's section doesn't match the fragment's symbol");
468 const MCSymbol *Base = Layout.getBaseSymbol(*MSD.Symbol);
470 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
472 bool IsReserved = !Base || OrigData.isCommon();
474 // Binding and Type share the same byte as upper and lower nibbles
475 uint8_t Binding = MCELF::GetBinding(OrigData);
476 uint8_t Type = MCELF::GetType(OrigData);
477 MCSymbolData *BaseSD = nullptr;
479 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
480 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
482 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
484 // Other and Visibility share the same byte with Visibility using the lower
486 uint8_t Visibility = MCELF::GetVisibility(OrigData);
487 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
490 uint64_t Value = SymbolValue(*MSD.Symbol, Layout);
493 const MCExpr *ESize = OrigData.getSize();
495 ESize = BaseSD->getSize();
499 if (!ESize->evaluateKnownAbsolute(Res, Layout))
500 report_fatal_error("Size expression must be absolute.");
504 // Write out the symbol table entry
505 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
506 MSD.SectionIndex, IsReserved);
509 // It is always valid to create a relocation with a symbol. It is preferable
510 // to use a relocation with a section if that is possible. Using the section
511 // allows us to omit some local symbols from the symbol table.
512 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
513 const MCSymbolRefExpr *RefA,
514 const MCSymbol *Sym, uint64_t C,
515 unsigned Type) const {
516 MCSymbolData *SD = Sym ? &Sym->getData() : nullptr;
518 // A PCRel relocation to an absolute value has no symbol (or section). We
519 // represent that with a relocation to a null section.
523 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
527 // The .odp creation emits a relocation against the symbol ".TOC." which
528 // create a R_PPC64_TOC relocation. However the relocation symbol name
529 // in final object creation should be NULL, since the symbol does not
530 // really exist, it is just the reference to TOC base for the current
531 // object file. Since the symbol is undefined, returning false results
532 // in a relocation with a null section which is the desired result.
533 case MCSymbolRefExpr::VK_PPC_TOCBASE:
536 // These VariantKind cause the relocation to refer to something other than
537 // the symbol itself, like a linker generated table. Since the address of
538 // symbol is not relevant, we cannot replace the symbol with the
539 // section and patch the difference in the addend.
540 case MCSymbolRefExpr::VK_GOT:
541 case MCSymbolRefExpr::VK_PLT:
542 case MCSymbolRefExpr::VK_GOTPCREL:
543 case MCSymbolRefExpr::VK_Mips_GOT:
544 case MCSymbolRefExpr::VK_PPC_GOT_LO:
545 case MCSymbolRefExpr::VK_PPC_GOT_HI:
546 case MCSymbolRefExpr::VK_PPC_GOT_HA:
550 // An undefined symbol is not in any section, so the relocation has to point
551 // to the symbol itself.
552 assert(Sym && "Expected a symbol");
553 if (Sym->isUndefined())
556 unsigned Binding = MCELF::GetBinding(*SD);
559 llvm_unreachable("Invalid Binding");
563 // If the symbol is weak, it might be overridden by a symbol in another
564 // file. The relocation has to point to the symbol so that the linker
567 case ELF::STB_GLOBAL:
568 // Global ELF symbols can be preempted by the dynamic linker. The relocation
569 // has to point to the symbol for a reason analogous to the STB_WEAK case.
573 // If a relocation points to a mergeable section, we have to be careful.
574 // If the offset is zero, a relocation with the section will encode the
575 // same information. With a non-zero offset, the situation is different.
576 // For example, a relocation can point 42 bytes past the end of a string.
577 // If we change such a relocation to use the section, the linker would think
578 // that it pointed to another string and subtracting 42 at runtime will
579 // produce the wrong value.
580 auto &Sec = cast<MCSectionELF>(Sym->getSection());
581 unsigned Flags = Sec.getFlags();
582 if (Flags & ELF::SHF_MERGE) {
586 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
587 // only handle section relocations to mergeable sections if using RELA.
