20 files changed, 260 insertions, 336 deletions

diff --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index 9420924..e142ac1 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -8,7 +8,6 @@
 
 #include "llvm/MC/MCAssembler.h"
 #include "llvm/ADT/ArrayRef.h"
-#include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringRef.h"
@@ -196,6 +195,7 @@ uint64_t MCAssembler::computeFragmentSize(const MCFragment &F) const {
   switch (F.getKind()) {
   case MCFragment::FT_Data:
   case MCFragment::FT_Relaxable:
+  case MCFragment::FT_Align:
   case MCFragment::FT_LEB:
   case MCFragment::FT_Dwarf:
   case MCFragment::FT_DwarfFrame:
@@ -226,28 +226,6 @@ uint64_t MCAssembler::computeFragmentSize(const MCFragment &F) const {
   case MCFragment::FT_SymbolId:
     return 4;
 
-  case MCFragment::FT_Align: {
-    const MCAlignFragment &AF = cast<MCAlignFragment>(F);
-    unsigned Offset = getFragmentOffset(AF);
-    unsigned Size = offsetToAlignment(Offset, AF.getAlignment());
-
-    // Insert extra Nops for code alignment if the target define
-    // shouldInsertExtraNopBytesForCodeAlign target hook.
-    if (AF.getParent()->useCodeAlign() && AF.hasEmitNops() &&
-        getBackend().shouldInsertExtraNopBytesForCodeAlign(AF, Size))
-      return Size;
-
-    // If we are padding with nops, force the padding to be larger than the
-    // minimum nop size.
-    if (Size > 0 && AF.hasEmitNops()) {
-      while (Size % getBackend().getMinimumNopSize())
-        Size += AF.getAlignment().value();
-    }
-    if (Size > AF.getMaxBytesToEmit())
-      return 0;
-    return Size;
-  }
-
   case MCFragment::FT_Org: {
     const MCOrgFragment &OF = cast<MCOrgFragment>(F);
     MCValue Value;
@@ -383,7 +361,7 @@ uint64_t MCAssembler::getSectionAddressSize(const MCSection &Sec) const {
 
 uint64_t MCAssembler::getSectionFileSize(const MCSection &Sec) const {
   // Virtual sections have no file size.
-  if (Sec.isVirtualSection())
+  if (Sec.isBssSection())
     return 0;
   return getSectionAddressSize(Sec);
 }
@@ -431,48 +409,45 @@ static void writeFragment(raw_ostream &OS, const MCAssembler &Asm,
     const auto &EF = cast<MCFragment>(F);
     OS << StringRef(EF.getContents().data(), EF.getContents().size());
     OS << StringRef(EF.getVarContents().data(), EF.getVarContents().size());
-    break;
-  }
+  } break;
+
   case MCFragment::FT_Align: {
     ++stats::EmittedAlignFragments;
-    const MCAlignFragment &AF = cast<MCAlignFragment>(F);
-    assert(AF.getFillLen() && "Invalid virtual align in concrete fragment!");
+    OS << StringRef(F.getContents().data(), F.getContents().size());
+    assert(F.getAlignFillLen() &&
+           "Invalid virtual align in concrete fragment!");
 
-    uint64_t Count = FragmentSize / AF.getFillLen();
-    assert(FragmentSize % AF.getFillLen() == 0 &&
+    uint64_t Count = (FragmentSize - F.getFixedSize()) / F.getAlignFillLen();
+    assert((FragmentSize - F.getFixedSize()) % F.getAlignFillLen() == 0 &&
            "computeFragmentSize computed size is incorrect");
 
-    // See if we are aligning with nops, and if so do that first to try to fill
-    // the Count bytes.  Then if that did not fill any bytes or there are any
-    // bytes left to fill use the Value and ValueSize to fill the rest.
-    // If we are aligning with nops, ask that target to emit the right data.
-    if (AF.hasEmitNops()) {
-      if (!Asm.getBackend().writeNopData(OS, Count, AF.getSubtargetInfo()))
-        report_fatal_error("unable to write nop sequence of " +
-                          Twine(Count) + " bytes");
-      break;
-    }
-
-    // Otherwise, write out in multiples of the value size.
-    for (uint64_t i = 0; i != Count; ++i) {
-      switch (AF.getFillLen()) {
-      default: llvm_unreachable("Invalid size!");
-      case 1:
-        OS << char(AF.getFill());
-        break;
-      case 2:
-        support::endian::write<uint16_t>(OS, AF.getFill(), Endian);
-        break;
-      case 4:
-        support::endian::write<uint32_t>(OS, AF.getFill(), Endian);
-        break;
-      case 8:
-        support::endian::write<uint64_t>(OS, AF.getFill(), Endian);
-        break;
+    // In the nops mode, call the backend hook to write `Count` nops.
+    if (F.hasAlignEmitNops()) {
+      if (!Asm.getBackend().writeNopData(OS, Count, F.getSubtargetInfo()))
+        reportFatalInternalError("unable to write nop sequence of " +
+                                 Twine(Count) + " bytes");
+    } else {
+      // Otherwise, write out in multiples of the value size.
+      for (uint64_t i = 0; i != Count; ++i) {
+        switch (F.getAlignFillLen()) {
+        default:
+          llvm_unreachable("Invalid size!");
+        case 1:
+          OS << char(F.getAlignFill());
+          break;
+        case 2:
+          support::endian::write<uint16_t>(OS, F.getAlignFill(), Endian);
+          break;
+        case 4:
+          support::endian::write<uint32_t>(OS, F.getAlignFill(), Endian);
+          break;
+        case 8:
+          support::endian::write<uint64_t>(OS, F.getAlignFill(), Endian);
+          break;
+        }
       }
     }
-    break;
-  }
+  } break;
 
   case MCFragment::FT_Fill: {
     ++stats::EmittedFillFragments;
@@ -583,42 +558,45 @@ void MCAssembler::writeSectionData(raw_ostream &OS,
                                    const MCSection *Sec) const {
   assert(getBackendPtr() && "Expected assembler backend");
 
-  // Ignore virtual sections.
-  if (Sec->isVirtualSection()) {
+  if (Sec->isBssSection()) {
     assert(getSectionFileSize(*Sec) == 0 && "Invalid size for section!");
 
