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,
259 uint64_t Offset, uint64_t Size, uint64_t Alignment,
260 const MCSectionELF &Section);
264 unsigned ELFObjectWriter::addToSectionTable(MCSectionELF *Sec) {
265 SectionTable.push_back(Sec);
266 ShStrTabBuilder.add(Sec->getSectionName());
267 return SectionTable.size();
270 void SymbolTableWriter::createSymtabShndx() {
271 if (!ShndxIndexes.empty())
274 ShndxIndexes.resize(NumWritten);
277 template <typename T> void SymbolTableWriter::write(T Value) {
278 EWriter.write(Value);
281 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
282 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
284 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
285 uint64_t size, uint8_t other,
286 uint32_t shndx, bool Reserved) {
287 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
292 if (!ShndxIndexes.empty()) {
294 ShndxIndexes.push_back(shndx);
296 ShndxIndexes.push_back(0);
299 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
302 write(name); // st_name
303 write(info); // st_info
304 write(other); // st_other
305 write(Index); // st_shndx
306 write(value); // st_value
307 write(size); // st_size
309 write(name); // st_name
310 write(uint32_t(value)); // st_value
311 write(uint32_t(size)); // st_size
312 write(info); // st_info
313 write(other); // st_other
314 write(Index); // st_shndx
320 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
321 const MCFixupKindInfo &FKI =
322 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
324 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
327 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
331 case MCSymbolRefExpr::VK_GOT:
332 case MCSymbolRefExpr::VK_PLT:
333 case MCSymbolRefExpr::VK_GOTPCREL:
334 case MCSymbolRefExpr::VK_GOTOFF:
335 case MCSymbolRefExpr::VK_TPOFF:
336 case MCSymbolRefExpr::VK_TLSGD:
337 case MCSymbolRefExpr::VK_GOTTPOFF:
338 case MCSymbolRefExpr::VK_INDNTPOFF:
339 case MCSymbolRefExpr::VK_NTPOFF:
340 case MCSymbolRefExpr::VK_GOTNTPOFF:
341 case MCSymbolRefExpr::VK_TLSLDM:
342 case MCSymbolRefExpr::VK_DTPOFF:
343 case MCSymbolRefExpr::VK_TLSLD:
348 ELFObjectWriter::~ELFObjectWriter()
351 // Emit the ELF header.
352 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
358 // emitWord method behaves differently for ELF32 and ELF64, writing
359 // 4 bytes in the former and 8 in the latter.
361 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
363 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
366 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
368 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
370 Write8(TargetObjectWriter->getOSABI());
371 Write8(0); // e_ident[EI_ABIVERSION]
373 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
375 Write16(ELF::ET_REL); // e_type
377 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
379 Write32(ELF::EV_CURRENT); // e_version
380 WriteWord(0); // e_entry, no entry point in .o file
381 WriteWord(0); // e_phoff, no program header for .o
382 WriteWord(0); // e_shoff = sec hdr table off in bytes
384 // e_flags = whatever the target wants
385 Write32(Asm.getELFHeaderEFlags());
387 // e_ehsize = ELF header size
388 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
390 Write16(0); // e_phentsize = prog header entry size
391 Write16(0); // e_phnum = # prog header entries = 0
393 // e_shentsize = Section header entry size
394 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
396 // e_shnum = # of section header ents
399 // e_shstrndx = Section # of '.shstrtab'
400 assert(ShstrtabIndex < ELF::SHN_LORESERVE);
401 Write16(ShstrtabIndex);
404 uint64_t ELFObjectWriter::SymbolValue(const MCSymbol &Sym,
405 const MCAsmLayout &Layout) {
406 MCSymbolData &Data = Sym.getData();
407 if (Data.isCommon() && Data.isExternal())
408 return Data.getCommonAlignment();
411 if (!Layout.getSymbolOffset(Sym, Res))
414 if (Layout.getAssembler().isThumbFunc(&Sym))
420 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
421 const MCAsmLayout &Layout) {
422 // The presence of symbol versions causes undefined symbols and
423 // versions declared with @@@ to be renamed.
