1 //===- lib/MC/ELFObjectWriter.cpp - ELF File Writer -----------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements ELF object file writer information.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/MC/MCELFObjectWriter.h"
15 #include "llvm/ADT/STLExtras.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/ADT/SmallString.h"
18 #include "llvm/ADT/StringMap.h"
19 #include "llvm/MC/MCAsmBackend.h"
20 #include "llvm/MC/MCAsmInfo.h"
21 #include "llvm/MC/MCAsmLayout.h"
22 #include "llvm/MC/MCAssembler.h"
23 #include "llvm/MC/MCContext.h"
24 #include "llvm/MC/MCELF.h"
25 #include "llvm/MC/MCELFSymbolFlags.h"
26 #include "llvm/MC/MCExpr.h"
27 #include "llvm/MC/MCFixupKindInfo.h"
28 #include "llvm/MC/MCObjectWriter.h"
29 #include "llvm/MC/MCSectionELF.h"
30 #include "llvm/MC/MCValue.h"
31 #include "llvm/Support/Compression.h"
32 #include "llvm/Support/Debug.h"
33 #include "llvm/Support/Endian.h"
34 #include "llvm/Support/ELF.h"
35 #include "llvm/Support/ErrorHandling.h"
40 #define DEBUG_TYPE "reloc-info"
43 class FragmentWriter {
47 FragmentWriter(bool IsLittleEndian);
48 template <typename T> void write(MCDataFragment &F, T Val);
51 typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
53 class SymbolTableWriter {
55 FragmentWriter &FWriter;
57 SectionIndexMapTy &SectionIndexMap;
59 // The symbol .symtab fragment we are writting to.
60 MCDataFragment *SymtabF;
62 // .symtab_shndx fragment we are writting to.
63 MCDataFragment *ShndxF;
65 // The numbel of symbols written so far.
68 void createSymtabShndx();
70 template <typename T> void write(MCDataFragment &F, T Value);
73 SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit,
74 SectionIndexMapTy &SectionIndexMap,
75 MCDataFragment *SymtabF);
77 void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
78 uint8_t other, uint32_t shndx, bool Reserved);
81 struct ELFRelocationEntry {
82 uint64_t Offset; // Where is the relocation.
83 bool UseSymbol; // Relocate with a symbol, not the section.
85 const MCSymbol *Symbol; // The symbol to relocate with.
86 const MCSectionData *Section; // The section to relocate with.
88 unsigned Type; // The type of the relocation.
89 uint64_t Addend; // The addend to use.
91 ELFRelocationEntry(uint64_t Offset, const MCSymbol *Symbol, unsigned Type,
93 : Offset(Offset), UseSymbol(true), Symbol(Symbol), Type(Type),
96 ELFRelocationEntry(uint64_t Offset, const MCSectionData *Section,
97 unsigned Type, uint64_t Addend)
98 : Offset(Offset), UseSymbol(false), Section(Section), Type(Type),
102 class ELFObjectWriter : public MCObjectWriter {
103 FragmentWriter FWriter;
107 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
108 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
109 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
110 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data,
111 bool Used, bool Renamed);
112 static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc);
113 static bool IsELFMetaDataSection(const MCSectionData &SD);
114 static uint64_t DataSectionSize(const MCSectionData &SD);
115 static uint64_t GetSectionFileSize(const MCAsmLayout &Layout,
116 const MCSectionData &SD);
117 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout,
118 const MCSectionData &SD);
120 void WriteDataSectionData(MCAssembler &Asm,
121 const MCAsmLayout &Layout,
122 const MCSectionELF &Section);
124 /*static bool isFixupKindX86RIPRel(unsigned Kind) {
125 return Kind == X86::reloc_riprel_4byte ||
126 Kind == X86::reloc_riprel_4byte_movq_load;
129 /// ELFSymbolData - Helper struct for containing some precomputed
130 /// information on symbols.
131 struct ELFSymbolData {
132 MCSymbolData *SymbolData;
133 uint64_t StringIndex;
134 uint32_t SectionIndex;
136 // Support lexicographic sorting.
137 bool operator<(const ELFSymbolData &RHS) const {
138 return SymbolData->getSymbol().getName() <
139 RHS.SymbolData->getSymbol().getName();
143 /// The target specific ELF writer instance.
144 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
146 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
147 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
148 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
150 llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>>
152 DenseMap<const MCSection*, uint64_t> SectionStringTableIndex;
155 /// @name Symbol Table Data
158 SmallString<256> StringTable;
159 std::vector<uint64_t> FileSymbolData;
160 std::vector<ELFSymbolData> LocalSymbolData;
161 std::vector<ELFSymbolData> ExternalSymbolData;
162 std::vector<ELFSymbolData> UndefinedSymbolData;
168 // This holds the symbol table index of the last local symbol.
169 unsigned LastLocalSymbolIndex;
170 // This holds the .strtab section index.
171 unsigned StringTableIndex;
172 // This holds the .symtab section index.
173 unsigned SymbolTableIndex;
175 unsigned ShstrtabIndex;
178 // TargetObjectWriter wrappers.
179 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
180 bool hasRelocationAddend() const {
181 return TargetObjectWriter->hasRelocationAddend();
183 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
184 bool IsPCRel) const {
185 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
189 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_ostream &_OS,
191 : MCObjectWriter(_OS, IsLittleEndian), FWriter(IsLittleEndian),
192 TargetObjectWriter(MOTW), NeedsGOT(false) {}
194 virtual ~ELFObjectWriter();
196 void WriteWord(uint64_t W) {
203 template <typename T> void write(MCDataFragment &F, T Value) {
204 FWriter.write(F, Value);
207 void WriteHeader(const MCAssembler &Asm,
208 uint64_t SectionDataSize,
209 unsigned NumberOfSections);
211 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
212 const MCAsmLayout &Layout);
214 void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm,
215 const MCAsmLayout &Layout,
216 SectionIndexMapTy &SectionIndexMap);
218 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
219 const MCSymbolRefExpr *RefA,
220 const MCSymbolData *SD, uint64_t C,
221 unsigned Type) const;
223 void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
224 const MCFragment *Fragment, const MCFixup &Fixup,
225 MCValue Target, bool &IsPCRel,
226 uint64_t &FixedValue) override;
228 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
231 // Map from a group section to the signature symbol
232 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
233 // Map from a signature symbol to the group section
234 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
235 // Map from a section to the section with the relocations
236 typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy;
237 // Map from a section to its offset
238 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy;
240 /// Compute the symbol table data
242 /// \param Asm - The assembler.
243 /// \param SectionIndexMap - Maps a section to its index.
244 /// \param RevGroupMap - Maps a signature symbol to the group section.
245 /// \param NumRegularSections - Number of non-relocation sections.
