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, const MCFixup &Fixup,
 197                                 const MCFragment *DF, MCValue &Target,
 198                                 const MCSubtargetInfo *STI, 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                                             STI, 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 &&
 286       getBackend().shouldForceRelocation(*this, Fixup, Target, STI)) {
 287     IsResolved = false;
 288     WasForced = true;
 289   }
 290
 291   // A linker relaxation target may emit ADD/SUB relocations for A-B+C. Let
 292   // recordRelocation handle non-VK_None cases like A@plt-B+C.
 293   if (!IsResolved && Target.getSymA() && Target.getSymB() &&
 294       Target.getSymA()->getKind() == MCSymbolRefExpr::VK_None &&
 295       getBackend().handleAddSubRelocations(Layout, *DF, Fixup, Target, Value))
 296     return true;
 297
 298   return IsResolved;
 299 }
 300
 301 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
 302                                           const MCFragment &F) const {
 303   assert(getBackendPtr() && "Requires assembler backend");
 304   switch (F.getKind()) {
 305   case MCFragment::FT_Data:
 306     return cast<MCDataFragment>(F).getContents().size();
 307   case MCFragment::FT_Relaxable:
 308     return cast<MCRelaxableFragment>(F).getContents().size();
 309   case MCFragment::FT_CompactEncodedInst:
 310     return cast<MCCompactEncodedInstFragment>(F).getContents().size();
 311   case MCFragment::FT_Fill: {
 312     auto &FF = cast<MCFillFragment>(F);
 313     int64_t NumValues = 0;
 314     if (!FF.getNumValues().evaluateKnownAbsolute(NumValues, Layout)) {
 315       getContext().reportError(FF.getLoc(),
 316                                "expected assembly-time absolute expression");
 317       return 0;
 318     }
 319     int64_t Size = NumValues * FF.getValueSize();
 320     if (Size < 0) {
 321       getContext().reportError(FF.getLoc(), "invalid number of bytes");
 322       return 0;
 323     }
 324     return Size;
 325   }
 326
 327   case MCFragment::FT_Nops:
 328     return cast<MCNopsFragment>(F).getNumBytes();
 329
 330   case MCFragment::FT_LEB:
 331     return cast<MCLEBFragment>(F).getContents().size();
 332
 333   case MCFragment::FT_BoundaryAlign:
 334     return cast<MCBoundaryAlignFragment>(F).getSize();
 335
 336   case MCFragment::FT_SymbolId:
 337     return 4;
 338
 339   case MCFragment::FT_Align: {
 340     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
 341     unsigned Offset = Layout.getFragmentOffset(&AF);
 342     unsigned Size = offsetToAlignment(Offset, AF.getAlignment());
 343
 344     // Insert extra Nops for code alignment if the target define
 345     // shouldInsertExtraNopBytesForCodeAlign target hook.
 346     if (AF.getParent()->useCodeAlign() && AF.hasEmitNops() &&
 347         getBackend().shouldInsertExtraNopBytesForCodeAlign(AF, Size))
 348       return Size;
 349
 350     // If we are padding with nops, force the padding to be larger than the
 351     // minimum nop size.
 352     if (Size > 0 && AF.hasEmitNops()) {
 353       while (Size % getBackend().getMinimumNopSize())
 354         Size += AF.getAlignment().value();
 355     }
 356     if (Size > AF.getMaxBytesToEmit())
 357       return 0;
 358     return Size;
 359   }
 360
 361   case MCFragment::FT_Org: {
 362     const MCOrgFragment &OF = cast<MCOrgFragment>(F);
 363     MCValue Value;
 364     if (!OF.getOffset().evaluateAsValue(Value, Layout)) {
 365       getContext().reportError(OF.getLoc(),
 366                                "expected assembly-time absolute expression");
 367         return 0;
 368     }
 369
 370     uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
 371     int64_t TargetLocation = Value.getConstant();
 372     if (const MCSymbolRefExpr *A = Value.getSymA()) {
 373       uint64_t Val;
 374       if (!Layout.getSymbolOffset(A->getSymbol(), Val)) {
 375         getContext().reportError(OF.getLoc(), "expected absolute expression");
 376         return 0;
 377       }
 378       TargetLocation += Val;
 379     }
 380     int64_t Size = TargetLocation - FragmentOffset;
 381     if (Size < 0 || Size >= 0x40000000) {
 382       getContext().reportError(
 383           OF.getLoc(), "invalid .org offset '" + Twine(TargetLocation) +
 384                            "' (at offset '" + Twine(FragmentOffset) + "')");
 385       return 0;
 386     }
 387     return Size;
 388   }
 389
 390   case MCFragment::FT_Dwarf:
 391     return cast<MCDwarfLineAddrFragment>(F).getContents().size();
 392   case MCFragment::FT_DwarfFrame:
 393     return cast<MCDwarfCallFrameFragment>(F).getContents().size();
 394   case MCFragment::FT_CVInlineLines:
 395     return cast<MCCVInlineLineTableFragment>(F).getContents().size();
 396   case MCFragment::FT_CVDefRange:
 397     return cast<MCCVDefRangeFragment>(F).getContents().size();
 398   case MCFragment::FT_PseudoProbe:
 399     return cast<MCPseudoProbeAddrFragment>(F).getContents().size();
 400   case MCFragment::FT_Dummy:
 401     llvm_unreachable("Should not have been added");
 402   }
 403
 404   llvm_unreachable("invalid fragment kind");
 405 }
 406
 407 void MCAsmLayout::layoutFragment(MCFragment *F) {
 408   MCFragment *Prev = F->getPrevNode();
 409
 410   // We should never try to recompute something which is valid.
