1 //===- lib/MC/ELFObjectWriter.cpp - ELF File Writer -----------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file implements ELF object file writer information. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "llvm/MC/MCELFObjectWriter.h" 15 #include "llvm/ADT/STLExtras.h" 16 #include "llvm/ADT/SmallPtrSet.h" 17 #include "llvm/ADT/SmallString.h" 18 #include "llvm/ADT/StringMap.h" 19 #include "llvm/MC/MCAsmBackend.h" 20 #include "llvm/MC/MCAsmInfo.h" 21 #include "llvm/MC/MCAsmLayout.h" 22 #include "llvm/MC/MCAssembler.h" 23 #include "llvm/MC/MCContext.h" 24 #include "llvm/MC/MCELF.h" 25 #include "llvm/MC/MCELFSymbolFlags.h" 26 #include "llvm/MC/MCExpr.h" 27 #include "llvm/MC/MCFixupKindInfo.h" 28 #include "llvm/MC/MCObjectWriter.h" 29 #include "llvm/MC/MCSectionELF.h" 30 #include "llvm/MC/MCValue.h" 31 #include "llvm/MC/StringTableBuilder.h" 32 #include "llvm/Support/Compression.h" 33 #include "llvm/Support/Debug.h" 34 #include "llvm/Support/ELF.h" 35 #include "llvm/Support/Endian.h" 36 #include "llvm/Support/ErrorHandling.h" 37 #include <vector> 38 using namespace llvm; 39 40 #undef DEBUG_TYPE 41 #define DEBUG_TYPE "reloc-info" 42 43 namespace { 44 class FragmentWriter { 45 bool IsLittleEndian; 46 47 public: 48 FragmentWriter(bool IsLittleEndian); 49 template <typename T> void write(MCDataFragment &F, T Val); 50 }; 51 52 typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy; 53 54 class SymbolTableWriter { 55 MCAssembler &Asm; 56 FragmentWriter &FWriter; 57 bool Is64Bit; 58 SectionIndexMapTy &SectionIndexMap; 59 60 // The symbol .symtab fragment we are writting to. 61 MCDataFragment *SymtabF; 62 63 // .symtab_shndx fragment we are writting to. 64 MCDataFragment *ShndxF; 65 66 // The numbel of symbols written so far. 67 unsigned NumWritten; 68 69 void createSymtabShndx(); 70 71 template <typename T> void write(MCDataFragment &F, T Value); 72 73 public: 74 SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit, 75 SectionIndexMapTy &SectionIndexMap, 76 MCDataFragment *SymtabF); 77 78 void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size, 79 uint8_t other, uint32_t shndx, bool Reserved); 80 }; 81 82 class ELFObjectWriter : public MCObjectWriter { 83 FragmentWriter FWriter; 84 85 protected: 86 87 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind); 88 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant); 89 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout); 90 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data, 91 bool Used, bool Renamed); 92 static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc); 93 static bool IsELFMetaDataSection(const MCSectionData &SD); 94 static uint64_t DataSectionSize(const MCSectionData &SD); 95 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout, 96 const MCSectionData &SD); 97 98 void writeDataSectionData(MCAssembler &Asm, const MCAsmLayout &Layout, 99 const MCSectionData &SD); 100 101 /// Helper struct for containing some precomputed information on symbols. 102 struct ELFSymbolData { 103 MCSymbolData *SymbolData; 104 uint64_t StringIndex; 105 uint32_t SectionIndex; 106 StringRef Name; 107 108 // Support lexicographic sorting. 109 bool operator<(const ELFSymbolData &RHS) const { 110 unsigned LHSType = MCELF::GetType(*SymbolData); 111 unsigned RHSType = MCELF::GetType(*RHS.SymbolData); 112 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION) 113 return false; 114 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION) 115 return true; 116 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION) 117 return SectionIndex < RHS.SectionIndex; 118 return Name < RHS.Name; 119 } 120 }; 121 122 /// The target specific ELF writer instance. 123 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter; 124 125 SmallPtrSet<const MCSymbol *, 16> UsedInReloc; 126 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc; 127 DenseMap<const MCSymbol *, const MCSymbol *> Renames; 128 129 llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>> 130 Relocations; 131 StringTableBuilder ShStrTabBuilder; 132 133 /// @} 134 /// @name Symbol Table Data 135 /// @{ 136 137 StringTableBuilder StrTabBuilder; 138 std::vector<uint64_t> FileSymbolData; 139 std::vector<ELFSymbolData> LocalSymbolData; 140 std::vector<ELFSymbolData> ExternalSymbolData; 141 std::vector<ELFSymbolData> UndefinedSymbolData; 142 143 /// @} 144 145 bool NeedsGOT; 146 147 // This holds the symbol table index of the last local symbol. 148 unsigned LastLocalSymbolIndex; 149 // This holds the .strtab section index. 150 unsigned StringTableIndex; 151 // This holds the .symtab section index. 152 unsigned SymbolTableIndex; 153 154 unsigned ShstrtabIndex; 155 156 157 // TargetObjectWriter wrappers. 158 bool is64Bit() const { return TargetObjectWriter->is64Bit(); } 159 bool hasRelocationAddend() const { 160 return TargetObjectWriter->hasRelocationAddend(); 161 } 162 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup, 163 bool IsPCRel) const { 164 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel); 165 } 166 167 public: 168 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS, 169 bool IsLittleEndian) 170 : MCObjectWriter(OS, IsLittleEndian), FWriter(IsLittleEndian), 171 TargetObjectWriter(MOTW), NeedsGOT(false) {} 172 173 void reset() override { 174 UsedInReloc.clear(); 175 WeakrefUsedInReloc.clear(); 176 Renames.clear(); 177 Relocations.clear(); 178 ShStrTabBuilder.clear(); 179 StrTabBuilder.clear(); 180 FileSymbolData.clear(); 181 LocalSymbolData.clear(); 182 ExternalSymbolData.clear(); 183 UndefinedSymbolData.clear(); 184 MCObjectWriter::reset(); 185 } 186 187 ~ELFObjectWriter() override; 188 189 void WriteWord(uint64_t W) { 190 if (is64Bit()) 191 Write64(W); 192 else 193 Write32(W); 194 } 195 196 template <typename T> void write(MCDataFragment &F, T Value) { 197 FWriter.write(F, Value); 198 } 199 200 void WriteHeader(const MCAssembler &Asm, 201 unsigned NumberOfSections); 202 203 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD, 204 const MCAsmLayout &Layout); 205 206 void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm, 207 const MCAsmLayout &Layout, 208 SectionIndexMapTy &SectionIndexMap); 209 210 bool shouldRelocateWithSymbol(const MCAssembler &Asm, 211 const MCSymbolRefExpr *RefA, 212 const MCSymbolData *SD, uint64_t C, 213 unsigned Type) const; 214 215 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout, 216 const MCFragment *Fragment, const MCFixup &Fixup, 217 MCValue Target, bool &IsPCRel, 218 uint64_t &FixedValue) override; 219 220 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm, 221 const MCSymbol *S); 222 223 // Map from a group section to the signature symbol 224 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy; 225 // Map from a signature symbol to the group section 226 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy; 227 // Map from a section to its offset 228 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy; 229 230 /// Compute the symbol table data 231 /// 232 /// \param Asm - The assembler. 233 /// \param SectionIndexMap - Maps a section to its index. 