Vendor import of lld trunk r304460:vendor/lld/lld-trunk-r304460

https://llvm.org/svn/llvm-project/lld/trunk@304460

18 files changed, 379 insertions, 214 deletions

diff --git a/ELF/InputSection.cpp b/ELF/InputSection.cpp
index 466656efbf08..4af05c1a187b 100644
--- a/ELF/InputSection.cpp
+++ b/ELF/InputSection.cpp
@@ -139,21 +139,24 @@ uint64_t SectionBase::getOffset(uint64_t Offset) const {
     return Offset;
   case Merge:
     const MergeInputSection *MS = cast<MergeInputSection>(this);
-    if (MS->MergeSec)
-      return MS->MergeSec->OutSecOff + MS->getOffset(Offset);
+    if (InputSection *IS = MS->getParent())
+      return IS->OutSecOff + MS->getOffset(Offset);
     return MS->getOffset(Offset);
   }
   llvm_unreachable("invalid section kind");
 }
 
 OutputSection *SectionBase::getOutputSection() {
+  InputSection *Sec;
   if (auto *IS = dyn_cast<InputSection>(this))
-    return IS->OutSec;
-  if (auto *MS = dyn_cast<MergeInputSection>(this))
-    return MS->MergeSec ? MS->MergeSec->OutSec : nullptr;
-  if (auto *EH = dyn_cast<EhInputSection>(this))
-    return EH->EHSec->OutSec;
-  return cast<OutputSection>(this);
+    Sec = IS;
+  else if (auto *MS = dyn_cast<MergeInputSection>(this))
+    Sec = MS->getParent();
+  else if (auto *EH = dyn_cast<EhInputSection>(this))
+    Sec = EH->getParent();
+  else
+    return cast<OutputSection>(this);
+  return Sec ? Sec->getParent() : nullptr;
 }
 
 // Uncompress section contents. Note that this function is called
@@ -181,9 +184,15 @@ uint64_t SectionBase::getOffset(const DefinedRegular &Sym) const {
   return getOffset(Sym.Value);
 }
 
-InputSectionBase *InputSectionBase::getLinkOrderDep() const {
-  if ((Flags & SHF_LINK_ORDER) && Link != 0)
-    return File->getSections()[Link];
+InputSection *InputSectionBase::getLinkOrderDep() const {
+  if ((Flags & SHF_LINK_ORDER) && Link != 0) {
+    InputSectionBase *L = File->getSections()[Link];
+    if (auto *IS = dyn_cast<InputSection>(L))
+      return IS;
+    error(
+        "Merge and .eh_frame sections are not supported with SHF_LINK_ORDER " +
+        toString(L));
+  }
   return nullptr;
 }
 
@@ -295,6 +304,10 @@ bool InputSectionBase::classof(const SectionBase *S) {
   return S->kind() != Output;
 }
 
+OutputSection *InputSection::getParent() const {
+  return cast_or_null<OutputSection>(Parent);
+}
+
 void InputSection::copyShtGroup(uint8_t *Buf) {
   assert(this->Type == SHT_GROUP);
 
@@ -309,7 +322,8 @@ void InputSection::copyShtGroup(uint8_t *Buf) {
   ArrayRef<InputSectionBase *> Sections = this->File->getSections();
   for (uint32_t Val : From.slice(1)) {
     uint32_t Index = read32(&Val, Config->Endianness);
-    write32(To++, Sections[Index]->OutSec->SectionIndex, Config->Endianness);
+    write32(To++, Sections[Index]->getOutputSection()->SectionIndex,
+            Config->Endianness);
   }
 }
 
@@ -342,7 +356,7 @@ void InputSection::copyRelocations(uint8_t *Buf, ArrayRef<RelTy> Rels) {
 
     // Output section VA is zero for -r, so r_offset is an offset within the
     // section, but for --emit-relocs it is an virtual address.
-    P->r_offset = RelocatedSection->OutSec->Addr +
+    P->r_offset = RelocatedSection->getOutputSection()->Addr +
                   RelocatedSection->getOffset(Rel.r_offset);
     P->setSymbolAndType(InX::SymTab->getSymbolIndex(&Body), Type,
                         Config->IsMips64EL);
@@ -596,7 +610,7 @@ void InputSection::relocateNonAlloc(uint8_t *Buf, ArrayRef<RelTy> Rels) {
       return;
     }
 
-    uint64_t AddrLoc = this->OutSec->Addr + Offset;
+    uint64_t AddrLoc = getParent()->Addr + Offset;
     uint64_t SymVA = 0;
     if (!Sym.isTls() || Out::TlsPhdr)
       SymVA = SignExtend64<sizeof(typename ELFT::uint) * 8>(
@@ -729,6 +743,10 @@ EhInputSection::EhInputSection(elf::ObjectFile<ELFT> *F,
   this->Live = true;
 }
 
+SyntheticSection *EhInputSection::getParent() const {
+  return cast_or_null<SyntheticSection>(Parent);
+}
+
 bool EhInputSection::classof(const SectionBase *S) {
   return S->kind() == InputSectionBase::EHFrame;
 }
@@ -797,6 +815,10 @@ static size_t findNull(ArrayRef<uint8_t> A, size_t EntSize) {
   return StringRef::npos;
 }
 
+SyntheticSection *MergeInputSection::getParent() const {
+  return cast_or_null<SyntheticSection>(Parent);
+}
+
 // Split SHF_STRINGS section. Such section is a sequence of
 // null-terminated strings.
 void MergeInputSection::splitStrings(ArrayRef<uint8_t> Data, size_t EntSize) {
diff --git a/ELF/InputSection.h b/ELF/InputSection.h
index 4ef4328e8a5d..97ca2133f905 100644
--- a/ELF/InputSection.h
+++ b/ELF/InputSection.h
@@ -120,7 +120,12 @@ public:
                    uint64_t Entsize, uint32_t Link, uint32_t Info,
                    uint32_t Alignment, ArrayRef<uint8_t> Data, StringRef Name,
                    Kind SectionKind);
-  OutputSection *OutSec = nullptr;
+
+  // Input sections are part of an output section. Special sections
+  // like .eh_frame and merge sections are first combined into a
+  // synthetic section that is then added to an output section. In all
+  // cases this points one level up.
+  SectionBase *Parent = nullptr;
 
   // Relocations that refer to this section.
   const void *FirstRelocation = nullptr;
@@ -158,7 +163,7 @@ public:
     return getFile<ELFT>()->getObj();
   }
 
-  InputSectionBase *getLinkOrderDep() const;
+  InputSection *getLinkOrderDep() const;
 
   void uncompress();
 
@@ -237,10 +242,7 @@ public:
   SectionPiece *getSectionPiece(uint64_t Offset);
   const SectionPiece *getSectionPiece(uint64_t Offset) const;
 
-  // MergeInputSections are aggregated to a synthetic input sections,
-  // and then added to an OutputSection. This pointer points to a
-  // synthetic MergeSyntheticSection which this section belongs to.
-  MergeSyntheticSection *MergeSec = nullptr;
+  SyntheticSection *getParent() const;
 
 private:
   void splitStrings(ArrayRef<uint8_t> A, size_t Size);
@@ -280,7 +282,8 @@ public:
   // Splittable sections are handled as a sequence of data
   // rather than a single large blob of data.
   std::vector<EhSectionPiece> Pieces;
-  SyntheticSection *EHSec = nullptr;
+
+  SyntheticSection *getParent() const;
 };
 
 // This is a section that is added directly to an output section
@@ -299,6 +302,8 @@ public:
   // beginning of the output section.
   template <class ELFT> void writeTo(uint8_t *Buf);
 
+  OutputSection *getParent() const;
+
   // The offset from beginning of the output sections this section was assigned
   // to. The writer sets a value.
   uint64_t OutSecOff = 0;
diff --git a/ELF/LinkerScript.cpp b/ELF/LinkerScript.cpp
index 99c464e3714c..75df2cd4bd5c 100644
--- a/ELF/LinkerScript.cpp
+++ b/ELF/LinkerScript.cpp
@@ -26,6 +26,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Casting.h"
+#include "llvm/Support/Compression.h"
 #include "llvm/Support/ELF.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -51,9 +52,8 @@ LinkerScript *elf::Script;
 
 uint64_t ExprValue::getValue() const {
   if (Sec) {
-    if (Sec->getOutputSection())
-      return alignTo(Sec->getOffset(Val) + Sec->getOutputSection()->Addr,
-                     Alignment);
+    if (OutputSection *OS = Sec->getOutputSection())
+      return alignTo(Sec->getOffset(Val) + OS->Addr, Alignment);
     error("unable to evaluate expression: input section " + Sec->Name +
           " has no output section assigned");
   }
@@ -85,29 +85,28 @@ template <class ELFT> static SymbolBody *addRegular(SymbolAssignment *Cmd) {
   return Sym->body();
 }
 
