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 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 some linkers (gold, 774 // but not bfd ld). 775 if (Flags & ELF::SHF_TLS) 776 return true; 777 778 // If the symbol is a thumb function the final relocation must set the lowest 779 // bit. With a symbol that is done by just having the symbol have that bit 780 // set, so we would lose the bit if we relocated with the section. 781 // FIXME: We could use the section but add the bit to the relocation value. 782 if (Asm.isThumbFunc(&Sym)) 783 return true; 784 785 if (TargetObjectWriter->needsRelocateWithSymbol(Type)) 786 return true; 787 return false; 788 } 789 790 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) { 791 const MCSymbol &Sym = Ref.getSymbol(); 792 793 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF) 794 return &Sym; 795 796 if (!Sym.isVariable()) 797 return nullptr; 798 799 const MCExpr *Expr = Sym.getVariableValue(); 800 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr); 801 if (!Inner) 802 return nullptr; 803 804 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF) 805 return &Inner->getSymbol(); 806 return nullptr; 807 } 808 809 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm, 810 const MCAsmLayout &Layout, 811 const MCFragment *Fragment, 812 const MCFixup &Fixup, 813 MCValue Target, 814 bool &IsPCRel, 815 uint64_t &FixedValue) { 816 const MCSectionData *FixupSection = Fragment->getParent(); 817 uint64_t C = Target.getConstant(); 818 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); 819 820 if (const MCSymbolRefExpr *RefB = Target.getSymB()) { 821 assert(RefB->getKind() == MCSymbolRefExpr::VK_None && 822 "Should not have constructed this"); 823 824 // Let A, B and C being the components of Target and R be the location of 825 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C). 826 // If it is pcrel, we want to compute (A - B + C - R). 827 828 // In general, ELF has no relocations for -B. It can only represent (A + C) 829 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can 830 // replace B to implement it: (A - R - K + C) 831 if (IsPCRel) 832 Asm.getContext().FatalError( 833 Fixup.getLoc(), 834 "No relocation available to represent this relative expression"); 835 836 const MCSymbol &SymB = RefB->getSymbol(); 837 838 if (SymB.isUndefined()) 839 Asm.getContext().FatalError( 840 Fixup.getLoc(), 841 Twine("symbol '") + SymB.getName() + 842 "' can not be undefined in a subtraction expression"); 843 844 assert(!SymB.isAbsolute() && "Should have been folded"); 845 const MCSection &SecB = SymB.getSection(); 846 if (&SecB != &FixupSection->getSection()) 847 Asm.getContext().FatalError( 848 Fixup.getLoc(), "Cannot represent a difference across sections"); 849 850 const MCSymbolData &SymBD = Asm.getSymbolData(SymB); 851 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD); 852 uint64_t K = SymBOffset - FixupOffset; 853 IsPCRel = true; 854 C -= K; 855 } 856 857 // We either rejected the fixup or folded B into C at this point. 858 const MCSymbolRefExpr *RefA = Target.getSymA(); 859 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr; 860 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr; 861 862 unsigned Type = GetRelocType(Target, Fixup, IsPCRel); 863 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type); 864 if (!RelocateWithSymbol && SymA && !SymA->isUndefined()) 865 C += Layout.getSymbolOffset(SymAD); 866 867 uint64_t Addend = 0; 868 if (hasRelocationAddend()) { 869 Addend = C; 870 C = 0; 871 } 872 873 FixedValue = C; 874 875 // FIXME: What is this!?!? 876 MCSymbolRefExpr::VariantKind Modifier = 877 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None; 878 if (RelocNeedsGOT(Modifier)) 879 NeedsGOT = true; 880 881 if (!RelocateWithSymbol) { 882 const MCSection *SecA = 883 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr; 884 const MCSectionData *SecAD = SecA ? &Asm.getSectionData(*SecA) : nullptr; 885 ELFRelocationEntry Rec(FixupOffset, SecAD, Type, Addend); 886 Relocations[FixupSection].push_back(Rec); 887 return; 888 } 889 890 if (SymA) { 891 if (const MCSymbol *R = Renames.lookup(SymA)) 892 SymA = R; 893 894 if (const MCSymbol *WeakRef = getWeakRef(*RefA)) 895 WeakrefUsedInReloc.insert(WeakRef); 896 else 897 UsedInReloc.insert(SymA); 898 } 899 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend); 900 Relocations[FixupSection].push_back(Rec); 901 return; 902 } 903 904 905 uint64_t 906 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm, 907 const MCSymbol *S) { 908 const MCSymbolData &SD = Asm.getSymbolData(*S); 909 return SD.getIndex(); 910 } 911 912 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout, 913 const MCSymbolData &Data, bool Used, 914 bool Renamed) { 915 const MCSymbol &Symbol = Data.getSymbol(); 916 if (Symbol.isVariable()) { 917 const MCExpr *Expr = Symbol.getVariableValue(); 918 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) { 919 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF) 920 return false; 921 } 922 } 923 924 if (Used) 925 return true; 926 927 if (Renamed) 928 return false; 929 930 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_") 931 return true; 932 933 if (Symbol.isVariable()) { 934 const MCSymbol *Base = Layout.getBaseSymbol(Symbol); 935 if (Base && Base->isUndefined()) 936 return false; 937 } 938 939 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL; 940 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal) 941 return false; 942 943 if (Symbol.isTemporary()) 944 return false; 945 946 return true; 947 } 948 949 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) { 950 if (Data.isExternal()) 951 return false; 952 953 const MCSymbol &Symbol = Data.getSymbol(); 954 if (Symbol.isDefined()) 955 return true; 956 957 if (isUsedInReloc) 958 return false; 959 960 return true; 961 } 962 963 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm, 964 SectionIndexMapTy &SectionIndexMap, 965 const RelMapTy &RelMap) { 966 unsigned Index = 1; 967 for (MCAssembler::iterator it = Asm.begin(), 968 ie = Asm.end(); it != ie; ++it) { 969 const MCSectionELF &Section = 970 static_cast<const MCSectionELF &>(it->getSection()); 971 if (Section.getType() != ELF::SHT_GROUP) 972 continue; 973 SectionIndexMap[&Section] = Index++; 974 } 975 976 for (MCAssembler::iterator it = Asm.begin(), 977 ie = Asm.end(); it != ie; ++it) { 978 const MCSectionELF &Section = 979 static_cast<const MCSectionELF &>(it->getSection()); 980 if (Section.getType() == ELF::SHT_GROUP || 981 Section.getType() == ELF::SHT_REL || 982 Section.getType() == ELF::SHT_RELA) 983 continue; 984 SectionIndexMap[&Section] = Index++; 985 const MCSectionELF *RelSection = RelMap.lookup(&Section); 986 if (RelSection) 987 SectionIndexMap[RelSection] = Index++; 988 } 989 } 990 991 void 992 ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout, 993 const SectionIndexMapTy &SectionIndexMap, 994 RevGroupMapTy RevGroupMap, 995 unsigned NumRegularSections) { 996 // FIXME: Is this the correct place to do this? 997 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed? 998 if (NeedsGOT) { 999 StringRef Name = "_GLOBAL_OFFSET_TABLE_"; 1000 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name); 1001 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym); 1002 Data.setExternal(true); 1003 MCELF::SetBinding(Data, ELF::STB_GLOBAL); 1004 } 1005 1006 // Add the data for the symbols. 1007 for (MCSymbolData &SD : Asm.symbols()) { 1008 const MCSymbol &Symbol = SD.getSymbol(); 1009 1010 bool Used = UsedInReloc.count(&Symbol); 1011 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol); 1012 bool isSignature = RevGroupMap.count(&Symbol); 1013 1014 if (!isInSymtab(Layout, SD, 1015 Used || WeakrefUsed || isSignature, 1016 Renames.count(&Symbol))) 1017 continue; 1018 1019 ELFSymbolData MSD; 1020 MSD.SymbolData = &SD; 1021 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol); 1022 1023 // Undefined symbols are global, but this is the first place we 1024 // are able to set it. 1025 bool Local = isLocal(SD, Used); 1026 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) { 1027 assert(BaseSymbol); 1028 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol); 1029 MCELF::SetBinding(SD, ELF::STB_GLOBAL); 1030 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL); 1031 } 1032 1033 if (!BaseSymbol) { 1034 MSD.SectionIndex = ELF::SHN_ABS; 1035 } else if (SD.isCommon()) { 1036 assert(!Local); 1037 MSD.SectionIndex = ELF::SHN_COMMON; 1038 } else if (BaseSymbol->isUndefined()) { 1039 if (isSignature && !Used) 1040 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]); 1041 else 1042 MSD.SectionIndex = ELF::SHN_UNDEF; 1043 if (!Used && WeakrefUsed) 1044 MCELF::SetBinding(SD, ELF::STB_WEAK); 1045 } else { 1046 const MCSectionELF &Section = 1047 static_cast<const MCSectionELF&>(BaseSymbol->getSection()); 1048 MSD.SectionIndex = SectionIndexMap.lookup(&Section); 1049 assert(MSD.SectionIndex && "Invalid section index!"); 1050 } 1051 1052 // The @@@ in symbol version is replaced with @ in undefined symbols and 1053 // @@ in defined ones. 1054 StringRef Name = Symbol.getName(); 1055 SmallString<32> Buf; 1056 size_t Pos = Name.find("@@@"); 1057 if (Pos != StringRef::npos) { 1058 Buf += Name.substr(0, Pos); 1059 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1; 1060 Buf += Name.substr(Pos + Skip); 1061 Name = Buf; 1062 } 1063 MSD.Name = StrTabBuilder.add(Name); 1064 1065 if (MSD.SectionIndex == ELF::SHN_UNDEF) 1066 UndefinedSymbolData.push_back(MSD); 1067 else if (Local) 1068 LocalSymbolData.push_back(MSD); 1069 else 1070 ExternalSymbolData.push_back(MSD); 1071 } 1072 1073 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i) 1074 StrTabBuilder.add(*i); 1075 1076 StrTabBuilder.finalize(); 1077 1078 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i) 1079 FileSymbolData.push_back(StrTabBuilder.getOffset(*i)); 1080 1081 for (ELFSymbolData& MSD : LocalSymbolData) 1082 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name); 1083 for (ELFSymbolData& MSD : ExternalSymbolData) 1084 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name); 1085 for (ELFSymbolData& MSD : UndefinedSymbolData) 1086 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name); 1087 1088 // Symbols are required to be in lexicographic order. 1089 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end()); 1090 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end()); 1091 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end()); 1092 1093 // Set the symbol indices. Local symbols must come before all other 1094 // symbols with non-local bindings. 1095 unsigned Index = FileSymbolData.size() + 1; 1096 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) 1097 LocalSymbolData[i].SymbolData->setIndex(Index++); 1098 1099 Index += NumRegularSections; 1100 1101 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) 1102 ExternalSymbolData[i].SymbolData->setIndex(Index++); 1103 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) 1104 UndefinedSymbolData[i].SymbolData->setIndex(Index++); 1105 } 1106 1107 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm, 1108 MCAsmLayout &Layout, 1109 RelMapTy &RelMap) { 1110 for (MCAssembler::const_iterator it = Asm.begin(), 1111 ie = Asm.end(); it != ie; ++it) { 1112 const MCSectionData &SD = *it; 1113 if (Relocations[&SD].empty()) 1114 continue; 1115 1116 MCContext &Ctx = Asm.getContext(); 1117 const MCSectionELF &Section = 1118 static_cast<const MCSectionELF&>(SD.getSection()); 1119 1120 const StringRef SectionName = Section.getSectionName(); 1121 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel"; 1122 RelaSectionName += SectionName; 1123 1124 unsigned EntrySize; 1125 if (hasRelocationAddend()) 1126 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela); 1127 else 1128 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel); 1129 1130 unsigned Flags = 0; 1131 StringRef Group = ""; 1132 if (Section.getFlags() & ELF::SHF_GROUP) { 1133 Flags = ELF::SHF_GROUP; 1134 Group = Section.getGroup()->getName(); 1135 } 1136 1137 const MCSectionELF *RelaSection = 1138 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ? 1139 ELF::SHT_RELA : ELF::SHT_REL, Flags, 1140 SectionKind::getReadOnly(), 1141 EntrySize, Group); 1142 RelMap[&Section] = RelaSection; 1143 Asm.getOrCreateSectionData(*RelaSection); 1144 } 1145 } 1146 1147 static SmallVector<char, 128> 1148 getUncompressedData(MCAsmLayout &Layout, 1149 MCSectionData::FragmentListType &Fragments) { 1150 SmallVector<char, 128> UncompressedData; 1151 for (const MCFragment &F : Fragments) { 1152 const SmallVectorImpl<char> *Contents; 1153 switch (F.getKind()) { 1154 case MCFragment::FT_Data: 1155 Contents = &cast<MCDataFragment>(F).getContents(); 1156 break; 1157 case MCFragment::FT_Dwarf: 1158 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents(); 1159 break; 1160 case MCFragment::FT_DwarfFrame: 1161 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents(); 1162 break; 1163 default: 1164 llvm_unreachable( 1165 "Not expecting any other fragment types in a debug_* section"); 1166 } 1167 UncompressedData.append(Contents->begin(), Contents->end()); 1168 } 1169 return UncompressedData; 1170 } 1171 1172 // Include the debug info compression header: 1173 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section, 1174 // useful for consumers to preallocate a buffer to decompress into. 1175 static bool 1176 prependCompressionHeader(uint64_t Size, 1177 SmallVectorImpl<char> &CompressedContents) { 1178 static const StringRef Magic = "ZLIB"; 1179 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size()) 1180 return false; 1181 if (sys::IsLittleEndianHost) 1182 sys::swapByteOrder(Size); 1183 CompressedContents.insert(CompressedContents.begin(), 1184 Magic.size() + sizeof(Size), 0); 1185 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin()); 1186 std::copy(reinterpret_cast<char *>(&Size), 1187 reinterpret_cast<char *>(&Size + 1), 1188 CompressedContents.begin() + Magic.size()); 1189 return true; 1190 } 1191 1192 // Return a single fragment containing the compressed contents of the whole 1193 // section. Null if the section was not compressed for any reason. 