234 /// \param RevGroupMap - Maps a signature symbol to the group section. 235 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout, 236 const SectionIndexMapTy &SectionIndexMap, 237 const RevGroupMapTy &RevGroupMap); 238 239 void computeIndexMap(MCAssembler &Asm, SectionIndexMapTy &SectionIndexMap); 240 241 MCSectionData *createRelocationSection(MCAssembler &Asm, 242 const MCSectionData &SD); 243 244 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout); 245 246 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout); 247 248 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout, 249 SectionIndexMapTy &SectionIndexMap); 250 251 // Create the sections that show up in the symbol table. Currently 252 // those are the .note.GNU-stack section and the group sections. 253 void createIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout, 254 GroupMapTy &GroupMap, RevGroupMapTy &RevGroupMap, 255 SectionIndexMapTy &SectionIndexMap); 256 257 void ExecutePostLayoutBinding(MCAssembler &Asm, 258 const MCAsmLayout &Layout) override; 259 260 void writeSectionHeader(ArrayRef<const MCSectionELF *> Sections, 261 MCAssembler &Asm, const GroupMapTy &GroupMap, 262 const MCAsmLayout &Layout, 263 const SectionIndexMapTy &SectionIndexMap, 264 const SectionOffsetMapTy &SectionOffsetMap); 265 266 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags, 267 uint64_t Address, uint64_t Offset, 268 uint64_t Size, uint32_t Link, uint32_t Info, 269 uint64_t Alignment, uint64_t EntrySize); 270 271 void WriteRelocationsFragment(const MCAssembler &Asm, 272 MCDataFragment *F, 273 const MCSectionData *SD); 274 275 bool 276 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 277 const MCSymbolData &DataA, 278 const MCSymbolData *DataB, 279 const MCFragment &FB, 280 bool InSet, 281 bool IsPCRel) const override; 282 283 bool isWeak(const MCSymbolData &SD) const override; 284 285 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override; 286 void writeSection(MCAssembler &Asm, 287 const SectionIndexMapTy &SectionIndexMap, 288 uint32_t GroupSymbolIndex, 289 uint64_t Offset, uint64_t Size, uint64_t Alignment, 290 const MCSectionELF &Section); 291 }; 292 } 293 294 FragmentWriter::FragmentWriter(bool IsLittleEndian) 295 : IsLittleEndian(IsLittleEndian) {} 296 297 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) { 298 if (IsLittleEndian) 299 Val = support::endian::byte_swap<T, support::little>(Val); 300 else 301 Val = support::endian::byte_swap<T, support::big>(Val); 302 const char *Start = (const char *)&Val; 303 F.getContents().append(Start, Start + sizeof(T)); 304 } 305 306 void SymbolTableWriter::createSymtabShndx() { 307 if (ShndxF) 308 return; 309 310 MCContext &Ctx = Asm.getContext(); 311 const MCSectionELF *SymtabShndxSection = 312 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, ""); 313 MCSectionData *SymtabShndxSD = 314 &Asm.getOrCreateSectionData(*SymtabShndxSection); 315 SymtabShndxSD->setAlignment(4); 316 ShndxF = new MCDataFragment(SymtabShndxSD); 317 unsigned Index = SectionIndexMap.size() + 1; 318 SectionIndexMap[SymtabShndxSection] = Index; 319 320 for (unsigned I = 0; I < NumWritten; ++I) 321 write(*ShndxF, uint32_t(0)); 322 } 323 324 template <typename T> 325 void SymbolTableWriter::write(MCDataFragment &F, T Value) { 326 FWriter.write(F, Value); 327 } 328 329 SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, 330 bool Is64Bit, 331 SectionIndexMapTy &SectionIndexMap, 332 MCDataFragment *SymtabF) 333 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit), 334 SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr), 335 NumWritten(0) {} 336 337 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value, 338 uint64_t size, uint8_t other, 339 uint32_t shndx, bool Reserved) { 340 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved; 341 342 if (LargeIndex) 343 createSymtabShndx(); 344 345 if (ShndxF) { 346 if (LargeIndex) 347 write(*ShndxF, shndx); 348 else 349 write(*ShndxF, uint32_t(0)); 350 } 351 352 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx; 353 354 if (Is64Bit) { 355 write(*SymtabF, name); // st_name 356 write(*SymtabF, info); // st_info 357 write(*SymtabF, other); // st_other 358 write(*SymtabF, Index); // st_shndx 359 write(*SymtabF, value); // st_value 360 write(*SymtabF, size); // st_size 361 } else { 362 write(*SymtabF, name); // st_name 363 write(*SymtabF, uint32_t(value)); // st_value 364 write(*SymtabF, uint32_t(size)); // st_size 365 write(*SymtabF, info); // st_info 366 write(*SymtabF, other); // st_other 367 write(*SymtabF, Index); // st_shndx 368 } 369 370 ++NumWritten; 371 } 372 373 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) { 374 const MCFixupKindInfo &FKI = 375 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind); 376 377 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel; 378 } 379 380 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) { 381 switch (Variant) { 382 default: 383 return false; 384 case MCSymbolRefExpr::VK_GOT: 385 case MCSymbolRefExpr::VK_PLT: 386 case MCSymbolRefExpr::VK_GOTPCREL: 387 case MCSymbolRefExpr::VK_GOTOFF: 388 case MCSymbolRefExpr::VK_TPOFF: 389 case MCSymbolRefExpr::VK_TLSGD: 390 case MCSymbolRefExpr::VK_GOTTPOFF: 391 case MCSymbolRefExpr::VK_INDNTPOFF: 392 case MCSymbolRefExpr::VK_NTPOFF: 393 case MCSymbolRefExpr::VK_GOTNTPOFF: 394 case MCSymbolRefExpr::VK_TLSLDM: 395 case MCSymbolRefExpr::VK_DTPOFF: 396 case MCSymbolRefExpr::VK_TLSLD: 397 return true; 398 } 399 } 400 401 ELFObjectWriter::~ELFObjectWriter() 402 {} 403 404 // Emit the ELF header. 405 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm, 406 unsigned NumberOfSections) { 407 // ELF Header 408 // ---------- 409 // 410 // Note 411 // ---- 412 // emitWord method behaves differently for ELF32 and ELF64, writing 413 // 4 bytes in the former and 8 in the latter. 414 415 Write8(0x7f); // e_ident[EI_MAG0] 416 Write8('E'); // e_ident[EI_MAG1] 417 Write8('L'); // e_ident[EI_MAG2] 418 Write8('F'); // e_ident[EI_MAG3] 419 420 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS] 421 422 // e_ident[EI_DATA] 423 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB); 424 425 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION] 426 // e_ident[EI_OSABI] 427 Write8(TargetObjectWriter->getOSABI()); 428 Write8(0); // e_ident[EI_ABIVERSION] 429 430 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD); 431 432 Write16(ELF::ET_REL); // e_type 433 434 Write16(TargetObjectWriter->getEMachine()); // e_machine = target 435 436 Write32(ELF::EV_CURRENT); // e_version 437 WriteWord(0); // e_entry, no entry point in .o file 438 WriteWord(0); // e_phoff, no program header for .o 439 WriteWord(0); // e_shoff = sec hdr table off in bytes 440 441 // e_flags = whatever the target wants 442 Write32(Asm.getELFHeaderEFlags()); 443 444 // e_ehsize = ELF header size 445 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr)); 446 447 Write16(0); // e_phentsize = prog header entry size 448 Write16(0); // e_phnum = # prog header entries = 0 449 450 // e_shentsize = Section header entry size 451 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr)); 452 453 // e_shnum = # of section header ents 454 if (NumberOfSections >= ELF::SHN_LORESERVE) 455 Write16(ELF::SHN_UNDEF); 456 else 457 Write16(NumberOfSections); 458 459 // e_shstrndx = Section # of '.shstrtab' 460 if (ShstrtabIndex >= ELF::SHN_LORESERVE) 461 Write16(ELF::SHN_XINDEX); 462 else 463 Write16(ShstrtabIndex); 464 } 465 466 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data, 467 const MCAsmLayout &Layout) { 468 if (Data.isCommon() && Data.isExternal()) 469 return Data.getCommonAlignment(); 470 471 uint64_t Res; 472 if (!Layout.getSymbolOffset(&Data, Res)) 473 return 0; 474 475 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol())) 476 Res |= 1; 477 478 return Res; 479 } 480 481 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm, 482 const MCAsmLayout &Layout) { 483 // The presence of symbol versions causes undefined symbols and 484 // versions declared with @@@ to be renamed. 