COFF: Create output sections early. NFCI.

[pcc]

Summary

With this, all output sections are created in one place. This will make
it simpler to implement merging of builtin sections.

[ruiu]

LGTM

Nice!

lld/COFF/Writer.cpp

336–397 ↗

(On Diff #141266)

auto -> uint32_t?

406 ↗

(On Diff #141266)

createSection -> CreateSection

462 ↗

(On Diff #141266)

sectionOrder -> SectionOrder

lld/trunk/COFF/Writer.cpp

private:
   void createMiscChunks();
   void createImportTables();
   void createExportTable();
   void assignAddresses();
   void removeEmptySections();
   void createSymbolAndStringTable();
   void openFile(StringRef OutputPath);
   template <typename PEHeaderTy> void writeHeader();
-  void createSEHTable(OutputSection *RData);
-  void createGuardCFTables(OutputSection *RData);
-  void createGLJmpTable(OutputSection *RData);
+  void createSEHTable();
+  void createGuardCFTables();
   void markSymbolsForRVATable(ObjFile *File,
                               ArrayRef<SectionChunk *> SymIdxChunks,
                               SymbolRVASet &TableSymbols);
-  void maybeAddRVATable(OutputSection *RData, SymbolRVASet TableSymbols,
-                        StringRef TableSym, StringRef CountSym);
+  void maybeAddRVATable(SymbolRVASet TableSymbols, StringRef TableSym,
+                        StringRef CountSym);
   void setSectionPermissions();
   void writeSections();
   void writeBuildId();
   void sortExceptionTable();
 
   llvm::Optional<coff_symbol16> createSymbol(Defined *D);
   size_t addEntryToStringTable(StringRef Str);
 
   OutputSection *findSection(StringRef Name);
-  OutputSection *createSection(StringRef Name);
-  void addBaserels(OutputSection *Dest);
-  void addBaserelBlocks(OutputSection *Dest, std::vector<Baserel> &V);
+  void addBaserels();
+  void addBaserelBlocks(std::vector<Baserel> &V);
 
   uint32_t getSizeOfInitializedData();
   std::map<StringRef, std::vector<DefinedImportData *>> binImports();
 
   std::unique_ptr<FileOutputBuffer> &Buffer;
   std::vector<OutputSection *> OutputSections;
   std::vector<char> Strtab;
   std::vector<llvm::object::coff_symbol16> OutputSymtab;
   IdataContents Idata;
   DelayLoadContents DelayIdata;
   EdataContents Edata;
   RVATableChunk *GuardFidsTable = nullptr;
   RVATableChunk *SEHTable = nullptr;
 
   DebugDirectoryChunk *DebugDirectory = nullptr;
   std::vector<Chunk *> DebugRecords;
   CVDebugRecordChunk *BuildId = nullptr;
   Optional<codeview::DebugInfo> PreviousBuildId;
   ArrayRef<uint8_t> SectionTable;
 
   uint64_t FileSize;
   uint32_t PointerToSymbolTable = 0;
   uint64_t SizeOfImage;
   uint64_t SizeOfHeaders;
+
+  OutputSection *TextSec;
+  OutputSection *RdataSec;
+  OutputSection *DataSec;
+  OutputSection *PdataSec;
+  OutputSection *IdataSec;
+  OutputSection *EdataSec;
+  OutputSection *DidatSec;
+  OutputSection *RsrcSec;
+  OutputSection *RelocSec;
 };
 } // anonymous namespace
 
 namespace lld {
 namespace coff {
 
 static Timer CodeLayoutTimer("Code Layout", Timer::root());
 static Timer DiskCommitTimer("Commit Output File", Timer::root());

 // The main function of the writer.
 void Writer::run() {
   ScopedTimer T1(CodeLayoutTimer);
 
   createSections();
   createMiscChunks();
   createImportTables();
   createExportTable();
-  if (Config->Relocatable)
-    createSection(".reloc");
   assignAddresses();
   removeEmptySections();
   setSectionPermissions();
   createSymbolAndStringTable();
 
   if (FileSize > UINT32_MAX)
     fatal("image size (" + Twine(FileSize) + ") " +
         "exceeds maximum allowable size (" + Twine(UINT32_MAX) + ")");
static void sortBySectionOrder(std::vector<Chunk *> &Chunks) {
   std::stable_sort(Chunks.begin(), Chunks.end(),
                    [=](const Chunk *A, const Chunk *B) {
                      return GetPriority(A) < GetPriority(B);
                    });
 }
 
