tools/llvm-objcopy/Object.cpp

   1 //===- Object.cpp ---------------------------------------------------------===//
   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 #include "Object.h"
  11 #include "llvm-objcopy.h"
  12 #include "llvm/ADT/ArrayRef.h"
  13 #include "llvm/ADT/STLExtras.h"
  14 #include "llvm/ADT/StringRef.h"
  15 #include "llvm/ADT/Twine.h"
  16 #include "llvm/ADT/iterator_range.h"
  17 #include "llvm/BinaryFormat/ELF.h"
  18 #include "llvm/Object/ELFObjectFile.h"
  19 #include "llvm/Support/ErrorHandling.h"
  20 #include "llvm/Support/FileOutputBuffer.h"
  21 #include <algorithm>
  22 #include <cstddef>
  23 #include <cstdint>
  24 #include <iterator>
  25 #include <utility>
  26 #include <vector>
  27
  28 using namespace llvm;
  29 using namespace object;
  30 using namespace ELF;
  31
  32 template <class ELFT> void Segment::writeHeader(FileOutputBuffer &Out) const {
  33   using Elf_Ehdr = typename ELFT::Ehdr;
  34   using Elf_Phdr = typename ELFT::Phdr;
  35
  36   uint8_t *Buf = Out.getBufferStart();
  37   Buf += sizeof(Elf_Ehdr) + Index * sizeof(Elf_Phdr);
  38   Elf_Phdr &Phdr = *reinterpret_cast<Elf_Phdr *>(Buf);
  39   Phdr.p_type = Type;
  40   Phdr.p_flags = Flags;
  41   Phdr.p_offset = Offset;
  42   Phdr.p_vaddr = VAddr;
  43   Phdr.p_paddr = PAddr;
  44   Phdr.p_filesz = FileSize;
  45   Phdr.p_memsz = MemSize;
  46   Phdr.p_align = Align;
  47 }
  48
  49 void Segment::writeSegment(FileOutputBuffer &Out) const {
  50   uint8_t *Buf = Out.getBufferStart() + Offset;
  51   // We want to maintain segments' interstitial data and contents exactly.
  52   // This lets us just copy segments directly.
  53   std::copy(std::begin(Contents), std::end(Contents), Buf);
  54 }
  55
  56 void SectionBase::removeSectionReferences(const SectionBase *Sec) {}
  57 void SectionBase::initialize(SectionTableRef SecTable) {}
  58 void SectionBase::finalize() {}
  59
  60 template <class ELFT>
  61 void SectionBase::writeHeader(FileOutputBuffer &Out) const {
  62   uint8_t *Buf = Out.getBufferStart();
  63   Buf += HeaderOffset;
  64   typename ELFT::Shdr &Shdr = *reinterpret_cast<typename ELFT::Shdr *>(Buf);
  65   Shdr.sh_name = NameIndex;
  66   Shdr.sh_type = Type;
  67   Shdr.sh_flags = Flags;
  68   Shdr.sh_addr = Addr;
  69   Shdr.sh_offset = Offset;
  70   Shdr.sh_size = Size;
  71   Shdr.sh_link = Link;
  72   Shdr.sh_info = Info;
  73   Shdr.sh_addralign = Align;
  74   Shdr.sh_entsize = EntrySize;
  75 }
  76
  77 void Section::writeSection(FileOutputBuffer &Out) const {
  78   if (Type == SHT_NOBITS)
  79     return;
  80   uint8_t *Buf = Out.getBufferStart() + Offset;
  81   std::copy(std::begin(Contents), std::end(Contents), Buf);
  82 }
  83
  84 void StringTableSection::addString(StringRef Name) {
  85   StrTabBuilder.add(Name);
  86   Size = StrTabBuilder.getSize();
  87 }
  88
  89 uint32_t StringTableSection::findIndex(StringRef Name) const {
  90   return StrTabBuilder.getOffset(Name);
  91 }
  92
  93 void StringTableSection::finalize() { StrTabBuilder.finalize(); }
  94
  95 void StringTableSection::writeSection(FileOutputBuffer &Out) const {
  96   StrTabBuilder.write(Out.getBufferStart() + Offset);
  97 }
  98
  99 static bool isValidReservedSectionIndex(uint16_t Index, uint16_t Machine) {
 100   switch (Index) {
 101   case SHN_ABS:
 102   case SHN_COMMON:
 103     return true;
 104   }
 105   if (Machine == EM_HEXAGON) {
 106     switch (Index) {
 107     case SHN_HEXAGON_SCOMMON:
 108     case SHN_HEXAGON_SCOMMON_2:
 109     case SHN_HEXAGON_SCOMMON_4:
 110     case SHN_HEXAGON_SCOMMON_8:
 111       return true;
 112     }
 113   }
 114   return false;
 115 }
 116
 117 uint16_t Symbol::getShndx() const {
 118   if (DefinedIn != nullptr) {
 119     return DefinedIn->Index;
 120   }
 121   switch (ShndxType) {
 122   // This means that we don't have a defined section but we do need to
 123   // output a legitimate section index.
