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 MCSymbolRefExpr *RefA,
219 const MCSymbolData *SD, uint64_t C,
220 unsigned Type) const;
222 void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
223 const MCFragment *Fragment, const MCFixup &Fixup,
224 MCValue Target, bool &IsPCRel,
225 uint64_t &FixedValue) override;
227 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
230 // Map from a group section to the signature symbol
231 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
232 // Map from a signature symbol to the group section
233 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
234 // Map from a section to the section with the relocations
235 typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy;
236 // Map from a section to its offset
237 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy;
239 /// Compute the symbol table data
241 /// \param Asm - The assembler.
242 /// \param SectionIndexMap - Maps a section to its index.
243 /// \param RevGroupMap - Maps a signature symbol to the group section.
244 /// \param NumRegularSections - Number of non-relocation sections.
245 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
246 const SectionIndexMapTy &SectionIndexMap,
247 RevGroupMapTy RevGroupMap,
248 unsigned NumRegularSections);
250 void ComputeIndexMap(MCAssembler &Asm,
251 SectionIndexMapTy &SectionIndexMap,
252 const RelMapTy &RelMap);
254 void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout,
257 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
259 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
260 const RelMapTy &RelMap);
262 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
263 SectionIndexMapTy &SectionIndexMap,
264 const RelMapTy &RelMap);
266 // Create the sections that show up in the symbol table. Currently
267 // those are the .note.GNU-stack section and the group sections.
268 void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
269 GroupMapTy &GroupMap,
270 RevGroupMapTy &RevGroupMap,
271 SectionIndexMapTy &SectionIndexMap,
272 const RelMapTy &RelMap);
274 void ExecutePostLayoutBinding(MCAssembler &Asm,
275 const MCAsmLayout &Layout) override;
277 void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap,
278 const MCAsmLayout &Layout,
279 const SectionIndexMapTy &SectionIndexMap,
280 const SectionOffsetMapTy &SectionOffsetMap);
282 void ComputeSectionOrder(MCAssembler &Asm,
283 std::vector<const MCSectionELF*> &Sections);
285 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
286 uint64_t Address, uint64_t Offset,
287 uint64_t Size, uint32_t Link, uint32_t Info,
288 uint64_t Alignment, uint64_t EntrySize);
290 void WriteRelocationsFragment(const MCAssembler &Asm,
292 const MCSectionData *SD);
295 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
296 const MCSymbolData &DataA,
297 const MCFragment &FB,
299 bool IsPCRel) const override;
301 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
302 void WriteSection(MCAssembler &Asm,
303 const SectionIndexMapTy &SectionIndexMap,
304 uint32_t GroupSymbolIndex,
305 uint64_t Offset, uint64_t Size, uint64_t Alignment,
306 const MCSectionELF &Section);
310 FragmentWriter::FragmentWriter(bool IsLittleEndian)
311 : IsLittleEndian(IsLittleEndian) {}
313 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
315 Val = support::endian::byte_swap<T, support::little>(Val);
317 Val = support::endian::byte_swap<T, support::big>(Val);
318 const char *Start = (const char *)&Val;
319 F.getContents().append(Start, Start + sizeof(T));
322 void SymbolTableWriter::createSymtabShndx() {
326 MCContext &Ctx = Asm.getContext();
327 const MCSectionELF *SymtabShndxSection =
328 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0,
329 SectionKind::getReadOnly(), 4, "");
330 MCSectionData *SymtabShndxSD =
331 &Asm.getOrCreateSectionData(*SymtabShndxSection);
332 SymtabShndxSD->setAlignment(4);
333 ShndxF = new MCDataFragment(SymtabShndxSD);
334 unsigned Index = SectionIndexMap.size() + 1;
335 SectionIndexMap[SymtabShndxSection] = Index;
337 for (unsigned I = 0; I < NumWritten; ++I)
338 write(*ShndxF, uint32_t(0));
341 template <typename T>
342 void SymbolTableWriter::write(MCDataFragment &F, T Value) {
343 FWriter.write(F, Value);
346 SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter,
348 SectionIndexMapTy &SectionIndexMap,
349 MCDataFragment *SymtabF)
350 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit),
351 SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr),
354 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
355 uint64_t size, uint8_t other,
356 uint32_t shndx, bool Reserved) {
357 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
364 write(*ShndxF, shndx);
366 write(*ShndxF, uint32_t(0));
369 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
371 raw_svector_ostream OS(SymtabF->getContents());
374 write(*SymtabF, name); // st_name
375 write(*SymtabF, info); // st_info
376 write(*SymtabF, other); // st_other
377 write(*SymtabF, Index); // st_shndx
378 write(*SymtabF, value); // st_value
379 write(*SymtabF, size); // st_size
381 write(*SymtabF, name); // st_name
382 write(*SymtabF, uint32_t(value)); // st_value
383 write(*SymtabF, uint32_t(size)); // st_size
384 write(*SymtabF, info); // st_info
385 write(*SymtabF, other); // st_other
386 write(*SymtabF, Index); // st_shndx
392 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
393 const MCFixupKindInfo &FKI =
394 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
396 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
399 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
403 case MCSymbolRefExpr::VK_GOT:
404 case MCSymbolRefExpr::VK_PLT:
405 case MCSymbolRefExpr::VK_GOTPCREL:
406 case MCSymbolRefExpr::VK_GOTOFF:
407 case MCSymbolRefExpr::VK_TPOFF:
408 case MCSymbolRefExpr::VK_TLSGD:
409 case MCSymbolRefExpr::VK_GOTTPOFF:
410 case MCSymbolRefExpr::VK_INDNTPOFF:
411 case MCSymbolRefExpr::VK_NTPOFF:
412 case MCSymbolRefExpr::VK_GOTNTPOFF:
413 case MCSymbolRefExpr::VK_TLSLDM:
414 case MCSymbolRefExpr::VK_DTPOFF:
415 case MCSymbolRefExpr::VK_TLSLD:
420 ELFObjectWriter::~ELFObjectWriter()
423 // Emit the ELF header.
