lib/MC/MCAssembler.cpp

   1 //===- lib/MC/MCAssembler.cpp - Assembler Backend Implementation ----------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #define DEBUG_TYPE "assembler"
  11 #include "llvm/MC/MCAssembler.h"
  12 #include "llvm/MC/MCAsmLayout.h"
  13 #include "llvm/MC/MCCodeEmitter.h"
  14 #include "llvm/MC/MCContext.h"
  15 #include "llvm/MC/MCExpr.h"
  16 #include "llvm/MC/MCObjectWriter.h"
  17 #include "llvm/MC/MCSection.h"
  18 #include "llvm/MC/MCSymbol.h"
  19 #include "llvm/MC/MCValue.h"
  20 #include "llvm/MC/MCDwarf.h"
  21 #include "llvm/ADT/OwningPtr.h"
  22 #include "llvm/ADT/Statistic.h"
  23 #include "llvm/ADT/StringExtras.h"
  24 #include "llvm/ADT/Twine.h"
  25 #include "llvm/Support/Debug.h"
  26 #include "llvm/Support/ErrorHandling.h"
  27 #include "llvm/Support/raw_ostream.h"
  28 #include "llvm/Target/TargetRegistry.h"
  29 #include "llvm/Target/TargetAsmBackend.h"
  30
  31 #include <vector>
  32 using namespace llvm;
  33
  34 namespace {
  35 namespace stats {
  36 STATISTIC(EmittedFragments, "Number of emitted assembler fragments");
  37 STATISTIC(EvaluateFixup, "Number of evaluated fixups");
  38 STATISTIC(FragmentLayouts, "Number of fragment layouts");
  39 STATISTIC(ObjectBytes, "Number of emitted object file bytes");
  40 STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
  41 STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
  42 }
  43 }
  44
  45 // FIXME FIXME FIXME: There are number of places in this file where we convert
  46 // what is a 64-bit assembler value used for computation into a value in the
  47 // object file, which may truncate it. We should detect that truncation where
  48 // invalid and report errors back.
  49
  50 /* *** */
  51
  52 MCAsmLayout::MCAsmLayout(MCAssembler &Asm)
  53   : Assembler(Asm), LastValidFragment()
  54  {
  55   // Compute the section layout order. Virtual sections must go last.
  56   for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
  57     if (!it->getSection().isVirtualSection())
  58       SectionOrder.push_back(&*it);
  59   for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
  60     if (it->getSection().isVirtualSection())
  61       SectionOrder.push_back(&*it);
  62 }
  63
  64 bool MCAsmLayout::isFragmentUpToDate(const MCFragment *F) const {
  65   const MCSectionData &SD = *F->getParent();
  66   const MCFragment *LastValid = LastValidFragment.lookup(&SD);
  67   if (!LastValid)
  68     return false;
  69   assert(LastValid->getParent() == F->getParent());
  70   return F->getLayoutOrder() <= LastValid->getLayoutOrder();
  71 }
  72
  73 void MCAsmLayout::Invalidate(MCFragment *F) {
  74   // If this fragment wasn't already up-to-date, we don't need to do anything.
  75   if (!isFragmentUpToDate(F))
  76     return;
  77
  78   // Otherwise, reset the last valid fragment to this fragment.
  79   const MCSectionData &SD = *F->getParent();
  80   LastValidFragment[&SD] = F;
  81 }
  82
  83 void MCAsmLayout::EnsureValid(const MCFragment *F) const {
  84   MCSectionData &SD = *F->getParent();
  85
  86   MCFragment *Cur = LastValidFragment[&SD];
  87   if (!Cur)
  88     Cur = &*SD.begin();
  89   else
  90     Cur = Cur->getNextNode();
  91
  92   // Advance the layout position until the fragment is up-to-date.
  93   while (!isFragmentUpToDate(F)) {
  94     const_cast<MCAsmLayout*>(this)->LayoutFragment(Cur);
  95     Cur = Cur->getNextNode();
  96   }
  97 }
  98
  99 uint64_t MCAsmLayout::getFragmentOffset(const MCFragment *F) const {
 100   EnsureValid(F);
 101   assert(F->Offset != ~UINT64_C(0) && "Address not set!");
 102   return F->Offset;
 103 }
 104
 105 uint64_t MCAsmLayout::getSymbolOffset(const MCSymbolData *SD) const {
 106   assert(SD->getFragment() && "Invalid getOffset() on undefined symbol!");
 107   return getFragmentOffset(SD->getFragment()) + SD->getOffset();
 108 }
 109
 110 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
 111   // The size is the last fragment's end offset.
