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) {
801 // Most TLS relocations use a got, so they need the symbol. Even those that
802 // are just an offset (@tpoff), require a symbol in some linkers (gold,
804 if (Flags & ELF::SHF_TLS)
807 if (TargetObjectWriter->needsRelocateWithSymbol(Type))
812 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
813 const MCAsmLayout &Layout,
814 const MCFragment *Fragment,
815 const MCFixup &Fixup,
818 uint64_t &FixedValue) {
819 const MCSectionData *FixupSection = Fragment->getParent();
820 uint64_t C = Target.getConstant();
821 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
823 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
824 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
825 "Should not have constructed this");
827 // Let A, B and C being the components of Target and R be the location of
828 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
829 // If it is pcrel, we want to compute (A - B + C - R).
831 // In general, ELF has no relocations for -B. It can only represent (A + C)
832 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
833 // replace B to implement it: (A - R - K + C)
835 Asm.getContext().FatalError(
837 "No relocation available to represent this relative expression");
839 const MCSymbol &SymB = RefB->getSymbol();
841 if (SymB.isUndefined())
842 Asm.getContext().FatalError(
844 Twine("symbol '") + SymB.getName() +
845 "' can not be undefined in a subtraction expression");
847 assert(!SymB.isAbsolute() && "Should have been folded");
848 const MCSection &SecB = SymB.getSection();
849 if (&SecB != &FixupSection->getSection())
850 Asm.getContext().FatalError(
851 Fixup.getLoc(), "Cannot represent a difference across sections");
853 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
854 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
855 uint64_t K = SymBOffset - FixupOffset;
860 // We either rejected the fixup or folded B into C at this point.
861 const MCSymbolRefExpr *RefA = Target.getSymA();
862 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
863 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
865 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
866 bool RelocateWithSymbol = shouldRelocateWithSymbol(RefA, SymAD, C, Type);
867 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
868 C += Layout.getSymbolOffset(SymAD);
871 if (hasRelocationAddend()) {
878 // FIXME: What is this!?!?
879 MCSymbolRefExpr::VariantKind Modifier =
880 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
881 if (RelocNeedsGOT(Modifier))
884 if (!RelocateWithSymbol) {
885 const MCSection *SecA =
886 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
887 const MCSectionData *SecAD = SecA ? &Asm.getSectionData(*SecA) : nullptr;
888 ELFRelocationEntry Rec(FixupOffset, SecAD, Type, Addend);
889 Relocations[FixupSection].push_back(Rec);
894 if (const MCSymbol *R = Renames.lookup(SymA))
897 if (RefA->getKind() == MCSymbolRefExpr::VK_WEAKREF)
898 WeakrefUsedInReloc.insert(SymA);
900 UsedInReloc.insert(SymA);
902 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
903 Relocations[FixupSection].push_back(Rec);
909 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
911 MCSymbolData &SD = Asm.getSymbolData(*S);
912 return SD.getIndex();
915 bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm,
916 const MCSymbolData &Data,
917 bool Used, bool Renamed) {
918 const MCSymbol &Symbol = Data.getSymbol();
919 if (Symbol.isVariable()) {
920 const MCExpr *Expr = Symbol.getVariableValue();
921 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
922 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
933 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
936 const MCSymbol &A = Symbol.AliasedSymbol();
937 if (Symbol.isVariable() && !A.isVariable() && A.isUndefined())
940 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
941 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
944 if (Symbol.isTemporary())
950 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isSignature,
951 bool isUsedInReloc) {
952 if (Data.isExternal())
955 const MCSymbol &Symbol = Data.getSymbol();
956 const MCSymbol &RefSymbol = Symbol.AliasedSymbol();
958 if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) {
959 if (isSignature && !isUsedInReloc)
968 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
969 SectionIndexMapTy &SectionIndexMap,
970 const RelMapTy &RelMap) {
972 for (MCAssembler::iterator it = Asm.begin(),
973 ie = Asm.end(); it != ie; ++it) {
974 const MCSectionELF &Section =
975 static_cast<const MCSectionELF &>(it->getSection());
976 if (Section.getType() != ELF::SHT_GROUP)
978 SectionIndexMap[&Section] = Index++;
981 for (MCAssembler::iterator it = Asm.begin(),
982 ie = Asm.end(); it != ie; ++it) {
983 const MCSectionELF &Section =
984 static_cast<const MCSectionELF &>(it->getSection());
985 if (Section.getType() == ELF::SHT_GROUP ||
986 Section.getType() == ELF::SHT_REL ||
987 Section.getType() == ELF::SHT_RELA)
989 SectionIndexMap[&Section] = Index++;
990 const MCSectionELF *RelSection = RelMap.lookup(&Section);
992 SectionIndexMap[RelSection] = Index++;
997 ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
998 const SectionIndexMapTy &SectionIndexMap,
999 RevGroupMapTy RevGroupMap,
1000 unsigned NumRegularSections) {
1001 // FIXME: Is this the correct place to do this?
