1 //===- lib/MC/ELFObjectWriter.cpp - ELF File Writer -----------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file implements ELF object file writer information. 11 // 12 //===----------------------------------------------------------------------===// 13 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/Endian.h" 35 #include "llvm/Support/ELF.h" 36 #include "llvm/Support/ErrorHandling.h" 37 #include <vector> 38 using namespace llvm; 39 40 #undef DEBUG_TYPE 41 #define DEBUG_TYPE "reloc-info" 42 43 namespace { 44 class FragmentWriter { 45 bool IsLittleEndian; 46 47 public: 48 FragmentWriter(bool IsLittleEndian); 49 template <typename T> void write(MCDataFragment &F, T Val); 50 }; 51 52 typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy; 53 54 class SymbolTableWriter { 55 MCAssembler &Asm; 56 FragmentWriter &FWriter; 57 bool Is64Bit; 58 SectionIndexMapTy &SectionIndexMap; 59 60 // The symbol .symtab fragment we are writting to. 61 MCDataFragment *SymtabF; 62 63 // .symtab_shndx fragment we are writting to. 64 MCDataFragment *ShndxF; 65 66 // The numbel of symbols written so far. 67 unsigned NumWritten; 68 69 void createSymtabShndx(); 70 71 template <typename T> void write(MCDataFragment &F, T Value); 72 73 public: 74 SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit, 75 SectionIndexMapTy &SectionIndexMap, 76 MCDataFragment *SymtabF); 77 78 void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size, 79 uint8_t other, uint32_t shndx, bool Reserved); 80 }; 81 82 struct ELFRelocationEntry { 83 uint64_t Offset; // Where is the relocation. 84 bool UseSymbol; // Relocate with a symbol, not the section. 85 union { 86 const MCSymbol *Symbol; // The symbol to relocate with. 87 const MCSectionData *Section; // The section to relocate with. 88 }; 89 unsigned Type; // The type of the relocation. 90 uint64_t Addend; // The addend to use. 91 92 ELFRelocationEntry(uint64_t Offset, const MCSymbol *Symbol, unsigned Type, 93 uint64_t Addend) 94 : Offset(Offset), UseSymbol(true), Symbol(Symbol), Type(Type), 95 Addend(Addend) {} 96 97 ELFRelocationEntry(uint64_t Offset, const MCSectionData *Section, 98 unsigned Type, uint64_t Addend) 99 : Offset(Offset), UseSymbol(false), Section(Section), Type(Type), 100 Addend(Addend) {} 101 }; 102 103 class ELFObjectWriter : public MCObjectWriter { 104 FragmentWriter FWriter; 105 106 protected: 107 108 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind); 109 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant); 110 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout); 111 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data, 112 bool Used, bool Renamed); 113 static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc); 114 static bool IsELFMetaDataSection(const MCSectionData &SD); 115 static uint64_t DataSectionSize(const MCSectionData &SD); 116 static uint64_t GetSectionFileSize(const MCAsmLayout &Layout, 117 const MCSectionData &SD); 118 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout, 119 const MCSectionData &SD); 120 121 void WriteDataSectionData(MCAssembler &Asm, 122 const MCAsmLayout &Layout, 123 const MCSectionELF &Section); 124 125 /*static bool isFixupKindX86RIPRel(unsigned Kind) { 126 return Kind == X86::reloc_riprel_4byte || 127 Kind == X86::reloc_riprel_4byte_movq_load; 128 }*/ 129 130 /// ELFSymbolData - Helper struct for containing some precomputed 131 /// information on symbols. 132 struct ELFSymbolData { 133 MCSymbolData *SymbolData; 134 uint64_t StringIndex; 135 uint32_t SectionIndex; 136 StringRef Name; 137 138 // Support lexicographic sorting. 139 bool operator<(const ELFSymbolData &RHS) const { 140 return Name < RHS.Name; 141 } 142 }; 143 144 /// The target specific ELF writer instance. 145 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter; 146 147 SmallPtrSet<const MCSymbol *, 16> UsedInReloc; 148 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc; 149 DenseMap<const MCSymbol *, const MCSymbol *> Renames; 150 151 llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>> 152 Relocations; 153 StringTableBuilder ShStrTabBuilder; 154 155 /// @} 156 /// @name Symbol Table Data 157 /// @{ 158 159 StringTableBuilder StrTabBuilder; 160 std::vector<uint64_t> FileSymbolData; 161 std::vector<ELFSymbolData> LocalSymbolData; 162 std::vector<ELFSymbolData> ExternalSymbolData; 163 std::vector<ELFSymbolData> UndefinedSymbolData; 164 165 /// @} 166 167 bool NeedsGOT; 168 169 // This holds the symbol table index of the last local symbol. 170 unsigned LastLocalSymbolIndex; 171 // This holds the .strtab section index. 172 unsigned StringTableIndex; 173 // This holds the .symtab section index. 174 unsigned SymbolTableIndex; 175 176 unsigned ShstrtabIndex; 177 178 179 // TargetObjectWriter wrappers. 180 bool is64Bit() const { return TargetObjectWriter->is64Bit(); } 181 bool hasRelocationAddend() const { 182 return TargetObjectWriter->hasRelocationAddend(); 183 } 184 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup, 185 bool IsPCRel) const { 186 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel); 187 } 188 189 public: 190 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_ostream &_OS, 191 bool IsLittleEndian) 192 : MCObjectWriter(_OS, IsLittleEndian), FWriter(IsLittleEndian), 193 TargetObjectWriter(MOTW), NeedsGOT(false) {} 194 195 virtual ~ELFObjectWriter(); 196 197 void WriteWord(uint64_t W) { 198 if (is64Bit()) 199 Write64(W); 200 else 201 Write32(W); 202 } 203 204 template <typename T> void write(MCDataFragment &F, T Value) { 205 FWriter.write(F, Value); 206 } 207 208 void WriteHeader(const MCAssembler &Asm, 209 uint64_t SectionDataSize, 210 unsigned NumberOfSections); 211 212 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD, 213 const MCAsmLayout &Layout); 214 215 void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm, 216 const MCAsmLayout &Layout, 217 SectionIndexMapTy &SectionIndexMap); 218 219 bool shouldRelocateWithSymbol(const MCAssembler &Asm, 220 const MCSymbolRefExpr *RefA, 221 const MCSymbolData *SD, uint64_t C, 222 unsigned Type) const; 223 224 void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout, 225 const MCFragment *Fragment, const MCFixup &Fixup, 226 MCValue Target, bool &IsPCRel, 227 uint64_t &FixedValue) override; 228 229 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm, 230 const MCSymbol *S); 231 232 // Map from a group section to the signature symbol 233 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy; 234 // Map from a signature symbol to the group section 235 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy; 236 // Map from a section to the section with the relocations 237 typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy; 238 // Map from a section to its offset 239 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy; 240 241 /// Compute the symbol table data 242 /// 243 /// \param Asm - The assembler. 244 /// \param SectionIndexMap - Maps a section to its index. 245 /// \param RevGroupMap - Maps a signature symbol to the group section. 246 /// \param NumRegularSections - Number of non-relocation sections. 247 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout, 248 const SectionIndexMapTy &SectionIndexMap, 249 const RevGroupMapTy &RevGroupMap, 250 unsigned NumRegularSections); 251 252 void ComputeIndexMap(MCAssembler &Asm, 253 SectionIndexMapTy &SectionIndexMap, 254 const RelMapTy &RelMap); 255 256 void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout, 257 RelMapTy &RelMap); 258 259 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout); 260 261 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 262 const RelMapTy &RelMap); 263 264 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout, 265 SectionIndexMapTy &SectionIndexMap, 266 const RelMapTy &RelMap); 267 268 // Create the sections that show up in the symbol table. Currently 269 // those are the .note.GNU-stack section and the group sections. 