 112   const MCFragment &F = SD->getFragmentList().back();
 113   return getFragmentOffset(&F) + getAssembler().ComputeFragmentSize(*this, F);
 114 }
 115
 116 uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
 117   // Virtual sections have no file size.
 118   if (SD->getSection().isVirtualSection())
 119     return 0;
 120
 121   // Otherwise, the file size is the same as the address space size.
 122   return getSectionAddressSize(SD);
 123 }
 124
 125 /* *** */
 126
 127 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
 128 }
 129
 130 MCFragment::~MCFragment() {
 131 }
 132
 133 MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
 134   : Kind(_Kind), Parent(_Parent), Atom(0), Offset(~UINT64_C(0))
 135 {
 136   if (Parent)
 137     Parent->getFragmentList().push_back(this);
 138 }
 139
 140 /* *** */
 141
 142 MCSectionData::MCSectionData() : Section(0) {}
 143
 144 MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
 145   : Section(&_Section),
 146     Ordinal(~UINT32_C(0)),
 147     Alignment(1),
 148     HasInstructions(false)
 149 {
 150   if (A)
 151     A->getSectionList().push_back(this);
 152 }
 153
 154 /* *** */
 155
 156 MCSymbolData::MCSymbolData() : Symbol(0) {}
 157
 158 MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
 159                            uint64_t _Offset, MCAssembler *A)
 160   : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
 161     IsExternal(false), IsPrivateExtern(false),
 162     CommonSize(0), SymbolSize(0), CommonAlign(0),
 163     Flags(0), Index(0)
 164 {
 165   if (A)
 166     A->getSymbolList().push_back(this);
 167 }
 168
 169 /* *** */
 170
 171 MCAssembler::MCAssembler(MCContext &Context_, TargetAsmBackend &Backend_,
 172                          MCCodeEmitter &Emitter_, MCObjectWriter &Writer_,
 173                          raw_ostream &OS_)
 174   : Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(Writer_),
 175     OS(OS_), RelaxAll(false), NoExecStack(false), SubsectionsViaSymbols(false)
 176 {
 177 }
 178
 179 MCAssembler::~MCAssembler() {
 180 }
 181
 182 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
 183   // Non-temporary labels should always be visible to the linker.
 184   if (!Symbol.isTemporary())
 185     return true;
 186
 187   // Absolute temporary labels are never visible.
 188   if (!Symbol.isInSection())
 189     return false;
 190
 191   // Otherwise, check if the section requires symbols even for temporary labels.
 192   return getBackend().doesSectionRequireSymbols(Symbol.getSection());
 193 }
 194
 195 const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
 196   // Linker visible symbols define atoms.
 197   if (isSymbolLinkerVisible(SD->getSymbol()))
 198     return SD;
 199
 200   // Absolute and undefined symbols have no defining atom.
 201   if (!SD->getFragment())
 202     return 0;
 203
 204   // Non-linker visible symbols in sections which can't be atomized have no
 205   // defining atom.
 206   if (!getBackend().isSectionAtomizable(
 207         SD->getFragment()->getParent()->getSection()))
 208     return 0;
 209
 210   // Otherwise, return the atom for the containing fragment.
 211   return SD->getFragment()->getAtom();
 212 }
 213
 214 bool MCAssembler::EvaluateFixup(const MCAsmLayout &Layout,
 215                                 const MCFixup &Fixup, const MCFragment *DF,
 216                                 MCValue &Target, uint64_t &Value) const {
 217   ++stats::EvaluateFixup;
 218
 219   if (!Fixup.getValue()->EvaluateAsRelocatable(Target, Layout))
 220     report_fatal_error("expected relocatable expression");
 221
 222   bool IsPCRel = Backend.getFixupKindInfo(
 223     Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
 224
 225   bool IsResolved;
 226   if (IsPCRel) {
 227     if (Target.getSymB()) {
 228       IsResolved = false;
 229     } else if (!Target.getSymA()) {
 230       IsResolved = false;
 231     } else {
 232       const MCSymbol &SA = Target.getSymA()->getSymbol();
 233       if (SA.AliasedSymbol().isUndefined()) {
 234         IsResolved = false;
 235       } else {
 236         const MCSymbolData &DataA = getSymbolData(SA);
 237         IsResolved =
 238           getWriter().IsSymbolRefDifferenceFullyResolvedImpl(*this, DataA,
 239                                                              *DF, false, true);
 240       }
 241     }
 242   } else {
 243     IsResolved = Target.isAbsolute();
 244   }
 245
 246   Value = Target.getConstant();
 247
 248   bool IsThumb = false;
 249   if (const MCSymbolRefExpr *A = Target.getSymA()) {
 250     const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
 251     if (Sym.isDefined())
 252       Value += Layout.getSymbolOffset(&getSymbolData(Sym));
 253     if (isThumbFunc(&Sym))
 254       IsThumb = true;
 255   }
 256   if (const MCSymbolRefExpr *B = Target.getSymB()) {
 257     const MCSymbol &Sym = B->getSymbol().AliasedSymbol();
 258     if (Sym.isDefined())
 259       Value -= Layout.getSymbolOffset(&getSymbolData(Sym));
 260   }
 261
 262
 263   bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
 264                          MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
 265   assert((ShouldAlignPC ? IsPCRel : true) &&
 266     "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
 267
 268   if (IsPCRel) {
 269     uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
 270
 271     // A number of ARM fixups in Thumb mode require that the effective PC
 272     // address be determined as the 32-bit aligned version of the actual offset.