425 for (const MCSymbol &Alias : Asm.symbols()) {
426 MCSymbolData &OriginalData = Alias.getData();
429 if (!Alias.isVariable())
431 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
434 const MCSymbol &Symbol = Ref->getSymbol();
435 MCSymbolData &SD = Asm.getSymbolData(Symbol);
437 StringRef AliasName = Alias.getName();
438 size_t Pos = AliasName.find('@');
439 if (Pos == StringRef::npos)
442 // Aliases defined with .symvar copy the binding from the symbol they alias.
443 // This is the first place we are able to copy this information.
444 OriginalData.setExternal(SD.isExternal());
445 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
447 StringRef Rest = AliasName.substr(Pos);
448 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
451 // FIXME: produce a better error message.
452 if (Symbol.isUndefined() && Rest.startswith("@@") &&
453 !Rest.startswith("@@@"))
454 report_fatal_error("A @@ version cannot be undefined");
456 Renames.insert(std::make_pair(&Symbol, &Alias));
460 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
461 uint8_t Type = newType;
463 // Propagation rules:
464 // IFUNC > FUNC > OBJECT > NOTYPE
465 // TLS_OBJECT > OBJECT > NOTYPE
467 // dont let the new type degrade the old type
471 case ELF::STT_GNU_IFUNC:
472 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
473 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
474 Type = ELF::STT_GNU_IFUNC;
477 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
478 Type == ELF::STT_TLS)
479 Type = ELF::STT_FUNC;
481 case ELF::STT_OBJECT:
482 if (Type == ELF::STT_NOTYPE)
483 Type = ELF::STT_OBJECT;
486 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
487 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
495 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
496 const MCAsmLayout &Layout) {
497 MCSymbolData &OrigData = MSD.Symbol->getData();
498 assert((!OrigData.getFragment() ||
499 (&OrigData.getFragment()->getParent()->getSection() ==
500 &MSD.Symbol->getSection())) &&
501 "The symbol's section doesn't match the fragment's symbol");
502 const MCSymbol *Base = Layout.getBaseSymbol(*MSD.Symbol);
504 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
506 bool IsReserved = !Base || OrigData.isCommon();
508 // Binding and Type share the same byte as upper and lower nibbles
509 uint8_t Binding = MCELF::GetBinding(OrigData);
510 uint8_t Type = MCELF::GetType(OrigData);
511 MCSymbolData *BaseSD = nullptr;
513 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
514 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
516 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
518 // Other and Visibility share the same byte with Visibility using the lower
520 uint8_t Visibility = MCELF::GetVisibility(OrigData);
521 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
524 uint64_t Value = SymbolValue(*MSD.Symbol, Layout);
527 const MCExpr *ESize = OrigData.getSize();
529 ESize = BaseSD->getSize();
533 if (!ESize->evaluateKnownAbsolute(Res, Layout))
534 report_fatal_error("Size expression must be absolute.");
538 // Write out the symbol table entry
539 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
540 MSD.SectionIndex, IsReserved);
543 void ELFObjectWriter::WriteSymbolTable(MCAssembler &Asm,
544 const MCAsmLayout &Layout,
545 SectionOffsetsTy &SectionOffsets) {
547 MCContext &Ctx = Asm.getContext();
549 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
552 MCSectionELF *SymtabSection =
553 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
554 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
555 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
556 SymbolTableIndex = addToSectionTable(SymtabSection);
558 // The string table must be emitted first because we need the index
559 // into the string table for all the symbol names.
561 SymbolTableWriter Writer(*this, is64Bit());
563 uint64_t Padding = OffsetToAlignment(OS.tell(), SymtabSD.getAlignment());
566 uint64_t SecStart = OS.tell();
568 // The first entry is the undefined symbol entry.
569 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
571 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
572 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
573 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
576 // Write the symbol table entries.