1194 static std::unique_ptr<MCDataFragment> 1195 getCompressedFragment(MCAsmLayout &Layout, 1196 MCSectionData::FragmentListType &Fragments) { 1197 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment()); 1198 1199 // Gather the uncompressed data from all the fragments, recording the 1200 // alignment fragment, if seen, and any fixups. 1201 SmallVector<char, 128> UncompressedData = 1202 getUncompressedData(Layout, Fragments); 1203 1204 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents(); 1205 1206 zlib::Status Success = zlib::compress( 1207 StringRef(UncompressedData.data(), UncompressedData.size()), 1208 CompressedContents); 1209 if (Success != zlib::StatusOK) 1210 return nullptr; 1211 1212 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) 1213 return nullptr; 1214 1215 return CompressedFragment; 1216 } 1217 1218 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>> 1219 DefiningSymbolMap; 1220 1221 static void UpdateSymbols(const MCAsmLayout &Layout, 1222 const std::vector<MCSymbolData *> &Symbols, 1223 MCFragment &NewFragment) { 1224 for (MCSymbolData *Sym : Symbols) { 1225 Sym->setOffset(Sym->getOffset() + 1226 Layout.getFragmentOffset(Sym->getFragment())); 1227 Sym->setFragment(&NewFragment); 1228 } 1229 } 1230 1231 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout, 1232 const DefiningSymbolMap &DefiningSymbols, 1233 const MCSectionELF &Section, 1234 MCSectionData &SD) { 1235 StringRef SectionName = Section.getSectionName(); 1236 MCSectionData::FragmentListType &Fragments = SD.getFragmentList(); 1237 1238 std::unique_ptr<MCDataFragment> CompressedFragment = 1239 getCompressedFragment(Layout, Fragments); 1240 1241 // Leave the section as-is if the fragments could not be compressed. 1242 if (!CompressedFragment) 1243 return; 1244 1245 // Update the fragment+offsets of any symbols referring to fragments in this 1246 // section to refer to the new fragment. 1247 auto I = DefiningSymbols.find(&SD); 1248 if (I != DefiningSymbols.end()) 1249 UpdateSymbols(Layout, I->second, *CompressedFragment); 1250 1251 // Invalidate the layout for the whole section since it will have new and 1252 // different fragments now. 1253 Layout.invalidateFragmentsFrom(&Fragments.front()); 1254 Fragments.clear(); 1255 1256 // Complete the initialization of the new fragment 1257 CompressedFragment->setParent(&SD); 1258 CompressedFragment->setLayoutOrder(0); 1259 Fragments.push_back(CompressedFragment.release()); 1260 1261 // Rename from .debug_* to .zdebug_* 1262 Asm.getContext().renameELFSection(&Section, 1263 (".z" + SectionName.drop_front(1)).str()); 1264 } 1265 1266 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm, 1267 MCAsmLayout &Layout) { 1268 if (!Asm.getContext().getAsmInfo()->compressDebugSections()) 1269 return; 1270 1271 DefiningSymbolMap DefiningSymbols; 1272 1273 for (MCSymbolData &SD : Asm.symbols()) 1274 if (MCFragment *F = SD.getFragment()) 1275 DefiningSymbols[F->getParent()].push_back(&SD); 1276 1277 for (MCSectionData &SD : Asm) { 1278 const MCSectionELF &Section = 1279 static_cast<const MCSectionELF &>(SD.getSection()); 1280 StringRef SectionName = Section.getSectionName(); 1281 1282 // Compressing debug_frame requires handling alignment fragments which is 1283 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow 1284 // for writing to arbitrary buffers) for little benefit. 1285 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame") 1286 continue; 1287 1288 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD); 1289 } 1290 } 1291 1292 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 1293 const RelMapTy &RelMap) { 1294 for (MCAssembler::const_iterator it = Asm.begin(), 1295 ie = Asm.end(); it != ie; ++it) { 1296 const MCSectionData &SD = *it; 1297 const MCSectionELF &Section = 1298 static_cast<const MCSectionELF&>(SD.getSection()); 1299 1300 const MCSectionELF *RelaSection = RelMap.lookup(&Section); 1301 if (!RelaSection) 1302 continue; 1303 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection); 1304 RelaSD.setAlignment(is64Bit() ? 