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/MCSectionELF.h"
  31 #include "llvm/MC/MCSymbol.h"
  32 #include "llvm/MC/MCValue.h"
  33 #include "llvm/Support/Alignment.h"
  34 #include "llvm/Support/Casting.h"
  35 #include "llvm/Support/Debug.h"
  36 #include "llvm/Support/EndianStream.h"
  37 #include "llvm/Support/ErrorHandling.h"
  38 #include "llvm/Support/LEB128.h"
  39 #include "llvm/Support/MathExtras.h"
  40 #include "llvm/Support/raw_ostream.h"
  41 #include <cassert>
  42 #include <cstdint>
  43 #include <cstring>
  44 #include <tuple>
  45 #include <utility>
  46
  47 using namespace llvm;
  48
  49 #define DEBUG_TYPE "assembler"
  50
  51 namespace {
  52 namespace stats {
  53
  54 STATISTIC(EmittedFragments, "Number of emitted assembler fragments - total");
  55 STATISTIC(EmittedRelaxableFragments,
  56           "Number of emitted assembler fragments - relaxable");
  57 STATISTIC(EmittedDataFragments,
  58           "Number of emitted assembler fragments - data");
  59 STATISTIC(EmittedCompactEncodedInstFragments,
  60           "Number of emitted assembler fragments - compact encoded inst");
  61 STATISTIC(EmittedAlignFragments,
  62           "Number of emitted assembler fragments - align");
  63 STATISTIC(EmittedFillFragments,
  64           "Number of emitted assembler fragments - fill");
  65 STATISTIC(EmittedNopsFragments, "Number of emitted assembler fragments - nops");
  66 STATISTIC(EmittedOrgFragments, "Number of emitted assembler fragments - org");
  67 STATISTIC(evaluateFixup, "Number of evaluated fixups");
  68 STATISTIC(FragmentLayouts, "Number of fragment layouts");
  69 STATISTIC(ObjectBytes, "Number of emitted object file bytes");
  70 STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
  71 STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
  72
  73 } // end namespace stats
  74 } // end anonymous namespace
  75
  76 // FIXME FIXME FIXME: There are number of places in this file where we convert
  77 // what is a 64-bit assembler value used for computation into a value in the
  78 // object file, which may truncate it. We should detect that truncation where
  79 // invalid and report errors back.
  80
  81 /* *** */
  82
  83 MCAssembler::MCAssembler(MCContext &Context,
  84                          std::unique_ptr<MCAsmBackend> Backend,
  85                          std::unique_ptr<MCCodeEmitter> Emitter,
  86                          std::unique_ptr<MCObjectWriter> Writer)
  87     : Context(Context), Backend(std::move(Backend)),
  88       Emitter(std::move(Emitter)), Writer(std::move(Writer)),
  89       BundleAlignSize(0), RelaxAll(false), SubsectionsViaSymbols(false),
  90       IncrementalLinkerCompatible(false), ELFHeaderEFlags(0) {
  91   VersionInfo.Major = 0; // Major version == 0 for "none specified"
  92 }
  93
  94 MCAssembler::~MCAssembler() = default;
  95
  96 void MCAssembler::reset() {
  97   Sections.clear();
  98   Symbols.clear();
  99   IndirectSymbols.clear();
 100   DataRegions.clear();
 101   LinkerOptions.clear();
 102   FileNames.clear();
 103   ThumbFuncs.clear();
 104   BundleAlignSize = 0;
 105   RelaxAll = false;
 106   SubsectionsViaSymbols = false;
 107   IncrementalLinkerCompatible = false;
 108   ELFHeaderEFlags = 0;
 109   LOHContainer.reset();
 110   VersionInfo.Major = 0;
 111   VersionInfo.SDKVersion = VersionTuple();
 112
 113   // reset objects owned by us
 114   if (getBackendPtr())
 115     getBackendPtr()->reset();
 116   if (getEmitterPtr())
 117     getEmitterPtr()->reset();
 118   if (getWriterPtr())
 119     getWriterPtr()->reset();
 120   getLOHContainer().reset();
 121 }
 122
 123 bool MCAssembler::registerSection(MCSection &Section) {
 124   if (Section.isRegistered())
 125     return false;
 126   Sections.push_back(&Section);
 127   Section.setIsRegistered(true);
 128   return true;
 129 }
 130
 131 bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
 132   if (ThumbFuncs.count(Symbol))
 133     return true;
 134
 135   if (!Symbol->isVariable())
 136     return false;
 137
 138   const MCExpr *Expr = Symbol->getVariableValue();
 139
 140   MCValue V;
 141   if (!Expr->evaluateAsRelocatable(V, nullptr, nullptr))
 142     return false;
 143
 144   if (V.getSymB() || V.getRefKind() != MCSymbolRefExpr::VK_None)
 145     return false;
 146
 147   const MCSymbolRefExpr *Ref = V.getSymA();
 148   if (!Ref)
 149     return false;
 150
 151   if (Ref->getKind() != MCSymbolRefExpr::VK_None)
 152     return false;
 153
 154   const MCSymbol &Sym = Ref->getSymbol();
 155   if (!isThumbFunc(&Sym))
 156     return false;
 157
 158   ThumbFuncs.insert(Symbol); // Cache it.
 159   return true;
 160 }
 161
 162 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
 163   // Non-temporary labels should always be visible to the linker.
 164   if (!Symbol.isTemporary())
 165     return true;
 166
 167   if (Symbol.isUsedInReloc())
 168     return true;
 169
 170   return false;
 171 }
 172
 173 const MCSymbol *MCAssembler::getAtom(const MCSymbol &S) const {
 174   // Linker visible symbols define atoms.
 175   if (isSymbolLinkerVisible(S))
 176     return &S;
 177
 178   // Absolute and undefined symbols have no defining atom.
 179   if (!S.isInSection())
 180     return nullptr;
 181
 182   // Non-linker visible symbols in sections which can't be atomized have no
 183   // defining atom.
 184   if (!getContext().getAsmInfo()->isSectionAtomizableBySymbols(
 185           *S.getFragment()->getParent()))
 186     return nullptr;
 187
 188   // Otherwise, return the atom for the containing fragment.
 189   return S.getFragment()->getAtom();
 190 }
 191
 192 bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
 193                                 const MCFixup &Fixup, const MCFragment *DF,
 194                                 MCValue &Target, uint64_t &Value,
 195                                 bool &WasForced) const {
 196   ++stats::evaluateFixup;
 197
 198   // FIXME: This code has some duplication with recordRelocation. We should
 199   // probably merge the two into a single callback that tries to evaluate a
 200   // fixup and records a relocation if one is needed.