1002 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
1004 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
1005 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
1006 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
1007 Data.setExternal(true);
1008 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
1011 // Index 0 is always the empty string.
1012 StringMap<uint64_t> StringIndexMap;
1013 StringTable += '\x00';
1015 // FIXME: We could optimize suffixes in strtab in the same way we
1016 // optimize them in shstrtab.
1018 for (MCAssembler::const_file_name_iterator it = Asm.file_names_begin(),
1019 ie = Asm.file_names_end();
1022 StringRef Name = *it;
1023 uint64_t &Entry = StringIndexMap[Name];
1025 Entry = StringTable.size();
1026 StringTable += Name;
1027 StringTable += '\x00';
1029 FileSymbolData.push_back(Entry);
1032 // Add the data for the symbols.
1033 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
1034 ie = Asm.symbol_end(); it != ie; ++it) {
1035 const MCSymbol &Symbol = it->getSymbol();
1037 bool Used = UsedInReloc.count(&Symbol);
1038 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
1039 bool isSignature = RevGroupMap.count(&Symbol);
1041 if (!isInSymtab(Asm, *it,
1042 Used || WeakrefUsed || isSignature,
1043 Renames.count(&Symbol)))
1047 MSD.SymbolData = it;
1048 const MCSymbol *BaseSymbol = getBaseSymbol(Layout, Symbol);
1050 // Undefined symbols are global, but this is the first place we
1051 // are able to set it.
1052 bool Local = isLocal(*it, isSignature, Used);
1053 if (!Local && MCELF::GetBinding(*it) == ELF::STB_LOCAL) {
1055 MCSymbolData &SD = Asm.getSymbolData(*BaseSymbol);
1056 MCELF::SetBinding(*it, ELF::STB_GLOBAL);
1057 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1061 MSD.SectionIndex = ELF::SHN_ABS;
1062 } else if (it->isCommon()) {
1064 MSD.SectionIndex = ELF::SHN_COMMON;
1065 } else if (BaseSymbol->isUndefined()) {
1066 if (isSignature && !Used)
1067 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]);
1069 MSD.SectionIndex = ELF::SHN_UNDEF;
1070 if (!Used && WeakrefUsed)
1071 MCELF::SetBinding(*it, ELF::STB_WEAK);
1073 const MCSectionELF &Section =
1074 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1075 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1076 assert(MSD.SectionIndex && "Invalid section index!");
1079 // The @@@ in symbol version is replaced with @ in undefined symbols and
1080 // @@ in defined ones.