 273     if (ShouldAlignPC) Offset &= ~0x3;
 274     Value -= Offset;
 275   }
 276
 277   // ARM fixups based from a thumb function address need to have the low
 278   // bit set. The actual value is always at least 16-bit aligned, so the
 279   // low bit is normally clear and available for use as an ISA flag for
 280   // interworking.
 281   if (IsThumb)
 282     Value |= 1;
 283
 284   return IsResolved;
 285 }
 286
 287 uint64_t MCAssembler::ComputeFragmentSize(const MCAsmLayout &Layout,
 288                                           const MCFragment &F) const {
 289   switch (F.getKind()) {
 290   case MCFragment::FT_Data:
 291     return cast<MCDataFragment>(F).getContents().size();
 292   case MCFragment::FT_Fill:
 293     return cast<MCFillFragment>(F).getSize();
 294   case MCFragment::FT_Inst:
 295     return cast<MCInstFragment>(F).getInstSize();
 296
 297   case MCFragment::FT_LEB:
 298     return cast<MCLEBFragment>(F).getContents().size();
 299
 300   case MCFragment::FT_Align: {
 301     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
 302     unsigned Offset = Layout.getFragmentOffset(&AF);
 303     unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
 304     if (Size > AF.getMaxBytesToEmit())
 305       return 0;
 306     return Size;
 307   }
 308
 309   case MCFragment::FT_Org: {
 310     MCOrgFragment &OF = cast<MCOrgFragment>(F);
 311     int64_t TargetLocation;
 312     if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, Layout))
 313       report_fatal_error("expected assembly-time absolute expression");
 314
 315     // FIXME: We need a way to communicate this error.
 316     uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
 317     int64_t Size = TargetLocation - FragmentOffset;
 318     if (Size < 0 || Size >= 0x40000000)
 319       report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
 320                          "' (at offset '" + Twine(FragmentOffset) + "')");
 321     return Size;
 322   }
 323
 324   case MCFragment::FT_Dwarf:
 325     return cast<MCDwarfLineAddrFragment>(F).getContents().size();
 326   case MCFragment::FT_DwarfFrame:
 327     return cast<MCDwarfCallFrameFragment>(F).getContents().size();
 328   }
 329
 330   assert(0 && "invalid fragment kind");
 331   return 0;
 332 }
 333
 334 void MCAsmLayout::LayoutFragment(MCFragment *F) {
 335   MCFragment *Prev = F->getPrevNode();
 336
 337   // We should never try to recompute something which is up-to-date.
 338   assert(!isFragmentUpToDate(F) && "Attempt to recompute up-to-date fragment!");
 339   // We should never try to compute the fragment layout if it's predecessor
 340   // isn't up-to-date.
 341   assert((!Prev || isFragmentUpToDate(Prev)) &&
 342          "Attempt to compute fragment before it's predecessor!");
 343
 344   ++stats::FragmentLayouts;
 345
 346   // Compute fragment offset and size.
 347   uint64_t Offset = 0;
 348   if (Prev)
 349     Offset += Prev->Offset + getAssembler().ComputeFragmentSize(*this, *Prev);
 350
 351   F->Offset = Offset;
 352   LastValidFragment[F->getParent()] = F;
 353 }
 354
 355 /// WriteFragmentData - Write the \arg F data to the output file.
 356 static void WriteFragmentData(const MCAssembler &Asm, const MCAsmLayout &Layout,
 357                               const MCFragment &F) {
 358   MCObjectWriter *OW = &Asm.getWriter();
 359   uint64_t Start = OW->getStream().tell();
 360   (void) Start;
 361
 362   ++stats::EmittedFragments;
 363
 364   // FIXME: Embed in fragments instead?