246 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
247 const SectionIndexMapTy &SectionIndexMap,
248 RevGroupMapTy RevGroupMap,
249 unsigned NumRegularSections);
251 void ComputeIndexMap(MCAssembler &Asm,
252 SectionIndexMapTy &SectionIndexMap,
253 const RelMapTy &RelMap);
255 void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout,
258 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
260 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
261 const RelMapTy &RelMap);
263 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
264 SectionIndexMapTy &SectionIndexMap,
265 const RelMapTy &RelMap);
267 // Create the sections that show up in the symbol table. Currently
268 // those are the .note.GNU-stack section and the group sections.
269 void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
270 GroupMapTy &GroupMap,
271 RevGroupMapTy &RevGroupMap,
272 SectionIndexMapTy &SectionIndexMap,
273 const RelMapTy &RelMap);
275 void ExecutePostLayoutBinding(MCAssembler &Asm,
276 const MCAsmLayout &Layout) override;
278 void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap,
279 const MCAsmLayout &Layout,
280 const SectionIndexMapTy &SectionIndexMap,
281 const SectionOffsetMapTy &SectionOffsetMap);
283 void ComputeSectionOrder(MCAssembler &Asm,
284 std::vector<const MCSectionELF*> &Sections);
286 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
287 uint64_t Address, uint64_t Offset,
288 uint64_t Size, uint32_t Link, uint32_t Info,
289 uint64_t Alignment, uint64_t EntrySize);
291 void WriteRelocationsFragment(const MCAssembler &Asm,
293 const MCSectionData *SD);
296 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
297 const MCSymbolData &DataA,
298 const MCFragment &FB,
300 bool IsPCRel) const override;
302 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
303 void WriteSection(MCAssembler &Asm,
304 const SectionIndexMapTy &SectionIndexMap,
305 uint32_t GroupSymbolIndex,
306 uint64_t Offset, uint64_t Size, uint64_t Alignment,
307 const MCSectionELF &Section);
311 FragmentWriter::FragmentWriter(bool IsLittleEndian)
312 : IsLittleEndian(IsLittleEndian) {}
314 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
316 Val = support::endian::byte_swap<T, support::little>(Val);
318 Val = support::endian::byte_swap<T, support::big>(Val);
319 const char *Start = (const char *)&Val;
320 F.getContents().append(Start, Start + sizeof(T));
323 void SymbolTableWriter::createSymtabShndx() {
327 MCContext &Ctx = Asm.getContext();
328 const MCSectionELF *SymtabShndxSection =
329 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0,
330 SectionKind::getReadOnly(), 4, "");
331 MCSectionData *SymtabShndxSD =
332 &Asm.getOrCreateSectionData(*SymtabShndxSection);
333 SymtabShndxSD->setAlignment(4);
334 ShndxF = new MCDataFragment(SymtabShndxSD);
335 unsigned Index = SectionIndexMap.size() + 1;
336 SectionIndexMap[SymtabShndxSection] = Index;
338 for (unsigned I = 0; I < NumWritten; ++I)
339 write(*ShndxF, uint32_t(0));
342 template <typename T>
343 void SymbolTableWriter::write(MCDataFragment &F, T Value) {
344 FWriter.write(F, Value);
347 SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter,
349 SectionIndexMapTy &SectionIndexMap,
350 MCDataFragment *SymtabF)
351 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit),
352 SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr),
355 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
356 uint64_t size, uint8_t other,
357 uint32_t shndx, bool Reserved) {
358 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
365 write(*ShndxF, shndx);
367 write(*ShndxF, uint32_t(0));
370 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
372 raw_svector_ostream OS(SymtabF->getContents());
375 write(*SymtabF, name); // st_name
376 write(*SymtabF, info); // st_info
377 write(*SymtabF, other); // st_other
378 write(*SymtabF, Index); // st_shndx
379 write(*SymtabF, value); // st_value
380 write(*SymtabF, size); // st_size
382 write(*SymtabF, name); // st_name
383 write(*SymtabF, uint32_t(value)); // st_value
384 write(*SymtabF, uint32_t(size)); // st_size
385 write(*SymtabF, info); // st_info
386 write(*SymtabF, other); // st_other
387 write(*SymtabF, Index); // st_shndx
393 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
394 const MCFixupKindInfo &FKI =
395 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
397 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
400 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
404 case MCSymbolRefExpr::VK_GOT:
405 case MCSymbolRefExpr::VK_PLT:
406 case MCSymbolRefExpr::VK_GOTPCREL:
407 case MCSymbolRefExpr::VK_GOTOFF:
408 case MCSymbolRefExpr::VK_TPOFF:
409 case MCSymbolRefExpr::VK_TLSGD:
410 case MCSymbolRefExpr::VK_GOTTPOFF:
411 case MCSymbolRefExpr::VK_INDNTPOFF:
412 case MCSymbolRefExpr::VK_NTPOFF:
413 case MCSymbolRefExpr::VK_GOTNTPOFF:
414 case MCSymbolRefExpr::VK_TLSLDM:
415 case MCSymbolRefExpr::VK_DTPOFF:
416 case MCSymbolRefExpr::VK_TLSLD:
421 ELFObjectWriter::~ELFObjectWriter()
424 // Emit the ELF header.
425 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
426 uint64_t SectionDataSize,
427 unsigned NumberOfSections) {
433 // emitWord method behaves differently for ELF32 and ELF64, writing
434 // 4 bytes in the former and 8 in the latter.
436 Write8(0x7f); // e_ident[EI_MAG0]
437 Write8('E'); // e_ident[EI_MAG1]
438 Write8('L'); // e_ident[EI_MAG2]
439 Write8('F'); // e_ident[EI_MAG3]
441 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
444 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
446 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
448 Write8(TargetObjectWriter->getOSABI());
449 Write8(0); // e_ident[EI_ABIVERSION]
451 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
453 Write16(ELF::ET_REL); // e_type
455 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
457 Write32(ELF::EV_CURRENT); // e_version
458 WriteWord(0); // e_entry, no entry point in .o file
459 WriteWord(0); // e_phoff, no program header for .o
460 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
461 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes
463 // e_flags = whatever the target wants
464 Write32(Asm.getELFHeaderEFlags());
466 // e_ehsize = ELF header size
467 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
469 Write16(0); // e_phentsize = prog header entry size
470 Write16(0); // e_phnum = # prog header entries = 0
472 // e_shentsize = Section header entry size
473 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
475 // e_shnum = # of section header ents
476 if (NumberOfSections >= ELF::SHN_LORESERVE)
477 Write16(ELF::SHN_UNDEF);
479 Write16(NumberOfSections);
481 // e_shstrndx = Section # of '.shstrtab'
482 if (ShstrtabIndex >= ELF::SHN_LORESERVE)
483 Write16(ELF::SHN_XINDEX);
485 Write16(ShstrtabIndex);
488 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &OrigData,
489 const MCAsmLayout &Layout) {
490 const MCSymbol &OrigSymbol = OrigData.getSymbol();
491 MCSymbolData *Data = &OrigData;
492 if (Data->isCommon() && Data->isExternal())
493 return Data->getCommonAlignment();
495 const MCSymbol *Symbol = &Data->getSymbol();
498 if (Symbol->isVariable()) {
499 const MCExpr *Expr = Symbol->getVariableValue();
501 if (!Expr->EvaluateAsValue(Value, &Layout))
502 llvm_unreachable("Invalid expression");
504 assert(!Value.getSymB());
506 Res = Value.getConstant();
508 if (const MCSymbolRefExpr *A = Value.getSymA()) {
509 Symbol = &A->getSymbol();
510 Data = &Layout.getAssembler().getSymbolData(*Symbol);
517 const MCAssembler &Asm = Layout.getAssembler();
518 if (Asm.isThumbFunc(&OrigSymbol))
521 if (!Symbol || !Symbol->isInSection())
524 Res += Layout.getSymbolOffset(Data);
529 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
530 const MCAsmLayout &Layout) {
531 // The presence of symbol versions causes undefined symbols and
532 // versions declared with @@@ to be renamed.