8 : 4); 1305 1306 MCDataFragment *F = new MCDataFragment(&RelaSD); 1307 WriteRelocationsFragment(Asm, F, &*it); 1308 } 1309 } 1310 1311 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type, 1312 uint64_t Flags, uint64_t Address, 1313 uint64_t Offset, uint64_t Size, 1314 uint32_t Link, uint32_t Info, 1315 uint64_t Alignment, 1316 uint64_t EntrySize) { 1317 Write32(Name); // sh_name: index into string table 1318 Write32(Type); // sh_type 1319 WriteWord(Flags); // sh_flags 1320 WriteWord(Address); // sh_addr 1321 WriteWord(Offset); // sh_offset 1322 WriteWord(Size); // sh_size 1323 Write32(Link); // sh_link 1324 Write32(Info); // sh_info 1325 WriteWord(Alignment); // sh_addralign 1326 WriteWord(EntrySize); // sh_entsize 1327 } 1328 1329 // ELF doesn't require relocations to be in any order. We sort by the r_offset, 1330 // just to match gnu as for easier comparison. The use type is an arbitrary way 1331 // of making the sort deterministic. 1332 static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) { 1333 const ELFRelocationEntry &A = *AP; 1334 const ELFRelocationEntry &B = *BP; 1335 if (A.Offset != B.Offset) 1336 return B.Offset - A.Offset; 1337 if (B.Type != A.Type) 1338 return A.Type - B.Type; 1339 llvm_unreachable("ELFRelocs might be unstable!"); 1340 } 1341 1342 static void sortRelocs(const MCAssembler &Asm, 1343 std::vector<ELFRelocationEntry> &Relocs) { 1344 array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel); 1345 } 1346 1347 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm, 1348 MCDataFragment *F, 1349 const MCSectionData *SD) { 1350 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD]; 1351 1352 sortRelocs(Asm, Relocs); 1353 1354 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) { 1355 const ELFRelocationEntry &Entry = Relocs[e - i - 1]; 1356 1357 unsigned Index; 1358 if (Entry.UseSymbol) { 1359 Index = getSymbolIndexInSymbolTable(Asm, Entry.Symbol); 1360 } else { 1361 const MCSectionData *Sec = Entry.Section; 1362 if (Sec) 1363 Index = Sec->getOrdinal() + FileSymbolData.size() + 1364 LocalSymbolData.size() + 1; 1365 else 1366 Index = 0; 1367 } 1368 1369 if (is64Bit()) { 1370 write(*F, Entry.Offset); 1371 if (TargetObjectWriter->isN64()) { 1372 write(*F, uint32_t(Index)); 1373 1374 write(*F, TargetObjectWriter->getRSsym(Entry.Type)); 1375 write(*F, TargetObjectWriter->getRType3(Entry.Type)); 1376 write(*F, TargetObjectWriter->getRType2(Entry.Type)); 1377 write(*F, TargetObjectWriter->getRType(Entry.Type)); 1378 } else { 1379 struct ELF::Elf64_Rela ERE64; 1380 ERE64.setSymbolAndType(Index, Entry.Type); 1381 write(*F, ERE64.r_info); 1382 } 1383 if (hasRelocationAddend()) 1384 write(*F, Entry.Addend); 1385 } else { 1386 write(*F, uint32_t(Entry.Offset)); 1387 1388 struct ELF::Elf32_Rela ERE32; 1389 ERE32.setSymbolAndType(Index, Entry.Type); 1390 write(*F, ERE32.r_info); 1391 1392 if (hasRelocationAddend()) 1393 write(*F, uint32_t(Entry.Addend)); 1394 } 1395 } 1396 } 1397 1398 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm, 1399 MCAsmLayout &Layout, 1400 SectionIndexMapTy &SectionIndexMap, 1401 const RelMapTy &RelMap) { 1402 MCContext &Ctx = Asm.getContext(); 1403 MCDataFragment *F; 1404 1405 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32; 1406 1407 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as. 1408 const MCSectionELF *ShstrtabSection = 1409 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0, 1410 SectionKind::getReadOnly()); 1411 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection); 1412 ShstrtabSD.setAlignment(1); 1413 1414 const MCSectionELF *SymtabSection = 1415 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, 1416 SectionKind::getReadOnly(), 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 SectionKind::getReadOnly()); 1424 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection); 1425 StrtabSD.setAlignment(1); 1426 1427 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1428 1429 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection); 1430 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection); 1431 StringTableIndex = SectionIndexMap.lookup(StrtabSection); 1432 1433 // Symbol table 1434 F = new MCDataFragment(&SymtabSD); 1435 WriteSymbolTable(F, Asm, Layout, SectionIndexMap); 1436 1437 F = new MCDataFragment(&StrtabSD); 1438 F->getContents().append(StrTabBuilder.data().begin(), 1439 StrTabBuilder.data().end()); 1440 1441 F = new MCDataFragment(&ShstrtabSD); 1442 1443 // Section header string table. 