 365   uint64_t FragmentSize = Asm.ComputeFragmentSize(Layout, F);
 366   switch (F.getKind()) {
 367   case MCFragment::FT_Align: {
 368     MCAlignFragment &AF = cast<MCAlignFragment>(F);
 369     uint64_t Count = FragmentSize / AF.getValueSize();
 370
 371     assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
 372
 373     // FIXME: This error shouldn't actually occur (the front end should emit
 374     // multiple .align directives to enforce the semantics it wants), but is
 375     // severe enough that we want to report it. How to handle this?
 376     if (Count * AF.getValueSize() != FragmentSize)
 377       report_fatal_error("undefined .align directive, value size '" +
 378                         Twine(AF.getValueSize()) +
 379                         "' is not a divisor of padding size '" +
 380                         Twine(FragmentSize) + "'");
 381
 382     // See if we are aligning with nops, and if so do that first to try to fill
 383     // the Count bytes.  Then if that did not fill any bytes or there are any
 384     // bytes left to fill use the the Value and ValueSize to fill the rest.
 385     // If we are aligning with nops, ask that target to emit the right data.
 386     if (AF.hasEmitNops()) {
 387       if (!Asm.getBackend().WriteNopData(Count, OW))
 388         report_fatal_error("unable to write nop sequence of " +
 389                           Twine(Count) + " bytes");
 390       break;
 391     }
 392
 393     // Otherwise, write out in multiples of the value size.
 394     for (uint64_t i = 0; i != Count; ++i) {
 395       switch (AF.getValueSize()) {
 396       default:
 397         assert(0 && "Invalid size!");
 398       case 1: OW->Write8 (uint8_t (AF.getValue())); break;
 399       case 2: OW->Write16(uint16_t(AF.getValue())); break;
 400       case 4: OW->Write32(uint32_t(AF.getValue())); break;
 401       case 8: OW->Write64(uint64_t(AF.getValue())); break;
 402       }
 403     }
 404     break;
 405   }
 406
 407   case MCFragment::FT_Data: {
 408     MCDataFragment &DF = cast<MCDataFragment>(F);
 409     assert(FragmentSize == DF.getContents().size() && "Invalid size!");
 410     OW->WriteBytes(DF.getContents().str());
 411     break;
 412   }
 413
 414   case MCFragment::FT_Fill: {
 415     MCFillFragment &FF = cast<MCFillFragment>(F);
 416
 417     assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
 418
 419     for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
 420       switch (FF.getValueSize()) {
 421       default:
 422         assert(0 && "Invalid size!");
 423       case 1: OW->Write8 (uint8_t (FF.getValue())); break;
 424       case 2: OW->Write16(uint16_t(FF.getValue())); break;
 425       case 4: OW->Write32(uint32_t(FF.getValue())); break;
 426       case 8: OW->Write64(uint64_t(FF.getValue())); break;
 427       }
 428     }
 429     break;
 430   }
 431
 432   case MCFragment::FT_Inst: {
 433     MCInstFragment &IF = cast<MCInstFragment>(F);
 434     OW->WriteBytes(StringRef(IF.getCode().begin(), IF.getCode().size()));
 435     break;
 436   }
 437
 438   case MCFragment::FT_LEB: {
 439     MCLEBFragment &LF = cast<MCLEBFragment>(F);
 440     OW->WriteBytes(LF.getContents().str());
 441     break;
 442   }
 443
 444   case MCFragment::FT_Org: {
 445     MCOrgFragment &OF = cast<MCOrgFragment>(F);
 446
 447     for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
 448       OW->Write8(uint8_t(OF.getValue()));
 449
 450     break;
 451   }
 452
 453   case MCFragment::FT_Dwarf: {
 454     const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
 455     OW->WriteBytes(OF.getContents().str());
 456     break;
 457   }
 458   case MCFragment::FT_DwarfFrame: {
 459     const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
 460     OW->WriteBytes(CF.getContents().str());
 461     break;
 462   }
 463   }
 464
 465   assert(OW->getStream().tell() - Start == FragmentSize);
 466 }
 467
 468 void MCAssembler::WriteSectionData(const MCSectionData *SD,
 469                                    const MCAsmLayout &Layout) const {
 470   // Ignore virtual sections.
 471   if (SD->getSection().isVirtualSection()) {
 472     assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
 473
 474     // Check that contents are only things legal inside a virtual section.
