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 isSignature,
114 static bool IsELFMetaDataSection(const MCSectionData &SD);
115 static uint64_t DataSectionSize(const MCSectionData &SD);
116 static uint64_t GetSectionFileSize(const MCAsmLayout &Layout,
117 const MCSectionData &SD);
118 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout,
119 const MCSectionData &SD);
121 void WriteDataSectionData(MCAssembler &Asm,
122 const MCAsmLayout &Layout,
123 const MCSectionELF &Section);
125 /*static bool isFixupKindX86RIPRel(unsigned Kind) {
126 return Kind == X86::reloc_riprel_4byte ||
127 Kind == X86::reloc_riprel_4byte_movq_load;
130 /// ELFSymbolData - Helper struct for containing some precomputed
131 /// information on symbols.
132 struct ELFSymbolData {
133 MCSymbolData *SymbolData;
134 uint64_t StringIndex;
135 uint32_t SectionIndex;
137 // Support lexicographic sorting.
138 bool operator<(const ELFSymbolData &RHS) const {
139 return SymbolData->getSymbol().getName() <
140 RHS.SymbolData->getSymbol().getName();
144 /// The target specific ELF writer instance.
145 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
147 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
148 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
149 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
151 llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>>
153 DenseMap<const MCSection*, uint64_t> SectionStringTableIndex;
156 /// @name Symbol Table Data
159 SmallString<256> StringTable;
160 std::vector<uint64_t> FileSymbolData;
161 std::vector<ELFSymbolData> LocalSymbolData;
162 std::vector<ELFSymbolData> ExternalSymbolData;
163 std::vector<ELFSymbolData> UndefinedSymbolData;
169 // This holds the symbol table index of the last local symbol.
170 unsigned LastLocalSymbolIndex;
171 // This holds the .strtab section index.
172 unsigned StringTableIndex;
173 // This holds the .symtab section index.
174 unsigned SymbolTableIndex;
176 unsigned ShstrtabIndex;
179 // TargetObjectWriter wrappers.
180 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
181 bool hasRelocationAddend() const {
182 return TargetObjectWriter->hasRelocationAddend();
184 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
185 bool IsPCRel) const {
186 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
190 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_ostream &_OS,
192 : MCObjectWriter(_OS, IsLittleEndian), FWriter(IsLittleEndian),
193 TargetObjectWriter(MOTW), NeedsGOT(false) {}
195 virtual ~ELFObjectWriter();
197 void WriteWord(uint64_t W) {
204 template <typename T> void write(MCDataFragment &F, T Value) {
205 FWriter.write(F, Value);
208 void WriteHeader(const MCAssembler &Asm,
209 uint64_t SectionDataSize,
210 unsigned NumberOfSections);
212 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
213 const MCAsmLayout &Layout);
215 void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm,
216 const MCAsmLayout &Layout,
217 SectionIndexMapTy &SectionIndexMap);
219 bool shouldRelocateWithSymbol(const 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 MCSymbolData *Data = &OrigData;
491 if (Data->isCommon() && Data->isExternal())
492 return Data->getCommonAlignment();
494 const MCSymbol *Symbol = &Data->getSymbol();
497 if (Symbol->isVariable()) {
498 const MCExpr *Expr = Symbol->getVariableValue();
500 if (!Expr->EvaluateAsRelocatable(Value, &Layout))
501 llvm_unreachable("Invalid expression");
503 assert(!Value.getSymB());
505 Res = Value.getConstant();
507 if (const MCSymbolRefExpr *A = Value.getSymA()) {
508 Symbol = &A->getSymbol();
509 Data = &Layout.getAssembler().getSymbolData(*Symbol);
516 if ((Data && Data->getFlags() & ELF_Other_ThumbFunc) ||
517 OrigData.getFlags() & ELF_Other_ThumbFunc)
520 if (!Symbol || !Symbol->isInSection())
523 Res += Layout.getSymbolOffset(Data);
528 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
529 const MCAsmLayout &Layout) {
530 // The presence of symbol versions causes undefined symbols and
531 // versions declared with @@@ to be renamed.
533 for (MCSymbolData &OriginalData : Asm.symbols()) {
534 const MCSymbol &Alias = OriginalData.getSymbol();
535 const MCSymbol &Symbol = Alias.AliasedSymbol();
536 MCSymbolData &SD = Asm.getSymbolData(Symbol);
539 if (&Symbol == &Alias)
542 StringRef AliasName = Alias.getName();
543 size_t Pos = AliasName.find('@');
544 if (Pos == StringRef::npos)
547 // Aliases defined with .symvar copy the binding from the symbol they alias.
548 // This is the first place we are able to copy this information.
549 OriginalData.setExternal(SD.isExternal());
550 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
552 StringRef Rest = AliasName.substr(Pos);
553 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
556 // FIXME: produce a better error message.
