1 files changed, 1154 insertions, 0 deletions

diff --git a/contrib/llvm-project/llvm/lib/MC/MCAssembler.cpp b/contrib/llvm-project/llvm/lib/MC/MCAssembler.cpp
new file mode 100644
index 000000000000..22a8e73e4af3
--- /dev/null
+++ b/contrib/llvm-project/llvm/lib/MC/MCAssembler.cpp
@@ -0,0 +1,1154 @@
+//===- lib/MC/MCAssembler.cpp - Assembler Backend Implementation ----------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#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"
+#include "llvm/ADT/Twine.h"
+#include "llvm/MC/MCAsmBackend.h"
+#include "llvm/MC/MCAsmInfo.h"
+#include "llvm/MC/MCAsmLayout.h"
+#include "llvm/MC/MCCodeEmitter.h"
+#include "llvm/MC/MCCodeView.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCDwarf.h"
+#include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCFixup.h"
+#include "llvm/MC/MCFixupKindInfo.h"
+#include "llvm/MC/MCFragment.h"
+#include "llvm/MC/MCInst.h"
+#include "llvm/MC/MCObjectWriter.h"
+#include "llvm/MC/MCSection.h"
+#include "llvm/MC/MCSectionELF.h"
+#include "llvm/MC/MCSymbol.h"
+#include "llvm/MC/MCValue.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/LEB128.h"
+#include "llvm/Support/MathExtras.h"
+#include "llvm/Support/raw_ostream.h"
+#include <cassert>
+#include <cstdint>
+#include <cstring>
+#include <tuple>
+#include <utility>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "assembler"
+
+namespace {
+namespace stats {
+
+STATISTIC(EmittedFragments, "Number of emitted assembler fragments - total");
+STATISTIC(EmittedRelaxableFragments,
+          "Number of emitted assembler fragments - relaxable");
+STATISTIC(EmittedDataFragments,
+          "Number of emitted assembler fragments - data");
+STATISTIC(EmittedCompactEncodedInstFragments,
+          "Number of emitted assembler fragments - compact encoded inst");
+STATISTIC(EmittedAlignFragments,
+          "Number of emitted assembler fragments - align");
+STATISTIC(EmittedFillFragments,
+          "Number of emitted assembler fragments - fill");
+STATISTIC(EmittedOrgFragments,
+          "Number of emitted assembler fragments - org");
+STATISTIC(evaluateFixup, "Number of evaluated fixups");
+STATISTIC(FragmentLayouts, "Number of fragment layouts");
+STATISTIC(ObjectBytes, "Number of emitted object file bytes");
+STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
+STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
+STATISTIC(PaddingFragmentsRelaxations,
+          "Number of Padding Fragments relaxations");
+STATISTIC(PaddingFragmentsBytes,
+          "Total size of all padding from adding Fragments");
+
+} // end namespace stats
+} // end anonymous namespace
+
+// FIXME FIXME FIXME: There are number of places in this file where we convert
+// what is a 64-bit assembler value used for computation into a value in the
+// object file, which may truncate it. We should detect that truncation where
+// invalid and report errors back.
+
+/* *** */
+
+MCAssembler::MCAssembler(MCContext &Context,
+                         std::unique_ptr<MCAsmBackend> Backend,
+                         std::unique_ptr<MCCodeEmitter> Emitter,
+                         std::unique_ptr<MCObjectWriter> Writer)
+    : Context(Context), Backend(std::move(Backend)),
+      Emitter(std::move(Emitter)), Writer(std::move(Writer)),
+      BundleAlignSize(0), RelaxAll(false), SubsectionsViaSymbols(false),
+      IncrementalLinkerCompatible(false), ELFHeaderEFlags(0) {
+  VersionInfo.Major = 0; // Major version == 0 for "none specified"
+}
+
+MCAssembler::~MCAssembler() = default;
+
+void MCAssembler::reset() {
+  Sections.clear();
+  Symbols.clear();
+  IndirectSymbols.clear();
+  DataRegions.clear();
+  LinkerOptions.clear();
+  FileNames.clear();
+  ThumbFuncs.clear();
+  BundleAlignSize = 0;
+  RelaxAll = false;
+  SubsectionsViaSymbols = false;
+  IncrementalLinkerCompatible = false;
+  ELFHeaderEFlags = 0;
+  LOHContainer.reset();
+  VersionInfo.Major = 0;
+  VersionInfo.SDKVersion = VersionTuple();
+
+  // reset objects owned by us
+  if (getBackendPtr())
+    getBackendPtr()->reset();
+  if (getEmitterPtr())
+    getEmitterPtr()->reset();
+  if (getWriterPtr())
+    getWriterPtr()->reset();
+  getLOHContainer().reset();
+}
+
+bool MCAssembler::registerSection(MCSection &Section) {
+  if (Section.isRegistered())
+    return false;
+  Sections.push_back(&Section);
+  Section.setIsRegistered(true);
+  return true;
+}
+
+bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
+  if (ThumbFuncs.count(Symbol))
+    return true;
+
+  if (!Symbol->isVariable())
+    return false;
+
+  const MCExpr *Expr = Symbol->getVariableValue();
+
+  MCValue V;
+  if (!Expr->evaluateAsRelocatable(V, nullptr, nullptr))
+    return false;
+
+  if (V.getSymB() || V.getRefKind() != MCSymbolRefExpr::VK_None)
+    return false;
+
+  const MCSymbolRefExpr *Ref = V.getSymA();
+  if (!Ref)
+    return false;
+
+  if (Ref->getKind() != MCSymbolRefExpr::VK_None)
+    return false;
+
+  const MCSymbol &Sym = Ref->getSymbol();
+  if (!isThumbFunc(&Sym))
+    return false;
+
+  ThumbFuncs.insert(Symbol); // Cache it.