-    // Check that contents are only things legal inside a virtual section.
+    // Ensure no fixups or non-zero bytes are written to BSS sections, catching
+    // errors in both input assembly code and MCStreamer API usage. Location is
+    // not tracked for efficiency.
+    auto Fn = [](char c) { return c != 0; };
     for (const MCFragment &F : *Sec) {
+      bool HasNonZero = false;
       switch (F.getKind()) {
-      default: llvm_unreachable("Invalid fragment in virtual section!");
-      case MCFragment::FT_Data: {
-        // Check that we aren't trying to write a non-zero contents (or fixups)
-        // into a virtual section. This is to support clients which use standard
-        // directives to fill the contents of virtual sections.
-        if (F.getFixups().size() || F.getVarFixups().size())
-          reportError(SMLoc(), Sec->getVirtualSectionKind() + " section '" +
-                                   Sec->getName() + "' cannot have fixups");
-        for (char C : F.getContents())
-          if (C) {
-            reportError(SMLoc(), Sec->getVirtualSectionKind() + " section '" +
-                                     Sec->getName() +
-                                     "' cannot have non-zero initializers");
-            break;
-          }
+      default:
+        reportFatalInternalError("BSS section '" + Sec->getName() +
+                                 "' contains invalid fragment");
+        break;
+      case MCFragment::FT_Data:
+      case MCFragment::FT_Relaxable:
+        HasNonZero =
+            any_of(F.getContents(), Fn) || any_of(F.getVarContents(), Fn);
         break;
-      }
       case MCFragment::FT_Align:
-        // Check that we aren't trying to write a non-zero value into a virtual
-        // section.
-        assert((cast<MCAlignFragment>(F).getFillLen() == 0 ||
-                cast<MCAlignFragment>(F).getFill() == 0) &&
-               "Invalid align in virtual section!");
+        // Disallowed for API usage. AsmParser changes non-zero fill values to
+        // 0.
+        assert(F.getAlignFill() == 0 && "Invalid align in virtual section!");
         break;
       case MCFragment::FT_Fill:
-        assert((cast<MCFillFragment>(F).getValue() == 0) &&
-               "Invalid fill in virtual section!");
+        HasNonZero = cast<MCFillFragment>(F).getValue() != 0;
         break;
       case MCFragment::FT_Org:
+        HasNonZero = cast<MCOrgFragment>(F).getValue() != 0;
+        break;
+      }
+      if (HasNonZero) {
+        reportError(SMLoc(), "BSS section '" + Sec->getName() +
+                                 "' cannot have non-zero bytes");
+        break;
+      }
+      if (F.getFixups().size() || F.getVarFixups().size()) {
+        reportError(SMLoc(),
+                    "BSS section '" + Sec->getName() + "' cannot have fixups");
         break;
       }
     }
@@ -722,34 +700,25 @@ void MCAssembler::layout() {
   for (MCSection &Sec : *this) {
     for (MCFragment &F : Sec) {
       // Process fragments with fixups here.
-      if (F.isEncoded()) {
-        auto Contents = F.getContents();
-        for (MCFixup &Fixup : F.getFixups()) {
+      auto Contents = F.getContents();
+      for (MCFixup &Fixup : F.getFixups()) {
+        uint64_t FixedValue;
+        MCValue Target;
+        evaluateFixup(F, Fixup, Target, FixedValue,
+                      /*RecordReloc=*/true, Contents);
+      }
+      if (F.getVarFixups().size()) {
+        // In the variable part, fixup offsets are relative to the fixed part's
+        // start. Extend the variable contents to the left to account for the
+        // fixed part size.
+        Contents = MutableArrayRef(F.getParent()->ContentStorage)
+                       .slice(F.VarContentStart - Contents.size(), F.getSize());
+        for (MCFixup &Fixup : F.getVarFixups()) {
           uint64_t FixedValue;
           MCValue Target;
           evaluateFixup(F, Fixup, Target, FixedValue,
                         /*RecordReloc=*/true, Contents);
         }
-        // In the variable part, fixup offsets are relative to the fixed part's
-        // start. Extend the variable contents to the left to account for the
-        // fixed part size.
-        auto VarFixups = F.getVarFixups();
-        if (VarFixups.size()) {
-          Contents =
-              MutableArrayRef(F.getParent()->ContentStorage)
-                  .slice(F.VarContentStart - Contents.size(), F.getSize());
-          for (MCFixup &Fixup : VarFixups) {
-            uint64_t FixedValue;
-            MCValue Target;
-            evaluateFixup(F, Fixup, Target, FixedValue,
-                          /*RecordReloc=*/true, Contents);
-          }
-        }
-      } else if (auto *AF = dyn_cast<MCAlignFragment>(&F)) {
-        // For RISC-V linker relaxation, an alignment relocation might be
-        // needed.
-        if (AF->hasEmitNops())
-          getBackend().shouldInsertFixupForCodeAlign(*this, *AF);
       }
     }
   }
@@ -953,15 +922,15 @@ bool MCAssembler::relaxDwarfCallFrameFragment(MCFragment &F) {
 }
 
 bool MCAssembler::relaxCVInlineLineTable(MCCVInlineLineTableFragment &F) {
-  unsigned OldSize = F.getContents().size();
+  unsigned OldSize = F.getVarContents().size();
   getContext().getCVContext().encodeInlineLineTable(*this, F);
-  return OldSize != F.getContents().size();
+  return OldSize != F.getVarContents().size();
 }
 
 bool MCAssembler::relaxCVDefRange(MCCVDefRangeFragment &F) {
-  unsigned OldSize = F.getContents().size();
+  unsigned OldSize = F.getVarContents().size();
   getContext().getCVContext().encodeDefRange(*this, F);
-  return OldSize != F.getContents().size();
+  return OldSize != F.getVarContents().size();
 }
 
 bool MCAssembler::relaxFill(MCFillFragment &F) {
@@ -1000,7 +969,32 @@ void MCAssembler::layoutSection(MCSection &Sec) {
   uint64_t Offset = 0;
   for (MCFragment &F : Sec) {
     F.Offset = Offset;
-    Offset += computeFragmentSize(F);
+    if (F.getKind() == MCFragment::FT_Align) {
+      Offset += F.getFixedSize();
+      unsigned Size = offsetToAlignment(Offset, F.getAlignment());
+      // In the nops mode, RISC-V style linker relaxation might adjust the size
+      // and add a fixup, even if `Size` is originally 0.
+      bool AlignFixup = false;
+      if (F.hasAlignEmitNops()) {
+        AlignFixup = getBackend().relaxAlign(F, Size);
+        // If the backend does not handle the fragment specially, pad with nops,
+        // but ensure that the padding is larger than the minimum nop size.
+        if (!AlignFixup)
+          while (Size % getBackend().getMinimumNopSize())
+            Size += F.getAlignment().value();
+      }
+      if (!AlignFixup && Size > F.getAlignMaxBytesToEmit())
+        Size = 0;
+      // Update the variable tail size, offset by FixedSize to prevent ubsan
+      // pointer-overflow in evaluateFixup. The content is ignored.
+      F.VarContentStart = F.getFixedSize();
+      F.VarContentEnd = F.VarContentStart + Size;
+      if (F.VarContentEnd > F.getParent()->ContentStorage.size())
+        F.getParent()->ContentStorage.resize(F.VarContentEnd);
+      Offset += Size;
+    } else {
+      Offset += computeFragmentSize(F);
+    }
   }
 }
 
diff --git a/llvm/lib/MC/MCCodeView.cpp b/llvm/lib/MC/MCCodeView.cpp
index 1f98251..7d528a5 100644
--- a/llvm/lib/MC/MCCodeView.cpp
+++ b/llvm/lib/MC/MCCodeView.cpp
@@ -26,8 +26,10 @@ using namespace llvm;
 using namespace llvm::codeview;
 
 void CodeViewContext::finish() {
-  if (StrTabFragment)
-    StrTabFragment->setContents(StrTab);
+  if (!StrTabFragment)
+    return;
+  assert(StrTabFragment->getKind() == MCFragment::FT_Data);
+  StrTabFragment->setVarContents(StrTab);
 }
 
 /// This is a valid number for use with .cv_loc if we've already seen a .cv_file
@@ -166,8 +168,9 @@ void CodeViewContext::emitStringTable(MCObjectStreamer &OS) {
   // somewhere else. If somebody wants two string tables in their .s file, one
   // will just be empty.
   if (!StrTabFragment) {
-    StrTabFragment = Ctx.allocFragment<MCFragment>();
-    OS.insert(StrTabFragment);
+    OS.newFragment();
+    StrTabFragment = OS.getCurrentFragment();
+    OS.newFragment();
   }
 
   OS.emitValueToAlignment(Align(4), 0);
@@ -603,7 +606,7 @@ void CodeViewContext::encodeInlineLineTable(const MCAssembler &Asm,
 
   compressAnnotation(BinaryAnnotationsOpCode::ChangeCodeLength, Buffer);
   compressAnnotation(std::min(EndSymLength, LocAfterLength), Buffer);
-  Frag.setContents(Buffer);
+  Frag.setVarContents(Buffer);
 }
 
 void CodeViewContext::encodeDefRange(const MCAssembler &Asm,
@@ -691,6 +694,6 @@ void CodeViewContext::encodeDefRange(const MCAssembler &Asm,
     }
   }
 