577 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
579 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
580 ELFSymbolData &MSD = LocalSymbolData[i];
581 WriteSymbol(Writer, MSD, Layout);
584 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
585 ELFSymbolData &MSD = ExternalSymbolData[i];
586 MCSymbolData &Data = MSD.Symbol->getData();
587 assert(((Data.getFlags() & ELF_STB_Global) ||
588 (Data.getFlags() & ELF_STB_Weak)) &&
589 "External symbol requires STB_GLOBAL or STB_WEAK flag");
590 WriteSymbol(Writer, MSD, Layout);
591 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
592 LastLocalSymbolIndex++;
595 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
596 ELFSymbolData &MSD = UndefinedSymbolData[i];
597 MCSymbolData &Data = MSD.Symbol->getData();
598 WriteSymbol(Writer, MSD, Layout);
599 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
600 LastLocalSymbolIndex++;
603 uint64_t SecEnd = OS.tell();
604 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
606 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
607 if (ShndxIndexes.empty())
610 SecStart = OS.tell();
611 MCSectionELF *SymtabShndxSection =
612 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
613 addToSectionTable(SymtabShndxSection);
614 MCSectionData *SymtabShndxSD =
615 &Asm.getOrCreateSectionData(*SymtabShndxSection);
616 SymtabShndxSD->setAlignment(4);
617 for (uint32_t Index : ShndxIndexes)
620 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
623 // It is always valid to create a relocation with a symbol. It is preferable
624 // to use a relocation with a section if that is possible. Using the section
625 // allows us to omit some local symbols from the symbol table.
626 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
627 const MCSymbolRefExpr *RefA,
628 const MCSymbol *Sym, uint64_t C,
629 unsigned Type) const {
630 MCSymbolData *SD = Sym ? &Sym->getData() : nullptr;
632 // A PCRel relocation to an absolute value has no symbol (or section). We
633 // represent that with a relocation to a null section.
637 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
641 // The .odp creation emits a relocation against the symbol ".TOC." which
642 // create a R_PPC64_TOC relocation. However the relocation symbol name
643 // in final object creation should be NULL, since the symbol does not
644 // really exist, it is just the reference to TOC base for the current
645 // object file. Since the symbol is undefined, returning false results
646 // in a relocation with a null section which is the desired result.
647 case MCSymbolRefExpr::VK_PPC_TOCBASE:
650 // These VariantKind cause the relocation to refer to something other than
651 // the symbol itself, like a linker generated table. Since the address of
652 // symbol is not relevant, we cannot replace the symbol with the
653 // section and patch the difference in the addend.
654 case MCSymbolRefExpr::VK_GOT:
655 case MCSymbolRefExpr::VK_PLT:
656 case MCSymbolRefExpr::VK_GOTPCREL:
657 case MCSymbolRefExpr::VK_Mips_GOT:
658 case MCSymbolRefExpr::VK_PPC_GOT_LO:
659 case MCSymbolRefExpr::VK_PPC_GOT_HI:
660 case MCSymbolRefExpr::VK_PPC_GOT_HA:
664 // An undefined symbol is not in any section, so the relocation has to point
665 // to the symbol itself.
666 assert(Sym && "Expected a symbol");
667 if (Sym->isUndefined())
670 unsigned Binding = MCELF::GetBinding(*SD);
673 llvm_unreachable("Invalid Binding");
677 // If the symbol is weak, it might be overridden by a symbol in another
678 // file. The relocation has to point to the symbol so that the linker
681 case ELF::STB_GLOBAL:
682 // Global ELF symbols can be preempted by the dynamic linker. The relocation
683 // has to point to the symbol for a reason analogous to the STB_WEAK case.
687 // If a relocation points to a mergeable section, we have to be careful.
688 // If the offset is zero, a relocation with the section will encode the
689 // same information. With a non-zero offset, the situation is different.
690 // For example, a relocation can point 42 bytes past the end of a string.
691 // If we change such a relocation to use the section, the linker would think
692 // that it pointed to another string and subtracting 42 at runtime will
693 // produce the wrong value.
694 auto &Sec = cast<MCSectionELF>(Sym->getSection());
695 unsigned Flags = Sec.getFlags();
696 if (Flags & ELF::SHF_MERGE) {
700 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
701 // only handle section relocations to mergeable sections if using RELA.
702 if (!hasRelocationAddend())
706 // Most TLS relocations use a got, so they need the symbol. Even those that
707 // are just an offset (@tpoff), require a symbol in gold versions before
708 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
709 // http://sourceware.org/PR16773.
710 if (Flags & ELF::SHF_TLS)
713 // If the symbol is a thumb function the final relocation must set the lowest
714 // bit. With a symbol that is done by just having the symbol have that bit
715 // set, so we would lose the bit if we relocated with the section.
716 // FIXME: We could use the section but add the bit to the relocation value.