485 486 for (MCSymbolData &OriginalData : Asm.symbols()) { 487 const MCSymbol &Alias = OriginalData.getSymbol(); 488 489 // Not an alias. 490 if (!Alias.isVariable()) 491 continue; 492 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue()); 493 if (!Ref) 494 continue; 495 const MCSymbol &Symbol = Ref->getSymbol(); 496 MCSymbolData &SD = Asm.getSymbolData(Symbol); 497 498 StringRef AliasName = Alias.getName(); 499 size_t Pos = AliasName.find('@'); 500 if (Pos == StringRef::npos) 501 continue; 502 503 // Aliases defined with .symvar copy the binding from the symbol they alias. 504 // This is the first place we are able to copy this information. 505 OriginalData.setExternal(SD.isExternal()); 506 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD)); 507 508 StringRef Rest = AliasName.substr(Pos); 509 if (!Symbol.isUndefined() && !Rest.startswith("@@@")) 510 continue; 511 512 // FIXME: produce a better error message. 513 if (Symbol.isUndefined() && Rest.startswith("@@") && 514 !Rest.startswith("@@@")) 515 report_fatal_error("A @@ version cannot be undefined"); 516 517 Renames.insert(std::make_pair(&Symbol, &Alias)); 518 } 519 } 520 521 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) { 522 uint8_t Type = newType; 523 524 // Propagation rules: 525 // IFUNC > FUNC > OBJECT > NOTYPE 526 // TLS_OBJECT > OBJECT > NOTYPE 527 // 528 // dont let the new type degrade the old type 529 switch (origType) { 530 default: 531 break; 532 case ELF::STT_GNU_IFUNC: 533 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT || 534 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS) 535 Type = ELF::STT_GNU_IFUNC; 536 break; 537 case ELF::STT_FUNC: 538 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE || 539 Type == ELF::STT_TLS) 540 Type = ELF::STT_FUNC; 541 break; 542 case ELF::STT_OBJECT: 543 if (Type == ELF::STT_NOTYPE) 544 Type = ELF::STT_OBJECT; 545 break; 546 case ELF::STT_TLS: 547 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE || 548 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC) 549 Type = ELF::STT_TLS; 550 break; 551 } 552 553 return Type; 554 } 555 556 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD, 557 const MCAsmLayout &Layout) { 558 MCSymbolData &OrigData = *MSD.SymbolData; 559 assert((!OrigData.getFragment() || 560 (&OrigData.getFragment()->getParent()->getSection() == 561 &OrigData.getSymbol().getSection())) && 562 "The symbol's section doesn't match the fragment's symbol"); 563 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol()); 564 565 // This has to be in sync with when computeSymbolTable uses SHN_ABS or 566 // SHN_COMMON. 567 bool IsReserved = !Base || OrigData.isCommon(); 568 569 // Binding and Type share the same byte as upper and lower nibbles 570 uint8_t Binding = MCELF::GetBinding(OrigData); 571 uint8_t Type = MCELF::GetType(OrigData); 572 MCSymbolData *BaseSD = nullptr; 573 if (Base) { 574 BaseSD = &Layout.getAssembler().getSymbolData(*Base); 575 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD)); 576 } 577 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift); 578 579 // Other and Visibility share the same byte with Visibility using the lower 580 // 2 bits 581 uint8_t Visibility = MCELF::GetVisibility(OrigData); 582 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift); 583 Other |= Visibility; 584 585 uint64_t Value = SymbolValue(OrigData, Layout); 586 uint64_t Size = 0; 587 588 const MCExpr *ESize = OrigData.getSize(); 589 if (!ESize && Base) 590 ESize = BaseSD->getSize(); 591 592 if (ESize) { 593 int64_t Res; 594 if (!ESize->evaluateKnownAbsolute(Res, Layout)) 595 report_fatal_error("Size expression must be absolute."); 596 Size = Res; 597 } 598 599 // Write out the symbol table entry 600 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other, 601 MSD.SectionIndex, IsReserved); 602 } 603 604 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF, 605 MCAssembler &Asm, 606 const MCAsmLayout &Layout, 607 SectionIndexMapTy &SectionIndexMap) { 608 // The string table must be emitted first because we need the index 609 // into the string table for all the symbol names. 610 611 // FIXME: Make sure the start of the symbol table is aligned. 612 613 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF); 614 615 // The first entry is the undefined symbol entry. 616 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false); 617 618 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) { 619 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, 620 ELF::STV_DEFAULT, ELF::SHN_ABS, true); 621 } 622 623 // Write the symbol table entries. 624 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1; 625 626 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) { 627 ELFSymbolData &MSD = LocalSymbolData[i]; 628 WriteSymbol(Writer, MSD, Layout); 629 } 630 631 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) { 632 ELFSymbolData &MSD = ExternalSymbolData[i]; 633 MCSymbolData &Data = *MSD.SymbolData; 634 assert(((Data.getFlags() & ELF_STB_Global) || 635 (Data.getFlags() & ELF_STB_Weak)) && 636 "External symbol requires STB_GLOBAL or STB_WEAK flag"); 637 WriteSymbol(Writer, MSD, Layout); 638 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 639 LastLocalSymbolIndex++; 640 } 641 642 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) { 643 ELFSymbolData &MSD = UndefinedSymbolData[i]; 644 MCSymbolData &Data = *MSD.SymbolData; 645 WriteSymbol(Writer, MSD, Layout); 646 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 647 LastLocalSymbolIndex++; 648 } 649 } 650 651 // It is always valid to create a relocation with a symbol. It is preferable 652 // to use a relocation with a section if that is possible. Using the section 653 // allows us to omit some local symbols from the symbol table. 654 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm, 655 const MCSymbolRefExpr *RefA, 656 const MCSymbolData *SD, 657 uint64_t C, 658 unsigned Type) const { 659 // A PCRel relocation to an absolute value has no symbol (or section). We 660 // represent that with a relocation to a null section. 