-OutputSection *LinkerScript::getOutputSection(const Twine &Loc,
-                                              StringRef Name) {
-  for (OutputSection *Sec : *OutputSections)
-    if (Sec->Name == Name)
-      return Sec;
-
-  static OutputSection Dummy("", 0, 0);
-  if (ErrorOnMissingSection)
-    error(Loc + ": undefined section " + Name);
-  return &Dummy;
+OutputSectionCommand *
+LinkerScript::createOutputSectionCommand(StringRef Name, StringRef Location) {
+  OutputSectionCommand *&CmdRef = NameToOutputSectionCommand[Name];
+  OutputSectionCommand *Cmd;
+  if (CmdRef && CmdRef->Location.empty()) {
+    // There was a forward reference.
+    Cmd = CmdRef;
+  } else {
+    Cmd = make<OutputSectionCommand>(Name);
+    if (!CmdRef)
+      CmdRef = Cmd;
+  }
+  Cmd->Location = Location;
+  return Cmd;
 }
 
-// This function is essentially the same as getOutputSection(Name)->Size,
-// but it won't print out an error message if a given section is not found.
-//
-// Linker script does not create an output section if its content is empty.
-// We want to allow SIZEOF(.foo) where .foo is a section which happened to
-// be empty. That is why this function is different from getOutputSection().
-uint64_t LinkerScript::getOutputSectionSize(StringRef Name) {
-  for (OutputSection *Sec : *OutputSections)
-    if (Sec->Name == Name)
-      return Sec->Size;
-  return 0;
+OutputSectionCommand *
+LinkerScript::getOrCreateOutputSectionCommand(StringRef Name) {
+  OutputSectionCommand *&CmdRef = NameToOutputSectionCommand[Name];
+  if (!CmdRef)
+    CmdRef = make<OutputSectionCommand>(Name);
+  return CmdRef;
 }
 
 void LinkerScript::setDot(Expr E, const Twine &Loc, bool InSec) {
@@ -291,11 +290,13 @@ LinkerScript::computeInputSections(const InputSectionDescription *Cmd) {
     size_t SizeBefore = Ret.size();
 
     for (InputSectionBase *Sec : InputSections) {
-      if (!isa<InputSection>(Sec))
+      if (Sec->Assigned)
         continue;
 
-      if (Sec->Assigned)
+      if (!Sec->Live) {
+        reportDiscarded(Sec);
         continue;
+      }
 
       // For -emit-relocs we have to ignore entries like
       //   .rela.dyn : { *(.rela.data) }
@@ -455,7 +456,7 @@ void LinkerScript::fabricateDefaultCommands() {
   // For each OutputSection that needs a VA fabricate an OutputSectionCommand
   // with an InputSectionDescription describing the InputSections
   for (OutputSection *Sec : *OutputSections) {
-    auto *OSCmd = make<OutputSectionCommand>(Sec->Name);
+    auto *OSCmd = createOutputSectionCommand(Sec->Name, "<internal>");
     OSCmd->Sec = Sec;
     SecToCommand[Sec] = OSCmd;
 
@@ -487,7 +488,7 @@ void LinkerScript::fabricateDefaultCommands() {
 // Add sections that didn't match any sections command.
 void LinkerScript::addOrphanSections(OutputSectionFactory &Factory) {
   for (InputSectionBase *S : InputSections) {
-    if (!S->Live || S->OutSec)
+    if (!S->Live || S->Parent)
       continue;
     StringRef Name = getOutputSectionName(S->Name);
     auto I = std::find_if(
@@ -590,7 +591,7 @@ void LinkerScript::process(BaseCommand &Base) {
   // It calculates and assigns the offsets for each section and also
   // updates the output section size.
   auto &Cmd = cast<InputSectionDescription>(Base);
-  for (InputSectionBase *Sec : Cmd.Sections) {
+  for (InputSection *Sec : Cmd.Sections) {
     // We tentatively added all synthetic sections at the beginning and removed
     // empty ones afterwards (because there is no way to know whether they were
     // going be empty or not other than actually running linker scripts.)
@@ -601,8 +602,8 @@ void LinkerScript::process(BaseCommand &Base) {
 
     if (!Sec->Live)
       continue;
-    assert(CurOutSec == Sec->OutSec);
-    output(cast<InputSection>(Sec));
+    assert(CurOutSec == Sec->getParent());
+    output(Sec);
   }
 }
 
@@ -842,7 +843,7 @@ void LinkerScript::placeOrphanSections() {
     // representations agree on which input sections to use.
     OutputSectionCommand *Cmd = getCmd(Sec);
     if (!Cmd) {
-      Cmd = make<OutputSectionCommand>(Name);
+      Cmd = createOutputSectionCommand(Name, "<internal>");
       Opt.Commands.insert(CmdIter, Cmd);
       ++CmdIndex;
 
@@ -919,9 +920,10 @@ void LinkerScript::synchronize() {
   }
 }
 
-static bool allocateHeaders(std::vector<PhdrEntry> &Phdrs,
-                            ArrayRef<OutputSection *> OutputSections,
-                            uint64_t Min) {
+static bool
+allocateHeaders(std::vector<PhdrEntry> &Phdrs,
+                ArrayRef<OutputSectionCommand *> OutputSectionCommands,
+                uint64_t Min) {
   auto FirstPTLoad =
       std::find_if(Phdrs.begin(), Phdrs.end(),
                    [](const PhdrEntry &E) { return E.p_type == PT_LOAD; });
@@ -938,16 +940,19 @@ static bool allocateHeaders(std::vector<PhdrEntry> &Phdrs,
 
   assert(FirstPTLoad->First == Out::ElfHeader);
   OutputSection *ActualFirst = nullptr;
-  for (OutputSection *Sec : OutputSections) {
+  for (OutputSectionCommand *Cmd : OutputSectionCommands) {
+    OutputSection *Sec = Cmd->Sec;
     if (Sec->FirstInPtLoad == Out::ElfHeader) {
       ActualFirst = Sec;
       break;
     }
   }
   if (ActualFirst) {
-    for (OutputSection *Sec : OutputSections)
+    for (OutputSectionCommand *Cmd : OutputSectionCommands) {
+      OutputSection *Sec = Cmd->Sec;
       if (Sec->FirstInPtLoad == Out::ElfHeader)
         Sec->FirstInPtLoad = ActualFirst;
+    }
     FirstPTLoad->First = ActualFirst;
   } else {
     Phdrs.erase(FirstPTLoad);
@@ -961,7 +966,9 @@ static bool allocateHeaders(std::vector<PhdrEntry> &Phdrs,
   return false;
 }
 
-void LinkerScript::assignAddresses(std::vector<PhdrEntry> &Phdrs) {
+void LinkerScript::assignAddresses(
+    std::vector<PhdrEntry> &Phdrs,
+    ArrayRef<OutputSectionCommand *> OutputSectionCommands) {
   // Assign addresses as instructed by linker script SECTIONS sub-commands.
   Dot = 0;
   ErrorOnMissingSection = true;
@@ -983,14 +990,15 @@ void LinkerScript::assignAddresses(std::vector<PhdrEntry> &Phdrs) {
   }
 
   uint64_t MinVA = std::numeric_limits<uint64_t>::max();
-  for (OutputSection *Sec : *OutputSections) {
+  for (OutputSectionCommand *Cmd : OutputSectionCommands) {
+    OutputSection *Sec = Cmd->Sec;
     if (Sec->Flags & SHF_ALLOC)
       MinVA = std::min<uint64_t>(MinVA, Sec->Addr);
     else
       Sec->Addr = 0;
   }
 
-  allocateHeaders(Phdrs, *OutputSections, MinVA);
+  allocateHeaders(Phdrs, OutputSectionCommands, MinVA);
 }
 
 // Creates program headers as instructed by PHDRS linker script command.
@@ -1068,6 +1076,33 @@ static void writeInt(uint8_t *Buf, uint64_t Data, uint64_t Size) {
     llvm_unreachable("unsupported Size argument");
 }
 
+// Compress section contents if this section contains debug info.
+template <class ELFT> void OutputSectionCommand::maybeCompress() {
+  typedef typename ELFT::Chdr Elf_Chdr;
+
+  // Compress only DWARF debug sections.
+  if (!Config->CompressDebugSections || (Sec->Flags & SHF_ALLOC) ||
+      !Name.startswith(".debug_"))
+    return;
+
+  // Create a section header.
+  Sec->ZDebugHeader.resize(sizeof(Elf_Chdr));
+  auto *Hdr = reinterpret_cast<Elf_Chdr *>(Sec->ZDebugHeader.data());
+  Hdr->ch_type = ELFCOMPRESS_ZLIB;
+  Hdr->ch_size = Sec->Size;
+  Hdr->ch_addralign = Sec->Alignment;
+
+  // Write section contents to a temporary buffer and compress it.
+  std::vector<uint8_t> Buf(Sec->Size);
+  writeTo<ELFT>(Buf.data());
+  if (Error E = zlib::compress(toStringRef(Buf), Sec->CompressedData))
+    fatal("compress failed: " + llvm::toString(std::move(E)));
+
+  // Update section headers.
+  Sec->Size = sizeof(Elf_Chdr) + Sec->CompressedData.size();
+  Sec->Flags |= SHF_COMPRESSED;
+}
+
 template <class ELFT> void OutputSectionCommand::writeTo(uint8_t *Buf) {
   Sec->Loc = Buf;
 
