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/MCAsmLayout.h" 21 #include "llvm/MC/MCAssembler.h" 22 #include "llvm/MC/MCContext.h" 23 #include "llvm/MC/MCELF.h" 24 #include "llvm/MC/MCELFSymbolFlags.h" 25 #include "llvm/MC/MCExpr.h" 26 #include "llvm/MC/MCFixupKindInfo.h" 27 #include "llvm/MC/MCObjectWriter.h" 28 #include "llvm/MC/MCSectionELF.h" 29 #include "llvm/MC/MCValue.h" 30 #include "llvm/Support/Debug.h" 31 #include "llvm/Support/ELF.h" 32 #include "llvm/Support/ErrorHandling.h" 33 #include <vector> 34 using namespace llvm; 35 36 #undef DEBUG_TYPE 37 #define DEBUG_TYPE "reloc-info" 38 39 namespace { 40 class ELFObjectWriter : public MCObjectWriter { 41 protected: 42 43 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind); 44 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant); 45 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout); 46 static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data, 47 bool Used, bool Renamed); 48 static bool isLocal(const MCSymbolData &Data, bool isSignature, 49 bool isUsedInReloc); 50 static bool IsELFMetaDataSection(const MCSectionData &SD); 51 static uint64_t DataSectionSize(const MCSectionData &SD); 52 static uint64_t GetSectionFileSize(const MCAsmLayout &Layout, 53 const MCSectionData &SD); 54 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout, 55 const MCSectionData &SD); 56 57 void WriteDataSectionData(MCAssembler &Asm, 58 const MCAsmLayout &Layout, 59 const MCSectionELF &Section); 60 61 /*static bool isFixupKindX86RIPRel(unsigned Kind) { 62 return Kind == X86::reloc_riprel_4byte || 63 Kind == X86::reloc_riprel_4byte_movq_load; 64 }*/ 65 66 /// ELFSymbolData - Helper struct for containing some precomputed 67 /// information on symbols. 68 struct ELFSymbolData { 69 MCSymbolData *SymbolData; 70 uint64_t StringIndex; 71 uint32_t SectionIndex; 72 73 // Support lexicographic sorting. 74 bool operator<(const ELFSymbolData &RHS) const { 75 return SymbolData->getSymbol().getName() < 76 RHS.SymbolData->getSymbol().getName(); 77 } 78 }; 79 80 /// The target specific ELF writer instance. 81 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter; 82 83 SmallPtrSet<const MCSymbol *, 16> UsedInReloc; 84 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc; 85 DenseMap<const MCSymbol *, const MCSymbol *> Renames; 86 87 llvm::DenseMap<const MCSectionData*, 88 std::vector<ELFRelocationEntry> > Relocations; 89 DenseMap<const MCSection*, uint64_t> SectionStringTableIndex; 90 91 /// @} 92 /// @name Symbol Table Data 93 /// @{ 94 95 SmallString<256> StringTable; 96 std::vector<uint64_t> FileSymbolData; 97 std::vector<ELFSymbolData> LocalSymbolData; 98 std::vector<ELFSymbolData> ExternalSymbolData; 99 std::vector<ELFSymbolData> UndefinedSymbolData; 100 101 /// @} 102 103 bool NeedsGOT; 104 105 bool NeedsSymtabShndx; 106 107 // This holds the symbol table index of the last local symbol. 108 unsigned LastLocalSymbolIndex; 109 // This holds the .strtab section index. 110 unsigned StringTableIndex; 111 // This holds the .symtab section index. 112 unsigned SymbolTableIndex; 113 114 unsigned ShstrtabIndex; 115 116 117 const MCSymbol *SymbolToReloc(const MCAssembler &Asm, 118 const MCValue &Target, 119 const MCFragment &F, 120 const MCFixup &Fixup, 121 bool IsPCRel) const; 122 123 // TargetObjectWriter wrappers. 124 const MCSymbol *ExplicitRelSym(const MCAssembler &Asm, 125 const MCValue &Target, 126 const MCFragment &F, 127 const MCFixup &Fixup, 128 bool IsPCRel) const { 129 return TargetObjectWriter->ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 130 } 131 const MCSymbol *undefinedExplicitRelSym(const MCValue &Target, 132 const MCFixup &Fixup, 133 bool IsPCRel) const { 134 return TargetObjectWriter->undefinedExplicitRelSym(Target, Fixup, 135 IsPCRel); 136 } 137 138 bool is64Bit() const { return TargetObjectWriter->is64Bit(); } 139 bool hasRelocationAddend() const { 140 return TargetObjectWriter->hasRelocationAddend(); 141 } 142 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup, 143 bool IsPCRel, bool IsRelocWithSymbol, 144 int64_t Addend) const { 145 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel, 146 IsRelocWithSymbol, Addend); 147 } 148 149 public: 150 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, 151 raw_ostream &_OS, bool IsLittleEndian) 152 : MCObjectWriter(_OS, IsLittleEndian), 153 TargetObjectWriter(MOTW), 154 NeedsGOT(false), NeedsSymtabShndx(false) { 155 } 156 157 virtual ~ELFObjectWriter(); 158 159 void WriteWord(uint64_t W) { 160 if (is64Bit()) 161 Write64(W); 162 else 163 Write32(W); 164 } 165 166 void StringLE16(char *buf, uint16_t Value) { 167 buf[0] = char(Value >> 0); 168 buf[1] = char(Value >> 8); 169 } 170 171 void StringLE32(char *buf, uint32_t Value) { 172 StringLE16(buf, uint16_t(Value >> 0)); 173 StringLE16(buf + 2, uint16_t(Value >> 16)); 174 } 175 176 void StringLE64(char *buf, uint64_t Value) { 177 StringLE32(buf, uint32_t(Value >> 0)); 178 StringLE32(buf + 4, uint32_t(Value >> 32)); 179 } 180 181 void StringBE16(char *buf ,uint16_t Value) { 182 buf[0] = char(Value >> 8); 183 buf[1] = char(Value >> 0); 184 } 185 186 void StringBE32(char *buf, uint32_t Value) { 187 StringBE16(buf, uint16_t(Value >> 16)); 188 StringBE16(buf + 2, uint16_t(Value >> 0)); 189 } 190 191 void StringBE64(char *buf, uint64_t Value) { 192 StringBE32(buf, uint32_t(Value >> 32)); 193 StringBE32(buf + 4, uint32_t(Value >> 0)); 194 } 195 196 void String8(MCDataFragment &F, uint8_t Value) { 197 char buf[1]; 198 buf[0] = Value; 199 F.getContents().append(&buf[0], &buf[1]); 200 } 201 202 void String16(MCDataFragment &F, uint16_t Value) { 203 char buf[2]; 204 if (isLittleEndian()) 205 StringLE16(buf, Value); 206 else 207 StringBE16(buf, Value); 208 F.getContents().append(&buf[0], &buf[2]); 209 } 210 211 void String32(MCDataFragment &F, uint32_t Value) { 212 char buf[4]; 213 if (isLittleEndian()) 214 StringLE32(buf, Value); 215 else 216 StringBE32(buf, Value); 217 F.getContents().append(&buf[0], &buf[4]); 218 } 219 220 void String64(MCDataFragment &F, uint64_t Value) { 221 char buf[8]; 222 if (isLittleEndian()) 223 StringLE64(buf, Value); 224 else 225 StringBE64(buf, Value); 226 F.getContents().append(&buf[0], &buf[8]); 227 } 228 229 void WriteHeader(const MCAssembler &Asm, 230 uint64_t SectionDataSize, 231 unsigned NumberOfSections); 232 233 void WriteSymbolEntry(MCDataFragment *SymtabF, 234 MCDataFragment *ShndxF, 235 uint64_t name, uint8_t info, 236 uint64_t value, uint64_t size, 237 uint8_t other, uint32_t shndx, 238 bool Reserved); 239 240 void WriteSymbol(MCDataFragment *SymtabF, MCDataFragment *ShndxF, 241 ELFSymbolData &MSD, 242 const MCAsmLayout &Layout); 243 244 typedef DenseMap<const MCSectionELF*, uint32_t> SectionIndexMapTy; 245 void WriteSymbolTable(MCDataFragment *SymtabF, 246 MCDataFragment *ShndxF, 247 const MCAssembler &Asm, 248 const MCAsmLayout &Layout, 249 const SectionIndexMapTy &SectionIndexMap); 250 251 void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout, 252 const MCFragment *Fragment, const MCFixup &Fixup, 253 MCValue Target, uint64_t &FixedValue) override; 254 255 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm, 256 const MCSymbol *S); 257 258 // Map from a group section to the signature symbol 259 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy; 260 // Map from a signature symbol to the group section 261 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy; 262 // Map from a section to the section with the relocations 263 typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy; 264 // Map from a section to its offset 265 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy; 266 267 /// ComputeSymbolTable - Compute the symbol table data 268 /// 269 /// \param Asm - The assembler. 270 /// \param SectionIndexMap - Maps a section to its index. 271 /// \param RevGroupMap - Maps a signature symbol to the group section. 272 /// \param NumRegularSections - Number of non-relocation sections. 273 void ComputeSymbolTable(MCAssembler &Asm, 274 const SectionIndexMapTy &SectionIndexMap, 275 RevGroupMapTy RevGroupMap, 276 unsigned NumRegularSections); 277 278 void ComputeIndexMap(MCAssembler &Asm, 279 SectionIndexMapTy &SectionIndexMap, 280 const RelMapTy &RelMap); 281 282 void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout, 283 RelMapTy &RelMap); 284 285 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 286 const RelMapTy &RelMap); 287 288 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout, 289 SectionIndexMapTy &SectionIndexMap, 290 const RelMapTy &RelMap); 291 292 // Create the sections that show up in the symbol table. Currently 293 // those are the .note.GNU-stack section and the group sections. 294 void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout, 295 GroupMapTy &GroupMap, 296 RevGroupMapTy &RevGroupMap, 297 SectionIndexMapTy &SectionIndexMap, 298 const RelMapTy &RelMap); 299 300 void ExecutePostLayoutBinding(MCAssembler &Asm, 301 const MCAsmLayout &Layout) override; 302 303 void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap, 304 const MCAsmLayout &Layout, 305 const SectionIndexMapTy &SectionIndexMap, 306 const SectionOffsetMapTy &SectionOffsetMap); 307 308 void ComputeSectionOrder(MCAssembler &Asm, 309 std::vector<const MCSectionELF*> &Sections); 310 311 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags, 312 uint64_t Address, uint64_t Offset, 313 uint64_t Size, uint32_t Link, uint32_t Info, 314 uint64_t Alignment, uint64_t EntrySize); 315 316 void WriteRelocationsFragment(const MCAssembler &Asm, 317 MCDataFragment *F, 318 const MCSectionData *SD); 319 320 bool 321 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 322 const MCSymbolData &DataA, 323 const MCFragment &FB, 324 bool InSet, 325 bool IsPCRel) const override; 326 327 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override; 328 void WriteSection(MCAssembler &Asm, 329 const SectionIndexMapTy &SectionIndexMap, 330 uint32_t GroupSymbolIndex, 331 uint64_t Offset, uint64_t Size, uint64_t Alignment, 332 const MCSectionELF &Section); 333 }; 334 } 335 336 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) { 337 const MCFixupKindInfo &FKI = 338 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind); 339 340 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel; 341 } 342 343 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) { 344 switch (Variant) { 345 default: 346 return false; 347 case MCSymbolRefExpr::VK_GOT: 348 case MCSymbolRefExpr::VK_PLT: 349 case MCSymbolRefExpr::VK_GOTPCREL: 350 case MCSymbolRefExpr::VK_GOTOFF: 351 case MCSymbolRefExpr::VK_TPOFF: 352 case MCSymbolRefExpr::VK_TLSGD: 353 case MCSymbolRefExpr::VK_GOTTPOFF: 354 case MCSymbolRefExpr::VK_INDNTPOFF: 355 case MCSymbolRefExpr::VK_NTPOFF: 356 case MCSymbolRefExpr::VK_GOTNTPOFF: 357 case MCSymbolRefExpr::VK_TLSLDM: 358 case MCSymbolRefExpr::VK_DTPOFF: 359 case MCSymbolRefExpr::VK_TLSLD: 360 return true; 361 } 362 } 363 364 ELFObjectWriter::~ELFObjectWriter() 365 {} 366 367 // Emit the ELF header. 368 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm, 369 uint64_t SectionDataSize, 370 unsigned NumberOfSections) { 371 // ELF Header 372 // ---------- 373 // 374 // Note 375 // ---- 376 // emitWord method behaves differently for ELF32 and ELF64, writing 377 // 4 bytes in the former and 8 in the latter. 378 379 Write8(0x7f); // e_ident[EI_MAG0] 380 Write8('E'); // e_ident[EI_MAG1] 381 Write8('L'); // e_ident[EI_MAG2] 382 Write8('F'); // e_ident[EI_MAG3] 383 384 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS] 385 386 // e_ident[EI_DATA] 387 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB); 388 389 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION] 390 // e_ident[EI_OSABI] 391 Write8(TargetObjectWriter->getOSABI()); 392 Write8(0); // e_ident[EI_ABIVERSION] 393 394 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD); 395 396 Write16(ELF::ET_REL); // e_type 397 398 Write16(TargetObjectWriter->getEMachine()); // e_machine = target 399 400 Write32(ELF::EV_CURRENT); // e_version 401 WriteWord(0); // e_entry, no entry point in .o file 402 WriteWord(0); // e_phoff, no program header for .o 403 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 404 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes 405 406 // e_flags = whatever the target wants 407 Write32(Asm.getELFHeaderEFlags()); 408 409 // e_ehsize = ELF header size 410 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr)); 411 412 Write16(0); // e_phentsize = prog header entry size 413 Write16(0); // e_phnum = # prog header entries = 0 414 415 // e_shentsize = Section header entry size 416 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr)); 417 418 // e_shnum = # of section header ents 419 if (NumberOfSections >= ELF::SHN_LORESERVE) 420 Write16(ELF::SHN_UNDEF); 421 else 422 Write16(NumberOfSections); 423 424 // e_shstrndx = Section # of '.shstrtab' 425 if (ShstrtabIndex >= ELF::SHN_LORESERVE) 426 Write16(ELF::SHN_XINDEX); 427 else 428 Write16(ShstrtabIndex); 429 } 430 431 void ELFObjectWriter::WriteSymbolEntry(MCDataFragment *SymtabF, 432 MCDataFragment *ShndxF, 433 uint64_t name, 434 uint8_t info, uint64_t value, 435 uint64_t size, uint8_t other, 436 uint32_t shndx, 437 bool Reserved) { 438 if (ShndxF) { 439 if (shndx >= ELF::SHN_LORESERVE && !Reserved) 440 String32(*ShndxF, shndx); 441 else 442 String32(*ShndxF, 0); 443 } 444 445 uint16_t Index = (shndx >= ELF::SHN_LORESERVE && !Reserved) ? 