 201
 202   // On error claim to have completely evaluated the fixup, to prevent any
 203   // further processing from being done.
 204   const MCExpr *Expr = Fixup.getValue();
 205   MCContext &Ctx = getContext();
 206   Value = 0;
 207   WasForced = false;
 208   if (!Expr->evaluateAsRelocatable(Target, &Layout, &Fixup)) {
 209     Ctx.reportError(Fixup.getLoc(), "expected relocatable expression");
 210     return true;
 211   }
 212   if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
 213     if (RefB->getKind() != MCSymbolRefExpr::VK_None) {
 214       Ctx.reportError(Fixup.getLoc(),
 215                       "unsupported subtraction of qualified symbol");
 216       return true;
 217     }
 218   }
 219
 220   assert(getBackendPtr() && "Expected assembler backend");
 221   bool IsTarget = getBackendPtr()->getFixupKindInfo(Fixup.getKind()).Flags &
 222                   MCFixupKindInfo::FKF_IsTarget;
 223
 224   if (IsTarget)
 225     return getBackend().evaluateTargetFixup(*this, Layout, Fixup, DF, Target,
 226                                             Value, WasForced);
 227
 228   unsigned FixupFlags = getBackendPtr()->getFixupKindInfo(Fixup.getKind()).Flags;
 229   bool IsPCRel = getBackendPtr()->getFixupKindInfo(Fixup.getKind()).Flags &
 230                  MCFixupKindInfo::FKF_IsPCRel;
 231
 232   bool IsResolved = false;
 233   if (IsPCRel) {
 234     if (Target.getSymB()) {
 235       IsResolved = false;
 236     } else if (!Target.getSymA()) {
 237       IsResolved = false;
 238     } else {
 239       const MCSymbolRefExpr *A = Target.getSymA();
 240       const MCSymbol &SA = A->getSymbol();
 241       if (A->getKind() != MCSymbolRefExpr::VK_None || SA.isUndefined()) {
 242         IsResolved = false;
 243       } else if (auto *Writer = getWriterPtr()) {
 244         IsResolved = (FixupFlags & MCFixupKindInfo::FKF_Constant) ||
 245                      Writer->isSymbolRefDifferenceFullyResolvedImpl(
 246                          *this, SA, *DF, false, true);
 247       }
 248     }
 249   } else {
 250     IsResolved = Target.isAbsolute();
 251   }
 252
 253   Value = Target.getConstant();
 254
 255   if (const MCSymbolRefExpr *A = Target.getSymA()) {
 256     const MCSymbol &Sym = A->getSymbol();
 257     if (Sym.isDefined())
 258       Value += Layout.getSymbolOffset(Sym);
 259   }
 260   if (const MCSymbolRefExpr *B = Target.getSymB()) {
 261     const MCSymbol &Sym = B->getSymbol();
 262     if (Sym.isDefined())
 263       Value -= Layout.getSymbolOffset(Sym);
 264   }
 265
 266   bool ShouldAlignPC = getBackend().getFixupKindInfo(Fixup.getKind()).Flags &
 267                        MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
 268   assert((ShouldAlignPC ? IsPCRel : true) &&
 269     "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
 270
 271   if (IsPCRel) {
 272     uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
 273
 274     // A number of ARM fixups in Thumb mode require that the effective PC
 275     // address be determined as the 32-bit aligned version of the actual offset.
 276     if (ShouldAlignPC) Offset &= ~0x3;
 277     Value -= Offset;
 278   }
 279
 280   // Let the backend force a relocation if needed.
 281   if (IsResolved && getBackend().shouldForceRelocation(*this, Fixup, Target)) {
 282     IsResolved = false;
 283     WasForced = true;
 284   }
 285
 286   return IsResolved;
 287 }
 288
 289 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
 290                                           const MCFragment &F) const {
 291   assert(getBackendPtr() && "Requires assembler backend");
 292   switch (F.getKind()) {
 293   case MCFragment::FT_Data:
 294     return cast<MCDataFragment>(F).getContents().size();
 295   case MCFragment::FT_Relaxable:
 296     return cast<MCRelaxableFragment>(F).getContents().size();
 297   case MCFragment::FT_CompactEncodedInst:
 298     return cast<MCCompactEncodedInstFragment>(F).getContents().size();
 299   case MCFragment::FT_Fill: {
 300     auto &FF = cast<MCFillFragment>(F);
 301     int64_t NumValues = 0;
 302     if (!FF.getNumValues().evaluateAsAbsolute(NumValues, Layout)) {
 303       getContext().reportError(FF.getLoc(),
 304                                "expected assembly-time absolute expression");
 305       return 0;
 306     }
 307     int64_t Size = NumValues * FF.getValueSize();
 308     if (Size < 0) {
 309       getContext().reportError(FF.getLoc(), "invalid number of bytes");
 310       return 0;
 311     }
 312     return Size;
 313   }
 314
 315   case MCFragment::FT_Nops:
 316     return cast<MCNopsFragment>(F).getNumBytes();
 317
 318   case MCFragment::FT_LEB:
 319     return cast<MCLEBFragment>(F).getContents().size();
 320
 321   case MCFragment::FT_BoundaryAlign:
 322     return cast<MCBoundaryAlignFragment>(F).getSize();
 323
 324   case MCFragment::FT_SymbolId:
 325     return 4;
 326
 327   case MCFragment::FT_Align: {
 328     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
 329     unsigned Offset = Layout.getFragmentOffset(&AF);
 330     unsigned Size = offsetToAlignment(Offset, Align(AF.getAlignment()));
 331
 332     // Insert extra Nops for code alignment if the target define
 333     // shouldInsertExtraNopBytesForCodeAlign target hook.
 334     if (AF.getParent()->UseCodeAlign() && AF.hasEmitNops() &&
 335         getBackend().shouldInsertExtraNopBytesForCodeAlign(AF, Size))
 336       return Size;
 337
 338     // If we are padding with nops, force the padding to be larger than the
 339     // minimum nop size.