557 if (Symbol.isUndefined() && Rest.startswith("@@") &&
558 !Rest.startswith("@@@"))
559 report_fatal_error("A @@ version cannot be undefined");
561 Renames.insert(std::make_pair(&Symbol, &Alias));
565 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
566 uint8_t Type = newType;
568 // Propagation rules:
569 // IFUNC > FUNC > OBJECT > NOTYPE
570 // TLS_OBJECT > OBJECT > NOTYPE
572 // dont let the new type degrade the old type
576 case ELF::STT_GNU_IFUNC:
577 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
578 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
579 Type = ELF::STT_GNU_IFUNC;
582 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
583 Type == ELF::STT_TLS)
584 Type = ELF::STT_FUNC;
586 case ELF::STT_OBJECT:
587 if (Type == ELF::STT_NOTYPE)
588 Type = ELF::STT_OBJECT;
591 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
592 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
600 static const MCSymbol *getBaseSymbol(const MCAsmLayout &Layout,
601 const MCSymbol &Symbol) {
602 if (!Symbol.isVariable())
605 const MCExpr *Expr = Symbol.getVariableValue();
607 if (!Expr->EvaluateAsRelocatable(Value, &Layout))
608 llvm_unreachable("Invalid Expression");
609 const MCSymbolRefExpr *RefB = Value.getSymB();
611 Layout.getAssembler().getContext().FatalError(
612 SMLoc(), Twine("symbol '") + RefB->getSymbol().getName() +
613 "' could not be evaluated in a subtraction expression");
615 const MCSymbolRefExpr *A = Value.getSymA();
618 return getBaseSymbol(Layout, A->getSymbol());
621 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
622 const MCAsmLayout &Layout) {
623 MCSymbolData &OrigData = *MSD.SymbolData;
624 assert((!OrigData.getFragment() ||
625 (&OrigData.getFragment()->getParent()->getSection() ==
626 &OrigData.getSymbol().getSection())) &&
627 "The symbol's section doesn't match the fragment's symbol");
628 const MCSymbol *Base = getBaseSymbol(Layout, OrigData.getSymbol());
630 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
632 bool IsReserved = !Base || OrigData.isCommon();
634 // Binding and Type share the same byte as upper and lower nibbles
635 uint8_t Binding = MCELF::GetBinding(OrigData);
636 uint8_t Type = MCELF::GetType(OrigData);
637 MCSymbolData *BaseSD = nullptr;
639 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
640 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
642 if (OrigData.getFlags() & ELF_Other_ThumbFunc)
643 Type = ELF::STT_FUNC;
644 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
646 // Other and Visibility share the same byte with Visibility using the lower
648 uint8_t Visibility = MCELF::GetVisibility(OrigData);
649 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
652 uint64_t Value = SymbolValue(OrigData, Layout);
655 const MCExpr *ESize = OrigData.getSize();
657 ESize = BaseSD->getSize();
661 if (!ESize->EvaluateAsAbsolute(Res, Layout))
662 report_fatal_error("Size expression must be absolute.");
666 // Write out the symbol table entry
667 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
668 MSD.SectionIndex, IsReserved);
671 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF,
673 const MCAsmLayout &Layout,
674 SectionIndexMapTy &SectionIndexMap) {
675 // The string table must be emitted first because we need the index
676 // into the string table for all the symbol names.
677 assert(StringTable.size() && "Missing string table");
679 // FIXME: Make sure the start of the symbol table is aligned.
681 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF);
683 // The first entry is the undefined symbol entry.
684 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
686 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
687 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
688 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
691 // Write the symbol table entries.
692 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
694 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
695 ELFSymbolData &MSD = LocalSymbolData[i];
696 WriteSymbol(Writer, MSD, Layout);
699 // Write out a symbol table entry for each regular section.
700 for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e;
702 const MCSectionELF &Section =
703 static_cast<const MCSectionELF&>(i->getSection());
704 if (Section.getType() == ELF::SHT_RELA ||
705 Section.getType() == ELF::SHT_REL ||
706 Section.getType() == ELF::SHT_STRTAB ||
707 Section.getType() == ELF::SHT_SYMTAB ||
708 Section.getType() == ELF::SHT_SYMTAB_SHNDX)
710 Writer.writeSymbol(0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT,
711 SectionIndexMap.lookup(&Section), false);
712 LastLocalSymbolIndex++;
715 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
716 ELFSymbolData &MSD = ExternalSymbolData[i];
717 MCSymbolData &Data = *MSD.SymbolData;
718 assert(((Data.getFlags() & ELF_STB_Global) ||
719 (Data.getFlags() & ELF_STB_Weak)) &&
720 "External symbol requires STB_GLOBAL or STB_WEAK flag");
721 WriteSymbol(Writer, MSD, Layout);
722 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
723 LastLocalSymbolIndex++;
726 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
727 ELFSymbolData &MSD = UndefinedSymbolData[i];
728 MCSymbolData &Data = *MSD.SymbolData;
729 WriteSymbol(Writer, MSD, Layout);
730 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
731 LastLocalSymbolIndex++;
735 // It is always valid to create a relocation with a symbol. It is preferable
736 // to use a relocation with a section if that is possible. Using the section
737 // allows us to omit some local symbols from the symbol table.
738 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCSymbolRefExpr *RefA,
739 const MCSymbolData *SD,
741 unsigned Type) const {
742 // A PCRel relocation to an absolute value has no symbol (or section). We
743 // represent that with a relocation to a null section.
747 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
751 // The .odp creation emits a relocation against the symbol ".TOC." which
752 // create a R_PPC64_TOC relocation. However the relocation symbol name
753 // in final object creation should be NULL, since the symbol does not
754 // really exist, it is just the reference to TOC base for the current
755 // object file. Since the symbol is undefined, returning false results
756 // in a relocation with a null section which is the desired result.
757 case MCSymbolRefExpr::VK_PPC_TOCBASE:
760 // These VariantKind cause the relocation to refer to something other than
761 // the symbol itself, like a linker generated table. Since the address of
762 // symbol is not relevant, we cannot replace the symbol with the
763 // section and patch the difference in the addend.
