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/Object/StringTableBuilder.h"
32 #include "llvm/Support/Compression.h"
33 #include "llvm/Support/Debug.h"
34 #include "llvm/Support/Endian.h"
35 #include "llvm/Support/ELF.h"
36 #include "llvm/Support/ErrorHandling.h"
41 #define DEBUG_TYPE "reloc-info"
44 class FragmentWriter {
48 FragmentWriter(bool IsLittleEndian);
49 template <typename T> void write(MCDataFragment &F, T Val);
52 typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
54 class SymbolTableWriter {
56 FragmentWriter &FWriter;
58 SectionIndexMapTy &SectionIndexMap;
60 // The symbol .symtab fragment we are writting to.
61 MCDataFragment *SymtabF;
63 // .symtab_shndx fragment we are writting to.
64 MCDataFragment *ShndxF;
66 // The numbel of symbols written so far.
69 void createSymtabShndx();
71 template <typename T> void write(MCDataFragment &F, T Value);
74 SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit,
75 SectionIndexMapTy &SectionIndexMap,
76 MCDataFragment *SymtabF);
78 void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
79 uint8_t other, uint32_t shndx, bool Reserved);
82 struct ELFRelocationEntry {
83 uint64_t Offset; // Where is the relocation.
84 bool UseSymbol; // Relocate with a symbol, not the section.
86 const MCSymbol *Symbol; // The symbol to relocate with.
87 const MCSectionData *Section; // The section to relocate with.
89 unsigned Type; // The type of the relocation.
90 uint64_t Addend; // The addend to use.
92 ELFRelocationEntry(uint64_t Offset, const MCSymbol *Symbol, unsigned Type,
94 : Offset(Offset), UseSymbol(true), Symbol(Symbol), Type(Type),
97 ELFRelocationEntry(uint64_t Offset, const MCSectionData *Section,
98 unsigned Type, uint64_t Addend)
99 : Offset(Offset), UseSymbol(false), Section(Section), Type(Type),
103 class ELFObjectWriter : public MCObjectWriter {
104 FragmentWriter FWriter;
108 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
109 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
110 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
111 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data,
112 bool Used, bool Renamed);
113 static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc);
114 static bool IsELFMetaDataSection(const MCSectionData &SD);
115 static uint64_t DataSectionSize(const MCSectionData &SD);
116 static uint64_t GetSectionFileSize(const MCAsmLayout &Layout,
117 const MCSectionData &SD);
118 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout,
119 const MCSectionData &SD);
121 void WriteDataSectionData(MCAssembler &Asm,
122 const MCAsmLayout &Layout,
123 const MCSectionELF &Section);
125 /*static bool isFixupKindX86RIPRel(unsigned Kind) {
126 return Kind == X86::reloc_riprel_4byte ||
127 Kind == X86::reloc_riprel_4byte_movq_load;
130 /// ELFSymbolData - Helper struct for containing some precomputed
131 /// information on symbols.
132 struct ELFSymbolData {
133 MCSymbolData *SymbolData;
134 uint64_t StringIndex;
135 uint32_t SectionIndex;
138 // Support lexicographic sorting.
139 bool operator<(const ELFSymbolData &RHS) const {
140 return Name < RHS.Name;
144 /// The target specific ELF writer instance.
145 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
147 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
148 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
149 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
151 llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>>
153 StringTableBuilder ShStrTabBuilder;
156 /// @name Symbol Table Data
159 StringTableBuilder StrTabBuilder;
160 std::vector<uint64_t> FileSymbolData;
161 std::vector<ELFSymbolData> LocalSymbolData;
162 std::vector<ELFSymbolData> ExternalSymbolData;
163 std::vector<ELFSymbolData> UndefinedSymbolData;
169 // This holds the symbol table index of the last local symbol.
170 unsigned LastLocalSymbolIndex;
171 // This holds the .strtab section index.
172 unsigned StringTableIndex;
173 // This holds the .symtab section index.
174 unsigned SymbolTableIndex;
176 unsigned ShstrtabIndex;
179 // TargetObjectWriter wrappers.
180 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
181 bool hasRelocationAddend() const {
182 return TargetObjectWriter->hasRelocationAddend();
184 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
185 bool IsPCRel) const {
186 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
190 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_ostream &_OS,
192 : MCObjectWriter(_OS, IsLittleEndian), FWriter(IsLittleEndian),
193 TargetObjectWriter(MOTW), NeedsGOT(false) {}
195 virtual ~ELFObjectWriter();
197 void WriteWord(uint64_t W) {
204 template <typename T> void write(MCDataFragment &F, T Value) {
205 FWriter.write(F, Value);
208 void WriteHeader(const MCAssembler &Asm,
209 uint64_t SectionDataSize,
210 unsigned NumberOfSections);
212 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
213 const MCAsmLayout &Layout);
215 void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm,
216 const MCAsmLayout &Layout,
217 SectionIndexMapTy &SectionIndexMap);
219 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
220 const MCSymbolRefExpr *RefA,
221 const MCSymbolData *SD, uint64_t C,
222 unsigned Type) const;
224 void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
225 const MCFragment *Fragment, const MCFixup &Fixup,
226 MCValue Target, bool &IsPCRel,
227 uint64_t &FixedValue) override;
229 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
232 // Map from a group section to the signature symbol
233 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
234 // Map from a signature symbol to the group section
235 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
236 // Map from a section to the section with the relocations
237 typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy;
238 // Map from a section to its offset
239 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy;
241 /// Compute the symbol table data
243 /// \param Asm - The assembler.
244 /// \param SectionIndexMap - Maps a section to its index.
245 /// \param RevGroupMap - Maps a signature symbol to the group section.
246 /// \param NumRegularSections - Number of non-relocation sections.
247 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
248 const SectionIndexMapTy &SectionIndexMap,
249 RevGroupMapTy RevGroupMap,
250 unsigned NumRegularSections);
252 void ComputeIndexMap(MCAssembler &Asm,
253 SectionIndexMapTy &SectionIndexMap,
254 const RelMapTy &RelMap);
256 void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout,
259 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
261 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
262 const RelMapTy &RelMap);
264 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
265 SectionIndexMapTy &SectionIndexMap,
266 const RelMapTy &RelMap);
268 // Create the sections that show up in the symbol table. Currently
269 // those are the .note.GNU-stack section and the group sections.
