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/MCAsmLayout.h"
21 #include "llvm/MC/MCAssembler.h"
22 #include "llvm/MC/MCContext.h"
23 #include "llvm/MC/MCELF.h"
24 #include "llvm/MC/MCELFSymbolFlags.h"
25 #include "llvm/MC/MCExpr.h"
26 #include "llvm/MC/MCFixupKindInfo.h"
27 #include "llvm/MC/MCObjectWriter.h"
28 #include "llvm/MC/MCSectionELF.h"
29 #include "llvm/MC/MCValue.h"
30 #include "llvm/Support/Debug.h"
31 #include "llvm/Support/Endian.h"
32 #include "llvm/Support/ELF.h"
33 #include "llvm/Support/ErrorHandling.h"
38 #define DEBUG_TYPE "reloc-info"
41 class FragmentWriter {
45 FragmentWriter(bool IsLittleEndian);
46 template <typename T> void write(MCDataFragment &F, T Val);
49 typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
51 class SymbolTableWriter {
53 FragmentWriter &FWriter;
55 SectionIndexMapTy &SectionIndexMap;
57 // The symbol .symtab fragment we are writting to.
58 MCDataFragment *SymtabF;
60 // .symtab_shndx fragment we are writting to.
61 MCDataFragment *ShndxF;
63 // The numbel of symbols written so far.
66 void createSymtabShndx();
68 template <typename T> void write(MCDataFragment &F, T Value);
71 SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit,
72 SectionIndexMapTy &SectionIndexMap,
73 MCDataFragment *SymtabF);
75 void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
76 uint8_t other, uint32_t shndx, bool Reserved);
79 struct ELFRelocationEntry {
80 uint64_t Offset; // Where is the relocation.
81 bool UseSymbol; // Relocate with a symbol, not the section.
83 const MCSymbol *Symbol; // The symbol to relocate with.
84 const MCSectionData *Section; // The section to relocate with.
86 unsigned Type; // The type of the relocation.
87 uint64_t Addend; // The addend to use.
89 ELFRelocationEntry(uint64_t Offset, const MCSymbol *Symbol, unsigned Type,
91 : Offset(Offset), UseSymbol(true), Symbol(Symbol), Type(Type),
94 ELFRelocationEntry(uint64_t Offset, const MCSectionData *Section,
95 unsigned Type, uint64_t Addend)
96 : Offset(Offset), UseSymbol(false), Section(Section), Type(Type),
100 class ELFObjectWriter : public MCObjectWriter {
101 FragmentWriter FWriter;
105 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
106 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
107 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
108 static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data,
109 bool Used, bool Renamed);
110 static bool isLocal(const MCSymbolData &Data, bool isSignature,
112 static bool IsELFMetaDataSection(const MCSectionData &SD);
113 static uint64_t DataSectionSize(const MCSectionData &SD);
114 static uint64_t GetSectionFileSize(const MCAsmLayout &Layout,
115 const MCSectionData &SD);
116 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout,
117 const MCSectionData &SD);
119 void WriteDataSectionData(MCAssembler &Asm,
120 const MCAsmLayout &Layout,
121 const MCSectionELF &Section);
123 /*static bool isFixupKindX86RIPRel(unsigned Kind) {
124 return Kind == X86::reloc_riprel_4byte ||
125 Kind == X86::reloc_riprel_4byte_movq_load;
128 /// ELFSymbolData - Helper struct for containing some precomputed
129 /// information on symbols.
130 struct ELFSymbolData {
131 MCSymbolData *SymbolData;
132 uint64_t StringIndex;
133 uint32_t SectionIndex;
135 // Support lexicographic sorting.
136 bool operator<(const ELFSymbolData &RHS) const {
137 return SymbolData->getSymbol().getName() <
138 RHS.SymbolData->getSymbol().getName();
142 /// The target specific ELF writer instance.
143 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
145 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
146 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
147 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
149 llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>>
151 DenseMap<const MCSection*, uint64_t> SectionStringTableIndex;
154 /// @name Symbol Table Data
157 SmallString<256> StringTable;
158 std::vector<uint64_t> FileSymbolData;
159 std::vector<ELFSymbolData> LocalSymbolData;
160 std::vector<ELFSymbolData> ExternalSymbolData;
161 std::vector<ELFSymbolData> UndefinedSymbolData;
167 // This holds the symbol table index of the last local symbol.
168 unsigned LastLocalSymbolIndex;
169 // This holds the .strtab section index.
170 unsigned StringTableIndex;
171 // This holds the .symtab section index.
172 unsigned SymbolTableIndex;
174 unsigned ShstrtabIndex;
177 // TargetObjectWriter wrappers.
178 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
179 bool hasRelocationAddend() const {
180 return TargetObjectWriter->hasRelocationAddend();
182 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
183 bool IsPCRel) const {
184 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
188 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_ostream &_OS,
190 : MCObjectWriter(_OS, IsLittleEndian), FWriter(IsLittleEndian),
191 TargetObjectWriter(MOTW), NeedsGOT(false) {}
193 virtual ~ELFObjectWriter();
195 void WriteWord(uint64_t W) {
202 template <typename T> void write(MCDataFragment &F, T Value) {
203 FWriter.write(F, Value);
206 void WriteHeader(const MCAssembler &Asm,
207 uint64_t SectionDataSize,
208 unsigned NumberOfSections);
210 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
211 const MCAsmLayout &Layout);
213 void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm,
214 const MCAsmLayout &Layout,
215 SectionIndexMapTy &SectionIndexMap);
217 bool shouldRelocateWithSymbol(const MCSymbolRefExpr *RefA,
218 const MCSymbolData *SD, uint64_t C,
219 unsigned Type) const;
221 void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
222 const MCFragment *Fragment, const MCFixup &Fixup,
223 MCValue Target, bool &IsPCRel,
224 uint64_t &FixedValue) override;
226 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
229 // Map from a group section to the signature symbol
230 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
231 // Map from a signature symbol to the group section
232 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
233 // Map from a section to the section with the relocations
234 typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy;
235 // Map from a section to its offset
236 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy;
238 /// Compute the symbol table data
240 /// \param Asm - The assembler.
