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 MCSymbolRefExpr *A = Target.getSymA();
 233       const MCSymbol &SA = A->getSymbol();
 234       if (A->getKind() != MCSymbolRefExpr::VK_None ||
 235           SA.AliasedSymbol().isUndefined()) {
 236         IsResolved = false;
 237       } else {
 238         const MCSymbolData &DataA = getSymbolData(SA);
 239         IsResolved =
 240           getWriter().IsSymbolRefDifferenceFullyResolvedImpl(*this, DataA,
 241                                                              *DF, false, true);
 242       }
 243     }
 244   } else {
 245     IsResolved = Target.isAbsolute();
 246   }
 247
 248   Value = Target.getConstant();
 249
 250   bool IsThumb = false;
 251   if (const MCSymbolRefExpr *A = Target.getSymA()) {
 252     const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
 253     if (Sym.isDefined())
 254       Value += Layout.getSymbolOffset(&getSymbolData(Sym));
 255     if (isThumbFunc(&Sym))
 256       IsThumb = true;
 257   }
 258   if (const MCSymbolRefExpr *B = Target.getSymB()) {
 259     const MCSymbol &Sym = B->getSymbol().AliasedSymbol();
 260     if (Sym.isDefined())
 261       Value -= Layout.getSymbolOffset(&getSymbolData(Sym));
 262   }
 263
 264
 265   bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
 266                          MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
 267   assert((ShouldAlignPC ? IsPCRel : true) &&
 268     "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
 269
 270   if (IsPCRel) {
 271     uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
 272
 273     // A number of ARM fixups in Thumb mode require that the effective PC
 274     // address be determined as the 32-bit aligned version of the actual offset.
 275     if (ShouldAlignPC) Offset &= ~0x3;
 276     Value -= Offset;
 277   }
 278
 279   // ARM fixups based from a thumb function address need to have the low
 280   // bit set. The actual value is always at least 16-bit aligned, so the
 281   // low bit is normally clear and available for use as an ISA flag for
 282   // interworking.
 283   if (IsThumb)
 284     Value |= 1;
 285
 286   return IsResolved;
 287 }
 288
 289 uint64_t MCAssembler::ComputeFragmentSize(const MCAsmLayout &Layout,
 290                                           const MCFragment &F) const {
 291   switch (F.getKind()) {
 292   case MCFragment::FT_Data:
 293     return cast<MCDataFragment>(F).getContents().size();
 294   case MCFragment::FT_Fill:
 295     return cast<MCFillFragment>(F).getSize();
 296   case MCFragment::FT_Inst:
 297     return cast<MCInstFragment>(F).getInstSize();
 298
 299   case MCFragment::FT_LEB:
 300     return cast<MCLEBFragment>(F).getContents().size();
 301
 302   case MCFragment::FT_Align: {
 303     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
 304     unsigned Offset = Layout.getFragmentOffset(&AF);
 305     unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
 306     if (Size > AF.getMaxBytesToEmit())
 307       return 0;
 308     return Size;
 309   }
 310
 311   case MCFragment::FT_Org: {
 312     MCOrgFragment &OF = cast<MCOrgFragment>(F);
 313     int64_t TargetLocation;
 314     if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, Layout))
 315       report_fatal_error("expected assembly-time absolute expression");
 316
 317     // FIXME: We need a way to communicate this error.
 318     uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
 319     int64_t Size = TargetLocation - FragmentOffset;
 320     if (Size < 0 || Size >= 0x40000000)
 321       report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
 322                          "' (at offset '" + Twine(FragmentOffset) + "')");
 323     return Size;
 324   }
 325
 326   case MCFragment::FT_Dwarf:
 327     return cast<MCDwarfLineAddrFragment>(F).getContents().size();
 328   case MCFragment::FT_DwarfFrame:
 329     return cast<MCDwarfCallFrameFragment>(F).getContents().size();
 330   }
 331
 332   assert(0 && "invalid fragment kind");
 333   return 0;
 334 }
 335
 336 void MCAsmLayout::LayoutFragment(MCFragment *F) {
 337   MCFragment *Prev = F->getPrevNode();
 338
 339   // We should never try to recompute something which is up-to-date.
