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/Support/Compression.h" 32 #include "llvm/Support/Debug.h" 33 #include "llvm/Support/Endian.h" 34 #include "llvm/Support/ELF.h" 35 #include "llvm/Support/ErrorHandling.h" 36 #include <vector> 37 using namespace llvm; 38 39 #undef DEBUG_TYPE 40 #define DEBUG_TYPE "reloc-info" 41 42 namespace { 43 class FragmentWriter { 44 bool IsLittleEndian; 45 46 public: 47 FragmentWriter(bool IsLittleEndian); 48 template <typename T> void write(MCDataFragment &F, T Val); 49 }; 50 51 typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy; 52 53 class SymbolTableWriter { 54 MCAssembler &Asm; 55 FragmentWriter &FWriter; 56 bool Is64Bit; 57 SectionIndexMapTy &SectionIndexMap; 58 59 // The symbol .symtab fragment we are writting to. 60 MCDataFragment *SymtabF; 61 62 // .symtab_shndx fragment we are writting to. 63 MCDataFragment *ShndxF; 64 65 // The numbel of symbols written so far. 66 unsigned NumWritten; 67 68 void createSymtabShndx(); 69 70 template <typename T> void write(MCDataFragment &F, T Value); 71 72 public: 73 SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit, 74 SectionIndexMapTy &SectionIndexMap, 75 MCDataFragment *SymtabF); 76 77 void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size, 78 uint8_t other, uint32_t shndx, bool Reserved); 79 }; 80 81 struct ELFRelocationEntry { 82 uint64_t Offset; // Where is the relocation. 83 bool UseSymbol; // Relocate with a symbol, not the section. 84 union { 85 const MCSymbol *Symbol; // The symbol to relocate with. 86 const MCSectionData *Section; // The section to relocate with. 87 }; 88 unsigned Type; // The type of the relocation. 89 uint64_t Addend; // The addend to use. 90 91 ELFRelocationEntry(uint64_t Offset, const MCSymbol *Symbol, unsigned Type, 92 uint64_t Addend) 93 : Offset(Offset), UseSymbol(true), Symbol(Symbol), Type(Type), 94 Addend(Addend) {} 95 96 ELFRelocationEntry(uint64_t Offset, const MCSectionData *Section, 97 unsigned Type, uint64_t Addend) 98 : Offset(Offset), UseSymbol(false), Section(Section), Type(Type), 99 Addend(Addend) {} 100 }; 101 102 class ELFObjectWriter : public MCObjectWriter { 103 FragmentWriter FWriter; 104 105 protected: 106 107 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind); 108 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant); 109 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout); 110 static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data, 111 bool Used, bool Renamed); 112 static bool isLocal(const MCSymbolData &Data, bool isSignature, 113 bool isUsedInReloc); 114 static bool IsELFMetaDataSection(const MCSectionData &SD); 115 static uint64_t DataSectionSize(const MCSectionData &SD); 116 static uint64_t GetSectionFileSize(const MCAsmLayout &Layout, 117 const MCSectionData &SD); 118 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout, 119 const MCSectionData &SD); 120 121 void WriteDataSectionData(MCAssembler &Asm, 122 const MCAsmLayout &Layout, 123 const MCSectionELF &Section); 124 125 /*static bool isFixupKindX86RIPRel(unsigned Kind) { 126 return Kind == X86::reloc_riprel_4byte || 127 Kind == X86::reloc_riprel_4byte_movq_load; 128 }*/ 129 130 /// ELFSymbolData - Helper struct for containing some precomputed 131 /// information on symbols. 132 struct ELFSymbolData { 133 MCSymbolData *SymbolData; 134 uint64_t StringIndex; 135 uint32_t SectionIndex; 136 137 // Support lexicographic sorting. 138 bool operator<(const ELFSymbolData &RHS) const { 139 return SymbolData->getSymbol().getName() < 140 RHS.SymbolData->getSymbol().getName(); 141 } 142 }; 143 144 /// The target specific ELF writer instance. 145 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter; 146 147 SmallPtrSet<const MCSymbol *, 16> UsedInReloc; 148 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc; 149 DenseMap<const MCSymbol *, const MCSymbol *> Renames; 150 151 llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>> 152 Relocations; 153 DenseMap<const MCSection*, uint64_t> SectionStringTableIndex; 154 155 /// @} 156 /// @name Symbol Table Data 157 /// @{ 158 159 SmallString<256> StringTable; 160 std::vector<uint64_t> FileSymbolData; 161 std::vector<ELFSymbolData> LocalSymbolData; 162 std::vector<ELFSymbolData> ExternalSymbolData; 163 std::vector<ELFSymbolData> UndefinedSymbolData; 164 165 /// @} 166 167 bool NeedsGOT; 168 169 // This holds the symbol table index of the last local symbol. 170 unsigned LastLocalSymbolIndex; 171 // This holds the .strtab section index. 172 unsigned StringTableIndex; 173 // This holds the .symtab section index. 174 unsigned SymbolTableIndex; 175 176 unsigned ShstrtabIndex; 177 178 179 // TargetObjectWriter wrappers. 180 bool is64Bit() const { return TargetObjectWriter->is64Bit(); } 181 bool hasRelocationAddend() const { 182 return TargetObjectWriter->hasRelocationAddend(); 183 } 184 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup, 185 bool IsPCRel) const { 186 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel); 187 } 188 189 public: 190 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_ostream &_OS, 191 bool IsLittleEndian) 192 : MCObjectWriter(_OS, IsLittleEndian), FWriter(IsLittleEndian), 193 TargetObjectWriter(MOTW), NeedsGOT(false) {} 194 195 virtual ~ELFObjectWriter(); 196 197 void WriteWord(uint64_t W) { 198 if (is64Bit()) 199 Write64(W); 200 else 201 Write32(W); 202 } 203 204 template <typename T> void write(MCDataFragment &F, T Value) { 205 FWriter.write(F, Value); 206 } 207 208 void WriteHeader(const MCAssembler &Asm, 209 uint64_t SectionDataSize, 210 unsigned NumberOfSections); 211 212 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD, 213 const MCAsmLayout &Layout); 214 215 void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm, 216 const MCAsmLayout &Layout, 217 SectionIndexMapTy &SectionIndexMap); 218 219 bool shouldRelocateWithSymbol(const MCSymbolRefExpr *RefA, 220 const MCSymbolData *SD, uint64_t C, 221 unsigned Type) const; 222 223 void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout, 224 const MCFragment *Fragment, const MCFixup &Fixup, 225 MCValue Target, bool &IsPCRel, 226 uint64_t &FixedValue) override; 227 228 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm, 229 const MCSymbol *S); 230 231 // Map from a group section to the signature symbol 232 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy; 233 // Map from a signature symbol to the group section 234 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy; 235 // Map from a section to the section with the relocations 236 typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy; 237 // Map from a section to its offset 238 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy; 239 240 /// Compute the symbol table data 241 /// 242 /// \param Asm - The assembler. 243 /// \param SectionIndexMap - Maps a section to its index. 244 /// \param RevGroupMap - Maps a signature symbol to the group section. 245 /// \param NumRegularSections - Number of non-relocation sections. 246 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout, 247 const SectionIndexMapTy &SectionIndexMap, 248 RevGroupMapTy RevGroupMap, 249 unsigned NumRegularSections); 250 251 void ComputeIndexMap(MCAssembler &Asm, 252 SectionIndexMapTy &SectionIndexMap, 253 const RelMapTy &RelMap); 254 255 void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout, 256 RelMapTy &RelMap); 257 258 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout); 259 260 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 261 const RelMapTy &RelMap); 262 263 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout, 264 SectionIndexMapTy &SectionIndexMap, 265 const RelMapTy &RelMap); 266 267 // Create the sections that show up in the symbol table. Currently 268 // those are the .note.GNU-stack section and the group sections. 