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 bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
75 static uint64_t SymbolValue(const MCSymbol &Sym, const MCAsmLayout &Layout);
76 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbol &Symbol,
77 bool Used, bool Renamed);
78 static bool isLocal(const MCSymbol &Symbol, bool isUsedInReloc);
80 /// Helper struct for containing some precomputed information on symbols.
81 struct ELFSymbolData {
82 const MCSymbol *Symbol;
84 uint32_t SectionIndex;
87 // Support lexicographic sorting.
88 bool operator<(const ELFSymbolData &RHS) const {
89 unsigned LHSType = MCELF::GetType(Symbol->getData());
90 unsigned RHSType = MCELF::GetType(RHS.Symbol->getData());
91 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
93 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
95 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
96 return SectionIndex < RHS.SectionIndex;
97 return Name < RHS.Name;
101 /// The target specific ELF writer instance.
102 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
104 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
105 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
106 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
108 llvm::DenseMap<const MCSectionELF *, std::vector<ELFRelocationEntry>>
110 StringTableBuilder ShStrTabBuilder;
113 /// @name Symbol Table Data
116 StringTableBuilder StrTabBuilder;
117 std::vector<uint64_t> FileSymbolData;
118 std::vector<ELFSymbolData> LocalSymbolData;
119 std::vector<ELFSymbolData> ExternalSymbolData;
120 std::vector<ELFSymbolData> UndefinedSymbolData;
126 // This holds the symbol table index of the last local symbol.
127 unsigned LastLocalSymbolIndex;
128 // This holds the .strtab section index.
129 unsigned StringTableIndex;
130 // This holds the .symtab section index.
131 unsigned SymbolTableIndex;
133 unsigned ShstrtabIndex;
135 // Sections in the order they are to be output in the section table.
136 std::vector<MCSectionELF *> SectionTable;
137 unsigned addToSectionTable(MCSectionELF *Sec);
139 // TargetObjectWriter wrappers.
140 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
141 bool hasRelocationAddend() const {
142 return TargetObjectWriter->hasRelocationAddend();
144 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
145 bool IsPCRel) const {
146 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
150 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
152 : MCObjectWriter(OS, IsLittleEndian), TargetObjectWriter(MOTW),
155 void reset() override {
157 WeakrefUsedInReloc.clear();
160 ShStrTabBuilder.clear();
161 StrTabBuilder.clear();
162 FileSymbolData.clear();
163 LocalSymbolData.clear();
164 ExternalSymbolData.clear();
165 UndefinedSymbolData.clear();
167 SectionTable.clear();
168 MCObjectWriter::reset();
171 ~ELFObjectWriter() override;
173 void WriteWord(uint64_t W) {
180 template <typename T> void write(T Val) {
182 support::endian::Writer<support::little>(OS).write(Val);
184 support::endian::Writer<support::big>(OS).write(Val);
187 void writeHeader(const MCAssembler &Asm);
189 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
190 const MCAsmLayout &Layout);
192 // Start and end offset of each section
193 typedef std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>
196 void WriteSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
197 SectionOffsetsTy &SectionOffsets);
199 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
200 const MCSymbolRefExpr *RefA,
201 const MCSymbol *Sym, uint64_t C,
202 unsigned Type) const;
204 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
205 const MCFragment *Fragment, const MCFixup &Fixup,
206 MCValue Target, bool &IsPCRel,
207 uint64_t &FixedValue) override;
209 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
212 // Map from a signature symbol to the group section index
213 typedef DenseMap<const MCSymbol *, unsigned> RevGroupMapTy;
215 /// Compute the symbol table data
217 /// \param Asm - The assembler.
218 /// \param SectionIndexMap - Maps a section to its index.
219 /// \param RevGroupMap - Maps a signature symbol to the group section.