764 case MCSymbolRefExpr::VK_GOT:
765 case MCSymbolRefExpr::VK_PLT:
766 case MCSymbolRefExpr::VK_GOTPCREL:
767 case MCSymbolRefExpr::VK_Mips_GOT:
768 case MCSymbolRefExpr::VK_PPC_GOT_LO:
769 case MCSymbolRefExpr::VK_PPC_GOT_HI:
770 case MCSymbolRefExpr::VK_PPC_GOT_HA:
774 // An undefined symbol is not in any section, so the relocation has to point
775 // to the symbol itself.
776 const MCSymbol &Sym = SD->getSymbol();
777 if (Sym.isUndefined())
780 unsigned Binding = MCELF::GetBinding(*SD);
783 llvm_unreachable("Invalid Binding");
787 // If the symbol is weak, it might be overridden by a symbol in another
788 // file. The relocation has to point to the symbol so that the linker
791 case ELF::STB_GLOBAL:
792 // Global ELF symbols can be preempted by the dynamic linker. The relocation
793 // has to point to the symbol for a reason analogous to the STB_WEAK case.
797 // If a relocation points to a mergeable section, we have to be careful.
798 // If the offset is zero, a relocation with the section will encode the
799 // same information. With a non-zero offset, the situation is different.
800 // For example, a relocation can point 42 bytes past the end of a string.
801 // If we change such a relocation to use the section, the linker would think
802 // that it pointed to another string and subtracting 42 at runtime will
803 // produce the wrong value.
804 auto &Sec = cast<MCSectionELF>(Sym.getSection());
805 unsigned Flags = Sec.getFlags();
806 if (Flags & ELF::SHF_MERGE) {
810 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
811 // only handle section relocations to mergeable sections if using RELA.
812 if (!hasRelocationAddend())
816 // Most TLS relocations use a got, so they need the symbol. Even those that
817 // are just an offset (@tpoff), require a symbol in some linkers (gold,
819 if (Flags & ELF::SHF_TLS)
822 // If the symbol is a thumb function the final relocation must set the lowest
823 // bit. With a symbol that is done by just having the symbol have that bit
824 // set, so we would lose the bit if we relocated with the section.
825 // FIXME: We could use the section but add the bit to the relocation value.
826 if (SD->getFlags() & ELF_Other_ThumbFunc)
829 if (TargetObjectWriter->needsRelocateWithSymbol(Type))
834 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
835 const MCAsmLayout &Layout,
836 const MCFragment *Fragment,
837 const MCFixup &Fixup,
840 uint64_t &FixedValue) {
841 const MCSectionData *FixupSection = Fragment->getParent();
842 uint64_t C = Target.getConstant();
843 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
845 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
846 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
847 "Should not have constructed this");
849 // Let A, B and C being the components of Target and R be the location of
850 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
851 // If it is pcrel, we want to compute (A - B + C - R).
853 // In general, ELF has no relocations for -B. It can only represent (A + C)
854 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
855 // replace B to implement it: (A - R - K + C)
857 Asm.getContext().FatalError(
859 "No relocation available to represent this relative expression");
861 const MCSymbol &SymB = RefB->getSymbol();
863 if (SymB.isUndefined())
864 Asm.getContext().FatalError(
866 Twine("symbol '") + SymB.getName() +
867 "' can not be undefined in a subtraction expression");
869 assert(!SymB.isAbsolute() && "Should have been folded");
870 const MCSection &SecB = SymB.getSection();
871 if (&SecB != &FixupSection->getSection())
872 Asm.getContext().FatalError(
873 Fixup.getLoc(), "Cannot represent a difference across sections");
875 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
876 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
877 uint64_t K = SymBOffset - FixupOffset;
882 // We either rejected the fixup or folded B into C at this point.
883 const MCSymbolRefExpr *RefA = Target.getSymA();
884 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
885 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
887 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
888 bool RelocateWithSymbol = shouldRelocateWithSymbol(RefA, SymAD, C, Type);
889 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
890 C += Layout.getSymbolOffset(SymAD);
893 if (hasRelocationAddend()) {
900 // FIXME: What is this!?!?
901 MCSymbolRefExpr::VariantKind Modifier =
902 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
903 if (RelocNeedsGOT(Modifier))
906 if (!RelocateWithSymbol) {
907 const MCSection *SecA =
908 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
909 const MCSectionData *SecAD = SecA ? &Asm.getSectionData(*SecA) : nullptr;
910 ELFRelocationEntry Rec(FixupOffset, SecAD, Type, Addend);
911 Relocations[FixupSection].push_back(Rec);
916 if (const MCSymbol *R = Renames.lookup(SymA))
919 if (RefA->getKind() == MCSymbolRefExpr::VK_WEAKREF)
920 WeakrefUsedInReloc.insert(SymA);
922 UsedInReloc.insert(SymA);
924 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
925 Relocations[FixupSection].push_back(Rec);
931 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
933 const MCSymbolData &SD = Asm.getSymbolData(*S);
934 return SD.getIndex();
937 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
938 const MCSymbolData &Data, bool Used,
940 const MCSymbol &Symbol = Data.getSymbol();
941 if (Symbol.isVariable()) {
942 const MCExpr *Expr = Symbol.getVariableValue();
943 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
944 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
955 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
958 if (Symbol.isVariable()) {
959 const MCSymbol *Base = getBaseSymbol(Layout, Symbol);
960 if (Base && Base->isUndefined())
964 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
965 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
968 if (Symbol.isTemporary())
974 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isSignature,
975 bool isUsedInReloc) {
976 if (Data.isExternal())
979 const MCSymbol &Symbol = Data.getSymbol();
980 const MCSymbol &RefSymbol = Symbol.AliasedSymbol();
982 if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) {
983 if (isSignature && !isUsedInReloc)
992 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
993 SectionIndexMapTy &SectionIndexMap,
994 const RelMapTy &RelMap) {
996 for (MCAssembler::iterator it = Asm.begin(),
997 ie = Asm.end(); it != ie; ++it) {
998 const MCSectionELF &Section =
999 static_cast<const MCSectionELF &>(it->getSection());
1000 if (Section.getType() != ELF::SHT_GROUP)
1002 SectionIndexMap[&Section] = Index++;
1005 for (MCAssembler::iterator it = Asm.begin(),
1006 ie = Asm.end(); it != ie; ++it) {
1007 const MCSectionELF &Section =
1008 static_cast<const MCSectionELF &>(it->getSection());
1009 if (Section.getType() == ELF::SHT_GROUP ||
1010 Section.getType() == ELF::SHT_REL ||
1011 Section.getType() == ELF::SHT_RELA)
1013 SectionIndexMap[&Section] = Index++;
1014 const MCSectionELF *RelSection = RelMap.lookup(&Section);
1016 SectionIndexMap[RelSection] = Index++;
1021 ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
1022 const SectionIndexMapTy &SectionIndexMap,
1023 RevGroupMapTy RevGroupMap,
1024 unsigned NumRegularSections) {
1025 // FIXME: Is this the correct place to do this?