270 void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
271 GroupMapTy &GroupMap,
272 RevGroupMapTy &RevGroupMap,
273 SectionIndexMapTy &SectionIndexMap,
274 const RelMapTy &RelMap);
276 void ExecutePostLayoutBinding(MCAssembler &Asm,
277 const MCAsmLayout &Layout) override;
279 void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap,
280 const MCAsmLayout &Layout,
281 const SectionIndexMapTy &SectionIndexMap,
282 const SectionOffsetMapTy &SectionOffsetMap);
284 void ComputeSectionOrder(MCAssembler &Asm,
285 std::vector<const MCSectionELF*> &Sections);
287 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
288 uint64_t Address, uint64_t Offset,
289 uint64_t Size, uint32_t Link, uint32_t Info,
290 uint64_t Alignment, uint64_t EntrySize);
292 void WriteRelocationsFragment(const MCAssembler &Asm,
294 const MCSectionData *SD);
297 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
298 const MCSymbolData &DataA,
299 const MCFragment &FB,
301 bool IsPCRel) const override;
303 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
304 void WriteSection(MCAssembler &Asm,
305 const SectionIndexMapTy &SectionIndexMap,
306 uint32_t GroupSymbolIndex,
307 uint64_t Offset, uint64_t Size, uint64_t Alignment,
308 const MCSectionELF &Section);
312 FragmentWriter::FragmentWriter(bool IsLittleEndian)
313 : IsLittleEndian(IsLittleEndian) {}
315 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
317 Val = support::endian::byte_swap<T, support::little>(Val);
319 Val = support::endian::byte_swap<T, support::big>(Val);
320 const char *Start = (const char *)&Val;
321 F.getContents().append(Start, Start + sizeof(T));
324 void SymbolTableWriter::createSymtabShndx() {
328 MCContext &Ctx = Asm.getContext();
329 const MCSectionELF *SymtabShndxSection =
330 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0,
331 SectionKind::getReadOnly(), 4, "");
332 MCSectionData *SymtabShndxSD =
333 &Asm.getOrCreateSectionData(*SymtabShndxSection);
334 SymtabShndxSD->setAlignment(4);
335 ShndxF = new MCDataFragment(SymtabShndxSD);
336 unsigned Index = SectionIndexMap.size() + 1;
337 SectionIndexMap[SymtabShndxSection] = Index;
339 for (unsigned I = 0; I < NumWritten; ++I)
340 write(*ShndxF, uint32_t(0));
343 template <typename T>
344 void SymbolTableWriter::write(MCDataFragment &F, T Value) {
345 FWriter.write(F, Value);
348 SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter,
350 SectionIndexMapTy &SectionIndexMap,
351 MCDataFragment *SymtabF)
352 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit),
353 SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr),
356 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
357 uint64_t size, uint8_t other,
358 uint32_t shndx, bool Reserved) {
359 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
366 write(*ShndxF, shndx);
368 write(*ShndxF, uint32_t(0));
371 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
373 raw_svector_ostream OS(SymtabF->getContents());
376 write(*SymtabF, name); // st_name
377 write(*SymtabF, info); // st_info
378 write(*SymtabF, other); // st_other
379 write(*SymtabF, Index); // st_shndx
380 write(*SymtabF, value); // st_value
381 write(*SymtabF, size); // st_size
383 write(*SymtabF, name); // st_name
384 write(*SymtabF, uint32_t(value)); // st_value
385 write(*SymtabF, uint32_t(size)); // st_size
386 write(*SymtabF, info); // st_info
387 write(*SymtabF, other); // st_other
388 write(*SymtabF, Index); // st_shndx
394 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
395 const MCFixupKindInfo &FKI =
396 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
398 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
401 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
405 case MCSymbolRefExpr::VK_GOT:
406 case MCSymbolRefExpr::VK_PLT:
407 case MCSymbolRefExpr::VK_GOTPCREL:
408 case MCSymbolRefExpr::VK_GOTOFF:
409 case MCSymbolRefExpr::VK_TPOFF:
410 case MCSymbolRefExpr::VK_TLSGD:
411 case MCSymbolRefExpr::VK_GOTTPOFF:
412 case MCSymbolRefExpr::VK_INDNTPOFF:
413 case MCSymbolRefExpr::VK_NTPOFF:
414 case MCSymbolRefExpr::VK_GOTNTPOFF:
415 case MCSymbolRefExpr::VK_TLSLDM:
416 case MCSymbolRefExpr::VK_DTPOFF:
417 case MCSymbolRefExpr::VK_TLSLD:
422 ELFObjectWriter::~ELFObjectWriter()
425 // Emit the ELF header.
426 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
427 uint64_t SectionDataSize,
428 unsigned NumberOfSections) {
434 // emitWord method behaves differently for ELF32 and ELF64, writing
435 // 4 bytes in the former and 8 in the latter.
437 Write8(0x7f); // e_ident[EI_MAG0]
438 Write8('E'); // e_ident[EI_MAG1]
439 Write8('L'); // e_ident[EI_MAG2]
440 Write8('F'); // e_ident[EI_MAG3]
442 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
445 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
447 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
449 Write8(TargetObjectWriter->getOSABI());
450 Write8(0); // e_ident[EI_ABIVERSION]
452 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
454 Write16(ELF::ET_REL); // e_type
456 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
458 Write32(ELF::EV_CURRENT); // e_version
459 WriteWord(0); // e_entry, no entry point in .o file
460 WriteWord(0); // e_phoff, no program header for .o
461 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
462 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes
464 // e_flags = whatever the target wants
465 Write32(Asm.getELFHeaderEFlags());
467 // e_ehsize = ELF header size
468 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
470 Write16(0); // e_phentsize = prog header entry size
471 Write16(0); // e_phnum = # prog header entries = 0
473 // e_shentsize = Section header entry size
474 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
476 // e_shnum = # of section header ents
477 if (NumberOfSections >= ELF::SHN_LORESERVE)
478 Write16(ELF::SHN_UNDEF);
480 Write16(NumberOfSections);
482 // e_shstrndx = Section # of '.shstrtab'
483 if (ShstrtabIndex >= ELF::SHN_LORESERVE)
484 Write16(ELF::SHN_XINDEX);
486 Write16(ShstrtabIndex);
489 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &OrigData,
490 const MCAsmLayout &Layout) {
491 MCSymbolData *Data = &OrigData;
492 if (Data->isCommon() && Data->isExternal())
493 return Data->getCommonAlignment();
495 const MCSymbol *Symbol = &Data->getSymbol();
496 MCAssembler &Asm = Layout.getAssembler();
497 bool IsThumb = Asm.isThumbFunc(Symbol);
499 // Given how we implement symver, we can end up with an symbol reference
500 // to an undefined symbol. Walk past it first.
