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      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/MCFixupKindInfo.h"
     17 #include "llvm/MC/MCObjectWriter.h"
     18 #include "llvm/MC/MCSection.h"
     19 #include "llvm/MC/MCSymbol.h"
     20 #include "llvm/MC/MCValue.h"
     21 #include "llvm/MC/MCDwarf.h"
     22 #include "llvm/MC/MCAsmBackend.h"
     23 #include "llvm/ADT/Statistic.h"
     24 #include "llvm/ADT/StringExtras.h"
     25 #include "llvm/ADT/Twine.h"
     26 #include "llvm/Support/Debug.h"
     27 #include "llvm/Support/ErrorHandling.h"
     28 #include "llvm/Support/raw_ostream.h"
     29 #include "llvm/Support/TargetRegistry.h"
     30 #include "llvm/Support/LEB128.h"
     31 
     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   const MCSymbol &S = SD->getSymbol();
    107 
    108   // If this is a variable, then recursively evaluate now.
    109   if (S.isVariable()) {
    110     MCValue Target;
    111     if (!S.getVariableValue()->EvaluateAsRelocatable(Target, *this))
    112       report_fatal_error("unable to evaluate offset for variable '" +
    113                          S.getName() + "'");
    114 
    115     // Verify that any used symbols are defined.
    116     if (Target.getSymA() && Target.getSymA()->getSymbol().isUndefined())
    117       report_fatal_error("unable to evaluate offset to undefined symbol '" +
    118                          Target.getSymA()->getSymbol().getName() + "'");
    119     if (Target.getSymB() && Target.getSymB()->getSymbol().isUndefined())
    120       report_fatal_error("unable to evaluate offset to undefined symbol '" +
    121                          Target.getSymB()->getSymbol().getName() + "'");
    122 
    123     uint64_t Offset = Target.getConstant();
    124     if (Target.getSymA())
    125       Offset += getSymbolOffset(&Assembler.getSymbolData(
    126                                   Target.getSymA()->getSymbol()));
    127     if (Target.getSymB())
    128       Offset -= getSymbolOffset(&Assembler.getSymbolData(
    129                                   Target.getSymB()->getSymbol()));
    130     return Offset;
    131   }
    132 
    133   assert(SD->getFragment() && "Invalid getOffset() on undefined symbol!");
    134   return getFragmentOffset(SD->getFragment()) + SD->getOffset();
    135 }
    136 
    137 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
    138   // The size is the last fragment's end offset.
    139   const MCFragment &F = SD->getFragmentList().back();
    140   return getFragmentOffset(&F) + getAssembler().computeFragmentSize(*this, F);
    141 }
    142 
    143 uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
    144   // Virtual sections have no file size.
    145   if (SD->getSection().isVirtualSection())
    146     return 0;
    147 
    148   // Otherwise, the file size is the same as the address space size.
    149   return getSectionAddressSize(SD);
    150 }
    151 
    152 /* *** */
    153 
    154 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
    155 }
    156 
    157 MCFragment::~MCFragment() {
    158 }
    159 
    160 MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
    161   : Kind(_Kind), Parent(_Parent), Atom(0), Offset(~UINT64_C(0)),
    162     LayoutOrder(~(0U))
    163 {
    164   if (Parent)
    165     Parent->getFragmentList().push_back(this);
    166 }
    167 
    168 /* *** */
    169 
    170 MCSectionData::MCSectionData() : Section(0) {}
    171 
    172 MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
    173   : Section(&_Section),
    174     Ordinal(~UINT32_C(0)),
    175     Alignment(1),
    176     HasInstructions(false)
    177 {
    178   if (A)
    179     A->getSectionList().push_back(this);
    180 }
    181 
    182 /* *** */
    183 
    184 MCSymbolData::MCSymbolData() : Symbol(0) {}
    185 
    186 MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
    187                            uint64_t _Offset, MCAssembler *A)
    188   : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
    189     IsExternal(false), IsPrivateExtern(false),
    190     CommonSize(0), SymbolSize(0), CommonAlign(0),
    191     Flags(0), Index(0)
    192 {
    193   if (A)
    194     A->getSymbolList().push_back(this);
    195 }
    196 
    197 /* *** */
    198 
    199 MCAssembler::MCAssembler(MCContext &Context_, MCAsmBackend &Backend_,
    200                          MCCodeEmitter &Emitter_, MCObjectWriter &Writer_,
    201                          raw_ostream &OS_)
    202   : Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(&Writer_),
    203     OS(OS_), RelaxAll(false), NoExecStack(false), SubsectionsViaSymbols(false)
    204 {
    205 }
    206 
    207 MCAssembler::~MCAssembler() {
    208 }
    209 
    210 void MCAssembler::setWriter(MCObjectWriter &ObjectWriter) {
    211   delete Writer;
    212   Writer = &ObjectWriter;
    213 }
    214 
    215 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
    216   // Non-temporary labels should always be visible to the linker.