424 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
425 uint64_t SectionDataSize,
426 unsigned NumberOfSections) {
432 // emitWord method behaves differently for ELF32 and ELF64, writing
433 // 4 bytes in the former and 8 in the latter.
435 Write8(0x7f); // e_ident[EI_MAG0]
436 Write8('E'); // e_ident[EI_MAG1]
437 Write8('L'); // e_ident[EI_MAG2]
438 Write8('F'); // e_ident[EI_MAG3]
440 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
443 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
445 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
447 Write8(TargetObjectWriter->getOSABI());
448 Write8(0); // e_ident[EI_ABIVERSION]
450 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
452 Write16(ELF::ET_REL); // e_type
454 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
456 Write32(ELF::EV_CURRENT); // e_version
457 WriteWord(0); // e_entry, no entry point in .o file
458 WriteWord(0); // e_phoff, no program header for .o
459 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
460 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes
462 // e_flags = whatever the target wants
463 Write32(Asm.getELFHeaderEFlags());
465 // e_ehsize = ELF header size
466 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
468 Write16(0); // e_phentsize = prog header entry size
469 Write16(0); // e_phnum = # prog header entries = 0
471 // e_shentsize = Section header entry size
472 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
474 // e_shnum = # of section header ents
475 if (NumberOfSections >= ELF::SHN_LORESERVE)
476 Write16(ELF::SHN_UNDEF);
478 Write16(NumberOfSections);
480 // e_shstrndx = Section # of '.shstrtab'
481 if (ShstrtabIndex >= ELF::SHN_LORESERVE)
482 Write16(ELF::SHN_XINDEX);
484 Write16(ShstrtabIndex);
487 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &OrigData,
488 const MCAsmLayout &Layout) {
489 MCSymbolData *Data = &OrigData;
490 if (Data->isCommon() && Data->isExternal())
491 return Data->getCommonAlignment();
493 const MCSymbol *Symbol = &Data->getSymbol();
496 if (Symbol->isVariable()) {
497 const MCExpr *Expr = Symbol->getVariableValue();
499 if (!Expr->EvaluateAsValue(Value, &Layout))
500 llvm_unreachable("Invalid expression");
502 assert(!Value.getSymB());
504 Res = Value.getConstant();
506 if (const MCSymbolRefExpr *A = Value.getSymA()) {
507 Symbol = &A->getSymbol();
508 Data = &Layout.getAssembler().getSymbolData(*Symbol);
515 if ((Data && Data->getFlags() & ELF_Other_ThumbFunc) ||
516 OrigData.getFlags() & ELF_Other_ThumbFunc)
519 if (!Symbol || !Symbol->isInSection())
522 Res += Layout.getSymbolOffset(Data);
527 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
528 const MCAsmLayout &Layout) {
529 // The presence of symbol versions causes undefined symbols and
530 // versions declared with @@@ to be renamed.
532 for (MCSymbolData &OriginalData : Asm.symbols()) {
533 const MCSymbol &Alias = OriginalData.getSymbol();
536 if (!Alias.isVariable())
538 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
541 const MCSymbol &Symbol = Ref->getSymbol();
542 MCSymbolData &SD = Asm.getSymbolData(Symbol);
544 StringRef AliasName = Alias.getName();
545 size_t Pos = AliasName.find('@');
546 if (Pos == StringRef::npos)
549 // Aliases defined with .symvar copy the binding from the symbol they alias.
550 // This is the first place we are able to copy this information.
551 OriginalData.setExternal(SD.isExternal());
552 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
554 StringRef Rest = AliasName.substr(Pos);
555 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
558 // FIXME: produce a better error message.
559 if (Symbol.isUndefined() && Rest.startswith("@@") &&
560 !Rest.startswith("@@@"))
561 report_fatal_error("A @@ version cannot be undefined");
563 Renames.insert(std::make_pair(&Symbol, &Alias));
567 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
568 uint8_t Type = newType;
570 // Propagation rules:
571 // IFUNC > FUNC > OBJECT > NOTYPE
572 // TLS_OBJECT > OBJECT > NOTYPE
574 // dont let the new type degrade the old type
578 case ELF::STT_GNU_IFUNC:
579 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
580 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
581 Type = ELF::STT_GNU_IFUNC;
584 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
585 Type == ELF::STT_TLS)
586 Type = ELF::STT_FUNC;
588 case ELF::STT_OBJECT:
589 if (Type == ELF::STT_NOTYPE)
590 Type = ELF::STT_OBJECT;
593 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
594 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
602 static const MCSymbol *getBaseSymbol(const MCAsmLayout &Layout,
603 const MCSymbol &Symbol) {
604 if (!Symbol.isVariable())
607 const MCExpr *Expr = Symbol.getVariableValue();
609 if (!Expr->EvaluateAsValue(Value, &Layout))
610 llvm_unreachable("Invalid Expression");
611 const MCSymbolRefExpr *RefB = Value.getSymB();
613 Layout.getAssembler().getContext().FatalError(
614 SMLoc(), Twine("symbol '") + RefB->getSymbol().getName() +
615 "' could not be evaluated in a subtraction expression");
617 const MCSymbolRefExpr *A = Value.getSymA();
620 return getBaseSymbol(Layout, A->getSymbol());
623 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
624 const MCAsmLayout &Layout) {
625 MCSymbolData &OrigData = *MSD.SymbolData;
626 assert((!OrigData.getFragment() ||
627 (&OrigData.getFragment()->getParent()->getSection() ==
628 &OrigData.getSymbol().getSection())) &&
629 "The symbol's section doesn't match the fragment's symbol");
630 const MCSymbol *Base = getBaseSymbol(Layout, OrigData.getSymbol());
632 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
634 bool IsReserved = !Base || OrigData.isCommon();
636 // Binding and Type share the same byte as upper and lower nibbles
637 uint8_t Binding = MCELF::GetBinding(OrigData);
638 uint8_t Type = MCELF::GetType(OrigData);
639 MCSymbolData *BaseSD = nullptr;
641 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
642 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
644 if (OrigData.getFlags() & ELF_Other_ThumbFunc)
645 Type = ELF::STT_FUNC;
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 MCSymbolRefExpr *RefA,
741 const MCSymbolData *SD,
743 unsigned Type) const {
744 // A PCRel relocation to an absolute value has no symbol (or section). We
745 // represent that with a relocation to a null section.
