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/MC/StringTableBuilder.h"
32 #include "llvm/Support/Compression.h"
33 #include "llvm/Support/Debug.h"
34 #include "llvm/Support/ELF.h"
35 #include "llvm/Support/Endian.h"
36 #include "llvm/Support/ErrorHandling.h"
41 #define DEBUG_TYPE "reloc-info"
44 class FragmentWriter {
48 FragmentWriter(bool IsLittleEndian);
49 template <typename T> void write(MCDataFragment &F, T Val);
52 typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
54 class SymbolTableWriter {
56 FragmentWriter &FWriter;
58 SectionIndexMapTy &SectionIndexMap;
60 // The symbol .symtab fragment we are writting to.
61 MCDataFragment *SymtabF;
63 // .symtab_shndx fragment we are writting to.
64 MCDataFragment *ShndxF;
66 // The numbel of symbols written so far.
69 void createSymtabShndx();
71 template <typename T> void write(MCDataFragment &F, T Value);
74 SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit,
75 SectionIndexMapTy &SectionIndexMap,
76 MCDataFragment *SymtabF);
78 void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
79 uint8_t other, uint32_t shndx, bool Reserved);
82 class ELFObjectWriter : public MCObjectWriter {
83 FragmentWriter FWriter;
87 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
88 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
89 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
90 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data,
91 bool Used, bool Renamed);
92 static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc);
93 static bool IsELFMetaDataSection(const MCSectionData &SD);
94 static uint64_t DataSectionSize(const MCSectionData &SD);
95 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout,
96 const MCSectionData &SD);
98 void writeDataSectionData(MCAssembler &Asm, const MCAsmLayout &Layout,
99 const MCSectionData &SD);
101 /// Helper struct for containing some precomputed information on symbols.
102 struct ELFSymbolData {
103 MCSymbolData *SymbolData;
104 uint64_t StringIndex;
105 uint32_t SectionIndex;
108 // Support lexicographic sorting.
109 bool operator<(const ELFSymbolData &RHS) const {
110 unsigned LHSType = MCELF::GetType(*SymbolData);
111 unsigned RHSType = MCELF::GetType(*RHS.SymbolData);
112 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
114 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
116 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
117 return SectionIndex < RHS.SectionIndex;
118 return Name < RHS.Name;
122 /// The target specific ELF writer instance.
123 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
125 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
126 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
127 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
129 llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>>
131 StringTableBuilder ShStrTabBuilder;
134 /// @name Symbol Table Data
137 StringTableBuilder StrTabBuilder;
138 std::vector<uint64_t> FileSymbolData;
139 std::vector<ELFSymbolData> LocalSymbolData;
140 std::vector<ELFSymbolData> ExternalSymbolData;
141 std::vector<ELFSymbolData> UndefinedSymbolData;
147 // This holds the symbol table index of the last local symbol.
148 unsigned LastLocalSymbolIndex;
149 // This holds the .strtab section index.
150 unsigned StringTableIndex;
151 // This holds the .symtab section index.
152 unsigned SymbolTableIndex;
154 unsigned ShstrtabIndex;
157 // TargetObjectWriter wrappers.
158 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
159 bool hasRelocationAddend() const {
160 return TargetObjectWriter->hasRelocationAddend();
162 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
163 bool IsPCRel) const {
164 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
168 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
170 : MCObjectWriter(OS, IsLittleEndian), FWriter(IsLittleEndian),
171 TargetObjectWriter(MOTW), NeedsGOT(false) {}
173 void reset() override {
175 WeakrefUsedInReloc.clear();
178 ShStrTabBuilder.clear();
179 StrTabBuilder.clear();
180 FileSymbolData.clear();
181 LocalSymbolData.clear();
182 ExternalSymbolData.clear();
183 UndefinedSymbolData.clear();
184 MCObjectWriter::reset();
187 ~ELFObjectWriter() override;
189 void WriteWord(uint64_t W) {
196 template <typename T> void write(MCDataFragment &F, T Value) {
197 FWriter.write(F, Value);
200 void WriteHeader(const MCAssembler &Asm,
201 unsigned NumberOfSections);
203 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
204 const MCAsmLayout &Layout);
206 void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm,
207 const MCAsmLayout &Layout,
208 SectionIndexMapTy &SectionIndexMap);
210 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
211 const MCSymbolRefExpr *RefA,
212 const MCSymbolData *SD, uint64_t C,
213 unsigned Type) const;
215 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
216 const MCFragment *Fragment, const MCFixup &Fixup,
217 MCValue Target, bool &IsPCRel,
218 uint64_t &FixedValue) override;
220 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
223 // Map from a group section to the signature symbol
224 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
225 // Map from a signature symbol to the group section
226 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
227 // Map from a section to its offset
228 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy;
230 /// Compute the symbol table data
232 /// \param Asm - The assembler.
233 /// \param SectionIndexMap - Maps a section to its index.
234 /// \param RevGroupMap - Maps a signature symbol to the group section.
235 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
236 const SectionIndexMapTy &SectionIndexMap,
237 const RevGroupMapTy &RevGroupMap);
239 void computeIndexMap(MCAssembler &Asm, SectionIndexMapTy &SectionIndexMap);
241 MCSectionData *createRelocationSection(MCAssembler &Asm,
242 const MCSectionData &SD);
244 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
246 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout);
248 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
249 SectionIndexMapTy &SectionIndexMap);
251 // Create the sections that show up in the symbol table. Currently
252 // those are the .note.GNU-stack section and the group sections.
