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