 475     for (MCSectionData::const_iterator it = SD->begin(),
 476            ie = SD->end(); it != ie; ++it) {
 477       switch (it->getKind()) {
 478       default:
 479         assert(0 && "Invalid fragment in virtual section!");
 480       case MCFragment::FT_Data: {
 481         // Check that we aren't trying to write a non-zero contents (or fixups)
 482         // into a virtual section. This is to support clients which use standard
 483         // directives to fill the contents of virtual sections.
 484         MCDataFragment &DF = cast<MCDataFragment>(*it);
 485         assert(DF.fixup_begin() == DF.fixup_end() &&
 486                "Cannot have fixups in virtual section!");
 487         for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
 488           assert(DF.getContents()[i] == 0 &&
 489                  "Invalid data value for virtual section!");
 490         break;
 491       }
 492       case MCFragment::FT_Align:
 493         // Check that we aren't trying to write a non-zero value into a virtual
 494         // section.
 495         assert((!cast<MCAlignFragment>(it)->getValueSize() ||
 496                 !cast<MCAlignFragment>(it)->getValue()) &&
 497                "Invalid align in virtual section!");
 498         break;
 499       case MCFragment::FT_Fill:
 500         assert(!cast<MCFillFragment>(it)->getValueSize() &&
 501                "Invalid fill in virtual section!");
 502         break;
 503       }
 504     }
 505
 506     return;
 507   }
 508
 509   uint64_t Start = getWriter().getStream().tell();
 510   (void) Start;
 511
 512   for (MCSectionData::const_iterator it = SD->begin(),
 513          ie = SD->end(); it != ie; ++it)
 514     WriteFragmentData(*this, Layout, *it);
 515
 516   assert(getWriter().getStream().tell() - Start ==
 517          Layout.getSectionAddressSize(SD));
 518 }
 519
 520
 521 uint64_t MCAssembler::HandleFixup(const MCAsmLayout &Layout,
 522                                   MCFragment &F,
 523                                   const MCFixup &Fixup) {
 524    // Evaluate the fixup.
 525    MCValue Target;
 526    uint64_t FixedValue;
 527    if (!EvaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
 528      // The fixup was unresolved, we need a relocation. Inform the object
 529      // writer of the relocation, and give it an opportunity to adjust the
 530      // fixup value if need be.
 531      getWriter().RecordRelocation(*this, Layout, &F, Fixup, Target, FixedValue);
 532    }
 533    return FixedValue;
 534  }
 535
 536 void MCAssembler::Finish() {
 537   DEBUG_WITH_TYPE("mc-dump", {
 538       llvm::errs() << "assembler backend - pre-layout\n--\n";
 539       dump(); });
 540
 541   // Create the layout object.
 542   MCAsmLayout Layout(*this);
 543
 544   // Create dummy fragments and assign section ordinals.
 545   unsigned SectionIndex = 0;
 546   for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
 547     // Create dummy fragments to eliminate any empty sections, this simplifies
 548     // layout.
 549     if (it->getFragmentList().empty())
 550       new MCDataFragment(it);
 551
 552     it->setOrdinal(SectionIndex++);
 553   }
 554
 555   // Assign layout order indices to sections and fragments.
 556   for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
 557     MCSectionData *SD = Layout.getSectionOrder()[i];
 558     SD->setLayoutOrder(i);
 559
 560     unsigned FragmentIndex = 0;
 561     for (MCSectionData::iterator it2 = SD->begin(),
 562            ie2 = SD->end(); it2 != ie2; ++it2)
 563       it2->setLayoutOrder(FragmentIndex++);
 564   }
 565
 566   // Layout until everything fits.
 567   while (LayoutOnce(Layout))
 568     continue;
 569
 570   DEBUG_WITH_TYPE("mc-dump", {
 571       llvm::errs() << "assembler backend - post-relaxation\n--\n";
 572       dump(); });
 573
 574   // Finalize the layout, including fragment lowering.
 575   FinishLayout(Layout);
 576
 577   DEBUG_WITH_TYPE("mc-dump", {
 578       llvm::errs() << "assembler backend - final-layout\n--\n";
 579       dump(); });
 580
 581   uint64_t StartOffset = OS.tell();
 582
 583   // Allow the object writer a chance to perform post-layout binding (for
 584   // example, to set the index fields in the symbol data).
 585   getWriter().ExecutePostLayoutBinding(*this, Layout);
 586
 587   // Evaluate and apply the fixups, generating relocation entries as necessary.