588 if (!hasRelocationAddend())
592 // Most TLS relocations use a got, so they need the symbol. Even those that
593 // are just an offset (@tpoff), require a symbol in gold versions before
594 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
595 // http://sourceware.org/PR16773.
596 if (Flags & ELF::SHF_TLS)
599 // If the symbol is a thumb function the final relocation must set the lowest
600 // bit. With a symbol that is done by just having the symbol have that bit
601 // set, so we would lose the bit if we relocated with the section.
602 // FIXME: We could use the section but add the bit to the relocation value.
603 if (Asm.isThumbFunc(Sym))
606 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
611 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
612 const MCSymbol &Sym = Ref.getSymbol();
614 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
617 if (!Sym.isVariable())
620 const MCExpr *Expr = Sym.getVariableValue();
621 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
625 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
626 return &Inner->getSymbol();
630 // True if the assembler knows nothing about the final value of the symbol.
631 // This doesn't cover the comdat issues, since in those cases the assembler
632 // can at least know that all symbols in the section will move together.
633 static bool isWeak(const MCSymbolData &D) {
634 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
637 switch (MCELF::GetBinding(D)) {
639 llvm_unreachable("Unknown binding");
642 case ELF::STB_GLOBAL:
645 case ELF::STB_GNU_UNIQUE:
650 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
651 const MCAsmLayout &Layout,
652 const MCFragment *Fragment,
653 const MCFixup &Fixup, MCValue Target,
654 bool &IsPCRel, uint64_t &FixedValue) {
655 const MCSectionELF &FixupSection = cast<MCSectionELF>(*Fragment->getParent());
656 uint64_t C = Target.getConstant();
657 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
659 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
660 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
661 "Should not have constructed this");
663 // Let A, B and C being the components of Target and R be the location of
664 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
665 // If it is pcrel, we want to compute (A - B + C - R).
667 // In general, ELF has no relocations for -B. It can only represent (A + C)
668 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
669 // replace B to implement it: (A - R - K + C)
671 Asm.getContext().reportFatalError(
673 "No relocation available to represent this relative expression");
675 const MCSymbol &SymB = RefB->getSymbol();
677 if (SymB.isUndefined())
678 Asm.getContext().reportFatalError(
680 Twine("symbol '") + SymB.getName() +
681 "' can not be undefined in a subtraction expression");
683 assert(!SymB.isAbsolute() && "Should have been folded");
684 const MCSection &SecB = SymB.getSection();
685 if (&SecB != &FixupSection)
686 Asm.getContext().reportFatalError(
687 Fixup.getLoc(), "Cannot represent a difference across sections");
689 if (::isWeak(SymB.getData()))
690 Asm.getContext().reportFatalError(
691 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
693 uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
694 uint64_t K = SymBOffset - FixupOffset;
699 // We either rejected the fixup or folded B into C at this point.