-  Frag.setContents(Contents);
-  Frag.setFixups(Fixups);
+  Frag.setVarContents(Contents);
+  Frag.setVarFixups(Fixups);
 }
diff --git a/llvm/lib/MC/MCDwarf.cpp b/llvm/lib/MC/MCDwarf.cpp
index b1dced7..e7c0d37 100644
--- a/llvm/lib/MC/MCDwarf.cpp
+++ b/llvm/lib/MC/MCDwarf.cpp
@@ -447,10 +447,17 @@ static void emitOneV5FileEntry(MCStreamer *MCOS, const MCDwarfFile &DwarfFile,
         StringRef(reinterpret_cast<const char *>(Cksum.data()), Cksum.size()));
   }
   if (HasAnySource) {
+    // From https://dwarfstd.org/issues/180201.1.html
+    // * The value is an empty null-terminated string if no source is available
+    StringRef Source = DwarfFile.Source.value_or(StringRef());
+    // * If the source is available but is an empty file then the value is a
+    // null-terminated single "\n".
+    if (DwarfFile.Source && DwarfFile.Source->empty())
+      Source = "\n";
     if (LineStr)
-      LineStr->emitRef(MCOS, DwarfFile.Source.value_or(StringRef()));
+      LineStr->emitRef(MCOS, Source);
     else {
-      MCOS->emitBytes(DwarfFile.Source.value_or(StringRef())); // Source and...
+      MCOS->emitBytes(Source);             // Source and...
       MCOS->emitBytes(StringRef("\0", 1)); // its null terminator.
     }
   }
diff --git a/llvm/lib/MC/MCELFStreamer.cpp b/llvm/lib/MC/MCELFStreamer.cpp
index 49071bd..b8cbaea5 100644
--- a/llvm/lib/MC/MCELFStreamer.cpp
+++ b/llvm/lib/MC/MCELFStreamer.cpp
@@ -88,7 +88,7 @@ void MCELFStreamer::changeSection(MCSection *Section, uint32_t Subsection) {
   if (SectionELF->getFlags() & ELF::SHF_GNU_RETAIN)
     getWriter().markGnuAbi();
 
-  changeSectionImpl(Section, Subsection);
+  MCObjectStreamer::changeSection(Section, Subsection);
   Asm.registerSymbol(*Section->getBeginSymbol());
 }
 
diff --git a/llvm/lib/MC/MCExpr.cpp b/llvm/lib/MC/MCExpr.cpp
index 22dff49..dbb2fd1 100644
--- a/llvm/lib/MC/MCExpr.cpp
+++ b/llvm/lib/MC/MCExpr.cpp
@@ -370,7 +370,6 @@ static void attemptToFoldSymbolOffsetDifference(const MCAssembler *Asm,
       }
 
       int64_t Num;
-      unsigned Count;
       if (DF) {
         Displacement += DF->getContents().size();
       } else if (F->getKind() == MCFragment::FT_Relaxable &&
@@ -379,11 +378,9 @@ static void attemptToFoldSymbolOffsetDifference(const MCAssembler *Asm,
         // After layout, during relocation generation, it can be treated as a
         // data fragment.
         Displacement += F->getSize();
-      } else if (auto *AF = dyn_cast<MCAlignFragment>(F);
-                 AF && Layout && AF->hasEmitNops() &&
-                 !Asm->getBackend().shouldInsertExtraNopBytesForCodeAlign(
-                     *AF, Count)) {
-        Displacement += Asm->computeFragmentSize(*AF);
+      } else if (F->getKind() == MCFragment::FT_Align && Layout &&
+                 F->isLinkerRelaxable()) {
+        Displacement += Asm->computeFragmentSize(*F);
       } else if (auto *FF = dyn_cast<MCFillFragment>(F);
                  FF && FF->getNumValues().evaluateAsAbsolute(Num)) {
         Displacement += Num * FF->getValueSize();
diff --git a/llvm/lib/MC/MCFragment.cpp b/llvm/lib/MC/MCFragment.cpp
index fe7afd4..3c395e5 100644
--- a/llvm/lib/MC/MCFragment.cpp
+++ b/llvm/lib/MC/MCFragment.cpp
@@ -72,17 +72,9 @@ LLVM_DUMP_METHOD void MCFragment::dump() const {
   };
 
   switch (getKind()) {
-  case MCFragment::FT_Align: {
-    const auto *AF = cast<MCAlignFragment>(this);
-    OS << " Align:" << AF->getAlignment().value() << " Fill:" << AF->getFill()
-       << " FillLen:" << unsigned(AF->getFillLen())
-       << " MaxBytesToEmit:" << AF->getMaxBytesToEmit();
-    if (AF->hasEmitNops())
-      OS << " Nops";
-    break;
-  }
   case MCFragment::FT_Data:
   case MCFragment::FT_Relaxable:
+  case MCFragment::FT_Align:
   case MCFragment::FT_LEB:
   case MCFragment::FT_Dwarf:
   case MCFragment::FT_DwarfFrame: {
@@ -91,8 +83,13 @@ LLVM_DUMP_METHOD void MCFragment::dump() const {
     auto Fixed = getContents();
     auto Var = getVarContents();
     OS << " Size:" << Fixed.size();
-    if (getKind() != MCFragment::FT_Data)
+    if (getKind() != MCFragment::FT_Data) {
       OS << '+' << Var.size();
+      // FT_Align uses getVarContents to track the size, but the content is
+      // ignored and not useful.
+      if (getKind() == MCFragment::FT_Align)
+        Var = {};
+    }
     OS << " [";
     for (unsigned i = 0, e = Fixed.size(); i != e; ++i) {
       if (i) OS << ",";
@@ -111,6 +108,13 @@ LLVM_DUMP_METHOD void MCFragment::dump() const {
       OS << ' ';
       getInst().dump_pretty(OS);
       break;
+    case MCFragment::FT_Align:
+      OS << "\n  Align:" << getAlignment().value() << " Fill:" << getAlignFill()
+         << " FillLen:" << unsigned(getAlignFillLen())
+         << " MaxBytesToEmit:" << getAlignMaxBytesToEmit();
+      if (hasAlignEmitNops())
+        OS << " Nops";
+      break;
     case MCFragment::FT_LEB: {
       OS << " Value:";
       getLEBValue().print(OS, nullptr);
diff --git a/llvm/lib/MC/MCMachOStreamer.cpp b/llvm/lib/MC/MCMachOStreamer.cpp
index 43598ef..8c3332c 100644
--- a/llvm/lib/MC/MCMachOStreamer.cpp
+++ b/llvm/lib/MC/MCMachOStreamer.cpp
@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/BinaryFormat/MachO.h"
@@ -132,8 +131,7 @@ public:
 } // end anonymous namespace.
 
 void MCMachOStreamer::changeSection(MCSection *Section, uint32_t Subsection) {
-  // Change the section normally.
-  changeSectionImpl(Section, Subsection);
+  MCObjectStreamer::changeSection(Section, Subsection);
 
   // Output a linker-local symbol so we don't need section-relative local
   // relocations. The linker hates us when we do that.
@@ -161,7 +159,7 @@ void MCMachOStreamer::emitLabel(MCSymbol *Symbol, SMLoc Loc) {
   // We have to create a new fragment if this is an atom defining symbol,
   // fragments cannot span atoms.
   if (cast<MCSymbolMachO>(Symbol)->isSymbolLinkerVisible())
-    insert(getContext().allocFragment<MCFragment>());
+    newFragment();
 
   MCObjectStreamer::emitLabel(Symbol, Loc);
 
