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 using namespace llvm;
  32
  33 namespace {
  34 namespace stats {
  35 STATISTIC(EmittedFragments, "Number of emitted assembler fragments");
  36 STATISTIC(EvaluateFixup, "Number of evaluated fixups");
  37 STATISTIC(FragmentLayouts, "Number of fragment layouts");
  38 STATISTIC(ObjectBytes, "Number of emitted object file bytes");
  39 STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
  40 STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
  41 }
  42 }
  43
  44 // FIXME FIXME FIXME: There are number of places in this file where we convert
  45 // what is a 64-bit assembler value used for computation into a value in the
  46 // object file, which may truncate it. We should detect that truncation where
  47 // invalid and report errors back.
  48
  49 /* *** */
  50
  51 MCAsmLayout::MCAsmLayout(MCAssembler &Asm)
  52   : Assembler(Asm), LastValidFragment()
  53  {
  54   // Compute the section layout order. Virtual sections must go last.
  55   for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
  56     if (!it->getSection().isVirtualSection())
  57       SectionOrder.push_back(&*it);
  58   for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
  59     if (it->getSection().isVirtualSection())
  60       SectionOrder.push_back(&*it);
  61 }
  62
  63 bool MCAsmLayout::isFragmentUpToDate(const MCFragment *F) const {
  64   const MCSectionData &SD = *F->getParent();
  65   const MCFragment *LastValid = LastValidFragment.lookup(&SD);
  66   if (!LastValid)
  67     return false;
  68   assert(LastValid->getParent() == F->getParent());
  69   return F->getLayoutOrder() <= LastValid->getLayoutOrder();
  70 }
  71
  72 void MCAsmLayout::Invalidate(MCFragment *F) {
  73   // If this fragment wasn't already up-to-date, we don't need to do anything.
  74   if (!isFragmentUpToDate(F))
  75     return;
  76
  77   // Otherwise, reset the last valid fragment to this fragment.
  78   const MCSectionData &SD = *F->getParent();
  79   LastValidFragment[&SD] = F;
  80 }
  81
  82 void MCAsmLayout::EnsureValid(const MCFragment *F) const {
  83   MCSectionData &SD = *F->getParent();
  84
  85   MCFragment *Cur = LastValidFragment[&SD];
  86   if (!Cur)
  87     Cur = &*SD.begin();
  88   else
  89     Cur = Cur->getNextNode();
  90
  91   // Advance the layout position until the fragment is up-to-date.
  92   while (!isFragmentUpToDate(F)) {
  93     const_cast<MCAsmLayout*>(this)->LayoutFragment(Cur);
  94     Cur = Cur->getNextNode();
  95   }
  96 }
  97
  98 uint64_t MCAsmLayout::getFragmentOffset(const MCFragment *F) const {
  99   EnsureValid(F);
 100   assert(F->Offset != ~UINT64_C(0) && "Address not set!");
 101   return F->Offset;
 102 }
 103
 104 uint64_t MCAsmLayout::getSymbolOffset(const MCSymbolData *SD) const {
 105   const MCSymbol &S = SD->getSymbol();
 106
 107   // If this is a variable, then recursively evaluate now.
 108   if (S.isVariable()) {
 109     MCValue Target;
 110     if (!S.getVariableValue()->EvaluateAsRelocatable(Target, *this))
 111       report_fatal_error("unable to evaluate offset for variable '" +
 112                          S.getName() + "'");
 113
 114     // Verify that any used symbols are defined.
 115     if (Target.getSymA() && Target.getSymA()->getSymbol().isUndefined())
 116       report_fatal_error("unable to evaluate offset to undefined symbol '" +
 117                          Target.getSymA()->getSymbol().getName() + "'");
 118     if (Target.getSymB() && Target.getSymB()->getSymbol().isUndefined())
 119       report_fatal_error("unable to evaluate offset to undefined symbol '" +
 120                          Target.getSymB()->getSymbol().getName() + "'");
 121
 122     uint64_t Offset = Target.getConstant();
 123     if (Target.getSymA())
 124       Offset += getSymbolOffset(&Assembler.getSymbolData(
 125                                   Target.getSymA()->getSymbol()));
 126     if (Target.getSymB())
 127       Offset -= getSymbolOffset(&Assembler.getSymbolData(
 128                                   Target.getSymB()->getSymbol()));
 129     return Offset;
 130   }
 131
 132   assert(SD->getFragment() && "Invalid getOffset() on undefined symbol!");
 133   return getFragmentOffset(SD->getFragment()) + SD->getOffset();
 134 }
 135
 136 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
 137   // The size is the last fragment's end offset.