 411   assert(!isFragmentValid(F) && "Attempt to recompute a valid fragment!");
 412   // We should never try to compute the fragment layout if its predecessor
 413   // isn't valid.
 414   assert((!Prev || isFragmentValid(Prev)) &&
 415          "Attempt to compute fragment before its predecessor!");
 416
 417   assert(!F->IsBeingLaidOut && "Already being laid out!");
 418   F->IsBeingLaidOut = true;
 419
 420   ++stats::FragmentLayouts;
 421
 422   // Compute fragment offset and size.
 423   if (Prev)
 424     F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
 425   else
 426     F->Offset = 0;
 427   F->IsBeingLaidOut = false;
 428   LastValidFragment[F->getParent()] = F;
 429
 430   // If bundling is enabled and this fragment has instructions in it, it has to
 431   // obey the bundling restrictions. With padding, we'll have:
 432   //
 433   //
 434   //        BundlePadding
 435   //             |||
 436   // -------------------------------------
 437   //   Prev  |##########|       F        |
 438   // -------------------------------------
 439   //                    ^
 440   //                    |
 441   //                    F->Offset
 442   //
 443   // The fragment's offset will point to after the padding, and its computed
 444   // size won't include the padding.
 445   //
 446   // When the -mc-relax-all flag is used, we optimize bundling by writting the
 447   // padding directly into fragments when the instructions are emitted inside
 448   // the streamer. When the fragment is larger than the bundle size, we need to
 449   // ensure that it's bundle aligned. This means that if we end up with
 450   // multiple fragments, we must emit bundle padding between fragments.
 451   //
 452   // ".align N" is an example of a directive that introduces multiple
 453   // fragments. We could add a special case to handle ".align N" by emitting
 454   // within-fragment padding (which would produce less padding when N is less
 455   // than the bundle size), but for now we don't.
 456   //
 457   if (Assembler.isBundlingEnabled() && F->hasInstructions()) {
 458     assert(isa<MCEncodedFragment>(F) &&
 459            "Only MCEncodedFragment implementations have instructions");
 460     MCEncodedFragment *EF = cast<MCEncodedFragment>(F);
 461     uint64_t FSize = Assembler.computeFragmentSize(*this, *EF);
 462
 463     if (!Assembler.getRelaxAll() && FSize > Assembler.getBundleAlignSize())
 464       report_fatal_error("Fragment can't be larger than a bundle size");
 465
 466     uint64_t RequiredBundlePadding =
 467         computeBundlePadding(Assembler, EF, EF->Offset, FSize);
 468     if (RequiredBundlePadding > UINT8_MAX)
 469       report_fatal_error("Padding cannot exceed 255 bytes");
 470     EF->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
 471     EF->Offset += RequiredBundlePadding;
 472   }
 473 }
 474
 475 bool MCAssembler::registerSymbol(const MCSymbol &Symbol) {
 476   bool Changed = !Symbol.isRegistered();
 477   if (Changed) {
 478     Symbol.setIsRegistered(true);
 479     Symbols.push_back(&Symbol);
 480   }
 481   return Changed;
 482 }
 483
 484 void MCAssembler::writeFragmentPadding(raw_ostream &OS,
 485                                        const MCEncodedFragment &EF,
 486                                        uint64_t FSize) const {
 487   assert(getBackendPtr() && "Expected assembler backend");
 488   // Should NOP padding be written out before this fragment?
 489   unsigned BundlePadding = EF.getBundlePadding();
 490   if (BundlePadding > 0) {
 491     assert(isBundlingEnabled() &&
 492            "Writing bundle padding with disabled bundling");
 493     assert(EF.hasInstructions() &&
 494            "Writing bundle padding for a fragment without instructions");
 495
 496     unsigned TotalLength = BundlePadding + static_cast<unsigned>(FSize);
 497     const MCSubtargetInfo *STI = EF.getSubtargetInfo();
 498     if (EF.alignToBundleEnd() && TotalLength > getBundleAlignSize()) {
 499       // If the padding itself crosses a bundle boundary, it must be emitted
 500       // in 2 pieces, since even nop instructions must not cross boundaries.
 501       //             v--------------v   <- BundleAlignSize
 502       //        v---------v             <- BundlePadding
 503       // ----------------------------
 504       // | Prev |####|####|    F    |
 505       // ----------------------------
 506       //        ^-------------------^   <- TotalLength
 507       unsigned DistanceToBoundary = TotalLength - getBundleAlignSize();
 508       if (!getBackend().writeNopData(OS, DistanceToBoundary, STI))
 509         report_fatal_error("unable to write NOP sequence of " +
 510                            Twine(DistanceToBoundary) + " bytes");
 511       BundlePadding -= DistanceToBoundary;
 512     }
 513     if (!getBackend().writeNopData(OS, BundlePadding, STI))
 514       report_fatal_error("unable to write NOP sequence of " +
 515                          Twine(BundlePadding) + " bytes");
 516   }
 517 }
 518
 519 /// Write the fragment \p F to the output file.
 520 static void writeFragment(raw_ostream &OS, const MCAssembler &Asm,
 521                           const MCAsmLayout &Layout, const MCFragment &F) {
 522   // FIXME: Embed in fragments instead?