749 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
753 // The .odp creation emits a relocation against the symbol ".TOC." which
754 // create a R_PPC64_TOC relocation. However the relocation symbol name
755 // in final object creation should be NULL, since the symbol does not
756 // really exist, it is just the reference to TOC base for the current
757 // object file. Since the symbol is undefined, returning false results
758 // in a relocation with a null section which is the desired result.
759 case MCSymbolRefExpr::VK_PPC_TOCBASE:
762 // These VariantKind cause the relocation to refer to something other than
763 // the symbol itself, like a linker generated table. Since the address of
764 // symbol is not relevant, we cannot replace the symbol with the
765 // section and patch the difference in the addend.
766 case MCSymbolRefExpr::VK_GOT:
767 case MCSymbolRefExpr::VK_PLT:
768 case MCSymbolRefExpr::VK_GOTPCREL:
769 case MCSymbolRefExpr::VK_Mips_GOT:
770 case MCSymbolRefExpr::VK_PPC_GOT_LO:
771 case MCSymbolRefExpr::VK_PPC_GOT_HI:
772 case MCSymbolRefExpr::VK_PPC_GOT_HA:
776 // An undefined symbol is not in any section, so the relocation has to point
777 // to the symbol itself.
778 const MCSymbol &Sym = SD->getSymbol();
779 if (Sym.isUndefined())
782 unsigned Binding = MCELF::GetBinding(*SD);
785 llvm_unreachable("Invalid Binding");
789 // If the symbol is weak, it might be overridden by a symbol in another
790 // file. The relocation has to point to the symbol so that the linker
793 case ELF::STB_GLOBAL:
794 // Global ELF symbols can be preempted by the dynamic linker. The relocation
795 // has to point to the symbol for a reason analogous to the STB_WEAK case.
799 // If a relocation points to a mergeable section, we have to be careful.
800 // If the offset is zero, a relocation with the section will encode the
801 // same information. With a non-zero offset, the situation is different.
802 // For example, a relocation can point 42 bytes past the end of a string.
803 // If we change such a relocation to use the section, the linker would think
804 // that it pointed to another string and subtracting 42 at runtime will
805 // produce the wrong value.
806 auto &Sec = cast<MCSectionELF>(Sym.getSection());
807 unsigned Flags = Sec.getFlags();
808 if (Flags & ELF::SHF_MERGE) {
812 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
813 // only handle section relocations to mergeable sections if using RELA.
814 if (!hasRelocationAddend())
818 // Most TLS relocations use a got, so they need the symbol. Even those that
819 // are just an offset (@tpoff), require a symbol in some linkers (gold,
821 if (Flags & ELF::SHF_TLS)
824 // If the symbol is a thumb function the final relocation must set the lowest
825 // bit. With a symbol that is done by just having the symbol have that bit
826 // set, so we would lose the bit if we relocated with the section.
827 // FIXME: We could use the section but add the bit to the relocation value.
828 if (SD->getFlags() & ELF_Other_ThumbFunc)
831 if (TargetObjectWriter->needsRelocateWithSymbol(Type))
836 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
837 const MCAsmLayout &Layout,
838 const MCFragment *Fragment,
839 const MCFixup &Fixup,
842 uint64_t &FixedValue) {
843 const MCSectionData *FixupSection = Fragment->getParent();
844 uint64_t C = Target.getConstant();
845 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
847 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
848 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
849 "Should not have constructed this");
851 // Let A, B and C being the components of Target and R be the location of
852 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
853 // If it is pcrel, we want to compute (A - B + C - R).
855 // In general, ELF has no relocations for -B. It can only represent (A + C)
856 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
857 // replace B to implement it: (A - R - K + C)
859 Asm.getContext().FatalError(
861 "No relocation available to represent this relative expression");
863 const MCSymbol &SymB = RefB->getSymbol();
865 if (SymB.isUndefined())
866 Asm.getContext().FatalError(
868 Twine("symbol '") + SymB.getName() +
869 "' can not be undefined in a subtraction expression");
871 assert(!SymB.isAbsolute() && "Should have been folded");
872 const MCSection &SecB = SymB.getSection();
873 if (&SecB != &FixupSection->getSection())
874 Asm.getContext().FatalError(
875 Fixup.getLoc(), "Cannot represent a difference across sections");
877 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
878 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
879 uint64_t K = SymBOffset - FixupOffset;
884 // We either rejected the fixup or folded B into C at this point.
885 const MCSymbolRefExpr *RefA = Target.getSymA();
886 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
887 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
889 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
890 bool RelocateWithSymbol = shouldRelocateWithSymbol(RefA, SymAD, C, Type);
891 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
892 C += Layout.getSymbolOffset(SymAD);
895 if (hasRelocationAddend()) {
902 // FIXME: What is this!?!?