 // Create output section objects and add them to OutputSections.
 void Writer::createSections() {
-  // First, bin chunks by name.
+  // First, create the builtin sections.
+  const uint32_t DATA = IMAGE_SCN_CNT_INITIALIZED_DATA;
+  const uint32_t BSS = IMAGE_SCN_CNT_UNINITIALIZED_DATA;
+  const uint32_t CODE = IMAGE_SCN_CNT_CODE;
+  const uint32_t DISCARDABLE = IMAGE_SCN_MEM_DISCARDABLE;
+  const uint32_t R = IMAGE_SCN_MEM_READ;
+  const uint32_t W = IMAGE_SCN_MEM_WRITE;
+  const uint32_t X = IMAGE_SCN_MEM_EXECUTE;
+
+  SmallDenseMap<StringRef, OutputSection *> Sections;
+  auto CreateSection = [&](StringRef Name, uint32_t Perms) {
+    auto Sec = make<OutputSection>(Name);
+    Sec->addPermissions(Perms);
+    OutputSections.push_back(Sec);
+    Sections[Name] = Sec;
+    return Sec;
+  };
+
+  // Try to match the section order used by link.exe.
+  TextSec = CreateSection(".text", CODE | R | X);
+  CreateSection(".bss", BSS | R | W);
+  RdataSec = CreateSection(".rdata", DATA | R);
+  DataSec = CreateSection(".data", DATA | R | W);
+  PdataSec = CreateSection(".pdata", DATA | R);
+  IdataSec = CreateSection(".idata", DATA | R);
+  EdataSec = CreateSection(".edata", DATA | R);
+  DidatSec = CreateSection(".didat", DATA | R);
+  RsrcSec = CreateSection(".rsrc", DATA | R);
+  RelocSec = CreateSection(".reloc", DATA | DISCARDABLE | R);
+
+  // Then bin chunks by name.
   std::map<StringRef, std::vector<Chunk *>> Map;
   for (Chunk *C : Symtab->getChunks()) {
     auto *SC = dyn_cast<SectionChunk>(C);
     if (SC && !SC->isLive()) {
       if (Config->Verbose)
         SC->printDiscardedMessage();
       continue;
     }
     Map[C->getSectionName()].push_back(C);
   }
 
   // Process an /order option.
   if (!Config->Order.empty())
     for (auto &Pair : Map)
       sortBySectionOrder(Pair.second);
 
   // Then create an OutputSection for each section.
   // '$' and all following characters in input section names are
   // discarded when determining output section. So, .text$foo
   // contributes to .text, for example. See PE/COFF spec 3.2.
-  SmallDenseMap<StringRef, OutputSection *> Sections;
   for (auto Pair : Map) {
     StringRef Name = getOutputSection(Pair.first);
     OutputSection *&Sec = Sections[Name];
     if (!Sec) {
       Sec = make<OutputSection>(Name);
       OutputSections.push_back(Sec);
     }
     std::vector<Chunk *> &Chunks = Pair.second;
     for (Chunk *C : Chunks) {
       Sec->addChunk(C);
       Sec->addPermissions(C->getPermissions());
     }
   }
+
+  // Finally, move some output sections to the end.
+  auto SectionOrder = [&](OutputSection *S) {
+    // .reloc should come last of all since it refers to RVAs of data in the
+    // previous sections.
+    if (S == RelocSec)
+      return 3;
+    // Move DISCARDABLE (or non-memory-mapped) sections to the end of file because
+    // the loader cannot handle holes.
+    if (S->getPermissions() & IMAGE_SCN_MEM_DISCARDABLE)
+      return 2;
+    // .rsrc should come at the end of the non-discardable sections because its
+    // size may change by the Win32 UpdateResources() function, causing
+    // subsequent sections to move (see https://crbug.com/827082).
+    if (S == RsrcSec)
+      return 1;
+    return 0;
+  };
+  std::stable_sort(OutputSections.begin(), OutputSections.end(),
+                   [&](OutputSection *S, OutputSection *T) {
+                     return SectionOrder(S) < SectionOrder(T);
+                   });
 }
 
 void Writer::createMiscChunks() {
-  OutputSection *RData = createSection(".rdata");
-
   for (auto &P : MergeChunk::Instances)
-    RData->addChunk(P.second);
+    RdataSec->addChunk(P.second);
 
