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 "MCELF.h" 15 #include "llvm/ADT/OwningPtr.h" 16 #include "llvm/ADT/SmallPtrSet.h" 17 #include "llvm/ADT/SmallString.h" 18 #include "llvm/ADT/STLExtras.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/MCELFObjectWriter.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/ErrorHandling.h" 33 #include "llvm/Support/ELF.h" 34 35 #include <vector> 36 using namespace llvm; 37 38 #undef DEBUG_TYPE 39 #define DEBUG_TYPE "reloc-info" 40 41 namespace { 42 class ELFObjectWriter : public MCObjectWriter { 43 protected: 44 45 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind); 46 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant); 47 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout); 48 static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data, 49 bool Used, bool Renamed); 50 static bool isLocal(const MCSymbolData &Data, bool isSignature, 51 bool isUsedInReloc); 52 static bool IsELFMetaDataSection(const MCSectionData &SD); 53 static uint64_t DataSectionSize(const MCSectionData &SD); 54 static uint64_t GetSectionFileSize(const MCAsmLayout &Layout, 55 const MCSectionData &SD); 56 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout, 57 const MCSectionData &SD); 58 59 void WriteDataSectionData(MCAssembler &Asm, 60 const MCAsmLayout &Layout, 61 const MCSectionELF &Section); 62 63 /*static bool isFixupKindX86RIPRel(unsigned Kind) { 64 return Kind == X86::reloc_riprel_4byte || 65 Kind == X86::reloc_riprel_4byte_movq_load; 66 }*/ 67 68 /// ELFSymbolData - Helper struct for containing some precomputed 69 /// information on symbols. 70 struct ELFSymbolData { 71 MCSymbolData *SymbolData; 72 uint64_t StringIndex; 73 uint32_t SectionIndex; 74 75 // Support lexicographic sorting. 76 bool operator<(const ELFSymbolData &RHS) const { 77 if (MCELF::GetType(*SymbolData) == ELF::STT_FILE) 78 return true; 79 if (MCELF::GetType(*RHS.SymbolData) == ELF::STT_FILE) 80 return false; 81 return SymbolData->getSymbol().getName() < 82 RHS.SymbolData->getSymbol().getName(); 83 } 84 }; 85 86 /// The target specific ELF writer instance. 87 llvm::OwningPtr<MCELFObjectTargetWriter> TargetObjectWriter; 88 89 SmallPtrSet<const MCSymbol *, 16> UsedInReloc; 90 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc; 91 DenseMap<const MCSymbol *, const MCSymbol *> Renames; 92 93 llvm::DenseMap<const MCSectionData*, 94 std::vector<ELFRelocationEntry> > Relocations; 95 DenseMap<const MCSection*, uint64_t> SectionStringTableIndex; 96 97 /// @} 98 /// @name Symbol Table Data 99 /// @{ 100 101 SmallString<256> StringTable; 102 std::vector<ELFSymbolData> LocalSymbolData; 103 std::vector<ELFSymbolData> ExternalSymbolData; 104 std::vector<ELFSymbolData> UndefinedSymbolData; 105 106 /// @} 107 108 bool NeedsGOT; 109 110 bool NeedsSymtabShndx; 111 112 // This holds the symbol table index of the last local symbol. 113 unsigned LastLocalSymbolIndex; 114 // This holds the .strtab section index. 115 unsigned StringTableIndex; 116 // This holds the .symtab section index. 117 unsigned SymbolTableIndex; 118 119 unsigned ShstrtabIndex; 120 121 122 const MCSymbol *SymbolToReloc(const MCAssembler &Asm, 123 const MCValue &Target, 124 const MCFragment &F, 125 const MCFixup &Fixup, 126 bool IsPCRel) const; 127 128 // TargetObjectWriter wrappers. 129 const MCSymbol *ExplicitRelSym(const MCAssembler &Asm, 130 const MCValue &Target, 131 const MCFragment &F, 132 const MCFixup &Fixup, 133 bool IsPCRel) const { 134 return TargetObjectWriter->ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 135 } 136 137 bool is64Bit() const { return TargetObjectWriter->is64Bit(); } 138 bool hasRelocationAddend() const { 139 return TargetObjectWriter->hasRelocationAddend(); 140 } 141 unsigned getEFlags() const { 142 return TargetObjectWriter->getEFlags(); 143 } 144 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup, 145 bool IsPCRel, bool IsRelocWithSymbol, 146 int64_t Addend) const { 147 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel, 148 IsRelocWithSymbol, Addend); 149 } 150 151 152 public: 153 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, 154 raw_ostream &_OS, bool IsLittleEndian) 155 : MCObjectWriter(_OS, IsLittleEndian), 156 TargetObjectWriter(MOTW), 157 NeedsGOT(false), NeedsSymtabShndx(false){ 158 } 159 160 virtual ~ELFObjectWriter(); 161 162 void WriteWord(uint64_t W) { 163 if (is64Bit()) 164 Write64(W); 165 else 166 Write32(W); 167 } 168 169 void StringLE16(char *buf, uint16_t Value) { 170 buf[0] = char(Value >> 0); 171 buf[1] = char(Value >> 8); 172 } 173 174 void StringLE32(char *buf, uint32_t Value) { 175 StringLE16(buf, uint16_t(Value >> 0)); 176 StringLE16(buf + 2, uint16_t(Value >> 16)); 177 } 178 179 void StringLE64(char *buf, uint64_t Value) { 180 StringLE32(buf, uint32_t(Value >> 0)); 181 StringLE32(buf + 4, uint32_t(Value >> 32)); 182 } 183 184 void StringBE16(char *buf ,uint16_t Value) { 185 buf[0] = char(Value >> 8); 186 buf[1] = char(Value >> 0); 187 } 188 189 void StringBE32(char *buf, uint32_t Value) { 190 StringBE16(buf, uint16_t(Value >> 16)); 191 StringBE16(buf + 2, uint16_t(Value >> 0)); 192 } 193 194 void StringBE64(char *buf, uint64_t Value) { 195 StringBE32(buf, uint32_t(Value >> 32)); 196 StringBE32(buf + 4, uint32_t(Value >> 0)); 197 } 198 199 void String8(MCDataFragment &F, uint8_t Value) { 200 char buf[1]; 201 buf[0] = Value; 202 F.getContents() += StringRef(buf, 1); 203 } 204 205 void String16(MCDataFragment &F, uint16_t Value) { 206 char buf[2]; 207 if (isLittleEndian()) 208 StringLE16(buf, Value); 209 else 210 StringBE16(buf, Value); 211 F.getContents() += StringRef(buf, 2); 212 } 213 214 void String32(MCDataFragment &F, uint32_t Value) { 215 char buf[4]; 216 if (isLittleEndian()) 217 StringLE32(buf, Value); 218 else 219 StringBE32(buf, Value); 220 F.getContents() += StringRef(buf, 4); 221 } 222 223 void String64(MCDataFragment &F, uint64_t Value) { 224 char buf[8]; 225 if (isLittleEndian()) 226 StringLE64(buf, Value); 227 else 228 StringBE64(buf, Value); 229 F.getContents() += StringRef(buf, 8); 230 } 231 232 void WriteHeader(uint64_t SectionDataSize, 233 unsigned NumberOfSections); 234 235 void WriteSymbolEntry(MCDataFragment *SymtabF, 236 MCDataFragment *ShndxF, 237 uint64_t name, uint8_t info, 238 uint64_t value, uint64_t size, 239 uint8_t other, uint32_t shndx, 240 bool Reserved); 241 242 void WriteSymbol(MCDataFragment *SymtabF, MCDataFragment *ShndxF, 243 ELFSymbolData &MSD, 244 const MCAsmLayout &Layout); 245 246 typedef DenseMap<const MCSectionELF*, uint32_t> SectionIndexMapTy; 247 void WriteSymbolTable(MCDataFragment *SymtabF, 248 MCDataFragment *ShndxF, 249 const MCAssembler &Asm, 250 const MCAsmLayout &Layout, 251 const SectionIndexMapTy &SectionIndexMap); 252 253 virtual void RecordRelocation(const MCAssembler &Asm, 254 const MCAsmLayout &Layout, 255 const MCFragment *Fragment, 256 const MCFixup &Fixup, 257 MCValue Target, uint64_t &FixedValue); 258 259 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm, 260 const MCSymbol *S); 261 262 // Map from a group section to the signature symbol 263 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy; 264 // Map from a signature symbol to the group section 265 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy; 266 // Map from a section to the section with the relocations 267 typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy; 268 // Map from a section to its offset 269 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy; 270 271 /// ComputeSymbolTable - Compute the symbol table data 272 /// 273 /// \param Asm - The assembler. 274 /// \param SectionIndexMap - Maps a section to its index. 275 /// \param RevGroupMap - Maps a signature symbol to the group section. 276 /// \param NumRegularSections - Number of non-relocation sections. 277 void ComputeSymbolTable(MCAssembler &Asm, 278 const SectionIndexMapTy &SectionIndexMap, 279 RevGroupMapTy RevGroupMap, 280 unsigned NumRegularSections); 281 282 void ComputeIndexMap(MCAssembler &Asm, 283 SectionIndexMapTy &SectionIndexMap, 284 const RelMapTy &RelMap); 285 286 void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout, 287 RelMapTy &RelMap); 288 289 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 290 const RelMapTy &RelMap); 291 292 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout, 293 SectionIndexMapTy &SectionIndexMap, 294 const RelMapTy &RelMap); 295 296 // Create the sections that show up in the symbol table. Currently 297 // those are the .note.GNU-stack section and the group sections. 298 void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout, 299 GroupMapTy &GroupMap, 300 RevGroupMapTy &RevGroupMap, 301 SectionIndexMapTy &SectionIndexMap, 302 const RelMapTy &RelMap); 303 304 virtual void ExecutePostLayoutBinding(MCAssembler &Asm, 305 const MCAsmLayout &Layout); 306 307 void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap, 308 const MCAsmLayout &Layout, 309 const SectionIndexMapTy &SectionIndexMap, 310 const SectionOffsetMapTy &SectionOffsetMap); 311 312 void ComputeSectionOrder(MCAssembler &Asm, 313 std::vector<const MCSectionELF*> &Sections); 314 315 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags, 316 uint64_t Address, uint64_t Offset, 317 uint64_t Size, uint32_t Link, uint32_t Info, 318 uint64_t Alignment, uint64_t EntrySize); 319 320 void WriteRelocationsFragment(const MCAssembler &Asm, 321 MCDataFragment *F, 322 const MCSectionData *SD); 323 324 virtual bool 325 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 326 const MCSymbolData &DataA, 327 const MCFragment &FB, 328 bool InSet, 329 bool IsPCRel) const; 330 331 virtual void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout); 332 void WriteSection(MCAssembler &Asm, 333 const SectionIndexMapTy &SectionIndexMap, 334 uint32_t GroupSymbolIndex, 335 uint64_t Offset, uint64_t Size, uint64_t Alignment, 336 const MCSectionELF &Section); 337 }; 338 } 339 340 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) { 341 const MCFixupKindInfo &FKI = 342 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind); 343 344 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel; 345 } 346 347 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) { 348 switch (Variant) { 349 default: 350 return false; 351 case MCSymbolRefExpr::VK_GOT: 352 case MCSymbolRefExpr::VK_PLT: 353 case MCSymbolRefExpr::VK_GOTPCREL: 354 case MCSymbolRefExpr::VK_GOTOFF: 355 case MCSymbolRefExpr::VK_TPOFF: 356 case MCSymbolRefExpr::VK_TLSGD: 357 case MCSymbolRefExpr::VK_GOTTPOFF: 358 case MCSymbolRefExpr::VK_INDNTPOFF: 359 case MCSymbolRefExpr::VK_NTPOFF: 360 case MCSymbolRefExpr::VK_GOTNTPOFF: 361 case MCSymbolRefExpr::VK_TLSLDM: 362 case MCSymbolRefExpr::VK_DTPOFF: 363 case MCSymbolRefExpr::VK_TLSLD: 364 return true; 365 } 366 } 367 368 ELFObjectWriter::~ELFObjectWriter() 369 {} 370 371 // Emit the ELF header. 372 void ELFObjectWriter::WriteHeader(uint64_t SectionDataSize, 373 unsigned NumberOfSections) { 374 // ELF Header 375 // ---------- 376 // 377 // Note 378 // ---- 379 // emitWord method behaves differently for ELF32 and ELF64, writing 380 // 4 bytes in the former and 8 in the latter. 381 382 Write8(0x7f); // e_ident[EI_MAG0] 383 Write8('E'); // e_ident[EI_MAG1] 384 Write8('L'); // e_ident[EI_MAG2] 385 Write8('F'); // e_ident[EI_MAG3] 386 387 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS] 388 389 // e_ident[EI_DATA] 390 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB); 391 392 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION] 393 // e_ident[EI_OSABI] 394 Write8(TargetObjectWriter->getOSABI()); 395 Write8(0); // e_ident[EI_ABIVERSION] 396 397 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD); 398 399 Write16(ELF::ET_REL); // e_type 400 401 Write16(TargetObjectWriter->getEMachine()); // e_machine = target 402 403 Write32(ELF::EV_CURRENT); // e_version 404 WriteWord(0); // e_entry, no entry point in .o file 405 WriteWord(0); // e_phoff, no program header for .o 406 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 407 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes 408 409 // e_flags = whatever the target wants 410 Write32(getEFlags()); 411 412 // e_ehsize = ELF header size 413 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr)); 414 415 Write16(0); // e_phentsize = prog header entry size 416 Write16(0); // e_phnum = # prog header entries = 0 417 418 // e_shentsize = Section header entry size 419 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr)); 420 421 // e_shnum = # of section header ents 422 if (NumberOfSections >= ELF::SHN_LORESERVE) 423 Write16(ELF::SHN_UNDEF); 424 else 425 Write16(NumberOfSections); 426 427 // e_shstrndx = Section # of '.shstrtab' 428 if (ShstrtabIndex >= ELF::SHN_LORESERVE) 429 Write16(ELF::SHN_XINDEX); 430 else 431 Write16(ShstrtabIndex); 432 } 433 434 void ELFObjectWriter::WriteSymbolEntry(MCDataFragment *SymtabF, 435 MCDataFragment *ShndxF, 436 uint64_t name, 437 uint8_t info, uint64_t value, 438 uint64_t size, uint8_t other, 439 uint32_t shndx, 440 bool Reserved) { 441 if (ShndxF) { 442 if (shndx >= ELF::SHN_LORESERVE && !Reserved) 443 String32(*ShndxF, shndx); 444 else 445 String32(*ShndxF, 0); 446 } 447 448 uint16_t Index = (shndx >= ELF::SHN_LORESERVE && !Reserved) ? 