717 if (Asm.isThumbFunc(Sym))
720 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
725 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
726 const MCSymbol &Sym = Ref.getSymbol();
728 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
731 if (!Sym.isVariable())
734 const MCExpr *Expr = Sym.getVariableValue();
735 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
739 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
740 return &Inner->getSymbol();
744 // True if the assembler knows nothing about the final value of the symbol.
745 // This doesn't cover the comdat issues, since in those cases the assembler
746 // can at least know that all symbols in the section will move together.
747 static bool isWeak(const MCSymbolData &D) {
748 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
751 switch (MCELF::GetBinding(D)) {
753 llvm_unreachable("Unknown binding");
756 case ELF::STB_GLOBAL:
759 case ELF::STB_GNU_UNIQUE:
764 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
765 const MCAsmLayout &Layout,
766 const MCFragment *Fragment,
767 const MCFixup &Fixup, MCValue Target,
768 bool &IsPCRel, uint64_t &FixedValue) {
769 const MCSectionData *FixupSectionD = Fragment->getParent();
770 const MCSectionELF &FixupSection =
771 cast<MCSectionELF>(FixupSectionD->getSection());
772 uint64_t C = Target.getConstant();
773 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
775 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
776 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
777 "Should not have constructed this");
779 // Let A, B and C being the components of Target and R be the location of
780 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
781 // If it is pcrel, we want to compute (A - B + C - R).
783 // In general, ELF has no relocations for -B. It can only represent (A + C)
784 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
785 // replace B to implement it: (A - R - K + C)
787 Asm.getContext().reportFatalError(
789 "No relocation available to represent this relative expression");
791 const MCSymbol &SymB = RefB->getSymbol();
793 if (SymB.isUndefined())
794 Asm.getContext().reportFatalError(
796 Twine("symbol '") + SymB.getName() +
797 "' can not be undefined in a subtraction expression");
799 assert(!SymB.isAbsolute() && "Should have been folded");
800 const MCSection &SecB = SymB.getSection();
801 if (&SecB != &FixupSection)
802 Asm.getContext().reportFatalError(
803 Fixup.getLoc(), "Cannot represent a difference across sections");
805 if (::isWeak(SymB.getData()))
806 Asm.getContext().reportFatalError(
807 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
809 uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
810 uint64_t K = SymBOffset - FixupOffset;
815 // We either rejected the fixup or folded B into C at this point.
816 const MCSymbolRefExpr *RefA = Target.getSymA();
817 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
819 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
820 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymA, C, Type);
821 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
822 C += Layout.getSymbolOffset(*SymA);
825 if (hasRelocationAddend()) {
832 // FIXME: What is this!?!?
833 MCSymbolRefExpr::VariantKind Modifier =
834 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
835 if (RelocNeedsGOT(Modifier))
838 if (!RelocateWithSymbol) {
839 const MCSection *SecA =
840 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
841 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
842 MCSymbol *SectionSymbol =
843 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
845 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
846 Relocations[&FixupSection].push_back(Rec);
851 if (const MCSymbol *R = Renames.lookup(SymA))
854 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
855 WeakrefUsedInReloc.insert(WeakRef);
857 UsedInReloc.insert(SymA);
859 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
860 Relocations[&FixupSection].push_back(Rec);
866 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
868 const MCSymbolData &SD = Asm.getSymbolData(*S);
869 return SD.getIndex();
872 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
873 const MCSymbol &Symbol, bool Used,
875 const MCSymbolData &Data = Symbol.getData();
876 if (Symbol.isVariable()) {
877 const MCExpr *Expr = Symbol.getVariableValue();
878 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
879 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
890 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
893 if (Symbol.isVariable()) {
894 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
895 if (Base && Base->isUndefined())
899 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
900 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
903 if (Symbol.isTemporary())
909 bool ELFObjectWriter::isLocal(const MCSymbol &Symbol, bool isUsedInReloc) {
910 const MCSymbolData &Data = Symbol.getData();
911 if (Data.isExternal())
914 if (Symbol.isDefined())
923 void ELFObjectWriter::computeSymbolTable(
924 MCAssembler &Asm, const MCAsmLayout &Layout,
925 const SectionIndexMapTy &SectionIndexMap,
926 const RevGroupMapTy &RevGroupMap) {
927 // FIXME: Is this the correct place to do this?