269 void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout, 270 GroupMapTy &GroupMap, 271 RevGroupMapTy &RevGroupMap, 272 SectionIndexMapTy &SectionIndexMap, 273 const RelMapTy &RelMap); 274 275 void ExecutePostLayoutBinding(MCAssembler &Asm, 276 const MCAsmLayout &Layout) override; 277 278 void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap, 279 const MCAsmLayout &Layout, 280 const SectionIndexMapTy &SectionIndexMap, 281 const SectionOffsetMapTy &SectionOffsetMap); 282 283 void ComputeSectionOrder(MCAssembler &Asm, 284 std::vector<const MCSectionELF*> &Sections); 285 286 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags, 287 uint64_t Address, uint64_t Offset, 288 uint64_t Size, uint32_t Link, uint32_t Info, 289 uint64_t Alignment, uint64_t EntrySize); 290 291 void WriteRelocationsFragment(const MCAssembler &Asm, 292 MCDataFragment *F, 293 const MCSectionData *SD); 294 295 bool 296 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 297 const MCSymbolData &DataA, 298 const MCFragment &FB, 299 bool InSet, 300 bool IsPCRel) const override; 301 302 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override; 303 void WriteSection(MCAssembler &Asm, 304 const SectionIndexMapTy &SectionIndexMap, 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, 330 SectionKind::getReadOnly(), 4, ""); 331 MCSectionData *SymtabShndxSD = 332 &Asm.getOrCreateSectionData(*SymtabShndxSection); 333 SymtabShndxSD->setAlignment(4); 334 ShndxF = new MCDataFragment(SymtabShndxSD); 335 unsigned Index = SectionIndexMap.size() + 1; 336 SectionIndexMap[SymtabShndxSection] = Index; 337 338 for (unsigned I = 0; I < NumWritten; ++I) 339 write(*ShndxF, uint32_t(0)); 340 } 341 342 template <typename T> 343 void SymbolTableWriter::write(MCDataFragment &F, T Value) { 344 FWriter.write(F, Value); 345 } 346 347 SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, 348 bool Is64Bit, 349 SectionIndexMapTy &SectionIndexMap, 350 MCDataFragment *SymtabF) 351 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit), 352 SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr), 353 NumWritten(0) {} 354 355 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value, 356 uint64_t size, uint8_t other, 357 uint32_t shndx, bool Reserved) { 358 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved; 359 360 if (LargeIndex) 361 createSymtabShndx(); 362 363 if (ShndxF) { 364 if (LargeIndex) 365 write(*ShndxF, shndx); 366 else 367 write(*ShndxF, uint32_t(0)); 368 } 369 370 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx; 371 372 raw_svector_ostream OS(SymtabF->getContents()); 373 374 if (Is64Bit) { 375 write(*SymtabF, name); // st_name 376 write(*SymtabF, info); // st_info 377 write(*SymtabF, other); // st_other 378 write(*SymtabF, Index); // st_shndx 379 write(*SymtabF, value); // st_value 380 write(*SymtabF, size); // st_size 381 } else { 382 write(*SymtabF, name); // st_name 383 write(*SymtabF, uint32_t(value)); // st_value 384 write(*SymtabF, uint32_t(size)); // st_size 385 write(*SymtabF, info); // st_info 386 write(*SymtabF, other); // st_other 387 write(*SymtabF, Index); // st_shndx 388 } 389 390 ++NumWritten; 391 } 392 393 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) { 394 const MCFixupKindInfo &FKI = 395 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind); 396 397 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel; 398 } 399 400 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) { 401 switch (Variant) { 402 default: 403 return false; 404 case MCSymbolRefExpr::VK_GOT: 405 case MCSymbolRefExpr::VK_PLT: 406 case MCSymbolRefExpr::VK_GOTPCREL: 407 case MCSymbolRefExpr::VK_GOTOFF: 408 case MCSymbolRefExpr::VK_TPOFF: 409 case MCSymbolRefExpr::VK_TLSGD: 410 case MCSymbolRefExpr::VK_GOTTPOFF: 411 case MCSymbolRefExpr::VK_INDNTPOFF: 412 case MCSymbolRefExpr::VK_NTPOFF: 413 case MCSymbolRefExpr::VK_GOTNTPOFF: 414 case MCSymbolRefExpr::VK_TLSLDM: 415 case MCSymbolRefExpr::VK_DTPOFF: 416 case MCSymbolRefExpr::VK_TLSLD: 417 return true; 418 } 419 } 420 421 ELFObjectWriter::~ELFObjectWriter() 422 {} 423 424 // Emit the ELF header. 425 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm, 426 uint64_t SectionDataSize, 427 unsigned NumberOfSections) { 428 // ELF Header 429 // ---------- 430 // 431 // Note 432 // ---- 433 // emitWord method behaves differently for ELF32 and ELF64, writing 434 // 4 bytes in the former and 8 in the latter. 435 436 Write8(0x7f); // e_ident[EI_MAG0] 437 Write8('E'); // e_ident[EI_MAG1] 438 Write8('L'); // e_ident[EI_MAG2] 439 Write8('F'); // e_ident[EI_MAG3] 440 441 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS] 442 443 // e_ident[EI_DATA] 444 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB); 445 446 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION] 447 // e_ident[EI_OSABI] 448 Write8(TargetObjectWriter->getOSABI()); 449 Write8(0); // e_ident[EI_ABIVERSION] 450 451 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD); 452 453 Write16(ELF::ET_REL); // e_type 454 455 Write16(TargetObjectWriter->getEMachine()); // e_machine = target 456 457 Write32(ELF::EV_CURRENT); // e_version 458 WriteWord(0); // e_entry, no entry point in .o file 459 WriteWord(0); // e_phoff, no program header for .o 460 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 461 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes 462 463 // e_flags = whatever the target wants 464 Write32(Asm.getELFHeaderEFlags()); 465 466 // e_ehsize = ELF header size 467 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr)); 468 469 Write16(0); // e_phentsize = prog header entry size 470 Write16(0); // e_phnum = # prog header entries = 0 471 472 // e_shentsize = Section header entry size 473 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr)); 474 475 // e_shnum = # of section header ents 476 if (NumberOfSections >= ELF::SHN_LORESERVE) 477 Write16(ELF::SHN_UNDEF); 478 else 479 Write16(NumberOfSections); 480 481 // e_shstrndx = Section # of '.shstrtab' 482 if (ShstrtabIndex >= ELF::SHN_LORESERVE) 483 Write16(ELF::SHN_XINDEX); 484 else 485 Write16(ShstrtabIndex); 486 } 487 488 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &OrigData, 489 const MCAsmLayout &Layout) { 490 MCSymbolData *Data = &OrigData; 491 if (Data->isCommon() && Data->isExternal()) 492 return Data->getCommonAlignment(); 493 494 const MCSymbol *Symbol = &Data->getSymbol(); 495 496 uint64_t Res = 0; 497 if (Symbol->isVariable()) { 498 const MCExpr *Expr = Symbol->getVariableValue(); 499 MCValue Value; 500 if (!Expr->EvaluateAsRelocatable(Value, &Layout)) 501 llvm_unreachable("Invalid expression"); 502 503 assert(!Value.getSymB()); 504 505 Res = Value.getConstant(); 506 507 if (const MCSymbolRefExpr *A = Value.getSymA()) { 508 Symbol = &A->getSymbol(); 509 Data = &Layout.getAssembler().getSymbolData(*Symbol); 510 } else { 511 Symbol = nullptr; 512 Data = nullptr; 513 } 514 } 515 516 if (Data && Data->getFlags() & ELF_Other_ThumbFunc) 517 Res |= 1; 518 519 if (!Symbol || !Symbol->isInSection()) 520 return Res; 521 522 Res += Layout.getSymbolOffset(Data); 523 524 return Res; 525 } 526 527 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm, 528 const MCAsmLayout &Layout) { 529 // The presence of symbol versions causes undefined symbols and 530 // versions declared with @@@ to be renamed. 531 532 for (MCSymbolData &OriginalData : Asm.symbols()) { 533 const MCSymbol &Alias = OriginalData.getSymbol(); 534 const MCSymbol &Symbol = Alias.AliasedSymbol(); 535 MCSymbolData &SD = Asm.getSymbolData(Symbol); 536 537 // Not an alias. 538 if (&Symbol == &Alias) 539 continue; 540 541 StringRef AliasName = Alias.getName(); 542 size_t Pos = AliasName.find('@'); 543 if (Pos == StringRef::npos) 544 continue; 545 546 // Aliases defined with .symvar copy the binding from the symbol they alias. 