vendor/llvm/llvm-trunk-r321017

1 files changed, 936 insertions, 0 deletions

diff --git a/tools/llvm-objcopy/Object.cpp b/tools/llvm-objcopy/Object.cpp
new file mode 100644
index 000000000000..bd5bcd7fc188
--- /dev/null
+++ b/tools/llvm-objcopy/Object.cpp
@@ -0,0 +1,936 @@
+//===- Object.cpp ---------------------------------------------------------===//
+//
+//                      The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "Object.h"
+#include "llvm-objcopy.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/ADT/iterator_range.h"
+#include "llvm/BinaryFormat/ELF.h"
+#include "llvm/Object/ELFObjectFile.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/FileOutputBuffer.h"
+#include <algorithm>
+#include <cstddef>
+#include <cstdint>
+#include <iterator>
+#include <utility>
+#include <vector>
+
+using namespace llvm;
+using namespace object;
+using namespace ELF;
+
+template <class ELFT> void Segment::writeHeader(FileOutputBuffer &Out) const {
+  using Elf_Ehdr = typename ELFT::Ehdr;
+  using Elf_Phdr = typename ELFT::Phdr;
+
+  uint8_t *Buf = Out.getBufferStart();
+  Buf += sizeof(Elf_Ehdr) + Index * sizeof(Elf_Phdr);
+  Elf_Phdr &Phdr = *reinterpret_cast<Elf_Phdr *>(Buf);
+  Phdr.p_type = Type;
+  Phdr.p_flags = Flags;
+  Phdr.p_offset = Offset;
+  Phdr.p_vaddr = VAddr;
+  Phdr.p_paddr = PAddr;
+  Phdr.p_filesz = FileSize;
+  Phdr.p_memsz = MemSize;
+  Phdr.p_align = Align;
+}
+
+void Segment::writeSegment(FileOutputBuffer &Out) const {
+  uint8_t *Buf = Out.getBufferStart() + Offset;
+  // We want to maintain segments' interstitial data and contents exactly.
+  // This lets us just copy segments directly.
+  std::copy(std::begin(Contents), std::end(Contents), Buf);
+}
+
+void SectionBase::removeSectionReferences(const SectionBase *Sec) {}
+void SectionBase::initialize(SectionTableRef SecTable) {}
+void SectionBase::finalize() {}
+
+template <class ELFT>
+void SectionBase::writeHeader(FileOutputBuffer &Out) const {
+  uint8_t *Buf = Out.getBufferStart();
+  Buf += HeaderOffset;
+  typename ELFT::Shdr &Shdr = *reinterpret_cast<typename ELFT::Shdr *>(Buf);
+  Shdr.sh_name = NameIndex;
+  Shdr.sh_type = Type;
+  Shdr.sh_flags = Flags;
+  Shdr.sh_addr = Addr;
+  Shdr.sh_offset = Offset;
+  Shdr.sh_size = Size;
+  Shdr.sh_link = Link;
+  Shdr.sh_info = Info;
+  Shdr.sh_addralign = Align;
+  Shdr.sh_entsize = EntrySize;
+}
+
+void Section::writeSection(FileOutputBuffer &Out) const {
+  if (Type == SHT_NOBITS)
+    return;
+  uint8_t *Buf = Out.getBufferStart() + Offset;
+  std::copy(std::begin(Contents), std::end(Contents), Buf);
+}
+
+void StringTableSection::addString(StringRef Name) {
+  StrTabBuilder.add(Name);
+  Size = StrTabBuilder.getSize();
+}
+
+uint32_t StringTableSection::findIndex(StringRef Name) const {
+  return StrTabBuilder.getOffset(Name);
+}
+
+void StringTableSection::finalize() { StrTabBuilder.finalize(); }
+
+void StringTableSection::writeSection(FileOutputBuffer &Out) const {
+  StrTabBuilder.write(Out.getBufferStart() + Offset);
+}
+
+static bool isValidReservedSectionIndex(uint16_t Index, uint16_t Machine) {
+  switch (Index) {
+  case SHN_ABS:
+  case SHN_COMMON:
+    return true;
+  }
+  if (Machine == EM_HEXAGON) {
+    switch (Index) {
+    case SHN_HEXAGON_SCOMMON:
+    case SHN_HEXAGON_SCOMMON_2:
+    case SHN_HEXAGON_SCOMMON_4:
+    case SHN_HEXAGON_SCOMMON_8:
+      return true;
+    }
+  }
+  return false;
+}
+
+uint16_t Symbol::getShndx() const {
+  if (DefinedIn != nullptr) {
+    return DefinedIn->Index;
+  }
+  switch (ShndxType) {
+  // This means that we don't have a defined section but we do need to
+  // output a legitimate section index.