+  return true;
+}
+
+bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
+  // Non-temporary labels should always be visible to the linker.
+  if (!Symbol.isTemporary())
+    return true;
+
+  // Absolute temporary labels are never visible.
+  if (!Symbol.isInSection())
+    return false;
+
+  if (Symbol.isUsedInReloc())
+    return true;
+
+  return false;
+}
+
+const MCSymbol *MCAssembler::getAtom(const MCSymbol &S) const {
+  // Linker visible symbols define atoms.
+  if (isSymbolLinkerVisible(S))
+    return &S;
+
+  // Absolute and undefined symbols have no defining atom.
+  if (!S.isInSection())
+    return nullptr;
+
+  // Non-linker visible symbols in sections which can't be atomized have no
+  // defining atom.
+  if (!getContext().getAsmInfo()->isSectionAtomizableBySymbols(
+          *S.getFragment()->getParent()))
+    return nullptr;
+
+  // Otherwise, return the atom for the containing fragment.
+  return S.getFragment()->getAtom();
+}
+
+bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
+                                const MCFixup &Fixup, const MCFragment *DF,
+                                MCValue &Target, uint64_t &Value,
+                                bool &WasForced) const {
+  ++stats::evaluateFixup;
+
+  // FIXME: This code has some duplication with recordRelocation. We should
+  // probably merge the two into a single callback that tries to evaluate a
+  // fixup and records a relocation if one is needed.
+
+  // On error claim to have completely evaluated the fixup, to prevent any
+  // further processing from being done.
+  const MCExpr *Expr = Fixup.getValue();
+  MCContext &Ctx = getContext();
+  Value = 0;
+  WasForced = false;
+  if (!Expr->evaluateAsRelocatable(Target, &Layout, &Fixup)) {
+    Ctx.reportError(Fixup.getLoc(), "expected relocatable expression");
+    return true;
+  }
+  if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
+    if (RefB->getKind() != MCSymbolRefExpr::VK_None) {
+      Ctx.reportError(Fixup.getLoc(),
+                      "unsupported subtraction of qualified symbol");
+      return true;
+    }
+  }
+
+  assert(getBackendPtr() && "Expected assembler backend");
+  bool IsPCRel = getBackendPtr()->getFixupKindInfo(Fixup.getKind()).Flags &
+                 MCFixupKindInfo::FKF_IsPCRel;
+
+  bool IsResolved = false;
+  if (IsPCRel) {
+    if (Target.getSymB()) {
+      IsResolved = false;
+    } else if (!Target.getSymA()) {
+      IsResolved = false;
+    } else {
+      const MCSymbolRefExpr *A = Target.getSymA();
+      const MCSymbol &SA = A->getSymbol();
+      if (A->getKind() != MCSymbolRefExpr::VK_None || SA.isUndefined()) {
+        IsResolved = false;
+      } else if (auto *Writer = getWriterPtr()) {
+        IsResolved = Writer->isSymbolRefDifferenceFullyResolvedImpl(
+            *this, SA, *DF, false, true);
+      }
+    }
+  } else {
+    IsResolved = Target.isAbsolute();
+  }
+
+  Value = Target.getConstant();
+
+  if (const MCSymbolRefExpr *A = Target.getSymA()) {
+    const MCSymbol &Sym = A->getSymbol();
+    if (Sym.isDefined())
+      Value += Layout.getSymbolOffset(Sym);
+  }
+  if (const MCSymbolRefExpr *B = Target.getSymB()) {
+    const MCSymbol &Sym = B->getSymbol();
+    if (Sym.isDefined())
+      Value -= Layout.getSymbolOffset(Sym);
+  }
+
+  bool ShouldAlignPC = getBackend().getFixupKindInfo(Fixup.getKind()).Flags &
+                       MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
+  assert((ShouldAlignPC ? IsPCRel : true) &&
+    "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
+
+  if (IsPCRel) {
+    uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
+
+    // A number of ARM fixups in Thumb mode require that the effective PC
+    // address be determined as the 32-bit aligned version of the actual offset.
+    if (ShouldAlignPC) Offset &= ~0x3;
+    Value -= Offset;
+  }
+
+  // Let the backend force a relocation if needed.
