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/OwningPtr.h" 16 #include "llvm/ADT/STLExtras.h" 17 #include "llvm/ADT/SmallPtrSet.h" 18 #include "llvm/ADT/SmallString.h" 19 #include "llvm/ADT/StringMap.h" 20 #include "llvm/MC/MCAsmBackend.h" 21 #include "llvm/MC/MCAsmLayout.h" 22 #include "llvm/MC/MCAssembler.h" 23 #include "llvm/MC/MCContext.h" 24 #include "llvm/MC/MCELF.h" 25 #include "llvm/MC/MCELFSymbolFlags.h" 26 #include "llvm/MC/MCExpr.h" 27 #include "llvm/MC/MCFixupKindInfo.h" 28 #include "llvm/MC/MCObjectWriter.h" 29 #include "llvm/MC/MCSectionELF.h" 30 #include "llvm/MC/MCValue.h" 31 #include "llvm/Support/Debug.h" 32 #include "llvm/Support/ELF.h" 33 #include "llvm/Support/ErrorHandling.h" 34 #include <vector> 35 using namespace llvm; 36 37 #undef DEBUG_TYPE 38 #define DEBUG_TYPE "reloc-info" 39 40 namespace { 41 class ELFObjectWriter : public MCObjectWriter { 42 protected: 43 44 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind); 45 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant); 46 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout); 47 static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data, 48 bool Used, bool Renamed); 49 static bool isLocal(const MCSymbolData &Data, bool isSignature, 50 bool isUsedInReloc); 51 static bool IsELFMetaDataSection(const MCSectionData &SD); 52 static uint64_t DataSectionSize(const MCSectionData &SD); 53 static uint64_t GetSectionFileSize(const MCAsmLayout &Layout, 54 const MCSectionData &SD); 55 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout, 56 const MCSectionData &SD); 57 58 void WriteDataSectionData(MCAssembler &Asm, 59 const MCAsmLayout &Layout, 60 const MCSectionELF &Section); 61 62 /*static bool isFixupKindX86RIPRel(unsigned Kind) { 63 return Kind == X86::reloc_riprel_4byte || 64 Kind == X86::reloc_riprel_4byte_movq_load; 65 }*/ 66 67 /// ELFSymbolData - Helper struct for containing some precomputed 68 /// information on symbols. 69 struct ELFSymbolData { 70 MCSymbolData *SymbolData; 71 uint64_t StringIndex; 72 uint32_t SectionIndex; 73 74 // Support lexicographic sorting. 75 bool operator<(const ELFSymbolData &RHS) const { 76 if (MCELF::GetType(*SymbolData) == ELF::STT_FILE) 77 return true; 78 if (MCELF::GetType(*RHS.SymbolData) == ELF::STT_FILE) 79 return false; 80 return SymbolData->getSymbol().getName() < 81 RHS.SymbolData->getSymbol().getName(); 82 } 83 }; 84 85 /// The target specific ELF writer instance. 86 llvm::OwningPtr<MCELFObjectTargetWriter> TargetObjectWriter; 87 88 SmallPtrSet<const MCSymbol *, 16> UsedInReloc; 89 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc; 90 DenseMap<const MCSymbol *, const MCSymbol *> Renames; 91 92 llvm::DenseMap<const MCSectionData*, 93 std::vector<ELFRelocationEntry> > Relocations; 94 DenseMap<const MCSection*, uint64_t> SectionStringTableIndex; 95 96 /// @} 97 /// @name Symbol Table Data 98 /// @{ 99 100 SmallString<256> StringTable; 101 std::vector<ELFSymbolData> LocalSymbolData; 102 std::vector<ELFSymbolData> ExternalSymbolData; 103 std::vector<ELFSymbolData> UndefinedSymbolData; 104 105 /// @} 106 107 bool NeedsGOT; 108 109 bool NeedsSymtabShndx; 110 111 // This holds the symbol table index of the last local symbol. 112 unsigned LastLocalSymbolIndex; 113 // This holds the .strtab section index. 114 unsigned StringTableIndex; 115 // This holds the .symtab section index. 116 unsigned SymbolTableIndex; 117 118 unsigned ShstrtabIndex; 119 120 121 const MCSymbol *SymbolToReloc(const MCAssembler &Asm, 122 const MCValue &Target, 123 const MCFragment &F, 124 const MCFixup &Fixup, 125 bool IsPCRel) const; 126 127 // TargetObjectWriter wrappers. 128 const MCSymbol *ExplicitRelSym(const MCAssembler &Asm, 129 const MCValue &Target, 130 const MCFragment &F, 131 const MCFixup &Fixup, 132 bool IsPCRel) const { 133 return TargetObjectWriter->ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 134 } 135 const MCSymbol *undefinedExplicitRelSym(const MCValue &Target, 136 const MCFixup &Fixup, 137 bool IsPCRel) const { 138 return TargetObjectWriter->undefinedExplicitRelSym(Target, Fixup, 139 IsPCRel); 140 } 141 142 bool is64Bit() const { return TargetObjectWriter->is64Bit(); } 143 bool hasRelocationAddend() const { 144 return TargetObjectWriter->hasRelocationAddend(); 145 } 146 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup, 147 bool IsPCRel, bool IsRelocWithSymbol, 148 int64_t Addend) const { 149 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel, 150 IsRelocWithSymbol, Addend); 151 } 152 153 public: 154 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, 155 raw_ostream &_OS, bool IsLittleEndian) 156 : MCObjectWriter(_OS, IsLittleEndian), 157 TargetObjectWriter(MOTW), 158 NeedsGOT(false), NeedsSymtabShndx(false) { 159 } 160 161 virtual ~ELFObjectWriter(); 162 163 void WriteWord(uint64_t W) { 164 if (is64Bit()) 165 Write64(W); 166 else 167 Write32(W); 168 } 169 170 void StringLE16(char *buf, uint16_t Value) { 171 buf[0] = char(Value >> 0); 172 buf[1] = char(Value >> 8); 173 } 174 175 void StringLE32(char *buf, uint32_t Value) { 176 StringLE16(buf, uint16_t(Value >> 0)); 177 StringLE16(buf + 2, uint16_t(Value >> 16)); 178 } 179 180 void StringLE64(char *buf, uint64_t Value) { 181 StringLE32(buf, uint32_t(Value >> 0)); 182 StringLE32(buf + 4, uint32_t(Value >> 32)); 183 } 184 185 void StringBE16(char *buf ,uint16_t Value) { 186 buf[0] = char(Value >> 8); 187 buf[1] = char(Value >> 0); 188 } 189 190 void StringBE32(char *buf, uint32_t Value) { 191 StringBE16(buf, uint16_t(Value >> 16)); 192 StringBE16(buf + 2, uint16_t(Value >> 0)); 193 } 194 195 void StringBE64(char *buf, uint64_t Value) { 196 StringBE32(buf, uint32_t(Value >> 32)); 197 StringBE32(buf + 4, uint32_t(Value >> 0)); 198 } 199 200 void String8(MCDataFragment &F, uint8_t Value) { 201 char buf[1]; 202 buf[0] = Value; 203 F.getContents().append(&buf[0], &buf[1]); 204 } 205 206 void String16(MCDataFragment &F, uint16_t Value) { 207 char buf[2]; 208 if (isLittleEndian()) 209 StringLE16(buf, Value); 210 else 211 StringBE16(buf, Value); 212 F.getContents().append(&buf[0], &buf[2]); 213 } 214 215 void String32(MCDataFragment &F, uint32_t Value) { 216 char buf[4]; 217 if (isLittleEndian()) 218 StringLE32(buf, Value); 219 else 220 StringBE32(buf, Value); 221 F.getContents().append(&buf[0], &buf[4]); 222 } 223 224 void String64(MCDataFragment &F, uint64_t Value) { 225 char buf[8]; 226 if (isLittleEndian()) 227 