 138   const MCFragment &F = SD->getFragmentList().back();
 139   return getFragmentOffset(&F) + getAssembler().ComputeFragmentSize(*this, F);
 140 }
 141
 142 uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
 143   // Virtual sections have no file size.
 144   if (SD->getSection().isVirtualSection())
 145     return 0;
 146
 147   // Otherwise, the file size is the same as the address space size.
 148   return getSectionAddressSize(SD);
 149 }
 150
 151 /* *** */
 152
 153 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
 154 }
 155
 156 MCFragment::~MCFragment() {
 157 }
 158
 159 MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
 160   : Kind(_Kind), Parent(_Parent), Atom(0), Offset(~UINT64_C(0))
 161 {
 162   if (Parent)
 163     Parent->getFragmentList().push_back(this);
 164 }
 165
 166 /* *** */
 167
 168 MCSectionData::MCSectionData() : Section(0) {}
 169
 170 MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
 171   : Section(&_Section),
 172     Ordinal(~UINT32_C(0)),
 173     Alignment(1),
 174     HasInstructions(false)
 175 {
 176   if (A)
 177     A->getSectionList().push_back(this);
 178 }
 179
 180 /* *** */
 181
 182 MCSymbolData::MCSymbolData() : Symbol(0) {}
 183
 184 MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
 185                            uint64_t _Offset, MCAssembler *A)
 186   : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
 187     IsExternal(false), IsPrivateExtern(false),
 188     CommonSize(0), SymbolSize(0), CommonAlign(0),
 189     Flags(0), Index(0)
 190 {
 191   if (A)
 192     A->getSymbolList().push_back(this);
 193 }
 194
 195 /* *** */
 196
 197 MCAssembler::MCAssembler(MCContext &Context_, TargetAsmBackend &Backend_,
 198                          MCCodeEmitter &Emitter_, MCObjectWriter &Writer_,
 199                          raw_ostream &OS_)
 200   : Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(Writer_),
 201     OS(OS_), RelaxAll(false), NoExecStack(false), SubsectionsViaSymbols(false)
 202 {
 203 }
 204
 205 MCAssembler::~MCAssembler() {
 206 }
 207
 208 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
 209   // Non-temporary labels should always be visible to the linker.
 210   if (!Symbol.isTemporary())
 211     return true;
 212
 213   // Absolute temporary labels are never visible.
 214   if (!Symbol.isInSection())
 215     return false;
 216
 217   // Otherwise, check if the section requires symbols even for temporary labels.
 218   return getBackend().doesSectionRequireSymbols(Symbol.getSection());
 219 }
 220
 221 const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
 222   // Linker visible symbols define atoms.
 223   if (isSymbolLinkerVisible(SD->getSymbol()))
 224     return SD;
 225
 226   // Absolute and undefined symbols have no defining atom.
 227   if (!SD->getFragment())
 228     return 0;
 229
 230   // Non-linker visible symbols in sections which can't be atomized have no
 231   // defining atom.
 232   if (!getBackend().isSectionAtomizable(
 233         SD->getFragment()->getParent()->getSection()))
 234     return 0;
 235
 236   // Otherwise, return the atom for the containing fragment.
 237   return SD->getFragment()->getAtom();
 238 }
 239
 240 bool MCAssembler::EvaluateFixup(const MCAsmLayout &Layout,
 241                                 const MCFixup &Fixup, const MCFragment *DF,
 242                                 MCValue &Target, uint64_t &Value) const {
 243   ++stats::EvaluateFixup;
 244
 245   if (!Fixup.getValue()->EvaluateAsRelocatable(Target, Layout))
 246     report_fatal_error("expected relocatable expression");
 247
 248   bool IsPCRel = Backend.getFixupKindInfo(
 249     Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
 250
 251   bool IsResolved;
 252   if (IsPCRel) {
 253     if (Target.getSymB()) {
 254       IsResolved = false;
 255     } else if (!Target.getSymA()) {
 256       IsResolved = false;
 257     } else {
 258       const MCSymbolRefExpr *A = Target.getSymA();
 259       const MCSymbol &SA = A->getSymbol();
 260       if (A->getKind() != MCSymbolRefExpr::VK_None ||
 261           SA.AliasedSymbol().isUndefined()) {
 262         IsResolved = false;
 263       } else {
 264         const MCSymbolData &DataA = getSymbolData(SA);
 265         IsResolved =
 266           getWriter().IsSymbolRefDifferenceFullyResolvedImpl(*this, DataA,
 267                                                              *DF, false, true);
 268       }
 269     }
 270   } else {
 271     IsResolved = Target.isAbsolute();
 272   }
 273
 274   Value = Target.getConstant();
 275
 276   bool IsThumb = false;
 277   if (const MCSymbolRefExpr *A = Target.getSymA()) {
 278     const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
 279     if (Sym.isDefined())
 280       Value += Layout.getSymbolOffset(&getSymbolData(Sym));
 281     if (isThumbFunc(&Sym))
 282       IsThumb = true;
 283   }
 284   if (const MCSymbolRefExpr *B = Target.getSymB()) {
 285     const MCSymbol &Sym = B->getSymbol().AliasedSymbol();
 286     if (Sym.isDefined())
 287       Value -= Layout.getSymbolOffset(&getSymbolData(Sym));
 288   }
 289
 290
 291   bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
 292                          MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
 293   assert((ShouldAlignPC ? IsPCRel : true) &&
 294     "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
 295
 296   if (IsPCRel) {
 297     uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
 298
 299     // A number of ARM fixups in Thumb mode require that the effective PC
 300     // address be determined as the 32-bit aligned version of the actual offset.