 124   case SYMBOL_SIMPLE_INDEX:
 125     return SHN_UNDEF;
 126   case SYMBOL_ABS:
 127   case SYMBOL_COMMON:
 128   case SYMBOL_HEXAGON_SCOMMON:
 129   case SYMBOL_HEXAGON_SCOMMON_2:
 130   case SYMBOL_HEXAGON_SCOMMON_4:
 131   case SYMBOL_HEXAGON_SCOMMON_8:
 132     return static_cast<uint16_t>(ShndxType);
 133   }
 134   llvm_unreachable("Symbol with invalid ShndxType encountered");
 135 }
 136
 137 void SymbolTableSection::addSymbol(StringRef Name, uint8_t Bind, uint8_t Type,
 138                                    SectionBase *DefinedIn, uint64_t Value,
 139                                    uint16_t Shndx, uint64_t Sz) {
 140   Symbol Sym;
 141   Sym.Name = Name;
 142   Sym.Binding = Bind;
 143   Sym.Type = Type;
 144   Sym.DefinedIn = DefinedIn;
 145   if (DefinedIn == nullptr) {
 146     if (Shndx >= SHN_LORESERVE)
 147       Sym.ShndxType = static_cast<SymbolShndxType>(Shndx);
 148     else
 149       Sym.ShndxType = SYMBOL_SIMPLE_INDEX;
 150   }
 151   Sym.Value = Value;
 152   Sym.Size = Sz;
 153   Sym.Index = Symbols.size();
 154   Symbols.emplace_back(llvm::make_unique<Symbol>(Sym));
 155   Size += this->EntrySize;
 156 }
 157
 158 void SymbolTableSection::removeSectionReferences(const SectionBase *Sec) {
 159   if (SymbolNames == Sec) {
 160     error("String table " + SymbolNames->Name +
 161           " cannot be removed because it is referenced by the symbol table " +
 162           this->Name);
 163   }
 164   auto Iter =
 165       std::remove_if(std::begin(Symbols), std::end(Symbols),
 166                      [=](const SymPtr &Sym) { return Sym->DefinedIn == Sec; });
 167   Size -= (std::end(Symbols) - Iter) * this->EntrySize;
 168   Symbols.erase(Iter, std::end(Symbols));
 169 }
 170
 171 void SymbolTableSection::initialize(SectionTableRef SecTable) {
 172   Size = 0;
 173   setStrTab(SecTable.getSectionOfType<StringTableSection>(
 174       Link,
 175       "Symbol table has link index of " + Twine(Link) +
 176           " which is not a valid index",
 177       "Symbol table has link index of " + Twine(Link) +
 178           " which is not a string table"));
 179 }
 180
 181 void SymbolTableSection::finalize() {
 182   // Make sure SymbolNames is finalized before getting name indexes.
 183   SymbolNames->finalize();
 184
 185   uint32_t MaxLocalIndex = 0;
 186   for (auto &Sym : Symbols) {
 187     Sym->NameIndex = SymbolNames->findIndex(Sym->Name);
 188     if (Sym->Binding == STB_LOCAL)
 189       MaxLocalIndex = std::max(MaxLocalIndex, Sym->Index);
 190   }
 191   // Now we need to set the Link and Info fields.
 192   Link = SymbolNames->Index;
 193   Info = MaxLocalIndex + 1;
 194 }
 195
 196 void SymbolTableSection::addSymbolNames() {
 197   // Add all of our strings to SymbolNames so that SymbolNames has the right
 198   // size before layout is decided.
 199   for (auto &Sym : Symbols)
 200     SymbolNames->addString(Sym->Name);
 201 }
 202
 203 const Symbol *SymbolTableSection::getSymbolByIndex(uint32_t Index) const {
 204   if (Symbols.size() <= Index)
 205     error("Invalid symbol index: " + Twine(Index));
 206   return Symbols[Index].get();
 207 }
 208
 209 template <class ELFT>
 210 void SymbolTableSectionImpl<ELFT>::writeSection(FileOutputBuffer &Out) const {
 211   uint8_t *Buf = Out.getBufferStart();
 212   Buf += Offset;
 213   typename ELFT::Sym *Sym = reinterpret_cast<typename ELFT::Sym *>(Buf);
 214   // Loop though symbols setting each entry of the symbol table.