241 /// \param SectionIndexMap - Maps a section to its index.
242 /// \param RevGroupMap - Maps a signature symbol to the group section.
243 /// \param NumRegularSections - Number of non-relocation sections.
244 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
245 const SectionIndexMapTy &SectionIndexMap,
246 RevGroupMapTy RevGroupMap,
247 unsigned NumRegularSections);
249 void ComputeIndexMap(MCAssembler &Asm,
250 SectionIndexMapTy &SectionIndexMap,
251 const RelMapTy &RelMap);
253 void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout,
256 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
257 const RelMapTy &RelMap);
259 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
260 SectionIndexMapTy &SectionIndexMap,
261 const RelMapTy &RelMap);
263 // Create the sections that show up in the symbol table. Currently
264 // those are the .note.GNU-stack section and the group sections.
265 void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
266 GroupMapTy &GroupMap,
267 RevGroupMapTy &RevGroupMap,
268 SectionIndexMapTy &SectionIndexMap,
269 const RelMapTy &RelMap);
271 void ExecutePostLayoutBinding(MCAssembler &Asm,
272 const MCAsmLayout &Layout) override;
274 void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap,
275 const MCAsmLayout &Layout,
276 const SectionIndexMapTy &SectionIndexMap,
277 const SectionOffsetMapTy &SectionOffsetMap);
279 void ComputeSectionOrder(MCAssembler &Asm,
280 std::vector<const MCSectionELF*> &Sections);
282 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
283 uint64_t Address, uint64_t Offset,
284 uint64_t Size, uint32_t Link, uint32_t Info,
285 uint64_t Alignment, uint64_t EntrySize);
287 void WriteRelocationsFragment(const MCAssembler &Asm,
289 const MCSectionData *SD);
292 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
293 const MCSymbolData &DataA,
294 const MCFragment &FB,
296 bool IsPCRel) const override;
298 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
299 void WriteSection(MCAssembler &Asm,
300 const SectionIndexMapTy &SectionIndexMap,
301 uint32_t GroupSymbolIndex,
302 uint64_t Offset, uint64_t Size, uint64_t Alignment,
303 const MCSectionELF &Section);
307 FragmentWriter::FragmentWriter(bool IsLittleEndian)
308 : IsLittleEndian(IsLittleEndian) {}
310 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
312 Val = support::endian::byte_swap<T, support::little>(Val);
314 Val = support::endian::byte_swap<T, support::big>(Val);
315 const char *Start = (const char *)&Val;
316 F.getContents().append(Start, Start + sizeof(T));
319 void SymbolTableWriter::createSymtabShndx() {
323 MCContext &Ctx = Asm.getContext();
324 const MCSectionELF *SymtabShndxSection =
325 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0,
326 SectionKind::getReadOnly(), 4, "");
327 MCSectionData *SymtabShndxSD =
328 &Asm.getOrCreateSectionData(*SymtabShndxSection);
329 SymtabShndxSD->setAlignment(4);
330 ShndxF = new MCDataFragment(SymtabShndxSD);
331 unsigned Index = SectionIndexMap.size() + 1;
332 SectionIndexMap[SymtabShndxSection] = Index;
334 for (unsigned I = 0; I < NumWritten; ++I)
335 write(*ShndxF, uint32_t(0));
338 template <typename T>
339 void SymbolTableWriter::write(MCDataFragment &F, T Value) {
340 FWriter.write(F, Value);
343 SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter,
345 SectionIndexMapTy &SectionIndexMap,
346 MCDataFragment *SymtabF)
347 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit),
348 SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr),
351 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
352 uint64_t size, uint8_t other,
353 uint32_t shndx, bool Reserved) {
354 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
361 write(*ShndxF, shndx);
363 write(*ShndxF, uint32_t(0));
366 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
368 raw_svector_ostream OS(SymtabF->getContents());
371 write(*SymtabF, name); // st_name
372 write(*SymtabF, info); // st_info
373 write(*SymtabF, other); // st_other
374 write(*SymtabF, Index); // st_shndx
375 write(*SymtabF, value); // st_value
376 write(*SymtabF, size); // st_size
378 write(*SymtabF, name); // st_name
379 write(*SymtabF, uint32_t(value)); // st_value
380 write(*SymtabF, uint32_t(size)); // st_size
381 write(*SymtabF, info); // st_info
382 write(*SymtabF, other); // st_other
383 write(*SymtabF, Index); // st_shndx
389 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
390 const MCFixupKindInfo &FKI =
391 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
393 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
396 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
400 case MCSymbolRefExpr::VK_GOT:
401 case MCSymbolRefExpr::VK_PLT:
402 case MCSymbolRefExpr::VK_GOTPCREL:
403 case MCSymbolRefExpr::VK_GOTOFF:
404 case MCSymbolRefExpr::VK_TPOFF:
405 case MCSymbolRefExpr::VK_TLSGD:
406 case MCSymbolRefExpr::VK_GOTTPOFF:
407 case MCSymbolRefExpr::VK_INDNTPOFF:
408 case MCSymbolRefExpr::VK_NTPOFF:
409 case MCSymbolRefExpr::VK_GOTNTPOFF:
410 case MCSymbolRefExpr::VK_TLSLDM:
411 case MCSymbolRefExpr::VK_DTPOFF:
412 case MCSymbolRefExpr::VK_TLSLD:
417 ELFObjectWriter::~ELFObjectWriter()
420 // Emit the ELF header.
421 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
422 uint64_t SectionDataSize,
423 unsigned NumberOfSections) {
429 // emitWord method behaves differently for ELF32 and ELF64, writing
430 // 4 bytes in the former and 8 in the latter.