1081 StringRef Name = Symbol.getName();
1082 SmallString<32> Buf;
1084 size_t Pos = Name.find("@@@");
1085 if (Pos != StringRef::npos) {
1086 Buf += Name.substr(0, Pos);
1087 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1088 Buf += Name.substr(Pos + Skip);
1092 uint64_t &Entry = StringIndexMap[Name];
1094 Entry = StringTable.size();
1095 StringTable += Name;
1096 StringTable += '\x00';
1098 MSD.StringIndex = Entry;
1099 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1100 UndefinedSymbolData.push_back(MSD);
1102 LocalSymbolData.push_back(MSD);
1104 ExternalSymbolData.push_back(MSD);
1107 // Symbols are required to be in lexicographic order.
1108 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1109 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1110 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1112 // Set the symbol indices. Local symbols must come before all other
1113 // symbols with non-local bindings.
1114 unsigned Index = FileSymbolData.size() + 1;
1115 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1116 LocalSymbolData[i].SymbolData->setIndex(Index++);
1118 Index += NumRegularSections;
1120 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1121 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1122 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1123 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1126 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm,
1127 MCAsmLayout &Layout,
1129 for (MCAssembler::const_iterator it = Asm.begin(),
1130 ie = Asm.end(); it != ie; ++it) {
1131 const MCSectionData &SD = *it;
1132 if (Relocations[&SD].empty())
1135 MCContext &Ctx = Asm.getContext();
1136 const MCSectionELF &Section =
1137 static_cast<const MCSectionELF&>(SD.getSection());
1139 const StringRef SectionName = Section.getSectionName();
1140 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1141 RelaSectionName += SectionName;
1144 if (hasRelocationAddend())
1145 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1147 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1150 StringRef Group = "";
1151 if (Section.getFlags() & ELF::SHF_GROUP) {
1152 Flags = ELF::SHF_GROUP;
1153 Group = Section.getGroup()->getName();
1156 const MCSectionELF *RelaSection =
1157 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ?
1158 ELF::SHT_RELA : ELF::SHT_REL, Flags,
1159 SectionKind::getReadOnly(),
1161 RelMap[&Section] = RelaSection;
1162 Asm.getOrCreateSectionData(*RelaSection);
1166 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
1167 const RelMapTy &RelMap) {
1168 for (MCAssembler::const_iterator it = Asm.begin(),
1169 ie = Asm.end(); it != ie; ++it) {
1170 const MCSectionData &SD = *it;
1171 const MCSectionELF &Section =
1172 static_cast<const MCSectionELF&>(SD.getSection());
1174 const MCSectionELF *RelaSection = RelMap.lookup(&Section);
1177 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
1178 RelaSD.setAlignment(is64Bit() ? 8 : 4);
1180 MCDataFragment *F = new MCDataFragment(&RelaSD);
1181 WriteRelocationsFragment(Asm, F, &*it);
1185 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1186 uint64_t Flags, uint64_t Address,
1187 uint64_t Offset, uint64_t Size,
1188 uint32_t Link, uint32_t Info,
1190 uint64_t EntrySize) {
1191 Write32(Name); // sh_name: index into string table
1192 Write32(Type); // sh_type
1193 WriteWord(Flags); // sh_flags
1194 WriteWord(Address); // sh_addr
1195 WriteWord(Offset); // sh_offset
1196 WriteWord(Size); // sh_size
1197 Write32(Link); // sh_link
1198 Write32(Info); // sh_info
1199 WriteWord(Alignment); // sh_addralign
1200 WriteWord(EntrySize); // sh_entsize
1203 // ELF doesn't require relocations to be in any order. We sort by the r_offset,
1204 // just to match gnu as for easier comparison. The use type is an arbitrary way
1205 // of making the sort deterministic.
