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 OrigData.getFlags() & ELF_Other_ThumbFunc) 518 Res |= 1; 519 520 if (!Symbol || !Symbol->isInSection()) 521 return Res; 522 523 Res += Layout.getSymbolOffset(Data); 524 525 return Res; 526 } 527 528 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm, 529 const MCAsmLayout &Layout) { 530 // The presence of symbol versions causes undefined symbols and 531 // versions declared with @@@ to be renamed. 532 533 for (MCSymbolData &OriginalData : Asm.symbols()) { 534 const MCSymbol &Alias = OriginalData.getSymbol(); 535 const MCSymbol &Symbol = Alias.AliasedSymbol(); 536 MCSymbolData &SD = Asm.getSymbolData(Symbol); 537 538 // Not an alias. 539 if (&Symbol == &Alias) 540 continue; 541 542 StringRef AliasName = Alias.getName(); 543 size_t Pos = AliasName.find('@'); 544 if (Pos == StringRef::npos) 545 continue; 546 547 // Aliases defined with .symvar copy the binding from the symbol they alias. 548 // This is the first place we are able to copy this information. 549 OriginalData.setExternal(SD.isExternal()); 550 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD)); 551 552 StringRef Rest = AliasName.substr(Pos); 553 if (!Symbol.isUndefined() && !Rest.startswith("@@@")) 554 continue; 555 556 // FIXME: produce a better error message. 557 if (Symbol.isUndefined() && Rest.startswith("@@") && 558 !Rest.startswith("@@@")) 559 report_fatal_error("A @@ version cannot be undefined"); 560 561 Renames.insert(std::make_pair(&Symbol, &Alias)); 562 } 563 } 564 565 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) { 566 uint8_t Type = newType; 567 568 // Propagation rules: 569 // IFUNC > FUNC > OBJECT > NOTYPE 570 // TLS_OBJECT > OBJECT > NOTYPE 571 // 572 // dont let the new type degrade the old type 573 switch (origType) { 574 default: 575 break; 576 case ELF::STT_GNU_IFUNC: 577 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT || 578 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS) 579 Type = ELF::STT_GNU_IFUNC; 580 break; 581 case ELF::STT_FUNC: 582 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE || 583 Type == ELF::STT_TLS) 584 Type = ELF::STT_FUNC; 585 break; 586 case ELF::STT_OBJECT: 587 if (Type == ELF::STT_NOTYPE) 588 Type = ELF::STT_OBJECT; 589 break; 590 case ELF::STT_TLS: 591 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE || 592 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC) 593 Type = ELF::STT_TLS; 594 break; 595 } 596 597 return Type; 598 } 599 600 static const MCSymbol *getBaseSymbol(const MCAsmLayout &Layout, 601 const MCSymbol &Symbol) { 602 if (!Symbol.isVariable()) 603 return &Symbol; 604 605 const MCExpr *Expr = Symbol.getVariableValue(); 606 MCValue Value; 607 if (!Expr->EvaluateAsRelocatable(Value, &Layout)) 608 llvm_unreachable("Invalid Expression"); 609 assert(!Value.getSymB()); 610 const MCSymbolRefExpr *A = Value.getSymA(); 611 if (!A) 612 return nullptr; 613 return getBaseSymbol(Layout, A->getSymbol()); 614 } 615 616 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD, 617 const MCAsmLayout &Layout) { 618 MCSymbolData &OrigData = *MSD.SymbolData; 619 assert((!OrigData.getFragment() || 620 (&OrigData.getFragment()->getParent()->getSection() == 621 &OrigData.getSymbol().getSection())) && 622 "The symbol's section doesn't match the fragment's symbol"); 623 const MCSymbol *Base = getBaseSymbol(Layout, OrigData.getSymbol()); 624 625 // This has to be in sync with when computeSymbolTable uses SHN_ABS or 626 // SHN_COMMON. 627 bool IsReserved = !Base || OrigData.isCommon(); 628 629 // Binding and Type share the same byte as upper and lower nibbles 630 uint8_t Binding = MCELF::GetBinding(OrigData); 631 uint8_t Type = MCELF::GetType(OrigData); 632 MCSymbolData *BaseSD = nullptr; 633 if (Base) { 634 BaseSD = &Layout.getAssembler().getSymbolData(*Base); 635 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD)); 636 } 637 if (OrigData.getFlags() & ELF_Other_ThumbFunc) 638 Type = ELF::STT_FUNC; 639 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift); 640 641 // Other and Visibility share the same byte with Visibility using the lower 642 // 2 bits 643 uint8_t Visibility = MCELF::GetVisibility(OrigData); 644 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift); 645 Other |= Visibility; 646 647 uint64_t Value = SymbolValue(OrigData, Layout); 648 uint64_t Size = 0; 649 650 const MCExpr *ESize = OrigData.getSize(); 651 if (!ESize && Base) 652 ESize = BaseSD->getSize(); 653 654 if (ESize) { 655 int64_t Res; 656 if (!ESize->EvaluateAsAbsolute(Res, Layout)) 657 report_fatal_error("Size expression must be absolute."); 658 Size = Res; 659 } 660 661 // Write out the symbol table entry 662 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other, 663 MSD.SectionIndex, IsReserved); 664 } 665 666 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF, 667 MCAssembler &Asm, 668 const MCAsmLayout &Layout, 669 SectionIndexMapTy &SectionIndexMap) { 670 // The string table must be emitted first because we need the index 671 // into the string table for all the symbol names. 672 assert(StringTable.size() && "Missing string table"); 673 674 // FIXME: Make sure the start of the symbol table is aligned. 675 676 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF); 677 678 // The first entry is the undefined symbol entry. 679 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false); 680 681 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) { 682 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, 683 ELF::STV_DEFAULT, ELF::SHN_ABS, true); 684 } 685 686 // Write the symbol table entries. 687 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1; 688 689 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) { 690 ELFSymbolData &MSD = LocalSymbolData[i]; 691 WriteSymbol(Writer, MSD, Layout); 692 } 693 694 // Write out a symbol table entry for each regular section. 