432 Write8(0x7f); // e_ident[EI_MAG0]
433 Write8('E'); // e_ident[EI_MAG1]
434 Write8('L'); // e_ident[EI_MAG2]
435 Write8('F'); // e_ident[EI_MAG3]
437 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
440 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
442 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
444 Write8(TargetObjectWriter->getOSABI());
445 Write8(0); // e_ident[EI_ABIVERSION]
447 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
449 Write16(ELF::ET_REL); // e_type
451 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
453 Write32(ELF::EV_CURRENT); // e_version
454 WriteWord(0); // e_entry, no entry point in .o file
455 WriteWord(0); // e_phoff, no program header for .o
456 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
457 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes
459 // e_flags = whatever the target wants
460 Write32(Asm.getELFHeaderEFlags());
462 // e_ehsize = ELF header size
463 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
465 Write16(0); // e_phentsize = prog header entry size
466 Write16(0); // e_phnum = # prog header entries = 0
468 // e_shentsize = Section header entry size
469 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
471 // e_shnum = # of section header ents
472 if (NumberOfSections >= ELF::SHN_LORESERVE)
473 Write16(ELF::SHN_UNDEF);
475 Write16(NumberOfSections);
477 // e_shstrndx = Section # of '.shstrtab'
478 if (ShstrtabIndex >= ELF::SHN_LORESERVE)
479 Write16(ELF::SHN_XINDEX);
481 Write16(ShstrtabIndex);
484 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &OrigData,
485 const MCAsmLayout &Layout) {
486 MCSymbolData *Data = &OrigData;
487 if (Data->isCommon() && Data->isExternal())
488 return Data->getCommonAlignment();
490 const MCSymbol *Symbol = &Data->getSymbol();
491 bool IsThumbFunc = OrigData.getFlags() & ELF_Other_ThumbFunc;
494 if (Symbol->isVariable()) {
495 const MCExpr *Expr = Symbol->getVariableValue();
497 if (!Expr->EvaluateAsRelocatable(Value, &Layout))
498 llvm_unreachable("Invalid expression");
500 assert(!Value.getSymB());
502 Res = Value.getConstant();
504 if (const MCSymbolRefExpr *A = Value.getSymA()) {
505 Symbol = &A->getSymbol();
506 Data = &Layout.getAssembler().getSymbolData(*Symbol);
516 if (!Symbol || !Symbol->isInSection())
519 Res += Layout.getSymbolOffset(Data);
524 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
525 const MCAsmLayout &Layout) {
526 // The presence of symbol versions causes undefined symbols and
527 // versions declared with @@@ to be renamed.
529 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
530 ie = Asm.symbol_end(); it != ie; ++it) {
531 const MCSymbol &Alias = it->getSymbol();
532 const MCSymbol &Symbol = Alias.AliasedSymbol();
533 MCSymbolData &SD = Asm.getSymbolData(Symbol);
536 if (&Symbol == &Alias)
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 it->setExternal(SD.isExternal());
547 MCELF::SetBinding(*it, 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->EvaluateAsRelocatable(Value, &Layout))
605 llvm_unreachable("Invalid Expression");
606 assert(!Value.getSymB());
607 const MCSymbolRefExpr *A = Value.getSymA();
610 return getBaseSymbol(Layout, A->getSymbol());
613 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
614 const MCAsmLayout &Layout) {
615 MCSymbolData &OrigData = *MSD.SymbolData;
616 const MCSymbol *Base = getBaseSymbol(Layout, OrigData.getSymbol());
618 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
620 bool IsReserved = !Base || OrigData.isCommon();
622 // Binding and Type share the same byte as upper and lower nibbles
623 uint8_t Binding = MCELF::GetBinding(OrigData);
624 uint8_t Type = MCELF::GetType(OrigData);
625 MCSymbolData *BaseSD = nullptr;
627 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
628 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
630 if (OrigData.getFlags() & ELF_Other_ThumbFunc)
631 Type = ELF::STT_FUNC;
632 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
634 // Other and Visibility share the same byte with Visibility using the lower
636 uint8_t Visibility = MCELF::GetVisibility(OrigData);
637 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
640 uint64_t Value = SymbolValue(OrigData, Layout);
641 if (OrigData.getFlags() & ELF_Other_ThumbFunc)
645 const MCExpr *ESize = OrigData.getSize();
647 ESize = BaseSD->getSize();
651 if (!ESize->EvaluateAsAbsolute(Res, Layout))
652 report_fatal_error("Size expression must be absolute.");
656 // Write out the symbol table entry
657 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
658 MSD.SectionIndex, IsReserved);
661 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF,
663 const MCAsmLayout &Layout,
664 SectionIndexMapTy &SectionIndexMap) {
665 // The string table must be emitted first because we need the index
666 // into the string table for all the symbol names.
667 assert(StringTable.size() && "Missing string table");
669 // FIXME: Make sure the start of the symbol table is aligned.
671 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF);
673 // The first entry is the undefined symbol entry.
674 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
676 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
677 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
678 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
681 // Write the symbol table entries.
682 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
684 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
685 ELFSymbolData &MSD = LocalSymbolData[i];
686 WriteSymbol(Writer, MSD, Layout);
689 // Write out a symbol table entry for each regular section.
690 for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e;
692 const MCSectionELF &Section =
693 static_cast<const MCSectionELF&>(i->getSection());
694 if (Section.getType() == ELF::SHT_RELA ||
695 Section.getType() == ELF::SHT_REL ||
696 Section.getType() == ELF::SHT_STRTAB ||
697 Section.getType() == ELF::SHT_SYMTAB ||
698 Section.getType() == ELF::SHT_SYMTAB_SHNDX)
700 Writer.writeSymbol(0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT,
701 SectionIndexMap.lookup(&Section), false);
702 LastLocalSymbolIndex++;
705 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
706 ELFSymbolData &MSD = ExternalSymbolData[i];
707 MCSymbolData &Data = *MSD.SymbolData;
708 assert(((Data.getFlags() & ELF_STB_Global) ||
709 (Data.getFlags() & ELF_STB_Weak)) &&
710 "External symbol requires STB_GLOBAL or STB_WEAK flag");
711 WriteSymbol(Writer, MSD, Layout);
712 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
713 LastLocalSymbolIndex++;
716 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
717 ELFSymbolData &MSD = UndefinedSymbolData[i];
718 MCSymbolData &Data = *MSD.SymbolData;
719 WriteSymbol(Writer, MSD, Layout);
720 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
721 LastLocalSymbolIndex++;
725 // It is always valid to create a relocation with a symbol. It is preferable
726 // to use a relocation with a section if that is possible. Using the section
727 // allows us to omit some local symbols from the symbol table.
