llvm/lib/MC/MCAssembler.cpp

   1 //===- lib/MC/MCAssembler.cpp - Assembler Backend Implementation ----------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "llvm/MC/MCAssembler.h"
  10 #include "llvm/ADT/ArrayRef.h"
  11 #include "llvm/ADT/SmallString.h"
  12 #include "llvm/ADT/SmallVector.h"
  13 #include "llvm/ADT/Statistic.h"
  14 #include "llvm/ADT/StringRef.h"
  15 #include "llvm/ADT/Twine.h"
  16 #include "llvm/MC/MCAsmBackend.h"
  17 #include "llvm/MC/MCAsmInfo.h"
  18 #include "llvm/MC/MCAsmLayout.h"
  19 #include "llvm/MC/MCCodeEmitter.h"
  20 #include "llvm/MC/MCCodeView.h"
  21 #include "llvm/MC/MCContext.h"
  22 #include "llvm/MC/MCDwarf.h"
  23 #include "llvm/MC/MCExpr.h"
  24 #include "llvm/MC/MCFixup.h"
  25 #include "llvm/MC/MCFixupKindInfo.h"
  26 #include "llvm/MC/MCFragment.h"
  27 #include "llvm/MC/MCInst.h"
  28 #include "llvm/MC/MCObjectWriter.h"
  29 #include "llvm/MC/MCSection.h"
  30 #include "llvm/MC/MCSymbol.h"
  31 #include "llvm/MC/MCValue.h"
  32 #include "llvm/Support/Alignment.h"
  33 #include "llvm/Support/Casting.h"
  34 #include "llvm/Support/Debug.h"
  35 #include "llvm/Support/EndianStream.h"
  36 #include "llvm/Support/ErrorHandling.h"
  37 #include "llvm/Support/LEB128.h"
  38 #include "llvm/Support/raw_ostream.h"
  39 #include <cassert>
  40 #include <cstdint>
  41 #include <tuple>
  42 #include <utility>
  43
  44 using namespace llvm;
  45
  46 namespace llvm {
  47 class MCSubtargetInfo;
  48 }
  49
  50 #define DEBUG_TYPE "assembler"
  51
  52 namespace {
  53 namespace stats {
  54
  55 STATISTIC(EmittedFragments, "Number of emitted assembler fragments - total");
  56 STATISTIC(EmittedRelaxableFragments,
  57           "Number of emitted assembler fragments - relaxable");
  58 STATISTIC(EmittedDataFragments,
  59           "Number of emitted assembler fragments - data");
  60 STATISTIC(EmittedCompactEncodedInstFragments,
  61           "Number of emitted assembler fragments - compact encoded inst");
  62 STATISTIC(EmittedAlignFragments,
  63           "Number of emitted assembler fragments - align");
  64 STATISTIC(EmittedFillFragments,
  65           "Number of emitted assembler fragments - fill");
  66 STATISTIC(EmittedNopsFragments, "Number of emitted assembler fragments - nops");
  67 STATISTIC(EmittedOrgFragments, "Number of emitted assembler fragments - org");
  68 STATISTIC(evaluateFixup, "Number of evaluated fixups");
  69 STATISTIC(FragmentLayouts, "Number of fragment layouts");
  70 STATISTIC(ObjectBytes, "Number of emitted object file bytes");
  71 STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
  72 STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
  73
  74 } // end namespace stats
  75 } // end anonymous namespace
  76
  77 // FIXME FIXME FIXME: There are number of places in this file where we convert
  78 // what is a 64-bit assembler value used for computation into a value in the
  79 // object file, which may truncate it. We should detect that truncation where
  80 // invalid and report errors back.
  81
  82 /* *** */
  83
  84 MCAssembler::MCAssembler(MCContext &Context,
  85                          std::unique_ptr<MCAsmBackend> Backend,
  86                          std::unique_ptr<MCCodeEmitter> Emitter,
  87                          std::unique_ptr<MCObjectWriter> Writer)
  88     : Context(Context), Backend(std::move(Backend)),
  89       Emitter(std::move(Emitter)), Writer(std::move(Writer)),
  90       BundleAlignSize(0), RelaxAll(false), SubsectionsViaSymbols(false),
  91       IncrementalLinkerCompatible(false), ELFHeaderEFlags(0) {
  92   VersionInfo.Major = 0; // Major version == 0 for "none specified"
  93   DarwinTargetVariantVersionInfo.Major = 0;
  94 }
  95
  96 MCAssembler::~MCAssembler() = default;
  97
  98 void MCAssembler::reset() {
  99   Sections.clear();
 100   Symbols.clear();
 101   IndirectSymbols.clear();
 102   DataRegions.clear();
 103   LinkerOptions.clear();
 104   FileNames.clear();
 105   ThumbFuncs.clear();
 106   BundleAlignSize = 0;
 107   RelaxAll = false;
 108   SubsectionsViaSymbols = false;
 109   IncrementalLinkerCompatible = false;
 110   ELFHeaderEFlags = 0;
 111   LOHContainer.reset();
 112   VersionInfo.Major = 0;
 113   VersionInfo.SDKVersion = VersionTuple();
 114   DarwinTargetVariantVersionInfo.Major = 0;
 115   DarwinTargetVariantVersionInfo.SDKVersion = VersionTuple();
 116
 117   // reset objects owned by us
 118   if (getBackendPtr())
 119     getBackendPtr()->reset();
 120   if (getEmitterPtr())
 121     getEmitterPtr()->reset();
 122   if (getWriterPtr())
 123     getWriterPtr()->reset();
 124   getLOHContainer().reset();
 125 }
 126
 127 bool MCAssembler::registerSection(MCSection &Section) {
 128   if (Section.isRegistered())
 129     return false;
 130   Sections.push_back(&Section);
 131   Section.setIsRegistered(true);
 132   return true;
 133 }
 134
 135 bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
 136   if (ThumbFuncs.count(Symbol))
 137     return true;
 138
 139   if (!Symbol->isVariable())
 140     return false;
 141
 142   const MCExpr *Expr = Symbol->getVariableValue();
 143
 144   MCValue V;
 145   if (!Expr->evaluateAsRelocatable(V, nullptr, nullptr))
 146     return false;
 147
 148   if (V.getSymB() || V.getRefKind() != MCSymbolRefExpr::VK_None)
 149     return false;
 150
 151   const MCSymbolRefExpr *Ref = V.getSymA();
 152   if (!Ref)
 153     return false;
 154
 155   if (Ref->getKind() != MCSymbolRefExpr::VK_None)
 156     return false;
 157
 158   const MCSymbol &Sym = Ref->getSymbol();
 159   if (!isThumbFunc(&Sym))
 160     return false;
 161
 162   ThumbFuncs.insert(Symbol); // Cache it.
 163   return true;
 164 }
 165
 166 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
 167   // Non-temporary labels should always be visible to the linker.