+  case SYMBOL_SIMPLE_INDEX:
+    return SHN_UNDEF;
+  case SYMBOL_ABS:
+  case SYMBOL_COMMON:
+  case SYMBOL_HEXAGON_SCOMMON:
+  case SYMBOL_HEXAGON_SCOMMON_2:
+  case SYMBOL_HEXAGON_SCOMMON_4:
+  case SYMBOL_HEXAGON_SCOMMON_8:
+    return static_cast<uint16_t>(ShndxType);
+  }
+  llvm_unreachable("Symbol with invalid ShndxType encountered");
+}
+
+void SymbolTableSection::addSymbol(StringRef Name, uint8_t Bind, uint8_t Type,
+                                   SectionBase *DefinedIn, uint64_t Value,
+                                   uint16_t Shndx, uint64_t Sz) {
+  Symbol Sym;
+  Sym.Name = Name;
+  Sym.Binding = Bind;
+  Sym.Type = Type;
+  Sym.DefinedIn = DefinedIn;
+  if (DefinedIn == nullptr) {
+    if (Shndx >= SHN_LORESERVE)
+      Sym.ShndxType = static_cast<SymbolShndxType>(Shndx);
+    else
+      Sym.ShndxType = SYMBOL_SIMPLE_INDEX;
+  }
+  Sym.Value = Value;
+  Sym.Size = Sz;
+  Sym.Index = Symbols.size();
+  Symbols.emplace_back(llvm::make_unique<Symbol>(Sym));
+  Size += this->EntrySize;
+}
+
+void SymbolTableSection::removeSectionReferences(const SectionBase *Sec) {
+  if (SymbolNames == Sec) {
+    error("String table " + SymbolNames->Name +
+          " cannot be removed because it is referenced by the symbol table " +
+          this->Name);
+  }
+  auto Iter =
+      std::remove_if(std::begin(Symbols), std::end(Symbols),
+                     [=](const SymPtr &Sym) { return Sym->DefinedIn == Sec; });
+  Size -= (std::end(Symbols) - Iter) * this->EntrySize;
+  Symbols.erase(Iter, std::end(Symbols));
+}
+
+void SymbolTableSection::initialize(SectionTableRef SecTable) {
+  Size = 0;
+  setStrTab(SecTable.getSectionOfType<StringTableSection>(
+      Link,
+      "Symbol table has link index of " + Twine(Link) +
+          " which is not a valid index",
+      "Symbol table has link index of " + Twine(Link) +
+          " which is not a string table"));
+}
+
+void SymbolTableSection::finalize() {
+  // Make sure SymbolNames is finalized before getting name indexes.
+  SymbolNames->finalize();
+
+  uint32_t MaxLocalIndex = 0;
+  for (auto &Sym : Symbols) {
+    Sym->NameIndex = SymbolNames->findIndex(Sym->Name);
+    if (Sym->Binding == STB_LOCAL)
+      MaxLocalIndex = std::max(MaxLocalIndex, Sym->Index);
+  }
+  // Now we need to set the Link and Info fields.
+  Link = SymbolNames->Index;
+  Info = MaxLocalIndex + 1;
+}
+
+void SymbolTableSection::addSymbolNames() {
+  // Add all of our strings to SymbolNames so that SymbolNames has the right
+  // size before layout is decided.
+  for (auto &Sym : Symbols)
+    SymbolNames->addString(Sym->Name);
+}
+
+const Symbol *SymbolTableSection::getSymbolByIndex(uint32_t Index) const {
+  if (Symbols.size() <= Index)
+    error("Invalid symbol index: " + Twine(Index));
+  return Symbols[Index].get();
+}
+
+template <class ELFT>
+void SymbolTableSectionImpl<ELFT>::writeSection(FileOutputBuffer &Out) const {
+  uint8_t *Buf = Out.getBufferStart();
+  Buf += Offset;
+  typename ELFT::Sym *Sym = reinterpret_cast<typename ELFT::Sym *>(Buf);
+  // Loop though symbols setting each entry of the symbol table.