1206 static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) {
1207 const ELFRelocationEntry &A = *AP;
1208 const ELFRelocationEntry &B = *BP;
1209 if (A.Offset != B.Offset)
1210 return B.Offset - A.Offset;
1211 if (B.Type != A.Type)
1212 return A.Type - B.Type;
1213 llvm_unreachable("ELFRelocs might be unstable!");
1216 static void sortRelocs(const MCAssembler &Asm,
1217 std::vector<ELFRelocationEntry> &Relocs) {
1218 array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
1221 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1223 const MCSectionData *SD) {
1224 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1226 sortRelocs(Asm, Relocs);
1228 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1229 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1232 if (Entry.UseSymbol) {
1233 Index = getSymbolIndexInSymbolTable(Asm, Entry.Symbol);
1235 const MCSectionData *Sec = Entry.Section;
1237 Index = Sec->getOrdinal() + FileSymbolData.size() +
1238 LocalSymbolData.size() + 1;
1244 write(*F, Entry.Offset);
1245 if (TargetObjectWriter->isN64()) {
1246 write(*F, uint32_t(Index));
1248 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1249 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1250 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1251 write(*F, TargetObjectWriter->getRType(Entry.Type));
1253 struct ELF::Elf64_Rela ERE64;
1254 ERE64.setSymbolAndType(Index, Entry.Type);
1255 write(*F, ERE64.r_info);
1257 if (hasRelocationAddend())
1258 write(*F, Entry.Addend);
1260 write(*F, uint32_t(Entry.Offset));
1262 struct ELF::Elf32_Rela ERE32;
1263 ERE32.setSymbolAndType(Index, Entry.Type);
1264 write(*F, ERE32.r_info);
1266 if (hasRelocationAddend())
1267 write(*F, uint32_t(Entry.Addend));
1272 static int compareBySuffix(const MCSectionELF *const *a,
1273 const MCSectionELF *const *b) {
1274 const StringRef &NameA = (*a)->getSectionName();
1275 const StringRef &NameB = (*b)->getSectionName();
1276 const unsigned sizeA = NameA.size();
1277 const unsigned sizeB = NameB.size();
1278 const unsigned len = std::min(sizeA, sizeB);
1279 for (unsigned int i = 0; i < len; ++i) {
1280 char ca = NameA[sizeA - i - 1];
1281 char cb = NameB[sizeB - i - 1];
1286 return sizeB - sizeA;
1289 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
1290 MCAsmLayout &Layout,
1291 SectionIndexMapTy &SectionIndexMap,
1292 const RelMapTy &RelMap) {
1293 MCContext &Ctx = Asm.getContext();
1296 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1298 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1299 const MCSectionELF *ShstrtabSection =
1300 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
1301 SectionKind::getReadOnly());
1302 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1303 ShstrtabSD.setAlignment(1);
1305 const MCSectionELF *SymtabSection =
1306 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1307 SectionKind::getReadOnly(),
1309 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1310 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1312 const MCSectionELF *StrtabSection;
1313 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
1314 SectionKind::getReadOnly());
1315 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1316 StrtabSD.setAlignment(1);
1318 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1320 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection);
1321 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection);
1322 StringTableIndex = SectionIndexMap.lookup(StrtabSection);
1325 F = new MCDataFragment(&SymtabSD);
1326 WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
1328 F = new MCDataFragment(&StrtabSD);
1329 F->getContents().append(StringTable.begin(), StringTable.end());
1331 F = new MCDataFragment(&ShstrtabSD);
1333 std::vector<const MCSectionELF*> Sections;
1334 for (MCAssembler::const_iterator it = Asm.begin(),
1335 ie = Asm.end(); it != ie; ++it) {
1336 const MCSectionELF &Section =
1337 static_cast<const MCSectionELF&>(it->getSection());
1338 Sections.push_back(&Section);
1340 array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix);
1342 // Section header string table.
1344 // The first entry of a string table holds a null character so skip
1347 F->getContents().push_back('\x00');
1349 for (unsigned int I = 0, E = Sections.size(); I != E; ++I) {
1350 const MCSectionELF &Section = *Sections[I];
1352 StringRef Name = Section.getSectionName();
1354 StringRef PreviousName = Sections[I - 1]->getSectionName();
1355 if (PreviousName.endswith(Name)) {
1356 SectionStringTableIndex[&Section] = Index - Name.size() - 1;
1360 // Remember the index into the string table so we can write it
1361 // into the sh_name field of the section header table.