253 void createIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
254 GroupMapTy &GroupMap, RevGroupMapTy &RevGroupMap,
255 SectionIndexMapTy &SectionIndexMap);
257 void ExecutePostLayoutBinding(MCAssembler &Asm,
258 const MCAsmLayout &Layout) override;
260 void writeSectionHeader(ArrayRef<const MCSectionELF *> Sections,
261 MCAssembler &Asm, const GroupMapTy &GroupMap,
262 const MCAsmLayout &Layout,
263 const SectionIndexMapTy &SectionIndexMap,
264 const SectionOffsetMapTy &SectionOffsetMap);
266 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
267 uint64_t Address, uint64_t Offset,
268 uint64_t Size, uint32_t Link, uint32_t Info,
269 uint64_t Alignment, uint64_t EntrySize);
271 void WriteRelocationsFragment(const MCAssembler &Asm,
273 const MCSectionData *SD);
276 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
277 const MCSymbolData &DataA,
278 const MCSymbolData *DataB,
279 const MCFragment &FB,
281 bool IsPCRel) const override;
283 bool isWeak(const MCSymbolData &SD) const override;
285 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
286 void writeSection(MCAssembler &Asm,
287 const SectionIndexMapTy &SectionIndexMap,
288 uint32_t GroupSymbolIndex,
289 uint64_t Offset, uint64_t Size, uint64_t Alignment,
290 const MCSectionELF &Section);
294 FragmentWriter::FragmentWriter(bool IsLittleEndian)
295 : IsLittleEndian(IsLittleEndian) {}
297 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
299 Val = support::endian::byte_swap<T, support::little>(Val);
301 Val = support::endian::byte_swap<T, support::big>(Val);
302 const char *Start = (const char *)&Val;
303 F.getContents().append(Start, Start + sizeof(T));
306 void SymbolTableWriter::createSymtabShndx() {
310 MCContext &Ctx = Asm.getContext();
311 const MCSectionELF *SymtabShndxSection =
312 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
313 MCSectionData *SymtabShndxSD =
314 &Asm.getOrCreateSectionData(*SymtabShndxSection);
315 SymtabShndxSD->setAlignment(4);
316 ShndxF = new MCDataFragment(SymtabShndxSD);
317 unsigned Index = SectionIndexMap.size() + 1;
318 SectionIndexMap[SymtabShndxSection] = Index;
320 for (unsigned I = 0; I < NumWritten; ++I)
321 write(*ShndxF, uint32_t(0));
324 template <typename T>
325 void SymbolTableWriter::write(MCDataFragment &F, T Value) {
326 FWriter.write(F, Value);
329 SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter,
331 SectionIndexMapTy &SectionIndexMap,
332 MCDataFragment *SymtabF)
333 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit),
334 SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr),
337 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
338 uint64_t size, uint8_t other,
339 uint32_t shndx, bool Reserved) {
340 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
347 write(*ShndxF, shndx);
349 write(*ShndxF, uint32_t(0));
352 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
355 write(*SymtabF, name); // st_name
356 write(*SymtabF, info); // st_info
357 write(*SymtabF, other); // st_other
358 write(*SymtabF, Index); // st_shndx
359 write(*SymtabF, value); // st_value
360 write(*SymtabF, size); // st_size
362 write(*SymtabF, name); // st_name
363 write(*SymtabF, uint32_t(value)); // st_value
364 write(*SymtabF, uint32_t(size)); // st_size
365 write(*SymtabF, info); // st_info
366 write(*SymtabF, other); // st_other
367 write(*SymtabF, Index); // st_shndx
373 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
374 const MCFixupKindInfo &FKI =
375 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
377 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
380 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
384 case MCSymbolRefExpr::VK_GOT:
385 case MCSymbolRefExpr::VK_PLT:
386 case MCSymbolRefExpr::VK_GOTPCREL:
387 case MCSymbolRefExpr::VK_GOTOFF:
388 case MCSymbolRefExpr::VK_TPOFF:
389 case MCSymbolRefExpr::VK_TLSGD:
390 case MCSymbolRefExpr::VK_GOTTPOFF:
391 case MCSymbolRefExpr::VK_INDNTPOFF:
392 case MCSymbolRefExpr::VK_NTPOFF:
393 case MCSymbolRefExpr::VK_GOTNTPOFF:
394 case MCSymbolRefExpr::VK_TLSLDM:
395 case MCSymbolRefExpr::VK_DTPOFF:
396 case MCSymbolRefExpr::VK_TLSLD:
401 ELFObjectWriter::~ELFObjectWriter()
404 // Emit the ELF header.
405 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
406 unsigned NumberOfSections) {
412 // emitWord method behaves differently for ELF32 and ELF64, writing
413 // 4 bytes in the former and 8 in the latter.
415 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
417 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
420 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
422 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
424 Write8(TargetObjectWriter->getOSABI());
425 Write8(0); // e_ident[EI_ABIVERSION]
427 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
429 Write16(ELF::ET_REL); // e_type
431 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
433 Write32(ELF::EV_CURRENT); // e_version
434 WriteWord(0); // e_entry, no entry point in .o file
435 WriteWord(0); // e_phoff, no program header for .o
436 WriteWord(0); // e_shoff = sec hdr table off in bytes
438 // e_flags = whatever the target wants
439 Write32(Asm.getELFHeaderEFlags());
441 // e_ehsize = ELF header size
442 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
444 Write16(0); // e_phentsize = prog header entry size
445 Write16(0); // e_phnum = # prog header entries = 0
447 // e_shentsize = Section header entry size
448 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
450 // e_shnum = # of section header ents
451 if (NumberOfSections >= ELF::SHN_LORESERVE)
452 Write16(ELF::SHN_UNDEF);
454 Write16(NumberOfSections);
456 // e_shstrndx = Section # of '.shstrtab'
457 if (ShstrtabIndex >= ELF::SHN_LORESERVE)
458 Write16(ELF::SHN_XINDEX);
460 Write16(ShstrtabIndex);
463 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
464 const MCAsmLayout &Layout) {
465 if (Data.isCommon() && Data.isExternal())
466 return Data.getCommonAlignment();
469 if (!Layout.getSymbolOffset(&Data, Res))
472 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
478 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
479 const MCAsmLayout &Layout) {
480 // The presence of symbol versions causes undefined symbols and
481 // versions declared with @@@ to be renamed.