695 for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e; 696 ++i) { 697 const MCSectionELF &Section = 698 static_cast<const MCSectionELF&>(i->getSection()); 699 if (Section.getType() == ELF::SHT_RELA || 700 Section.getType() == ELF::SHT_REL || 701 Section.getType() == ELF::SHT_STRTAB || 702 Section.getType() == ELF::SHT_SYMTAB || 703 Section.getType() == ELF::SHT_SYMTAB_SHNDX) 704 continue; 705 Writer.writeSymbol(0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT, 706 SectionIndexMap.lookup(&Section), false); 707 LastLocalSymbolIndex++; 708 } 709 710 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) { 711 ELFSymbolData &MSD = ExternalSymbolData[i]; 712 MCSymbolData &Data = *MSD.SymbolData; 713 assert(((Data.getFlags() & ELF_STB_Global) || 714 (Data.getFlags() & ELF_STB_Weak)) && 715 "External symbol requires STB_GLOBAL or STB_WEAK flag"); 716 WriteSymbol(Writer, MSD, Layout); 717 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 718 LastLocalSymbolIndex++; 719 } 720 721 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) { 722 ELFSymbolData &MSD = UndefinedSymbolData[i]; 723 MCSymbolData &Data = *MSD.SymbolData; 724 WriteSymbol(Writer, MSD, Layout); 725 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 726 LastLocalSymbolIndex++; 727 } 728 } 729 730 // It is always valid to create a relocation with a symbol. It is preferable 731 // to use a relocation with a section if that is possible. Using the section 732 // allows us to omit some local symbols from the symbol table. 733 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCSymbolRefExpr *RefA, 734 const MCSymbolData *SD, 735 uint64_t C, 736 unsigned Type) const { 737 // A PCRel relocation to an absolute value has no symbol (or section). We 738 // represent that with a relocation to a null section. 739 if (!RefA) 740 return false; 741 742 MCSymbolRefExpr::VariantKind Kind = RefA->getKind(); 743 switch (Kind) { 744 default: 745 break; 746 // The .odp creation emits a relocation against the symbol ".TOC." which 747 // create a R_PPC64_TOC relocation. However the relocation symbol name 748 // in final object creation should be NULL, since the symbol does not 749 // really exist, it is just the reference to TOC base for the current 750 // object file. Since the symbol is undefined, returning false results 751 // in a relocation with a null section which is the desired result. 752 case MCSymbolRefExpr::VK_PPC_TOCBASE: 753 return false; 754 755 // These VariantKind cause the relocation to refer to something other than 756 // the symbol itself, like a linker generated table. Since the address of 757 // symbol is not relevant, we cannot replace the symbol with the 758 // section and patch the difference in the addend. 759 case MCSymbolRefExpr::VK_GOT: 760 case MCSymbolRefExpr::VK_PLT: 761 case MCSymbolRefExpr::VK_GOTPCREL: 762 case MCSymbolRefExpr::VK_Mips_GOT: 763 case MCSymbolRefExpr::VK_PPC_GOT_LO: 764 case MCSymbolRefExpr::VK_PPC_GOT_HI: 765 case MCSymbolRefExpr::VK_PPC_GOT_HA: 766 return true; 767 } 768 769 // An undefined symbol is not in any section, so the relocation has to point 770 // to the symbol itself. 771 const MCSymbol &Sym = SD->getSymbol(); 772 if (Sym.isUndefined()) 773 return true; 774 775 unsigned Binding = MCELF::GetBinding(*SD); 776 switch(Binding) { 777 default: 778 llvm_unreachable("Invalid Binding"); 779 case ELF::STB_LOCAL: 780 break; 781 case ELF::STB_WEAK: 782 // If the symbol is weak, it might be overridden by a symbol in another 783 // file. The relocation has to point to the symbol so that the linker 784 // can update it. 785 return true; 786 case ELF::STB_GLOBAL: 787 // Global ELF symbols can be preempted by the dynamic linker. The relocation 788 // has to point to the symbol for a reason analogous to the STB_WEAK case. 789 return true; 790 } 791 792 // If a relocation points to a mergeable section, we have to be careful. 793 // If the offset is zero, a relocation with the section will encode the 794 // same information. With a non-zero offset, the situation is different. 795 // For example, a relocation can point 42 bytes past the end of a string. 796 // If we change such a relocation to use the section, the linker would think 797 // that it pointed to another string and subtracting 42 at runtime will 798 // produce the wrong value. 799 auto &Sec = cast<MCSectionELF>(Sym.getSection()); 800 unsigned Flags = Sec.getFlags(); 801 if (Flags & ELF::SHF_MERGE) { 802 if (C != 0) 803 return true; 804 805 // It looks like gold has a bug (http://sourceware.org/PR16794) and can 806 // only handle section relocations to mergeable sections if using RELA. 807 if (!hasRelocationAddend()) 808 return true; 809 } 810 811 // Most TLS relocations use a got, so they need the symbol. Even those that 812 // are just an offset (@tpoff), require a symbol in some linkers (gold, 813 // but not bfd ld). 814 if (Flags & ELF::SHF_TLS) 815 return true; 816 817 // If the symbol is a thumb function the final relocation must set the lowest 818 // bit. With a symbol that is done by just having the symbol have that bit 819 // set, so we would lose the bit if we relocated with the section. 820 // FIXME: We could use the section but add the bit to the relocation value. 821 if (SD->getFlags() & ELF_Other_ThumbFunc) 822 return true; 823 824 if (TargetObjectWriter->needsRelocateWithSymbol(Type)) 825 return true; 826 return false; 827 } 828 829 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm, 830 const MCAsmLayout &Layout, 831 const MCFragment *Fragment, 832 const MCFixup &Fixup, 833 MCValue Target, 834 bool &IsPCRel, 835 uint64_t &FixedValue) { 836 const MCSectionData *FixupSection = Fragment->getParent(); 837 uint64_t C = Target.getConstant(); 838 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); 839 840 if (const MCSymbolRefExpr *RefB = Target.getSymB()) { 841 assert(RefB->getKind() == MCSymbolRefExpr::VK_None && 842 "Should not have constructed this"); 843 844 // Let A, B and C being the components of Target and R be the location of 845 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C). 