StringLE64(buf, Value); 228 else 229 StringBE64(buf, Value); 230 F.getContents().append(&buf[0], &buf[8]); 231 } 232 233 void WriteHeader(const MCAssembler &Asm, 234 uint64_t SectionDataSize, 235 unsigned NumberOfSections); 236 237 void WriteSymbolEntry(MCDataFragment *SymtabF, 238 MCDataFragment *ShndxF, 239 uint64_t name, uint8_t info, 240 uint64_t value, uint64_t size, 241 uint8_t other, uint32_t shndx, 242 bool Reserved); 243 244 void WriteSymbol(MCDataFragment *SymtabF, MCDataFragment *ShndxF, 245 ELFSymbolData &MSD, 246 const MCAsmLayout &Layout); 247 248 typedef DenseMap<const MCSectionELF*, uint32_t> SectionIndexMapTy; 249 void WriteSymbolTable(MCDataFragment *SymtabF, 250 MCDataFragment *ShndxF, 251 const MCAssembler &Asm, 252 const MCAsmLayout &Layout, 253 const SectionIndexMapTy &SectionIndexMap); 254 255 virtual void RecordRelocation(const MCAssembler &Asm, 256 const MCAsmLayout &Layout, 257 const MCFragment *Fragment, 258 const MCFixup &Fixup, 259 MCValue Target, uint64_t &FixedValue); 260 261 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm, 262 const MCSymbol *S); 263 264 // Map from a group section to the signature symbol 265 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy; 266 // Map from a signature symbol to the group section 267 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy; 268 // Map from a section to the section with the relocations 269 typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy; 270 // Map from a section to its offset 271 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy; 272 273 /// ComputeSymbolTable - Compute the symbol table data 274 /// 275 /// \param Asm - The assembler. 276 /// \param SectionIndexMap - Maps a section to its index. 277 /// \param RevGroupMap - Maps a signature symbol to the group section. 278 /// \param NumRegularSections - Number of non-relocation sections. 279 void ComputeSymbolTable(MCAssembler &Asm, 280 const SectionIndexMapTy &SectionIndexMap, 281 RevGroupMapTy RevGroupMap, 282 unsigned NumRegularSections); 283 284 void ComputeIndexMap(MCAssembler &Asm, 285 SectionIndexMapTy &SectionIndexMap, 286 const RelMapTy &RelMap); 287 288 void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout, 289 RelMapTy &RelMap); 290 291 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 292 const RelMapTy &RelMap); 293 294 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout, 295 SectionIndexMapTy &SectionIndexMap, 296 const RelMapTy &RelMap); 297 298 // Create the sections that show up in the symbol table. Currently 299 // those are the .note.GNU-stack section and the group sections. 300 void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout, 301 GroupMapTy &GroupMap, 302 RevGroupMapTy &RevGroupMap, 303 SectionIndexMapTy &SectionIndexMap, 304 const RelMapTy &RelMap); 305 306 virtual void ExecutePostLayoutBinding(MCAssembler &Asm, 307 const MCAsmLayout &Layout); 308 309 void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap, 310 const MCAsmLayout &Layout, 311 const SectionIndexMapTy &SectionIndexMap, 312 const SectionOffsetMapTy &SectionOffsetMap); 313 314 void ComputeSectionOrder(MCAssembler &Asm, 315 std::vector<const MCSectionELF*> &Sections); 316 317 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags, 318 uint64_t Address, uint64_t Offset, 319 uint64_t Size, uint32_t Link, uint32_t Info, 320 uint64_t Alignment, uint64_t EntrySize); 321 322 void WriteRelocationsFragment(const MCAssembler &Asm, 323 MCDataFragment *F, 324 const MCSectionData *SD); 325 326 virtual bool 327 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 328 const MCSymbolData &DataA, 329 const MCFragment &FB, 330 bool InSet, 331 bool IsPCRel) const; 332 333 virtual void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout); 334 void WriteSection(MCAssembler &Asm, 335 const SectionIndexMapTy &SectionIndexMap, 336 uint32_t GroupSymbolIndex, 337 uint64_t Offset, uint64_t Size, uint64_t Alignment, 338 const MCSectionELF &Section); 339 }; 340 } 341 342 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) { 343 const MCFixupKindInfo &FKI = 344 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind); 345 346 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel; 347 } 348 349 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) { 350 switch (Variant) { 351 default: 352 return false; 353 case MCSymbolRefExpr::VK_GOT: 354 case MCSymbolRefExpr::VK_PLT: 355 case MCSymbolRefExpr::VK_GOTPCREL: 356 case MCSymbolRefExpr::VK_GOTOFF: 357 case MCSymbolRefExpr::VK_TPOFF: 358 case MCSymbolRefExpr::VK_TLSGD: 359 case MCSymbolRefExpr::VK_GOTTPOFF: 360 case MCSymbolRefExpr::VK_INDNTPOFF: 361 case MCSymbolRefExpr::VK_NTPOFF: 362 case MCSymbolRefExpr::VK_GOTNTPOFF: 363 case MCSymbolRefExpr::VK_TLSLDM: 364 case MCSymbolRefExpr::VK_DTPOFF: 365 case MCSymbolRefExpr::VK_TLSLD: 366 return true; 367 } 368 } 369 370 ELFObjectWriter::~ELFObjectWriter() 371 {} 372 373 // Emit the ELF header. 374 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm, 375 uint64_t SectionDataSize, 376 unsigned NumberOfSections) { 377 // ELF Header 378 // ---------- 379 // 380 // Note 381 // ---- 382 // emitWord method behaves differently for ELF32 and ELF64, writing 383 // 4 bytes in the former and 8 in the latter. 384 385 Write8(0x7f); // e_ident[EI_MAG0] 386 Write8('E'); // e_ident[EI_MAG1] 387 Write8('L'); // e_ident[EI_MAG2] 388 Write8('F'); // e_ident[EI_MAG3] 389 390 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS] 391 392 // e_ident[EI_DATA] 393 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB); 394 395 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION] 396 // e_ident[EI_OSABI] 397 Write8(TargetObjectWriter->getOSABI()); 398 Write8(0); // e_ident[EI_ABIVERSION] 399 400 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD); 401 402 Write16(ELF::ET_REL); // e_type 403 404 Write16(TargetObjectWriter->getEMachine()); // e_machine = target 405 406 Write32(ELF::EV_CURRENT); // e_version 407 WriteWord(0); // e_entry, no entry point in .o file 408 WriteWord(0); // e_phoff, no program header for .o 409 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 410 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes 411 412 // e_flags = whatever the target wants 413 Write32(Asm.getELFHeaderEFlags()); 414 415 // e_ehsize = ELF header size 416 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr)); 417 418 Write16(0); // e_phentsize = prog header entry size 419 Write16(0); // e_phnum = # prog header entries = 0 420 421 // e_shentsize = Section header entry size 422 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr)); 423 424 // e_shnum = # of section header ents 425 if (NumberOfSections >= ELF::SHN_LORESERVE) 426 Write16(ELF::SHN_UNDEF); 427 else 428 Write16(NumberOfSections); 429 430 // e_shstrndx = Section # of '.shstrtab' 431 if (ShstrtabIndex >= ELF::SHN_LORESERVE) 432 Write16(ELF::SHN_XINDEX); 433 else 434 Write16(ShstrtabIndex); 435 } 436 437 void ELFObjectWriter::WriteSymbolEntry(MCDataFragment *SymtabF, 438 MCDataFragment *ShndxF, 439 uint64_t name, 440 uint8_t info, uint64_t value, 441 uint64_t size, uint8_t other, 442 uint32_t shndx, 443 bool Reserved) { 444 if (ShndxF) { 445 if (shndx >= ELF::SHN_LORESERVE && !Reserved) 446 String32(*ShndxF, shndx); 447 else 448 String32(*ShndxF, 0); 449 } 450 451 uint16_t Index = (shndx >= ELF::SHN_LORESERVE && !Reserved) ? 