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 void writeSymbolTable(MCContext &Ctx, const MCAsmLayout &Layout,
190 SectionOffsetsTy &SectionOffsets);
192 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
193 const MCSymbolRefExpr *RefA,
194 const MCSymbol *Sym, uint64_t C,
195 unsigned Type) const;
197 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
198 const MCFragment *Fragment, const MCFixup &Fixup,
199 MCValue Target, bool &IsPCRel,
200 uint64_t &FixedValue) override;
202 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
205 // Map from a signature symbol to the group section index
206 typedef DenseMap<const MCSymbol *, unsigned> RevGroupMapTy;
208 /// Compute the symbol table data
210 /// \param Asm - The assembler.
211 /// \param SectionIndexMap - Maps a section to its index.
212 /// \param RevGroupMap - Maps a signature symbol to the group section.
213 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
214 const SectionIndexMapTy &SectionIndexMap,
215 const RevGroupMapTy &RevGroupMap);
217 MCSectionELF *createRelocationSection(MCContext &Ctx,
218 const MCSectionELF &Sec);
220 const MCSectionELF *createStringTable(MCContext &Ctx);
222 void ExecutePostLayoutBinding(MCAssembler &Asm,
223 const MCAsmLayout &Layout) override;
225 void writeSectionHeader(const MCAssembler &Asm, const MCAsmLayout &Layout,
226 const SectionIndexMapTy &SectionIndexMap,
227 const SectionOffsetsTy &SectionOffsets);
229 void writeSectionData(const MCAssembler &Asm, MCSection &Sec,
230 const MCAsmLayout &Layout);
232 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
233 uint64_t Address, uint64_t Offset, uint64_t Size,
234 uint32_t Link, uint32_t Info, uint64_t Alignment,
237 void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
239 bool IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
240 const MCSymbol &SymA,
241 const MCFragment &FB,
243 bool IsPCRel) const override;
245 bool isWeak(const MCSymbol &Sym) const override;
247 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
248 void writeSection(const SectionIndexMapTy &SectionIndexMap,
249 uint32_t GroupSymbolIndex, uint64_t Offset, uint64_t Size,
250 const MCSectionELF &Section);
254 unsigned ELFObjectWriter::addToSectionTable(const MCSectionELF *Sec) {
255 SectionTable.push_back(Sec);
256 StrTabBuilder.add(Sec->getSectionName());
257 return SectionTable.size();
260 void SymbolTableWriter::createSymtabShndx() {
261 if (!ShndxIndexes.empty())
264 ShndxIndexes.resize(NumWritten);
267 template <typename T> void SymbolTableWriter::write(T Value) {
268 EWriter.write(Value);
271 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
272 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
274 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
275 uint64_t size, uint8_t other,
276 uint32_t shndx, bool Reserved) {
277 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
282 if (!ShndxIndexes.empty()) {
284 ShndxIndexes.push_back(shndx);
286 ShndxIndexes.push_back(0);
289 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
292 write(name); // st_name
293 write(info); // st_info
294 write(other); // st_other
295 write(Index); // st_shndx
296 write(value); // st_value
297 write(size); // st_size
299 write(name); // st_name
300 write(uint32_t(value)); // st_value
301 write(uint32_t(size)); // st_size
302 write(info); // st_info
303 write(other); // st_other
304 write(Index); // st_shndx
310 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
311 const MCFixupKindInfo &FKI =
312 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
314 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
317 ELFObjectWriter::~ELFObjectWriter()
320 // Emit the ELF header.
321 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
327 // emitWord method behaves differently for ELF32 and ELF64, writing
328 // 4 bytes in the former and 8 in the latter.