@@ -1084,7 +1119,12 @@ template <class ELFT> void OutputSectionCommand::writeTo(uint8_t *Buf) {
     return;
 
   // Write leading padding.
-  ArrayRef<InputSection *> Sections = Sec->Sections;
+  std::vector<InputSection *> Sections;
+  for (BaseCommand *Cmd : Commands)
+    if (auto *ISD = dyn_cast<InputSectionDescription>(Cmd))
+      for (InputSection *IS : ISD->Sections)
+        if (IS->Live)
+          Sections.push_back(IS);
   uint32_t Filler = getFiller();
   if (Filler)
     fill(Buf, Sections.empty() ? Sec->Size : Sections[0]->OutSecOff, Filler);
@@ -1161,3 +1201,8 @@ template void OutputSectionCommand::writeTo<ELF32LE>(uint8_t *Buf);
 template void OutputSectionCommand::writeTo<ELF32BE>(uint8_t *Buf);
 template void OutputSectionCommand::writeTo<ELF64LE>(uint8_t *Buf);
 template void OutputSectionCommand::writeTo<ELF64BE>(uint8_t *Buf);
+
+template void OutputSectionCommand::maybeCompress<ELF32LE>();
+template void OutputSectionCommand::maybeCompress<ELF32BE>();
+template void OutputSectionCommand::maybeCompress<ELF64LE>();
+template void OutputSectionCommand::maybeCompress<ELF64BE>();
diff --git a/ELF/LinkerScript.h b/ELF/LinkerScript.h
index 08f60f4517a7..a708ea7f61d5 100644
--- a/ELF/LinkerScript.h
+++ b/ELF/LinkerScript.h
@@ -137,6 +137,7 @@ struct OutputSectionCommand : BaseCommand {
   std::string MemoryRegionName;
 
   template <class ELFT> void writeTo(uint8_t *Buf);
+  template <class ELFT> void maybeCompress();
   uint32_t getFiller();
 };
 
@@ -221,6 +222,8 @@ struct ScriptConfiguration {
 
 class LinkerScript final {
   llvm::DenseMap<OutputSection *, OutputSectionCommand *> SecToCommand;
+  llvm::DenseMap<StringRef, OutputSectionCommand *> NameToOutputSectionCommand;
+
   void assignSymbol(SymbolAssignment *Cmd, bool InSec);
   void setDot(Expr E, const Twine &Loc, bool InSec);
 
@@ -241,7 +244,6 @@ class LinkerScript final {
   void process(BaseCommand &Base);
 
   OutputSection *Aether;
-  bool ErrorOnMissingSection = false;
 
   uint64_t Dot;
   uint64_t ThreadBssOffset = 0;
@@ -251,11 +253,14 @@ class LinkerScript final {
   MemoryRegion *CurMemRegion = nullptr;
 
 public:
+  bool ErrorOnMissingSection = false;
+  OutputSectionCommand *createOutputSectionCommand(StringRef Name,
+                                                   StringRef Location);
+  OutputSectionCommand *getOrCreateOutputSectionCommand(StringRef Name);
+
   OutputSectionCommand *getCmd(OutputSection *Sec) const;
   bool hasPhdrsCommands() { return !Opt.PhdrsCommands.empty(); }
   uint64_t getDot() { return Dot; }
-  OutputSection *getOutputSection(const Twine &Loc, StringRef S);
-  uint64_t getOutputSectionSize(StringRef S);
   void discard(ArrayRef<InputSectionBase *> V);
 
   ExprValue getSymbolValue(const Twine &Loc, StringRef S);
@@ -277,7 +282,8 @@ public:
   void placeOrphanSections();
   void processNonSectionCommands();
   void synchronize();
-  void assignAddresses(std::vector<PhdrEntry> &Phdrs);
+  void assignAddresses(std::vector<PhdrEntry> &Phdrs,
+                       ArrayRef<OutputSectionCommand *> OutputSectionCommands);
 
   void addSymbol(SymbolAssignment *Cmd);
   void processCommands(OutputSectionFactory &Factory);
diff --git a/ELF/MarkLive.cpp b/ELF/MarkLive.cpp
index ee499265886e..b77c84ff75a0 100644
--- a/ELF/MarkLive.cpp
+++ b/ELF/MarkLive.cpp
@@ -220,7 +220,8 @@ template <class ELFT> void elf::markLive() {
 
   auto MarkSymbol = [&](const SymbolBody *Sym) {
     if (auto *D = dyn_cast_or_null<DefinedRegular>(Sym))
-      Enqueue({cast<InputSectionBase>(D->Section), D->Value});
+      if (auto *IS = cast_or_null<InputSectionBase>(D->Section))
+        Enqueue({IS, D->Value});
   };
 
   // Add GC root symbols.
diff --git a/ELF/OutputSections.cpp b/ELF/OutputSections.cpp
index f117690c3828..4f8906a32081 100644
--- a/ELF/OutputSections.cpp
+++ b/ELF/OutputSections.cpp
@@ -16,7 +16,6 @@
 #include "SyntheticSections.h"
 #include "Target.h"
 #include "Threads.h"
-#include "llvm/Support/Compression.h"
 #include "llvm/Support/Dwarf.h"
 #include "llvm/Support/MD5.h"
 #include "llvm/Support/MathExtras.h"
@@ -76,46 +75,19 @@ static bool compareByFilePosition(InputSection *A, InputSection *B) {
   if (A->kind() == InputSectionBase::Synthetic ||
       B->kind() == InputSectionBase::Synthetic)
     return false;
-  auto *LA = cast<InputSection>(A->getLinkOrderDep());
-  auto *LB = cast<InputSection>(B->getLinkOrderDep());
-  OutputSection *AOut = LA->OutSec;
-  OutputSection *BOut = LB->OutSec;
+  InputSection *LA = A->getLinkOrderDep();
+  InputSection *LB = B->getLinkOrderDep();
+  OutputSection *AOut = LA->getParent();
+  OutputSection *BOut = LB->getParent();
   if (AOut != BOut)
     return AOut->SectionIndex < BOut->SectionIndex;
   return LA->OutSecOff < LB->OutSecOff;
 }
 
-// Compress section contents if this section contains debug info.
-template <class ELFT> void OutputSection::maybeCompress() {
-  typedef typename ELFT::Chdr Elf_Chdr;
-
-  // Compress only DWARF debug sections.
-  if (!Config->CompressDebugSections || (Flags & SHF_ALLOC) ||
-      !Name.startswith(".debug_"))
-    return;
-
-  // Create a section header.
-  ZDebugHeader.resize(sizeof(Elf_Chdr));
-  auto *Hdr = reinterpret_cast<Elf_Chdr *>(ZDebugHeader.data());
-  Hdr->ch_type = ELFCOMPRESS_ZLIB;
-  Hdr->ch_size = Size;
-  Hdr->ch_addralign = Alignment;
-
-  // Write section contents to a temporary buffer and compress it.
-  std::vector<uint8_t> Buf(Size);
-  Script->getCmd(this)->writeTo<ELFT>(Buf.data());
-  if (Error E = zlib::compress(toStringRef(Buf), CompressedData))
-    fatal("compress failed: " + llvm::toString(std::move(E)));
-
-  // Update section headers.
-  Size = sizeof(Elf_Chdr) + CompressedData.size();
-  Flags |= SHF_COMPRESSED;
-}
-
 template <class ELFT> static void finalizeShtGroup(OutputSection *Sec) {
   // sh_link field for SHT_GROUP sections should contain the section index of
   // the symbol table.
-  Sec->Link = InX::SymTab->OutSec->SectionIndex;
+  Sec->Link = InX::SymTab->getParent()->SectionIndex;
 
   // sh_info then contain index of an entry in symbol table section which
   // provides signature of the section group.
@@ -135,7 +107,7 @@ template <class ELFT> void OutputSection::finalize() {
     // need to translate the InputSection sh_link to the OutputSection sh_link,
     // all InputSections in the OutputSection have the same dependency.
     if (auto *D = this->Sections.front()->getLinkOrderDep())
-      this->Link = D->OutSec->SectionIndex;
+      this->Link = D->getParent()->SectionIndex;
   }
 
   uint32_t Type = this->Type;
@@ -151,11 +123,11 @@ template <class ELFT> void OutputSection::finalize() {
   if (isa<SyntheticSection>(First))
     return;
 