 168   if (!Symbol.isTemporary())
 169     return true;
 170
 171   if (Symbol.isUsedInReloc())
 172     return true;
 173
 174   return false;
 175 }
 176
 177 const MCSymbol *MCAssembler::getAtom(const MCSymbol &S) const {
 178   // Linker visible symbols define atoms.
 179   if (isSymbolLinkerVisible(S))
 180     return &S;
 181
 182   // Absolute and undefined symbols have no defining atom.
 183   if (!S.isInSection())
 184     return nullptr;
 185
 186   // Non-linker visible symbols in sections which can't be atomized have no
 187   // defining atom.
 188   if (!getContext().getAsmInfo()->isSectionAtomizableBySymbols(
 189           *S.getFragment()->getParent()))
 190     return nullptr;
 191
 192   // Otherwise, return the atom for the containing fragment.
 193   return S.getFragment()->getAtom();
 194 }
 195
 196 bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
 197                                 const MCFixup &Fixup, const MCFragment *DF,
 198                                 MCValue &Target, uint64_t &Value,
 199                                 bool &WasForced) const {
 200   ++stats::evaluateFixup;
 201
 202   // FIXME: This code has some duplication with recordRelocation. We should
 203   // probably merge the two into a single callback that tries to evaluate a
 204   // fixup and records a relocation if one is needed.
 205
 206   // On error claim to have completely evaluated the fixup, to prevent any
 207   // further processing from being done.
 208   const MCExpr *Expr = Fixup.getValue();
 209   MCContext &Ctx = getContext();
 210   Value = 0;
 211   WasForced = false;
 212   if (!Expr->evaluateAsRelocatable(Target, &Layout, &Fixup)) {
 213     Ctx.reportError(Fixup.getLoc(), "expected relocatable expression");
 214     return true;
 215   }
 216   if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
 217     if (RefB->getKind() != MCSymbolRefExpr::VK_None) {
 218       Ctx.reportError(Fixup.getLoc(),
 219                       "unsupported subtraction of qualified symbol");
 220       return true;
 221     }
 222   }
 223
 224   assert(getBackendPtr() && "Expected assembler backend");
 225   bool IsTarget = getBackendPtr()->getFixupKindInfo(Fixup.getKind()).Flags &
 226                   MCFixupKindInfo::FKF_IsTarget;
 227
 228   if (IsTarget)
 229     return getBackend().evaluateTargetFixup(*this, Layout, Fixup, DF, Target,
 230                                             Value, WasForced);
 231
 232   unsigned FixupFlags = getBackendPtr()->getFixupKindInfo(Fixup.getKind()).Flags;
 233   bool IsPCRel = getBackendPtr()->getFixupKindInfo(Fixup.getKind()).Flags &
 234                  MCFixupKindInfo::FKF_IsPCRel;
 235
 236   bool IsResolved = false;
 237   if (IsPCRel) {
 238     if (Target.getSymB()) {
 239       IsResolved = false;
 240     } else if (!Target.getSymA()) {
 241       IsResolved = false;
 242     } else {
 243       const MCSymbolRefExpr *A = Target.getSymA();
 244       const MCSymbol &SA = A->getSymbol();
 245       if (A->getKind() != MCSymbolRefExpr::VK_None || SA.isUndefined()) {
 246         IsResolved = false;
 247       } else if (auto *Writer = getWriterPtr()) {
 248         IsResolved = (FixupFlags & MCFixupKindInfo::FKF_Constant) ||
 249                      Writer->isSymbolRefDifferenceFullyResolvedImpl(
 250                          *this, SA, *DF, false, true);
 251       }
 252     }
 253   } else {
 254     IsResolved = Target.isAbsolute();
 255   }
 256
 257   Value = Target.getConstant();
 258
 259   if (const MCSymbolRefExpr *A = Target.getSymA()) {
 260     const MCSymbol &Sym = A->getSymbol();
 261     if (Sym.isDefined())
 262       Value += Layout.getSymbolOffset(Sym);
 263   }
 264   if (const MCSymbolRefExpr *B = Target.getSymB()) {
 265     const MCSymbol &Sym = B->getSymbol();
 266     if (Sym.isDefined())
 267       Value -= Layout.getSymbolOffset(Sym);
 268   }
 269
 270   bool ShouldAlignPC = getBackend().getFixupKindInfo(Fixup.getKind()).Flags &
 271                        MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
 272   assert((ShouldAlignPC ? IsPCRel : true) &&
 273     "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
 274
 275   if (IsPCRel) {
 276     uint64_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
 277
 278     // A number of ARM fixups in Thumb mode require that the effective PC
 279     // address be determined as the 32-bit aligned version of the actual offset.
 280     if (ShouldAlignPC) Offset &= ~0x3;
 281     Value -= Offset;
 282   }
 283
 284   // Let the backend force a relocation if needed.
 285   if (IsResolved && getBackend().shouldForceRelocation(*this, Fixup, Target)) {
 286     IsResolved = false;
 287     WasForced = true;
 288   }
 289
 290   // A linker relaxation target may emit ADD/SUB relocations for A-B+C. Let
 291   // recordRelocation handle non-VK_None cases like A@plt-B+C.
 292   if (!IsResolved && Target.getSymA() && Target.getSymB() &&
 293       Target.getSymA()->getKind() == MCSymbolRefExpr::VK_None &&
 294       getBackend().handleAddSubRelocations(Layout, *DF, Fixup, Target, Value))
 295     return true;
 296
 297   return IsResolved;
 298 }
 299
 300 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
 301                                           const MCFragment &F) const {
 302   assert(getBackendPtr() && "Requires assembler backend");
 303   switch (F.getKind()) {
 304   case MCFragment::FT_Data:
 305     return cast<MCDataFragment>(F).getContents().size();
 306   case MCFragment::FT_Relaxable:
 307     return cast<MCRelaxableFragment>(F).getContents().size();
 308   case MCFragment::FT_CompactEncodedInst:
 309     return cast<MCCompactEncodedInstFragment>(F).getContents().size();
 310   case MCFragment::FT_Fill: {
 311     auto &FF = cast<MCFillFragment>(F);
 312     int64_t NumValues = 0;
 313     if (!FF.getNumValues().evaluateKnownAbsolute(NumValues, Layout)) {
 314       getContext().reportError(FF.getLoc(),
 315                                "expected assembly-time absolute expression");
 316       return 0;
 317     }
 318     int64_t Size = NumValues * FF.getValueSize();
 319     if (Size < 0) {
 320       getContext().reportError(FF.getLoc(), "invalid number of bytes");
 321       return 0;
 322     }
 323     return Size;
 324   }
 325
 326   case MCFragment::FT_Nops:
 327     return cast<MCNopsFragment>(F).getNumBytes();
 328
 329   case MCFragment::FT_LEB:
 330     return cast<MCLEBFragment>(F).getContents().size();
 331
 332   case MCFragment::FT_BoundaryAlign:
 333     return cast<MCBoundaryAlignFragment>(F).getSize();
 334
 335   case MCFragment::FT_SymbolId:
 336     return 4;
 337
 338   case MCFragment::FT_Align: {
 339     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
 340     unsigned Offset = Layout.getFragmentOffset(&AF);
 341     unsigned Size = offsetToAlignment(Offset, AF.getAlignment());
 342
 343     // Insert extra Nops for code alignment if the target define
 344     // shouldInsertExtraNopBytesForCodeAlign target hook.