846 // If it is pcrel, we want to compute (A - B + C - R). 847 848 // In general, ELF has no relocations for -B. It can only represent (A + C) 849 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can 850 // replace B to implement it: (A - R - K + C) 851 if (IsPCRel) 852 Asm.getContext().FatalError( 853 Fixup.getLoc(), 854 "No relocation available to represent this relative expression"); 855 856 const MCSymbol &SymB = RefB->getSymbol(); 857 858 if (SymB.isUndefined()) 859 Asm.getContext().FatalError( 860 Fixup.getLoc(), 861 Twine("symbol '") + SymB.getName() + 862 "' can not be undefined in a subtraction expression"); 863 864 assert(!SymB.isAbsolute() && "Should have been folded"); 865 const MCSection &SecB = SymB.getSection(); 866 if (&SecB != &FixupSection->getSection()) 867 Asm.getContext().FatalError( 868 Fixup.getLoc(), "Cannot represent a difference across sections"); 869 870 const MCSymbolData &SymBD = Asm.getSymbolData(SymB); 871 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD); 872 uint64_t K = SymBOffset - FixupOffset; 873 IsPCRel = true; 874 C -= K; 875 } 876 877 // We either rejected the fixup or folded B into C at this point. 878 const MCSymbolRefExpr *RefA = Target.getSymA(); 879 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr; 880 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr; 881 882 unsigned Type = GetRelocType(Target, Fixup, IsPCRel); 883 bool RelocateWithSymbol = shouldRelocateWithSymbol(RefA, SymAD, C, Type); 884 if (!RelocateWithSymbol && SymA && !SymA->isUndefined()) 885 C += Layout.getSymbolOffset(SymAD); 886 887 uint64_t Addend = 0; 888 if (hasRelocationAddend()) { 889 Addend = C; 890 C = 0; 891 } 892 893 FixedValue = C; 894 895 // FIXME: What is this!?!? 896 MCSymbolRefExpr::VariantKind Modifier = 897 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None; 898 if (RelocNeedsGOT(Modifier)) 899 NeedsGOT = true; 900 901 if (!RelocateWithSymbol) { 902 const MCSection *SecA = 903 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr; 904 const MCSectionData *SecAD = SecA ? &Asm.getSectionData(*SecA) : nullptr; 905 ELFRelocationEntry Rec(FixupOffset, SecAD, Type, Addend); 906 Relocations[FixupSection].push_back(Rec); 907 return; 908 } 909 910 if (SymA) { 911 if (const MCSymbol *R = Renames.lookup(SymA)) 912 SymA = R; 913 914 if (RefA->getKind() == MCSymbolRefExpr::VK_WEAKREF) 915 WeakrefUsedInReloc.insert(SymA); 916 else 917 UsedInReloc.insert(SymA); 918 } 919 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend); 920 Relocations[FixupSection].push_back(Rec); 921 return; 922 } 923 924 925 uint64_t 926 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm, 927 const MCSymbol *S) { 928 MCSymbolData &SD = Asm.getSymbolData(*S); 929 return SD.getIndex(); 930 } 931 932 bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm, 933 const MCSymbolData &Data, 934 bool Used, bool Renamed) { 935 const MCSymbol &Symbol = Data.getSymbol(); 936 if (Symbol.isVariable()) { 937 const MCExpr *Expr = Symbol.getVariableValue(); 938 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) { 939 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF) 940 return false; 941 } 942 } 943 944 if (Used) 945 return true; 946 947 if (Renamed) 948 return false; 949 950 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_") 951 return true; 952 953 const MCSymbol &A = Symbol.AliasedSymbol(); 954 if (Symbol.isVariable() && !A.isVariable() && A.isUndefined()) 955 return false; 956 957 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL; 958 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal) 959 return false; 960 961 if (Symbol.isTemporary()) 962 return false; 963 964 return true; 965 } 966 967 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isSignature, 968 bool isUsedInReloc) { 969 if (Data.isExternal()) 970 return false; 971 972 const MCSymbol &Symbol = Data.getSymbol(); 973 const MCSymbol &RefSymbol = Symbol.AliasedSymbol(); 974 975 if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) { 976 if (isSignature && !isUsedInReloc) 977 return true; 978 979 return false; 980 } 981 982 return true; 983 } 984 985 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm, 986 SectionIndexMapTy &SectionIndexMap, 987 const RelMapTy &RelMap) { 988 unsigned Index = 1; 989 for (MCAssembler::iterator it = Asm.begin(), 990 ie = Asm.end(); it != ie; ++it) { 991 const MCSectionELF &Section = 992 static_cast<const MCSectionELF &>(it->getSection()); 993 if (Section.getType() != ELF::SHT_GROUP) 994 continue; 995 SectionIndexMap[&Section] = Index++; 996 } 997 998 for (MCAssembler::iterator it = Asm.begin(), 999 ie = Asm.end(); it != ie; ++it) { 1000 const MCSectionELF &Section = 1001 static_cast<const MCSectionELF &>(it->getSection()); 1002 if (Section.getType() == ELF::SHT_GROUP || 1003 Section.getType() == ELF::SHT_REL || 1004 Section.getType() == ELF::SHT_RELA) 1005 continue; 1006 SectionIndexMap[&Section] = Index++; 1007 const MCSectionELF *RelSection = RelMap.lookup(&Section); 1008 if (RelSection) 1009 SectionIndexMap[RelSection] = Index++; 1010 } 1011 } 1012 1013 void 1014 ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout, 1015 const SectionIndexMapTy &SectionIndexMap, 1016 RevGroupMapTy RevGroupMap, 1017 unsigned NumRegularSections) { 1018 // FIXME: Is this the correct place to do this? 1019 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed? 1020 if (NeedsGOT) { 1021 StringRef Name = "_GLOBAL_OFFSET_TABLE_"; 1022 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name); 1023 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym); 1024 Data.setExternal(true); 1025 MCELF::SetBinding(Data, ELF::STB_GLOBAL); 1026 } 1027 1028 // Index 0 is always the empty string. 1029 StringMap<uint64_t> StringIndexMap; 1030 StringTable += '\x00'; 1031 1032 // FIXME: We could optimize suffixes in strtab in the same way we 1033 // optimize them in shstrtab. 