728 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCSymbolRefExpr *RefA,
729 const MCSymbolData *SD,
731 unsigned Type) const {
732 // A PCRel relocation to an absolute value has no symbol (or section). We
733 // represent that with a relocation to a null section.
737 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
741 // The .odp creation emits a relocation against the symbol ".TOC." which
742 // create a R_PPC64_TOC relocation. However the relocation symbol name
743 // in final object creation should be NULL, since the symbol does not
744 // really exist, it is just the reference to TOC base for the current
745 // object file. Since the symbol is undefined, returning false results
746 // in a relocation with a null section which is the desired result.
747 case MCSymbolRefExpr::VK_PPC_TOCBASE:
750 // These VariantKind cause the relocation to refer to something other than
751 // the symbol itself, like a linker generated table. Since the address of
752 // symbol is not relevant, we cannot replace the symbol with the
753 // section and patch the difference in the addend.
754 case MCSymbolRefExpr::VK_GOT:
755 case MCSymbolRefExpr::VK_PLT:
756 case MCSymbolRefExpr::VK_GOTPCREL:
757 case MCSymbolRefExpr::VK_Mips_GOT:
758 case MCSymbolRefExpr::VK_PPC_GOT_LO:
759 case MCSymbolRefExpr::VK_PPC_GOT_HI:
760 case MCSymbolRefExpr::VK_PPC_GOT_HA:
764 // An undefined symbol is not in any section, so the relocation has to point
765 // to the symbol itself.
766 const MCSymbol &Sym = SD->getSymbol();
767 if (Sym.isUndefined())
770 unsigned Binding = MCELF::GetBinding(*SD);
773 llvm_unreachable("Invalid Binding");
777 // If the symbol is weak, it might be overridden by a symbol in another
778 // file. The relocation has to point to the symbol so that the linker
781 case ELF::STB_GLOBAL:
782 // Global ELF symbols can be preempted by the dynamic linker. The relocation
783 // has to point to the symbol for a reason analogous to the STB_WEAK case.
787 // If a relocation points to a mergeable section, we have to be careful.
788 // If the offset is zero, a relocation with the section will encode the
789 // same information. With a non-zero offset, the situation is different.
790 // For example, a relocation can point 42 bytes past the end of a string.
791 // If we change such a relocation to use the section, the linker would think
792 // that it pointed to another string and subtracting 42 at runtime will
793 // produce the wrong value.
794 auto &Sec = cast<MCSectionELF>(Sym.getSection());
795 unsigned Flags = Sec.getFlags();
796 if (Flags & ELF::SHF_MERGE) {
800 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
801 // only handle section relocations to mergeable sections if using RELA.
802 if (!hasRelocationAddend())
806 // Most TLS relocations use a got, so they need the symbol. Even those that
807 // are just an offset (@tpoff), require a symbol in some linkers (gold,
809 if (Flags & ELF::SHF_TLS)
812 if (TargetObjectWriter->needsRelocateWithSymbol(Type))
817 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
818 const MCAsmLayout &Layout,
819 const MCFragment *Fragment,
820 const MCFixup &Fixup,
823 uint64_t &FixedValue) {
824 const MCSectionData *FixupSection = Fragment->getParent();
825 uint64_t C = Target.getConstant();
826 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
828 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
829 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
830 "Should not have constructed this");
832 // Let A, B and C being the components of Target and R be the location of
833 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
834 // If it is pcrel, we want to compute (A - B + C - R).
836 // In general, ELF has no relocations for -B. It can only represent (A + C)
837 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
838 // replace B to implement it: (A - R - K + C)
840 Asm.getContext().FatalError(
842 "No relocation available to represent this relative expression");
844 const MCSymbol &SymB = RefB->getSymbol();
846 if (SymB.isUndefined())
847 Asm.getContext().FatalError(
849 Twine("symbol '") + SymB.getName() +
850 "' can not be undefined in a subtraction expression");
852 assert(!SymB.isAbsolute() && "Should have been folded");
853 const MCSection &SecB = SymB.getSection();
854 if (&SecB != &FixupSection->getSection())
855 Asm.getContext().FatalError(
856 Fixup.getLoc(), "Cannot represent a difference across sections");
858 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
859 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
860 uint64_t K = SymBOffset - FixupOffset;
865 // We either rejected the fixup or folded B into C at this point.
866 const MCSymbolRefExpr *RefA = Target.getSymA();
867 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
868 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
870 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
871 bool RelocateWithSymbol = shouldRelocateWithSymbol(RefA, SymAD, C, Type);
872 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
873 C += Layout.getSymbolOffset(SymAD);
876 if (hasRelocationAddend()) {
883 // FIXME: What is this!?!?