 588   for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
 589     for (MCSectionData::iterator it2 = it->begin(),
 590            ie2 = it->end(); it2 != ie2; ++it2) {
 591       MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
 592       if (DF) {
 593         for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
 594                ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
 595           MCFixup &Fixup = *it3;
 596           uint64_t FixedValue = HandleFixup(Layout, *DF, Fixup);
 597           getBackend().ApplyFixup(Fixup, DF->getContents().data(),
 598                                   DF->getContents().size(), FixedValue);
 599         }
 600       }
 601       MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
 602       if (IF) {
 603         for (MCInstFragment::fixup_iterator it3 = IF->fixup_begin(),
 604                ie3 = IF->fixup_end(); it3 != ie3; ++it3) {
 605           MCFixup &Fixup = *it3;
 606           uint64_t FixedValue = HandleFixup(Layout, *IF, Fixup);
 607           getBackend().ApplyFixup(Fixup, IF->getCode().data(),
 608                                   IF->getCode().size(), FixedValue);
 609         }
 610       }
 611     }
 612   }
 613
 614   // Write the object file.
 615   getWriter().WriteObject(*this, Layout);
 616
 617   stats::ObjectBytes += OS.tell() - StartOffset;
 618 }
 619
 620 bool MCAssembler::FixupNeedsRelaxation(const MCFixup &Fixup,
 621                                        const MCFragment *DF,
 622                                        const MCAsmLayout &Layout) const {
 623   if (getRelaxAll())
 624     return true;
 625
 626   // If we cannot resolve the fixup value, it requires relaxation.
 627   MCValue Target;
 628   uint64_t Value;
 629   if (!EvaluateFixup(Layout, Fixup, DF, Target, Value))
 630     return true;
 631
 632   // Otherwise, relax if the value is too big for a (signed) i8.
 633   //
 634   // FIXME: This is target dependent!
 635   return int64_t(Value) != int64_t(int8_t(Value));
 636 }
 637
 638 bool MCAssembler::FragmentNeedsRelaxation(const MCInstFragment *IF,
 639                                           const MCAsmLayout &Layout) const {
 640   // If this inst doesn't ever need relaxation, ignore it. This occurs when we
 641   // are intentionally pushing out inst fragments, or because we relaxed a
 642   // previous instruction to one that doesn't need relaxation.
 643   if (!getBackend().MayNeedRelaxation(IF->getInst()))
 644     return false;
 645
 646   for (MCInstFragment::const_fixup_iterator it = IF->fixup_begin(),
 647          ie = IF->fixup_end(); it != ie; ++it)
 648     if (FixupNeedsRelaxation(*it, IF, Layout))
 649       return true;
 650
 651   return false;
 652 }
 653
 654 bool MCAssembler::RelaxInstruction(MCAsmLayout &Layout,
 655                                    MCInstFragment &IF) {
 656   if (!FragmentNeedsRelaxation(&IF, Layout))
 657     return false;
 658
 659   ++stats::RelaxedInstructions;
 660
 661   // FIXME-PERF: We could immediately lower out instructions if we can tell
 662   // they are fully resolved, to avoid retesting on later passes.
 663
 664   // Relax the fragment.
 665
 666   MCInst Relaxed;
 667   getBackend().RelaxInstruction(IF.getInst(), Relaxed);
 668
 669   // Encode the new instruction.
 670   //
 671   // FIXME-PERF: If it matters, we could let the target do this. It can
 672   // probably do so more efficiently in many cases.
 673   SmallVector<MCFixup, 4> Fixups;
 674   SmallString<256> Code;
 675   raw_svector_ostream VecOS(Code);
 676   getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups);
 677   VecOS.flush();
 678
 679   // Update the instruction fragment.
 680   IF.setInst(Relaxed);
 681   IF.getCode() = Code;
 682   IF.getFixups().clear();
 683   // FIXME: Eliminate copy.