1362 SectionStringTableIndex[&Section] = Index;
1364 Index += Name.size() + 1;
1365 F->getContents().append(Name.begin(), Name.end());
1366 F->getContents().push_back('\x00');
1370 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm,
1371 MCAsmLayout &Layout,
1372 GroupMapTy &GroupMap,
1373 RevGroupMapTy &RevGroupMap,
1374 SectionIndexMapTy &SectionIndexMap,
1375 const RelMapTy &RelMap) {
1376 // Create the .note.GNU-stack section if needed.
1377 MCContext &Ctx = Asm.getContext();
1378 if (Asm.getNoExecStack()) {
1379 const MCSectionELF *GnuStackSection =
1380 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0,
1381 SectionKind::getReadOnly());
1382 Asm.getOrCreateSectionData(*GnuStackSection);
1386 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1388 const MCSectionELF &Section =
1389 static_cast<const MCSectionELF&>(it->getSection());
1390 if (!(Section.getFlags() & ELF::SHF_GROUP))
1393 const MCSymbol *SignatureSymbol = Section.getGroup();
1394 Asm.getOrCreateSymbolData(*SignatureSymbol);
1395 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1397 Group = Ctx.CreateELFGroupSection();
1398 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1399 Data.setAlignment(4);
1400 MCDataFragment *F = new MCDataFragment(&Data);
1401 write(*F, uint32_t(ELF::GRP_COMDAT));
1403 GroupMap[Group] = SignatureSymbol;
1406 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1408 // Add sections to the groups
1409 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1411 const MCSectionELF &Section =
1412 static_cast<const MCSectionELF&>(it->getSection());
1413 if (!(Section.getFlags() & ELF::SHF_GROUP))
1415 const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1416 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1417 // FIXME: we could use the previous fragment
1418 MCDataFragment *F = new MCDataFragment(&Data);
1419 uint32_t Index = SectionIndexMap.lookup(&Section);
1424 void ELFObjectWriter::WriteSection(MCAssembler &Asm,
1425 const SectionIndexMapTy &SectionIndexMap,
1426 uint32_t GroupSymbolIndex,
1427 uint64_t Offset, uint64_t Size,
1429 const MCSectionELF &Section) {
1430 uint64_t sh_link = 0;
1431 uint64_t sh_info = 0;
1433 switch(Section.getType()) {
1434 case ELF::SHT_DYNAMIC:
1435 sh_link = SectionStringTableIndex[&Section];
1440 case ELF::SHT_RELA: {
1441 const MCSectionELF *SymtabSection;
1442 const MCSectionELF *InfoSection;
1443 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB,
1445 SectionKind::getReadOnly());
1446 sh_link = SectionIndexMap.lookup(SymtabSection);
1447 assert(sh_link && ".symtab not found");
1449 // Remove ".rel" and ".rela" prefixes.