 340     if (Size > 0 && AF.hasEmitNops()) {
 341       while (Size % getBackend().getMinimumNopSize())
 342         Size += AF.getAlignment();
 343     }
 344     if (Size > AF.getMaxBytesToEmit())
 345       return 0;
 346     return Size;
 347   }
 348
 349   case MCFragment::FT_Org: {
 350     const MCOrgFragment &OF = cast<MCOrgFragment>(F);
 351     MCValue Value;
 352     if (!OF.getOffset().evaluateAsValue(Value, Layout)) {
 353       getContext().reportError(OF.getLoc(),
 354                                "expected assembly-time absolute expression");
 355         return 0;
 356     }
 357
 358     uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
 359     int64_t TargetLocation = Value.getConstant();
 360     if (const MCSymbolRefExpr *A = Value.getSymA()) {
 361       uint64_t Val;
 362       if (!Layout.getSymbolOffset(A->getSymbol(), Val)) {
 363         getContext().reportError(OF.getLoc(), "expected absolute expression");
 364         return 0;
 365       }
 366       TargetLocation += Val;
 367     }
 368     int64_t Size = TargetLocation - FragmentOffset;
 369     if (Size < 0 || Size >= 0x40000000) {
 370       getContext().reportError(
 371           OF.getLoc(), "invalid .org offset '" + Twine(TargetLocation) +
 372                            "' (at offset '" + Twine(FragmentOffset) + "')");
 373       return 0;
 374     }
 375     return Size;
 376   }
 377
 378   case MCFragment::FT_Dwarf:
 379     return cast<MCDwarfLineAddrFragment>(F).getContents().size();
 380   case MCFragment::FT_DwarfFrame:
 381     return cast<MCDwarfCallFrameFragment>(F).getContents().size();
 382   case MCFragment::FT_CVInlineLines:
 383     return cast<MCCVInlineLineTableFragment>(F).getContents().size();
 384   case MCFragment::FT_CVDefRange:
 385     return cast<MCCVDefRangeFragment>(F).getContents().size();
 386   case MCFragment::FT_PseudoProbe:
 387     return cast<MCPseudoProbeAddrFragment>(F).getContents().size();
 388   case MCFragment::FT_Dummy:
 389     llvm_unreachable("Should not have been added");
 390   }
 391
 392   llvm_unreachable("invalid fragment kind");
 393 }
 394
 395 void MCAsmLayout::layoutFragment(MCFragment *F) {
 396   MCFragment *Prev = F->getPrevNode();
 397
 398   // We should never try to recompute something which is valid.
 399   assert(!isFragmentValid(F) && "Attempt to recompute a valid fragment!");
 400   // We should never try to compute the fragment layout if its predecessor
 401   // isn't valid.
 402   assert((!Prev || isFragmentValid(Prev)) &&
 403          "Attempt to compute fragment before its predecessor!");
 404
 405   assert(!F->IsBeingLaidOut && "Already being laid out!");
 406   F->IsBeingLaidOut = true;
 407
 408   ++stats::FragmentLayouts;
 409
 410   // Compute fragment offset and size.
 411   if (Prev)
 412     F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
 413   else
 414     F->Offset = 0;
 415   F->IsBeingLaidOut = false;
 416   LastValidFragment[F->getParent()] = F;
 417
 418   // If bundling is enabled and this fragment has instructions in it, it has to
 419   // obey the bundling restrictions. With padding, we'll have:
 420   //
 421   //
 422   //        BundlePadding
 423   //             |||
 424   // -------------------------------------
 425   //   Prev  |##########|       F        |
 426   // -------------------------------------
 427   //                    ^
 428   //                    |
 429   //                    F->Offset
 430   //
 431   // The fragment's offset will point to after the padding, and its computed
 432   // size won't include the padding.
 433   //
 434   // When the -mc-relax-all flag is used, we optimize bundling by writting the
 435   // padding directly into fragments when the instructions are emitted inside
 436   // the streamer. When the fragment is larger than the bundle size, we need to
 437   // ensure that it's bundle aligned. This means that if we end up with
 438   // multiple fragments, we must emit bundle padding between fragments.
 439   //
 440   // ".align N" is an example of a directive that introduces multiple
 441   // fragments. We could add a special case to handle ".align N" by emitting
 442   // within-fragment padding (which would produce less padding when N is less
 443   // than the bundle size), but for now we don't.
 444   //
 445   if (Assembler.isBundlingEnabled() && F->hasInstructions()) {
 446     assert(isa<MCEncodedFragment>(F) &&
 447            "Only MCEncodedFragment implementations have instructions");
 448     MCEncodedFragment *EF = cast<MCEncodedFragment>(F);
 449     uint64_t FSize = Assembler.computeFragmentSize(*this, *EF);
 450
 451     if (!Assembler.getRelaxAll() && FSize > Assembler.getBundleAlignSize())
 452       report_fatal_error("Fragment can't be larger than a bundle size");
 453
 454     uint64_t RequiredBundlePadding =
 455         computeBundlePadding(Assembler, EF, EF->Offset, FSize);
 456     if (RequiredBundlePadding > UINT8_MAX)
 457       report_fatal_error("Padding cannot exceed 255 bytes");
 458     EF->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
 459     EF->Offset += RequiredBundlePadding;
 460   }
 461 }
 462
 463 void MCAssembler::registerSymbol(const MCSymbol &Symbol, bool *Created) {
 464   bool New = !Symbol.isRegistered();
 465   if (Created)
 466     *Created = New;
 467   if (New) {
 468     Symbol.setIsRegistered(true);
 469     Symbols.push_back(&Symbol);
 470   }
 471 }
 472
 473 void MCAssembler::writeFragmentPadding(raw_ostream &OS,
 474                                        const MCEncodedFragment &EF,
 475                                        uint64_t FSize) const {
 476   assert(getBackendPtr() && "Expected assembler backend");
 477   // Should NOP padding be written out before this fragment?
 478   unsigned BundlePadding = EF.getBundlePadding();
 479   if (BundlePadding > 0) {
 480     assert(isBundlingEnabled() &&
 481            "Writing bundle padding with disabled bundling");
 482     assert(EF.hasInstructions() &&
 483            "Writing bundle padding for a fragment without instructions");
 484
 485     unsigned TotalLength = BundlePadding + static_cast<unsigned>(FSize);
 486     if (EF.alignToBundleEnd() && TotalLength > getBundleAlignSize()) {
 487       // If the padding itself crosses a bundle boundary, it must be emitted
 488       // in 2 pieces, since even nop instructions must not cross boundaries.