903 MCSymbolRefExpr::VariantKind Modifier =
904 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
905 if (RelocNeedsGOT(Modifier))
908 if (!RelocateWithSymbol) {
909 const MCSection *SecA =
910 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
911 const MCSectionData *SecAD = SecA ? &Asm.getSectionData(*SecA) : nullptr;
912 ELFRelocationEntry Rec(FixupOffset, SecAD, Type, Addend);
913 Relocations[FixupSection].push_back(Rec);
918 if (const MCSymbol *R = Renames.lookup(SymA))
921 if (RefA->getKind() == MCSymbolRefExpr::VK_WEAKREF)
922 WeakrefUsedInReloc.insert(SymA);
924 UsedInReloc.insert(SymA);
926 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
927 Relocations[FixupSection].push_back(Rec);
933 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
935 const MCSymbolData &SD = Asm.getSymbolData(*S);
936 return SD.getIndex();
939 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
940 const MCSymbolData &Data, bool Used,
942 const MCSymbol &Symbol = Data.getSymbol();
943 if (Symbol.isVariable()) {
944 const MCExpr *Expr = Symbol.getVariableValue();
945 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
946 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
957 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
960 if (Symbol.isVariable()) {
961 const MCSymbol *Base = getBaseSymbol(Layout, Symbol);
962 if (Base && Base->isUndefined())
966 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
967 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
970 if (Symbol.isTemporary())
976 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
977 if (Data.isExternal())
980 const MCSymbol &Symbol = Data.getSymbol();
981 if (Symbol.isDefined())
990 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
991 SectionIndexMapTy &SectionIndexMap,
992 const RelMapTy &RelMap) {
994 for (MCAssembler::iterator it = Asm.begin(),
995 ie = Asm.end(); it != ie; ++it) {
996 const MCSectionELF &Section =
997 static_cast<const MCSectionELF &>(it->getSection());
998 if (Section.getType() != ELF::SHT_GROUP)
1000 SectionIndexMap[&Section] = Index++;
1003 for (MCAssembler::iterator it = Asm.begin(),
1004 ie = Asm.end(); it != ie; ++it) {
1005 const MCSectionELF &Section =
1006 static_cast<const MCSectionELF &>(it->getSection());
1007 if (Section.getType() == ELF::SHT_GROUP ||
1008 Section.getType() == ELF::SHT_REL ||
1009 Section.getType() == ELF::SHT_RELA)
1011 SectionIndexMap[&Section] = Index++;
1012 const MCSectionELF *RelSection = RelMap.lookup(&Section);
1014 SectionIndexMap[RelSection] = Index++;
1019 ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
1020 const SectionIndexMapTy &SectionIndexMap,
1021 RevGroupMapTy RevGroupMap,
1022 unsigned NumRegularSections) {
1023 // FIXME: Is this the correct place to do this?
1024 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
1026 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
1027 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
1028 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
1029 Data.setExternal(true);
1030 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
1033 // Index 0 is always the empty string.
1034 StringMap<uint64_t> StringIndexMap;
1035 StringTable += '\x00';
1037 // FIXME: We could optimize suffixes in strtab in the same way we
1038 // optimize them in shstrtab.
1040 for (MCAssembler::const_file_name_iterator it = Asm.file_names_begin(),
1041 ie = Asm.file_names_end();
1044 StringRef Name = *it;
1045 uint64_t &Entry = StringIndexMap[Name];
1047 Entry = StringTable.size();
1048 StringTable += Name;
1049 StringTable += '\x00';
1051 FileSymbolData.push_back(Entry);
1054 // Add the data for the symbols.
1055 for (MCSymbolData &SD : Asm.symbols()) {
1056 const MCSymbol &Symbol = SD.getSymbol();
1058 bool Used = UsedInReloc.count(&Symbol);
1059 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
1060 bool isSignature = RevGroupMap.count(&Symbol);
1062 if (!isInSymtab(Layout, SD,
1063 Used || WeakrefUsed || isSignature,
1064 Renames.count(&Symbol)))
1068 MSD.SymbolData = &SD;
1069 const MCSymbol *BaseSymbol = getBaseSymbol(Layout, Symbol);
1071 // Undefined symbols are global, but this is the first place we
1072 // are able to set it.
1073 bool Local = isLocal(SD, Used);
1074 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1076 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1077 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1078 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1082 MSD.SectionIndex = ELF::SHN_ABS;
1083 } else if (SD.isCommon()) {
1085 MSD.SectionIndex = ELF::SHN_COMMON;
1086 } else if (BaseSymbol->isUndefined()) {
1087 if (isSignature && !Used)
1088 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]);
1090 MSD.SectionIndex = ELF::SHN_UNDEF;
1091 if (!Used && WeakrefUsed)
1092 MCELF::SetBinding(SD, ELF::STB_WEAK);
1094 const MCSectionELF &Section =
1095 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1096 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1097 assert(MSD.SectionIndex && "Invalid section index!");
1100 // The @@@ in symbol version is replaced with @ in undefined symbols and
1101 // @@ in defined ones.
1102 StringRef Name = Symbol.getName();
1103 SmallString<32> Buf;
1105 size_t Pos = Name.find("@@@");
1106 if (Pos != StringRef::npos) {
1107 Buf += Name.substr(0, Pos);
1108 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1109 Buf += Name.substr(Pos + Skip);
1113 uint64_t &Entry = StringIndexMap[Name];
1115 Entry = StringTable.size();
1116 StringTable += Name;
1117 StringTable += '\x00';
1119 MSD.StringIndex = Entry;
1120 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1121 UndefinedSymbolData.push_back(MSD);
1123 LocalSymbolData.push_back(MSD);
1125 ExternalSymbolData.push_back(MSD);
1128 // Symbols are required to be in lexicographic order.
1129 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1130 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1131 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1133 // Set the symbol indices. Local symbols must come before all other
1134 // symbols with non-local bindings.