 345     if (AF.getParent()->useCodeAlign() && AF.hasEmitNops() &&
 346         getBackend().shouldInsertExtraNopBytesForCodeAlign(AF, Size))
 347       return Size;
 348
 349     // If we are padding with nops, force the padding to be larger than the
 350     // minimum nop size.
 351     if (Size > 0 && AF.hasEmitNops()) {
 352       while (Size % getBackend().getMinimumNopSize())
 353         Size += AF.getAlignment().value();
 354     }
 355     if (Size > AF.getMaxBytesToEmit())
 356       return 0;
 357     return Size;
 358   }
 359
 360   case MCFragment::FT_Org: {
 361     const MCOrgFragment &OF = cast<MCOrgFragment>(F);
 362     MCValue Value;
 363     if (!OF.getOffset().evaluateAsValue(Value, Layout)) {
 364       getContext().reportError(OF.getLoc(),
 365                                "expected assembly-time absolute expression");
 366         return 0;
 367     }
 368
 369     uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
 370     int64_t TargetLocation = Value.getConstant();
 371     if (const MCSymbolRefExpr *A = Value.getSymA()) {
 372       uint64_t Val;
 373       if (!Layout.getSymbolOffset(A->getSymbol(), Val)) {
 374         getContext().reportError(OF.getLoc(), "expected absolute expression");
 375         return 0;
 376       }
 377       TargetLocation += Val;
 378     }
 379     int64_t Size = TargetLocation - FragmentOffset;
 380     if (Size < 0 || Size >= 0x40000000) {
 381       getContext().reportError(
 382           OF.getLoc(), "invalid .org offset '" + Twine(TargetLocation) +
 383                            "' (at offset '" + Twine(FragmentOffset) + "')");
 384       return 0;
 385     }
 386     return Size;
 387   }
 388
 389   case MCFragment::FT_Dwarf:
 390     return cast<MCDwarfLineAddrFragment>(F).getContents().size();
 391   case MCFragment::FT_DwarfFrame:
 392     return cast<MCDwarfCallFrameFragment>(F).getContents().size();
 393   case MCFragment::FT_CVInlineLines:
 394     return cast<MCCVInlineLineTableFragment>(F).getContents().size();
 395   case MCFragment::FT_CVDefRange:
 396     return cast<MCCVDefRangeFragment>(F).getContents().size();
 397   case MCFragment::FT_PseudoProbe:
 398     return cast<MCPseudoProbeAddrFragment>(F).getContents().size();
 399   case MCFragment::FT_Dummy:
 400     llvm_unreachable("Should not have been added");
 401   }
 402
 403   llvm_unreachable("invalid fragment kind");
 404 }
 405
 406 void MCAsmLayout::layoutFragment(MCFragment *F) {
 407   MCFragment *Prev = F->getPrevNode();
 408
 409   // We should never try to recompute something which is valid.
 410   assert(!isFragmentValid(F) && "Attempt to recompute a valid fragment!");
 411   // We should never try to compute the fragment layout if its predecessor
 412   // isn't valid.
 413   assert((!Prev || isFragmentValid(Prev)) &&
 414          "Attempt to compute fragment before its predecessor!");
 415
 416   assert(!F->IsBeingLaidOut && "Already being laid out!");
 417   F->IsBeingLaidOut = true;
 418
 419   ++stats::FragmentLayouts;
 420
 421   // Compute fragment offset and size.
 422   if (Prev)
 423     F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
 424   else
 425     F->Offset = 0;
 426   F->IsBeingLaidOut = false;
 427   LastValidFragment[F->getParent()] = F;
 428
 429   // If bundling is enabled and this fragment has instructions in it, it has to
 430   // obey the bundling restrictions. With padding, we'll have:
 431   //
 432   //
 433   //        BundlePadding
 434   //             |||
 435   // -------------------------------------
 436   //   Prev  |##########|       F        |
 437   // -------------------------------------
 438   //                    ^
 439   //                    |
 440   //                    F->Offset
 441   //
 442   // The fragment's offset will point to after the padding, and its computed
 443   // size won't include the padding.
 444   //
 445   // When the -mc-relax-all flag is used, we optimize bundling by writting the
 446   // padding directly into fragments when the instructions are emitted inside
 447   // the streamer. When the fragment is larger than the bundle size, we need to
 448   // ensure that it's bundle aligned. This means that if we end up with
 449   // multiple fragments, we must emit bundle padding between fragments.
 450   //
 451   // ".align N" is an example of a directive that introduces multiple
 452   // fragments. We could add a special case to handle ".align N" by emitting
 453   // within-fragment padding (which would produce less padding when N is less
 454   // than the bundle size), but for now we don't.
 455   //
 456   if (Assembler.isBundlingEnabled() && F->hasInstructions()) {
 457     assert(isa<MCEncodedFragment>(F) &&
 458            "Only MCEncodedFragment implementations have instructions");
 459     MCEncodedFragment *EF = cast<MCEncodedFragment>(F);
 460     uint64_t FSize = Assembler.computeFragmentSize(*this, *EF);
 461
 462     if (!Assembler.getRelaxAll() && FSize > Assembler.getBundleAlignSize())
 463       report_fatal_error("Fragment can't be larger than a bundle size");
 464
 465     uint64_t RequiredBundlePadding =
 466         computeBundlePadding(Assembler, EF, EF->Offset, FSize);
 467     if (RequiredBundlePadding > UINT8_MAX)
 468       report_fatal_error("Padding cannot exceed 255 bytes");
 469     EF->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
 470     EF->Offset += RequiredBundlePadding;
 471   }
 472 }
 473
 474 bool MCAssembler::registerSymbol(const MCSymbol &Symbol) {
 475   bool Changed = !Symbol.isRegistered();
 476   if (Changed) {
 477     Symbol.setIsRegistered(true);
 478     Symbols.push_back(&Symbol);
 479   }
 480   return Changed;
 481 }
 482
 483 void MCAssembler::writeFragmentPadding(raw_ostream &OS,
 484                                        const MCEncodedFragment &EF,
 485                                        uint64_t FSize) const {
 486   assert(getBackendPtr() && "Expected assembler backend");
 487   // Should NOP padding be written out before this fragment?