 301     if (ShouldAlignPC) Offset &= ~0x3;
 302     Value -= Offset;
 303   }
 304
 305   // ARM fixups based from a thumb function address need to have the low
 306   // bit set. The actual value is always at least 16-bit aligned, so the
 307   // low bit is normally clear and available for use as an ISA flag for
 308   // interworking.
 309   if (IsThumb)
 310     Value |= 1;
 311
 312   return IsResolved;
 313 }
 314
 315 uint64_t MCAssembler::ComputeFragmentSize(const MCAsmLayout &Layout,
 316                                           const MCFragment &F) const {
 317   switch (F.getKind()) {
 318   case MCFragment::FT_Data:
 319     return cast<MCDataFragment>(F).getContents().size();
 320   case MCFragment::FT_Fill:
 321     return cast<MCFillFragment>(F).getSize();
 322   case MCFragment::FT_Inst:
 323     return cast<MCInstFragment>(F).getInstSize();
 324
 325   case MCFragment::FT_LEB:
 326     return cast<MCLEBFragment>(F).getContents().size();
 327
 328   case MCFragment::FT_Align: {
 329     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
 330     unsigned Offset = Layout.getFragmentOffset(&AF);
 331     unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
 332     if (Size > AF.getMaxBytesToEmit())
 333       return 0;
 334     return Size;
 335   }
 336
 337   case MCFragment::FT_Org: {
 338     MCOrgFragment &OF = cast<MCOrgFragment>(F);
 339     int64_t TargetLocation;
 340     if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, Layout))
 341       report_fatal_error("expected assembly-time absolute expression");
 342
 343     // FIXME: We need a way to communicate this error.
 344     uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
 345     int64_t Size = TargetLocation - FragmentOffset;
 346     if (Size < 0 || Size >= 0x40000000)
 347       report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
 348                          "' (at offset '" + Twine(FragmentOffset) + "')");
 349     return Size;
 350   }
 351
 352   case MCFragment::FT_Dwarf:
 353     return cast<MCDwarfLineAddrFragment>(F).getContents().size();
 354   case MCFragment::FT_DwarfFrame:
 355     return cast<MCDwarfCallFrameFragment>(F).getContents().size();
 356   }
 357
 358   assert(0 && "invalid fragment kind");
 359   return 0;
 360 }
 361
 362 void MCAsmLayout::LayoutFragment(MCFragment *F) {
 363   MCFragment *Prev = F->getPrevNode();
 364
 365   // We should never try to recompute something which is up-to-date.
 366   assert(!isFragmentUpToDate(F) && "Attempt to recompute up-to-date fragment!");
 367   // We should never try to compute the fragment layout if it's predecessor
 368   // isn't up-to-date.
 369   assert((!Prev || isFragmentUpToDate(Prev)) &&
 370          "Attempt to compute fragment before it's predecessor!");
 371
 372   ++stats::FragmentLayouts;
 373
 374   // Compute fragment offset and size.
 375   uint64_t Offset = 0;
 376   if (Prev)
 377     Offset += Prev->Offset + getAssembler().ComputeFragmentSize(*this, *Prev);
 378
 379   F->Offset = Offset;
 380   LastValidFragment[F->getParent()] = F;
 381 }
 382
 383 /// WriteFragmentData - Write the \arg F data to the output file.