-  this->Link = InX::SymTab->OutSec->SectionIndex;
+  this->Link = InX::SymTab->getParent()->SectionIndex;
   // sh_info for SHT_REL[A] sections should contain the section header index of
   // the section to which the relocation applies.
   InputSectionBase *S = First->getRelocatedSection();
-  this->Info = S->OutSec->SectionIndex;
+  Info = S->getOutputSection()->SectionIndex;
 }
 
 static uint64_t updateOffset(uint64_t Off, InputSection *S) {
@@ -167,7 +139,7 @@ static uint64_t updateOffset(uint64_t Off, InputSection *S) {
 void OutputSection::addSection(InputSection *S) {
   assert(S->Live);
   Sections.push_back(S);
-  S->OutSec = this;
+  S->Parent = this;
   this->updateAlignment(S->Alignment);
 
   // The actual offsets will be computed by assignAddresses. For now, use
@@ -351,7 +323,7 @@ static bool canMergeToProgbits(unsigned Type) {
          Type == SHT_NOTE;
 }
 
-static void reportDiscarded(InputSectionBase *IS) {
+void elf::reportDiscarded(InputSectionBase *IS) {
   if (!Config->PrintGcSections)
     return;
   message("removing unused section from '" + IS->Name + "' in file '" +
@@ -437,8 +409,3 @@ template void OutputSection::finalize<ELF32LE>();
 template void OutputSection::finalize<ELF32BE>();
 template void OutputSection::finalize<ELF64LE>();
 template void OutputSection::finalize<ELF64BE>();
-
-template void OutputSection::maybeCompress<ELF32LE>();
-template void OutputSection::maybeCompress<ELF32BE>();
-template void OutputSection::maybeCompress<ELF64LE>();
-template void OutputSection::maybeCompress<ELF64BE>();
diff --git a/ELF/OutputSections.h b/ELF/OutputSections.h
index 08655a9ed67b..326348cd5a20 100644
--- a/ELF/OutputSections.h
+++ b/ELF/OutputSections.h
@@ -83,7 +83,6 @@ public:
   void sortInitFini();
   void sortCtorsDtors();
   template <class ELFT> void finalize();
-  template <class ELFT> void maybeCompress();
   void assignOffsets();
   std::vector<InputSection *> Sections;
 
@@ -149,6 +148,7 @@ private:
 };
 
 uint64_t getHeaderSize();
+void reportDiscarded(InputSectionBase *IS);
 
 } // namespace elf
 } // namespace lld
diff --git a/ELF/Relocations.cpp b/ELF/Relocations.cpp
index 5564ea246eeb..54cc6dd89d46 100644
--- a/ELF/Relocations.cpp
+++ b/ELF/Relocations.cpp
@@ -360,9 +360,9 @@ static bool isStaticLinkTimeConstant(RelExpr E, uint32_t Type,
   // These expressions always compute a constant
   if (isRelExprOneOf<R_SIZE, R_GOT_FROM_END, R_GOT_OFF, R_MIPS_GOT_LOCAL_PAGE,
                      R_MIPS_GOT_OFF, R_MIPS_GOT_OFF32, R_MIPS_GOT_GP_PC,
-                     R_MIPS_TLSGD, R_GOT_PAGE_PC, R_GOT_PC, R_PLT_PC,
-                     R_TLSGD_PC, R_TLSGD, R_PPC_PLT_OPD, R_TLSDESC_CALL,
-                     R_TLSDESC_PAGE, R_HINT>(E))
+                     R_MIPS_TLSGD, R_GOT_PAGE_PC, R_GOT_PC,
+                     R_GOTONLY_PC_FROM_END, R_PLT_PC, R_TLSGD_PC, R_TLSGD,
+                     R_PPC_PLT_OPD, R_TLSDESC_CALL, R_TLSDESC_PAGE, R_HINT>(E))
     return true;
 
   // These never do, except if the entire file is position dependent or if
@@ -1015,7 +1015,7 @@ ThunkSection *ThunkCreator::getISThunkSec(InputSection *IS, OutputSection *OS) {
   ThunkSection *TS = ThunkedSections.lookup(IS);
   if (TS)
     return TS;
-  auto *TOS = cast<OutputSection>(IS->OutSec);
+  auto *TOS = IS->getParent();
   TS = make<ThunkSection>(TOS, IS->OutSecOff);
   ThunkSections[TOS].push_back(TS);
   ThunkedSections[IS] = TS;
diff --git a/ELF/ScriptParser.cpp b/ELF/ScriptParser.cpp
index 4b77e35b9bae..02212fa8ba14 100644
--- a/ELF/ScriptParser.cpp
+++ b/ELF/ScriptParser.cpp
@@ -55,6 +55,7 @@ public:
 
 private:
   void addFile(StringRef Path);
+  OutputSection *checkSection(OutputSectionCommand *Cmd, StringRef Loccation);
 
   void readAsNeeded();
   void readEntry();
@@ -564,8 +565,8 @@ uint32_t ScriptParser::readFill() {
 
 OutputSectionCommand *
 ScriptParser::readOutputSectionDescription(StringRef OutSec) {
-  OutputSectionCommand *Cmd = make<OutputSectionCommand>(OutSec);
-  Cmd->Location = getCurrentLocation();
+  OutputSectionCommand *Cmd =
+      Script->createOutputSectionCommand(OutSec, getCurrentLocation());
 
   // Read an address expression.
   // https://sourceware.org/binutils/docs/ld/Output-Section-Address.html
@@ -819,6 +820,16 @@ StringRef ScriptParser::readParenLiteral() {
   return Tok;
 }
 
+OutputSection *ScriptParser::checkSection(OutputSectionCommand *Cmd,
+                                          StringRef Location) {
+  if (Cmd->Location.empty() && Script->ErrorOnMissingSection)
+    error(Location + ": undefined section " + Cmd->Name);
+  if (Cmd->Sec)
+    return Cmd->Sec;
+  static OutputSection Dummy("", 0, 0);
+  return &Dummy;
+}
+
 Expr ScriptParser::readPrimary() {
   if (peek() == "(")
     return readParenExpr();
@@ -847,9 +858,8 @@ Expr ScriptParser::readPrimary() {
   }
   if (Tok == "ADDR") {
     StringRef Name = readParenLiteral();
-    return [=]() -> ExprValue {
-      return {Script->getOutputSection(Location, Name), 0};
-    };
+    OutputSectionCommand *Cmd = Script->getOrCreateOutputSectionCommand(Name);
+    return [=]() -> ExprValue { return {checkSection(Cmd, Location), 0}; };
   }
   if (Tok == "ALIGN") {
     expect("(");
@@ -867,7 +877,8 @@ Expr ScriptParser::readPrimary() {
   }
   if (Tok == "ALIGNOF") {
     StringRef Name = readParenLiteral();
-    return [=] { return Script->getOutputSection(Location, Name)->Alignment; };
+    OutputSectionCommand *Cmd = Script->getOrCreateOutputSectionCommand(Name);
+    return [=] { return checkSection(Cmd, Location)->Alignment; };
   }
   if (Tok == "ASSERT")
     return readAssertExpr();
@@ -912,7 +923,8 @@ Expr ScriptParser::readPrimary() {
   }
   if (Tok == "LOADADDR") {
     StringRef Name = readParenLiteral();
-    return [=] { return Script->getOutputSection(Location, Name)->getLMA(); };
+    OutputSectionCommand *Cmd = Script->getOrCreateOutputSectionCommand(Name);
+    return [=] { return checkSection(Cmd, Location)->getLMA(); };
   }
   if (Tok == "ORIGIN") {
     StringRef Name = readParenLiteral();
@@ -930,7 +942,11 @@ Expr ScriptParser::readPrimary() {
   }
   if (Tok == "SIZEOF") {
     StringRef Name = readParenLiteral();
-    return [=] { return Script->getOutputSectionSize(Name); };
+    OutputSectionCommand *Cmd = Script->getOrCreateOutputSectionCommand(Name);
+    // Linker script does not create an output section if its content is empty.
+    // We want to allow SIZEOF(.foo) where .foo is a section which happened to
+    // be empty.
+    return [=] { return Cmd->Sec ? Cmd->Sec->Size : 0; };
   }
   if (Tok == "SIZEOF_HEADERS")
     return [=] { return elf::getHeaderSize(); };
diff --git a/ELF/Symbols.cpp b/ELF/Symbols.cpp
index 7ce1f5354b1b..67e57d9c8f00 100644
--- a/ELF/Symbols.cpp
+++ b/ELF/Symbols.cpp
@@ -101,12 +101,12 @@ static uint64_t getSymVA(const SymbolBody &Body, int64_t &Addend) {
   case SymbolBody::DefinedCommonKind:
     if (!Config->DefineCommon)
       return 0;
-    return InX::Common->OutSec->Addr + InX::Common->OutSecOff +
+    return InX::Common->getParent()->Addr + InX::Common->OutSecOff +
            cast<DefinedCommon>(Body).Offset;
   case SymbolBody::SharedKind: {
     auto &SS = cast<SharedSymbol>(Body);
     if (SS.NeedsCopy)
-      return SS.CopyRelSec->OutSec->Addr + SS.CopyRelSec->OutSecOff +
+      return SS.CopyRelSec->getParent()->Addr + SS.CopyRelSec->OutSecOff +
              SS.CopyRelSecOff;
     if (SS.NeedsPltAddr)
       return Body.getPltVA();
@@ -207,13 +207,13 @@ OutputSection *SymbolBody::getOutputSection() const {
 