446 uint16_t(ELF::SHN_XINDEX) : shndx; 447 448 if (is64Bit()) { 449 String32(*SymtabF, name); // st_name 450 String8(*SymtabF, info); // st_info 451 String8(*SymtabF, other); // st_other 452 String16(*SymtabF, Index); // st_shndx 453 String64(*SymtabF, value); // st_value 454 String64(*SymtabF, size); // st_size 455 } else { 456 String32(*SymtabF, name); // st_name 457 String32(*SymtabF, value); // st_value 458 String32(*SymtabF, size); // st_size 459 String8(*SymtabF, info); // st_info 460 String8(*SymtabF, other); // st_other 461 String16(*SymtabF, Index); // st_shndx 462 } 463 } 464 465 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data, 466 const MCAsmLayout &Layout) { 467 if (Data.isCommon() && Data.isExternal()) 468 return Data.getCommonAlignment(); 469 470 const MCSymbol &Symbol = Data.getSymbol(); 471 472 if (Symbol.isAbsolute() && Symbol.isVariable()) { 473 if (const MCExpr *Value = Symbol.getVariableValue()) { 474 int64_t IntValue; 475 if (Value->EvaluateAsAbsolute(IntValue, Layout)) 476 return (uint64_t)IntValue; 477 } 478 } 479 480 if (!Symbol.isInSection()) 481 return 0; 482 483 484 if (Data.getFragment()) { 485 if (Data.getFlags() & ELF_Other_ThumbFunc) 486 return Layout.getSymbolOffset(&Data)+1; 487 else 488 return Layout.getSymbolOffset(&Data); 489 } 490 491 return 0; 492 } 493 494 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm, 495 const MCAsmLayout &Layout) { 496 // The presence of symbol versions causes undefined symbols and 497 // versions declared with @@@ to be renamed. 498 499 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(), 500 ie = Asm.symbol_end(); it != ie; ++it) { 501 const MCSymbol &Alias = it->getSymbol(); 502 const MCSymbol &Symbol = Alias.AliasedSymbol(); 503 MCSymbolData &SD = Asm.getSymbolData(Symbol); 504 505 // Not an alias. 506 if (&Symbol == &Alias) 507 continue; 508 509 StringRef AliasName = Alias.getName(); 510 size_t Pos = AliasName.find('@'); 511 if (Pos == StringRef::npos) 512 continue; 513 514 // Aliases defined with .symvar copy the binding from the symbol they alias. 515 // This is the first place we are able to copy this information. 516 it->setExternal(SD.isExternal()); 517 MCELF::SetBinding(*it, MCELF::GetBinding(SD)); 518 519 StringRef Rest = AliasName.substr(Pos); 520 if (!Symbol.isUndefined() && !Rest.startswith("@@@")) 521 continue; 522 523 // FIXME: produce a better error message. 524 if (Symbol.isUndefined() && Rest.startswith("@@") && 525 !Rest.startswith("@@@")) 526 report_fatal_error("A @@ version cannot be undefined"); 527 528 Renames.insert(std::make_pair(&Symbol, &Alias)); 529 } 530 } 531 532 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) { 533 uint8_t Type = newType; 534 535 // Propagation rules: 536 // IFUNC > FUNC > OBJECT > NOTYPE 537 // TLS_OBJECT > OBJECT > NOTYPE 538 // 539 // dont let the new type degrade the old type 540 switch (origType) { 541 default: 542 break; 543 case ELF::STT_GNU_IFUNC: 544 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT || 545 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS) 546 Type = ELF::STT_GNU_IFUNC; 547 break; 548 case ELF::STT_FUNC: 549 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE || 550 Type == ELF::STT_TLS) 551 Type = ELF::STT_FUNC; 552 break; 553 case ELF::STT_OBJECT: 554 if (Type == ELF::STT_NOTYPE) 555 Type = ELF::STT_OBJECT; 556 break; 557 case ELF::STT_TLS: 558 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE || 559 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC) 560 Type = ELF::STT_TLS; 561 break; 562 } 563 564 return Type; 565 } 566 567 void ELFObjectWriter::WriteSymbol(MCDataFragment *SymtabF, 568 MCDataFragment *ShndxF, 569 ELFSymbolData &MSD, 570 const MCAsmLayout &Layout) { 571 MCSymbolData &OrigData = *MSD.SymbolData; 572 MCSymbolData &Data = 573 Layout.getAssembler().getSymbolData(OrigData.getSymbol().AliasedSymbol()); 574 575 bool IsReserved = Data.isCommon() || Data.getSymbol().isAbsolute() || 576 Data.getSymbol().isVariable(); 577 578 // Binding and Type share the same byte as upper and lower nibbles 579 uint8_t Binding = MCELF::GetBinding(OrigData); 580 uint8_t Type = mergeTypeForSet(MCELF::GetType(OrigData), MCELF::GetType(Data)); 581 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift); 582 583 // Other and Visibility share the same byte with Visibility using the lower 584 // 2 bits 585 uint8_t Visibility = MCELF::GetVisibility(OrigData); 586 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift); 587 Other |= Visibility; 588 589 uint64_t Value = SymbolValue(Data, Layout); 590 uint64_t Size = 0; 591 592 assert(!(Data.isCommon() && !Data.isExternal())); 593 594 const MCExpr *ESize = Data.getSize(); 595 if (ESize) { 596 int64_t Res; 597 if (!ESize->EvaluateAsAbsolute(Res, Layout)) 598 report_fatal_error("Size expression must be absolute."); 599 Size = Res; 600 } 601 602 // Write out the symbol table entry 603 WriteSymbolEntry(SymtabF, ShndxF, MSD.StringIndex, Info, Value, 604 Size, Other, MSD.SectionIndex, IsReserved); 605 } 606 607 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF, 608 MCDataFragment *ShndxF, 609 const MCAssembler &Asm, 610 const MCAsmLayout &Layout, 611 const SectionIndexMapTy &SectionIndexMap) { 612 // The string table must be emitted first because we need the index 613 // into the string table for all the symbol names. 614 assert(StringTable.size() && "Missing string table"); 615 616 // FIXME: Make sure the start of the symbol table is aligned. 617 618 // The first entry is the undefined symbol entry. 619 WriteSymbolEntry(SymtabF, ShndxF, 0, 0, 0, 0, 0, 0, false); 620 621 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) { 622 WriteSymbolEntry(SymtabF, ShndxF, FileSymbolData[i], 623 ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, 624 ELF::STV_DEFAULT, ELF::SHN_ABS, true); 625 } 626 627 // Write the symbol table entries. 628 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1; 629 630 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) { 631 ELFSymbolData &MSD = LocalSymbolData[i]; 632 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 633 } 634 635 // Write out a symbol table entry for each regular section. 