501 if (Symbol->isVariable()) {
502 const MCExpr *Expr = Symbol->getVariableValue();
503 if (auto *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
504 if (Ref->getKind() == MCSymbolRefExpr::VK_None) {
505 Symbol = &Ref->getSymbol();
506 Data = &Asm.getOrCreateSymbolData(*Symbol);
511 if (!Symbol->isVariable() && !Data->getFragment())
514 uint64_t Res = Layout.getSymbolOffset(Data);
522 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
523 const MCAsmLayout &Layout) {
524 // The presence of symbol versions causes undefined symbols and
525 // versions declared with @@@ to be renamed.
527 for (MCSymbolData &OriginalData : Asm.symbols()) {
528 const MCSymbol &Alias = OriginalData.getSymbol();
531 if (!Alias.isVariable())
533 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
536 const MCSymbol &Symbol = Ref->getSymbol();
537 MCSymbolData &SD = Asm.getSymbolData(Symbol);
539 StringRef AliasName = Alias.getName();
540 size_t Pos = AliasName.find('@');
541 if (Pos == StringRef::npos)
544 // Aliases defined with .symvar copy the binding from the symbol they alias.
545 // This is the first place we are able to copy this information.
546 OriginalData.setExternal(SD.isExternal());
547 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
549 StringRef Rest = AliasName.substr(Pos);
550 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
553 // FIXME: produce a better error message.
554 if (Symbol.isUndefined() && Rest.startswith("@@") &&
555 !Rest.startswith("@@@"))
556 report_fatal_error("A @@ version cannot be undefined");
558 Renames.insert(std::make_pair(&Symbol, &Alias));
562 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
563 uint8_t Type = newType;
565 // Propagation rules:
566 // IFUNC > FUNC > OBJECT > NOTYPE
567 // TLS_OBJECT > OBJECT > NOTYPE
569 // dont let the new type degrade the old type
573 case ELF::STT_GNU_IFUNC:
574 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
575 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
576 Type = ELF::STT_GNU_IFUNC;
579 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
580 Type == ELF::STT_TLS)
581 Type = ELF::STT_FUNC;
583 case ELF::STT_OBJECT:
584 if (Type == ELF::STT_NOTYPE)
585 Type = ELF::STT_OBJECT;
588 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
589 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
597 static const MCSymbol *getBaseSymbol(const MCAsmLayout &Layout,
598 const MCSymbol &Symbol) {
599 if (!Symbol.isVariable())
602 const MCExpr *Expr = Symbol.getVariableValue();
604 if (!Expr->EvaluateAsValue(Value, &Layout))
605 llvm_unreachable("Invalid Expression");
606 const MCSymbolRefExpr *RefB = Value.getSymB();
608 Layout.getAssembler().getContext().FatalError(
609 SMLoc(), Twine("symbol '") + RefB->getSymbol().getName() +
610 "' could not be evaluated in a subtraction expression");
612 const MCSymbolRefExpr *A = Value.getSymA();
615 return getBaseSymbol(Layout, A->getSymbol());
618 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
619 const MCAsmLayout &Layout) {
620 MCSymbolData &OrigData = *MSD.SymbolData;
621 assert((!OrigData.getFragment() ||
622 (&OrigData.getFragment()->getParent()->getSection() ==
623 &OrigData.getSymbol().getSection())) &&
624 "The symbol's section doesn't match the fragment's symbol");
625 const MCSymbol *Base = getBaseSymbol(Layout, OrigData.getSymbol());
627 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
629 bool IsReserved = !Base || OrigData.isCommon();
631 // Binding and Type share the same byte as upper and lower nibbles
632 uint8_t Binding = MCELF::GetBinding(OrigData);
633 uint8_t Type = MCELF::GetType(OrigData);
634 MCSymbolData *BaseSD = nullptr;
636 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
637 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
639 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
641 // Other and Visibility share the same byte with Visibility using the lower
643 uint8_t Visibility = MCELF::GetVisibility(OrigData);
644 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
647 uint64_t Value = SymbolValue(OrigData, Layout);
650 const MCExpr *ESize = OrigData.getSize();
652 ESize = BaseSD->getSize();
656 if (!ESize->EvaluateAsAbsolute(Res, Layout))
657 report_fatal_error("Size expression must be absolute.");
661 // Write out the symbol table entry
662 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
663 MSD.SectionIndex, IsReserved);
666 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF,
668 const MCAsmLayout &Layout,
669 SectionIndexMapTy &SectionIndexMap) {
670 // The string table must be emitted first because we need the index
671 // into the string table for all the symbol names.
673 // FIXME: Make sure the start of the symbol table is aligned.
675 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF);
677 // The first entry is the undefined symbol entry.
678 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
680 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
681 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
682 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
685 // Write the symbol table entries.
686 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
688 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
689 ELFSymbolData &MSD = LocalSymbolData[i];
690 WriteSymbol(Writer, MSD, Layout);
693 // Write out a symbol table entry for each regular section.
694 for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e;
696 const MCSectionELF &Section =
697 static_cast<const MCSectionELF&>(i->getSection());
698 if (Section.getType() == ELF::SHT_RELA ||
699 Section.getType() == ELF::SHT_REL ||
700 Section.getType() == ELF::SHT_STRTAB ||
701 Section.getType() == ELF::SHT_SYMTAB ||
702 Section.getType() == ELF::SHT_SYMTAB_SHNDX)
704 Writer.writeSymbol(0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT,
705 SectionIndexMap.lookup(&Section), false);
706 LastLocalSymbolIndex++;
709 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
710 ELFSymbolData &MSD = ExternalSymbolData[i];
711 MCSymbolData &Data = *MSD.SymbolData;
712 assert(((Data.getFlags() & ELF_STB_Global) ||
713 (Data.getFlags() & ELF_STB_Weak)) &&
714 "External symbol requires STB_GLOBAL or STB_WEAK flag");
715 WriteSymbol(Writer, MSD, Layout);
716 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
717 LastLocalSymbolIndex++;
720 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
721 ELFSymbolData &MSD = UndefinedSymbolData[i];
722 MCSymbolData &Data = *MSD.SymbolData;
723 WriteSymbol(Writer, MSD, Layout);
724 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
725 LastLocalSymbolIndex++;
729 // It is always valid to create a relocation with a symbol. It is preferable
730 // to use a relocation with a section if that is possible. Using the section
731 // allows us to omit some local symbols from the symbol table.