220 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
221 const SectionIndexMapTy &SectionIndexMap,
222 const RevGroupMapTy &RevGroupMap);
224 MCSectionELF *createRelocationSection(MCAssembler &Asm,
225 const MCSectionELF &Sec);
227 const MCSectionELF *createSectionHeaderStringTable();
228 const MCSectionELF *createStringTable(MCContext &Ctx);
230 void ExecutePostLayoutBinding(MCAssembler &Asm,
231 const MCAsmLayout &Layout) override;
233 void writeSectionHeader(MCAssembler &Asm, const MCAsmLayout &Layout,
234 const SectionIndexMapTy &SectionIndexMap,
235 const SectionOffsetsTy &SectionOffsets);
237 void writeSectionData(const MCAssembler &Asm, const MCSectionData &SD,
238 const MCAsmLayout &Layout);
240 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
241 uint64_t Address, uint64_t Offset, uint64_t Size,
242 uint32_t Link, uint32_t Info, uint64_t Alignment,
245 void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
247 bool IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
248 const MCSymbol &SymA,
249 const MCFragment &FB,
251 bool IsPCRel) const override;
253 bool isWeak(const MCSymbol &Sym) const override;
255 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
256 void writeSection(MCAssembler &Asm,
257 const SectionIndexMapTy &SectionIndexMap,
258 uint32_t GroupSymbolIndex, uint64_t Offset, uint64_t Size,
259 const MCSectionELF &Section);
263 unsigned ELFObjectWriter::addToSectionTable(MCSectionELF *Sec) {
264 SectionTable.push_back(Sec);
265 ShStrTabBuilder.add(Sec->getSectionName());
266 return SectionTable.size();
269 void SymbolTableWriter::createSymtabShndx() {
270 if (!ShndxIndexes.empty())
273 ShndxIndexes.resize(NumWritten);
276 template <typename T> void SymbolTableWriter::write(T Value) {
277 EWriter.write(Value);
280 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
281 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
283 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
284 uint64_t size, uint8_t other,
285 uint32_t shndx, bool Reserved) {
286 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
291 if (!ShndxIndexes.empty()) {
293 ShndxIndexes.push_back(shndx);
295 ShndxIndexes.push_back(0);
298 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
301 write(name); // st_name
302 write(info); // st_info
303 write(other); // st_other
304 write(Index); // st_shndx
305 write(value); // st_value
306 write(size); // st_size
308 write(name); // st_name
309 write(uint32_t(value)); // st_value
310 write(uint32_t(size)); // st_size
311 write(info); // st_info
312 write(other); // st_other
313 write(Index); // st_shndx
319 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
320 const MCFixupKindInfo &FKI =
321 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
323 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
326 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
330 case MCSymbolRefExpr::VK_GOT:
331 case MCSymbolRefExpr::VK_PLT:
332 case MCSymbolRefExpr::VK_GOTPCREL:
333 case MCSymbolRefExpr::VK_GOTOFF:
334 case MCSymbolRefExpr::VK_TPOFF:
335 case MCSymbolRefExpr::VK_TLSGD:
336 case MCSymbolRefExpr::VK_GOTTPOFF:
337 case MCSymbolRefExpr::VK_INDNTPOFF:
338 case MCSymbolRefExpr::VK_NTPOFF:
339 case MCSymbolRefExpr::VK_GOTNTPOFF:
340 case MCSymbolRefExpr::VK_TLSLDM:
341 case MCSymbolRefExpr::VK_DTPOFF:
342 case MCSymbolRefExpr::VK_TLSLD:
347 ELFObjectWriter::~ELFObjectWriter()
350 // Emit the ELF header.
351 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
357 // emitWord method behaves differently for ELF32 and ELF64, writing
358 // 4 bytes in the former and 8 in the latter.
360 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
362 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
365 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
367 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
369 Write8(TargetObjectWriter->getOSABI());
370 Write8(0); // e_ident[EI_ABIVERSION]
372 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
374 Write16(ELF::ET_REL); // e_type
376 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
378 Write32(ELF::EV_CURRENT); // e_version
379 WriteWord(0); // e_entry, no entry point in .o file
380 WriteWord(0); // e_phoff, no program header for .o
381 WriteWord(0); // e_shoff = sec hdr table off in bytes
383 // e_flags = whatever the target wants
384 Write32(Asm.getELFHeaderEFlags());
386 // e_ehsize = ELF header size
387 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
389 Write16(0); // e_phentsize = prog header entry size
390 Write16(0); // e_phnum = # prog header entries = 0
392 // e_shentsize = Section header entry size
393 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
395 // e_shnum = # of section header ents
398 // e_shstrndx = Section # of '.shstrtab'
399 assert(ShstrtabIndex < ELF::SHN_LORESERVE);
400 Write16(ShstrtabIndex);
403 uint64_t ELFObjectWriter::SymbolValue(const MCSymbol &Sym,
404 const MCAsmLayout &Layout) {
405 MCSymbolData &Data = Sym.getData();
406 if (Data.isCommon() && Data.isExternal())
407 return Data.getCommonAlignment();
410 if (!Layout.getSymbolOffset(Sym, Res))
413 if (Layout.getAssembler().isThumbFunc(&Sym))
419 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
420 const MCAsmLayout &Layout) {
421 // The presence of symbol versions causes undefined symbols and
422 // versions declared with @@@ to be renamed.
424 for (const MCSymbol &Alias : Asm.symbols()) {
425 MCSymbolData &OriginalData = Alias.getData();
428 if (!Alias.isVariable())
430 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
433 const MCSymbol &Symbol = Ref->getSymbol();
434 MCSymbolData &SD = Asm.getSymbolData(Symbol);
436 StringRef AliasName = Alias.getName();
437 size_t Pos = AliasName.find('@');
438 if (Pos == StringRef::npos)
441 // Aliases defined with .symvar copy the binding from the symbol they alias.
442 // This is the first place we are able to copy this information.
443 OriginalData.setExternal(SD.isExternal());
444 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
446 StringRef Rest = AliasName.substr(Pos);
447 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
450 // FIXME: produce a better error message.
