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 RelMapTy &RelMap); 253 254 MCSectionData *createRelocationSection(MCAssembler &Asm, 255 const MCSectionData &SD); 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); 264 265 // Create the sections that show up in the symbol table. Currently 266 // those are the .note.GNU-stack section and the group sections. 267 void createIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout, 268 GroupMapTy &GroupMap, 269 RevGroupMapTy &RevGroupMap, 270 SectionIndexMapTy &SectionIndexMap, 271 RelMapTy &RelMap); 272 273 void ExecutePostLayoutBinding(MCAssembler &Asm, 274 const MCAsmLayout &Layout) override; 275 276 void writeSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap, 277 const MCAsmLayout &Layout, 278 const SectionIndexMapTy &SectionIndexMap, 279 const RelMapTy &RelMap, 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 const RelMapTy &RelMap, 305 uint32_t GroupSymbolIndex, 306 uint64_t Offset, uint64_t Size, uint64_t Alignment, 307 const MCSectionELF &Section); 308 }; 309 } 310 311 FragmentWriter::FragmentWriter(bool IsLittleEndian) 312 : IsLittleEndian(IsLittleEndian) {} 313 314 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) { 315 if (IsLittleEndian) 316 Val = support::endian::byte_swap<T, support::little>(Val); 317 else 318 Val = support::endian::byte_swap<T, support::big>(Val); 319 const char *Start = (const char *)&Val; 320 F.getContents().append(Start, Start + sizeof(T)); 321 } 322 323 void SymbolTableWriter::createSymtabShndx() { 324 if (ShndxF) 325 return; 326 327 MCContext &Ctx = Asm.getContext(); 328 const MCSectionELF *SymtabShndxSection = 329 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 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 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 MCSectionData &SD = *it; 963 const MCSectionELF &Section = 964 static_cast<const MCSectionELF &>(SD.getSection()); 965 if (Section.getType() == ELF::SHT_GROUP || 966 Section.getType() == ELF::SHT_REL || 967 Section.getType() == ELF::SHT_RELA) 968 continue; 969 SectionIndexMap[&Section] = Index++; 970 if (MCSectionData *RelSD = createRelocationSection(Asm, SD)) { 971 const MCSectionELF *RelSection = 972 static_cast<const MCSectionELF *>(&RelSD->getSection()); 973 RelMap[RelSection] = &Section; 974 SectionIndexMap[RelSection] = Index++; 975 } 976 } 977 } 978 979 void 980 ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout, 981 const SectionIndexMapTy &SectionIndexMap, 982 const RevGroupMapTy &RevGroupMap, 983 unsigned NumRegularSections) { 984 // FIXME: Is this the correct place to do this? 985 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed? 986 if (NeedsGOT) { 987 StringRef Name = "_GLOBAL_OFFSET_TABLE_"; 988 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name); 989 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym); 990 Data.setExternal(true); 991 MCELF::SetBinding(Data, ELF::STB_GLOBAL); 992 } 993 994 // Add the data for the symbols. 995 for (MCSymbolData &SD : Asm.symbols()) { 996 const MCSymbol &Symbol = SD.getSymbol(); 997 998 bool Used = UsedInReloc.count(&Symbol); 999 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol); 1000 bool isSignature = RevGroupMap.count(&Symbol); 1001 1002 if (!isInSymtab(Layout, SD, 1003 Used || WeakrefUsed || isSignature, 1004 Renames.count(&Symbol))) 1005 continue; 1006 1007 ELFSymbolData MSD; 1008 MSD.SymbolData = &SD; 1009 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol); 1010 1011 // Undefined symbols are global, but this is the first place we 1012 // are able to set it. 1013 bool Local = isLocal(SD, Used); 1014 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) { 1015 assert(BaseSymbol); 1016 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol); 1017 MCELF::SetBinding(SD, ELF::STB_GLOBAL); 1018 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL); 1019 } 1020 1021 if (!BaseSymbol) { 