452 uint16_t(ELF::SHN_XINDEX) : shndx; 453 454 if (is64Bit()) { 455 String32(*SymtabF, name); // st_name 456 String8(*SymtabF, info); // st_info 457 String8(*SymtabF, other); // st_other 458 String16(*SymtabF, Index); // st_shndx 459 String64(*SymtabF, value); // st_value 460 String64(*SymtabF, size); // st_size 461 } else { 462 String32(*SymtabF, name); // st_name 463 String32(*SymtabF, value); // st_value 464 String32(*SymtabF, size); // st_size 465 String8(*SymtabF, info); // st_info 466 String8(*SymtabF, other); // st_other 467 String16(*SymtabF, Index); // st_shndx 468 } 469 } 470 471 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data, 472 const MCAsmLayout &Layout) { 473 if (Data.isCommon() && Data.isExternal()) 474 return Data.getCommonAlignment(); 475 476 const MCSymbol &Symbol = Data.getSymbol(); 477 478 if (Symbol.isAbsolute() && Symbol.isVariable()) { 479 if (const MCExpr *Value = Symbol.getVariableValue()) { 480 int64_t IntValue; 481 if (Value->EvaluateAsAbsolute(IntValue, Layout)) 482 return (uint64_t)IntValue; 483 } 484 } 485 486 if (!Symbol.isInSection()) 487 return 0; 488 489 490 if (Data.getFragment()) { 491 if (Data.getFlags() & ELF_Other_ThumbFunc) 492 return Layout.getSymbolOffset(&Data)+1; 493 else 494 return Layout.getSymbolOffset(&Data); 495 } 496 497 return 0; 498 } 499 500 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm, 501 const MCAsmLayout &Layout) { 502 // The presence of symbol versions causes undefined symbols and 503 // versions declared with @@@ to be renamed. 504 505 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(), 506 ie = Asm.symbol_end(); it != ie; ++it) { 507 const MCSymbol &Alias = it->getSymbol(); 508 const MCSymbol &Symbol = Alias.AliasedSymbol(); 509 MCSymbolData &SD = Asm.getSymbolData(Symbol); 510 511 // Not an alias. 512 if (&Symbol == &Alias) 513 continue; 514 515 StringRef AliasName = Alias.getName(); 516 size_t Pos = AliasName.find('@'); 517 if (Pos == StringRef::npos) 518 continue; 519 520 // Aliases defined with .symvar copy the binding from the symbol they alias. 521 // This is the first place we are able to copy this information. 522 it->setExternal(SD.isExternal()); 523 MCELF::SetBinding(*it, MCELF::GetBinding(SD)); 524 525 StringRef Rest = AliasName.substr(Pos); 526 if (!Symbol.isUndefined() && !Rest.startswith("@@@")) 527 continue; 528 529 // FIXME: produce a better error message. 530 if (Symbol.isUndefined() && Rest.startswith("@@") && 531 !Rest.startswith("@@@")) 532 report_fatal_error("A @@ version cannot be undefined"); 533 534 Renames.insert(std::make_pair(&Symbol, &Alias)); 535 } 536 } 537 538 void ELFObjectWriter::WriteSymbol(MCDataFragment *SymtabF, 539 MCDataFragment *ShndxF, 540 ELFSymbolData &MSD, 541 const MCAsmLayout &Layout) { 542 MCSymbolData &OrigData = *MSD.SymbolData; 543 MCSymbolData &Data = 544 Layout.getAssembler().getSymbolData(OrigData.getSymbol().AliasedSymbol()); 545 546 bool IsReserved = Data.isCommon() || Data.getSymbol().isAbsolute() || 547 Data.getSymbol().isVariable(); 548 549 // Binding and Type share the same byte as upper and lower nibbles 550 uint8_t Binding = MCELF::GetBinding(OrigData); 551 uint8_t Type = MCELF::GetType(Data); 552 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift); 553 554 // Other and Visibility share the same byte with Visability using the lower 555 // 2 bits 556 uint8_t Visibility = MCELF::GetVisibility(OrigData); 557 uint8_t Other = MCELF::getOther(OrigData) << 558 (ELF_Other_Shift - ELF_STV_Shift); 559 Other |= Visibility; 560 561 uint64_t Value = SymbolValue(Data, Layout); 562 uint64_t Size = 0; 563 564 assert(!(Data.isCommon() && !Data.isExternal())); 565 566 const MCExpr *ESize = Data.getSize(); 567 if (ESize) { 568 int64_t Res; 569 if (!ESize->EvaluateAsAbsolute(Res, Layout)) 570 report_fatal_error("Size expression must be absolute."); 571 Size = Res; 572 } 573 574 // Write out the symbol table entry 575 WriteSymbolEntry(SymtabF, ShndxF, MSD.StringIndex, Info, Value, 576 Size, Other, MSD.SectionIndex, IsReserved); 577 } 578 579 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF, 580 MCDataFragment *ShndxF, 581 const MCAssembler &Asm, 582 const MCAsmLayout &Layout, 583 const SectionIndexMapTy &SectionIndexMap) { 584 // The string table must be emitted first because we need the index 585 // into the string table for all the symbol names. 586 assert(StringTable.size() && "Missing string table"); 587 588 // FIXME: Make sure the start of the symbol table is aligned. 589 590 // The first entry is the undefined symbol entry. 591 WriteSymbolEntry(SymtabF, ShndxF, 0, 0, 0, 0, 0, 0, false); 592 593 // Write the symbol table entries. 594 LastLocalSymbolIndex = LocalSymbolData.size() + 1; 595 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) { 596 ELFSymbolData &MSD = LocalSymbolData[i]; 597 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 598 } 599 600 // Write out a symbol table entry for each regular section. 