 489       //             v--------------v   <- BundleAlignSize
 490       //        v---------v             <- BundlePadding
 491       // ----------------------------
 492       // | Prev |####|####|    F    |
 493       // ----------------------------
 494       //        ^-------------------^   <- TotalLength
 495       unsigned DistanceToBoundary = TotalLength - getBundleAlignSize();
 496       if (!getBackend().writeNopData(OS, DistanceToBoundary))
 497         report_fatal_error("unable to write NOP sequence of " +
 498                            Twine(DistanceToBoundary) + " bytes");
 499       BundlePadding -= DistanceToBoundary;
 500     }
 501     if (!getBackend().writeNopData(OS, BundlePadding))
 502       report_fatal_error("unable to write NOP sequence of " +
 503                          Twine(BundlePadding) + " bytes");
 504   }
 505 }
 506
 507 /// Write the fragment \p F to the output file.
 508 static void writeFragment(raw_ostream &OS, const MCAssembler &Asm,
 509                           const MCAsmLayout &Layout, const MCFragment &F) {
 510   // FIXME: Embed in fragments instead?
 511   uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
 512
 513   support::endianness Endian = Asm.getBackend().Endian;
 514
 515   if (const MCEncodedFragment *EF = dyn_cast<MCEncodedFragment>(&F))
 516     Asm.writeFragmentPadding(OS, *EF, FragmentSize);
 517
 518   // This variable (and its dummy usage) is to participate in the assert at
 519   // the end of the function.
 520   uint64_t Start = OS.tell();
 521   (void) Start;
 522
 523   ++stats::EmittedFragments;
 524
 525   switch (F.getKind()) {
 526   case MCFragment::FT_Align: {
 527     ++stats::EmittedAlignFragments;
 528     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
 529     assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
 530
 531     uint64_t Count = FragmentSize / AF.getValueSize();
 532
 533     // FIXME: This error shouldn't actually occur (the front end should emit
 534     // multiple .align directives to enforce the semantics it wants), but is
 535     // severe enough that we want to report it. How to handle this?
 536     if (Count * AF.getValueSize() != FragmentSize)
 537       report_fatal_error("undefined .align directive, value size '" +
 538                         Twine(AF.getValueSize()) +
 539                         "' is not a divisor of padding size '" +
 540                         Twine(FragmentSize) + "'");
 541
 542     // See if we are aligning with nops, and if so do that first to try to fill
 543     // the Count bytes.  Then if that did not fill any bytes or there are any
 544     // bytes left to fill use the Value and ValueSize to fill the rest.
 545     // If we are aligning with nops, ask that target to emit the right data.
 546     if (AF.hasEmitNops()) {
 547       if (!Asm.getBackend().writeNopData(OS, Count))
 548         report_fatal_error("unable to write nop sequence of " +
 549                           Twine(Count) + " bytes");
 550       break;
 551     }
 552
 553     // Otherwise, write out in multiples of the value size.
 554     for (uint64_t i = 0; i != Count; ++i) {
 555       switch (AF.getValueSize()) {
 556       default: llvm_unreachable("Invalid size!");
 557       case 1: OS << char(AF.getValue()); break;
 558       case 2:
 559         support::endian::write<uint16_t>(OS, AF.getValue(), Endian);
 560         break;
 561       case 4:
 562         support::endian::write<uint32_t>(OS, AF.getValue(), Endian);
 563         break;
 564       case 8:
 565         support::endian::write<uint64_t>(OS, AF.getValue(), Endian);
 566         break;
 567       }
 568     }
 569     break;
 570   }
 571
 572   case MCFragment::FT_Data:
 573     ++stats::EmittedDataFragments;
 574     OS << cast<MCDataFragment>(F).getContents();
 575     break;
 576
 577   case MCFragment::FT_Relaxable:
 578     ++stats::EmittedRelaxableFragments;
 579     OS << cast<MCRelaxableFragment>(F).getContents();
 580     break;
 581
 582   case MCFragment::FT_CompactEncodedInst:
 583     ++stats::EmittedCompactEncodedInstFragments;
 584     OS << cast<MCCompactEncodedInstFragment>(F).getContents();
 585     break;
 586
 587   case MCFragment::FT_Fill: {
 588     ++stats::EmittedFillFragments;
 589     const MCFillFragment &FF = cast<MCFillFragment>(F);
 590     uint64_t V = FF.getValue();
 591     unsigned VSize = FF.getValueSize();
 592     const unsigned MaxChunkSize = 16;
 593     char Data[MaxChunkSize];
 594     assert(0 < VSize && VSize <= MaxChunkSize && "Illegal fragment fill size");
 595     // Duplicate V into Data as byte vector to reduce number of
 596     // writes done. As such, do endian conversion here.
 597     for (unsigned I = 0; I != VSize; ++I) {
 598       unsigned index = Endian == support::little ? I : (VSize - I - 1);
 599       Data[I] = uint8_t(V >> (index * 8));
 600     }
 601     for (unsigned I = VSize; I < MaxChunkSize; ++I)
 602       Data[I] = Data[I - VSize];
 603
 604     // Set to largest multiple of VSize in Data.
 605     const unsigned NumPerChunk = MaxChunkSize / VSize;
 606     // Set ChunkSize to largest multiple of VSize in Data
 607     const unsigned ChunkSize = VSize * NumPerChunk;
 608
 609     // Do copies by chunk.
 610     StringRef Ref(Data, ChunkSize);
 611     for (uint64_t I = 0, E = FragmentSize / ChunkSize; I != E; ++I)
 612       OS << Ref;
 613
 614     // do remainder if needed.
 615     unsigned TrailingCount = FragmentSize % ChunkSize;
 616     if (TrailingCount)
 617       OS.write(Data, TrailingCount);
 618     break;
 619   }
 620
 621   case MCFragment::FT_Nops: {
 622     ++stats::EmittedNopsFragments;
 623     const MCNopsFragment &NF = cast<MCNopsFragment>(F);
 624     int64_t NumBytes = NF.getNumBytes();
 625     int64_t ControlledNopLength = NF.getControlledNopLength();
 626     int64_t MaximumNopLength = Asm.getBackend().getMaximumNopSize();
 627
 628     assert(NumBytes > 0 && "Expected positive NOPs fragment size");
 629     assert(ControlledNopLength >= 0 && "Expected non-negative NOP size");
 630
 631     if (ControlledNopLength > MaximumNopLength) {
 632       Asm.getContext().reportError(NF.getLoc(),
 633                                    "illegal NOP size " +
 634                                        std::to_string(ControlledNopLength) +
 635                                        ". (expected within [0, " +
 636                                        std::to_string(MaximumNopLength) + "])");
 637       // Clamp the NOP length as reportError does not stop the execution
 638       // immediately.