+  for (auto &Symbol : Symbols) {
+    Sym->st_name = Symbol->NameIndex;
+    Sym->st_value = Symbol->Value;
+    Sym->st_size = Symbol->Size;
+    Sym->setBinding(Symbol->Binding);
+    Sym->setType(Symbol->Type);
+    Sym->st_shndx = Symbol->getShndx();
+    ++Sym;
+  }
+}
+
+template <class SymTabType>
+void RelocSectionWithSymtabBase<SymTabType>::removeSectionReferences(
+    const SectionBase *Sec) {
+  if (Symbols == Sec) {
+    error("Symbol table " + Symbols->Name + " cannot be removed because it is "
+                                            "referenced by the relocation "
+                                            "section " +
+          this->Name);
+  }
+}
+
+template <class SymTabType>
+void RelocSectionWithSymtabBase<SymTabType>::initialize(
+    SectionTableRef SecTable) {
+  setSymTab(SecTable.getSectionOfType<SymTabType>(
+      Link,
+      "Link field value " + Twine(Link) + " in section " + Name + " is invalid",
+      "Link field value " + Twine(Link) + " in section " + Name +
+          " is not a symbol table"));
+
+  if (Info != SHN_UNDEF)
+    setSection(SecTable.getSection(Info,
+                                   "Info field value " + Twine(Info) +
+                                       " in section " + Name + " is invalid"));
+  else
+    setSection(nullptr);
+}
+
+template <class SymTabType>
+void RelocSectionWithSymtabBase<SymTabType>::finalize() {
+  this->Link = Symbols->Index;
+  if (SecToApplyRel != nullptr)
+    this->Info = SecToApplyRel->Index;
+}
+
+template <class ELFT>
+void setAddend(Elf_Rel_Impl<ELFT, false> &Rel, uint64_t Addend) {}
+
+template <class ELFT>
+void setAddend(Elf_Rel_Impl<ELFT, true> &Rela, uint64_t Addend) {
+  Rela.r_addend = Addend;
+}
+
+template <class ELFT>
+template <class T>
+void RelocationSection<ELFT>::writeRel(T *Buf) const {
+  for (const auto &Reloc : Relocations) {
+    Buf->r_offset = Reloc.Offset;
+    setAddend(*Buf, Reloc.Addend);
+    Buf->setSymbolAndType(Reloc.RelocSymbol->Index, Reloc.Type, false);
+    ++Buf;
+  }
+}
+
+template <class ELFT>
+void RelocationSection<ELFT>::writeSection(FileOutputBuffer &Out) const {
+  uint8_t *Buf = Out.getBufferStart() + Offset;
+  if (Type == SHT_REL)
+    writeRel(reinterpret_cast<Elf_Rel *>(Buf));
+  else
+    writeRel(reinterpret_cast<Elf_Rela *>(Buf));
+}
+
+void DynamicRelocationSection::writeSection(FileOutputBuffer &Out) const {
+  std::copy(std::begin(Contents), std::end(Contents),
+            Out.getBufferStart() + Offset);
+}
+
+void SectionWithStrTab::removeSectionReferences(const SectionBase *Sec) {
+  if (StrTab == Sec) {
+    error("String table " + StrTab->Name + " cannot be removed because it is "
+                                           "referenced by the section " +
+          this->Name);
+  }
+}
+
+bool SectionWithStrTab::classof(const SectionBase *S) {
+  return isa<DynamicSymbolTableSection>(S) || isa<DynamicSection>(S);
+}
+
+void SectionWithStrTab::initialize(SectionTableRef SecTable) {
+  auto StrTab = SecTable.getSection(Link,
+                                    "Link field value " + Twine(Link) +
+                                        " in section " + Name + " is invalid");
+  if (StrTab->Type != SHT_STRTAB) {
+    error("Link field value " + Twine(Link) + " in section " + Name +
+          " is not a string table");
+  }
+  setStrTab(StrTab);
+}
+
+void SectionWithStrTab::finalize() { this->Link = StrTab->Index; }
+
+// Returns true IFF a section is wholly inside the range of a segment
+static bool sectionWithinSegment(const SectionBase &Section,
+                                 const Segment &Segment) {
+  // If a section is empty it should be treated like it has a size of 1. This is
+  // to clarify the case when an empty section lies on a boundary between two
+  // segments and ensures that the section "belongs" to the second segment and
+  // not the first.
+  uint64_t SecSize = Section.Size ? Section.Size : 1;
+  return Segment.Offset <= Section.OriginalOffset &&
+         Segment.Offset + Segment.FileSize >= Section.OriginalOffset + SecSize;
+}
+
+// Returns true IFF a segment's original offset is inside of another segment's
+// range.
+static bool segmentOverlapsSegment(const Segment &Child,
+                                   const Segment &Parent) {
+
+  return Parent.OriginalOffset <= Child.OriginalOffset &&
+         Parent.OriginalOffset + Parent.FileSize > Child.OriginalOffset;
+}
+
+static bool compareSegments(const Segment *A, const Segment *B) {
+  // Any segment without a parent segment should come before a segment
+  // that has a parent segment.
+  if (A->OriginalOffset < B->OriginalOffset)
+    return true;
+  if (A->OriginalOffset > B->OriginalOffset)
+    return false;
+  return A->Index < B->Index;
+}
+
+template <class ELFT>
+void Object<ELFT>::readProgramHeaders(const ELFFile<ELFT> &ElfFile) {
+  uint32_t Index = 0;
+  for (const auto &Phdr : unwrapOrError(ElfFile.program_headers())) {
+    ArrayRef<uint8_t> Data{ElfFile.base() + Phdr.p_offset,
+                           (size_t)Phdr.p_filesz};
+    Segments.emplace_back(llvm::make_unique<Segment>(Data));
+    Segment &Seg = *Segments.back();
+    Seg.Type = Phdr.p_type;
+    Seg.Flags = Phdr.p_flags;
+    Seg.OriginalOffset = Phdr.p_offset;
+    Seg.Offset = Phdr.p_offset;
+    Seg.VAddr = Phdr.p_vaddr;
+    Seg.PAddr = Phdr.p_paddr;
+    Seg.FileSize = Phdr.p_filesz;
+    Seg.MemSize = Phdr.p_memsz;
+    Seg.Align = Phdr.p_align;
+    Seg.Index = Index++;
+    for (auto &Section : Sections) {
+      if (sectionWithinSegment(*Section, Seg)) {
+        Seg.addSection(&*Section);
+        if (!Section->ParentSegment ||
+            Section->ParentSegment->Offset > Seg.Offset) {
+          Section->ParentSegment = &Seg;
+        }
+      }
+    }
+  }
+  // Now we do an O(n^2) loop through the segments in order to match up
+  // segments.