534 for (MCSymbolData &OriginalData : Asm.symbols()) {
535 const MCSymbol &Alias = OriginalData.getSymbol();
538 if (!Alias.isVariable())
540 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
543 const MCSymbol &Symbol = Ref->getSymbol();
544 MCSymbolData &SD = Asm.getSymbolData(Symbol);
546 StringRef AliasName = Alias.getName();
547 size_t Pos = AliasName.find('@');
548 if (Pos == StringRef::npos)
551 // Aliases defined with .symvar copy the binding from the symbol they alias.
552 // This is the first place we are able to copy this information.
553 OriginalData.setExternal(SD.isExternal());
554 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
556 StringRef Rest = AliasName.substr(Pos);
557 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
560 // FIXME: produce a better error message.
561 if (Symbol.isUndefined() && Rest.startswith("@@") &&
562 !Rest.startswith("@@@"))
563 report_fatal_error("A @@ version cannot be undefined");
565 Renames.insert(std::make_pair(&Symbol, &Alias));
569 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
570 uint8_t Type = newType;
572 // Propagation rules:
573 // IFUNC > FUNC > OBJECT > NOTYPE
574 // TLS_OBJECT > OBJECT > NOTYPE
576 // dont let the new type degrade the old type
580 case ELF::STT_GNU_IFUNC:
581 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
582 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
583 Type = ELF::STT_GNU_IFUNC;
586 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
587 Type == ELF::STT_TLS)
588 Type = ELF::STT_FUNC;
590 case ELF::STT_OBJECT:
591 if (Type == ELF::STT_NOTYPE)
592 Type = ELF::STT_OBJECT;
595 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
596 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
604 static const MCSymbol *getBaseSymbol(const MCAsmLayout &Layout,
605 const MCSymbol &Symbol) {
606 if (!Symbol.isVariable())
609 const MCExpr *Expr = Symbol.getVariableValue();
611 if (!Expr->EvaluateAsValue(Value, &Layout))
612 llvm_unreachable("Invalid Expression");
613 const MCSymbolRefExpr *RefB = Value.getSymB();
615 Layout.getAssembler().getContext().FatalError(
616 SMLoc(), Twine("symbol '") + RefB->getSymbol().getName() +
617 "' could not be evaluated in a subtraction expression");
619 const MCSymbolRefExpr *A = Value.getSymA();
622 return getBaseSymbol(Layout, A->getSymbol());
625 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
626 const MCAsmLayout &Layout) {
627 MCSymbolData &OrigData = *MSD.SymbolData;
628 assert((!OrigData.getFragment() ||
629 (&OrigData.getFragment()->getParent()->getSection() ==
630 &OrigData.getSymbol().getSection())) &&
631 "The symbol's section doesn't match the fragment's symbol");
632 const MCSymbol *Base = getBaseSymbol(Layout, OrigData.getSymbol());
634 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
636 bool IsReserved = !Base || OrigData.isCommon();
638 // Binding and Type share the same byte as upper and lower nibbles
639 uint8_t Binding = MCELF::GetBinding(OrigData);
640 uint8_t Type = MCELF::GetType(OrigData);
641 MCSymbolData *BaseSD = nullptr;
643 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
644 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
646 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
648 // Other and Visibility share the same byte with Visibility using the lower
650 uint8_t Visibility = MCELF::GetVisibility(OrigData);
651 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
654 uint64_t Value = SymbolValue(OrigData, Layout);
657 const MCExpr *ESize = OrigData.getSize();
659 ESize = BaseSD->getSize();
663 if (!ESize->EvaluateAsAbsolute(Res, Layout))
664 report_fatal_error("Size expression must be absolute.");
668 // Write out the symbol table entry
669 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
670 MSD.SectionIndex, IsReserved);
673 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF,
675 const MCAsmLayout &Layout,
676 SectionIndexMapTy &SectionIndexMap) {
677 // The string table must be emitted first because we need the index
678 // into the string table for all the symbol names.
679 assert(StringTable.size() && "Missing string table");
681 // FIXME: Make sure the start of the symbol table is aligned.
683 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF);
685 // The first entry is the undefined symbol entry.
686 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
688 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
689 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
690 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
693 // Write the symbol table entries.
694 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
696 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
697 ELFSymbolData &MSD = LocalSymbolData[i];
698 WriteSymbol(Writer, MSD, Layout);
701 // Write out a symbol table entry for each regular section.
702 for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e;
704 const MCSectionELF &Section =
705 static_cast<const MCSectionELF&>(i->getSection());
706 if (Section.getType() == ELF::SHT_RELA ||
707 Section.getType() == ELF::SHT_REL ||
708 Section.getType() == ELF::SHT_STRTAB ||
709 Section.getType() == ELF::SHT_SYMTAB ||
710 Section.getType() == ELF::SHT_SYMTAB_SHNDX)
712 Writer.writeSymbol(0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT,
713 SectionIndexMap.lookup(&Section), false);
714 LastLocalSymbolIndex++;
717 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
718 ELFSymbolData &MSD = ExternalSymbolData[i];
719 MCSymbolData &Data = *MSD.SymbolData;
720 assert(((Data.getFlags() & ELF_STB_Global) ||
721 (Data.getFlags() & ELF_STB_Weak)) &&
722 "External symbol requires STB_GLOBAL or STB_WEAK flag");
723 WriteSymbol(Writer, MSD, Layout);
724 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
725 LastLocalSymbolIndex++;
728 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
729 ELFSymbolData &MSD = UndefinedSymbolData[i];
730 MCSymbolData &Data = *MSD.SymbolData;
731 WriteSymbol(Writer, MSD, Layout);
732 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
733 LastLocalSymbolIndex++;
737 // It is always valid to create a relocation with a symbol. It is preferable
738 // to use a relocation with a section if that is possible. Using the section
739 // allows us to omit some local symbols from the symbol table.