451 if (Symbol.isUndefined() && Rest.startswith("@@") &&
452 !Rest.startswith("@@@"))
453 report_fatal_error("A @@ version cannot be undefined");
455 Renames.insert(std::make_pair(&Symbol, &Alias));
459 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
460 uint8_t Type = newType;
462 // Propagation rules:
463 // IFUNC > FUNC > OBJECT > NOTYPE
464 // TLS_OBJECT > OBJECT > NOTYPE
466 // dont let the new type degrade the old type
470 case ELF::STT_GNU_IFUNC:
471 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
472 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
473 Type = ELF::STT_GNU_IFUNC;
476 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
477 Type == ELF::STT_TLS)
478 Type = ELF::STT_FUNC;
480 case ELF::STT_OBJECT:
481 if (Type == ELF::STT_NOTYPE)
482 Type = ELF::STT_OBJECT;
485 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
486 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
494 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
495 const MCAsmLayout &Layout) {
496 MCSymbolData &OrigData = MSD.Symbol->getData();
497 assert((!OrigData.getFragment() ||
498 (&OrigData.getFragment()->getParent()->getSection() ==
499 &MSD.Symbol->getSection())) &&
500 "The symbol's section doesn't match the fragment's symbol");
501 const MCSymbol *Base = Layout.getBaseSymbol(*MSD.Symbol);
503 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
505 bool IsReserved = !Base || OrigData.isCommon();
507 // Binding and Type share the same byte as upper and lower nibbles
508 uint8_t Binding = MCELF::GetBinding(OrigData);
509 uint8_t Type = MCELF::GetType(OrigData);
510 MCSymbolData *BaseSD = nullptr;
512 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
513 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
515 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
517 // Other and Visibility share the same byte with Visibility using the lower
519 uint8_t Visibility = MCELF::GetVisibility(OrigData);
520 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
523 uint64_t Value = SymbolValue(*MSD.Symbol, Layout);
526 const MCExpr *ESize = OrigData.getSize();
528 ESize = BaseSD->getSize();
532 if (!ESize->evaluateKnownAbsolute(Res, Layout))
533 report_fatal_error("Size expression must be absolute.");
537 // Write out the symbol table entry
538 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
539 MSD.SectionIndex, IsReserved);
542 void ELFObjectWriter::WriteSymbolTable(MCAssembler &Asm,
543 const MCAsmLayout &Layout,
544 SectionOffsetsTy &SectionOffsets) {
546 MCContext &Ctx = Asm.getContext();
548 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
551 MCSectionELF *SymtabSection =
552 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
553 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
554 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
555 SymbolTableIndex = addToSectionTable(SymtabSection);
557 // The string table must be emitted first because we need the index
558 // into the string table for all the symbol names.
560 SymbolTableWriter Writer(*this, is64Bit());
562 uint64_t Padding = OffsetToAlignment(OS.tell(), SymtabSD.getAlignment());
565 uint64_t SecStart = OS.tell();
567 // The first entry is the undefined symbol entry.
568 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
570 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
571 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
572 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
575 // Write the symbol table entries.
576 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
578 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
579 ELFSymbolData &MSD = LocalSymbolData[i];
580 WriteSymbol(Writer, MSD, Layout);
583 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
584 ELFSymbolData &MSD = ExternalSymbolData[i];
585 MCSymbolData &Data = MSD.Symbol->getData();
586 assert(((Data.getFlags() & ELF_STB_Global) ||
587 (Data.getFlags() & ELF_STB_Weak)) &&
588 "External symbol requires STB_GLOBAL or STB_WEAK flag");
589 WriteSymbol(Writer, MSD, Layout);
590 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
591 LastLocalSymbolIndex++;
594 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
595 ELFSymbolData &MSD = UndefinedSymbolData[i];
596 MCSymbolData &Data = MSD.Symbol->getData();
597 WriteSymbol(Writer, MSD, Layout);
598 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
599 LastLocalSymbolIndex++;
602 uint64_t SecEnd = OS.tell();
603 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
605 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
606 if (ShndxIndexes.empty())
609 SecStart = OS.tell();
610 MCSectionELF *SymtabShndxSection =
611 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
612 addToSectionTable(SymtabShndxSection);
613 MCSectionData *SymtabShndxSD =
614 &Asm.getOrCreateSectionData(*SymtabShndxSection);
615 SymtabShndxSD->setAlignment(4);
616 for (uint32_t Index : ShndxIndexes)
619 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
622 // It is always valid to create a relocation with a symbol. It is preferable
623 // to use a relocation with a section if that is possible. Using the section
624 // allows us to omit some local symbols from the symbol table.
625 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
626 const MCSymbolRefExpr *RefA,
627 const MCSymbol *Sym, uint64_t C,
628 unsigned Type) const {
629 MCSymbolData *SD = Sym ? &Sym->getData() : nullptr;
631 // A PCRel relocation to an absolute value has no symbol (or section). We
632 // represent that with a relocation to a null section.