1034 1035 for (MCAssembler::const_file_name_iterator it = Asm.file_names_begin(), 1036 ie = Asm.file_names_end(); 1037 it != ie; 1038 ++it) { 1039 StringRef Name = *it; 1040 uint64_t &Entry = StringIndexMap[Name]; 1041 if (!Entry) { 1042 Entry = StringTable.size(); 1043 StringTable += Name; 1044 StringTable += '\x00'; 1045 } 1046 FileSymbolData.push_back(Entry); 1047 } 1048 1049 // Add the data for the symbols. 1050 for (MCSymbolData &SD : Asm.symbols()) { 1051 const MCSymbol &Symbol = SD.getSymbol(); 1052 1053 bool Used = UsedInReloc.count(&Symbol); 1054 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol); 1055 bool isSignature = RevGroupMap.count(&Symbol); 1056 1057 if (!isInSymtab(Asm, SD, 1058 Used || WeakrefUsed || isSignature, 1059 Renames.count(&Symbol))) 1060 continue; 1061 1062 ELFSymbolData MSD; 1063 MSD.SymbolData = &SD; 1064 const MCSymbol *BaseSymbol = getBaseSymbol(Layout, Symbol); 1065 1066 // Undefined symbols are global, but this is the first place we 1067 // are able to set it. 1068 bool Local = isLocal(SD, isSignature, Used); 1069 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) { 1070 assert(BaseSymbol); 1071 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol); 1072 MCELF::SetBinding(SD, ELF::STB_GLOBAL); 1073 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL); 1074 } 1075 1076 if (!BaseSymbol) { 1077 MSD.SectionIndex = ELF::SHN_ABS; 1078 } else if (SD.isCommon()) { 1079 assert(!Local); 1080 MSD.SectionIndex = ELF::SHN_COMMON; 1081 } else if (BaseSymbol->isUndefined()) { 1082 if (isSignature && !Used) 1083 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]); 1084 else 1085 MSD.SectionIndex = ELF::SHN_UNDEF; 1086 if (!Used && WeakrefUsed) 1087 MCELF::SetBinding(SD, ELF::STB_WEAK); 1088 } else { 1089 const MCSectionELF &Section = 1090 static_cast<const MCSectionELF&>(BaseSymbol->getSection()); 1091 MSD.SectionIndex = SectionIndexMap.lookup(&Section); 1092 assert(MSD.SectionIndex && "Invalid section index!"); 1093 } 1094 1095 // The @@@ in symbol version is replaced with @ in undefined symbols and 1096 // @@ in defined ones. 1097 StringRef Name = Symbol.getName(); 1098 SmallString<32> Buf; 1099 1100 size_t Pos = Name.find("@@@"); 1101 if (Pos != StringRef::npos) { 1102 Buf += Name.substr(0, Pos); 1103 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1; 1104 Buf += Name.substr(Pos + Skip); 1105 Name = Buf; 1106 } 1107 1108 uint64_t &Entry = StringIndexMap[Name]; 1109 if (!Entry) { 1110 Entry = StringTable.size(); 1111 StringTable += Name; 1112 StringTable += '\x00'; 1113 } 1114 MSD.StringIndex = Entry; 1115 if (MSD.SectionIndex == ELF::SHN_UNDEF) 1116 UndefinedSymbolData.push_back(MSD); 1117 else if (Local) 1118 LocalSymbolData.push_back(MSD); 1119 else 1120 ExternalSymbolData.push_back(MSD); 1121 } 1122 1123 // Symbols are required to be in lexicographic order. 1124 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end()); 1125 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end()); 1126 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end()); 1127 1128 // Set the symbol indices. Local symbols must come before all other 1129 // symbols with non-local bindings. 1130 unsigned Index = FileSymbolData.size() + 1; 1131 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) 1132 LocalSymbolData[i].SymbolData->setIndex(Index++); 1133 1134 Index += NumRegularSections; 1135 1136 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) 1137 ExternalSymbolData[i].SymbolData->setIndex(Index++); 1138 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) 1139 UndefinedSymbolData[i].SymbolData->setIndex(Index++); 1140 } 1141 1142 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm, 1143 MCAsmLayout &Layout, 1144 RelMapTy &RelMap) { 1145 for (MCAssembler::const_iterator it = Asm.begin(), 1146 ie = Asm.end(); it != ie; ++it) { 1147 const MCSectionData &SD = *it; 1148 if (Relocations[&SD].empty()) 1149 continue; 1150 1151 MCContext &Ctx = Asm.getContext(); 1152 const MCSectionELF &Section = 1153 static_cast<const MCSectionELF&>(SD.getSection()); 1154 1155 const StringRef SectionName = Section.getSectionName(); 1156 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel"; 1157 RelaSectionName += SectionName; 1158 1159 unsigned EntrySize; 1160 if (hasRelocationAddend()) 1161 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela); 1162 else 1163 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel); 1164 1165 unsigned Flags = 0; 1166 StringRef Group = ""; 1167 if (Section.getFlags() & ELF::SHF_GROUP) { 1168 Flags = ELF::SHF_GROUP; 1169 Group = Section.getGroup()->getName(); 1170 } 1171 1172 const MCSectionELF *RelaSection = 1173 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ? 1174 ELF::SHT_RELA : ELF::SHT_REL, Flags, 1175 SectionKind::getReadOnly(), 1176 EntrySize, Group); 1177 RelMap[&Section] = RelaSection; 1178 Asm.getOrCreateSectionData(*RelaSection); 1179 } 1180 } 1181 1182 static SmallVector<char, 128> 1183 getUncompressedData(MCAsmLayout &Layout, 1184 MCSectionData::FragmentListType &Fragments) { 1185 SmallVector<char, 128> UncompressedData; 1186 for (const MCFragment &F : Fragments) { 1187 const SmallVectorImpl<char> *Contents; 1188 switch (F.getKind()) { 1189 case MCFragment::FT_Data: 1190 Contents = &cast<MCDataFragment>(F).getContents(); 1191 break; 1192 case MCFragment::FT_Dwarf: 1193 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents(); 1194 break; 1195 case MCFragment::FT_DwarfFrame: 1196 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents(); 1197 break; 1198 default: 1199 llvm_unreachable( 1200 "Not expecting any other fragment types in a debug_* section"); 1201 } 1202 UncompressedData.append(Contents->begin(), Contents->end()); 1203 } 1204 return UncompressedData; 1205 } 1206 1207 // Include the debug info compression header: 1208 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section, 1209 // useful for consumers to preallocate a buffer to decompress into. 1210 static bool 1211 prependCompressionHeader(uint64_t Size, 1212 SmallVectorImpl<char> &CompressedContents) { 1213 static const StringRef Magic = "ZLIB"; 1214 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size()) 1215 return false; 1216 if (sys::IsLittleEndianHost) 1217 Size = sys::SwapByteOrder(Size); 1218 CompressedContents.insert(CompressedContents.begin(), 1219 Magic.size() + sizeof(Size), 0); 1220 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin()); 1221 std::copy(reinterpret_cast<char *>(&Size), 1222 reinterpret_cast<char *>(&Size + 1), 1223 CompressedContents.begin() + Magic.size()); 1224 return true; 1225 } 1226 1227 // Return a single fragment containing the compressed contents of the whole 1228 // section. Null if the section was not compressed for any reason. 