884 MCSymbolRefExpr::VariantKind Modifier =
885 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
886 if (RelocNeedsGOT(Modifier))
889 if (!RelocateWithSymbol) {
890 const MCSection *SecA =
891 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
892 const MCSectionData *SecAD = SecA ? &Asm.getSectionData(*SecA) : nullptr;
893 ELFRelocationEntry Rec(FixupOffset, SecAD, Type, Addend);
894 Relocations[FixupSection].push_back(Rec);
899 if (const MCSymbol *R = Renames.lookup(SymA))
902 if (RefA->getKind() == MCSymbolRefExpr::VK_WEAKREF)
903 WeakrefUsedInReloc.insert(SymA);
905 UsedInReloc.insert(SymA);
907 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
908 Relocations[FixupSection].push_back(Rec);
914 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
916 MCSymbolData &SD = Asm.getSymbolData(*S);
917 return SD.getIndex();
920 bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm,
921 const MCSymbolData &Data,
922 bool Used, bool Renamed) {
923 const MCSymbol &Symbol = Data.getSymbol();
924 if (Symbol.isVariable()) {
925 const MCExpr *Expr = Symbol.getVariableValue();
926 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
927 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
938 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
941 const MCSymbol &A = Symbol.AliasedSymbol();
942 if (Symbol.isVariable() && !A.isVariable() && A.isUndefined())
945 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
946 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
949 if (Symbol.isTemporary())
955 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isSignature,
956 bool isUsedInReloc) {
957 if (Data.isExternal())
960 const MCSymbol &Symbol = Data.getSymbol();
961 const MCSymbol &RefSymbol = Symbol.AliasedSymbol();
963 if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) {
964 if (isSignature && !isUsedInReloc)
973 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
974 SectionIndexMapTy &SectionIndexMap,
975 const RelMapTy &RelMap) {
977 for (MCAssembler::iterator it = Asm.begin(),
978 ie = Asm.end(); it != ie; ++it) {
979 const MCSectionELF &Section =
980 static_cast<const MCSectionELF &>(it->getSection());
981 if (Section.getType() != ELF::SHT_GROUP)
983 SectionIndexMap[&Section] = Index++;
986 for (MCAssembler::iterator it = Asm.begin(),
987 ie = Asm.end(); it != ie; ++it) {
988 const MCSectionELF &Section =
989 static_cast<const MCSectionELF &>(it->getSection());
990 if (Section.getType() == ELF::SHT_GROUP ||
991 Section.getType() == ELF::SHT_REL ||
992 Section.getType() == ELF::SHT_RELA)
994 SectionIndexMap[&Section] = Index++;
995 const MCSectionELF *RelSection = RelMap.lookup(&Section);
997 SectionIndexMap[RelSection] = Index++;
1002 ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
1003 const SectionIndexMapTy &SectionIndexMap,
1004 RevGroupMapTy RevGroupMap,
1005 unsigned NumRegularSections) {
1006 // FIXME: Is this the correct place to do this?
1007 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
1009 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
1010 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
1011 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
1012 Data.setExternal(true);
1013 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
1016 // Index 0 is always the empty string.
1017 StringMap<uint64_t> StringIndexMap;
1018 StringTable += '\x00';
1020 // FIXME: We could optimize suffixes in strtab in the same way we
1021 // optimize them in shstrtab.
1023 for (MCAssembler::const_file_name_iterator it = Asm.file_names_begin(),
1024 ie = Asm.file_names_end();
1027 StringRef Name = *it;
1028 uint64_t &Entry = StringIndexMap[Name];
1030 Entry = StringTable.size();
1031 StringTable += Name;
1032 StringTable += '\x00';
1034 FileSymbolData.push_back(Entry);
1037 // Add the data for the symbols.
1038 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
1039 ie = Asm.symbol_end(); it != ie; ++it) {
1040 const MCSymbol &Symbol = it->getSymbol();
1042 bool Used = UsedInReloc.count(&Symbol);
1043 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
1044 bool isSignature = RevGroupMap.count(&Symbol);
1046 if (!isInSymtab(Asm, *it,
1047 Used || WeakrefUsed || isSignature,
1048 Renames.count(&Symbol)))
1052 MSD.SymbolData = it;
1053 const MCSymbol *BaseSymbol = getBaseSymbol(Layout, Symbol);
1055 // Undefined symbols are global, but this is the first place we
1056 // are able to set it.
1057 bool Local = isLocal(*it, isSignature, Used);
1058 if (!Local && MCELF::GetBinding(*it) == ELF::STB_LOCAL) {
1060 MCSymbolData &SD = Asm.getSymbolData(*BaseSymbol);
1061 MCELF::SetBinding(*it, ELF::STB_GLOBAL);
1062 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1066 MSD.SectionIndex = ELF::SHN_ABS;
1067 } else if (it->isCommon()) {
1069 MSD.SectionIndex = ELF::SHN_COMMON;
1070 } else if (BaseSymbol->isUndefined()) {
1071 if (isSignature && !Used)
1072 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]);
1074 MSD.SectionIndex = ELF::SHN_UNDEF;
1075 if (!Used && WeakrefUsed)
1076 MCELF::SetBinding(*it, ELF::STB_WEAK);
1078 const MCSectionELF &Section =
1079 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1080 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1081 assert(MSD.SectionIndex && "Invalid section index!");
1084 // The @@@ in symbol version is replaced with @ in undefined symbols and
1085 // @@ in defined ones.
1086 StringRef Name = Symbol.getName();
1087 SmallString<32> Buf;
1089 size_t Pos = Name.find("@@@");
1090 if (Pos != StringRef::npos) {
1091 Buf += Name.substr(0, Pos);
1092 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1093 Buf += Name.substr(Pos + Skip);
1097 uint64_t &Entry = StringIndexMap[Name];
1099 Entry = StringTable.size();
1100 StringTable += Name;
1101 StringTable += '\x00';
1103 MSD.StringIndex = Entry;
1104 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1105 UndefinedSymbolData.push_back(MSD);
1107 LocalSymbolData.push_back(MSD);
1109 ExternalSymbolData.push_back(MSD);
1112 // Symbols are required to be in lexicographic order.
1113 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1114 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1115 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1117 // Set the symbol indices. Local symbols must come before all other
1118 // symbols with non-local bindings.
1119 unsigned Index = FileSymbolData.size() + 1;
1120 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1121 LocalSymbolData[i].SymbolData->setIndex(Index++);
1123 Index += NumRegularSections;
1125 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1126 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1127 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1128 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1131 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm,
1132 MCAsmLayout &Layout,
1134 for (MCAssembler::const_iterator it = Asm.begin(),
1135 ie = Asm.end(); it != ie; ++it) {
1136 const MCSectionData &SD = *it;
1137 if (Relocations[&SD].empty())
1140 MCContext &Ctx = Asm.getContext();
1141 const MCSectionELF &Section =
1142 static_cast<const MCSectionELF&>(SD.getSection());
1144 const StringRef SectionName = Section.getSectionName();
1145 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1146 RelaSectionName += SectionName;
1149 if (hasRelocationAddend())
1150 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1152 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1155 StringRef Group = "";
1156 if (Section.getFlags() & ELF::SHF_GROUP) {
1157 Flags = ELF::SHF_GROUP;
1158 Group = Section.getGroup()->getName();
1161 const MCSectionELF *RelaSection =
1162 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ?