928 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
930 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
931 MCSymbol *Sym = Asm.getContext().getOrCreateSymbol(Name);
932 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
933 Data.setExternal(true);
934 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
937 // Add the data for the symbols.
938 for (const MCSymbol &Symbol : Asm.symbols()) {
939 MCSymbolData &SD = Symbol.getData();
941 bool Used = UsedInReloc.count(&Symbol);
942 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
943 bool isSignature = RevGroupMap.count(&Symbol);
945 if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
946 Renames.count(&Symbol)))
950 MSD.Symbol = &Symbol;
951 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
953 // Undefined symbols are global, but this is the first place we
954 // are able to set it.
955 bool Local = isLocal(Symbol, Used);
956 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
958 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
959 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
960 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
964 MSD.SectionIndex = ELF::SHN_ABS;
965 } else if (SD.isCommon()) {
967 MSD.SectionIndex = ELF::SHN_COMMON;
968 } else if (BaseSymbol->isUndefined()) {
969 if (isSignature && !Used)
970 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
972 MSD.SectionIndex = ELF::SHN_UNDEF;
973 if (!Used && WeakrefUsed)
974 MCELF::SetBinding(SD, ELF::STB_WEAK);
976 const MCSectionELF &Section =
977 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
978 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
979 assert(MSD.SectionIndex && "Invalid section index!");
982 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
985 // FIXME: All name handling should be done before we get to the writer,
986 // including dealing with GNU-style version suffixes. Fixing this isn't
989 // We thus have to be careful to not perform the symbol version replacement
992 // The ELF format is used on Windows by the MCJIT engine. Thus, on
993 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
994 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
995 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
996 // the EFLObjectWriter should not interpret the "@@@" sub-string as
997 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
998 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
999 // "__imp_?" or "__imp_@?".
1001 // It would have been interesting to perform the MS mangling prefix check
1002 // only when the target triple is of the form *-pc-windows-elf. But, it
1003 // seems that this information is not easily accessible from the
1005 StringRef Name = Symbol.getName();
1006 if (!Name.startswith("?") && !Name.startswith("@?") &&
1007 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1008 // This symbol isn't following the MSVC C++ name mangling convention. We
1009 // can thus safely interpret the @@@ in symbol names as specifying symbol
1011 SmallString<32> Buf;
1012 size_t Pos = Name.find("@@@");
1013 if (Pos != StringRef::npos) {
1014 Buf += Name.substr(0, Pos);
1015 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1016 Buf += Name.substr(Pos + Skip);
1021 // Sections have their own string table
1022 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1023 MSD.Name = StrTabBuilder.add(Name);
1025 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1026 UndefinedSymbolData.push_back(MSD);
1028 LocalSymbolData.push_back(MSD);
1030 ExternalSymbolData.push_back(MSD);
1033 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1034 StrTabBuilder.add(*i);
1036 StrTabBuilder.finalize(StringTableBuilder::ELF);
1038 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1039 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1041 for (ELFSymbolData &MSD : LocalSymbolData)
1042 MSD.StringIndex = MCELF::GetType(MSD.Symbol->getData()) == ELF::STT_SECTION
1044 : StrTabBuilder.getOffset(MSD.Name);
1045 for (ELFSymbolData &MSD : ExternalSymbolData)
1046 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1047 for (ELFSymbolData& MSD : UndefinedSymbolData)
1048 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1050 // Symbols are required to be in lexicographic order.
1051 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1052 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1053 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1055 // Set the symbol indices. Local symbols must come before all other
1056 // symbols with non-local bindings.