1022 MSD.SectionIndex = ELF::SHN_ABS; 1023 } else if (SD.isCommon()) { 1024 assert(!Local); 1025 MSD.SectionIndex = ELF::SHN_COMMON; 1026 } else if (BaseSymbol->isUndefined()) { 1027 if (isSignature && !Used) 1028 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap.lookup(&Symbol)); 1029 else 1030 MSD.SectionIndex = ELF::SHN_UNDEF; 1031 if (!Used && WeakrefUsed) 1032 MCELF::SetBinding(SD, ELF::STB_WEAK); 1033 } else { 1034 const MCSectionELF &Section = 1035 static_cast<const MCSectionELF&>(BaseSymbol->getSection()); 1036 MSD.SectionIndex = SectionIndexMap.lookup(&Section); 1037 assert(MSD.SectionIndex && "Invalid section index!"); 1038 } 1039 1040 // The @@@ in symbol version is replaced with @ in undefined symbols and @@ 1041 // in defined ones. 1042 // 1043 // FIXME: All name handling should be done before we get to the writer, 1044 // including dealing with GNU-style version suffixes. Fixing this isn't 1045 // trivial. 1046 // 1047 // We thus have to be careful to not perform the symbol version replacement 1048 // blindly: 1049 // 1050 // The ELF format is used on Windows by the MCJIT engine. Thus, on 1051 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS 1052 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC 1053 // C++ name mangling can legally have "@@@" as a sub-string. In that case, 1054 // the EFLObjectWriter should not interpret the "@@@" sub-string as 1055 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore 1056 // checks for the MSVC C++ name mangling prefix which is either "?", "@?", 1057 // "__imp_?" or "__imp_@?". 1058 // 1059 // It would have been interesting to perform the MS mangling prefix check 1060 // only when the target triple is of the form *-pc-windows-elf. But, it 1061 // seems that this information is not easily accessible from the 1062 // ELFObjectWriter. 1063 StringRef Name = Symbol.getName(); 1064 if (!Name.startswith("?") && !Name.startswith("@?") && 1065 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) { 1066 // This symbol isn't following the MSVC C++ name mangling convention. We 1067 // can thus safely interpret the @@@ in symbol names as specifying symbol 1068 // versioning. 1069 SmallString<32> Buf; 1070 size_t Pos = Name.find("@@@"); 1071 if (Pos != StringRef::npos) { 1072 Buf += Name.substr(0, Pos); 1073 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1; 1074 Buf += Name.substr(Pos + Skip); 1075 Name = Buf; 1076 } 1077 } 1078 1079 // Sections have their own string table 1080 if (MCELF::GetType(SD) != ELF::STT_SECTION) 1081 MSD.Name = StrTabBuilder.add(Name); 1082 1083 if (MSD.SectionIndex == ELF::SHN_UNDEF) 1084 UndefinedSymbolData.push_back(MSD); 1085 else if (Local) 1086 LocalSymbolData.push_back(MSD); 1087 else 1088 ExternalSymbolData.push_back(MSD); 1089 } 1090 1091 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i) 1092 StrTabBuilder.add(*i); 1093 1094 StrTabBuilder.finalize(StringTableBuilder::ELF); 1095 1096 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i) 1097 FileSymbolData.push_back(StrTabBuilder.getOffset(*i)); 1098 1099 for (ELFSymbolData &MSD : LocalSymbolData) 1100 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION 1101 ? 0 1102 : StrTabBuilder.getOffset(MSD.Name); 1103 for (ELFSymbolData &MSD : ExternalSymbolData) 1104 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name); 1105 for (ELFSymbolData& MSD : UndefinedSymbolData) 1106 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name); 1107 1108 // Symbols are required to be in lexicographic order. 1109 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end()); 1110 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end()); 1111 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end()); 1112 1113 // Set the symbol indices. Local symbols must come before all other 1114 // symbols with non-local bindings. 