+  for (auto &Child : Segments) {
+    for (auto &Parent : Segments) {
+      // Every segment will overlap with itself but we don't want a segment to
+      // be it's own parent so we avoid that situation.
+      if (&Child != &Parent && segmentOverlapsSegment(*Child, *Parent)) {
+        // We want a canonical "most parental" segment but this requires
+        // inspecting the ParentSegment.
+        if (compareSegments(Parent.get(), Child.get()))
+          if (Child->ParentSegment == nullptr ||
+              compareSegments(Parent.get(), Child->ParentSegment)) {
+            Child->ParentSegment = Parent.get();
+          }
+      }
+    }
+  }
+}
+
+template <class ELFT>
+void Object<ELFT>::initSymbolTable(const object::ELFFile<ELFT> &ElfFile,
+                                   SymbolTableSection *SymTab,
+                                   SectionTableRef SecTable) {
+  const Elf_Shdr &Shdr = *unwrapOrError(ElfFile.getSection(SymTab->Index));
+  StringRef StrTabData = unwrapOrError(ElfFile.getStringTableForSymtab(Shdr));
+
+  for (const auto &Sym : unwrapOrError(ElfFile.symbols(&Shdr))) {
+    SectionBase *DefSection = nullptr;
+    StringRef Name = unwrapOrError(Sym.getName(StrTabData));
+
+    if (Sym.st_shndx >= SHN_LORESERVE) {
+      if (!isValidReservedSectionIndex(Sym.st_shndx, Machine)) {
+        error(
+            "Symbol '" + Name +
+            "' has unsupported value greater than or equal to SHN_LORESERVE: " +
+            Twine(Sym.st_shndx));
+      }
+    } else if (Sym.st_shndx != SHN_UNDEF) {
+      DefSection = SecTable.getSection(
+          Sym.st_shndx,
+          "Symbol '" + Name + "' is defined in invalid section with index " +
+              Twine(Sym.st_shndx));
+    }
+
+    SymTab->addSymbol(Name, Sym.getBinding(), Sym.getType(), DefSection,
+                      Sym.getValue(), Sym.st_shndx, Sym.st_size);
+  }
+}
+
+template <class ELFT>
+static void getAddend(uint64_t &ToSet, const Elf_Rel_Impl<ELFT, false> &Rel) {}
+
+template <class ELFT>
+static void getAddend(uint64_t &ToSet, const Elf_Rel_Impl<ELFT, true> &Rela) {
+  ToSet = Rela.r_addend;
+}
+
+template <class ELFT, class T>
+void initRelocations(RelocationSection<ELFT> *Relocs,
+                     SymbolTableSection *SymbolTable, T RelRange) {
+  for (const auto &Rel : RelRange) {
+    Relocation ToAdd;
+    ToAdd.Offset = Rel.r_offset;
+    getAddend(ToAdd.Addend, Rel);
+    ToAdd.Type = Rel.getType(false);
+    ToAdd.RelocSymbol = SymbolTable->getSymbolByIndex(Rel.getSymbol(false));
+    Relocs->addRelocation(ToAdd);
+  }
+}
+
+SectionBase *SectionTableRef::getSection(uint16_t Index, Twine ErrMsg) {
+  if (Index == SHN_UNDEF || Index > Sections.size())
+    error(ErrMsg);
+  return Sections[Index - 1].get();
+}
+
+template <class T>
+T *SectionTableRef::getSectionOfType(uint16_t Index, Twine IndexErrMsg,
+                                     Twine TypeErrMsg) {
+  if (T *Sec = dyn_cast<T>(getSection(Index, IndexErrMsg)))
+    return Sec;
+  error(TypeErrMsg);
+}
+
+template <class ELFT>
+std::unique_ptr<SectionBase>
+Object<ELFT>::makeSection(const object::ELFFile<ELFT> &ElfFile,
+                          const Elf_Shdr &Shdr) {
+  ArrayRef<uint8_t> Data;
+  switch (Shdr.sh_type) {
+  case SHT_REL:
+  case SHT_RELA:
+    if (Shdr.sh_flags & SHF_ALLOC) {
+      Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
+      return llvm::make_unique<DynamicRelocationSection>(Data);
+    }
+    return llvm::make_unique<RelocationSection<ELFT>>();
+  case SHT_STRTAB:
+    // If a string table is allocated we don't want to mess with it. That would
+    // mean altering the memory image. There are no special link types or
+    // anything so we can just use a Section.