449 uint16_t(ELF::SHN_XINDEX) : shndx; 450 451 if (is64Bit()) { 452 String32(*SymtabF, name); // st_name 453 String8(*SymtabF, info); // st_info 454 String8(*SymtabF, other); // st_other 455 String16(*SymtabF, Index); // st_shndx 456 String64(*SymtabF, value); // st_value 457 String64(*SymtabF, size); // st_size 458 } else { 459 String32(*SymtabF, name); // st_name 460 String32(*SymtabF, value); // st_value 461 String32(*SymtabF, size); // st_size 462 String8(*SymtabF, info); // st_info 463 String8(*SymtabF, other); // st_other 464 String16(*SymtabF, Index); // st_shndx 465 } 466 } 467 468 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data, 469 const MCAsmLayout &Layout) { 470 if (Data.isCommon() && Data.isExternal()) 471 return Data.getCommonAlignment(); 472 473 const MCSymbol &Symbol = Data.getSymbol(); 474 475 if (Symbol.isAbsolute() && Symbol.isVariable()) { 476 if (const MCExpr *Value = Symbol.getVariableValue()) { 477 int64_t IntValue; 478 if (Value->EvaluateAsAbsolute(IntValue, Layout)) 479 return (uint64_t)IntValue; 480 } 481 } 482 483 if (!Symbol.isInSection()) 484 return 0; 485 486 487 if (Data.getFragment()) { 488 if (Data.getFlags() & ELF_Other_ThumbFunc) 489 return Layout.getSymbolOffset(&Data)+1; 490 else 491 return Layout.getSymbolOffset(&Data); 492 } 493 494 return 0; 495 } 496 497 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm, 498 const MCAsmLayout &Layout) { 499 // The presence of symbol versions causes undefined symbols and 500 // versions declared with @@@ to be renamed. 501 502 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(), 503 ie = Asm.symbol_end(); it != ie; ++it) { 504 const MCSymbol &Alias = it->getSymbol(); 505 const MCSymbol &Symbol = Alias.AliasedSymbol(); 506 MCSymbolData &SD = Asm.getSymbolData(Symbol); 507 508 // Not an alias. 509 if (&Symbol == &Alias) 510 continue; 511 512 StringRef AliasName = Alias.getName(); 513 size_t Pos = AliasName.find('@'); 514 if (Pos == StringRef::npos) 515 continue; 516 517 // Aliases defined with .symvar copy the binding from the symbol they alias. 518 // This is the first place we are able to copy this information. 519 it->setExternal(SD.isExternal()); 520 MCELF::SetBinding(*it, MCELF::GetBinding(SD)); 521 522 StringRef Rest = AliasName.substr(Pos); 523 if (!Symbol.isUndefined() && !Rest.startswith("@@@")) 524 continue; 525 526 // FIXME: produce a better error message. 527 if (Symbol.isUndefined() && Rest.startswith("@@") && 528 !Rest.startswith("@@@")) 529 report_fatal_error("A @@ version cannot be undefined"); 530 531 Renames.insert(std::make_pair(&Symbol, &Alias)); 532 } 533 } 534 535 void ELFObjectWriter::WriteSymbol(MCDataFragment *SymtabF, 536 MCDataFragment *ShndxF, 537 ELFSymbolData &MSD, 538 const MCAsmLayout &Layout) { 539 MCSymbolData &OrigData = *MSD.SymbolData; 540 MCSymbolData &Data = 541 Layout.getAssembler().getSymbolData(OrigData.getSymbol().AliasedSymbol()); 542 543 bool IsReserved = Data.isCommon() || Data.getSymbol().isAbsolute() || 544 Data.getSymbol().isVariable(); 545 546 uint8_t Binding = MCELF::GetBinding(OrigData); 547 uint8_t Visibility = MCELF::GetVisibility(OrigData); 548 uint8_t Type = MCELF::GetType(Data); 549 550 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift); 551 uint8_t Other = Visibility; 552 553 uint64_t Value = SymbolValue(Data, Layout); 554 uint64_t Size = 0; 555 556 assert(!(Data.isCommon() && !Data.isExternal())); 557 558 const MCExpr *ESize = Data.getSize(); 559 if (ESize) { 560 int64_t Res; 561 if (!ESize->EvaluateAsAbsolute(Res, Layout)) 562 report_fatal_error("Size expression must be absolute."); 563 Size = Res; 564 } 565 566 // Write out the symbol table entry 567 WriteSymbolEntry(SymtabF, ShndxF, MSD.StringIndex, Info, Value, 568 Size, Other, MSD.SectionIndex, IsReserved); 569 } 570 571 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF, 572 MCDataFragment *ShndxF, 573 const MCAssembler &Asm, 574 const MCAsmLayout &Layout, 575 const SectionIndexMapTy &SectionIndexMap) { 576 // The string table must be emitted first because we need the index 577 // into the string table for all the symbol names. 578 assert(StringTable.size() && "Missing string table"); 579 580 // FIXME: Make sure the start of the symbol table is aligned. 581 582 // The first entry is the undefined symbol entry. 583 WriteSymbolEntry(SymtabF, ShndxF, 0, 0, 0, 0, 0, 0, false); 584 585 // Write the symbol table entries. 586 LastLocalSymbolIndex = LocalSymbolData.size() + 1; 587 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) { 588 ELFSymbolData &MSD = LocalSymbolData[i]; 589 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 590 } 591 592 // Write out a symbol table entry for each regular section. 