 384 static void WriteFragmentData(const MCAssembler &Asm, const MCAsmLayout &Layout,
 385                               const MCFragment &F) {
 386   MCObjectWriter *OW = &Asm.getWriter();
 387   uint64_t Start = OW->getStream().tell();
 388   (void) Start;
 389
 390   ++stats::EmittedFragments;
 391
 392   // FIXME: Embed in fragments instead?
 393   uint64_t FragmentSize = Asm.ComputeFragmentSize(Layout, F);
 394   switch (F.getKind()) {
 395   case MCFragment::FT_Align: {
 396     MCAlignFragment &AF = cast<MCAlignFragment>(F);
 397     uint64_t Count = FragmentSize / AF.getValueSize();
 398
 399     assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
 400
 401     // FIXME: This error shouldn't actually occur (the front end should emit
 402     // multiple .align directives to enforce the semantics it wants), but is
 403     // severe enough that we want to report it. How to handle this?
 404     if (Count * AF.getValueSize() != FragmentSize)
 405       report_fatal_error("undefined .align directive, value size '" +
 406                         Twine(AF.getValueSize()) +
 407                         "' is not a divisor of padding size '" +
 408                         Twine(FragmentSize) + "'");
 409
 410     // See if we are aligning with nops, and if so do that first to try to fill
 411     // the Count bytes.  Then if that did not fill any bytes or there are any
 412     // bytes left to fill use the the Value and ValueSize to fill the rest.
 413     // If we are aligning with nops, ask that target to emit the right data.
 414     if (AF.hasEmitNops()) {
 415       if (!Asm.getBackend().WriteNopData(Count, OW))
 416         report_fatal_error("unable to write nop sequence of " +
 417                           Twine(Count) + " bytes");
 418       break;
 419     }
 420
 421     // Otherwise, write out in multiples of the value size.
 422     for (uint64_t i = 0; i != Count; ++i) {
 423       switch (AF.getValueSize()) {
 424       default:
 425         assert(0 && "Invalid size!");
 426       case 1: OW->Write8 (uint8_t (AF.getValue())); break;
 427       case 2: OW->Write16(uint16_t(AF.getValue())); break;
 428       case 4: OW->Write32(uint32_t(AF.getValue())); break;
 429       case 8: OW->Write64(uint64_t(AF.getValue())); break;
 430       }
 431     }
 432     break;
 433   }
 434
 435   case MCFragment::FT_Data: {
 436     MCDataFragment &DF = cast<MCDataFragment>(F);
 437     assert(FragmentSize == DF.getContents().size() && "Invalid size!");
 438     OW->WriteBytes(DF.getContents().str());
 439     break;
 440   }
 441
 442   case MCFragment::FT_Fill: {
 443     MCFillFragment &FF = cast<MCFillFragment>(F);
 444
 445     assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
 446
 447     for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
 448       switch (FF.getValueSize()) {
 449       default:
 450         assert(0 && "Invalid size!");
 451       case 1: OW->Write8 (uint8_t (FF.getValue())); break;
 452       case 2: OW->Write16(uint16_t(FF.getValue())); break;
 453       case 4: OW->Write32(uint32_t(FF.getValue())); break;
 454       case 8: OW->Write64(uint64_t(FF.getValue())); break;
 455       }
 456     }
 457     break;
 458   }
 459
 460   case MCFragment::FT_Inst: {
 461     MCInstFragment &IF = cast<MCInstFragment>(F);
 462     OW->WriteBytes(StringRef(IF.getCode().begin(), IF.getCode().size()));
 463     break;
 464   }
 465
 466   case MCFragment::FT_LEB: {
 467     MCLEBFragment &LF = cast<MCLEBFragment>(F);
 468     OW->WriteBytes(LF.getContents().str());
 469     break;
 470   }
 471
 472   case MCFragment::FT_Org: {
 473     MCOrgFragment &OF = cast<MCOrgFragment>(F);
 474
 475     for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
 476       OW->Write8(uint8_t(OF.getValue()));
 477
 478     break;
 479   }
 480
 481   case MCFragment::FT_Dwarf: {
 482     const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
 483     OW->WriteBytes(OF.getContents().str());
 484     break;
 485   }
 486   case MCFragment::FT_DwarfFrame: {
 487     const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
 488     OW->WriteBytes(CF.getContents().str());
 489     break;
 490   }
 491   }
 492
 493   assert(OW->getStream().tell() - Start == FragmentSize);
 494 }
 495
 496 void MCAssembler::WriteSectionData(const MCSectionData *SD,
 497                                    const MCAsmLayout &Layout) const {
 498   // Ignore virtual sections.
 499   if (SD->getSection().isVirtualSection()) {
 500     assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
 501
 502     // Check that contents are only things legal inside a virtual section.