    217   if (!Symbol.isTemporary())
    218     return true;
    219 
    220   // Absolute temporary labels are never visible.
    221   if (!Symbol.isInSection())
    222     return false;
    223 
    224   // Otherwise, check if the section requires symbols even for temporary labels.
    225   return getBackend().doesSectionRequireSymbols(Symbol.getSection());
    226 }
    227 
    228 const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
    229   // Linker visible symbols define atoms.
    230   if (isSymbolLinkerVisible(SD->getSymbol()))
    231     return SD;
    232 
    233   // Absolute and undefined symbols have no defining atom.
    234   if (!SD->getFragment())
    235     return 0;
    236 
    237   // Non-linker visible symbols in sections which can't be atomized have no
    238   // defining atom.
    239   if (!getBackend().isSectionAtomizable(
    240         SD->getFragment()->getParent()->getSection()))
    241     return 0;
    242 
    243   // Otherwise, return the atom for the containing fragment.
    244   return SD->getFragment()->getAtom();
    245 }
    246 
    247 bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
    248                                 const MCFixup &Fixup, const MCFragment *DF,
    249                                 MCValue &Target, uint64_t &Value) const {
    250   ++stats::evaluateFixup;
    251 
    252   if (!Fixup.getValue()->EvaluateAsRelocatable(Target, Layout))
    253     getContext().FatalError(Fixup.getLoc(), "expected relocatable expression");
    254 
    255   bool IsPCRel = Backend.getFixupKindInfo(
    256     Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
    257 
    258   bool IsResolved;
    259   if (IsPCRel) {
    260     if (Target.getSymB()) {
    261       IsResolved = false;
    262     } else if (!Target.getSymA()) {
    263       IsResolved = false;
    264     } else {
    265       const MCSymbolRefExpr *A = Target.getSymA();
    266       const MCSymbol &SA = A->getSymbol();
    267       if (A->getKind() != MCSymbolRefExpr::VK_None ||
    268           SA.AliasedSymbol().isUndefined()) {
    269         IsResolved = false;
    270       } else {
    271         const MCSymbolData &DataA = getSymbolData(SA);
    272         IsResolved =
    273           getWriter().IsSymbolRefDifferenceFullyResolvedImpl(*this, DataA,
    274                                                              *DF, false, true);
    275       }
    276     }
    277   } else {
    278     IsResolved = Target.isAbsolute();
    279   }
    280 
    281   Value = Target.getConstant();
    282 
    283   if (const MCSymbolRefExpr *A = Target.getSymA()) {
    284     const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
    285     if (Sym.isDefined())
    286       Value += Layout.getSymbolOffset(&getSymbolData(Sym));
    287   }
    288   if (const MCSymbolRefExpr *B = Target.getSymB()) {
    289     const MCSymbol &Sym = B->getSymbol().AliasedSymbol();
    290     if (Sym.isDefined())
    291       Value -= Layout.getSymbolOffset(&getSymbolData(Sym));
    292   }
    293 
    294 
    295   bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
    296                          MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
    297   assert((ShouldAlignPC ? IsPCRel : true) &&
    298     "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
    299 
    300   if (IsPCRel) {
    301     uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
    302 
    303     // A number of ARM fixups in Thumb mode require that the effective PC
    304     // address be determined as the 32-bit aligned version of the actual offset.