1163 ELF::SHT_RELA : ELF::SHT_REL, Flags,
1164 SectionKind::getReadOnly(),
1166 RelMap[&Section] = RelaSection;
1167 Asm.getOrCreateSectionData(*RelaSection);
1171 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
1172 const RelMapTy &RelMap) {
1173 for (MCAssembler::const_iterator it = Asm.begin(),
1174 ie = Asm.end(); it != ie; ++it) {
1175 const MCSectionData &SD = *it;
1176 const MCSectionELF &Section =
1177 static_cast<const MCSectionELF&>(SD.getSection());
1179 const MCSectionELF *RelaSection = RelMap.lookup(&Section);
1182 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
1183 RelaSD.setAlignment(is64Bit() ? 8 : 4);
1185 MCDataFragment *F = new MCDataFragment(&RelaSD);
1186 WriteRelocationsFragment(Asm, F, &*it);
1190 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1191 uint64_t Flags, uint64_t Address,
1192 uint64_t Offset, uint64_t Size,
1193 uint32_t Link, uint32_t Info,
1195 uint64_t EntrySize) {
1196 Write32(Name); // sh_name: index into string table
1197 Write32(Type); // sh_type
1198 WriteWord(Flags); // sh_flags
1199 WriteWord(Address); // sh_addr
1200 WriteWord(Offset); // sh_offset
1201 WriteWord(Size); // sh_size
1202 Write32(Link); // sh_link
1203 Write32(Info); // sh_info
1204 WriteWord(Alignment); // sh_addralign
1205 WriteWord(EntrySize); // sh_entsize
1208 // ELF doesn't require relocations to be in any order. We sort by the r_offset,
1209 // just to match gnu as for easier comparison. The use type is an arbitrary way
1210 // of making the sort deterministic.
1211 static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) {
1212 const ELFRelocationEntry &A = *AP;
1213 const ELFRelocationEntry &B = *BP;
1214 if (A.Offset != B.Offset)
1215 return B.Offset - A.Offset;
1216 if (B.Type != A.Type)
1217 return A.Type - B.Type;
1218 llvm_unreachable("ELFRelocs might be unstable!");
1221 static void sortRelocs(const MCAssembler &Asm,
1222 std::vector<ELFRelocationEntry> &Relocs) {
1223 array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
1226 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1228 const MCSectionData *SD) {
1229 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1231 sortRelocs(Asm, Relocs);
1233 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1234 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1237 if (Entry.UseSymbol) {
1238 Index = getSymbolIndexInSymbolTable(Asm, Entry.Symbol);
1240 const MCSectionData *Sec = Entry.Section;
1242 Index = Sec->getOrdinal() + FileSymbolData.size() +
1243 LocalSymbolData.size() + 1;
1249 write(*F, Entry.Offset);
1250 if (TargetObjectWriter->isN64()) {
1251 write(*F, uint32_t(Index));
1253 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1254 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1255 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1256 write(*F, TargetObjectWriter->getRType(Entry.Type));
1258 struct ELF::Elf64_Rela ERE64;
1259 ERE64.setSymbolAndType(Index, Entry.Type);
1260 write(*F, ERE64.r_info);
1262 if (hasRelocationAddend())
1263 write(*F, Entry.Addend);
1265 write(*F, uint32_t(Entry.Offset));
1267 struct ELF::Elf32_Rela ERE32;
1268 ERE32.setSymbolAndType(Index, Entry.Type);
1269 write(*F, ERE32.r_info);
1271 if (hasRelocationAddend())
1272 write(*F, uint32_t(Entry.Addend));
1277 static int compareBySuffix(const MCSectionELF *const *a,
1278 const MCSectionELF *const *b) {
1279 const StringRef &NameA = (*a)->getSectionName();
1280 const StringRef &NameB = (*b)->getSectionName();
1281 const unsigned sizeA = NameA.size();
1282 const unsigned sizeB = NameB.size();
1283 const unsigned len = std::min(sizeA, sizeB);
1284 for (unsigned int i = 0; i < len; ++i) {
1285 char ca = NameA[sizeA - i - 1];
1286 char cb = NameB[sizeB - i - 1];
1291 return sizeB - sizeA;
1294 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
1295 MCAsmLayout &Layout,
1296 SectionIndexMapTy &SectionIndexMap,
1297 const RelMapTy &RelMap) {
1298 MCContext &Ctx = Asm.getContext();
1301 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1303 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1304 const MCSectionELF *ShstrtabSection =
1305 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
1306 SectionKind::getReadOnly());
1307 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1308 ShstrtabSD.setAlignment(1);
1310 const MCSectionELF *SymtabSection =
1311 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1312 SectionKind::getReadOnly(),
1314 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1315 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1317 const MCSectionELF *StrtabSection;
1318 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
1319 SectionKind::getReadOnly());
1320 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1321 StrtabSD.setAlignment(1);
1323 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1325 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection);
1326 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection);
1327 StringTableIndex = SectionIndexMap.lookup(StrtabSection);
1330 F = new MCDataFragment(&SymtabSD);
1331 WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
1333 F = new MCDataFragment(&StrtabSD);
1334 F->getContents().append(StringTable.begin(), StringTable.end());
1336 F = new MCDataFragment(&ShstrtabSD);
1338 std::vector<const MCSectionELF*> Sections;
1339 for (MCAssembler::const_iterator it = Asm.begin(),
1340 ie = Asm.end(); it != ie; ++it) {
1341 const MCSectionELF &Section =
1342 static_cast<const MCSectionELF&>(it->getSection());
1343 Sections.push_back(&Section);
1345 array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix);
1347 // Section header string table.