 503     for (MCSectionData::const_iterator it = SD->begin(),
 504            ie = SD->end(); it != ie; ++it) {
 505       switch (it->getKind()) {
 506       default:
 507         assert(0 && "Invalid fragment in virtual section!");
 508       case MCFragment::FT_Data: {
 509         // Check that we aren't trying to write a non-zero contents (or fixups)
 510         // into a virtual section. This is to support clients which use standard
 511         // directives to fill the contents of virtual sections.
 512         MCDataFragment &DF = cast<MCDataFragment>(*it);
 513         assert(DF.fixup_begin() == DF.fixup_end() &&
 514                "Cannot have fixups in virtual section!");
 515         for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
 516           assert(DF.getContents()[i] == 0 &&
 517                  "Invalid data value for virtual section!");
 518         break;
 519       }
 520       case MCFragment::FT_Align:
 521         // Check that we aren't trying to write a non-zero value into a virtual
 522         // section.
 523         assert((!cast<MCAlignFragment>(it)->getValueSize() ||
 524                 !cast<MCAlignFragment>(it)->getValue()) &&
 525                "Invalid align in virtual section!");
 526         break;
 527       case MCFragment::FT_Fill:
 528         assert(!cast<MCFillFragment>(it)->getValueSize() &&
 529                "Invalid fill in virtual section!");
 530         break;
 531       }
 532     }
 533
 534     return;
 535   }
 536
 537   uint64_t Start = getWriter().getStream().tell();
 538   (void) Start;
 539
 540   for (MCSectionData::const_iterator it = SD->begin(),
 541          ie = SD->end(); it != ie; ++it)
 542     WriteFragmentData(*this, Layout, *it);
 543
 544   assert(getWriter().getStream().tell() - Start ==
 545          Layout.getSectionAddressSize(SD));
 546 }
 547
 548
 549 uint64_t MCAssembler::HandleFixup(const MCAsmLayout &Layout,
 550                                   MCFragment &F,
 551                                   const MCFixup &Fixup) {
 552    // Evaluate the fixup.
 553    MCValue Target;
 554    uint64_t FixedValue;
 555    if (!EvaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
 556      // The fixup was unresolved, we need a relocation. Inform the object
 557      // writer of the relocation, and give it an opportunity to adjust the
 558      // fixup value if need be.
 559      getWriter().RecordRelocation(*this, Layout, &F, Fixup, Target, FixedValue);
 560    }
 561    return FixedValue;
 562  }
 563
 564 void MCAssembler::Finish() {
 565   DEBUG_WITH_TYPE("mc-dump", {
 566       llvm::errs() << "assembler backend - pre-layout\n--\n";
 567       dump(); });
 568
 569   // Create the layout object.
 570   MCAsmLayout Layout(*this);
 571
 572   // Create dummy fragments and assign section ordinals.
 573   unsigned SectionIndex = 0;
 574   for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
 575     // Create dummy fragments to eliminate any empty sections, this simplifies
 576     // layout.
 577     if (it->getFragmentList().empty())
 578       new MCDataFragment(it);
 579
 580     it->setOrdinal(SectionIndex++);
 581   }
 582
 583   // Assign layout order indices to sections and fragments.
 584   for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
 585     MCSectionData *SD = Layout.getSectionOrder()[i];
 586     SD->setLayoutOrder(i);
 587
 588     unsigned FragmentIndex = 0;
 589     for (MCSectionData::iterator it2 = SD->begin(),
 590            ie2 = SD->end(); it2 != ie2; ++it2)
 591       it2->setLayoutOrder(FragmentIndex++);
 592   }
 593
 594   // Layout until everything fits.
 595   while (LayoutOnce(Layout))
 596     continue;
 597
 598   DEBUG_WITH_TYPE("mc-dump", {
 599       llvm::errs() << "assembler backend - post-relaxation\n--\n";
 600       dump(); });
 601
 602   // Finalize the layout, including fragment lowering.
 603   FinishLayout(Layout);
 604
 605   DEBUG_WITH_TYPE("mc-dump", {
 606       llvm::errs() << "assembler backend - final-layout\n--\n";
 607       dump(); });
 608
 609   uint64_t StartOffset = OS.tell();
 610
 611   // Allow the object writer a chance to perform post-layout binding (for
 612   // example, to set the index fields in the symbol data).
 613   getWriter().ExecutePostLayoutBinding(*this, Layout);
 614
 615   // Evaluate and apply the fixups, generating relocation entries as necessary.