1229 static std::unique_ptr<MCDataFragment> 1230 getCompressedFragment(MCAsmLayout &Layout, 1231 MCSectionData::FragmentListType &Fragments) { 1232 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment()); 1233 1234 // Gather the uncompressed data from all the fragments, recording the 1235 // alignment fragment, if seen, and any fixups. 1236 SmallVector<char, 128> UncompressedData = 1237 getUncompressedData(Layout, Fragments); 1238 1239 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents(); 1240 1241 zlib::Status Success = zlib::compress( 1242 StringRef(UncompressedData.data(), UncompressedData.size()), 1243 CompressedContents); 1244 if (Success != zlib::StatusOK) 1245 return nullptr; 1246 1247 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) 1248 return nullptr; 1249 1250 return CompressedFragment; 1251 } 1252 1253 static void UpdateSymbols(const MCAsmLayout &Layout, const MCSectionData &SD, 1254 MCAssembler::symbol_range Symbols, 1255 MCFragment *NewFragment) { 1256 for (MCSymbolData &Data : Symbols) { 1257 MCFragment *F = Data.getFragment(); 1258 if (F && F->getParent() == &SD) { 1259 Data.setOffset(Data.getOffset() + 1260 Layout.getFragmentOffset(Data.Fragment)); 1261 Data.setFragment(NewFragment); 1262 } 1263 } 1264 } 1265 1266 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout, 1267 const MCSectionELF &Section, 1268 MCSectionData &SD) { 1269 StringRef SectionName = Section.getSectionName(); 1270 MCSectionData::FragmentListType &Fragments = SD.getFragmentList(); 1271 1272 std::unique_ptr<MCDataFragment> CompressedFragment = 1273 getCompressedFragment(Layout, Fragments); 1274 1275 // Leave the section as-is if the fragments could not be compressed. 1276 if (!CompressedFragment) 1277 return; 1278 1279 // Update the fragment+offsets of any symbols referring to fragments in this 1280 // section to refer to the new fragment. 1281 UpdateSymbols(Layout, SD, Asm.symbols(), CompressedFragment.get()); 1282 1283 // Invalidate the layout for the whole section since it will have new and 1284 // different fragments now. 1285 Layout.invalidateFragmentsFrom(&Fragments.front()); 1286 Fragments.clear(); 1287 1288 // Complete the initialization of the new fragment 1289 CompressedFragment->setParent(&SD); 1290 CompressedFragment->setLayoutOrder(0); 1291 Fragments.push_back(CompressedFragment.release()); 1292 1293 // Rename from .debug_* to .zdebug_* 1294 Asm.getContext().renameELFSection(&Section, 1295 (".z" + SectionName.drop_front(1)).str()); 1296 } 1297 1298 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm, 1299 MCAsmLayout &Layout) { 1300 if (!Asm.getContext().getAsmInfo()->compressDebugSections()) 1301 return; 1302 1303 for (MCSectionData &SD : Asm) { 1304 const MCSectionELF &Section = 1305 static_cast<const MCSectionELF &>(SD.getSection()); 1306 StringRef SectionName = Section.getSectionName(); 1307 1308 // Compressing debug_frame requires handling alignment fragments which is 1309 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow 1310 // for writing to arbitrary buffers) for little benefit. 1311 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame") 1312 continue; 1313 1314 CompressDebugSection(Asm, Layout, Section, SD); 1315 } 1316 } 1317 1318 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 1319 const RelMapTy &RelMap) { 1320 for (MCAssembler::const_iterator it = Asm.begin(), 1321 ie = Asm.end(); it != ie; ++it) { 1322 const MCSectionData &SD = *it; 1323 const MCSectionELF &Section = 1324 static_cast<const MCSectionELF&>(SD.getSection()); 1325 1326 const MCSectionELF *RelaSection = RelMap.lookup(&Section); 1327 if (!RelaSection) 1328 continue; 1329 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection); 1330 RelaSD.setAlignment(is64Bit() ? 8 : 4); 1331 1332 MCDataFragment *F = new MCDataFragment(&RelaSD); 1333 WriteRelocationsFragment(Asm, F, &*it); 1334 } 1335 } 1336 1337 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type, 1338 uint64_t Flags, uint64_t Address, 1339 uint64_t Offset, uint64_t Size, 1340 uint32_t Link, uint32_t Info, 1341 uint64_t Alignment, 1342 uint64_t EntrySize) { 1343 Write32(Name); // sh_name: index into string table 1344 Write32(Type); // sh_type 1345 WriteWord(Flags); // sh_flags 1346 WriteWord(Address); // sh_addr 1347 WriteWord(Offset); // sh_offset 1348 WriteWord(Size); // sh_size 1349 Write32(Link); // sh_link 1350 Write32(Info); // sh_info 1351 WriteWord(Alignment); // sh_addralign 1352 WriteWord(EntrySize); // sh_entsize 1353 } 1354 1355 // ELF doesn't require relocations to be in any order. We sort by the r_offset, 1356 // just to match gnu as for easier comparison. The use type is an arbitrary way 1357 // of making the sort deterministic. 