1444 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { 1445 const MCSectionELF &Section = 1446 static_cast<const MCSectionELF&>(it->getSection()); 1447 ShStrTabBuilder.add(Section.getSectionName()); 1448 } 1449 ShStrTabBuilder.finalize(); 1450 F->getContents().append(ShStrTabBuilder.data().begin(), 1451 ShStrTabBuilder.data().end()); 1452 } 1453 1454 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm, 1455 MCAsmLayout &Layout, 1456 GroupMapTy &GroupMap, 1457 RevGroupMapTy &RevGroupMap, 1458 SectionIndexMapTy &SectionIndexMap, 1459 const RelMapTy &RelMap) { 1460 // Create the .note.GNU-stack section if needed. 1461 MCContext &Ctx = Asm.getContext(); 1462 if (Asm.getNoExecStack()) { 1463 const MCSectionELF *GnuStackSection = 1464 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0, 1465 SectionKind::getReadOnly()); 1466 Asm.getOrCreateSectionData(*GnuStackSection); 1467 } 1468 1469 // Build the groups 1470 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1471 it != ie; ++it) { 1472 const MCSectionELF &Section = 1473 static_cast<const MCSectionELF&>(it->getSection()); 1474 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1475 continue; 1476 1477 const MCSymbol *SignatureSymbol = Section.getGroup(); 1478 Asm.getOrCreateSymbolData(*SignatureSymbol); 1479 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol]; 1480 if (!Group) { 1481 Group = Ctx.CreateELFGroupSection(); 1482 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1483 Data.setAlignment(4); 1484 MCDataFragment *F = new MCDataFragment(&Data); 1485 write(*F, uint32_t(ELF::GRP_COMDAT)); 1486 } 1487 GroupMap[Group] = SignatureSymbol; 1488 } 1489 1490 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1491 1492 // Add sections to the groups 1493 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1494 it != ie; ++it) { 1495 const MCSectionELF &Section = 1496 static_cast<const MCSectionELF&>(it->getSection()); 1497 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1498 continue; 1499 const MCSectionELF *Group = RevGroupMap[Section.getGroup()]; 1500 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1501 // FIXME: we could use the previous fragment 1502 MCDataFragment *F = new MCDataFragment(&Data); 1503 uint32_t Index = SectionIndexMap.lookup(&Section); 1504 write(*F, Index); 1505 } 1506 } 1507 1508 void ELFObjectWriter::WriteSection(MCAssembler &Asm, 1509 const SectionIndexMapTy &SectionIndexMap, 1510 uint32_t GroupSymbolIndex, 1511 uint64_t Offset, uint64_t Size, 1512 uint64_t Alignment, 1513 const MCSectionELF &Section) { 1514 uint64_t sh_link = 0; 1515 uint64_t sh_info = 0; 1516 1517 switch(Section.getType()) { 1518 case ELF::SHT_DYNAMIC: 1519 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName()); 1520 sh_info = 0; 1521 break; 1522 1523 case ELF::SHT_REL: 1524 case ELF::SHT_RELA: { 1525 const MCSectionELF *SymtabSection; 1526 const MCSectionELF *InfoSection; 1527 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 1528 0, 1529 SectionKind::getReadOnly()); 1530 sh_link = SectionIndexMap.lookup(SymtabSection); 1531 assert(sh_link && ".symtab not found"); 1532 1533 // Remove ".rel" and ".rela" prefixes. 1534 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5; 1535 StringRef SectionName = Section.getSectionName().substr(SecNameLen); 1536 StringRef GroupName = 1537 Section.getGroup() ? Section.getGroup()->getName() : ""; 1538 1539 InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS, 1540 0, SectionKind::getReadOnly(), 1541 0, GroupName); 1542 sh_info = SectionIndexMap.lookup(InfoSection); 1543 break; 1544 } 1545 1546 case ELF::SHT_SYMTAB: 1547 case ELF::SHT_DYNSYM: 1548 sh_link = StringTableIndex; 1549 sh_info = LastLocalSymbolIndex; 1550 break; 1551 1552 case ELF::SHT_SYMTAB_SHNDX: 1553 sh_link = SymbolTableIndex; 1554 break; 1555 1556 case ELF::SHT_PROGBITS: 1557 case ELF::SHT_STRTAB: 1558 case ELF::SHT_NOBITS: 1559 case ELF::SHT_NOTE: 1560 case ELF::SHT_NULL: 1561 case ELF::SHT_ARM_ATTRIBUTES: 1562 case ELF::SHT_INIT_ARRAY: 1563 case ELF::SHT_FINI_ARRAY: 1564 case ELF::SHT_PREINIT_ARRAY: 1565 case ELF::SHT_X86_64_UNWIND: 1566 case ELF::SHT_MIPS_REGINFO: 1567 case ELF::SHT_MIPS_OPTIONS: 1568 case ELF::SHT_MIPS_ABIFLAGS: 1569 // Nothing to do. 1570 break; 1571 1572 case ELF::SHT_GROUP: 1573 sh_link = SymbolTableIndex; 1574 sh_info = GroupSymbolIndex; 1575 break; 1576 1577 default: 1578 llvm_unreachable("FIXME: sh_type value not supported!"); 1579 } 1580 1581 