+    if (Shdr.sh_flags & SHF_ALLOC) {
+      Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
+      return llvm::make_unique<Section>(Data);
+    }
+    return llvm::make_unique<StringTableSection>();
+  case SHT_HASH:
+  case SHT_GNU_HASH:
+    // Hash tables should refer to SHT_DYNSYM which we're not going to change.
+    // Because of this we don't need to mess with the hash tables either.
+    Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
+    return llvm::make_unique<Section>(Data);
+  case SHT_DYNSYM:
+    Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
+    return llvm::make_unique<DynamicSymbolTableSection>(Data);
+  case SHT_DYNAMIC:
+    Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
+    return llvm::make_unique<DynamicSection>(Data);
+  case SHT_SYMTAB: {
+    auto SymTab = llvm::make_unique<SymbolTableSectionImpl<ELFT>>();
+    SymbolTable = SymTab.get();
+    return std::move(SymTab);
+  }
+  case SHT_NOBITS:
+    return llvm::make_unique<Section>(Data);
+  default:
+    Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
+    return llvm::make_unique<Section>(Data);
+  }
+}
+
+template <class ELFT>
+SectionTableRef Object<ELFT>::readSectionHeaders(const ELFFile<ELFT> &ElfFile) {
+  uint32_t Index = 0;
+  for (const auto &Shdr : unwrapOrError(ElfFile.sections())) {
+    if (Index == 0) {
+      ++Index;
+      continue;
+    }
+    SecPtr Sec = makeSection(ElfFile, Shdr);
+    Sec->Name = unwrapOrError(ElfFile.getSectionName(&Shdr));
+    Sec->Type = Shdr.sh_type;
+    Sec->Flags = Shdr.sh_flags;
+    Sec->Addr = Shdr.sh_addr;
+    Sec->Offset = Shdr.sh_offset;
+    Sec->OriginalOffset = Shdr.sh_offset;
+    Sec->Size = Shdr.sh_size;
+    Sec->Link = Shdr.sh_link;
+    Sec->Info = Shdr.sh_info;
+    Sec->Align = Shdr.sh_addralign;
+    Sec->EntrySize = Shdr.sh_entsize;
+    Sec->Index = Index++;
+    Sections.push_back(std::move(Sec));
+  }
+
+  SectionTableRef SecTable(Sections);
+
+  // Now that all of the sections have been added we can fill out some extra
+  // details about symbol tables. We need the symbol table filled out before
+  // any relocations.
+  if (SymbolTable) {
+    SymbolTable->initialize(SecTable);
+    initSymbolTable(ElfFile, SymbolTable, SecTable);
+  }
+
+  // Now that all sections and symbols have been added we can add
+  // relocations that reference symbols and set the link and info fields for
+  // relocation sections.
+  for (auto &Section : Sections) {
+    if (Section.get() == SymbolTable)
+      continue;
+    Section->initialize(SecTable);
+    if (auto RelSec = dyn_cast<RelocationSection<ELFT>>(Section.get())) {
+      auto Shdr = unwrapOrError(ElfFile.sections()).begin() + RelSec->Index;
+      if (RelSec->Type == SHT_REL)
+        initRelocations(RelSec, SymbolTable, unwrapOrError(ElfFile.rels(Shdr)));
+      else
+        initRelocations(RelSec, SymbolTable,
+                        unwrapOrError(ElfFile.relas(Shdr)));
+    }
+  }
+
+  return SecTable;
+}
+
+template <class ELFT> Object<ELFT>::Object(const ELFObjectFile<ELFT> &Obj) {
+  const auto &ElfFile = *Obj.getELFFile();
+  const auto &Ehdr = *ElfFile.getHeader();
+
+  std::copy(Ehdr.e_ident, Ehdr.e_ident + 16, Ident);
+  Type = Ehdr.e_type;
+  Machine = Ehdr.e_machine;
+  Version = Ehdr.e_version;
+  Entry = Ehdr.e_entry;
+  Flags = Ehdr.e_flags;
+
+  SectionTableRef SecTable = readSectionHeaders(ElfFile);
+  readProgramHeaders(ElfFile);
+
+  SectionNames = SecTable.getSectionOfType<StringTableSection>(
+      Ehdr.e_shstrndx,
+      "e_shstrndx field value " + Twine(Ehdr.e_shstrndx) + " in elf header " +
+          " is invalid",
+      "e_shstrndx field value " + Twine(Ehdr.e_shstrndx) + " in elf header " +
+          " is not a string table");
+}
+
+template <class ELFT>
+void Object<ELFT>::writeHeader(FileOutputBuffer &Out) const {
+  uint8_t *Buf = Out.getBufferStart();
+  Elf_Ehdr &Ehdr = *reinterpret_cast<Elf_Ehdr *>(Buf);
+  std::copy(Ident, Ident + 16, Ehdr.e_ident);
+  Ehdr.e_type = Type;
+  Ehdr.e_machine = Machine;
+  Ehdr.e_version = Version;
+  Ehdr.e_entry = Entry;
+  Ehdr.e_phoff = sizeof(Elf_Ehdr);