330 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
332 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
335 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
337 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
339 Write8(TargetObjectWriter->getOSABI());
340 Write8(0); // e_ident[EI_ABIVERSION]
342 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
344 Write16(ELF::ET_REL); // e_type
346 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
348 Write32(ELF::EV_CURRENT); // e_version
349 WriteWord(0); // e_entry, no entry point in .o file
350 WriteWord(0); // e_phoff, no program header for .o
351 WriteWord(0); // e_shoff = sec hdr table off in bytes
353 // e_flags = whatever the target wants
354 Write32(Asm.getELFHeaderEFlags());
356 // e_ehsize = ELF header size
357 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
359 Write16(0); // e_phentsize = prog header entry size
360 Write16(0); // e_phnum = # prog header entries = 0
362 // e_shentsize = Section header entry size
363 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
365 // e_shnum = # of section header ents
368 // e_shstrndx = Section # of '.shstrtab'
369 assert(StringTableIndex < ELF::SHN_LORESERVE);
370 Write16(StringTableIndex);
373 uint64_t ELFObjectWriter::SymbolValue(const MCSymbol &Sym,
374 const MCAsmLayout &Layout) {
375 MCSymbolData &Data = Sym.getData();
376 if (Data.isCommon() && Data.isExternal())
377 return Data.getCommonAlignment();
380 if (!Layout.getSymbolOffset(Sym, Res))
383 if (Layout.getAssembler().isThumbFunc(&Sym))
389 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
390 const MCAsmLayout &Layout) {
391 // The presence of symbol versions causes undefined symbols and
392 // versions declared with @@@ to be renamed.
394 for (const MCSymbol &Alias : Asm.symbols()) {
395 MCSymbolData &OriginalData = Alias.getData();
398 if (!Alias.isVariable())
400 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
403 const MCSymbol &Symbol = Ref->getSymbol();
404 MCSymbolData &SD = Asm.getSymbolData(Symbol);
406 StringRef AliasName = Alias.getName();
407 size_t Pos = AliasName.find('@');
408 if (Pos == StringRef::npos)
411 // Aliases defined with .symvar copy the binding from the symbol they alias.
412 // This is the first place we are able to copy this information.
413 OriginalData.setExternal(SD.isExternal());
414 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
416 StringRef Rest = AliasName.substr(Pos);
417 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
420 // FIXME: produce a better error message.
421 if (Symbol.isUndefined() && Rest.startswith("@@") &&
422 !Rest.startswith("@@@"))
423 report_fatal_error("A @@ version cannot be undefined");
425 Renames.insert(std::make_pair(&Symbol, &Alias));
429 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
430 uint8_t Type = newType;
432 // Propagation rules:
433 // IFUNC > FUNC > OBJECT > NOTYPE
434 // TLS_OBJECT > OBJECT > NOTYPE
436 // dont let the new type degrade the old type
440 case ELF::STT_GNU_IFUNC:
441 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
442 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
443 Type = ELF::STT_GNU_IFUNC;
446 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
447 Type == ELF::STT_TLS)
448 Type = ELF::STT_FUNC;
450 case ELF::STT_OBJECT:
451 if (Type == ELF::STT_NOTYPE)
452 Type = ELF::STT_OBJECT;
455 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
456 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
464 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
465 const MCAsmLayout &Layout) {
466 MCSymbolData &OrigData = MSD.Symbol->getData();
467 assert((!OrigData.getFragment() ||
468 (OrigData.getFragment()->getParent() == &MSD.Symbol->getSection())) &&
469 "The symbol's section doesn't match the fragment's symbol");
470 const MCSymbol *Base = Layout.getBaseSymbol(*MSD.Symbol);
472 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
474 bool IsReserved = !Base || OrigData.isCommon();
476 // Binding and Type share the same byte as upper and lower nibbles
477 uint8_t Binding = MCELF::GetBinding(OrigData);
478 uint8_t Type = MCELF::GetType(OrigData);
479 MCSymbolData *BaseSD = nullptr;
481 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
482 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
484 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
486 // Other and Visibility share the same byte with Visibility using the lower
488 uint8_t Visibility = MCELF::GetVisibility(OrigData);
489 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
492 uint64_t Value = SymbolValue(*MSD.Symbol, Layout);
495 const MCExpr *ESize = OrigData.getSize();
497 ESize = BaseSD->getSize();
501 if (!ESize->evaluateKnownAbsolute(Res, Layout))
502 report_fatal_error("Size expression must be absolute.");
506 // Write out the symbol table entry
507 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
508 MSD.SectionIndex, IsReserved);
511 void ELFObjectWriter::writeSymbolTable(MCContext &Ctx,
512 const MCAsmLayout &Layout,
513 SectionOffsetsTy &SectionOffsets) {
514 const MCSectionELF *SymtabSection = SectionTable[SymbolTableIndex - 1];
516 // The string table must be emitted first because we need the index
517 // into the string table for all the symbol names.
519 SymbolTableWriter Writer(*this, is64Bit());
522 OffsetToAlignment(OS.tell(), SymtabSection->getAlignment());
525 uint64_t SecStart = OS.tell();
527 // The first entry is the undefined symbol entry.