 616   for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
 617     for (MCSectionData::iterator it2 = it->begin(),
 618            ie2 = it->end(); it2 != ie2; ++it2) {
 619       MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
 620       if (DF) {
 621         for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
 622                ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
 623           MCFixup &Fixup = *it3;
 624           uint64_t FixedValue = HandleFixup(Layout, *DF, Fixup);
 625           getBackend().ApplyFixup(Fixup, DF->getContents().data(),
 626                                   DF->getContents().size(), FixedValue);
 627         }
 628       }
 629       MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
 630       if (IF) {
 631         for (MCInstFragment::fixup_iterator it3 = IF->fixup_begin(),
 632                ie3 = IF->fixup_end(); it3 != ie3; ++it3) {
 633           MCFixup &Fixup = *it3;
 634           uint64_t FixedValue = HandleFixup(Layout, *IF, Fixup);
 635           getBackend().ApplyFixup(Fixup, IF->getCode().data(),
 636                                   IF->getCode().size(), FixedValue);
 637         }
 638       }
 639     }
 640   }
 641
 642   // Write the object file.
 643   getWriter().WriteObject(*this, Layout);
 644
 645   stats::ObjectBytes += OS.tell() - StartOffset;
 646 }
 647
 648 bool MCAssembler::FixupNeedsRelaxation(const MCFixup &Fixup,
 649                                        const MCFragment *DF,
 650                                        const MCAsmLayout &Layout) const {
 651   if (getRelaxAll())
 652     return true;
 653
 654   // If we cannot resolve the fixup value, it requires relaxation.
 655   MCValue Target;
 656   uint64_t Value;
 657   if (!EvaluateFixup(Layout, Fixup, DF, Target, Value))
 658     return true;
 659
 660   // Otherwise, relax if the value is too big for a (signed) i8.
 661   //
 662   // FIXME: This is target dependent!
 663   return int64_t(Value) != int64_t(int8_t(Value));
 664 }
 665
 666 bool MCAssembler::FragmentNeedsRelaxation(const MCInstFragment *IF,
 667                                           const MCAsmLayout &Layout) const {
 668   // If this inst doesn't ever need relaxation, ignore it. This occurs when we
 669   // are intentionally pushing out inst fragments, or because we relaxed a
 670   // previous instruction to one that doesn't need relaxation.
 671   if (!getBackend().MayNeedRelaxation(IF->getInst()))
 672     return false;
 673
 674   for (MCInstFragment::const_fixup_iterator it = IF->fixup_begin(),
 675          ie = IF->fixup_end(); it != ie; ++it)
 676     if (FixupNeedsRelaxation(*it, IF, Layout))
 677       return true;
 678
 679   return false;
 680 }
 681
 682 bool MCAssembler::RelaxInstruction(MCAsmLayout &Layout,
 683                                    MCInstFragment &IF) {
 684   if (!FragmentNeedsRelaxation(&IF, Layout))
 685     return false;
 686
 687   ++stats::RelaxedInstructions;
 688
 689   // FIXME-PERF: We could immediately lower out instructions if we can tell
 690   // they are fully resolved, to avoid retesting on later passes.
 691
 692   // Relax the fragment.
 693
 694   MCInst Relaxed;
 695   getBackend().RelaxInstruction(IF.getInst(), Relaxed);
 696
 697   // Encode the new instruction.
 698   //
 699   // FIXME-PERF: If it matters, we could let the target do this. It can
 700   // probably do so more efficiently in many cases.
 701   SmallVector<MCFixup, 4> Fixups;
 702   SmallString<256> Code;
 703   raw_svector_ostream VecOS(Code);
 704   getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups);
 705   VecOS.flush();
 706
 707   // Update the instruction fragment.
 708   IF.setInst(Relaxed);
 709   IF.getCode() = Code;
 710   IF.getFixups().clear();
 711   // FIXME: Eliminate copy.