1115 unsigned Index = FileSymbolData.size() + 1; 1116 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) 1117 LocalSymbolData[i].SymbolData->setIndex(Index++); 1118 1119 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) 1120 ExternalSymbolData[i].SymbolData->setIndex(Index++); 1121 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) 1122 UndefinedSymbolData[i].SymbolData->setIndex(Index++); 1123 } 1124 1125 MCSectionData * 1126 ELFObjectWriter::createRelocationSection(MCAssembler &Asm, 1127 const MCSectionData &SD) { 1128 if (Relocations[&SD].empty()) 1129 return nullptr; 1130 1131 MCContext &Ctx = Asm.getContext(); 1132 const MCSectionELF &Section = 1133 static_cast<const MCSectionELF &>(SD.getSection()); 1134 1135 const StringRef SectionName = Section.getSectionName(); 1136 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel"; 1137 RelaSectionName += SectionName; 1138 1139 unsigned EntrySize; 1140 if (hasRelocationAddend()) 1141 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela); 1142 else 1143 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel); 1144 1145 unsigned Flags = 0; 1146 StringRef Group = ""; 1147 if (Section.getFlags() & ELF::SHF_GROUP) { 1148 Flags = ELF::SHF_GROUP; 1149 Group = Section.getGroup()->getName(); 1150 } 1151 1152 const MCSectionELF *RelaSection = Ctx.getELFSection( 1153 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL, 1154 Flags, EntrySize, Group, true); 1155 return &Asm.getOrCreateSectionData(*RelaSection); 1156 } 1157 1158 static SmallVector<char, 128> 1159 getUncompressedData(MCAsmLayout &Layout, 1160 MCSectionData::FragmentListType &Fragments) { 1161 SmallVector<char, 128> UncompressedData; 1162 for (const MCFragment &F : Fragments) { 1163 const SmallVectorImpl<char> *Contents; 1164 switch (F.getKind()) { 1165 case MCFragment::FT_Data: 1166 Contents = &cast<MCDataFragment>(F).getContents(); 1167 break; 1168 case MCFragment::FT_Dwarf: 1169 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents(); 1170 break; 1171 case MCFragment::FT_DwarfFrame: 1172 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents(); 1173 break; 1174 default: 1175 llvm_unreachable( 1176 "Not expecting any other fragment types in a debug_* section"); 1177 } 1178 UncompressedData.append(Contents->begin(), Contents->end()); 1179 } 1180 return UncompressedData; 1181 } 1182 1183 // Include the debug info compression header: 1184 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section, 1185 // useful for consumers to preallocate a buffer to decompress into. 1186 static bool 1187 prependCompressionHeader(uint64_t Size, 1188 SmallVectorImpl<char> &CompressedContents) { 1189 const StringRef Magic = "ZLIB"; 1190 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size()) 1191 return false; 1192 if (sys::IsLittleEndianHost) 1193 sys::swapByteOrder(Size); 1194 CompressedContents.insert(CompressedContents.begin(), 1195 Magic.size() + sizeof(Size), 0); 1196 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin()); 1197 std::copy(reinterpret_cast<char *>(&Size), 1198 reinterpret_cast<char *>(&Size + 1), 1199 CompressedContents.begin() + Magic.size()); 1200 return true; 1201 } 1202 1203 // Return a single fragment containing the compressed contents of the whole 1204 // section. Null if the section was not compressed for any reason. 1205 static std::unique_ptr<MCDataFragment> 1206 getCompressedFragment(MCAsmLayout &Layout, 1207 MCSectionData::FragmentListType &Fragments) { 1208 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment()); 1209 1210 // Gather the uncompressed data from all the fragments, recording the 1211 // alignment fragment, if seen, and any fixups. 