483 for (MCSymbolData &OriginalData : Asm.symbols()) {
484 const MCSymbol &Alias = OriginalData.getSymbol();
487 if (!Alias.isVariable())
489 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
492 const MCSymbol &Symbol = Ref->getSymbol();
493 MCSymbolData &SD = Asm.getSymbolData(Symbol);
495 StringRef AliasName = Alias.getName();
496 size_t Pos = AliasName.find('@');
497 if (Pos == StringRef::npos)
500 // Aliases defined with .symvar copy the binding from the symbol they alias.
501 // This is the first place we are able to copy this information.
502 OriginalData.setExternal(SD.isExternal());
503 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
505 StringRef Rest = AliasName.substr(Pos);
506 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
509 // FIXME: produce a better error message.
510 if (Symbol.isUndefined() && Rest.startswith("@@") &&
511 !Rest.startswith("@@@"))
512 report_fatal_error("A @@ version cannot be undefined");
514 Renames.insert(std::make_pair(&Symbol, &Alias));
518 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
519 uint8_t Type = newType;
521 // Propagation rules:
522 // IFUNC > FUNC > OBJECT > NOTYPE
523 // TLS_OBJECT > OBJECT > NOTYPE
525 // dont let the new type degrade the old type
529 case ELF::STT_GNU_IFUNC:
530 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
531 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
532 Type = ELF::STT_GNU_IFUNC;
535 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
536 Type == ELF::STT_TLS)
537 Type = ELF::STT_FUNC;
539 case ELF::STT_OBJECT:
540 if (Type == ELF::STT_NOTYPE)
541 Type = ELF::STT_OBJECT;
544 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
545 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
553 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
554 const MCAsmLayout &Layout) {
555 MCSymbolData &OrigData = *MSD.SymbolData;
556 assert((!OrigData.getFragment() ||
557 (&OrigData.getFragment()->getParent()->getSection() ==
558 &OrigData.getSymbol().getSection())) &&
559 "The symbol's section doesn't match the fragment's symbol");
560 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
562 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
564 bool IsReserved = !Base || OrigData.isCommon();
566 // Binding and Type share the same byte as upper and lower nibbles
567 uint8_t Binding = MCELF::GetBinding(OrigData);
568 uint8_t Type = MCELF::GetType(OrigData);
569 MCSymbolData *BaseSD = nullptr;
571 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
572 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
574 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
576 // Other and Visibility share the same byte with Visibility using the lower
578 uint8_t Visibility = MCELF::GetVisibility(OrigData);
579 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
582 uint64_t Value = SymbolValue(OrigData, Layout);
585 const MCExpr *ESize = OrigData.getSize();
587 ESize = BaseSD->getSize();
591 if (!ESize->evaluateKnownAbsolute(Res, Layout))
592 report_fatal_error("Size expression must be absolute.");
596 // Write out the symbol table entry
597 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
598 MSD.SectionIndex, IsReserved);
601 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF,
603 const MCAsmLayout &Layout,
604 SectionIndexMapTy &SectionIndexMap) {
605 // The string table must be emitted first because we need the index
606 // into the string table for all the symbol names.
608 // FIXME: Make sure the start of the symbol table is aligned.
610 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF);
612 // The first entry is the undefined symbol entry.
613 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
615 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
616 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
617 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
620 // Write the symbol table entries.
621 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
623 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
624 ELFSymbolData &MSD = LocalSymbolData[i];
625 WriteSymbol(Writer, MSD, Layout);
628 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
629 ELFSymbolData &MSD = ExternalSymbolData[i];
630 MCSymbolData &Data = *MSD.SymbolData;
631 assert(((Data.getFlags() & ELF_STB_Global) ||
632 (Data.getFlags() & ELF_STB_Weak)) &&
633 "External symbol requires STB_GLOBAL or STB_WEAK flag");
634 WriteSymbol(Writer, MSD, Layout);
635 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
636 LastLocalSymbolIndex++;
639 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
640 ELFSymbolData &MSD = UndefinedSymbolData[i];
641 MCSymbolData &Data = *MSD.SymbolData;
642 WriteSymbol(Writer, MSD, Layout);
643 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
644 LastLocalSymbolIndex++;
648 // It is always valid to create a relocation with a symbol. It is preferable
649 // to use a relocation with a section if that is possible. Using the section
650 // allows us to omit some local symbols from the symbol table.
651 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
652 const MCSymbolRefExpr *RefA,
653 const MCSymbolData *SD,
655 unsigned Type) const {
656 // A PCRel relocation to an absolute value has no symbol (or section). We
657 // represent that with a relocation to a null section.
661 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
665 // The .odp creation emits a relocation against the symbol ".TOC." which
666 // create a R_PPC64_TOC relocation. However the relocation symbol name
667 // in final object creation should be NULL, since the symbol does not
668 // really exist, it is just the reference to TOC base for the current
669 // object file. Since the symbol is undefined, returning false results
670 // in a relocation with a null section which is the desired result.
671 case MCSymbolRefExpr::VK_PPC_TOCBASE:
674 // These VariantKind cause the relocation to refer to something other than
675 // the symbol itself, like a linker generated table. Since the address of
676 // symbol is not relevant, we cannot replace the symbol with the
677 // section and patch the difference in the addend.