1358 static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) { 1359 const ELFRelocationEntry &A = *AP; 1360 const ELFRelocationEntry &B = *BP; 1361 if (A.Offset != B.Offset) 1362 return B.Offset - A.Offset; 1363 if (B.Type != A.Type) 1364 return A.Type - B.Type; 1365 llvm_unreachable("ELFRelocs might be unstable!"); 1366 } 1367 1368 static void sortRelocs(const MCAssembler &Asm, 1369 std::vector<ELFRelocationEntry> &Relocs) { 1370 array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel); 1371 } 1372 1373 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm, 1374 MCDataFragment *F, 1375 const MCSectionData *SD) { 1376 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD]; 1377 1378 sortRelocs(Asm, Relocs); 1379 1380 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) { 1381 const ELFRelocationEntry &Entry = Relocs[e - i - 1]; 1382 1383 unsigned Index; 1384 if (Entry.UseSymbol) { 1385 Index = getSymbolIndexInSymbolTable(Asm, Entry.Symbol); 1386 } else { 1387 const MCSectionData *Sec = Entry.Section; 1388 if (Sec) 1389 Index = Sec->getOrdinal() + FileSymbolData.size() + 1390 LocalSymbolData.size() + 1; 1391 else 1392 Index = 0; 1393 } 1394 1395 if (is64Bit()) { 1396 write(*F, Entry.Offset); 1397 if (TargetObjectWriter->isN64()) { 1398 write(*F, uint32_t(Index)); 1399 1400 write(*F, TargetObjectWriter->getRSsym(Entry.Type)); 1401 write(*F, TargetObjectWriter->getRType3(Entry.Type)); 1402 write(*F, TargetObjectWriter->getRType2(Entry.Type)); 1403 write(*F, TargetObjectWriter->getRType(Entry.Type)); 1404 } else { 1405 struct ELF::Elf64_Rela ERE64; 1406 ERE64.setSymbolAndType(Index, Entry.Type); 1407 write(*F, ERE64.r_info); 1408 } 1409 if (hasRelocationAddend()) 1410 write(*F, Entry.Addend); 1411 } else { 1412 write(*F, uint32_t(Entry.Offset)); 1413 1414 struct ELF::Elf32_Rela ERE32; 1415 ERE32.setSymbolAndType(Index, Entry.Type); 1416 write(*F, ERE32.r_info); 1417 1418 if (hasRelocationAddend()) 1419 write(*F, uint32_t(Entry.Addend)); 1420 } 1421 } 1422 } 1423 1424 static int compareBySuffix(const MCSectionELF *const *a, 1425 const MCSectionELF *const *b) { 1426 const StringRef &NameA = (*a)->getSectionName(); 1427 const StringRef &NameB = (*b)->getSectionName(); 1428 const unsigned sizeA = NameA.size(); 1429 const unsigned sizeB = NameB.size(); 1430 const unsigned len = std::min(sizeA, sizeB); 1431 for (unsigned int i = 0; i < len; ++i) { 1432 char ca = NameA[sizeA - i - 1]; 1433 char cb = NameB[sizeB - i - 1]; 1434 if (ca != cb) 1435 return cb - ca; 1436 } 1437 1438 return sizeB - sizeA; 1439 } 1440 1441 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm, 1442 MCAsmLayout &Layout, 1443 SectionIndexMapTy &SectionIndexMap, 1444 const RelMapTy &RelMap) { 1445 MCContext &Ctx = Asm.getContext(); 1446 MCDataFragment *F; 1447 1448 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32; 1449 1450 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as. 1451 const MCSectionELF *ShstrtabSection = 1452 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0, 1453 SectionKind::getReadOnly()); 1454 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection); 1455 ShstrtabSD.setAlignment(1); 1456 1457 const MCSectionELF *SymtabSection = 1458 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, 1459 SectionKind::getReadOnly(), 1460 EntrySize, ""); 1461 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection); 1462 SymtabSD.setAlignment(is64Bit() ? 8 : 4); 1463 1464 const MCSectionELF *StrtabSection; 1465 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0, 1466 SectionKind::getReadOnly()); 1467 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection); 1468 StrtabSD.setAlignment(1); 1469 1470 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1471 1472 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection); 1473 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection); 1474 StringTableIndex = SectionIndexMap.lookup(StrtabSection); 1475 1476 // Symbol table 1477 F = new MCDataFragment(&SymtabSD); 1478 WriteSymbolTable(F, Asm, Layout, SectionIndexMap); 1479 1480 F = new MCDataFragment(&StrtabSD); 1481 F->getContents().append(StringTable.begin(), StringTable.end()); 1482 1483 F = new MCDataFragment(&ShstrtabSD); 1484 1485 std::vector<const MCSectionELF*> Sections; 1486 for (MCAssembler::const_iterator it = Asm.begin(), 1487 ie = Asm.end(); it != ie; ++it) { 1488 const MCSectionELF &Section = 1489 static_cast<const MCSectionELF&>(it->getSection()); 1490 Sections.push_back(&Section); 1491 } 1492 array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix); 1493 1494 // Section header string table. 1495 // 1496 // The first entry of a string table holds a null character so skip 1497 // section 0. 1498 uint64_t Index = 1; 1499 F->getContents().push_back('\x00'); 1500 1501 for (unsigned int I = 0, E = Sections.size(); I != E; ++I) { 1502 const MCSectionELF &Section = *Sections[I]; 1503 1504 StringRef Name = Section.getSectionName(); 1505 if (I != 0) { 1506 StringRef PreviousName = Sections[I - 1]->getSectionName(); 1507 if (PreviousName.endswith(Name)) { 1508 SectionStringTableIndex[&Section] = Index - Name.size() - 1; 1509 continue; 1510 } 1511 } 1512 // Remember the index into the string table so we can write it 1513 // into the sh_name field of the section header table. 1514 SectionStringTableIndex[&Section] = Index; 1515 1516 Index += Name.size() + 1; 1517 F->getContents().append(Name.begin(), Name.end()); 1518 F->getContents().push_back('\x00'); 1519 } 1520 } 1521 1522 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm, 1523 MCAsmLayout &Layout, 1524 GroupMapTy &GroupMap, 1525 RevGroupMapTy &RevGroupMap, 1526 SectionIndexMapTy &SectionIndexMap, 1527 const RelMapTy &RelMap) { 1528 // Create the .note.GNU-stack section if needed. 