 215   for (auto &Symbol : Symbols) {
 216     Sym->st_name = Symbol->NameIndex;
 217     Sym->st_value = Symbol->Value;
 218     Sym->st_size = Symbol->Size;
 219     Sym->setBinding(Symbol->Binding);
 220     Sym->setType(Symbol->Type);
 221     Sym->st_shndx = Symbol->getShndx();
 222     ++Sym;
 223   }
 224 }
 225
 226 template <class SymTabType>
 227 void RelocSectionWithSymtabBase<SymTabType>::removeSectionReferences(
 228     const SectionBase *Sec) {
 229   if (Symbols == Sec) {
 230     error("Symbol table " + Symbols->Name +
 231           " cannot be removed because it is "
 232           "referenced by the relocation "
 233           "section " +
 234           this->Name);
 235   }
 236 }
 237
 238 template <class SymTabType>
 239 void RelocSectionWithSymtabBase<SymTabType>::initialize(
 240     SectionTableRef SecTable) {
 241   setSymTab(SecTable.getSectionOfType<SymTabType>(
 242       Link,
 243       "Link field value " + Twine(Link) + " in section " + Name + " is invalid",
 244       "Link field value " + Twine(Link) + " in section " + Name +
 245           " is not a symbol table"));
 246
 247   if (Info != SHN_UNDEF)
 248     setSection(SecTable.getSection(Info, "Info field value " + Twine(Info) +
 249                                              " in section " + Name +
 250                                              " is invalid"));
 251   else
 252     setSection(nullptr);
 253 }
 254
 255 template <class SymTabType>
 256 void RelocSectionWithSymtabBase<SymTabType>::finalize() {
 257   this->Link = Symbols->Index;
 258   if (SecToApplyRel != nullptr)
 259     this->Info = SecToApplyRel->Index;
 260 }
 261
 262 template <class ELFT>
 263 void setAddend(Elf_Rel_Impl<ELFT, false> &Rel, uint64_t Addend) {}
 264
 265 template <class ELFT>
 266 void setAddend(Elf_Rel_Impl<ELFT, true> &Rela, uint64_t Addend) {
 267   Rela.r_addend = Addend;
 268 }
 269
 270 template <class ELFT>
 271 template <class T>
 272 void RelocationSection<ELFT>::writeRel(T *Buf) const {
 273   for (const auto &Reloc : Relocations) {
 274     Buf->r_offset = Reloc.Offset;
 275     setAddend(*Buf, Reloc.Addend);
 276     Buf->setSymbolAndType(Reloc.RelocSymbol->Index, Reloc.Type, false);
 277     ++Buf;
 278   }
 279 }
 280
 281 template <class ELFT>
 282 void RelocationSection<ELFT>::writeSection(FileOutputBuffer &Out) const {
 283   uint8_t *Buf = Out.getBufferStart() + Offset;
 284   if (Type == SHT_REL)
 285     writeRel(reinterpret_cast<Elf_Rel *>(Buf));
 286   else
 287     writeRel(reinterpret_cast<Elf_Rela *>(Buf));
 288 }
 289
 290 void DynamicRelocationSection::writeSection(FileOutputBuffer &Out) const {
 291   std::copy(std::begin(Contents), std::end(Contents),
 292             Out.getBufferStart() + Offset);
 293 }
 294
 295 void SectionWithStrTab::removeSectionReferences(const SectionBase *Sec) {
 296   if (StrTab == Sec) {
 297     error("String table " + StrTab->Name +
 298           " cannot be removed because it is "
 299           "referenced by the section " +
 300           this->Name);
 301   }
 302 }
 303
 304 bool SectionWithStrTab::classof(const SectionBase *S) {
 305   return isa<DynamicSymbolTableSection>(S) || isa<DynamicSection>(S);
 306 }
 307
 308 void SectionWithStrTab::initialize(SectionTableRef SecTable) {
 309   auto StrTab =
 310       SecTable.getSection(Link, "Link field value " + Twine(Link) +
 311                                     " in section " + Name + " is invalid");
 312   if (StrTab->Type != SHT_STRTAB) {
 313     error("Link field value " + Twine(Link) + " in section " + Name +
 314           " is not a string table");
 315   }
 316   setStrTab(StrTab);
 317 }
 318
 319 void SectionWithStrTab::finalize() { this->Link = StrTab->Index; }
 320
 321 // Returns true IFF a section is wholly inside the range of a segment
 322 static bool sectionWithinSegment(const SectionBase &Section,
 323                                  const Segment &Segment) {
 324   // If a section is empty it should be treated like it has a size of 1. This is
 325   // to clarify the case when an empty section lies on a boundary between two
 326   // segments and ensures that the section "belongs" to the second segment and
 327   // not the first.
 328   uint64_t SecSize = Section.Size ? Section.Size : 1;
 329   return Segment.Offset <= Section.OriginalOffset &&
 330          Segment.Offset + Segment.FileSize >= Section.OriginalOffset + SecSize;
 331 }
 332
 333 // Returns true IFF a segment's original offset is inside of another segment's
 334 // range.
 335 static bool segmentOverlapsSegment(const Segment &Child,
 336                                    const Segment &Parent) {
 337
 338   return Parent.OriginalOffset <= Child.OriginalOffset &&
 339          Parent.OriginalOffset + Parent.FileSize > Child.OriginalOffset;
 340 }
 341
 342 static bool compareSegments(const Segment *A, const Segment *B) {
 343   // Any segment without a parent segment should come before a segment
 344   // that has a parent segment.
 345   if (A->OriginalOffset < B->OriginalOffset)
 346     return true;
 347   if (A->OriginalOffset > B->OriginalOffset)
 348     return false;
 349   return A->Index < B->Index;
 350 }
 351
 352 template <class ELFT>
 353 void Object<ELFT>::readProgramHeaders(const ELFFile<ELFT> &ElfFile) {
 354   uint32_t Index = 0;
 355   for (const auto &Phdr : unwrapOrError(ElfFile.program_headers())) {
 356     ArrayRef<uint8_t> Data{ElfFile.base() + Phdr.p_offset,
 357                            (size_t)Phdr.p_filesz};
 358     Segments.emplace_back(llvm::make_unique<Segment>(Data));
 359     Segment &Seg = *Segments.back();
 360     Seg.Type = Phdr.p_type;
 361     Seg.Flags = Phdr.p_flags;
 362     Seg.OriginalOffset = Phdr.p_offset;
 363     Seg.Offset = Phdr.p_offset;
 364     Seg.VAddr = Phdr.p_vaddr;
 365     Seg.PAddr = Phdr.p_paddr;
 366     Seg.FileSize = Phdr.p_filesz;
 367     Seg.MemSize = Phdr.p_memsz;
 368     Seg.Align = Phdr.p_align;
 369     Seg.Index = Index++;
 370     for (auto &Section : Sections) {
 371       if (sectionWithinSegment(*Section, Seg)) {
 372         Seg.addSection(&*Section);
 373         if (!Section->ParentSegment ||
 374             Section->ParentSegment->Offset > Seg.Offset) {
 375           Section->ParentSegment = &Seg;
 376         }
 377       }
 378     }
 379   }
 380   // Now we do an O(n^2) loop through the segments in order to match up
 381   // segments.