 639       ControlledNopLength = MaximumNopLength;
 640     }
 641
 642     // Use maximum value if the size of each NOP is not specified
 643     if (!ControlledNopLength)
 644       ControlledNopLength = MaximumNopLength;
 645
 646     while (NumBytes) {
 647       uint64_t NumBytesToEmit =
 648           (uint64_t)std::min(NumBytes, ControlledNopLength);
 649       assert(NumBytesToEmit && "try to emit empty NOP instruction");
 650       if (!Asm.getBackend().writeNopData(OS, NumBytesToEmit)) {
 651         report_fatal_error("unable to write nop sequence of the remaining " +
 652                            Twine(NumBytesToEmit) + " bytes");
 653         break;
 654       }
 655       NumBytes -= NumBytesToEmit;
 656     }
 657     break;
 658   }
 659
 660   case MCFragment::FT_LEB: {
 661     const MCLEBFragment &LF = cast<MCLEBFragment>(F);
 662     OS << LF.getContents();
 663     break;
 664   }
 665
 666   case MCFragment::FT_BoundaryAlign: {
 667     if (!Asm.getBackend().writeNopData(OS, FragmentSize))
 668       report_fatal_error("unable to write nop sequence of " +
 669                          Twine(FragmentSize) + " bytes");
 670     break;
 671   }
 672
 673   case MCFragment::FT_SymbolId: {
 674     const MCSymbolIdFragment &SF = cast<MCSymbolIdFragment>(F);
 675     support::endian::write<uint32_t>(OS, SF.getSymbol()->getIndex(), Endian);
 676     break;
 677   }
 678
 679   case MCFragment::FT_Org: {
 680     ++stats::EmittedOrgFragments;
 681     const MCOrgFragment &OF = cast<MCOrgFragment>(F);
 682
 683     for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
 684       OS << char(OF.getValue());
 685
 686     break;
 687   }
 688
 689   case MCFragment::FT_Dwarf: {
 690     const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
 691     OS << OF.getContents();
 692     break;
 693   }
 694   case MCFragment::FT_DwarfFrame: {
 695     const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
 696     OS << CF.getContents();
 697     break;
 698   }
 699   case MCFragment::FT_CVInlineLines: {
 700     const auto &OF = cast<MCCVInlineLineTableFragment>(F);
 701     OS << OF.getContents();
 702     break;
 703   }
 704   case MCFragment::FT_CVDefRange: {
 705     const auto &DRF = cast<MCCVDefRangeFragment>(F);
 706     OS << DRF.getContents();
 707     break;
 708   }
 709   case MCFragment::FT_PseudoProbe: {
 710     const MCPseudoProbeAddrFragment &PF = cast<MCPseudoProbeAddrFragment>(F);
 711     OS << PF.getContents();
 712     break;
 713   }
 714   case MCFragment::FT_Dummy:
 715     llvm_unreachable("Should not have been added");
 716   }
 717
 718   assert(OS.tell() - Start == FragmentSize &&
 719          "The stream should advance by fragment size");
 720 }
 721
 722 void MCAssembler::writeSectionData(raw_ostream &OS, const MCSection *Sec,
 723                                    const MCAsmLayout &Layout) const {
 724   assert(getBackendPtr() && "Expected assembler backend");
 725
 726   // Ignore virtual sections.
 727   if (Sec->isVirtualSection()) {
 728     assert(Layout.getSectionFileSize(Sec) == 0 && "Invalid size for section!");
 729
 730     // Check that contents are only things legal inside a virtual section.
 731     for (const MCFragment &F : *Sec) {
 732       switch (F.getKind()) {
 733       default: llvm_unreachable("Invalid fragment in virtual section!");
 734       case MCFragment::FT_Data: {
 735         // Check that we aren't trying to write a non-zero contents (or fixups)
 736         // into a virtual section. This is to support clients which use standard
 737         // directives to fill the contents of virtual sections.
 738         const MCDataFragment &DF = cast<MCDataFragment>(F);
 739         if (DF.fixup_begin() != DF.fixup_end())
 740           getContext().reportError(SMLoc(), Sec->getVirtualSectionKind() +
 741                                                 " section '" + Sec->getName() +
 742                                                 "' cannot have fixups");
 743         for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
 744           if (DF.getContents()[i]) {
 745             getContext().reportError(SMLoc(),
 746                                      Sec->getVirtualSectionKind() +
 747                                          " section '" + Sec->getName() +
 748                                          "' cannot have non-zero initializers");
 749             break;
 750           }
 751         break;
 752       }
 753       case MCFragment::FT_Align:
 754         // Check that we aren't trying to write a non-zero value into a virtual
 755         // section.
 756         assert((cast<MCAlignFragment>(F).getValueSize() == 0 ||
 757                 cast<MCAlignFragment>(F).getValue() == 0) &&
 758                "Invalid align in virtual section!");
 759         break;
 760       case MCFragment::FT_Fill:
 761         assert((cast<MCFillFragment>(F).getValue() == 0) &&
 762                "Invalid fill in virtual section!");
 763         break;
 764       case MCFragment::FT_Org:
 765         break;
 766       }
 767     }
 768
 769     return;
 770   }
 771
 772   uint64_t Start = OS.tell();
 773   (void)Start;
 774
 775   for (const MCFragment &F : *Sec)
 776     writeFragment(OS, *this, Layout, F);
 777
 778   assert(getContext().hadError() ||
 779          OS.tell() - Start == Layout.getSectionAddressSize(Sec));
 780 }
 781
 782 std::tuple<MCValue, uint64_t, bool>
 783 MCAssembler::handleFixup(const MCAsmLayout &Layout, MCFragment &F,
 784                          const MCFixup &Fixup) {
 785   // Evaluate the fixup.
 786   MCValue Target;
 787   uint64_t FixedValue;
 788   bool WasForced;
 789   bool IsResolved = evaluateFixup(Layout, Fixup, &F, Target, FixedValue,
 790                                   WasForced);
 791   if (!IsResolved) {
 792     // The fixup was unresolved, we need a relocation. Inform the object
 793     // writer of the relocation, and give it an opportunity to adjust the
 794     // fixup value if need be.