636 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
640 // The .odp creation emits a relocation against the symbol ".TOC." which
641 // create a R_PPC64_TOC relocation. However the relocation symbol name
642 // in final object creation should be NULL, since the symbol does not
643 // really exist, it is just the reference to TOC base for the current
644 // object file. Since the symbol is undefined, returning false results
645 // in a relocation with a null section which is the desired result.
646 case MCSymbolRefExpr::VK_PPC_TOCBASE:
649 // These VariantKind cause the relocation to refer to something other than
650 // the symbol itself, like a linker generated table. Since the address of
651 // symbol is not relevant, we cannot replace the symbol with the
652 // section and patch the difference in the addend.
653 case MCSymbolRefExpr::VK_GOT:
654 case MCSymbolRefExpr::VK_PLT:
655 case MCSymbolRefExpr::VK_GOTPCREL:
656 case MCSymbolRefExpr::VK_Mips_GOT:
657 case MCSymbolRefExpr::VK_PPC_GOT_LO:
658 case MCSymbolRefExpr::VK_PPC_GOT_HI:
659 case MCSymbolRefExpr::VK_PPC_GOT_HA:
663 // An undefined symbol is not in any section, so the relocation has to point
664 // to the symbol itself.
665 assert(Sym && "Expected a symbol");
666 if (Sym->isUndefined())
669 unsigned Binding = MCELF::GetBinding(*SD);
672 llvm_unreachable("Invalid Binding");
676 // If the symbol is weak, it might be overridden by a symbol in another
677 // file. The relocation has to point to the symbol so that the linker
680 case ELF::STB_GLOBAL:
681 // Global ELF symbols can be preempted by the dynamic linker. The relocation
682 // has to point to the symbol for a reason analogous to the STB_WEAK case.
686 // If a relocation points to a mergeable section, we have to be careful.
687 // If the offset is zero, a relocation with the section will encode the
688 // same information. With a non-zero offset, the situation is different.
689 // For example, a relocation can point 42 bytes past the end of a string.
690 // If we change such a relocation to use the section, the linker would think
691 // that it pointed to another string and subtracting 42 at runtime will
692 // produce the wrong value.
693 auto &Sec = cast<MCSectionELF>(Sym->getSection());
694 unsigned Flags = Sec.getFlags();
695 if (Flags & ELF::SHF_MERGE) {
699 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
700 // only handle section relocations to mergeable sections if using RELA.
701 if (!hasRelocationAddend())
705 // Most TLS relocations use a got, so they need the symbol. Even those that
706 // are just an offset (@tpoff), require a symbol in gold versions before
707 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
708 // http://sourceware.org/PR16773.
709 if (Flags & ELF::SHF_TLS)
712 // If the symbol is a thumb function the final relocation must set the lowest
713 // bit. With a symbol that is done by just having the symbol have that bit
714 // set, so we would lose the bit if we relocated with the section.
715 // FIXME: We could use the section but add the bit to the relocation value.
716 if (Asm.isThumbFunc(Sym))
719 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
724 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
725 const MCSymbol &Sym = Ref.getSymbol();
727 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
730 if (!Sym.isVariable())
733 const MCExpr *Expr = Sym.getVariableValue();
734 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
738 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
739 return &Inner->getSymbol();
743 // True if the assembler knows nothing about the final value of the symbol.
744 // This doesn't cover the comdat issues, since in those cases the assembler
745 // can at least know that all symbols in the section will move together.
746 static bool isWeak(const MCSymbolData &D) {
747 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
750 switch (MCELF::GetBinding(D)) {
752 llvm_unreachable("Unknown binding");
755 case ELF::STB_GLOBAL:
758 case ELF::STB_GNU_UNIQUE:
763 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
764 const MCAsmLayout &Layout,
765 const MCFragment *Fragment,
766 const MCFixup &Fixup, MCValue Target,
767 bool &IsPCRel, uint64_t &FixedValue) {
768 const MCSectionData *FixupSectionD = Fragment->getParent();
769 const MCSectionELF &FixupSection =
770 cast<MCSectionELF>(FixupSectionD->getSection());
771 uint64_t C = Target.getConstant();
772 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
774 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
775 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
776 "Should not have constructed this");
778 // Let A, B and C being the components of Target and R be the location of
779 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
780 // If it is pcrel, we want to compute (A - B + C - R).