1026 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
1028 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
1029 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
1030 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
1031 Data.setExternal(true);
1032 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
1035 // Index 0 is always the empty string.
1036 StringMap<uint64_t> StringIndexMap;
1037 StringTable += '\x00';
1039 // FIXME: We could optimize suffixes in strtab in the same way we
1040 // optimize them in shstrtab.
1042 for (MCAssembler::const_file_name_iterator it = Asm.file_names_begin(),
1043 ie = Asm.file_names_end();
1046 StringRef Name = *it;
1047 uint64_t &Entry = StringIndexMap[Name];
1049 Entry = StringTable.size();
1050 StringTable += Name;
1051 StringTable += '\x00';
1053 FileSymbolData.push_back(Entry);
1056 // Add the data for the symbols.
1057 for (MCSymbolData &SD : Asm.symbols()) {
1058 const MCSymbol &Symbol = SD.getSymbol();
1060 bool Used = UsedInReloc.count(&Symbol);
1061 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
1062 bool isSignature = RevGroupMap.count(&Symbol);
1064 if (!isInSymtab(Layout, SD,
1065 Used || WeakrefUsed || isSignature,
1066 Renames.count(&Symbol)))
1070 MSD.SymbolData = &SD;
1071 const MCSymbol *BaseSymbol = getBaseSymbol(Layout, Symbol);
1073 // Undefined symbols are global, but this is the first place we
1074 // are able to set it.
1075 bool Local = isLocal(SD, isSignature, Used);
1076 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1078 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1079 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1080 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1084 MSD.SectionIndex = ELF::SHN_ABS;
1085 } else if (SD.isCommon()) {
1087 MSD.SectionIndex = ELF::SHN_COMMON;
1088 } else if (BaseSymbol->isUndefined()) {
1089 if (isSignature && !Used)
1090 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]);
1092 MSD.SectionIndex = ELF::SHN_UNDEF;
1093 if (!Used && WeakrefUsed)
1094 MCELF::SetBinding(SD, ELF::STB_WEAK);
1096 const MCSectionELF &Section =
1097 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1098 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1099 assert(MSD.SectionIndex && "Invalid section index!");
1102 // The @@@ in symbol version is replaced with @ in undefined symbols and
1103 // @@ in defined ones.
1104 StringRef Name = Symbol.getName();
1105 SmallString<32> Buf;
1107 size_t Pos = Name.find("@@@");
1108 if (Pos != StringRef::npos) {
1109 Buf += Name.substr(0, Pos);
1110 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1111 Buf += Name.substr(Pos + Skip);
1115 uint64_t &Entry = StringIndexMap[Name];
1117 Entry = StringTable.size();
1118 StringTable += Name;
1119 StringTable += '\x00';
1121 MSD.StringIndex = Entry;
1122 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1123 UndefinedSymbolData.push_back(MSD);
1125 LocalSymbolData.push_back(MSD);
1127 ExternalSymbolData.push_back(MSD);
1130 // Symbols are required to be in lexicographic order.
1131 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1132 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1133 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1135 // Set the symbol indices. Local symbols must come before all other
1136 // symbols with non-local bindings.
1137 unsigned Index = FileSymbolData.size() + 1;
1138 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1139 LocalSymbolData[i].SymbolData->setIndex(Index++);
1141 Index += NumRegularSections;
1143 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1144 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1145 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1146 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1149 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm,
1150 MCAsmLayout &Layout,
1152 for (MCAssembler::const_iterator it = Asm.begin(),
1153 ie = Asm.end(); it != ie; ++it) {
1154 const MCSectionData &SD = *it;
1155 if (Relocations[&SD].empty())
1158 MCContext &Ctx = Asm.getContext();
1159 const MCSectionELF &Section =
1160 static_cast<const MCSectionELF&>(SD.getSection());
1162 const StringRef SectionName = Section.getSectionName();
1163 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1164 RelaSectionName += SectionName;
1167 if (hasRelocationAddend())
1168 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1170 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1173 StringRef Group = "";
1174 if (Section.getFlags() & ELF::SHF_GROUP) {
1175 Flags = ELF::SHF_GROUP;
1176 Group = Section.getGroup()->getName();
1179 const MCSectionELF *RelaSection =
1180 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ?