    305     if (ShouldAlignPC) Offset &= ~0x3;
    306     Value -= Offset;
    307   }
    308 
    309   // Let the backend adjust the fixup value if necessary, including whether
    310   // we need a relocation.
    311   Backend.processFixupValue(*this, Layout, Fixup, DF, Target, Value,
    312                             IsResolved);
    313 
    314   return IsResolved;
    315 }
    316 
    317 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
    318                                           const MCFragment &F) const {
    319   switch (F.getKind()) {
    320   case MCFragment::FT_Data:
    321     return cast<MCDataFragment>(F).getContents().size();
    322   case MCFragment::FT_Fill:
    323     return cast<MCFillFragment>(F).getSize();
    324   case MCFragment::FT_Inst:
    325     return cast<MCInstFragment>(F).getInstSize();
    326 
    327   case MCFragment::FT_LEB:
    328     return cast<MCLEBFragment>(F).getContents().size();
    329 
    330   case MCFragment::FT_Align: {
    331     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
    332     unsigned Offset = Layout.getFragmentOffset(&AF);
    333     unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
    334     // If we are padding with nops, force the padding to be larger than the
    335     // minimum nop size.
    336     if (Size > 0 && AF.hasEmitNops()) {
    337       while (Size % getBackend().getMinimumNopSize())
    338         Size += AF.getAlignment();
    339     }
    340     if (Size > AF.getMaxBytesToEmit())
    341       return 0;
    342     return Size;
    343   }
    344 
    345   case MCFragment::FT_Org: {
    346     MCOrgFragment &OF = cast<MCOrgFragment>(F);
    347     int64_t TargetLocation;
    348     if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, Layout))
    349       report_fatal_error("expected assembly-time absolute expression");
    350 
    351     // FIXME: We need a way to communicate this error.
    352     uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
    353     int64_t Size = TargetLocation - FragmentOffset;
    354     if (Size < 0 || Size >= 0x40000000)
    355       report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
    356                          "' (at offset '" + Twine(FragmentOffset) + "')");
    357     return Size;
    358   }
    359 
    360   case MCFragment::FT_Dwarf:
    361     return cast<MCDwarfLineAddrFragment>(F).getContents().size();
    362   case MCFragment::FT_DwarfFrame:
    363     return cast<MCDwarfCallFrameFragment>(F).getContents().size();
    364   }
    365 
    366   llvm_unreachable("invalid fragment kind");
    367 }
    368 
    369 void MCAsmLayout::LayoutFragment(MCFragment *F) {
    370   MCFragment *Prev = F->getPrevNode();
    371 
    372   // We should never try to recompute something which is up-to-date.
    373   assert(!isFragmentUpToDate(F) && "Attempt to recompute up-to-date fragment!");
    374   // We should never try to compute the fragment layout if it's predecessor
    375   // isn't up-to-date.
    376   assert((!Prev || isFragmentUpToDate(Prev)) &&
    377          "Attempt to compute fragment before it's predecessor!");
    378 
    379   ++stats::FragmentLayouts;
    380 
    381   // Compute fragment offset and size.
    382   uint64_t Offset = 0;
    383   if (Prev)
    384     Offset += Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
    385 
    386   F->Offset = Offset;
    387   LastValidFragment[F->getParent()] = F;
    388 }
    389 
    390 /// WriteFragmentData - Write the \arg F data to the output file.
    391 static void WriteFragmentData(const MCAssembler &Asm, const MCAsmLayout &Layout,
    392                               const MCFragment &F) {
    393   MCObjectWriter *OW = &Asm.getWriter();
    394   uint64_t Start = OW->getStream().tell();
    395   (void) Start;
    396 
    397   ++stats::EmittedFragments;
    398 
    399   // FIXME: Embed in fragments instead?