1135 unsigned Index = FileSymbolData.size() + 1;
1136 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1137 LocalSymbolData[i].SymbolData->setIndex(Index++);
1139 Index += NumRegularSections;
1141 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1142 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1143 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1144 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1147 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm,
1148 MCAsmLayout &Layout,
1150 for (MCAssembler::const_iterator it = Asm.begin(),
1151 ie = Asm.end(); it != ie; ++it) {
1152 const MCSectionData &SD = *it;
1153 if (Relocations[&SD].empty())
1156 MCContext &Ctx = Asm.getContext();
1157 const MCSectionELF &Section =
1158 static_cast<const MCSectionELF&>(SD.getSection());
1160 const StringRef SectionName = Section.getSectionName();
1161 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1162 RelaSectionName += SectionName;
1165 if (hasRelocationAddend())
1166 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1168 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1171 StringRef Group = "";
1172 if (Section.getFlags() & ELF::SHF_GROUP) {
1173 Flags = ELF::SHF_GROUP;
1174 Group = Section.getGroup()->getName();
1177 const MCSectionELF *RelaSection =
1178 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ?
1179 ELF::SHT_RELA : ELF::SHT_REL, Flags,
1180 SectionKind::getReadOnly(),
1182 RelMap[&Section] = RelaSection;
1183 Asm.getOrCreateSectionData(*RelaSection);
1187 static SmallVector<char, 128>
1188 getUncompressedData(MCAsmLayout &Layout,
1189 MCSectionData::FragmentListType &Fragments) {
1190 SmallVector<char, 128> UncompressedData;
1191 for (const MCFragment &F : Fragments) {
1192 const SmallVectorImpl<char> *Contents;
1193 switch (F.getKind()) {
1194 case MCFragment::FT_Data:
1195 Contents = &cast<MCDataFragment>(F).getContents();
1197 case MCFragment::FT_Dwarf:
1198 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1200 case MCFragment::FT_DwarfFrame:
1201 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1205 "Not expecting any other fragment types in a debug_* section");
1207 UncompressedData.append(Contents->begin(), Contents->end());
1209 return UncompressedData;
1212 // Include the debug info compression header:
1213 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1214 // useful for consumers to preallocate a buffer to decompress into.
1216 prependCompressionHeader(uint64_t Size,
1217 SmallVectorImpl<char> &CompressedContents) {
1218 static const StringRef Magic = "ZLIB";
1219 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1221 if (sys::IsLittleEndianHost)
1222 Size = sys::SwapByteOrder(Size);
1223 CompressedContents.insert(CompressedContents.begin(),
1224 Magic.size() + sizeof(Size), 0);
1225 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1226 std::copy(reinterpret_cast<char *>(&Size),
1227 reinterpret_cast<char *>(&Size + 1),
1228 CompressedContents.begin() + Magic.size());
1232 // Return a single fragment containing the compressed contents of the whole
1233 // section. Null if the section was not compressed for any reason.
1234 static std::unique_ptr<MCDataFragment>
1235 getCompressedFragment(MCAsmLayout &Layout,
1236 MCSectionData::FragmentListType &Fragments) {
1237 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1239 // Gather the uncompressed data from all the fragments, recording the
1240 // alignment fragment, if seen, and any fixups.
1241 SmallVector<char, 128> UncompressedData =
1242 getUncompressedData(Layout, Fragments);
1244 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1246 zlib::Status Success = zlib::compress(
1247 StringRef(UncompressedData.data(), UncompressedData.size()),
1248 CompressedContents);
1249 if (Success != zlib::StatusOK)
1252 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1255 return CompressedFragment;
1258 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1261 static void UpdateSymbols(const MCAsmLayout &Layout,
1262 const std::vector<MCSymbolData *> &Symbols,
1263 MCFragment &NewFragment) {
1264 for (MCSymbolData *Sym : Symbols) {
1265 Sym->setOffset(Sym->getOffset() +
1266 Layout.getFragmentOffset(Sym->getFragment()));
1267 Sym->setFragment(&NewFragment);
1271 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1272 const DefiningSymbolMap &DefiningSymbols,
1273 const MCSectionELF &Section,
1274 MCSectionData &SD) {
1275 StringRef SectionName = Section.getSectionName();
1276 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1278 std::unique_ptr<MCDataFragment> CompressedFragment =
1279 getCompressedFragment(Layout, Fragments);
1281 // Leave the section as-is if the fragments could not be compressed.
1282 if (!CompressedFragment)
1285 // Update the fragment+offsets of any symbols referring to fragments in this
1286 // section to refer to the new fragment.
1287 auto I = DefiningSymbols.find(&SD);
1288 if (I != DefiningSymbols.end())
1289 UpdateSymbols(Layout, I->second, *CompressedFragment);
1291 // Invalidate the layout for the whole section since it will have new and
1292 // different fragments now.
1293 Layout.invalidateFragmentsFrom(&Fragments.front());
1296 // Complete the initialization of the new fragment
1297 CompressedFragment->setParent(&SD);
1298 CompressedFragment->setLayoutOrder(0);
1299 Fragments.push_back(CompressedFragment.release());
1301 // Rename from .debug_* to .zdebug_*
1302 Asm.getContext().renameELFSection(&Section,
1303 (".z" + SectionName.drop_front(1)).str());
1306 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1307 MCAsmLayout &Layout) {
1308 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1311 DefiningSymbolMap DefiningSymbols;
1313 for (MCSymbolData &SD : Asm.symbols())
1314 if (MCFragment *F = SD.getFragment())
1315 DefiningSymbols[F->getParent()].push_back(&SD);
1317 for (MCSectionData &SD : Asm) {
1318 const MCSectionELF &Section =
1319 static_cast<const MCSectionELF &>(SD.getSection());
1320 StringRef SectionName = Section.getSectionName();
1322 // Compressing debug_frame requires handling alignment fragments which is
1323 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1324 // for writing to arbitrary buffers) for little benefit.