 488   unsigned BundlePadding = EF.getBundlePadding();
 489   if (BundlePadding > 0) {
 490     assert(isBundlingEnabled() &&
 491            "Writing bundle padding with disabled bundling");
 492     assert(EF.hasInstructions() &&
 493            "Writing bundle padding for a fragment without instructions");
 494
 495     unsigned TotalLength = BundlePadding + static_cast<unsigned>(FSize);
 496     const MCSubtargetInfo *STI = EF.getSubtargetInfo();
 497     if (EF.alignToBundleEnd() && TotalLength > getBundleAlignSize()) {
 498       // If the padding itself crosses a bundle boundary, it must be emitted
 499       // in 2 pieces, since even nop instructions must not cross boundaries.
 500       //             v--------------v   <- BundleAlignSize
 501       //        v---------v             <- BundlePadding
 502       // ----------------------------
 503       // | Prev |####|####|    F    |
 504       // ----------------------------
 505       //        ^-------------------^   <- TotalLength
 506       unsigned DistanceToBoundary = TotalLength - getBundleAlignSize();
 507       if (!getBackend().writeNopData(OS, DistanceToBoundary, STI))
 508         report_fatal_error("unable to write NOP sequence of " +
 509                            Twine(DistanceToBoundary) + " bytes");
 510       BundlePadding -= DistanceToBoundary;
 511     }
 512     if (!getBackend().writeNopData(OS, BundlePadding, STI))
 513       report_fatal_error("unable to write NOP sequence of " +
 514                          Twine(BundlePadding) + " bytes");
 515   }
 516 }
 517
 518 /// Write the fragment \p F to the output file.
 519 static void writeFragment(raw_ostream &OS, const MCAssembler &Asm,
 520                           const MCAsmLayout &Layout, const MCFragment &F) {
 521   // FIXME: Embed in fragments instead?
 522   uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
 523
 524   llvm::endianness Endian = Asm.getBackend().Endian;
 525
 526   if (const MCEncodedFragment *EF = dyn_cast<MCEncodedFragment>(&F))
 527     Asm.writeFragmentPadding(OS, *EF, FragmentSize);
 528
 529   // This variable (and its dummy usage) is to participate in the assert at
 530   // the end of the function.
 531   uint64_t Start = OS.tell();
 532   (void) Start;
 533
 534   ++stats::EmittedFragments;
 535
 536   switch (F.getKind()) {
 537   case MCFragment::FT_Align: {
 538     ++stats::EmittedAlignFragments;
 539     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
 540     assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
 541
 542     uint64_t Count = FragmentSize / AF.getValueSize();
 543
 544     // FIXME: This error shouldn't actually occur (the front end should emit
 545     // multiple .align directives to enforce the semantics it wants), but is
 546     // severe enough that we want to report it. How to handle this?
 547     if (Count * AF.getValueSize() != FragmentSize)
 548       report_fatal_error("undefined .align directive, value size '" +
 549                         Twine(AF.getValueSize()) +
 550                         "' is not a divisor of padding size '" +
 551                         Twine(FragmentSize) + "'");
 552
 553     // See if we are aligning with nops, and if so do that first to try to fill
 554     // the Count bytes.  Then if that did not fill any bytes or there are any
 555     // bytes left to fill use the Value and ValueSize to fill the rest.
 556     // If we are aligning with nops, ask that target to emit the right data.
 557     if (AF.hasEmitNops()) {
 558       if (!Asm.getBackend().writeNopData(OS, Count, AF.getSubtargetInfo()))
 559         report_fatal_error("unable to write nop sequence of " +
 560                           Twine(Count) + " bytes");
 561       break;
 562     }
 563
 564     // Otherwise, write out in multiples of the value size.
 565     for (uint64_t i = 0; i != Count; ++i) {
 566       switch (AF.getValueSize()) {
 567       default: llvm_unreachable("Invalid size!");
 568       case 1: OS << char(AF.getValue()); break;
 569       case 2:
 570         support::endian::write<uint16_t>(OS, AF.getValue(), Endian);
 571         break;
 572       case 4:
 573         support::endian::write<uint32_t>(OS, AF.getValue(), Endian);
 574         break;
 575       case 8:
 576         support::endian::write<uint64_t>(OS, AF.getValue(), Endian);
 577         break;
 578       }
 579     }
 580     break;
 581   }
 582
 583   case MCFragment::FT_Data:
 584     ++stats::EmittedDataFragments;
 585     OS << cast<MCDataFragment>(F).getContents();
 586     break;
 587
 588   case MCFragment::FT_Relaxable:
 589     ++stats::EmittedRelaxableFragments;
 590     OS << cast<MCRelaxableFragment>(F).getContents();
 591     break;
 592
 593   case MCFragment::FT_CompactEncodedInst:
 594     ++stats::EmittedCompactEncodedInstFragments;
 595     OS << cast<MCCompactEncodedInstFragment>(F).getContents();
 596     break;
 597
 598   case MCFragment::FT_Fill: {
 599     ++stats::EmittedFillFragments;
 600     const MCFillFragment &FF = cast<MCFillFragment>(F);
 601     uint64_t V = FF.getValue();
 602     unsigned VSize = FF.getValueSize();
 603     const unsigned MaxChunkSize = 16;
 604     char Data[MaxChunkSize];
 605     assert(0 < VSize && VSize <= MaxChunkSize && "Illegal fragment fill size");
 606     // Duplicate V into Data as byte vector to reduce number of
 607     // writes done. As such, do endian conversion here.
 608     for (unsigned I = 0; I != VSize; ++I) {
 609       unsigned index = Endian == llvm::endianness::little ? I : (VSize - I - 1);
 610       Data[I] = uint8_t(V >> (index * 8));
 611     }
 612     for (unsigned I = VSize; I < MaxChunkSize; ++I)
 613       Data[I] = Data[I - VSize];
 614
 615     // Set to largest multiple of VSize in Data.
 616     const unsigned NumPerChunk = MaxChunkSize / VSize;
 617     // Set ChunkSize to largest multiple of VSize in Data
 618     const unsigned ChunkSize = VSize * NumPerChunk;
 619
 620     // Do copies by chunk.
 621     StringRef Ref(Data, ChunkSize);
 622     for (uint64_t I = 0, E = FragmentSize / ChunkSize; I != E; ++I)
 623       OS << Ref;
 624
 625     // do remainder if needed.