 340   assert(!isFragmentUpToDate(F) && "Attempt to recompute up-to-date fragment!");
 341   // We should never try to compute the fragment layout if it's predecessor
 342   // isn't up-to-date.
 343   assert((!Prev || isFragmentUpToDate(Prev)) &&
 344          "Attempt to compute fragment before it's predecessor!");
 345
 346   ++stats::FragmentLayouts;
 347
 348   // Compute fragment offset and size.
 349   uint64_t Offset = 0;
 350   if (Prev)
 351     Offset += Prev->Offset + getAssembler().ComputeFragmentSize(*this, *Prev);
 352
 353   F->Offset = Offset;
 354   LastValidFragment[F->getParent()] = F;
 355 }
 356
 357 /// WriteFragmentData - Write the \arg F data to the output file.
 358 static void WriteFragmentData(const MCAssembler &Asm, const MCAsmLayout &Layout,
 359                               const MCFragment &F) {
 360   MCObjectWriter *OW = &Asm.getWriter();
 361   uint64_t Start = OW->getStream().tell();
 362   (void) Start;
 363
 364   ++stats::EmittedFragments;
 365
 366   // FIXME: Embed in fragments instead?
 367   uint64_t FragmentSize = Asm.ComputeFragmentSize(Layout, F);
 368   switch (F.getKind()) {
 369   case MCFragment::FT_Align: {
 370     MCAlignFragment &AF = cast<MCAlignFragment>(F);
 371     uint64_t Count = FragmentSize / AF.getValueSize();
 372
 373     assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
 374
 375     // FIXME: This error shouldn't actually occur (the front end should emit
 376     // multiple .align directives to enforce the semantics it wants), but is
 377     // severe enough that we want to report it. How to handle this?
 378     if (Count * AF.getValueSize() != FragmentSize)
 379       report_fatal_error("undefined .align directive, value size '" +
 380                         Twine(AF.getValueSize()) +
 381                         "' is not a divisor of padding size '" +
 382                         Twine(FragmentSize) + "'");
 383
 384     // See if we are aligning with nops, and if so do that first to try to fill
 385     // the Count bytes.  Then if that did not fill any bytes or there are any
 386     // bytes left to fill use the the Value and ValueSize to fill the rest.
 387     // If we are aligning with nops, ask that target to emit the right data.
 388     if (AF.hasEmitNops()) {
 389       if (!Asm.getBackend().WriteNopData(Count, OW))
 390         report_fatal_error("unable to write nop sequence of " +
 391                           Twine(Count) + " bytes");
 392       break;
 393     }
 394
 395     // Otherwise, write out in multiples of the value size.
 396     for (uint64_t i = 0; i != Count; ++i) {
 397       switch (AF.getValueSize()) {
 398       default:
 399         assert(0 && "Invalid size!");
 400       case 1: OW->Write8 (uint8_t (AF.getValue())); break;
 401       case 2: OW->Write16(uint16_t(AF.getValue())); break;
 402       case 4: OW->Write32(uint32_t(AF.getValue())); break;
 403       case 8: OW->Write64(uint64_t(AF.getValue())); break;
 404       }
 405     }
 406     break;
 407   }
 408
 409   case MCFragment::FT_Data: {
 410     MCDataFragment &DF = cast<MCDataFragment>(F);
 411     assert(FragmentSize == DF.getContents().size() && "Invalid size!");
 412     OW->WriteBytes(DF.getContents().str());
 413     break;
 414   }
 415
 416   case MCFragment::FT_Fill: {
 417     MCFillFragment &FF = cast<MCFillFragment>(F);
 418
 419     assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
 420
 421     for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
 422       switch (FF.getValueSize()) {
 423       default:
 424         assert(0 && "Invalid size!");
 425       case 1: OW->Write8 (uint8_t (FF.getValue())); break;
 426       case 2: OW->Write16(uint16_t(FF.getValue())); break;
 427       case 4: OW->Write32(uint32_t(FF.getValue())); break;
 428       case 8: OW->Write64(uint64_t(FF.getValue())); break;
 429       }