 382   for (auto &Child : Segments) {
 383     for (auto &Parent : Segments) {
 384       // Every segment will overlap with itself but we don't want a segment to
 385       // be it's own parent so we avoid that situation.
 386       if (&Child != &Parent && segmentOverlapsSegment(*Child, *Parent)) {
 387         // We want a canonical "most parental" segment but this requires
 388         // inspecting the ParentSegment.
 389         if (compareSegments(Parent.get(), Child.get()))
 390           if (Child->ParentSegment == nullptr ||
 391               compareSegments(Parent.get(), Child->ParentSegment)) {
 392             Child->ParentSegment = Parent.get();
 393           }
 394       }
 395     }
 396   }
 397 }
 398
 399 template <class ELFT>
 400 void Object<ELFT>::initSymbolTable(const object::ELFFile<ELFT> &ElfFile,
 401                                    SymbolTableSection *SymTab,
 402                                    SectionTableRef SecTable) {
 403   const Elf_Shdr &Shdr = *unwrapOrError(ElfFile.getSection(SymTab->Index));
 404   StringRef StrTabData = unwrapOrError(ElfFile.getStringTableForSymtab(Shdr));
 405
 406   for (const auto &Sym : unwrapOrError(ElfFile.symbols(&Shdr))) {
 407     SectionBase *DefSection = nullptr;
 408     StringRef Name = unwrapOrError(Sym.getName(StrTabData));
 409
 410     if (Sym.st_shndx >= SHN_LORESERVE) {
 411       if (!isValidReservedSectionIndex(Sym.st_shndx, Machine)) {
 412         error(
 413             "Symbol '" + Name +
 414             "' has unsupported value greater than or equal to SHN_LORESERVE: " +
 415             Twine(Sym.st_shndx));
 416       }
 417     } else if (Sym.st_shndx != SHN_UNDEF) {
 418       DefSection = SecTable.getSection(
 419           Sym.st_shndx, "Symbol '" + Name +
 420                             "' is defined in invalid section with index " +
 421                             Twine(Sym.st_shndx));
 422     }
 423
 424     SymTab->addSymbol(Name, Sym.getBinding(), Sym.getType(), DefSection,
 425                       Sym.getValue(), Sym.st_shndx, Sym.st_size);
 426   }
 427 }
 428
 429 template <class ELFT>
 430 static void getAddend(uint64_t &ToSet, const Elf_Rel_Impl<ELFT, false> &Rel) {}
 431
 432 template <class ELFT>
 433 static void getAddend(uint64_t &ToSet, const Elf_Rel_Impl<ELFT, true> &Rela) {
 434   ToSet = Rela.r_addend;
 435 }
 436
 437 template <class ELFT, class T>
 438 void initRelocations(RelocationSection<ELFT> *Relocs,
 439                      SymbolTableSection *SymbolTable, T RelRange) {
 440   for (const auto &Rel : RelRange) {
 441     Relocation ToAdd;
 442     ToAdd.Offset = Rel.r_offset;
 443     getAddend(ToAdd.Addend, Rel);
 444     ToAdd.Type = Rel.getType(false);
 445     ToAdd.RelocSymbol = SymbolTable->getSymbolByIndex(Rel.getSymbol(false));
 446     Relocs->addRelocation(ToAdd);
 447   }
 448 }
 449
 450 SectionBase *SectionTableRef::getSection(uint16_t Index, Twine ErrMsg) {
 451   if (Index == SHN_UNDEF || Index > Sections.size())
 452     error(ErrMsg);
 453   return Sections[Index - 1].get();
 454 }
 455
 456 template <class T>
 457 T *SectionTableRef::getSectionOfType(uint16_t Index, Twine IndexErrMsg,
 458                                      Twine TypeErrMsg) {
 459   if (T *Sec = dyn_cast<T>(getSection(Index, IndexErrMsg)))
 460     return Sec;
 461   error(TypeErrMsg);
 462 }
 463
 464 template <class ELFT>
 465 std::unique_ptr<SectionBase>
 466 Object<ELFT>::makeSection(const object::ELFFile<ELFT> &ElfFile,
 467                           const Elf_Shdr &Shdr) {
 468   ArrayRef<uint8_t> Data;
 469   switch (Shdr.sh_type) {
 470   case SHT_REL:
 471   case SHT_RELA:
 472     if (Shdr.sh_flags & SHF_ALLOC) {
 473       Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
 474       return llvm::make_unique<DynamicRelocationSection>(Data);
 475     }
 476     return llvm::make_unique<RelocationSection<ELFT>>();
 477   case SHT_STRTAB:
 478     // If a string table is allocated we don't want to mess with it. That would
 479     // mean altering the memory image. There are no special link types or
 480     // anything so we can just use a Section.