    400   uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
    401   switch (F.getKind()) {
    402   case MCFragment::FT_Align: {
    403     MCAlignFragment &AF = cast<MCAlignFragment>(F);
    404     uint64_t Count = FragmentSize / AF.getValueSize();
    405 
    406     assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
    407 
    408     // FIXME: This error shouldn't actually occur (the front end should emit
    409     // multiple .align directives to enforce the semantics it wants), but is
    410     // severe enough that we want to report it. How to handle this?
    411     if (Count * AF.getValueSize() != FragmentSize)
    412       report_fatal_error("undefined .align directive, value size '" +
    413                         Twine(AF.getValueSize()) +
    414                         "' is not a divisor of padding size '" +
    415                         Twine(FragmentSize) + "'");
    416 
    417     // See if we are aligning with nops, and if so do that first to try to fill
    418     // the Count bytes.  Then if that did not fill any bytes or there are any
    419     // bytes left to fill use the Value and ValueSize to fill the rest.
    420     // If we are aligning with nops, ask that target to emit the right data.
    421     if (AF.hasEmitNops()) {
    422       if (!Asm.getBackend().writeNopData(Count, OW))
    423         report_fatal_error("unable to write nop sequence of " +
    424                           Twine(Count) + " bytes");
    425       break;
    426     }
    427 
    428     // Otherwise, write out in multiples of the value size.
    429     for (uint64_t i = 0; i != Count; ++i) {
    430       switch (AF.getValueSize()) {
    431       default: llvm_unreachable("Invalid size!");
    432       case 1: OW->Write8 (uint8_t (AF.getValue())); break;
    433       case 2: OW->Write16(uint16_t(AF.getValue())); break;
    434       case 4: OW->Write32(uint32_t(AF.getValue())); break;
    435       case 8: OW->Write64(uint64_t(AF.getValue())); break;
    436       }
    437     }
    438     break;
    439   }
    440 
    441   case MCFragment::FT_Data: {
    442     MCDataFragment &DF = cast<MCDataFragment>(F);
    443     assert(FragmentSize == DF.getContents().size() && "Invalid size!");
    444     OW->WriteBytes(DF.getContents().str());
    445     break;
    446   }
    447 
    448   case MCFragment::FT_Fill: {
    449     MCFillFragment &FF = cast<MCFillFragment>(F);
    450 
    451     assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
    452 
    453     for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
    454       switch (FF.getValueSize()) {
    455       default: llvm_unreachable("Invalid size!");
    456       case 1: OW->Write8 (uint8_t (FF.getValue())); break;
    457       case 2: OW->Write16(uint16_t(FF.getValue())); break;
    458       case 4: OW->Write32(uint32_t(FF.getValue())); break;
    459       case 8: OW->Write64(uint64_t(FF.getValue())); break;
    460       }
    461     }
    462     break;
    463   }
    464 
    465   case MCFragment::FT_Inst: {
    466     MCInstFragment &IF = cast<MCInstFragment>(F);
    467     OW->WriteBytes(StringRef(IF.getCode().begin(), IF.getCode().size()));
    468     break;
    469   }
    470 
    471   case MCFragment::FT_LEB: {
    472     MCLEBFragment &LF = cast<MCLEBFragment>(F);
    473     OW->WriteBytes(LF.getContents().str());
    474     break;
    475   }
    476 
    477   case MCFragment::FT_Org: {
    478     MCOrgFragment &OF = cast<MCOrgFragment>(F);
    479 
    480     for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
    481       OW->Write8(uint8_t(OF.getValue()));
    482 
    483     break;
    484   }
    485 
    486   case MCFragment::FT_Dwarf: {
    487     const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
    488     OW->WriteBytes(OF.getContents().str());
    489     break;
    490   }
    491   case MCFragment::FT_DwarfFrame: {
    492     const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
    493     OW->WriteBytes(CF.getContents().str());
    494     break;
    495   }
    496   }
    497 
    498   assert(OW->getStream().tell() - Start == FragmentSize);
    499 }
    500 
    501 void MCAssembler::writeSectionData(const MCSectionData *SD,
    502                                    const MCAsmLayout &Layout) const {
    503   // Ignore virtual sections.