 430     }
 431     break;
 432   }
 433
 434   case MCFragment::FT_Inst: {
 435     MCInstFragment &IF = cast<MCInstFragment>(F);
 436     OW->WriteBytes(StringRef(IF.getCode().begin(), IF.getCode().size()));
 437     break;
 438   }
 439
 440   case MCFragment::FT_LEB: {
 441     MCLEBFragment &LF = cast<MCLEBFragment>(F);
 442     OW->WriteBytes(LF.getContents().str());
 443     break;
 444   }
 445
 446   case MCFragment::FT_Org: {
 447     MCOrgFragment &OF = cast<MCOrgFragment>(F);
 448
 449     for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
 450       OW->Write8(uint8_t(OF.getValue()));
 451
 452     break;
 453   }
 454
 455   case MCFragment::FT_Dwarf: {
 456     const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
 457     OW->WriteBytes(OF.getContents().str());
 458     break;
 459   }
 460   case MCFragment::FT_DwarfFrame: {
 461     const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
 462     OW->WriteBytes(CF.getContents().str());
 463     break;
 464   }
 465   }
 466
 467   assert(OW->getStream().tell() - Start == FragmentSize);
 468 }
 469
 470 void MCAssembler::WriteSectionData(const MCSectionData *SD,
 471                                    const MCAsmLayout &Layout) const {
 472   // Ignore virtual sections.
 473   if (SD->getSection().isVirtualSection()) {
 474     assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
 475
 476     // Check that contents are only things legal inside a virtual section.
 477     for (MCSectionData::const_iterator it = SD->begin(),
 478            ie = SD->end(); it != ie; ++it) {
 479       switch (it->getKind()) {
 480       default:
 481         assert(0 && "Invalid fragment in virtual section!");
 482       case MCFragment::FT_Data: {
 483         // Check that we aren't trying to write a non-zero contents (or fixups)
 484         // into a virtual section. This is to support clients which use standard
 485         // directives to fill the contents of virtual sections.
 486         MCDataFragment &DF = cast<MCDataFragment>(*it);
 487         assert(DF.fixup_begin() == DF.fixup_end() &&
 488                "Cannot have fixups in virtual section!");
 489         for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
 490           assert(DF.getContents()[i] == 0 &&
 491                  "Invalid data value for virtual section!");
 492         break;
 493       }
 494       case MCFragment::FT_Align:
 495         // Check that we aren't trying to write a non-zero value into a virtual
 496         // section.
 497         assert((!cast<MCAlignFragment>(it)->getValueSize() ||
 498                 !cast<MCAlignFragment>(it)->getValue()) &&
 499                "Invalid align in virtual section!");
 500         break;
 501       case MCFragment::FT_Fill:
 502         assert(!cast<MCFillFragment>(it)->getValueSize() &&
 503                "Invalid fill in virtual section!");
 504         break;
 505       }
 506     }
 507
 508     return;
 509   }
 510
 511   uint64_t Start = getWriter().getStream().tell();
 512   (void) Start;
 513
 514   for (MCSectionData::const_iterator it = SD->begin(),
 515          ie = SD->end(); it != ie; ++it)
 516     WriteFragmentData(*this, Layout, *it);
 517
 518   assert(getWriter().getStream().tell() - Start ==
 519          Layout.getSectionAddressSize(SD));
 520 }
 521
 522
 523 uint64_t MCAssembler::HandleFixup(const MCAsmLayout &Layout,
 524                                   MCFragment &F,
 525                                   const MCFixup &Fixup) {
 526    // Evaluate the fixup.
 527    MCValue Target;
 528    uint64_t FixedValue;
 529    if (!EvaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
 530      // The fixup was unresolved, we need a relocation. Inform the object
 531      // writer of the relocation, and give it an opportunity to adjust the
 532      // fixup value if need be.