740 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
741 const MCSymbolRefExpr *RefA,
742 const MCSymbolData *SD,
744 unsigned Type) const {
745 // A PCRel relocation to an absolute value has no symbol (or section). We
746 // represent that with a relocation to a null section.
750 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
754 // The .odp creation emits a relocation against the symbol ".TOC." which
755 // create a R_PPC64_TOC relocation. However the relocation symbol name
756 // in final object creation should be NULL, since the symbol does not
757 // really exist, it is just the reference to TOC base for the current
758 // object file. Since the symbol is undefined, returning false results
759 // in a relocation with a null section which is the desired result.
760 case MCSymbolRefExpr::VK_PPC_TOCBASE:
763 // These VariantKind cause the relocation to refer to something other than
764 // the symbol itself, like a linker generated table. Since the address of
765 // symbol is not relevant, we cannot replace the symbol with the
766 // section and patch the difference in the addend.
767 case MCSymbolRefExpr::VK_GOT:
768 case MCSymbolRefExpr::VK_PLT:
769 case MCSymbolRefExpr::VK_GOTPCREL:
770 case MCSymbolRefExpr::VK_Mips_GOT:
771 case MCSymbolRefExpr::VK_PPC_GOT_LO:
772 case MCSymbolRefExpr::VK_PPC_GOT_HI:
773 case MCSymbolRefExpr::VK_PPC_GOT_HA:
777 // An undefined symbol is not in any section, so the relocation has to point
778 // to the symbol itself.
779 const MCSymbol &Sym = SD->getSymbol();
780 if (Sym.isUndefined())
783 unsigned Binding = MCELF::GetBinding(*SD);
786 llvm_unreachable("Invalid Binding");
790 // If the symbol is weak, it might be overridden by a symbol in another
791 // file. The relocation has to point to the symbol so that the linker
794 case ELF::STB_GLOBAL:
795 // Global ELF symbols can be preempted by the dynamic linker. The relocation
796 // has to point to the symbol for a reason analogous to the STB_WEAK case.
800 // If a relocation points to a mergeable section, we have to be careful.
801 // If the offset is zero, a relocation with the section will encode the
802 // same information. With a non-zero offset, the situation is different.
803 // For example, a relocation can point 42 bytes past the end of a string.
804 // If we change such a relocation to use the section, the linker would think
805 // that it pointed to another string and subtracting 42 at runtime will
806 // produce the wrong value.
807 auto &Sec = cast<MCSectionELF>(Sym.getSection());
808 unsigned Flags = Sec.getFlags();
809 if (Flags & ELF::SHF_MERGE) {
813 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
814 // only handle section relocations to mergeable sections if using RELA.
815 if (!hasRelocationAddend())
819 // Most TLS relocations use a got, so they need the symbol. Even those that
820 // are just an offset (@tpoff), require a symbol in some linkers (gold,
822 if (Flags & ELF::SHF_TLS)
825 // If the symbol is a thumb function the final relocation must set the lowest
826 // bit. With a symbol that is done by just having the symbol have that bit
827 // set, so we would lose the bit if we relocated with the section.
828 // FIXME: We could use the section but add the bit to the relocation value.
829 if (Asm.isThumbFunc(&Sym))
832 if (TargetObjectWriter->needsRelocateWithSymbol(Type))
837 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
838 const MCAsmLayout &Layout,
839 const MCFragment *Fragment,
840 const MCFixup &Fixup,
843 uint64_t &FixedValue) {
844 const MCSectionData *FixupSection = Fragment->getParent();
845 uint64_t C = Target.getConstant();
846 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
848 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
849 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
850 "Should not have constructed this");
852 // Let A, B and C being the components of Target and R be the location of
853 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
854 // If it is pcrel, we want to compute (A - B + C - R).
856 // In general, ELF has no relocations for -B. It can only represent (A + C)
857 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
858 // replace B to implement it: (A - R - K + C)
860 Asm.getContext().FatalError(
862 "No relocation available to represent this relative expression");
864 const MCSymbol &SymB = RefB->getSymbol();
866 if (SymB.isUndefined())
867 Asm.getContext().FatalError(
869 Twine("symbol '") + SymB.getName() +
870 "' can not be undefined in a subtraction expression");
872 assert(!SymB.isAbsolute() && "Should have been folded");
873 const MCSection &SecB = SymB.getSection();
874 if (&SecB != &FixupSection->getSection())
875 Asm.getContext().FatalError(
876 Fixup.getLoc(), "Cannot represent a difference across sections");
878 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
879 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
880 uint64_t K = SymBOffset - FixupOffset;
885 // We either rejected the fixup or folded B into C at this point.
886 const MCSymbolRefExpr *RefA = Target.getSymA();
887 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
888 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
890 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
891 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
892 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
893 C += Layout.getSymbolOffset(SymAD);
896 if (hasRelocationAddend()) {
903 // FIXME: What is this!?!?
904 MCSymbolRefExpr::VariantKind Modifier =
905 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
906 if (RelocNeedsGOT(Modifier))
909 if (!RelocateWithSymbol) {
910 const MCSection *SecA =
911 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
912 const MCSectionData *SecAD = SecA ? &Asm.getSectionData(*SecA) : nullptr;
913 ELFRelocationEntry Rec(FixupOffset, SecAD, Type, Addend);
914 Relocations[FixupSection].push_back(Rec);
919 if (const MCSymbol *R = Renames.lookup(SymA))
922 if (RefA->getKind() == MCSymbolRefExpr::VK_WEAKREF)
923 WeakrefUsedInReloc.insert(SymA);
925 UsedInReloc.insert(SymA);
927 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
928 Relocations[FixupSection].push_back(Rec);
934 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
936 const MCSymbolData &SD = Asm.getSymbolData(*S);
937 return SD.getIndex();
940 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
941 const MCSymbolData &Data, bool Used,
943 const MCSymbol &Symbol = Data.getSymbol();
944 if (Symbol.isVariable()) {
945 const MCExpr *Expr = Symbol.getVariableValue();
946 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
947 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
958 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
961 if (Symbol.isVariable()) {
962 const MCSymbol *Base = getBaseSymbol(Layout, Symbol);
963 if (Base && Base->isUndefined())
967 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
968 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
971 if (Symbol.isTemporary())
977 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
978 if (Data.isExternal())
981 const MCSymbol &Symbol = Data.getSymbol();
982 if (Symbol.isDefined())
991 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
992 SectionIndexMapTy &SectionIndexMap,
993 const RelMapTy &RelMap) {
995 for (MCAssembler::iterator it = Asm.begin(),
996 ie = Asm.end(); it != ie; ++it) {
997 const MCSectionELF &Section =
998 static_cast<const MCSectionELF &>(it->getSection());
999 if (Section.getType() != ELF::SHT_GROUP)
1001 SectionIndexMap[&Section] = Index++;
1004 for (MCAssembler::iterator it = Asm.begin(),
1005 ie = Asm.end(); it != ie; ++it) {
1006 const MCSectionELF &Section =
1007 static_cast<const MCSectionELF &>(it->getSection());
1008 if (Section.getType() == ELF::SHT_GROUP ||
1009 Section.getType() == ELF::SHT_REL ||
1010 Section.getType() == ELF::SHT_RELA)
1012 SectionIndexMap[&Section] = Index++;
1013 const MCSectionELF *RelSection = RelMap.lookup(&Section);
1015 SectionIndexMap[RelSection] = Index++;
1020 ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
1021 const SectionIndexMapTy &SectionIndexMap,
1022 RevGroupMapTy RevGroupMap,
1023 unsigned NumRegularSections) {
1024 // FIXME: Is this the correct place to do this?