732 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
733 const MCSymbolRefExpr *RefA,
734 const MCSymbolData *SD,
736 unsigned Type) const {
737 // A PCRel relocation to an absolute value has no symbol (or section). We
738 // represent that with a relocation to a null section.
742 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
746 // The .odp creation emits a relocation against the symbol ".TOC." which
747 // create a R_PPC64_TOC relocation. However the relocation symbol name
748 // in final object creation should be NULL, since the symbol does not
749 // really exist, it is just the reference to TOC base for the current
750 // object file. Since the symbol is undefined, returning false results
751 // in a relocation with a null section which is the desired result.
752 case MCSymbolRefExpr::VK_PPC_TOCBASE:
755 // These VariantKind cause the relocation to refer to something other than
756 // the symbol itself, like a linker generated table. Since the address of
757 // symbol is not relevant, we cannot replace the symbol with the
758 // section and patch the difference in the addend.
759 case MCSymbolRefExpr::VK_GOT:
760 case MCSymbolRefExpr::VK_PLT:
761 case MCSymbolRefExpr::VK_GOTPCREL:
762 case MCSymbolRefExpr::VK_Mips_GOT:
763 case MCSymbolRefExpr::VK_PPC_GOT_LO:
764 case MCSymbolRefExpr::VK_PPC_GOT_HI:
765 case MCSymbolRefExpr::VK_PPC_GOT_HA:
769 // An undefined symbol is not in any section, so the relocation has to point
770 // to the symbol itself.
771 const MCSymbol &Sym = SD->getSymbol();
772 if (Sym.isUndefined())
775 unsigned Binding = MCELF::GetBinding(*SD);
778 llvm_unreachable("Invalid Binding");
782 // If the symbol is weak, it might be overridden by a symbol in another
783 // file. The relocation has to point to the symbol so that the linker
786 case ELF::STB_GLOBAL:
787 // Global ELF symbols can be preempted by the dynamic linker. The relocation
788 // has to point to the symbol for a reason analogous to the STB_WEAK case.
792 // If a relocation points to a mergeable section, we have to be careful.
793 // If the offset is zero, a relocation with the section will encode the
794 // same information. With a non-zero offset, the situation is different.
795 // For example, a relocation can point 42 bytes past the end of a string.
796 // If we change such a relocation to use the section, the linker would think
797 // that it pointed to another string and subtracting 42 at runtime will
798 // produce the wrong value.
799 auto &Sec = cast<MCSectionELF>(Sym.getSection());
800 unsigned Flags = Sec.getFlags();
801 if (Flags & ELF::SHF_MERGE) {
805 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
806 // only handle section relocations to mergeable sections if using RELA.
807 if (!hasRelocationAddend())
811 // Most TLS relocations use a got, so they need the symbol. Even those that
812 // are just an offset (@tpoff), require a symbol in some linkers (gold,
814 if (Flags & ELF::SHF_TLS)
817 // If the symbol is a thumb function the final relocation must set the lowest
818 // bit. With a symbol that is done by just having the symbol have that bit
819 // set, so we would lose the bit if we relocated with the section.
820 // FIXME: We could use the section but add the bit to the relocation value.
821 if (Asm.isThumbFunc(&Sym))
824 if (TargetObjectWriter->needsRelocateWithSymbol(Type))
829 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
830 const MCAsmLayout &Layout,
831 const MCFragment *Fragment,
832 const MCFixup &Fixup,
835 uint64_t &FixedValue) {
836 const MCSectionData *FixupSection = Fragment->getParent();
837 uint64_t C = Target.getConstant();
838 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
840 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
841 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
842 "Should not have constructed this");
844 // Let A, B and C being the components of Target and R be the location of
845 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
846 // If it is pcrel, we want to compute (A - B + C - R).
848 // In general, ELF has no relocations for -B. It can only represent (A + C)
849 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
850 // replace B to implement it: (A - R - K + C)
852 Asm.getContext().FatalError(
854 "No relocation available to represent this relative expression");
856 const MCSymbol &SymB = RefB->getSymbol();
858 if (SymB.isUndefined())
859 Asm.getContext().FatalError(
861 Twine("symbol '") + SymB.getName() +
862 "' can not be undefined in a subtraction expression");
864 assert(!SymB.isAbsolute() && "Should have been folded");
865 const MCSection &SecB = SymB.getSection();
866 if (&SecB != &FixupSection->getSection())
867 Asm.getContext().FatalError(
868 Fixup.getLoc(), "Cannot represent a difference across sections");
870 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
871 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
872 uint64_t K = SymBOffset - FixupOffset;
877 // We either rejected the fixup or folded B into C at this point.
878 const MCSymbolRefExpr *RefA = Target.getSymA();
879 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
880 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
882 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
883 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
884 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
885 C += Layout.getSymbolOffset(SymAD);
888 if (hasRelocationAddend()) {
895 // FIXME: What is this!?!?
896 MCSymbolRefExpr::VariantKind Modifier =
897 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
898 if (RelocNeedsGOT(Modifier))
901 if (!RelocateWithSymbol) {
902 const MCSection *SecA =
903 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
904 const MCSectionData *SecAD = SecA ? &Asm.getSectionData(*SecA) : nullptr;
905 ELFRelocationEntry Rec(FixupOffset, SecAD, Type, Addend);
906 Relocations[FixupSection].push_back(Rec);
911 if (const MCSymbol *R = Renames.lookup(SymA))
914 if (RefA->getKind() == MCSymbolRefExpr::VK_WEAKREF)
915 WeakrefUsedInReloc.insert(SymA);
917 UsedInReloc.insert(SymA);
919 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
920 Relocations[FixupSection].push_back(Rec);
926 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
928 const MCSymbolData &SD = Asm.getSymbolData(*S);
929 return SD.getIndex();
932 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
933 const MCSymbolData &Data, bool Used,
935 const MCSymbol &Symbol = Data.getSymbol();
936 if (Symbol.isVariable()) {
937 const MCExpr *Expr = Symbol.getVariableValue();
938 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
939 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
950 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
953 if (Symbol.isVariable()) {
954 const MCSymbol *Base = getBaseSymbol(Layout, Symbol);
955 if (Base && Base->isUndefined())
959 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
960 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
963 if (Symbol.isTemporary())
969 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
970 if (Data.isExternal())
973 const MCSymbol &Symbol = Data.getSymbol();
974 if (Symbol.isDefined())
983 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
984 SectionIndexMapTy &SectionIndexMap,
985 const RelMapTy &RelMap) {
987 for (MCAssembler::iterator it = Asm.begin(),
988 ie = Asm.end(); it != ie; ++it) {
989 const MCSectionELF &Section =
990 static_cast<const MCSectionELF &>(it->getSection());
991 if (Section.getType() != ELF::SHT_GROUP)
993 SectionIndexMap[&Section] = Index++;
996 for (MCAssembler::iterator it = Asm.begin(),
997 ie = Asm.end(); it != ie; ++it) {
998 const MCSectionELF &Section =
999 static_cast<const MCSectionELF &>(it->getSection());
1000 if (Section.getType() == ELF::SHT_GROUP ||
1001 Section.getType() == ELF::SHT_REL ||
1002 Section.getType() == ELF::SHT_RELA)
1004 SectionIndexMap[&Section] = Index++;
1005 const MCSectionELF *RelSection = RelMap.lookup(&Section);
1007 SectionIndexMap[RelSection] = Index++;
1012 ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
1013 const SectionIndexMapTy &SectionIndexMap,
1014 RevGroupMapTy RevGroupMap,
1015 unsigned NumRegularSections) {
1016 // FIXME: Is this the correct place to do this?