    504   if (SD->getSection().isVirtualSection()) {
    505     assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
    506 
    507     // Check that contents are only things legal inside a virtual section.
    508     for (MCSectionData::const_iterator it = SD->begin(),
    509            ie = SD->end(); it != ie; ++it) {
    510       switch (it->getKind()) {
    511       default: llvm_unreachable("Invalid fragment in virtual section!");
    512       case MCFragment::FT_Data: {
    513         // Check that we aren't trying to write a non-zero contents (or fixups)
    514         // into a virtual section. This is to support clients which use standard
    515         // directives to fill the contents of virtual sections.
    516         MCDataFragment &DF = cast<MCDataFragment>(*it);
    517         assert(DF.fixup_begin() == DF.fixup_end() &&
    518                "Cannot have fixups in virtual section!");
    519         for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
    520           assert(DF.getContents()[i] == 0 &&
    521                  "Invalid data value for virtual section!");
    522         break;
    523       }
    524       case MCFragment::FT_Align:
    525         // Check that we aren't trying to write a non-zero value into a virtual
    526         // section.
    527         assert((!cast<MCAlignFragment>(it)->getValueSize() ||
    528                 !cast<MCAlignFragment>(it)->getValue()) &&
    529                "Invalid align in virtual section!");
    530         break;
    531       case MCFragment::FT_Fill:
    532         assert(!cast<MCFillFragment>(it)->getValueSize() &&
    533                "Invalid fill in virtual section!");
    534         break;
    535       }
    536     }
    537 
    538     return;
    539   }
    540 
    541   uint64_t Start = getWriter().getStream().tell();
    542   (void) Start;
    543 
    544   for (MCSectionData::const_iterator it = SD->begin(),
    545          ie = SD->end(); it != ie; ++it)
    546     WriteFragmentData(*this, Layout, *it);
    547 
    548   assert(getWriter().getStream().tell() - Start ==
    549          Layout.getSectionAddressSize(SD));
    550 }
    551 
    552 
    553 uint64_t MCAssembler::handleFixup(const MCAsmLayout &Layout,
    554                                   MCFragment &F,
    555                                   const MCFixup &Fixup) {
    556    // Evaluate the fixup.
    557    MCValue Target;
    558    uint64_t FixedValue;
    559    if (!evaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
    560      // The fixup was unresolved, we need a relocation. Inform the object
    561      // writer of the relocation, and give it an opportunity to adjust the
    562      // fixup value if need be.
    563      getWriter().RecordRelocation(*this, Layout, &F, Fixup, Target, FixedValue);
    564    }
    565    return FixedValue;
    566  }
    567 
    568 void MCAssembler::Finish() {
    569   DEBUG_WITH_TYPE("mc-dump", {
    570       llvm::errs() << "assembler backend - pre-layout\n--\n";
    571       dump(); });
    572 
    573   // Create the layout object.
    574   MCAsmLayout Layout(*this);
    575 
    576   // Create dummy fragments and assign section ordinals.
    577   unsigned SectionIndex = 0;
    578   for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
    579     // Create dummy fragments to eliminate any empty sections, this simplifies
    580     // layout.
    581     if (it->getFragmentList().empty())
    582       new MCDataFragment(it);
    583 
    584     it->setOrdinal(SectionIndex++);
    585   }
    586 
    587   // Assign layout order indices to sections and fragments.
    588   for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
    589     MCSectionData *SD = Layout.getSectionOrder()[i];
    590     SD->setLayoutOrder(i);
    591 
    592     unsigned FragmentIndex = 0;
    593     for (MCSectionData::iterator it2 = SD->begin(),
    594            ie2 = SD->end(); it2 != ie2; ++it2)
    595       it2->setLayoutOrder(FragmentIndex++);
    596   }
    597 
    598   // Layout until everything fits.