1025 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
1027 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
1028 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
1029 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
1030 Data.setExternal(true);
1031 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
1034 // Index 0 is always the empty string.
1035 StringMap<uint64_t> StringIndexMap;
1036 StringTable += '\x00';
1038 // FIXME: We could optimize suffixes in strtab in the same way we
1039 // optimize them in shstrtab.
1041 for (MCAssembler::const_file_name_iterator it = Asm.file_names_begin(),
1042 ie = Asm.file_names_end();
1045 StringRef Name = *it;
1046 uint64_t &Entry = StringIndexMap[Name];
1048 Entry = StringTable.size();
1049 StringTable += Name;
1050 StringTable += '\x00';
1052 FileSymbolData.push_back(Entry);
1055 // Add the data for the symbols.
1056 for (MCSymbolData &SD : Asm.symbols()) {
1057 const MCSymbol &Symbol = SD.getSymbol();
1059 bool Used = UsedInReloc.count(&Symbol);
1060 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
1061 bool isSignature = RevGroupMap.count(&Symbol);
1063 if (!isInSymtab(Layout, SD,
1064 Used || WeakrefUsed || isSignature,
1065 Renames.count(&Symbol)))
1069 MSD.SymbolData = &SD;
1070 const MCSymbol *BaseSymbol = getBaseSymbol(Layout, Symbol);
1072 // Undefined symbols are global, but this is the first place we
1073 // are able to set it.
1074 bool Local = isLocal(SD, Used);
1075 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1077 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1078 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1079 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1083 MSD.SectionIndex = ELF::SHN_ABS;
1084 } else if (SD.isCommon()) {
1086 MSD.SectionIndex = ELF::SHN_COMMON;
1087 } else if (BaseSymbol->isUndefined()) {
1088 if (isSignature && !Used)
1089 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]);
1091 MSD.SectionIndex = ELF::SHN_UNDEF;
1092 if (!Used && WeakrefUsed)
1093 MCELF::SetBinding(SD, ELF::STB_WEAK);
1095 const MCSectionELF &Section =
1096 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1097 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1098 assert(MSD.SectionIndex && "Invalid section index!");
1101 // The @@@ in symbol version is replaced with @ in undefined symbols and
1102 // @@ in defined ones.
1103 StringRef Name = Symbol.getName();
1104 SmallString<32> Buf;
1106 size_t Pos = Name.find("@@@");
1107 if (Pos != StringRef::npos) {
1108 Buf += Name.substr(0, Pos);
1109 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1110 Buf += Name.substr(Pos + Skip);
1114 uint64_t &Entry = StringIndexMap[Name];
1116 Entry = StringTable.size();
1117 StringTable += Name;
1118 StringTable += '\x00';
1120 MSD.StringIndex = Entry;
1121 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1122 UndefinedSymbolData.push_back(MSD);
1124 LocalSymbolData.push_back(MSD);
1126 ExternalSymbolData.push_back(MSD);
1129 // Symbols are required to be in lexicographic order.
1130 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1131 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1132 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1134 // Set the symbol indices. Local symbols must come before all other
1135 // symbols with non-local bindings.
1136 unsigned Index = FileSymbolData.size() + 1;
1137 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1138 LocalSymbolData[i].SymbolData->setIndex(Index++);
1140 Index += NumRegularSections;
1142 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1143 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1144 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1145 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1148 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm,
1149 MCAsmLayout &Layout,
1151 for (MCAssembler::const_iterator it = Asm.begin(),
1152 ie = Asm.end(); it != ie; ++it) {
1153 const MCSectionData &SD = *it;
1154 if (Relocations[&SD].empty())
1157 MCContext &Ctx = Asm.getContext();
1158 const MCSectionELF &Section =
1159 static_cast<const MCSectionELF&>(SD.getSection());
1161 const StringRef SectionName = Section.getSectionName();
1162 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1163 RelaSectionName += SectionName;
1166 if (hasRelocationAddend())
1167 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1169 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1172 StringRef Group = "";
1173 if (Section.getFlags() & ELF::SHF_GROUP) {
1174 Flags = ELF::SHF_GROUP;
1175 Group = Section.getGroup()->getName();
1178 const MCSectionELF *RelaSection =
1179 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ?
1180 ELF::SHT_RELA : ELF::SHT_REL, Flags,
1181 SectionKind::getReadOnly(),
1183 RelMap[&Section] = RelaSection;
1184 Asm.getOrCreateSectionData(*RelaSection);
1188 static SmallVector<char, 128>
1189 getUncompressedData(MCAsmLayout &Layout,
1190 MCSectionData::FragmentListType &Fragments) {
1191 SmallVector<char, 128> UncompressedData;
1192 for (const MCFragment &F : Fragments) {
1193 const SmallVectorImpl<char> *Contents;
1194 switch (F.getKind()) {
1195 case MCFragment::FT_Data:
1196 Contents = &cast<MCDataFragment>(F).getContents();
1198 case MCFragment::FT_Dwarf:
1199 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1201 case MCFragment::FT_DwarfFrame:
1202 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1206 "Not expecting any other fragment types in a debug_* section");
1208 UncompressedData.append(Contents->begin(), Contents->end());
1210 return UncompressedData;
1213 // Include the debug info compression header:
1214 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1215 // useful for consumers to preallocate a buffer to decompress into.
1217 prependCompressionHeader(uint64_t Size,
1218 SmallVectorImpl<char> &CompressedContents) {
1219 static const StringRef Magic = "ZLIB";
1220 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1222 if (sys::IsLittleEndianHost)
1223 Size = sys::SwapByteOrder(Size);
1224 CompressedContents.insert(CompressedContents.begin(),
1225 Magic.size() + sizeof(Size), 0);
1226 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1227 std::copy(reinterpret_cast<char *>(&Size),
1228 reinterpret_cast<char *>(&Size + 1),
1229 CompressedContents.begin() + Magic.size());
1233 // Return a single fragment containing the compressed contents of the whole
1234 // section. Null if the section was not compressed for any reason.