1325 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1328 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1332 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
1333 const RelMapTy &RelMap) {
1334 for (MCAssembler::const_iterator it = Asm.begin(),
1335 ie = Asm.end(); it != ie; ++it) {
1336 const MCSectionData &SD = *it;
1337 const MCSectionELF &Section =
1338 static_cast<const MCSectionELF&>(SD.getSection());
1340 const MCSectionELF *RelaSection = RelMap.lookup(&Section);
1343 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
1344 RelaSD.setAlignment(is64Bit() ? 8 : 4);
1346 MCDataFragment *F = new MCDataFragment(&RelaSD);
1347 WriteRelocationsFragment(Asm, F, &*it);
1351 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1352 uint64_t Flags, uint64_t Address,
1353 uint64_t Offset, uint64_t Size,
1354 uint32_t Link, uint32_t Info,
1356 uint64_t EntrySize) {
1357 Write32(Name); // sh_name: index into string table
1358 Write32(Type); // sh_type
1359 WriteWord(Flags); // sh_flags
1360 WriteWord(Address); // sh_addr
1361 WriteWord(Offset); // sh_offset
1362 WriteWord(Size); // sh_size
1363 Write32(Link); // sh_link
1364 Write32(Info); // sh_info
1365 WriteWord(Alignment); // sh_addralign
1366 WriteWord(EntrySize); // sh_entsize
1369 // ELF doesn't require relocations to be in any order. We sort by the r_offset,
1370 // just to match gnu as for easier comparison. The use type is an arbitrary way
1371 // of making the sort deterministic.
1372 static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) {
1373 const ELFRelocationEntry &A = *AP;
1374 const ELFRelocationEntry &B = *BP;
1375 if (A.Offset != B.Offset)
1376 return B.Offset - A.Offset;
1377 if (B.Type != A.Type)
1378 return A.Type - B.Type;
1379 llvm_unreachable("ELFRelocs might be unstable!");
1382 static void sortRelocs(const MCAssembler &Asm,
1383 std::vector<ELFRelocationEntry> &Relocs) {
1384 array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
1387 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1389 const MCSectionData *SD) {
1390 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1392 sortRelocs(Asm, Relocs);
1394 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1395 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1398 if (Entry.UseSymbol) {
1399 Index = getSymbolIndexInSymbolTable(Asm, Entry.Symbol);
1401 const MCSectionData *Sec = Entry.Section;
1403 Index = Sec->getOrdinal() + FileSymbolData.size() +
1404 LocalSymbolData.size() + 1;
1410 write(*F, Entry.Offset);
1411 if (TargetObjectWriter->isN64()) {
1412 write(*F, uint32_t(Index));
1414 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1415 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1416 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1417 write(*F, TargetObjectWriter->getRType(Entry.Type));
1419 struct ELF::Elf64_Rela ERE64;
1420 ERE64.setSymbolAndType(Index, Entry.Type);
1421 write(*F, ERE64.r_info);
1423 if (hasRelocationAddend())
1424 write(*F, Entry.Addend);
1426 write(*F, uint32_t(Entry.Offset));
1428 struct ELF::Elf32_Rela ERE32;
1429 ERE32.setSymbolAndType(Index, Entry.Type);
1430 write(*F, ERE32.r_info);
1432 if (hasRelocationAddend())
1433 write(*F, uint32_t(Entry.Addend));
1438 static int compareBySuffix(const MCSectionELF *const *a,
1439 const MCSectionELF *const *b) {
1440 const StringRef &NameA = (*a)->getSectionName();
1441 const StringRef &NameB = (*b)->getSectionName();
1442 const unsigned sizeA = NameA.size();
1443 const unsigned sizeB = NameB.size();
1444 const unsigned len = std::min(sizeA, sizeB);
1445 for (unsigned int i = 0; i < len; ++i) {
1446 char ca = NameA[sizeA - i - 1];
1447 char cb = NameB[sizeB - i - 1];
1452 return sizeB - sizeA;
1455 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
1456 MCAsmLayout &Layout,
1457 SectionIndexMapTy &SectionIndexMap,
1458 const RelMapTy &RelMap) {
1459 MCContext &Ctx = Asm.getContext();
1462 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1464 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1465 const MCSectionELF *ShstrtabSection =
1466 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
1467 SectionKind::getReadOnly());
1468 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1469 ShstrtabSD.setAlignment(1);
1471 const MCSectionELF *SymtabSection =
1472 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1473 SectionKind::getReadOnly(),
1475 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1476 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1478 const MCSectionELF *StrtabSection;
1479 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
1480 SectionKind::getReadOnly());
1481 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1482 StrtabSD.setAlignment(1);
1484 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1486 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection);
1487 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection);
1488 StringTableIndex = SectionIndexMap.lookup(StrtabSection);
1491 F = new MCDataFragment(&SymtabSD);
1492 WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
1494 F = new MCDataFragment(&StrtabSD);
1495 F->getContents().append(StringTable.begin(), StringTable.end());
1497 F = new MCDataFragment(&ShstrtabSD);
1499 std::vector<const MCSectionELF*> Sections;
1500 for (MCAssembler::const_iterator it = Asm.begin(),
1501 ie = Asm.end(); it != ie; ++it) {
1502 const MCSectionELF &Section =
1503 static_cast<const MCSectionELF&>(it->getSection());
1504 Sections.push_back(&Section);
1506 array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix);
1508 // Section header string table.
1510 // The first entry of a string table holds a null character so skip
1513 F->getContents().push_back('\x00');
1515 for (unsigned int I = 0, E = Sections.size(); I != E; ++I) {
1516 const MCSectionELF &Section = *Sections[I];
1518 StringRef Name = Section.getSectionName();
1520 StringRef PreviousName = Sections[I - 1]->getSectionName();
1521 if (PreviousName.endswith(Name)) {
1522 SectionStringTableIndex[&Section] = Index - Name.size() - 1;
1526 // Remember the index into the string table so we can write it
1527 // into the sh_name field of the section header table.