636 for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e; 637 ++i) { 638 const MCSectionELF &Section = 639 static_cast<const MCSectionELF&>(i->getSection()); 640 if (Section.getType() == ELF::SHT_RELA || 641 Section.getType() == ELF::SHT_REL || 642 Section.getType() == ELF::SHT_STRTAB || 643 Section.getType() == ELF::SHT_SYMTAB || 644 Section.getType() == ELF::SHT_SYMTAB_SHNDX) 645 continue; 646 WriteSymbolEntry(SymtabF, ShndxF, 0, ELF::STT_SECTION, 0, 0, 647 ELF::STV_DEFAULT, SectionIndexMap.lookup(&Section), 648 false); 649 LastLocalSymbolIndex++; 650 } 651 652 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) { 653 ELFSymbolData &MSD = ExternalSymbolData[i]; 654 MCSymbolData &Data = *MSD.SymbolData; 655 assert(((Data.getFlags() & ELF_STB_Global) || 656 (Data.getFlags() & ELF_STB_Weak)) && 657 "External symbol requires STB_GLOBAL or STB_WEAK flag"); 658 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 659 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 660 LastLocalSymbolIndex++; 661 } 662 663 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) { 664 ELFSymbolData &MSD = UndefinedSymbolData[i]; 665 MCSymbolData &Data = *MSD.SymbolData; 666 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 667 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 668 LastLocalSymbolIndex++; 669 } 670 } 671 672 const MCSymbol *ELFObjectWriter::SymbolToReloc(const MCAssembler &Asm, 673 const MCValue &Target, 674 const MCFragment &F, 675 const MCFixup &Fixup, 676 bool IsPCRel) const { 677 const MCSymbol &Symbol = Target.getSymA()->getSymbol(); 678 const MCSymbol &ASymbol = Symbol.AliasedSymbol(); 679 const MCSymbol *Renamed = Renames.lookup(&Symbol); 680 const MCSymbolData &SD = Asm.getSymbolData(Symbol); 681 682 if (ASymbol.isUndefined()) { 683 if (Renamed) 684 return Renamed; 685 return undefinedExplicitRelSym(Target, Fixup, IsPCRel); 686 } 687 688 if (SD.isExternal()) { 689 if (Renamed) 690 return Renamed; 691 return &Symbol; 692 } 693 694 const MCSectionELF &Section = 695 static_cast<const MCSectionELF&>(ASymbol.getSection()); 696 const SectionKind secKind = Section.getKind(); 697 698 if (secKind.isBSS()) 699 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 700 701 if (secKind.isThreadLocal()) { 702 if (Renamed) 703 return Renamed; 704 return &Symbol; 705 } 706 707 MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind(); 708 const MCSectionELF &Sec2 = 709 static_cast<const MCSectionELF&>(F.getParent()->getSection()); 710 711 if (&Sec2 != &Section && 712 (Kind == MCSymbolRefExpr::VK_PLT || 713 Kind == MCSymbolRefExpr::VK_GOTPCREL || 714 Kind == MCSymbolRefExpr::VK_GOTOFF)) { 715 if (Renamed) 716 return Renamed; 717 return &Symbol; 718 } 719 720 if (Section.getFlags() & ELF::SHF_MERGE) { 721 if (Target.getConstant() == 0) 722 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 723 if (Renamed) 724 return Renamed; 725 return &Symbol; 726 } 727 728 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 729 730 } 731 732 733 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm, 734 const MCAsmLayout &Layout, 735 const MCFragment *Fragment, 736 const MCFixup &Fixup, 737 MCValue Target, 738 uint64_t &FixedValue) { 739 int64_t Addend = 0; 740 int Index = 0; 741 int64_t Value = Target.getConstant(); 742 const MCSymbol *RelocSymbol = NULL; 743 744 bool IsPCRel = isFixupKindPCRel(Asm, Fixup.getKind()); 745 if (!Target.isAbsolute()) { 746 const MCSymbol &Symbol = Target.getSymA()->getSymbol(); 747 const MCSymbol &ASymbol = Symbol.AliasedSymbol(); 748 RelocSymbol = SymbolToReloc(Asm, Target, *Fragment, Fixup, IsPCRel); 749 750 if (const MCSymbolRefExpr *RefB = Target.getSymB()) { 751 const MCSymbol &SymbolB = RefB->getSymbol(); 752 MCSymbolData &SDB = Asm.getSymbolData(SymbolB); 753 IsPCRel = true; 754 755 if (!SDB.getFragment()) 756 Asm.getContext().FatalError( 757 Fixup.getLoc(), 758 Twine("symbol '") + SymbolB.getName() + 759 "' can not be undefined in a subtraction expression"); 760 761 // Offset of the symbol in the section 762 int64_t a = Layout.getSymbolOffset(&SDB); 763 764 // Offset of the relocation in the section 765 int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); 766 Value += b - a; 767 } 768 769 if (!RelocSymbol) { 770 MCSymbolData &SD = Asm.getSymbolData(ASymbol); 771 MCFragment *F = SD.getFragment(); 772 773 if (F) { 774 Index = F->getParent()->getOrdinal() + 1; 775 // Offset of the symbol in the section 776 Value += Layout.getSymbolOffset(&SD); 777 } else { 778 Index = 0; 779 } 780 } else { 781 if (Asm.getSymbolData(Symbol).getFlags() & ELF_Other_Weakref) 782 WeakrefUsedInReloc.insert(RelocSymbol); 783 else 784 UsedInReloc.insert(RelocSymbol); 785 Index = -1; 786 } 787 Addend = Value; 788 if (hasRelocationAddend()) 789 Value = 0; 790 } 791 792 FixedValue = Value; 793 unsigned Type = GetRelocType(Target, Fixup, IsPCRel, 794 (RelocSymbol != 0), Addend); 795 MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ? 796 MCSymbolRefExpr::VK_None : Target.getSymA()->getKind(); 797 if (RelocNeedsGOT(Modifier)) 798 NeedsGOT = true; 799 800 uint64_t RelocOffset = Layout.getFragmentOffset(Fragment) + 801 Fixup.getOffset(); 802 803 if (!hasRelocationAddend()) 804 Addend = 0; 805 806 if (is64Bit()) 807 assert(isInt<64>(Addend)); 808 else 809 assert(isInt<32>(Addend)); 810 811 ELFRelocationEntry ERE(RelocOffset, Index, Type, RelocSymbol, Addend, Fixup); 812 Relocations[Fragment->getParent()].push_back(ERE); 813 } 814 815 816 uint64_t 817 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm, 818 const MCSymbol *S) { 819 MCSymbolData &SD = Asm.getSymbolData(*S); 820 return SD.getIndex(); 821 } 822 823 bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm, 824 const MCSymbolData &Data, 825 bool Used, bool Renamed) { 826 if (Data.getFlags() & ELF_Other_Weakref) 827 return false; 828 829 if (Used) 830 return true; 831 832 if (Renamed) 833 return false; 834 835 const MCSymbol &Symbol = Data.getSymbol(); 836 837 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_") 838 return true; 839 840 const MCSymbol &A = Symbol.AliasedSymbol(); 841 if (Symbol.isVariable() && !A.isVariable() && A.isUndefined()) 842 return false; 843 844 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL; 845 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal) 846 return false; 847 848 if (Symbol.isTemporary()) 849 return false; 850 851 return true; 852 } 853 854 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isSignature, 855 bool isUsedInReloc) { 856 if (Data.isExternal()) 857 return false; 858 859 const MCSymbol &Symbol = Data.getSymbol(); 860 const MCSymbol &RefSymbol = Symbol.AliasedSymbol(); 861 862 if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) { 863 if (isSignature && !isUsedInReloc) 864 return true; 865 866 return false; 867 } 868 869 return true; 870 } 871 872 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm, 873 SectionIndexMapTy &SectionIndexMap, 874 const RelMapTy &RelMap) { 875 unsigned Index = 1; 876 for (MCAssembler::iterator it = Asm.begin(), 877 ie = Asm.end(); it != ie; ++it) { 878 const MCSectionELF &Section = 879 static_cast<const MCSectionELF &>(it->getSection()); 880 if (Section.getType() != ELF::SHT_GROUP) 881 continue; 882 SectionIndexMap[&Section] = Index++; 883 } 884 885 for (MCAssembler::iterator it = Asm.begin(), 886 ie = Asm.end(); it != ie; ++it) { 887 const MCSectionELF &Section = 888 static_cast<const MCSectionELF &>(it->getSection()); 889 if (Section.getType() == ELF::SHT_GROUP || 890 Section.getType() == ELF::SHT_REL || 891 Section.getType() == ELF::SHT_RELA) 892 continue; 893 SectionIndexMap[&Section] = Index++; 894 const MCSectionELF *RelSection = RelMap.lookup(&Section); 895 if (RelSection) 896 SectionIndexMap[RelSection] = Index++; 897 } 898 } 899 900 void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm, 901 const SectionIndexMapTy &SectionIndexMap, 902 RevGroupMapTy RevGroupMap, 903 unsigned NumRegularSections) { 904 // FIXME: Is this the correct place to do this? 905 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed? 906 if (NeedsGOT) { 907 StringRef Name = "_GLOBAL_OFFSET_TABLE_"; 908 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name); 909 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym); 910 Data.setExternal(true); 911 MCELF::SetBinding(Data, ELF::STB_GLOBAL); 912 } 913 914 // Index 0 is always the empty string. 915 StringMap<uint64_t> StringIndexMap; 916 StringTable += '\x00'; 917 918 // FIXME: We could optimize suffixes in strtab in the same way we 919 // optimize them in shstrtab. 920 921 for (MCAssembler::const_file_name_iterator it = Asm.file_names_begin(), 922 ie = Asm.file_names_end(); 923 it != ie; 924 ++it) { 925 StringRef Name = *it; 926 uint64_t &Entry = StringIndexMap[Name]; 927 if (!Entry) { 928 Entry = StringTable.size(); 929 StringTable += Name; 930 StringTable += '\x00'; 931 } 932 FileSymbolData.push_back(Entry); 933 } 934 935 // Add the data for the symbols. 936 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(), 937 ie = Asm.symbol_end(); it != ie; ++it) { 938 const MCSymbol &Symbol = it->getSymbol(); 939 940 bool Used = UsedInReloc.count(&Symbol); 941 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol); 942 bool isSignature = RevGroupMap.count(&Symbol); 943 944 if (!isInSymtab(Asm, *it, 945 Used || WeakrefUsed || isSignature, 946 Renames.count(&Symbol))) 947 continue; 948 949 ELFSymbolData MSD; 950 MSD.SymbolData = it; 951 const MCSymbol &RefSymbol = Symbol.AliasedSymbol(); 952 953 // Undefined symbols are global, but this is the first place we 954 // are able to set it. 955 bool Local = isLocal(*it, isSignature, Used); 956 if (!Local && MCELF::GetBinding(*it) == ELF::STB_LOCAL) { 957 MCSymbolData &SD = Asm.getSymbolData(RefSymbol); 958 MCELF::SetBinding(*it, ELF::STB_GLOBAL); 959 MCELF::SetBinding(SD, ELF::STB_GLOBAL); 960 } 961 962 if (RefSymbol.isUndefined() && !Used && WeakrefUsed) 963 MCELF::SetBinding(*it, ELF::STB_WEAK); 964 965 if (it->isCommon()) { 966 assert(!Local); 967 MSD.SectionIndex = ELF::SHN_COMMON; 968 } else if (Symbol.isAbsolute() || RefSymbol.isVariable()) { 969 MSD.SectionIndex = ELF::SHN_ABS; 970 } else if (RefSymbol.isUndefined()) { 971 if (isSignature && !Used) 972 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]); 973 else 974 MSD.SectionIndex = ELF::SHN_UNDEF; 975 } else { 976 const MCSectionELF &Section = 977 static_cast<const MCSectionELF&>(RefSymbol.getSection()); 978 MSD.SectionIndex = SectionIndexMap.lookup(&Section); 979 if (MSD.SectionIndex >= ELF::SHN_LORESERVE) 980 NeedsSymtabShndx = true; 981 assert(MSD.SectionIndex && "Invalid section index!"); 982 } 983 984 // The @@@ in symbol version is replaced with @ in undefined symbols and 985 // @@ in defined ones. 986 StringRef Name = Symbol.getName(); 987 SmallString<32> Buf; 988 989 size_t Pos = Name.find("@@@"); 990 if (Pos != StringRef::npos) { 991 Buf += Name.substr(0, Pos); 992 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1; 993 Buf += Name.substr(Pos + Skip); 994 Name = Buf; 995 } 996 997 uint64_t &Entry = StringIndexMap[Name]; 998 if (!Entry) { 999 Entry = StringTable.size(); 1000 StringTable += Name; 1001 StringTable += '\x00'; 1002 } 1003 MSD.StringIndex = Entry; 1004 if (MSD.SectionIndex == ELF::SHN_UNDEF) 1005 UndefinedSymbolData.push_back(MSD); 1006 else if (Local) 1007 LocalSymbolData.push_back(MSD); 1008 else 1009 ExternalSymbolData.push_back(MSD); 1010 } 1011 1012 // Symbols are required to be in lexicographic order. 1013 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end()); 1014 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end()); 1015 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end()); 1016 1017 // Set the symbol indices. Local symbols must come before all other 1018 // symbols with non-local bindings. 1019 unsigned Index = FileSymbolData.size() + 1; 1020 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) 1021 LocalSymbolData[i].SymbolData->setIndex(Index++); 1022 1023 Index += NumRegularSections; 1024 1025 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) 1026 ExternalSymbolData[i].SymbolData->setIndex(Index++); 1027 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) 1028 UndefinedSymbolData[i].SymbolData->setIndex(Index++); 1029 1030 if (Index >= ELF::SHN_LORESERVE) 1031 NeedsSymtabShndx = true; 1032 } 1033 1034 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm, 1035 MCAsmLayout &Layout, 1036 RelMapTy &RelMap) { 1037 for (MCAssembler::const_iterator it = Asm.begin(), 1038 ie = Asm.end(); it != ie; ++it) { 1039 const MCSectionData &SD = *it; 1040 if (Relocations[&SD].empty()) 1041 continue; 1042 1043 MCContext &Ctx = Asm.getContext(); 1044 const MCSectionELF &Section = 1045 static_cast<const MCSectionELF&>(SD.getSection()); 1046 1047 const StringRef SectionName = Section.getSectionName(); 1048 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel"; 1049 RelaSectionName += SectionName; 1050 1051 unsigned EntrySize; 1052 if (hasRelocationAddend()) 1053 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela); 1054 else 1055 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel); 1056 1057 unsigned Flags = 0; 1058 StringRef Group = ""; 1059 if (Section.getFlags() & ELF::SHF_GROUP) { 1060 Flags = ELF::SHF_GROUP; 1061 Group = Section.getGroup()->getName(); 1062 } 1063 1064 const MCSectionELF *RelaSection = 1065 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ? 