1017 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
1019 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
1020 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
1021 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
1022 Data.setExternal(true);
1023 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
1026 // Add the data for the symbols.
1027 for (MCSymbolData &SD : Asm.symbols()) {
1028 const MCSymbol &Symbol = SD.getSymbol();
1030 bool Used = UsedInReloc.count(&Symbol);
1031 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
1032 bool isSignature = RevGroupMap.count(&Symbol);
1034 if (!isInSymtab(Layout, SD,
1035 Used || WeakrefUsed || isSignature,
1036 Renames.count(&Symbol)))
1040 MSD.SymbolData = &SD;
1041 const MCSymbol *BaseSymbol = getBaseSymbol(Layout, Symbol);
1043 // Undefined symbols are global, but this is the first place we
1044 // are able to set it.
1045 bool Local = isLocal(SD, Used);
1046 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1048 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1049 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1050 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1054 MSD.SectionIndex = ELF::SHN_ABS;
1055 } else if (SD.isCommon()) {
1057 MSD.SectionIndex = ELF::SHN_COMMON;
1058 } else if (BaseSymbol->isUndefined()) {
1059 if (isSignature && !Used)
1060 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]);
1062 MSD.SectionIndex = ELF::SHN_UNDEF;
1063 if (!Used && WeakrefUsed)
1064 MCELF::SetBinding(SD, ELF::STB_WEAK);
1066 const MCSectionELF &Section =
1067 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1068 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1069 assert(MSD.SectionIndex && "Invalid section index!");
1072 // The @@@ in symbol version is replaced with @ in undefined symbols and
1073 // @@ in defined ones.
1074 StringRef Name = Symbol.getName();
1075 SmallString<32> Buf;
1076 size_t Pos = Name.find("@@@");
1077 if (Pos != StringRef::npos) {
1078 Buf += Name.substr(0, Pos);
1079 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1080 Buf += Name.substr(Pos + Skip);
1083 MSD.Name = StrTabBuilder.add(Name);
1085 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1086 UndefinedSymbolData.push_back(MSD);
1088 LocalSymbolData.push_back(MSD);
1090 ExternalSymbolData.push_back(MSD);
1093 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1094 StrTabBuilder.add(*i);
1096 StrTabBuilder.finalize();
1098 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1099 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1101 for (ELFSymbolData& MSD : LocalSymbolData)
1102 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1103 for (ELFSymbolData& MSD : ExternalSymbolData)
1104 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1105 for (ELFSymbolData& MSD : UndefinedSymbolData)
1106 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1108 // Symbols are required to be in lexicographic order.
1109 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1110 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1111 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1113 // Set the symbol indices. Local symbols must come before all other
1114 // symbols with non-local bindings.
1115 unsigned Index = FileSymbolData.size() + 1;
1116 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1117 LocalSymbolData[i].SymbolData->setIndex(Index++);
1119 Index += NumRegularSections;
1121 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1122 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1123 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1124 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1127 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm,
1128 MCAsmLayout &Layout,
1130 for (MCAssembler::const_iterator it = Asm.begin(),
1131 ie = Asm.end(); it != ie; ++it) {
1132 const MCSectionData &SD = *it;
1133 if (Relocations[&SD].empty())
1136 MCContext &Ctx = Asm.getContext();
1137 const MCSectionELF &Section =
1138 static_cast<const MCSectionELF&>(SD.getSection());
1140 const StringRef SectionName = Section.getSectionName();
1141 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1142 RelaSectionName += SectionName;
1145 if (hasRelocationAddend())
1146 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1148 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1151 StringRef Group = "";
1152 if (Section.getFlags() & ELF::SHF_GROUP) {
1153 Flags = ELF::SHF_GROUP;
1154 Group = Section.getGroup()->getName();
1157 const MCSectionELF *RelaSection =
1158 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ?
1159 ELF::SHT_RELA : ELF::SHT_REL, Flags,
1160 SectionKind::getReadOnly(),
1162 RelMap[&Section] = RelaSection;
1163 Asm.getOrCreateSectionData(*RelaSection);
1167 static SmallVector<char, 128>
1168 getUncompressedData(MCAsmLayout &Layout,
1169 MCSectionData::FragmentListType &Fragments) {
1170 SmallVector<char, 128> UncompressedData;
1171 for (const MCFragment &F : Fragments) {
1172 const SmallVectorImpl<char> *Contents;
1173 switch (F.getKind()) {
1174 case MCFragment::FT_Data:
1175 Contents = &cast<MCDataFragment>(F).getContents();
1177 case MCFragment::FT_Dwarf:
1178 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1180 case MCFragment::FT_DwarfFrame:
1181 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1185 "Not expecting any other fragment types in a debug_* section");
1187 UncompressedData.append(Contents->begin(), Contents->end());
1189 return UncompressedData;
1192 // Include the debug info compression header:
1193 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1194 // useful for consumers to preallocate a buffer to decompress into.