547 // This is the first place we are able to copy this information. 548 OriginalData.setExternal(SD.isExternal()); 549 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD)); 550 551 StringRef Rest = AliasName.substr(Pos); 552 if (!Symbol.isUndefined() && !Rest.startswith("@@@")) 553 continue; 554 555 // FIXME: produce a better error message. 556 if (Symbol.isUndefined() && Rest.startswith("@@") && 557 !Rest.startswith("@@@")) 558 report_fatal_error("A @@ version cannot be undefined"); 559 560 Renames.insert(std::make_pair(&Symbol, &Alias)); 561 } 562 } 563 564 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) { 565 uint8_t Type = newType; 566 567 // Propagation rules: 568 // IFUNC > FUNC > OBJECT > NOTYPE 569 // TLS_OBJECT > OBJECT > NOTYPE 570 // 571 // dont let the new type degrade the old type 572 switch (origType) { 573 default: 574 break; 575 case ELF::STT_GNU_IFUNC: 576 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT || 577 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS) 578 Type = ELF::STT_GNU_IFUNC; 579 break; 580 case ELF::STT_FUNC: 581 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE || 582 Type == ELF::STT_TLS) 583 Type = ELF::STT_FUNC; 584 break; 585 case ELF::STT_OBJECT: 586 if (Type == ELF::STT_NOTYPE) 587 Type = ELF::STT_OBJECT; 588 break; 589 case ELF::STT_TLS: 590 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE || 591 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC) 592 Type = ELF::STT_TLS; 593 break; 594 } 595 596 return Type; 597 } 598 599 static const MCSymbol *getBaseSymbol(const MCAsmLayout &Layout, 600 const MCSymbol &Symbol) { 601 if (!Symbol.isVariable()) 602 return &Symbol; 603 604 const MCExpr *Expr = Symbol.getVariableValue(); 605 MCValue Value; 606 if (!Expr->EvaluateAsRelocatable(Value, &Layout)) 607 llvm_unreachable("Invalid Expression"); 608 assert(!Value.getSymB()); 609 const MCSymbolRefExpr *A = Value.getSymA(); 610 if (!A) 611 return nullptr; 612 return getBaseSymbol(Layout, A->getSymbol()); 613 } 614 615 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD, 616 const MCAsmLayout &Layout) { 617 MCSymbolData &OrigData = *MSD.SymbolData; 618 assert((!OrigData.getFragment() || 619 (&OrigData.getFragment()->getParent()->getSection() == 620 &OrigData.getSymbol().getSection())) && 621 "The symbol's section doesn't match the fragment's symbol"); 622 const MCSymbol *Base = getBaseSymbol(Layout, OrigData.getSymbol()); 623 624 // This has to be in sync with when computeSymbolTable uses SHN_ABS or 625 // SHN_COMMON. 626 bool IsReserved = !Base || OrigData.isCommon(); 627 628 // Binding and Type share the same byte as upper and lower nibbles 629 uint8_t Binding = MCELF::GetBinding(OrigData); 630 uint8_t Type = MCELF::GetType(OrigData); 631 MCSymbolData *BaseSD = nullptr; 632 if (Base) { 633 BaseSD = &Layout.getAssembler().getSymbolData(*Base); 634 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD)); 635 } 636 if (OrigData.getFlags() & ELF_Other_ThumbFunc) 637 Type = ELF::STT_FUNC; 638 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift); 639 640 // Other and Visibility share the same byte with Visibility using the lower 641 // 2 bits 642 uint8_t Visibility = MCELF::GetVisibility(OrigData); 643 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift); 644 Other |= Visibility; 645 646 uint64_t Value = SymbolValue(OrigData, Layout); 647 if (OrigData.getFlags() & ELF_Other_ThumbFunc) 648 Value |= 1; 649 uint64_t Size = 0; 650 651 const MCExpr *ESize = OrigData.getSize(); 652 if (!ESize && Base) 653 ESize = BaseSD->getSize(); 654 655 if (ESize) { 656 int64_t Res; 657 if (!ESize->EvaluateAsAbsolute(Res, Layout)) 658 report_fatal_error("Size expression must be absolute."); 659 Size = Res; 660 } 661 662 // Write out the symbol table entry 663 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other, 664 MSD.SectionIndex, IsReserved); 665 } 666 667 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF, 668 MCAssembler &Asm, 669 const MCAsmLayout &Layout, 670 SectionIndexMapTy &SectionIndexMap) { 671 // The string table must be emitted first because we need the index 672 // into the string table for all the symbol names. 673 assert(StringTable.size() && "Missing string table"); 674 675 // FIXME: Make sure the start of the symbol table is aligned. 676 677 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF); 678 679 // The first entry is the undefined symbol entry. 680 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false); 681 682 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) { 683 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, 684 ELF::STV_DEFAULT, ELF::SHN_ABS, true); 685 } 686 687 // Write the symbol table entries. 688 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1; 689 690 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) { 691 ELFSymbolData &MSD = LocalSymbolData[i]; 692 WriteSymbol(Writer, MSD, Layout); 693 } 694 695 // Write out a symbol table entry for each regular section. 696 for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e; 697 ++i) { 698 const MCSectionELF &Section = 699 static_cast<const MCSectionELF&>(i->getSection()); 700 if (Section.getType() == ELF::SHT_RELA || 701 Section.getType() == ELF::SHT_REL || 702 Section.getType() == ELF::SHT_STRTAB || 703 Section.getType() == ELF::SHT_SYMTAB || 704 Section.getType() == ELF::SHT_SYMTAB_SHNDX) 705 continue; 706 Writer.writeSymbol(0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT, 707 SectionIndexMap.lookup(&Section), false); 708 LastLocalSymbolIndex++; 709 } 710 711 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) { 712 ELFSymbolData &MSD = ExternalSymbolData[i]; 713 MCSymbolData &Data = *MSD.SymbolData; 714 assert(((Data.getFlags() & ELF_STB_Global) || 715 (Data.getFlags() & ELF_STB_Weak)) && 716 "External symbol requires STB_GLOBAL or STB_WEAK flag"); 717 WriteSymbol(Writer, MSD, Layout); 718 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 719 LastLocalSymbolIndex++; 720 } 721 722 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) { 723 ELFSymbolData &MSD = UndefinedSymbolData[i]; 724 MCSymbolData &Data = *MSD.SymbolData; 725 WriteSymbol(Writer, MSD, Layout); 726 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 727 LastLocalSymbolIndex++; 728 } 729 } 730 731 // It is always valid to create a relocation with a symbol. It is preferable 732 // to use a relocation with a section if that is possible. Using the section 733 // allows us to omit some local symbols from the symbol table. 734 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCSymbolRefExpr *RefA, 735 const MCSymbolData *SD, 736 uint64_t C, 737 unsigned Type) const { 738 // A PCRel relocation to an absolute value has no symbol (or section). We 739 // represent that with a relocation to a null section. 740 if (!RefA) 741 return false; 742 743 MCSymbolRefExpr::VariantKind Kind = RefA->getKind(); 744 switch (Kind) { 745 default: 746 break; 747 // The .odp creation emits a relocation against the symbol ".TOC." which 748 // create a R_PPC64_TOC relocation. However the relocation symbol name 749 // in final object creation should be NULL, since the symbol does not 750 // really exist, it is just the reference to TOC base for the current 751 // object file. Since the symbol is undefined, returning false results 752 // in a relocation with a null section which is the desired result. 753 case MCSymbolRefExpr::VK_PPC_TOCBASE: 754 return false; 755 756 // These VariantKind cause the relocation to refer to something other than 757 // the symbol itself, like a linker generated table. Since the address of 758 // symbol is not relevant, we cannot replace the symbol with the 759 // section and patch the difference in the addend. 