270 void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout, 271 GroupMapTy &GroupMap, 272 RevGroupMapTy &RevGroupMap, 273 SectionIndexMapTy &SectionIndexMap, 274 const RelMapTy &RelMap); 275 276 void ExecutePostLayoutBinding(MCAssembler &Asm, 277 const MCAsmLayout &Layout) override; 278 279 void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap, 280 const MCAsmLayout &Layout, 281 const SectionIndexMapTy &SectionIndexMap, 282 const SectionOffsetMapTy &SectionOffsetMap); 283 284 void ComputeSectionOrder(MCAssembler &Asm, 285 std::vector<const MCSectionELF*> &Sections); 286 287 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags, 288 uint64_t Address, uint64_t Offset, 289 uint64_t Size, uint32_t Link, uint32_t Info, 290 uint64_t Alignment, uint64_t EntrySize); 291 292 void WriteRelocationsFragment(const MCAssembler &Asm, 293 MCDataFragment *F, 294 const MCSectionData *SD); 295 296 bool 297 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 298 const MCSymbolData &DataA, 299 const MCFragment &FB, 300 bool InSet, 301 bool IsPCRel) const override; 302 303 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override; 304 void WriteSection(MCAssembler &Asm, 305 const SectionIndexMapTy &SectionIndexMap, 306 uint32_t GroupSymbolIndex, 307 uint64_t Offset, uint64_t Size, uint64_t Alignment, 308 const MCSectionELF &Section); 309 }; 310 } 311 312 FragmentWriter::FragmentWriter(bool IsLittleEndian) 313 : IsLittleEndian(IsLittleEndian) {} 314 315 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) { 316 if (IsLittleEndian) 317 Val = support::endian::byte_swap<T, support::little>(Val); 318 else 319 Val = support::endian::byte_swap<T, support::big>(Val); 320 const char *Start = (const char *)&Val; 321 F.getContents().append(Start, Start + sizeof(T)); 322 } 323 324 void SymbolTableWriter::createSymtabShndx() { 325 if (ShndxF) 326 return; 327 328 MCContext &Ctx = Asm.getContext(); 329 const MCSectionELF *SymtabShndxSection = 330 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 331 SectionKind::getReadOnly(), 4, ""); 332 MCSectionData *SymtabShndxSD = 333 &Asm.getOrCreateSectionData(*SymtabShndxSection); 334 SymtabShndxSD->setAlignment(4); 335 ShndxF = new MCDataFragment(SymtabShndxSD); 336 unsigned Index = SectionIndexMap.size() + 1; 337 SectionIndexMap[SymtabShndxSection] = Index; 338 339 for (unsigned I = 0; I < NumWritten; ++I) 340 write(*ShndxF, uint32_t(0)); 341 } 342 343 template <typename T> 344 void SymbolTableWriter::write(MCDataFragment &F, T Value) { 345 FWriter.write(F, Value); 346 } 347 348 SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, 349 bool Is64Bit, 350 SectionIndexMapTy &SectionIndexMap, 351 MCDataFragment *SymtabF) 352 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit), 353 SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr), 354 NumWritten(0) {} 355 356 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value, 357 uint64_t size, uint8_t other, 358 uint32_t shndx, bool Reserved) { 359 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved; 360 361 if (LargeIndex) 362 createSymtabShndx(); 363 364 if (ShndxF) { 365 if (LargeIndex) 366 write(*ShndxF, shndx); 367 else 368 write(*ShndxF, uint32_t(0)); 369 } 370 371 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx; 372 373 raw_svector_ostream OS(SymtabF->getContents()); 374 375 if (Is64Bit) { 376 write(*SymtabF, name); // st_name 377 write(*SymtabF, info); // st_info 378 write(*SymtabF, other); // st_other 379 write(*SymtabF, Index); // st_shndx 380 write(*SymtabF, value); // st_value 381 write(*SymtabF, size); // st_size 382 } else { 383 write(*SymtabF, name); // st_name 384 write(*SymtabF, uint32_t(value)); // st_value 385 write(*SymtabF, uint32_t(size)); // st_size 386 write(*SymtabF, info); // st_info 387 write(*SymtabF, other); // st_other 388 write(*SymtabF, Index); // st_shndx 389 } 390 391 ++NumWritten; 392 } 393 394 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) { 395 const MCFixupKindInfo &FKI = 396 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind); 397 398 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel; 399 } 400 401 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) { 402 switch (Variant) { 403 default: 404 return false; 405 case MCSymbolRefExpr::VK_GOT: 406 case MCSymbolRefExpr::VK_PLT: 407 case MCSymbolRefExpr::VK_GOTPCREL: 408 case MCSymbolRefExpr::VK_GOTOFF: 409 case MCSymbolRefExpr::VK_TPOFF: 410 case MCSymbolRefExpr::VK_TLSGD: 411 case MCSymbolRefExpr::VK_GOTTPOFF: 412 case MCSymbolRefExpr::VK_INDNTPOFF: 413 case MCSymbolRefExpr::VK_NTPOFF: 414 case MCSymbolRefExpr::VK_GOTNTPOFF: 415 case MCSymbolRefExpr::VK_TLSLDM: 416 case MCSymbolRefExpr::VK_DTPOFF: 417 case MCSymbolRefExpr::VK_TLSLD: 418 return true; 419 } 420 } 421 422 ELFObjectWriter::~ELFObjectWriter() 423 {} 424 425 // Emit the ELF header. 426 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm, 427 uint64_t SectionDataSize, 428 unsigned NumberOfSections) { 429 // ELF Header 430 // ---------- 431 // 432 // Note 433 // ---- 434 // emitWord method behaves differently for ELF32 and ELF64, writing 435 // 4 bytes in the former and 8 in the latter. 436 437 Write8(0x7f); // e_ident[EI_MAG0] 438 Write8('E'); // e_ident[EI_MAG1] 439 Write8('L'); // e_ident[EI_MAG2] 440 Write8('F'); // e_ident[EI_MAG3] 441 442 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS] 443 444 // e_ident[EI_DATA] 445 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB); 446 447 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION] 448 // e_ident[EI_OSABI] 449 Write8(TargetObjectWriter->getOSABI()); 450 Write8(0); // e_ident[EI_ABIVERSION] 451 452 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD); 453 454 Write16(ELF::ET_REL); // e_type 455 456 Write16(TargetObjectWriter->getEMachine()); // e_machine = target 457 458 Write32(ELF::EV_CURRENT); // e_version 459 WriteWord(0); // e_entry, no entry point in .o file 460 WriteWord(0); // e_phoff, no program header for .o 461 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 462 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes 463 464 // e_flags = whatever the target wants 465 Write32(Asm.getELFHeaderEFlags()); 466 467 // e_ehsize = ELF header size 468 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr)); 469 470 Write16(0); // e_phentsize = prog header entry size 471 Write16(0); // e_phnum = # prog header entries = 0 472 473 // e_shentsize = Section header entry size 474 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr)); 475 476 // e_shnum = # of section header ents 477 if (NumberOfSections >= ELF::SHN_LORESERVE) 478 Write16(ELF::SHN_UNDEF); 479 else 480 Write16(NumberOfSections); 481 482 // e_shstrndx = Section # of '.shstrtab' 483 if (ShstrtabIndex >= ELF::SHN_LORESERVE) 484 Write16(ELF::SHN_XINDEX); 485 else 486 Write16(ShstrtabIndex); 487 } 488 489 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data, 490 const MCAsmLayout &Layout) { 491 if (Data.isCommon() && Data.isExternal()) 492 return Data.getCommonAlignment(); 493 494 uint64_t Res; 495 if (!Layout.getSymbolOffset(&Data, Res)) 496 return 0; 497 498 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol())) 499 Res |= 1; 500 501 return Res; 502 } 503 504 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm, 505 const MCAsmLayout &Layout) { 506 // The presence of symbol versions causes undefined symbols and 507 // versions declared with @@@ to be renamed. 