528 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
530 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
531 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
532 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
535 // Write the symbol table entries.
536 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
538 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
539 ELFSymbolData &MSD = LocalSymbolData[i];
540 WriteSymbol(Writer, MSD, Layout);
543 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
544 ELFSymbolData &MSD = ExternalSymbolData[i];
545 MCSymbolData &Data = MSD.Symbol->getData();
546 assert(((Data.getFlags() & ELF_STB_Global) ||
547 (Data.getFlags() & ELF_STB_Weak)) &&
548 "External symbol requires STB_GLOBAL or STB_WEAK flag");
549 WriteSymbol(Writer, MSD, Layout);
550 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
551 LastLocalSymbolIndex++;
554 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
555 ELFSymbolData &MSD = UndefinedSymbolData[i];
556 MCSymbolData &Data = MSD.Symbol->getData();
557 WriteSymbol(Writer, MSD, Layout);
558 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
559 LastLocalSymbolIndex++;
562 uint64_t SecEnd = OS.tell();
563 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
565 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
566 if (ShndxIndexes.empty()) {
567 assert(SymtabShndxSectionIndex == 0);
570 assert(SymtabShndxSectionIndex != 0);
572 SecStart = OS.tell();
573 const MCSectionELF *SymtabShndxSection =
574 SectionTable[SymtabShndxSectionIndex - 1];
575 for (uint32_t Index : ShndxIndexes)
578 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
581 // It is always valid to create a relocation with a symbol. It is preferable
582 // to use a relocation with a section if that is possible. Using the section
583 // allows us to omit some local symbols from the symbol table.
584 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
585 const MCSymbolRefExpr *RefA,
586 const MCSymbol *Sym, uint64_t C,
587 unsigned Type) const {
588 MCSymbolData *SD = Sym ? &Sym->getData() : nullptr;
590 // A PCRel relocation to an absolute value has no symbol (or section). We
591 // represent that with a relocation to a null section.
595 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
599 // The .odp creation emits a relocation against the symbol ".TOC." which
600 // create a R_PPC64_TOC relocation. However the relocation symbol name
601 // in final object creation should be NULL, since the symbol does not
602 // really exist, it is just the reference to TOC base for the current
603 // object file. Since the symbol is undefined, returning false results
604 // in a relocation with a null section which is the desired result.
605 case MCSymbolRefExpr::VK_PPC_TOCBASE:
608 // These VariantKind cause the relocation to refer to something other than
609 // the symbol itself, like a linker generated table. Since the address of
610 // symbol is not relevant, we cannot replace the symbol with the
611 // section and patch the difference in the addend.
612 case MCSymbolRefExpr::VK_GOT:
613 case MCSymbolRefExpr::VK_PLT:
614 case MCSymbolRefExpr::VK_GOTPCREL:
615 case MCSymbolRefExpr::VK_Mips_GOT:
616 case MCSymbolRefExpr::VK_PPC_GOT_LO:
617 case MCSymbolRefExpr::VK_PPC_GOT_HI:
618 case MCSymbolRefExpr::VK_PPC_GOT_HA:
622 // An undefined symbol is not in any section, so the relocation has to point
623 // to the symbol itself.
624 assert(Sym && "Expected a symbol");
625 if (Sym->isUndefined())
628 unsigned Binding = MCELF::GetBinding(*SD);
631 llvm_unreachable("Invalid Binding");
635 // If the symbol is weak, it might be overridden by a symbol in another
636 // file. The relocation has to point to the symbol so that the linker
639 case ELF::STB_GLOBAL:
640 // Global ELF symbols can be preempted by the dynamic linker. The relocation
641 // has to point to the symbol for a reason analogous to the STB_WEAK case.
645 // If a relocation points to a mergeable section, we have to be careful.
646 // If the offset is zero, a relocation with the section will encode the
647 // same information. With a non-zero offset, the situation is different.
648 // For example, a relocation can point 42 bytes past the end of a string.
649 // If we change such a relocation to use the section, the linker would think
650 // that it pointed to another string and subtracting 42 at runtime will
651 // produce the wrong value.
652 auto &Sec = cast<MCSectionELF>(Sym->getSection());
653 unsigned Flags = Sec.getFlags();
654 if (Flags & ELF::SHF_MERGE) {
658 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
659 // only handle section relocations to mergeable sections if using RELA.