1066 ELF::SHT_RELA : ELF::SHT_REL, Flags, 1067 SectionKind::getReadOnly(), 1068 EntrySize, Group); 1069 RelMap[&Section] = RelaSection; 1070 Asm.getOrCreateSectionData(*RelaSection); 1071 } 1072 } 1073 1074 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 1075 const RelMapTy &RelMap) { 1076 for (MCAssembler::const_iterator it = Asm.begin(), 1077 ie = Asm.end(); it != ie; ++it) { 1078 const MCSectionData &SD = *it; 1079 const MCSectionELF &Section = 1080 static_cast<const MCSectionELF&>(SD.getSection()); 1081 1082 const MCSectionELF *RelaSection = RelMap.lookup(&Section); 1083 if (!RelaSection) 1084 continue; 1085 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection); 1086 RelaSD.setAlignment(is64Bit() ? 8 : 4); 1087 1088 MCDataFragment *F = new MCDataFragment(&RelaSD); 1089 WriteRelocationsFragment(Asm, F, &*it); 1090 } 1091 } 1092 1093 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type, 1094 uint64_t Flags, uint64_t Address, 1095 uint64_t Offset, uint64_t Size, 1096 uint32_t Link, uint32_t Info, 1097 uint64_t Alignment, 1098 uint64_t EntrySize) { 1099 Write32(Name); // sh_name: index into string table 1100 Write32(Type); // sh_type 1101 WriteWord(Flags); // sh_flags 1102 WriteWord(Address); // sh_addr 1103 WriteWord(Offset); // sh_offset 1104 WriteWord(Size); // sh_size 1105 Write32(Link); // sh_link 1106 Write32(Info); // sh_info 1107 WriteWord(Alignment); // sh_addralign 1108 WriteWord(EntrySize); // sh_entsize 1109 } 1110 1111 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm, 1112 MCDataFragment *F, 1113 const MCSectionData *SD) { 1114 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD]; 1115 1116 // Sort the relocation entries. Most targets just sort by r_offset, but some 1117 // (e.g., MIPS) have additional constraints. 1118 TargetObjectWriter->sortRelocs(Asm, Relocs); 1119 1120 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) { 1121 ELFRelocationEntry entry = Relocs[e - i - 1]; 1122 1123 if (!entry.Index) 1124 ; 1125 else if (entry.Index < 0) 1126 entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol); 1127 else 1128 entry.Index += FileSymbolData.size() + LocalSymbolData.size(); 1129 if (is64Bit()) { 1130 String64(*F, entry.r_offset); 1131 if (TargetObjectWriter->isN64()) { 1132 String32(*F, entry.Index); 1133 1134 String8(*F, TargetObjectWriter->getRSsym(entry.Type)); 1135 String8(*F, TargetObjectWriter->getRType3(entry.Type)); 1136 String8(*F, TargetObjectWriter->getRType2(entry.Type)); 1137 String8(*F, TargetObjectWriter->getRType(entry.Type)); 1138 } 1139 else { 1140 struct ELF::Elf64_Rela ERE64; 1141 ERE64.setSymbolAndType(entry.Index, entry.Type); 1142 String64(*F, ERE64.r_info); 1143 } 1144 if (hasRelocationAddend()) 1145 String64(*F, entry.r_addend); 1146 } else { 1147 String32(*F, entry.r_offset); 1148 1149 struct ELF::Elf32_Rela ERE32; 1150 ERE32.setSymbolAndType(entry.Index, entry.Type); 1151 String32(*F, ERE32.r_info); 1152 1153 if (hasRelocationAddend()) 1154 String32(*F, entry.r_addend); 1155 } 1156 } 1157 } 1158 1159 static int compareBySuffix(const MCSectionELF *const *a, 1160 const MCSectionELF *const *b) { 1161 const StringRef &NameA = (*a)->getSectionName(); 1162 const StringRef &NameB = (*b)->getSectionName(); 1163 const unsigned sizeA = NameA.size(); 1164 const unsigned sizeB = NameB.size(); 1165 const unsigned len = std::min(sizeA, sizeB); 1166 for (unsigned int i = 0; i < len; ++i) { 1167 char ca = NameA[sizeA - i - 1]; 1168 char cb = NameB[sizeB - i - 1]; 1169 if (ca != cb) 1170 return cb - ca; 1171 } 1172 1173 return sizeB - sizeA; 1174 } 1175 1176 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm, 1177 MCAsmLayout &Layout, 1178 SectionIndexMapTy &SectionIndexMap, 1179 const RelMapTy &RelMap) { 1180 MCContext &Ctx = Asm.getContext(); 1181 MCDataFragment *F; 1182 1183 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32; 1184 1185 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as. 1186 const MCSectionELF *ShstrtabSection = 1187 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0, 1188 SectionKind::getReadOnly()); 1189 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection); 1190 ShstrtabSD.setAlignment(1); 1191 1192 const MCSectionELF *SymtabSection = 1193 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, 1194 SectionKind::getReadOnly(), 1195 EntrySize, ""); 1196 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection); 1197 SymtabSD.setAlignment(is64Bit() ? 8 : 4); 1198 1199 MCSectionData *SymtabShndxSD = NULL; 1200 1201 if (NeedsSymtabShndx) { 1202 const MCSectionELF *SymtabShndxSection = 1203 Ctx.getELFSection(".symtab_shndx", ELF::SHT_SYMTAB_SHNDX, 0, 1204 SectionKind::getReadOnly(), 4, ""); 1205 SymtabShndxSD = &Asm.getOrCreateSectionData(*SymtabShndxSection); 1206 SymtabShndxSD->setAlignment(4); 1207 } 1208 1209 const MCSectionELF *StrtabSection; 1210 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0, 1211 SectionKind::getReadOnly()); 1212 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection); 1213 StrtabSD.setAlignment(1); 1214 1215 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1216 1217 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection); 1218 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection); 1219 StringTableIndex = SectionIndexMap.lookup(StrtabSection); 1220 1221 // Symbol table 1222 F = new MCDataFragment(&SymtabSD); 1223 MCDataFragment *ShndxF = NULL; 1224 if (NeedsSymtabShndx) { 1225 ShndxF = new MCDataFragment(SymtabShndxSD); 1226 } 1227 WriteSymbolTable(F, ShndxF, Asm, Layout, SectionIndexMap); 1228 1229 F = new MCDataFragment(&StrtabSD); 1230 F->getContents().append(StringTable.begin(), StringTable.end()); 1231 1232 F = new MCDataFragment(&ShstrtabSD); 1233 1234 std::vector<const MCSectionELF*> Sections; 1235 for (MCAssembler::const_iterator it = Asm.begin(), 1236 ie = Asm.end(); it != ie; ++it) { 1237 const MCSectionELF &Section = 1238 static_cast<const MCSectionELF&>(it->getSection()); 1239 Sections.push_back(&Section); 1240 } 1241 array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix); 1242 1243 // Section header string table. 1244 // 1245 // The first entry of a string table holds a null character so skip 1246 // section 0. 1247 uint64_t Index = 1; 1248 F->getContents().push_back('\x00'); 1249 1250 for (unsigned int I = 0, E = Sections.size(); I != E; ++I) { 1251 const MCSectionELF &Section = *Sections[I]; 1252 1253 StringRef Name = Section.getSectionName(); 1254 if (I != 0) { 1255 StringRef PreviousName = Sections[I - 1]->getSectionName(); 1256 if (PreviousName.endswith(Name)) { 1257 SectionStringTableIndex[&Section] = Index - Name.size() - 1; 1258 continue; 1259 } 1260 } 1261 // Remember the index into the string table so we can write it 1262 // into the sh_name field of the section header table. 