 523   uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
 524
 525   llvm::endianness Endian = Asm.getBackend().Endian;
 526
 527   if (const MCEncodedFragment *EF = dyn_cast<MCEncodedFragment>(&F))
 528     Asm.writeFragmentPadding(OS, *EF, FragmentSize);
 529
 530   // This variable (and its dummy usage) is to participate in the assert at
 531   // the end of the function.
 532   uint64_t Start = OS.tell();
 533   (void) Start;
 534
 535   ++stats::EmittedFragments;
 536
 537   switch (F.getKind()) {
 538   case MCFragment::FT_Align: {
 539     ++stats::EmittedAlignFragments;
 540     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
 541     assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
 542
 543     uint64_t Count = FragmentSize / AF.getValueSize();
 544
 545     // FIXME: This error shouldn't actually occur (the front end should emit
 546     // multiple .align directives to enforce the semantics it wants), but is
 547     // severe enough that we want to report it. How to handle this?
 548     if (Count * AF.getValueSize() != FragmentSize)
 549       report_fatal_error("undefined .align directive, value size '" +
 550                         Twine(AF.getValueSize()) +
 551                         "' is not a divisor of padding size '" +
 552                         Twine(FragmentSize) + "'");
 553
 554     // See if we are aligning with nops, and if so do that first to try to fill
 555     // the Count bytes.  Then if that did not fill any bytes or there are any
 556     // bytes left to fill use the Value and ValueSize to fill the rest.
 557     // If we are aligning with nops, ask that target to emit the right data.
 558     if (AF.hasEmitNops()) {
 559       if (!Asm.getBackend().writeNopData(OS, Count, AF.getSubtargetInfo()))
 560         report_fatal_error("unable to write nop sequence of " +
 561                           Twine(Count) + " bytes");
 562       break;
 563     }
 564
 565     // Otherwise, write out in multiples of the value size.
 566     for (uint64_t i = 0; i != Count; ++i) {
 567       switch (AF.getValueSize()) {
 568       default: llvm_unreachable("Invalid size!");
 569       case 1: OS << char(AF.getValue()); break;
 570       case 2:
 571         support::endian::write<uint16_t>(OS, AF.getValue(), Endian);
 572         break;
 573       case 4:
 574         support::endian::write<uint32_t>(OS, AF.getValue(), Endian);
 575         break;
 576       case 8:
 577         support::endian::write<uint64_t>(OS, AF.getValue(), Endian);
 578         break;
 579       }
 580     }
 581     break;
 582   }
 583
 584   case MCFragment::FT_Data:
 585     ++stats::EmittedDataFragments;
 586     OS << cast<MCDataFragment>(F).getContents();
 587     break;
 588
 589   case MCFragment::FT_Relaxable:
 590     ++stats::EmittedRelaxableFragments;
 591     OS << cast<MCRelaxableFragment>(F).getContents();
 592     break;
 593
 594   case MCFragment::FT_CompactEncodedInst:
 595     ++stats::EmittedCompactEncodedInstFragments;
 596     OS << cast<MCCompactEncodedInstFragment>(F).getContents();
 597     break;
 598
 599   case MCFragment::FT_Fill: {
 600     ++stats::EmittedFillFragments;
 601     const MCFillFragment &FF = cast<MCFillFragment>(F);
 602     uint64_t V = FF.getValue();
 603     unsigned VSize = FF.getValueSize();
 604     const unsigned MaxChunkSize = 16;
 605     char Data[MaxChunkSize];
 606     assert(0 < VSize && VSize <= MaxChunkSize && "Illegal fragment fill size");
 607     // Duplicate V into Data as byte vector to reduce number of
 608     // writes done. As such, do endian conversion here.
 609     for (unsigned I = 0; I != VSize; ++I) {
 610       unsigned index = Endian == llvm::endianness::little ? I : (VSize - I - 1);
 611       Data[I] = uint8_t(V >> (index * 8));
 612     }
 613     for (unsigned I = VSize; I < MaxChunkSize; ++I)
 614       Data[I] = Data[I - VSize];
 615
 616     // Set to largest multiple of VSize in Data.
 617     const unsigned NumPerChunk = MaxChunkSize / VSize;
 618     // Set ChunkSize to largest multiple of VSize in Data
 619     const unsigned ChunkSize = VSize * NumPerChunk;
 620
 621     // Do copies by chunk.
 622     StringRef Ref(Data, ChunkSize);
 623     for (uint64_t I = 0, E = FragmentSize / ChunkSize; I != E; ++I)
 624       OS << Ref;
 625
 626     // do remainder if needed.
 627     unsigned TrailingCount = FragmentSize % ChunkSize;
 628     if (TrailingCount)
 629       OS.write(Data, TrailingCount);
 630     break;
 631   }
 632
 633   case MCFragment::FT_Nops: {
 634     ++stats::EmittedNopsFragments;
 635     const MCNopsFragment &NF = cast<MCNopsFragment>(F);
 636
 637     int64_t NumBytes = NF.getNumBytes();
 638     int64_t ControlledNopLength = NF.getControlledNopLength();
 639     int64_t MaximumNopLength =
 640         Asm.getBackend().getMaximumNopSize(*NF.getSubtargetInfo());
 641
 642     assert(NumBytes > 0 && "Expected positive NOPs fragment size");
 643     assert(ControlledNopLength >= 0 && "Expected non-negative NOP size");
 644
 645     if (ControlledNopLength > MaximumNopLength) {
 646       Asm.getContext().reportError(NF.getLoc(),
 647                                    "illegal NOP size " +
 648                                        std::to_string(ControlledNopLength) +
 649                                        ". (expected within [0, " +
 650                                        std::to_string(MaximumNopLength) + "])");
 651       // Clamp the NOP length as reportError does not stop the execution
 652       // immediately.