660 if (!hasRelocationAddend())
664 // Most TLS relocations use a got, so they need the symbol. Even those that
665 // are just an offset (@tpoff), require a symbol in gold versions before
666 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
667 // http://sourceware.org/PR16773.
668 if (Flags & ELF::SHF_TLS)
671 // If the symbol is a thumb function the final relocation must set the lowest
672 // bit. With a symbol that is done by just having the symbol have that bit
673 // set, so we would lose the bit if we relocated with the section.
674 // FIXME: We could use the section but add the bit to the relocation value.
675 if (Asm.isThumbFunc(Sym))
678 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
683 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
684 const MCSymbol &Sym = Ref.getSymbol();
686 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
689 if (!Sym.isVariable())
692 const MCExpr *Expr = Sym.getVariableValue();
693 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
697 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
698 return &Inner->getSymbol();
702 // True if the assembler knows nothing about the final value of the symbol.
703 // This doesn't cover the comdat issues, since in those cases the assembler
704 // can at least know that all symbols in the section will move together.
705 static bool isWeak(const MCSymbolData &D) {
706 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
709 switch (MCELF::GetBinding(D)) {
711 llvm_unreachable("Unknown binding");
714 case ELF::STB_GLOBAL:
717 case ELF::STB_GNU_UNIQUE:
722 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
723 const MCAsmLayout &Layout,
724 const MCFragment *Fragment,
725 const MCFixup &Fixup, MCValue Target,
726 bool &IsPCRel, uint64_t &FixedValue) {
727 const MCSectionELF &FixupSection = cast<MCSectionELF>(*Fragment->getParent());
728 uint64_t C = Target.getConstant();
729 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
731 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
732 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
733 "Should not have constructed this");
735 // Let A, B and C being the components of Target and R be the location of
736 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
737 // If it is pcrel, we want to compute (A - B + C - R).
739 // In general, ELF has no relocations for -B. It can only represent (A + C)
740 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
741 // replace B to implement it: (A - R - K + C)
743 Asm.getContext().reportFatalError(
745 "No relocation available to represent this relative expression");
747 const MCSymbol &SymB = RefB->getSymbol();
749 if (SymB.isUndefined())
750 Asm.getContext().reportFatalError(
752 Twine("symbol '") + SymB.getName() +
753 "' can not be undefined in a subtraction expression");
755 assert(!SymB.isAbsolute() && "Should have been folded");
756 const MCSection &SecB = SymB.getSection();
757 if (&SecB != &FixupSection)
758 Asm.getContext().reportFatalError(
759 Fixup.getLoc(), "Cannot represent a difference across sections");
761 if (::isWeak(SymB.getData()))
762 Asm.getContext().reportFatalError(
763 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
765 uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
766 uint64_t K = SymBOffset - FixupOffset;
771 // We either rejected the fixup or folded B into C at this point.
772 const MCSymbolRefExpr *RefA = Target.getSymA();
773 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
775 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
776 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymA, C, Type);
777 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
778 C += Layout.getSymbolOffset(*SymA);
781 if (hasRelocationAddend()) {
788 if (!RelocateWithSymbol) {
789 const MCSection *SecA =
790 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
791 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
792 const MCSymbol *SectionSymbol = ELFSec ? ELFSec->getBeginSymbol() : nullptr;
793 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
794 Relocations[&FixupSection].push_back(Rec);
799 if (const MCSymbol *R = Renames.lookup(SymA))
802 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
803 WeakrefUsedInReloc.insert(WeakRef);
805 UsedInReloc.insert(SymA);
807 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
808 Relocations[&FixupSection].push_back(Rec);
814 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
816 assert(S->hasData());
817 return S->getIndex();
820 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
821 const MCSymbol &Symbol, bool Used,
823 const MCSymbolData &Data = Symbol.getData();
824 if (Symbol.isVariable()) {
825 const MCExpr *Expr = Symbol.getVariableValue();
826 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
827 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
838 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
841 if (Symbol.isVariable()) {
842 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
843 if (Base && Base->isUndefined())
847 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
848 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
851 if (MCELF::GetType(Data) == ELF::STT_SECTION)
854 if (Symbol.isTemporary())
860 bool ELFObjectWriter::isLocal(const MCSymbol &Symbol, bool isUsedInReloc) {
861 const MCSymbolData &Data = Symbol.getData();
862 if (Data.isExternal())
865 if (Symbol.isDefined())
874 void ELFObjectWriter::computeSymbolTable(
875 MCAssembler &Asm, const MCAsmLayout &Layout,
876 const SectionIndexMapTy &SectionIndexMap,
877 const RevGroupMapTy &RevGroupMap) {
878 MCContext &Ctx = Asm.getContext();
880 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
881 MCSectionELF *SymtabSection =
882 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
883 SymtabSection->setAlignment(is64Bit() ? 8 : 4);
884 SymbolTableIndex = addToSectionTable(SymtabSection);
886 // Add the data for the symbols.