+  if (IsResolved && getBackend().shouldForceRelocation(*this, Fixup, Target)) {
+    IsResolved = false;
+    WasForced = true;
+  }
+
+  return IsResolved;
+}
+
+uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
+                                          const MCFragment &F) const {
+  assert(getBackendPtr() && "Requires assembler backend");
+  switch (F.getKind()) {
+  case MCFragment::FT_Data:
+    return cast<MCDataFragment>(F).getContents().size();
+  case MCFragment::FT_Relaxable:
+    return cast<MCRelaxableFragment>(F).getContents().size();
+  case MCFragment::FT_CompactEncodedInst:
+    return cast<MCCompactEncodedInstFragment>(F).getContents().size();
+  case MCFragment::FT_Fill: {
+    auto &FF = cast<MCFillFragment>(F);
+    int64_t NumValues = 0;
+    if (!FF.getNumValues().evaluateAsAbsolute(NumValues, Layout)) {
+      getContext().reportError(FF.getLoc(),
+                               "expected assembly-time absolute expression");
+      return 0;
+    }
+    int64_t Size = NumValues * FF.getValueSize();
+    if (Size < 0) {
+      getContext().reportError(FF.getLoc(), "invalid number of bytes");
+      return 0;
+    }
+    return Size;
+  }
+
+  case MCFragment::FT_LEB:
+    return cast<MCLEBFragment>(F).getContents().size();
+
+  case MCFragment::FT_Padding:
+    return cast<MCPaddingFragment>(F).getSize();
+
+  case MCFragment::FT_SymbolId:
+    return 4;
+
+  case MCFragment::FT_Align: {
+    const MCAlignFragment &AF = cast<MCAlignFragment>(F);
+    unsigned Offset = Layout.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();
+    }
+    if (Size > AF.getMaxBytesToEmit())
+      return 0;
+    return Size;
+  }
+
+  case MCFragment::FT_Org: {
+    const MCOrgFragment &OF = cast<MCOrgFragment>(F);
+    MCValue Value;
+    if (!OF.getOffset().evaluateAsValue(Value, Layout)) {
+      getContext().reportError(OF.getLoc(),
+                               "expected assembly-time absolute expression");
+        return 0;
+    }
+
+    uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
+    int64_t TargetLocation = Value.getConstant();
+    if (const MCSymbolRefExpr *A = Value.getSymA()) {
+      uint64_t Val;
+      if (!Layout.getSymbolOffset(A->getSymbol(), Val)) {
+        getContext().reportError(OF.getLoc(), "expected absolute expression");
+        return 0;
+      }
+      TargetLocation += Val;
+    }
+    int64_t Size = TargetLocation - FragmentOffset;
+    if (Size < 0 || Size >= 0x40000000) {
+      getContext().reportError(
+          OF.getLoc(), "invalid .org offset '" + Twine(TargetLocation) +
+                           "' (at offset '" + Twine(FragmentOffset) + "')");
+      return 0;
+    }
+    return Size;
+  }
+
+  case MCFragment::FT_Dwarf:
+    return cast<MCDwarfLineAddrFragment>(F).getContents().size();
+  case MCFragment::FT_DwarfFrame:
+    return cast<MCDwarfCallFrameFragment>(F).getContents().size();
+  case MCFragment::FT_CVInlineLines:
+    return cast<MCCVInlineLineTableFragment>(F).getContents().size();
+  case MCFragment::FT_CVDefRange:
+    return cast<MCCVDefRangeFragment>(F).getContents().size();
+  case MCFragment::FT_Dummy:
+    llvm_unreachable("Should not have been added");
+  }
+
+  llvm_unreachable("invalid fragment kind");
+}
+
+void MCAsmLayout::layoutFragment(MCFragment *F) {
+  MCFragment *Prev = F->getPrevNode();
+
+  // We should never try to recompute something which is valid.
+  assert(!isFragmentValid(F) && "Attempt to recompute a valid fragment!");
+  // We should never try to compute the fragment layout if its predecessor
+  // isn't valid.
+  assert((!Prev || isFragmentValid(Prev)) &&
+         "Attempt to compute fragment before its predecessor!");
+
+  ++stats::FragmentLayouts;
+
+  // Compute fragment offset and size.
+  if (Prev)
+    F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
+  else
+    F->Offset = 0;
+  LastValidFragment[F->getParent()] = F;
+
+  // If bundling is enabled and this fragment has instructions in it, it has to
+  // obey the bundling restrictions. With padding, we'll have:
+  //
+  //
+  //        BundlePadding
+  //             |||
+  // -------------------------------------
+  //   Prev  |##########|       F        |
+  // -------------------------------------
+  //                    ^
+  //                    |
+  //                    F->Offset
+  //
+  // The fragment's offset will point to after the padding, and its computed
+  // size won't include the padding.
+  //
+  // When the -mc-relax-all flag is used, we optimize bundling by writting the
+  // padding directly into fragments when the instructions are emitted inside
+  // the streamer. When the fragment is larger than the bundle size, we need to
+  // ensure that it's bundle aligned. This means that if we end up with
+  // multiple fragments, we must emit bundle padding between fragments.
+  //
+  // ".align N" is an example of a directive that introduces multiple
+  // fragments. We could add a special case to handle ".align N" by emitting
+  // within-fragment padding (which would produce less padding when N is less
+  // than the bundle size), but for now we don't.
+  //
+  if (Assembler.isBundlingEnabled() && F->hasInstructions()) {
+    assert(isa<MCEncodedFragment>(F) &&
+           "Only MCEncodedFragment implementations have instructions");
+    MCEncodedFragment *EF = cast<MCEncodedFragment>(F);
+    uint64_t FSize = Assembler.computeFragmentSize(*this, *EF);
+
+    if (!Assembler.getRelaxAll() && FSize > Assembler.getBundleAlignSize())
+      report_fatal_error("Fragment can't be larger than a bundle size");
+
+    uint64_t RequiredBundlePadding =
+        computeBundlePadding(Assembler, EF, EF->Offset, FSize);
+    if (RequiredBundlePadding > UINT8_MAX)
+      report_fatal_error("Padding cannot exceed 255 bytes");
+    EF->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
+    EF->Offset += RequiredBundlePadding;
+  }
+}
+
+void MCAssembler::registerSymbol(const MCSymbol &Symbol, bool *Created) {
+  bool New = !Symbol.isRegistered();
+  if (Created)
+    *Created = New;
+  if (New) {
+    Symbol.setIsRegistered(true);
+    Symbols.push_back(&Symbol);
+  }
+}
+
+void MCAssembler::writeFragmentPadding(raw_ostream &OS,
+                                       const MCEncodedFragment &EF,
+                                       uint64_t FSize) const {
+  assert(getBackendPtr() && "Expected assembler backend");
+  // Should NOP padding be written out before this fragment?