700 const MCSymbolRefExpr *RefA = Target.getSymA();
701 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
703 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
704 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymA, C, Type);
705 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
706 C += Layout.getSymbolOffset(*SymA);
709 if (hasRelocationAddend()) {
716 if (!RelocateWithSymbol) {
717 const MCSection *SecA =
718 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
719 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
720 const MCSymbol *SectionSymbol = ELFSec ? ELFSec->getBeginSymbol() : nullptr;
721 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
722 Relocations[&FixupSection].push_back(Rec);
727 if (const MCSymbol *R = Renames.lookup(SymA))
730 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
731 WeakrefUsedInReloc.insert(WeakRef);
733 UsedInReloc.insert(SymA);
735 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
736 Relocations[&FixupSection].push_back(Rec);
742 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
744 assert(S->hasData());
745 return S->getIndex();
748 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
749 const MCSymbol &Symbol, bool Used,
751 const MCSymbolData &Data = Symbol.getData();
752 if (Symbol.isVariable()) {
753 const MCExpr *Expr = Symbol.getVariableValue();
754 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
755 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
766 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
769 if (Symbol.isVariable()) {
770 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
771 if (Base && Base->isUndefined())
775 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
776 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
779 if (MCELF::GetType(Data) == ELF::STT_SECTION)
782 if (Symbol.isTemporary())
788 bool ELFObjectWriter::isLocal(const MCSymbol &Symbol, bool isUsedInReloc) {
789 const MCSymbolData &Data = Symbol.getData();
790 if (Data.isExternal())
793 if (Symbol.isDefined())
802 void ELFObjectWriter::computeSymbolTable(
803 MCAssembler &Asm, const MCAsmLayout &Layout,
804 const SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap,
805 SectionOffsetsTy &SectionOffsets) {
806 MCContext &Ctx = Asm.getContext();
807 SymbolTableWriter Writer(*this, is64Bit());
810 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
811 MCSectionELF *SymtabSection =
812 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
813 SymtabSection->setAlignment(is64Bit() ? 8 : 4);
814 SymbolTableIndex = addToSectionTable(SymtabSection);
817 OffsetToAlignment(OS.tell(), SymtabSection->getAlignment());
820 uint64_t SecStart = OS.tell();
822 // The first entry is the undefined symbol entry.
823 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
825 // Add the data for the symbols.
826 bool HasLargeSectionIndex = false;
827 for (const MCSymbol &Symbol : Asm.symbols()) {
828 MCSymbolData &SD = Symbol.getData();
830 bool Used = UsedInReloc.count(&Symbol);
831 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
832 bool isSignature = RevGroupMap.count(&Symbol);
834 if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
835 Renames.count(&Symbol)))
839 MSD.Symbol = &Symbol;
840 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
842 // Undefined symbols are global, but this is the first place we
843 // are able to set it.
844 bool Local = isLocal(Symbol, Used);
845 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
847 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
848 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
849 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
853 MSD.SectionIndex = ELF::SHN_ABS;
854 } else if (SD.isCommon()) {
856 MSD.SectionIndex = ELF::SHN_COMMON;
857 } else if (BaseSymbol->isUndefined()) {
858 if (isSignature && !Used) {
859 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
860 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
861 HasLargeSectionIndex = true;
863 MSD.SectionIndex = ELF::SHN_UNDEF;
865 if (!Used && WeakrefUsed)
866 MCELF::SetBinding(SD, ELF::STB_WEAK);
868 const MCSectionELF &Section =
869 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
870 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
871 assert(MSD.SectionIndex && "Invalid section index!");
872 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
873 HasLargeSectionIndex = true;
876 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
879 // FIXME: All name handling should be done before we get to the writer,
880 // including dealing with GNU-style version suffixes. Fixing this isn't
883 // We thus have to be careful to not perform the symbol version replacement
886 // The ELF format is used on Windows by the MCJIT engine. Thus, on
887 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
888 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
889 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
890 // the EFLObjectWriter should not interpret the "@@@" sub-string as
891 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
892 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
893 // "__imp_?" or "__imp_@?".
895 // It would have been interesting to perform the MS mangling prefix check
896 // only when the target triple is of the form *-pc-windows-elf. But, it
897 // seems that this information is not easily accessible from the
899 StringRef Name = Symbol.getName();
900 if (!Name.startswith("?") && !Name.startswith("@?") &&
901 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
902 // This symbol isn't following the MSVC C++ name mangling convention. We
903 // can thus safely interpret the @@@ in symbol names as specifying symbol
906 size_t Pos = Name.find("@@@");
907 if (Pos != StringRef::npos) {
908 Buf += Name.substr(0, Pos);
909 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
910 Buf += Name.substr(Pos + Skip);
915 // Sections have their own string table
916 if (MCELF::GetType(SD) != ELF::STT_SECTION)
917 MSD.Name = StrTabBuilder.add(Name);
919 if (MSD.SectionIndex == ELF::SHN_UNDEF)
920 UndefinedSymbolData.push_back(MSD);
922 LocalSymbolData.push_back(MSD);
924 ExternalSymbolData.push_back(MSD);
927 if (HasLargeSectionIndex) {
928 MCSectionELF *SymtabShndxSection =
929 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
930 SymtabShndxSectionIndex = addToSectionTable(SymtabShndxSection);
931 SymtabShndxSection->setAlignment(4);
934 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
935 StrTabBuilder.add(*i);
937 StrTabBuilder.finalize(StringTableBuilder::ELF);
939 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
940 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
942 // Symbols are required to be in lexicographic order.