    599   while (layoutOnce(Layout))
    600     continue;
    601 
    602   DEBUG_WITH_TYPE("mc-dump", {
    603       llvm::errs() << "assembler backend - post-relaxation\n--\n";
    604       dump(); });
    605 
    606   // Finalize the layout, including fragment lowering.
    607   finishLayout(Layout);
    608 
    609   DEBUG_WITH_TYPE("mc-dump", {
    610       llvm::errs() << "assembler backend - final-layout\n--\n";
    611       dump(); });
    612 
    613   uint64_t StartOffset = OS.tell();
    614 
    615   // Allow the object writer a chance to perform post-layout binding (for
    616   // example, to set the index fields in the symbol data).
    617   getWriter().ExecutePostLayoutBinding(*this, Layout);
    618 
    619   // Evaluate and apply the fixups, generating relocation entries as necessary.
    620   for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
    621     for (MCSectionData::iterator it2 = it->begin(),
    622            ie2 = it->end(); it2 != ie2; ++it2) {
    623       MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
    624       if (DF) {
    625         for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
    626                ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
    627           MCFixup &Fixup = *it3;
    628           uint64_t FixedValue = handleFixup(Layout, *DF, Fixup);
    629           getBackend().applyFixup(Fixup, DF->getContents().data(),
    630                                   DF->getContents().size(), FixedValue);
    631         }
    632       }
    633       MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
    634       if (IF) {
    635         for (MCInstFragment::fixup_iterator it3 = IF->fixup_begin(),
    636                ie3 = IF->fixup_end(); it3 != ie3; ++it3) {
    637           MCFixup &Fixup = *it3;
    638           uint64_t FixedValue = handleFixup(Layout, *IF, Fixup);
    639           getBackend().applyFixup(Fixup, IF->getCode().data(),
    640                                   IF->getCode().size(), FixedValue);
    641         }
    642       }
    643     }
    644   }
    645 
    646   // Write the object file.
    647   getWriter().WriteObject(*this, Layout);
    648 
    649   stats::ObjectBytes += OS.tell() - StartOffset;
    650 }
    651 
    652 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
    653                                        const MCInstFragment *DF,
    654                                        const MCAsmLayout &Layout) const {
    655   if (getRelaxAll())
    656     return true;
    657 
    658   // If we cannot resolve the fixup value, it requires relaxation.
    659   MCValue Target;
    660   uint64_t Value;
    661   if (!evaluateFixup(Layout, Fixup, DF, Target, Value))
    662     return true;
    663 
    664   return getBackend().fixupNeedsRelaxation(Fixup, Value, DF, Layout);
    665 }
    666 
    667 bool MCAssembler::fragmentNeedsRelaxation(const MCInstFragment *IF,
    668                                           const MCAsmLayout &Layout) const {
    669   // If this inst doesn't ever need relaxation, ignore it. This occurs when we
    670   // are intentionally pushing out inst fragments, or because we relaxed a
    671   // previous instruction to one that doesn't need relaxation.
    672   if (!getBackend().mayNeedRelaxation(IF->getInst()))
    673     return false;
    674 
    675   for (MCInstFragment::const_fixup_iterator it = IF->fixup_begin(),
    676          ie = IF->fixup_end(); it != ie; ++it)
    677     if (fixupNeedsRelaxation(*it, IF, Layout))
    678       return true;
    679 
    680   return false;
    681 }
    682 
    683 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
    684                                    MCInstFragment &IF) {
    685   if (!fragmentNeedsRelaxation(&IF, Layout))
    686     return false;
    687 
    688   ++stats::RelaxedInstructions;
    689 
    690   // FIXME-PERF: We could immediately lower out instructions if we can tell
    691   // they are fully resolved, to avoid retesting on later passes.
    692 
    693   // Relax the fragment.
    694 
    695   MCInst Relaxed;
    696   getBackend().relaxInstruction(IF.getInst(), Relaxed);
    697 
    698   // Encode the new instruction.