1528 SectionStringTableIndex[&Section] = Index;
1530 Index += Name.size() + 1;
1531 F->getContents().append(Name.begin(), Name.end());
1532 F->getContents().push_back('\x00');
1536 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm,
1537 MCAsmLayout &Layout,
1538 GroupMapTy &GroupMap,
1539 RevGroupMapTy &RevGroupMap,
1540 SectionIndexMapTy &SectionIndexMap,
1541 const RelMapTy &RelMap) {
1542 // Create the .note.GNU-stack section if needed.
1543 MCContext &Ctx = Asm.getContext();
1544 if (Asm.getNoExecStack()) {
1545 const MCSectionELF *GnuStackSection =
1546 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0,
1547 SectionKind::getReadOnly());
1548 Asm.getOrCreateSectionData(*GnuStackSection);
1552 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1554 const MCSectionELF &Section =
1555 static_cast<const MCSectionELF&>(it->getSection());
1556 if (!(Section.getFlags() & ELF::SHF_GROUP))
1559 const MCSymbol *SignatureSymbol = Section.getGroup();
1560 Asm.getOrCreateSymbolData(*SignatureSymbol);
1561 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1563 Group = Ctx.CreateELFGroupSection();
1564 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1565 Data.setAlignment(4);
1566 MCDataFragment *F = new MCDataFragment(&Data);
1567 write(*F, uint32_t(ELF::GRP_COMDAT));
1569 GroupMap[Group] = SignatureSymbol;
1572 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1574 // Add sections to the groups
1575 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1577 const MCSectionELF &Section =
1578 static_cast<const MCSectionELF&>(it->getSection());
1579 if (!(Section.getFlags() & ELF::SHF_GROUP))
1581 const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1582 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1583 // FIXME: we could use the previous fragment
1584 MCDataFragment *F = new MCDataFragment(&Data);
1585 uint32_t Index = SectionIndexMap.lookup(&Section);
1590 void ELFObjectWriter::WriteSection(MCAssembler &Asm,
1591 const SectionIndexMapTy &SectionIndexMap,
1592 uint32_t GroupSymbolIndex,
1593 uint64_t Offset, uint64_t Size,
1595 const MCSectionELF &Section) {
1596 uint64_t sh_link = 0;
1597 uint64_t sh_info = 0;
1599 switch(Section.getType()) {
1600 case ELF::SHT_DYNAMIC:
1601 sh_link = SectionStringTableIndex[&Section];
1606 case ELF::SHT_RELA: {
1607 const MCSectionELF *SymtabSection;
1608 const MCSectionELF *InfoSection;
1609 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB,
1611 SectionKind::getReadOnly());
1612 sh_link = SectionIndexMap.lookup(SymtabSection);
1613 assert(sh_link && ".symtab not found");
1615 // Remove ".rel" and ".rela" prefixes.
1616 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1617 StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1618 StringRef GroupName =
1619 Section.getGroup() ? Section.getGroup()->getName() : "";
1621 InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS,
1622 0, SectionKind::getReadOnly(),
1624 sh_info = SectionIndexMap.lookup(InfoSection);
1628 case ELF::SHT_SYMTAB:
1629 case ELF::SHT_DYNSYM:
1630 sh_link = StringTableIndex;
1631 sh_info = LastLocalSymbolIndex;
1634 case ELF::SHT_SYMTAB_SHNDX:
1635 sh_link = SymbolTableIndex;
1638 case ELF::SHT_PROGBITS:
1639 case ELF::SHT_STRTAB:
1640 case ELF::SHT_NOBITS:
1643 case ELF::SHT_ARM_ATTRIBUTES:
1644 case ELF::SHT_INIT_ARRAY:
1645 case ELF::SHT_FINI_ARRAY:
1646 case ELF::SHT_PREINIT_ARRAY:
1647 case ELF::SHT_X86_64_UNWIND:
1648 case ELF::SHT_MIPS_REGINFO:
1649 case ELF::SHT_MIPS_OPTIONS:
1653 case ELF::SHT_GROUP:
1654 sh_link = SymbolTableIndex;
1655 sh_info = GroupSymbolIndex;
1659 assert(0 && "FIXME: sh_type value not supported!");
1663 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1664 Section.getType() == ELF::SHT_ARM_EXIDX) {
1665 StringRef SecName(Section.getSectionName());
1666 if (SecName == ".ARM.exidx") {
1667 sh_link = SectionIndexMap.lookup(
1668 Asm.getContext().getELFSection(".text",
1670 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC,
1671 SectionKind::getText()));
1672 } else if (SecName.startswith(".ARM.exidx")) {
1673 StringRef GroupName =
1674 Section.getGroup() ? Section.getGroup()->getName() : "";
1675 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
1676 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS,
1677 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText(), 0,
1682 WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(),
1683 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1684 Alignment, Section.getEntrySize());
1687 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1688 return SD.getOrdinal() == ~UINT32_C(0) &&
1689 !SD.getSection().isVirtualSection();
1692 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1694 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1696 const MCFragment &F = *i;
1697 assert(F.getKind() == MCFragment::FT_Data);
1698 Ret += cast<MCDataFragment>(F).getContents().size();
1703 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
1704 const MCSectionData &SD) {
1705 if (IsELFMetaDataSection(SD))
1706 return DataSectionSize(SD);
1707 return Layout.getSectionFileSize(&SD);
1710 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1711 const MCSectionData &SD) {
1712 if (IsELFMetaDataSection(SD))
1713 return DataSectionSize(SD);
1714 return Layout.getSectionAddressSize(&SD);
1717 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
1718 const MCAsmLayout &Layout,
1719 const MCSectionELF &Section) {
1720 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1722 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1723 WriteZeros(Padding);
1725 if (IsELFMetaDataSection(SD)) {
1726 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1728 const MCFragment &F = *i;
1729 assert(F.getKind() == MCFragment::FT_Data);
1730 WriteBytes(cast<MCDataFragment>(F).getContents());
1733 Asm.writeSectionData(&SD, Layout);
1737 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm,
1738 const GroupMapTy &GroupMap,
1739 const MCAsmLayout &Layout,
1740 const SectionIndexMapTy &SectionIndexMap,
1741 const SectionOffsetMapTy &SectionOffsetMap) {
1742 const unsigned NumSections = Asm.size() + 1;
1744 std::vector<const MCSectionELF*> Sections;
1745 Sections.resize(NumSections - 1);
1747 for (SectionIndexMapTy::const_iterator i=
1748 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
1749 const std::pair<const MCSectionELF*, uint32_t> &p = *i;
1750 Sections[p.second - 1] = p.first;
1753 // Null section first.