+  unsigned BundlePadding = EF.getBundlePadding();
+  if (BundlePadding > 0) {
+    assert(isBundlingEnabled() &&
+           "Writing bundle padding with disabled bundling");
+    assert(EF.hasInstructions() &&
+           "Writing bundle padding for a fragment without instructions");
+
+    unsigned TotalLength = BundlePadding + static_cast<unsigned>(FSize);
+    if (EF.alignToBundleEnd() && TotalLength > getBundleAlignSize()) {
+      // If the padding itself crosses a bundle boundary, it must be emitted
+      // in 2 pieces, since even nop instructions must not cross boundaries.
+      //             v--------------v   <- BundleAlignSize
+      //        v---------v             <- BundlePadding
+      // ----------------------------
+      // | Prev |####|####|    F    |
+      // ----------------------------
+      //        ^-------------------^   <- TotalLength
+      unsigned DistanceToBoundary = TotalLength - getBundleAlignSize();
+      if (!getBackend().writeNopData(OS, DistanceToBoundary))
+        report_fatal_error("unable to write NOP sequence of " +
+                           Twine(DistanceToBoundary) + " bytes");
+      BundlePadding -= DistanceToBoundary;
+    }
+    if (!getBackend().writeNopData(OS, BundlePadding))
+      report_fatal_error("unable to write NOP sequence of " +
+                         Twine(BundlePadding) + " bytes");
+  }
+}
+
+/// Write the fragment \p F to the output file.
+static void writeFragment(raw_ostream &OS, const MCAssembler &Asm,
+                          const MCAsmLayout &Layout, const MCFragment &F) {
+  // FIXME: Embed in fragments instead?
+  uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
+
+  support::endianness Endian = Asm.getBackend().Endian;
+
+  if (const MCEncodedFragment *EF = dyn_cast<MCEncodedFragment>(&F))
+    Asm.writeFragmentPadding(OS, *EF, FragmentSize);
+
+  // This variable (and its dummy usage) is to participate in the assert at
+  // the end of the function.
+  uint64_t Start = OS.tell();
+  (void) Start;
+
+  ++stats::EmittedFragments;
+
+  switch (F.getKind()) {
+  case MCFragment::FT_Align: {
+    ++stats::EmittedAlignFragments;
+    const MCAlignFragment &AF = cast<MCAlignFragment>(F);
+    assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
+
+    uint64_t Count = FragmentSize / AF.getValueSize();
+
+    // FIXME: This error shouldn't actually occur (the front end should emit
+    // multiple .align directives to enforce the semantics it wants), but is
+    // severe enough that we want to report it. How to handle this?
+    if (Count * AF.getValueSize() != FragmentSize)
+      report_fatal_error("undefined .align directive, value size '" +
+                        Twine(AF.getValueSize()) +
+                        "' is not a divisor of padding size '" +
+                        Twine(FragmentSize) + "'");
+
+    // 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))
+        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.getValueSize()) {
+      default: llvm_unreachable("Invalid size!");
+      case 1: OS << char(AF.getValue()); break;
+      case 2:
+        support::endian::write<uint16_t>(OS, AF.getValue(), Endian);
+        break;
+      case 4:
+        support::endian::write<uint32_t>(OS, AF.getValue(), Endian);
+        break;
+      case 8:
+        support::endian::write<uint64_t>(OS, AF.getValue(), Endian);
+        break;
+      }
+    }
+    break;
+  }
+
+  case MCFragment::FT_Data:
+    ++stats::EmittedDataFragments;
+    OS << cast<MCDataFragment>(F).getContents();
+    break;
+
+  case MCFragment::FT_Relaxable:
+    ++stats::EmittedRelaxableFragments;
+    OS << cast<MCRelaxableFragment>(F).getContents();
+    break;
+
+  case MCFragment::FT_CompactEncodedInst:
+    ++stats::EmittedCompactEncodedInstFragments;
+    OS << cast<MCCompactEncodedInstFragment>(F).getContents();
+    break;
+
+  case MCFragment::FT_Fill: {
+    ++stats::EmittedFillFragments;
+    const MCFillFragment &FF = cast<MCFillFragment>(F);
+    uint64_t V = FF.getValue();
+    unsigned VSize = FF.getValueSize();
+    const unsigned MaxChunkSize = 16;
+    char Data[MaxChunkSize];
+    // Duplicate V into Data as byte vector to reduce number of
+    // writes done. As such, do endian conversion here.
+    for (unsigned I = 0; I != VSize; ++I) {
+      unsigned index = Endian == support::little ? I : (VSize - I - 1);
+      Data[I] = uint8_t(V >> (index * 8));
+    }
+    for (unsigned I = VSize; I < MaxChunkSize; ++I)
+      Data[I] = Data[I - VSize];
+
+    // Set to largest multiple of VSize in Data.
+    const unsigned NumPerChunk = MaxChunkSize / VSize;
+    // Set ChunkSize to largest multiple of VSize in Data
+    const unsigned ChunkSize = VSize * NumPerChunk;
+
+    // Do copies by chunk.