661 if (!RefA) 662 return false; 663 664 MCSymbolRefExpr::VariantKind Kind = RefA->getKind(); 665 switch (Kind) { 666 default: 667 break; 668 // The .odp creation emits a relocation against the symbol ".TOC." which 669 // create a R_PPC64_TOC relocation. However the relocation symbol name 670 // in final object creation should be NULL, since the symbol does not 671 // really exist, it is just the reference to TOC base for the current 672 // object file. Since the symbol is undefined, returning false results 673 // in a relocation with a null section which is the desired result. 674 case MCSymbolRefExpr::VK_PPC_TOCBASE: 675 return false; 676 677 // These VariantKind cause the relocation to refer to something other than 678 // the symbol itself, like a linker generated table. Since the address of 679 // symbol is not relevant, we cannot replace the symbol with the 680 // section and patch the difference in the addend. 681 case MCSymbolRefExpr::VK_GOT: 682 case MCSymbolRefExpr::VK_PLT: 683 case MCSymbolRefExpr::VK_GOTPCREL: 684 case MCSymbolRefExpr::VK_Mips_GOT: 685 case MCSymbolRefExpr::VK_PPC_GOT_LO: 686 case MCSymbolRefExpr::VK_PPC_GOT_HI: 687 case MCSymbolRefExpr::VK_PPC_GOT_HA: 688 return true; 689 } 690 691 // An undefined symbol is not in any section, so the relocation has to point 692 // to the symbol itself. 693 const MCSymbol &Sym = SD->getSymbol(); 694 if (Sym.isUndefined()) 695 return true; 696 697 unsigned Binding = MCELF::GetBinding(*SD); 698 switch(Binding) { 699 default: 700 llvm_unreachable("Invalid Binding"); 701 case ELF::STB_LOCAL: 702 break; 703 case ELF::STB_WEAK: 704 // If the symbol is weak, it might be overridden by a symbol in another 705 // file. The relocation has to point to the symbol so that the linker 706 // can update it. 707 return true; 708 case ELF::STB_GLOBAL: 709 // Global ELF symbols can be preempted by the dynamic linker. The relocation 710 // has to point to the symbol for a reason analogous to the STB_WEAK case. 711 return true; 712 } 713 714 // If a relocation points to a mergeable section, we have to be careful. 715 // If the offset is zero, a relocation with the section will encode the 716 // same information. With a non-zero offset, the situation is different. 717 // For example, a relocation can point 42 bytes past the end of a string. 718 // If we change such a relocation to use the section, the linker would think 719 // that it pointed to another string and subtracting 42 at runtime will 720 // produce the wrong value. 721 auto &Sec = cast<MCSectionELF>(Sym.getSection()); 722 unsigned Flags = Sec.getFlags(); 723 if (Flags & ELF::SHF_MERGE) { 724 if (C != 0) 725 return true; 726 727 // It looks like gold has a bug (http://sourceware.org/PR16794) and can 728 // only handle section relocations to mergeable sections if using RELA. 729 if (!hasRelocationAddend()) 730 return true; 731 } 732 733 // Most TLS relocations use a got, so they need the symbol. Even those that 734 // are just an offset (@tpoff), require a symbol in gold versions before 735 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed 736 // http://sourceware.org/PR16773. 737 if (Flags & ELF::SHF_TLS) 738 return true; 739 740 // If the symbol is a thumb function the final relocation must set the lowest 741 // bit. With a symbol that is done by just having the symbol have that bit 742 // set, so we would lose the bit if we relocated with the section. 743 // FIXME: We could use the section but add the bit to the relocation value. 744 if (Asm.isThumbFunc(&Sym)) 745 return true; 746 747 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type)) 748 return true; 749 return false; 750 } 751 752 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) { 753 const MCSymbol &Sym = Ref.getSymbol(); 754 755 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF) 756 return &Sym; 757 758 if (!Sym.isVariable()) 759 return nullptr; 760 761 const MCExpr *Expr = Sym.getVariableValue(); 762 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr); 763 if (!Inner) 764 return nullptr; 765 766 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF) 767 return &Inner->getSymbol(); 768 return nullptr; 769 } 770 771 static bool isWeak(const MCSymbolData &D) { 772 return D.getFlags() & ELF_STB_Weak || MCELF::GetType(D) == ELF::STT_GNU_IFUNC; 773 } 774 775 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm, 776 const MCAsmLayout &Layout, 777 const MCFragment *Fragment, 778 const MCFixup &Fixup, MCValue Target, 779 bool &IsPCRel, uint64_t &FixedValue) { 780 const MCSectionData *FixupSection = Fragment->getParent(); 781 uint64_t C = Target.getConstant(); 782 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); 783 784 if (const MCSymbolRefExpr *RefB = Target.getSymB()) { 785 assert(RefB->getKind() == MCSymbolRefExpr::VK_None && 786 "Should not have constructed this"); 787 788 // Let A, B and C being the components of Target and R be the location of 789 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C). 790 // If it is pcrel, we want to compute (A - B + C - R). 791 792 // In general, ELF has no relocations for -B. It can only represent (A + C) 793 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can 794 // replace B to implement it: (A - R - K + C) 795 if (IsPCRel) 796 Asm.getContext().FatalError( 797 Fixup.getLoc(), 798 "No relocation available to represent this relative expression"); 799 800 const MCSymbol &SymB = RefB->getSymbol(); 801 802 if (SymB.isUndefined()) 803 Asm.getContext().FatalError( 804 Fixup.getLoc(), 805 Twine("symbol '") + SymB.getName() + 806 "' can not be undefined in a subtraction expression"); 807 808 assert(!SymB.isAbsolute() && "Should have been folded"); 809 const MCSection &SecB = SymB.getSection(); 810 if (&SecB != &FixupSection->getSection()) 811 Asm.getContext().FatalError( 812 Fixup.getLoc(), "Cannot represent a difference across sections"); 813 814 const MCSymbolData &SymBD = Asm.getSymbolData(SymB); 815 if (::isWeak(SymBD)) 816 Asm.getContext().FatalError( 817 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol"); 818 819 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD); 820 uint64_t K = SymBOffset - FixupOffset; 821 IsPCRel = true; 822 C -= K; 823 } 824 825 // We either rejected the fixup or folded B into C at this point. 