678 case MCSymbolRefExpr::VK_GOT:
679 case MCSymbolRefExpr::VK_PLT:
680 case MCSymbolRefExpr::VK_GOTPCREL:
681 case MCSymbolRefExpr::VK_Mips_GOT:
682 case MCSymbolRefExpr::VK_PPC_GOT_LO:
683 case MCSymbolRefExpr::VK_PPC_GOT_HI:
684 case MCSymbolRefExpr::VK_PPC_GOT_HA:
688 // An undefined symbol is not in any section, so the relocation has to point
689 // to the symbol itself.
690 const MCSymbol &Sym = SD->getSymbol();
691 if (Sym.isUndefined())
694 unsigned Binding = MCELF::GetBinding(*SD);
697 llvm_unreachable("Invalid Binding");
701 // If the symbol is weak, it might be overridden by a symbol in another
702 // file. The relocation has to point to the symbol so that the linker
705 case ELF::STB_GLOBAL:
706 // Global ELF symbols can be preempted by the dynamic linker. The relocation
707 // has to point to the symbol for a reason analogous to the STB_WEAK case.
711 // If a relocation points to a mergeable section, we have to be careful.
712 // If the offset is zero, a relocation with the section will encode the
713 // same information. With a non-zero offset, the situation is different.
714 // For example, a relocation can point 42 bytes past the end of a string.
715 // If we change such a relocation to use the section, the linker would think
716 // that it pointed to another string and subtracting 42 at runtime will
717 // produce the wrong value.
718 auto &Sec = cast<MCSectionELF>(Sym.getSection());
719 unsigned Flags = Sec.getFlags();
720 if (Flags & ELF::SHF_MERGE) {
724 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
725 // only handle section relocations to mergeable sections if using RELA.
726 if (!hasRelocationAddend())
730 // Most TLS relocations use a got, so they need the symbol. Even those that
731 // are just an offset (@tpoff), require a symbol in gold versions before
732 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
733 // http://sourceware.org/PR16773.
734 if (Flags & ELF::SHF_TLS)
737 // If the symbol is a thumb function the final relocation must set the lowest
738 // bit. With a symbol that is done by just having the symbol have that bit
739 // set, so we would lose the bit if we relocated with the section.
740 // FIXME: We could use the section but add the bit to the relocation value.
741 if (Asm.isThumbFunc(&Sym))
744 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
749 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
750 const MCSymbol &Sym = Ref.getSymbol();
752 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
755 if (!Sym.isVariable())
758 const MCExpr *Expr = Sym.getVariableValue();
759 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
763 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
764 return &Inner->getSymbol();
768 // True if the assembler knows nothing about the final value of the symbol.
769 // This doesn't cover the comdat issues, since in those cases the assembler
770 // can at least know that all symbols in the section will move together.
771 static bool isWeak(const MCSymbolData &D) {
772 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
775 switch (MCELF::GetBinding(D)) {
777 llvm_unreachable("Unknown binding");
780 case ELF::STB_GLOBAL:
783 case ELF::STB_GNU_UNIQUE:
788 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
789 const MCAsmLayout &Layout,
790 const MCFragment *Fragment,
791 const MCFixup &Fixup, MCValue Target,
792 bool &IsPCRel, uint64_t &FixedValue) {
793 const MCSectionData *FixupSection = Fragment->getParent();
794 uint64_t C = Target.getConstant();
795 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
797 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
798 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
799 "Should not have constructed this");
801 // Let A, B and C being the components of Target and R be the location of
802 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
803 // If it is pcrel, we want to compute (A - B + C - R).
805 // In general, ELF has no relocations for -B. It can only represent (A + C)
806 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
807 // replace B to implement it: (A - R - K + C)
809 Asm.getContext().FatalError(
811 "No relocation available to represent this relative expression");
813 const MCSymbol &SymB = RefB->getSymbol();
815 if (SymB.isUndefined())
816 Asm.getContext().FatalError(
818 Twine("symbol '") + SymB.getName() +
819 "' can not be undefined in a subtraction expression");
821 assert(!SymB.isAbsolute() && "Should have been folded");
822 const MCSection &SecB = SymB.getSection();
823 if (&SecB != &FixupSection->getSection())
824 Asm.getContext().FatalError(
825 Fixup.getLoc(), "Cannot represent a difference across sections");
827 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
829 Asm.getContext().FatalError(
830 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
832 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
833 uint64_t K = SymBOffset - FixupOffset;
838 // We either rejected the fixup or folded B into C at this point.
839 const MCSymbolRefExpr *RefA = Target.getSymA();
840 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
841 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
843 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
844 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
845 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
846 C += Layout.getSymbolOffset(SymAD);
849 if (hasRelocationAddend()) {
856 // FIXME: What is this!?!?