782 // In general, ELF has no relocations for -B. It can only represent (A + C)
783 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
784 // replace B to implement it: (A - R - K + C)
786 Asm.getContext().reportFatalError(
788 "No relocation available to represent this relative expression");
790 const MCSymbol &SymB = RefB->getSymbol();
792 if (SymB.isUndefined())
793 Asm.getContext().reportFatalError(
795 Twine("symbol '") + SymB.getName() +
796 "' can not be undefined in a subtraction expression");
798 assert(!SymB.isAbsolute() && "Should have been folded");
799 const MCSection &SecB = SymB.getSection();
800 if (&SecB != &FixupSection)
801 Asm.getContext().reportFatalError(
802 Fixup.getLoc(), "Cannot represent a difference across sections");
804 if (::isWeak(SymB.getData()))
805 Asm.getContext().reportFatalError(
806 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
808 uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
809 uint64_t K = SymBOffset - FixupOffset;
814 // We either rejected the fixup or folded B into C at this point.
815 const MCSymbolRefExpr *RefA = Target.getSymA();
816 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
818 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
819 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymA, C, Type);
820 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
821 C += Layout.getSymbolOffset(*SymA);
824 if (hasRelocationAddend()) {
831 // FIXME: What is this!?!?
832 MCSymbolRefExpr::VariantKind Modifier =
833 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
834 if (RelocNeedsGOT(Modifier))
837 if (!RelocateWithSymbol) {
838 const MCSection *SecA =
839 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
840 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
841 MCSymbol *SectionSymbol =
842 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
844 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
845 Relocations[&FixupSection].push_back(Rec);
850 if (const MCSymbol *R = Renames.lookup(SymA))
853 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
854 WeakrefUsedInReloc.insert(WeakRef);
856 UsedInReloc.insert(SymA);
858 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
859 Relocations[&FixupSection].push_back(Rec);
865 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
867 const MCSymbolData &SD = Asm.getSymbolData(*S);
868 return SD.getIndex();
871 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
872 const MCSymbol &Symbol, bool Used,
874 const MCSymbolData &Data = Symbol.getData();
875 if (Symbol.isVariable()) {
876 const MCExpr *Expr = Symbol.getVariableValue();
877 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
878 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
889 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
892 if (Symbol.isVariable()) {
893 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
894 if (Base && Base->isUndefined())
898 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
899 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
902 if (Symbol.isTemporary())
908 bool ELFObjectWriter::isLocal(const MCSymbol &Symbol, bool isUsedInReloc) {
909 const MCSymbolData &Data = Symbol.getData();
910 if (Data.isExternal())
913 if (Symbol.isDefined())
922 void ELFObjectWriter::computeSymbolTable(
923 MCAssembler &Asm, const MCAsmLayout &Layout,
924 const SectionIndexMapTy &SectionIndexMap,
925 const RevGroupMapTy &RevGroupMap) {
926 // FIXME: Is this the correct place to do this?
927 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
929 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
930 MCSymbol *Sym = Asm.getContext().getOrCreateSymbol(Name);
931 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
932 Data.setExternal(true);
933 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
936 // Add the data for the symbols.
937 for (const MCSymbol &Symbol : Asm.symbols()) {
938 MCSymbolData &SD = Symbol.getData();
940 bool Used = UsedInReloc.count(&Symbol);
941 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
942 bool isSignature = RevGroupMap.count(&Symbol);
944 if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
945 Renames.count(&Symbol)))
949 MSD.Symbol = &Symbol;
950 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
952 // Undefined symbols are global, but this is the first place we
953 // are able to set it.
954 bool Local = isLocal(Symbol, Used);
955 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
957 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
958 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
959 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
963 MSD.SectionIndex = ELF::SHN_ABS;
964 } else if (SD.isCommon()) {
966 MSD.SectionIndex = ELF::SHN_COMMON;
967 } else if (BaseSymbol->isUndefined()) {
968 if (isSignature && !Used)
969 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
971 MSD.SectionIndex = ELF::SHN_UNDEF;
972 if (!Used && WeakrefUsed)
973 MCELF::SetBinding(SD, ELF::STB_WEAK);
975 const MCSectionELF &Section =
976 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
977 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
978 assert(MSD.SectionIndex && "Invalid section index!");
981 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
984 // FIXME: All name handling should be done before we get to the writer,
985 // including dealing with GNU-style version suffixes. Fixing this isn't
988 // We thus have to be careful to not perform the symbol version replacement
991 // The ELF format is used on Windows by the MCJIT engine. Thus, on
992 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
993 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
994 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
995 // the EFLObjectWriter should not interpret the "@@@" sub-string as
996 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
997 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
998 // "__imp_?" or "__imp_@?".