@@ -393,7 +391,7 @@ void MCMachOStreamer::emitZerofill(MCSection *Section, MCSymbol *Symbol,
   // On darwin all virtual sections have zerofill type. Disallow the usage of
   // .zerofill in non-virtual functions. If something similar is needed, use
   // .space or .zero.
-  if (!Section->isVirtualSection()) {
+  if (!Section->isBssSection()) {
     getContext().reportError(
         Loc, "The usage of .zerofill is restricted to sections of "
              "ZEROFILL type. Use .zero or .space instead.");
@@ -479,7 +477,8 @@ void MCMachOStreamer::finalizeCGProfile() {
   // and set its size now so that it's accounted for in layout.
   MCSection *CGProfileSection = Asm.getContext().getMachOSection(
       "__LLVM", "__cg_profile", 0, SectionKind::getMetadata());
-  changeSection(CGProfileSection);
+  // Call the base class changeSection to omit the linker-local label.
+  MCObjectStreamer::changeSection(CGProfileSection);
   // For each entry, reserve space for 2 32-bit indices and a 64-bit count.
   size_t SectionBytes =
       W.getCGProfile().size() * (2 * sizeof(uint32_t) + sizeof(uint64_t));
@@ -511,7 +510,8 @@ void MCMachOStreamer::createAddrSigSection() {
   // to be computed immediately after in order for it to be exported correctly.
   MCSection *AddrSigSection =
       Asm.getContext().getObjectFileInfo()->getAddrSigSection();
-  changeSection(AddrSigSection);
+  // Call the base class changeSection to omit the linker-local label.
+  MCObjectStreamer::changeSection(AddrSigSection);
   auto *Frag = cast<MCFragment>(AddrSigSection->curFragList()->Head);
   // We will generate a series of pointer-sized symbol relocations at offset
   // 0x0. Set the section size to be large enough to contain a single pointer
diff --git a/llvm/lib/MC/MCObjectStreamer.cpp b/llvm/lib/MC/MCObjectStreamer.cpp
index f61dda6..89f4da5 100644
--- a/llvm/lib/MC/MCObjectStreamer.cpp
+++ b/llvm/lib/MC/MCObjectStreamer.cpp
@@ -19,7 +19,6 @@
 #include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCSymbol.h"
-#include "llvm/MC/MCValue.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/SourceMgr.h"
 using namespace llvm;
@@ -33,6 +32,7 @@ MCObjectStreamer::MCObjectStreamer(MCContext &Context,
           Context, std::move(TAB), std::move(Emitter), std::move(OW))),
       EmitEHFrame(true), EmitDebugFrame(false) {
   assert(Assembler->getBackendPtr() && Assembler->getEmitterPtr());
+  IsObj = true;
   setAllowAutoPadding(Assembler->getBackend().allowAutoPadding());
   if (Context.getTargetOptions() && Context.getTargetOptions()->MCRelaxAll)
     Assembler->setRelaxAll(true);
@@ -46,6 +46,25 @@ MCAssembler *MCObjectStreamer::getAssemblerPtr() {
   return nullptr;
 }
 
+void MCObjectStreamer::newFragment() {
+  addFragment(getContext().allocFragment<MCFragment>());
+}
+
+void MCObjectStreamer::insert(MCFragment *F) {
+  assert(F->getKind() != MCFragment::FT_Data &&
+         "F should have a variable-size tail");
+  addFragment(F);
+  newFragment();
+}
+
+void MCObjectStreamer::appendContents(size_t Num, char Elt) {
+  CurFrag->appendContents(Num, Elt);
+}
+
+void MCObjectStreamer::addFixup(const MCExpr *Value, MCFixupKind Kind) {
+  CurFrag->addFixup(MCFixup::create(CurFrag->getFixedSize(), Value, Kind));
+}
+
 // As a compile-time optimization, avoid allocating and evaluating an MCExpr
 // tree for (Hi - Lo) when Hi and Lo are offsets into the same fragment's fixed
 // part.
@@ -106,18 +125,6 @@ void MCObjectStreamer::emitFrames(MCAsmBackend *MAB) {
     MCDwarfFrameEmitter::Emit(*this, MAB, false);
 }
 
-MCFragment *MCObjectStreamer::getOrCreateDataFragment() {
-  // TODO: Start a new fragment whenever finalizing the variable-size tail of a
-  // previous one, so that all getOrCreateDataFragment calls can be replaced
-  // with getCurrentFragment
-  auto *F = getCurrentFragment();
-  if (F->getKind() != MCFragment::FT_Data) {
-    F = getContext().allocFragment<MCFragment>();
-    insert(F);
-  }
-  return F;
-}
-
 void MCObjectStreamer::visitUsedSymbol(const MCSymbol &Sym) {
   Assembler->registerSymbol(Sym);
 }
@@ -131,7 +138,7 @@ void MCObjectStreamer::emitCFISections(bool EH, bool Debug) {
 void MCObjectStreamer::emitValueImpl(const MCExpr *Value, unsigned Size,
                                      SMLoc Loc) {
   MCStreamer::emitValueImpl(Value, Size, Loc);
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
 
   MCDwarfLineEntry::make(this, getCurrentSectionOnly());
 
@@ -180,7 +187,7 @@ void MCObjectStreamer::emitLabel(MCSymbol *Symbol, SMLoc Loc) {
   // If there is a current fragment, mark the symbol as pointing into it.
   // Otherwise queue the label and set its fragment pointer when we emit the
   // next fragment.
-  MCFragment *F = getOrCreateDataFragment();
+  MCFragment *F = getCurrentFragment();
   Symbol->setFragment(F);
   Symbol->setOffset(F->getContents().size());
 
@@ -214,7 +221,7 @@ void MCObjectStreamer::emitULEB128Value(const MCExpr *Value) {
     emitULEB128IntValue(IntValue);
     return;
   }
-  auto *F = getOrCreateDataFragment();
+  auto *F = getCurrentFragment();
   F->makeLEB(false, Value);
   newFragment();
 }
@@ -225,7 +232,7 @@ void MCObjectStreamer::emitSLEB128Value(const MCExpr *Value) {
     emitSLEB128IntValue(IntValue);
     return;
   }
-  auto *F = getOrCreateDataFragment();
+  auto *F = getCurrentFragment();
   F->makeLEB(true, Value);
   newFragment();
 }
@@ -236,11 +243,6 @@ void MCObjectStreamer::emitWeakReference(MCSymbol *Alias,
 }
 
 void MCObjectStreamer::changeSection(MCSection *Section, uint32_t Subsection) {
-  changeSectionImpl(Section, Subsection);
-}
-
-bool MCObjectStreamer::changeSectionImpl(MCSection *Section,
-                                         uint32_t Subsection) {
   assert(Section && "Cannot switch to a null section!");
   getContext().clearDwarfLocSeen();
 
@@ -259,7 +261,7 @@ bool MCObjectStreamer::changeSectionImpl(MCSection *Section,
   Section->CurFragList = &Subsections[I].second;
   CurFrag = Section->CurFragList->Tail;
 
-  return getAssembler().registerSection(*Section);
+  getAssembler().registerSection(*Section);
 }
 
 void MCObjectStreamer::switchSectionNoPrint(MCSection *Section) {
@@ -291,18 +293,6 @@ bool MCObjectStreamer::mayHaveInstructions(MCSection &Sec) const {
 
 void MCObjectStreamer::emitInstruction(const MCInst &Inst,
                                        const MCSubtargetInfo &STI) {
-  const MCSection &Sec = *getCurrentSectionOnly();
-  if (Sec.isVirtualSection()) {
-    getContext().reportError(Inst.getLoc(), Twine(Sec.getVirtualSectionKind()) +
-                                                " section '" + Sec.getName() +
-                                                "' cannot have instructions");
-    return;
-  }
-  emitInstructionImpl(Inst, STI);
-}
-
-void MCObjectStreamer::emitInstructionImpl(const MCInst &Inst,
-                                           const MCSubtargetInfo &STI) {
   MCStreamer::emitInstruction(Inst, STI);
 
   MCSection *Sec = getCurrentSectionOnly();
@@ -336,7 +326,7 @@ void MCObjectStreamer::emitInstructionImpl(const MCInst &Inst,
 
 void MCObjectStreamer::emitInstToData(const MCInst &Inst,
                                       const MCSubtargetInfo &STI) {
-  MCFragment *F = getOrCreateDataFragment();
+  MCFragment *F = getCurrentFragment();
 
   // Append the instruction to the data fragment.
   size_t FixupStartIndex = F->getFixups().size();
@@ -368,7 +358,7 @@ void MCObjectStreamer::emitInstToData(const MCInst &Inst,
 
 void MCObjectStreamer::emitInstToFragment(const MCInst &Inst,
                                           const MCSubtargetInfo &STI) {
-  auto *F = getOrCreateDataFragment();
+  auto *F = getCurrentFragment();
   SmallVector<char, 16> Data;
   SmallVector<MCFixup, 1> Fixups;
   getAssembler().getEmitter().encodeInstruction(Inst, Data, Fixups, STI);
@@ -379,6 +369,7 @@ void MCObjectStreamer::emitInstToFragment(const MCInst &Inst,
   F->setVarContents(Data);
   F->setVarFixups(Fixups);
   F->setInst(Inst);
+  newFragment();
 }
 
 void MCObjectStreamer::emitDwarfLocDirective(unsigned FileNo, unsigned Line,
@@ -440,10 +431,11 @@ void MCObjectStreamer::emitDwarfAdvanceLineAddr(int64_t LineDelta,
     return;
   }
 