+    StringRef Ref(Data, ChunkSize);
+    for (uint64_t I = 0, E = FragmentSize / ChunkSize; I != E; ++I)
+      OS << Ref;
+
+    // do remainder if needed.
+    unsigned TrailingCount = FragmentSize % ChunkSize;
+    if (TrailingCount)
+      OS.write(Data, TrailingCount);
+    break;
+  }
+
+  case MCFragment::FT_LEB: {
+    const MCLEBFragment &LF = cast<MCLEBFragment>(F);
+    OS << LF.getContents();
+    break;
+  }
+
+  case MCFragment::FT_Padding: {
+    if (!Asm.getBackend().writeNopData(OS, FragmentSize))
+      report_fatal_error("unable to write nop sequence of " +
+                         Twine(FragmentSize) + " bytes");
+    break;
+  }
+
+  case MCFragment::FT_SymbolId: {
+    const MCSymbolIdFragment &SF = cast<MCSymbolIdFragment>(F);
+    support::endian::write<uint32_t>(OS, SF.getSymbol()->getIndex(), Endian);
+    break;
+  }
+
+  case MCFragment::FT_Org: {
+    ++stats::EmittedOrgFragments;
+    const MCOrgFragment &OF = cast<MCOrgFragment>(F);
+
+    for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
+      OS << char(OF.getValue());
+
+    break;
+  }
+
+  case MCFragment::FT_Dwarf: {
+    const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
+    OS << OF.getContents();
+    break;
+  }
+  case MCFragment::FT_DwarfFrame: {
+    const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
+    OS << CF.getContents();
+    break;
+  }
+  case MCFragment::FT_CVInlineLines: {
+    const auto &OF = cast<MCCVInlineLineTableFragment>(F);
+    OS << OF.getContents();
+    break;
+  }
+  case MCFragment::FT_CVDefRange: {
+    const auto &DRF = cast<MCCVDefRangeFragment>(F);
+    OS << DRF.getContents();
+    break;
+  }
+  case MCFragment::FT_Dummy:
+    llvm_unreachable("Should not have been added");
+  }
+
+  assert(OS.tell() - Start == FragmentSize &&
+         "The stream should advance by fragment size");
+}
+
+void MCAssembler::writeSectionData(raw_ostream &OS, const MCSection *Sec,
+                                   const MCAsmLayout &Layout) const {
+  assert(getBackendPtr() && "Expected assembler backend");
+
+  // Ignore virtual sections.
+  if (Sec->isVirtualSection()) {
+    assert(Layout.getSectionFileSize(Sec) == 0 && "Invalid size for section!");
+
+    // Check that contents are only things legal inside a virtual section.
+    for (const MCFragment &F : *Sec) {
+      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.
+        const MCDataFragment &DF = cast<MCDataFragment>(F);
+        if (DF.fixup_begin() != DF.fixup_end())
+          report_fatal_error("cannot have fixups in virtual section!");
+        for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
+          if (DF.getContents()[i]) {
+            if (auto *ELFSec = dyn_cast<const MCSectionELF>(Sec))
+              report_fatal_error("non-zero initializer found in section '" +
+                  ELFSec->getSectionName() + "'");
+            else
+              report_fatal_error("non-zero initializer found in virtual section");
+          }
+        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).getValueSize() == 0 ||
+                cast<MCAlignFragment>(F).getValue() == 0) &&
+               "Invalid align in virtual section!");
+        break;
+      case MCFragment::FT_Fill:
+        assert((cast<MCFillFragment>(F).getValue() == 0) &&
+               "Invalid fill in virtual section!");
+        break;
+      }
+    }
+
+    return;
+  }
+
+  uint64_t Start = OS.tell();
+  (void)Start;
+
+  for (const MCFragment &F : *Sec)
+    writeFragment(OS, *this, Layout, F);
+
+  assert(OS.tell() - Start == Layout.getSectionAddressSize(Sec));
+}
+
+std::tuple<MCValue, uint64_t, bool>
+MCAssembler::handleFixup(const MCAsmLayout &Layout, MCFragment &F,
+                         const MCFixup &Fixup) {
+  // Evaluate the fixup.
+  MCValue Target;
+  uint64_t FixedValue;
+  bool WasForced;
+  bool IsResolved = evaluateFixup(Layout, Fixup, &F, Target, FixedValue,
+                                  WasForced);
+  if (!IsResolved) {
+    // The fixup was unresolved, we need a relocation. Inform the object
+    // writer of the relocation, and give it an opportunity to adjust the
+    // fixup value if need be.
+    if (Target.getSymA() && Target.getSymB() &&
+        getBackend().requiresDiffExpressionRelocations()) {
+      // The fixup represents the difference between two symbols, which the
+      // backend has indicated must be resolved at link time. Split up the fixup
+      // into two relocations, one for the add, and one for the sub, and emit
+      // both of these. The constant will be associated with the add half of the
+      // expression.
+      MCFixup FixupAdd = MCFixup::createAddFor(Fixup);
+      MCValue TargetAdd =
+          MCValue::get(Target.getSymA(), nullptr, Target.getConstant());
+      getWriter().recordRelocation(*this, Layout, &F, FixupAdd, TargetAdd,
+                                   FixedValue);
+      MCFixup FixupSub = MCFixup::createSubFor(Fixup);
+      MCValue TargetSub = MCValue::get(Target.getSymB());
+      getWriter().recordRelocation(*this, Layout, &F, FixupSub, TargetSub,
+                                   FixedValue);
+    } else {
+      getWriter().recordRelocation(*this, Layout, &F, Fixup, Target,
+                                   FixedValue);
+    }
+  }
+  return std::make_tuple(Target, FixedValue, IsResolved);
+}
+
+void MCAssembler::layout(MCAsmLayout &Layout) {
+  assert(getBackendPtr() && "Expected assembler backend");
+  DEBUG_WITH_TYPE("mc-dump", {
+      errs() << "assembler backend - pre-layout\n--\n";
+      dump(); });
+
+  // Create dummy fragments and assign section ordinals.