593 for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e; 594 ++i) { 595 const MCSectionELF &Section = 596 static_cast<const MCSectionELF&>(i->getSection()); 597 if (Section.getType() == ELF::SHT_RELA || 598 Section.getType() == ELF::SHT_REL || 599 Section.getType() == ELF::SHT_STRTAB || 600 Section.getType() == ELF::SHT_SYMTAB || 601 Section.getType() == ELF::SHT_SYMTAB_SHNDX) 602 continue; 603 WriteSymbolEntry(SymtabF, ShndxF, 0, ELF::STT_SECTION, 0, 0, 604 ELF::STV_DEFAULT, SectionIndexMap.lookup(&Section), 605 false); 606 LastLocalSymbolIndex++; 607 } 608 609 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) { 610 ELFSymbolData &MSD = ExternalSymbolData[i]; 611 MCSymbolData &Data = *MSD.SymbolData; 612 assert(((Data.getFlags() & ELF_STB_Global) || 613 (Data.getFlags() & ELF_STB_Weak)) && 614 "External symbol requires STB_GLOBAL or STB_WEAK flag"); 615 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 616 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 617 LastLocalSymbolIndex++; 618 } 619 620 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) { 621 ELFSymbolData &MSD = UndefinedSymbolData[i]; 622 MCSymbolData &Data = *MSD.SymbolData; 623 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 624 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 625 LastLocalSymbolIndex++; 626 } 627 } 628 629 const MCSymbol *ELFObjectWriter::SymbolToReloc(const MCAssembler &Asm, 630 const MCValue &Target, 631 const MCFragment &F, 632 const MCFixup &Fixup, 633 bool IsPCRel) const { 634 const MCSymbol &Symbol = Target.getSymA()->getSymbol(); 635 const MCSymbol &ASymbol = Symbol.AliasedSymbol(); 636 const MCSymbol *Renamed = Renames.lookup(&Symbol); 637 const MCSymbolData &SD = Asm.getSymbolData(Symbol); 638 639 if (ASymbol.isUndefined()) { 640 if (Renamed) 641 return Renamed; 642 return &ASymbol; 643 } 644 645 if (SD.isExternal()) { 646 if (Renamed) 647 return Renamed; 648 return &Symbol; 649 } 650 651 const MCSectionELF &Section = 652 static_cast<const MCSectionELF&>(ASymbol.getSection()); 653 const SectionKind secKind = Section.getKind(); 654 655 if (secKind.isBSS()) 656 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 657 658 if (secKind.isThreadLocal()) { 659 if (Renamed) 660 return Renamed; 661 return &Symbol; 662 } 663 664 MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind(); 665 const MCSectionELF &Sec2 = 666 static_cast<const MCSectionELF&>(F.getParent()->getSection()); 667 668 if (&Sec2 != &Section && 669 (Kind == MCSymbolRefExpr::VK_PLT || 670 Kind == MCSymbolRefExpr::VK_GOTPCREL || 671 Kind == MCSymbolRefExpr::VK_GOTOFF)) { 672 if (Renamed) 673 return Renamed; 674 return &Symbol; 675 } 676 677 if (Section.getFlags() & ELF::SHF_MERGE) { 678 if (Target.getConstant() == 0) 679 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 680 if (Renamed) 681 return Renamed; 682 return &Symbol; 683 } 684 685 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 686 687 } 688 689 690 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm, 691 const MCAsmLayout &Layout, 692 const MCFragment *Fragment, 693 const MCFixup &Fixup, 694 MCValue Target, 695 uint64_t &FixedValue) { 696 int64_t Addend = 0; 697 int Index = 0; 698 int64_t Value = Target.getConstant(); 699 const MCSymbol *RelocSymbol = NULL; 700 701 bool IsPCRel = isFixupKindPCRel(Asm, Fixup.getKind()); 702 if (!Target.isAbsolute()) { 703 const MCSymbol &Symbol = Target.getSymA()->getSymbol(); 704 const MCSymbol &ASymbol = Symbol.AliasedSymbol(); 705 RelocSymbol = SymbolToReloc(Asm, Target, *Fragment, Fixup, IsPCRel); 706 707 if (const MCSymbolRefExpr *RefB = Target.getSymB()) { 708 const MCSymbol &SymbolB = RefB->getSymbol(); 709 MCSymbolData &SDB = Asm.getSymbolData(SymbolB); 710 IsPCRel = true; 711 712 // Offset of the symbol in the section 713 int64_t a = Layout.getSymbolOffset(&SDB); 714 715 // Offset of the relocation in the section 716 int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); 717 Value += b - a; 718 } 719 720 if (!RelocSymbol) { 721 MCSymbolData &SD = Asm.getSymbolData(ASymbol); 722 MCFragment *F = SD.getFragment(); 723 724 Index = F->getParent()->getOrdinal() + 1; 725 726 // Offset of the symbol in the section 727 Value += Layout.getSymbolOffset(&SD); 728 } else { 729 if (Asm.getSymbolData(Symbol).getFlags() & ELF_Other_Weakref) 730 WeakrefUsedInReloc.insert(RelocSymbol); 731 else 732 UsedInReloc.insert(RelocSymbol); 733 Index = -1; 734 } 735 Addend = Value; 736 // Compensate for the addend on i386. 737 if (is64Bit()) 738 Value = 0; 739 } 740 741 FixedValue = Value; 742 unsigned Type = GetRelocType(Target, Fixup, IsPCRel, 743 (RelocSymbol != 0), Addend); 744 MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ? 745 MCSymbolRefExpr::VK_None : Target.getSymA()->getKind(); 746 if (RelocNeedsGOT(Modifier)) 747 NeedsGOT = true; 748 749 uint64_t RelocOffset = Layout.getFragmentOffset(Fragment) + 750 Fixup.getOffset(); 751 752 // FIXME: no tests cover this. Is adjustFixupOffset dead code? 753 TargetObjectWriter->adjustFixupOffset(Fixup, RelocOffset); 754 755 if (!hasRelocationAddend()) 756 Addend = 0; 757 758 if (is64Bit()) 759 assert(isInt<64>(Addend)); 760 else 761 assert(isInt<32>(Addend)); 762 763 ELFRelocationEntry ERE(RelocOffset, Index, Type, RelocSymbol, Addend, Fixup); 764 Relocations[Fragment->getParent()].push_back(ERE); 765 } 766 767 768 uint64_t 769 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm, 770 const MCSymbol *S) { 771 MCSymbolData &SD = Asm.getSymbolData(*S); 772 return SD.getIndex(); 773 } 774 775 bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm, 776 const MCSymbolData &Data, 777 bool Used, bool Renamed) { 778 if (Data.getFlags() & ELF_Other_Weakref) 779 return false; 780 781 if (Used) 782 return true; 783 784 if (Renamed) 785 return false; 786 787 const MCSymbol &Symbol = Data.getSymbol(); 788 789 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_") 790 return true; 791 792 const MCSymbol &A = Symbol.AliasedSymbol(); 793 if (Symbol.isVariable() && !A.isVariable() && A.isUndefined()) 794 return false; 795 796 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL; 797 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal) 798 return false; 799 800 if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined()) 801 return false; 802 803 if (Symbol.isTemporary()) 804 return false; 805 806 return true; 807 } 808 809 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isSignature, 810 bool isUsedInReloc) { 811 if (Data.isExternal()) 812 return false; 813 814 const MCSymbol &Symbol = Data.getSymbol(); 815 const MCSymbol &RefSymbol = Symbol.AliasedSymbol(); 816 817 if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) { 818 if (isSignature && !isUsedInReloc) 819 return true; 820 821 return false; 822 } 823 824 return true; 825 } 826 827 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm, 828 SectionIndexMapTy &SectionIndexMap, 829 const RelMapTy &RelMap) { 830 unsigned Index = 1; 831 for (MCAssembler::iterator it = Asm.begin(), 832 ie = Asm.end(); it != ie; ++it) { 833 const MCSectionELF &Section = 834 static_cast<const MCSectionELF &>(it->getSection()); 835 if (Section.getType() != ELF::SHT_GROUP) 836 continue; 837 SectionIndexMap[&Section] = Index++; 838 } 839 840 for (MCAssembler::iterator it = Asm.begin(), 841 ie = Asm.end(); it != ie; ++it) { 842 const MCSectionELF &Section = 843 static_cast<const MCSectionELF &>(it->getSection()); 844 if (Section.getType() == ELF::SHT_GROUP || 845 Section.getType() == ELF::SHT_REL || 846 Section.getType() == ELF::SHT_RELA) 847 continue; 848 SectionIndexMap[&Section] = Index++; 849 const MCSectionELF *RelSection = RelMap.lookup(&Section); 850 if (RelSection) 851 SectionIndexMap[RelSection] = Index++; 852 } 853 } 854 855 void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm, 856 const SectionIndexMapTy &SectionIndexMap, 857 RevGroupMapTy RevGroupMap, 858 unsigned NumRegularSections) { 859 // FIXME: Is this the correct place to do this? 860 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed? 861 if (NeedsGOT) { 862 llvm::StringRef Name = "_GLOBAL_OFFSET_TABLE_"; 863 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name); 864 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym); 865 Data.setExternal(true); 866 MCELF::SetBinding(Data, ELF::STB_GLOBAL); 867 } 868 869 // Index 0 is always the empty string. 870 StringMap<uint64_t> StringIndexMap; 871 StringTable += '\x00'; 872 873 // FIXME: We could optimize suffixes in strtab in the same way we 874 // optimize them in shstrtab. 875 876 // Add the data for the symbols. 877 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(), 878 ie = Asm.symbol_end(); it != ie; ++it) { 879 const MCSymbol &Symbol = it->getSymbol(); 880 881 bool Used = UsedInReloc.count(&Symbol); 882 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol); 883 bool isSignature = RevGroupMap.count(&Symbol); 884 885 if (!isInSymtab(Asm, *it, 886 Used || WeakrefUsed || isSignature, 887 Renames.count(&Symbol))) 888 continue; 889 890 ELFSymbolData MSD; 891 MSD.SymbolData = it; 892 const MCSymbol &RefSymbol = Symbol.AliasedSymbol(); 893 894 // Undefined symbols are global, but this is the first place we 895 // are able to set it. 896 bool Local = isLocal(*it, isSignature, Used); 897 if (!Local && MCELF::GetBinding(*it) == ELF::STB_LOCAL) { 898 MCSymbolData &SD = Asm.getSymbolData(RefSymbol); 899 MCELF::SetBinding(*it, ELF::STB_GLOBAL); 900 MCELF::SetBinding(SD, ELF::STB_GLOBAL); 901 } 902 903 if (RefSymbol.isUndefined() && !Used && WeakrefUsed) 904 MCELF::SetBinding(*it, ELF::STB_WEAK); 905 906 if (it->isCommon()) { 907 assert(!Local); 908 MSD.SectionIndex = ELF::SHN_COMMON; 909 } else if (Symbol.isAbsolute() || RefSymbol.isVariable()) { 910 MSD.SectionIndex = ELF::SHN_ABS; 911 } else if (RefSymbol.isUndefined()) { 912 if (isSignature && !Used) 913 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]); 914 else 915 MSD.SectionIndex = ELF::SHN_UNDEF; 916 } else { 917 const MCSectionELF &Section = 918 static_cast<const MCSectionELF&>(RefSymbol.getSection()); 919 MSD.SectionIndex = SectionIndexMap.lookup(&Section); 920 if (MSD.SectionIndex >= ELF::SHN_LORESERVE) 921 NeedsSymtabShndx = true; 922 assert(MSD.SectionIndex && "Invalid section index!"); 923 } 924 925 // The @@@ in symbol version is replaced with @ in undefined symbols and 926 // @@ in defined ones. 927 StringRef Name = Symbol.getName(); 928 SmallString<32> Buf; 929 930 size_t Pos = Name.find("@@@"); 931 if (Pos != StringRef::npos) { 932 Buf += Name.substr(0, Pos); 933 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1; 934 Buf += Name.substr(Pos + Skip); 935 Name = Buf; 936 } 937 938 uint64_t &Entry = StringIndexMap[Name]; 939 if (!Entry) { 940 Entry = StringTable.size(); 941 StringTable += Name; 942 StringTable += '\x00'; 943 } 944 MSD.StringIndex = Entry; 945 if (MSD.SectionIndex == ELF::SHN_UNDEF) 946 UndefinedSymbolData.push_back(MSD); 947 else if (Local) 948 LocalSymbolData.push_back(MSD); 949 else 950 ExternalSymbolData.push_back(MSD); 951 } 952 953 // Symbols are required to be in lexicographic order. 954 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end()); 955 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end()); 956 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end()); 957 958 // Set the symbol indices. Local symbols must come before all other 959 // symbols with non-local bindings. 960 unsigned Index = 1; 961 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) 962 LocalSymbolData[i].SymbolData->setIndex(Index++); 963 964 Index += NumRegularSections; 965 966 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) 967 ExternalSymbolData[i].SymbolData->setIndex(Index++); 968 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) 969 UndefinedSymbolData[i].SymbolData->setIndex(Index++); 970 971 if (NumRegularSections > ELF::SHN_LORESERVE) 972 NeedsSymtabShndx = true; 973 } 974 975 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm, 976 MCAsmLayout &Layout, 977 RelMapTy &RelMap) { 978 for (MCAssembler::const_iterator it = Asm.begin(), 979 ie = Asm.end(); it != ie; ++it) { 980 const MCSectionData &SD = *it; 981 if (Relocations[&SD].empty()) 982 continue; 983 984 MCContext &Ctx = Asm.getContext(); 985 const MCSectionELF &Section = 986 static_cast<const MCSectionELF&>(SD.getSection()); 987 988 const StringRef SectionName = Section.getSectionName(); 989 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel"; 990 RelaSectionName += SectionName; 991 992 unsigned EntrySize; 993 if (hasRelocationAddend()) 994 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela); 995 else 996 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel); 997 998 const MCSectionELF *RelaSection = 999 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ? 1000 ELF::SHT_RELA : ELF::SHT_REL, 0, 1001 SectionKind::getReadOnly(), 1002 EntrySize, ""); 1003 RelMap[&Section] = RelaSection; 1004 Asm.getOrCreateSectionData(*RelaSection); 1005 } 1006 } 1007 1008 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 1009 const RelMapTy &RelMap) { 1010 for (MCAssembler::const_iterator it = Asm.begin(), 1011 ie = Asm.end(); it != ie; ++it) { 1012 const MCSectionData &SD = *it; 1013 const MCSectionELF &Section = 1014 static_cast<const MCSectionELF&>(SD.getSection()); 1015 1016 const MCSectionELF *RelaSection = RelMap.lookup(&Section); 1017 if (!RelaSection) 1018 continue; 1019 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection); 1020 RelaSD.setAlignment(is64Bit() ? 