943 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
944 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
945 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
947 // Set the symbol indices. Local symbols must come before all other
948 // symbols with non-local bindings.
949 unsigned Index = FileSymbolData.size() + 1;
951 for (ELFSymbolData &MSD : LocalSymbolData) {
952 MSD.StringIndex = MCELF::GetType(MSD.Symbol->getData()) == ELF::STT_SECTION
954 : StrTabBuilder.getOffset(MSD.Name);
955 MSD.Symbol->setIndex(Index++);
957 for (ELFSymbolData &MSD : ExternalSymbolData) {
958 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
959 MSD.Symbol->setIndex(Index++);
961 for (ELFSymbolData &MSD : UndefinedSymbolData) {
962 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
963 MSD.Symbol->setIndex(Index++);
966 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
967 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
968 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
971 // Write the symbol table entries.
972 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
974 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
975 ELFSymbolData &MSD = LocalSymbolData[i];
976 WriteSymbol(Writer, MSD, Layout);
979 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
980 ELFSymbolData &MSD = ExternalSymbolData[i];
981 MCSymbolData &Data = MSD.Symbol->getData();
982 assert(((Data.getFlags() & ELF_STB_Global) ||
983 (Data.getFlags() & ELF_STB_Weak)) &&
984 "External symbol requires STB_GLOBAL or STB_WEAK flag");
985 WriteSymbol(Writer, MSD, Layout);
986 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
987 LastLocalSymbolIndex++;
990 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
991 ELFSymbolData &MSD = UndefinedSymbolData[i];
992 MCSymbolData &Data = MSD.Symbol->getData();
993 WriteSymbol(Writer, MSD, Layout);
994 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
995 LastLocalSymbolIndex++;
998 uint64_t SecEnd = OS.tell();
999 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
1001 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
1002 if (ShndxIndexes.empty()) {
1003 assert(SymtabShndxSectionIndex == 0);
1006 assert(SymtabShndxSectionIndex != 0);
1008 SecStart = OS.tell();
1009 const MCSectionELF *SymtabShndxSection =
1010 SectionTable[SymtabShndxSectionIndex - 1];
1011 for (uint32_t Index : ShndxIndexes)
1014 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
1018 ELFObjectWriter::createRelocationSection(MCContext &Ctx,
1019 const MCSectionELF &Sec) {
1020 if (Relocations[&Sec].empty())
1023 const StringRef SectionName = Sec.getSectionName();
1024 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1025 RelaSectionName += SectionName;
1028 if (hasRelocationAddend())
1029 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1031 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1034 if (Sec.getFlags() & ELF::SHF_GROUP)
1035 Flags = ELF::SHF_GROUP;
1037 MCSectionELF *RelaSection = Ctx.createELFRelSection(
1038 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1039 Flags, EntrySize, Sec.getGroup(), &Sec);
1040 RelaSection->setAlignment(is64Bit() ? 8 : 4);
1044 static SmallVector<char, 128>
1045 getUncompressedData(const MCAsmLayout &Layout,
1046 const MCSection::FragmentListType &Fragments) {
1047 SmallVector<char, 128> UncompressedData;
1048 for (const MCFragment &F : Fragments) {
1049 const SmallVectorImpl<char> *Contents;
1050 switch (F.getKind()) {
1051 case MCFragment::FT_Data:
1052 Contents = &cast<MCDataFragment>(F).getContents();
1054 case MCFragment::FT_Dwarf:
1055 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1057 case MCFragment::FT_DwarfFrame:
1058 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1062 "Not expecting any other fragment types in a debug_* section");
1064 UncompressedData.append(Contents->begin(), Contents->end());
1066 return UncompressedData;
1069 // Include the debug info compression header:
1070 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1071 // useful for consumers to preallocate a buffer to decompress into.