1000 // It would have been interesting to perform the MS mangling prefix check
1001 // only when the target triple is of the form *-pc-windows-elf. But, it
1002 // seems that this information is not easily accessible from the
1004 StringRef Name = Symbol.getName();
1005 if (!Name.startswith("?") && !Name.startswith("@?") &&
1006 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1007 // This symbol isn't following the MSVC C++ name mangling convention. We
1008 // can thus safely interpret the @@@ in symbol names as specifying symbol
1010 SmallString<32> Buf;
1011 size_t Pos = Name.find("@@@");
1012 if (Pos != StringRef::npos) {
1013 Buf += Name.substr(0, Pos);
1014 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1015 Buf += Name.substr(Pos + Skip);
1020 // Sections have their own string table
1021 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1022 MSD.Name = StrTabBuilder.add(Name);
1024 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1025 UndefinedSymbolData.push_back(MSD);
1027 LocalSymbolData.push_back(MSD);
1029 ExternalSymbolData.push_back(MSD);
1032 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1033 StrTabBuilder.add(*i);
1035 StrTabBuilder.finalize(StringTableBuilder::ELF);
1037 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1038 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1040 for (ELFSymbolData &MSD : LocalSymbolData)
1041 MSD.StringIndex = MCELF::GetType(MSD.Symbol->getData()) == ELF::STT_SECTION
1043 : StrTabBuilder.getOffset(MSD.Name);
1044 for (ELFSymbolData &MSD : ExternalSymbolData)
1045 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1046 for (ELFSymbolData& MSD : UndefinedSymbolData)
1047 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1049 // Symbols are required to be in lexicographic order.
1050 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1051 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1052 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1054 // Set the symbol indices. Local symbols must come before all other
1055 // symbols with non-local bindings.
1056 unsigned Index = FileSymbolData.size() + 1;
1057 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1058 LocalSymbolData[i].Symbol->getData().setIndex(Index++);
1060 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1061 ExternalSymbolData[i].Symbol->getData().setIndex(Index++);
1062 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1063 UndefinedSymbolData[i].Symbol->getData().setIndex(Index++);
1067 ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1068 const MCSectionELF &Sec) {
1069 if (Relocations[&Sec].empty())
1072 MCContext &Ctx = Asm.getContext();
1073 const StringRef SectionName = Sec.getSectionName();
1074 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1075 RelaSectionName += SectionName;
1078 if (hasRelocationAddend())
1079 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1081 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1084 if (Sec.getFlags() & ELF::SHF_GROUP)
1085 Flags = ELF::SHF_GROUP;
1087 MCSectionELF *RelaSection = Ctx.createELFRelSection(
1088 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1089 Flags, EntrySize, Sec.getGroup(), &Sec);
1090 MCSectionData &RelSD = Asm.getOrCreateSectionData(*RelaSection);
1091 RelSD.setAlignment(is64Bit() ? 8 : 4);
1095 static SmallVector<char, 128>
1096 getUncompressedData(const MCAsmLayout &Layout,
1097 const MCSectionData::FragmentListType &Fragments) {
1098 SmallVector<char, 128> UncompressedData;
1099 for (const MCFragment &F : Fragments) {
1100 const SmallVectorImpl<char> *Contents;
1101 switch (F.getKind()) {
1102 case MCFragment::FT_Data:
1103 Contents = &cast<MCDataFragment>(F).getContents();
1105 case MCFragment::FT_Dwarf:
1106 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1108 case MCFragment::FT_DwarfFrame:
1109 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1113 "Not expecting any other fragment types in a debug_* section");
1115 UncompressedData.append(Contents->begin(), Contents->end());
1117 return UncompressedData;
1120 // Include the debug info compression header:
1121 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1122 // useful for consumers to preallocate a buffer to decompress into.
1124 prependCompressionHeader(uint64_t Size,
1125 SmallVectorImpl<char> &CompressedContents) {
1126 const StringRef Magic = "ZLIB";
1127 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1129 if (sys::IsLittleEndianHost)
1130 sys::swapByteOrder(Size);
1131 CompressedContents.insert(CompressedContents.begin(),
1132 Magic.size() + sizeof(Size), 0);
1133 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1134 std::copy(reinterpret_cast<char *>(&Size),
1135 reinterpret_cast<char *>(&Size + 1),
1136 CompressedContents.begin() + Magic.size());
1140 void ELFObjectWriter::writeSectionData(const MCAssembler &Asm,
1141 const MCSectionData &SD,
1142 const MCAsmLayout &Layout) {
1143 MCSectionELF &Section = static_cast<MCSectionELF &>(SD.getSection());
1144 StringRef SectionName = Section.getSectionName();
1146 // Compressing debug_frame requires handling alignment fragments which is
1147 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1148 // for writing to arbitrary buffers) for little benefit.
1149 if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
1150 !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
1151 Asm.writeSectionData(&SD, Layout);
1155 // Gather the uncompressed data from all the fragments.