826 const MCSymbolRefExpr *RefA = Target.getSymA(); 827 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr; 828 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr; 829 830 unsigned Type = GetRelocType(Target, Fixup, IsPCRel); 831 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type); 832 if (!RelocateWithSymbol && SymA && !SymA->isUndefined()) 833 C += Layout.getSymbolOffset(SymAD); 834 835 uint64_t Addend = 0; 836 if (hasRelocationAddend()) { 837 Addend = C; 838 C = 0; 839 } 840 841 FixedValue = C; 842 843 // FIXME: What is this!?!? 844 MCSymbolRefExpr::VariantKind Modifier = 845 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None; 846 if (RelocNeedsGOT(Modifier)) 847 NeedsGOT = true; 848 849 if (!RelocateWithSymbol) { 850 const MCSection *SecA = 851 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr; 852 auto *ELFSec = cast_or_null<MCSectionELF>(SecA); 853 MCSymbol *SectionSymbol = 854 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec) 855 : nullptr; 856 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend); 857 Relocations[FixupSection].push_back(Rec); 858 return; 859 } 860 861 if (SymA) { 862 if (const MCSymbol *R = Renames.lookup(SymA)) 863 SymA = R; 864 865 if (const MCSymbol *WeakRef = getWeakRef(*RefA)) 866 WeakrefUsedInReloc.insert(WeakRef); 867 else 868 UsedInReloc.insert(SymA); 869 } 870 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend); 871 Relocations[FixupSection].push_back(Rec); 872 return; 873 } 874 875 876 uint64_t 877 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm, 878 const MCSymbol *S) { 879 const MCSymbolData &SD = Asm.getSymbolData(*S); 880 return SD.getIndex(); 881 } 882 883 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout, 884 const MCSymbolData &Data, bool Used, 885 bool Renamed) { 886 const MCSymbol &Symbol = Data.getSymbol(); 887 if (Symbol.isVariable()) { 888 const MCExpr *Expr = Symbol.getVariableValue(); 889 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) { 890 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF) 891 return false; 892 } 893 } 894 895 if (Used) 896 return true; 897 898 if (Renamed) 899 return false; 900 901 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_") 902 return true; 903 904 if (Symbol.isVariable()) { 905 const MCSymbol *Base = Layout.getBaseSymbol(Symbol); 906 if (Base && Base->isUndefined()) 907 return false; 908 } 909 910 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL; 911 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal) 912 return false; 913 914 if (Symbol.isTemporary()) 915 return false; 916 917 return true; 918 } 919 920 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) { 921 if (Data.isExternal()) 922 return false; 923 924 const MCSymbol &Symbol = Data.getSymbol(); 925 if (Symbol.isDefined()) 926 return true; 927 928 if (isUsedInReloc) 929 return false; 930 931 return true; 932 } 933 934 void ELFObjectWriter::computeIndexMap(MCAssembler &Asm, 935 SectionIndexMapTy &SectionIndexMap) { 936 unsigned Index = 1; 937 for (MCAssembler::iterator it = Asm.begin(), 938 ie = Asm.end(); it != ie; ++it) { 939 const MCSectionELF &Section = 940 static_cast<const MCSectionELF &>(it->getSection()); 941 if (Section.getType() != ELF::SHT_GROUP) 942 continue; 943 SectionIndexMap[&Section] = Index++; 944 } 945 946 for (MCAssembler::iterator it = Asm.begin(), 947 ie = Asm.end(); it != ie; ++it) { 948 const MCSectionData &SD = *it; 949 const MCSectionELF &Section = 950 static_cast<const MCSectionELF &>(SD.getSection()); 951 if (Section.getType() == ELF::SHT_GROUP || 952 Section.getType() == ELF::SHT_REL || 953 Section.getType() == ELF::SHT_RELA) 954 continue; 955 SectionIndexMap[&Section] = Index++; 956 if (MCSectionData *RelSD = createRelocationSection(Asm, SD)) { 957 const MCSectionELF *RelSection = 958 static_cast<const MCSectionELF *>(&RelSD->getSection()); 959 SectionIndexMap[RelSection] = Index++; 960 } 961 } 962 } 963 964 void ELFObjectWriter::computeSymbolTable( 965 MCAssembler &Asm, const MCAsmLayout &Layout, 966 const SectionIndexMapTy &SectionIndexMap, 967 const RevGroupMapTy &RevGroupMap) { 968 // FIXME: Is this the correct place to do this? 969 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed? 970 if (NeedsGOT) { 971 StringRef Name = "_GLOBAL_OFFSET_TABLE_"; 972 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name); 973 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym); 974 Data.setExternal(true); 975 MCELF::SetBinding(Data, ELF::STB_GLOBAL); 976 } 977 978 // Add the data for the symbols. 979 for (MCSymbolData &SD : Asm.symbols()) { 980 const MCSymbol &Symbol = SD.getSymbol(); 981 982 bool Used = UsedInReloc.count(&Symbol); 983 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol); 984 bool isSignature = RevGroupMap.count(&Symbol); 985 986 if (!isInSymtab(Layout, SD, 987 Used || WeakrefUsed || isSignature, 988 Renames.count(&Symbol))) 989 continue; 990 991 ELFSymbolData MSD; 992 MSD.SymbolData = &SD; 993 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol); 994 995 // Undefined symbols are global, but this is the first place we 996 // are able to set it. 997 bool Local = isLocal(SD, Used); 998 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) { 999 assert(BaseSymbol); 1000 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol); 1001 MCELF::SetBinding(SD, ELF::STB_GLOBAL); 1002 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL); 1003 } 1004 1005 if (!BaseSymbol) { 1006 MSD.SectionIndex = ELF::SHN_ABS; 1007 } else if (SD.isCommon()) { 1008 assert(!Local); 1009 MSD.SectionIndex = ELF::SHN_COMMON; 1010 } else if (BaseSymbol->isUndefined()) { 1011 if (isSignature && !Used) 1012 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap.lookup(&Symbol)); 1013 else 1014 MSD.SectionIndex = ELF::SHN_UNDEF; 1015 if (!Used && WeakrefUsed) 1016 MCELF::SetBinding(SD, ELF::STB_WEAK); 1017 } else { 1018 const MCSectionELF &Section = 1019 static_cast<const MCSectionELF&>(BaseSymbol->getSection()); 1020 MSD.SectionIndex = SectionIndexMap.lookup(&Section); 1021 assert(MSD.SectionIndex && "Invalid section index!"); 1022 } 1023 1024 // The @@@ in symbol version is replaced with @ in undefined symbols and @@ 1025 // in defined ones. 1026 // 1027 // FIXME: All name handling should be done before we get to the writer, 1028 // including dealing with GNU-style version suffixes. Fixing this isn't 1029 // trivial. 1030 // 1031 // We thus have to be careful to not perform the symbol version replacement 1032 // blindly: 1033 // 1034 // The ELF format is used on Windows by the MCJIT engine. Thus, on 1035 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS 1036 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC 1037 // C++ name mangling can legally have "@@@" as a sub-string. In that case, 1038 // the EFLObjectWriter should not interpret the "@@@" sub-string as 1039 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore 1040 // checks for the MSVC C++ name mangling prefix which is either "?", "@?", 1041 // "__imp_?" or "__imp_@?". 1042 // 1043 // It would have been interesting to perform the MS mangling prefix check 1044 // only when the target triple is of the form *-pc-windows-elf. But, it 1045 // seems that this information is not easily accessible from the 1046 // ELFObjectWriter. 1047 StringRef Name = Symbol.getName(); 1048 if (!Name.startswith("?") && !Name.startswith("@?") && 1049 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) { 1050 // This symbol isn't following the MSVC C++ name mangling convention. We 1051 // can thus safely interpret the @@@ in symbol names as specifying symbol 1052 // versioning. 