1450 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1451 StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1452 StringRef GroupName =
1453 Section.getGroup() ? Section.getGroup()->getName() : "";
1455 InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS,
1456 0, SectionKind::getReadOnly(),
1458 sh_info = SectionIndexMap.lookup(InfoSection);
1462 case ELF::SHT_SYMTAB:
1463 case ELF::SHT_DYNSYM:
1464 sh_link = StringTableIndex;
1465 sh_info = LastLocalSymbolIndex;
1468 case ELF::SHT_SYMTAB_SHNDX:
1469 sh_link = SymbolTableIndex;
1472 case ELF::SHT_PROGBITS:
1473 case ELF::SHT_STRTAB:
1474 case ELF::SHT_NOBITS:
1477 case ELF::SHT_ARM_ATTRIBUTES:
1478 case ELF::SHT_INIT_ARRAY:
1479 case ELF::SHT_FINI_ARRAY:
1480 case ELF::SHT_PREINIT_ARRAY:
1481 case ELF::SHT_X86_64_UNWIND:
1482 case ELF::SHT_MIPS_REGINFO:
1483 case ELF::SHT_MIPS_OPTIONS:
1487 case ELF::SHT_GROUP:
1488 sh_link = SymbolTableIndex;
1489 sh_info = GroupSymbolIndex;
1493 assert(0 && "FIXME: sh_type value not supported!");
1497 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1498 Section.getType() == ELF::SHT_ARM_EXIDX) {
1499 StringRef SecName(Section.getSectionName());
1500 if (SecName == ".ARM.exidx") {
1501 sh_link = SectionIndexMap.lookup(
1502 Asm.getContext().getELFSection(".text",
1504 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC,
1505 SectionKind::getText()));
1506 } else if (SecName.startswith(".ARM.exidx")) {
1507 StringRef GroupName =
1508 Section.getGroup() ? Section.getGroup()->getName() : "";
1509 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
1510 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS,
1511 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText(), 0,
1516 WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(),
1517 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1518 Alignment, Section.getEntrySize());
1521 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1522 return SD.getOrdinal() == ~UINT32_C(0) &&
1523 !SD.getSection().isVirtualSection();
1526 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1528 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1530 const MCFragment &F = *i;
1531 assert(F.getKind() == MCFragment::FT_Data);
1532 Ret += cast<MCDataFragment>(F).getContents().size();
1537 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
1538 const MCSectionData &SD) {
1539 if (IsELFMetaDataSection(SD))
1540 return DataSectionSize(SD);
1541 return Layout.getSectionFileSize(&SD);
1544 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1545 const MCSectionData &SD) {
1546 if (IsELFMetaDataSection(SD))
1547 return DataSectionSize(SD);
1548 return Layout.getSectionAddressSize(&SD);
1551 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
1552 const MCAsmLayout &Layout,
1553 const MCSectionELF &Section) {
1554 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1556 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1557 WriteZeros(Padding);
1559 if (IsELFMetaDataSection(SD)) {
1560 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1562 const MCFragment &F = *i;
1563 assert(F.getKind() == MCFragment::FT_Data);
1564 WriteBytes(cast<MCDataFragment>(F).getContents());
1567 Asm.writeSectionData(&SD, Layout);
1571 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm,
1572 const GroupMapTy &GroupMap,
1573 const MCAsmLayout &Layout,
1574 const SectionIndexMapTy &SectionIndexMap,
1575 const SectionOffsetMapTy &SectionOffsetMap) {
1576 const unsigned NumSections = Asm.size() + 1;
1578 std::vector<const MCSectionELF*> Sections;
1579 Sections.resize(NumSections - 1);
1581 for (SectionIndexMapTy::const_iterator i=
1582 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
1583 const std::pair<const MCSectionELF*, uint32_t> &p = *i;
1584 Sections[p.second - 1] = p.first;
1587 // Null section first.