 684   for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
 685     IF.getFixups().push_back(Fixups[i]);
 686
 687   return true;
 688 }
 689
 690 bool MCAssembler::RelaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
 691   int64_t Value = 0;
 692   uint64_t OldSize = LF.getContents().size();
 693   LF.getValue().EvaluateAsAbsolute(Value, Layout);
 694   SmallString<8> &Data = LF.getContents();
 695   Data.clear();
 696   raw_svector_ostream OSE(Data);
 697   if (LF.isSigned())
 698     MCObjectWriter::EncodeSLEB128(Value, OSE);
 699   else
 700     MCObjectWriter::EncodeULEB128(Value, OSE);
 701   OSE.flush();
 702   return OldSize != LF.getContents().size();
 703 }
 704
 705 bool MCAssembler::RelaxDwarfLineAddr(MCAsmLayout &Layout,
 706                                      MCDwarfLineAddrFragment &DF) {
 707   int64_t AddrDelta = 0;
 708   uint64_t OldSize = DF.getContents().size();
 709   bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
 710   (void)IsAbs;
 711   assert(IsAbs);
 712   int64_t LineDelta;
 713   LineDelta = DF.getLineDelta();
 714   SmallString<8> &Data = DF.getContents();
 715   Data.clear();
 716   raw_svector_ostream OSE(Data);
 717   MCDwarfLineAddr::Encode(LineDelta, AddrDelta, OSE);
 718   OSE.flush();
 719   return OldSize != Data.size();
 720 }
 721
 722 bool MCAssembler::RelaxDwarfCallFrameFragment(MCAsmLayout &Layout,
 723                                               MCDwarfCallFrameFragment &DF) {
 724   int64_t AddrDelta = 0;
 725   uint64_t OldSize = DF.getContents().size();
 726   bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
 727   (void)IsAbs;
 728   assert(IsAbs);
 729   SmallString<8> &Data = DF.getContents();
 730   Data.clear();
 731   raw_svector_ostream OSE(Data);
 732   MCDwarfFrameEmitter::EncodeAdvanceLoc(AddrDelta, OSE);
 733   OSE.flush();
 734   return OldSize != Data.size();
 735 }
 736
 737 bool MCAssembler::LayoutSectionOnce(MCAsmLayout &Layout,
 738                                     MCSectionData &SD) {
 739   MCFragment *FirstInvalidFragment = NULL;
 740   // Scan for fragments that need relaxation.
 741   for (MCSectionData::iterator it2 = SD.begin(),
 742          ie2 = SD.end(); it2 != ie2; ++it2) {
 743     // Check if this is an fragment that needs relaxation.
 744     bool relaxedFrag = false;
 745     switch(it2->getKind()) {
 746     default:
 747           break;
 748     case MCFragment::FT_Inst:
 749       relaxedFrag = RelaxInstruction(Layout, *cast<MCInstFragment>(it2));
 750       break;
 751     case MCFragment::FT_Dwarf:
 752       relaxedFrag = RelaxDwarfLineAddr(Layout,
 753                                        *cast<MCDwarfLineAddrFragment>(it2));
 754       break;
 755     case MCFragment::FT_DwarfFrame:
 756       relaxedFrag =
 757         RelaxDwarfCallFrameFragment(Layout,
 758                                     *cast<MCDwarfCallFrameFragment>(it2));
 759       break;
 760     case MCFragment::FT_LEB:
 761       relaxedFrag = RelaxLEB(Layout, *cast<MCLEBFragment>(it2));
 762       break;
 763     }
 764     // Update the layout, and remember that we relaxed.
 765     if (relaxedFrag && !FirstInvalidFragment)
 766       FirstInvalidFragment = it2;
 767   }
 768   if (FirstInvalidFragment) {
 769     Layout.Invalidate(FirstInvalidFragment);
 770     return true;
 771   }
 772   return false;
 773 }
 774
 775 bool MCAssembler::LayoutOnce(MCAsmLayout &Layout) {
 776   ++stats::RelaxationSteps;
 777
 778   bool WasRelaxed = false;
 779   for (iterator it = begin(), ie = end(); it != ie; ++it) {
 780     MCSectionData &SD = *it;
 781     while(LayoutSectionOnce(Layout, SD))
 782       WasRelaxed = true;
 783   }
 784
 785   return WasRelaxed;
 786 }
 787
 788 void MCAssembler::FinishLayout(MCAsmLayout &Layout) {
 789   // The layout is done. Mark every fragment as valid.