887 bool HasLargeSectionIndex = false;
888 for (const MCSymbol &Symbol : Asm.symbols()) {
889 MCSymbolData &SD = Symbol.getData();
891 bool Used = UsedInReloc.count(&Symbol);
892 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
893 bool isSignature = RevGroupMap.count(&Symbol);
895 if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
896 Renames.count(&Symbol)))
900 MSD.Symbol = &Symbol;
901 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
903 // Undefined symbols are global, but this is the first place we
904 // are able to set it.
905 bool Local = isLocal(Symbol, Used);
906 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
908 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
909 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
910 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
914 MSD.SectionIndex = ELF::SHN_ABS;
915 } else if (SD.isCommon()) {
917 MSD.SectionIndex = ELF::SHN_COMMON;
918 } else if (BaseSymbol->isUndefined()) {
919 if (isSignature && !Used) {
920 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
921 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
922 HasLargeSectionIndex = true;
924 MSD.SectionIndex = ELF::SHN_UNDEF;
926 if (!Used && WeakrefUsed)
927 MCELF::SetBinding(SD, ELF::STB_WEAK);
929 const MCSectionELF &Section =
930 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
931 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
932 assert(MSD.SectionIndex && "Invalid section index!");
933 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
934 HasLargeSectionIndex = true;
937 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
940 // FIXME: All name handling should be done before we get to the writer,
941 // including dealing with GNU-style version suffixes. Fixing this isn't
944 // We thus have to be careful to not perform the symbol version replacement
947 // The ELF format is used on Windows by the MCJIT engine. Thus, on
948 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
949 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
950 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
951 // the EFLObjectWriter should not interpret the "@@@" sub-string as
952 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
953 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
954 // "__imp_?" or "__imp_@?".
956 // It would have been interesting to perform the MS mangling prefix check
957 // only when the target triple is of the form *-pc-windows-elf. But, it
958 // seems that this information is not easily accessible from the
960 StringRef Name = Symbol.getName();
961 if (!Name.startswith("?") && !Name.startswith("@?") &&
962 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
963 // This symbol isn't following the MSVC C++ name mangling convention. We
964 // can thus safely interpret the @@@ in symbol names as specifying symbol
967 size_t Pos = Name.find("@@@");
968 if (Pos != StringRef::npos) {
969 Buf += Name.substr(0, Pos);
970 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
971 Buf += Name.substr(Pos + Skip);
976 // Sections have their own string table
977 if (MCELF::GetType(SD) != ELF::STT_SECTION)
978 MSD.Name = StrTabBuilder.add(Name);
980 if (MSD.SectionIndex == ELF::SHN_UNDEF)
981 UndefinedSymbolData.push_back(MSD);
983 LocalSymbolData.push_back(MSD);
985 ExternalSymbolData.push_back(MSD);
988 if (HasLargeSectionIndex) {
989 MCSectionELF *SymtabShndxSection =
990 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
991 SymtabShndxSectionIndex = addToSectionTable(SymtabShndxSection);
992 SymtabShndxSection->setAlignment(4);
995 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
996 StrTabBuilder.add(*i);
998 StrTabBuilder.finalize(StringTableBuilder::ELF);
1000 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1001 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1003 for (ELFSymbolData &MSD : LocalSymbolData)
1004 MSD.StringIndex = MCELF::GetType(MSD.Symbol->getData()) == ELF::STT_SECTION
1006 : StrTabBuilder.getOffset(MSD.Name);
1007 for (ELFSymbolData &MSD : ExternalSymbolData)
1008 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1009 for (ELFSymbolData& MSD : UndefinedSymbolData)
1010 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1012 // Symbols are required to be in lexicographic order.
1013 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1014 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1015 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1017 // Set the symbol indices. Local symbols must come before all other
1018 // symbols with non-local bindings.