 626     unsigned TrailingCount = FragmentSize % ChunkSize;
 627     if (TrailingCount)
 628       OS.write(Data, TrailingCount);
 629     break;
 630   }
 631
 632   case MCFragment::FT_Nops: {
 633     ++stats::EmittedNopsFragments;
 634     const MCNopsFragment &NF = cast<MCNopsFragment>(F);
 635
 636     int64_t NumBytes = NF.getNumBytes();
 637     int64_t ControlledNopLength = NF.getControlledNopLength();
 638     int64_t MaximumNopLength =
 639         Asm.getBackend().getMaximumNopSize(*NF.getSubtargetInfo());
 640
 641     assert(NumBytes > 0 && "Expected positive NOPs fragment size");
 642     assert(ControlledNopLength >= 0 && "Expected non-negative NOP size");
 643
 644     if (ControlledNopLength > MaximumNopLength) {
 645       Asm.getContext().reportError(NF.getLoc(),
 646                                    "illegal NOP size " +
 647                                        std::to_string(ControlledNopLength) +
 648                                        ". (expected within [0, " +
 649                                        std::to_string(MaximumNopLength) + "])");
 650       // Clamp the NOP length as reportError does not stop the execution
 651       // immediately.
 652       ControlledNopLength = MaximumNopLength;
 653     }
 654
 655     // Use maximum value if the size of each NOP is not specified
 656     if (!ControlledNopLength)
 657       ControlledNopLength = MaximumNopLength;
 658
 659     while (NumBytes) {
 660       uint64_t NumBytesToEmit =
 661           (uint64_t)std::min(NumBytes, ControlledNopLength);
 662       assert(NumBytesToEmit && "try to emit empty NOP instruction");
 663       if (!Asm.getBackend().writeNopData(OS, NumBytesToEmit,
 664                                          NF.getSubtargetInfo())) {
 665         report_fatal_error("unable to write nop sequence of the remaining " +
 666                            Twine(NumBytesToEmit) + " bytes");
 667         break;
 668       }
 669       NumBytes -= NumBytesToEmit;
 670     }
 671     break;
 672   }
 673
 674   case MCFragment::FT_LEB: {
 675     const MCLEBFragment &LF = cast<MCLEBFragment>(F);
 676     OS << LF.getContents();
 677     break;
 678   }
 679
 680   case MCFragment::FT_BoundaryAlign: {
 681     const MCBoundaryAlignFragment &BF = cast<MCBoundaryAlignFragment>(F);
 682     if (!Asm.getBackend().writeNopData(OS, FragmentSize, BF.getSubtargetInfo()))
 683       report_fatal_error("unable to write nop sequence of " +
 684                          Twine(FragmentSize) + " bytes");
 685     break;
 686   }
 687
 688   case MCFragment::FT_SymbolId: {
 689     const MCSymbolIdFragment &SF = cast<MCSymbolIdFragment>(F);
 690     support::endian::write<uint32_t>(OS, SF.getSymbol()->getIndex(), Endian);
 691     break;
 692   }
 693
 694   case MCFragment::FT_Org: {
 695     ++stats::EmittedOrgFragments;
 696     const MCOrgFragment &OF = cast<MCOrgFragment>(F);
 697
 698     for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
 699       OS << char(OF.getValue());
 700
 701     break;
 702   }
 703
 704   case MCFragment::FT_Dwarf: {
 705     const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
 706     OS << OF.getContents();
 707     break;
 708   }
 709   case MCFragment::FT_DwarfFrame: {
 710     const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
 711     OS << CF.getContents();
 712     break;
 713   }
 714   case MCFragment::FT_CVInlineLines: {
 715     const auto &OF = cast<MCCVInlineLineTableFragment>(F);
 716     OS << OF.getContents();
 717     break;
 718   }
 719   case MCFragment::FT_CVDefRange: {
 720     const auto &DRF = cast<MCCVDefRangeFragment>(F);
 721     OS << DRF.getContents();
 722     break;
 723   }
 724   case MCFragment::FT_PseudoProbe: {
 725     const MCPseudoProbeAddrFragment &PF = cast<MCPseudoProbeAddrFragment>(F);
 726     OS << PF.getContents();
 727     break;
 728   }
 729   case MCFragment::FT_Dummy:
 730     llvm_unreachable("Should not have been added");
 731   }
 732
 733   assert(OS.tell() - Start == FragmentSize &&
 734          "The stream should advance by fragment size");
 735 }
 736
 737 void MCAssembler::writeSectionData(raw_ostream &OS, const MCSection *Sec,
 738                                    const MCAsmLayout &Layout) const {
 739   assert(getBackendPtr() && "Expected assembler backend");
 740
 741   // Ignore virtual sections.
 742   if (Sec->isVirtualSection()) {
 743     assert(Layout.getSectionFileSize(Sec) == 0 && "Invalid size for section!");
 744
 745     // Check that contents are only things legal inside a virtual section.
 746     for (const MCFragment &F : *Sec) {
 747       switch (F.getKind()) {
 748       default: llvm_unreachable("Invalid fragment in virtual section!");
 749       case MCFragment::FT_Data: {
 750         // Check that we aren't trying to write a non-zero contents (or fixups)
 751         // into a virtual section. This is to support clients which use standard
 752         // directives to fill the contents of virtual sections.
 753         const MCDataFragment &DF = cast<MCDataFragment>(F);
 754         if (DF.fixup_begin() != DF.fixup_end())
 755           getContext().reportError(SMLoc(), Sec->getVirtualSectionKind() +
 756                                                 " section '" + Sec->getName() +
 757                                                 "' cannot have fixups");
 758         for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
 759           if (DF.getContents()[i]) {
 760             getContext().reportError(SMLoc(),
 761                                      Sec->getVirtualSectionKind() +
 762                                          " section '" + Sec->getName() +
 763                                          "' cannot have non-zero initializers");
 764             break;
 765           }
 766         break;
 767       }
 768       case MCFragment::FT_Align:
 769         // Check that we aren't trying to write a non-zero value into a virtual
 770         // section.
 771         assert((cast<MCAlignFragment>(F).getValueSize() == 0 ||
 772                 cast<MCAlignFragment>(F).getValue() == 0) &&
 773                "Invalid align in virtual section!");
 774         break;
 775       case MCFragment::FT_Fill:
 776         assert((cast<MCFillFragment>(F).getValue() == 0) &&
 777                "Invalid fill in virtual section!");
 778         break;
 779       case MCFragment::FT_Org:
 780         break;
 781       }
 782     }
 783
 784     return;
 785   }
 786
 787   uint64_t Start = OS.tell();
 788   (void)Start;
 789
 790   for (const MCFragment &F : *Sec)
 791     writeFragment(OS, *this, Layout, F);
 792
 793   assert(getContext().hadError() ||
 794          OS.tell() - Start == Layout.getSectionAddressSize(Sec));
 795 }
 796
 797 std::tuple<MCValue, uint64_t, bool>
 798 MCAssembler::handleFixup(const MCAsmLayout &Layout, MCFragment &F,
 799                          const MCFixup &Fixup) {
 800   // Evaluate the fixup.