508 509 for (MCSymbolData &OriginalData : Asm.symbols()) { 510 const MCSymbol &Alias = OriginalData.getSymbol(); 511 512 // Not an alias. 513 if (!Alias.isVariable()) 514 continue; 515 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue()); 516 if (!Ref) 517 continue; 518 const MCSymbol &Symbol = Ref->getSymbol(); 519 MCSymbolData &SD = Asm.getSymbolData(Symbol); 520 521 StringRef AliasName = Alias.getName(); 522 size_t Pos = AliasName.find('@'); 523 if (Pos == StringRef::npos) 524 continue; 525 526 // Aliases defined with .symvar copy the binding from the symbol they alias. 527 // This is the first place we are able to copy this information. 528 OriginalData.setExternal(SD.isExternal()); 529 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD)); 530 531 StringRef Rest = AliasName.substr(Pos); 532 if (!Symbol.isUndefined() && !Rest.startswith("@@@")) 533 continue; 534 535 // FIXME: produce a better error message. 536 if (Symbol.isUndefined() && Rest.startswith("@@") && 537 !Rest.startswith("@@@")) 538 report_fatal_error("A @@ version cannot be undefined"); 539 540 Renames.insert(std::make_pair(&Symbol, &Alias)); 541 } 542 } 543 544 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) { 545 uint8_t Type = newType; 546 547 // Propagation rules: 548 // IFUNC > FUNC > OBJECT > NOTYPE 549 // TLS_OBJECT > OBJECT > NOTYPE 550 // 551 // dont let the new type degrade the old type 552 switch (origType) { 553 default: 554 break; 555 case ELF::STT_GNU_IFUNC: 556 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT || 557 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS) 558 Type = ELF::STT_GNU_IFUNC; 559 break; 560 case ELF::STT_FUNC: 561 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE || 562 Type == ELF::STT_TLS) 563 Type = ELF::STT_FUNC; 564 break; 565 case ELF::STT_OBJECT: 566 if (Type == ELF::STT_NOTYPE) 567 Type = ELF::STT_OBJECT; 568 break; 569 case ELF::STT_TLS: 570 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE || 571 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC) 572 Type = ELF::STT_TLS; 573 break; 574 } 575 576 return Type; 577 } 578 579 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD, 580 const MCAsmLayout &Layout) { 581 MCSymbolData &OrigData = *MSD.SymbolData; 582 assert((!OrigData.getFragment() || 583 (&OrigData.getFragment()->getParent()->getSection() == 584 &OrigData.getSymbol().getSection())) && 585 "The symbol's section doesn't match the fragment's symbol"); 586 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol()); 587 588 // This has to be in sync with when computeSymbolTable uses SHN_ABS or 589 // SHN_COMMON. 590 bool IsReserved = !Base || OrigData.isCommon(); 591 592 // Binding and Type share the same byte as upper and lower nibbles 593 uint8_t Binding = MCELF::GetBinding(OrigData); 594 uint8_t Type = MCELF::GetType(OrigData); 595 MCSymbolData *BaseSD = nullptr; 596 if (Base) { 597 BaseSD = &Layout.getAssembler().getSymbolData(*Base); 598 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD)); 599 } 600 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift); 601 602 // Other and Visibility share the same byte with Visibility using the lower 603 // 2 bits 604 uint8_t Visibility = MCELF::GetVisibility(OrigData); 605 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift); 606 Other |= Visibility; 607 608 uint64_t Value = SymbolValue(OrigData, Layout); 609 uint64_t Size = 0; 610 611 const MCExpr *ESize = OrigData.getSize(); 612 if (!ESize && Base) 613 ESize = BaseSD->getSize(); 614 615 if (ESize) { 616 int64_t Res; 617 if (!ESize->EvaluateAsAbsolute(Res, Layout)) 618 report_fatal_error("Size expression must be absolute."); 619 Size = Res; 620 } 621 622 // Write out the symbol table entry 623 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other, 624 MSD.SectionIndex, IsReserved); 625 } 626 627 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF, 628 MCAssembler &Asm, 629 const MCAsmLayout &Layout, 630 SectionIndexMapTy &SectionIndexMap) { 631 // The string table must be emitted first because we need the index 632 // into the string table for all the symbol names. 633 634 // FIXME: Make sure the start of the symbol table is aligned. 635 636 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF); 637 638 // The first entry is the undefined symbol entry. 639 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false); 640 641 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) { 642 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, 643 ELF::STV_DEFAULT, ELF::SHN_ABS, true); 644 } 645 646 // Write the symbol table entries. 647 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1; 648 649 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) { 650 ELFSymbolData &MSD = LocalSymbolData[i]; 651 WriteSymbol(Writer, MSD, Layout); 652 } 653 654 // Write out a symbol table entry for each regular section. 655 for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e; 656 ++i) { 657 const MCSectionELF &Section = 658 static_cast<const MCSectionELF&>(i->getSection()); 659 if (Section.getType() == ELF::SHT_RELA || 660 Section.getType() == ELF::SHT_REL || 661 Section.getType() == ELF::SHT_STRTAB || 662 Section.getType() == ELF::SHT_SYMTAB || 663 Section.getType() == ELF::SHT_SYMTAB_SHNDX) 664 continue; 665 Writer.writeSymbol(0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT, 666 SectionIndexMap.lookup(&Section), false); 667 LastLocalSymbolIndex++; 668 } 669 670 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) { 671 ELFSymbolData &MSD = ExternalSymbolData[i]; 672 MCSymbolData &Data = *MSD.SymbolData; 673 assert(((Data.getFlags() & ELF_STB_Global) || 674 (Data.getFlags() & ELF_STB_Weak)) && 675 "External symbol requires STB_GLOBAL or STB_WEAK flag"); 676 WriteSymbol(Writer, MSD, Layout); 677 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 678 LastLocalSymbolIndex++; 679 } 680 681 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) { 682 ELFSymbolData &MSD = UndefinedSymbolData[i]; 683 MCSymbolData &Data = *MSD.SymbolData; 684 WriteSymbol(Writer, MSD, Layout); 685 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 686 LastLocalSymbolIndex++; 687 } 688 } 689 690 // It is always valid to create a relocation with a symbol. It is preferable 691 // to use a relocation with a section if that is possible. Using the section 692 // allows us to omit some local symbols from the symbol table. 693 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm, 694 const MCSymbolRefExpr *RefA, 695 const MCSymbolData *SD, 696 uint64_t C, 697 unsigned Type) const { 698 // A PCRel relocation to an absolute value has no symbol (or section). We 699 // represent that with a relocation to a null section. 700 if (!RefA) 701 return false; 702 703 MCSymbolRefExpr::VariantKind Kind = RefA->getKind(); 704 switch (Kind) { 705 default: 706 break; 707 // The .odp creation emits a relocation against the symbol ".TOC." which 708 // create a R_PPC64_TOC relocation. However the relocation symbol name 709 // in final object creation should be NULL, since the symbol does not 710 // really exist, it is just the reference to TOC base for the current 711 // object file. Since the symbol is undefined, returning false results 712 // in a relocation with a null section which is the desired result. 713 case MCSymbolRefExpr::VK_PPC_TOCBASE: 714 return false; 715 716 // These VariantKind cause the relocation to refer to something other than 717 // the symbol itself, like a linker generated table. Since the address of 718 // symbol is not relevant, we cannot replace the symbol with the 719 // section and patch the difference in the addend. 