1196 prependCompressionHeader(uint64_t Size,
1197 SmallVectorImpl<char> &CompressedContents) {
1198 static const StringRef Magic = "ZLIB";
1199 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1201 if (sys::IsLittleEndianHost)
1202 Size = sys::SwapByteOrder(Size);
1203 CompressedContents.insert(CompressedContents.begin(),
1204 Magic.size() + sizeof(Size), 0);
1205 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1206 std::copy(reinterpret_cast<char *>(&Size),
1207 reinterpret_cast<char *>(&Size + 1),
1208 CompressedContents.begin() + Magic.size());
1212 // Return a single fragment containing the compressed contents of the whole
1213 // section. Null if the section was not compressed for any reason.
1214 static std::unique_ptr<MCDataFragment>
1215 getCompressedFragment(MCAsmLayout &Layout,
1216 MCSectionData::FragmentListType &Fragments) {
1217 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1219 // Gather the uncompressed data from all the fragments, recording the
1220 // alignment fragment, if seen, and any fixups.
1221 SmallVector<char, 128> UncompressedData =
1222 getUncompressedData(Layout, Fragments);
1224 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1226 zlib::Status Success = zlib::compress(
1227 StringRef(UncompressedData.data(), UncompressedData.size()),
1228 CompressedContents);
1229 if (Success != zlib::StatusOK)
1232 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1235 return CompressedFragment;
1238 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1241 static void UpdateSymbols(const MCAsmLayout &Layout,
1242 const std::vector<MCSymbolData *> &Symbols,
1243 MCFragment &NewFragment) {
1244 for (MCSymbolData *Sym : Symbols) {
1245 Sym->setOffset(Sym->getOffset() +
1246 Layout.getFragmentOffset(Sym->getFragment()));
1247 Sym->setFragment(&NewFragment);
1251 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1252 const DefiningSymbolMap &DefiningSymbols,
1253 const MCSectionELF &Section,
1254 MCSectionData &SD) {
1255 StringRef SectionName = Section.getSectionName();
1256 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1258 std::unique_ptr<MCDataFragment> CompressedFragment =
1259 getCompressedFragment(Layout, Fragments);
1261 // Leave the section as-is if the fragments could not be compressed.
1262 if (!CompressedFragment)
1265 // Update the fragment+offsets of any symbols referring to fragments in this
1266 // section to refer to the new fragment.
1267 auto I = DefiningSymbols.find(&SD);
1268 if (I != DefiningSymbols.end())
1269 UpdateSymbols(Layout, I->second, *CompressedFragment);
1271 // Invalidate the layout for the whole section since it will have new and
1272 // different fragments now.
1273 Layout.invalidateFragmentsFrom(&Fragments.front());
1276 // Complete the initialization of the new fragment
1277 CompressedFragment->setParent(&SD);
1278 CompressedFragment->setLayoutOrder(0);
1279 Fragments.push_back(CompressedFragment.release());
1281 // Rename from .debug_* to .zdebug_*
1282 Asm.getContext().renameELFSection(&Section,
1283 (".z" + SectionName.drop_front(1)).str());
1286 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1287 MCAsmLayout &Layout) {
1288 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1291 DefiningSymbolMap DefiningSymbols;
1293 for (MCSymbolData &SD : Asm.symbols())
1294 if (MCFragment *F = SD.getFragment())
1295 DefiningSymbols[F->getParent()].push_back(&SD);
1297 for (MCSectionData &SD : Asm) {
1298 const MCSectionELF &Section =
1299 static_cast<const MCSectionELF &>(SD.getSection());
1300 StringRef SectionName = Section.getSectionName();
1302 // Compressing debug_frame requires handling alignment fragments which is
1303 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1304 // for writing to arbitrary buffers) for little benefit.
1305 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1308 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1312 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
1313 const RelMapTy &RelMap) {
1314 for (MCAssembler::const_iterator it = Asm.begin(),
1315 ie = Asm.end(); it != ie; ++it) {
1316 const MCSectionData &SD = *it;
1317 const MCSectionELF &Section =
1318 static_cast<const MCSectionELF&>(SD.getSection());
1320 const MCSectionELF *RelaSection = RelMap.lookup(&Section);
1323 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
1324 RelaSD.setAlignment(is64Bit() ? 8 : 4);
1326 MCDataFragment *F = new MCDataFragment(&RelaSD);
1327 WriteRelocationsFragment(Asm, F, &*it);
1331 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1332 uint64_t Flags, uint64_t Address,
1333 uint64_t Offset, uint64_t Size,
1334 uint32_t Link, uint32_t Info,
1336 uint64_t EntrySize) {
1337 Write32(Name); // sh_name: index into string table
1338 Write32(Type); // sh_type
1339 WriteWord(Flags); // sh_flags
1340 WriteWord(Address); // sh_addr
1341 WriteWord(Offset); // sh_offset
1342 WriteWord(Size); // sh_size
1343 Write32(Link); // sh_link
1344 Write32(Info); // sh_info
1345 WriteWord(Alignment); // sh_addralign
1346 WriteWord(EntrySize); // sh_entsize
1349 // ELF doesn't require relocations to be in any order. We sort by the r_offset,
1350 // just to match gnu as for easier comparison. The use type is an arbitrary way
1351 // of making the sort deterministic.
1352 static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) {
1353 const ELFRelocationEntry &A = *AP;
1354 const ELFRelocationEntry &B = *BP;
1355 if (A.Offset != B.Offset)
1356 return B.Offset - A.Offset;
1357 if (B.Type != A.Type)
1358 return A.Type - B.Type;
1359 llvm_unreachable("ELFRelocs might be unstable!");
1362 static void sortRelocs(const MCAssembler &Asm,
1363 std::vector<ELFRelocationEntry> &Relocs) {
1364 array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
1367 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1369 const MCSectionData *SD) {
1370 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1372 sortRelocs(Asm, Relocs);
1374 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1375 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1378 if (Entry.UseSymbol) {
1379 Index = getSymbolIndexInSymbolTable(Asm, Entry.Symbol);
1381 const MCSectionData *Sec = Entry.Section;
1383 Index = Sec->getOrdinal() + FileSymbolData.size() +
1384 LocalSymbolData.size() + 1;
1390 write(*F, Entry.Offset);
1391 if (TargetObjectWriter->isN64()) {
1392 write(*F, uint32_t(Index));
1394 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1395 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1396 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1397 write(*F, TargetObjectWriter->getRType(Entry.Type));
1399 struct ELF::Elf64_Rela ERE64;
1400 ERE64.setSymbolAndType(Index, Entry.Type);
1401 write(*F, ERE64.r_info);
1403 if (hasRelocationAddend())
1404 write(*F, Entry.Addend);
1406 write(*F, uint32_t(Entry.Offset));
1408 struct ELF::Elf32_Rela ERE32;
1409 ERE32.setSymbolAndType(Index, Entry.Type);
1410 write(*F, ERE32.r_info);
1412 if (hasRelocationAddend())
1413 write(*F, uint32_t(Entry.Addend));
1418 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
1419 MCAsmLayout &Layout,
1420 SectionIndexMapTy &SectionIndexMap,
1421 const RelMapTy &RelMap) {
1422 MCContext &Ctx = Asm.getContext();
1425 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1427 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1428 const MCSectionELF *ShstrtabSection =
1429 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
1430 SectionKind::getReadOnly());
1431 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1432 ShstrtabSD.setAlignment(1);
1434 const MCSectionELF *SymtabSection =
1435 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1436 SectionKind::getReadOnly(),
1438 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1439 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1441 const MCSectionELF *StrtabSection;
1442 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
1443 SectionKind::getReadOnly());
1444 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1445 StrtabSD.setAlignment(1);
1447 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1449 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection);
1450 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection);
1451 StringTableIndex = SectionIndexMap.lookup(StrtabSection);
1454 F = new MCDataFragment(&SymtabSD);
1455 WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
1457 F = new MCDataFragment(&StrtabSD);
1458 F->getContents().append(StrTabBuilder.data().begin(),
1459 StrTabBuilder.data().end());
1461 F = new MCDataFragment(&ShstrtabSD);
1463 // Section header string table.