   // Create thunks for locally-dllimported symbols.
   if (!Symtab->LocalImportChunks.empty()) {
     for (Chunk *C : Symtab->LocalImportChunks)
-      RData->addChunk(C);
+      RdataSec->addChunk(C);
   }
 
   // Create Debug Information Chunks
   if (Config->Debug) {
     DebugDirectory = make<DebugDirectoryChunk>(DebugRecords);
 
     // Make a CVDebugRecordChunk even when /DEBUG:CV is not specified.  We
     // output a PDB no matter what, and this chunk provides the only means of
     // allowing a debugger to match a PDB and an executable.  So we need it even
     // if we're ultimately not going to write CodeView data to the PDB.
     auto *CVChunk = make<CVDebugRecordChunk>();
     BuildId = CVChunk;
     DebugRecords.push_back(CVChunk);
 
-    RData->addChunk(DebugDirectory);
+    RdataSec->addChunk(DebugDirectory);
     for (Chunk *C : DebugRecords)
-      RData->addChunk(C);
+      RdataSec->addChunk(C);
   }
 
   // Create SEH table. x86-only.
   if (Config->Machine == I386)
-    createSEHTable(RData);
+    createSEHTable();
 
   // Create /guard:cf tables if requested.
   if (Config->GuardCF != GuardCFLevel::Off)
-    createGuardCFTables(RData);
+    createGuardCFTables();
 }
 
 // Create .idata section for the DLL-imported symbol table.
 // The format of this section is inherently Windows-specific.
 // IdataContents class abstracted away the details for us,
 // so we just let it create chunks and add them to the section.
 void Writer::createImportTables() {
   if (ImportFile::Instances.empty())
     return;
 
   // Initialize DLLOrder so that import entries are ordered in
   // the same order as in the command line. (That affects DLL
   // initialization order, and this ordering is MSVC-compatible.)
   for (ImportFile *File : ImportFile::Instances) {
     if (!File->Live)
       continue;
 
     std::string DLL = StringRef(File->DLLName).lower();
     if (Config->DLLOrder.count(DLL) == 0)
       Config->DLLOrder[DLL] = Config->DLLOrder.size();
   }
 
-  OutputSection *Text = createSection(".text");
   for (ImportFile *File : ImportFile::Instances) {
     if (!File->Live)
       continue;
 
     if (DefinedImportThunk *Thunk = File->ThunkSym)
-      Text->addChunk(Thunk->getChunk());
+      TextSec->addChunk(Thunk->getChunk());
 
     if (Config->DelayLoads.count(StringRef(File->DLLName).lower())) {
       if (!File->ThunkSym)
         fatal("cannot delay-load " + toString(File) +
               " due to import of data: " + toString(*File->ImpSym));
       DelayIdata.add(File->ImpSym);
     } else {
       Idata.add(File->ImpSym);
     }
   }
 
-  if (!Idata.empty()) {
-    OutputSection *Sec = createSection(".idata");
+  if (!Idata.empty())
     for (Chunk *C : Idata.getChunks())
-      Sec->addChunk(C);
-  }
+      IdataSec->addChunk(C);
 
   if (!DelayIdata.empty()) {
     Defined *Helper = cast<Defined>(Config->DelayLoadHelper);
     DelayIdata.create(Helper);
-    OutputSection *Sec = createSection(".didat");
     for (Chunk *C : DelayIdata.getChunks())
-      Sec->addChunk(C);
-    Sec = createSection(".data");
+      DidatSec->addChunk(C);
     for (Chunk *C : DelayIdata.getDataChunks())
-      Sec->addChunk(C);
-    Sec = createSection(".text");
+      DataSec->addChunk(C);
     for (Chunk *C : DelayIdata.getCodeChunks())
-      Sec->addChunk(C);
+      TextSec->addChunk(C);
   }
 }
 
 void Writer::createExportTable() {
   if (Config->Exports.empty())
     return;
-  OutputSection *Sec = createSection(".edata");
   for (Chunk *C : Edata.Chunks)
-    Sec->addChunk(C);
+    EdataSec->addChunk(C);
 }
 