 653       ControlledNopLength = MaximumNopLength;
 654     }
 655
 656     // Use maximum value if the size of each NOP is not specified
 657     if (!ControlledNopLength)
 658       ControlledNopLength = MaximumNopLength;
 659
 660     while (NumBytes) {
 661       uint64_t NumBytesToEmit =
 662           (uint64_t)std::min(NumBytes, ControlledNopLength);
 663       assert(NumBytesToEmit && "try to emit empty NOP instruction");
 664       if (!Asm.getBackend().writeNopData(OS, NumBytesToEmit,
 665                                          NF.getSubtargetInfo())) {
 666         report_fatal_error("unable to write nop sequence of the remaining " +
 667                            Twine(NumBytesToEmit) + " bytes");
 668         break;
 669       }
 670       NumBytes -= NumBytesToEmit;
 671     }
 672     break;
 673   }
 674
 675   case MCFragment::FT_LEB: {
 676     const MCLEBFragment &LF = cast<MCLEBFragment>(F);
 677     OS << LF.getContents();
 678     break;
 679   }
 680
 681   case MCFragment::FT_BoundaryAlign: {
 682     const MCBoundaryAlignFragment &BF = cast<MCBoundaryAlignFragment>(F);
 683     if (!Asm.getBackend().writeNopData(OS, FragmentSize, BF.getSubtargetInfo()))
 684       report_fatal_error("unable to write nop sequence of " +
 685                          Twine(FragmentSize) + " bytes");
 686     break;
 687   }
 688
 689   case MCFragment::FT_SymbolId: {
 690     const MCSymbolIdFragment &SF = cast<MCSymbolIdFragment>(F);
 691     support::endian::write<uint32_t>(OS, SF.getSymbol()->getIndex(), Endian);
 692     break;
 693   }
 694
 695   case MCFragment::FT_Org: {
 696     ++stats::EmittedOrgFragments;
 697     const MCOrgFragment &OF = cast<MCOrgFragment>(F);
 698
 699     for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
 700       OS << char(OF.getValue());
 701
 702     break;
 703   }
 704
 705   case MCFragment::FT_Dwarf: {
 706     const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
 707     OS << OF.getContents();
 708     break;
 709   }
 710   case MCFragment::FT_DwarfFrame: {
 711     const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
 712     OS << CF.getContents();
 713     break;
 714   }
 715   case MCFragment::FT_CVInlineLines: {
 716     const auto &OF = cast<MCCVInlineLineTableFragment>(F);
 717     OS << OF.getContents();
 718     break;
 719   }
 720   case MCFragment::FT_CVDefRange: {
 721     const auto &DRF = cast<MCCVDefRangeFragment>(F);
 722     OS << DRF.getContents();
 723     break;
 724   }
 725   case MCFragment::FT_PseudoProbe: {
 726     const MCPseudoProbeAddrFragment &PF = cast<MCPseudoProbeAddrFragment>(F);
 727     OS << PF.getContents();
 728     break;
 729   }
 730   case MCFragment::FT_Dummy:
 731     llvm_unreachable("Should not have been added");
 732   }
 733
 734   assert(OS.tell() - Start == FragmentSize &&
 735          "The stream should advance by fragment size");
 736 }
 737
 738 void MCAssembler::writeSectionData(raw_ostream &OS, const MCSection *Sec,
 739                                    const MCAsmLayout &Layout) const {
 740   assert(getBackendPtr() && "Expected assembler backend");
 741
 742   // Ignore virtual sections.
 743   if (Sec->isVirtualSection()) {
 744     assert(Layout.getSectionFileSize(Sec) == 0 && "Invalid size for section!");
 745
 746     // Check that contents are only things legal inside a virtual section.
 747     for (const MCFragment &F : *Sec) {
 748       switch (F.getKind()) {
 749       default: llvm_unreachable("Invalid fragment in virtual section!");
 750       case MCFragment::FT_Data: {
 751         // Check that we aren't trying to write a non-zero contents (or fixups)
 752         // into a virtual section. This is to support clients which use standard
 753         // directives to fill the contents of virtual sections.
 754         const MCDataFragment &DF = cast<MCDataFragment>(F);
 755         if (DF.fixup_begin() != DF.fixup_end())
 756           getContext().reportError(SMLoc(), Sec->getVirtualSectionKind() +
 757                                                 " section '" + Sec->getName() +
 758                                                 "' cannot have fixups");
 759         for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
 760           if (DF.getContents()[i]) {
 761             getContext().reportError(SMLoc(),
 762                                      Sec->getVirtualSectionKind() +
 763                                          " section '" + Sec->getName() +
 764                                          "' cannot have non-zero initializers");
 765             break;
 766           }
 767         break;
 768       }
 769       case MCFragment::FT_Align:
 770         // Check that we aren't trying to write a non-zero value into a virtual
 771         // section.
 772         assert((cast<MCAlignFragment>(F).getValueSize() == 0 ||
 773                 cast<MCAlignFragment>(F).getValue() == 0) &&
 774                "Invalid align in virtual section!");
 775         break;
 776       case MCFragment::FT_Fill:
 777         assert((cast<MCFillFragment>(F).getValue() == 0) &&
 778                "Invalid fill in virtual section!");
 779         break;
 780       case MCFragment::FT_Org:
 781         break;
 782       }
 783     }
 784
 785     return;
 786   }
 787
 788   uint64_t Start = OS.tell();
 789   (void)Start;
 790
 791   for (const MCFragment &F : *Sec)
 792     writeFragment(OS, *this, Layout, F);
 793
 794   assert(getContext().hadError() ||
 795          OS.tell() - Start == Layout.getSectionAddressSize(Sec));
 796 }
 797
 798 std::tuple<MCValue, uint64_t, bool>
 799 MCAssembler::handleFixup(const MCAsmLayout &Layout, MCFragment &F,
 800                          const MCFixup &Fixup, const MCSubtargetInfo *STI) {
 801   // Evaluate the fixup.