+  Ehdr.e_flags = Flags;
+  Ehdr.e_ehsize = sizeof(Elf_Ehdr);
+  Ehdr.e_phentsize = sizeof(Elf_Phdr);
+  Ehdr.e_phnum = Segments.size();
+  Ehdr.e_shentsize = sizeof(Elf_Shdr);
+  if (WriteSectionHeaders) {
+    Ehdr.e_shoff = SHOffset;
+    Ehdr.e_shnum = Sections.size() + 1;
+    Ehdr.e_shstrndx = SectionNames->Index;
+  } else {
+    Ehdr.e_shoff = 0;
+    Ehdr.e_shnum = 0;
+    Ehdr.e_shstrndx = 0;
+  }
+}
+
+template <class ELFT>
+void Object<ELFT>::writeProgramHeaders(FileOutputBuffer &Out) const {
+  for (auto &Phdr : Segments)
+    Phdr->template writeHeader<ELFT>(Out);
+}
+
+template <class ELFT>
+void Object<ELFT>::writeSectionHeaders(FileOutputBuffer &Out) const {
+  uint8_t *Buf = Out.getBufferStart() + SHOffset;
+  // This reference serves to write the dummy section header at the begining
+  // of the file. It is not used for anything else
+  Elf_Shdr &Shdr = *reinterpret_cast<Elf_Shdr *>(Buf);
+  Shdr.sh_name = 0;
+  Shdr.sh_type = SHT_NULL;
+  Shdr.sh_flags = 0;
+  Shdr.sh_addr = 0;
+  Shdr.sh_offset = 0;
+  Shdr.sh_size = 0;
+  Shdr.sh_link = 0;
+  Shdr.sh_info = 0;
+  Shdr.sh_addralign = 0;
+  Shdr.sh_entsize = 0;
+
+  for (auto &Section : Sections)
+    Section->template writeHeader<ELFT>(Out);
+}
+
+template <class ELFT>
+void Object<ELFT>::writeSectionData(FileOutputBuffer &Out) const {
+  for (auto &Section : Sections)
+    Section->writeSection(Out);
+}
+
+template <class ELFT>
+void Object<ELFT>::removeSections(
+    std::function<bool(const SectionBase &)> ToRemove) {
+
+  auto Iter = std::stable_partition(
+      std::begin(Sections), std::end(Sections), [=](const SecPtr &Sec) {
+        if (ToRemove(*Sec))
+          return false;
+        if (auto RelSec = dyn_cast<RelocationSectionBase>(Sec.get())) {
+          if (auto ToRelSec = RelSec->getSection())
+            return !ToRemove(*ToRelSec);
+        }
+        return true;
+      });
+  if (SymbolTable != nullptr && ToRemove(*SymbolTable))
+    SymbolTable = nullptr;
+  if (ToRemove(*SectionNames)) {
+    if (WriteSectionHeaders)
+      error("Cannot remove " + SectionNames->Name +
+            " because it is the section header string table.");
+    SectionNames = nullptr;
+  }
+  // Now make sure there are no remaining references to the sections that will
+  // be removed. Sometimes it is impossible to remove a reference so we emit
+  // an error here instead.
+  for (auto &RemoveSec : make_range(Iter, std::end(Sections))) {
+    for (auto &Segment : Segments)
+      Segment->removeSection(RemoveSec.get());
+    for (auto &KeepSec : make_range(std::begin(Sections), Iter))
+      KeepSec->removeSectionReferences(RemoveSec.get());
+  }
+  // Now finally get rid of them all togethor.
+  Sections.erase(Iter, std::end(Sections));
+}
+
+template <class ELFT> void ELFObject<ELFT>::sortSections() {
+  // Put all sections in offset order. Maintain the ordering as closely as
+  // possible while meeting that demand however.
+  auto CompareSections = [](const SecPtr &A, const SecPtr &B) {
+    return A->OriginalOffset < B->OriginalOffset;
+  };
+  std::stable_sort(std::begin(this->Sections), std::end(this->Sections),
+                   CompareSections);
+}
+
+static uint64_t alignToAddr(uint64_t Offset, uint64_t Addr, uint64_t Align) {
+  // Calculate Diff such that (Offset + Diff) & -Align == Addr & -Align.
+  if (Align == 0)
+    Align = 1;
+  auto Diff =
+      static_cast<int64_t>(Addr % Align) - static_cast<int64_t>(Offset % Align);
+  // We only want to add to Offset, however, so if Diff < 0 we can add Align and
+  // (Offset + Diff) & -Align == Addr & -Align will still hold.
+  if (Diff < 0)
+    Diff += Align;
+  return Offset + Diff;
+}
+
+// Orders segments such that if x = y->ParentSegment then y comes before x.
+static void OrderSegments(std::vector<Segment *> &Segments) {
+  std::stable_sort(std::begin(Segments), std::end(Segments), compareSegments);
+}
+
+// This function finds a consistent layout for a list of segments starting from
+// an Offset. It assumes that Segments have been sorted by OrderSegments and
+// returns an Offset one past the end of the last segment.