   if (auto *S = dyn_cast<SharedSymbol>(this)) {
     if (S->NeedsCopy)
-      return S->CopyRelSec->OutSec;
+      return S->CopyRelSec->getParent();
     return nullptr;
   }
 
   if (isa<DefinedCommon>(this)) {
     if (Config->DefineCommon)
-      return InX::Common->OutSec;
+      return InX::Common->getParent();
     return nullptr;
   }
 
diff --git a/ELF/SyntheticSections.cpp b/ELF/SyntheticSections.cpp
index d3db32613a8a..223fc9a0fd07 100644
--- a/ELF/SyntheticSections.cpp
+++ b/ELF/SyntheticSections.cpp
@@ -48,8 +48,8 @@ using namespace lld;
 using namespace lld::elf;
 
 uint64_t SyntheticSection::getVA() const {
-  if (this->OutSec)
-    return this->OutSec->Addr + this->OutSecOff;
+  if (OutputSection *Sec = getParent())
+    return Sec->Addr + OutSecOff;
   return 0;
 }
 
@@ -367,8 +367,8 @@ BssSection::BssSection(StringRef Name)
     : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_NOBITS, 0, Name) {}
 
 size_t BssSection::reserveSpace(uint64_t Size, uint32_t Alignment) {
-  if (OutSec)
-    OutSec->updateAlignment(Alignment);
+  if (OutputSection *Sec = getParent())
+    Sec->updateAlignment(Alignment);
   this->Size = alignTo(this->Size, Alignment) + Size;
   this->Alignment = std::max(this->Alignment, Alignment);
   return this->Size - Size;
@@ -494,7 +494,7 @@ void EhFrameSection<ELFT>::addSectionAux(EhInputSection *Sec,
 template <class ELFT>
 void EhFrameSection<ELFT>::addSection(InputSectionBase *C) {
   auto *Sec = cast<EhInputSection>(C);
-  Sec->EHSec = this;
+  Sec->Parent = this;
   updateAlignment(Sec->Alignment);
   Sections.push_back(Sec);
   for (auto *DS : Sec->DependentSections)
@@ -579,7 +579,7 @@ uint64_t EhFrameSection<ELFT>::getFdePc(uint8_t *Buf, size_t FdeOff,
   if ((Enc & 0x70) == DW_EH_PE_absptr)
     return Addr;
   if ((Enc & 0x70) == DW_EH_PE_pcrel)
-    return Addr + this->OutSec->Addr + Off;
+    return Addr + getParent()->Addr + Off;
   fatal("unknown FDE size relative encoding");
 }
 
@@ -610,7 +610,7 @@ template <class ELFT> void EhFrameSection<ELFT>::writeTo(uint8_t *Buf) {
       uint8_t Enc = getFdeEncoding<ELFT>(Cie->Piece);
       for (SectionPiece *Fde : Cie->FdePieces) {
         uint64_t Pc = getFdePc(Buf, Fde->OutputOff, Enc);
-        uint64_t FdeVA = this->OutSec->Addr + Fde->OutputOff;
+        uint64_t FdeVA = getParent()->Addr + Fde->OutputOff;
         In<ELFT>::EhFrameHdr->addFde(Pc, FdeVA);
       }
     }
@@ -698,8 +698,7 @@ void MipsGotSection::addEntry(SymbolBody &Sym, int64_t Addend, RelExpr Expr) {
     // sections referenced by GOT relocations. Then later in the `finalize`
     // method calculate number of "pages" required to cover all saved output
     // section and allocate appropriate number of GOT entries.
-    auto *DefSym = cast<DefinedRegular>(&Sym);
-    PageIndexMap.insert({DefSym->Section->getOutputSection(), 0});
+    PageIndexMap.insert({Sym.getOutputSection(), 0});
     return;
   }
   if (Sym.isTls()) {
@@ -766,8 +765,7 @@ static uint64_t getMipsPageCount(uint64_t Size) {
 
 uint64_t MipsGotSection::getPageEntryOffset(const SymbolBody &B,
                                             int64_t Addend) const {
-  const OutputSection *OutSec =
-      cast<DefinedRegular>(&B)->Section->getOutputSection();
+  const OutputSection *OutSec = B.getOutputSection();
   uint64_t SecAddr = getMipsPageAddr(OutSec->Addr);
   uint64_t SymAddr = getMipsPageAddr(B.getVA(Addend));
   uint64_t Index = PageIndexMap.lookup(OutSec) + (SymAddr - SecAddr) / 0xffff;
@@ -1071,11 +1069,11 @@ template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
   if (this->Size)
     return; // Already finalized.
 
-  this->Link = InX::DynStrTab->OutSec->SectionIndex;
-  if (In<ELFT>::RelaDyn->OutSec->Size > 0) {
+  this->Link = InX::DynStrTab->getParent()->SectionIndex;
+  if (In<ELFT>::RelaDyn->getParent()->Size > 0) {
     bool IsRela = Config->IsRela;
     add({IsRela ? DT_RELA : DT_REL, In<ELFT>::RelaDyn});
-    add({IsRela ? DT_RELASZ : DT_RELSZ, In<ELFT>::RelaDyn->OutSec->Size});
+    add({IsRela ? DT_RELASZ : DT_RELSZ, In<ELFT>::RelaDyn->getParent()->Size});
     add({IsRela ? DT_RELAENT : DT_RELENT,
          uint64_t(IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel))});
 
@@ -1088,9 +1086,9 @@ template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
         add({IsRela ? DT_RELACOUNT : DT_RELCOUNT, NumRelativeRels});
     }
   }
-  if (In<ELFT>::RelaPlt->OutSec->Size > 0) {
+  if (In<ELFT>::RelaPlt->getParent()->Size > 0) {
     add({DT_JMPREL, In<ELFT>::RelaPlt});
-    add({DT_PLTRELSZ, In<ELFT>::RelaPlt->OutSec->Size});
+    add({DT_PLTRELSZ, In<ELFT>::RelaPlt->getParent()->Size});
     add({Config->EMachine == EM_MIPS ? DT_MIPS_PLTGOT : DT_PLTGOT,
          InX::GotPlt});
     add({DT_PLTREL, uint64_t(Config->IsRela ? DT_RELA : DT_REL)});
@@ -1152,7 +1150,7 @@ template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
       add({DT_MIPS_RLD_MAP, InX::MipsRldMap});
   }
 
-  this->OutSec->Link = this->Link;
+  getParent()->Link = this->Link;
 
   // +1 for DT_NULL
   this->Size = (Entries.size() + 1) * this->Entsize;
@@ -1168,7 +1166,7 @@ template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *Buf) {
       P->d_un.d_ptr = E.OutSec->Addr;
       break;
     case Entry::InSecAddr:
-      P->d_un.d_ptr = E.InSec->OutSec->Addr + E.InSec->OutSecOff;
+      P->d_un.d_ptr = E.InSec->getParent()->Addr + E.InSec->OutSecOff;
       break;
     case Entry::SecSize:
       P->d_un.d_val = E.OutSec->Size;
@@ -1185,7 +1183,7 @@ template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *Buf) {
 }
 
 uint64_t DynamicReloc::getOffset() const {
-  return InputSec->OutSec->Addr + InputSec->getOffset(OffsetInSec);
+  return InputSec->getOutputSection()->Addr + InputSec->getOffset(OffsetInSec);
 }
 
 int64_t DynamicReloc::getAddend() const {
@@ -1258,11 +1256,11 @@ template <class ELFT> unsigned RelocationSection<ELFT>::getRelocOffset() {
 }
 
 template <class ELFT> void RelocationSection<ELFT>::finalizeContents() {
-  this->Link = InX::DynSymTab ? InX::DynSymTab->OutSec->SectionIndex
-                              : InX::SymTab->OutSec->SectionIndex;
+  this->Link = InX::DynSymTab ? InX::DynSymTab->getParent()->SectionIndex
+                              : InX::SymTab->getParent()->SectionIndex;
 
   // Set required output section properties.
-  this->OutSec->Link = this->Link;
+  getParent()->Link = this->Link;
 }
 