1181 ELF::SHT_RELA : ELF::SHT_REL, Flags,
1182 SectionKind::getReadOnly(),
1184 RelMap[&Section] = RelaSection;
1185 Asm.getOrCreateSectionData(*RelaSection);
1189 static SmallVector<char, 128>
1190 getUncompressedData(MCAsmLayout &Layout,
1191 MCSectionData::FragmentListType &Fragments) {
1192 SmallVector<char, 128> UncompressedData;
1193 for (const MCFragment &F : Fragments) {
1194 const SmallVectorImpl<char> *Contents;
1195 switch (F.getKind()) {
1196 case MCFragment::FT_Data:
1197 Contents = &cast<MCDataFragment>(F).getContents();
1199 case MCFragment::FT_Dwarf:
1200 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1202 case MCFragment::FT_DwarfFrame:
1203 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1207 "Not expecting any other fragment types in a debug_* section");
1209 UncompressedData.append(Contents->begin(), Contents->end());
1211 return UncompressedData;
1214 // Include the debug info compression header:
1215 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1216 // useful for consumers to preallocate a buffer to decompress into.
1218 prependCompressionHeader(uint64_t Size,
1219 SmallVectorImpl<char> &CompressedContents) {
1220 static const StringRef Magic = "ZLIB";
1221 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1223 if (sys::IsLittleEndianHost)
1224 Size = sys::SwapByteOrder(Size);
1225 CompressedContents.insert(CompressedContents.begin(),
1226 Magic.size() + sizeof(Size), 0);
1227 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1228 std::copy(reinterpret_cast<char *>(&Size),
1229 reinterpret_cast<char *>(&Size + 1),
1230 CompressedContents.begin() + Magic.size());
1234 // Return a single fragment containing the compressed contents of the whole
1235 // section. Null if the section was not compressed for any reason.
1236 static std::unique_ptr<MCDataFragment>
1237 getCompressedFragment(MCAsmLayout &Layout,
1238 MCSectionData::FragmentListType &Fragments) {
1239 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1241 // Gather the uncompressed data from all the fragments, recording the
1242 // alignment fragment, if seen, and any fixups.
1243 SmallVector<char, 128> UncompressedData =
1244 getUncompressedData(Layout, Fragments);
1246 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1248 zlib::Status Success = zlib::compress(
1249 StringRef(UncompressedData.data(), UncompressedData.size()),
1250 CompressedContents);
1251 if (Success != zlib::StatusOK)
1254 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1257 return CompressedFragment;
1260 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1263 static void UpdateSymbols(const MCAsmLayout &Layout,
1264 const std::vector<MCSymbolData *> &Symbols,
1265 MCFragment &NewFragment) {
1266 for (MCSymbolData *Sym : Symbols) {
1267 Sym->setOffset(Sym->getOffset() +
1268 Layout.getFragmentOffset(Sym->getFragment()));
1269 Sym->setFragment(&NewFragment);
1273 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1274 const DefiningSymbolMap &DefiningSymbols,
1275 const MCSectionELF &Section,
1276 MCSectionData &SD) {
1277 StringRef SectionName = Section.getSectionName();
1278 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1280 std::unique_ptr<MCDataFragment> CompressedFragment =
1281 getCompressedFragment(Layout, Fragments);
1283 // Leave the section as-is if the fragments could not be compressed.
1284 if (!CompressedFragment)
1287 // Update the fragment+offsets of any symbols referring to fragments in this
1288 // section to refer to the new fragment.
1289 auto I = DefiningSymbols.find(&SD);
1290 if (I != DefiningSymbols.end())
1291 UpdateSymbols(Layout, I->second, *CompressedFragment);
1293 // Invalidate the layout for the whole section since it will have new and
1294 // different fragments now.
1295 Layout.invalidateFragmentsFrom(&Fragments.front());
1298 // Complete the initialization of the new fragment
1299 CompressedFragment->setParent(&SD);
1300 CompressedFragment->setLayoutOrder(0);
1301 Fragments.push_back(CompressedFragment.release());
1303 // Rename from .debug_* to .zdebug_*
1304 Asm.getContext().renameELFSection(&Section,
1305 (".z" + SectionName.drop_front(1)).str());
1308 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1309 MCAsmLayout &Layout) {
1310 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1313 DefiningSymbolMap DefiningSymbols;
1315 for (MCSymbolData &SD : Asm.symbols())
1316 if (MCFragment *F = SD.getFragment())
1317 DefiningSymbols[F->getParent()].push_back(&SD);
1319 for (MCSectionData &SD : Asm) {
1320 const MCSectionELF &Section =
1321 static_cast<const MCSectionELF &>(SD.getSection());
1322 StringRef SectionName = Section.getSectionName();
1324 // Compressing debug_frame requires handling alignment fragments which is
1325 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1326 // for writing to arbitrary buffers) for little benefit.
1327 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1330 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1334 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
1335 const RelMapTy &RelMap) {
1336 for (MCAssembler::const_iterator it = Asm.begin(),
1337 ie = Asm.end(); it != ie; ++it) {
1338 const MCSectionData &SD = *it;
1339 const MCSectionELF &Section =
1340 static_cast<const MCSectionELF&>(SD.getSection());
1342 const MCSectionELF *RelaSection = RelMap.lookup(&Section);
1345 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
1346 RelaSD.setAlignment(is64Bit() ? 8 : 4);
1348 MCDataFragment *F = new MCDataFragment(&RelaSD);
1349 WriteRelocationsFragment(Asm, F, &*it);
1353 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1354 uint64_t Flags, uint64_t Address,
1355 uint64_t Offset, uint64_t Size,
1356 uint32_t Link, uint32_t Info,
1358 uint64_t EntrySize) {
1359 Write32(Name); // sh_name: index into string table
1360 Write32(Type); // sh_type
1361 WriteWord(Flags); // sh_flags
1362 WriteWord(Address); // sh_addr
1363 WriteWord(Offset); // sh_offset
1364 WriteWord(Size); // sh_size
1365 Write32(Link); // sh_link
1366 Write32(Info); // sh_info
1367 WriteWord(Alignment); // sh_addralign
1368 WriteWord(EntrySize); // sh_entsize
1371 // ELF doesn't require relocations to be in any order. We sort by the r_offset,
1372 // just to match gnu as for easier comparison. The use type is an arbitrary way
1373 // of making the sort deterministic.