601 for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e; 602 ++i) { 603 const MCSectionELF &Section = 604 static_cast<const MCSectionELF&>(i->getSection()); 605 if (Section.getType() == ELF::SHT_RELA || 606 Section.getType() == ELF::SHT_REL || 607 Section.getType() == ELF::SHT_STRTAB || 608 Section.getType() == ELF::SHT_SYMTAB || 609 Section.getType() == ELF::SHT_SYMTAB_SHNDX) 610 continue; 611 WriteSymbolEntry(SymtabF, ShndxF, 0, ELF::STT_SECTION, 0, 0, 612 ELF::STV_DEFAULT, SectionIndexMap.lookup(&Section), 613 false); 614 LastLocalSymbolIndex++; 615 } 616 617 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) { 618 ELFSymbolData &MSD = ExternalSymbolData[i]; 619 MCSymbolData &Data = *MSD.SymbolData; 620 assert(((Data.getFlags() & ELF_STB_Global) || 621 (Data.getFlags() & ELF_STB_Weak)) && 622 "External symbol requires STB_GLOBAL or STB_WEAK flag"); 623 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 624 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 625 LastLocalSymbolIndex++; 626 } 627 628 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) { 629 ELFSymbolData &MSD = UndefinedSymbolData[i]; 630 MCSymbolData &Data = *MSD.SymbolData; 631 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 632 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 633 LastLocalSymbolIndex++; 634 } 635 } 636 637 const MCSymbol *ELFObjectWriter::SymbolToReloc(const MCAssembler &Asm, 638 const MCValue &Target, 639 const MCFragment &F, 640 const MCFixup &Fixup, 641 bool IsPCRel) const { 642 const MCSymbol &Symbol = Target.getSymA()->getSymbol(); 643 const MCSymbol &ASymbol = Symbol.AliasedSymbol(); 644 const MCSymbol *Renamed = Renames.lookup(&Symbol); 645 const MCSymbolData &SD = Asm.getSymbolData(Symbol); 646 647 if (ASymbol.isUndefined()) { 648 if (Renamed) 649 return Renamed; 650 return undefinedExplicitRelSym(Target, Fixup, IsPCRel); 651 } 652 653 if (SD.isExternal()) { 654 if (Renamed) 655 return Renamed; 656 return &Symbol; 657 } 658 659 const MCSectionELF &Section = 660 static_cast<const MCSectionELF&>(ASymbol.getSection()); 661 const SectionKind secKind = Section.getKind(); 662 663 if (secKind.isBSS()) 664 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 665 666 if (secKind.isThreadLocal()) { 667 if (Renamed) 668 return Renamed; 669 return &Symbol; 670 } 671 672 MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind(); 673 const MCSectionELF &Sec2 = 674 static_cast<const MCSectionELF&>(F.getParent()->getSection()); 675 676 if (&Sec2 != &Section && 677 (Kind == MCSymbolRefExpr::VK_PLT || 678 Kind == MCSymbolRefExpr::VK_GOTPCREL || 679 Kind == MCSymbolRefExpr::VK_GOTOFF)) { 680 if (Renamed) 681 return Renamed; 682 return &Symbol; 683 } 684 685 if (Section.getFlags() & ELF::SHF_MERGE) { 686 if (Target.getConstant() == 0) 687 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 688 if (Renamed) 689 return Renamed; 690 return &Symbol; 691 } 692 693 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 694 695 } 696 697 698 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm, 699 const MCAsmLayout &Layout, 700 const MCFragment *Fragment, 701 const MCFixup &Fixup, 702 MCValue Target, 703 uint64_t &FixedValue) { 704 int64_t Addend = 0; 705 int Index = 0; 706 int64_t Value = Target.getConstant(); 707 const MCSymbol *RelocSymbol = NULL; 708 709 bool IsPCRel = isFixupKindPCRel(Asm, Fixup.getKind()); 710 if (!Target.isAbsolute()) { 711 const MCSymbol &Symbol = Target.getSymA()->getSymbol(); 712 const MCSymbol &ASymbol = Symbol.AliasedSymbol(); 713 RelocSymbol = SymbolToReloc(Asm, Target, *Fragment, Fixup, IsPCRel); 714 715 if (const MCSymbolRefExpr *RefB = Target.getSymB()) { 716 const MCSymbol &SymbolB = RefB->getSymbol(); 717 MCSymbolData &SDB = Asm.getSymbolData(SymbolB); 718 IsPCRel = true; 719 720 // Offset of the symbol in the section 721 int64_t a = Layout.getSymbolOffset(&SDB); 722 723 // Offset of the relocation in the section 724 int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); 725 Value += b - a; 726 } 727 728 if (!RelocSymbol) { 729 MCSymbolData &SD = Asm.getSymbolData(ASymbol); 730 MCFragment *F = SD.getFragment(); 731 732 if (F) { 733 Index = F->getParent()->getOrdinal() + 1; 734 // Offset of the symbol in the section 735 Value += Layout.getSymbolOffset(&SD); 736 } else { 737 Index = 0; 738 } 739 } else { 740 if (Asm.getSymbolData(Symbol).getFlags() & ELF_Other_Weakref) 741 WeakrefUsedInReloc.insert(RelocSymbol); 742 else 743 UsedInReloc.insert(RelocSymbol); 744 Index = -1; 745 } 746 Addend = Value; 747 if (hasRelocationAddend()) 748 Value = 0; 749 } 750 751 FixedValue = Value; 752 unsigned Type = GetRelocType(Target, Fixup, IsPCRel, 753 (RelocSymbol != 0), Addend); 754 MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ? 755 MCSymbolRefExpr::VK_None : Target.getSymA()->getKind(); 756 if (RelocNeedsGOT(Modifier)) 757 NeedsGOT = true; 758 759 uint64_t RelocOffset = Layout.getFragmentOffset(Fragment) + 760 Fixup.getOffset(); 761 762 // FIXME: no tests cover this. Is adjustFixupOffset dead code? 763 TargetObjectWriter->adjustFixupOffset(Fixup, RelocOffset); 764 765 if (!hasRelocationAddend()) 766 Addend = 0; 767 768 if (is64Bit()) 769 assert(isInt<64>(Addend)); 770 else 771 assert(isInt<32>(Addend)); 772 773 ELFRelocationEntry ERE(RelocOffset, Index, Type, RelocSymbol, Addend, Fixup); 774 Relocations[Fragment->getParent()].push_back(ERE); 775 } 776 777 778 uint64_t 779 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm, 780 const MCSymbol *S) { 781 MCSymbolData &SD = Asm.getSymbolData(*S); 782 return SD.getIndex(); 783 } 784 785 bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm, 786 const MCSymbolData &Data, 787 bool Used, bool Renamed) { 788 if (Data.getFlags() & ELF_Other_Weakref) 789 return false; 790 791 if (Used) 792 return true; 793 794 if (Renamed) 795 return false; 796 797 const MCSymbol &Symbol = Data.getSymbol(); 798 799 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_") 800 return true; 801 802 const MCSymbol &A = Symbol.AliasedSymbol(); 803 if (Symbol.isVariable() && !A.isVariable() && A.isUndefined()) 804 return false; 805 806 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL; 807 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal) 808 return false; 809 810 if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined()) 811 return false; 812 813 if (Symbol.isTemporary()) 814 return false; 815 816 return true; 817 } 818 819 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isSignature, 820 bool isUsedInReloc) { 821 if (Data.isExternal()) 822 return false; 823 824 const MCSymbol &Symbol = Data.getSymbol(); 825 const MCSymbol &RefSymbol = Symbol.AliasedSymbol(); 826 827 if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) { 828 if (isSignature && !isUsedInReloc) 829 return true; 830 831 return false; 832 } 833 834 return true; 835 } 836 837 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm, 838 SectionIndexMapTy &SectionIndexMap, 839 const RelMapTy &RelMap) { 840 unsigned Index = 1; 841 for (MCAssembler::iterator it = Asm.begin(), 842 ie = Asm.end(); it != ie; ++it) { 843 const MCSectionELF &Section = 844 static_cast<const MCSectionELF &>(it->getSection()); 845 if (Section.getType() != ELF::SHT_GROUP) 846 continue; 847 SectionIndexMap[&Section] = Index++; 848 } 849 850 for (MCAssembler::iterator it = Asm.begin(), 851 ie = Asm.end(); it != ie; ++it) { 852 const MCSectionELF &Section = 853 static_cast<const MCSectionELF &>(it->getSection()); 854 if (Section.getType() == ELF::SHT_GROUP || 855 Section.getType() == ELF::SHT_REL || 856 Section.getType() == ELF::SHT_RELA) 857 continue; 858 SectionIndexMap[&Section] = Index++; 859 const MCSectionELF *RelSection = RelMap.lookup(&Section); 860 if (RelSection) 861 SectionIndexMap[RelSection] = Index++; 862 } 863 } 864 865 void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm, 866 const SectionIndexMapTy &SectionIndexMap, 867 RevGroupMapTy RevGroupMap, 868 unsigned NumRegularSections) { 869 // FIXME: Is this the correct place to do this? 870 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed? 871 if (NeedsGOT) { 872 StringRef Name = "_GLOBAL_OFFSET_TABLE_"; 873 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name); 874 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym); 875 Data.setExternal(true); 876 MCELF::SetBinding(Data, ELF::STB_GLOBAL); 877 } 878 879 // Index 0 is always the empty string. 880 StringMap<uint64_t> StringIndexMap; 881 StringTable += '\x00'; 882 883 // FIXME: We could optimize suffixes in strtab in the same way we 884 // optimize them in shstrtab. 885 886 // Add the data for the symbols. 887 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(), 888 ie = Asm.symbol_end(); it != ie; ++it) { 889 const MCSymbol &Symbol = it->getSymbol(); 890 891 bool Used = UsedInReloc.count(&Symbol); 892 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol); 893 bool isSignature = RevGroupMap.count(&Symbol); 894 895 if (!isInSymtab(Asm, *it, 896 Used || WeakrefUsed || isSignature, 897 Renames.count(&Symbol))) 898 continue; 899 900 ELFSymbolData MSD; 901 MSD.SymbolData = it; 902 const MCSymbol &RefSymbol = Symbol.AliasedSymbol(); 903 904 // Undefined symbols are global, but this is the first place we 905 // are able to set it. 906 bool Local = isLocal(*it, isSignature, Used); 907 if (!Local && MCELF::GetBinding(*it) == ELF::STB_LOCAL) { 908 MCSymbolData &SD = Asm.getSymbolData(RefSymbol); 909 MCELF::SetBinding(*it, ELF::STB_GLOBAL); 910 MCELF::SetBinding(SD, ELF::STB_GLOBAL); 911 } 912 913 if (RefSymbol.isUndefined() && !Used && WeakrefUsed) 914 MCELF::SetBinding(*it, ELF::STB_WEAK); 915 916 if (it->isCommon()) { 917 assert(!Local); 918 MSD.SectionIndex = ELF::SHN_COMMON; 919 } else if (Symbol.isAbsolute() || RefSymbol.isVariable()) { 920 MSD.SectionIndex = ELF::SHN_ABS; 921 } else if (RefSymbol.isUndefined()) { 922 if (isSignature && !Used) 923 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]); 924 else 925 MSD.SectionIndex = ELF::SHN_UNDEF; 926 } else { 927 const MCSectionELF &Section = 928 static_cast<const MCSectionELF&>(RefSymbol.getSection()); 929 MSD.SectionIndex = SectionIndexMap.lookup(&Section); 930 if (MSD.SectionIndex >= ELF::SHN_LORESERVE) 931 NeedsSymtabShndx = true; 932 assert(MSD.SectionIndex && "Invalid section index!"); 933 } 934 935 // The @@@ in symbol version is replaced with @ in undefined symbols and 936 // @@ in defined ones. 937 StringRef Name = Symbol.getName(); 938 SmallString<32> Buf; 939 940 size_t Pos = Name.find("@@@"); 941 if (Pos != StringRef::npos) { 942 Buf += Name.substr(0, Pos); 943 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1; 944 Buf += Name.substr(Pos + Skip); 945 Name = Buf; 946 } 947 948 uint64_t &Entry = StringIndexMap[Name]; 949 if (!Entry) { 950 Entry = StringTable.size(); 951 StringTable += Name; 952 StringTable += '\x00'; 953 } 954 MSD.StringIndex = Entry; 955 if (MSD.SectionIndex == ELF::SHN_UNDEF) 956 UndefinedSymbolData.push_back(MSD); 957 else if (Local) 958 LocalSymbolData.push_back(MSD); 959 else 960 ExternalSymbolData.push_back(MSD); 961 } 962 963 // Symbols are required to be in lexicographic order. 964 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end()); 965 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end()); 966 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end()); 967 968 // Set the symbol indices. Local symbols must come before all other 969 // symbols with non-local bindings. 970 unsigned Index = 1; 971 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) 972 LocalSymbolData[i].SymbolData->setIndex(Index++); 973 974 Index += NumRegularSections; 975 976 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) 977 ExternalSymbolData[i].SymbolData->setIndex(Index++); 978 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) 979 UndefinedSymbolData[i].SymbolData->setIndex(Index++); 980 981 if (Index >= ELF::SHN_LORESERVE) 982 NeedsSymtabShndx = true; 983 } 984 985 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm, 986 MCAsmLayout &Layout, 987 RelMapTy &RelMap) { 988 for (MCAssembler::const_iterator it = Asm.begin(), 989 ie = Asm.end(); it != ie; ++it) { 990 const MCSectionData &SD = *it; 991 if (Relocations[&SD].empty()) 992 continue; 993 994 MCContext &Ctx = Asm.getContext(); 995 const MCSectionELF &Section = 996 static_cast<const MCSectionELF&>(SD.getSection()); 997 998 const StringRef SectionName = Section.getSectionName(); 999 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel"; 1000 RelaSectionName += SectionName; 1001 1002 unsigned EntrySize; 1003 if (hasRelocationAddend()) 1004 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela); 1005 else 1006 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel); 1007 1008 const MCSectionELF *RelaSection = 1009 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ? 1010 ELF::SHT_RELA : ELF::SHT_REL, 0, 1011 SectionKind::getReadOnly(), 1012 EntrySize, ""); 1013 RelMap[&Section] = RelaSection; 1014 Asm.getOrCreateSectionData(*RelaSection); 1015 } 1016 } 1017 1018 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 1019 const RelMapTy &RelMap) { 1020 for (MCAssembler::const_iterator it = Asm.begin(), 1021 ie = Asm.end(); it != ie; ++it) { 1022 const MCSectionData &SD = *it; 1023 const MCSectionELF &Section = 1024 static_cast<const MCSectionELF&>(SD.getSection()); 1025 1026 const MCSectionELF *RelaSection = RelMap.lookup(&Section); 1027 if (!RelaSection) 1028 continue; 1029 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection); 1030 RelaSD.setAlignment(is64Bit() ? 