    699   //
    700   // FIXME-PERF: If it matters, we could let the target do this. It can
    701   // probably do so more efficiently in many cases.
    702   SmallVector<MCFixup, 4> Fixups;
    703   SmallString<256> Code;
    704   raw_svector_ostream VecOS(Code);
    705   getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups);
    706   VecOS.flush();
    707 
    708   // Update the instruction fragment.
    709   IF.setInst(Relaxed);
    710   IF.getCode() = Code;
    711   IF.getFixups().clear();
    712   // FIXME: Eliminate copy.
    713   for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
    714     IF.getFixups().push_back(Fixups[i]);
    715 
    716   return true;
    717 }
    718 
    719 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
    720   int64_t Value = 0;
    721   uint64_t OldSize = LF.getContents().size();
    722   bool IsAbs = LF.getValue().EvaluateAsAbsolute(Value, Layout);
    723   (void)IsAbs;
    724   assert(IsAbs);
    725   SmallString<8> &Data = LF.getContents();
    726   Data.clear();
    727   raw_svector_ostream OSE(Data);
    728   if (LF.isSigned())
    729     encodeSLEB128(Value, OSE);
    730   else
    731     encodeULEB128(Value, OSE);
    732   OSE.flush();
    733   return OldSize != LF.getContents().size();
    734 }
    735 
    736 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
    737                                      MCDwarfLineAddrFragment &DF) {
    738   int64_t AddrDelta = 0;
    739   uint64_t OldSize = DF.getContents().size();
    740   bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
    741   (void)IsAbs;
    742   assert(IsAbs);
    743   int64_t LineDelta;
    744   LineDelta = DF.getLineDelta();
    745   SmallString<8> &Data = DF.getContents();
    746   Data.clear();
    747   raw_svector_ostream OSE(Data);
    748   MCDwarfLineAddr::Encode(LineDelta, AddrDelta, OSE);
    749   OSE.flush();
    750   return OldSize != Data.size();
    751 }
    752 
    753 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
    754                                               MCDwarfCallFrameFragment &DF) {
    755   int64_t AddrDelta = 0;
    756   uint64_t OldSize = DF.getContents().size();
    757   bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
    758   (void)IsAbs;
    759   assert(IsAbs);
    760   SmallString<8> &Data = DF.getContents();
    761   Data.clear();
    762   raw_svector_ostream OSE(Data);
    763   MCDwarfFrameEmitter::EncodeAdvanceLoc(AddrDelta, OSE);
    764   OSE.flush();
    765   return OldSize != Data.size();
    766 }
    767 
    768 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout,
    769                                     MCSectionData &SD) {
    770   MCFragment *FirstInvalidFragment = NULL;
    771   // Scan for fragments that need relaxation.
    772   for (MCSectionData::iterator it2 = SD.begin(),
    773          ie2 = SD.end(); it2 != ie2; ++it2) {
    774     // Check if this is an fragment that needs relaxation.
    775     bool relaxedFrag = false;
    776     switch(it2->getKind()) {
    777     default:
    778           break;
    779     case MCFragment::FT_Inst:
    780       relaxedFrag = relaxInstruction(Layout, *cast<MCInstFragment>(it2));
    781       break;
    782     case MCFragment::FT_Dwarf:
    783       relaxedFrag = relaxDwarfLineAddr(Layout,
    784                                        *cast<MCDwarfLineAddrFragment>(it2));
    785       break;
    786     case MCFragment::FT_DwarfFrame:
    787       relaxedFrag =
    788         relaxDwarfCallFrameFragment(Layout,
    789                                     *cast<MCDwarfCallFrameFragment>(it2));
    790       break;
    791     case MCFragment::FT_LEB:
    792       relaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(it2));
    793       break;
    794     }
    795     // Update the layout, and remember that we relaxed.