8 : 4); 1021 1022 MCDataFragment *F = new MCDataFragment(&RelaSD); 1023 WriteRelocationsFragment(Asm, F, &*it); 1024 } 1025 } 1026 1027 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type, 1028 uint64_t Flags, uint64_t Address, 1029 uint64_t Offset, uint64_t Size, 1030 uint32_t Link, uint32_t Info, 1031 uint64_t Alignment, 1032 uint64_t EntrySize) { 1033 Write32(Name); // sh_name: index into string table 1034 Write32(Type); // sh_type 1035 WriteWord(Flags); // sh_flags 1036 WriteWord(Address); // sh_addr 1037 WriteWord(Offset); // sh_offset 1038 WriteWord(Size); // sh_size 1039 Write32(Link); // sh_link 1040 Write32(Info); // sh_info 1041 WriteWord(Alignment); // sh_addralign 1042 WriteWord(EntrySize); // sh_entsize 1043 } 1044 1045 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm, 1046 MCDataFragment *F, 1047 const MCSectionData *SD) { 1048 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD]; 1049 1050 // Sort the relocation entries. Most targets just sort by r_offset, but some 1051 // (e.g., MIPS) have additional constraints. 1052 TargetObjectWriter->sortRelocs(Asm, Relocs); 1053 1054 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) { 1055 ELFRelocationEntry entry = Relocs[e - i - 1]; 1056 1057 if (!entry.Index) 1058 ; 1059 else if (entry.Index < 0) 1060 entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol); 1061 else 1062 entry.Index += LocalSymbolData.size(); 1063 if (is64Bit()) { 1064 String64(*F, entry.r_offset); 1065 if (TargetObjectWriter->isN64()) { 1066 String32(*F, entry.Index); 1067 1068 String8(*F, TargetObjectWriter->getRSsym(entry.Type)); 1069 String8(*F, TargetObjectWriter->getRType3(entry.Type)); 1070 String8(*F, TargetObjectWriter->getRType2(entry.Type)); 1071 String8(*F, TargetObjectWriter->getRType(entry.Type)); 1072 } 1073 else { 1074 struct ELF::Elf64_Rela ERE64; 1075 ERE64.setSymbolAndType(entry.Index, entry.Type); 1076 String64(*F, ERE64.r_info); 1077 } 1078 if (hasRelocationAddend()) 1079 String64(*F, entry.r_addend); 1080 } else { 1081 String32(*F, entry.r_offset); 1082 1083 struct ELF::Elf32_Rela ERE32; 1084 ERE32.setSymbolAndType(entry.Index, entry.Type); 1085 String32(*F, ERE32.r_info); 1086 1087 if (hasRelocationAddend()) 1088 String32(*F, entry.r_addend); 1089 } 1090 } 1091 } 1092 1093 static int compareBySuffix(const void *a, const void *b) { 1094 const MCSectionELF *secA = *static_cast<const MCSectionELF* const *>(a); 1095 const MCSectionELF *secB = *static_cast<const MCSectionELF* const *>(b); 1096 const StringRef &NameA = secA->getSectionName(); 1097 const StringRef &NameB = secB->getSectionName(); 1098 const unsigned sizeA = NameA.size(); 1099 const unsigned sizeB = NameB.size(); 1100 const unsigned len = std::min(sizeA, sizeB); 1101 for (unsigned int i = 0; i < len; ++i) { 1102 char ca = NameA[sizeA - i - 1]; 1103 char cb = NameB[sizeB - i - 1]; 1104 if (ca != cb) 1105 return cb - ca; 1106 } 1107 1108 return sizeB - sizeA; 1109 } 1110 1111 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm, 1112 MCAsmLayout &Layout, 1113 SectionIndexMapTy &SectionIndexMap, 1114 const RelMapTy &RelMap) { 1115 MCContext &Ctx = Asm.getContext(); 1116 MCDataFragment *F; 1117 1118 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32; 1119 1120 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as. 1121 const MCSectionELF *ShstrtabSection = 1122 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0, 1123 SectionKind::getReadOnly()); 1124 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection); 1125 ShstrtabSD.setAlignment(1); 1126 1127 const MCSectionELF *SymtabSection = 1128 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, 1129 SectionKind::getReadOnly(), 1130 EntrySize, ""); 1131 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection); 1132 SymtabSD.setAlignment(is64Bit() ? 8 : 4); 1133 1134 MCSectionData *SymtabShndxSD = NULL; 1135 1136 if (NeedsSymtabShndx) { 1137 const MCSectionELF *SymtabShndxSection = 1138 Ctx.getELFSection(".symtab_shndx", ELF::SHT_SYMTAB_SHNDX, 0, 1139 SectionKind::getReadOnly(), 4, ""); 1140 SymtabShndxSD = &Asm.getOrCreateSectionData(*SymtabShndxSection); 1141 SymtabShndxSD->setAlignment(4); 1142 } 1143 1144 const MCSectionELF *StrtabSection; 1145 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0, 1146 SectionKind::getReadOnly()); 1147 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection); 1148 StrtabSD.setAlignment(1); 1149 1150 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1151 1152 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection); 1153 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection); 1154 StringTableIndex = SectionIndexMap.lookup(StrtabSection); 1155 1156 // Symbol table 1157 F = new MCDataFragment(&SymtabSD); 1158 MCDataFragment *ShndxF = NULL; 1159 if (NeedsSymtabShndx) { 1160 ShndxF = new MCDataFragment(SymtabShndxSD); 1161 } 1162 WriteSymbolTable(F, ShndxF, Asm, Layout, SectionIndexMap); 1163 1164 F = new MCDataFragment(&StrtabSD); 1165 F->getContents().append(StringTable.begin(), StringTable.end()); 1166 1167 F = new MCDataFragment(&ShstrtabSD); 1168 1169 std::vector<const MCSectionELF*> Sections; 1170 for (MCAssembler::const_iterator it = Asm.begin(), 1171 ie = Asm.end(); it != ie; ++it) { 1172 const MCSectionELF &Section = 1173 static_cast<const MCSectionELF&>(it->getSection()); 1174 Sections.push_back(&Section); 1175 } 1176 array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix); 1177 1178 // Section header string table. 1179 // 1180 // The first entry of a string table holds a null character so skip 1181 // section 0. 1182 uint64_t Index = 1; 1183 F->getContents() += '\x00'; 1184 1185 for (unsigned int I = 0, E = Sections.size(); I != E; ++I) { 1186 const MCSectionELF &Section = *Sections[I]; 1187 1188 StringRef Name = Section.getSectionName(); 1189 if (I != 0) { 1190 StringRef PreviousName = Sections[I - 1]->getSectionName(); 1191 if (PreviousName.endswith(Name)) { 1192 SectionStringTableIndex[&Section] = Index - Name.size() - 1; 1193 continue; 1194 } 1195 } 1196 // Remember the index into the string table so we can write it 1197 // into the sh_name field of the section header table. 