 // The Windows loader doesn't seem to like empty sections,
 // so we remove them if any.
 void Writer::removeEmptySections() {
   auto IsEmpty = [](OutputSection *S) { return S->getVirtualSize() == 0; };
   OutputSections.erase(
       std::remove_if(OutputSections.begin(), OutputSections.end(), IsEmpty),
void Writer::createSymbolAndStringTable() {
   // We position the symbol table to be adjacent to the end of the last section.
   uint64_t FileOff = FileSize;
   PointerToSymbolTable = FileOff;
   FileOff += OutputSymtab.size() * sizeof(coff_symbol16);
   FileOff += 4 + Strtab.size();
   FileSize = alignTo(FileOff, SectorSize);
 }
 
-static int sectionIndex(OutputSection *S) {
-  // Move DISCARDABLE (or non-memory-mapped) sections to the end of file because
-  // the loader cannot handle holes.
-  if (S->getPermissions() & IMAGE_SCN_MEM_DISCARDABLE)
-    return 101;
-
-  // Try to match the section order used by link.exe. In particular, it's
-  // important that .reloc comes last since it refers to RVA's of data in
-  // the previous sections. .rsrc should come late because its size may
-  // change by the Win32 UpdateResources() function, causing subsequent
-  // sections to move (see https://crbug.com/827082).
-  return StringSwitch<int>(S->Name)
-      .Case(".text", 1)
-      .Case(".bss", 2)
-      .Case(".rdata", 3)
-      .Case(".data", 4)
-      .Case(".pdata", 5)
-      .Case(".idata", 6)
-      .Case(".rsrc", 99)
-      .Case(".reloc", 100)
-      .Default(50); // Default to somewhere in the middle.
-}
-
 // Visits all sections to assign incremental, non-overlapping RVAs and
 // file offsets.
 void Writer::assignAddresses() {
   SizeOfHeaders = DOSStubSize + sizeof(PEMagic) + sizeof(coff_file_header) +
                   sizeof(data_directory) * NumberfOfDataDirectory +
                   sizeof(coff_section) * OutputSections.size();
   SizeOfHeaders +=
       Config->is64() ? sizeof(pe32plus_header) : sizeof(pe32_header);
   SizeOfHeaders = alignTo(SizeOfHeaders, SectorSize);
   uint64_t RVA = PageSize; // The first page is kept unmapped.
   FileSize = SizeOfHeaders;
 
-  // Reorder the sections.
-  std::stable_sort(OutputSections.begin(), OutputSections.end(),
-                   [](OutputSection *S, OutputSection *T) {
-                     return sectionIndex(S) < sectionIndex(T);
-                   });
-
   for (OutputSection *Sec : OutputSections) {
-    if (Sec->Name == ".reloc")
-      addBaserels(Sec);
+    if (Sec == RelocSec)
+      addBaserels();
     uint64_t RawSize = 0, VirtualSize = 0;
     Sec->Header.VirtualAddress = RVA;
     for (Chunk *C : Sec->getChunks()) {
       VirtualSize = alignTo(VirtualSize, C->Alignment);
       C->setRVA(RVA + VirtualSize);
       C->OutputSectionOff = VirtualSize;
       C->finalizeContents();
       VirtualSize += C->getSize();
template <typename PEHeaderTy> void Writer::writeHeader() {
   if (Config->GuardCF != GuardCFLevel::Off)
     PE->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_GUARD_CF;
   if (Config->Machine == I386 && !SEHTable &&
       !Symtab->findUnderscore("_load_config_used"))
     PE->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_NO_SEH;
   if (Config->TerminalServerAware)
     PE->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_TERMINAL_SERVER_AWARE;
   PE->NumberOfRvaAndSize = NumberfOfDataDirectory;
-  if (OutputSection *Text = findSection(".text")) {
-    PE->BaseOfCode = Text->getRVA();
-    PE->SizeOfCode = Text->getRawSize();
+  if (TextSec->getVirtualSize()) {
+    PE->BaseOfCode = TextSec->getRVA();
+    PE->SizeOfCode = TextSec->getRawSize();
   }
   PE->SizeOfInitializedData = getSizeOfInitializedData();
 