 795     getWriter().recordRelocation(*this, Layout, &F, Fixup, Target, FixedValue);
 796   }
 797   return std::make_tuple(Target, FixedValue, IsResolved);
 798 }
 799
 800 void MCAssembler::layout(MCAsmLayout &Layout) {
 801   assert(getBackendPtr() && "Expected assembler backend");
 802   DEBUG_WITH_TYPE("mc-dump", {
 803       errs() << "assembler backend - pre-layout\n--\n";
 804       dump(); });
 805
 806   // Create dummy fragments and assign section ordinals.
 807   unsigned SectionIndex = 0;
 808   for (MCSection &Sec : *this) {
 809     // Create dummy fragments to eliminate any empty sections, this simplifies
 810     // layout.
 811     if (Sec.getFragmentList().empty())
 812       new MCDataFragment(&Sec);
 813
 814     Sec.setOrdinal(SectionIndex++);
 815   }
 816
 817   // Assign layout order indices to sections and fragments.
 818   for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
 819     MCSection *Sec = Layout.getSectionOrder()[i];
 820     Sec->setLayoutOrder(i);
 821
 822     unsigned FragmentIndex = 0;
 823     for (MCFragment &Frag : *Sec)
 824       Frag.setLayoutOrder(FragmentIndex++);
 825   }
 826
 827   // Layout until everything fits.
 828   while (layoutOnce(Layout)) {
 829     if (getContext().hadError())
 830       return;
 831     // Size of fragments in one section can depend on the size of fragments in
 832     // another. If any fragment has changed size, we have to re-layout (and
 833     // as a result possibly further relax) all.
 834     for (MCSection &Sec : *this)
 835       Layout.invalidateFragmentsFrom(&*Sec.begin());
 836   }
 837
 838   DEBUG_WITH_TYPE("mc-dump", {
 839       errs() << "assembler backend - post-relaxation\n--\n";
 840       dump(); });
 841
 842   // Finalize the layout, including fragment lowering.
 843   finishLayout(Layout);
 844
 845   DEBUG_WITH_TYPE("mc-dump", {
 846       errs() << "assembler backend - final-layout\n--\n";
 847       dump(); });
 848
 849   // Allow the object writer a chance to perform post-layout binding (for
 850   // example, to set the index fields in the symbol data).
 851   getWriter().executePostLayoutBinding(*this, Layout);
 852
 853   // Evaluate and apply the fixups, generating relocation entries as necessary.
 854   for (MCSection &Sec : *this) {
 855     for (MCFragment &Frag : Sec) {
 856       ArrayRef<MCFixup> Fixups;
 857       MutableArrayRef<char> Contents;
 858       const MCSubtargetInfo *STI = nullptr;
 859
 860       // Process MCAlignFragment and MCEncodedFragmentWithFixups here.
 861       switch (Frag.getKind()) {
 862       default:
 863         continue;
 864       case MCFragment::FT_Align: {
 865         MCAlignFragment &AF = cast<MCAlignFragment>(Frag);
 866         // Insert fixup type for code alignment if the target define
 867         // shouldInsertFixupForCodeAlign target hook.
 868         if (Sec.UseCodeAlign() && AF.hasEmitNops())
 869           getBackend().shouldInsertFixupForCodeAlign(*this, Layout, AF);
 870         continue;
 871       }
 872       case MCFragment::FT_Data: {
 873         MCDataFragment &DF = cast<MCDataFragment>(Frag);
 874         Fixups = DF.getFixups();
 875         Contents = DF.getContents();
 876         STI = DF.getSubtargetInfo();
 877         assert(!DF.hasInstructions() || STI != nullptr);
 878         break;
 879       }
 880       case MCFragment::FT_Relaxable: {
 881         MCRelaxableFragment &RF = cast<MCRelaxableFragment>(Frag);
 882         Fixups = RF.getFixups();
 883         Contents = RF.getContents();
 884         STI = RF.getSubtargetInfo();
 885         assert(!RF.hasInstructions() || STI != nullptr);
 886         break;
 887       }
 888       case MCFragment::FT_CVDefRange: {
 889         MCCVDefRangeFragment &CF = cast<MCCVDefRangeFragment>(Frag);
 890         Fixups = CF.getFixups();
 891         Contents = CF.getContents();
 892         break;
 893       }
 894       case MCFragment::FT_Dwarf: {
 895         MCDwarfLineAddrFragment &DF = cast<MCDwarfLineAddrFragment>(Frag);
 896         Fixups = DF.getFixups();
 897         Contents = DF.getContents();
 898         break;
 899       }
 900       case MCFragment::FT_DwarfFrame: {
 901         MCDwarfCallFrameFragment &DF = cast<MCDwarfCallFrameFragment>(Frag);
 902         Fixups = DF.getFixups();
 903         Contents = DF.getContents();
 904         break;
 905       }
 906       case MCFragment::FT_PseudoProbe: {
 907         MCPseudoProbeAddrFragment &PF = cast<MCPseudoProbeAddrFragment>(Frag);
 908         Fixups = PF.getFixups();
 909         Contents = PF.getContents();
 910         break;
 911       }
 912       }
 913       for (const MCFixup &Fixup : Fixups) {
 914         uint64_t FixedValue;
 915         bool IsResolved;
 916         MCValue Target;
 917         std::tie(Target, FixedValue, IsResolved) =
 918             handleFixup(Layout, Frag, Fixup);
 919         getBackend().applyFixup(*this, Fixup, Target, Contents, FixedValue,
 920                                 IsResolved, STI);
 921       }
 922     }
 923   }
 924 }
 925
 926 void MCAssembler::Finish() {
 927   // Create the layout object.
 928   MCAsmLayout Layout(*this);
 929   layout(Layout);
 930
 931   // Write the object file.
 932   stats::ObjectBytes += getWriter().writeObject(*this, Layout);
 933 }
 934
 935 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
 936                                        const MCRelaxableFragment *DF,
 937                                        const MCAsmLayout &Layout) const {
 938   assert(getBackendPtr() && "Expected assembler backend");
 939   MCValue Target;
 940   uint64_t Value;
 941   bool WasForced;
 942   bool Resolved = evaluateFixup(Layout, Fixup, DF, Target, Value, WasForced);
 943   if (Target.getSymA() &&
 944       Target.getSymA()->getKind() == MCSymbolRefExpr::VK_X86_ABS8 &&
 945       Fixup.getKind() == FK_Data_1)
 946     return false;
 947   return getBackend().fixupNeedsRelaxationAdvanced(Fixup, Resolved, Value, DF,
 948                                                    Layout, WasForced);
 949 }
 950
 951 bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
 952                                           const MCAsmLayout &Layout) const {
 953   assert(getBackendPtr() && "Expected assembler backend");
 954   // If this inst doesn't ever need relaxation, ignore it. This occurs when we
 955   // are intentionally pushing out inst fragments, or because we relaxed a
 956   // previous instruction to one that doesn't need relaxation.