 SymbolTableBaseSection::SymbolTableBaseSection(StringTableSection &StrTabSec)
@@ -1293,14 +1291,14 @@ static bool sortMipsSymbols(const SymbolTableEntry &L,
 // function. (For .dynsym, we don't do that because symbols for
 // dynamic linking are inherently all globals.)
 void SymbolTableBaseSection::finalizeContents() {
-  this->OutSec->Link = StrTabSec.OutSec->SectionIndex;
+  getParent()->Link = StrTabSec.getParent()->SectionIndex;
 
   // If it is a .dynsym, there should be no local symbols, but we need
   // to do a few things for the dynamic linker.
   if (this->Type == SHT_DYNSYM) {
     // Section's Info field has the index of the first non-local symbol.
     // Because the first symbol entry is a null entry, 1 is the first.
-    this->OutSec->Info = 1;
+    getParent()->Info = 1;
 
     if (InX::GnuHashTab) {
       // NB: It also sorts Symbols to meet the GNU hash table requirements.
@@ -1326,7 +1324,7 @@ void SymbolTableBaseSection::postThunkContents() {
                S.Symbol->symbol()->computeBinding() == STB_LOCAL;
       });
   size_t NumLocals = It - Symbols.begin();
-  this->OutSec->Info = NumLocals + 1;
+  getParent()->Info = NumLocals + 1;
 }
 
 void SymbolTableBaseSection::addSymbol(SymbolBody *B) {
@@ -1344,8 +1342,7 @@ size_t SymbolTableBaseSection::getSymbolIndex(SymbolBody *Body) {
     // This is used for -r, so we have to handle multiple section
     // symbols being combined.
     if (Body->Type == STT_SECTION && E.Symbol->Type == STT_SECTION)
-      return cast<DefinedRegular>(Body)->Section->getOutputSection() ==
-             cast<DefinedRegular>(E.Symbol)->Section->getOutputSection();
+      return Body->getOutputSection() == E.Symbol->getOutputSection();
     return false;
   });
   if (I == Symbols.end())
@@ -1456,7 +1453,7 @@ GnuHashTableSection::GnuHashTableSection()
 }
 
 void GnuHashTableSection::finalizeContents() {
-  this->OutSec->Link = InX::DynSymTab->OutSec->SectionIndex;
+  getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
 
   // Computes bloom filter size in word size. We want to allocate 8
   // bits for each symbol. It must be a power of two.
@@ -1590,7 +1587,7 @@ HashTableSection<ELFT>::HashTableSection()
 }
 
 template <class ELFT> void HashTableSection<ELFT>::finalizeContents() {
-  this->OutSec->Link = InX::DynSymTab->OutSec->SectionIndex;
+  getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
 
   unsigned NumEntries = 2;                            // nbucket and nchain.
   NumEntries += InX::DynSymTab->getNumSymbols(); // The chain entries.
@@ -1801,7 +1798,7 @@ void GdbIndexSection::finalizeContents() {
 
   for (InputSectionBase *S : InputSections)
     if (InputSection *IS = dyn_cast<InputSection>(S))
-      if (IS->OutSec && IS->Name == ".debug_info")
+      if (IS->getParent() && IS->Name == ".debug_info")
         readDwarf(IS);
 
   SymbolTable.finalizeContents();
@@ -1846,7 +1843,7 @@ void GdbIndexSection::writeTo(uint8_t *Buf) {
 
   // Write the address area.
   for (AddressEntry &E : AddressArea) {
-    uint64_t BaseAddr = E.Section->OutSec->Addr + E.Section->getOffset(0);
+    uint64_t BaseAddr = E.Section->getParent()->Addr + E.Section->getOffset(0);
     write64le(Buf, BaseAddr + E.LowAddress);
     write64le(Buf + 8, BaseAddr + E.HighAddress);
     write32le(Buf + 16, E.CuIndex);
@@ -1906,7 +1903,7 @@ template <class ELFT> void EhFrameHeader<ELFT>::writeTo(uint8_t *Buf) {
   Buf[1] = DW_EH_PE_pcrel | DW_EH_PE_sdata4;
   Buf[2] = DW_EH_PE_udata4;
   Buf[3] = DW_EH_PE_datarel | DW_EH_PE_sdata4;
-  write32<E>(Buf + 4, In<ELFT>::EhFrame->OutSec->Addr - this->getVA() - 4);
+  write32<E>(Buf + 4, In<ELFT>::EhFrame->getParent()->Addr - this->getVA() - 4);
   write32<E>(Buf + 8, Fdes.size());
   Buf += 12;
 
@@ -1948,12 +1945,12 @@ template <class ELFT> void VersionDefinitionSection<ELFT>::finalizeContents() {
   for (VersionDefinition &V : Config->VersionDefinitions)
     V.NameOff = InX::DynStrTab->addString(V.Name);
 
-  this->OutSec->Link = InX::DynStrTab->OutSec->SectionIndex;
+  getParent()->Link = InX::DynStrTab->getParent()->SectionIndex;
 
   // sh_info should be set to the number of definitions. This fact is missed in
   // documentation, but confirmed by binutils community:
   // https://sourceware.org/ml/binutils/2014-11/msg00355.html
-  this->OutSec->Info = getVerDefNum();
+  getParent()->Info = getVerDefNum();
 }
 
 template <class ELFT>
@@ -2001,7 +1998,7 @@ VersionTableSection<ELFT>::VersionTableSection()
 template <class ELFT> void VersionTableSection<ELFT>::finalizeContents() {
   // At the moment of june 2016 GNU docs does not mention that sh_link field
   // should be set, but Sun docs do. Also readelf relies on this field.
-  this->OutSec->Link = InX::DynSymTab->OutSec->SectionIndex;
+  getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
 }
 
 template <class ELFT> size_t VersionTableSection<ELFT>::getSize() const {
@@ -2093,8 +2090,8 @@ template <class ELFT> void VersionNeedSection<ELFT>::writeTo(uint8_t *Buf) {
 }
 
 template <class ELFT> void VersionNeedSection<ELFT>::finalizeContents() {
-  this->OutSec->Link = InX::DynStrTab->OutSec->SectionIndex;
-  this->OutSec->Info = Needed.size();
+  getParent()->Link = InX::DynStrTab->getParent()->SectionIndex;
+  getParent()->Info = Needed.size();
 }
 
 template <class ELFT> size_t VersionNeedSection<ELFT>::getSize() const {
@@ -2115,7 +2112,7 @@ MergeSyntheticSection::MergeSyntheticSection(StringRef Name, uint32_t Type,
 
 void MergeSyntheticSection::addSection(MergeInputSection *MS) {
   assert(!Finalized);
-  MS->MergeSec = this;
+  MS->Parent = this;
   Sections.push_back(MS);
 }
 
@@ -2186,13 +2183,23 @@ ARMExidxSentinelSection::ARMExidxSentinelSection()
 // This section will have been sorted last in the .ARM.exidx table.
 // This table entry will have the form:
 // | PREL31 upper bound of code that has exception tables | EXIDX_CANTUNWIND |
+// The sentinel must have the PREL31 value of an address higher than any
+// address described by any other table entry.
 void ARMExidxSentinelSection::writeTo(uint8_t *Buf) {
-  // Get the InputSection before us, we are by definition last
-  auto RI = this->OutSec->Sections.rbegin();
-  InputSection *LE = *(++RI);
-  InputSection *LC = cast<InputSection>(LE->getLinkOrderDep());
-  uint64_t S = LC->OutSec->Addr + LC->getOffset(LC->getSize());
-  uint64_t P = this->getVA();
+  // The Sections are sorted in order of ascending PREL31 address with the
+  // sentinel last. We need to find the InputSection that precedes the
+  // sentinel. By construction the Sentinel is in the last
+  // InputSectionDescription as the InputSection that precedes it.
+  OutputSectionCommand *C = Script->getCmd(getParent());
+  auto ISD = std::find_if(C->Commands.rbegin(), C->Commands.rend(),
+                          [](const BaseCommand *Base) {
+                            return isa<InputSectionDescription>(Base);
+                          });
+  auto L = cast<InputSectionDescription>(*ISD);
+  InputSection *Highest = L->Sections[L->Sections.size() - 2];
+  InputSection *LS = Highest->getLinkOrderDep();
+  uint64_t S = LS->getParent()->Addr + LS->getOffset(LS->getSize());
+  uint64_t P = getVA();
   Target->relocateOne(Buf, R_ARM_PREL31, S - P);
   write32le(Buf + 4, 0x1);
 }
@@ -2200,7 +2207,7 @@ void ARMExidxSentinelSection::writeTo(uint8_t *Buf) {
 ThunkSection::ThunkSection(OutputSection *OS, uint64_t Off)
     : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS,
                        Config->Wordsize, ".text.thunk") {
-  this->OutSec = OS;
+  this->Parent = OS;
   this->OutSecOff = Off;
 }
 
diff --git a/ELF/SyntheticSections.h b/ELF/SyntheticSections.h
index 61cc03de222e..b47d2fab24ec 100644
--- a/ELF/SyntheticSections.h
+++ b/ELF/SyntheticSections.h
@@ -53,7 +53,7 @@ public:
   virtual bool empty() const { return false; }
   uint64_t getVA() const;
 