8 : 4); 1031 1032 MCDataFragment *F = new MCDataFragment(&RelaSD); 1033 WriteRelocationsFragment(Asm, F, &*it); 1034 } 1035 } 1036 1037 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type, 1038 uint64_t Flags, uint64_t Address, 1039 uint64_t Offset, uint64_t Size, 1040 uint32_t Link, uint32_t Info, 1041 uint64_t Alignment, 1042 uint64_t EntrySize) { 1043 Write32(Name); // sh_name: index into string table 1044 Write32(Type); // sh_type 1045 WriteWord(Flags); // sh_flags 1046 WriteWord(Address); // sh_addr 1047 WriteWord(Offset); // sh_offset 1048 WriteWord(Size); // sh_size 1049 Write32(Link); // sh_link 1050 Write32(Info); // sh_info 1051 WriteWord(Alignment); // sh_addralign 1052 WriteWord(EntrySize); // sh_entsize 1053 } 1054 1055 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm, 1056 MCDataFragment *F, 1057 const MCSectionData *SD) { 1058 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD]; 1059 1060 // Sort the relocation entries. Most targets just sort by r_offset, but some 1061 // (e.g., MIPS) have additional constraints. 1062 TargetObjectWriter->sortRelocs(Asm, Relocs); 1063 1064 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) { 1065 ELFRelocationEntry entry = Relocs[e - i - 1]; 1066 1067 if (!entry.Index) 1068 ; 1069 else if (entry.Index < 0) 1070 entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol); 1071 else 1072 entry.Index += LocalSymbolData.size(); 1073 if (is64Bit()) { 1074 String64(*F, entry.r_offset); 1075 if (TargetObjectWriter->isN64()) { 1076 String32(*F, entry.Index); 1077 1078 String8(*F, TargetObjectWriter->getRSsym(entry.Type)); 1079 String8(*F, TargetObjectWriter->getRType3(entry.Type)); 1080 String8(*F, TargetObjectWriter->getRType2(entry.Type)); 1081 String8(*F, TargetObjectWriter->getRType(entry.Type)); 1082 } 1083 else { 1084 struct ELF::Elf64_Rela ERE64; 1085 ERE64.setSymbolAndType(entry.Index, entry.Type); 1086 String64(*F, ERE64.r_info); 1087 } 1088 if (hasRelocationAddend()) 1089 String64(*F, entry.r_addend); 1090 } else { 1091 String32(*F, entry.r_offset); 1092 1093 struct ELF::Elf32_Rela ERE32; 1094 ERE32.setSymbolAndType(entry.Index, entry.Type); 1095 String32(*F, ERE32.r_info); 1096 1097 if (hasRelocationAddend()) 1098 String32(*F, entry.r_addend); 1099 } 1100 } 1101 } 1102 1103 static int compareBySuffix(const void *a, const void *b) { 1104 const MCSectionELF *secA = *static_cast<const MCSectionELF* const *>(a); 1105 const MCSectionELF *secB = *static_cast<const MCSectionELF* const *>(b); 1106 const StringRef &NameA = secA->getSectionName(); 1107 const StringRef &NameB = secB->getSectionName(); 1108 const unsigned sizeA = NameA.size(); 1109 const unsigned sizeB = NameB.size(); 1110 const unsigned len = std::min(sizeA, sizeB); 1111 for (unsigned int i = 0; i < len; ++i) { 1112 char ca = NameA[sizeA - i - 1]; 1113 char cb = NameB[sizeB - i - 1]; 1114 if (ca != cb) 1115 return cb - ca; 1116 } 1117 1118 return sizeB - sizeA; 1119 } 1120 1121 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm, 1122 MCAsmLayout &Layout, 1123 SectionIndexMapTy &SectionIndexMap, 1124 const RelMapTy &RelMap) { 1125 MCContext &Ctx = Asm.getContext(); 1126 MCDataFragment *F; 1127 1128 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32; 1129 1130 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as. 1131 const MCSectionELF *ShstrtabSection = 1132 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0, 1133 SectionKind::getReadOnly()); 1134 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection); 1135 ShstrtabSD.setAlignment(1); 1136 1137 const MCSectionELF *SymtabSection = 1138 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, 1139 SectionKind::getReadOnly(), 1140 EntrySize, ""); 1141 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection); 1142 SymtabSD.setAlignment(is64Bit() ? 8 : 4); 1143 1144 MCSectionData *SymtabShndxSD = NULL; 1145 1146 if (NeedsSymtabShndx) { 1147 const MCSectionELF *SymtabShndxSection = 1148 Ctx.getELFSection(".symtab_shndx", ELF::SHT_SYMTAB_SHNDX, 0, 1149 SectionKind::getReadOnly(), 4, ""); 1150 SymtabShndxSD = &Asm.getOrCreateSectionData(*SymtabShndxSection); 1151 SymtabShndxSD->setAlignment(4); 1152 } 1153 1154 const MCSectionELF *StrtabSection; 1155 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0, 1156 SectionKind::getReadOnly()); 1157 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection); 1158 StrtabSD.setAlignment(1); 1159 1160 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1161 1162 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection); 1163 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection); 1164 StringTableIndex = SectionIndexMap.lookup(StrtabSection); 1165 1166 // Symbol table 1167 F = new MCDataFragment(&SymtabSD); 1168 MCDataFragment *ShndxF = NULL; 1169 if (NeedsSymtabShndx) { 1170 ShndxF = new MCDataFragment(SymtabShndxSD); 1171 } 1172 WriteSymbolTable(F, ShndxF, Asm, Layout, SectionIndexMap); 1173 1174 F = new MCDataFragment(&StrtabSD); 1175 F->getContents().append(StringTable.begin(), StringTable.end()); 1176 1177 F = new MCDataFragment(&ShstrtabSD); 1178 1179 std::vector<const MCSectionELF*> Sections; 1180 for (MCAssembler::const_iterator it = Asm.begin(), 1181 ie = Asm.end(); it != ie; ++it) { 1182 const MCSectionELF &Section = 1183 static_cast<const MCSectionELF&>(it->getSection()); 1184 Sections.push_back(&Section); 1185 } 1186 array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix); 1187 1188 // Section header string table. 1189 // 1190 // The first entry of a string table holds a null character so skip 1191 // section 0. 1192 uint64_t Index = 1; 1193 F->getContents().push_back('\x00'); 1194 1195 for (unsigned int I = 0, E = Sections.size(); I != E; ++I) { 1196 const MCSectionELF &Section = *Sections[I]; 1197 1198 StringRef Name = Section.getSectionName(); 1199 if (I != 0) { 1200 StringRef PreviousName = Sections[I - 1]->getSectionName(); 1201 if (PreviousName.endswith(Name)) { 1202 SectionStringTableIndex[&Section] = Index - Name.size() - 1; 1203 continue; 1204 } 1205 } 1206 // Remember the index into the string table so we can write it 1207 // into the sh_name field of the section header table. 