1212 SmallVector<char, 128> UncompressedData = 1213 getUncompressedData(Layout, Fragments); 1214 1215 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents(); 1216 1217 zlib::Status Success = zlib::compress( 1218 StringRef(UncompressedData.data(), UncompressedData.size()), 1219 CompressedContents); 1220 if (Success != zlib::StatusOK) 1221 return nullptr; 1222 1223 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) 1224 return nullptr; 1225 1226 return CompressedFragment; 1227 } 1228 1229 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>> 1230 DefiningSymbolMap; 1231 1232 static void UpdateSymbols(const MCAsmLayout &Layout, 1233 const std::vector<MCSymbolData *> &Symbols, 1234 MCFragment &NewFragment) { 1235 for (MCSymbolData *Sym : Symbols) { 1236 Sym->setOffset(Sym->getOffset() + 1237 Layout.getFragmentOffset(Sym->getFragment())); 1238 Sym->setFragment(&NewFragment); 1239 } 1240 } 1241 1242 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout, 1243 const DefiningSymbolMap &DefiningSymbols, 1244 const MCSectionELF &Section, 1245 MCSectionData &SD) { 1246 StringRef SectionName = Section.getSectionName(); 1247 MCSectionData::FragmentListType &Fragments = SD.getFragmentList(); 1248 1249 std::unique_ptr<MCDataFragment> CompressedFragment = 1250 getCompressedFragment(Layout, Fragments); 1251 1252 // Leave the section as-is if the fragments could not be compressed. 1253 if (!CompressedFragment) 1254 return; 1255 1256 // Update the fragment+offsets of any symbols referring to fragments in this 1257 // section to refer to the new fragment. 1258 auto I = DefiningSymbols.find(&SD); 1259 if (I != DefiningSymbols.end()) 1260 UpdateSymbols(Layout, I->second, *CompressedFragment); 1261 1262 // Invalidate the layout for the whole section since it will have new and 1263 // different fragments now. 1264 Layout.invalidateFragmentsFrom(&Fragments.front()); 1265 Fragments.clear(); 1266 1267 // Complete the initialization of the new fragment 1268 CompressedFragment->setParent(&SD); 1269 CompressedFragment->setLayoutOrder(0); 1270 Fragments.push_back(CompressedFragment.release()); 1271 1272 // Rename from .debug_* to .zdebug_* 1273 Asm.getContext().renameELFSection(&Section, 1274 (".z" + SectionName.drop_front(1)).str()); 1275 } 1276 1277 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm, 1278 MCAsmLayout &Layout) { 1279 if (!Asm.getContext().getAsmInfo()->compressDebugSections()) 1280 return; 1281 1282 DefiningSymbolMap DefiningSymbols; 1283 1284 for (MCSymbolData &SD : Asm.symbols()) 1285 if (MCFragment *F = SD.getFragment()) 1286 DefiningSymbols[F->getParent()].push_back(&SD); 1287 1288 for (MCSectionData &SD : Asm) { 1289 const MCSectionELF &Section = 1290 static_cast<const MCSectionELF &>(SD.getSection()); 1291 StringRef SectionName = Section.getSectionName(); 1292 1293 // Compressing debug_frame requires handling alignment fragments which is 1294 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow 1295 // for writing to arbitrary buffers) for little benefit. 1296 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame") 1297 continue; 1298 1299 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD); 1300 } 1301 } 1302 1303 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 1304 const RelMapTy &RelMap) { 1305 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { 1306 MCSectionData &RelSD = *it; 1307 const MCSectionELF &RelSection = 1308 static_cast<const MCSectionELF &>(RelSD.getSection()); 1309 1310 unsigned Type = RelSection.getType(); 1311 if (Type != ELF::SHT_REL && Type != ELF::SHT_RELA) 1312 continue; 1313 1314 const MCSectionELF *Section = RelMap.lookup(&RelSection); 1315 MCSectionData &SD = Asm.getOrCreateSectionData(*Section); 1316 RelSD.setAlignment(is64Bit() ? 