-  static bool classof(const InputSectionBase *D) {
+  static bool classof(const SectionBase *D) {
     return D->kind() == InputSectionBase::Synthetic;
   }
 };
diff --git a/ELF/Target.cpp b/ELF/Target.cpp
index cf7d912ad829..b6c6e7089365 100644
--- a/ELF/Target.cpp
+++ b/ELF/Target.cpp
@@ -62,10 +62,10 @@ static void or32be(uint8_t *P, int32_t V) { write32be(P, read32be(P) | V); }
 template <class ELFT> static std::string getErrorLoc(const uint8_t *Loc) {
   for (InputSectionBase *D : InputSections) {
     auto *IS = dyn_cast_or_null<InputSection>(D);
-    if (!IS || !IS->OutSec)
+    if (!IS || !IS->getParent())
       continue;
 
-    uint8_t *ISLoc = cast<OutputSection>(IS->OutSec)->Loc + IS->OutSecOff;
+    uint8_t *ISLoc = IS->getParent()->Loc + IS->OutSecOff;
     if (ISLoc <= Loc && Loc < ISLoc + IS->getSize())
       return IS->template getLocation<ELFT>(Loc - ISLoc) + ": ";
   }
diff --git a/ELF/Writer.cpp b/ELF/Writer.cpp
index 77d6412f80ad..258d5e26ef7f 100644
--- a/ELF/Writer.cpp
+++ b/ELF/Writer.cpp
@@ -261,23 +261,26 @@ template <class ELFT> void Writer<ELFT>::run() {
     if (!Config->Relocatable)
       fixSectionAlignments();
     Script->fabricateDefaultCommands();
+  } else {
+    Script->synchronize();
   }
 
   for (BaseCommand *Base : Script->Opt.Commands)
     if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base))
       OutputSectionCommands.push_back(Cmd);
 
+  clearOutputSections();
   // If -compressed-debug-sections is specified, we need to compress
   // .debug_* sections. Do it right now because it changes the size of
   // output sections.
-  parallelForEach(OutputSections.begin(), OutputSections.end(),
-                  [](OutputSection *S) { S->maybeCompress<ELFT>(); });
+  parallelForEach(
+      OutputSectionCommands.begin(), OutputSectionCommands.end(),
+      [](OutputSectionCommand *Cmd) { Cmd->maybeCompress<ELFT>(); });
 
   if (Config->Relocatable) {
     assignFileOffsets();
   } else {
-    Script->synchronize();
-    Script->assignAddresses(Phdrs);
+    Script->assignAddresses(Phdrs, OutputSectionCommands);
 
     // Remove empty PT_LOAD to avoid causing the dynamic linker to try to mmap a
     // 0 sized region. This has to be done late since only after assignAddresses
@@ -300,13 +303,13 @@ template <class ELFT> void Writer<ELFT>::run() {
   openFile();
   if (ErrorCount)
     return;
+
   if (!Config->OFormatBinary) {
     writeHeader();
     writeSections();
   } else {
     writeSectionsBinary();
   }
-  clearOutputSections();
 
   // Backfill .note.gnu.build-id section content. This is done at last
   // because the content is usually a hash value of the entire output file.
@@ -613,27 +616,27 @@ bool elf::isRelroSection(const OutputSection *Sec) {
   // .got contains pointers to external symbols. They are resolved by
   // the dynamic linker when a module is loaded into memory, and after
   // that they are not expected to change. So, it can be in RELRO.
-  if (InX::Got && Sec == InX::Got->OutSec)
+  if (InX::Got && Sec == InX::Got->getParent())
     return true;
 
   // .got.plt contains pointers to external function symbols. They are
   // by default resolved lazily, so we usually cannot put it into RELRO.
   // However, if "-z now" is given, the lazy symbol resolution is
   // disabled, which enables us to put it into RELRO.
-  if (Sec == InX::GotPlt->OutSec)
+  if (Sec == InX::GotPlt->getParent())
     return Config->ZNow;
 
   // .dynamic section contains data for the dynamic linker, and
   // there's no need to write to it at runtime, so it's better to put
   // it into RELRO.
-  if (Sec == InX::Dynamic->OutSec)
+  if (Sec == InX::Dynamic->getParent())
     return true;
 
   // .bss.rel.ro is used for copy relocations for read-only symbols.
   // Since the dynamic linker needs to process copy relocations, the
   // section cannot be read-only, but once initialized, they shouldn't
   // change.
-  if (Sec == InX::BssRelRo->OutSec)
+  if (Sec == InX::BssRelRo->getParent())
     return true;
 
   // Sections with some special names are put into RELRO. This is a
@@ -1112,9 +1115,9 @@ template <class ELFT> void Writer<ELFT>::sortSections() {
 static void applySynthetic(const std::vector<SyntheticSection *> &Sections,
                            std::function<void(SyntheticSection *)> Fn) {
   for (SyntheticSection *SS : Sections)
-    if (SS && SS->OutSec && !SS->empty()) {
+    if (SS && SS->getParent() && !SS->empty()) {
       Fn(SS);
-      SS->OutSec->assignOffsets();
+      SS->getParent()->assignOffsets();
     }
 }
 
@@ -1130,16 +1133,15 @@ static void removeUnusedSyntheticSections(std::vector<OutputSection *> &V) {
     SyntheticSection *SS = dyn_cast<SyntheticSection>(S);
     if (!SS)
       return;
-    if (!SS->empty() || !SS->OutSec)
+    OutputSection *OS = SS->getParent();
+    if (!SS->empty() || !OS)
       continue;
-
-    SS->OutSec->Sections.erase(std::find(SS->OutSec->Sections.begin(),
-                                         SS->OutSec->Sections.end(), SS));
+    OS->Sections.erase(std::find(OS->Sections.begin(), OS->Sections.end(), SS));
     SS->Live = false;
     // If there are no other sections in the output section, remove it from the
     // output.
-    if (SS->OutSec->Sections.empty())
-      V.erase(std::find(V.begin(), V.end(), SS->OutSec));
+    if (OS->Sections.empty())
+      V.erase(std::find(V.begin(), V.end(), OS));
   }
 }
 
@@ -1427,8 +1429,8 @@ template <class ELFT> std::vector<PhdrEntry> Writer<ELFT>::createPhdrs() {
 
   // Add an entry for .dynamic.
   if (InX::DynSymTab)
-    AddHdr(PT_DYNAMIC, InX::Dynamic->OutSec->getPhdrFlags())
-        ->add(InX::Dynamic->OutSec);
+    AddHdr(PT_DYNAMIC, InX::Dynamic->getParent()->getPhdrFlags())
+        ->add(InX::Dynamic->getParent());
 
   // PT_GNU_RELRO includes all sections that should be marked as
   // read-only by dynamic linker after proccessing relocations.
@@ -1441,9 +1443,9 @@ template <class ELFT> std::vector<PhdrEntry> Writer<ELFT>::createPhdrs() {
 
   // PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
   if (!In<ELFT>::EhFrame->empty() && In<ELFT>::EhFrameHdr &&
-      In<ELFT>::EhFrame->OutSec && In<ELFT>::EhFrameHdr->OutSec)
-    AddHdr(PT_GNU_EH_FRAME, In<ELFT>::EhFrameHdr->OutSec->getPhdrFlags())
-        ->add(In<ELFT>::EhFrameHdr->OutSec);
+      In<ELFT>::EhFrame->getParent() && In<ELFT>::EhFrameHdr->getParent())
+    AddHdr(PT_GNU_EH_FRAME, In<ELFT>::EhFrameHdr->getParent()->getPhdrFlags())
+        ->add(In<ELFT>::EhFrameHdr->getParent());
 
   // PT_OPENBSD_RANDOMIZE is an OpenBSD-specific feature. That makes
   // the dynamic linker fill the segment with random data.
@@ -1556,9 +1558,11 @@ static uint64_t setOffset(OutputSection *Sec, uint64_t Off) {
 
 template <class ELFT> void Writer<ELFT>::assignFileOffsetsBinary() {
   uint64_t Off = 0;
-  for (OutputSection *Sec : OutputSections)
+  for (OutputSectionCommand *Cmd : OutputSectionCommands) {
+    OutputSection *Sec = Cmd->Sec;
     if (Sec->Flags & SHF_ALLOC)
       Off = setOffset(Sec, Off);
+  }
   FileSize = alignTo(Off, Config->Wordsize);
 }
 