1235 static std::unique_ptr<MCDataFragment>
1236 getCompressedFragment(MCAsmLayout &Layout,
1237 MCSectionData::FragmentListType &Fragments) {
1238 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1240 // Gather the uncompressed data from all the fragments, recording the
1241 // alignment fragment, if seen, and any fixups.
1242 SmallVector<char, 128> UncompressedData =
1243 getUncompressedData(Layout, Fragments);
1245 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1247 zlib::Status Success = zlib::compress(
1248 StringRef(UncompressedData.data(), UncompressedData.size()),
1249 CompressedContents);
1250 if (Success != zlib::StatusOK)
1253 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1256 return CompressedFragment;
1259 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1262 static void UpdateSymbols(const MCAsmLayout &Layout,
1263 const std::vector<MCSymbolData *> &Symbols,
1264 MCFragment &NewFragment) {
1265 for (MCSymbolData *Sym : Symbols) {
1266 Sym->setOffset(Sym->getOffset() +
1267 Layout.getFragmentOffset(Sym->getFragment()));
1268 Sym->setFragment(&NewFragment);
1272 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1273 const DefiningSymbolMap &DefiningSymbols,
1274 const MCSectionELF &Section,
1275 MCSectionData &SD) {
1276 StringRef SectionName = Section.getSectionName();
1277 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1279 std::unique_ptr<MCDataFragment> CompressedFragment =
1280 getCompressedFragment(Layout, Fragments);
1282 // Leave the section as-is if the fragments could not be compressed.
1283 if (!CompressedFragment)
1286 // Update the fragment+offsets of any symbols referring to fragments in this
1287 // section to refer to the new fragment.
1288 auto I = DefiningSymbols.find(&SD);
1289 if (I != DefiningSymbols.end())
1290 UpdateSymbols(Layout, I->second, *CompressedFragment);
1292 // Invalidate the layout for the whole section since it will have new and
1293 // different fragments now.
1294 Layout.invalidateFragmentsFrom(&Fragments.front());
1297 // Complete the initialization of the new fragment
1298 CompressedFragment->setParent(&SD);
1299 CompressedFragment->setLayoutOrder(0);
1300 Fragments.push_back(CompressedFragment.release());
1302 // Rename from .debug_* to .zdebug_*
1303 Asm.getContext().renameELFSection(&Section,
1304 (".z" + SectionName.drop_front(1)).str());
1307 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1308 MCAsmLayout &Layout) {
1309 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1312 DefiningSymbolMap DefiningSymbols;
1314 for (MCSymbolData &SD : Asm.symbols())
1315 if (MCFragment *F = SD.getFragment())
1316 DefiningSymbols[F->getParent()].push_back(&SD);
1318 for (MCSectionData &SD : Asm) {
1319 const MCSectionELF &Section =
1320 static_cast<const MCSectionELF &>(SD.getSection());
1321 StringRef SectionName = Section.getSectionName();
1323 // Compressing debug_frame requires handling alignment fragments which is
1324 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1325 // for writing to arbitrary buffers) for little benefit.
1326 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1329 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1333 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
1334 const RelMapTy &RelMap) {
1335 for (MCAssembler::const_iterator it = Asm.begin(),
1336 ie = Asm.end(); it != ie; ++it) {
1337 const MCSectionData &SD = *it;
1338 const MCSectionELF &Section =
1339 static_cast<const MCSectionELF&>(SD.getSection());
1341 const MCSectionELF *RelaSection = RelMap.lookup(&Section);
1344 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
1345 RelaSD.setAlignment(is64Bit() ? 8 : 4);
1347 MCDataFragment *F = new MCDataFragment(&RelaSD);
1348 WriteRelocationsFragment(Asm, F, &*it);
1352 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1353 uint64_t Flags, uint64_t Address,
1354 uint64_t Offset, uint64_t Size,
1355 uint32_t Link, uint32_t Info,
1357 uint64_t EntrySize) {
1358 Write32(Name); // sh_name: index into string table
1359 Write32(Type); // sh_type
1360 WriteWord(Flags); // sh_flags
1361 WriteWord(Address); // sh_addr
1362 WriteWord(Offset); // sh_offset
1363 WriteWord(Size); // sh_size
1364 Write32(Link); // sh_link
1365 Write32(Info); // sh_info
1366 WriteWord(Alignment); // sh_addralign
1367 WriteWord(EntrySize); // sh_entsize
1370 // ELF doesn't require relocations to be in any order. We sort by the r_offset,
1371 // just to match gnu as for easier comparison. The use type is an arbitrary way
1372 // of making the sort deterministic.
1373 static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) {
1374 const ELFRelocationEntry &A = *AP;
1375 const ELFRelocationEntry &B = *BP;
1376 if (A.Offset != B.Offset)
1377 return B.Offset - A.Offset;
1378 if (B.Type != A.Type)
1379 return A.Type - B.Type;
1380 llvm_unreachable("ELFRelocs might be unstable!");
1383 static void sortRelocs(const MCAssembler &Asm,
1384 std::vector<ELFRelocationEntry> &Relocs) {
1385 array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
1388 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1390 const MCSectionData *SD) {
1391 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1393 sortRelocs(Asm, Relocs);
1395 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1396 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1399 if (Entry.UseSymbol) {
1400 Index = getSymbolIndexInSymbolTable(Asm, Entry.Symbol);
1402 const MCSectionData *Sec = Entry.Section;
1404 Index = Sec->getOrdinal() + FileSymbolData.size() +
1405 LocalSymbolData.size() + 1;
1411 write(*F, Entry.Offset);
1412 if (TargetObjectWriter->isN64()) {
1413 write(*F, uint32_t(Index));
1415 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1416 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1417 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1418 write(*F, TargetObjectWriter->getRType(Entry.Type));
1420 struct ELF::Elf64_Rela ERE64;
1421 ERE64.setSymbolAndType(Index, Entry.Type);
1422 write(*F, ERE64.r_info);
1424 if (hasRelocationAddend())
1425 write(*F, Entry.Addend);
1427 write(*F, uint32_t(Entry.Offset));
1429 struct ELF::Elf32_Rela ERE32;
1430 ERE32.setSymbolAndType(Index, Entry.Type);
1431 write(*F, ERE32.r_info);
1433 if (hasRelocationAddend())
1434 write(*F, uint32_t(Entry.Addend));
1439 static int compareBySuffix(const MCSectionELF *const *a,
1440 const MCSectionELF *const *b) {
1441 const StringRef &NameA = (*a)->getSectionName();
1442 const StringRef &NameB = (*b)->getSectionName();
1443 const unsigned sizeA = NameA.size();
1444 const unsigned sizeB = NameB.size();
1445 const unsigned len = std::min(sizeA, sizeB);
1446 for (unsigned int i = 0; i < len; ++i) {
1447 char ca = NameA[sizeA - i - 1];
1448 char cb = NameB[sizeB - i - 1];
1453 return sizeB - sizeA;
1456 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
1457 MCAsmLayout &Layout,
1458 SectionIndexMapTy &SectionIndexMap,
1459 const RelMapTy &RelMap) {
1460 MCContext &Ctx = Asm.getContext();
1463 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1465 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1466 const MCSectionELF *ShstrtabSection =
1467 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
1468 SectionKind::getReadOnly());
1469 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1470 ShstrtabSD.setAlignment(1);
1472 const MCSectionELF *SymtabSection =
1473 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1474 SectionKind::getReadOnly(),
1476 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1477 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1479 const MCSectionELF *StrtabSection;
1480 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
1481 SectionKind::getReadOnly());
1482 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1483 StrtabSD.setAlignment(1);
1485 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1487 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection);
1488 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection);
1489 StringTableIndex = SectionIndexMap.lookup(StrtabSection);
1492 F = new MCDataFragment(&SymtabSD);
1493 WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
1495 F = new MCDataFragment(&StrtabSD);
1496 F->getContents().append(StringTable.begin(), StringTable.end());
1498 F = new MCDataFragment(&ShstrtabSD);
1500 std::vector<const MCSectionELF*> Sections;
1501 for (MCAssembler::const_iterator it = Asm.begin(),
1502 ie = Asm.end(); it != ie; ++it) {
1503 const MCSectionELF &Section =
1504 static_cast<const MCSectionELF&>(it->getSection());
1505 Sections.push_back(&Section);
1507 array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix);
1509 // Section header string table.