1019 unsigned Index = FileSymbolData.size() + 1;
1020 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1021 LocalSymbolData[i].Symbol->setIndex(Index++);
1023 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1024 ExternalSymbolData[i].Symbol->setIndex(Index++);
1025 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1026 UndefinedSymbolData[i].Symbol->setIndex(Index++);
1030 ELFObjectWriter::createRelocationSection(MCContext &Ctx,
1031 const MCSectionELF &Sec) {
1032 if (Relocations[&Sec].empty())
1035 const StringRef SectionName = Sec.getSectionName();
1036 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1037 RelaSectionName += SectionName;
1040 if (hasRelocationAddend())
1041 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1043 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1046 if (Sec.getFlags() & ELF::SHF_GROUP)
1047 Flags = ELF::SHF_GROUP;
1049 MCSectionELF *RelaSection = Ctx.createELFRelSection(
1050 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1051 Flags, EntrySize, Sec.getGroup(), &Sec);
1052 RelaSection->setAlignment(is64Bit() ? 8 : 4);
1056 static SmallVector<char, 128>
1057 getUncompressedData(const MCAsmLayout &Layout,
1058 const MCSection::FragmentListType &Fragments) {
1059 SmallVector<char, 128> UncompressedData;
1060 for (const MCFragment &F : Fragments) {
1061 const SmallVectorImpl<char> *Contents;
1062 switch (F.getKind()) {
1063 case MCFragment::FT_Data:
1064 Contents = &cast<MCDataFragment>(F).getContents();
1066 case MCFragment::FT_Dwarf:
1067 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1069 case MCFragment::FT_DwarfFrame:
1070 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1074 "Not expecting any other fragment types in a debug_* section");
1076 UncompressedData.append(Contents->begin(), Contents->end());
1078 return UncompressedData;
1081 // Include the debug info compression header:
1082 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1083 // useful for consumers to preallocate a buffer to decompress into.
1085 prependCompressionHeader(uint64_t Size,
1086 SmallVectorImpl<char> &CompressedContents) {
1087 const StringRef Magic = "ZLIB";
1088 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1090 if (sys::IsLittleEndianHost)
1091 sys::swapByteOrder(Size);
1092 CompressedContents.insert(CompressedContents.begin(),
1093 Magic.size() + sizeof(Size), 0);
1094 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1095 std::copy(reinterpret_cast<char *>(&Size),
1096 reinterpret_cast<char *>(&Size + 1),
1097 CompressedContents.begin() + Magic.size());
1101 void ELFObjectWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
1102 const MCAsmLayout &Layout) {
1103 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1104 StringRef SectionName = Section.getSectionName();
1106 // Compressing debug_frame requires handling alignment fragments which is
1107 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1108 // for writing to arbitrary buffers) for little benefit.
1109 if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
1110 !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
1111 Asm.writeSectionData(&Section, Layout);
1115 // Gather the uncompressed data from all the fragments.
1116 const MCSection::FragmentListType &Fragments = Section.getFragmentList();
1117 SmallVector<char, 128> UncompressedData =
1118 getUncompressedData(Layout, Fragments);
1120 SmallVector<char, 128> CompressedContents;
1121 zlib::Status Success = zlib::compress(
1122 StringRef(UncompressedData.data(), UncompressedData.size()),
1123 CompressedContents);
1124 if (Success != zlib::StatusOK) {
1125 Asm.writeSectionData(&Section, Layout);
1129 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
1130 Asm.writeSectionData(&Section, Layout);
1133 Asm.getContext().renameELFSection(&Section,
1134 (".z" + SectionName.drop_front(1)).str());
1135 OS << CompressedContents;
1138 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1139 uint64_t Flags, uint64_t Address,
1140 uint64_t Offset, uint64_t Size,
1141 uint32_t Link, uint32_t Info,
1143 uint64_t EntrySize) {
1144 Write32(Name); // sh_name: index into string table
1145 Write32(Type); // sh_type
1146 WriteWord(Flags); // sh_flags
1147 WriteWord(Address); // sh_addr
1148 WriteWord(Offset); // sh_offset
1149 WriteWord(Size); // sh_size
1150 Write32(Link); // sh_link
1151 Write32(Info); // sh_info
1152 WriteWord(Alignment); // sh_addralign
1153 WriteWord(EntrySize); // sh_entsize
1156 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1157 const MCSectionELF &Sec) {
1158 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1160 // Sort the relocation entries. Most targets just sort by Offset, but some
1161 // (e.g., MIPS) have additional constraints.