1263 SectionStringTableIndex[&Section] = Index; 1264 1265 Index += Name.size() + 1; 1266 F->getContents().append(Name.begin(), Name.end()); 1267 F->getContents().push_back('\x00'); 1268 } 1269 } 1270 1271 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm, 1272 MCAsmLayout &Layout, 1273 GroupMapTy &GroupMap, 1274 RevGroupMapTy &RevGroupMap, 1275 SectionIndexMapTy &SectionIndexMap, 1276 const RelMapTy &RelMap) { 1277 // Create the .note.GNU-stack section if needed. 1278 MCContext &Ctx = Asm.getContext(); 1279 if (Asm.getNoExecStack()) { 1280 const MCSectionELF *GnuStackSection = 1281 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0, 1282 SectionKind::getReadOnly()); 1283 Asm.getOrCreateSectionData(*GnuStackSection); 1284 } 1285 1286 // Build the groups 1287 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1288 it != ie; ++it) { 1289 const MCSectionELF &Section = 1290 static_cast<const MCSectionELF&>(it->getSection()); 1291 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1292 continue; 1293 1294 const MCSymbol *SignatureSymbol = Section.getGroup(); 1295 Asm.getOrCreateSymbolData(*SignatureSymbol); 1296 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol]; 1297 if (!Group) { 1298 Group = Ctx.CreateELFGroupSection(); 1299 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1300 Data.setAlignment(4); 1301 MCDataFragment *F = new MCDataFragment(&Data); 1302 String32(*F, ELF::GRP_COMDAT); 1303 } 1304 GroupMap[Group] = SignatureSymbol; 1305 } 1306 1307 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1308 1309 // Add sections to the groups 1310 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1311 it != ie; ++it) { 1312 const MCSectionELF &Section = 1313 static_cast<const MCSectionELF&>(it->getSection()); 1314 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1315 continue; 1316 const MCSectionELF *Group = RevGroupMap[Section.getGroup()]; 1317 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1318 // FIXME: we could use the previous fragment 1319 MCDataFragment *F = new MCDataFragment(&Data); 1320 unsigned Index = SectionIndexMap.lookup(&Section); 1321 String32(*F, Index); 1322 } 1323 } 1324 1325 void ELFObjectWriter::WriteSection(MCAssembler &Asm, 1326 const SectionIndexMapTy &SectionIndexMap, 1327 uint32_t GroupSymbolIndex, 1328 uint64_t Offset, uint64_t Size, 1329 uint64_t Alignment, 1330 const MCSectionELF &Section) { 1331 uint64_t sh_link = 0; 1332 uint64_t sh_info = 0; 1333 1334 switch(Section.getType()) { 1335 case ELF::SHT_DYNAMIC: 1336 sh_link = SectionStringTableIndex[&Section]; 1337 sh_info = 0; 1338 break; 1339 1340 case ELF::SHT_REL: 1341 case ELF::SHT_RELA: { 1342 const MCSectionELF *SymtabSection; 1343 const MCSectionELF *InfoSection; 1344 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 1345 0, 1346 SectionKind::getReadOnly()); 1347 sh_link = SectionIndexMap.lookup(SymtabSection); 1348 assert(sh_link && ".symtab not found"); 1349 1350 // Remove ".rel" and ".rela" prefixes. 1351 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5; 1352 StringRef SectionName = Section.getSectionName().substr(SecNameLen); 1353 StringRef GroupName = 1354 Section.getGroup() ? Section.getGroup()->getName() : ""; 1355 1356 InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS, 1357 0, SectionKind::getReadOnly(), 1358 0, GroupName); 1359 sh_info = SectionIndexMap.lookup(InfoSection); 1360 break; 1361 } 1362 1363 case ELF::SHT_SYMTAB: 1364 case ELF::SHT_DYNSYM: 1365 sh_link = StringTableIndex; 1366 sh_info = LastLocalSymbolIndex; 1367 break; 1368 1369 case ELF::SHT_SYMTAB_SHNDX: 1370 sh_link = SymbolTableIndex; 1371 break; 1372 1373 case ELF::SHT_PROGBITS: 1374 case ELF::SHT_STRTAB: 1375 case ELF::SHT_NOBITS: 1376 case ELF::SHT_NOTE: 1377 case ELF::SHT_NULL: 1378 case ELF::SHT_ARM_ATTRIBUTES: 1379 case ELF::SHT_INIT_ARRAY: 1380 case ELF::SHT_FINI_ARRAY: 1381 case ELF::SHT_PREINIT_ARRAY: 1382 case ELF::SHT_X86_64_UNWIND: 1383 case ELF::SHT_MIPS_REGINFO: 1384 case ELF::SHT_MIPS_OPTIONS: 1385 // Nothing to do. 1386 break; 1387 1388 case ELF::SHT_GROUP: 1389 sh_link = SymbolTableIndex; 1390 sh_info = GroupSymbolIndex; 1391 break; 1392 1393 default: 1394 assert(0 && "FIXME: sh_type value not supported!"); 1395 break; 1396 } 1397 1398 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM && 1399 Section.getType() == ELF::SHT_ARM_EXIDX) { 1400 StringRef SecName(Section.getSectionName()); 1401 if (SecName == ".ARM.exidx") { 1402 sh_link = SectionIndexMap.lookup( 1403 Asm.getContext().getELFSection(".text", 1404 ELF::SHT_PROGBITS, 1405 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, 1406 SectionKind::getText())); 1407 } else if (SecName.startswith(".ARM.exidx")) { 1408 StringRef GroupName = 1409 Section.getGroup() ? Section.getGroup()->getName() : ""; 1410 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection( 1411 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS, 1412 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText(), 0, 1413 GroupName)); 1414 } 1415 } 1416 1417 WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(), 1418 Section.getFlags(), 0, Offset, Size, sh_link, sh_info, 1419 Alignment, Section.getEntrySize()); 1420 } 1421 1422 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) { 1423 return SD.getOrdinal() == ~UINT32_C(0) && 1424 !SD.getSection().isVirtualSection(); 1425 } 1426 1427 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) { 1428 uint64_t Ret = 0; 1429 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1430 ++i) { 1431 const MCFragment &F = *i; 1432 assert(F.getKind() == MCFragment::FT_Data); 1433 Ret += cast<MCDataFragment>(F).getContents().size(); 1434 } 1435 return Ret; 1436 } 1437 1438 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout, 1439 const MCSectionData &SD) { 1440 if (IsELFMetaDataSection(SD)) 1441 return DataSectionSize(SD); 1442 return Layout.getSectionFileSize(&SD); 1443 } 1444 1445 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout, 1446 const MCSectionData &SD) { 1447 if (IsELFMetaDataSection(SD)) 1448 return DataSectionSize(SD); 1449 return Layout.getSectionAddressSize(&SD); 1450 } 1451 1452 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm, 1453 const MCAsmLayout &Layout, 1454 const MCSectionELF &Section) { 1455 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1456 1457 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment()); 1458 WriteZeros(Padding); 1459 1460 if (IsELFMetaDataSection(SD)) { 1461 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1462 ++i) { 1463 const MCFragment &F = *i; 1464 assert(F.getKind() == MCFragment::FT_Data); 1465 WriteBytes(cast<MCDataFragment>(F).getContents()); 1466 } 1467 } else { 1468 Asm.writeSectionData(&SD, Layout); 1469 } 1470 } 1471 1472 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm, 1473 const GroupMapTy &GroupMap, 1474 const MCAsmLayout &Layout, 1475 const SectionIndexMapTy &SectionIndexMap, 1476 const SectionOffsetMapTy &SectionOffsetMap) { 1477 const unsigned NumSections = Asm.size() + 1; 1478 1479 std::vector<const MCSectionELF*> Sections; 1480 Sections.resize(NumSections - 1); 1481 1482 for (SectionIndexMapTy::const_iterator i= 1483 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) { 1484 const std::pair<const MCSectionELF*, uint32_t> &p = *i; 1485 Sections[p.second - 1] = p.first; 1486 } 1487 1488 // Null section first. 