1073 prependCompressionHeader(uint64_t Size,
1074 SmallVectorImpl<char> &CompressedContents) {
1075 const StringRef Magic = "ZLIB";
1076 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1078 if (sys::IsLittleEndianHost)
1079 sys::swapByteOrder(Size);
1080 CompressedContents.insert(CompressedContents.begin(),
1081 Magic.size() + sizeof(Size), 0);
1082 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1083 std::copy(reinterpret_cast<char *>(&Size),
1084 reinterpret_cast<char *>(&Size + 1),
1085 CompressedContents.begin() + Magic.size());
1089 void ELFObjectWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
1090 const MCAsmLayout &Layout) {
1091 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1092 StringRef SectionName = Section.getSectionName();
1094 // Compressing debug_frame requires handling alignment fragments which is
1095 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1096 // for writing to arbitrary buffers) for little benefit.
1097 if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
1098 !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
1099 Asm.writeSectionData(&Section, Layout);
1103 // Gather the uncompressed data from all the fragments.
1104 const MCSection::FragmentListType &Fragments = Section.getFragmentList();
1105 SmallVector<char, 128> UncompressedData =
1106 getUncompressedData(Layout, Fragments);
1108 SmallVector<char, 128> CompressedContents;
1109 zlib::Status Success = zlib::compress(
1110 StringRef(UncompressedData.data(), UncompressedData.size()),
1111 CompressedContents);
1112 if (Success != zlib::StatusOK) {
1113 Asm.writeSectionData(&Section, Layout);
1117 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
1118 Asm.writeSectionData(&Section, Layout);
1121 Asm.getContext().renameELFSection(&Section,
1122 (".z" + SectionName.drop_front(1)).str());
1123 OS << CompressedContents;
1126 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1127 uint64_t Flags, uint64_t Address,
1128 uint64_t Offset, uint64_t Size,
1129 uint32_t Link, uint32_t Info,
1131 uint64_t EntrySize) {
1132 Write32(Name); // sh_name: index into string table
1133 Write32(Type); // sh_type
1134 WriteWord(Flags); // sh_flags
1135 WriteWord(Address); // sh_addr
1136 WriteWord(Offset); // sh_offset
1137 WriteWord(Size); // sh_size
1138 Write32(Link); // sh_link
1139 Write32(Info); // sh_info
1140 WriteWord(Alignment); // sh_addralign
1141 WriteWord(EntrySize); // sh_entsize
1144 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1145 const MCSectionELF &Sec) {
1146 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1148 // Sort the relocation entries. Most targets just sort by Offset, but some
1149 // (e.g., MIPS) have additional constraints.