1511 // The first entry of a string table holds a null character so skip
1514 F->getContents().push_back('\x00');
1516 for (unsigned int I = 0, E = Sections.size(); I != E; ++I) {
1517 const MCSectionELF &Section = *Sections[I];
1519 StringRef Name = Section.getSectionName();
1521 StringRef PreviousName = Sections[I - 1]->getSectionName();
1522 if (PreviousName.endswith(Name)) {
1523 SectionStringTableIndex[&Section] = Index - Name.size() - 1;
1527 // Remember the index into the string table so we can write it
1528 // into the sh_name field of the section header table.
1529 SectionStringTableIndex[&Section] = Index;
1531 Index += Name.size() + 1;
1532 F->getContents().append(Name.begin(), Name.end());
1533 F->getContents().push_back('\x00');
1537 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm,
1538 MCAsmLayout &Layout,
1539 GroupMapTy &GroupMap,
1540 RevGroupMapTy &RevGroupMap,
1541 SectionIndexMapTy &SectionIndexMap,
1542 const RelMapTy &RelMap) {
1543 // Create the .note.GNU-stack section if needed.
1544 MCContext &Ctx = Asm.getContext();
1545 if (Asm.getNoExecStack()) {
1546 const MCSectionELF *GnuStackSection =
1547 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0,
1548 SectionKind::getReadOnly());
1549 Asm.getOrCreateSectionData(*GnuStackSection);
1553 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1555 const MCSectionELF &Section =
1556 static_cast<const MCSectionELF&>(it->getSection());
1557 if (!(Section.getFlags() & ELF::SHF_GROUP))
1560 const MCSymbol *SignatureSymbol = Section.getGroup();
1561 Asm.getOrCreateSymbolData(*SignatureSymbol);
1562 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1564 Group = Ctx.CreateELFGroupSection();
1565 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1566 Data.setAlignment(4);
1567 MCDataFragment *F = new MCDataFragment(&Data);
1568 write(*F, uint32_t(ELF::GRP_COMDAT));
1570 GroupMap[Group] = SignatureSymbol;
1573 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1575 // Add sections to the groups
1576 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1578 const MCSectionELF &Section =
1579 static_cast<const MCSectionELF&>(it->getSection());
1580 if (!(Section.getFlags() & ELF::SHF_GROUP))
1582 const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1583 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1584 // FIXME: we could use the previous fragment
1585 MCDataFragment *F = new MCDataFragment(&Data);
1586 uint32_t Index = SectionIndexMap.lookup(&Section);
1591 void ELFObjectWriter::WriteSection(MCAssembler &Asm,
1592 const SectionIndexMapTy &SectionIndexMap,
1593 uint32_t GroupSymbolIndex,
1594 uint64_t Offset, uint64_t Size,
1596 const MCSectionELF &Section) {
1597 uint64_t sh_link = 0;
1598 uint64_t sh_info = 0;
1600 switch(Section.getType()) {
1601 case ELF::SHT_DYNAMIC:
1602 sh_link = SectionStringTableIndex[&Section];
1607 case ELF::SHT_RELA: {
1608 const MCSectionELF *SymtabSection;
1609 const MCSectionELF *InfoSection;
1610 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB,
1612 SectionKind::getReadOnly());
1613 sh_link = SectionIndexMap.lookup(SymtabSection);
1614 assert(sh_link && ".symtab not found");
1616 // Remove ".rel" and ".rela" prefixes.