1198 SectionStringTableIndex[&Section] = Index; 1199 1200 Index += Name.size() + 1; 1201 F->getContents() += Name; 1202 F->getContents() += '\x00'; 1203 } 1204 } 1205 1206 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm, 1207 MCAsmLayout &Layout, 1208 GroupMapTy &GroupMap, 1209 RevGroupMapTy &RevGroupMap, 1210 SectionIndexMapTy &SectionIndexMap, 1211 const RelMapTy &RelMap) { 1212 // Create the .note.GNU-stack section if needed. 1213 MCContext &Ctx = Asm.getContext(); 1214 if (Asm.getNoExecStack()) { 1215 const MCSectionELF *GnuStackSection = 1216 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0, 1217 SectionKind::getReadOnly()); 1218 Asm.getOrCreateSectionData(*GnuStackSection); 1219 } 1220 1221 // Build the groups 1222 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1223 it != ie; ++it) { 1224 const MCSectionELF &Section = 1225 static_cast<const MCSectionELF&>(it->getSection()); 1226 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1227 continue; 1228 1229 const MCSymbol *SignatureSymbol = Section.getGroup(); 1230 Asm.getOrCreateSymbolData(*SignatureSymbol); 1231 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol]; 1232 if (!Group) { 1233 Group = Ctx.CreateELFGroupSection(); 1234 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1235 Data.setAlignment(4); 1236 MCDataFragment *F = new MCDataFragment(&Data); 1237 String32(*F, ELF::GRP_COMDAT); 1238 } 1239 GroupMap[Group] = SignatureSymbol; 1240 } 1241 1242 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1243 1244 // Add sections to the groups 1245 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1246 it != ie; ++it) { 1247 const MCSectionELF &Section = 1248 static_cast<const MCSectionELF&>(it->getSection()); 1249 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1250 continue; 1251 const MCSectionELF *Group = RevGroupMap[Section.getGroup()]; 1252 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1253 // FIXME: we could use the previous fragment 1254 MCDataFragment *F = new MCDataFragment(&Data); 1255 unsigned Index = SectionIndexMap.lookup(&Section); 1256 String32(*F, Index); 1257 } 1258 } 1259 1260 void ELFObjectWriter::WriteSection(MCAssembler &Asm, 1261 const SectionIndexMapTy &SectionIndexMap, 1262 uint32_t GroupSymbolIndex, 1263 uint64_t Offset, uint64_t Size, 1264 uint64_t Alignment, 1265 const MCSectionELF &Section) { 1266 uint64_t sh_link = 0; 1267 uint64_t sh_info = 0; 1268 1269 switch(Section.getType()) { 1270 case ELF::SHT_DYNAMIC: 1271 sh_link = SectionStringTableIndex[&Section]; 1272 sh_info = 0; 1273 break; 1274 1275 case ELF::SHT_REL: 1276 case ELF::SHT_RELA: { 1277 const MCSectionELF *SymtabSection; 1278 const MCSectionELF *InfoSection; 1279 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 1280 0, 1281 SectionKind::getReadOnly()); 1282 sh_link = SectionIndexMap.lookup(SymtabSection); 1283 assert(sh_link && ".symtab not found"); 1284 1285 // Remove ".rel" and ".rela" prefixes. 1286 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5; 1287 StringRef SectionName = Section.getSectionName().substr(SecNameLen); 1288 1289 InfoSection = Asm.getContext().getELFSection(SectionName, 1290 ELF::SHT_PROGBITS, 0, 1291 SectionKind::getReadOnly()); 1292 sh_info = SectionIndexMap.lookup(InfoSection); 1293 break; 1294 } 1295 1296 case ELF::SHT_SYMTAB: 1297 case ELF::SHT_DYNSYM: 1298 sh_link = StringTableIndex; 1299 sh_info = LastLocalSymbolIndex; 1300 break; 1301 1302 case ELF::SHT_SYMTAB_SHNDX: 1303 sh_link = SymbolTableIndex; 1304 break; 1305 1306 case ELF::SHT_PROGBITS: 1307 case ELF::SHT_STRTAB: 1308 case ELF::SHT_NOBITS: 1309 case ELF::SHT_NOTE: 1310 case ELF::SHT_NULL: 1311 case ELF::SHT_ARM_ATTRIBUTES: 1312 case ELF::SHT_INIT_ARRAY: 1313 case ELF::SHT_FINI_ARRAY: 1314 case ELF::SHT_PREINIT_ARRAY: 1315 case ELF::SHT_X86_64_UNWIND: 1316 // Nothing to do. 1317 break; 1318 1319 case ELF::SHT_GROUP: 1320 sh_link = SymbolTableIndex; 1321 sh_info = GroupSymbolIndex; 1322 break; 1323 1324 default: 1325 assert(0 && "FIXME: sh_type value not supported!"); 1326 break; 1327 } 1328 1329 WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(), 1330 Section.getFlags(), 0, Offset, Size, sh_link, sh_info, 1331 Alignment, Section.getEntrySize()); 1332 } 1333 1334 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) { 1335 return SD.getOrdinal() == ~UINT32_C(0) && 1336 !SD.getSection().isVirtualSection(); 1337 } 1338 1339 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) { 1340 uint64_t Ret = 0; 1341 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1342 ++i) { 1343 const MCFragment &F = *i; 1344 assert(F.getKind() == MCFragment::FT_Data); 1345 Ret += cast<MCDataFragment>(F).getContents().size(); 1346 } 1347 return Ret; 1348 } 1349 1350 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout, 1351 const MCSectionData &SD) { 1352 if (IsELFMetaDataSection(SD)) 1353 return DataSectionSize(SD); 1354 return Layout.getSectionFileSize(&SD); 1355 } 1356 1357 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout, 1358 const MCSectionData &SD) { 1359 if (IsELFMetaDataSection(SD)) 1360 return DataSectionSize(SD); 1361 return Layout.getSectionAddressSize(&SD); 1362 } 1363 1364 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm, 1365 const MCAsmLayout &Layout, 1366 const MCSectionELF &Section) { 1367 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1368 1369 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment()); 1370 WriteZeros(Padding); 1371 1372 if (IsELFMetaDataSection(SD)) { 1373 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1374 ++i) { 1375 const MCFragment &F = *i; 1376 assert(F.getKind() == MCFragment::FT_Data); 1377 WriteBytes(cast<MCDataFragment>(F).getContents().str()); 1378 } 1379 } else { 1380 Asm.writeSectionData(&SD, Layout); 1381 } 1382 } 1383 1384 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm, 1385 const GroupMapTy &GroupMap, 1386 const MCAsmLayout &Layout, 1387 const SectionIndexMapTy &SectionIndexMap, 1388 const SectionOffsetMapTy &SectionOffsetMap) { 1389 const unsigned NumSections = Asm.size() + 1; 1390 1391 std::vector<const MCSectionELF*> Sections; 1392 Sections.resize(NumSections - 1); 1393 1394 for (SectionIndexMapTy::const_iterator i= 1395 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) { 1396 const std::pair<const MCSectionELF*, uint32_t> &p = *i; 1397 Sections[p.second - 1] = p.first; 1398 } 1399 1400 // Null section first. 