760 case MCSymbolRefExpr::VK_GOT: 761 case MCSymbolRefExpr::VK_PLT: 762 case MCSymbolRefExpr::VK_GOTPCREL: 763 case MCSymbolRefExpr::VK_Mips_GOT: 764 case MCSymbolRefExpr::VK_PPC_GOT_LO: 765 case MCSymbolRefExpr::VK_PPC_GOT_HI: 766 case MCSymbolRefExpr::VK_PPC_GOT_HA: 767 return true; 768 } 769 770 // An undefined symbol is not in any section, so the relocation has to point 771 // to the symbol itself. 772 const MCSymbol &Sym = SD->getSymbol(); 773 if (Sym.isUndefined()) 774 return true; 775 776 unsigned Binding = MCELF::GetBinding(*SD); 777 switch(Binding) { 778 default: 779 llvm_unreachable("Invalid Binding"); 780 case ELF::STB_LOCAL: 781 break; 782 case ELF::STB_WEAK: 783 // If the symbol is weak, it might be overridden by a symbol in another 784 // file. The relocation has to point to the symbol so that the linker 785 // can update it. 786 return true; 787 case ELF::STB_GLOBAL: 788 // Global ELF symbols can be preempted by the dynamic linker. The relocation 789 // has to point to the symbol for a reason analogous to the STB_WEAK case. 790 return true; 791 } 792 793 // If a relocation points to a mergeable section, we have to be careful. 794 // If the offset is zero, a relocation with the section will encode the 795 // same information. With a non-zero offset, the situation is different. 796 // For example, a relocation can point 42 bytes past the end of a string. 797 // If we change such a relocation to use the section, the linker would think 798 // that it pointed to another string and subtracting 42 at runtime will 799 // produce the wrong value. 800 auto &Sec = cast<MCSectionELF>(Sym.getSection()); 801 unsigned Flags = Sec.getFlags(); 802 if (Flags & ELF::SHF_MERGE) { 803 if (C != 0) 804 return true; 805 806 // It looks like gold has a bug (http://sourceware.org/PR16794) and can 807 // only handle section relocations to mergeable sections if using RELA. 808 if (!hasRelocationAddend()) 809 return true; 810 } 811 812 // Most TLS relocations use a got, so they need the symbol. Even those that 813 // are just an offset (@tpoff), require a symbol in some linkers (gold, 814 // but not bfd ld). 815 if (Flags & ELF::SHF_TLS) 816 return true; 817 818 // If the symbol is a thumb function the final relocation must set the lowest 819 // bit. With a symbol that is done by just having the symbol have that bit 820 // set, so we would lose the bit if we relocated with the section. 821 // FIXME: We could use the section but add the bit to the relocation value. 822 if (SD->getFlags() & ELF_Other_ThumbFunc) 823 return true; 824 825 if (TargetObjectWriter->needsRelocateWithSymbol(Type)) 826 return true; 827 return false; 828 } 829 830 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm, 831 const MCAsmLayout &Layout, 832 const MCFragment *Fragment, 833 const MCFixup &Fixup, 834 MCValue Target, 835 bool &IsPCRel, 836 uint64_t &FixedValue) { 837 const MCSectionData *FixupSection = Fragment->getParent(); 838 uint64_t C = Target.getConstant(); 839 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); 840 841 if (const MCSymbolRefExpr *RefB = Target.getSymB()) { 842 assert(RefB->getKind() == MCSymbolRefExpr::VK_None && 843 "Should not have constructed this"); 844 845 // Let A, B and C being the components of Target and R be the location of 846 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C). 847 // If it is pcrel, we want to compute (A - B + C - R). 848 849 // In general, ELF has no relocations for -B. It can only represent (A + C) 850 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can 851 // replace B to implement it: (A - R - K + C) 852 if (IsPCRel) 853 Asm.getContext().FatalError( 854 Fixup.getLoc(), 855 "No relocation available to represent this relative expression"); 856 857 const MCSymbol &SymB = RefB->getSymbol(); 858 859 if (SymB.isUndefined()) 860 Asm.getContext().FatalError( 861 Fixup.getLoc(), 862 Twine("symbol '") + SymB.getName() + 863 "' can not be undefined in a subtraction expression"); 864 865 assert(!SymB.isAbsolute() && "Should have been folded"); 866 const MCSection &SecB = SymB.getSection(); 867 if (&SecB != &FixupSection->getSection()) 868 Asm.getContext().FatalError( 869 Fixup.getLoc(), "Cannot represent a difference across sections"); 870 871 const MCSymbolData &SymBD = Asm.getSymbolData(SymB); 872 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD); 873 uint64_t K = SymBOffset - FixupOffset; 874 IsPCRel = true; 875 C -= K; 876 } 877 878 // We either rejected the fixup or folded B into C at this point. 879 const MCSymbolRefExpr *RefA = Target.getSymA(); 880 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr; 881 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr; 882 883 unsigned Type = GetRelocType(Target, Fixup, IsPCRel); 884 bool RelocateWithSymbol = shouldRelocateWithSymbol(RefA, SymAD, C, Type); 885 if (!RelocateWithSymbol && SymA && !SymA->isUndefined()) 886 C += Layout.getSymbolOffset(SymAD); 887 888 uint64_t Addend = 0; 889 if (hasRelocationAddend()) { 890 Addend = C; 891 C = 0; 892 } 893 894 FixedValue = C; 895 896 // FIXME: What is this!?!? 897 MCSymbolRefExpr::VariantKind Modifier = 898 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None; 899 if (RelocNeedsGOT(Modifier)) 900 NeedsGOT = true; 901 902 if (!RelocateWithSymbol) { 903 const MCSection *SecA = 904 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr; 905 const MCSectionData *SecAD = SecA ? &Asm.getSectionData(*SecA) : nullptr; 906 ELFRelocationEntry Rec(FixupOffset, SecAD, Type, Addend); 907 Relocations[FixupSection].push_back(Rec); 908 return; 909 } 910 911 if (SymA) { 912 if (const MCSymbol *R = Renames.lookup(SymA)) 913 SymA = R; 914 915 if (RefA->getKind() == MCSymbolRefExpr::VK_WEAKREF) 916 WeakrefUsedInReloc.insert(SymA); 917 else 918 UsedInReloc.insert(SymA); 919 } 920 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend); 921 Relocations[FixupSection].push_back(Rec); 922 return; 923 } 924 925 926 uint64_t 927 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm, 928 const MCSymbol *S) { 929 MCSymbolData &SD = Asm.getSymbolData(*S); 930 return SD.getIndex(); 931 } 932 933 bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm, 934 const MCSymbolData &Data, 935 bool Used, bool Renamed) { 936 const MCSymbol &Symbol = Data.getSymbol(); 937 if (Symbol.isVariable()) { 938 const MCExpr *Expr = Symbol.getVariableValue(); 939 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) { 940 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF) 941 return false; 942 } 943 } 944 945 if (Used) 946 return true; 947 948 if (Renamed) 949 return false; 950 951 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_") 952 return true; 953 954 const MCSymbol &A = Symbol.AliasedSymbol(); 955 if (Symbol.isVariable() && !A.isVariable() && A.isUndefined()) 956 return false; 957 958 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL; 959 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal) 960 return false; 961 962 if (Symbol.isTemporary()) 963 return false; 964 965 return true; 966 } 967 968 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isSignature, 969 bool isUsedInReloc) { 970 if (Data.isExternal()) 971 return false; 972 973 const MCSymbol &Symbol = Data.getSymbol(); 974 const MCSymbol &RefSymbol = Symbol.AliasedSymbol(); 975 976 if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) { 977 if (isSignature && !isUsedInReloc) 978 return true; 979 980 return false; 981 } 982 983 return true; 984 } 985 986 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm, 987 SectionIndexMapTy &SectionIndexMap, 988 const RelMapTy &RelMap) { 989 unsigned Index = 1; 990 for (MCAssembler::iterator it = Asm.begin(), 991 ie = Asm.end(); it != ie; ++it) { 992 const MCSectionELF &Section = 993 static_cast<const MCSectionELF &>(it->getSection()); 994 if (Section.getType() != ELF::SHT_GROUP) 995 continue; 996 SectionIndexMap[&Section] = Index++; 997 } 998 999 for (MCAssembler::iterator it = Asm.begin(), 1000 ie = Asm.end(); it != ie; ++it) { 1001 const MCSectionELF &Section = 1002 static_cast<const MCSectionELF &>(it->getSection()); 1003 if (Section.getType() == ELF::SHT_GROUP || 1004 Section.getType() == ELF::SHT_REL || 1005 Section.getType() == ELF::SHT_RELA) 1006 continue; 1007 SectionIndexMap[&Section] = Index++; 1008 const MCSectionELF *RelSection = RelMap.lookup(&Section); 1009 if (RelSection) 1010 SectionIndexMap[RelSection] = Index++; 1011 } 1012 } 1013 1014 void 1015 ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout, 1016 const SectionIndexMapTy &SectionIndexMap, 1017 RevGroupMapTy RevGroupMap, 1018 unsigned NumRegularSections) { 1019 // FIXME: Is this the correct place to do this? 1020 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed? 1021 if (NeedsGOT) { 1022 StringRef Name = "_GLOBAL_OFFSET_TABLE_"; 1023 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name); 1024 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym); 1025 Data.setExternal(true); 1026 MCELF::SetBinding(Data, ELF::STB_GLOBAL); 1027 } 1028 1029 // Index 0 is always the empty string. 