1374 static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) {
1375 const ELFRelocationEntry &A = *AP;
1376 const ELFRelocationEntry &B = *BP;
1377 if (A.Offset != B.Offset)
1378 return B.Offset - A.Offset;
1379 if (B.Type != A.Type)
1380 return A.Type - B.Type;
1381 llvm_unreachable("ELFRelocs might be unstable!");
1384 static void sortRelocs(const MCAssembler &Asm,
1385 std::vector<ELFRelocationEntry> &Relocs) {
1386 array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
1389 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1391 const MCSectionData *SD) {
1392 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1394 sortRelocs(Asm, Relocs);
1396 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1397 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1400 if (Entry.UseSymbol) {
1401 Index = getSymbolIndexInSymbolTable(Asm, Entry.Symbol);
1403 const MCSectionData *Sec = Entry.Section;
1405 Index = Sec->getOrdinal() + FileSymbolData.size() +
1406 LocalSymbolData.size() + 1;
1412 write(*F, Entry.Offset);
1413 if (TargetObjectWriter->isN64()) {
1414 write(*F, uint32_t(Index));
1416 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1417 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1418 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1419 write(*F, TargetObjectWriter->getRType(Entry.Type));
1421 struct ELF::Elf64_Rela ERE64;
1422 ERE64.setSymbolAndType(Index, Entry.Type);
1423 write(*F, ERE64.r_info);
1425 if (hasRelocationAddend())
1426 write(*F, Entry.Addend);
1428 write(*F, uint32_t(Entry.Offset));
1430 struct ELF::Elf32_Rela ERE32;
1431 ERE32.setSymbolAndType(Index, Entry.Type);
1432 write(*F, ERE32.r_info);
1434 if (hasRelocationAddend())
1435 write(*F, uint32_t(Entry.Addend));
1440 static int compareBySuffix(const MCSectionELF *const *a,
1441 const MCSectionELF *const *b) {
1442 const StringRef &NameA = (*a)->getSectionName();
1443 const StringRef &NameB = (*b)->getSectionName();
1444 const unsigned sizeA = NameA.size();
1445 const unsigned sizeB = NameB.size();
1446 const unsigned len = std::min(sizeA, sizeB);
1447 for (unsigned int i = 0; i < len; ++i) {
1448 char ca = NameA[sizeA - i - 1];
1449 char cb = NameB[sizeB - i - 1];
1454 return sizeB - sizeA;
1457 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
1458 MCAsmLayout &Layout,
1459 SectionIndexMapTy &SectionIndexMap,
1460 const RelMapTy &RelMap) {
1461 MCContext &Ctx = Asm.getContext();
1464 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1466 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1467 const MCSectionELF *ShstrtabSection =
1468 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
1469 SectionKind::getReadOnly());
1470 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1471 ShstrtabSD.setAlignment(1);
1473 const MCSectionELF *SymtabSection =
1474 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1475 SectionKind::getReadOnly(),
1477 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1478 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1480 const MCSectionELF *StrtabSection;
1481 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
1482 SectionKind::getReadOnly());
1483 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1484 StrtabSD.setAlignment(1);
1486 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1488 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection);
1489 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection);
1490 StringTableIndex = SectionIndexMap.lookup(StrtabSection);
1493 F = new MCDataFragment(&SymtabSD);
1494 WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
1496 F = new MCDataFragment(&StrtabSD);
1497 F->getContents().append(StringTable.begin(), StringTable.end());
1499 F = new MCDataFragment(&ShstrtabSD);
1501 std::vector<const MCSectionELF*> Sections;
1502 for (MCAssembler::const_iterator it = Asm.begin(),
1503 ie = Asm.end(); it != ie; ++it) {
1504 const MCSectionELF &Section =
1505 static_cast<const MCSectionELF&>(it->getSection());
1506 Sections.push_back(&Section);
1508 array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix);
1510 // Section header string table.
1512 // The first entry of a string table holds a null character so skip
1515 F->getContents().push_back('\x00');
1517 for (unsigned int I = 0, E = Sections.size(); I != E; ++I) {
1518 const MCSectionELF &Section = *Sections[I];
1520 StringRef Name = Section.getSectionName();
1522 StringRef PreviousName = Sections[I - 1]->getSectionName();
1523 if (PreviousName.endswith(Name)) {
1524 SectionStringTableIndex[&Section] = Index - Name.size() - 1;
1528 // Remember the index into the string table so we can write it
1529 // into the sh_name field of the section header table.
1530 SectionStringTableIndex[&Section] = Index;
1532 Index += Name.size() + 1;
1533 F->getContents().append(Name.begin(), Name.end());
1534 F->getContents().push_back('\x00');
1538 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm,
1539 MCAsmLayout &Layout,
1540 GroupMapTy &GroupMap,
1541 RevGroupMapTy &RevGroupMap,
1542 SectionIndexMapTy &SectionIndexMap,
1543 const RelMapTy &RelMap) {
1544 // Create the .note.GNU-stack section if needed.