+  unsigned SectionIndex = 0;
+  for (MCSection &Sec : *this) {
+    // Create dummy fragments to eliminate any empty sections, this simplifies
+    // layout.
+    if (Sec.getFragmentList().empty())
+      new MCDataFragment(&Sec);
+
+    Sec.setOrdinal(SectionIndex++);
+  }
+
+  // Assign layout order indices to sections and fragments.
+  for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
+    MCSection *Sec = Layout.getSectionOrder()[i];
+    Sec->setLayoutOrder(i);
+
+    unsigned FragmentIndex = 0;
+    for (MCFragment &Frag : *Sec)
+      Frag.setLayoutOrder(FragmentIndex++);
+  }
+
+  // Layout until everything fits.
+  while (layoutOnce(Layout))
+    if (getContext().hadError())
+      return;
+
+  DEBUG_WITH_TYPE("mc-dump", {
+      errs() << "assembler backend - post-relaxation\n--\n";
+      dump(); });
+
+  // Finalize the layout, including fragment lowering.
+  finishLayout(Layout);
+
+  DEBUG_WITH_TYPE("mc-dump", {
+      errs() << "assembler backend - final-layout\n--\n";
+      dump(); });
+
+  // Allow the object writer a chance to perform post-layout binding (for
+  // example, to set the index fields in the symbol data).
+  getWriter().executePostLayoutBinding(*this, Layout);
+
+  // Evaluate and apply the fixups, generating relocation entries as necessary.
+  for (MCSection &Sec : *this) {
+    for (MCFragment &Frag : Sec) {
+      // Data and relaxable fragments both have fixups.  So only process
+      // those here.
+      // FIXME: Is there a better way to do this?  MCEncodedFragmentWithFixups
+      // being templated makes this tricky.
+      if (isa<MCEncodedFragment>(&Frag) &&
+          isa<MCCompactEncodedInstFragment>(&Frag))
+        continue;
+      if (!isa<MCEncodedFragment>(&Frag) && !isa<MCCVDefRangeFragment>(&Frag) &&
+          !isa<MCAlignFragment>(&Frag))
+        continue;
+      ArrayRef<MCFixup> Fixups;
+      MutableArrayRef<char> Contents;
+      const MCSubtargetInfo *STI = nullptr;
+      if (auto *FragWithFixups = dyn_cast<MCDataFragment>(&Frag)) {
+        Fixups = FragWithFixups->getFixups();
+        Contents = FragWithFixups->getContents();
+        STI = FragWithFixups->getSubtargetInfo();
+        assert(!FragWithFixups->hasInstructions() || STI != nullptr);
+      } else if (auto *FragWithFixups = dyn_cast<MCRelaxableFragment>(&Frag)) {
+        Fixups = FragWithFixups->getFixups();
+        Contents = FragWithFixups->getContents();
+        STI = FragWithFixups->getSubtargetInfo();
+        assert(!FragWithFixups->hasInstructions() || STI != nullptr);
+      } else if (auto *FragWithFixups = dyn_cast<MCCVDefRangeFragment>(&Frag)) {
+        Fixups = FragWithFixups->getFixups();
+        Contents = FragWithFixups->getContents();
+      } else if (auto *FragWithFixups = dyn_cast<MCDwarfLineAddrFragment>(&Frag)) {
+        Fixups = FragWithFixups->getFixups();
+        Contents = FragWithFixups->getContents();
+      } else if (auto *AF = dyn_cast<MCAlignFragment>(&Frag)) {
+        // Insert fixup type for code alignment if the target define
+        // shouldInsertFixupForCodeAlign target hook.
+        if (Sec.UseCodeAlign() && AF->hasEmitNops()) {
+          getBackend().shouldInsertFixupForCodeAlign(*this, Layout, *AF);
+        }
+        continue;
+      } else if (auto *FragWithFixups =
+                     dyn_cast<MCDwarfCallFrameFragment>(&Frag)) {
+        Fixups = FragWithFixups->getFixups();
+        Contents = FragWithFixups->getContents();
+      } else
+        llvm_unreachable("Unknown fragment with fixups!");
+      for (const MCFixup &Fixup : Fixups) {
+        uint64_t FixedValue;
+        bool IsResolved;
+        MCValue Target;
+        std::tie(Target, FixedValue, IsResolved) =
+            handleFixup(Layout, Frag, Fixup);
+        getBackend().applyFixup(*this, Fixup, Target, Contents, FixedValue,
+                                IsResolved, STI);
+      }
+    }
+  }
+}
+
+void MCAssembler::Finish() {
+  // Create the layout object.
+  MCAsmLayout Layout(*this);
+  layout(Layout);
+
+  // Write the object file.