1030 StringMap<uint64_t> StringIndexMap; 1031 StringTable += '\x00'; 1032 1033 // FIXME: We could optimize suffixes in strtab in the same way we 1034 // optimize them in shstrtab. 1035 1036 for (MCAssembler::const_file_name_iterator it = Asm.file_names_begin(), 1037 ie = Asm.file_names_end(); 1038 it != ie; 1039 ++it) { 1040 StringRef Name = *it; 1041 uint64_t &Entry = StringIndexMap[Name]; 1042 if (!Entry) { 1043 Entry = StringTable.size(); 1044 StringTable += Name; 1045 StringTable += '\x00'; 1046 } 1047 FileSymbolData.push_back(Entry); 1048 } 1049 1050 // Add the data for the symbols. 1051 for (MCSymbolData &SD : Asm.symbols()) { 1052 const MCSymbol &Symbol = SD.getSymbol(); 1053 1054 bool Used = UsedInReloc.count(&Symbol); 1055 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol); 1056 bool isSignature = RevGroupMap.count(&Symbol); 1057 1058 if (!isInSymtab(Asm, SD, 1059 Used || WeakrefUsed || isSignature, 1060 Renames.count(&Symbol))) 1061 continue; 1062 1063 ELFSymbolData MSD; 1064 MSD.SymbolData = &SD; 1065 const MCSymbol *BaseSymbol = getBaseSymbol(Layout, Symbol); 1066 1067 // Undefined symbols are global, but this is the first place we 1068 // are able to set it. 1069 bool Local = isLocal(SD, isSignature, Used); 1070 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) { 1071 assert(BaseSymbol); 1072 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol); 1073 MCELF::SetBinding(SD, ELF::STB_GLOBAL); 1074 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL); 1075 } 1076 1077 if (!BaseSymbol) { 1078 MSD.SectionIndex = ELF::SHN_ABS; 1079 } else if (SD.isCommon()) { 1080 assert(!Local); 1081 MSD.SectionIndex = ELF::SHN_COMMON; 1082 } else if (BaseSymbol->isUndefined()) { 1083 if (isSignature && !Used) 1084 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]); 1085 else 1086 MSD.SectionIndex = ELF::SHN_UNDEF; 1087 if (!Used && WeakrefUsed) 1088 MCELF::SetBinding(SD, ELF::STB_WEAK); 1089 } else { 1090 const MCSectionELF &Section = 1091 static_cast<const MCSectionELF&>(BaseSymbol->getSection()); 1092 MSD.SectionIndex = SectionIndexMap.lookup(&Section); 1093 assert(MSD.SectionIndex && "Invalid section index!"); 1094 } 1095 1096 // The @@@ in symbol version is replaced with @ in undefined symbols and 1097 // @@ in defined ones. 1098 StringRef Name = Symbol.getName(); 1099 SmallString<32> Buf; 1100 1101 size_t Pos = Name.find("@@@"); 1102 if (Pos != StringRef::npos) { 1103 Buf += Name.substr(0, Pos); 1104 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1; 1105 Buf += Name.substr(Pos + Skip); 1106 Name = Buf; 1107 } 1108 1109 uint64_t &Entry = StringIndexMap[Name]; 1110 if (!Entry) { 1111 Entry = StringTable.size(); 1112 StringTable += Name; 1113 StringTable += '\x00'; 1114 } 1115 MSD.StringIndex = Entry; 1116 if (MSD.SectionIndex == ELF::SHN_UNDEF) 1117 UndefinedSymbolData.push_back(MSD); 1118 else if (Local) 1119 LocalSymbolData.push_back(MSD); 1120 else 1121 ExternalSymbolData.push_back(MSD); 1122 } 1123 1124 // Symbols are required to be in lexicographic order. 1125 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end()); 1126 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end()); 1127 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end()); 1128 1129 // Set the symbol indices. Local symbols must come before all other 1130 // symbols with non-local bindings. 1131 unsigned Index = FileSymbolData.size() + 1; 1132 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) 1133 LocalSymbolData[i].SymbolData->setIndex(Index++); 1134 1135 Index += NumRegularSections; 1136 1137 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) 1138 ExternalSymbolData[i].SymbolData->setIndex(Index++); 1139 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) 1140 UndefinedSymbolData[i].SymbolData->setIndex(Index++); 1141 } 1142 1143 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm, 1144 MCAsmLayout &Layout, 1145 RelMapTy &RelMap) { 1146 for (MCAssembler::const_iterator it = Asm.begin(), 1147 ie = Asm.end(); it != ie; ++it) { 1148 const MCSectionData &SD = *it; 1149 if (Relocations[&SD].empty()) 1150 continue; 1151 1152 MCContext &Ctx = Asm.getContext(); 1153 const MCSectionELF &Section = 1154 static_cast<const MCSectionELF&>(SD.getSection()); 1155 1156 const StringRef SectionName = Section.getSectionName(); 1157 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel"; 1158 RelaSectionName += SectionName; 1159 1160 unsigned EntrySize; 1161 if (hasRelocationAddend()) 1162 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela); 1163 else 1164 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel); 1165 1166 unsigned Flags = 0; 1167 StringRef Group = ""; 1168 if (Section.getFlags() & ELF::SHF_GROUP) { 1169 Flags = ELF::SHF_GROUP; 1170 Group = Section.getGroup()->getName(); 1171 } 1172 1173 const MCSectionELF *RelaSection = 1174 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ? 1175 ELF::SHT_RELA : ELF::SHT_REL, Flags, 1176 SectionKind::getReadOnly(), 1177 EntrySize, Group); 1178 RelMap[&Section] = RelaSection; 1179 Asm.getOrCreateSectionData(*RelaSection); 1180 } 1181 } 1182 1183 static SmallVector<char, 128> 1184 getUncompressedData(MCAsmLayout &Layout, 1185 MCSectionData::FragmentListType &Fragments) { 1186 SmallVector<char, 128> UncompressedData; 1187 for (const MCFragment &F : Fragments) { 1188 const SmallVectorImpl<char> *Contents; 1189 switch (F.getKind()) { 1190 case MCFragment::FT_Data: 1191 Contents = &cast<MCDataFragment>(F).getContents(); 1192 break; 1193 case MCFragment::FT_Dwarf: 1194 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents(); 1195 break; 1196 case MCFragment::FT_DwarfFrame: 1197 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents(); 1198 break; 1199 default: 1200 llvm_unreachable( 1201 "Not expecting any other fragment types in a debug_* section"); 1202 } 1203 UncompressedData.append(Contents->begin(), Contents->end()); 1204 } 1205 return UncompressedData; 1206 } 1207 1208 // Include the debug info compression header: 1209 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section, 1210 // useful for consumers to preallocate a buffer to decompress into. 1211 static bool 1212 prependCompressionHeader(uint64_t Size, 1213 SmallVectorImpl<char> &CompressedContents) { 1214 static const StringRef Magic = "ZLIB"; 1215 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size()) 1216 return false; 1217 if (sys::IsLittleEndianHost) 1218 Size = sys::SwapByteOrder(Size); 1219 CompressedContents.insert(CompressedContents.begin(), 1220 Magic.size() + sizeof(Size), 0); 1221 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin()); 1222 std::copy(reinterpret_cast<char *>(&Size), 1223 reinterpret_cast<char *>(&Size + 1), 1224 CompressedContents.begin() + Magic.size()); 1225 return true; 1226 } 1227 1228 // Return a single fragment containing the compressed contents of the whole 1229 // section. Null if the section was not compressed for any reason. 