1545 MCContext &Ctx = Asm.getContext();
1546 if (Asm.getNoExecStack()) {
1547 const MCSectionELF *GnuStackSection =
1548 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0,
1549 SectionKind::getReadOnly());
1550 Asm.getOrCreateSectionData(*GnuStackSection);
1554 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1556 const MCSectionELF &Section =
1557 static_cast<const MCSectionELF&>(it->getSection());
1558 if (!(Section.getFlags() & ELF::SHF_GROUP))
1561 const MCSymbol *SignatureSymbol = Section.getGroup();
1562 Asm.getOrCreateSymbolData(*SignatureSymbol);
1563 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1565 Group = Ctx.CreateELFGroupSection();
1566 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1567 Data.setAlignment(4);
1568 MCDataFragment *F = new MCDataFragment(&Data);
1569 write(*F, uint32_t(ELF::GRP_COMDAT));
1571 GroupMap[Group] = SignatureSymbol;
1574 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1576 // Add sections to the groups
1577 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1579 const MCSectionELF &Section =
1580 static_cast<const MCSectionELF&>(it->getSection());
1581 if (!(Section.getFlags() & ELF::SHF_GROUP))
1583 const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1584 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1585 // FIXME: we could use the previous fragment
1586 MCDataFragment *F = new MCDataFragment(&Data);
1587 uint32_t Index = SectionIndexMap.lookup(&Section);
1592 void ELFObjectWriter::WriteSection(MCAssembler &Asm,
1593 const SectionIndexMapTy &SectionIndexMap,
1594 uint32_t GroupSymbolIndex,
1595 uint64_t Offset, uint64_t Size,
1597 const MCSectionELF &Section) {
1598 uint64_t sh_link = 0;
1599 uint64_t sh_info = 0;
1601 switch(Section.getType()) {
1602 case ELF::SHT_DYNAMIC:
1603 sh_link = SectionStringTableIndex[&Section];
1608 case ELF::SHT_RELA: {
1609 const MCSectionELF *SymtabSection;
1610 const MCSectionELF *InfoSection;
1611 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB,
1613 SectionKind::getReadOnly());
1614 sh_link = SectionIndexMap.lookup(SymtabSection);
1615 assert(sh_link && ".symtab not found");
1617 // Remove ".rel" and ".rela" prefixes.
1618 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1619 StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1620 StringRef GroupName =
1621 Section.getGroup() ? Section.getGroup()->getName() : "";
1623 InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS,
1624 0, SectionKind::getReadOnly(),
1626 sh_info = SectionIndexMap.lookup(InfoSection);
1630 case ELF::SHT_SYMTAB:
1631 case ELF::SHT_DYNSYM:
1632 sh_link = StringTableIndex;
1633 sh_info = LastLocalSymbolIndex;
1636 case ELF::SHT_SYMTAB_SHNDX:
1637 sh_link = SymbolTableIndex;
1640 case ELF::SHT_PROGBITS:
1641 case ELF::SHT_STRTAB:
1642 case ELF::SHT_NOBITS:
1645 case ELF::SHT_ARM_ATTRIBUTES:
1646 case ELF::SHT_INIT_ARRAY:
1647 case ELF::SHT_FINI_ARRAY:
1648 case ELF::SHT_PREINIT_ARRAY:
1649 case ELF::SHT_X86_64_UNWIND:
1650 case ELF::SHT_MIPS_REGINFO:
1651 case ELF::SHT_MIPS_OPTIONS:
1655 case ELF::SHT_GROUP:
1656 sh_link = SymbolTableIndex;
1657 sh_info = GroupSymbolIndex;
1661 assert(0 && "FIXME: sh_type value not supported!");
1665 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1666 Section.getType() == ELF::SHT_ARM_EXIDX) {
1667 StringRef SecName(Section.getSectionName());
1668 if (SecName == ".ARM.exidx") {
1669 sh_link = SectionIndexMap.lookup(
1670 Asm.getContext().getELFSection(".text",
1672 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC,
1673 SectionKind::getText()));
1674 } else if (SecName.startswith(".ARM.exidx")) {
1675 StringRef GroupName =
1676 Section.getGroup() ? Section.getGroup()->getName() : "";
1677 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
1678 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS,
1679 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText(), 0,
1684 WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(),
1685 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1686 Alignment, Section.getEntrySize());
1689 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1690 return SD.getOrdinal() == ~UINT32_C(0) &&
1691 !SD.getSection().isVirtualSection();
1694 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1696 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1698 const MCFragment &F = *i;
1699 assert(F.getKind() == MCFragment::FT_Data);
1700 Ret += cast<MCDataFragment>(F).getContents().size();
1705 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
1706 const MCSectionData &SD) {
1707 if (IsELFMetaDataSection(SD))
1708 return DataSectionSize(SD);
1709 return Layout.getSectionFileSize(&SD);
1712 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1713 const MCSectionData &SD) {
1714 if (IsELFMetaDataSection(SD))
1715 return DataSectionSize(SD);
1716 return Layout.getSectionAddressSize(&SD);
1719 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
1720 const MCAsmLayout &Layout,
1721 const MCSectionELF &Section) {
1722 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1724 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1725 WriteZeros(Padding);
1727 if (IsELFMetaDataSection(SD)) {
1728 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1730 const MCFragment &F = *i;
1731 assert(F.getKind() == MCFragment::FT_Data);
1732 WriteBytes(cast<MCDataFragment>(F).getContents());
1735 Asm.writeSectionData(&SD, Layout);
1739 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm,
1740 const GroupMapTy &GroupMap,
1741 const MCAsmLayout &Layout,
1742 const SectionIndexMapTy &SectionIndexMap,
1743 const SectionOffsetMapTy &SectionOffsetMap) {
1744 const unsigned NumSections = Asm.size() + 1;
1746 std::vector<const MCSectionELF*> Sections;
1747 Sections.resize(NumSections - 1);
1749 for (SectionIndexMapTy::const_iterator i=
1750 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
1751 const std::pair<const MCSectionELF*, uint32_t> &p = *i;
1752 Sections[p.second - 1] = p.first;
1755 // Null section first.