8 : 4); 1317 1318 MCDataFragment *F = new MCDataFragment(&RelSD); 1319 WriteRelocationsFragment(Asm, F, &SD); 1320 } 1321 } 1322 1323 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type, 1324 uint64_t Flags, uint64_t Address, 1325 uint64_t Offset, uint64_t Size, 1326 uint32_t Link, uint32_t Info, 1327 uint64_t Alignment, 1328 uint64_t EntrySize) { 1329 Write32(Name); // sh_name: index into string table 1330 Write32(Type); // sh_type 1331 WriteWord(Flags); // sh_flags 1332 WriteWord(Address); // sh_addr 1333 WriteWord(Offset); // sh_offset 1334 WriteWord(Size); // sh_size 1335 Write32(Link); // sh_link 1336 Write32(Info); // sh_info 1337 WriteWord(Alignment); // sh_addralign 1338 WriteWord(EntrySize); // sh_entsize 1339 } 1340 1341 // ELF doesn't require relocations to be in any order. We sort by the r_offset, 1342 // just to match gnu as for easier comparison. The use type is an arbitrary way 1343 // of making the sort deterministic. 1344 static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) { 1345 const ELFRelocationEntry &A = *AP; 1346 const ELFRelocationEntry &B = *BP; 1347 if (A.Offset != B.Offset) 1348 return B.Offset - A.Offset; 1349 if (B.Type != A.Type) 1350 return A.Type - B.Type; 1351 llvm_unreachable("ELFRelocs might be unstable!"); 1352 } 1353 1354 static void sortRelocs(const MCAssembler &Asm, 1355 std::vector<ELFRelocationEntry> &Relocs) { 1356 array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel); 1357 } 1358 1359 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm, 1360 MCDataFragment *F, 1361 const MCSectionData *SD) { 1362 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD]; 1363 1364 sortRelocs(Asm, Relocs); 1365 1366 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) { 1367 const ELFRelocationEntry &Entry = Relocs[e - i - 1]; 1368 unsigned Index = 1369 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0; 1370 1371 if (is64Bit()) { 1372 write(*F, Entry.Offset); 1373 if (TargetObjectWriter->isN64()) { 1374 write(*F, uint32_t(Index)); 1375 1376 write(*F, TargetObjectWriter->getRSsym(Entry.Type)); 1377 write(*F, TargetObjectWriter->getRType3(Entry.Type)); 1378 write(*F, TargetObjectWriter->getRType2(Entry.Type)); 1379 write(*F, TargetObjectWriter->getRType(Entry.Type)); 1380 } else { 1381 struct ELF::Elf64_Rela ERE64; 1382 ERE64.setSymbolAndType(Index, Entry.Type); 1383 write(*F, ERE64.r_info); 1384 } 1385 if (hasRelocationAddend()) 1386 write(*F, Entry.Addend); 1387 } else { 1388 write(*F, uint32_t(Entry.Offset)); 1389 1390 struct ELF::Elf32_Rela ERE32; 1391 ERE32.setSymbolAndType(Index, Entry.Type); 1392 write(*F, ERE32.r_info); 1393 1394 if (hasRelocationAddend()) 1395 write(*F, uint32_t(Entry.Addend)); 1396 } 1397 } 1398 } 1399 1400 void ELFObjectWriter::CreateMetadataSections( 1401 MCAssembler &Asm, MCAsmLayout &Layout, SectionIndexMapTy &SectionIndexMap) { 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 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection); 1411 ShstrtabSD.setAlignment(1); 1412 ShstrtabIndex = SectionIndexMap.size() + 1; 1413 SectionIndexMap[ShstrtabSection] = ShstrtabIndex; 1414 1415 const MCSectionELF *SymtabSection = 1416 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, 1417 EntrySize, ""); 1418 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection); 1419 SymtabSD.setAlignment(is64Bit() ? 8 : 4); 1420 SymbolTableIndex = SectionIndexMap.size() + 1; 1421 SectionIndexMap[SymtabSection] = SymbolTableIndex; 1422 1423 const MCSectionELF *StrtabSection; 1424 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0); 1425 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection); 1426 StrtabSD.setAlignment(1); 1427 StringTableIndex = SectionIndexMap.size() + 1; 1428 SectionIndexMap[StrtabSection] = StringTableIndex; 1429 1430 // Symbol table 1431 F = new MCDataFragment(&SymtabSD); 1432 WriteSymbolTable(F, Asm, Layout, SectionIndexMap); 1433 1434 F = new MCDataFragment(&StrtabSD); 1435 F->getContents().append(StrTabBuilder.data().begin(), 1436 StrTabBuilder.data().end()); 1437 1438 F = new MCDataFragment(&ShstrtabSD); 1439 1440 // Section header string table. 