1489 uint64_t FirstSectionSize = 1490 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0; 1491 uint32_t FirstSectionLink = 1492 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0; 1493 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0); 1494 1495 for (unsigned i = 0; i < NumSections - 1; ++i) { 1496 const MCSectionELF &Section = *Sections[i]; 1497 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1498 uint32_t GroupSymbolIndex; 1499 if (Section.getType() != ELF::SHT_GROUP) 1500 GroupSymbolIndex = 0; 1501 else 1502 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, 1503 GroupMap.lookup(&Section)); 1504 1505 uint64_t Size = GetSectionAddressSize(Layout, SD); 1506 1507 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex, 1508 SectionOffsetMap.lookup(&Section), Size, 1509 SD.getAlignment(), Section); 1510 } 1511 } 1512 1513 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm, 1514 std::vector<const MCSectionELF*> &Sections) { 1515 for (MCAssembler::iterator it = Asm.begin(), 1516 ie = Asm.end(); it != ie; ++it) { 1517 const MCSectionELF &Section = 1518 static_cast<const MCSectionELF &>(it->getSection()); 1519 if (Section.getType() == ELF::SHT_GROUP) 1520 Sections.push_back(&Section); 1521 } 1522 1523 for (MCAssembler::iterator it = Asm.begin(), 1524 ie = Asm.end(); it != ie; ++it) { 1525 const MCSectionELF &Section = 1526 static_cast<const MCSectionELF &>(it->getSection()); 1527 if (Section.getType() != ELF::SHT_GROUP && 1528 Section.getType() != ELF::SHT_REL && 1529 Section.getType() != ELF::SHT_RELA) 1530 Sections.push_back(&Section); 1531 } 1532 1533 for (MCAssembler::iterator it = Asm.begin(), 1534 ie = Asm.end(); it != ie; ++it) { 1535 const MCSectionELF &Section = 1536 static_cast<const MCSectionELF &>(it->getSection()); 1537 if (Section.getType() == ELF::SHT_REL || 1538 Section.getType() == ELF::SHT_RELA) 1539 Sections.push_back(&Section); 1540 } 1541 } 1542 1543 void ELFObjectWriter::WriteObject(MCAssembler &Asm, 1544 const MCAsmLayout &Layout) { 1545 GroupMapTy GroupMap; 1546 RevGroupMapTy RevGroupMap; 1547 SectionIndexMapTy SectionIndexMap; 1548 1549 unsigned NumUserSections = Asm.size(); 1550 1551 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap; 1552 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1553 1554 const unsigned NumUserAndRelocSections = Asm.size(); 1555 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap, 1556 RevGroupMap, SectionIndexMap, RelMap); 1557 const unsigned AllSections = Asm.size(); 1558 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections; 1559 1560 unsigned NumRegularSections = NumUserSections + NumIndexedSections; 1561 1562 // Compute symbol table information. 1563 ComputeSymbolTable(Asm, SectionIndexMap, RevGroupMap, NumRegularSections); 1564 1565 1566 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1567 1568 CreateMetadataSections(const_cast<MCAssembler&>(Asm), 1569 const_cast<MCAsmLayout&>(Layout), 1570 SectionIndexMap, 1571 RelMap); 1572 1573 uint64_t NaturalAlignment = is64Bit() ? 8 : 4; 1574 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 1575 sizeof(ELF::Elf32_Ehdr); 1576 uint64_t FileOff = HeaderSize; 1577 1578 std::vector<const MCSectionELF*> Sections; 1579 ComputeSectionOrder(Asm, Sections); 1580 unsigned NumSections = Sections.size(); 1581 SectionOffsetMapTy SectionOffsetMap; 1582 for (unsigned i = 0; i < NumRegularSections + 1; ++i) { 1583 const MCSectionELF &Section = *Sections[i]; 1584 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1585 1586 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1587 1588 // Remember the offset into the file for this section. 1589 SectionOffsetMap[&Section] = FileOff; 1590 1591 // Get the size of the section in the output file (including padding). 1592 FileOff += GetSectionFileSize(Layout, SD); 1593 } 1594 1595 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment); 1596 1597 const unsigned SectionHeaderOffset = FileOff - HeaderSize; 1598 1599 uint64_t SectionHeaderEntrySize = is64Bit() ? 1600 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr); 1601 FileOff += (NumSections + 1) * SectionHeaderEntrySize; 1602 1603 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) { 1604 const MCSectionELF &Section = *Sections[i]; 1605 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1606 1607 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1608 1609 // Remember the offset into the file for this section. 1610 SectionOffsetMap[&Section] = FileOff; 1611 1612 // Get the size of the section in the output file (including padding). 1613 FileOff += GetSectionFileSize(Layout, SD); 1614 } 1615 1616 // Write out the ELF header ... 1617 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1); 1618 1619 // ... then the regular sections ... 1620 // + because of .shstrtab 1621 for (unsigned i = 0; i < NumRegularSections + 1; ++i) 1622 WriteDataSectionData(Asm, Layout, *Sections[i]); 1623 1624 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment); 1625 WriteZeros(Padding); 1626 1627 // ... then the section header table ... 1628 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap, 1629 SectionOffsetMap); 1630 1631 // ... and then the remaining sections ... 1632 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) 1633 WriteDataSectionData(Asm, Layout, *Sections[i]); 1634 } 1635 1636 bool 1637 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 1638 const MCSymbolData &DataA, 1639 const MCFragment &FB, 1640 bool InSet, 1641 bool IsPCRel) const { 1642 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC) 1643 return false; 1644 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl( 1645 Asm, DataA, FB,InSet, IsPCRel); 1646 } 1647 1648 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW, 1649 raw_ostream &OS, 1650 bool IsLittleEndian) { 1651 return new ELFObjectWriter(MOTW, OS, IsLittleEndian); 1652 } 1653