1756 uint64_t FirstSectionSize =
1757 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
1758 uint32_t FirstSectionLink =
1759 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1760 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1762 for (unsigned i = 0; i < NumSections - 1; ++i) {
1763 const MCSectionELF &Section = *Sections[i];
1764 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1765 uint32_t GroupSymbolIndex;
1766 if (Section.getType() != ELF::SHT_GROUP)
1767 GroupSymbolIndex = 0;
1769 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1770 GroupMap.lookup(&Section));
1772 uint64_t Size = GetSectionAddressSize(Layout, SD);
1774 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex,
1775 SectionOffsetMap.lookup(&Section), Size,
1776 SD.getAlignment(), Section);
1780 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
1781 std::vector<const MCSectionELF*> &Sections) {
1782 for (MCAssembler::iterator it = Asm.begin(),
1783 ie = Asm.end(); it != ie; ++it) {
1784 const MCSectionELF &Section =
1785 static_cast<const MCSectionELF &>(it->getSection());
1786 if (Section.getType() == ELF::SHT_GROUP)
1787 Sections.push_back(&Section);
1790 for (MCAssembler::iterator it = Asm.begin(),
1791 ie = Asm.end(); it != ie; ++it) {
1792 const MCSectionELF &Section =
1793 static_cast<const MCSectionELF &>(it->getSection());
1794 if (Section.getType() != ELF::SHT_GROUP &&
1795 Section.getType() != ELF::SHT_REL &&
1796 Section.getType() != ELF::SHT_RELA)
1797 Sections.push_back(&Section);
1800 for (MCAssembler::iterator it = Asm.begin(),
1801 ie = Asm.end(); it != ie; ++it) {
1802 const MCSectionELF &Section =
1803 static_cast<const MCSectionELF &>(it->getSection());
1804 if (Section.getType() == ELF::SHT_REL ||
1805 Section.getType() == ELF::SHT_RELA)
1806 Sections.push_back(&Section);
1810 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1811 const MCAsmLayout &Layout) {
1812 GroupMapTy GroupMap;
1813 RevGroupMapTy RevGroupMap;
1814 SectionIndexMapTy SectionIndexMap;
1816 unsigned NumUserSections = Asm.size();
1818 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1820 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap;
1821 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1823 const unsigned NumUserAndRelocSections = Asm.size();
1824 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
1825 RevGroupMap, SectionIndexMap, RelMap);
1826 const unsigned AllSections = Asm.size();
1827 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections;
1829 unsigned NumRegularSections = NumUserSections + NumIndexedSections;
1831 // Compute symbol table information.
1832 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
1833 NumRegularSections);
1835 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1837 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1838 const_cast<MCAsmLayout&>(Layout),
1842 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1843 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
1844 sizeof(ELF::Elf32_Ehdr);
1845 uint64_t FileOff = HeaderSize;
1847 std::vector<const MCSectionELF*> Sections;
1848 ComputeSectionOrder(Asm, Sections);
1849 unsigned NumSections = Sections.size();
1850 SectionOffsetMapTy SectionOffsetMap;
1851 for (unsigned i = 0; i < NumRegularSections + 1; ++i) {
1852 const MCSectionELF &Section = *Sections[i];
1853 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1855 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1857 // Remember the offset into the file for this section.
1858 SectionOffsetMap[&Section] = FileOff;
1860 // Get the size of the section in the output file (including padding).
1861 FileOff += GetSectionFileSize(Layout, SD);
1864 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1866 const unsigned SectionHeaderOffset = FileOff - HeaderSize;
1868 uint64_t SectionHeaderEntrySize = is64Bit() ?
1869 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr);
1870 FileOff += (NumSections + 1) * SectionHeaderEntrySize;
1872 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) {
1873 const MCSectionELF &Section = *Sections[i];
1874 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1876 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1878 // Remember the offset into the file for this section.
1879 SectionOffsetMap[&Section] = FileOff;
1881 // Get the size of the section in the output file (including padding).
1882 FileOff += GetSectionFileSize(Layout, SD);
1885 // Write out the ELF header ...
1886 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
1888 // ... then the regular sections ...
1889 // + because of .shstrtab
1890 for (unsigned i = 0; i < NumRegularSections + 1; ++i)
1891 WriteDataSectionData(Asm, Layout, *Sections[i]);
1893 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1894 WriteZeros(Padding);
1896 // ... then the section header table ...
1897 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap,
1900 // ... and then the remaining sections ...
1901 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i)
1902 WriteDataSectionData(Asm, Layout, *Sections[i]);
1906 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
1907 const MCSymbolData &DataA,
1908 const MCFragment &FB,
1910 bool IsPCRel) const {
1911 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC)
1913 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1914 Asm, DataA, FB,InSet, IsPCRel);
1917 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1919 bool IsLittleEndian) {
1920 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);