1208 SectionStringTableIndex[&Section] = Index; 1209 1210 Index += Name.size() + 1; 1211 F->getContents().append(Name.begin(), Name.end()); 1212 F->getContents().push_back('\x00'); 1213 } 1214 } 1215 1216 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm, 1217 MCAsmLayout &Layout, 1218 GroupMapTy &GroupMap, 1219 RevGroupMapTy &RevGroupMap, 1220 SectionIndexMapTy &SectionIndexMap, 1221 const RelMapTy &RelMap) { 1222 // Create the .note.GNU-stack section if needed. 1223 MCContext &Ctx = Asm.getContext(); 1224 if (Asm.getNoExecStack()) { 1225 const MCSectionELF *GnuStackSection = 1226 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0, 1227 SectionKind::getReadOnly()); 1228 Asm.getOrCreateSectionData(*GnuStackSection); 1229 } 1230 1231 // Build the groups 1232 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1233 it != ie; ++it) { 1234 const MCSectionELF &Section = 1235 static_cast<const MCSectionELF&>(it->getSection()); 1236 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1237 continue; 1238 1239 const MCSymbol *SignatureSymbol = Section.getGroup(); 1240 Asm.getOrCreateSymbolData(*SignatureSymbol); 1241 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol]; 1242 if (!Group) { 1243 Group = Ctx.CreateELFGroupSection(); 1244 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1245 Data.setAlignment(4); 1246 MCDataFragment *F = new MCDataFragment(&Data); 1247 String32(*F, ELF::GRP_COMDAT); 1248 } 1249 GroupMap[Group] = SignatureSymbol; 1250 } 1251 1252 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1253 1254 // Add sections to the groups 1255 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1256 it != ie; ++it) { 1257 const MCSectionELF &Section = 1258 static_cast<const MCSectionELF&>(it->getSection()); 1259 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1260 continue; 1261 const MCSectionELF *Group = RevGroupMap[Section.getGroup()]; 1262 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1263 // FIXME: we could use the previous fragment 1264 MCDataFragment *F = new MCDataFragment(&Data); 1265 unsigned Index = SectionIndexMap.lookup(&Section); 1266 String32(*F, Index); 1267 } 1268 } 1269 1270 void ELFObjectWriter::WriteSection(MCAssembler &Asm, 1271 const SectionIndexMapTy &SectionIndexMap, 1272 uint32_t GroupSymbolIndex, 1273 uint64_t Offset, uint64_t Size, 1274 uint64_t Alignment, 1275 const MCSectionELF &Section) { 1276 uint64_t sh_link = 0; 1277 uint64_t sh_info = 0; 1278 1279 switch(Section.getType()) { 1280 case ELF::SHT_DYNAMIC: 1281 sh_link = SectionStringTableIndex[&Section]; 1282 sh_info = 0; 1283 break; 1284 1285 case ELF::SHT_REL: 1286 case ELF::SHT_RELA: { 1287 const MCSectionELF *SymtabSection; 1288 const MCSectionELF *InfoSection; 1289 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 1290 0, 1291 SectionKind::getReadOnly()); 1292 sh_link = SectionIndexMap.lookup(SymtabSection); 1293 assert(sh_link && ".symtab not found"); 1294 1295 // Remove ".rel" and ".rela" prefixes. 1296 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5; 1297 StringRef SectionName = Section.getSectionName().substr(SecNameLen); 1298 1299 InfoSection = Asm.getContext().getELFSection(SectionName, 1300 ELF::SHT_PROGBITS, 0, 1301 SectionKind::getReadOnly()); 1302 sh_info = SectionIndexMap.lookup(InfoSection); 1303 break; 1304 } 1305 1306 case ELF::SHT_SYMTAB: 1307 case ELF::SHT_DYNSYM: 1308 sh_link = StringTableIndex; 1309 sh_info = LastLocalSymbolIndex; 1310 break; 1311 1312 case ELF::SHT_SYMTAB_SHNDX: 1313 sh_link = SymbolTableIndex; 1314 break; 1315 1316 case ELF::SHT_PROGBITS: 1317 case ELF::SHT_STRTAB: 1318 case ELF::SHT_NOBITS: 1319 case ELF::SHT_NOTE: 1320 case ELF::SHT_NULL: 1321 case ELF::SHT_ARM_ATTRIBUTES: 1322 case ELF::SHT_INIT_ARRAY: 1323 case ELF::SHT_FINI_ARRAY: 1324 case ELF::SHT_PREINIT_ARRAY: 1325 case ELF::SHT_X86_64_UNWIND: 1326 case ELF::SHT_MIPS_REGINFO: 1327 case ELF::SHT_MIPS_OPTIONS: 1328 // Nothing to do. 1329 break; 1330 1331 case ELF::SHT_GROUP: 1332 sh_link = SymbolTableIndex; 1333 sh_info = GroupSymbolIndex; 1334 break; 1335 1336 default: 1337 assert(0 && "FIXME: sh_type value not supported!"); 1338 break; 1339 } 1340 1341 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM && 1342 Section.getType() == ELF::SHT_ARM_EXIDX) { 1343 StringRef SecName(Section.getSectionName()); 1344 if (SecName == ".ARM.exidx") { 1345 sh_link = SectionIndexMap.lookup( 1346 Asm.getContext().getELFSection(".text", 1347 ELF::SHT_PROGBITS, 1348 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, 1349 SectionKind::getText())); 1350 } else if (SecName.startswith(".ARM.exidx")) { 1351 sh_link = SectionIndexMap.lookup( 1352 Asm.getContext().getELFSection(SecName.substr(sizeof(".ARM.exidx") - 1), 1353 ELF::SHT_PROGBITS, 1354 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, 1355 SectionKind::getText())); 1356 } 1357 } 1358 1359 WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(), 1360 Section.getFlags(), 0, Offset, Size, sh_link, sh_info, 1361 Alignment, Section.getEntrySize()); 1362 } 1363 1364 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) { 1365 return SD.getOrdinal() == ~UINT32_C(0) && 1366 !SD.getSection().isVirtualSection(); 1367 } 1368 1369 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) { 1370 uint64_t Ret = 0; 1371 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1372 ++i) { 1373 const MCFragment &F = *i; 1374 assert(F.getKind() == MCFragment::FT_Data); 1375 Ret += cast<MCDataFragment>(F).getContents().size(); 1376 } 1377 return Ret; 1378 } 1379 1380 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout, 1381 const MCSectionData &SD) { 1382 if (IsELFMetaDataSection(SD)) 1383 return DataSectionSize(SD); 1384 return Layout.getSectionFileSize(&SD); 1385 } 1386 1387 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout, 1388 const MCSectionData &SD) { 1389 if (IsELFMetaDataSection(SD)) 1390 return DataSectionSize(SD); 1391 return Layout.getSectionAddressSize(&SD); 1392 } 1393 1394 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm, 1395 const MCAsmLayout &Layout, 1396 const MCSectionELF &Section) { 1397 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1398 1399 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment()); 1400 WriteZeros(Padding); 1401 1402 if (IsELFMetaDataSection(SD)) { 1403 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1404 ++i) { 1405 const MCFragment &F = *i; 1406 assert(F.getKind() == MCFragment::FT_Data); 1407 WriteBytes(cast<MCDataFragment>(F).getContents()); 1408 } 1409 } else { 1410 Asm.writeSectionData(&SD, Layout); 1411 } 1412 } 1413 1414 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm, 1415 const GroupMapTy &GroupMap, 1416 const MCAsmLayout &Layout, 1417 const SectionIndexMapTy &SectionIndexMap, 1418 const SectionOffsetMapTy &SectionOffsetMap) { 1419 const unsigned NumSections = Asm.size() + 1; 1420 1421 std::vector<const MCSectionELF*> Sections; 1422 Sections.resize(NumSections - 1); 1423 1424 for (SectionIndexMapTy::const_iterator i= 1425 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) { 1426 const std::pair<const MCSectionELF*, uint32_t> &p = *i; 1427 Sections[p.second - 1] = p.first; 1428 } 1429 1430 // Null section first. 