 957   if (!getBackend().mayNeedRelaxation(F->getInst(), *F->getSubtargetInfo()))
 958     return false;
 959
 960   for (const MCFixup &Fixup : F->getFixups())
 961     if (fixupNeedsRelaxation(Fixup, F, Layout))
 962       return true;
 963
 964   return false;
 965 }
 966
 967 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
 968                                    MCRelaxableFragment &F) {
 969   assert(getEmitterPtr() &&
 970          "Expected CodeEmitter defined for relaxInstruction");
 971   if (!fragmentNeedsRelaxation(&F, Layout))
 972     return false;
 973
 974   ++stats::RelaxedInstructions;
 975
 976   // FIXME-PERF: We could immediately lower out instructions if we can tell
 977   // they are fully resolved, to avoid retesting on later passes.
 978
 979   // Relax the fragment.
 980
 981   MCInst Relaxed = F.getInst();
 982   getBackend().relaxInstruction(Relaxed, *F.getSubtargetInfo());
 983
 984   // Encode the new instruction.
 985   //
 986   // FIXME-PERF: If it matters, we could let the target do this. It can
 987   // probably do so more efficiently in many cases.
 988   SmallVector<MCFixup, 4> Fixups;
 989   SmallString<256> Code;
 990   raw_svector_ostream VecOS(Code);
 991   getEmitter().encodeInstruction(Relaxed, VecOS, Fixups, *F.getSubtargetInfo());
 992
 993   // Update the fragment.
 994   F.setInst(Relaxed);
 995   F.getContents() = Code;
 996   F.getFixups() = Fixups;
 997
 998   return true;
 999 }
1000
1001 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
1002   uint64_t OldSize = LF.getContents().size();
1003   int64_t Value;
1004   bool Abs = LF.getValue().evaluateKnownAbsolute(Value, Layout);
1005   if (!Abs)
1006     report_fatal_error("sleb128 and uleb128 expressions must be absolute");
1007   SmallString<8> &Data = LF.getContents();
1008   Data.clear();
1009   raw_svector_ostream OSE(Data);
1010   // The compiler can generate EH table assembly that is impossible to assemble
1011   // without either adding padding to an LEB fragment or adding extra padding
1012   // to a later alignment fragment. To accommodate such tables, relaxation can
1013   // only increase an LEB fragment size here, not decrease it. See PR35809.
1014   if (LF.isSigned())
1015     encodeSLEB128(Value, OSE, OldSize);
1016   else
1017     encodeULEB128(Value, OSE, OldSize);
1018   return OldSize != LF.getContents().size();
1019 }
1020
1021 /// Check if the branch crosses the boundary.
1022 ///
1023 /// \param StartAddr start address of the fused/unfused branch.
1024 /// \param Size size of the fused/unfused branch.
1025 /// \param BoundaryAlignment alignment requirement of the branch.
1026 /// \returns true if the branch cross the boundary.
1027 static bool mayCrossBoundary(uint64_t StartAddr, uint64_t Size,
1028                              Align BoundaryAlignment) {
1029   uint64_t EndAddr = StartAddr + Size;
1030   return (StartAddr >> Log2(BoundaryAlignment)) !=
1031          ((EndAddr - 1) >> Log2(BoundaryAlignment));
1032 }
1033
1034 /// Check if the branch is against the boundary.
1035 ///
1036 /// \param StartAddr start address of the fused/unfused branch.
1037 /// \param Size size of the fused/unfused branch.
1038 /// \param BoundaryAlignment alignment requirement of the branch.
1039 /// \returns true if the branch is against the boundary.
1040 static bool isAgainstBoundary(uint64_t StartAddr, uint64_t Size,
1041                               Align BoundaryAlignment) {
1042   uint64_t EndAddr = StartAddr + Size;
1043   return (EndAddr & (BoundaryAlignment.value() - 1)) == 0;
1044 }
1045
1046 /// Check if the branch needs padding.
1047 ///
1048 /// \param StartAddr start address of the fused/unfused branch.
1049 /// \param Size size of the fused/unfused branch.
1050 /// \param BoundaryAlignment alignment requirement of the branch.
1051 /// \returns true if the branch needs padding.
1052 static bool needPadding(uint64_t StartAddr, uint64_t Size,
1053                         Align BoundaryAlignment) {
1054   return mayCrossBoundary(StartAddr, Size, BoundaryAlignment) ||
1055          isAgainstBoundary(StartAddr, Size, BoundaryAlignment);
1056 }
1057
1058 bool MCAssembler::relaxBoundaryAlign(MCAsmLayout &Layout,
1059                                      MCBoundaryAlignFragment &BF) {
1060   // BoundaryAlignFragment that doesn't need to align any fragment should not be
1061   // relaxed.