1053 SmallString<32> Buf; 1054 size_t Pos = Name.find("@@@"); 1055 if (Pos != StringRef::npos) { 1056 Buf += Name.substr(0, Pos); 1057 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1; 1058 Buf += Name.substr(Pos + Skip); 1059 Name = Buf; 1060 } 1061 } 1062 1063 // Sections have their own string table 1064 if (MCELF::GetType(SD) != ELF::STT_SECTION) 1065 MSD.Name = StrTabBuilder.add(Name); 1066 1067 if (MSD.SectionIndex == ELF::SHN_UNDEF) 1068 UndefinedSymbolData.push_back(MSD); 1069 else if (Local) 1070 LocalSymbolData.push_back(MSD); 1071 else 1072 ExternalSymbolData.push_back(MSD); 1073 } 1074 1075 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i) 1076 StrTabBuilder.add(*i); 1077 1078 StrTabBuilder.finalize(StringTableBuilder::ELF); 1079 1080 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i) 1081 FileSymbolData.push_back(StrTabBuilder.getOffset(*i)); 1082 1083 for (ELFSymbolData &MSD : LocalSymbolData) 1084 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION 1085 ? 0 1086 : StrTabBuilder.getOffset(MSD.Name); 1087 for (ELFSymbolData &MSD : ExternalSymbolData) 1088 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name); 1089 for (ELFSymbolData& MSD : UndefinedSymbolData) 1090 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name); 1091 1092 // Symbols are required to be in lexicographic order. 1093 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end()); 1094 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end()); 1095 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end()); 1096 1097 // Set the symbol indices. Local symbols must come before all other 1098 // symbols with non-local bindings. 1099 unsigned Index = FileSymbolData.size() + 1; 1100 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) 1101 LocalSymbolData[i].SymbolData->setIndex(Index++); 1102 1103 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) 1104 ExternalSymbolData[i].SymbolData->setIndex(Index++); 1105 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) 1106 UndefinedSymbolData[i].SymbolData->setIndex(Index++); 1107 } 1108 1109 MCSectionData * 1110 ELFObjectWriter::createRelocationSection(MCAssembler &Asm, 1111 const MCSectionData &SD) { 1112 if (Relocations[&SD].empty()) 1113 return nullptr; 1114 1115 MCContext &Ctx = Asm.getContext(); 1116 const MCSectionELF &Section = 1117 static_cast<const MCSectionELF &>(SD.getSection()); 1118 1119 const StringRef SectionName = Section.getSectionName(); 1120 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel"; 1121 RelaSectionName += SectionName; 1122 1123 unsigned EntrySize; 1124 if (hasRelocationAddend()) 1125 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela); 1126 else 1127 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel); 1128 1129 unsigned Flags = 0; 1130 if (Section.getFlags() & ELF::SHF_GROUP) 1131 Flags = ELF::SHF_GROUP; 1132 1133 const MCSectionELF *RelaSection = Ctx.createELFRelSection( 1134 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL, 1135 Flags, EntrySize, Section.getGroup(), &Section); 1136 return &Asm.getOrCreateSectionData(*RelaSection); 1137 } 1138 1139 static SmallVector<char, 128> 1140 getUncompressedData(MCAsmLayout &Layout, 1141 MCSectionData::FragmentListType &Fragments) { 1142 SmallVector<char, 128> UncompressedData; 1143 for (const MCFragment &F : Fragments) { 1144 const SmallVectorImpl<char> *Contents; 1145 switch (F.getKind()) { 1146 case MCFragment::FT_Data: 1147 Contents = &cast<MCDataFragment>(F).getContents(); 1148 break; 1149 case MCFragment::FT_Dwarf: 1150 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents(); 1151 break; 1152 case MCFragment::FT_DwarfFrame: 1153 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents(); 1154 break; 1155 default: 1156 llvm_unreachable( 1157 "Not expecting any other fragment types in a debug_* section"); 1158 } 1159 UncompressedData.append(Contents->begin(), Contents->end()); 1160 } 1161 return UncompressedData; 1162 } 1163 1164 // Include the debug info compression header: 1165 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section, 1166 // useful for consumers to preallocate a buffer to decompress into. 1167 static bool 1168 prependCompressionHeader(uint64_t Size, 1169 SmallVectorImpl<char> &CompressedContents) { 1170 const StringRef Magic = "ZLIB"; 1171 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size()) 1172 return false; 1173 if (sys::IsLittleEndianHost) 1174 sys::swapByteOrder(Size); 1175 CompressedContents.insert(CompressedContents.begin(), 1176 Magic.size() + sizeof(Size), 0); 1177 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin()); 1178 std::copy(reinterpret_cast<char *>(&Size), 1179 reinterpret_cast<char *>(&Size + 1), 1180 CompressedContents.begin() + Magic.size()); 1181 return true; 1182 } 1183 1184 // Return a single fragment containing the compressed contents of the whole 1185 // section. Null if the section was not compressed for any reason. 1186 static std::unique_ptr<MCDataFragment> 1187 getCompressedFragment(MCAsmLayout &Layout, 1188 MCSectionData::FragmentListType &Fragments) { 1189 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment()); 1190 1191 // Gather the uncompressed data from all the fragments, recording the 1192 // alignment fragment, if seen, and any fixups. 1193 SmallVector<char, 128> UncompressedData = 1194 getUncompressedData(Layout, Fragments); 1195 1196 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents(); 1197 1198 zlib::Status Success = zlib::compress( 1199 StringRef(UncompressedData.data(), UncompressedData.size()), 1200 CompressedContents); 1201 if (Success != zlib::StatusOK) 1202 return nullptr; 1203 1204 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) 1205 return nullptr; 1206 1207 return CompressedFragment; 1208 } 1209 1210 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>> 1211 DefiningSymbolMap; 1212 1213 static void UpdateSymbols(const MCAsmLayout &Layout, 1214 const std::vector<MCSymbolData *> &Symbols, 1215 MCFragment &NewFragment) { 1216 for (MCSymbolData *Sym : Symbols) { 1217 Sym->setOffset(Sym->getOffset() + 1218 Layout.getFragmentOffset(Sym->getFragment())); 1219 Sym->setFragment(&NewFragment); 1220 } 1221 } 1222 1223 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout, 1224 const DefiningSymbolMap &DefiningSymbols, 1225 const MCSectionELF &Section, 1226 MCSectionData &SD) { 1227 StringRef SectionName = Section.getSectionName(); 1228 MCSectionData::FragmentListType &Fragments = SD.getFragmentList(); 1229 1230 std::unique_ptr<MCDataFragment> CompressedFragment = 1231 getCompressedFragment(Layout, Fragments); 1232 1233 // Leave the section as-is if the fragments could not be compressed. 1234 if (!CompressedFragment) 1235 return; 1236 1237 // Update the fragment+offsets of any symbols referring to fragments in this 1238 // section to refer to the new fragment. 