1156 const MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1157 SmallVector<char, 128> UncompressedData =
1158 getUncompressedData(Layout, Fragments);
1160 SmallVector<char, 128> CompressedContents;
1161 zlib::Status Success = zlib::compress(
1162 StringRef(UncompressedData.data(), UncompressedData.size()),
1163 CompressedContents);
1164 if (Success != zlib::StatusOK) {
1165 Asm.writeSectionData(&SD, Layout);
1169 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
1170 Asm.writeSectionData(&SD, Layout);
1173 Asm.getContext().renameELFSection(&Section,
1174 (".z" + SectionName.drop_front(1)).str());
1175 OS << CompressedContents;
1178 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1179 uint64_t Flags, uint64_t Address,
1180 uint64_t Offset, uint64_t Size,
1181 uint32_t Link, uint32_t Info,
1183 uint64_t EntrySize) {
1184 Write32(Name); // sh_name: index into string table
1185 Write32(Type); // sh_type
1186 WriteWord(Flags); // sh_flags
1187 WriteWord(Address); // sh_addr
1188 WriteWord(Offset); // sh_offset
1189 WriteWord(Size); // sh_size
1190 Write32(Link); // sh_link
1191 Write32(Info); // sh_info
1192 WriteWord(Alignment); // sh_addralign
1193 WriteWord(EntrySize); // sh_entsize
1196 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1197 const MCSectionELF &Sec) {
1198 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1200 // Sort the relocation entries. Most targets just sort by Offset, but some
1201 // (e.g., MIPS) have additional constraints.
1202 TargetObjectWriter->sortRelocs(Asm, Relocs);
1204 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1205 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1207 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1210 write(Entry.Offset);
1211 if (TargetObjectWriter->isN64()) {
1212 write(uint32_t(Index));
1214 write(TargetObjectWriter->getRSsym(Entry.Type));
1215 write(TargetObjectWriter->getRType3(Entry.Type));
1216 write(TargetObjectWriter->getRType2(Entry.Type));
1217 write(TargetObjectWriter->getRType(Entry.Type));
1219 struct ELF::Elf64_Rela ERE64;
1220 ERE64.setSymbolAndType(Index, Entry.Type);
1221 write(ERE64.r_info);
1223 if (hasRelocationAddend())
1224 write(Entry.Addend);
1226 write(uint32_t(Entry.Offset));
1228 struct ELF::Elf32_Rela ERE32;
1229 ERE32.setSymbolAndType(Index, Entry.Type);
1230 write(ERE32.r_info);
1232 if (hasRelocationAddend())
1233 write(uint32_t(Entry.Addend));
1238 const MCSectionELF *ELFObjectWriter::createSectionHeaderStringTable() {
1239 const MCSectionELF *ShstrtabSection = SectionTable[ShstrtabIndex - 1];
1240 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1241 OS << ShStrTabBuilder.data();
1242 return ShstrtabSection;
1245 const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
1246 MCSectionELF *StrtabSection =
1247 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1248 StringTableIndex = addToSectionTable(StrtabSection);
1249 OS << StrTabBuilder.data();
1250 return StrtabSection;
1253 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1254 const SectionIndexMapTy &SectionIndexMap,
1255 uint32_t GroupSymbolIndex,
1256 uint64_t Offset, uint64_t Size,
1257 const MCSectionELF &Section) {
1258 uint64_t sh_link = 0;
1259 uint64_t sh_info = 0;
1261 switch(Section.getType()) {
1266 case ELF::SHT_DYNAMIC:
1267 llvm_unreachable("SHT_DYNAMIC in a relocatable object");
1270 case ELF::SHT_RELA: {
1271 sh_link = SymbolTableIndex;
1272 assert(sh_link && ".symtab not found");
1273 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1274 sh_info = SectionIndexMap.lookup(InfoSection);
1278 case ELF::SHT_SYMTAB:
1279 case ELF::SHT_DYNSYM:
1280 sh_link = StringTableIndex;
1281 sh_info = LastLocalSymbolIndex;
1284 case ELF::SHT_SYMTAB_SHNDX:
1285 sh_link = SymbolTableIndex;
1288 case ELF::SHT_GROUP:
1289 sh_link = SymbolTableIndex;
1290 sh_info = GroupSymbolIndex;
1294 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1295 Section.getType() == ELF::SHT_ARM_EXIDX)
1296 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1298 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1299 Section.getType(), Section.getFlags(), 0, Offset, Size,
1300 sh_link, sh_info, Section.getAlignment(),
1301 Section.getEntrySize());
1304 void ELFObjectWriter::writeSectionHeader(
1305 MCAssembler &Asm, const MCAsmLayout &Layout,
1306 const SectionIndexMapTy &SectionIndexMap,
1307 const SectionOffsetsTy &SectionOffsets) {
1308 const unsigned NumSections = SectionTable.size();
1310 // Null section first.
1311 uint64_t FirstSectionSize =
1312 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1313 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1315 for (MCSectionELF *Section : SectionTable) {
1316 const MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1317 uint32_t GroupSymbolIndex;
1318 unsigned Type = Section->getType();
1319 if (Type != ELF::SHT_GROUP)
1320 GroupSymbolIndex = 0;
1322 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section->getGroup());
1324 const std::pair<uint64_t, uint64_t> &Offsets =
1325 SectionOffsets.find(Section)->second;
1326 uint64_t Size = Type == ELF::SHT_NOBITS ? Layout.getSectionAddressSize(&SD)
1327 : Offsets.second - Offsets.first;
1329 writeSection(Asm, SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1334 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1335 const MCAsmLayout &Layout) {
1336 MCContext &Ctx = Asm.getContext();
1337 MCSectionELF *ShstrtabSection =
1338 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1339 ShstrtabIndex = addToSectionTable(ShstrtabSection);
1341 RevGroupMapTy RevGroupMap;
1342 SectionIndexMapTy SectionIndexMap;
1344 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1346 // Write out the ELF header ...