857 MCSymbolRefExpr::VariantKind Modifier =
858 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
859 if (RelocNeedsGOT(Modifier))
862 if (!RelocateWithSymbol) {
863 const MCSection *SecA =
864 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
865 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
866 MCSymbol *SectionSymbol =
867 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
869 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
870 Relocations[FixupSection].push_back(Rec);
875 if (const MCSymbol *R = Renames.lookup(SymA))
878 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
879 WeakrefUsedInReloc.insert(WeakRef);
881 UsedInReloc.insert(SymA);
883 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
884 Relocations[FixupSection].push_back(Rec);
890 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
892 const MCSymbolData &SD = Asm.getSymbolData(*S);
893 return SD.getIndex();
896 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
897 const MCSymbolData &Data, bool Used,
899 const MCSymbol &Symbol = Data.getSymbol();
900 if (Symbol.isVariable()) {
901 const MCExpr *Expr = Symbol.getVariableValue();
902 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
903 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
914 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
917 if (Symbol.isVariable()) {
918 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
919 if (Base && Base->isUndefined())
923 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
924 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
927 if (Symbol.isTemporary())
933 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
934 if (Data.isExternal())
937 const MCSymbol &Symbol = Data.getSymbol();
938 if (Symbol.isDefined())
947 void ELFObjectWriter::computeIndexMap(MCAssembler &Asm,
948 SectionIndexMapTy &SectionIndexMap) {
950 for (MCAssembler::iterator it = Asm.begin(),
951 ie = Asm.end(); it != ie; ++it) {
952 const MCSectionELF &Section =
953 static_cast<const MCSectionELF &>(it->getSection());
954 if (Section.getType() != ELF::SHT_GROUP)
956 SectionIndexMap[&Section] = Index++;
959 std::vector<const MCSectionELF *> RelSections;
961 for (MCAssembler::iterator it = Asm.begin(),
962 ie = Asm.end(); it != ie; ++it) {
963 const MCSectionData &SD = *it;
964 const MCSectionELF &Section =
965 static_cast<const MCSectionELF &>(SD.getSection());
966 if (Section.getType() == ELF::SHT_GROUP ||
967 Section.getType() == ELF::SHT_REL ||
968 Section.getType() == ELF::SHT_RELA)
970 SectionIndexMap[&Section] = Index++;
971 if (MCSectionData *RelSD = createRelocationSection(Asm, SD)) {
972 const MCSectionELF *RelSection =
973 static_cast<const MCSectionELF *>(&RelSD->getSection());
974 RelSections.push_back(RelSection);
978 // Put relocation sections close together. The linker reads them
979 // first, so this improves cache locality.
980 for (const MCSectionELF * Sec: RelSections)
981 SectionIndexMap[Sec] = Index++;
984 void ELFObjectWriter::computeSymbolTable(
985 MCAssembler &Asm, const MCAsmLayout &Layout,
986 const SectionIndexMapTy &SectionIndexMap,
987 const RevGroupMapTy &RevGroupMap) {
988 // FIXME: Is this the correct place to do this?
989 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
991 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
992 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
993 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
994 Data.setExternal(true);
995 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
998 // Add the data for the symbols.
999 for (MCSymbolData &SD : Asm.symbols()) {
1000 const MCSymbol &Symbol = SD.getSymbol();
1002 bool Used = UsedInReloc.count(&Symbol);
1003 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
1004 bool isSignature = RevGroupMap.count(&Symbol);
1006 if (!isInSymtab(Layout, SD,
1007 Used || WeakrefUsed || isSignature,
1008 Renames.count(&Symbol)))
1012 MSD.SymbolData = &SD;
1013 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
1015 // Undefined symbols are global, but this is the first place we
1016 // are able to set it.
1017 bool Local = isLocal(SD, Used);
1018 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1020 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1021 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1022 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1026 MSD.SectionIndex = ELF::SHN_ABS;
1027 } else if (SD.isCommon()) {
1029 MSD.SectionIndex = ELF::SHN_COMMON;
1030 } else if (BaseSymbol->isUndefined()) {
1031 if (isSignature && !Used)
1032 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap.lookup(&Symbol));
1034 MSD.SectionIndex = ELF::SHN_UNDEF;
1035 if (!Used && WeakrefUsed)
1036 MCELF::SetBinding(SD, ELF::STB_WEAK);
1038 const MCSectionELF &Section =
1039 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1040 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1041 assert(MSD.SectionIndex && "Invalid section index!");
1044 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
1047 // FIXME: All name handling should be done before we get to the writer,
1048 // including dealing with GNU-style version suffixes. Fixing this isn't
1051 // We thus have to be careful to not perform the symbol version replacement
1054 // The ELF format is used on Windows by the MCJIT engine. Thus, on
1055 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
1056 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
1057 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
1058 // the EFLObjectWriter should not interpret the "@@@" sub-string as
1059 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
1060 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
1061 // "__imp_?" or "__imp_@?".
1063 // It would have been interesting to perform the MS mangling prefix check
1064 // only when the target triple is of the form *-pc-windows-elf. But, it
1065 // seems that this information is not easily accessible from the
1067 StringRef Name = Symbol.getName();
1068 if (!Name.startswith("?") && !Name.startswith("@?") &&
1069 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1070 // This symbol isn't following the MSVC C++ name mangling convention. We
1071 // can thus safely interpret the @@@ in symbol names as specifying symbol
1073 SmallString<32> Buf;
1074 size_t Pos = Name.find("@@@");
1075 if (Pos != StringRef::npos) {
1076 Buf += Name.substr(0, Pos);
1077 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1078 Buf += Name.substr(Pos + Skip);
1083 // Sections have their own string table
1084 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1085 MSD.Name = StrTabBuilder.add(Name);
1087 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1088 UndefinedSymbolData.push_back(MSD);
1090 LocalSymbolData.push_back(MSD);
1092 ExternalSymbolData.push_back(MSD);
1095 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1096 StrTabBuilder.add(*i);
1098 StrTabBuilder.finalize(StringTableBuilder::ELF);
1100 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1101 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1103 for (ELFSymbolData &MSD : LocalSymbolData)
1104 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1106 : StrTabBuilder.getOffset(MSD.Name);
1107 for (ELFSymbolData &MSD : ExternalSymbolData)
1108 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1109 for (ELFSymbolData& MSD : UndefinedSymbolData)
1110 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1112 // Symbols are required to be in lexicographic order.
1113 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1114 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1115 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1117 // Set the symbol indices. Local symbols must come before all other
1118 // symbols with non-local bindings.