1057 unsigned Index = FileSymbolData.size() + 1;
1058 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1059 LocalSymbolData[i].Symbol->getData().setIndex(Index++);
1061 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1062 ExternalSymbolData[i].Symbol->getData().setIndex(Index++);
1063 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1064 UndefinedSymbolData[i].Symbol->getData().setIndex(Index++);
1068 ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1069 const MCSectionELF &Sec) {
1070 if (Relocations[&Sec].empty())
1073 MCContext &Ctx = Asm.getContext();
1074 const StringRef SectionName = Sec.getSectionName();
1075 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1076 RelaSectionName += SectionName;
1079 if (hasRelocationAddend())
1080 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1082 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1085 if (Sec.getFlags() & ELF::SHF_GROUP)
1086 Flags = ELF::SHF_GROUP;
1088 MCSectionELF *RelaSection = Ctx.createELFRelSection(
1089 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1090 Flags, EntrySize, Sec.getGroup(), &Sec);
1091 MCSectionData &RelSD = Asm.getOrCreateSectionData(*RelaSection);
1092 RelSD.setAlignment(is64Bit() ? 8 : 4);
1096 static SmallVector<char, 128>
1097 getUncompressedData(const MCAsmLayout &Layout,
1098 const MCSectionData::FragmentListType &Fragments) {
1099 SmallVector<char, 128> UncompressedData;
1100 for (const MCFragment &F : Fragments) {
1101 const SmallVectorImpl<char> *Contents;
1102 switch (F.getKind()) {
1103 case MCFragment::FT_Data:
1104 Contents = &cast<MCDataFragment>(F).getContents();
1106 case MCFragment::FT_Dwarf:
1107 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1109 case MCFragment::FT_DwarfFrame:
1110 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1114 "Not expecting any other fragment types in a debug_* section");
1116 UncompressedData.append(Contents->begin(), Contents->end());
1118 return UncompressedData;
1121 // Include the debug info compression header:
1122 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1123 // useful for consumers to preallocate a buffer to decompress into.
1125 prependCompressionHeader(uint64_t Size,
1126 SmallVectorImpl<char> &CompressedContents) {
1127 const StringRef Magic = "ZLIB";
1128 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1130 if (sys::IsLittleEndianHost)
1131 sys::swapByteOrder(Size);
1132 CompressedContents.insert(CompressedContents.begin(),
1133 Magic.size() + sizeof(Size), 0);
1134 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1135 std::copy(reinterpret_cast<char *>(&Size),
1136 reinterpret_cast<char *>(&Size + 1),
1137 CompressedContents.begin() + Magic.size());
1141 void ELFObjectWriter::writeSectionData(const MCAssembler &Asm,
1142 const MCSectionData &SD,
1143 const MCAsmLayout &Layout) {
1144 MCSectionELF &Section = static_cast<MCSectionELF &>(SD.getSection());
1145 StringRef SectionName = Section.getSectionName();
1147 // Compressing debug_frame requires handling alignment fragments which is
1148 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1149 // for writing to arbitrary buffers) for little benefit.
1150 if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
1151 !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
1152 Asm.writeSectionData(&SD, Layout);
1156 // Gather the uncompressed data from all the fragments.
1157 const MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1158 SmallVector<char, 128> UncompressedData =
1159 getUncompressedData(Layout, Fragments);
1161 SmallVector<char, 128> CompressedContents;
1162 zlib::Status Success = zlib::compress(
1163 StringRef(UncompressedData.data(), UncompressedData.size()),
1164 CompressedContents);
1165 if (Success != zlib::StatusOK) {
1166 Asm.writeSectionData(&SD, Layout);
1170 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
1171 Asm.writeSectionData(&SD, Layout);
1174 Asm.getContext().renameELFSection(&Section,
1175 (".z" + SectionName.drop_front(1)).str());
1176 OS << CompressedContents;
1179 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1180 uint64_t Flags, uint64_t Address,
1181 uint64_t Offset, uint64_t Size,
1182 uint32_t Link, uint32_t Info,
1184 uint64_t EntrySize) {
1185 Write32(Name); // sh_name: index into string table
1186 Write32(Type); // sh_type
1187 WriteWord(Flags); // sh_flags
1188 WriteWord(Address); // sh_addr
1189 WriteWord(Offset); // sh_offset
1190 WriteWord(Size); // sh_size
1191 Write32(Link); // sh_link
1192 Write32(Info); // sh_info
1193 WriteWord(Alignment); // sh_addralign
1194 WriteWord(EntrySize); // sh_entsize
1197 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1198 const MCSectionELF &Sec) {
1199 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1201 // Sort the relocation entries. Most targets just sort by Offset, but some
1202 // (e.g., MIPS) have additional constraints.