 801   MCValue Target;
 802   uint64_t FixedValue;
 803   bool WasForced;
 804   bool IsResolved = evaluateFixup(Layout, Fixup, &F, Target, FixedValue,
 805                                   WasForced);
 806   if (!IsResolved) {
 807     // The fixup was unresolved, we need a relocation. Inform the object
 808     // writer of the relocation, and give it an opportunity to adjust the
 809     // fixup value if need be.
 810     getWriter().recordRelocation(*this, Layout, &F, Fixup, Target, FixedValue);
 811   }
 812   return std::make_tuple(Target, FixedValue, IsResolved);
 813 }
 814
 815 void MCAssembler::layout(MCAsmLayout &Layout) {
 816   assert(getBackendPtr() && "Expected assembler backend");
 817   DEBUG_WITH_TYPE("mc-dump", {
 818       errs() << "assembler backend - pre-layout\n--\n";
 819       dump(); });
 820
 821   // Create dummy fragments and assign section ordinals.
 822   unsigned SectionIndex = 0;
 823   for (MCSection &Sec : *this) {
 824     // Create dummy fragments to eliminate any empty sections, this simplifies
 825     // layout.
 826     if (Sec.getFragmentList().empty())
 827       new MCDataFragment(&Sec);
 828
 829     Sec.setOrdinal(SectionIndex++);
 830   }
 831
 832   // Assign layout order indices to sections and fragments.
 833   for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
 834     MCSection *Sec = Layout.getSectionOrder()[i];
 835     Sec->setLayoutOrder(i);
 836
 837     unsigned FragmentIndex = 0;
 838     for (MCFragment &Frag : *Sec)
 839       Frag.setLayoutOrder(FragmentIndex++);
 840   }
 841
 842   // Layout until everything fits.
 843   while (layoutOnce(Layout)) {
 844     if (getContext().hadError())
 845       return;
 846     // Size of fragments in one section can depend on the size of fragments in
 847     // another. If any fragment has changed size, we have to re-layout (and
 848     // as a result possibly further relax) all.
 849     for (MCSection &Sec : *this)
 850       Layout.invalidateFragmentsFrom(&*Sec.begin());
 851   }
 852
 853   DEBUG_WITH_TYPE("mc-dump", {
 854       errs() << "assembler backend - post-relaxation\n--\n";
 855       dump(); });
 856
 857   // Finalize the layout, including fragment lowering.
 858   finishLayout(Layout);
 859
 860   DEBUG_WITH_TYPE("mc-dump", {
 861       errs() << "assembler backend - final-layout\n--\n";
 862       dump(); });
 863
 864   // Allow the object writer a chance to perform post-layout binding (for
 865   // example, to set the index fields in the symbol data).
 866   getWriter().executePostLayoutBinding(*this, Layout);
 867
 868   // Evaluate and apply the fixups, generating relocation entries as necessary.
 869   for (MCSection &Sec : *this) {
 870     for (MCFragment &Frag : Sec) {
 871       ArrayRef<MCFixup> Fixups;
 872       MutableArrayRef<char> Contents;
 873       const MCSubtargetInfo *STI = nullptr;
 874
 875       // Process MCAlignFragment and MCEncodedFragmentWithFixups here.
 876       switch (Frag.getKind()) {
 877       default:
 878         continue;
 879       case MCFragment::FT_Align: {
 880         MCAlignFragment &AF = cast<MCAlignFragment>(Frag);
 881         // Insert fixup type for code alignment if the target define
 882         // shouldInsertFixupForCodeAlign target hook.
 883         if (Sec.useCodeAlign() && AF.hasEmitNops())
 884           getBackend().shouldInsertFixupForCodeAlign(*this, Layout, AF);
 885         continue;
 886       }
 887       case MCFragment::FT_Data: {
 888         MCDataFragment &DF = cast<MCDataFragment>(Frag);
 889         Fixups = DF.getFixups();
 890         Contents = DF.getContents();
 891         STI = DF.getSubtargetInfo();
 892         assert(!DF.hasInstructions() || STI != nullptr);
 893         break;
 894       }
 895       case MCFragment::FT_Relaxable: {
 896         MCRelaxableFragment &RF = cast<MCRelaxableFragment>(Frag);
 897         Fixups = RF.getFixups();
 898         Contents = RF.getContents();
 899         STI = RF.getSubtargetInfo();
 900         assert(!RF.hasInstructions() || STI != nullptr);
 901         break;
 902       }
 903       case MCFragment::FT_CVDefRange: {
 904         MCCVDefRangeFragment &CF = cast<MCCVDefRangeFragment>(Frag);
 905         Fixups = CF.getFixups();
 906         Contents = CF.getContents();
 907         break;
 908       }
 909       case MCFragment::FT_Dwarf: {
 910         MCDwarfLineAddrFragment &DF = cast<MCDwarfLineAddrFragment>(Frag);
 911         Fixups = DF.getFixups();
 912         Contents = DF.getContents();
 913         break;
 914       }
 915       case MCFragment::FT_DwarfFrame: {
 916         MCDwarfCallFrameFragment &DF = cast<MCDwarfCallFrameFragment>(Frag);
 917         Fixups = DF.getFixups();
 918         Contents = DF.getContents();
 919         break;
 920       }
 921       case MCFragment::FT_PseudoProbe: {
 922         MCPseudoProbeAddrFragment &PF = cast<MCPseudoProbeAddrFragment>(Frag);
 923         Fixups = PF.getFixups();
 924         Contents = PF.getContents();
 925         break;
 926       }
 927       }
 928       for (const MCFixup &Fixup : Fixups) {
 929         uint64_t FixedValue;
 930         bool IsResolved;
 931         MCValue Target;
 932         std::tie(Target, FixedValue, IsResolved) =
 933             handleFixup(Layout, Frag, Fixup);
 934         getBackend().applyFixup(*this, Fixup, Target, Contents, FixedValue,
 935                                 IsResolved, STI);
 936       }
 937     }
 938   }
 939 }
 940
 941 void MCAssembler::Finish() {
 942   // Create the layout object.
 943   MCAsmLayout Layout(*this);
 944   layout(Layout);
 945
 946   // Write the object file.