1162 TargetObjectWriter->sortRelocs(Asm, Relocs);
1164 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1165 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1167 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1170 write(Entry.Offset);
1171 if (TargetObjectWriter->isN64()) {
1172 write(uint32_t(Index));
1174 write(TargetObjectWriter->getRSsym(Entry.Type));
1175 write(TargetObjectWriter->getRType3(Entry.Type));
1176 write(TargetObjectWriter->getRType2(Entry.Type));
1177 write(TargetObjectWriter->getRType(Entry.Type));
1179 struct ELF::Elf64_Rela ERE64;
1180 ERE64.setSymbolAndType(Index, Entry.Type);
1181 write(ERE64.r_info);
1183 if (hasRelocationAddend())
1184 write(Entry.Addend);
1186 write(uint32_t(Entry.Offset));
1188 struct ELF::Elf32_Rela ERE32;
1189 ERE32.setSymbolAndType(Index, Entry.Type);
1190 write(ERE32.r_info);
1192 if (hasRelocationAddend())
1193 write(uint32_t(Entry.Addend));
1198 const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
1199 const MCSectionELF *StrtabSection = SectionTable[StringTableIndex - 1];
1200 OS << StrTabBuilder.data();
1201 return StrtabSection;
1204 void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
1205 uint32_t GroupSymbolIndex, uint64_t Offset,
1206 uint64_t Size, const MCSectionELF &Section) {
1207 uint64_t sh_link = 0;
1208 uint64_t sh_info = 0;
1210 switch(Section.getType()) {
1215 case ELF::SHT_DYNAMIC:
1216 llvm_unreachable("SHT_DYNAMIC in a relocatable object");
1219 case ELF::SHT_RELA: {
1220 sh_link = SymbolTableIndex;
1221 assert(sh_link && ".symtab not found");
1222 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1223 sh_info = SectionIndexMap.lookup(InfoSection);
1227 case ELF::SHT_SYMTAB:
1228 case ELF::SHT_DYNSYM:
1229 sh_link = StringTableIndex;
1230 sh_info = LastLocalSymbolIndex;
1233 case ELF::SHT_SYMTAB_SHNDX:
1234 sh_link = SymbolTableIndex;
1237 case ELF::SHT_GROUP:
1238 sh_link = SymbolTableIndex;
1239 sh_info = GroupSymbolIndex;
1243 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1244 Section.getType() == ELF::SHT_ARM_EXIDX)
1245 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1247 WriteSecHdrEntry(StrTabBuilder.getOffset(Section.getSectionName()),
1248 Section.getType(), Section.getFlags(), 0, Offset, Size,
1249 sh_link, sh_info, Section.getAlignment(),
1250 Section.getEntrySize());
1253 void ELFObjectWriter::writeSectionHeader(
1254 const MCAssembler &Asm, const MCAsmLayout &Layout,
1255 const SectionIndexMapTy &SectionIndexMap,
1256 const SectionOffsetsTy &SectionOffsets) {
1257 const unsigned NumSections = SectionTable.size();
1259 // Null section first.
1260 uint64_t FirstSectionSize =
1261 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1262 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1264 for (const MCSectionELF *Section : SectionTable) {
1265 uint32_t GroupSymbolIndex;
1266 unsigned Type = Section->getType();
1267 if (Type != ELF::SHT_GROUP)
1268 GroupSymbolIndex = 0;
1270 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section->getGroup());
1272 const std::pair<uint64_t, uint64_t> &Offsets =
1273 SectionOffsets.find(Section)->second;
1275 if (Type == ELF::SHT_NOBITS)
1276 Size = Layout.getSectionAddressSize(Section);
1278 Size = Offsets.second - Offsets.first;
1280 writeSection(SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1285 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1286 const MCAsmLayout &Layout) {
1287 MCContext &Ctx = Asm.getContext();
1288 MCSectionELF *StrtabSection =
1289 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1290 StringTableIndex = addToSectionTable(StrtabSection);
1292 RevGroupMapTy RevGroupMap;
1293 SectionIndexMapTy SectionIndexMap;
1295 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1297 // Write out the ELF header ...
1300 // ... then the sections ...
1301 SectionOffsetsTy SectionOffsets;
1302 std::vector<MCSectionELF *> Groups;
1303 std::vector<MCSectionELF *> Relocations;
1304 for (MCSection &Sec : Asm) {
1305 MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
1307 uint64_t Padding = OffsetToAlignment(OS.tell(), Section.getAlignment());
1308 WriteZeros(Padding);
1310 // Remember the offset into the file for this section.