   // Write data directory
   auto *Dir = reinterpret_cast<data_directory *>(Buf);
   Buf += sizeof(*Dir) * NumberfOfDataDirectory;
-  if (OutputSection *Sec = findSection(".edata")) {
-    Dir[EXPORT_TABLE].RelativeVirtualAddress = Sec->getRVA();
-    Dir[EXPORT_TABLE].Size = Sec->getVirtualSize();
+  if (EdataSec->getVirtualSize()) {
+    Dir[EXPORT_TABLE].RelativeVirtualAddress = EdataSec->getRVA();
+    Dir[EXPORT_TABLE].Size = EdataSec->getVirtualSize();
   }
   if (!Idata.empty()) {
     Dir[IMPORT_TABLE].RelativeVirtualAddress = Idata.getDirRVA();
     Dir[IMPORT_TABLE].Size = Idata.getDirSize();
     Dir[IAT].RelativeVirtualAddress = Idata.getIATRVA();
     Dir[IAT].Size = Idata.getIATSize();
   }
-  if (OutputSection *Sec = findSection(".rsrc")) {
-    Dir[RESOURCE_TABLE].RelativeVirtualAddress = Sec->getRVA();
-    Dir[RESOURCE_TABLE].Size = Sec->getVirtualSize();
-  }
-  if (OutputSection *Sec = findSection(".pdata")) {
-    Dir[EXCEPTION_TABLE].RelativeVirtualAddress = Sec->getRVA();
-    Dir[EXCEPTION_TABLE].Size = Sec->getVirtualSize();
-  }
-  if (OutputSection *Sec = findSection(".reloc")) {
-    Dir[BASE_RELOCATION_TABLE].RelativeVirtualAddress = Sec->getRVA();
-    Dir[BASE_RELOCATION_TABLE].Size = Sec->getVirtualSize();
+  if (RsrcSec->getVirtualSize()) {
+    Dir[RESOURCE_TABLE].RelativeVirtualAddress = RsrcSec->getRVA();
+    Dir[RESOURCE_TABLE].Size = RsrcSec->getVirtualSize();
+  }
+  if (PdataSec->getVirtualSize()) {
+    Dir[EXCEPTION_TABLE].RelativeVirtualAddress = PdataSec->getRVA();
+    Dir[EXCEPTION_TABLE].Size = PdataSec->getVirtualSize();
+  }
+  if (RelocSec->getVirtualSize()) {
+    Dir[BASE_RELOCATION_TABLE].RelativeVirtualAddress = RelocSec->getRVA();
+    Dir[BASE_RELOCATION_TABLE].Size = RelocSec->getVirtualSize();
   }
   if (Symbol *Sym = Symtab->findUnderscore("_tls_used")) {
     if (Defined *B = dyn_cast<Defined>(Sym)) {
       Dir[TLS_TABLE].RelativeVirtualAddress = B->getRVA();
       Dir[TLS_TABLE].Size = Config->is64()
                                 ? sizeof(object::coff_tls_directory64)
                                 : sizeof(object::coff_tls_directory32);
     }

 }
 
 void Writer::openFile(StringRef Path) {
   Buffer = CHECK(
       FileOutputBuffer::create(Path, FileSize, FileOutputBuffer::F_executable),
       "failed to open " + Path);
 }
 
-void Writer::createSEHTable(OutputSection *RData) {
+void Writer::createSEHTable() {
   SymbolRVASet Handlers;
   for (ObjFile *File : ObjFile::Instances) {
     // FIXME: We should error here instead of earlier unless /safeseh:no was
     // passed.
     if (!File->hasSafeSEH())
       return;
 
     markSymbolsForRVATable(File, File->getSXDataChunks(), Handlers);
   }
 
-  maybeAddRVATable(RData, std::move(Handlers), "__safe_se_handler_table",
+  maybeAddRVATable(std::move(Handlers), "__safe_se_handler_table",
                    "__safe_se_handler_count");
 }
 