 712   for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
 713     IF.getFixups().push_back(Fixups[i]);
 714
 715   return true;
 716 }
 717
 718 bool MCAssembler::RelaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
 719   int64_t Value = 0;
 720   uint64_t OldSize = LF.getContents().size();
 721   bool IsAbs = LF.getValue().EvaluateAsAbsolute(Value, Layout);
 722   (void)IsAbs;
 723   assert(IsAbs);
 724   SmallString<8> &Data = LF.getContents();
 725   Data.clear();
 726   raw_svector_ostream OSE(Data);
 727   if (LF.isSigned())
 728     MCObjectWriter::EncodeSLEB128(Value, OSE);
 729   else
 730     MCObjectWriter::EncodeULEB128(Value, OSE);
 731   OSE.flush();
 732   return OldSize != LF.getContents().size();
 733 }
 734
 735 bool MCAssembler::RelaxDwarfLineAddr(MCAsmLayout &Layout,
 736                                      MCDwarfLineAddrFragment &DF) {
 737   int64_t AddrDelta = 0;
 738   uint64_t OldSize = DF.getContents().size();
 739   bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
 740   (void)IsAbs;
 741   assert(IsAbs);
 742   int64_t LineDelta;
 743   LineDelta = DF.getLineDelta();
 744   SmallString<8> &Data = DF.getContents();
 745   Data.clear();
 746   raw_svector_ostream OSE(Data);
 747   MCDwarfLineAddr::Encode(LineDelta, AddrDelta, OSE);
 748   OSE.flush();
 749   return OldSize != Data.size();
 750 }
 751
 752 bool MCAssembler::RelaxDwarfCallFrameFragment(MCAsmLayout &Layout,
 753                                               MCDwarfCallFrameFragment &DF) {
 754   int64_t AddrDelta = 0;
 755   uint64_t OldSize = DF.getContents().size();
 756   bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
 757   (void)IsAbs;
 758   assert(IsAbs);
 759   SmallString<8> &Data = DF.getContents();
 760   Data.clear();
 761   raw_svector_ostream OSE(Data);
 762   MCDwarfFrameEmitter::EncodeAdvanceLoc(AddrDelta, OSE);
 763   OSE.flush();
 764   return OldSize != Data.size();
 765 }
 766
 767 bool MCAssembler::LayoutSectionOnce(MCAsmLayout &Layout,
 768                                     MCSectionData &SD) {
 769   MCFragment *FirstInvalidFragment = NULL;
 770   // Scan for fragments that need relaxation.
 771   for (MCSectionData::iterator it2 = SD.begin(),
 772          ie2 = SD.end(); it2 != ie2; ++it2) {
 773     // Check if this is an fragment that needs relaxation.
 774     bool relaxedFrag = false;
 775     switch(it2->getKind()) {
 776     default:
 777           break;
 778     case MCFragment::FT_Inst:
 779       relaxedFrag = RelaxInstruction(Layout, *cast<MCInstFragment>(it2));
 780       break;
 781     case MCFragment::FT_Dwarf:
 782       relaxedFrag = RelaxDwarfLineAddr(Layout,
 783                                        *cast<MCDwarfLineAddrFragment>(it2));
 784       break;
 785     case MCFragment::FT_DwarfFrame:
 786       relaxedFrag =
 787         RelaxDwarfCallFrameFragment(Layout,
 788                                     *cast<MCDwarfCallFrameFragment>(it2));
 789       break;
 790     case MCFragment::FT_LEB:
 791       relaxedFrag = RelaxLEB(Layout, *cast<MCLEBFragment>(it2));
 792       break;
 793     }
 794     // Update the layout, and remember that we relaxed.
 795     if (relaxedFrag && !FirstInvalidFragment)
 796       FirstInvalidFragment = it2;
 797   }
 798   if (FirstInvalidFragment) {
 799     Layout.Invalidate(FirstInvalidFragment);
 800     return true;
 801   }
 802   return false;
 803 }
 804
 805 bool MCAssembler::LayoutOnce(MCAsmLayout &Layout) {
 806   ++stats::RelaxationSteps;
 807
 808   bool WasRelaxed = false;
 809   for (iterator it = begin(), ie = end(); it != ie; ++it) {
 810     MCSectionData &SD = *it;
 811     while(LayoutSectionOnce(Layout, SD))
 812       WasRelaxed = true;
 813   }
 814
 815   return WasRelaxed;
 816 }
 817
 818 void MCAssembler::FinishLayout(MCAsmLayout &Layout) {
 819   // The layout is done. Mark every fragment as valid.