 481     if (Shdr.sh_flags & SHF_ALLOC) {
 482       Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
 483       return llvm::make_unique<Section>(Data);
 484     }
 485     return llvm::make_unique<StringTableSection>();
 486   case SHT_HASH:
 487   case SHT_GNU_HASH:
 488     // Hash tables should refer to SHT_DYNSYM which we're not going to change.
 489     // Because of this we don't need to mess with the hash tables either.
 490     Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
 491     return llvm::make_unique<Section>(Data);
 492   case SHT_DYNSYM:
 493     Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
 494     return llvm::make_unique<DynamicSymbolTableSection>(Data);
 495   case SHT_DYNAMIC:
 496     Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
 497     return llvm::make_unique<DynamicSection>(Data);
 498   case SHT_SYMTAB: {
 499     auto SymTab = llvm::make_unique<SymbolTableSectionImpl<ELFT>>();
 500     SymbolTable = SymTab.get();
 501     return std::move(SymTab);
 502   }
 503   case SHT_NOBITS:
 504     return llvm::make_unique<Section>(Data);
 505   default:
 506     Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
 507     return llvm::make_unique<Section>(Data);
 508   }
 509 }
 510
 511 template <class ELFT>
 512 SectionTableRef Object<ELFT>::readSectionHeaders(const ELFFile<ELFT> &ElfFile) {
 513   uint32_t Index = 0;
 514   for (const auto &Shdr : unwrapOrError(ElfFile.sections())) {
 515     if (Index == 0) {
 516       ++Index;
 517       continue;
 518     }
 519     SecPtr Sec = makeSection(ElfFile, Shdr);
 520     Sec->Name = unwrapOrError(ElfFile.getSectionName(&Shdr));
 521     Sec->Type = Shdr.sh_type;
 522     Sec->Flags = Shdr.sh_flags;
 523     Sec->Addr = Shdr.sh_addr;
 524     Sec->Offset = Shdr.sh_offset;
 525     Sec->OriginalOffset = Shdr.sh_offset;
 526     Sec->Size = Shdr.sh_size;
 527     Sec->Link = Shdr.sh_link;
 528     Sec->Info = Shdr.sh_info;
 529     Sec->Align = Shdr.sh_addralign;
 530     Sec->EntrySize = Shdr.sh_entsize;
 531     Sec->Index = Index++;
 532     Sections.push_back(std::move(Sec));
 533   }
 534
 535   SectionTableRef SecTable(Sections);
 536
 537   // Now that all of the sections have been added we can fill out some extra
 538   // details about symbol tables. We need the symbol table filled out before
 539   // any relocations.
 540   if (SymbolTable) {
 541     SymbolTable->initialize(SecTable);
 542     initSymbolTable(ElfFile, SymbolTable, SecTable);
 543   }
 544
 545   // Now that all sections and symbols have been added we can add
 546   // relocations that reference symbols and set the link and info fields for
 547   // relocation sections.
 548   for (auto &Section : Sections) {
 549     if (Section.get() == SymbolTable)
 550       continue;
 551     Section->initialize(SecTable);
 552     if (auto RelSec = dyn_cast<RelocationSection<ELFT>>(Section.get())) {
 553       auto Shdr = unwrapOrError(ElfFile.sections()).begin() + RelSec->Index;
 554       if (RelSec->Type == SHT_REL)
 555         initRelocations(RelSec, SymbolTable, unwrapOrError(ElfFile.rels(Shdr)));
 556       else
 557         initRelocations(RelSec, SymbolTable,
 558                         unwrapOrError(ElfFile.relas(Shdr)));
 559     }
 560   }
 561
 562   return SecTable;
 563 }
 564
 565 template <class ELFT> Object<ELFT>::Object(const ELFObjectFile<ELFT> &Obj) {
 566   const auto &ElfFile = *Obj.getELFFile();
 567   const auto &Ehdr = *ElfFile.getHeader();
 568
 569   std::copy(Ehdr.e_ident, Ehdr.e_ident + 16, Ident);
 570   Type = Ehdr.e_type;
 571   Machine = Ehdr.e_machine;
 572   Version = Ehdr.e_version;
 573   Entry = Ehdr.e_entry;
 574   Flags = Ehdr.e_flags;
 575
 576   SectionTableRef SecTable = readSectionHeaders(ElfFile);
 577   readProgramHeaders(ElfFile);
 578
 579   SectionNames = SecTable.getSectionOfType<StringTableSection>(
 580       Ehdr.e_shstrndx,
 581       "e_shstrndx field value " + Twine(Ehdr.e_shstrndx) + " in elf header " +
 582           " is invalid",
 583       "e_shstrndx field value " + Twine(Ehdr.e_shstrndx) + " in elf header " +
 584           " is not a string table");
 585 }
 586
 587 template <class ELFT>
 588 void Object<ELFT>::writeHeader(FileOutputBuffer &Out) const {
 589   uint8_t *Buf = Out.getBufferStart();
 590   Elf_Ehdr &Ehdr = *reinterpret_cast<Elf_Ehdr *>(Buf);
 591   std::copy(Ident, Ident + 16, Ehdr.e_ident);
 592   Ehdr.e_type = Type;
 593   Ehdr.e_machine = Machine;
 594   Ehdr.e_version = Version;
 595   Ehdr.e_entry = Entry;
 596   Ehdr.e_phoff = sizeof(Elf_Ehdr);