 802   MCValue Target;
 803   uint64_t FixedValue;
 804   bool WasForced;
 805   bool IsResolved =
 806       evaluateFixup(Layout, Fixup, &F, Target, STI, FixedValue, WasForced);
 807   if (!IsResolved) {
 808     // The fixup was unresolved, we need a relocation. Inform the object
 809     // writer of the relocation, and give it an opportunity to adjust the
 810     // fixup value if need be.
 811     getWriter().recordRelocation(*this, Layout, &F, Fixup, Target, FixedValue);
 812   }
 813   return std::make_tuple(Target, FixedValue, IsResolved);
 814 }
 815
 816 void MCAssembler::layout(MCAsmLayout &Layout) {
 817   assert(getBackendPtr() && "Expected assembler backend");
 818   DEBUG_WITH_TYPE("mc-dump", {
 819       errs() << "assembler backend - pre-layout\n--\n";
 820       dump(); });
 821
 822   // Create dummy fragments and assign section ordinals.
 823   unsigned SectionIndex = 0;
 824   for (MCSection &Sec : *this) {
 825     // Create dummy fragments to eliminate any empty sections, this simplifies
 826     // layout.
 827     if (Sec.getFragmentList().empty())
 828       new MCDataFragment(&Sec);
 829
 830     Sec.setOrdinal(SectionIndex++);
 831   }
 832
 833   // Assign layout order indices to sections and fragments.
 834   for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
 835     MCSection *Sec = Layout.getSectionOrder()[i];
 836     Sec->setLayoutOrder(i);
 837
 838     unsigned FragmentIndex = 0;
 839     for (MCFragment &Frag : *Sec)
 840       Frag.setLayoutOrder(FragmentIndex++);
 841   }
 842
 843   // Layout until everything fits.
 844   while (layoutOnce(Layout)) {
 845     if (getContext().hadError())
 846       return;
 847     // Size of fragments in one section can depend on the size of fragments in
 848     // another. If any fragment has changed size, we have to re-layout (and
 849     // as a result possibly further relax) all.
 850     for (MCSection &Sec : *this)
 851       Layout.invalidateFragmentsFrom(&*Sec.begin());
 852   }
 853
 854   DEBUG_WITH_TYPE("mc-dump", {
 855       errs() << "assembler backend - post-relaxation\n--\n";
 856       dump(); });
 857
 858   // Finalize the layout, including fragment lowering.
 859   finishLayout(Layout);
 860
 861   DEBUG_WITH_TYPE("mc-dump", {
 862       errs() << "assembler backend - final-layout\n--\n";
 863       dump(); });
 864
 865   // Allow the object writer a chance to perform post-layout binding (for
 866   // example, to set the index fields in the symbol data).
 867   getWriter().executePostLayoutBinding(*this, Layout);
 868
 869   // Evaluate and apply the fixups, generating relocation entries as necessary.
 870   for (MCSection &Sec : *this) {
 871     for (MCFragment &Frag : Sec) {
 872       ArrayRef<MCFixup> Fixups;
 873       MutableArrayRef<char> Contents;
 874       const MCSubtargetInfo *STI = nullptr;
 875
 876       // Process MCAlignFragment and MCEncodedFragmentWithFixups here.
 877       switch (Frag.getKind()) {
 878       default:
 879         continue;
 880       case MCFragment::FT_Align: {
 881         MCAlignFragment &AF = cast<MCAlignFragment>(Frag);
 882         // Insert fixup type for code alignment if the target define
 883         // shouldInsertFixupForCodeAlign target hook.
 884         if (Sec.useCodeAlign() && AF.hasEmitNops())
 885           getBackend().shouldInsertFixupForCodeAlign(*this, Layout, AF);
 886         continue;
 887       }
 888       case MCFragment::FT_Data: {
 889         MCDataFragment &DF = cast<MCDataFragment>(Frag);
 890         Fixups = DF.getFixups();
 891         Contents = DF.getContents();
 892         STI = DF.getSubtargetInfo();
 893         assert(!DF.hasInstructions() || STI != nullptr);
 894         break;
 895       }
 896       case MCFragment::FT_Relaxable: {
 897         MCRelaxableFragment &RF = cast<MCRelaxableFragment>(Frag);
 898         Fixups = RF.getFixups();
 899         Contents = RF.getContents();
 900         STI = RF.getSubtargetInfo();
 901         assert(!RF.hasInstructions() || STI != nullptr);
 902         break;
 903       }
 904       case MCFragment::FT_CVDefRange: {
 905         MCCVDefRangeFragment &CF = cast<MCCVDefRangeFragment>(Frag);
 906         Fixups = CF.getFixups();
 907         Contents = CF.getContents();
 908         break;
 909       }
 910       case MCFragment::FT_Dwarf: {
 911         MCDwarfLineAddrFragment &DF = cast<MCDwarfLineAddrFragment>(Frag);
 912         Fixups = DF.getFixups();
 913         Contents = DF.getContents();
 914         break;
 915       }
 916       case MCFragment::FT_DwarfFrame: {
 917         MCDwarfCallFrameFragment &DF = cast<MCDwarfCallFrameFragment>(Frag);
 918         Fixups = DF.getFixups();
 919         Contents = DF.getContents();
 920         break;
 921       }
 922       case MCFragment::FT_LEB: {
 923         auto &LF = cast<MCLEBFragment>(Frag);
 924         Fixups = LF.getFixups();
 925         Contents = LF.getContents();
 926         break;
 927       }
 928       case MCFragment::FT_PseudoProbe: {
 929         MCPseudoProbeAddrFragment &PF = cast<MCPseudoProbeAddrFragment>(Frag);
 930         Fixups = PF.getFixups();
 931         Contents = PF.getContents();
 932         break;
 933       }
 934       }
 935       for (const MCFixup &Fixup : Fixups) {
 936         uint64_t FixedValue;
 937         bool IsResolved;
 938         MCValue Target;
 939         std::tie(Target, FixedValue, IsResolved) =
 940             handleFixup(Layout, Frag, Fixup, STI);
 941         getBackend().applyFixup(*this, Fixup, Target, Contents, FixedValue,
 942                                 IsResolved, STI);
 943       }
 944     }
 945   }
 946 }
 947
 948 void MCAssembler::Finish() {
 949   // Create the layout object.