1230 static std::unique_ptr<MCDataFragment> 1231 getCompressedFragment(MCAsmLayout &Layout, 1232 MCSectionData::FragmentListType &Fragments) { 1233 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment()); 1234 1235 // Gather the uncompressed data from all the fragments, recording the 1236 // alignment fragment, if seen, and any fixups. 1237 SmallVector<char, 128> UncompressedData = 1238 getUncompressedData(Layout, Fragments); 1239 1240 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents(); 1241 1242 zlib::Status Success = zlib::compress( 1243 StringRef(UncompressedData.data(), UncompressedData.size()), 1244 CompressedContents); 1245 if (Success != zlib::StatusOK) 1246 return nullptr; 1247 1248 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) 1249 return nullptr; 1250 1251 return CompressedFragment; 1252 } 1253 1254 static void UpdateSymbols(const MCAsmLayout &Layout, const MCSectionData &SD, 1255 MCAssembler::symbol_range Symbols, 1256 MCFragment *NewFragment) { 1257 for (MCSymbolData &Data : Symbols) { 1258 MCFragment *F = Data.getFragment(); 1259 if (F && F->getParent() == &SD) { 1260 Data.setOffset(Data.getOffset() + 1261 Layout.getFragmentOffset(Data.Fragment)); 1262 Data.setFragment(NewFragment); 1263 } 1264 } 1265 } 1266 1267 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout, 1268 const MCSectionELF &Section, 1269 MCSectionData &SD) { 1270 StringRef SectionName = Section.getSectionName(); 1271 MCSectionData::FragmentListType &Fragments = SD.getFragmentList(); 1272 1273 std::unique_ptr<MCDataFragment> CompressedFragment = 1274 getCompressedFragment(Layout, Fragments); 1275 1276 // Leave the section as-is if the fragments could not be compressed. 1277 if (!CompressedFragment) 1278 return; 1279 1280 // Update the fragment+offsets of any symbols referring to fragments in this 1281 // section to refer to the new fragment. 1282 UpdateSymbols(Layout, SD, Asm.symbols(), CompressedFragment.get()); 1283 1284 // Invalidate the layout for the whole section since it will have new and 1285 // different fragments now. 1286 Layout.invalidateFragmentsFrom(&Fragments.front()); 1287 Fragments.clear(); 1288 1289 // Complete the initialization of the new fragment 1290 CompressedFragment->setParent(&SD); 1291 CompressedFragment->setLayoutOrder(0); 1292 Fragments.push_back(CompressedFragment.release()); 1293 1294 // Rename from .debug_* to .zdebug_* 1295 Asm.getContext().renameELFSection(&Section, 1296 (".z" + SectionName.drop_front(1)).str()); 1297 } 1298 1299 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm, 1300 MCAsmLayout &Layout) { 1301 if (!Asm.getContext().getAsmInfo()->compressDebugSections()) 1302 return; 1303 1304 for (MCSectionData &SD : Asm) { 1305 const MCSectionELF &Section = 1306 static_cast<const MCSectionELF &>(SD.getSection()); 1307 StringRef SectionName = Section.getSectionName(); 1308 1309 // Compressing debug_frame requires handling alignment fragments which is 1310 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow 1311 // for writing to arbitrary buffers) for little benefit. 1312 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame") 1313 continue; 1314 1315 CompressDebugSection(Asm, Layout, Section, SD); 1316 } 1317 } 1318 1319 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 1320 const RelMapTy &RelMap) { 1321 for (MCAssembler::const_iterator it = Asm.begin(), 1322 ie = Asm.end(); it != ie; ++it) { 1323 const MCSectionData &SD = *it; 1324 const MCSectionELF &Section = 1325 static_cast<const MCSectionELF&>(SD.getSection()); 1326 1327 const MCSectionELF *RelaSection = RelMap.lookup(&Section); 1328 if (!RelaSection) 1329 continue; 1330 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection); 1331 RelaSD.setAlignment(is64Bit() ? 8 : 4); 1332 1333 MCDataFragment *F = new MCDataFragment(&RelaSD); 1334 WriteRelocationsFragment(Asm, F, &*it); 1335 } 1336 } 1337 1338 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type, 1339 uint64_t Flags, uint64_t Address, 1340 uint64_t Offset, uint64_t Size, 1341 uint32_t Link, uint32_t Info, 1342 uint64_t Alignment, 1343 uint64_t EntrySize) { 1344 Write32(Name); // sh_name: index into string table 1345 Write32(Type); // sh_type 1346 WriteWord(Flags); // sh_flags 1347 WriteWord(Address); // sh_addr 1348 WriteWord(Offset); // sh_offset 1349 WriteWord(Size); // sh_size 1350 Write32(Link); // sh_link 1351 Write32(Info); // sh_info 1352 WriteWord(Alignment); // sh_addralign 1353 WriteWord(EntrySize); // sh_entsize 1354 } 1355 1356 // ELF doesn't require relocations to be in any order. We sort by the r_offset, 1357 // just to match gnu as for easier comparison. The use type is an arbitrary way 1358 // of making the sort deterministic. 1359 static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) { 1360 const ELFRelocationEntry &A = *AP; 1361 const ELFRelocationEntry &B = *BP; 1362 if (A.Offset != B.Offset) 1363 return B.Offset - A.Offset; 1364 if (B.Type != A.Type) 1365 return A.Type - B.Type; 1366 llvm_unreachable("ELFRelocs might be unstable!"); 1367 } 1368 1369 static void sortRelocs(const MCAssembler &Asm, 1370 std::vector<ELFRelocationEntry> &Relocs) { 1371 array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel); 1372 } 1373 1374 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm, 1375 MCDataFragment *F, 1376 const MCSectionData *SD) { 1377 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD]; 1378 1379 sortRelocs(Asm, Relocs); 1380 1381 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) { 1382 const ELFRelocationEntry &Entry = Relocs[e - i - 1]; 1383 1384 unsigned Index; 1385 if (Entry.UseSymbol) { 1386 Index = getSymbolIndexInSymbolTable(Asm, Entry.Symbol); 1387 } else { 1388 const MCSectionData *Sec = Entry.Section; 1389 if (Sec) 1390 Index = Sec->getOrdinal() + FileSymbolData.size() + 1391 LocalSymbolData.size() + 1; 1392 else 1393 Index = 0; 1394 } 1395 1396 if (is64Bit()) { 1397 write(*F, Entry.Offset); 1398 if (TargetObjectWriter->isN64()) { 1399 write(*F, uint32_t(Index)); 1400 1401 write(*F, TargetObjectWriter->getRSsym(Entry.Type)); 1402 write(*F, TargetObjectWriter->getRType3(Entry.Type)); 1403 write(*F, TargetObjectWriter->getRType2(Entry.Type)); 1404 write(*F, TargetObjectWriter->getRType(Entry.Type)); 1405 } else { 1406 struct ELF::Elf64_Rela ERE64; 1407 ERE64.setSymbolAndType(Index, Entry.Type); 1408 write(*F, ERE64.r_info); 1409 } 1410 if (hasRelocationAddend()) 1411 write(*F, Entry.Addend); 1412 } else { 1413 write(*F, uint32_t(Entry.Offset)); 1414 1415 struct ELF::Elf32_Rela ERE32; 1416 ERE32.setSymbolAndType(Index, Entry.Type); 1417 write(*F, ERE32.r_info); 1418 1419 if (hasRelocationAddend()) 1420 write(*F, uint32_t(Entry.Addend)); 1421 } 1422 } 1423 } 1424 1425 static int compareBySuffix(const MCSectionELF *const *a, 1426 const MCSectionELF *const *b) { 1427 const StringRef &NameA = (*a)->getSectionName(); 1428 const StringRef &NameB = (*b)->getSectionName(); 1429 const unsigned sizeA = NameA.size(); 1430 const unsigned sizeB = NameB.size(); 1431 const unsigned len = std::min(sizeA, sizeB); 1432 for (unsigned int i = 0; i < len; ++i) { 1433 char ca = NameA[sizeA - i - 1]; 1434 char cb = NameB[sizeB - i - 1]; 1435 if (ca != cb) 1436 return cb - ca; 1437 } 1438 1439 return sizeB - sizeA; 1440 } 1441 1442 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm, 1443 MCAsmLayout &Layout, 1444 SectionIndexMapTy &SectionIndexMap, 1445 const RelMapTy &RelMap) { 1446 MCContext &Ctx = Asm.getContext(); 1447 MCDataFragment *F; 1448 1449 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32; 1450 1451 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as. 1452 const MCSectionELF *ShstrtabSection = 1453 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0, 1454 SectionKind::getReadOnly()); 1455 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection); 1456 ShstrtabSD.setAlignment(1); 1457 1458 const MCSectionELF *SymtabSection = 1459 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, 1460 SectionKind::getReadOnly(), 1461 EntrySize, ""); 1462 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection); 1463 SymtabSD.setAlignment(is64Bit() ? 