+  stats::ObjectBytes += getWriter().writeObject(*this, Layout);
+}
+
+bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
+                                       const MCRelaxableFragment *DF,
+                                       const MCAsmLayout &Layout) const {
+  assert(getBackendPtr() && "Expected assembler backend");
+  MCValue Target;
+  uint64_t Value;
+  bool WasForced;
+  bool Resolved = evaluateFixup(Layout, Fixup, DF, Target, Value, WasForced);
+  if (Target.getSymA() &&
+      Target.getSymA()->getKind() == MCSymbolRefExpr::VK_X86_ABS8 &&
+      Fixup.getKind() == FK_Data_1)
+    return false;
+  return getBackend().fixupNeedsRelaxationAdvanced(Fixup, Resolved, Value, DF,
+                                                   Layout, WasForced);
+}
+
+bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
+                                          const MCAsmLayout &Layout) const {
+  assert(getBackendPtr() && "Expected assembler backend");
+  // If this inst doesn't ever need relaxation, ignore it. This occurs when we
+  // are intentionally pushing out inst fragments, or because we relaxed a
+  // previous instruction to one that doesn't need relaxation.
+  if (!getBackend().mayNeedRelaxation(F->getInst(), *F->getSubtargetInfo()))
+    return false;
+
+  for (const MCFixup &Fixup : F->getFixups())
+    if (fixupNeedsRelaxation(Fixup, F, Layout))
+      return true;
+
+  return false;
+}
+
+bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
+                                   MCRelaxableFragment &F) {
+  assert(getEmitterPtr() &&
+         "Expected CodeEmitter defined for relaxInstruction");
+  if (!fragmentNeedsRelaxation(&F, Layout))
+    return false;
+
+  ++stats::RelaxedInstructions;
+
+  // FIXME-PERF: We could immediately lower out instructions if we can tell
+  // they are fully resolved, to avoid retesting on later passes.
+
+  // Relax the fragment.
+
+  MCInst Relaxed;
+  getBackend().relaxInstruction(F.getInst(), *F.getSubtargetInfo(), Relaxed);
+
+  // Encode the new instruction.
+  //
+  // FIXME-PERF: If it matters, we could let the target do this. It can
+  // probably do so more efficiently in many cases.
+  SmallVector<MCFixup, 4> Fixups;
+  SmallString<256> Code;
+  raw_svector_ostream VecOS(Code);
+  getEmitter().encodeInstruction(Relaxed, VecOS, Fixups, *F.getSubtargetInfo());
+
+  // Update the fragment.
+  F.setInst(Relaxed);
+  F.getContents() = Code;
+  F.getFixups() = Fixups;
+
+  return true;
+}
+
+bool MCAssembler::relaxPaddingFragment(MCAsmLayout &Layout,
+                                       MCPaddingFragment &PF) {
+  assert(getBackendPtr() && "Expected assembler backend");
+  uint64_t OldSize = PF.getSize();
+  if (!getBackend().relaxFragment(&PF, Layout))
+    return false;
+  uint64_t NewSize = PF.getSize();
+
+  ++stats::PaddingFragmentsRelaxations;
+  stats::PaddingFragmentsBytes += NewSize;
+  stats::PaddingFragmentsBytes -= OldSize;
+  return true;
+}
+
+bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
+  uint64_t OldSize = LF.getContents().size();
+  int64_t Value;
+  bool Abs = LF.getValue().evaluateKnownAbsolute(Value, Layout);
+  if (!Abs)
+    report_fatal_error("sleb128 and uleb128 expressions must be absolute");
+  SmallString<8> &Data = LF.getContents();
+  Data.clear();
+  raw_svector_ostream OSE(Data);
+  // The compiler can generate EH table assembly that is impossible to assemble
+  // without either adding padding to an LEB fragment or adding extra padding
+  // to a later alignment fragment. To accommodate such tables, relaxation can
+  // only increase an LEB fragment size here, not decrease it. See PR35809.
+  if (LF.isSigned())
+    encodeSLEB128(Value, OSE, OldSize);
+  else
+    encodeULEB128(Value, OSE, OldSize);
+  return OldSize != LF.getContents().size();
+}
+
+bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
+                                     MCDwarfLineAddrFragment &DF) {
+  MCContext &Context = Layout.getAssembler().getContext();
+  uint64_t OldSize = DF.getContents().size();
+  int64_t AddrDelta;
+  bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
+  assert(Abs && "We created a line delta with an invalid expression");
+  (void)Abs;
+  int64_t LineDelta;
+  LineDelta = DF.getLineDelta();
+  SmallVectorImpl<char> &Data = DF.getContents();
+  Data.clear();
+  raw_svector_ostream OSE(Data);
+  DF.getFixups().clear();
+
+  if (!getBackend().requiresDiffExpressionRelocations()) {
+    MCDwarfLineAddr::Encode(Context, getDWARFLinetableParams(), LineDelta,
+                            AddrDelta, OSE);
+  } else {
+    uint32_t Offset;
+    uint32_t Size;
+    bool SetDelta = MCDwarfLineAddr::FixedEncode(Context,
+                                                 getDWARFLinetableParams(),
+                                                 LineDelta, AddrDelta,
+                                                 OSE, &Offset, &Size);
+    // Add Fixups for address delta or new address.