1150 TargetObjectWriter->sortRelocs(Asm, Relocs);
1152 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1153 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1155 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1158 write(Entry.Offset);
1159 if (TargetObjectWriter->isN64()) {
1160 write(uint32_t(Index));
1162 write(TargetObjectWriter->getRSsym(Entry.Type));
1163 write(TargetObjectWriter->getRType3(Entry.Type));
1164 write(TargetObjectWriter->getRType2(Entry.Type));
1165 write(TargetObjectWriter->getRType(Entry.Type));
1167 struct ELF::Elf64_Rela ERE64;
1168 ERE64.setSymbolAndType(Index, Entry.Type);
1169 write(ERE64.r_info);
1171 if (hasRelocationAddend())
1172 write(Entry.Addend);
1174 write(uint32_t(Entry.Offset));
1176 struct ELF::Elf32_Rela ERE32;
1177 ERE32.setSymbolAndType(Index, Entry.Type);
1178 write(ERE32.r_info);
1180 if (hasRelocationAddend())
1181 write(uint32_t(Entry.Addend));
1186 const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
1187 const MCSectionELF *StrtabSection = SectionTable[StringTableIndex - 1];
1188 OS << StrTabBuilder.data();
1189 return StrtabSection;
1192 void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
1193 uint32_t GroupSymbolIndex, uint64_t Offset,
1194 uint64_t Size, const MCSectionELF &Section) {
1195 uint64_t sh_link = 0;
1196 uint64_t sh_info = 0;
1198 switch(Section.getType()) {
1203 case ELF::SHT_DYNAMIC:
1204 llvm_unreachable("SHT_DYNAMIC in a relocatable object");
1207 case ELF::SHT_RELA: {
1208 sh_link = SymbolTableIndex;
1209 assert(sh_link && ".symtab not found");
1210 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1211 sh_info = SectionIndexMap.lookup(InfoSection);
1215 case ELF::SHT_SYMTAB:
1216 case ELF::SHT_DYNSYM:
1217 sh_link = StringTableIndex;
1218 sh_info = LastLocalSymbolIndex;
1221 case ELF::SHT_SYMTAB_SHNDX:
1222 sh_link = SymbolTableIndex;
1225 case ELF::SHT_GROUP:
1226 sh_link = SymbolTableIndex;
1227 sh_info = GroupSymbolIndex;
1231 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1232 Section.getType() == ELF::SHT_ARM_EXIDX)
1233 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1235 WriteSecHdrEntry(StrTabBuilder.getOffset(Section.getSectionName()),
1236 Section.getType(), Section.getFlags(), 0, Offset, Size,
1237 sh_link, sh_info, Section.getAlignment(),
1238 Section.getEntrySize());
1241 void ELFObjectWriter::writeSectionHeader(
1242 const MCAssembler &Asm, const MCAsmLayout &Layout,
1243 const SectionIndexMapTy &SectionIndexMap,
1244 const SectionOffsetsTy &SectionOffsets) {
1245 const unsigned NumSections = SectionTable.size();
1247 // Null section first.
1248 uint64_t FirstSectionSize =
1249 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1250 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1252 for (const MCSectionELF *Section : SectionTable) {
1253 uint32_t GroupSymbolIndex;
1254 unsigned Type = Section->getType();
1255 if (Type != ELF::SHT_GROUP)
1256 GroupSymbolIndex = 0;
1258 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section->getGroup());
1260 const std::pair<uint64_t, uint64_t> &Offsets =
1261 SectionOffsets.find(Section)->second;
1263 if (Type == ELF::SHT_NOBITS)
1264 Size = Layout.getSectionAddressSize(Section);
1266 Size = Offsets.second - Offsets.first;
1268 writeSection(SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1273 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1274 const MCAsmLayout &Layout) {
1275 MCContext &Ctx = Asm.getContext();
1276 MCSectionELF *StrtabSection =
1277 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1278 StringTableIndex = addToSectionTable(StrtabSection);
1280 RevGroupMapTy RevGroupMap;
1281 SectionIndexMapTy SectionIndexMap;
1283 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1285 // Write out the ELF header ...
1288 // ... then the sections ...
1289 SectionOffsetsTy SectionOffsets;
1290 std::vector<MCSectionELF *> Groups;
1291 std::vector<MCSectionELF *> Relocations;
1292 for (MCSection &Sec : Asm) {
1293 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1295 uint64_t Padding = OffsetToAlignment(OS.tell(), Section.getAlignment());
1296 WriteZeros(Padding);
1298 // Remember the offset into the file for this section.