 533      getWriter().RecordRelocation(*this, Layout, &F, Fixup, Target, FixedValue);
 534    }
 535    return FixedValue;
 536  }
 537
 538 void MCAssembler::Finish() {
 539   DEBUG_WITH_TYPE("mc-dump", {
 540       llvm::errs() << "assembler backend - pre-layout\n--\n";
 541       dump(); });
 542
 543   // Create the layout object.
 544   MCAsmLayout Layout(*this);
 545
 546   // Create dummy fragments and assign section ordinals.
 547   unsigned SectionIndex = 0;
 548   for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
 549     // Create dummy fragments to eliminate any empty sections, this simplifies
 550     // layout.
 551     if (it->getFragmentList().empty())
 552       new MCDataFragment(it);
 553
 554     it->setOrdinal(SectionIndex++);
 555   }
 556
 557   // Assign layout order indices to sections and fragments.
 558   for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
 559     MCSectionData *SD = Layout.getSectionOrder()[i];
 560     SD->setLayoutOrder(i);
 561
 562     unsigned FragmentIndex = 0;
 563     for (MCSectionData::iterator it2 = SD->begin(),
 564            ie2 = SD->end(); it2 != ie2; ++it2)
 565       it2->setLayoutOrder(FragmentIndex++);
 566   }
 567
 568   // Layout until everything fits.
 569   while (LayoutOnce(Layout))
 570     continue;
 571
 572   DEBUG_WITH_TYPE("mc-dump", {
 573       llvm::errs() << "assembler backend - post-relaxation\n--\n";
 574       dump(); });
 575
 576   // Finalize the layout, including fragment lowering.
 577   FinishLayout(Layout);
 578
 579   DEBUG_WITH_TYPE("mc-dump", {
 580       llvm::errs() << "assembler backend - final-layout\n--\n";
 581       dump(); });
 582
 583   uint64_t StartOffset = OS.tell();
 584
 585   // Allow the object writer a chance to perform post-layout binding (for
 586   // example, to set the index fields in the symbol data).
 587   getWriter().ExecutePostLayoutBinding(*this, Layout);
 588
 589   // Evaluate and apply the fixups, generating relocation entries as necessary.
 590   for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
 591     for (MCSectionData::iterator it2 = it->begin(),
 592            ie2 = it->end(); it2 != ie2; ++it2) {
 593       MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
 594       if (DF) {
 595         for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
 596                ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
 597           MCFixup &Fixup = *it3;
 598           uint64_t FixedValue = HandleFixup(Layout, *DF, Fixup);
 599           getBackend().ApplyFixup(Fixup, DF->getContents().data(),
 600                                   DF->getContents().size(), FixedValue);
 601         }
 602       }
 603       MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
 604       if (IF) {
 605         for (MCInstFragment::fixup_iterator it3 = IF->fixup_begin(),
 606                ie3 = IF->fixup_end(); it3 != ie3; ++it3) {
 607           MCFixup &Fixup = *it3;
 608           uint64_t FixedValue = HandleFixup(Layout, *IF, Fixup);
 609           getBackend().ApplyFixup(Fixup, IF->getCode().data(),
 610                                   IF->getCode().size(), FixedValue);
 611         }
 612       }
 613     }
 614   }
 615
 616   // Write the object file.
 617   getWriter().WriteObject(*this, Layout);
 618
 619   stats::ObjectBytes += OS.tell() - StartOffset;
 620 }
 621
 622 bool MCAssembler::FixupNeedsRelaxation(const MCFixup &Fixup,
 623                                        const MCFragment *DF,
 624                                        const MCAsmLayout &Layout) const {
 625   if (getRelaxAll())
 626     return true;
 627
 628   // If we cannot resolve the fixup value, it requires relaxation.
 629   MCValue Target;
 630   uint64_t Value;
 631   if (!EvaluateFixup(Layout, Fixup, DF, Target, Value))
 632     return true;
 633
 634   // Otherwise, relax if the value is too big for a (signed) i8.