-  auto *F = getOrCreateDataFragment();
+  auto *F = getCurrentFragment();
   F->Kind = MCFragment::FT_Dwarf;
   F->setDwarfAddrDelta(buildSymbolDiff(*this, Label, LastLabel, SMLoc()));
   F->setDwarfLineDelta(LineDelta);
+  newFragment();
 }
 
 void MCObjectStreamer::emitDwarfLineEndEntry(MCSection *Section,
@@ -471,9 +463,10 @@ void MCObjectStreamer::emitDwarfLineEndEntry(MCSection *Section,
 void MCObjectStreamer::emitDwarfAdvanceFrameAddr(const MCSymbol *LastLabel,
                                                  const MCSymbol *Label,
                                                  SMLoc Loc) {
-  auto *F = getOrCreateDataFragment();
+  auto *F = getCurrentFragment();
   F->Kind = MCFragment::FT_DwarfFrame;
   F->setDwarfAddrDelta(buildSymbolDiff(*this, Label, LastLabel, Loc));
+  newFragment();
 }
 
 void MCObjectStreamer::emitCVLocDirective(unsigned FunctionId, unsigned FileNo,
@@ -532,7 +525,7 @@ void MCObjectStreamer::emitCVFileChecksumOffsetDirective(unsigned FileNo) {
 
 void MCObjectStreamer::emitBytes(StringRef Data) {
   MCDwarfLineEntry::make(this, getCurrentSectionOnly());
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   DF->appendContents(ArrayRef(Data.data(), Data.size()));
 }
 
@@ -541,28 +534,21 @@ void MCObjectStreamer::emitValueToAlignment(Align Alignment, int64_t Fill,
                                             unsigned MaxBytesToEmit) {
   if (MaxBytesToEmit == 0)
     MaxBytesToEmit = Alignment.value();
-  insert(getContext().allocFragment<MCAlignFragment>(Alignment, Fill, FillLen,
-                                                     MaxBytesToEmit));
+  MCFragment *F = getCurrentFragment();
+  F->makeAlign(Alignment, Fill, FillLen, MaxBytesToEmit);
+  newFragment();
 
   // Update the maximum alignment on the current section if necessary.
-  MCSection *CurSec = getCurrentSectionOnly();
-  CurSec->ensureMinAlignment(Alignment);
+  F->getParent()->ensureMinAlignment(Alignment);
 }
 
 void MCObjectStreamer::emitCodeAlignment(Align Alignment,
                                          const MCSubtargetInfo *STI,
                                          unsigned MaxBytesToEmit) {
+  auto *F = getCurrentFragment();
   emitValueToAlignment(Alignment, 0, 1, MaxBytesToEmit);
-  auto *F = cast<MCAlignFragment>(getCurrentFragment());
-  F->setEmitNops(true, STI);
-  // With RISC-V style linker relaxation, mark the section as linker-relaxable
-  // if the alignment is larger than the minimum NOP size.
-  unsigned Size;
-  if (getAssembler().getBackend().shouldInsertExtraNopBytesForCodeAlign(*F,
-                                                                        Size)) {
-    getCurrentSectionOnly()->setLinkerRelaxable();
-    newFragment();
-  }
+  F->u.align.EmitNops = true;
+  F->STI = STI;
 }
 
 void MCObjectStreamer::emitValueToOffset(const MCExpr *Offset,
diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index 77bf843..d0b6ea4 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -3404,11 +3404,10 @@ bool AsmParser::parseDirectiveAlign(bool IsPow2, uint8_t ValueSize) {
   const MCSection *Section = getStreamer().getCurrentSectionOnly();
   assert(Section && "must have section to emit alignment");
 
-  if (HasFillExpr && FillExpr != 0 && Section->isVirtualSection()) {
+  if (HasFillExpr && FillExpr != 0 && Section->isBssSection()) {
     ReturnVal |=
-        Warning(FillExprLoc, "ignoring non-zero fill value in " +
-                                 Section->getVirtualSectionKind() +
-                                 " section '" + Section->getName() + "'");
+        Warning(FillExprLoc, "ignoring non-zero fill value in BSS section '" +
+                                 Section->getName() + "'");
     FillExpr = 0;
   }
 
diff --git a/llvm/lib/MC/MCParser/MCTargetAsmParser.cpp b/llvm/lib/MC/MCParser/MCTargetAsmParser.cpp
index 7f09349..d7b0546 100644
--- a/llvm/lib/MC/MCParser/MCTargetAsmParser.cpp
+++ b/llvm/lib/MC/MCParser/MCTargetAsmParser.cpp
@@ -8,8 +8,8 @@
 
 #include "llvm/MC/MCParser/MCTargetAsmParser.h"
 #include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCObjectStreamer.h"
 #include "llvm/MC/MCRegister.h"
-#include "llvm/MC/MCStreamer.h"
 
 using namespace llvm;
 
@@ -25,8 +25,9 @@ MCSubtargetInfo &MCTargetAsmParser::copySTI() {
   STI = &STICopy;
   // The returned STI will likely be modified. Create a new fragment to prevent
   // mixing STI values within a fragment.
-  if (getStreamer().getCurrentFragment())
-    getStreamer().newFragment();
+  auto &S = getStreamer();
+  if (S.isObj() && S.getCurrentFragment())
+    static_cast<MCObjectStreamer &>(S).newFragment();
   return STICopy;
 }
 
diff --git a/llvm/lib/MC/MCSection.cpp b/llvm/lib/MC/MCSection.cpp
index 9367145..023f7f2 100644
--- a/llvm/lib/MC/MCSection.cpp
+++ b/llvm/lib/MC/MCSection.cpp
@@ -18,10 +18,10 @@
 
 using namespace llvm;
 
-MCSection::MCSection(SectionVariant V, StringRef Name, bool IsText,
-                     bool IsVirtual, MCSymbol *Begin)
+MCSection::MCSection(SectionVariant V, StringRef Name, bool IsText, bool IsBss,
+                     MCSymbol *Begin)
     : Begin(Begin), HasInstructions(false), IsRegistered(false), IsText(IsText),
-      IsVirtual(IsVirtual), LinkerRelaxable(false), Name(Name), Variant(V) {
+      IsBss(IsBss), LinkerRelaxable(false), Name(Name), Variant(V) {
   // The initial subsection number is 0. Create a fragment list.
   CurFragList = &Subsections.emplace_back(0u, FragList{}).second;
 }
@@ -34,8 +34,6 @@ MCSymbol *MCSection::getEndSymbol(MCContext &Ctx) {
 
 bool MCSection::hasEnded() const { return End && End->isInSection(); }
 
-StringRef MCSection::getVirtualSectionKind() const { return "virtual"; }
-
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 LLVM_DUMP_METHOD void MCSection::dump(
     DenseMap<const MCFragment *, SmallVector<const MCSymbol *, 0>> *FragToSyms)
@@ -60,16 +58,6 @@ LLVM_DUMP_METHOD void MCSection::dump(
 }
 #endif
 
-void MCFragment::setContents(ArrayRef<char> Contents) {
-  auto &S = getParent()->ContentStorage;
-  if (ContentStart + Contents.size() > ContentEnd) {
-    ContentStart = S.size();
-    S.resize_for_overwrite(S.size() + Contents.size());
-  }
-  ContentEnd = ContentStart + Contents.size();
-  llvm::copy(Contents, S.begin() + ContentStart);
-}
-
 void MCFragment::setVarContents(ArrayRef<char> Contents) {
   auto &S = getParent()->ContentStorage;
   if (VarContentStart + Contents.size() > VarContentEnd) {
@@ -96,16 +84,6 @@ void MCFragment::appendFixups(ArrayRef<MCFixup> Fixups) {
   FixupEnd = S.size();
 }
 