 597   Ehdr.e_flags = Flags;
 598   Ehdr.e_ehsize = sizeof(Elf_Ehdr);
 599   Ehdr.e_phentsize = sizeof(Elf_Phdr);
 600   Ehdr.e_phnum = Segments.size();
 601   Ehdr.e_shentsize = sizeof(Elf_Shdr);
 602   if (WriteSectionHeaders) {
 603     Ehdr.e_shoff = SHOffset;
 604     Ehdr.e_shnum = Sections.size() + 1;
 605     Ehdr.e_shstrndx = SectionNames->Index;
 606   } else {
 607     Ehdr.e_shoff = 0;
 608     Ehdr.e_shnum = 0;
 609     Ehdr.e_shstrndx = 0;
 610   }
 611 }
 612
 613 template <class ELFT>
 614 void Object<ELFT>::writeProgramHeaders(FileOutputBuffer &Out) const {
 615   for (auto &Phdr : Segments)
 616     Phdr->template writeHeader<ELFT>(Out);
 617 }
 618
 619 template <class ELFT>
 620 void Object<ELFT>::writeSectionHeaders(FileOutputBuffer &Out) const {
 621   uint8_t *Buf = Out.getBufferStart() + SHOffset;
 622   // This reference serves to write the dummy section header at the begining
 623   // of the file. It is not used for anything else
 624   Elf_Shdr &Shdr = *reinterpret_cast<Elf_Shdr *>(Buf);
 625   Shdr.sh_name = 0;
 626   Shdr.sh_type = SHT_NULL;
 627   Shdr.sh_flags = 0;
 628   Shdr.sh_addr = 0;
 629   Shdr.sh_offset = 0;
 630   Shdr.sh_size = 0;
 631   Shdr.sh_link = 0;
 632   Shdr.sh_info = 0;
 633   Shdr.sh_addralign = 0;
 634   Shdr.sh_entsize = 0;
 635
 636   for (auto &Section : Sections)
 637     Section->template writeHeader<ELFT>(Out);
 638 }
 639
 640 template <class ELFT>
 641 void Object<ELFT>::writeSectionData(FileOutputBuffer &Out) const {
 642   for (auto &Section : Sections)
 643     Section->writeSection(Out);
 644 }
 645
 646 template <class ELFT>
 647 void Object<ELFT>::removeSections(
 648     std::function<bool(const SectionBase &)> ToRemove) {
 649
 650   auto Iter = std::stable_partition(
 651       std::begin(Sections), std::end(Sections), [=](const SecPtr &Sec) {
 652         if (ToRemove(*Sec))
 653           return false;
 654         if (auto RelSec = dyn_cast<RelocationSectionBase>(Sec.get())) {
 655           if (auto ToRelSec = RelSec->getSection())
 656             return !ToRemove(*ToRelSec);
 657         }
 658         return true;
 659       });
 660   if (SymbolTable != nullptr && ToRemove(*SymbolTable))
 661     SymbolTable = nullptr;
 662   if (ToRemove(*SectionNames)) {
 663     if (WriteSectionHeaders)
 664       error("Cannot remove " + SectionNames->Name +
 665             " because it is the section header string table.");
 666     SectionNames = nullptr;
 667   }
 668   // Now make sure there are no remaining references to the sections that will
 669   // be removed. Sometimes it is impossible to remove a reference so we emit
 670   // an error here instead.
 671   for (auto &RemoveSec : make_range(Iter, std::end(Sections))) {
 672     for (auto &Segment : Segments)
 673       Segment->removeSection(RemoveSec.get());
 674     for (auto &KeepSec : make_range(std::begin(Sections), Iter))
 675       KeepSec->removeSectionReferences(RemoveSec.get());
 676   }
 677   // Now finally get rid of them all togethor.
 678   Sections.erase(Iter, std::end(Sections));
 679 }
 680
 681 template <class ELFT> void ELFObject<ELFT>::sortSections() {
 682   // Put all sections in offset order. Maintain the ordering as closely as
 683   // possible while meeting that demand however.
 684   auto CompareSections = [](const SecPtr &A, const SecPtr &B) {
 685     return A->OriginalOffset < B->OriginalOffset;
 686   };
 687   std::stable_sort(std::begin(this->Sections), std::end(this->Sections),
 688                    CompareSections);
 689 }
 690
 691 static uint64_t alignToAddr(uint64_t Offset, uint64_t Addr, uint64_t Align) {
 692   // Calculate Diff such that (Offset + Diff) & -Align == Addr & -Align.
 693   if (Align == 0)
 694     Align = 1;
 695   auto Diff =
 696       static_cast<int64_t>(Addr % Align) - static_cast<int64_t>(Offset % Align);
 697   // We only want to add to Offset, however, so if Diff < 0 we can add Align and
 698   // (Offset + Diff) & -Align == Addr & -Align will still hold.
 699   if (Diff < 0)
 700     Diff += Align;
 701   return Offset + Diff;
 702 }
 703
 704 // Orders segments such that if x = y->ParentSegment then y comes before x.
 705 static void OrderSegments(std::vector<Segment *> &Segments) {
 706   std::stable_sort(std::begin(Segments), std::end(Segments), compareSegments);
 707 }
 708
 709 // This function finds a consistent layout for a list of segments starting from
 710 // an Offset. It assumes that Segments have been sorted by OrderSegments and
 711 // returns an Offset one past the end of the last segment.