 790   for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
 791     Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
 792   }
 793 }
 794
 795 // Debugging methods
 796
 797 namespace llvm {
 798
 799 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
 800   OS << "<MCFixup" << " Offset:" << AF.getOffset()
 801      << " Value:" << *AF.getValue()
 802      << " Kind:" << AF.getKind() << ">";
 803   return OS;
 804 }
 805
 806 }
 807
 808 void MCFragment::dump() {
 809   raw_ostream &OS = llvm::errs();
 810
 811   OS << "<";
 812   switch (getKind()) {
 813   case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
 814   case MCFragment::FT_Data:  OS << "MCDataFragment"; break;
 815   case MCFragment::FT_Fill:  OS << "MCFillFragment"; break;
 816   case MCFragment::FT_Inst:  OS << "MCInstFragment"; break;
 817   case MCFragment::FT_Org:   OS << "MCOrgFragment"; break;
 818   case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
 819   case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
 820   case MCFragment::FT_LEB:   OS << "MCLEBFragment"; break;
 821   }
 822
 823   OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
 824      << " Offset:" << Offset << ">";
 825
 826   switch (getKind()) {
 827   case MCFragment::FT_Align: {
 828     const MCAlignFragment *AF = cast<MCAlignFragment>(this);
 829     if (AF->hasEmitNops())
 830       OS << " (emit nops)";
 831     OS << "\n       ";
 832     OS << " Alignment:" << AF->getAlignment()
 833        << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
 834        << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
 835     break;
 836   }
 837   case MCFragment::FT_Data:  {
 838     const MCDataFragment *DF = cast<MCDataFragment>(this);
 839     OS << "\n       ";
 840     OS << " Contents:[";
 841     const SmallVectorImpl<char> &Contents = DF->getContents();
 842     for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
 843       if (i) OS << ",";
 844       OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
 845     }
 846     OS << "] (" << Contents.size() << " bytes)";
 847
 848     if (!DF->getFixups().empty()) {
 849       OS << ",\n       ";
 850       OS << " Fixups:[";
 851       for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
 852              ie = DF->fixup_end(); it != ie; ++it) {
 853         if (it != DF->fixup_begin()) OS << ",\n                ";
 854         OS << *it;
 855       }
 856       OS << "]";
 857     }
 858     break;
 859   }
 860   case MCFragment::FT_Fill:  {
 861     const MCFillFragment *FF = cast<MCFillFragment>(this);
 862     OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
 863        << " Size:" << FF->getSize();
 864     break;
 865   }
 866   case MCFragment::FT_Inst:  {
 867     const MCInstFragment *IF = cast<MCInstFragment>(this);
 868     OS << "\n       ";
 869     OS << " Inst:";
 870     IF->getInst().dump_pretty(OS);
 871     break;
 872   }
 873   case MCFragment::FT_Org:  {
 874     const MCOrgFragment *OF = cast<MCOrgFragment>(this);
 875     OS << "\n       ";
 876     OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
 877     break;
 878   }
 879   case MCFragment::FT_Dwarf:  {
 880     const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
 881     OS << "\n       ";
 882     OS << " AddrDelta:" << OF->getAddrDelta()
 883        << " LineDelta:" << OF->getLineDelta();
 884     break;
 885   }
 886   case MCFragment::FT_DwarfFrame:  {
 887     const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
 888     OS << "\n       ";
 889     OS << " AddrDelta:" << CF->getAddrDelta();
 890     break;
 891   }
 892   case MCFragment::FT_LEB: {
 893     const MCLEBFragment *LF = cast<MCLEBFragment>(this);
 894     OS << "\n       ";
 895     OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
 896     break;
 897   }
 898   }
 899   OS << ">";
 900 }
 901
 902 void MCSectionData::dump() {
 903   raw_ostream &OS = llvm::errs();
 904
 905   OS << "<MCSectionData";
 906   OS << " Alignment:" << getAlignment() << " Fragments:[\n      ";
 907   for (iterator it = begin(), ie = end(); it != ie; ++it) {
 908     if (it != begin()) OS << ",\n      ";
 909     it->dump();
 910   }
 911   OS << "]>";
 912 }
 913
 914 void MCSymbolData::dump() {
 915   raw_ostream &OS = llvm::errs();
 916
 917   OS << "<MCSymbolData Symbol:" << getSymbol()
 918      << " Fragment:" << getFragment() << " Offset:" << getOffset()
 919      << " Flags:" << getFlags() << " Index:" << getIndex();
 920   if (isCommon())
 921     OS << " (common, size:" << getCommonSize()
 922        << " align: " << getCommonAlignment() << ")";
 923   if (isExternal())
 924     OS << " (external)";
 925   if (isPrivateExtern())
 926     OS << " (private extern)";
 927   OS << ">";
 928 }
 929
 930 void MCAssembler::dump() {
 931   raw_ostream &OS = llvm::errs();
 932
 933   OS << "<MCAssembler\n";
 934   OS << "  Sections:[\n    ";
 935   for (iterator it = begin(), ie = end(); it != ie; ++it) {
 936     if (it != begin()) OS << ",\n    ";
 937     it->dump();
 938   }
 939   OS << "],\n";
 940   OS << "  Symbols:[";
 941
 942   for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
 943     if (it != symbol_begin()) OS << ",\n           ";
 944     it->dump();
 945   }
 946   OS << "]>\n";
 947 }