1299 uint64_t SecStart = OS.tell();
1301 const MCSymbol *SignatureSymbol = Section.getGroup();
1302 writeSectionData(Asm, Section, Layout);
1304 uint64_t SecEnd = OS.tell();
1305 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1307 MCSectionELF *RelSection = createRelocationSection(Ctx, Section);
1309 if (SignatureSymbol) {
1310 Asm.getOrCreateSymbolData(*SignatureSymbol);
1311 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1313 MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1314 GroupIdx = addToSectionTable(Group);
1315 Group->setAlignment(4);
1316 Groups.push_back(Group);
1318 GroupMembers[SignatureSymbol].push_back(&Section);
1320 GroupMembers[SignatureSymbol].push_back(RelSection);
1323 SectionIndexMap[&Section] = addToSectionTable(&Section);
1325 SectionIndexMap[RelSection] = addToSectionTable(RelSection);
1326 Relocations.push_back(RelSection);
1330 for (MCSectionELF *Group : Groups) {
1331 uint64_t Padding = OffsetToAlignment(OS.tell(), Group->getAlignment());
1332 WriteZeros(Padding);
1334 // Remember the offset into the file for this section.
1335 uint64_t SecStart = OS.tell();
1337 const MCSymbol *SignatureSymbol = Group->getGroup();
1338 assert(SignatureSymbol);
1339 write(uint32_t(ELF::GRP_COMDAT));
1340 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1341 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1345 uint64_t SecEnd = OS.tell();
1346 SectionOffsets[Group] = std::make_pair(SecStart, SecEnd);
1349 // Compute symbol table information.
1350 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, SectionOffsets);
1352 for (MCSectionELF *RelSection : Relocations) {
1353 uint64_t Padding = OffsetToAlignment(OS.tell(), RelSection->getAlignment());
1354 WriteZeros(Padding);
1356 // Remember the offset into the file for this section.
1357 uint64_t SecStart = OS.tell();
1359 writeRelocations(Asm, *RelSection->getAssociatedSection());
1361 uint64_t SecEnd = OS.tell();
1362 SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
1366 uint64_t SecStart = OS.tell();
1367 const MCSectionELF *Sec = createStringTable(Ctx);
1368 uint64_t SecEnd = OS.tell();
1369 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1372 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1373 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1374 WriteZeros(Padding);
1376 const unsigned SectionHeaderOffset = OS.tell();
1378 // ... then the section header table ...
1379 writeSectionHeader(Asm, Layout, SectionIndexMap, SectionOffsets);
1381 uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
1382 ? (uint16_t)ELF::SHN_UNDEF
1383 : SectionTable.size() + 1;
1384 if (sys::IsLittleEndianHost != IsLittleEndian)
1385 sys::swapByteOrder(NumSections);
1386 unsigned NumSectionsOffset;
1389 uint64_t Val = SectionHeaderOffset;
1390 if (sys::IsLittleEndianHost != IsLittleEndian)
1391 sys::swapByteOrder(Val);
1392 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1393 offsetof(ELF::Elf64_Ehdr, e_shoff));
1394 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1396 uint32_t Val = SectionHeaderOffset;
1397 if (sys::IsLittleEndianHost != IsLittleEndian)
1398 sys::swapByteOrder(Val);
1399 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1400 offsetof(ELF::Elf32_Ehdr, e_shoff));
1401 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1403 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1407 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1408 const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
1409 bool InSet, bool IsPCRel) const {
1412 if (::isWeak(SymA.getData()))
1415 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
1419 bool ELFObjectWriter::isWeak(const MCSymbol &Sym) const {
1420 const MCSymbolData &SD = Sym.getData();
1424 // It is invalid to replace a reference to a global in a comdat
1425 // with a reference to a local since out of comdat references
1426 // to a local are forbidden.
1427 // We could try to return false for more cases, like the reference
1428 // being in the same comdat or Sym being an alias to another global,
1429 // but it is not clear if it is worth the effort.
1430 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1433 if (!Sym.isInSection())
1436 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1437 return Sec.getGroup();
1440 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1441 raw_pwrite_stream &OS,
1442 bool IsLittleEndian) {
1443 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);