 950   MCAsmLayout Layout(*this);
 951   layout(Layout);
 952
 953   // Write the object file.
 954   stats::ObjectBytes += getWriter().writeObject(*this, Layout);
 955 }
 956
 957 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
 958                                        const MCRelaxableFragment *DF,
 959                                        const MCAsmLayout &Layout) const {
 960   assert(getBackendPtr() && "Expected assembler backend");
 961   MCValue Target;
 962   uint64_t Value;
 963   bool WasForced;
 964   bool Resolved = evaluateFixup(Layout, Fixup, DF, Target,
 965                                 DF->getSubtargetInfo(), Value, WasForced);
 966   if (Target.getSymA() &&
 967       Target.getSymA()->getKind() == MCSymbolRefExpr::VK_X86_ABS8 &&
 968       Fixup.getKind() == FK_Data_1)
 969     return false;
 970   return getBackend().fixupNeedsRelaxationAdvanced(Fixup, Resolved, Value, DF,
 971                                                    Layout, WasForced);
 972 }
 973
 974 bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
 975                                           const MCAsmLayout &Layout) const {
 976   assert(getBackendPtr() && "Expected assembler backend");
 977   // If this inst doesn't ever need relaxation, ignore it. This occurs when we
 978   // are intentionally pushing out inst fragments, or because we relaxed a
 979   // previous instruction to one that doesn't need relaxation.
 980   if (!getBackend().mayNeedRelaxation(F->getInst(), *F->getSubtargetInfo()))
 981     return false;
 982
 983   for (const MCFixup &Fixup : F->getFixups())
 984     if (fixupNeedsRelaxation(Fixup, F, Layout))
 985       return true;
 986
 987   return false;
 988 }
 989
 990 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
 991                                    MCRelaxableFragment &F) {
 992   assert(getEmitterPtr() &&
 993          "Expected CodeEmitter defined for relaxInstruction");
 994   if (!fragmentNeedsRelaxation(&F, Layout))
 995     return false;
 996
 997   ++stats::RelaxedInstructions;
 998
 999   // FIXME-PERF: We could immediately lower out instructions if we can tell
1000   // they are fully resolved, to avoid retesting on later passes.
1001
1002   // Relax the fragment.
1003
1004   MCInst Relaxed = F.getInst();
1005   getBackend().relaxInstruction(Relaxed, *F.getSubtargetInfo());
1006
1007   // Encode the new instruction.
1008   F.setInst(Relaxed);
1009   F.getFixups().clear();
1010   F.getContents().clear();
1011   getEmitter().encodeInstruction(Relaxed, F.getContents(), F.getFixups(),
1012                                  *F.getSubtargetInfo());
1013   return true;
1014 }
1015
1016 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
1017   const unsigned OldSize = static_cast<unsigned>(LF.getContents().size());
1018   unsigned PadTo = OldSize;
1019   int64_t Value;
1020   SmallVectorImpl<char> &Data = LF.getContents();
1021   LF.getFixups().clear();
1022   // Use evaluateKnownAbsolute for Mach-O as a hack: .subsections_via_symbols
1023   // requires that .uleb128 A-B is foldable where A and B reside in different
1024   // fragments. This is used by __gcc_except_table.
1025   bool Abs = getSubsectionsViaSymbols()
1026                  ? LF.getValue().evaluateKnownAbsolute(Value, Layout)
1027                  : LF.getValue().evaluateAsAbsolute(Value, Layout);
1028   if (!Abs) {
1029     bool Relaxed, UseZeroPad;
1030     std::tie(Relaxed, UseZeroPad) = getBackend().relaxLEB128(LF, Layout, Value);
1031     if (!Relaxed) {
1032       getContext().reportError(LF.getValue().getLoc(),
1033                                Twine(LF.isSigned() ? ".s" : ".u") +
1034                                    "leb128 expression is not absolute");
1035       LF.setValue(MCConstantExpr::create(0, Context));
1036     }
1037     uint8_t Tmp[10]; // maximum size: ceil(64/7)
1038     PadTo = std::max(PadTo, encodeULEB128(uint64_t(Value), Tmp));
1039     if (UseZeroPad)
1040       Value = 0;
1041   }
1042   Data.clear();
1043   raw_svector_ostream OSE(Data);
1044   // The compiler can generate EH table assembly that is impossible to assemble
1045   // without either adding padding to an LEB fragment or adding extra padding
1046   // to a later alignment fragment. To accommodate such tables, relaxation can
1047   // only increase an LEB fragment size here, not decrease it. See PR35809.