 947   stats::ObjectBytes += getWriter().writeObject(*this, Layout);
 948 }
 949
 950 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
 951                                        const MCRelaxableFragment *DF,
 952                                        const MCAsmLayout &Layout) const {
 953   assert(getBackendPtr() && "Expected assembler backend");
 954   MCValue Target;
 955   uint64_t Value;
 956   bool WasForced;
 957   bool Resolved = evaluateFixup(Layout, Fixup, DF, Target, Value, WasForced);
 958   if (Target.getSymA() &&
 959       Target.getSymA()->getKind() == MCSymbolRefExpr::VK_X86_ABS8 &&
 960       Fixup.getKind() == FK_Data_1)
 961     return false;
 962   return getBackend().fixupNeedsRelaxationAdvanced(Fixup, Resolved, Value, DF,
 963                                                    Layout, WasForced);
 964 }
 965
 966 bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
 967                                           const MCAsmLayout &Layout) const {
 968   assert(getBackendPtr() && "Expected assembler backend");
 969   // If this inst doesn't ever need relaxation, ignore it. This occurs when we
 970   // are intentionally pushing out inst fragments, or because we relaxed a
 971   // previous instruction to one that doesn't need relaxation.
 972   if (!getBackend().mayNeedRelaxation(F->getInst(), *F->getSubtargetInfo()))
 973     return false;
 974
 975   for (const MCFixup &Fixup : F->getFixups())
 976     if (fixupNeedsRelaxation(Fixup, F, Layout))
 977       return true;
 978
 979   return false;
 980 }
 981
 982 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
 983                                    MCRelaxableFragment &F) {
 984   assert(getEmitterPtr() &&
 985          "Expected CodeEmitter defined for relaxInstruction");
 986   if (!fragmentNeedsRelaxation(&F, Layout))
 987     return false;
 988
 989   ++stats::RelaxedInstructions;
 990
 991   // FIXME-PERF: We could immediately lower out instructions if we can tell
 992   // they are fully resolved, to avoid retesting on later passes.
 993
 994   // Relax the fragment.
 995
 996   MCInst Relaxed = F.getInst();
 997   getBackend().relaxInstruction(Relaxed, *F.getSubtargetInfo());
 998
 999   // Encode the new instruction.
1000   F.setInst(Relaxed);
1001   F.getFixups().clear();
1002   F.getContents().clear();
1003   getEmitter().encodeInstruction(Relaxed, F.getContents(), F.getFixups(),
1004                                  *F.getSubtargetInfo());
1005   return true;
1006 }
1007
1008 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
1009   uint64_t OldSize = LF.getContents().size();
1010   int64_t Value;
1011   bool Abs = LF.getValue().evaluateKnownAbsolute(Value, Layout);
1012   if (!Abs) {
1013     getContext().reportError(LF.getValue().getLoc(),
1014                              Twine(LF.isSigned() ? ".s" : ".u") +
1015                                  "leb128 expression is not absolute");
1016   }
1017   SmallString<8> &Data = LF.getContents();
1018   Data.clear();
1019   raw_svector_ostream OSE(Data);
1020   // The compiler can generate EH table assembly that is impossible to assemble
1021   // without either adding padding to an LEB fragment or adding extra padding
1022   // to a later alignment fragment. To accommodate such tables, relaxation can
1023   // only increase an LEB fragment size here, not decrease it. See PR35809.
1024   if (LF.isSigned())
1025     encodeSLEB128(Value, OSE, OldSize);
1026   else
1027     encodeULEB128(Value, OSE, OldSize);
1028   return OldSize != LF.getContents().size();
1029 }
1030
1031 /// Check if the branch crosses the boundary.
1032 ///
1033 /// \param StartAddr start address of the fused/unfused branch.
1034 /// \param Size size of the fused/unfused branch.
1035 /// \param BoundaryAlignment alignment requirement of the branch.
1036 /// \returns true if the branch cross the boundary.
1037 static bool mayCrossBoundary(uint64_t StartAddr, uint64_t Size,
1038                              Align BoundaryAlignment) {
1039   uint64_t EndAddr = StartAddr + Size;
1040   return (StartAddr >> Log2(BoundaryAlignment)) !=
1041          ((EndAddr - 1) >> Log2(BoundaryAlignment));
1042 }
1043
1044 /// Check if the branch is against the boundary.
1045 ///
1046 /// \param StartAddr start address of the fused/unfused branch.
1047 /// \param Size size of the fused/unfused branch.
1048 /// \param BoundaryAlignment alignment requirement of the branch.
1049 /// \returns true if the branch is against the boundary.
1050 static bool isAgainstBoundary(uint64_t StartAddr, uint64_t Size,
1051                               Align BoundaryAlignment) {
1052   uint64_t EndAddr = StartAddr + Size;
1053   return (EndAddr & (BoundaryAlignment.value() - 1)) == 0;
1054 }
1055
1056 /// Check if the branch needs padding.
1057 ///
1058 /// \param StartAddr start address of the fused/unfused branch.
1059 /// \param Size size of the fused/unfused branch.
1060 /// \param BoundaryAlignment alignment requirement of the branch.
1061 /// \returns true if the branch needs padding.
1062 static bool needPadding(uint64_t StartAddr, uint64_t Size,
1063                         Align BoundaryAlignment) {
1064   return mayCrossBoundary(StartAddr, Size, BoundaryAlignment) ||
1065          isAgainstBoundary(StartAddr, Size, BoundaryAlignment);
1066 }
1067
1068 bool MCAssembler::relaxBoundaryAlign(MCAsmLayout &Layout,
1069                                      MCBoundaryAlignFragment &BF) {
1070   // BoundaryAlignFragment that doesn't need to align any fragment should not be
1071   // relaxed.