1441 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { 1442 const MCSectionELF &Section = 1443 static_cast<const MCSectionELF&>(it->getSection()); 1444 ShStrTabBuilder.add(Section.getSectionName()); 1445 } 1446 ShStrTabBuilder.finalize(StringTableBuilder::ELF); 1447 F->getContents().append(ShStrTabBuilder.data().begin(), 1448 ShStrTabBuilder.data().end()); 1449 } 1450 1451 void ELFObjectWriter::createIndexedSections(MCAssembler &Asm, 1452 MCAsmLayout &Layout, 1453 GroupMapTy &GroupMap, 1454 RevGroupMapTy &RevGroupMap, 1455 SectionIndexMapTy &SectionIndexMap, 1456 RelMapTy &RelMap) { 1457 MCContext &Ctx = Asm.getContext(); 1458 1459 // Build the groups 1460 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1461 it != ie; ++it) { 1462 const MCSectionELF &Section = 1463 static_cast<const MCSectionELF&>(it->getSection()); 1464 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1465 continue; 1466 1467 const MCSymbol *SignatureSymbol = Section.getGroup(); 1468 Asm.getOrCreateSymbolData(*SignatureSymbol); 1469 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol]; 1470 if (!Group) { 1471 Group = Ctx.CreateELFGroupSection(); 1472 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1473 Data.setAlignment(4); 1474 MCDataFragment *F = new MCDataFragment(&Data); 1475 write(*F, uint32_t(ELF::GRP_COMDAT)); 1476 } 1477 GroupMap[Group] = SignatureSymbol; 1478 } 1479 1480 computeIndexMap(Asm, SectionIndexMap, RelMap); 1481 1482 // Add sections to the groups 1483 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1484 it != ie; ++it) { 1485 const MCSectionELF &Section = 1486 static_cast<const MCSectionELF&>(it->getSection()); 1487 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1488 continue; 1489 const MCSectionELF *Group = RevGroupMap[Section.getGroup()]; 1490 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1491 // FIXME: we could use the previous fragment 1492 MCDataFragment *F = new MCDataFragment(&Data); 1493 uint32_t Index = SectionIndexMap.lookup(&Section); 1494 write(*F, Index); 1495 } 1496 } 1497 1498 void ELFObjectWriter::writeSection(MCAssembler &Asm, 1499 const SectionIndexMapTy &SectionIndexMap, 1500 const RelMapTy &RelMap, 1501 uint32_t GroupSymbolIndex, 1502 uint64_t Offset, uint64_t Size, 1503 uint64_t Alignment, 1504 const MCSectionELF &Section) { 1505 uint64_t sh_link = 0; 1506 uint64_t sh_info = 0; 1507 1508 switch(Section.getType()) { 1509 case ELF::SHT_DYNAMIC: 1510 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName()); 1511 sh_info = 0; 1512 break; 1513 1514 case ELF::SHT_REL: 1515 case ELF::SHT_RELA: { 1516 sh_link = SymbolTableIndex; 1517 assert(sh_link && ".symtab not found"); 1518 const MCSectionELF *InfoSection = RelMap.find(&Section)->second; 1519 sh_info = SectionIndexMap.lookup(InfoSection); 1520 break; 1521 } 1522 1523 case ELF::SHT_SYMTAB: 1524 case ELF::SHT_DYNSYM: 1525 sh_link = StringTableIndex; 1526 sh_info = LastLocalSymbolIndex; 1527 break; 1528 1529 case ELF::SHT_SYMTAB_SHNDX: 1530 sh_link = SymbolTableIndex; 1531 break; 1532 1533 case ELF::SHT_PROGBITS: 1534 case ELF::SHT_STRTAB: 1535 case ELF::SHT_NOBITS: 1536 case ELF::SHT_NOTE: 1537 case ELF::SHT_NULL: 1538 case ELF::SHT_ARM_ATTRIBUTES: 1539 case ELF::SHT_INIT_ARRAY: 1540 case ELF::SHT_FINI_ARRAY: 1541 case ELF::SHT_PREINIT_ARRAY: 1542 case ELF::SHT_X86_64_UNWIND: 1543 case ELF::SHT_MIPS_REGINFO: 1544 case ELF::SHT_MIPS_OPTIONS: 1545 case ELF::SHT_MIPS_ABIFLAGS: 1546 // Nothing to do. 1547 break; 1548 1549 case ELF::SHT_GROUP: 1550 sh_link = SymbolTableIndex; 1551 sh_info = GroupSymbolIndex; 1552 break; 1553 1554 default: 1555 llvm_unreachable("FIXME: sh_type value not supported!"); 1556 } 1557 1558 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM && 1559 Section.getType() == ELF::SHT_ARM_EXIDX) { 1560 StringRef SecName(Section.getSectionName()); 1561 if (SecName == ".ARM.exidx") { 1562 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection( 1563 ".text", ELF::SHT_PROGBITS, ELF::SHF_EXECINSTR | ELF::SHF_ALLOC)); 1564 } else if (SecName.startswith(".ARM.exidx")) { 1565 StringRef GroupName = 1566 Section.getGroup() ? Section.getGroup()->getName() : ""; 1567 