+    const MCExpr *FixupExpr;
+    if (SetDelta) {
+      FixupExpr = &DF.getAddrDelta();
+    } else {
+      const MCBinaryExpr *ABE = cast<MCBinaryExpr>(&DF.getAddrDelta());
+      FixupExpr = ABE->getLHS();
+    }
+    DF.getFixups().push_back(
+        MCFixup::create(Offset, FixupExpr,
+                        MCFixup::getKindForSize(Size, false /*isPCRel*/)));
+  }
+
+  return OldSize != Data.size();
+}
+
+bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
+                                              MCDwarfCallFrameFragment &DF) {
+  MCContext &Context = Layout.getAssembler().getContext();
+  uint64_t OldSize = DF.getContents().size();
+  int64_t AddrDelta;
+  bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
+  assert(Abs && "We created call frame with an invalid expression");
+  (void) Abs;
+  SmallVectorImpl<char> &Data = DF.getContents();
+  Data.clear();
+  raw_svector_ostream OSE(Data);
+  DF.getFixups().clear();
+
+  if (getBackend().requiresDiffExpressionRelocations()) {
+    uint32_t Offset;
+    uint32_t Size;
+    MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE, &Offset,
+                                          &Size);
+    if (Size) {
+      DF.getFixups().push_back(MCFixup::create(
+          Offset, &DF.getAddrDelta(),
+          MCFixup::getKindForSizeInBits(Size /*In bits.*/, false /*isPCRel*/)));
+    }
+  } else {
+    MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
+  }
+
+  return OldSize != Data.size();
+}
+
+bool MCAssembler::relaxCVInlineLineTable(MCAsmLayout &Layout,
+                                         MCCVInlineLineTableFragment &F) {
+  unsigned OldSize = F.getContents().size();
+  getContext().getCVContext().encodeInlineLineTable(Layout, F);
+  return OldSize != F.getContents().size();
+}
+
+bool MCAssembler::relaxCVDefRange(MCAsmLayout &Layout,
+                                  MCCVDefRangeFragment &F) {
+  unsigned OldSize = F.getContents().size();
+  getContext().getCVContext().encodeDefRange(Layout, F);
+  return OldSize != F.getContents().size();
+}
+
+bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSection &Sec) {
+  // Holds the first fragment which needed relaxing during this layout. It will
+  // remain NULL if none were relaxed.
+  // When a fragment is relaxed, all the fragments following it should get
+  // invalidated because their offset is going to change.
+  MCFragment *FirstRelaxedFragment = nullptr;
+
+  // Attempt to relax all the fragments in the section.
+  for (MCSection::iterator I = Sec.begin(), IE = Sec.end(); I != IE; ++I) {
+    // Check if this is a fragment that needs relaxation.
+    bool RelaxedFrag = false;
+    switch(I->getKind()) {
+    default:
+      break;
+    case MCFragment::FT_Relaxable:
+      assert(!getRelaxAll() &&
+             "Did not expect a MCRelaxableFragment in RelaxAll mode");
+      RelaxedFrag = relaxInstruction(Layout, *cast<MCRelaxableFragment>(I));
+      break;
+    case MCFragment::FT_Dwarf:
+      RelaxedFrag = relaxDwarfLineAddr(Layout,
+                                       *cast<MCDwarfLineAddrFragment>(I));
+      break;
+    case MCFragment::FT_DwarfFrame:
+      RelaxedFrag =
+        relaxDwarfCallFrameFragment(Layout,
+                                    *cast<MCDwarfCallFrameFragment>(I));
+      break;
+    case MCFragment::FT_LEB:
+      RelaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(I));
+      break;
+    case MCFragment::FT_Padding:
+      RelaxedFrag = relaxPaddingFragment(Layout, *cast<MCPaddingFragment>(I));
+      break;
+    case MCFragment::FT_CVInlineLines:
+      RelaxedFrag =
+          relaxCVInlineLineTable(Layout, *cast<MCCVInlineLineTableFragment>(I));
+      break;
+    case MCFragment::FT_CVDefRange:
+      RelaxedFrag = relaxCVDefRange(Layout, *cast<MCCVDefRangeFragment>(I));
+      break;
+    }
+    if (RelaxedFrag && !FirstRelaxedFragment)
+      FirstRelaxedFragment = &*I;
+  }
+  if (FirstRelaxedFragment) {
+    Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
+    return true;
+  }
+  return false;
+}
+
+bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
+  ++stats::RelaxationSteps;
+
+  bool WasRelaxed = false;
+  for (iterator it = begin(), ie = end(); it != ie; ++it) {
+    MCSection &Sec = *it;
+    while (layoutSectionOnce(Layout, Sec))
+      WasRelaxed = true;
+  }
+
+  return WasRelaxed;
+}
+
+void MCAssembler::finishLayout(MCAsmLayout &Layout) {
+  assert(getBackendPtr() && "Expected assembler backend");
+  // The layout is done. Mark every fragment as valid.
+  for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
+    MCSection &Section = *Layout.getSectionOrder()[i];
+    Layout.getFragmentOffset(&*Section.rbegin());
+    computeFragmentSize(Layout, *Section.rbegin());
+  }
+  getBackend().finishLayout(*this, Layout);
+}
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+LLVM_DUMP_METHOD void MCAssembler::dump() const{
+  raw_ostream &OS = errs();
+
+  OS << "<MCAssembler\n";
+  OS << "  Sections:[\n    ";
+  for (const_iterator it = begin(), ie = end(); it != ie; ++it) {
+    if (it != begin()) OS << ",\n    ";
+    it->dump();
+  }
+  OS << "],\n";
+  OS << "  Symbols:[";
+
+  for (const_symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
+    if (it != symbol_begin()) OS << ",\n           ";
+    OS << "(";
+    it->dump();
+    OS << ", Index:" << it->getIndex() << ", ";
+    OS << ")";
+  }
+  OS << "]>\n";
+}
+#endif