1311 uint64_t SecStart = OS.tell();
1313 const MCSymbol *SignatureSymbol = Section.getGroup();
1314 writeSectionData(Asm, Section, Layout);
1316 uint64_t SecEnd = OS.tell();
1317 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1319 MCSectionELF *RelSection = createRelocationSection(Ctx, Section);
1321 if (SignatureSymbol) {
1322 Asm.getOrCreateSymbolData(*SignatureSymbol);
1323 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1325 MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1326 GroupIdx = addToSectionTable(Group);
1327 Group->setAlignment(4);
1328 Groups.push_back(Group);
1330 GroupMembers[SignatureSymbol].push_back(&Section);
1332 GroupMembers[SignatureSymbol].push_back(RelSection);
1335 SectionIndexMap[&Section] = addToSectionTable(&Section);
1337 SectionIndexMap[RelSection] = addToSectionTable(RelSection);
1338 Relocations.push_back(RelSection);
1342 for (MCSectionELF *Group : Groups) {
1343 uint64_t Padding = OffsetToAlignment(OS.tell(), Group->getAlignment());
1344 WriteZeros(Padding);
1346 // Remember the offset into the file for this section.
1347 uint64_t SecStart = OS.tell();
1349 const MCSymbol *SignatureSymbol = Group->getGroup();
1350 assert(SignatureSymbol);
1351 write(uint32_t(ELF::GRP_COMDAT));
1352 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1353 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1357 uint64_t SecEnd = OS.tell();
1358 SectionOffsets[Group] = std::make_pair(SecStart, SecEnd);
1361 // Compute symbol table information.
1362 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1364 for (MCSectionELF *RelSection : Relocations) {
1365 uint64_t Padding = OffsetToAlignment(OS.tell(), RelSection->getAlignment());
1366 WriteZeros(Padding);
1368 // Remember the offset into the file for this section.
1369 uint64_t SecStart = OS.tell();
1371 writeRelocations(Asm, *RelSection->getAssociatedSection());
1373 uint64_t SecEnd = OS.tell();
1374 SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
1377 writeSymbolTable(Ctx, Layout, SectionOffsets);
1380 uint64_t SecStart = OS.tell();
1381 const MCSectionELF *Sec = createStringTable(Ctx);
1382 uint64_t SecEnd = OS.tell();
1383 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1386 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1387 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1388 WriteZeros(Padding);
1390 const unsigned SectionHeaderOffset = OS.tell();
1392 // ... then the section header table ...
1393 writeSectionHeader(Asm, Layout, SectionIndexMap, SectionOffsets);
1395 uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
1396 ? (uint16_t)ELF::SHN_UNDEF
1397 : SectionTable.size() + 1;
1398 if (sys::IsLittleEndianHost != IsLittleEndian)
1399 sys::swapByteOrder(NumSections);
1400 unsigned NumSectionsOffset;
1403 uint64_t Val = SectionHeaderOffset;
1404 if (sys::IsLittleEndianHost != IsLittleEndian)
1405 sys::swapByteOrder(Val);
1406 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1407 offsetof(ELF::Elf64_Ehdr, e_shoff));
1408 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1410 uint32_t Val = SectionHeaderOffset;
1411 if (sys::IsLittleEndianHost != IsLittleEndian)
1412 sys::swapByteOrder(Val);
1413 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1414 offsetof(ELF::Elf32_Ehdr, e_shoff));
1415 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1417 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1421 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1422 const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
1423 bool InSet, bool IsPCRel) const {
1426 if (::isWeak(SymA.getData()))
1429 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
1433 bool ELFObjectWriter::isWeak(const MCSymbol &Sym) const {
1434 const MCSymbolData &SD = Sym.getData();
1438 // It is invalid to replace a reference to a global in a comdat
1439 // with a reference to a local since out of comdat references
1440 // to a local are forbidden.
1441 // We could try to return false for more cases, like the reference
1442 // being in the same comdat or Sym being an alias to another global,
1443 // but it is not clear if it is worth the effort.
1444 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1447 if (!Sym.isInSection())
1450 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1451 return Sec.getGroup();
1454 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1455 raw_pwrite_stream &OS,
1456 bool IsLittleEndian) {
1457 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);