1119 unsigned Index = FileSymbolData.size() + 1;
1120 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1121 LocalSymbolData[i].SymbolData->setIndex(Index++);
1123 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1124 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1125 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1126 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1130 ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1131 const MCSectionData &SD) {
1132 if (Relocations[&SD].empty())
1135 MCContext &Ctx = Asm.getContext();
1136 const MCSectionELF &Section =
1137 static_cast<const MCSectionELF &>(SD.getSection());
1139 const StringRef SectionName = Section.getSectionName();
1140 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1141 RelaSectionName += SectionName;
1144 if (hasRelocationAddend())
1145 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1147 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1150 if (Section.getFlags() & ELF::SHF_GROUP)
1151 Flags = ELF::SHF_GROUP;
1153 const MCSectionELF *RelaSection = Ctx.createELFRelSection(
1154 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1155 Flags, EntrySize, Section.getGroup(), &Section);
1156 return &Asm.getOrCreateSectionData(*RelaSection);
1159 static SmallVector<char, 128>
1160 getUncompressedData(MCAsmLayout &Layout,
1161 MCSectionData::FragmentListType &Fragments) {
1162 SmallVector<char, 128> UncompressedData;
1163 for (const MCFragment &F : Fragments) {
1164 const SmallVectorImpl<char> *Contents;
1165 switch (F.getKind()) {
1166 case MCFragment::FT_Data:
1167 Contents = &cast<MCDataFragment>(F).getContents();
1169 case MCFragment::FT_Dwarf:
1170 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1172 case MCFragment::FT_DwarfFrame:
1173 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1177 "Not expecting any other fragment types in a debug_* section");
1179 UncompressedData.append(Contents->begin(), Contents->end());
1181 return UncompressedData;
1184 // Include the debug info compression header:
1185 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1186 // useful for consumers to preallocate a buffer to decompress into.
1188 prependCompressionHeader(uint64_t Size,
1189 SmallVectorImpl<char> &CompressedContents) {
1190 const StringRef Magic = "ZLIB";
1191 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1193 if (sys::IsLittleEndianHost)
1194 sys::swapByteOrder(Size);
1195 CompressedContents.insert(CompressedContents.begin(),
1196 Magic.size() + sizeof(Size), 0);
1197 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1198 std::copy(reinterpret_cast<char *>(&Size),
1199 reinterpret_cast<char *>(&Size + 1),
1200 CompressedContents.begin() + Magic.size());
1204 // Return a single fragment containing the compressed contents of the whole
1205 // section. Null if the section was not compressed for any reason.
1206 static std::unique_ptr<MCDataFragment>
1207 getCompressedFragment(MCAsmLayout &Layout,
1208 MCSectionData::FragmentListType &Fragments) {
1209 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1211 // Gather the uncompressed data from all the fragments, recording the
1212 // alignment fragment, if seen, and any fixups.
1213 SmallVector<char, 128> UncompressedData =
1214 getUncompressedData(Layout, Fragments);
1216 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1218 zlib::Status Success = zlib::compress(
1219 StringRef(UncompressedData.data(), UncompressedData.size()),
1220 CompressedContents);
1221 if (Success != zlib::StatusOK)
1224 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1227 return CompressedFragment;
1230 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1233 static void UpdateSymbols(const MCAsmLayout &Layout,
1234 const std::vector<MCSymbolData *> &Symbols,
1235 MCFragment &NewFragment) {
1236 for (MCSymbolData *Sym : Symbols) {
1237 Sym->setOffset(Sym->getOffset() +
1238 Layout.getFragmentOffset(Sym->getFragment()));
1239 Sym->setFragment(&NewFragment);
1243 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1244 const DefiningSymbolMap &DefiningSymbols,
1245 const MCSectionELF &Section,
1246 MCSectionData &SD) {
1247 StringRef SectionName = Section.getSectionName();
1248 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1250 std::unique_ptr<MCDataFragment> CompressedFragment =
1251 getCompressedFragment(Layout, Fragments);
1253 // Leave the section as-is if the fragments could not be compressed.
1254 if (!CompressedFragment)
1257 // Update the fragment+offsets of any symbols referring to fragments in this
1258 // section to refer to the new fragment.
1259 auto I = DefiningSymbols.find(&SD);
1260 if (I != DefiningSymbols.end())
1261 UpdateSymbols(Layout, I->second, *CompressedFragment);
1263 // Invalidate the layout for the whole section since it will have new and
1264 // different fragments now.
1265 Layout.invalidateFragmentsFrom(&Fragments.front());
1268 // Complete the initialization of the new fragment
1269 CompressedFragment->setParent(&SD);
1270 CompressedFragment->setLayoutOrder(0);
1271 Fragments.push_back(CompressedFragment.release());
1273 // Rename from .debug_* to .zdebug_*
1274 Asm.getContext().renameELFSection(&Section,
1275 (".z" + SectionName.drop_front(1)).str());
1278 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1279 MCAsmLayout &Layout) {
1280 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1283 DefiningSymbolMap DefiningSymbols;
1285 for (MCSymbolData &SD : Asm.symbols())
1286 if (MCFragment *F = SD.getFragment())
1287 DefiningSymbols[F->getParent()].push_back(&SD);
1289 for (MCSectionData &SD : Asm) {
1290 const MCSectionELF &Section =
1291 static_cast<const MCSectionELF &>(SD.getSection());
1292 StringRef SectionName = Section.getSectionName();
1294 // Compressing debug_frame requires handling alignment fragments which is
1295 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1296 // for writing to arbitrary buffers) for little benefit.