1048   if (LF.isSigned())
1049     encodeSLEB128(Value, OSE, PadTo);
1050   else
1051     encodeULEB128(Value, OSE, PadTo);
1052   return OldSize != LF.getContents().size();
1053 }
1054
1055 /// Check if the branch crosses the boundary.
1056 ///
1057 /// \param StartAddr start address of the fused/unfused branch.
1058 /// \param Size size of the fused/unfused branch.
1059 /// \param BoundaryAlignment alignment requirement of the branch.
1060 /// \returns true if the branch cross the boundary.
1061 static bool mayCrossBoundary(uint64_t StartAddr, uint64_t Size,
1062                              Align BoundaryAlignment) {
1063   uint64_t EndAddr = StartAddr + Size;
1064   return (StartAddr >> Log2(BoundaryAlignment)) !=
1065          ((EndAddr - 1) >> Log2(BoundaryAlignment));
1066 }
1067
1068 /// Check if the branch is against the boundary.
1069 ///
1070 /// \param StartAddr start address of the fused/unfused branch.
1071 /// \param Size size of the fused/unfused branch.
1072 /// \param BoundaryAlignment alignment requirement of the branch.
1073 /// \returns true if the branch is against the boundary.
1074 static bool isAgainstBoundary(uint64_t StartAddr, uint64_t Size,
1075                               Align BoundaryAlignment) {
1076   uint64_t EndAddr = StartAddr + Size;
1077   return (EndAddr & (BoundaryAlignment.value() - 1)) == 0;
1078 }
1079
1080 /// Check if the branch needs padding.
1081 ///
1082 /// \param StartAddr start address of the fused/unfused branch.
1083 /// \param Size size of the fused/unfused branch.
1084 /// \param BoundaryAlignment alignment requirement of the branch.
1085 /// \returns true if the branch needs padding.
1086 static bool needPadding(uint64_t StartAddr, uint64_t Size,
1087                         Align BoundaryAlignment) {
1088   return mayCrossBoundary(StartAddr, Size, BoundaryAlignment) ||
1089          isAgainstBoundary(StartAddr, Size, BoundaryAlignment);
1090 }
1091
1092 bool MCAssembler::relaxBoundaryAlign(MCAsmLayout &Layout,
1093                                      MCBoundaryAlignFragment &BF) {
1094   // BoundaryAlignFragment that doesn't need to align any fragment should not be
1095   // relaxed.
1096   if (!BF.getLastFragment())
1097     return false;
1098
1099   uint64_t AlignedOffset = Layout.getFragmentOffset(&BF);
1100   uint64_t AlignedSize = 0;
1101   for (const MCFragment *F = BF.getLastFragment(); F != &BF;
1102        F = F->getPrevNode())
1103     AlignedSize += computeFragmentSize(Layout, *F);
1104
1105   Align BoundaryAlignment = BF.getAlignment();
1106   uint64_t NewSize = needPadding(AlignedOffset, AlignedSize, BoundaryAlignment)
1107                          ? offsetToAlignment(AlignedOffset, BoundaryAlignment)
1108                          : 0U;
1109   if (NewSize == BF.getSize())
1110     return false;
1111   BF.setSize(NewSize);
1112   Layout.invalidateFragmentsFrom(&BF);
1113   return true;
1114 }
1115
1116 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
1117                                      MCDwarfLineAddrFragment &DF) {
1118
1119   bool WasRelaxed;
1120   if (getBackend().relaxDwarfLineAddr(DF, Layout, WasRelaxed))
1121     return WasRelaxed;
1122
1123   MCContext &Context = Layout.getAssembler().getContext();
1124   uint64_t OldSize = DF.getContents().size();
1125   int64_t AddrDelta;
1126   bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1127   assert(Abs && "We created a line delta with an invalid expression");
1128   (void)Abs;
1129   int64_t LineDelta;
1130   LineDelta = DF.getLineDelta();
1131   SmallVectorImpl<char> &Data = DF.getContents();
1132   Data.clear();
1133   DF.getFixups().clear();
1134
1135   MCDwarfLineAddr::encode(Context, getDWARFLinetableParams(), LineDelta,
1136                           AddrDelta, Data);
1137   return OldSize != Data.size();
1138 }
1139
1140 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
1141                                               MCDwarfCallFrameFragment &DF) {
1142   bool WasRelaxed;
1143   if (getBackend().relaxDwarfCFA(DF, Layout, WasRelaxed))
1144     return WasRelaxed;
1145
1146   MCContext &Context = Layout.getAssembler().getContext();
1147   int64_t Value;
1148   bool Abs = DF.getAddrDelta().evaluateAsAbsolute(Value, Layout);
1149   if (!Abs) {
1150     getContext().reportError(DF.getAddrDelta().getLoc(),
1151                              "invalid CFI advance_loc expression");
1152     DF.setAddrDelta(MCConstantExpr::create(0, Context));
1153     return false;
1154   }
1155
1156   SmallVectorImpl<char> &Data = DF.getContents();
1157   uint64_t OldSize = Data.size();
1158   Data.clear();
1159   DF.getFixups().clear();
1160
1161   MCDwarfFrameEmitter::encodeAdvanceLoc(Context, Value, Data);
1162   return OldSize != Data.size();
1163 }
1164
1165 bool MCAssembler::relaxCVInlineLineTable(MCAsmLayout &Layout,