720 case MCSymbolRefExpr::VK_GOT: 721 case MCSymbolRefExpr::VK_PLT: 722 case MCSymbolRefExpr::VK_GOTPCREL: 723 case MCSymbolRefExpr::VK_Mips_GOT: 724 case MCSymbolRefExpr::VK_PPC_GOT_LO: 725 case MCSymbolRefExpr::VK_PPC_GOT_HI: 726 case MCSymbolRefExpr::VK_PPC_GOT_HA: 727 return true; 728 } 729 730 // An undefined symbol is not in any section, so the relocation has to point 731 // to the symbol itself. 732 const MCSymbol &Sym = SD->getSymbol(); 733 if (Sym.isUndefined()) 734 return true; 735 736 unsigned Binding = MCELF::GetBinding(*SD); 737 switch(Binding) { 738 default: 739 llvm_unreachable("Invalid Binding"); 740 case ELF::STB_LOCAL: 741 break; 742 case ELF::STB_WEAK: 743 // If the symbol is weak, it might be overridden by a symbol in another 744 // file. The relocation has to point to the symbol so that the linker 745 // can update it. 746 return true; 747 case ELF::STB_GLOBAL: 748 // Global ELF symbols can be preempted by the dynamic linker. The relocation 749 // has to point to the symbol for a reason analogous to the STB_WEAK case. 750 return true; 751 } 752 753 // If a relocation points to a mergeable section, we have to be careful. 754 // If the offset is zero, a relocation with the section will encode the 755 // same information. With a non-zero offset, the situation is different. 756 // For example, a relocation can point 42 bytes past the end of a string. 757 // If we change such a relocation to use the section, the linker would think 758 // that it pointed to another string and subtracting 42 at runtime will 759 // produce the wrong value. 760 auto &Sec = cast<MCSectionELF>(Sym.getSection()); 761 unsigned Flags = Sec.getFlags(); 762 if (Flags & ELF::SHF_MERGE) { 763 if (C != 0) 764 return true; 765 766 // It looks like gold has a bug (http://sourceware.org/PR16794) and can 767 // only handle section relocations to mergeable sections if using RELA. 768 if (!hasRelocationAddend()) 769 return true; 770 } 771 772 // Most TLS relocations use a got, so they need the symbol. Even those that 773 // are just an offset (@tpoff), require a symbol in gold versions before 774 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed 775 // http://sourceware.org/PR16773. 776 if (Flags & ELF::SHF_TLS) 777 return true; 778 779 // If the symbol is a thumb function the final relocation must set the lowest 780 // bit. With a symbol that is done by just having the symbol have that bit 781 // set, so we would lose the bit if we relocated with the section. 782 // FIXME: We could use the section but add the bit to the relocation value. 783 if (Asm.isThumbFunc(&Sym)) 784 return true; 785 786 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type)) 787 return true; 788 return false; 789 } 790 791 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) { 792 const MCSymbol &Sym = Ref.getSymbol(); 793 794 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF) 795 return &Sym; 796 797 if (!Sym.isVariable()) 798 return nullptr; 799 800 const MCExpr *Expr = Sym.getVariableValue(); 801 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr); 802 if (!Inner) 803 return nullptr; 804 805 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF) 806 return &Inner->getSymbol(); 807 return nullptr; 808 } 809 810 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm, 811 const MCAsmLayout &Layout, 812 const MCFragment *Fragment, 813 const MCFixup &Fixup, 814 MCValue Target, 815 bool &IsPCRel, 816 uint64_t &FixedValue) { 817 const MCSectionData *FixupSection = Fragment->getParent(); 818 uint64_t C = Target.getConstant(); 819 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); 820 821 if (const MCSymbolRefExpr *RefB = Target.getSymB()) { 822 assert(RefB->getKind() == MCSymbolRefExpr::VK_None && 823 "Should not have constructed this"); 824 825 // Let A, B and C being the components of Target and R be the location of 826 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C). 827 // If it is pcrel, we want to compute (A - B + C - R). 828 829 // In general, ELF has no relocations for -B. It can only represent (A + C) 830 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can 831 // replace B to implement it: (A - R - K + C) 832 if (IsPCRel) 833 Asm.getContext().FatalError( 834 Fixup.getLoc(), 835 "No relocation available to represent this relative expression"); 836 837 const MCSymbol &SymB = RefB->getSymbol(); 838 839 if (SymB.isUndefined()) 840 Asm.getContext().FatalError( 841 Fixup.getLoc(), 842 Twine("symbol '") + SymB.getName() + 843 "' can not be undefined in a subtraction expression"); 844 845 assert(!SymB.isAbsolute() && "Should have been folded"); 846 const MCSection &SecB = SymB.getSection(); 847 if (&SecB != &FixupSection->getSection()) 848 Asm.getContext().FatalError( 849 Fixup.getLoc(), "Cannot represent a difference across sections"); 850 851 const MCSymbolData &SymBD = Asm.getSymbolData(SymB); 852 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD); 853 uint64_t K = SymBOffset - FixupOffset; 854 IsPCRel = true; 855 C -= K; 856 } 857 858 // We either rejected the fixup or folded B into C at this point. 859 const MCSymbolRefExpr *RefA = Target.getSymA(); 860 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr; 861 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr; 862 863 unsigned Type = GetRelocType(Target, Fixup, IsPCRel); 864 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type); 865 if (!RelocateWithSymbol && SymA && !SymA->isUndefined()) 866 C += Layout.getSymbolOffset(SymAD); 867 868 uint64_t Addend = 0; 869 if (hasRelocationAddend()) { 870 Addend = C; 871 C = 0; 872 } 873 874 FixedValue = C; 875 876 // FIXME: What is this!?!? 877 MCSymbolRefExpr::VariantKind Modifier = 878 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None; 879 if (RelocNeedsGOT(Modifier)) 880 NeedsGOT = true; 881 882 if (!RelocateWithSymbol) { 883 const MCSection *SecA = 884 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr; 885 const MCSectionData *SecAD = SecA ? &Asm.getSectionData(*SecA) : nullptr; 886 ELFRelocationEntry Rec(FixupOffset, SecAD, Type, Addend); 887 Relocations[FixupSection].push_back(Rec); 888 return; 889 } 890 891 if (SymA) { 892 if (const MCSymbol *R = Renames.lookup(SymA)) 893 SymA = R; 894 895 if (const MCSymbol *WeakRef = getWeakRef(*RefA)) 896 WeakrefUsedInReloc.insert(WeakRef); 897 else 898 UsedInReloc.insert(SymA); 899 } 900 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend); 901 Relocations[FixupSection].push_back(Rec); 902 return; 903 } 904 905 906 uint64_t 907 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm, 908 const MCSymbol *S) { 909 const MCSymbolData &SD = Asm.getSymbolData(*S); 910 return SD.getIndex(); 911 } 912 913 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout, 914 const MCSymbolData &Data, bool Used, 915 bool Renamed) { 916 const MCSymbol &Symbol = Data.getSymbol(); 917 if (Symbol.isVariable()) { 918 const MCExpr *Expr = Symbol.getVariableValue(); 919 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) { 920 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF) 921 return false; 922 } 923 } 924 925 if (Used) 926 return true; 927 928 if (Renamed) 929 return false; 930 931 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_") 932 return true; 933 934 if (Symbol.isVariable()) { 935 const MCSymbol *Base = Layout.getBaseSymbol(Symbol); 936 if (Base && Base->isUndefined()) 937 return false; 938 } 939 940 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL; 941 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal) 942 return false; 943 944 if (Symbol.isTemporary()) 945 return false; 946 947 return true; 948 } 949 950 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) { 951 if (Data.isExternal()) 952 return false; 953 954 const MCSymbol &Symbol = Data.getSymbol(); 955 if (Symbol.isDefined()) 956 return true; 957 958 if (isUsedInReloc) 959 return false; 960 961 return true; 962 } 963 964 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm, 965 SectionIndexMapTy &SectionIndexMap, 966 const RelMapTy &RelMap) { 967 unsigned Index = 1; 968 for (MCAssembler::iterator it = Asm.begin(), 969 ie = Asm.end(); it != ie; ++it) { 970 const MCSectionELF &Section = 971 static_cast<const MCSectionELF &>(it->getSection()); 972 if (Section.getType() != ELF::SHT_GROUP) 973 continue; 974 SectionIndexMap[&Section] = Index++; 975 } 976 977 for (MCAssembler::iterator it = Asm.begin(), 978 ie = Asm.end(); it != ie; ++it) { 979 const MCSectionELF &Section = 980 static_cast<const MCSectionELF &>(it->getSection()); 981 if (Section.getType() == ELF::SHT_GROUP || 982 Section.getType() == ELF::SHT_REL || 983 Section.getType() == ELF::SHT_RELA) 984 continue; 985 SectionIndexMap[&Section] = Index++; 986 const MCSectionELF *RelSection = RelMap.lookup(&Section); 987 if (RelSection) 988 SectionIndexMap[RelSection] = Index++; 989 } 990 } 991 992 void 993 ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout, 994 const SectionIndexMapTy &SectionIndexMap, 995 const RevGroupMapTy &RevGroupMap, 996 unsigned NumRegularSections) { 997 // FIXME: Is this the correct place to do this? 998 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed? 999 if (NeedsGOT) { 1000 StringRef Name = "_GLOBAL_OFFSET_TABLE_"; 1001 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name); 1002 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym); 1003 Data.setExternal(true); 1004 MCELF::SetBinding(Data, ELF::STB_GLOBAL); 1005 } 1006 1007 // Add the data for the symbols. 1008 for (MCSymbolData &SD : Asm.symbols()) { 1009 const MCSymbol &Symbol = SD.getSymbol(); 1010 1011 bool Used = UsedInReloc.count(&Symbol); 1012 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol); 1013 bool isSignature = RevGroupMap.count(&Symbol); 1014 1015 if (!isInSymtab(Layout, SD, 1016 Used || WeakrefUsed || isSignature, 1017 Renames.count(&Symbol))) 1018 continue; 1019 1020 ELFSymbolData MSD; 1021 MSD.SymbolData = &SD; 1022 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol); 1023 1024 // Undefined symbols are global, but this is the first place we 1025 // are able to set it. 1026 bool Local = isLocal(SD, Used); 1027 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) { 1028 assert(BaseSymbol); 1029 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol); 1030 MCELF::SetBinding(SD, ELF::STB_GLOBAL); 1031 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL); 1032 } 1033 1034 if (!BaseSymbol) { 1035 MSD.SectionIndex = ELF::SHN_ABS; 1036 } else if (SD.isCommon()) { 1037 assert(!Local); 1038 MSD.SectionIndex = ELF::SHN_COMMON; 1039 } else if (BaseSymbol->isUndefined()) { 1040 if (isSignature && !Used) 1041 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap.lookup(&Symbol)); 1042 else 1043 MSD.SectionIndex = ELF::SHN_UNDEF; 1044 if (!Used && WeakrefUsed) 1045 MCELF::SetBinding(SD, ELF::STB_WEAK); 1046 } else { 1047 const MCSectionELF &Section = 1048 static_cast<const MCSectionELF&>(BaseSymbol->getSection()); 1049 MSD.SectionIndex = SectionIndexMap.lookup(&Section); 1050 assert(MSD.SectionIndex && "Invalid section index!"); 1051 } 1052 1053 // The @@@ in symbol version is replaced with @ in undefined symbols and 1054 // @@ in defined ones. 1055 StringRef Name = Symbol.getName(); 1056 SmallString<32> Buf; 1057 size_t Pos = Name.find("@@@"); 1058 if (Pos != StringRef::npos) { 1059 Buf += Name.substr(0, Pos); 1060 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1; 1061 Buf += Name.substr(Pos + Skip); 1062 Name = Buf; 1063 } 1064 MSD.Name = StrTabBuilder.add(Name); 1065 1066 if (MSD.SectionIndex == ELF::SHN_UNDEF) 1067 UndefinedSymbolData.push_back(MSD); 1068 else if (Local) 1069 LocalSymbolData.push_back(MSD); 1070 else 1071 ExternalSymbolData.push_back(MSD); 1072 } 1073 1074 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i) 1075 StrTabBuilder.add(*i); 1076 1077 StrTabBuilder.finalize(StringTableBuilder::ELF); 1078 1079 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i) 1080 FileSymbolData.push_back(StrTabBuilder.getOffset(*i)); 1081 1082 for (ELFSymbolData& MSD : LocalSymbolData) 1083 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name); 1084 for (ELFSymbolData& MSD : ExternalSymbolData) 1085 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name); 1086 for (ELFSymbolData& MSD : UndefinedSymbolData) 1087 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name); 1088 1089 // Symbols are required to be in lexicographic order. 1090 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end()); 1091 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end()); 1092 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end()); 1093 1094 // Set the symbol indices. Local symbols must come before all other 1095 // symbols with non-local bindings. 1096 unsigned Index = FileSymbolData.size() + 1; 1097 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) 1098 LocalSymbolData[i].SymbolData->setIndex(Index++); 1099 1100 Index += NumRegularSections; 1101 1102 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) 1103 ExternalSymbolData[i].SymbolData->setIndex(Index++); 1104 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) 1105 UndefinedSymbolData[i].SymbolData->setIndex(Index++); 1106 } 1107 1108 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm, 1109 MCAsmLayout &Layout, 1110 RelMapTy &RelMap) { 1111 for (MCAssembler::const_iterator it = Asm.begin(), 1112 ie = Asm.end(); it != ie; ++it) { 1113 const MCSectionData &SD = *it; 1114 if (Relocations[&SD].empty()) 1115 continue; 1116 1117 MCContext &Ctx = Asm.getContext(); 1118 const MCSectionELF &Section = 1119 static_cast<const MCSectionELF&>(SD.getSection()); 1120 1121 const StringRef SectionName = Section.getSectionName(); 1122 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel"; 1123 RelaSectionName += SectionName; 1124 1125 unsigned EntrySize; 1126 if (hasRelocationAddend()) 1127 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela); 1128 else 1129 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel); 1130 1131 unsigned Flags = 0; 1132 StringRef Group = ""; 1133 if (Section.getFlags() & ELF::SHF_GROUP) { 1134 Flags = ELF::SHF_GROUP; 1135 Group = Section.getGroup()->getName(); 1136 } 1137 1138 const MCSectionELF *RelaSection = 1139 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ? 1140 ELF::SHT_RELA : ELF::SHT_REL, Flags, 1141 SectionKind::getReadOnly(), 1142 EntrySize, Group); 1143 RelMap[&Section] = RelaSection; 1144 Asm.getOrCreateSectionData(*RelaSection); 1145 } 1146 } 1147 1148 static SmallVector<char, 128> 1149 getUncompressedData(MCAsmLayout &Layout, 1150 MCSectionData::FragmentListType &Fragments) { 1151 SmallVector<char, 128> UncompressedData; 1152 for (const MCFragment &F : Fragments) { 1153 const SmallVectorImpl<char> *Contents; 1154 switch (F.getKind()) { 1155 case MCFragment::FT_Data: 1156 Contents = &cast<MCDataFragment>(F).getContents(); 1157 break; 1158 case MCFragment::FT_Dwarf: 1159 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents(); 1160 break; 1161 case MCFragment::FT_DwarfFrame: 1162 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents(); 1163 break; 1164 default: 1165 llvm_unreachable( 1166 "Not expecting any other fragment types in a debug_* section"); 1167 } 1168 UncompressedData.append(Contents->begin(), Contents->end()); 1169 } 1170 return UncompressedData; 1171 } 1172 1173 // Include the debug info compression header: 1174 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section, 1175 // useful for consumers to preallocate a buffer to decompress into. 1176 static bool 1177 prependCompressionHeader(uint64_t Size, 1178 SmallVectorImpl<char> &CompressedContents) { 1179 static const StringRef Magic = "ZLIB"; 1180 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size()) 1181 return false; 1182 if (sys::IsLittleEndianHost) 1183 sys::swapByteOrder(Size); 1184 CompressedContents.insert(CompressedContents.begin(), 1185 Magic.size() + sizeof(Size), 0); 1186 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin()); 1187 std::copy(reinterpret_cast<char *>(&Size), 1188 reinterpret_cast<char *>(&Size + 1), 1189 CompressedContents.begin() + Magic.size()); 1190 return true; 1191 } 1192 1193 // Return a single fragment containing the compressed contents of the whole 1194 // section. Null if the section was not compressed for any reason. 