1401 uint64_t FirstSectionSize = 1402 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0; 1403 uint32_t FirstSectionLink = 1404 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0; 1405 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0); 1406 1407 for (unsigned i = 0; i < NumSections - 1; ++i) { 1408 const MCSectionELF &Section = *Sections[i]; 1409 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1410 uint32_t GroupSymbolIndex; 1411 if (Section.getType() != ELF::SHT_GROUP) 1412 GroupSymbolIndex = 0; 1413 else 1414 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, 1415 GroupMap.lookup(&Section)); 1416 1417 uint64_t Size = GetSectionAddressSize(Layout, SD); 1418 1419 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex, 1420 SectionOffsetMap.lookup(&Section), Size, 1421 SD.getAlignment(), Section); 1422 } 1423 } 1424 1425 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm, 1426 std::vector<const MCSectionELF*> &Sections) { 1427 for (MCAssembler::iterator it = Asm.begin(), 1428 ie = Asm.end(); it != ie; ++it) { 1429 const MCSectionELF &Section = 1430 static_cast<const MCSectionELF &>(it->getSection()); 1431 if (Section.getType() == ELF::SHT_GROUP) 1432 Sections.push_back(&Section); 1433 } 1434 1435 for (MCAssembler::iterator it = Asm.begin(), 1436 ie = Asm.end(); it != ie; ++it) { 1437 const MCSectionELF &Section = 1438 static_cast<const MCSectionELF &>(it->getSection()); 1439 if (Section.getType() != ELF::SHT_GROUP && 1440 Section.getType() != ELF::SHT_REL && 1441 Section.getType() != ELF::SHT_RELA) 1442 Sections.push_back(&Section); 1443 } 1444 1445 for (MCAssembler::iterator it = Asm.begin(), 1446 ie = Asm.end(); it != ie; ++it) { 1447 const MCSectionELF &Section = 1448 static_cast<const MCSectionELF &>(it->getSection()); 1449 if (Section.getType() == ELF::SHT_REL || 1450 Section.getType() == ELF::SHT_RELA) 1451 Sections.push_back(&Section); 1452 } 1453 } 1454 1455 void ELFObjectWriter::WriteObject(MCAssembler &Asm, 1456 const MCAsmLayout &Layout) { 1457 GroupMapTy GroupMap; 1458 RevGroupMapTy RevGroupMap; 1459 SectionIndexMapTy SectionIndexMap; 1460 1461 unsigned NumUserSections = Asm.size(); 1462 1463 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap; 1464 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1465 1466 const unsigned NumUserAndRelocSections = Asm.size(); 1467 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap, 1468 RevGroupMap, SectionIndexMap, RelMap); 1469 const unsigned AllSections = Asm.size(); 1470 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections; 1471 1472 unsigned NumRegularSections = NumUserSections + NumIndexedSections; 1473 1474 // Compute symbol table information. 1475 ComputeSymbolTable(Asm, SectionIndexMap, RevGroupMap, NumRegularSections); 1476 1477 1478 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1479 1480 CreateMetadataSections(const_cast<MCAssembler&>(Asm), 1481 const_cast<MCAsmLayout&>(Layout), 1482 SectionIndexMap, 1483 RelMap); 1484 1485 uint64_t NaturalAlignment = is64Bit() ? 8 : 4; 1486 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 1487 sizeof(ELF::Elf32_Ehdr); 1488 uint64_t FileOff = HeaderSize; 1489 1490 std::vector<const MCSectionELF*> Sections; 1491 ComputeSectionOrder(Asm, Sections); 1492 unsigned NumSections = Sections.size(); 1493 SectionOffsetMapTy SectionOffsetMap; 1494 for (unsigned i = 0; i < NumRegularSections + 1; ++i) { 1495 const MCSectionELF &Section = *Sections[i]; 1496 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1497 1498 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1499 1500 // Remember the offset into the file for this section. 1501 SectionOffsetMap[&Section] = FileOff; 1502 1503 // Get the size of the section in the output file (including padding). 1504 FileOff += GetSectionFileSize(Layout, SD); 1505 } 1506 1507 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment); 1508 1509 const unsigned SectionHeaderOffset = FileOff - HeaderSize; 1510 1511 uint64_t SectionHeaderEntrySize = is64Bit() ? 1512 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr); 1513 FileOff += (NumSections + 1) * SectionHeaderEntrySize; 1514 1515 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) { 1516 const MCSectionELF &Section = *Sections[i]; 1517 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1518 1519 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1520 1521 // Remember the offset into the file for this section. 1522 SectionOffsetMap[&Section] = FileOff; 1523 1524 // Get the size of the section in the output file (including padding). 1525 FileOff += GetSectionFileSize(Layout, SD); 1526 } 1527 1528 // Write out the ELF header ... 1529 WriteHeader(SectionHeaderOffset, NumSections + 1); 1530 1531 // ... then the regular sections ... 1532 // + because of .shstrtab 1533 for (unsigned i = 0; i < NumRegularSections + 1; ++i) 1534 WriteDataSectionData(Asm, Layout, *Sections[i]); 1535 1536 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment); 1537 WriteZeros(Padding); 1538 1539 // ... then the section header table ... 1540 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap, 1541 SectionOffsetMap); 1542 1543 // ... and then the remaining sections ... 1544 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) 1545 WriteDataSectionData(Asm, Layout, *Sections[i]); 1546 } 1547 1548 bool 1549 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 1550 const MCSymbolData &DataA, 1551 const MCFragment &FB, 1552 bool InSet, 1553 bool IsPCRel) const { 1554 if (DataA.getFlags() & ELF_STB_Weak) 1555 return false; 1556 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl( 1557 Asm, DataA, FB,InSet, IsPCRel); 1558 } 1559 1560 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW, 1561 raw_ostream &OS, 1562 bool IsLittleEndian) { 1563 return new ELFObjectWriter(MOTW, OS, IsLittleEndian); 1564 } 1565