 // Add a symbol to an RVA set. Two symbols may have the same RVA, but an RVA set
 // cannot contain duplicates. Therefore, the set is uniqued by Chunk and the
 // symbol's offset into that Chunk.
 static void addSymbolToRVASet(SymbolRVASet &RVASet, Defined *S) {
   Chunk *C = S->getChunk();
for (Symbol *Ref : SC->symbols()) {
       }
     }
   }
 }
 
 // Create the guard function id table. This is a table of RVAs of all
 // address-taken functions. It is sorted and uniqued, just like the safe SEH
 // table.
-void Writer::createGuardCFTables(OutputSection *RData) {
+void Writer::createGuardCFTables() {
   SymbolRVASet AddressTakenSyms;
   SymbolRVASet LongJmpTargets;
   for (ObjFile *File : ObjFile::Instances) {
     // If the object was compiled with /guard:cf, the address taken symbols
     // are in .gfids$y sections, and the longjmp targets are in .gljmp$y
     // sections. If the object was not compiled with /guard:cf, we assume there
     // were no setjmp targets, and that all code symbols with relocations are
     // possibly address-taken.
     if (File->hasGuardCF()) {
       markSymbolsForRVATable(File, File->getGuardFidChunks(), AddressTakenSyms);
       markSymbolsForRVATable(File, File->getGuardLJmpChunks(), LongJmpTargets);
     } else {
       markSymbolsWithRelocations(File, AddressTakenSyms);
     }
   }
 
   // Mark the image entry as address-taken.
   if (Config->Entry)
     addSymbolToRVASet(AddressTakenSyms, cast<Defined>(Config->Entry));
 
-  maybeAddRVATable(RData, std::move(AddressTakenSyms), "__guard_fids_table",
+  maybeAddRVATable(std::move(AddressTakenSyms), "__guard_fids_table",
                    "__guard_fids_count");
 
   // Add the longjmp target table unless the user told us not to.
   if (Config->GuardCF == GuardCFLevel::Full)
-    maybeAddRVATable(RData, std::move(LongJmpTargets), "__guard_longjmp_table",
+    maybeAddRVATable(std::move(LongJmpTargets), "__guard_longjmp_table",
                      "__guard_longjmp_count");
 
   // Set __guard_flags, which will be used in the load config to indicate that
   // /guard:cf was enabled.
   uint32_t GuardFlags = uint32_t(coff_guard_flags::CFInstrumented) |
                         uint32_t(coff_guard_flags::HasFidTable);
   if (Config->GuardCF == GuardCFLevel::Full)
     GuardFlags |= uint32_t(coff_guard_flags::HasLongJmpTable);
for (uint32_t SymIndex : SymIndices) {
       }
     }
   }
 }
 
 // Replace the absolute table symbol with a synthetic symbol pointing to
 // TableChunk so that we can emit base relocations for it and resolve section
 // relative relocations.
-void Writer::maybeAddRVATable(OutputSection *RData,
-                              SymbolRVASet TableSymbols,
-                              StringRef TableSym, StringRef CountSym) {
+void Writer::maybeAddRVATable(SymbolRVASet TableSymbols, StringRef TableSym,
+                              StringRef CountSym) {
   if (TableSymbols.empty())
     return;
 
   RVATableChunk *TableChunk = make<RVATableChunk>(std::move(TableSymbols));
-  RData->addChunk(TableChunk);
+  RdataSec->addChunk(TableChunk);
 
   Symbol *T = Symtab->findUnderscore(TableSym);
   Symbol *C = Symtab->findUnderscore(CountSym);
   replaceSymbol<DefinedSynthetic>(T, T->getName(), TableChunk);
   cast<DefinedAbsolute>(C)->setVA(TableChunk->getSize() / 4);
 }
 
 // Handles /section options to allow users to overwrite
void Writer::writeBuildId() {
   Buf += DOSStubSize + sizeof(PEMagic);
   object::coff_file_header *CoffHeader =
       reinterpret_cast<coff_file_header *>(Buf);
   CoffHeader->TimeDateStamp = Hash;
 }
 