1588 uint64_t FirstSectionSize =
1589 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
1590 uint32_t FirstSectionLink =
1591 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1592 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1594 for (unsigned i = 0; i < NumSections - 1; ++i) {
1595 const MCSectionELF &Section = *Sections[i];
1596 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1597 uint32_t GroupSymbolIndex;
1598 if (Section.getType() != ELF::SHT_GROUP)
1599 GroupSymbolIndex = 0;
1601 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1602 GroupMap.lookup(&Section));
1604 uint64_t Size = GetSectionAddressSize(Layout, SD);
1606 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex,
1607 SectionOffsetMap.lookup(&Section), Size,
1608 SD.getAlignment(), Section);
1612 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
1613 std::vector<const MCSectionELF*> &Sections) {
1614 for (MCAssembler::iterator it = Asm.begin(),
1615 ie = Asm.end(); it != ie; ++it) {
1616 const MCSectionELF &Section =
1617 static_cast<const MCSectionELF &>(it->getSection());
1618 if (Section.getType() == ELF::SHT_GROUP)
1619 Sections.push_back(&Section);
1622 for (MCAssembler::iterator it = Asm.begin(),
1623 ie = Asm.end(); it != ie; ++it) {
1624 const MCSectionELF &Section =
1625 static_cast<const MCSectionELF &>(it->getSection());
1626 if (Section.getType() != ELF::SHT_GROUP &&
1627 Section.getType() != ELF::SHT_REL &&
1628 Section.getType() != ELF::SHT_RELA)
1629 Sections.push_back(&Section);
1632 for (MCAssembler::iterator it = Asm.begin(),
1633 ie = Asm.end(); it != ie; ++it) {
1634 const MCSectionELF &Section =
1635 static_cast<const MCSectionELF &>(it->getSection());
1636 if (Section.getType() == ELF::SHT_REL ||
1637 Section.getType() == ELF::SHT_RELA)
1638 Sections.push_back(&Section);
1642 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1643 const MCAsmLayout &Layout) {
1644 GroupMapTy GroupMap;
1645 RevGroupMapTy RevGroupMap;
1646 SectionIndexMapTy SectionIndexMap;
1648 unsigned NumUserSections = Asm.size();
1650 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap;
1651 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1653 const unsigned NumUserAndRelocSections = Asm.size();
1654 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
1655 RevGroupMap, SectionIndexMap, RelMap);
1656 const unsigned AllSections = Asm.size();
1657 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections;
1659 unsigned NumRegularSections = NumUserSections + NumIndexedSections;
1661 // Compute symbol table information.
1662 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
1663 NumRegularSections);
1665 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1667 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1668 const_cast<MCAsmLayout&>(Layout),
1672 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1673 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
1674 sizeof(ELF::Elf32_Ehdr);
1675 uint64_t FileOff = HeaderSize;
1677 std::vector<const MCSectionELF*> Sections;
1678 ComputeSectionOrder(Asm, Sections);
1679 unsigned NumSections = Sections.size();
1680 SectionOffsetMapTy SectionOffsetMap;
1681 for (unsigned i = 0; i < NumRegularSections + 1; ++i) {
1682 const MCSectionELF &Section = *Sections[i];
1683 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1685 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1687 // Remember the offset into the file for this section.
1688 SectionOffsetMap[&Section] = FileOff;
1690 // Get the size of the section in the output file (including padding).
1691 FileOff += GetSectionFileSize(Layout, SD);
1694 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1696 const unsigned SectionHeaderOffset = FileOff - HeaderSize;
1698 uint64_t SectionHeaderEntrySize = is64Bit() ?
1699 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr);
1700 FileOff += (NumSections + 1) * SectionHeaderEntrySize;
1702 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) {
1703 const MCSectionELF &Section = *Sections[i];
1704 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1706 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1708 // Remember the offset into the file for this section.
1709 SectionOffsetMap[&Section] = FileOff;
1711 // Get the size of the section in the output file (including padding).
1712 FileOff += GetSectionFileSize(Layout, SD);
1715 // Write out the ELF header ...
1716 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
1718 // ... then the regular sections ...
1719 // + because of .shstrtab
1720 for (unsigned i = 0; i < NumRegularSections + 1; ++i)
1721 WriteDataSectionData(Asm, Layout, *Sections[i]);
1723 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1724 WriteZeros(Padding);
1726 // ... then the section header table ...
1727 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap,
1730 // ... and then the remaining sections ...
1731 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i)
1732 WriteDataSectionData(Asm, Layout, *Sections[i]);
1736 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
1737 const MCSymbolData &DataA,
1738 const MCFragment &FB,
1740 bool IsPCRel) const {
1741 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC)
1743 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1744 Asm, DataA, FB,InSet, IsPCRel);
1747 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1749 bool IsLittleEndian) {
1750 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);