1203 TargetObjectWriter->sortRelocs(Asm, Relocs);
1205 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1206 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1208 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1211 write(Entry.Offset);
1212 if (TargetObjectWriter->isN64()) {
1213 write(uint32_t(Index));
1215 write(TargetObjectWriter->getRSsym(Entry.Type));
1216 write(TargetObjectWriter->getRType3(Entry.Type));
1217 write(TargetObjectWriter->getRType2(Entry.Type));
1218 write(TargetObjectWriter->getRType(Entry.Type));
1220 struct ELF::Elf64_Rela ERE64;
1221 ERE64.setSymbolAndType(Index, Entry.Type);
1222 write(ERE64.r_info);
1224 if (hasRelocationAddend())
1225 write(Entry.Addend);
1227 write(uint32_t(Entry.Offset));
1229 struct ELF::Elf32_Rela ERE32;
1230 ERE32.setSymbolAndType(Index, Entry.Type);
1231 write(ERE32.r_info);
1233 if (hasRelocationAddend())
1234 write(uint32_t(Entry.Addend));
1239 const MCSectionELF *ELFObjectWriter::createSectionHeaderStringTable() {
1240 const MCSectionELF *ShstrtabSection = SectionTable[ShstrtabIndex - 1];
1241 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1242 OS << ShStrTabBuilder.data();
1243 return ShstrtabSection;
1246 const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
1247 MCSectionELF *StrtabSection =
1248 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1249 StringTableIndex = addToSectionTable(StrtabSection);
1250 OS << StrTabBuilder.data();
1251 return StrtabSection;
1254 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1255 const SectionIndexMapTy &SectionIndexMap,
1256 uint32_t GroupSymbolIndex,
1257 uint64_t Offset, uint64_t Size,
1259 const MCSectionELF &Section) {
1260 uint64_t sh_link = 0;
1261 uint64_t sh_info = 0;
1263 switch(Section.getType()) {
1268 case ELF::SHT_DYNAMIC:
1269 llvm_unreachable("SHT_DYNAMIC in a relocatable object");
1272 case ELF::SHT_RELA: {
1273 sh_link = SymbolTableIndex;
1274 assert(sh_link && ".symtab not found");
1275 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1276 sh_info = SectionIndexMap.lookup(InfoSection);
1280 case ELF::SHT_SYMTAB:
1281 case ELF::SHT_DYNSYM:
1282 sh_link = StringTableIndex;
1283 sh_info = LastLocalSymbolIndex;
1286 case ELF::SHT_SYMTAB_SHNDX:
1287 sh_link = SymbolTableIndex;
1290 case ELF::SHT_GROUP:
1291 sh_link = SymbolTableIndex;
1292 sh_info = GroupSymbolIndex;
1296 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1297 Section.getType() == ELF::SHT_ARM_EXIDX)
1298 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1300 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1302 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1303 Alignment, Section.getEntrySize());
1306 void ELFObjectWriter::writeSectionHeader(
1307 MCAssembler &Asm, const MCAsmLayout &Layout,
1308 const SectionIndexMapTy &SectionIndexMap,
1309 const SectionOffsetsTy &SectionOffsets) {
1310 const unsigned NumSections = SectionTable.size();
1312 // Null section first.
1313 uint64_t FirstSectionSize =
1314 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1315 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1317 for (MCSectionELF *Section : SectionTable) {
1318 const MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1319 uint32_t GroupSymbolIndex;
1320 unsigned Type = Section->getType();
1321 if (Type != ELF::SHT_GROUP)
1322 GroupSymbolIndex = 0;
1324 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section->getGroup());
1326 const std::pair<uint64_t, uint64_t> &Offsets =
1327 SectionOffsets.find(Section)->second;
1328 uint64_t Size = Type == ELF::SHT_NOBITS ? Layout.getSectionAddressSize(&SD)
1329 : Offsets.second - Offsets.first;
1331 writeSection(Asm, SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1332 SD.getAlignment(), *Section);
1336 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1337 const MCAsmLayout &Layout) {
1338 MCContext &Ctx = Asm.getContext();
1339 MCSectionELF *ShstrtabSection =
1340 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1341 ShstrtabIndex = addToSectionTable(ShstrtabSection);
1343 RevGroupMapTy RevGroupMap;
1344 SectionIndexMapTy SectionIndexMap;
1346 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1348 // Write out the ELF header ...
1351 // ... then the sections ...