 // Sort .pdata section contents according to PE/COFF spec 5.5.
 void Writer::sortExceptionTable() {
-  OutputSection *Sec = findSection(".pdata");
-  if (!Sec)
+  if (PdataSec->getVirtualSize() == 0)
     return;
   // We assume .pdata contains function table entries only.
-  uint8_t *Begin = Buffer->getBufferStart() + Sec->getFileOff();
-  uint8_t *End = Begin + Sec->getVirtualSize();
+  uint8_t *Begin = Buffer->getBufferStart() + PdataSec->getFileOff();
+  uint8_t *End = Begin + PdataSec->getVirtualSize();
   if (Config->Machine == AMD64) {
     struct Entry { ulittle32_t Begin, End, Unwind; };
     sort(parallel::par, (Entry *)Begin, (Entry *)End,
          [](const Entry &A, const Entry &B) { return A.Begin < B.Begin; });
     return;
   }
   if (Config->Machine == ARMNT || Config->Machine == ARM64) {
     struct Entry { ulittle32_t Begin, Unwind; };

 uint32_t Writer::getSizeOfInitializedData() {
   uint32_t Res = 0;
   for (OutputSection *S : OutputSections)
     if (S->getPermissions() & IMAGE_SCN_CNT_INITIALIZED_DATA)
       Res += S->getRawSize();
   return Res;
 }
 
-// Returns an existing section or create a new one if not found.
-OutputSection *Writer::createSection(StringRef Name) {
-  if (auto *Sec = findSection(Name))
-    return Sec;
-  const auto DATA = IMAGE_SCN_CNT_INITIALIZED_DATA;
-  const auto BSS = IMAGE_SCN_CNT_UNINITIALIZED_DATA;
-  const auto CODE = IMAGE_SCN_CNT_CODE;
-  const auto DISCARDABLE = IMAGE_SCN_MEM_DISCARDABLE;
-  const auto R = IMAGE_SCN_MEM_READ;
-  const auto W = IMAGE_SCN_MEM_WRITE;
-  const auto X = IMAGE_SCN_MEM_EXECUTE;
-  uint32_t Perms = StringSwitch<uint32_t>(Name)
-                       .Case(".bss", BSS | R | W)
-                       .Case(".data", DATA | R | W)
-                       .Cases(".didat", ".edata", ".idata", ".rdata", DATA | R)
-                       .Case(".reloc", DATA | DISCARDABLE | R)
-                       .Case(".text", CODE | R | X)
-                       .Default(0);
-  if (!Perms)
-    llvm_unreachable("unknown section name");
-  auto Sec = make<OutputSection>(Name);
-  Sec->addPermissions(Perms);
-  OutputSections.push_back(Sec);
-  return Sec;
-}
-
-// Dest is .reloc section. Add contents to that section.
-void Writer::addBaserels(OutputSection *Dest) {
+// Add base relocations to .reloc section.
+void Writer::addBaserels() {
+  if (!Config->Relocatable)
+    return;
   std::vector<Baserel> V;
   for (OutputSection *Sec : OutputSections) {
-    if (Sec == Dest)
+    if (Sec == RelocSec)
       continue;
     // Collect all locations for base relocations.
     for (Chunk *C : Sec->getChunks())
       C->getBaserels(&V);
     // Add the addresses to .reloc section.
     if (!V.empty())
-      addBaserelBlocks(Dest, V);
+      addBaserelBlocks(V);
     V.clear();
   }
 }
 
 // Add addresses to .reloc section. Note that addresses are grouped by page.
-void Writer::addBaserelBlocks(OutputSection *Dest, std::vector<Baserel> &V) {
+void Writer::addBaserelBlocks(std::vector<Baserel> &V) {
   const uint32_t Mask = ~uint32_t(PageSize - 1);
   uint32_t Page = V[0].RVA & Mask;
   size_t I = 0, J = 1;
   for (size_t E = V.size(); J < E; ++J) {
     uint32_t P = V[J].RVA & Mask;
     if (P == Page)
       continue;
-    Dest->addChunk(make<BaserelChunk>(Page, &V[I], &V[0] + J));
+    RelocSec->addChunk(make<BaserelChunk>(Page, &V[I], &V[0] + J));
     I = J;
     Page = P;
   }
   if (I == J)
     return;
-  Dest->addChunk(make<BaserelChunk>(Page, &V[I], &V[0] + J));
+  RelocSec->addChunk(make<BaserelChunk>(Page, &V[I], &V[0] + J));
 }