+static uint64_t LayoutSegments(std::vector<Segment *> &Segments,
+                               uint64_t Offset) {
+  assert(std::is_sorted(std::begin(Segments), std::end(Segments),
+                        compareSegments));
+  // The only way a segment should move is if a section was between two
+  // segments and that section was removed. If that section isn't in a segment
+  // then it's acceptable, but not ideal, to simply move it to after the
+  // segments. So we can simply layout segments one after the other accounting
+  // for alignment.
+  for (auto &Segment : Segments) {
+    // We assume that segments have been ordered by OriginalOffset and Index
+    // such that a parent segment will always come before a child segment in
+    // OrderedSegments. This means that the Offset of the ParentSegment should
+    // already be set and we can set our offset relative to it.
+    if (Segment->ParentSegment != nullptr) {
+      auto Parent = Segment->ParentSegment;
+      Segment->Offset =
+          Parent->Offset + Segment->OriginalOffset - Parent->OriginalOffset;
+    } else {
+      Offset = alignToAddr(Offset, Segment->VAddr, Segment->Align);
+      Segment->Offset = Offset;
+    }
+    Offset = std::max(Offset, Segment->Offset + Segment->FileSize);
+  }
+  return Offset;
+}
+
+// This function finds a consistent layout for a list of sections. It assumes
+// that the ->ParentSegment of each section has already been laid out. The
+// supplied starting Offset is used for the starting offset of any section that
+// does not have a ParentSegment. It returns either the offset given if all
+// sections had a ParentSegment or an offset one past the last section if there
+// was a section that didn't have a ParentSegment.
+template <class SecPtr>
+static uint64_t LayoutSections(std::vector<SecPtr> &Sections, uint64_t Offset) {
+  // Now the offset of every segment has been set we can assign the offsets
+  // of each section. For sections that are covered by a segment we should use
+  // the segment's original offset and the section's original offset to compute
+  // the offset from the start of the segment. Using the offset from the start
+  // of the segment we can assign a new offset to the section. For sections not
+  // covered by segments we can just bump Offset to the next valid location.
+  uint32_t Index = 1;
+  for (auto &Section : Sections) {
+    Section->Index = Index++;
+    if (Section->ParentSegment != nullptr) {
+      auto Segment = Section->ParentSegment;
+      Section->Offset =
+          Segment->Offset + (Section->OriginalOffset - Segment->OriginalOffset);
+    } else {
+      Offset = alignTo(Offset, Section->Align == 0 ? 1 : Section->Align);
+      Section->Offset = Offset;
+      if (Section->Type != SHT_NOBITS)
+        Offset += Section->Size;
+    }
+  }
+  return Offset;
+}
+
+template <class ELFT> void ELFObject<ELFT>::assignOffsets() {
+  // We need a temporary list of segments that has a special order to it
+  // so that we know that anytime ->ParentSegment is set that segment has
+  // already had its offset properly set.
+  std::vector<Segment *> OrderedSegments;
+  for (auto &Segment : this->Segments)
+    OrderedSegments.push_back(Segment.get());
+  OrderSegments(OrderedSegments);
+  // The size of ELF + program headers will not change so it is ok to assume
+  // that the first offset of the first segment is a good place to start
+  // outputting sections. This covers both the standard case and the PT_PHDR
+  // case.
+  uint64_t Offset;
+  if (!OrderedSegments.empty()) {
+    Offset = OrderedSegments[0]->Offset;
+  } else {
+    Offset = sizeof(Elf_Ehdr);
+  }
+  Offset = LayoutSegments(OrderedSegments, Offset);
+  Offset = LayoutSections(this->Sections, Offset);
+  // If we need to write the section header table out then we need to align the
+  // Offset so that SHOffset is valid.
+  if (this->WriteSectionHeaders)
+    Offset = alignTo(Offset, sizeof(typename ELFT::Addr));
+  this->SHOffset = Offset;
+}
+
+template <class ELFT> size_t ELFObject<ELFT>::totalSize() const {
+  // We already have the section header offset so we can calculate the total
+  // size by just adding up the size of each section header.
+  auto NullSectionSize = this->WriteSectionHeaders ? sizeof(Elf_Shdr) : 0;
+  return this->SHOffset + this->Sections.size() * sizeof(Elf_Shdr) +
+         NullSectionSize;
+}
+
+template <class ELFT> void ELFObject<ELFT>::write(FileOutputBuffer &Out) const {
+  this->writeHeader(Out);
+  this->writeProgramHeaders(Out);
+  this->writeSectionData(Out);
+  if (this->WriteSectionHeaders)
+    this->writeSectionHeaders(Out);
+}
+
+template <class ELFT> void ELFObject<ELFT>::finalize() {
+  // Make sure we add the names of all the sections.