1464 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1465 const MCSectionELF &Section =
1466 static_cast<const MCSectionELF&>(it->getSection());
1467 ShStrTabBuilder.add(Section.getSectionName());
1469 ShStrTabBuilder.finalize();
1470 F->getContents().append(ShStrTabBuilder.data().begin(),
1471 ShStrTabBuilder.data().end());
1474 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm,
1475 MCAsmLayout &Layout,
1476 GroupMapTy &GroupMap,
1477 RevGroupMapTy &RevGroupMap,
1478 SectionIndexMapTy &SectionIndexMap,
1479 const RelMapTy &RelMap) {
1480 // Create the .note.GNU-stack section if needed.
1481 MCContext &Ctx = Asm.getContext();
1482 if (Asm.getNoExecStack()) {
1483 const MCSectionELF *GnuStackSection =
1484 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0,
1485 SectionKind::getReadOnly());
1486 Asm.getOrCreateSectionData(*GnuStackSection);
1490 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1492 const MCSectionELF &Section =
1493 static_cast<const MCSectionELF&>(it->getSection());
1494 if (!(Section.getFlags() & ELF::SHF_GROUP))
1497 const MCSymbol *SignatureSymbol = Section.getGroup();
1498 Asm.getOrCreateSymbolData(*SignatureSymbol);
1499 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1501 Group = Ctx.CreateELFGroupSection();
1502 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1503 Data.setAlignment(4);
1504 MCDataFragment *F = new MCDataFragment(&Data);
1505 write(*F, uint32_t(ELF::GRP_COMDAT));
1507 GroupMap[Group] = SignatureSymbol;
1510 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1512 // Add sections to the groups
1513 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1515 const MCSectionELF &Section =
1516 static_cast<const MCSectionELF&>(it->getSection());
1517 if (!(Section.getFlags() & ELF::SHF_GROUP))
1519 const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1520 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1521 // FIXME: we could use the previous fragment
1522 MCDataFragment *F = new MCDataFragment(&Data);
1523 uint32_t Index = SectionIndexMap.lookup(&Section);
1528 void ELFObjectWriter::WriteSection(MCAssembler &Asm,
1529 const SectionIndexMapTy &SectionIndexMap,
1530 uint32_t GroupSymbolIndex,
1531 uint64_t Offset, uint64_t Size,
1533 const MCSectionELF &Section) {
1534 uint64_t sh_link = 0;
1535 uint64_t sh_info = 0;
1537 switch(Section.getType()) {
1538 case ELF::SHT_DYNAMIC:
1539 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1544 case ELF::SHT_RELA: {
1545 const MCSectionELF *SymtabSection;
1546 const MCSectionELF *InfoSection;
1547 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB,
1549 SectionKind::getReadOnly());
1550 sh_link = SectionIndexMap.lookup(SymtabSection);
1551 assert(sh_link && ".symtab not found");
1553 // Remove ".rel" and ".rela" prefixes.
1554 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1555 StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1556 StringRef GroupName =
1557 Section.getGroup() ? Section.getGroup()->getName() : "";
1559 InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS,
1560 0, SectionKind::getReadOnly(),
1562 sh_info = SectionIndexMap.lookup(InfoSection);
1566 case ELF::SHT_SYMTAB:
1567 case ELF::SHT_DYNSYM:
1568 sh_link = StringTableIndex;
1569 sh_info = LastLocalSymbolIndex;
1572 case ELF::SHT_SYMTAB_SHNDX:
1573 sh_link = SymbolTableIndex;
1576 case ELF::SHT_PROGBITS:
1577 case ELF::SHT_STRTAB:
1578 case ELF::SHT_NOBITS:
1581 case ELF::SHT_ARM_ATTRIBUTES:
1582 case ELF::SHT_INIT_ARRAY:
1583 case ELF::SHT_FINI_ARRAY:
1584 case ELF::SHT_PREINIT_ARRAY:
1585 case ELF::SHT_X86_64_UNWIND:
1586 case ELF::SHT_MIPS_REGINFO:
1587 case ELF::SHT_MIPS_OPTIONS:
1591 case ELF::SHT_GROUP:
1592 sh_link = SymbolTableIndex;
1593 sh_info = GroupSymbolIndex;
1597 assert(0 && "FIXME: sh_type value not supported!");
1601 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1602 Section.getType() == ELF::SHT_ARM_EXIDX) {
1603 StringRef SecName(Section.getSectionName());
1604 if (SecName == ".ARM.exidx") {
1605 sh_link = SectionIndexMap.lookup(
1606 Asm.getContext().getELFSection(".text",
1608 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC,
1609 SectionKind::getText()));
1610 } else if (SecName.startswith(".ARM.exidx")) {
1611 StringRef GroupName =
1612 Section.getGroup() ? Section.getGroup()->getName() : "";
1613 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
1614 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS,
1615 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText(), 0,
1620 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1622 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1623 Alignment, Section.getEntrySize());
1626 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1627 return SD.getOrdinal() == ~UINT32_C(0) &&
1628 !SD.getSection().isVirtualSection();
1631 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1633 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1635 const MCFragment &F = *i;
1636 assert(F.getKind() == MCFragment::FT_Data);
1637 Ret += cast<MCDataFragment>(F).getContents().size();
1642 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
1643 const MCSectionData &SD) {
1644 if (IsELFMetaDataSection(SD))
1645 return DataSectionSize(SD);
1646 return Layout.getSectionFileSize(&SD);
1649 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1650 const MCSectionData &SD) {
1651 if (IsELFMetaDataSection(SD))
1652 return DataSectionSize(SD);
1653 return Layout.getSectionAddressSize(&SD);
1656 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
1657 const MCAsmLayout &Layout,
1658 const MCSectionELF &Section) {
1659 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1661 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1662 WriteZeros(Padding);
1664 if (IsELFMetaDataSection(SD)) {
1665 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1667 const MCFragment &F = *i;
1668 assert(F.getKind() == MCFragment::FT_Data);
1669 WriteBytes(cast<MCDataFragment>(F).getContents());
1672 Asm.writeSectionData(&SD, Layout);
1676 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm,
1677 const GroupMapTy &GroupMap,
1678 const MCAsmLayout &Layout,
1679 const SectionIndexMapTy &SectionIndexMap,
1680 const SectionOffsetMapTy &SectionOffsetMap) {
1681 const unsigned NumSections = Asm.size() + 1;
1683 std::vector<const MCSectionELF*> Sections;
1684 Sections.resize(NumSections - 1);
1686 for (SectionIndexMapTy::const_iterator i=
1687 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
1688 const std::pair<const MCSectionELF*, uint32_t> &p = *i;
1689 Sections[p.second - 1] = p.first;
1692 // Null section first.