 635   //
 636   // FIXME: This is target dependent!
 637   return int64_t(Value) != int64_t(int8_t(Value));
 638 }
 639
 640 bool MCAssembler::FragmentNeedsRelaxation(const MCInstFragment *IF,
 641                                           const MCAsmLayout &Layout) const {
 642   // If this inst doesn't ever need relaxation, ignore it. This occurs when we
 643   // are intentionally pushing out inst fragments, or because we relaxed a
 644   // previous instruction to one that doesn't need relaxation.
 645   if (!getBackend().MayNeedRelaxation(IF->getInst()))
 646     return false;
 647
 648   for (MCInstFragment::const_fixup_iterator it = IF->fixup_begin(),
 649          ie = IF->fixup_end(); it != ie; ++it)
 650     if (FixupNeedsRelaxation(*it, IF, Layout))
 651       return true;
 652
 653   return false;
 654 }
 655
 656 bool MCAssembler::RelaxInstruction(MCAsmLayout &Layout,
 657                                    MCInstFragment &IF) {
 658   if (!FragmentNeedsRelaxation(&IF, Layout))
 659     return false;
 660
 661   ++stats::RelaxedInstructions;
 662
 663   // FIXME-PERF: We could immediately lower out instructions if we can tell
 664   // they are fully resolved, to avoid retesting on later passes.
 665
 666   // Relax the fragment.
 667
 668   MCInst Relaxed;
 669   getBackend().RelaxInstruction(IF.getInst(), Relaxed);
 670
 671   // Encode the new instruction.
 672   //
 673   // FIXME-PERF: If it matters, we could let the target do this. It can
 674   // probably do so more efficiently in many cases.
 675   SmallVector<MCFixup, 4> Fixups;
 676   SmallString<256> Code;
 677   raw_svector_ostream VecOS(Code);
 678   getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups);
 679   VecOS.flush();
 680
 681   // Update the instruction fragment.
 682   IF.setInst(Relaxed);
 683   IF.getCode() = Code;
 684   IF.getFixups().clear();
 685   // FIXME: Eliminate copy.
 686   for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
 687     IF.getFixups().push_back(Fixups[i]);
 688
 689   return true;
 690 }
 691
 692 bool MCAssembler::RelaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
 693   int64_t Value = 0;
 694   uint64_t OldSize = LF.getContents().size();
 695   LF.getValue().EvaluateAsAbsolute(Value, Layout);
 696   SmallString<8> &Data = LF.getContents();
 697   Data.clear();
 698   raw_svector_ostream OSE(Data);
 699   if (LF.isSigned())
 700     MCObjectWriter::EncodeSLEB128(Value, OSE);
 701   else
 702     MCObjectWriter::EncodeULEB128(Value, OSE);
 703   OSE.flush();
 704   return OldSize != LF.getContents().size();
 705 }
 706
 707 bool MCAssembler::RelaxDwarfLineAddr(MCAsmLayout &Layout,
 708                                      MCDwarfLineAddrFragment &DF) {
 709   int64_t AddrDelta = 0;
 710   uint64_t OldSize = DF.getContents().size();
 711   bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
 712   (void)IsAbs;
 713   assert(IsAbs);
 714   int64_t LineDelta;
 715   LineDelta = DF.getLineDelta();
 716   SmallString<8> &Data = DF.getContents();
 717   Data.clear();
 718   raw_svector_ostream OSE(Data);
 719   MCDwarfLineAddr::Encode(LineDelta, AddrDelta, OSE);
 720   OSE.flush();
 721   return OldSize != Data.size();
 722 }
 723
 724 bool MCAssembler::RelaxDwarfCallFrameFragment(MCAsmLayout &Layout,
 725                                               MCDwarfCallFrameFragment &DF) {
 726   int64_t AddrDelta = 0;
 727   uint64_t OldSize = DF.getContents().size();
 728   bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
 729   (void)IsAbs;
 730   assert(IsAbs);
 731   SmallString<8> &Data = DF.getContents();
 732   Data.clear();
 733   raw_svector_ostream OSE(Data);
 734   MCDwarfFrameEmitter::EncodeAdvanceLoc(AddrDelta, OSE);
 735   OSE.flush();
 736   return OldSize != Data.size();
 737 }
 738
 739 bool MCAssembler::LayoutSectionOnce(MCAsmLayout &Layout,
 740                                     MCSectionData &SD) {
 741   MCFragment *FirstInvalidFragment = NULL;
 742   // Scan for fragments that need relaxation.