+  if (this->SectionNames != nullptr)
+    for (const auto &Section : this->Sections) {
+      this->SectionNames->addString(Section->Name);
+    }
+  // Make sure we add the names of all the symbols.
+  if (this->SymbolTable != nullptr)
+    this->SymbolTable->addSymbolNames();
+
+  sortSections();
+  assignOffsets();
+
+  // Finalize SectionNames first so that we can assign name indexes.
+  if (this->SectionNames != nullptr)
+    this->SectionNames->finalize();
+  // Finally now that all offsets and indexes have been set we can finalize any
+  // remaining issues.
+  uint64_t Offset = this->SHOffset + sizeof(Elf_Shdr);
+  for (auto &Section : this->Sections) {
+    Section->HeaderOffset = Offset;
+    Offset += sizeof(Elf_Shdr);
+    if (this->WriteSectionHeaders)
+      Section->NameIndex = this->SectionNames->findIndex(Section->Name);
+    Section->finalize();
+  }
+}
+
+template <class ELFT> size_t BinaryObject<ELFT>::totalSize() const {
+  return TotalSize;
+}
+
+template <class ELFT>
+void BinaryObject<ELFT>::write(FileOutputBuffer &Out) const {
+  for (auto &Section : this->Sections) {
+    if ((Section->Flags & SHF_ALLOC) == 0)
+      continue;
+    Section->writeSection(Out);
+  }
+}
+
+template <class ELFT> void BinaryObject<ELFT>::finalize() {
+  // TODO: Create a filter range to construct OrderedSegments from so that this
+  // code can be deduped with assignOffsets above. This should also solve the
+  // todo below for LayoutSections.
+  // We need a temporary list of segments that has a special order to it
+  // so that we know that anytime ->ParentSegment is set that segment has
+  // already had it's offset properly set. We only want to consider the segments
+  // that will affect layout of allocated sections so we only add those.
+  std::vector<Segment *> OrderedSegments;
+  for (auto &Section : this->Sections) {
+    if ((Section->Flags & SHF_ALLOC) != 0 &&
+        Section->ParentSegment != nullptr) {
+      OrderedSegments.push_back(Section->ParentSegment);
+    }
+  }
+  OrderSegments(OrderedSegments);
+  // Because we add a ParentSegment for each section we might have duplicate
+  // segments in OrderedSegments. If there were duplicates then LayoutSegments
+  // would do very strange things.
+  auto End =
+      std::unique(std::begin(OrderedSegments), std::end(OrderedSegments));
+  OrderedSegments.erase(End, std::end(OrderedSegments));
+
+  // Modify the first segment so that there is no gap at the start. This allows
+  // our layout algorithm to proceed as expected while not out writing out the
+  // gap at the start.
+  if (!OrderedSegments.empty()) {
+    auto Seg = OrderedSegments[0];
+    auto Sec = Seg->firstSection();
+    auto Diff = Sec->OriginalOffset - Seg->OriginalOffset;
+    Seg->OriginalOffset += Diff;
+    // The size needs to be shrunk as well
+    Seg->FileSize -= Diff;
+    Seg->MemSize -= Diff;
+    // The VAddr needs to be adjusted so that the alignment is correct as well
+    Seg->VAddr += Diff;
+    Seg->PAddr = Seg->VAddr;
+    // We don't want this to be shifted by alignment so we need to set the
+    // alignment to zero.
+    Seg->Align = 0;
+  }
+
+  uint64_t Offset = LayoutSegments(OrderedSegments, 0);
+
+  // TODO: generalize LayoutSections to take a range. Pass a special range
+  // constructed from an iterator that skips values for which a predicate does
+  // not hold. Then pass such a range to LayoutSections instead of constructing
+  // AllocatedSections here.
+  std::vector<SectionBase *> AllocatedSections;
+  for (auto &Section : this->Sections) {
+    if ((Section->Flags & SHF_ALLOC) == 0)
+      continue;
+    AllocatedSections.push_back(Section.get());
+  }
+  LayoutSections(AllocatedSections, Offset);
+
+  // Now that every section has been laid out we just need to compute the total
+  // file size. This might not be the same as the offset returned by
+  // LayoutSections, because we want to truncate the last segment to the end of
+  // its last section, to match GNU objcopy's behaviour.
+  TotalSize = 0;
+  for (const auto &Section : AllocatedSections) {
+    if (Section->Type != SHT_NOBITS)
+      TotalSize = std::max(TotalSize, Section->Offset + Section->Size);
+  }
+}
+
+namespace llvm {
+
+template class Object<ELF64LE>;
+template class Object<ELF64BE>;
+template class Object<ELF32LE>;
+template class Object<ELF32BE>;
+
+template class ELFObject<ELF64LE>;
+template class ELFObject<ELF64BE>;
+template class ELFObject<ELF32LE>;
+template class ELFObject<ELF32BE>;
+
+template class BinaryObject<ELF64LE>;
+template class BinaryObject<ELF64BE>;
+template class BinaryObject<ELF32LE>;
+template class BinaryObject<ELF32BE>;
+
+} // end namespace llvm