 712 static uint64_t LayoutSegments(std::vector<Segment *> &Segments,
 713                                uint64_t Offset) {
 714   assert(std::is_sorted(std::begin(Segments), std::end(Segments),
 715                         compareSegments));
 716   // The only way a segment should move is if a section was between two
 717   // segments and that section was removed. If that section isn't in a segment
 718   // then it's acceptable, but not ideal, to simply move it to after the
 719   // segments. So we can simply layout segments one after the other accounting
 720   // for alignment.
 721   for (auto &Segment : Segments) {
 722     // We assume that segments have been ordered by OriginalOffset and Index
 723     // such that a parent segment will always come before a child segment in
 724     // OrderedSegments. This means that the Offset of the ParentSegment should
 725     // already be set and we can set our offset relative to it.
 726     if (Segment->ParentSegment != nullptr) {
 727       auto Parent = Segment->ParentSegment;
 728       Segment->Offset =
 729           Parent->Offset + Segment->OriginalOffset - Parent->OriginalOffset;
 730     } else {
 731       Offset = alignToAddr(Offset, Segment->VAddr, Segment->Align);
 732       Segment->Offset = Offset;
 733     }
 734     Offset = std::max(Offset, Segment->Offset + Segment->FileSize);
 735   }
 736   return Offset;
 737 }
 738
 739 // This function finds a consistent layout for a list of sections. It assumes
 740 // that the ->ParentSegment of each section has already been laid out. The
 741 // supplied starting Offset is used for the starting offset of any section that
 742 // does not have a ParentSegment. It returns either the offset given if all
 743 // sections had a ParentSegment or an offset one past the last section if there
 744 // was a section that didn't have a ParentSegment.
 745 template <class SecPtr>
 746 static uint64_t LayoutSections(std::vector<SecPtr> &Sections, uint64_t Offset) {
 747   // Now the offset of every segment has been set we can assign the offsets
 748   // of each section. For sections that are covered by a segment we should use
 749   // the segment's original offset and the section's original offset to compute
 750   // the offset from the start of the segment. Using the offset from the start
 751   // of the segment we can assign a new offset to the section. For sections not
 752   // covered by segments we can just bump Offset to the next valid location.
 753   uint32_t Index = 1;
 754   for (auto &Section : Sections) {
 755     Section->Index = Index++;
 756     if (Section->ParentSegment != nullptr) {
 757       auto Segment = Section->ParentSegment;
 758       Section->Offset =
 759           Segment->Offset + (Section->OriginalOffset - Segment->OriginalOffset);
 760     } else {
 761       Offset = alignTo(Offset, Section->Align == 0 ? 1 : Section->Align);
 762       Section->Offset = Offset;
 763       if (Section->Type != SHT_NOBITS)
 764         Offset += Section->Size;
 765     }
 766   }
 767   return Offset;
 768 }
 769
 770 template <class ELFT> void ELFObject<ELFT>::assignOffsets() {
 771   // We need a temporary list of segments that has a special order to it
 772   // so that we know that anytime ->ParentSegment is set that segment has
 773   // already had its offset properly set.
 774   std::vector<Segment *> OrderedSegments;
 775   for (auto &Segment : this->Segments)
 776     OrderedSegments.push_back(Segment.get());
 777   OrderSegments(OrderedSegments);
 778   // The size of ELF + program headers will not change so it is ok to assume
 779   // that the first offset of the first segment is a good place to start
 780   // outputting sections. This covers both the standard case and the PT_PHDR
 781   // case.
 782   uint64_t Offset;
 783   if (!OrderedSegments.empty()) {
 784     Offset = OrderedSegments[0]->Offset;
 785   } else {
 786     Offset = sizeof(Elf_Ehdr);
 787   }
 788   Offset = LayoutSegments(OrderedSegments, Offset);
 789   Offset = LayoutSections(this->Sections, Offset);
 790   // If we need to write the section header table out then we need to align the
 791   // Offset so that SHOffset is valid.
 792   if (this->WriteSectionHeaders)
 793     Offset = alignTo(Offset, sizeof(typename ELFT::Addr));
 794   this->SHOffset = Offset;
 795 }
 796
 797 template <class ELFT> size_t ELFObject<ELFT>::totalSize() const {
 798   // We already have the section header offset so we can calculate the total
 799   // size by just adding up the size of each section header.
 800   auto NullSectionSize = this->WriteSectionHeaders ? sizeof(Elf_Shdr) : 0;
 801   return this->SHOffset + this->Sections.size() * sizeof(Elf_Shdr) +
 802          NullSectionSize;
 803 }
 804
 805 template <class ELFT> void ELFObject<ELFT>::write(FileOutputBuffer &Out) const {
 806   this->writeHeader(Out);
 807   this->writeProgramHeaders(Out);
 808   this->writeSectionData(Out);
 809   if (this->WriteSectionHeaders)
 810     this->writeSectionHeaders(Out);
 811 }
 812
 813 template <class ELFT> void ELFObject<ELFT>::finalize() {
 814   // Make sure we add the names of all the sections.
 815   if (this->SectionNames != nullptr)
 816     for (const auto &Section : this->Sections) {
 817       this->SectionNames->addString(Section->Name);
 818     }
 819   // Make sure we add the names of all the symbols.