 743   for (MCSectionData::iterator it2 = SD.begin(),
 744          ie2 = SD.end(); it2 != ie2; ++it2) {
 745     // Check if this is an fragment that needs relaxation.
 746     bool relaxedFrag = false;
 747     switch(it2->getKind()) {
 748     default:
 749           break;
 750     case MCFragment::FT_Inst:
 751       relaxedFrag = RelaxInstruction(Layout, *cast<MCInstFragment>(it2));
 752       break;
 753     case MCFragment::FT_Dwarf:
 754       relaxedFrag = RelaxDwarfLineAddr(Layout,
 755                                        *cast<MCDwarfLineAddrFragment>(it2));
 756       break;
 757     case MCFragment::FT_DwarfFrame:
 758       relaxedFrag =
 759         RelaxDwarfCallFrameFragment(Layout,
 760                                     *cast<MCDwarfCallFrameFragment>(it2));
 761       break;
 762     case MCFragment::FT_LEB:
 763       relaxedFrag = RelaxLEB(Layout, *cast<MCLEBFragment>(it2));
 764       break;
 765     }
 766     // Update the layout, and remember that we relaxed.
 767     if (relaxedFrag && !FirstInvalidFragment)
 768       FirstInvalidFragment = it2;
 769   }
 770   if (FirstInvalidFragment) {
 771     Layout.Invalidate(FirstInvalidFragment);
 772     return true;
 773   }
 774   return false;
 775 }
 776
 777 bool MCAssembler::LayoutOnce(MCAsmLayout &Layout) {
 778   ++stats::RelaxationSteps;
 779
 780   bool WasRelaxed = false;
 781   for (iterator it = begin(), ie = end(); it != ie; ++it) {
 782     MCSectionData &SD = *it;
 783     while(LayoutSectionOnce(Layout, SD))
 784       WasRelaxed = true;
 785   }
 786
 787   return WasRelaxed;
 788 }
 789
 790 void MCAssembler::FinishLayout(MCAsmLayout &Layout) {
 791   // The layout is done. Mark every fragment as valid.
 792   for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
 793     Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
 794   }
 795 }
 796
 797 // Debugging methods
 798
 799 namespace llvm {
 800
 801 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
 802   OS << "<MCFixup" << " Offset:" << AF.getOffset()
 803      << " Value:" << *AF.getValue()
 804      << " Kind:" << AF.getKind() << ">";
 805   return OS;
 806 }
 807
 808 }
 809
 810 void MCFragment::dump() {
 811   raw_ostream &OS = llvm::errs();
 812
 813   OS << "<";
 814   switch (getKind()) {
 815   case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
 816   case MCFragment::FT_Data:  OS << "MCDataFragment"; break;
 817   case MCFragment::FT_Fill:  OS << "MCFillFragment"; break;
 818   case MCFragment::FT_Inst:  OS << "MCInstFragment"; break;
 819   case MCFragment::FT_Org:   OS << "MCOrgFragment"; break;
 820   case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
 821   case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
 822   case MCFragment::FT_LEB:   OS << "MCLEBFragment"; break;
 823   }
 824
 825   OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
 826      << " Offset:" << Offset << ">";
 827
 828   switch (getKind()) {
 829   case MCFragment::FT_Align: {
 830     const MCAlignFragment *AF = cast<MCAlignFragment>(this);
 831     if (AF->hasEmitNops())
 832       OS << " (emit nops)";
 833     OS << "\n       ";
 834     OS << " Alignment:" << AF->getAlignment()
 835        << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
 836        << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
 837     break;
 838   }
 839   case MCFragment::FT_Data:  {
 840     const MCDataFragment *DF = cast<MCDataFragment>(this);
 841     OS << "\n       ";
 842     OS << " Contents:[";