8 : 4); 1464 1465 const MCSectionELF *StrtabSection; 1466 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0, 1467 SectionKind::getReadOnly()); 1468 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection); 1469 StrtabSD.setAlignment(1); 1470 1471 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1472 1473 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection); 1474 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection); 1475 StringTableIndex = SectionIndexMap.lookup(StrtabSection); 1476 1477 // Symbol table 1478 F = new MCDataFragment(&SymtabSD); 1479 WriteSymbolTable(F, Asm, Layout, SectionIndexMap); 1480 1481 F = new MCDataFragment(&StrtabSD); 1482 F->getContents().append(StringTable.begin(), StringTable.end()); 1483 1484 F = new MCDataFragment(&ShstrtabSD); 1485 1486 std::vector<const MCSectionELF*> Sections; 1487 for (MCAssembler::const_iterator it = Asm.begin(), 1488 ie = Asm.end(); it != ie; ++it) { 1489 const MCSectionELF &Section = 1490 static_cast<const MCSectionELF&>(it->getSection()); 1491 Sections.push_back(&Section); 1492 } 1493 array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix); 1494 1495 // Section header string table. 1496 // 1497 // The first entry of a string table holds a null character so skip 1498 // section 0. 1499 uint64_t Index = 1; 1500 F->getContents().push_back('\x00'); 1501 1502 for (unsigned int I = 0, E = Sections.size(); I != E; ++I) { 1503 const MCSectionELF &Section = *Sections[I]; 1504 1505 StringRef Name = Section.getSectionName(); 1506 if (I != 0) { 1507 StringRef PreviousName = Sections[I - 1]->getSectionName(); 1508 if (PreviousName.endswith(Name)) { 1509 SectionStringTableIndex[&Section] = Index - Name.size() - 1; 1510 continue; 1511 } 1512 } 1513 // Remember the index into the string table so we can write it 1514 // into the sh_name field of the section header table. 1515 SectionStringTableIndex[&Section] = Index; 1516 1517 Index += Name.size() + 1; 1518 F->getContents().append(Name.begin(), Name.end()); 1519 F->getContents().push_back('\x00'); 1520 } 1521 } 1522 1523 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm, 1524 MCAsmLayout &Layout, 1525 GroupMapTy &GroupMap, 1526 RevGroupMapTy &RevGroupMap, 1527 SectionIndexMapTy &SectionIndexMap, 1528 const RelMapTy &RelMap) { 1529 // Create the .note.GNU-stack section if needed. 1530 MCContext &Ctx = Asm.getContext(); 1531 if (Asm.getNoExecStack()) { 1532 const MCSectionELF *GnuStackSection = 1533 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0, 1534 SectionKind::getReadOnly()); 1535 Asm.getOrCreateSectionData(*GnuStackSection); 1536 } 1537 1538 // Build the groups 1539 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1540 it != ie; ++it) { 1541 const MCSectionELF &Section = 1542 static_cast<const MCSectionELF&>(it->getSection()); 1543 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1544 continue; 1545 1546 const MCSymbol *SignatureSymbol = Section.getGroup(); 1547 Asm.getOrCreateSymbolData(*SignatureSymbol); 1548 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol]; 1549 if (!Group) { 1550 Group = Ctx.CreateELFGroupSection(); 1551 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1552 Data.setAlignment(4); 1553 MCDataFragment *F = new MCDataFragment(&Data); 1554 write(*F, uint32_t(ELF::GRP_COMDAT)); 1555 } 1556 GroupMap[Group] = SignatureSymbol; 1557 } 1558 1559 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1560 1561 // Add sections to the groups 1562 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1563 it != ie; ++it) { 1564 const MCSectionELF &Section = 1565 static_cast<const MCSectionELF&>(it->getSection()); 1566 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1567 continue; 1568 const MCSectionELF *Group = RevGroupMap[Section.getGroup()]; 1569 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1570 // FIXME: we could use the previous fragment 1571 MCDataFragment *F = new MCDataFragment(&Data); 1572 uint32_t Index = SectionIndexMap.lookup(&Section); 1573 write(*F, Index); 1574 } 1575 } 1576 1577 void ELFObjectWriter::WriteSection(MCAssembler &Asm, 1578 const SectionIndexMapTy &SectionIndexMap, 1579 uint32_t GroupSymbolIndex, 1580 uint64_t Offset, uint64_t Size, 1581 uint64_t Alignment, 1582 const MCSectionELF &Section) { 1583 uint64_t sh_link = 0; 1584 uint64_t sh_info = 0; 1585 1586 switch(Section.getType()) { 1587 case ELF::SHT_DYNAMIC: 1588 sh_link = SectionStringTableIndex[&Section]; 1589 sh_info = 0; 1590 break; 1591 1592 case ELF::SHT_REL: 1593 case ELF::SHT_RELA: { 1594 const MCSectionELF *SymtabSection; 1595 const MCSectionELF *InfoSection; 1596 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 1597 0, 1598 SectionKind::getReadOnly()); 1599 sh_link = SectionIndexMap.lookup(SymtabSection); 1600 assert(sh_link && ".symtab not found"); 1601 1602 // Remove ".rel" and ".rela" prefixes. 1603 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5; 1604 StringRef SectionName = Section.getSectionName().substr(SecNameLen); 1605 StringRef GroupName = 1606 Section.getGroup() ? Section.getGroup()->getName() : ""; 1607 1608 InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS, 1609 0, SectionKind::getReadOnly(), 1610 0, GroupName); 1611 sh_info = SectionIndexMap.lookup(InfoSection); 1612 break; 1613 } 1614 1615 case ELF::SHT_SYMTAB: 1616 case ELF::SHT_DYNSYM: 1617 sh_link = StringTableIndex; 1618 sh_info = LastLocalSymbolIndex; 1619 break; 1620 1621 case ELF::SHT_SYMTAB_SHNDX: 1622 sh_link = SymbolTableIndex; 1623 break; 1624 1625 case ELF::SHT_PROGBITS: 1626 case ELF::SHT_STRTAB: 1627 case ELF::SHT_NOBITS: 1628 case ELF::SHT_NOTE: 1629 case ELF::SHT_NULL: 1630 case ELF::SHT_ARM_ATTRIBUTES: 1631 case ELF::SHT_INIT_ARRAY: 1632 case ELF::SHT_FINI_ARRAY: 1633 case ELF::SHT_PREINIT_ARRAY: 1634 case ELF::SHT_X86_64_UNWIND: 1635 case ELF::SHT_MIPS_REGINFO: 1636 case ELF::SHT_MIPS_OPTIONS: 1637 // Nothing to do. 1638 break; 1639 1640 case ELF::SHT_GROUP: 1641 sh_link = SymbolTableIndex; 1642 sh_info = GroupSymbolIndex; 1643 break; 1644 1645 default: 1646 assert(0 && "FIXME: sh_type value not supported!"); 1647 break; 1648 } 1649 1650 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM && 1651 Section.getType() == ELF::SHT_ARM_EXIDX) { 1652 StringRef SecName(Section.getSectionName()); 1653 if (SecName == ".ARM.exidx") { 1654 sh_link = SectionIndexMap.lookup( 1655 Asm.getContext().getELFSection(".text", 1656 ELF::SHT_PROGBITS, 1657 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, 1658 SectionKind::getText())); 1659 } else if (SecName.startswith(".ARM.exidx")) { 1660 StringRef GroupName = 1661 Section.getGroup() ? Section.getGroup()->getName() : ""; 1662 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection( 1663 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS, 1664 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText(), 0, 1665 GroupName)); 1666 } 1667 } 1668 1669 WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(), 1670 Section.getFlags(), 0, Offset, Size, sh_link, sh_info, 1671 Alignment, Section.getEntrySize()); 1672 } 1673 1674 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) { 1675 return SD.getOrdinal() == ~UINT32_C(0) && 1676 !SD.getSection().isVirtualSection(); 1677 } 1678 1679 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) { 1680 uint64_t Ret = 0; 1681 