1754 uint64_t FirstSectionSize =
1755 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
1756 uint32_t FirstSectionLink =
1757 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1758 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1760 for (unsigned i = 0; i < NumSections - 1; ++i) {
1761 const MCSectionELF &Section = *Sections[i];
1762 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1763 uint32_t GroupSymbolIndex;
1764 if (Section.getType() != ELF::SHT_GROUP)
1765 GroupSymbolIndex = 0;
1767 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1768 GroupMap.lookup(&Section));
1770 uint64_t Size = GetSectionAddressSize(Layout, SD);
1772 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex,
1773 SectionOffsetMap.lookup(&Section), Size,
1774 SD.getAlignment(), Section);
1778 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
1779 std::vector<const MCSectionELF*> &Sections) {
1780 for (MCAssembler::iterator it = Asm.begin(),
1781 ie = Asm.end(); it != ie; ++it) {
1782 const MCSectionELF &Section =
1783 static_cast<const MCSectionELF &>(it->getSection());
1784 if (Section.getType() == ELF::SHT_GROUP)
1785 Sections.push_back(&Section);
1788 for (MCAssembler::iterator it = Asm.begin(),
1789 ie = Asm.end(); it != ie; ++it) {
1790 const MCSectionELF &Section =
1791 static_cast<const MCSectionELF &>(it->getSection());
1792 if (Section.getType() != ELF::SHT_GROUP &&
1793 Section.getType() != ELF::SHT_REL &&
1794 Section.getType() != ELF::SHT_RELA)
1795 Sections.push_back(&Section);
1798 for (MCAssembler::iterator it = Asm.begin(),
1799 ie = Asm.end(); it != ie; ++it) {
1800 const MCSectionELF &Section =
1801 static_cast<const MCSectionELF &>(it->getSection());
1802 if (Section.getType() == ELF::SHT_REL ||
1803 Section.getType() == ELF::SHT_RELA)
1804 Sections.push_back(&Section);
1808 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1809 const MCAsmLayout &Layout) {
1810 GroupMapTy GroupMap;
1811 RevGroupMapTy RevGroupMap;
1812 SectionIndexMapTy SectionIndexMap;
1814 unsigned NumUserSections = Asm.size();
1816 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1818 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap;
1819 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1821 const unsigned NumUserAndRelocSections = Asm.size();
1822 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
1823 RevGroupMap, SectionIndexMap, RelMap);
1824 const unsigned AllSections = Asm.size();
1825 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections;
1827 unsigned NumRegularSections = NumUserSections + NumIndexedSections;
1829 // Compute symbol table information.
1830 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
1831 NumRegularSections);
1833 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1835 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1836 const_cast<MCAsmLayout&>(Layout),
1840 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1841 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
1842 sizeof(ELF::Elf32_Ehdr);
1843 uint64_t FileOff = HeaderSize;
1845 std::vector<const MCSectionELF*> Sections;
1846 ComputeSectionOrder(Asm, Sections);
1847 unsigned NumSections = Sections.size();
1848 SectionOffsetMapTy SectionOffsetMap;
1849 for (unsigned i = 0; i < NumRegularSections + 1; ++i) {
1850 const MCSectionELF &Section = *Sections[i];
1851 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1853 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1855 // Remember the offset into the file for this section.
1856 SectionOffsetMap[&Section] = FileOff;
1858 // Get the size of the section in the output file (including padding).
1859 FileOff += GetSectionFileSize(Layout, SD);
1862 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1864 const unsigned SectionHeaderOffset = FileOff - HeaderSize;
1866 uint64_t SectionHeaderEntrySize = is64Bit() ?
1867 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr);
1868 FileOff += (NumSections + 1) * SectionHeaderEntrySize;
1870 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) {
1871 const MCSectionELF &Section = *Sections[i];
1872 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1874 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1876 // Remember the offset into the file for this section.
1877 SectionOffsetMap[&Section] = FileOff;
1879 // Get the size of the section in the output file (including padding).
1880 FileOff += GetSectionFileSize(Layout, SD);
1883 // Write out the ELF header ...
1884 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
1886 // ... then the regular sections ...
1887 // + because of .shstrtab
1888 for (unsigned i = 0; i < NumRegularSections + 1; ++i)
1889 WriteDataSectionData(Asm, Layout, *Sections[i]);
1891 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1892 WriteZeros(Padding);
1894 // ... then the section header table ...
1895 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap,
1898 // ... and then the remaining sections ...
1899 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i)
1900 WriteDataSectionData(Asm, Layout, *Sections[i]);
1904 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
1905 const MCSymbolData &DataA,
1906 const MCFragment &FB,
1908 bool IsPCRel) const {
1909 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC)
1911 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1912 Asm, DataA, FB,InSet, IsPCRel);
1915 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1917 bool IsLittleEndian) {
1918 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);