@@ -1568,11 +1572,12 @@ template <class ELFT> void Writer<ELFT>::assignFileOffsets() {
   Off = setOffset(Out::ElfHeader, Off);
   Off = setOffset(Out::ProgramHeaders, Off);
 
-  for (OutputSection *Sec : OutputSections)
-    Off = setOffset(Sec, Off);
+  for (OutputSectionCommand *Cmd : OutputSectionCommands)
+    Off = setOffset(Cmd->Sec, Off);
 
   SectionHeaderOff = alignTo(Off, Config->Wordsize);
-  FileSize = SectionHeaderOff + (OutputSections.size() + 1) * sizeof(Elf_Shdr);
+  FileSize =
+      SectionHeaderOff + (OutputSectionCommands.size() + 1) * sizeof(Elf_Shdr);
 }
 
 // Finalize the program headers. We call this function after we assign
@@ -1695,16 +1700,15 @@ template <class ELFT> void Writer<ELFT>::fixPredefinedSymbols() {
 
   // Setup MIPS _gp_disp/__gnu_local_gp symbols which should
   // be equal to the _gp symbol's value.
-  if (Config->EMachine == EM_MIPS) {
-    if (!ElfSym::MipsGp->Value) {
-      // Find GP-relative section with the lowest address
-      // and use this address to calculate default _gp value.
-      uint64_t Gp = -1;
-      for (const OutputSection *OS : OutputSections)
-        if ((OS->Flags & SHF_MIPS_GPREL) && OS->Addr < Gp)
-          Gp = OS->Addr;
-      if (Gp != (uint64_t)-1)
-        ElfSym::MipsGp->Value = Gp + 0x7ff0;
+  if (Config->EMachine == EM_MIPS && !ElfSym::MipsGp->Value) {
+    // Find GP-relative section with the lowest address
+    // and use this address to calculate default _gp value.
+    for (const OutputSectionCommand *Cmd : OutputSectionCommands) {
+      OutputSection *OS = Cmd->Sec;
+      if (OS->Flags & SHF_MIPS_GPREL) {
+        ElfSym::MipsGp->Value = OS->Addr + 0x7ff0;
+        break;
+      }
     }
   }
 }
@@ -1728,7 +1732,7 @@ template <class ELFT> void Writer<ELFT>::writeHeader() {
   EHdr->e_phnum = Phdrs.size();
   EHdr->e_shentsize = sizeof(Elf_Shdr);
   EHdr->e_shnum = OutputSectionCommands.size() + 1;
-  EHdr->e_shstrndx = InX::ShStrTab->OutSec->SectionIndex;
+  EHdr->e_shstrndx = InX::ShStrTab->getParent()->SectionIndex;
 
   if (Config->EMachine == EM_ARM)
     // We don't currently use any features incompatible with EF_ARM_EABI_VER5,
@@ -1804,7 +1808,7 @@ template <class ELFT> void Writer<ELFT>::writeSections() {
 
   OutputSection *EhFrameHdr =
       (In<ELFT>::EhFrameHdr && !In<ELFT>::EhFrameHdr->empty())
-          ? In<ELFT>::EhFrameHdr->OutSec
+          ? In<ELFT>::EhFrameHdr->getParent()
           : nullptr;
 
   // In -r or -emit-relocs mode, write the relocation sections first as in
@@ -1832,7 +1836,7 @@ template <class ELFT> void Writer<ELFT>::writeSections() {
 }
 
 template <class ELFT> void Writer<ELFT>::writeBuildId() {
-  if (!InX::BuildId || !InX::BuildId->OutSec)
+  if (!InX::BuildId || !InX::BuildId->getParent())
     return;
 
   // Compute a hash of all sections of the output file.
diff --git a/test/ELF/gc-absolute.s b/test/ELF/gc-absolute.s
new file mode 100644
index 000000000000..29e671678ee7
--- /dev/null
+++ b/test/ELF/gc-absolute.s
@@ -0,0 +1,7 @@
+# REQUIRES: x86
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: ld.lld %t -o %t2 -shared --gc-sections
+
+.global foo
+foo = 0x123
diff --git a/test/ELF/i386-gotpc-dynamic.s b/test/ELF/i386-gotpc-dynamic.s
new file mode 100644
index 000000000000..da8a607d5753
--- /dev/null
+++ b/test/ELF/i386-gotpc-dynamic.s
@@ -0,0 +1,32 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=i686-pc-linux %s -o %t.o
+# RUN: ld.lld %t.o -o %t.so -shared
+# RUN: llvm-readobj -s %t.so | FileCheck %s
+# RUN: llvm-objdump -d %t.so | FileCheck --check-prefix=DISASM %s
+
+# CHECK:       Section {
+# CHECK:        Index: 7
+# CHECK-NEXT:   Name: .got
+# CHECK-NEXT:   Type: SHT_PROGBITS
+# CHECK-NEXT:   Flags [
+# CHECK-NEXT:     SHF_ALLOC
+# CHECK-NEXT:     SHF_WRITE
+# CHECK-NEXT:   ]
+# CHECK-NEXT:   Address: 0x2030
+# CHECK-NEXT:   Offset:
+# CHECK-NEXT:   Size:
+# CHECK-NEXT:   Link:
+# CHECK-NEXT:   Info:
+# CHECK-NEXT:   AddressAlignment:
+# CHECK-NEXT:   EntrySize:
+# CHECK-NEXT: }
+
+## 0x1000 + 4144 = 0x2030
+# DISASM: 1000: {{.*}} movl $4144, %eax
+
+.section .foo,"ax",@progbits
+foo:
+ movl $bar@got-., %eax # R_386_GOTPC
+
+.local bar
+bar:
diff --git a/test/ELF/mips64-eh-abs-reloc.s b/test/ELF/mips64-eh-abs-reloc.s
new file mode 100644
index 000000000000..7bc500137992
--- /dev/null
+++ b/test/ELF/mips64-eh-abs-reloc.s
@@ -0,0 +1,38 @@
+# Having an R_MIPS_64 relocation in eh_frame would previously crash LLD
+# REQUIRES: mips
+# RUN: llvm-mc -filetype=obj -triple=mips64-unknown-freebsd %s -o %t.o
+# RUN: llvm-readobj -r %t.o | FileCheck %s -check-prefix OBJ
+# RUN: ld.lld --eh-frame-hdr -shared -z notext -o %t.so %t.o
+# RUN: llvm-readobj -r %t.so | FileCheck %s -check-prefix PIC-RELOCS
+
+# Linking this as a PIE executable would also previously crash
+# RUN: llvm-mc -filetype=obj -triple=mips64-unknown-freebsd %S/Inputs/archive2.s -o %t-foo.o
+# -pie needs -z notext because of the R_MIPS_64 relocation
+# RUN: ld.lld --eh-frame-hdr -Bdynamic -pie -z notext -o %t-pie-dynamic.exe %t.o %t-foo.o
+# RUN: llvm-readobj -r %t-pie-dynamic.exe | FileCheck %s -check-prefix PIC-RELOCS
+
+
+# OBJ:       Section ({{.*}}) .rela.text {
+# OBJ-NEXT:    0x0 R_MIPS_GPREL16/R_MIPS_SUB/R_MIPS_HI16 foo 0x0
+# OBJ-NEXT:  }
+# OBJ-NEXT:  Section ({{.*}}) .rela.eh_frame {
+# OBJ-NEXT:    0x1C R_MIPS_64/R_MIPS_NONE/R_MIPS_NONE .text 0x0
+# OBJ-NEXT:  }
+
+# PIC-RELOCS: Relocations [
+# PIC-RELOCS-NEXT:  Section (7) .rela.dyn {
+# PIC-RELOCS-NEXT:    {{0x.+}} R_MIPS_REL32/R_MIPS_64/R_MIPS_NONE - 0x10000
+# PIC-RELOCS-NEXT:  }
+# PIC-RELOCS-NEXT:]
+
+
+.globl foo
+
+bar:
+.cfi_startproc
+lui	$11, %hi(%neg(%gp_rel(foo)))
+.cfi_endproc
+
+.globl __start
+__start:
+b bar
diff --git a/test/ELF/section-metadata-err.s b/test/ELF/section-metadata-err.s
new file mode 100644
index 000000000000..f3b5842945cb
--- /dev/null
+++ b/test/ELF/section-metadata-err.s
@@ -0,0 +1,15 @@
+# REQUIRES: x86
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+# RUN: not ld.lld %t.o -o %t 2>&1 | FileCheck %s
+
+# CHECK: error: Merge and .eh_frame sections are not supported with SHF_LINK_ORDER {{.*}}section-metadata-err.s.tmp.o:(.foo)
+
+.global _start
+_start:
+.quad .foo
+
+.section .foo,"aM",@progbits,8
+.quad 0
+
+.section bar,"ao",@progbits,.foo