1062   if (!BF.getLastFragment())
1063     return false;
1064
1065   uint64_t AlignedOffset = Layout.getFragmentOffset(&BF);
1066   uint64_t AlignedSize = 0;
1067   for (const MCFragment *F = BF.getLastFragment(); F != &BF;
1068        F = F->getPrevNode())
1069     AlignedSize += computeFragmentSize(Layout, *F);
1070
1071   Align BoundaryAlignment = BF.getAlignment();
1072   uint64_t NewSize = needPadding(AlignedOffset, AlignedSize, BoundaryAlignment)
1073                          ? offsetToAlignment(AlignedOffset, BoundaryAlignment)
1074                          : 0U;
1075   if (NewSize == BF.getSize())
1076     return false;
1077   BF.setSize(NewSize);
1078   Layout.invalidateFragmentsFrom(&BF);
1079   return true;
1080 }
1081
1082 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
1083                                      MCDwarfLineAddrFragment &DF) {
1084
1085   bool WasRelaxed;
1086   if (getBackend().relaxDwarfLineAddr(DF, Layout, WasRelaxed))
1087     return WasRelaxed;
1088
1089   MCContext &Context = Layout.getAssembler().getContext();
1090   uint64_t OldSize = DF.getContents().size();
1091   int64_t AddrDelta;
1092   bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1093   assert(Abs && "We created a line delta with an invalid expression");
1094   (void)Abs;
1095   int64_t LineDelta;
1096   LineDelta = DF.getLineDelta();
1097   SmallVectorImpl<char> &Data = DF.getContents();
1098   Data.clear();
1099   raw_svector_ostream OSE(Data);
1100   DF.getFixups().clear();
1101
1102   MCDwarfLineAddr::Encode(Context, getDWARFLinetableParams(), LineDelta,
1103                           AddrDelta, OSE);
1104   return OldSize != Data.size();
1105 }
1106
1107 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
1108                                               MCDwarfCallFrameFragment &DF) {
1109   bool WasRelaxed;
1110   if (getBackend().relaxDwarfCFA(DF, Layout, WasRelaxed))
1111     return WasRelaxed;
1112
1113   MCContext &Context = Layout.getAssembler().getContext();
1114   uint64_t OldSize = DF.getContents().size();
1115   int64_t AddrDelta;
1116   bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1117   assert(Abs && "We created call frame with an invalid expression");
1118   (void) Abs;
1119   SmallVectorImpl<char> &Data = DF.getContents();
1120   Data.clear();
1121   raw_svector_ostream OSE(Data);
1122   DF.getFixups().clear();
1123
1124   MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
1125   return OldSize != Data.size();
1126 }
1127
1128 bool MCAssembler::relaxCVInlineLineTable(MCAsmLayout &Layout,
1129                                          MCCVInlineLineTableFragment &F) {
1130   unsigned OldSize = F.getContents().size();
1131   getContext().getCVContext().encodeInlineLineTable(Layout, F);
1132   return OldSize != F.getContents().size();
1133 }
1134
1135 bool MCAssembler::relaxCVDefRange(MCAsmLayout &Layout,
1136                                   MCCVDefRangeFragment &F) {
1137   unsigned OldSize = F.getContents().size();
1138   getContext().getCVContext().encodeDefRange(Layout, F);
1139   return OldSize != F.getContents().size();
1140 }
1141
1142 bool MCAssembler::relaxPseudoProbeAddr(MCAsmLayout &Layout,
1143                                        MCPseudoProbeAddrFragment &PF) {
1144   uint64_t OldSize = PF.getContents().size();
1145   int64_t AddrDelta;
1146   bool Abs = PF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1147   assert(Abs && "We created a pseudo probe with an invalid expression");
1148   (void)Abs;
1149   SmallVectorImpl<char> &Data = PF.getContents();
1150   Data.clear();
1151   raw_svector_ostream OSE(Data);
1152   PF.getFixups().clear();
1153
1154   // AddrDelta is a signed integer
1155   encodeSLEB128(AddrDelta, OSE, OldSize);
1156   return OldSize != Data.size();
1157 }
1158
1159 bool MCAssembler::relaxFragment(MCAsmLayout &Layout, MCFragment &F) {
1160   switch(F.getKind()) {
1161   default:
1162     return false;
1163   case MCFragment::FT_Relaxable:
1164     assert(!getRelaxAll() &&
1165            "Did not expect a MCRelaxableFragment in RelaxAll mode");
1166     return relaxInstruction(Layout, cast<MCRelaxableFragment>(F));
1167   case MCFragment::FT_Dwarf:
1168     return relaxDwarfLineAddr(Layout, cast<MCDwarfLineAddrFragment>(F));
1169   case MCFragment::FT_DwarfFrame:
1170     return relaxDwarfCallFrameFragment(Layout,
1171                                        cast<MCDwarfCallFrameFragment>(F));
1172   case MCFragment::FT_LEB:
1173     return relaxLEB(Layout, cast<MCLEBFragment>(F));
1174   case MCFragment::FT_BoundaryAlign:
1175     return relaxBoundaryAlign(Layout, cast<MCBoundaryAlignFragment>(F));
1176   case MCFragment::FT_CVInlineLines:
1177     return relaxCVInlineLineTable(Layout, cast<MCCVInlineLineTableFragment>(F));
1178   case MCFragment::FT_CVDefRange:
1179     return relaxCVDefRange(Layout, cast<MCCVDefRangeFragment>(F));
1180   case MCFragment::FT_PseudoProbe:
1181     return relaxPseudoProbeAddr(Layout, cast<MCPseudoProbeAddrFragment>(F));
1182   }
1183 }
1184
1185 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSection &Sec) {
1186   // Holds the first fragment which needed relaxing during this layout. It will
1187   // remain NULL if none were relaxed.
1188   // When a fragment is relaxed, all the fragments following it should get
1189   // invalidated because their offset is going to change.
1190   MCFragment *FirstRelaxedFragment = nullptr;
1191
1192   // Attempt to relax all the fragments in the section.
1193   for (MCFragment &Frag : Sec) {
1194     // Check if this is a fragment that needs relaxation.
1195     bool RelaxedFrag = relaxFragment(Layout, Frag);
1196     if (RelaxedFrag && !FirstRelaxedFragment)
1197       FirstRelaxedFragment = &Frag;
1198   }
1199   if (FirstRelaxedFragment) {
1200     Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
1201     return true;
1202   }
1203   return false;
1204 }
1205
1206 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
1207   ++stats::RelaxationSteps;
1208
1209   bool WasRelaxed = false;
1210   for (MCSection &Sec : *this) {
1211     while (layoutSectionOnce(Layout, Sec))
1212       WasRelaxed = true;
1213   }
1214
1215   return WasRelaxed;
1216 }
1217
1218 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
1219   assert(getBackendPtr() && "Expected assembler backend");
1220   // The layout is done. Mark every fragment as valid.
1221   for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
1222     MCSection &Section = *Layout.getSectionOrder()[i];
1223     Layout.getFragmentOffset(&*Section.getFragmentList().rbegin());
1224     computeFragmentSize(Layout, *Section.getFragmentList().rbegin());
1225   }
1226   getBackend().finishLayout(*this, Layout);
1227 }
1228
1229 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1230 LLVM_DUMP_METHOD void MCAssembler::dump() const{
1231   raw_ostream &OS = errs();
1232
1233   OS << "<MCAssembler\n";
1234   OS << "  Sections:[\n    ";
1235   for (const_iterator it = begin(), ie = end(); it != ie; ++it) {
1236     if (it != begin()) OS << ",\n    ";
1237     it->dump();
1238   }
1239   OS << "],\n";
1240   OS << "  Symbols:[";
1241
1242   for (const_symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1243     if (it != symbol_begin()) OS << ",\n           ";
1244     OS << "(";
1245     it->dump();
1246     OS << ", Index:" << it->getIndex() << ", ";
1247     OS << ")";
1248   }
1249   OS << "]>\n";
1250 }
1251 #endif