1617 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1618 StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1619 StringRef GroupName =
1620 Section.getGroup() ? Section.getGroup()->getName() : "";
1622 InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS,
1623 0, SectionKind::getReadOnly(),
1625 sh_info = SectionIndexMap.lookup(InfoSection);
1629 case ELF::SHT_SYMTAB:
1630 case ELF::SHT_DYNSYM:
1631 sh_link = StringTableIndex;
1632 sh_info = LastLocalSymbolIndex;
1635 case ELF::SHT_SYMTAB_SHNDX:
1636 sh_link = SymbolTableIndex;
1639 case ELF::SHT_PROGBITS:
1640 case ELF::SHT_STRTAB:
1641 case ELF::SHT_NOBITS:
1644 case ELF::SHT_ARM_ATTRIBUTES:
1645 case ELF::SHT_INIT_ARRAY:
1646 case ELF::SHT_FINI_ARRAY:
1647 case ELF::SHT_PREINIT_ARRAY:
1648 case ELF::SHT_X86_64_UNWIND:
1649 case ELF::SHT_MIPS_REGINFO:
1650 case ELF::SHT_MIPS_OPTIONS:
1654 case ELF::SHT_GROUP:
1655 sh_link = SymbolTableIndex;
1656 sh_info = GroupSymbolIndex;
1660 assert(0 && "FIXME: sh_type value not supported!");
1664 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1665 Section.getType() == ELF::SHT_ARM_EXIDX) {
1666 StringRef SecName(Section.getSectionName());
1667 if (SecName == ".ARM.exidx") {
1668 sh_link = SectionIndexMap.lookup(
1669 Asm.getContext().getELFSection(".text",
1671 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC,
1672 SectionKind::getText()));
1673 } else if (SecName.startswith(".ARM.exidx")) {
1674 StringRef GroupName =
1675 Section.getGroup() ? Section.getGroup()->getName() : "";
1676 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
1677 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS,
1678 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText(), 0,
1683 WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(),
1684 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1685 Alignment, Section.getEntrySize());
1688 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1689 return SD.getOrdinal() == ~UINT32_C(0) &&
1690 !SD.getSection().isVirtualSection();
1693 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1695 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1697 const MCFragment &F = *i;
1698 assert(F.getKind() == MCFragment::FT_Data);
1699 Ret += cast<MCDataFragment>(F).getContents().size();
1704 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
1705 const MCSectionData &SD) {
1706 if (IsELFMetaDataSection(SD))
1707 return DataSectionSize(SD);
1708 return Layout.getSectionFileSize(&SD);
1711 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1712 const MCSectionData &SD) {
1713 if (IsELFMetaDataSection(SD))
1714 return DataSectionSize(SD);
1715 return Layout.getSectionAddressSize(&SD);
1718 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
1719 const MCAsmLayout &Layout,
1720 const MCSectionELF &Section) {
1721 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1723 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1724 WriteZeros(Padding);
1726 if (IsELFMetaDataSection(SD)) {
1727 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1729 const MCFragment &F = *i;
1730 assert(F.getKind() == MCFragment::FT_Data);
1731 WriteBytes(cast<MCDataFragment>(F).getContents());
1734 Asm.writeSectionData(&SD, Layout);
1738 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm,
1739 const GroupMapTy &GroupMap,
1740 const MCAsmLayout &Layout,
1741 const SectionIndexMapTy &SectionIndexMap,
1742 const SectionOffsetMapTy &SectionOffsetMap) {
1743 const unsigned NumSections = Asm.size() + 1;
1745 std::vector<const MCSectionELF*> Sections;
1746 Sections.resize(NumSections - 1);
1748 for (SectionIndexMapTy::const_iterator i=
1749 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
1750 const std::pair<const MCSectionELF*, uint32_t> &p = *i;
1751 Sections[p.second - 1] = p.first;
1754 // Null section first.
1755 uint64_t FirstSectionSize =
1756 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
1757 uint32_t FirstSectionLink =
1758 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1759 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1761 for (unsigned i = 0; i < NumSections - 1; ++i) {
1762 const MCSectionELF &Section = *Sections[i];
1763 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1764 uint32_t GroupSymbolIndex;
1765 if (Section.getType() != ELF::SHT_GROUP)
1766 GroupSymbolIndex = 0;
1768 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1769 GroupMap.lookup(&Section));
1771 uint64_t Size = GetSectionAddressSize(Layout, SD);
1773 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex,
1774 SectionOffsetMap.lookup(&Section), Size,
1775 SD.getAlignment(), Section);
1779 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
1780 std::vector<const MCSectionELF*> &Sections) {
1781 for (MCAssembler::iterator it = Asm.begin(),
1782 ie = Asm.end(); it != ie; ++it) {
1783 const MCSectionELF &Section =
1784 static_cast<const MCSectionELF &>(it->getSection());
1785 if (Section.getType() == ELF::SHT_GROUP)
1786 Sections.push_back(&Section);
1789 for (MCAssembler::iterator it = Asm.begin(),
1790 ie = Asm.end(); it != ie; ++it) {
1791 const MCSectionELF &Section =
1792 static_cast<const MCSectionELF &>(it->getSection());
1793 if (Section.getType() != ELF::SHT_GROUP &&
1794 Section.getType() != ELF::SHT_REL &&
1795 Section.getType() != ELF::SHT_RELA)
1796 Sections.push_back(&Section);
1799 for (MCAssembler::iterator it = Asm.begin(),
1800 ie = Asm.end(); it != ie; ++it) {
1801 const MCSectionELF &Section =
1802 static_cast<const MCSectionELF &>(it->getSection());
1803 if (Section.getType() == ELF::SHT_REL ||
1804 Section.getType() == ELF::SHT_RELA)
1805 Sections.push_back(&Section);
1809 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1810 const MCAsmLayout &Layout) {
1811 GroupMapTy GroupMap;
1812 RevGroupMapTy RevGroupMap;
1813 SectionIndexMapTy SectionIndexMap;
1815 unsigned NumUserSections = Asm.size();
1817 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1819 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap;
1820 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1822 const unsigned NumUserAndRelocSections = Asm.size();
1823 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
1824 RevGroupMap, SectionIndexMap, RelMap);
1825 const unsigned AllSections = Asm.size();
1826 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections;
1828 unsigned NumRegularSections = NumUserSections + NumIndexedSections;
1830 // Compute symbol table information.
1831 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
1832 NumRegularSections);
1834 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1836 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1837 const_cast<MCAsmLayout&>(Layout),
1841 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1842 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
1843 sizeof(ELF::Elf32_Ehdr);
1844 uint64_t FileOff = HeaderSize;
1846 std::vector<const MCSectionELF*> Sections;
1847 ComputeSectionOrder(Asm, Sections);
1848 unsigned NumSections = Sections.size();
1849 SectionOffsetMapTy SectionOffsetMap;
1850 for (unsigned i = 0; i < NumRegularSections + 1; ++i) {
1851 const MCSectionELF &Section = *Sections[i];
1852 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1854 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1856 // Remember the offset into the file for this section.
1857 SectionOffsetMap[&Section] = FileOff;
1859 // Get the size of the section in the output file (including padding).
1860 FileOff += GetSectionFileSize(Layout, SD);
1863 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1865 const unsigned SectionHeaderOffset = FileOff - HeaderSize;
1867 uint64_t SectionHeaderEntrySize = is64Bit() ?
1868 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr);
1869 FileOff += (NumSections + 1) * SectionHeaderEntrySize;
1871 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) {
1872 const MCSectionELF &Section = *Sections[i];
1873 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1875 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1877 // Remember the offset into the file for this section.
1878 SectionOffsetMap[&Section] = FileOff;
1880 // Get the size of the section in the output file (including padding).
1881 FileOff += GetSectionFileSize(Layout, SD);
1884 // Write out the ELF header ...
1885 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
1887 // ... then the regular sections ...
1888 // + because of .shstrtab
1889 for (unsigned i = 0; i < NumRegularSections + 1; ++i)
1890 WriteDataSectionData(Asm, Layout, *Sections[i]);
1892 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1893 WriteZeros(Padding);
1895 // ... then the section header table ...
1896 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap,
1899 // ... and then the remaining sections ...
1900 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i)
1901 WriteDataSectionData(Asm, Layout, *Sections[i]);
1905 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
1906 const MCSymbolData &DataA,
1907 const MCFragment &FB,
1909 bool IsPCRel) const {
1910 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC)
1912 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1913 Asm, DataA, FB,InSet, IsPCRel);
1916 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1918 bool IsLittleEndian) {
1919 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);