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1682 ++i) { 1683 const MCFragment &F = *i; 1684 assert(F.getKind() == MCFragment::FT_Data); 1685 Ret += cast<MCDataFragment>(F).getContents().size(); 1686 } 1687 return Ret; 1688 } 1689 1690 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout, 1691 const MCSectionData &SD) { 1692 if (IsELFMetaDataSection(SD)) 1693 return DataSectionSize(SD); 1694 return Layout.getSectionFileSize(&SD); 1695 } 1696 1697 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout, 1698 const MCSectionData &SD) { 1699 if (IsELFMetaDataSection(SD)) 1700 return DataSectionSize(SD); 1701 return Layout.getSectionAddressSize(&SD); 1702 } 1703 1704 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm, 1705 const MCAsmLayout &Layout, 1706 const MCSectionELF &Section) { 1707 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1708 1709 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment()); 1710 WriteZeros(Padding); 1711 1712 if (IsELFMetaDataSection(SD)) { 1713 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1714 ++i) { 1715 const MCFragment &F = *i; 1716 assert(F.getKind() == MCFragment::FT_Data); 1717 WriteBytes(cast<MCDataFragment>(F).getContents()); 1718 } 1719 } else { 1720 Asm.writeSectionData(&SD, Layout); 1721 } 1722 } 1723 1724 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm, 1725 const GroupMapTy &GroupMap, 1726 const MCAsmLayout &Layout, 1727 const SectionIndexMapTy &SectionIndexMap, 1728 const SectionOffsetMapTy &SectionOffsetMap) { 1729 const unsigned NumSections = Asm.size() + 1; 1730 1731 std::vector<const MCSectionELF*> Sections; 1732 Sections.resize(NumSections - 1); 1733 1734 for (SectionIndexMapTy::const_iterator i= 1735 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) { 1736 const std::pair<const MCSectionELF*, uint32_t> &p = *i; 1737 Sections[p.second - 1] = p.first; 1738 } 1739 1740 // Null section first. 1741 uint64_t FirstSectionSize = 1742 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0; 1743 uint32_t FirstSectionLink = 1744 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0; 1745 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0); 1746 1747 for (unsigned i = 0; i < NumSections - 1; ++i) { 1748 const MCSectionELF &Section = *Sections[i]; 1749 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1750 uint32_t GroupSymbolIndex; 1751 if (Section.getType() != ELF::SHT_GROUP) 1752 GroupSymbolIndex = 0; 1753 else 1754 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, 1755 GroupMap.lookup(&Section)); 1756 1757 uint64_t Size = GetSectionAddressSize(Layout, SD); 1758 1759 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex, 1760 SectionOffsetMap.lookup(&Section), Size, 1761 SD.getAlignment(), Section); 1762 } 1763 } 1764 1765 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm, 1766 std::vector<const MCSectionELF*> &Sections) { 1767 for (MCAssembler::iterator it = Asm.begin(), 1768 ie = Asm.end(); it != ie; ++it) { 1769 const MCSectionELF &Section = 1770 static_cast<const MCSectionELF &>(it->getSection()); 1771 if (Section.getType() == ELF::SHT_GROUP) 1772 Sections.push_back(&Section); 1773 } 1774 1775 for (MCAssembler::iterator it = Asm.begin(), 1776 ie = Asm.end(); it != ie; ++it) { 1777 const MCSectionELF &Section = 1778 static_cast<const MCSectionELF &>(it->getSection()); 1779 if (Section.getType() != ELF::SHT_GROUP && 1780 Section.getType() != ELF::SHT_REL && 1781 Section.getType() != ELF::SHT_RELA) 1782 Sections.push_back(&Section); 1783 } 1784 1785 for (MCAssembler::iterator it = Asm.begin(), 1786 ie = Asm.end(); it != ie; ++it) { 1787 const MCSectionELF &Section = 1788 static_cast<const MCSectionELF &>(it->getSection()); 1789 if (Section.getType() == ELF::SHT_REL || 1790 Section.getType() == ELF::SHT_RELA) 1791 Sections.push_back(&Section); 1792 } 1793 } 1794 1795 void ELFObjectWriter::WriteObject(MCAssembler &Asm, 1796 const MCAsmLayout &Layout) { 1797 GroupMapTy GroupMap; 1798 RevGroupMapTy RevGroupMap; 1799 SectionIndexMapTy SectionIndexMap; 1800 1801 unsigned NumUserSections = Asm.size(); 1802 1803 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout)); 1804 1805 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap; 1806 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1807 1808 const unsigned NumUserAndRelocSections = Asm.size(); 1809 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap, 1810 RevGroupMap, SectionIndexMap, RelMap); 1811 const unsigned AllSections = Asm.size(); 1812 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections; 1813 1814 unsigned NumRegularSections = NumUserSections + NumIndexedSections; 1815 1816 // Compute symbol table information. 1817 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, 1818 NumRegularSections); 1819 1820 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1821 1822 CreateMetadataSections(const_cast<MCAssembler&>(Asm), 1823 const_cast<MCAsmLayout&>(Layout), 1824 SectionIndexMap, 1825 RelMap); 1826 1827 uint64_t NaturalAlignment = is64Bit() ? 8 : 4; 1828 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 1829 sizeof(ELF::Elf32_Ehdr); 1830 uint64_t FileOff = HeaderSize; 1831 1832 std::vector<const MCSectionELF*> Sections; 1833 ComputeSectionOrder(Asm, Sections); 1834 unsigned NumSections = Sections.size(); 1835 SectionOffsetMapTy SectionOffsetMap; 1836 for (unsigned i = 0; i < NumRegularSections + 1; ++i) { 1837 const MCSectionELF &Section = *Sections[i]; 1838 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1839 1840 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1841 1842 // Remember the offset into the file for this section. 1843 SectionOffsetMap[&Section] = FileOff; 1844 1845 // Get the size of the section in the output file (including padding). 1846 FileOff += GetSectionFileSize(Layout, SD); 1847 } 1848 1849 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment); 1850 1851 const unsigned SectionHeaderOffset = FileOff - HeaderSize; 1852 1853 uint64_t SectionHeaderEntrySize = is64Bit() ? 1854 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr); 1855 FileOff += (NumSections + 1) * SectionHeaderEntrySize; 1856 1857 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) { 1858 const MCSectionELF &Section = *Sections[i]; 1859 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1860 1861 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1862 1863 // Remember the offset into the file for this section. 1864 SectionOffsetMap[&Section] = FileOff; 1865 1866 // Get the size of the section in the output file (including padding). 1867 FileOff += GetSectionFileSize(Layout, SD); 1868 } 1869 1870 // Write out the ELF header ... 1871 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1); 1872 1873 // ... then the regular sections ... 1874 // + because of .shstrtab 1875 for (unsigned i = 0; i < NumRegularSections + 1; ++i) 1876 WriteDataSectionData(Asm, Layout, *Sections[i]); 1877 1878 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment); 1879 WriteZeros(Padding); 1880 1881 // ... then the section header table ... 1882 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap, 1883 SectionOffsetMap); 1884 1885 // ... and then the remaining sections ... 1886 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) 1887 WriteDataSectionData(Asm, Layout, *Sections[i]); 1888 } 1889 1890 bool 1891 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 1892 const MCSymbolData &DataA, 1893 const MCFragment &FB, 1894 bool InSet, 1895 bool IsPCRel) const { 1896 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC) 1897 return false; 1898 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl( 1899 Asm, DataA, FB,InSet, IsPCRel); 1900 } 1901 1902 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW, 1903 raw_ostream &OS, 1904 bool IsLittleEndian) { 1905 return new ELFObjectWriter(MOTW, OS, IsLittleEndian); 1906 } 1907