1349 // The first entry of a string table holds a null character so skip
1352 F->getContents().push_back('\x00');
1354 for (unsigned int I = 0, E = Sections.size(); I != E; ++I) {
1355 const MCSectionELF &Section = *Sections[I];
1357 StringRef Name = Section.getSectionName();
1359 StringRef PreviousName = Sections[I - 1]->getSectionName();
1360 if (PreviousName.endswith(Name)) {
1361 SectionStringTableIndex[&Section] = Index - Name.size() - 1;
1365 // Remember the index into the string table so we can write it
1366 // into the sh_name field of the section header table.
1367 SectionStringTableIndex[&Section] = Index;
1369 Index += Name.size() + 1;
1370 F->getContents().append(Name.begin(), Name.end());
1371 F->getContents().push_back('\x00');
1375 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm,
1376 MCAsmLayout &Layout,
1377 GroupMapTy &GroupMap,
1378 RevGroupMapTy &RevGroupMap,
1379 SectionIndexMapTy &SectionIndexMap,
1380 const RelMapTy &RelMap) {
1381 // Create the .note.GNU-stack section if needed.
1382 MCContext &Ctx = Asm.getContext();
1383 if (Asm.getNoExecStack()) {
1384 const MCSectionELF *GnuStackSection =
1385 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0,
1386 SectionKind::getReadOnly());
1387 Asm.getOrCreateSectionData(*GnuStackSection);
1391 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1393 const MCSectionELF &Section =
1394 static_cast<const MCSectionELF&>(it->getSection());
1395 if (!(Section.getFlags() & ELF::SHF_GROUP))
1398 const MCSymbol *SignatureSymbol = Section.getGroup();
1399 Asm.getOrCreateSymbolData(*SignatureSymbol);
1400 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1402 Group = Ctx.CreateELFGroupSection();
1403 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1404 Data.setAlignment(4);
1405 MCDataFragment *F = new MCDataFragment(&Data);
1406 write(*F, uint32_t(ELF::GRP_COMDAT));
1408 GroupMap[Group] = SignatureSymbol;
1411 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1413 // Add sections to the groups
1414 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1416 const MCSectionELF &Section =
1417 static_cast<const MCSectionELF&>(it->getSection());
1418 if (!(Section.getFlags() & ELF::SHF_GROUP))
1420 const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1421 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1422 // FIXME: we could use the previous fragment
1423 MCDataFragment *F = new MCDataFragment(&Data);
1424 uint32_t Index = SectionIndexMap.lookup(&Section);
1429 void ELFObjectWriter::WriteSection(MCAssembler &Asm,
1430 const SectionIndexMapTy &SectionIndexMap,
1431 uint32_t GroupSymbolIndex,
1432 uint64_t Offset, uint64_t Size,
1434 const MCSectionELF &Section) {
1435 uint64_t sh_link = 0;
1436 uint64_t sh_info = 0;
1438 switch(Section.getType()) {
1439 case ELF::SHT_DYNAMIC:
1440 sh_link = SectionStringTableIndex[&Section];
1445 case ELF::SHT_RELA: {
1446 const MCSectionELF *SymtabSection;
1447 const MCSectionELF *InfoSection;
1448 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB,
1450 SectionKind::getReadOnly());
1451 sh_link = SectionIndexMap.lookup(SymtabSection);
1452 assert(sh_link && ".symtab not found");
1454 // Remove ".rel" and ".rela" prefixes.
1455 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1456 StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1457 StringRef GroupName =
1458 Section.getGroup() ? Section.getGroup()->getName() : "";
1460 InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS,
1461 0, SectionKind::getReadOnly(),
1463 sh_info = SectionIndexMap.lookup(InfoSection);
1467 case ELF::SHT_SYMTAB:
1468 case ELF::SHT_DYNSYM:
1469 sh_link = StringTableIndex;
1470 sh_info = LastLocalSymbolIndex;
1473 case ELF::SHT_SYMTAB_SHNDX:
1474 sh_link = SymbolTableIndex;
1477 case ELF::SHT_PROGBITS:
1478 case ELF::SHT_STRTAB:
1479 case ELF::SHT_NOBITS:
1482 case ELF::SHT_ARM_ATTRIBUTES:
1483 case ELF::SHT_INIT_ARRAY:
1484 case ELF::SHT_FINI_ARRAY:
1485 case ELF::SHT_PREINIT_ARRAY:
1486 case ELF::SHT_X86_64_UNWIND:
1487 case ELF::SHT_MIPS_REGINFO:
1488 case ELF::SHT_MIPS_OPTIONS:
1492 case ELF::SHT_GROUP:
1493 sh_link = SymbolTableIndex;
1494 sh_info = GroupSymbolIndex;
1498 assert(0 && "FIXME: sh_type value not supported!");
1502 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1503 Section.getType() == ELF::SHT_ARM_EXIDX) {
1504 StringRef SecName(Section.getSectionName());
1505 if (SecName == ".ARM.exidx") {
1506 sh_link = SectionIndexMap.lookup(
1507 Asm.getContext().getELFSection(".text",
1509 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC,
1510 SectionKind::getText()));
1511 } else if (SecName.startswith(".ARM.exidx")) {
1512 StringRef GroupName =
1513 Section.getGroup() ? Section.getGroup()->getName() : "";
1514 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
1515 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS,
1516 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText(), 0,
1521 WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(),
1522 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1523 Alignment, Section.getEntrySize());
1526 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1527 return SD.getOrdinal() == ~UINT32_C(0) &&
1528 !SD.getSection().isVirtualSection();
1531 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1533 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1535 const MCFragment &F = *i;
1536 assert(F.getKind() == MCFragment::FT_Data);
1537 Ret += cast<MCDataFragment>(F).getContents().size();
1542 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
1543 const MCSectionData &SD) {
1544 if (IsELFMetaDataSection(SD))
1545 return DataSectionSize(SD);
1546 return Layout.getSectionFileSize(&SD);
1549 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1550 const MCSectionData &SD) {
1551 if (IsELFMetaDataSection(SD))
1552 return DataSectionSize(SD);
1553 return Layout.getSectionAddressSize(&SD);
1556 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
1557 const MCAsmLayout &Layout,
1558 const MCSectionELF &Section) {
1559 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1561 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1562 WriteZeros(Padding);
1564 if (IsELFMetaDataSection(SD)) {
1565 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1567 const MCFragment &F = *i;
1568 assert(F.getKind() == MCFragment::FT_Data);
1569 WriteBytes(cast<MCDataFragment>(F).getContents());
1572 Asm.writeSectionData(&SD, Layout);
1576 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm,
1577 const GroupMapTy &GroupMap,
1578 const MCAsmLayout &Layout,
1579 const SectionIndexMapTy &SectionIndexMap,
1580 const SectionOffsetMapTy &SectionOffsetMap) {
1581 const unsigned NumSections = Asm.size() + 1;
1583 std::vector<const MCSectionELF*> Sections;
1584 Sections.resize(NumSections - 1);
1586 for (SectionIndexMapTy::const_iterator i=
1587 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
1588 const std::pair<const MCSectionELF*, uint32_t> &p = *i;
1589 Sections[p.second - 1] = p.first;
1592 // Null section first.