1297 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1300 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1304 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) {
1305 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1306 MCSectionData &RelSD = *it;
1307 const MCSectionELF &RelSection =
1308 static_cast<const MCSectionELF &>(RelSD.getSection());
1310 unsigned Type = RelSection.getType();
1311 if (Type != ELF::SHT_REL && Type != ELF::SHT_RELA)
1314 const MCSectionELF *Section = RelSection.getAssociatedSection();
1315 MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1316 RelSD.setAlignment(is64Bit() ? 8 : 4);
1318 MCDataFragment *F = new MCDataFragment(&RelSD);
1319 WriteRelocationsFragment(Asm, F, &SD);
1323 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1324 uint64_t Flags, uint64_t Address,
1325 uint64_t Offset, uint64_t Size,
1326 uint32_t Link, uint32_t Info,
1328 uint64_t EntrySize) {
1329 Write32(Name); // sh_name: index into string table
1330 Write32(Type); // sh_type
1331 WriteWord(Flags); // sh_flags
1332 WriteWord(Address); // sh_addr
1333 WriteWord(Offset); // sh_offset
1334 WriteWord(Size); // sh_size
1335 Write32(Link); // sh_link
1336 Write32(Info); // sh_info
1337 WriteWord(Alignment); // sh_addralign
1338 WriteWord(EntrySize); // sh_entsize
1341 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1343 const MCSectionData *SD) {
1344 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1346 // Sort the relocation entries. Most targets just sort by Offset, but some
1347 // (e.g., MIPS) have additional constraints.
1348 TargetObjectWriter->sortRelocs(Asm, Relocs);
1350 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1351 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1353 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1356 write(*F, Entry.Offset);
1357 if (TargetObjectWriter->isN64()) {
1358 write(*F, uint32_t(Index));
1360 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1361 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1362 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1363 write(*F, TargetObjectWriter->getRType(Entry.Type));
1365 struct ELF::Elf64_Rela ERE64;
1366 ERE64.setSymbolAndType(Index, Entry.Type);
1367 write(*F, ERE64.r_info);
1369 if (hasRelocationAddend())
1370 write(*F, Entry.Addend);
1372 write(*F, uint32_t(Entry.Offset));
1374 struct ELF::Elf32_Rela ERE32;
1375 ERE32.setSymbolAndType(Index, Entry.Type);
1376 write(*F, ERE32.r_info);
1378 if (hasRelocationAddend())
1379 write(*F, uint32_t(Entry.Addend));
1384 void ELFObjectWriter::CreateMetadataSections(
1385 MCAssembler &Asm, MCAsmLayout &Layout, SectionIndexMapTy &SectionIndexMap) {
1386 MCContext &Ctx = Asm.getContext();
1389 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1391 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1392 const MCSectionELF *ShstrtabSection =
1393 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1394 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1395 ShstrtabSD.setAlignment(1);
1396 ShstrtabIndex = SectionIndexMap.size() + 1;
1397 SectionIndexMap[ShstrtabSection] = ShstrtabIndex;
1399 const MCSectionELF *SymtabSection =
1400 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1402 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1403 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1404 SymbolTableIndex = SectionIndexMap.size() + 1;
1405 SectionIndexMap[SymtabSection] = SymbolTableIndex;
1407 const MCSectionELF *StrtabSection;
1408 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1409 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1410 StrtabSD.setAlignment(1);
1411 StringTableIndex = SectionIndexMap.size() + 1;
1412 SectionIndexMap[StrtabSection] = StringTableIndex;
1415 F = new MCDataFragment(&SymtabSD);
1416 WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
1418 F = new MCDataFragment(&StrtabSD);
1419 F->getContents().append(StrTabBuilder.data().begin(),
1420 StrTabBuilder.data().end());
1422 F = new MCDataFragment(&ShstrtabSD);
1424 // Section header string table.
1425 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1426 const MCSectionELF &Section =
1427 static_cast<const MCSectionELF&>(it->getSection());
1428 ShStrTabBuilder.add(Section.getSectionName());
1430 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1431 F->getContents().append(ShStrTabBuilder.data().begin(),
1432 ShStrTabBuilder.data().end());
1435 void ELFObjectWriter::createIndexedSections(
1436 MCAssembler &Asm, MCAsmLayout &Layout, GroupMapTy &GroupMap,
1437 RevGroupMapTy &RevGroupMap, SectionIndexMapTy &SectionIndexMap) {
1438 MCContext &Ctx = Asm.getContext();
1441 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1443 const MCSectionELF &Section =
1444 static_cast<const MCSectionELF&>(it->getSection());
1445 if (!(Section.getFlags() & ELF::SHF_GROUP))
1448 const MCSymbol *SignatureSymbol = Section.getGroup();
1449 Asm.getOrCreateSymbolData(*SignatureSymbol);
1450 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1452 Group = Ctx.CreateELFGroupSection();
1453 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1454 Data.setAlignment(4);
1455 MCDataFragment *F = new MCDataFragment(&Data);
1456 write(*F, uint32_t(ELF::GRP_COMDAT));
1458 GroupMap[Group] = SignatureSymbol;
1461 computeIndexMap(Asm, SectionIndexMap);
1463 // Add sections to the groups
1464 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1466 const MCSectionELF &Section =
1467 static_cast<const MCSectionELF&>(it->getSection());
1468 if (!(Section.getFlags() & ELF::SHF_GROUP))
1470 const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1471 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1472 // FIXME: we could use the previous fragment
1473 MCDataFragment *F = new MCDataFragment(&Data);
1474 uint32_t Index = SectionIndexMap.lookup(&Section);
1479 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1480 const SectionIndexMapTy &SectionIndexMap,
1481 uint32_t GroupSymbolIndex,
1482 uint64_t Offset, uint64_t Size,
1484 const MCSectionELF &Section) {
1485 uint64_t sh_link = 0;
1486 uint64_t sh_info = 0;
1488 switch(Section.getType()) {
1493 case ELF::SHT_DYNAMIC:
1494 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1498 case ELF::SHT_RELA: {