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection( 1568 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS, 1569 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, 0, GroupName)); 1570 } 1571 } 1572 1573 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()), 1574 Section.getType(), 1575 Section.getFlags(), 0, Offset, Size, sh_link, sh_info, 1576 Alignment, Section.getEntrySize()); 1577 } 1578 1579 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) { 1580 return SD.getOrdinal() == ~UINT32_C(0) && 1581 !SD.getSection().isVirtualSection(); 1582 } 1583 1584 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) { 1585 uint64_t Ret = 0; 1586 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1587 ++i) { 1588 const MCFragment &F = *i; 1589 assert(F.getKind() == MCFragment::FT_Data); 1590 Ret += cast<MCDataFragment>(F).getContents().size(); 1591 } 1592 return Ret; 1593 } 1594 1595 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout, 1596 const MCSectionData &SD) { 1597 if (IsELFMetaDataSection(SD)) 1598 return DataSectionSize(SD); 1599 return Layout.getSectionFileSize(&SD); 1600 } 1601 1602 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout, 1603 const MCSectionData &SD) { 1604 if (IsELFMetaDataSection(SD)) 1605 return DataSectionSize(SD); 1606 return Layout.getSectionAddressSize(&SD); 1607 } 1608 1609 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm, 1610 const MCAsmLayout &Layout, 1611 const MCSectionELF &Section) { 1612 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1613 1614 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment()); 1615 WriteZeros(Padding); 1616 1617 if (IsELFMetaDataSection(SD)) { 1618 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1619 ++i) { 1620 const MCFragment &F = *i; 1621 assert(F.getKind() == MCFragment::FT_Data); 1622 WriteBytes(cast<MCDataFragment>(F).getContents()); 1623 } 1624 } else { 1625 Asm.writeSectionData(&SD, Layout); 1626 } 1627 } 1628 1629 void ELFObjectWriter::writeSectionHeader( 1630 MCAssembler &Asm, const GroupMapTy &GroupMap, const MCAsmLayout &Layout, 1631 const SectionIndexMapTy &SectionIndexMap, const RelMapTy &RelMap, 1632 const SectionOffsetMapTy &SectionOffsetMap) { 1633 const unsigned NumSections = Asm.size() + 1; 1634 1635 std::vector<const MCSectionELF*> Sections; 1636 Sections.resize(NumSections - 1); 1637 1638 for (SectionIndexMapTy::const_iterator i= 1639 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) { 1640 const std::pair<const MCSectionELF*, uint32_t> &p = *i; 1641 Sections[p.second - 1] = p.first; 1642 } 1643 1644 // Null section first. 1645 uint64_t FirstSectionSize = 1646 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0; 1647 uint32_t FirstSectionLink = 1648 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0; 1649 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0); 1650 1651 for (unsigned i = 0; i < NumSections - 1; ++i) { 1652 const MCSectionELF &Section = *Sections[i]; 1653 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1654 uint32_t GroupSymbolIndex; 1655 if (Section.getType() != ELF::SHT_GROUP) 1656 GroupSymbolIndex = 0; 1657 else 1658 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, 1659 GroupMap.lookup(&Section)); 1660 1661 uint64_t Size = GetSectionAddressSize(Layout, SD); 1662 1663 writeSection(Asm, SectionIndexMap, RelMap, GroupSymbolIndex, 1664 SectionOffsetMap.lookup(&Section), Size, 1665 SD.getAlignment(), Section); 1666 } 1667 } 1668 1669 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm, 1670 std::vector<const MCSectionELF*> &Sections) { 1671 for (MCAssembler::iterator it = Asm.begin(), 1672 ie = Asm.end(); it != ie; ++it) { 1673 const MCSectionELF &Section = 1674 static_cast<const MCSectionELF &>(it->getSection()); 1675 if (Section.getType() == ELF::SHT_GROUP) 1676 Sections.push_back(&Section); 1677 } 1678 1679 for (MCAssembler::iterator it = Asm.begin(), 1680 ie = Asm.end(); it != ie; ++it) { 