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