1499 sh_link = SymbolTableIndex;
1500 assert(sh_link && ".symtab not found");
1501 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1502 sh_info = SectionIndexMap.lookup(InfoSection);
1506 case ELF::SHT_SYMTAB:
1507 case ELF::SHT_DYNSYM:
1508 sh_link = StringTableIndex;
1509 sh_info = LastLocalSymbolIndex;
1512 case ELF::SHT_SYMTAB_SHNDX:
1513 sh_link = SymbolTableIndex;
1516 case ELF::SHT_GROUP:
1517 sh_link = SymbolTableIndex;
1518 sh_info = GroupSymbolIndex;
1522 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1523 Section.getType() == ELF::SHT_ARM_EXIDX)
1524 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1526 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1528 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1529 Alignment, Section.getEntrySize());
1532 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1533 return SD.getOrdinal() == ~UINT32_C(0) &&
1534 !SD.getSection().isVirtualSection();
1537 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1539 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1541 const MCFragment &F = *i;
1542 assert(F.getKind() == MCFragment::FT_Data);
1543 Ret += cast<MCDataFragment>(F).getContents().size();
1548 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1549 const MCSectionData &SD) {
1550 if (IsELFMetaDataSection(SD))
1551 return DataSectionSize(SD);
1552 return Layout.getSectionAddressSize(&SD);
1555 void ELFObjectWriter::writeDataSectionData(MCAssembler &Asm,
1556 const MCAsmLayout &Layout,
1557 const MCSectionData &SD) {
1558 if (IsELFMetaDataSection(SD)) {
1559 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1561 const MCFragment &F = *i;
1562 assert(F.getKind() == MCFragment::FT_Data);
1563 WriteBytes(cast<MCDataFragment>(F).getContents());
1566 Asm.writeSectionData(&SD, Layout);
1570 void ELFObjectWriter::writeSectionHeader(
1571 ArrayRef<const MCSectionELF *> Sections, MCAssembler &Asm,
1572 const GroupMapTy &GroupMap, const MCAsmLayout &Layout,
1573 const SectionIndexMapTy &SectionIndexMap,
1574 const SectionOffsetMapTy &SectionOffsetMap) {
1575 const unsigned NumSections = Asm.size();
1577 // Null section first.
1578 uint64_t FirstSectionSize =
1579 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1580 uint32_t FirstSectionLink =
1581 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1582 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1584 for (unsigned i = 0; i < NumSections; ++i) {
1585 const MCSectionELF &Section = *Sections[i];
1586 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1587 uint32_t GroupSymbolIndex;
1588 if (Section.getType() != ELF::SHT_GROUP)
1589 GroupSymbolIndex = 0;
1591 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1592 GroupMap.lookup(&Section));
1594 uint64_t Size = GetSectionAddressSize(Layout, SD);
1596 writeSection(Asm, SectionIndexMap, GroupSymbolIndex,
1597 SectionOffsetMap.lookup(&Section), Size, SD.getAlignment(),
1602 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1603 const MCAsmLayout &Layout) {
1604 GroupMapTy GroupMap;
1605 RevGroupMapTy RevGroupMap;
1606 SectionIndexMapTy SectionIndexMap;
1608 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1609 createIndexedSections(Asm, const_cast<MCAsmLayout &>(Layout), GroupMap,
1610 RevGroupMap, SectionIndexMap);
1612 // Compute symbol table information.
1613 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1615 WriteRelocations(Asm, const_cast<MCAsmLayout &>(Layout));
1617 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1618 const_cast<MCAsmLayout&>(Layout),
1621 unsigned NumSections = Asm.size();
1622 std::vector<const MCSectionELF*> Sections;
1623 Sections.resize(NumSections);
1625 for (auto &Pair : SectionIndexMap)
1626 Sections[Pair.second - 1] = Pair.first;
1628 SectionOffsetMapTy SectionOffsetMap;
1630 // Write out the ELF header ...
1631 WriteHeader(Asm, NumSections + 1);
1633 // ... then the sections ...
1634 for (unsigned i = 0; i < NumSections; ++i) {
1635 const MCSectionELF &Section = *Sections[i];
1636 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1637 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1638 WriteZeros(Padding);
1640 // Remember the offset into the file for this section.
1641 SectionOffsetMap[&Section] = OS.tell();
1643 writeDataSectionData(Asm, Layout, SD);
1646 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1647 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1648 WriteZeros(Padding);
1650 const unsigned SectionHeaderOffset = OS.tell();
1652 // ... then the section header table ...
1653 writeSectionHeader(Sections, Asm, GroupMap, Layout, SectionIndexMap,
1657 uint64_t Val = SectionHeaderOffset;
1658 if (sys::IsLittleEndianHost != IsLittleEndian)
1659 sys::swapByteOrder(Val);
1660 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1661 offsetof(ELF::Elf64_Ehdr, e_shoff));
1663 uint32_t Val = SectionHeaderOffset;
1664 if (sys::IsLittleEndianHost != IsLittleEndian)
1665 sys::swapByteOrder(Val);
1666 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1667 offsetof(ELF::Elf32_Ehdr, e_shoff));
1671 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1672 const MCAssembler &Asm, const MCSymbolData &DataA,
1673 const MCSymbolData *DataB, const MCFragment &FB, bool InSet,
1674 bool IsPCRel) const {
1675 if (!InSet && (::isWeak(DataA) || (DataB && ::isWeak(*DataB))))
1677 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1678 Asm, DataA, DataB, FB, InSet, IsPCRel);
1681 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {
1685 const MCSymbol &Sym = SD.getSymbol();
1686 if (!Sym.isInSection())
1689 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1690 if (!Sec.getGroup())
1693 // It is invalid to replace a reference to a global in a comdat
1694 // with a reference to a local since out of comdat references
1695 // to a local are forbidden.
1696 // We could try to return false for more cases, like the reference
1697 // being in the same comdat or Sym being an alias to another global,
1698 // but it is not clear if it is worth the effort.
1703 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1704 raw_pwrite_stream &OS,
1705 bool IsLittleEndian) {
1706 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);