 843     const SmallVectorImpl<char> &Contents = DF->getContents();
 844     for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
 845       if (i) OS << ",";
 846       OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
 847     }
 848     OS << "] (" << Contents.size() << " bytes)";
 849
 850     if (!DF->getFixups().empty()) {
 851       OS << ",\n       ";
 852       OS << " Fixups:[";
 853       for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
 854              ie = DF->fixup_end(); it != ie; ++it) {
 855         if (it != DF->fixup_begin()) OS << ",\n                ";
 856         OS << *it;
 857       }
 858       OS << "]";
 859     }
 860     break;
 861   }
 862   case MCFragment::FT_Fill:  {
 863     const MCFillFragment *FF = cast<MCFillFragment>(this);
 864     OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
 865        << " Size:" << FF->getSize();
 866     break;
 867   }
 868   case MCFragment::FT_Inst:  {
 869     const MCInstFragment *IF = cast<MCInstFragment>(this);
 870     OS << "\n       ";
 871     OS << " Inst:";
 872     IF->getInst().dump_pretty(OS);
 873     break;
 874   }
 875   case MCFragment::FT_Org:  {
 876     const MCOrgFragment *OF = cast<MCOrgFragment>(this);
 877     OS << "\n       ";
 878     OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
 879     break;
 880   }
 881   case MCFragment::FT_Dwarf:  {
 882     const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
 883     OS << "\n       ";
 884     OS << " AddrDelta:" << OF->getAddrDelta()
 885        << " LineDelta:" << OF->getLineDelta();
 886     break;
 887   }
 888   case MCFragment::FT_DwarfFrame:  {
 889     const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
 890     OS << "\n       ";
 891     OS << " AddrDelta:" << CF->getAddrDelta();
 892     break;
 893   }
 894   case MCFragment::FT_LEB: {
 895     const MCLEBFragment *LF = cast<MCLEBFragment>(this);
 896     OS << "\n       ";
 897     OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
 898     break;
 899   }
 900   }
 901   OS << ">";
 902 }
 903
 904 void MCSectionData::dump() {
 905   raw_ostream &OS = llvm::errs();
 906
 907   OS << "<MCSectionData";
 908   OS << " Alignment:" << getAlignment() << " Fragments:[\n      ";
 909   for (iterator it = begin(), ie = end(); it != ie; ++it) {
 910     if (it != begin()) OS << ",\n      ";
 911     it->dump();
 912   }
 913   OS << "]>";
 914 }
 915
 916 void MCSymbolData::dump() {
 917   raw_ostream &OS = llvm::errs();
 918
 919   OS << "<MCSymbolData Symbol:" << getSymbol()
 920      << " Fragment:" << getFragment() << " Offset:" << getOffset()
 921      << " Flags:" << getFlags() << " Index:" << getIndex();
 922   if (isCommon())
 923     OS << " (common, size:" << getCommonSize()
 924        << " align: " << getCommonAlignment() << ")";
 925   if (isExternal())
 926     OS << " (external)";
 927   if (isPrivateExtern())
 928     OS << " (private extern)";
 929   OS << ">";
 930 }
 931
 932 void MCAssembler::dump() {
 933   raw_ostream &OS = llvm::errs();
 934
 935   OS << "<MCAssembler\n";
 936   OS << "  Sections:[\n    ";
 937   for (iterator it = begin(), ie = end(); it != ie; ++it) {
 938     if (it != begin()) OS << ",\n    ";
 939     it->dump();
 940   }
 941   OS << "],\n";
 942   OS << "  Symbols:[";
 943
 944   for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
 945     if (it != symbol_begin()) OS << ",\n           ";
 946     it->dump();
 947   }
 948   OS << "]>\n";
 949 }