1593 uint64_t FirstSectionSize =
1594 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
1595 uint32_t FirstSectionLink =
1596 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1597 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1599 for (unsigned i = 0; i < NumSections - 1; ++i) {
1600 const MCSectionELF &Section = *Sections[i];
1601 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1602 uint32_t GroupSymbolIndex;
1603 if (Section.getType() != ELF::SHT_GROUP)
1604 GroupSymbolIndex = 0;
1606 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1607 GroupMap.lookup(&Section));
1609 uint64_t Size = GetSectionAddressSize(Layout, SD);
1611 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex,
1612 SectionOffsetMap.lookup(&Section), Size,
1613 SD.getAlignment(), Section);
1617 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
1618 std::vector<const MCSectionELF*> &Sections) {
1619 for (MCAssembler::iterator it = Asm.begin(),
1620 ie = Asm.end(); it != ie; ++it) {
1621 const MCSectionELF &Section =
1622 static_cast<const MCSectionELF &>(it->getSection());
1623 if (Section.getType() == ELF::SHT_GROUP)
1624 Sections.push_back(&Section);
1627 for (MCAssembler::iterator it = Asm.begin(),
1628 ie = Asm.end(); it != ie; ++it) {
1629 const MCSectionELF &Section =
1630 static_cast<const MCSectionELF &>(it->getSection());
1631 if (Section.getType() != ELF::SHT_GROUP &&
1632 Section.getType() != ELF::SHT_REL &&
1633 Section.getType() != ELF::SHT_RELA)
1634 Sections.push_back(&Section);
1637 for (MCAssembler::iterator it = Asm.begin(),
1638 ie = Asm.end(); it != ie; ++it) {
1639 const MCSectionELF &Section =
1640 static_cast<const MCSectionELF &>(it->getSection());
1641 if (Section.getType() == ELF::SHT_REL ||
1642 Section.getType() == ELF::SHT_RELA)
1643 Sections.push_back(&Section);
1647 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1648 const MCAsmLayout &Layout) {
1649 GroupMapTy GroupMap;
1650 RevGroupMapTy RevGroupMap;
1651 SectionIndexMapTy SectionIndexMap;
1653 unsigned NumUserSections = Asm.size();
1655 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap;
1656 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1658 const unsigned NumUserAndRelocSections = Asm.size();
1659 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
1660 RevGroupMap, SectionIndexMap, RelMap);
1661 const unsigned AllSections = Asm.size();
1662 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections;
1664 unsigned NumRegularSections = NumUserSections + NumIndexedSections;
1666 // Compute symbol table information.
1667 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
1668 NumRegularSections);
1670 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1672 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1673 const_cast<MCAsmLayout&>(Layout),
1677 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1678 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
1679 sizeof(ELF::Elf32_Ehdr);
1680 uint64_t FileOff = HeaderSize;
1682 std::vector<const MCSectionELF*> Sections;
1683 ComputeSectionOrder(Asm, Sections);
1684 unsigned NumSections = Sections.size();
1685 SectionOffsetMapTy SectionOffsetMap;
1686 for (unsigned i = 0; i < NumRegularSections + 1; ++i) {
1687 const MCSectionELF &Section = *Sections[i];
1688 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1690 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1692 // Remember the offset into the file for this section.
1693 SectionOffsetMap[&Section] = FileOff;
1695 // Get the size of the section in the output file (including padding).
1696 FileOff += GetSectionFileSize(Layout, SD);
1699 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1701 const unsigned SectionHeaderOffset = FileOff - HeaderSize;
1703 uint64_t SectionHeaderEntrySize = is64Bit() ?
1704 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr);
1705 FileOff += (NumSections + 1) * SectionHeaderEntrySize;
1707 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) {
1708 const MCSectionELF &Section = *Sections[i];
1709 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1711 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1713 // Remember the offset into the file for this section.
1714 SectionOffsetMap[&Section] = FileOff;
1716 // Get the size of the section in the output file (including padding).
1717 FileOff += GetSectionFileSize(Layout, SD);
1720 // Write out the ELF header ...
1721 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
1723 // ... then the regular sections ...
1724 // + because of .shstrtab
1725 for (unsigned i = 0; i < NumRegularSections + 1; ++i)
1726 WriteDataSectionData(Asm, Layout, *Sections[i]);
1728 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1729 WriteZeros(Padding);
1731 // ... then the section header table ...
1732 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap,
1735 // ... and then the remaining sections ...
1736 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i)
1737 WriteDataSectionData(Asm, Layout, *Sections[i]);
1741 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
1742 const MCSymbolData &DataA,
1743 const MCFragment &FB,
1745 bool IsPCRel) const {
1746 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC)
1748 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1749 Asm, DataA, FB,InSet, IsPCRel);
1752 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1754 bool IsLittleEndian) {
1755 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);