1239 auto I = DefiningSymbols.find(&SD); 1240 if (I != DefiningSymbols.end()) 1241 UpdateSymbols(Layout, I->second, *CompressedFragment); 1242 1243 // Invalidate the layout for the whole section since it will have new and 1244 // different fragments now. 1245 Layout.invalidateFragmentsFrom(&Fragments.front()); 1246 Fragments.clear(); 1247 1248 // Complete the initialization of the new fragment 1249 CompressedFragment->setParent(&SD); 1250 CompressedFragment->setLayoutOrder(0); 1251 Fragments.push_back(CompressedFragment.release()); 1252 1253 // Rename from .debug_* to .zdebug_* 1254 Asm.getContext().renameELFSection(&Section, 1255 (".z" + SectionName.drop_front(1)).str()); 1256 } 1257 1258 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm, 1259 MCAsmLayout &Layout) { 1260 if (!Asm.getContext().getAsmInfo()->compressDebugSections()) 1261 return; 1262 1263 DefiningSymbolMap DefiningSymbols; 1264 1265 for (MCSymbolData &SD : Asm.symbols()) 1266 if (MCFragment *F = SD.getFragment()) 1267 DefiningSymbols[F->getParent()].push_back(&SD); 1268 1269 for (MCSectionData &SD : Asm) { 1270 const MCSectionELF &Section = 1271 static_cast<const MCSectionELF &>(SD.getSection()); 1272 StringRef SectionName = Section.getSectionName(); 1273 1274 // Compressing debug_frame requires handling alignment fragments which is 1275 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow 1276 // for writing to arbitrary buffers) for little benefit. 1277 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame") 1278 continue; 1279 1280 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD); 1281 } 1282 } 1283 1284 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) { 1285 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { 1286 MCSectionData &RelSD = *it; 1287 const MCSectionELF &RelSection = 1288 static_cast<const MCSectionELF &>(RelSD.getSection()); 1289 1290 unsigned Type = RelSection.getType(); 1291 if (Type != ELF::SHT_REL && Type != ELF::SHT_RELA) 1292 continue; 1293 1294 const MCSectionELF *Section = RelSection.getAssociatedSection(); 1295 MCSectionData &SD = Asm.getOrCreateSectionData(*Section); 1296 RelSD.setAlignment(is64Bit() ? 8 : 4); 1297 1298 MCDataFragment *F = new MCDataFragment(&RelSD); 1299 WriteRelocationsFragment(Asm, F, &SD); 1300 } 1301 } 1302 1303 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type, 1304 uint64_t Flags, uint64_t Address, 1305 uint64_t Offset, uint64_t Size, 1306 uint32_t Link, uint32_t Info, 1307 uint64_t Alignment, 1308 uint64_t EntrySize) { 1309 Write32(Name); // sh_name: index into string table 1310 Write32(Type); // sh_type 1311 WriteWord(Flags); // sh_flags 1312 WriteWord(Address); // sh_addr 1313 WriteWord(Offset); // sh_offset 1314 WriteWord(Size); // sh_size 1315 Write32(Link); // sh_link 1316 Write32(Info); // sh_info 1317 WriteWord(Alignment); // sh_addralign 1318 WriteWord(EntrySize); // sh_entsize 1319 } 1320 1321 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm, 1322 MCDataFragment *F, 1323 const MCSectionData *SD) { 1324 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD]; 1325 1326 // Sort the relocation entries. Most targets just sort by Offset, but some 1327 // (e.g., MIPS) have additional constraints. 1328 TargetObjectWriter->sortRelocs(Asm, Relocs); 1329 1330 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) { 1331 const ELFRelocationEntry &Entry = Relocs[e - i - 1]; 1332 unsigned Index = 1333 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0; 1334 1335 if (is64Bit()) { 1336 write(*F, Entry.Offset); 1337 if (TargetObjectWriter->isN64()) { 1338 write(*F, uint32_t(Index)); 1339 1340 write(*F, TargetObjectWriter->getRSsym(Entry.Type)); 1341 write(*F, TargetObjectWriter->getRType3(Entry.Type)); 1342 write(*F, TargetObjectWriter->getRType2(Entry.Type)); 1343 write(*F, TargetObjectWriter->getRType(Entry.Type)); 1344 } else { 1345 struct ELF::Elf64_Rela ERE64; 1346 ERE64.setSymbolAndType(Index, Entry.Type); 1347 write(*F, ERE64.r_info); 1348 } 1349 if (hasRelocationAddend()) 1350 write(*F, Entry.Addend); 1351 } else { 1352 write(*F, uint32_t(Entry.Offset)); 1353 1354 struct ELF::Elf32_Rela ERE32; 1355 ERE32.setSymbolAndType(Index, Entry.Type); 1356 write(*F, ERE32.r_info); 1357 1358 if (hasRelocationAddend()) 1359 write(*F, uint32_t(Entry.Addend)); 1360 } 1361 } 1362 } 1363 1364 void ELFObjectWriter::CreateMetadataSections( 1365 MCAssembler &Asm, MCAsmLayout &Layout, SectionIndexMapTy &SectionIndexMap) { 1366 MCContext &Ctx = Asm.getContext(); 1367 MCDataFragment *F; 1368 1369 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32; 1370 1371 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as. 1372 const MCSectionELF *ShstrtabSection = 1373 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0); 1374 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection); 1375 ShstrtabSD.setAlignment(1); 1376 ShstrtabIndex = SectionIndexMap.size() + 1; 1377 SectionIndexMap[ShstrtabSection] = ShstrtabIndex; 1378 1379 const MCSectionELF *SymtabSection = 1380 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, 1381 EntrySize, ""); 1382 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection); 1383 SymtabSD.setAlignment(is64Bit() ? 8 : 4); 1384 SymbolTableIndex = SectionIndexMap.size() + 1; 1385 SectionIndexMap[SymtabSection] = SymbolTableIndex; 1386 1387 const MCSectionELF *StrtabSection; 1388 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0); 1389 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection); 1390 StrtabSD.setAlignment(1); 1391 StringTableIndex = SectionIndexMap.size() + 1; 1392 SectionIndexMap[StrtabSection] = StringTableIndex; 1393 1394 // Symbol table 1395 F = new MCDataFragment(&SymtabSD); 1396 WriteSymbolTable(F, Asm, Layout, SectionIndexMap); 1397 1398 F = new MCDataFragment(&StrtabSD); 1399 F->getContents().append(StrTabBuilder.data().begin(), 1400 StrTabBuilder.data().end()); 1401 1402 F = new MCDataFragment(&ShstrtabSD); 1403 1404 // Section header string table. 1405 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { 1406 const MCSectionELF &Section = 1407 static_cast<const MCSectionELF&>(it->getSection()); 1408 ShStrTabBuilder.add(Section.getSectionName()); 1409 } 1410 ShStrTabBuilder.finalize(StringTableBuilder::ELF); 1411 F->getContents().append(ShStrTabBuilder.data().begin(), 1412 ShStrTabBuilder.data().end()); 1413 } 1414 1415 void ELFObjectWriter::createIndexedSections( 1416 MCAssembler &Asm, MCAsmLayout &Layout, GroupMapTy &GroupMap, 1417 RevGroupMapTy &RevGroupMap, SectionIndexMapTy &SectionIndexMap) { 1418 MCContext &Ctx = Asm.getContext(); 1419 1420 // Build the groups 1421 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1422 it != ie; ++it) { 1423 const MCSectionELF &Section = 1424 static_cast<const MCSectionELF&>(it->getSection()); 1425 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1426 continue; 1427 1428 const MCSymbol *SignatureSymbol = Section.getGroup(); 1429 Asm.getOrCreateSymbolData(*SignatureSymbol); 1430 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol]; 1431 if (!Group) { 1432 Group = Ctx.CreateELFGroupSection(); 1433 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1434 Data.setAlignment(4); 1435 MCDataFragment *F = new MCDataFragment(&Data); 1436 write(*F, uint32_t(ELF::GRP_COMDAT)); 1437 } 1438 GroupMap[Group] = SignatureSymbol; 1439 } 1440 1441 computeIndexMap(Asm, SectionIndexMap); 1442 1443 // Add sections to the groups 1444 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1445 it != ie; ++it) { 1446 const MCSectionELF &Section = 1447 static_cast<const MCSectionELF&>(it->getSection()); 1448 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1449 continue; 1450 const MCSectionELF *Group = RevGroupMap[Section.getGroup()]; 1451 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1452 // FIXME: we could use the previous fragment 1453 MCDataFragment *F = new MCDataFragment(&Data); 1454 uint32_t Index = SectionIndexMap.lookup(&Section); 1455 write(*F, Index); 1456 } 1457 } 1458 1459 void ELFObjectWriter::writeSection(MCAssembler &Asm, 1460 const SectionIndexMapTy &SectionIndexMap, 1461 uint32_t GroupSymbolIndex, 1462 uint64_t Offset, uint64_t Size, 1463 uint64_t Alignment, 1464 const MCSectionELF &Section) { 1465 uint64_t sh_link = 0; 1466 uint64_t sh_info = 0; 1467 1468 switch(Section.getType()) { 1469 default: 1470 // Nothing to do. 1471 break; 1472 1473 case ELF::SHT_DYNAMIC: 1474 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName()); 1475 break; 1476 1477 case ELF::SHT_REL: 1478 case ELF::SHT_RELA: { 1479 sh_link = SymbolTableIndex; 1480 assert(sh_link && ".symtab not found"); 1481 const MCSectionELF *InfoSection = Section.getAssociatedSection(); 1482 sh_info = SectionIndexMap.lookup(InfoSection); 1483 break; 1484 } 1485 1486 case ELF::SHT_SYMTAB: 1487 case ELF::SHT_DYNSYM: 1488 sh_link = StringTableIndex; 1489 sh_info = LastLocalSymbolIndex; 1490 break; 1491 1492 case ELF::SHT_SYMTAB_SHNDX: 1493 sh_link = SymbolTableIndex; 1494 break; 1495 1496 case ELF::SHT_GROUP: 1497 sh_link = SymbolTableIndex; 1498 sh_info = GroupSymbolIndex; 1499 break; 1500 } 1501 1502 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM && 1503 Section.getType() == ELF::SHT_ARM_EXIDX) 1504 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection()); 1505 1506 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()), 1507 Section.getType(), 1508 Section.getFlags(), 0, Offset, Size, sh_link, sh_info, 1509 Alignment, Section.getEntrySize()); 1510 } 1511 1512 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) { 1513 return SD.getOrdinal() == ~UINT32_C(0) && 1514 !SD.getSection().isVirtualSection(); 1515 } 1516 1517 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) { 1518 uint64_t Ret = 0; 1519 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1520 ++i) { 1521 const MCFragment &F = *i; 1522 assert(F.getKind() == MCFragment::FT_Data); 1523 Ret += cast<MCDataFragment>(F).getContents().size(); 1524 } 1525 return Ret; 1526 } 1527 1528 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout, 1529 const MCSectionData &SD) { 1530 if (IsELFMetaDataSection(SD)) 1531 return DataSectionSize(SD); 1532 return Layout.getSectionAddressSize(&SD); 1533 } 1534 1535 void ELFObjectWriter::writeDataSectionData(MCAssembler &Asm, 1536 const MCAsmLayout &Layout, 1537 const MCSectionData &SD) { 1538 if (IsELFMetaDataSection(SD)) { 1539 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1540 ++i) { 1541 const MCFragment &F = *i; 1542 assert(F.getKind() == MCFragment::FT_Data); 1543 WriteBytes(cast<MCDataFragment>(F).getContents()); 1544 } 1545 } else { 1546 Asm.writeSectionData(&SD, Layout); 1547 } 1548 } 1549 1550 void ELFObjectWriter::writeSectionHeader( 1551 ArrayRef<const MCSectionELF *> Sections, MCAssembler &Asm, 1552 const GroupMapTy &GroupMap, const MCAsmLayout &Layout, 1553 const SectionIndexMapTy &SectionIndexMap, 1554 const SectionOffsetMapTy &SectionOffsetMap) { 1555 const unsigned NumSections = Asm.size(); 1556 1557 // Null section first. 1558 uint64_t FirstSectionSize = 1559 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0; 1560 uint32_t FirstSectionLink = 1561 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0; 1562 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0); 1563 1564 for (unsigned i = 0; i < NumSections; ++i) { 1565 const MCSectionELF &Section = *Sections[i]; 1566 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1567 uint32_t GroupSymbolIndex; 1568 if (Section.getType() != ELF::SHT_GROUP) 1569 GroupSymbolIndex = 0; 1570 else 1571 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, 1572 GroupMap.lookup(&Section)); 1573 1574 uint64_t Size = GetSectionAddressSize(Layout, SD); 1575 1576 writeSection(Asm, SectionIndexMap, GroupSymbolIndex, 1577 SectionOffsetMap.lookup(&Section), Size, SD.getAlignment(), 1578 Section); 1579 } 1580 } 1581 1582 void ELFObjectWriter::WriteObject(MCAssembler &Asm, 1583 const MCAsmLayout &Layout) { 1584 GroupMapTy GroupMap; 1585 RevGroupMapTy RevGroupMap; 1586 SectionIndexMapTy SectionIndexMap; 1587 1588 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout)); 1589 createIndexedSections(Asm, const_cast<MCAsmLayout &>(Layout), GroupMap, 1590 RevGroupMap, SectionIndexMap); 1591 1592 // Compute symbol table information. 1593 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap); 1594 1595 WriteRelocations(Asm, const_cast<MCAsmLayout &>(Layout)); 1596 1597 CreateMetadataSections(const_cast<MCAssembler&>(Asm), 1598 const_cast<MCAsmLayout&>(Layout), 1599 SectionIndexMap); 1600 1601 unsigned NumSections = Asm.size(); 1602 std::vector<const MCSectionELF*> Sections; 1603 Sections.resize(NumSections); 1604 1605 for (auto &Pair : SectionIndexMap) 1606 Sections[Pair.second - 1] = Pair.first; 1607 1608 SectionOffsetMapTy SectionOffsetMap; 1609 1610 // Write out the ELF header ... 1611 WriteHeader(Asm, NumSections + 1); 1612 1613 // ... then the sections ... 1614 for (unsigned i = 0; i < NumSections; ++i) { 1615 const MCSectionELF &Section = *Sections[i]; 1616 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1617 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment()); 1618 WriteZeros(Padding); 1619 1620 // Remember the offset into the file for this section. 1621 SectionOffsetMap[&Section] = OS.tell(); 1622 1623 writeDataSectionData(Asm, Layout, SD); 1624 } 1625 1626 uint64_t NaturalAlignment = is64Bit() ? 8 : 4; 1627 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment); 1628 WriteZeros(Padding); 1629 1630 const unsigned SectionHeaderOffset = OS.tell(); 1631 1632 // ... then the section header table ... 1633 writeSectionHeader(Sections, Asm, GroupMap, Layout, SectionIndexMap, 1634 SectionOffsetMap); 1635 1636 if (is64Bit()) { 1637 uint64_t Val = SectionHeaderOffset; 1638 if (sys::IsLittleEndianHost != IsLittleEndian) 1639 sys::swapByteOrder(Val); 1640 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val), 1641 offsetof(ELF::Elf64_Ehdr, e_shoff)); 1642 } else { 1643 uint32_t Val = SectionHeaderOffset; 1644 if (sys::IsLittleEndianHost != IsLittleEndian) 1645 sys::swapByteOrder(Val); 1646 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val), 1647 offsetof(ELF::Elf32_Ehdr, e_shoff)); 1648 } 1649 } 1650 1651 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl( 1652 const MCAssembler &Asm, const MCSymbolData &DataA, 1653 const MCSymbolData *DataB, const MCFragment &FB, bool InSet, 1654 bool IsPCRel) const { 1655 if (!InSet && (::isWeak(DataA) || (DataB && ::isWeak(*DataB)))) 1656 return false; 1657 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl( 1658 Asm, DataA, DataB, FB, InSet, IsPCRel); 1659 } 1660 1661 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const { 1662 return ::isWeak(SD); 1663 } 1664 1665 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW, 1666 raw_pwrite_stream &OS, 1667 bool IsLittleEndian) { 1668 return new ELFObjectWriter(MOTW, OS, IsLittleEndian); 1669 } 1670