1166                                          MCCVInlineLineTableFragment &F) {
1167   unsigned OldSize = F.getContents().size();
1168   getContext().getCVContext().encodeInlineLineTable(Layout, F);
1169   return OldSize != F.getContents().size();
1170 }
1171
1172 bool MCAssembler::relaxCVDefRange(MCAsmLayout &Layout,
1173                                   MCCVDefRangeFragment &F) {
1174   unsigned OldSize = F.getContents().size();
1175   getContext().getCVContext().encodeDefRange(Layout, F);
1176   return OldSize != F.getContents().size();
1177 }
1178
1179 bool MCAssembler::relaxPseudoProbeAddr(MCAsmLayout &Layout,
1180                                        MCPseudoProbeAddrFragment &PF) {
1181   uint64_t OldSize = PF.getContents().size();
1182   int64_t AddrDelta;
1183   bool Abs = PF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1184   assert(Abs && "We created a pseudo probe with an invalid expression");
1185   (void)Abs;
1186   SmallVectorImpl<char> &Data = PF.getContents();
1187   Data.clear();
1188   raw_svector_ostream OSE(Data);
1189   PF.getFixups().clear();
1190
1191   // AddrDelta is a signed integer
1192   encodeSLEB128(AddrDelta, OSE, OldSize);
1193   return OldSize != Data.size();
1194 }
1195
1196 bool MCAssembler::relaxFragment(MCAsmLayout &Layout, MCFragment &F) {
1197   switch(F.getKind()) {
1198   default:
1199     return false;
1200   case MCFragment::FT_Relaxable:
1201     assert(!getRelaxAll() &&
1202            "Did not expect a MCRelaxableFragment in RelaxAll mode");
1203     return relaxInstruction(Layout, cast<MCRelaxableFragment>(F));
1204   case MCFragment::FT_Dwarf:
1205     return relaxDwarfLineAddr(Layout, cast<MCDwarfLineAddrFragment>(F));
1206   case MCFragment::FT_DwarfFrame:
1207     return relaxDwarfCallFrameFragment(Layout,
1208                                        cast<MCDwarfCallFrameFragment>(F));
1209   case MCFragment::FT_LEB:
1210     return relaxLEB(Layout, cast<MCLEBFragment>(F));
1211   case MCFragment::FT_BoundaryAlign:
1212     return relaxBoundaryAlign(Layout, cast<MCBoundaryAlignFragment>(F));
1213   case MCFragment::FT_CVInlineLines:
1214     return relaxCVInlineLineTable(Layout, cast<MCCVInlineLineTableFragment>(F));
1215   case MCFragment::FT_CVDefRange:
1216     return relaxCVDefRange(Layout, cast<MCCVDefRangeFragment>(F));
1217   case MCFragment::FT_PseudoProbe:
1218     return relaxPseudoProbeAddr(Layout, cast<MCPseudoProbeAddrFragment>(F));
1219   }
1220 }
1221
1222 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSection &Sec) {
1223   // Holds the first fragment which needed relaxing during this layout. It will
1224   // remain NULL if none were relaxed.
1225   // When a fragment is relaxed, all the fragments following it should get
1226   // invalidated because their offset is going to change.
1227   MCFragment *FirstRelaxedFragment = nullptr;
1228
1229   // Attempt to relax all the fragments in the section.
1230   for (MCFragment &Frag : Sec) {
1231     // Check if this is a fragment that needs relaxation.
1232     bool RelaxedFrag = relaxFragment(Layout, Frag);
1233     if (RelaxedFrag && !FirstRelaxedFragment)
1234       FirstRelaxedFragment = &Frag;
1235   }
1236   if (FirstRelaxedFragment) {
1237     Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
1238     return true;
1239   }
1240   return false;
1241 }
1242
1243 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
1244   ++stats::RelaxationSteps;
1245
1246   bool WasRelaxed = false;
1247   for (MCSection &Sec : *this) {
1248     while (layoutSectionOnce(Layout, Sec))
1249       WasRelaxed = true;
1250   }
1251
1252   return WasRelaxed;
1253 }
1254
1255 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
1256   assert(getBackendPtr() && "Expected assembler backend");
1257   // The layout is done. Mark every fragment as valid.
1258   for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
1259     MCSection &Section = *Layout.getSectionOrder()[i];
1260     Layout.getFragmentOffset(&*Section.getFragmentList().rbegin());
1261     computeFragmentSize(Layout, *Section.getFragmentList().rbegin());
1262   }
1263   getBackend().finishLayout(*this, Layout);
1264 }
1265
1266 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1267 LLVM_DUMP_METHOD void MCAssembler::dump() const{
1268   raw_ostream &OS = errs();
1269
1270   OS << "<MCAssembler\n";
1271   OS << "  Sections:[\n    ";
1272   for (const_iterator it = begin(), ie = end(); it != ie; ++it) {
1273     if (it != begin()) OS << ",\n    ";
1274     it->dump();
1275   }
1276   OS << "],\n";
1277   OS << "  Symbols:[";
1278
1279   for (const_symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1280     if (it != symbol_begin()) OS << ",\n           ";
1281     OS << "(";
1282     it->dump();
1283     OS << ", Index:" << it->getIndex() << ", ";
1284     OS << ")";
1285   }
1286   OS << "]>\n";
1287 }
1288 #endif