1693 uint64_t FirstSectionSize =
1694 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
1695 uint32_t FirstSectionLink =
1696 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1697 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1699 for (unsigned i = 0; i < NumSections - 1; ++i) {
1700 const MCSectionELF &Section = *Sections[i];
1701 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1702 uint32_t GroupSymbolIndex;
1703 if (Section.getType() != ELF::SHT_GROUP)
1704 GroupSymbolIndex = 0;
1706 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1707 GroupMap.lookup(&Section));
1709 uint64_t Size = GetSectionAddressSize(Layout, SD);
1711 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex,
1712 SectionOffsetMap.lookup(&Section), Size,
1713 SD.getAlignment(), Section);
1717 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
1718 std::vector<const MCSectionELF*> &Sections) {
1719 for (MCAssembler::iterator it = Asm.begin(),
1720 ie = Asm.end(); it != ie; ++it) {
1721 const MCSectionELF &Section =
1722 static_cast<const MCSectionELF &>(it->getSection());
1723 if (Section.getType() == ELF::SHT_GROUP)
1724 Sections.push_back(&Section);
1727 for (MCAssembler::iterator it = Asm.begin(),
1728 ie = Asm.end(); it != ie; ++it) {
1729 const MCSectionELF &Section =
1730 static_cast<const MCSectionELF &>(it->getSection());
1731 if (Section.getType() != ELF::SHT_GROUP &&
1732 Section.getType() != ELF::SHT_REL &&
1733 Section.getType() != ELF::SHT_RELA)
1734 Sections.push_back(&Section);
1737 for (MCAssembler::iterator it = Asm.begin(),
1738 ie = Asm.end(); it != ie; ++it) {
1739 const MCSectionELF &Section =
1740 static_cast<const MCSectionELF &>(it->getSection());
1741 if (Section.getType() == ELF::SHT_REL ||
1742 Section.getType() == ELF::SHT_RELA)
1743 Sections.push_back(&Section);
1747 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1748 const MCAsmLayout &Layout) {
1749 GroupMapTy GroupMap;
1750 RevGroupMapTy RevGroupMap;
1751 SectionIndexMapTy SectionIndexMap;
1753 unsigned NumUserSections = Asm.size();
1755 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1757 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap;
1758 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1760 const unsigned NumUserAndRelocSections = Asm.size();
1761 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
1762 RevGroupMap, SectionIndexMap, RelMap);
1763 const unsigned AllSections = Asm.size();
1764 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections;
1766 unsigned NumRegularSections = NumUserSections + NumIndexedSections;
1768 // Compute symbol table information.
1769 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
1770 NumRegularSections);
1772 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1774 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1775 const_cast<MCAsmLayout&>(Layout),
1779 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1780 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
1781 sizeof(ELF::Elf32_Ehdr);
1782 uint64_t FileOff = HeaderSize;
1784 std::vector<const MCSectionELF*> Sections;
1785 ComputeSectionOrder(Asm, Sections);
1786 unsigned NumSections = Sections.size();
1787 SectionOffsetMapTy SectionOffsetMap;
1788 for (unsigned i = 0; i < NumRegularSections + 1; ++i) {
1789 const MCSectionELF &Section = *Sections[i];
1790 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1792 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1794 // Remember the offset into the file for this section.
1795 SectionOffsetMap[&Section] = FileOff;
1797 // Get the size of the section in the output file (including padding).
1798 FileOff += GetSectionFileSize(Layout, SD);
1801 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1803 const unsigned SectionHeaderOffset = FileOff - HeaderSize;
1805 uint64_t SectionHeaderEntrySize = is64Bit() ?
1806 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr);
1807 FileOff += (NumSections + 1) * SectionHeaderEntrySize;
1809 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) {
1810 const MCSectionELF &Section = *Sections[i];
1811 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1813 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1815 // Remember the offset into the file for this section.
1816 SectionOffsetMap[&Section] = FileOff;
1818 // Get the size of the section in the output file (including padding).
1819 FileOff += GetSectionFileSize(Layout, SD);
1822 // Write out the ELF header ...
1823 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
1825 // ... then the regular sections ...
1826 // + because of .shstrtab
1827 for (unsigned i = 0; i < NumRegularSections + 1; ++i)
1828 WriteDataSectionData(Asm, Layout, *Sections[i]);
1830 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1831 WriteZeros(Padding);
1833 // ... then the section header table ...
1834 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap,
1837 // ... and then the remaining sections ...
1838 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i)
1839 WriteDataSectionData(Asm, Layout, *Sections[i]);
1843 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
1844 const MCSymbolData &DataA,
1845 const MCFragment &FB,
1847 bool IsPCRel) const {
1848 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC)
1850 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1851 Asm, DataA, FB,InSet, IsPCRel);
1854 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1856 bool IsLittleEndian) {
1857 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);