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM && 1582 Section.getType() == ELF::SHT_ARM_EXIDX) { 1583 StringRef SecName(Section.getSectionName()); 1584 if (SecName == ".ARM.exidx") { 1585 sh_link = SectionIndexMap.lookup( 1586 Asm.getContext().getELFSection(".text", 1587 ELF::SHT_PROGBITS, 1588 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, 1589 SectionKind::getText())); 1590 } else if (SecName.startswith(".ARM.exidx")) { 1591 StringRef GroupName = 1592 Section.getGroup() ? Section.getGroup()->getName() : ""; 1593 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection( 1594 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS, 1595 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText(), 0, 1596 GroupName)); 1597 } 1598 } 1599 1600 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()), 1601 Section.getType(), 1602 Section.getFlags(), 0, Offset, Size, sh_link, sh_info, 1603 Alignment, Section.getEntrySize()); 1604 } 1605 1606 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) { 1607 return SD.getOrdinal() == ~UINT32_C(0) && 1608 !SD.getSection().isVirtualSection(); 1609 } 1610 1611 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) { 1612 uint64_t Ret = 0; 1613 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1614 ++i) { 1615 const MCFragment &F = *i; 1616 assert(F.getKind() == MCFragment::FT_Data); 1617 Ret += cast<MCDataFragment>(F).getContents().size(); 1618 } 1619 return Ret; 1620 } 1621 1622 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout, 1623 const MCSectionData &SD) { 1624 if (IsELFMetaDataSection(SD)) 1625 return DataSectionSize(SD); 1626 return Layout.getSectionFileSize(&SD); 1627 } 1628 1629 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout, 1630 const MCSectionData &SD) { 1631 if (IsELFMetaDataSection(SD)) 1632 return DataSectionSize(SD); 1633 return Layout.getSectionAddressSize(&SD); 1634 } 1635 1636 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm, 1637 const MCAsmLayout &Layout, 1638 const MCSectionELF &Section) { 1639 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1640 1641 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment()); 1642 WriteZeros(Padding); 1643 1644 if (IsELFMetaDataSection(SD)) { 1645 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1646 ++i) { 1647 const MCFragment &F = *i; 1648 assert(F.getKind() == MCFragment::FT_Data); 1649 WriteBytes(cast<MCDataFragment>(F).getContents()); 1650 } 1651 } else { 1652 Asm.writeSectionData(&SD, Layout); 1653 } 1654 } 1655 1656 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm, 1657 const GroupMapTy &GroupMap, 1658 const MCAsmLayout &Layout, 1659 const SectionIndexMapTy &SectionIndexMap, 1660 const SectionOffsetMapTy &SectionOffsetMap) { 1661 const unsigned NumSections = Asm.size() + 1; 1662 1663 std::vector<const MCSectionELF*> Sections; 1664 Sections.resize(NumSections - 1); 1665 1666 for (SectionIndexMapTy::const_iterator i= 1667 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) { 1668 const std::pair<const MCSectionELF*, uint32_t> &p = *i; 1669 Sections[p.second - 1] = p.first; 1670 } 1671 1672 // Null section first. 1673 uint64_t FirstSectionSize = 1674 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0; 1675 uint32_t FirstSectionLink = 1676 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0; 1677 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0); 1678 1679 for (unsigned i = 0; i < NumSections - 1; ++i) { 1680 const MCSectionELF &Section = *Sections[i]; 1681 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1682 uint32_t GroupSymbolIndex; 1683 if (Section.getType() != ELF::SHT_GROUP) 1684 GroupSymbolIndex = 0; 1685 else 1686 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, 1687 GroupMap.lookup(&Section)); 1688 1689 uint64_t Size = GetSectionAddressSize(Layout, SD); 1690 1691 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex, 1692 SectionOffsetMap.lookup(&Section), Size, 1693 SD.getAlignment(), Section); 1694 } 1695 } 1696 1697 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm, 1698 std::vector<const MCSectionELF*> &Sections) { 1699 for (MCAssembler::iterator it = Asm.begin(), 1700 ie = Asm.end(); it != ie; ++it) { 1701 const MCSectionELF &Section = 1702 static_cast<const MCSectionELF &>(it->getSection()); 1703 if (Section.getType() == ELF::SHT_GROUP) 1704 Sections.push_back(&Section); 1705 } 1706 1707 for (MCAssembler::iterator it = Asm.begin(), 1708 ie = Asm.end(); it != ie; ++it) { 1709 const MCSectionELF &Section = 1710 static_cast<const MCSectionELF &>(it->getSection()); 1711 if (Section.getType() != ELF::SHT_GROUP && 1712 Section.getType() != ELF::SHT_REL && 1713 Section.getType() != ELF::SHT_RELA) 1714 Sections.push_back(&Section); 1715 } 1716 1717 for (MCAssembler::iterator it = Asm.begin(), 1718 ie = Asm.end(); it != ie; ++it) { 1719 const MCSectionELF &Section = 1720 static_cast<const MCSectionELF &>(it->getSection()); 1721 if (Section.getType() == ELF::SHT_REL || 1722 Section.getType() == ELF::SHT_RELA) 1723 Sections.push_back(&Section); 1724 } 1725 } 1726 1727 void ELFObjectWriter::WriteObject(MCAssembler &Asm, 1728 const MCAsmLayout &Layout) { 1729 GroupMapTy GroupMap; 1730 RevGroupMapTy RevGroupMap; 1731 SectionIndexMapTy SectionIndexMap; 1732 1733 unsigned NumUserSections = Asm.size(); 1734 1735 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout)); 1736 1737 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap; 1738 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1739 1740 const unsigned NumUserAndRelocSections = Asm.size(); 1741 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap, 1742 RevGroupMap, SectionIndexMap, RelMap); 1743 const unsigned AllSections = Asm.size(); 1744 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections; 1745 1746 unsigned NumRegularSections = NumUserSections + NumIndexedSections; 1747 1748 // Compute symbol table information. 1749 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, 1750 NumRegularSections); 1751 1752 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1753 1754 CreateMetadataSections(const_cast<MCAssembler&>(Asm), 1755 const_cast<MCAsmLayout&>(Layout), 1756 SectionIndexMap, 1757 RelMap); 1758 1759 uint64_t NaturalAlignment = is64Bit() ? 8 : 4; 1760 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 1761 sizeof(ELF::Elf32_Ehdr); 1762 uint64_t FileOff = HeaderSize; 1763 1764 std::vector<const MCSectionELF*> Sections; 1765 ComputeSectionOrder(Asm, Sections); 1766 unsigned NumSections = Sections.size(); 1767 SectionOffsetMapTy SectionOffsetMap; 1768 for (unsigned i = 0; i < NumRegularSections + 1; ++i) { 1769 const MCSectionELF &Section = *Sections[i]; 1770 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1771 1772 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1773 1774 // Remember the offset into the file for this section. 1775 SectionOffsetMap[&Section] = FileOff; 1776 1777 // Get the size of the section in the output file (including padding). 1778 FileOff += GetSectionFileSize(Layout, SD); 1779 } 1780 1781 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment); 1782 1783 const unsigned SectionHeaderOffset = FileOff - HeaderSize; 1784 1785 uint64_t SectionHeaderEntrySize = is64Bit() ? 1786 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr); 1787 FileOff += (NumSections + 1) * SectionHeaderEntrySize; 1788 1789 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) { 1790 const MCSectionELF &Section = *Sections[i]; 1791 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1792 1793 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1794 1795 // Remember the offset into the file for this section. 1796 SectionOffsetMap[&Section] = FileOff; 1797 1798 // Get the size of the section in the output file (including padding). 1799 FileOff += GetSectionFileSize(Layout, SD); 1800 } 1801 1802 // Write out the ELF header ... 1803 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1); 1804 1805 // ... then the regular sections ... 1806 // + because of .shstrtab 1807 for (unsigned i = 0; i < NumRegularSections + 1; ++i) 1808 WriteDataSectionData(Asm, Layout, *Sections[i]); 1809 1810 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment); 1811 WriteZeros(Padding); 1812 1813 // ... then the section header table ... 1814 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap, 1815 SectionOffsetMap); 1816 1817 // ... and then the remaining sections ... 1818 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) 1819 WriteDataSectionData(Asm, Layout, *Sections[i]); 1820 } 1821 1822 bool 1823 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 1824 const MCSymbolData &DataA, 1825 const MCFragment &FB, 1826 bool InSet, 1827 bool IsPCRel) const { 1828 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC) 1829 return false; 1830 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl( 1831 Asm, DataA, FB,InSet, IsPCRel); 1832 } 1833 1834 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW, 1835 raw_ostream &OS, 1836 bool IsLittleEndian) { 1837 return new ELFObjectWriter(MOTW, OS, IsLittleEndian); 1838 } 1839