-void MCFragment::setFixups(ArrayRef<MCFixup> Fixups) {
-  auto &S = getParent()->FixupStorage;
-  if (FixupStart + Fixups.size() > FixupEnd) {
-    FixupStart = S.size();
-    S.resize_for_overwrite(S.size() + Fixups.size());
-  }
-  FixupEnd = FixupStart + Fixups.size();
-  llvm::copy(Fixups, S.begin() + FixupStart);
-}
-
 void MCFragment::setVarFixups(ArrayRef<MCFixup> Fixups) {
   auto &S = getParent()->FixupStorage;
   if (VarFixupStart + Fixups.size() > VarFixupEnd) {
diff --git a/llvm/lib/MC/MCSectionCOFF.cpp b/llvm/lib/MC/MCSectionCOFF.cpp
index 94e29ce..5bf1473 100644
--- a/llvm/lib/MC/MCSectionCOFF.cpp
+++ b/llvm/lib/MC/MCSectionCOFF.cpp
@@ -115,7 +115,3 @@ void MCSectionCOFF::printSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
 }
 
 bool MCSectionCOFF::useCodeAlign() const { return isText(); }
-
-StringRef MCSectionCOFF::getVirtualSectionKind() const {
-  return "IMAGE_SCN_CNT_UNINITIALIZED_DATA";
-}
diff --git a/llvm/lib/MC/MCSectionELF.cpp b/llvm/lib/MC/MCSectionELF.cpp
index 299fe40..ef33f9c 100644
--- a/llvm/lib/MC/MCSectionELF.cpp
+++ b/llvm/lib/MC/MCSectionELF.cpp
@@ -215,5 +215,3 @@ void MCSectionELF::printSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
 bool MCSectionELF::useCodeAlign() const {
   return getFlags() & ELF::SHF_EXECINSTR;
 }
-
-StringRef MCSectionELF::getVirtualSectionKind() const { return "SHT_NOBITS"; }
diff --git a/llvm/lib/MC/MCStreamer.cpp b/llvm/lib/MC/MCStreamer.cpp
index c3ecf8f..30198c9 100644
--- a/llvm/lib/MC/MCStreamer.cpp
+++ b/llvm/lib/MC/MCStreamer.cpp
@@ -1404,7 +1404,7 @@ MCSymbol *MCStreamer::endSection(MCSection *Section) {
   return Sym;
 }
 
-void MCStreamer::insert(MCFragment *F) {
+void MCStreamer::addFragment(MCFragment *F) {
   auto *Sec = CurFrag->getParent();
   F->setParent(Sec);
   F->setLayoutOrder(CurFrag->getLayoutOrder() + 1);
@@ -1413,10 +1413,6 @@ void MCStreamer::insert(MCFragment *F) {
   Sec->curFragList()->Tail = F;
 }
 
-void MCStreamer::newFragment() {
-  insert(getContext().allocFragment<MCFragment>());
-}
-
 static VersionTuple
 targetVersionOrMinimumSupportedOSVersion(const Triple &Target,
                                          VersionTuple TargetVersion) {
diff --git a/llvm/lib/MC/MCWin64EH.cpp b/llvm/lib/MC/MCWin64EH.cpp
index e8b26bf..72a8dd7 100644
--- a/llvm/lib/MC/MCWin64EH.cpp
+++ b/llvm/lib/MC/MCWin64EH.cpp
@@ -318,15 +318,13 @@ static void EmitUnwindInfo(MCStreamer &streamer, WinEH::FrameInfo *info) {
 
   // Emit the epilog instructions.
   if (EnableUnwindV2) {
-    MCFragment *DF = OS->getOrCreateDataFragment();
-
     bool IsLast = true;
     for (const auto &Epilog : llvm::reverse(info->EpilogMap)) {
       if (IsLast) {
         IsLast = false;
         uint8_t Flags = LastEpilogIsAtEnd ? 0x01 : 0;
-        streamer.emitInt8(EpilogSize);
-        streamer.emitInt8((Flags << 4) | Win64EH::UOP_Epilog);
+        OS->emitInt8(EpilogSize);
+        OS->emitInt8((Flags << 4) | Win64EH::UOP_Epilog);
 
         if (LastEpilogIsAtEnd)
           continue;
@@ -337,9 +335,8 @@ static void EmitUnwindInfo(MCStreamer &streamer, WinEH::FrameInfo *info) {
       // layout has been completed.
       auto *MCE = MCUnwindV2EpilogTargetExpr::create(*info, Epilog.second,
                                                      EpilogSize, context);
-      MCFixup Fixup = MCFixup::create(DF->getContents().size(), MCE, FK_Data_2);
-      DF->addFixup(Fixup);
-      DF->appendContents(2, 0);
+      OS->addFixup(MCE, FK_Data_2);
+      OS->appendContents(2, 0);
     }
   }
   if (AddPaddingEpilogCode)
diff --git a/llvm/lib/MC/MCWinCOFFStreamer.cpp b/llvm/lib/MC/MCWinCOFFStreamer.cpp
index 3398775..9369bea 100644
--- a/llvm/lib/MC/MCWinCOFFStreamer.cpp
+++ b/llvm/lib/MC/MCWinCOFFStreamer.cpp
@@ -153,7 +153,7 @@ void MCWinCOFFStreamer::initSections(bool NoExecStack,
 }
 
 void MCWinCOFFStreamer::changeSection(MCSection *Section, uint32_t Subsection) {
-  changeSectionImpl(Section, Subsection);
+  MCObjectStreamer::changeSection(Section, Subsection);
   // Ensure that the first and the second symbols relative to the section are
   // the section symbol and the COMDAT symbol.
   getAssembler().registerSymbol(*Section->getBeginSymbol());
@@ -278,35 +278,28 @@ void MCWinCOFFStreamer::emitCOFFSymbolIndex(MCSymbol const *Symbol) {
 
 void MCWinCOFFStreamer::emitCOFFSectionIndex(const MCSymbol *Symbol) {
   visitUsedSymbol(*Symbol);
-  MCFragment *DF = getOrCreateDataFragment();
   const MCSymbolRefExpr *SRE = MCSymbolRefExpr::create(Symbol, getContext());
-  MCFixup Fixup = MCFixup::create(DF->getContents().size(), SRE, FK_SecRel_2);
-  DF->addFixup(Fixup);
-  DF->appendContents(2, 0);
+  addFixup(SRE, FK_SecRel_2);
+  appendContents(2, 0);
 }
 
 void MCWinCOFFStreamer::emitCOFFSecRel32(const MCSymbol *Symbol,
                                          uint64_t Offset) {
   visitUsedSymbol(*Symbol);
-  MCFragment *DF = getOrCreateDataFragment();
   // Create Symbol A for the relocation relative reference.
   const MCExpr *MCE = MCSymbolRefExpr::create(Symbol, getContext());
   // Add the constant offset, if given.
   if (Offset)
     MCE = MCBinaryExpr::createAdd(
         MCE, MCConstantExpr::create(Offset, getContext()), getContext());
-  // Build the secrel32 relocation.
-  MCFixup Fixup = MCFixup::create(DF->getContents().size(), MCE, FK_SecRel_4);
-  // Record the relocation.
-  DF->addFixup(Fixup);
+  addFixup(MCE, FK_SecRel_4);
   // Emit 4 bytes (zeros) to the object file.
-  DF->appendContents(4, 0);
+  appendContents(4, 0);
 }
 
 void MCWinCOFFStreamer::emitCOFFImgRel32(const MCSymbol *Symbol,
                                          int64_t Offset) {
   visitUsedSymbol(*Symbol);
-  MCFragment *DF = getOrCreateDataFragment();
   // Create Symbol A for the relocation relative reference.
   const MCExpr *MCE = MCSymbolRefExpr::create(
       Symbol, MCSymbolRefExpr::VK_COFF_IMGREL32, getContext());
@@ -314,40 +307,29 @@ void MCWinCOFFStreamer::emitCOFFImgRel32(const MCSymbol *Symbol,
   if (Offset)
     MCE = MCBinaryExpr::createAdd(
         MCE, MCConstantExpr::create(Offset, getContext()), getContext());
-  // Build the imgrel relocation.
-  MCFixup Fixup = MCFixup::create(DF->getContents().size(), MCE, FK_Data_4);
-  // Record the relocation.
-  DF->addFixup(Fixup);
+  addFixup(MCE, FK_Data_4);
   // Emit 4 bytes (zeros) to the object file.
-  DF->appendContents(4, 0);
+  appendContents(4, 0);
 }
 