1352 SectionOffsetsTy SectionOffsets;
1353 bool ComputedSymtab = false;
1354 for (const MCSectionData &SD : Asm) {
1355 MCSectionELF &Section = static_cast<MCSectionELF &>(SD.getSection());
1357 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1358 WriteZeros(Padding);
1360 // Remember the offset into the file for this section.
1361 uint64_t SecStart = OS.tell();
1363 const MCSymbol *SignatureSymbol = Section.getGroup();
1364 unsigned Type = Section.getType();
1365 if (Type == ELF::SHT_GROUP) {
1366 assert(SignatureSymbol);
1367 write(uint32_t(ELF::GRP_COMDAT));
1368 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1369 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1372 } else if (Type == ELF::SHT_REL || Type == ELF::SHT_RELA) {
1373 if (!ComputedSymtab) {
1374 // Compute symbol table information.
1375 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1376 ComputedSymtab = true;
1378 writeRelocations(Asm, *Section.getAssociatedSection());
1380 writeSectionData(Asm, SD, Layout);
1383 uint64_t SecEnd = OS.tell();
1384 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1386 if (Type == ELF::SHT_GROUP || Type == ELF::SHT_REL || Type == ELF::SHT_RELA)
1389 MCSectionELF *RelSection = createRelocationSection(Asm, Section);
1391 if (SignatureSymbol) {
1392 Asm.getOrCreateSymbolData(*SignatureSymbol);
1393 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1395 MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1396 GroupIdx = addToSectionTable(Group);
1397 MCSectionData *GroupD = &Asm.getOrCreateSectionData(*Group);
1398 GroupD->setAlignment(4);
1400 GroupMembers[SignatureSymbol].push_back(&Section);
1402 GroupMembers[SignatureSymbol].push_back(RelSection);
1405 SectionIndexMap[&Section] = addToSectionTable(&Section);
1407 SectionIndexMap[RelSection] = addToSectionTable(RelSection);
1410 if (!ComputedSymtab) {
1411 // Compute symbol table information.
1412 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1413 ComputedSymtab = true;
1416 WriteSymbolTable(Asm, Layout, SectionOffsets);
1419 uint64_t SecStart = OS.tell();
1420 const MCSectionELF *Sec = createStringTable(Ctx);
1421 uint64_t SecEnd = OS.tell();
1422 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1426 uint64_t SecStart = OS.tell();
1427 const MCSectionELF *Sec = createSectionHeaderStringTable();
1428 uint64_t SecEnd = OS.tell();
1429 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1432 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1433 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1434 WriteZeros(Padding);
1436 const unsigned SectionHeaderOffset = OS.tell();
1438 // ... then the section header table ...
1439 writeSectionHeader(Asm, Layout, SectionIndexMap, SectionOffsets);
1441 uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
1442 ? (uint16_t)ELF::SHN_UNDEF
1443 : SectionTable.size() + 1;
1444 if (sys::IsLittleEndianHost != IsLittleEndian)
1445 sys::swapByteOrder(NumSections);
1446 unsigned NumSectionsOffset;
1449 uint64_t Val = SectionHeaderOffset;
1450 if (sys::IsLittleEndianHost != IsLittleEndian)
1451 sys::swapByteOrder(Val);
1452 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1453 offsetof(ELF::Elf64_Ehdr, e_shoff));
1454 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1456 uint32_t Val = SectionHeaderOffset;
1457 if (sys::IsLittleEndianHost != IsLittleEndian)
1458 sys::swapByteOrder(Val);
1459 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1460 offsetof(ELF::Elf32_Ehdr, e_shoff));
1461 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1463 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1467 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1468 const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
1469 bool InSet, bool IsPCRel) const {
1472 if (::isWeak(SymA.getData()))
1475 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
1479 bool ELFObjectWriter::isWeak(const MCSymbol &Sym) const {
1480 const MCSymbolData &SD = Sym.getData();
1484 // It is invalid to replace a reference to a global in a comdat
1485 // with a reference to a local since out of comdat references
1486 // to a local are forbidden.
1487 // We could try to return false for more cases, like the reference
1488 // being in the same comdat or Sym being an alias to another global,
1489 // but it is not clear if it is worth the effort.
1490 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1493 if (!Sym.isInSection())
1496 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1497 return Sec.getGroup();
1500 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1501 raw_pwrite_stream &OS,
1502 bool IsLittleEndian) {
1503 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);