1072   if (!BF.getLastFragment())
1073     return false;
1074
1075   uint64_t AlignedOffset = Layout.getFragmentOffset(&BF);
1076   uint64_t AlignedSize = 0;
1077   for (const MCFragment *F = BF.getLastFragment(); F != &BF;
1078        F = F->getPrevNode())
1079     AlignedSize += computeFragmentSize(Layout, *F);
1080
1081   Align BoundaryAlignment = BF.getAlignment();
1082   uint64_t NewSize = needPadding(AlignedOffset, AlignedSize, BoundaryAlignment)
1083                          ? offsetToAlignment(AlignedOffset, BoundaryAlignment)
1084                          : 0U;
1085   if (NewSize == BF.getSize())
1086     return false;
1087   BF.setSize(NewSize);
1088   Layout.invalidateFragmentsFrom(&BF);
1089   return true;
1090 }
1091
1092 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
1093                                      MCDwarfLineAddrFragment &DF) {
1094
1095   bool WasRelaxed;
1096   if (getBackend().relaxDwarfLineAddr(DF, Layout, WasRelaxed))
1097     return WasRelaxed;
1098
1099   MCContext &Context = Layout.getAssembler().getContext();
1100   uint64_t OldSize = DF.getContents().size();
1101   int64_t AddrDelta;
1102   bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1103   assert(Abs && "We created a line delta with an invalid expression");
1104   (void)Abs;
1105   int64_t LineDelta;
1106   LineDelta = DF.getLineDelta();
1107   SmallVectorImpl<char> &Data = DF.getContents();
1108   Data.clear();
1109   DF.getFixups().clear();
1110
1111   MCDwarfLineAddr::encode(Context, getDWARFLinetableParams(), LineDelta,
1112                           AddrDelta, Data);
1113   return OldSize != Data.size();
1114 }
1115
1116 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
1117                                               MCDwarfCallFrameFragment &DF) {
1118   bool WasRelaxed;
1119   if (getBackend().relaxDwarfCFA(DF, Layout, WasRelaxed))
1120     return WasRelaxed;
1121
1122   MCContext &Context = Layout.getAssembler().getContext();
1123   int64_t Value;
1124   bool Abs = DF.getAddrDelta().evaluateAsAbsolute(Value, Layout);
1125   if (!Abs) {
1126     getContext().reportError(DF.getAddrDelta().getLoc(),
1127                              "invalid CFI advance_loc expression");
1128     DF.setAddrDelta(MCConstantExpr::create(0, Context));
1129     return false;
1130   }
1131
1132   SmallVectorImpl<char> &Data = DF.getContents();
1133   uint64_t OldSize = Data.size();
1134   Data.clear();
1135   DF.getFixups().clear();
1136
1137   MCDwarfFrameEmitter::encodeAdvanceLoc(Context, Value, Data);
1138   return OldSize != Data.size();
1139 }
1140
1141 bool MCAssembler::relaxCVInlineLineTable(MCAsmLayout &Layout,
1142                                          MCCVInlineLineTableFragment &F) {
1143   unsigned OldSize = F.getContents().size();
1144   getContext().getCVContext().encodeInlineLineTable(Layout, F);
1145   return OldSize != F.getContents().size();
1146 }
1147
1148 bool MCAssembler::relaxCVDefRange(MCAsmLayout &Layout,
1149                                   MCCVDefRangeFragment &F) {
1150   unsigned OldSize = F.getContents().size();
1151   getContext().getCVContext().encodeDefRange(Layout, F);
1152   return OldSize != F.getContents().size();
1153 }
1154
1155 bool MCAssembler::relaxPseudoProbeAddr(MCAsmLayout &Layout,
1156                                        MCPseudoProbeAddrFragment &PF) {
1157   uint64_t OldSize = PF.getContents().size();
1158   int64_t AddrDelta;
1159   bool Abs = PF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1160   assert(Abs && "We created a pseudo probe with an invalid expression");
1161   (void)Abs;
1162   SmallVectorImpl<char> &Data = PF.getContents();
1163   Data.clear();
1164   raw_svector_ostream OSE(Data);
1165   PF.getFixups().clear();
1166
1167   // AddrDelta is a signed integer
1168   encodeSLEB128(AddrDelta, OSE, OldSize);
1169   return OldSize != Data.size();
1170 }
1171
1172 bool MCAssembler::relaxFragment(MCAsmLayout &Layout, MCFragment &F) {
1173   switch(F.getKind()) {
1174   default:
1175     return false;
1176   case MCFragment::FT_Relaxable:
1177     assert(!getRelaxAll() &&
1178            "Did not expect a MCRelaxableFragment in RelaxAll mode");
1179     return relaxInstruction(Layout, cast<MCRelaxableFragment>(F));
1180   case MCFragment::FT_Dwarf:
1181     return relaxDwarfLineAddr(Layout, cast<MCDwarfLineAddrFragment>(F));
1182   case MCFragment::FT_DwarfFrame:
1183     return relaxDwarfCallFrameFragment(Layout,
1184                                        cast<MCDwarfCallFrameFragment>(F));
1185   case MCFragment::FT_LEB:
1186     return relaxLEB(Layout, cast<MCLEBFragment>(F));
1187   case MCFragment::FT_BoundaryAlign:
1188     return relaxBoundaryAlign(Layout, cast<MCBoundaryAlignFragment>(F));
1189   case MCFragment::FT_CVInlineLines:
1190     return relaxCVInlineLineTable(Layout, cast<MCCVInlineLineTableFragment>(F));
1191   case MCFragment::FT_CVDefRange:
1192     return relaxCVDefRange(Layout, cast<MCCVDefRangeFragment>(F));
1193   case MCFragment::FT_PseudoProbe:
1194     return relaxPseudoProbeAddr(Layout, cast<MCPseudoProbeAddrFragment>(F));
1195   }
1196 }
1197
1198 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSection &Sec) {
1199   // Holds the first fragment which needed relaxing during this layout. It will
1200   // remain NULL if none were relaxed.
1201   // When a fragment is relaxed, all the fragments following it should get
1202   // invalidated because their offset is going to change.
1203   MCFragment *FirstRelaxedFragment = nullptr;
1204
1205   // Attempt to relax all the fragments in the section.
1206   for (MCFragment &Frag : Sec) {
1207     // Check if this is a fragment that needs relaxation.
1208     bool RelaxedFrag = relaxFragment(Layout, Frag);
1209     if (RelaxedFrag && !FirstRelaxedFragment)
1210       FirstRelaxedFragment = &Frag;
1211   }
1212   if (FirstRelaxedFragment) {
1213     Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
1214     return true;
1215   }
1216   return false;
1217 }
1218
1219 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
1220   ++stats::RelaxationSteps;
1221
1222   bool WasRelaxed = false;
1223   for (MCSection &Sec : *this) {
1224     while (layoutSectionOnce(Layout, Sec))
1225       WasRelaxed = true;
1226   }
1227
1228   return WasRelaxed;
1229 }
1230
1231 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
1232   assert(getBackendPtr() && "Expected assembler backend");
1233   // The layout is done. Mark every fragment as valid.
1234   for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
1235     MCSection &Section = *Layout.getSectionOrder()[i];
1236     Layout.getFragmentOffset(&*Section.getFragmentList().rbegin());
1237     computeFragmentSize(Layout, *Section.getFragmentList().rbegin());
1238   }
1239   getBackend().finishLayout(*this, Layout);
1240 }
1241
1242 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1243 LLVM_DUMP_METHOD void MCAssembler::dump() const{
1244   raw_ostream &OS = errs();
1245
1246   OS << "<MCAssembler\n";
1247   OS << "  Sections:[\n    ";
1248   for (const_iterator it = begin(), ie = end(); it != ie; ++it) {
1249     if (it != begin()) OS << ",\n    ";
1250     it->dump();
1251   }
1252   OS << "],\n";
1253   OS << "  Symbols:[";
1254
1255   for (const_symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1256     if (it != symbol_begin()) OS << ",\n           ";
1257     OS << "(";
1258     it->dump();
1259     OS << ", Index:" << it->getIndex() << ", ";
1260     OS << ")";
1261   }
1262   OS << "]>\n";
1263 }
1264 #endif