1431 uint64_t FirstSectionSize = 1432 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0; 1433 uint32_t FirstSectionLink = 1434 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0; 1435 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0); 1436 1437 for (unsigned i = 0; i < NumSections - 1; ++i) { 1438 const MCSectionELF &Section = *Sections[i]; 1439 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1440 uint32_t GroupSymbolIndex; 1441 if (Section.getType() != ELF::SHT_GROUP) 1442 GroupSymbolIndex = 0; 1443 else 1444 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, 1445 GroupMap.lookup(&Section)); 1446 1447 uint64_t Size = GetSectionAddressSize(Layout, SD); 1448 1449 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex, 1450 SectionOffsetMap.lookup(&Section), Size, 1451 SD.getAlignment(), Section); 1452 } 1453 } 1454 1455 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm, 1456 std::vector<const MCSectionELF*> &Sections) { 1457 for (MCAssembler::iterator it = Asm.begin(), 1458 ie = Asm.end(); it != ie; ++it) { 1459 const MCSectionELF &Section = 1460 static_cast<const MCSectionELF &>(it->getSection()); 1461 if (Section.getType() == ELF::SHT_GROUP) 1462 Sections.push_back(&Section); 1463 } 1464 1465 for (MCAssembler::iterator it = Asm.begin(), 1466 ie = Asm.end(); it != ie; ++it) { 1467 const MCSectionELF &Section = 1468 static_cast<const MCSectionELF &>(it->getSection()); 1469 if (Section.getType() != ELF::SHT_GROUP && 1470 Section.getType() != ELF::SHT_REL && 1471 Section.getType() != ELF::SHT_RELA) 1472 Sections.push_back(&Section); 1473 } 1474 1475 for (MCAssembler::iterator it = Asm.begin(), 1476 ie = Asm.end(); it != ie; ++it) { 1477 const MCSectionELF &Section = 1478 static_cast<const MCSectionELF &>(it->getSection()); 1479 if (Section.getType() == ELF::SHT_REL || 1480 Section.getType() == ELF::SHT_RELA) 1481 Sections.push_back(&Section); 1482 } 1483 } 1484 1485 void ELFObjectWriter::WriteObject(MCAssembler &Asm, 1486 const MCAsmLayout &Layout) { 1487 GroupMapTy GroupMap; 1488 RevGroupMapTy RevGroupMap; 1489 SectionIndexMapTy SectionIndexMap; 1490 1491 unsigned NumUserSections = Asm.size(); 1492 1493 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap; 1494 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1495 1496 const unsigned NumUserAndRelocSections = Asm.size(); 1497 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap, 1498 RevGroupMap, SectionIndexMap, RelMap); 1499 const unsigned AllSections = Asm.size(); 1500 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections; 1501 1502 unsigned NumRegularSections = NumUserSections + NumIndexedSections; 1503 1504 // Compute symbol table information. 1505 ComputeSymbolTable(Asm, SectionIndexMap, RevGroupMap, NumRegularSections); 1506 1507 1508 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1509 1510 CreateMetadataSections(const_cast<MCAssembler&>(Asm), 1511 const_cast<MCAsmLayout&>(Layout), 1512 SectionIndexMap, 1513 RelMap); 1514 1515 uint64_t NaturalAlignment = is64Bit() ? 8 : 4; 1516 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 1517 sizeof(ELF::Elf32_Ehdr); 1518 uint64_t FileOff = HeaderSize; 1519 1520 std::vector<const MCSectionELF*> Sections; 1521 ComputeSectionOrder(Asm, Sections); 1522 unsigned NumSections = Sections.size(); 1523 SectionOffsetMapTy SectionOffsetMap; 1524 for (unsigned i = 0; i < NumRegularSections + 1; ++i) { 1525 const MCSectionELF &Section = *Sections[i]; 1526 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1527 1528 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1529 1530 // Remember the offset into the file for this section. 1531 SectionOffsetMap[&Section] = FileOff; 1532 1533 // Get the size of the section in the output file (including padding). 1534 FileOff += GetSectionFileSize(Layout, SD); 1535 } 1536 1537 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment); 1538 1539 const unsigned SectionHeaderOffset = FileOff - HeaderSize; 1540 1541 uint64_t SectionHeaderEntrySize = is64Bit() ? 1542 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr); 1543 FileOff += (NumSections + 1) * SectionHeaderEntrySize; 1544 1545 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) { 1546 const MCSectionELF &Section = *Sections[i]; 1547 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1548 1549 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1550 1551 // Remember the offset into the file for this section. 1552 SectionOffsetMap[&Section] = FileOff; 1553 1554 // Get the size of the section in the output file (including padding). 1555 FileOff += GetSectionFileSize(Layout, SD); 1556 } 1557 1558 // Write out the ELF header ... 1559 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1); 1560 1561 // ... then the regular sections ... 1562 // + because of .shstrtab 1563 for (unsigned i = 0; i < NumRegularSections + 1; ++i) 1564 WriteDataSectionData(Asm, Layout, *Sections[i]); 1565 1566 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment); 1567 WriteZeros(Padding); 1568 1569 // ... then the section header table ... 1570 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap, 1571 SectionOffsetMap); 1572 1573 // ... and then the remaining sections ... 1574 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) 1575 WriteDataSectionData(Asm, Layout, *Sections[i]); 1576 } 1577 1578 bool 1579 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 1580 const MCSymbolData &DataA, 1581 const MCFragment &FB, 1582 bool InSet, 1583 bool IsPCRel) const { 1584 if (DataA.getFlags() & ELF_STB_Weak) 1585 return false; 1586 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl( 1587 Asm, DataA, FB,InSet, IsPCRel); 1588 } 1589 1590 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW, 1591 raw_ostream &OS, 1592 bool IsLittleEndian) { 1593 return new ELFObjectWriter(MOTW, OS, IsLittleEndian); 1594 } 1595