1195 static std::unique_ptr<MCDataFragment> 1196 getCompressedFragment(MCAsmLayout &Layout, 1197 MCSectionData::FragmentListType &Fragments) { 1198 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment()); 1199 1200 // Gather the uncompressed data from all the fragments, recording the 1201 // alignment fragment, if seen, and any fixups. 1202 SmallVector<char, 128> UncompressedData = 1203 getUncompressedData(Layout, Fragments); 1204 1205 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents(); 1206 1207 zlib::Status Success = zlib::compress( 1208 StringRef(UncompressedData.data(), UncompressedData.size()), 1209 CompressedContents); 1210 if (Success != zlib::StatusOK) 1211 return nullptr; 1212 1213 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) 1214 return nullptr; 1215 1216 return CompressedFragment; 1217 } 1218 1219 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>> 1220 DefiningSymbolMap; 1221 1222 static void UpdateSymbols(const MCAsmLayout &Layout, 1223 const std::vector<MCSymbolData *> &Symbols, 1224 MCFragment &NewFragment) { 1225 for (MCSymbolData *Sym : Symbols) { 1226 Sym->setOffset(Sym->getOffset() + 1227 Layout.getFragmentOffset(Sym->getFragment())); 1228 Sym->setFragment(&NewFragment); 1229 } 1230 } 1231 1232 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout, 1233 const DefiningSymbolMap &DefiningSymbols, 1234 const MCSectionELF &Section, 1235 MCSectionData &SD) { 1236 StringRef SectionName = Section.getSectionName(); 1237 MCSectionData::FragmentListType &Fragments = SD.getFragmentList(); 1238 1239 std::unique_ptr<MCDataFragment> CompressedFragment = 1240 getCompressedFragment(Layout, Fragments); 1241 1242 // Leave the section as-is if the fragments could not be compressed. 1243 if (!CompressedFragment) 1244 return; 1245 1246 // Update the fragment+offsets of any symbols referring to fragments in this 1247 // section to refer to the new fragment. 1248 auto I = DefiningSymbols.find(&SD); 1249 if (I != DefiningSymbols.end()) 1250 UpdateSymbols(Layout, I->second, *CompressedFragment); 1251 1252 // Invalidate the layout for the whole section since it will have new and 1253 // different fragments now. 1254 Layout.invalidateFragmentsFrom(&Fragments.front()); 1255 Fragments.clear(); 1256 1257 // Complete the initialization of the new fragment 1258 CompressedFragment->setParent(&SD); 1259 CompressedFragment->setLayoutOrder(0); 1260 Fragments.push_back(CompressedFragment.release()); 1261 1262 // Rename from .debug_* to .zdebug_* 1263 Asm.getContext().renameELFSection(&Section, 1264 (".z" + SectionName.drop_front(1)).str()); 1265 } 1266 1267 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm, 1268 MCAsmLayout &Layout) { 1269 if (!Asm.getContext().getAsmInfo()->compressDebugSections()) 1270 return; 1271 1272 DefiningSymbolMap DefiningSymbols; 1273 1274 for (MCSymbolData &SD : Asm.symbols()) 1275 if (MCFragment *F = SD.getFragment()) 1276 DefiningSymbols[F->getParent()].push_back(&SD); 1277 1278 for (MCSectionData &SD : Asm) { 1279 const MCSectionELF &Section = 1280 static_cast<const MCSectionELF &>(SD.getSection()); 1281 StringRef SectionName = Section.getSectionName(); 1282 1283 // Compressing debug_frame requires handling alignment fragments which is 1284 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow 1285 // for writing to arbitrary buffers) for little benefit. 1286 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame") 1287 continue; 1288 1289 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD); 1290 } 1291 } 1292 1293 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 1294 const RelMapTy &RelMap) { 1295 for (MCAssembler::const_iterator it = Asm.begin(), 1296 ie = Asm.end(); it != ie; ++it) { 1297 const MCSectionData &SD = *it; 1298 const MCSectionELF &Section = 1299 static_cast<const MCSectionELF&>(SD.getSection()); 1300 1301 const MCSectionELF *RelaSection = RelMap.lookup(&Section); 1302 if (!RelaSection) 1303 continue; 1304 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection); 1305 RelaSD.setAlignment(is64Bit() ? 8 : 4); 1306 1307 MCDataFragment *F = new MCDataFragment(&RelaSD); 1308 WriteRelocationsFragment(Asm, F, &*it); 1309 } 1310 } 1311 1312 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type, 1313 uint64_t Flags, uint64_t Address, 1314 uint64_t Offset, uint64_t Size, 1315 uint32_t Link, uint32_t Info, 1316 uint64_t Alignment, 1317 uint64_t EntrySize) { 1318 Write32(Name); // sh_name: index into string table 1319 Write32(Type); // sh_type 1320 WriteWord(Flags); // sh_flags 1321 WriteWord(Address); // sh_addr 1322 WriteWord(Offset); // sh_offset 1323 WriteWord(Size); // sh_size 1324 Write32(Link); // sh_link 1325 Write32(Info); // sh_info 1326 WriteWord(Alignment); // sh_addralign 1327 WriteWord(EntrySize); // sh_entsize 1328 } 1329 1330 // ELF doesn't require relocations to be in any order. We sort by the r_offset, 1331 // just to match gnu as for easier comparison. The use type is an arbitrary way 1332 // of making the sort deterministic. 1333 static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) { 1334 const ELFRelocationEntry &A = *AP; 1335 const ELFRelocationEntry &B = *BP; 1336 if (A.Offset != B.Offset) 1337 return B.Offset - A.Offset; 1338 if (B.Type != A.Type) 1339 return A.Type - B.Type; 1340 llvm_unreachable("ELFRelocs might be unstable!"); 1341 } 1342 1343 static void sortRelocs(const MCAssembler &Asm, 1344 std::vector<ELFRelocationEntry> &Relocs) { 1345 array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel); 1346 } 1347 1348 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm, 1349 MCDataFragment *F, 1350 const MCSectionData *SD) { 1351 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD]; 1352 1353 sortRelocs(Asm, Relocs); 1354 1355 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) { 1356 const ELFRelocationEntry &Entry = Relocs[e - i - 1]; 1357 1358 unsigned Index; 1359 if (Entry.UseSymbol) { 1360 Index = getSymbolIndexInSymbolTable(Asm, Entry.Symbol); 1361 } else { 1362 const MCSectionData *Sec = Entry.Section; 1363 if (Sec) 1364 Index = Sec->getOrdinal() + FileSymbolData.size() + 1365 LocalSymbolData.size() + 1; 1366 else 1367 Index = 0; 1368 } 1369 1370 if (is64Bit()) { 1371 write(*F, Entry.Offset); 1372 if (TargetObjectWriter->isN64()) { 1373 write(*F, uint32_t(Index)); 1374 1375 write(*F, TargetObjectWriter->getRSsym(Entry.Type)); 1376 write(*F, TargetObjectWriter->getRType3(Entry.Type)); 1377 write(*F, TargetObjectWriter->getRType2(Entry.Type)); 1378 write(*F, TargetObjectWriter->getRType(Entry.Type)); 1379 } else { 1380 struct ELF::Elf64_Rela ERE64; 1381 ERE64.setSymbolAndType(Index, Entry.Type); 1382 write(*F, ERE64.r_info); 1383 } 1384 if (hasRelocationAddend()) 1385 write(*F, Entry.Addend); 1386 } else { 1387 write(*F, uint32_t(Entry.Offset)); 1388 1389 struct ELF::Elf32_Rela ERE32; 1390 ERE32.setSymbolAndType(Index, Entry.Type); 1391 write(*F, ERE32.r_info); 1392 1393 if (hasRelocationAddend()) 1394 write(*F, uint32_t(Entry.Addend)); 1395 } 1396 } 1397 } 1398 1399 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm, 1400 MCAsmLayout &Layout, 1401 SectionIndexMapTy &SectionIndexMap, 1402 const RelMapTy &RelMap) { 1403 MCContext &Ctx = Asm.getContext(); 1404 MCDataFragment *F; 1405 1406 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32; 1407 1408 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as. 1409 const MCSectionELF *ShstrtabSection = 1410 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0, 1411 SectionKind::getReadOnly()); 1412 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection); 1413 ShstrtabSD.setAlignment(1); 1414 1415 const MCSectionELF *SymtabSection = 1416 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, 1417 SectionKind::getReadOnly(), 1418 EntrySize, ""); 1419 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection); 1420 SymtabSD.setAlignment(is64Bit() ? 