1681 const MCSectionELF &Section = 1682 static_cast<const MCSectionELF &>(it->getSection()); 1683 if (Section.getType() != ELF::SHT_GROUP && 1684 Section.getType() != ELF::SHT_REL && 1685 Section.getType() != ELF::SHT_RELA) 1686 Sections.push_back(&Section); 1687 } 1688 1689 for (MCAssembler::iterator it = Asm.begin(), 1690 ie = Asm.end(); it != ie; ++it) { 1691 const MCSectionELF &Section = 1692 static_cast<const MCSectionELF &>(it->getSection()); 1693 if (Section.getType() == ELF::SHT_REL || 1694 Section.getType() == ELF::SHT_RELA) 1695 Sections.push_back(&Section); 1696 } 1697 } 1698 1699 void ELFObjectWriter::WriteObject(MCAssembler &Asm, 1700 const MCAsmLayout &Layout) { 1701 GroupMapTy GroupMap; 1702 RevGroupMapTy RevGroupMap; 1703 SectionIndexMapTy SectionIndexMap; 1704 1705 unsigned NumUserSections = Asm.size(); 1706 1707 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout)); 1708 1709 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap; 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 1728 uint64_t NaturalAlignment = is64Bit() ? 8 : 4; 1729 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 1730 sizeof(ELF::Elf32_Ehdr); 1731 uint64_t FileOff = HeaderSize; 1732 1733 std::vector<const MCSectionELF*> Sections; 1734 ComputeSectionOrder(Asm, Sections); 1735 unsigned NumSections = Sections.size(); 1736 SectionOffsetMapTy SectionOffsetMap; 1737 for (unsigned i = 0; i < NumRegularSections + 1; ++i) { 1738 const MCSectionELF &Section = *Sections[i]; 1739 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1740 1741 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1742 1743 // Remember the offset into the file for this section. 1744 SectionOffsetMap[&Section] = FileOff; 1745 1746 // Get the size of the section in the output file (including padding). 1747 FileOff += GetSectionFileSize(Layout, SD); 1748 } 1749 1750 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment); 1751 1752 const unsigned SectionHeaderOffset = FileOff - HeaderSize; 1753 1754 uint64_t SectionHeaderEntrySize = is64Bit() ? 1755 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr); 1756 FileOff += (NumSections + 1) * SectionHeaderEntrySize; 1757 1758 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) { 1759 const MCSectionELF &Section = *Sections[i]; 1760 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1761 1762 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1763 1764 // Remember the offset into the file for this section. 1765 SectionOffsetMap[&Section] = FileOff; 1766 1767 // Get the size of the section in the output file (including padding). 1768 FileOff += GetSectionFileSize(Layout, SD); 1769 } 1770 1771 // Write out the ELF header ... 1772 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1); 1773 1774 // ... then the regular sections ... 1775 // + because of .shstrtab 1776 for (unsigned i = 0; i < NumRegularSections + 1; ++i) 1777 WriteDataSectionData(Asm, Layout, *Sections[i]); 1778 1779 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment); 1780 WriteZeros(Padding); 1781 1782 // ... then the section header table ... 1783 writeSectionHeader(Asm, GroupMap, Layout, SectionIndexMap, RelMap, 1784 SectionOffsetMap); 1785 1786 // ... and then the remaining sections ... 1787 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) 1788 WriteDataSectionData(Asm, Layout, *Sections[i]); 1789 } 1790 1791 bool 1792 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 1793 const MCSymbolData &DataA, 1794 const MCFragment &FB, 1795 bool InSet, 1796 bool IsPCRel) const { 1797 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC) 1798 return false; 1799 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl( 1800 Asm, DataA, FB,InSet, IsPCRel); 1801 } 1802 1803 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW, 1804 raw_ostream &OS, 1805 bool IsLittleEndian) { 1806 return new ELFObjectWriter(MOTW, OS, IsLittleEndian); 1807 } 1808