 void MCWinCOFFStreamer::emitCOFFSecNumber(MCSymbol const *Symbol) {
   visitUsedSymbol(*Symbol);
-  MCFragment *DF = getOrCreateDataFragment();
   // Create Symbol for section number.
   const MCExpr *MCE = MCCOFFSectionNumberTargetExpr::create(
       *Symbol, this->getWriter(), getContext());
-  // Build the relocation.
-  MCFixup Fixup = MCFixup::create(DF->getContents().size(), MCE, FK_Data_4);
-  // Record the relocation.
-  DF->addFixup(Fixup);
+  addFixup(MCE, FK_Data_4);
   // Emit 4 bytes (zeros) to the object file.
-  DF->appendContents(4, 0);
+  appendContents(4, 0);
 }
 
 void MCWinCOFFStreamer::emitCOFFSecOffset(MCSymbol const *Symbol) {
   visitUsedSymbol(*Symbol);
-  MCFragment *DF = getOrCreateDataFragment();
   // Create Symbol for section offset.
   const MCExpr *MCE =
       MCCOFFSectionOffsetTargetExpr::create(*Symbol, getContext());
-  // Build the relocation.
-  MCFixup Fixup = MCFixup::create(DF->getContents().size(), MCE, FK_Data_4);
-  // Record the relocation.
-  DF->addFixup(Fixup);
+  addFixup(MCE, FK_Data_4);
   // Emit 4 bytes (zeros) to the object file.
-  DF->appendContents(4, 0);
+  appendContents(4, 0);
 }
 
 void MCWinCOFFStreamer::emitCommonSymbol(MCSymbol *S, uint64_t Size,
diff --git a/llvm/lib/MC/MCXCOFFStreamer.cpp b/llvm/lib/MC/MCXCOFFStreamer.cpp
index 4d45296..63381b4 100644
--- a/llvm/lib/MC/MCXCOFFStreamer.cpp
+++ b/llvm/lib/MC/MCXCOFFStreamer.cpp
@@ -89,7 +89,7 @@ void MCXCOFFStreamer::emitXCOFFSymbolLinkageWithVisibility(
 void MCXCOFFStreamer::emitXCOFFRefDirective(const MCSymbol *Symbol) {
   // Add a Fixup here to later record a relocation of type R_REF to prevent the
   // ref symbol from being garbage collected (by the binder).
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   const MCSymbolRefExpr *SRE = MCSymbolRefExpr::create(Symbol, getContext());
   std::optional<MCFixupKind> MaybeKind =
       getAssembler().getBackend().getFixupKind("R_REF");
diff --git a/llvm/lib/MC/MachObjectWriter.cpp b/llvm/lib/MC/MachObjectWriter.cpp
index 3291dd7..48d2fc6 100644
--- a/llvm/lib/MC/MachObjectWriter.cpp
+++ b/llvm/lib/MC/MachObjectWriter.cpp
@@ -131,7 +131,7 @@ uint64_t MachObjectWriter::getPaddingSize(const MCAssembler &Asm,
     return 0;
 
   const MCSection &NextSec = *SectionOrder[Next];
-  if (NextSec.isVirtualSection())
+  if (NextSec.isBssSection())
     return 0;
   return offsetToAlignment(EndAddr, NextSec.getAlign());
 }
@@ -267,7 +267,7 @@ void MachObjectWriter::writeSection(const MCAssembler &Asm,
   const MCSectionMachO &Section = cast<MCSectionMachO>(Sec);
 
   // The offset is unused for virtual sections.
-  if (Section.isVirtualSection()) {
+  if (Section.isBssSection()) {
     assert(Asm.getSectionFileSize(Sec) == 0 && "Invalid file size!");
     FileOffset = 0;
   }
@@ -682,13 +682,13 @@ void MachObjectWriter::computeSectionAddresses(const MCAssembler &Asm) {
   unsigned i = 0;
   // Compute the section layout order. Virtual sections must go last.
   for (MCSection &Sec : Asm) {
-    if (!Sec.isVirtualSection()) {
+    if (!Sec.isBssSection()) {
       SectionOrder.push_back(&Sec);
       cast<MCSectionMachO>(Sec).setLayoutOrder(i++);
     }
   }
   for (MCSection &Sec : Asm) {
-    if (Sec.isVirtualSection()) {
+    if (Sec.isBssSection()) {
       SectionOrder.push_back(&Sec);
       cast<MCSectionMachO>(Sec).setLayoutOrder(i++);
     }
@@ -797,11 +797,8 @@ uint64_t MachObjectWriter::writeObject() {
                      UndefinedSymbolData);
 
   if (!CGProfile.empty()) {
-    MCSection *CGProfileSection = getContext().getMachOSection(
-        "__LLVM", "__cg_profile", 0, SectionKind::getMetadata());
-    auto &Frag = *CGProfileSection->begin();
-    Frag.clearContents();
-    raw_svector_ostream OS(Frag.getContentsForAppending());
+    SmallString<0> Content;
+    raw_svector_ostream OS(Content);
     for (const MCObjectWriter::CGProfileEntry &CGPE : CGProfile) {
       uint32_t FromIndex = CGPE.From->getSymbol().getIndex();
       uint32_t ToIndex = CGPE.To->getSymbol().getIndex();
@@ -809,7 +806,9 @@ uint64_t MachObjectWriter::writeObject() {
       support::endian::write(OS, ToIndex, W.Endian);
       support::endian::write(OS, CGPE.Count, W.Endian);
     }
-    Frag.doneAppending();
+    MCSection *Sec = getContext().getMachOSection("__LLVM", "__cg_profile", 0,
+                                                  SectionKind::getMetadata());
+    llvm::copy(OS.str(), Sec->curFragList()->Head->getContents().data());
   }
 
   unsigned NumSections = Asm.end() - Asm.begin();
@@ -883,7 +882,7 @@ uint64_t MachObjectWriter::writeObject() {
 
     VMSize = std::max(VMSize, Address + Size);
 
-    if (Sec.isVirtualSection())
+    if (Sec.isBssSection())
       continue;
 
     SectionDataSize = std::max(SectionDataSize, Address + Size);
@@ -915,7 +914,7 @@ uint64_t MachObjectWriter::writeObject() {
     unsigned Flags = Sec.getTypeAndAttributes();
     if (Sec.hasInstructions())
       Flags |= MachO::S_ATTR_SOME_INSTRUCTIONS;
-    if (!cast<MCSectionMachO>(Sec).isVirtualSection() &&
+    if (!cast<MCSectionMachO>(Sec).isBssSection() &&
         !isUInt<32>(SectionStart)) {
       getContext().reportError(
           SMLoc(), "cannot encode offset of section; object file too large");
diff --git a/llvm/lib/MC/WasmObjectWriter.cpp b/llvm/lib/MC/WasmObjectWriter.cpp
index 7af240a..3b99af4 100644
--- a/llvm/lib/MC/WasmObjectWriter.cpp
+++ b/llvm/lib/MC/WasmObjectWriter.cpp
@@ -696,14 +696,15 @@ static void addData(SmallVectorImpl<char> &DataBytes,
     if (Frag.hasInstructions())
       report_fatal_error("only data supported in data sections");
 