8 : 4); 1421 1422 const MCSectionELF *StrtabSection; 1423 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0, 1424 SectionKind::getReadOnly()); 1425 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection); 1426 StrtabSD.setAlignment(1); 1427 1428 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1429 1430 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection); 1431 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection); 1432 StringTableIndex = SectionIndexMap.lookup(StrtabSection); 1433 1434 // Symbol table 1435 F = new MCDataFragment(&SymtabSD); 1436 WriteSymbolTable(F, Asm, Layout, SectionIndexMap); 1437 1438 F = new MCDataFragment(&StrtabSD); 1439 F->getContents().append(StrTabBuilder.data().begin(), 1440 StrTabBuilder.data().end()); 1441 1442 F = new MCDataFragment(&ShstrtabSD); 1443 1444 // Section header string table. 1445 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { 1446 const MCSectionELF &Section = 1447 static_cast<const MCSectionELF&>(it->getSection()); 1448 ShStrTabBuilder.add(Section.getSectionName()); 1449 } 1450 ShStrTabBuilder.finalize(StringTableBuilder::ELF); 1451 F->getContents().append(ShStrTabBuilder.data().begin(), 1452 ShStrTabBuilder.data().end()); 1453 } 1454 1455 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm, 1456 MCAsmLayout &Layout, 1457 GroupMapTy &GroupMap, 1458 RevGroupMapTy &RevGroupMap, 1459 SectionIndexMapTy &SectionIndexMap, 1460 const RelMapTy &RelMap) { 1461 // Create the .note.GNU-stack section if needed. 1462 MCContext &Ctx = Asm.getContext(); 1463 if (Asm.getNoExecStack()) { 1464 const MCSectionELF *GnuStackSection = 1465 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0, 1466 SectionKind::getReadOnly()); 1467 Asm.getOrCreateSectionData(*GnuStackSection); 1468 } 1469 1470 // Build the groups 1471 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1472 it != ie; ++it) { 1473 const MCSectionELF &Section = 1474 static_cast<const MCSectionELF&>(it->getSection()); 1475 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1476 continue; 1477 1478 const MCSymbol *SignatureSymbol = Section.getGroup(); 1479 Asm.getOrCreateSymbolData(*SignatureSymbol); 1480 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol]; 1481 if (!Group) { 1482 Group = Ctx.CreateELFGroupSection(); 1483 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1484 Data.setAlignment(4); 1485 MCDataFragment *F = new MCDataFragment(&Data); 1486 write(*F, uint32_t(ELF::GRP_COMDAT)); 1487 } 1488 GroupMap[Group] = SignatureSymbol; 1489 } 1490 1491 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1492 1493 // Add sections to the groups 1494 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1495 it != ie; ++it) { 1496 const MCSectionELF &Section = 1497 static_cast<const MCSectionELF&>(it->getSection()); 1498 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1499 continue; 1500 const MCSectionELF *Group = RevGroupMap[Section.getGroup()]; 1501 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1502 // FIXME: we could use the previous fragment 1503 MCDataFragment *F = new MCDataFragment(&Data); 1504 uint32_t Index = SectionIndexMap.lookup(&Section); 1505 write(*F, Index); 1506 } 1507 } 1508 1509 void ELFObjectWriter::WriteSection(MCAssembler &Asm, 1510 const SectionIndexMapTy &SectionIndexMap, 1511 uint32_t GroupSymbolIndex, 1512 uint64_t Offset, uint64_t Size, 1513 uint64_t Alignment, 1514 const MCSectionELF &Section) { 1515 uint64_t sh_link = 0; 1516 uint64_t sh_info = 0; 1517 1518 switch(Section.getType()) { 1519 case ELF::SHT_DYNAMIC: 1520 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName()); 1521 sh_info = 0; 1522 break; 1523 1524 case ELF::SHT_REL: 1525 case ELF::SHT_RELA: { 1526 const MCSectionELF *SymtabSection; 1527 const MCSectionELF *InfoSection; 1528 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 1529 0, 1530 SectionKind::getReadOnly()); 1531 sh_link = SectionIndexMap.lookup(SymtabSection); 1532 assert(sh_link && ".symtab not found"); 1533 1534 // Remove ".rel" and ".rela" prefixes. 1535 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5; 1536 StringRef SectionName = Section.getSectionName().substr(SecNameLen); 1537 StringRef GroupName = 1538 Section.getGroup() ? Section.getGroup()->getName() : ""; 1539 1540 InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS, 1541 0, SectionKind::getReadOnly(), 1542 0, GroupName); 1543 sh_info = SectionIndexMap.lookup(InfoSection); 1544 break; 1545 } 1546 1547 case ELF::SHT_SYMTAB: 1548 case ELF::SHT_DYNSYM: 1549 sh_link = StringTableIndex; 1550 sh_info = LastLocalSymbolIndex; 1551 break; 1552 1553 case ELF::SHT_SYMTAB_SHNDX: 1554 sh_link = SymbolTableIndex; 1555 break; 1556 1557 case ELF::SHT_PROGBITS: 1558 case ELF::SHT_STRTAB: 1559 case ELF::SHT_NOBITS: 1560 case ELF::SHT_NOTE: 1561 case ELF::SHT_NULL: 1562 case ELF::SHT_ARM_ATTRIBUTES: 1563 case ELF::SHT_INIT_ARRAY: 1564 case ELF::SHT_FINI_ARRAY: 1565 case ELF::SHT_PREINIT_ARRAY: 1566 case ELF::SHT_X86_64_UNWIND: 1567 case ELF::SHT_MIPS_REGINFO: 1568 case ELF::SHT_MIPS_OPTIONS: 1569 case ELF::SHT_MIPS_ABIFLAGS: 1570 // Nothing to do. 1571 break; 1572 1573 case ELF::SHT_GROUP: 1574 sh_link = SymbolTableIndex; 1575 sh_info = GroupSymbolIndex; 1576 break; 1577 1578 default: 1579 llvm_unreachable("FIXME: sh_type value not supported!"); 1580 } 1581 1582 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM && 1583 Section.getType() == ELF::SHT_ARM_EXIDX) { 1584 StringRef SecName(Section.getSectionName()); 1585 if (SecName == ".ARM.exidx") { 1586 sh_link = SectionIndexMap.lookup( 1587 Asm.getContext().getELFSection(".text", 1588 ELF::SHT_PROGBITS, 1589 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, 1590 SectionKind::getText())); 1591 } else if (SecName.startswith(".ARM.exidx")) { 1592 StringRef GroupName = 1593 Section.getGroup() ? Section.getGroup()->getName() : ""; 1594 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection( 1595 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS, 1596 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText(), 0, 1597 GroupName)); 1598 } 1599 } 1600 1601 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()), 1602 Section.getType(), 1603 Section.getFlags(), 0, Offset, Size, sh_link, sh_info, 1604 Alignment, Section.getEntrySize()); 1605 } 1606 1607 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) { 1608 return SD.getOrdinal() == ~UINT32_C(0) && 1609 !SD.getSection().isVirtualSection(); 1610 } 1611 1612 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) { 1613 uint64_t Ret = 0; 1614 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1615 ++i) { 1616 const MCFragment &F = *i; 1617 assert(F.getKind() == MCFragment::FT_Data); 1618 Ret += cast<MCDataFragment>(F).getContents().size(); 1619 } 1620 return Ret; 1621 } 1622 1623 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout, 1624 const MCSectionData &SD) { 1625 if (IsELFMetaDataSection(SD)) 1626 return DataSectionSize(SD); 1627 return Layout.getSectionFileSize(&SD); 1628 } 1629 1630 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout, 1631 const MCSectionData &SD) { 1632 if (IsELFMetaDataSection(SD)) 1633 return DataSectionSize(SD); 1634 return Layout.getSectionAddressSize(&SD); 1635 } 1636 1637 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm, 1638 const MCAsmLayout &Layout, 1639 const MCSectionELF &Section) { 1640 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1641 1642 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment()); 1643 WriteZeros(Padding); 1644 1645 if (IsELFMetaDataSection(SD)) { 1646 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1647 ++i) { 1648 const MCFragment &F = *i; 1649 assert(F.getKind() == MCFragment::FT_Data); 1650 WriteBytes(cast<MCDataFragment>(F).getContents()); 1651 } 1652 } else { 1653 Asm.writeSectionData(&SD, Layout); 1654 } 1655 } 1656 1657 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm, 1658 const GroupMapTy &GroupMap, 1659 const MCAsmLayout &Layout, 1660 const SectionIndexMapTy &SectionIndexMap, 1661 const SectionOffsetMapTy &SectionOffsetMap) { 1662 const unsigned NumSections = Asm.size() + 1; 1663 1664 std::vector<const MCSectionELF*> Sections; 1665 Sections.resize(NumSections - 1); 1666 1667 for (SectionIndexMapTy::const_iterator i= 1668 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) { 1669 const std::pair<const MCSectionELF*, uint32_t> &p = *i; 1670 Sections[p.second - 1] = p.first; 1671 } 1672 1673 // Null section first. 1674 uint64_t FirstSectionSize = 1675 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0; 1676 uint32_t FirstSectionLink = 1677 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0; 1678 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0); 1679 1680 for (unsigned i = 0; i < NumSections - 1; ++i) { 1681 const MCSectionELF &Section = *Sections[i]; 1682 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1683 uint32_t GroupSymbolIndex; 1684 if (Section.getType() != ELF::SHT_GROUP) 1685 GroupSymbolIndex = 0; 1686 else 1687 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, 1688 GroupMap.lookup(&Section)); 1689 1690 uint64_t Size = GetSectionAddressSize(Layout, SD); 1691 1692 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex, 1693 SectionOffsetMap.lookup(&Section), Size, 1694 SD.getAlignment(), Section); 1695 } 1696 } 1697 1698 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm, 1699 std::vector<const MCSectionELF*> &Sections) { 1700 for (MCAssembler::iterator it = Asm.begin(), 1701 ie = Asm.end(); it != ie; ++it) { 1702 const MCSectionELF &Section = 1703 static_cast<const MCSectionELF &>(it->getSection()); 1704 if (Section.getType() == ELF::SHT_GROUP) 1705 Sections.push_back(&Section); 1706 } 1707 1708 for (MCAssembler::iterator it = Asm.begin(), 1709 ie = Asm.end(); it != ie; ++it) { 1710 const MCSectionELF &Section = 1711 static_cast<const MCSectionELF &>(it->getSection()); 1712 if (Section.getType() != ELF::SHT_GROUP && 1713 Section.getType() != ELF::SHT_REL && 1714 Section.getType() != ELF::SHT_RELA) 1715 Sections.push_back(&Section); 1716 } 1717 1718 for (MCAssembler::iterator it = Asm.begin(), 1719 ie = Asm.end(); it != ie; ++it) { 1720 const MCSectionELF &Section = 1721 static_cast<const MCSectionELF &>(it->getSection()); 1722 if (Section.getType() == ELF::SHT_REL || 1723 Section.getType() == ELF::SHT_RELA) 1724 Sections.push_back(&Section); 1725 } 1726 } 1727 1728 void ELFObjectWriter::WriteObject(MCAssembler &Asm, 1729 const MCAsmLayout &Layout) { 1730 GroupMapTy GroupMap; 1731 RevGroupMapTy RevGroupMap; 1732 SectionIndexMapTy SectionIndexMap; 1733 1734 unsigned NumUserSections = Asm.size(); 1735 1736 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout)); 1737 1738 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap; 1739 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1740 1741 const unsigned NumUserAndRelocSections = Asm.size(); 1742 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap, 1743 RevGroupMap, SectionIndexMap, RelMap); 1744 const unsigned AllSections = Asm.size(); 1745 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections; 1746 1747 unsigned NumRegularSections = NumUserSections + NumIndexedSections; 1748 1749 // Compute symbol table information. 1750 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, 1751 NumRegularSections); 1752 1753 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1754 1755 CreateMetadataSections(const_cast<MCAssembler&>(Asm), 1756 const_cast<MCAsmLayout&>(Layout), 1757 SectionIndexMap, 1758 RelMap); 1759 1760 uint64_t NaturalAlignment = is64Bit() ? 8 : 4; 1761 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 1762 sizeof(ELF::Elf32_Ehdr); 1763 uint64_t FileOff = HeaderSize; 1764 1765 std::vector<const MCSectionELF*> Sections; 1766 ComputeSectionOrder(Asm, Sections); 1767 unsigned NumSections = Sections.size(); 1768 SectionOffsetMapTy SectionOffsetMap; 1769 for (unsigned i = 0; i < NumRegularSections + 1; ++i) { 1770 const MCSectionELF &Section = *Sections[i]; 1771 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1772 1773 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1774 1775 // Remember the offset into the file for this section. 1776 SectionOffsetMap[&Section] = FileOff; 1777 1778 // Get the size of the section in the output file (including padding). 1779 FileOff += GetSectionFileSize(Layout, SD); 1780 } 1781 1782 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment); 1783 1784 const unsigned SectionHeaderOffset = FileOff - HeaderSize; 1785 1786 uint64_t SectionHeaderEntrySize = is64Bit() ? 1787 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr); 1788 FileOff += (NumSections + 1) * SectionHeaderEntrySize; 1789 1790 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) { 1791 const MCSectionELF &Section = *Sections[i]; 1792 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1793 1794 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1795 1796 // Remember the offset into the file for this section. 1797 SectionOffsetMap[&Section] = FileOff; 1798 1799 // Get the size of the section in the output file (including padding). 1800 FileOff += GetSectionFileSize(Layout, SD); 1801 } 1802 1803 // Write out the ELF header ... 1804 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1); 1805 1806 // ... then the regular sections ... 1807 // + because of .shstrtab 1808 for (unsigned i = 0; i < NumRegularSections + 1; ++i) 1809 WriteDataSectionData(Asm, Layout, *Sections[i]); 1810 1811 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment); 1812 WriteZeros(Padding); 1813 1814 // ... then the section header table ... 1815 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap, 1816 SectionOffsetMap); 1817 1818 // ... and then the remaining sections ... 1819 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) 1820 WriteDataSectionData(Asm, Layout, *Sections[i]); 1821 } 1822 1823 bool 1824 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 1825 const MCSymbolData &DataA, 1826 const MCFragment &FB, 1827 bool InSet, 1828 bool IsPCRel) const { 1829 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC) 1830 return false; 1831 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl( 1832 Asm, DataA, FB,InSet, IsPCRel); 1833 } 1834 1835 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW, 1836 raw_ostream &OS, 1837 bool IsLittleEndian) { 1838 return new ELFObjectWriter(MOTW, OS, IsLittleEndian); 1839 } 1840