1529 MCContext &Ctx = Asm.getContext(); 1530 if (Asm.getNoExecStack()) { 1531 const MCSectionELF *GnuStackSection = 1532 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0, 1533 SectionKind::getReadOnly()); 1534 Asm.getOrCreateSectionData(*GnuStackSection); 1535 } 1536 1537 // Build the groups 1538 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1539 it != ie; ++it) { 1540 const MCSectionELF &Section = 1541 static_cast<const MCSectionELF&>(it->getSection()); 1542 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1543 continue; 1544 1545 const MCSymbol *SignatureSymbol = Section.getGroup(); 1546 Asm.getOrCreateSymbolData(*SignatureSymbol); 1547 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol]; 1548 if (!Group) { 1549 Group = Ctx.CreateELFGroupSection(); 1550 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1551 Data.setAlignment(4); 1552 MCDataFragment *F = new MCDataFragment(&Data); 1553 write(*F, uint32_t(ELF::GRP_COMDAT)); 1554 } 1555 GroupMap[Group] = SignatureSymbol; 1556 } 1557 1558 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1559 1560 // Add sections to the groups 1561 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1562 it != ie; ++it) { 1563 const MCSectionELF &Section = 1564 static_cast<const MCSectionELF&>(it->getSection()); 1565 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1566 continue; 1567 const MCSectionELF *Group = RevGroupMap[Section.getGroup()]; 1568 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1569 // FIXME: we could use the previous fragment 1570 MCDataFragment *F = new MCDataFragment(&Data); 1571 uint32_t Index = SectionIndexMap.lookup(&Section); 1572 write(*F, Index); 1573 } 1574 } 1575 1576 void ELFObjectWriter::WriteSection(MCAssembler &Asm, 1577 const SectionIndexMapTy &SectionIndexMap, 1578 uint32_t GroupSymbolIndex, 1579 uint64_t Offset, uint64_t Size, 1580 uint64_t Alignment, 1581 const MCSectionELF &Section) { 1582 uint64_t sh_link = 0; 1583 uint64_t sh_info = 0; 1584 1585 switch(Section.getType()) { 1586 case ELF::SHT_DYNAMIC: 1587 sh_link = SectionStringTableIndex[&Section]; 1588 sh_info = 0; 1589 break; 1590 1591 case ELF::SHT_REL: 1592 case ELF::SHT_RELA: { 1593 const MCSectionELF *SymtabSection; 1594 const MCSectionELF *InfoSection; 1595 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 1596 0, 1597 SectionKind::getReadOnly()); 1598 sh_link = SectionIndexMap.lookup(SymtabSection); 1599 assert(sh_link && ".symtab not found"); 1600 1601 // Remove ".rel" and ".rela" prefixes. 1602 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5; 1603 StringRef SectionName = Section.getSectionName().substr(SecNameLen); 1604 StringRef GroupName = 1605 Section.getGroup() ? Section.getGroup()->getName() : ""; 1606 1607 InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS, 1608 0, SectionKind::getReadOnly(), 1609 0, GroupName); 1610 sh_info = SectionIndexMap.lookup(InfoSection); 1611 break; 1612 } 1613 1614 case ELF::SHT_SYMTAB: 1615 case ELF::SHT_DYNSYM: 1616 sh_link = StringTableIndex; 1617 sh_info = LastLocalSymbolIndex; 1618 break; 1619 1620 case ELF::SHT_SYMTAB_SHNDX: 1621 sh_link = SymbolTableIndex; 1622 break; 1623 1624 case ELF::SHT_PROGBITS: 1625 case ELF::SHT_STRTAB: 1626 case ELF::SHT_NOBITS: 1627 case ELF::SHT_NOTE: 1628 case ELF::SHT_NULL: 1629 case ELF::SHT_ARM_ATTRIBUTES: 1630 case ELF::SHT_INIT_ARRAY: 1631 case ELF::SHT_FINI_ARRAY: 1632 case ELF::SHT_PREINIT_ARRAY: 1633 case ELF::SHT_X86_64_UNWIND: 1634 case ELF::SHT_MIPS_REGINFO: 1635 case ELF::SHT_MIPS_OPTIONS: 1636 // Nothing to do. 1637 break; 1638 1639 case ELF::SHT_GROUP: 1640 sh_link = SymbolTableIndex; 1641 sh_info = GroupSymbolIndex; 1642 break; 1643 1644 default: 1645 assert(0 && "FIXME: sh_type value not supported!"); 1646 break; 1647 } 1648 1649 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM && 1650 Section.getType() == ELF::SHT_ARM_EXIDX) { 1651 StringRef SecName(Section.getSectionName()); 1652 if (SecName == ".ARM.exidx") { 1653 sh_link = SectionIndexMap.lookup( 1654 Asm.getContext().getELFSection(".text", 1655 ELF::SHT_PROGBITS, 1656 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, 1657 SectionKind::getText())); 1658 } else if (SecName.startswith(".ARM.exidx")) { 1659 StringRef GroupName = 1660 Section.getGroup() ? Section.getGroup()->getName() : ""; 1661 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection( 1662 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS, 1663 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText(), 0, 1664 GroupName)); 1665 } 1666 } 1667 1668 WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(), 1669 Section.getFlags(), 0, Offset, Size, sh_link, sh_info, 1670 Alignment, Section.getEntrySize()); 1671 } 1672 1673 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) { 1674 return SD.getOrdinal() == ~UINT32_C(0) && 1675 !SD.getSection().isVirtualSection(); 1676 } 1677 1678 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) { 1679 uint64_t Ret = 0; 1680 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1681 ++i) { 1682 const MCFragment &F = *i; 1683 assert(F.getKind() == MCFragment::FT_Data); 1684 Ret += cast<MCDataFragment>(F).getContents().size(); 1685 } 1686 return Ret; 1687 } 1688 1689 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout, 1690 const MCSectionData &SD) { 1691 if (IsELFMetaDataSection(SD)) 1692 return DataSectionSize(SD); 1693 return Layout.getSectionFileSize(&SD); 1694 } 1695 1696 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout, 1697 const MCSectionData &SD) { 1698 if (IsELFMetaDataSection(SD)) 1699 return DataSectionSize(SD); 1700 return Layout.getSectionAddressSize(&SD); 1701 } 1702 1703 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm, 1704 const MCAsmLayout &Layout, 1705 const MCSectionELF &Section) { 1706 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1707 1708 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment()); 1709 WriteZeros(Padding); 1710 1711 if (IsELFMetaDataSection(SD)) { 1712 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1713 ++i) { 1714 const MCFragment &F = *i; 1715 assert(F.getKind() == MCFragment::FT_Data); 1716 WriteBytes(cast<MCDataFragment>(F).getContents()); 1717 } 1718 } else { 1719 Asm.writeSectionData(&SD, Layout); 1720 } 1721 } 1722 1723 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm, 1724 const GroupMapTy &GroupMap, 1725 const MCAsmLayout &Layout, 1726 const SectionIndexMapTy &SectionIndexMap, 1727 const SectionOffsetMapTy &SectionOffsetMap) { 1728 const unsigned NumSections = Asm.size() + 1; 1729 1730 std::vector<const MCSectionELF*> Sections; 1731 Sections.resize(NumSections - 1); 1732 1733 for (SectionIndexMapTy::const_iterator i= 1734 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) { 1735 const std::pair<const MCSectionELF*, uint32_t> &p = *i; 1736 Sections[p.second - 1] = p.first; 1737 } 1738 1739 // Null section first. 