-    if (auto *Align = dyn_cast<MCAlignFragment>(&Frag)) {
-      if (Align->getFillLen() != 1)
+    llvm::append_range(DataBytes, Frag.getContents());
+    if (Frag.getKind() == MCFragment::FT_Align) {
+      if (Frag.getAlignFillLen() != 1)
         report_fatal_error("only byte values supported for alignment");
       // If nops are requested, use zeros, as this is the data section.
-      uint8_t Value = Align->hasEmitNops() ? 0 : Align->getFill();
+      uint8_t Value = Frag.hasAlignEmitNops() ? 0 : Frag.getAlignFill();
       uint64_t Size =
-          std::min<uint64_t>(alignTo(DataBytes.size(), Align->getAlignment()),
-                             DataBytes.size() + Align->getMaxBytesToEmit());
+          std::min<uint64_t>(alignTo(DataBytes.size(), Frag.getAlignment()),
+                             DataBytes.size() + Frag.getAlignMaxBytesToEmit());
       DataBytes.resize(Size, Value);
     } else if (auto *Fill = dyn_cast<MCFillFragment>(&Frag)) {
       int64_t NumValues;
@@ -711,12 +712,10 @@ static void addData(SmallVectorImpl<char> &DataBytes,
         llvm_unreachable("The fill should be an assembler constant");
       DataBytes.insert(DataBytes.end(), Fill->getValueSize() * NumValues,
                        Fill->getValue());
+    } else if (Frag.getKind() == MCFragment::FT_LEB) {
+      llvm::append_range(DataBytes, Frag.getVarContents());
     } else {
-      llvm::append_range(DataBytes, Frag.getContents());
-      if (Frag.getKind() == MCFragment::FT_LEB)
-        llvm::append_range(DataBytes, Frag.getVarContents());
-      else
-        assert(Frag.getKind() == MCFragment::FT_Data);
+      assert(Frag.getKind() == MCFragment::FT_Data);
     }
   }
 
@@ -1858,23 +1857,9 @@ uint64_t WasmObjectWriter::writeOneObject(MCAssembler &Asm,
     auto IT = WS.begin();
     if (IT == WS.end())
       continue;
-    const MCFragment &EmptyFrag = *IT;
-    if (EmptyFrag.getKind() != MCFragment::FT_Data)
-      report_fatal_error(".init_array section should be aligned");
-
-    const MCFragment *nextFrag = EmptyFrag.getNext();
-    while (nextFrag != nullptr) {
-      const MCFragment &AlignFrag = *nextFrag;
-      if (AlignFrag.getKind() != MCFragment::FT_Align)
-        report_fatal_error(".init_array section should be aligned");
-      if (cast<MCAlignFragment>(AlignFrag).getAlignment() !=
-          Align(is64Bit() ? 8 : 4))
-        report_fatal_error(
-            ".init_array section should be aligned for pointers");
-
-      const MCFragment &Frag = *AlignFrag.getNext();
-      nextFrag = Frag.getNext();
-      if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data)
+    for (auto *Frag = &*IT; Frag; Frag = Frag->getNext()) {
+      if (Frag->hasInstructions() || (Frag->getKind() != MCFragment::FT_Align &&
+                                      Frag->getKind() != MCFragment::FT_Data))
         report_fatal_error("only data supported in .init_array section");
 
       uint16_t Priority = UINT16_MAX;
@@ -1886,9 +1871,8 @@ uint64_t WasmObjectWriter::writeOneObject(MCAssembler &Asm,
         if (WS.getName().substr(PrefixLength + 1).getAsInteger(10, Priority))
           report_fatal_error("invalid .init_array section priority");
       }
-      const auto &DataFrag = Frag;
-      assert(llvm::all_of(DataFrag.getContents(), [](char C) { return !C; }));
-      for (const MCFixup &Fixup : DataFrag.getFixups()) {
+      assert(llvm::all_of(Frag->getContents(), [](char C) { return !C; }));
+      for (const MCFixup &Fixup : Frag->getFixups()) {
         assert(Fixup.getKind() ==
                MCFixup::getDataKindForSize(is64Bit() ? 8 : 4));
         const MCExpr *Expr = Fixup.getValue();
diff --git a/llvm/lib/MC/WinCOFFObjectWriter.cpp b/llvm/lib/MC/WinCOFFObjectWriter.cpp
index ee4d957..6ad4334 100644
--- a/llvm/lib/MC/WinCOFFObjectWriter.cpp
+++ b/llvm/lib/MC/WinCOFFObjectWriter.cpp
@@ -179,7 +179,7 @@ private:
   void SetSymbolName(COFFSymbol &S);
   void SetSectionName(COFFSection &S);
 
-  bool IsPhysicalSection(COFFSection *S);
+  bool isUninitializedData(const COFFSection &S);
 
   // Entity writing methods.
   void WriteFileHeader(const COFF::header &Header);
@@ -453,8 +453,8 @@ void WinCOFFWriter::SetSymbolName(COFFSymbol &S) {
     std::memcpy(S.Data.Name, S.Name.c_str(), S.Name.size());
 }
 
-bool WinCOFFWriter::IsPhysicalSection(COFFSection *S) {
-  return (S->Header.Characteristics & COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA) ==
+bool WinCOFFWriter::isUninitializedData(const COFFSection &S) {
+  return (S.Header.Characteristics & COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA) !=
          0;
 }
 
@@ -606,6 +606,9 @@ void WinCOFFWriter::writeSection(const COFFSection &Sec) {
     assert(AuxSyms.size() == 1 && AuxSyms[0].AuxType == ATSectionDefinition);
     AuxSymbol &SecDef = AuxSyms[0];
     SecDef.Aux.SectionDefinition.CheckSum = CRC;
+  } else if (isUninitializedData(Sec)) {
+    // Error if fixups or non-zero bytes are present.
+    writeSectionContents(*Sec.MCSection);
   }
 
   // Write relocations for this section.
@@ -745,7 +748,7 @@ void WinCOFFWriter::assignFileOffsets() {
 
     Sec->Header.SizeOfRawData = Asm->getSectionAddressSize(Section);
 
-    if (IsPhysicalSection(Sec)) {
+    if (!isUninitializedData(*Sec)) {
       Sec->Header.PointerToRawData = Offset;
       Offset += Sec->Header.SizeOfRawData;
     }
@@ -1067,10 +1070,8 @@ uint64_t WinCOFFWriter::writeObject() {
 
   // Create the contents of the .llvm_addrsig section.
   if (Mode != DwoOnly && OWriter.getEmitAddrsigSection()) {
-    auto *Sec = getContext().getCOFFSection(".llvm_addrsig",
-                                            COFF::IMAGE_SCN_LNK_REMOVE);
-    auto *Frag = Sec->curFragList()->Head;
-    raw_svector_ostream OS(Frag->getContentsForAppending());
+    SmallString<0> Content;
+    raw_svector_ostream OS(Content);
     for (const MCSymbol *S : OWriter.AddrsigSyms) {
       if (!S->isRegistered())
         continue;
@@ -1085,15 +1086,15 @@ uint64_t WinCOFFWriter::writeObject() {
              "executePostLayoutBinding!");
       encodeULEB128(SectionMap[TargetSection]->Symbol->getIndex(), OS);
     }
-    Frag->doneAppending();
+    auto *Sec = getContext().getCOFFSection(".llvm_addrsig",
+                                            COFF::IMAGE_SCN_LNK_REMOVE);
+    Sec->curFragList()->Tail->setVarContents(OS.str());
   }
 
   // Create the contents of the .llvm.call-graph-profile section.
   if (Mode != DwoOnly && !OWriter.getCGProfile().empty()) {
-    auto *Sec = getContext().getCOFFSection(".llvm.call-graph-profile",
-                                            COFF::IMAGE_SCN_LNK_REMOVE);
-    auto *Frag = Sec->curFragList()->Head;
-    raw_svector_ostream OS(Frag->getContentsForAppending());
+    SmallString<0> Content;
+    raw_svector_ostream OS(Content);
     for (const auto &CGPE : OWriter.getCGProfile()) {
       uint32_t FromIndex = CGPE.From->getSymbol().getIndex();
       uint32_t ToIndex = CGPE.To->getSymbol().getIndex();
@@ -1101,7 +1102,9 @@ uint64_t WinCOFFWriter::writeObject() {
       support::endian::write(OS, ToIndex, W.Endian);
       support::endian::write(OS, CGPE.Count, W.Endian);
     }
-    Frag->doneAppending();
+    auto *Sec = getContext().getCOFFSection(".llvm.call-graph-profile",
+                                            COFF::IMAGE_SCN_LNK_REMOVE);
+    Sec->curFragList()->Tail->setVarContents(OS.str());
   }
 
   assignFileOffsets();