 820   if (this->SymbolTable != nullptr)
 821     this->SymbolTable->addSymbolNames();
 822
 823   sortSections();
 824   assignOffsets();
 825
 826   // Finalize SectionNames first so that we can assign name indexes.
 827   if (this->SectionNames != nullptr)
 828     this->SectionNames->finalize();
 829   // Finally now that all offsets and indexes have been set we can finalize any
 830   // remaining issues.
 831   uint64_t Offset = this->SHOffset + sizeof(Elf_Shdr);
 832   for (auto &Section : this->Sections) {
 833     Section->HeaderOffset = Offset;
 834     Offset += sizeof(Elf_Shdr);
 835     if (this->WriteSectionHeaders)
 836       Section->NameIndex = this->SectionNames->findIndex(Section->Name);
 837     Section->finalize();
 838   }
 839 }
 840
 841 template <class ELFT> size_t BinaryObject<ELFT>::totalSize() const {
 842   return TotalSize;
 843 }
 844
 845 template <class ELFT>
 846 void BinaryObject<ELFT>::write(FileOutputBuffer &Out) const {
 847   for (auto &Section : this->Sections) {
 848     if ((Section->Flags & SHF_ALLOC) == 0)
 849       continue;
 850     Section->writeSection(Out);
 851   }
 852 }
 853
 854 template <class ELFT> void BinaryObject<ELFT>::finalize() {
 855   // TODO: Create a filter range to construct OrderedSegments from so that this
 856   // code can be deduped with assignOffsets above. This should also solve the
 857   // todo below for LayoutSections.
 858   // We need a temporary list of segments that has a special order to it
 859   // so that we know that anytime ->ParentSegment is set that segment has
 860   // already had it's offset properly set. We only want to consider the segments
 861   // that will affect layout of allocated sections so we only add those.
 862   std::vector<Segment *> OrderedSegments;
 863   for (auto &Section : this->Sections) {
 864     if ((Section->Flags & SHF_ALLOC) != 0 &&
 865         Section->ParentSegment != nullptr) {
 866       OrderedSegments.push_back(Section->ParentSegment);
 867     }
 868   }
 869   OrderSegments(OrderedSegments);
 870   // Because we add a ParentSegment for each section we might have duplicate
 871   // segments in OrderedSegments. If there were duplicates then LayoutSegments
 872   // would do very strange things.
 873   auto End =
 874       std::unique(std::begin(OrderedSegments), std::end(OrderedSegments));
 875   OrderedSegments.erase(End, std::end(OrderedSegments));
 876
 877   // Modify the first segment so that there is no gap at the start. This allows
 878   // our layout algorithm to proceed as expected while not out writing out the
 879   // gap at the start.
 880   if (!OrderedSegments.empty()) {
 881     auto Seg = OrderedSegments[0];
 882     auto Sec = Seg->firstSection();
 883     auto Diff = Sec->OriginalOffset - Seg->OriginalOffset;
 884     Seg->OriginalOffset += Diff;
 885     // The size needs to be shrunk as well
 886     Seg->FileSize -= Diff;
 887     Seg->MemSize -= Diff;
 888     // The VAddr needs to be adjusted so that the alignment is correct as well
 889     Seg->VAddr += Diff;
 890     Seg->PAddr = Seg->VAddr;
 891     // We don't want this to be shifted by alignment so we need to set the
 892     // alignment to zero.
 893     Seg->Align = 0;
 894   }
 895
 896   uint64_t Offset = LayoutSegments(OrderedSegments, 0);
 897
 898   // TODO: generalize LayoutSections to take a range. Pass a special range
 899   // constructed from an iterator that skips values for which a predicate does
 900   // not hold. Then pass such a range to LayoutSections instead of constructing
 901   // AllocatedSections here.
 902   std::vector<SectionBase *> AllocatedSections;
 903   for (auto &Section : this->Sections) {
 904     if ((Section->Flags & SHF_ALLOC) == 0)
 905       continue;
 906     AllocatedSections.push_back(Section.get());
 907   }
 908   LayoutSections(AllocatedSections, Offset);
 909
 910   // Now that every section has been laid out we just need to compute the total
 911   // file size. This might not be the same as the offset returned by
 912   // LayoutSections, because we want to truncate the last segment to the end of
 913   // its last section, to match GNU objcopy's behaviour.
 914   TotalSize = 0;
 915   for (const auto &Section : AllocatedSections) {
 916     if (Section->Type != SHT_NOBITS)
 917       TotalSize = std::max(TotalSize, Section->Offset + Section->Size);
 918   }
 919 }
 920
 921 namespace llvm {
 922
 923 template class Object<ELF64LE>;
 924 template class Object<ELF64BE>;
 925 template class Object<ELF32LE>;
 926 template class Object<ELF32BE>;
 927
 928 template class ELFObject<ELF64LE>;
 929 template class ELFObject<ELF64BE>;
 930 template class ELFObject<ELF32LE>;
 931 template class ELFObject<ELF32BE>;
 932
 933 template class BinaryObject<ELF64LE>;
 934 template class BinaryObject<ELF64BE>;
 935 template class BinaryObject<ELF32LE>;
 936 template class BinaryObject<ELF32BE>;
 937
 938 } // end namespace llvm