1740 uint64_t FirstSectionSize = 1741 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0; 1742 uint32_t FirstSectionLink = 1743 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0; 1744 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0); 1745 1746 for (unsigned i = 0; i < NumSections - 1; ++i) { 1747 const MCSectionELF &Section = *Sections[i]; 1748 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1749 uint32_t GroupSymbolIndex; 1750 if (Section.getType() != ELF::SHT_GROUP) 1751 GroupSymbolIndex = 0; 1752 else 1753 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, 1754 GroupMap.lookup(&Section)); 1755 1756 uint64_t Size = GetSectionAddressSize(Layout, SD); 1757 1758 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex, 1759 SectionOffsetMap.lookup(&Section), Size, 1760 SD.getAlignment(), Section); 1761 } 1762 } 1763 1764 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm, 1765 std::vector<const MCSectionELF*> &Sections) { 1766 for (MCAssembler::iterator it = Asm.begin(), 1767 ie = Asm.end(); it != ie; ++it) { 1768 const MCSectionELF &Section = 1769 static_cast<const MCSectionELF &>(it->getSection()); 1770 if (Section.getType() == ELF::SHT_GROUP) 1771 Sections.push_back(&Section); 1772 } 1773 1774 for (MCAssembler::iterator it = Asm.begin(), 1775 ie = Asm.end(); it != ie; ++it) { 1776 const MCSectionELF &Section = 1777 static_cast<const MCSectionELF &>(it->getSection()); 1778 if (Section.getType() != ELF::SHT_GROUP && 1779 Section.getType() != ELF::SHT_REL && 1780 Section.getType() != ELF::SHT_RELA) 1781 Sections.push_back(&Section); 1782 } 1783 1784 for (MCAssembler::iterator it = Asm.begin(), 1785 ie = Asm.end(); it != ie; ++it) { 1786 const MCSectionELF &Section = 1787 static_cast<const MCSectionELF &>(it->getSection()); 1788 if (Section.getType() == ELF::SHT_REL || 1789 Section.getType() == ELF::SHT_RELA) 1790 Sections.push_back(&Section); 1791 } 1792 } 1793 1794 void ELFObjectWriter::WriteObject(MCAssembler &Asm, 1795 const MCAsmLayout &Layout) { 1796 GroupMapTy GroupMap; 1797 RevGroupMapTy RevGroupMap; 1798 SectionIndexMapTy SectionIndexMap; 1799 1800 unsigned NumUserSections = Asm.size(); 1801 1802 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout)); 1803 1804 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap; 1805 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1806 1807 const unsigned NumUserAndRelocSections = Asm.size(); 1808 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap, 1809 RevGroupMap, SectionIndexMap, RelMap); 1810 const unsigned AllSections = Asm.size(); 1811 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections; 1812 1813 unsigned NumRegularSections = NumUserSections + NumIndexedSections; 1814 1815 // Compute symbol table information. 1816 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, 1817 NumRegularSections); 1818 1819 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1820 1821 CreateMetadataSections(const_cast<MCAssembler&>(Asm), 1822 const_cast<MCAsmLayout&>(Layout), 1823 SectionIndexMap, 1824 RelMap); 1825 1826 uint64_t NaturalAlignment = is64Bit() ? 8 : 4; 1827 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 1828 sizeof(ELF::Elf32_Ehdr); 1829 uint64_t FileOff = HeaderSize; 1830 1831 std::vector<const MCSectionELF*> Sections; 1832 ComputeSectionOrder(Asm, Sections); 1833 unsigned NumSections = Sections.size(); 1834 SectionOffsetMapTy SectionOffsetMap; 1835 for (unsigned i = 0; i < NumRegularSections + 1; ++i) { 1836 const MCSectionELF &Section = *Sections[i]; 1837 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1838 1839 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1840 1841 // Remember the offset into the file for this section. 1842 SectionOffsetMap[&Section] = FileOff; 1843 1844 // Get the size of the section in the output file (including padding). 1845 FileOff += GetSectionFileSize(Layout, SD); 1846 } 1847 1848 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment); 1849 1850 const unsigned SectionHeaderOffset = FileOff - HeaderSize; 1851 1852 uint64_t SectionHeaderEntrySize = is64Bit() ? 1853 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr); 1854 FileOff += (NumSections + 1) * SectionHeaderEntrySize; 1855 1856 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) { 1857 const MCSectionELF &Section = *Sections[i]; 1858 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1859 1860 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1861 1862 // Remember the offset into the file for this section. 1863 SectionOffsetMap[&Section] = FileOff; 1864 1865 // Get the size of the section in the output file (including padding). 1866 FileOff += GetSectionFileSize(Layout, SD); 1867 } 1868 1869 // Write out the ELF header ... 1870 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1); 1871 1872 // ... then the regular sections ... 1873 // + because of .shstrtab 1874 for (unsigned i = 0; i < NumRegularSections + 1; ++i) 1875 WriteDataSectionData(Asm, Layout, *Sections[i]); 1876 1877 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment); 1878 WriteZeros(Padding); 1879 1880 // ... then the section header table ... 1881 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap, 1882 SectionOffsetMap); 1883 1884 // ... and then the remaining sections ... 1885 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) 1886 WriteDataSectionData(Asm, Layout, *Sections[i]); 1887 } 1888 1889 bool 1890 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 1891 const MCSymbolData &DataA, 1892 const MCFragment &FB, 1893 bool InSet, 1894 bool IsPCRel) const { 1895 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC) 1896 return false; 1897 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl( 1898 Asm, DataA, FB,InSet, IsPCRel); 1899 } 1900 1901 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW, 1902 raw_ostream &OS, 1903 bool IsLittleEndian) { 1904 return new ELFObjectWriter(MOTW, OS, IsLittleEndian); 1905 } 1906