1349 // ... then the sections ...
1350 SectionOffsetsTy SectionOffsets;
1351 bool ComputedSymtab = false;
1352 for (const MCSectionData &SD : Asm) {
1353 MCSectionELF &Section = static_cast<MCSectionELF &>(SD.getSection());
1355 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1356 WriteZeros(Padding);
1358 // Remember the offset into the file for this section.
1359 uint64_t SecStart = OS.tell();
1361 const MCSymbol *SignatureSymbol = Section.getGroup();
1362 unsigned Type = Section.getType();
1363 if (Type == ELF::SHT_GROUP) {
1364 assert(SignatureSymbol);
1365 write(uint32_t(ELF::GRP_COMDAT));
1366 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1367 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1370 } else if (Type == ELF::SHT_REL || Type == ELF::SHT_RELA) {
1371 if (!ComputedSymtab) {
1372 // Compute symbol table information.
1373 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1374 ComputedSymtab = true;
1376 writeRelocations(Asm, *Section.getAssociatedSection());
1378 writeSectionData(Asm, SD, Layout);
1381 uint64_t SecEnd = OS.tell();
1382 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1384 if (Type == ELF::SHT_GROUP || Type == ELF::SHT_REL || Type == ELF::SHT_RELA)
1387 MCSectionELF *RelSection = createRelocationSection(Asm, Section);
1389 if (SignatureSymbol) {
1390 Asm.getOrCreateSymbolData(*SignatureSymbol);
1391 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1393 MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1394 GroupIdx = addToSectionTable(Group);
1395 MCSectionData *GroupD = &Asm.getOrCreateSectionData(*Group);
1396 GroupD->setAlignment(4);
1398 GroupMembers[SignatureSymbol].push_back(&Section);
1400 GroupMembers[SignatureSymbol].push_back(RelSection);
1403 SectionIndexMap[&Section] = addToSectionTable(&Section);
1405 SectionIndexMap[RelSection] = addToSectionTable(RelSection);
1408 if (!ComputedSymtab) {
1409 // Compute symbol table information.
1410 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1411 ComputedSymtab = true;
1414 WriteSymbolTable(Asm, Layout, SectionOffsets);
1417 uint64_t SecStart = OS.tell();
1418 const MCSectionELF *Sec = createStringTable(Ctx);
1419 uint64_t SecEnd = OS.tell();
1420 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1424 uint64_t SecStart = OS.tell();
1425 const MCSectionELF *Sec = createSectionHeaderStringTable();
1426 uint64_t SecEnd = OS.tell();
1427 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1430 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1431 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1432 WriteZeros(Padding);
1434 const unsigned SectionHeaderOffset = OS.tell();
1436 // ... then the section header table ...
1437 writeSectionHeader(Asm, Layout, SectionIndexMap, SectionOffsets);
1439 uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
1440 ? (uint16_t)ELF::SHN_UNDEF
1441 : SectionTable.size() + 1;
1442 if (sys::IsLittleEndianHost != IsLittleEndian)
1443 sys::swapByteOrder(NumSections);
1444 unsigned NumSectionsOffset;
1447 uint64_t Val = SectionHeaderOffset;
1448 if (sys::IsLittleEndianHost != IsLittleEndian)
1449 sys::swapByteOrder(Val);
1450 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1451 offsetof(ELF::Elf64_Ehdr, e_shoff));
1452 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1454 uint32_t Val = SectionHeaderOffset;
1455 if (sys::IsLittleEndianHost != IsLittleEndian)
1456 sys::swapByteOrder(Val);
1457 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1458 offsetof(ELF::Elf32_Ehdr, e_shoff));
1459 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1461 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1465 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1466 const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
1467 bool InSet, bool IsPCRel) const {
1470 if (::isWeak(SymA.getData()))
1473 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
1477 bool ELFObjectWriter::isWeak(const MCSymbol &Sym) const {
1478 const MCSymbolData &SD = Sym.getData();
1482 // It is invalid to replace a reference to a global in a comdat
1483 // with a reference to a local since out of comdat references
1484 // to a local are forbidden.
1485 // We could try to return false for more cases, like the reference
1486 // being in the same comdat or Sym being an alias to another global,
1487 // but it is not clear if it is worth the effort.
1488 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1491 if (!Sym.isInSection())
1494 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1495 return Sec.getGroup();
1498 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1499 raw_pwrite_stream &OS,
1500 bool IsLittleEndian) {
1501 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);