 820   for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
 821     Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
 822   }
 823 }
 824
 825 // Debugging methods
 826
 827 namespace llvm {
 828
 829 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
 830   OS << "<MCFixup" << " Offset:" << AF.getOffset()
 831      << " Value:" << *AF.getValue()
 832      << " Kind:" << AF.getKind() << ">";
 833   return OS;
 834 }
 835
 836 }
 837
 838 void MCFragment::dump() {
 839   raw_ostream &OS = llvm::errs();
 840
 841   OS << "<";
 842   switch (getKind()) {
 843   case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
 844   case MCFragment::FT_Data:  OS << "MCDataFragment"; break;
 845   case MCFragment::FT_Fill:  OS << "MCFillFragment"; break;
 846   case MCFragment::FT_Inst:  OS << "MCInstFragment"; break;
 847   case MCFragment::FT_Org:   OS << "MCOrgFragment"; break;
 848   case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
 849   case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
 850   case MCFragment::FT_LEB:   OS << "MCLEBFragment"; break;
 851   }
 852
 853   OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
 854      << " Offset:" << Offset << ">";
 855
 856   switch (getKind()) {
 857   case MCFragment::FT_Align: {
 858     const MCAlignFragment *AF = cast<MCAlignFragment>(this);
 859     if (AF->hasEmitNops())
 860       OS << " (emit nops)";
 861     OS << "\n       ";
 862     OS << " Alignment:" << AF->getAlignment()
 863        << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
 864        << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
 865     break;
 866   }
 867   case MCFragment::FT_Data:  {
 868     const MCDataFragment *DF = cast<MCDataFragment>(this);
 869     OS << "\n       ";
 870     OS << " Contents:[";
 871     const SmallVectorImpl<char> &Contents = DF->getContents();
 872     for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
 873       if (i) OS << ",";
 874       OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
 875     }
 876     OS << "] (" << Contents.size() << " bytes)";
 877
 878     if (!DF->getFixups().empty()) {
 879       OS << ",\n       ";
 880       OS << " Fixups:[";
 881       for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
 882              ie = DF->fixup_end(); it != ie; ++it) {
 883         if (it != DF->fixup_begin()) OS << ",\n                ";
 884         OS << *it;
 885       }
 886       OS << "]";
 887     }
 888     break;
 889   }
 890   case MCFragment::FT_Fill:  {
 891     const MCFillFragment *FF = cast<MCFillFragment>(this);
 892     OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
 893        << " Size:" << FF->getSize();
 894     break;
 895   }
 896   case MCFragment::FT_Inst:  {
 897     const MCInstFragment *IF = cast<MCInstFragment>(this);
 898     OS << "\n       ";
 899     OS << " Inst:";
 900     IF->getInst().dump_pretty(OS);
 901     break;
 902   }
 903   case MCFragment::FT_Org:  {
 904     const MCOrgFragment *OF = cast<MCOrgFragment>(this);
 905     OS << "\n       ";
 906     OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
 907     break;
 908   }
 909   case MCFragment::FT_Dwarf:  {
 910     const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
 911     OS << "\n       ";
 912     OS << " AddrDelta:" << OF->getAddrDelta()
 913        << " LineDelta:" << OF->getLineDelta();
 914     break;
 915   }
 916   case MCFragment::FT_DwarfFrame:  {
 917     const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
 918     OS << "\n       ";
 919     OS << " AddrDelta:" << CF->getAddrDelta();
 920     break;
 921   }
 922   case MCFragment::FT_LEB: {
 923     const MCLEBFragment *LF = cast<MCLEBFragment>(this);
 924     OS << "\n       ";
 925     OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
 926     break;
 927   }
 928   }
 929   OS << ">";
 930 }
 931
 932 void MCSectionData::dump() {
 933   raw_ostream &OS = llvm::errs();
 934
 935   OS << "<MCSectionData";
 936   OS << " Alignment:" << getAlignment() << " Fragments:[\n      ";
 937   for (iterator it = begin(), ie = end(); it != ie; ++it) {
 938     if (it != begin()) OS << ",\n      ";
 939     it->dump();
 940   }
 941   OS << "]>";
 942 }
 943
 944 void MCSymbolData::dump() {
 945   raw_ostream &OS = llvm::errs();
 946
 947   OS << "<MCSymbolData Symbol:" << getSymbol()
 948      << " Fragment:" << getFragment() << " Offset:" << getOffset()
 949      << " Flags:" << getFlags() << " Index:" << getIndex();
 950   if (isCommon())
 951     OS << " (common, size:" << getCommonSize()
 952        << " align: " << getCommonAlignment() << ")";
 953   if (isExternal())
 954     OS << " (external)";
 955   if (isPrivateExtern())
 956     OS << " (private extern)";
 957   OS << ">";
 958 }
 959
 960 void MCAssembler::dump() {
 961   raw_ostream &OS = llvm::errs();
 962
 963   OS << "<MCAssembler\n";
 964   OS << "  Sections:[\n    ";
 965   for (iterator it = begin(), ie = end(); it != ie; ++it) {
 966     if (it != begin()) OS << ",\n    ";
 967     it->dump();
 968   }
 969   OS << "],\n";
 970   OS << "  Symbols:[";
 971
 972   for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
 973     if (it != symbol_begin()) OS << ",\n           ";
 974     it->dump();
 975   }
 976   OS << "]>\n";
 977 }