    796     if (relaxedFrag && !FirstInvalidFragment)
    797       FirstInvalidFragment = it2;
    798   }
    799   if (FirstInvalidFragment) {
    800     Layout.Invalidate(FirstInvalidFragment);
    801     return true;
    802   }
    803   return false;
    804 }
    805 
    806 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
    807   ++stats::RelaxationSteps;
    808 
    809   bool WasRelaxed = false;
    810   for (iterator it = begin(), ie = end(); it != ie; ++it) {
    811     MCSectionData &SD = *it;
    812     while(layoutSectionOnce(Layout, SD))
    813       WasRelaxed = true;
    814   }
    815 
    816   return WasRelaxed;
    817 }
    818 
    819 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
    820   // The layout is done. Mark every fragment as valid.
    821   for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
    822     Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
    823   }
    824 }
    825 
    826 // Debugging methods
    827 
    828 namespace llvm {
    829 
    830 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
    831   OS << "<MCFixup" << " Offset:" << AF.getOffset()
    832      << " Value:" << *AF.getValue()
    833      << " Kind:" << AF.getKind() << ">";
    834   return OS;
    835 }
    836 
    837 }
    838 
    839 #ifndef NDEBUG
    840 void MCFragment::dump() {
    841   raw_ostream &OS = llvm::errs();
    842 
    843   OS << "<";
    844   switch (getKind()) {
    845   case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
    846   case MCFragment::FT_Data:  OS << "MCDataFragment"; break;
    847   case MCFragment::FT_Fill:  OS << "MCFillFragment"; break;
    848   case MCFragment::FT_Inst:  OS << "MCInstFragment"; break;
    849   case MCFragment::FT_Org:   OS << "MCOrgFragment"; break;
    850   case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
    851   case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
    852   case MCFragment::FT_LEB:   OS << "MCLEBFragment"; break;
    853   }
    854 
    855   OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
    856      << " Offset:" << Offset << ">";
    857 
    858   switch (getKind()) {
    859   case MCFragment::FT_Align: {
    860     const MCAlignFragment *AF = cast<MCAlignFragment>(this);
    861     if (AF->hasEmitNops())
    862       OS << " (emit nops)";
    863     OS << "\n       ";
    864     OS << " Alignment:" << AF->getAlignment()
    865        << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
    866        << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
    867     break;
    868   }
    869   case MCFragment::FT_Data:  {
    870     const MCDataFragment *DF = cast<MCDataFragment>(this);
    871     OS << "\n       ";
    872     OS << " Contents:[";
    873     const SmallVectorImpl<char> &Contents = DF->getContents();
    874     for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
    875       if (i) OS << ",";
    876       OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
    877     }
    878     OS << "] (" << Contents.size() << " bytes)";
    879 
    880     if (!DF->getFixups().empty()) {
    881       OS << ",\n       ";
    882       OS << " Fixups:[";
    883       for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
    884              ie = DF->fixup_end(); it != ie; ++it) {
    885         if (it != DF->fixup_begin()) OS << ",\n                ";
    886         OS << *it;
    887       }
    888       OS << "]";
    889     }
    890     break;
    891   }
    892   case MCFragment::FT_Fill:  {
    893     const MCFillFragment *FF = cast<MCFillFragment>(this);
    894     OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
    895        << " Size:" << FF->getSize();
    896     break;
    897   }
    898   case MCFragment::FT_Inst:  {
    899     const MCInstFragment *IF = cast<MCInstFragment>(this);
    900     OS << "\n       ";
    901     OS << " Inst:";
    902     IF->getInst().dump_pretty(OS);
    903     break;
    904   }
    905   case MCFragment::FT_Org:  {
    906     const MCOrgFragment *OF = cast<MCOrgFragment>(this);
    907     OS << "\n       ";
    908     OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
    909     break;
    910   }
    911   case MCFragment::FT_Dwarf:  {
    912     const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
    913     OS << "\n       ";
    914     OS << " AddrDelta:" << OF->getAddrDelta()
    915        << " LineDelta:" << OF->getLineDelta();
    916     break;
    917   }
    918   case MCFragment::FT_DwarfFrame:  {
    919     const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
    920     OS << "\n       ";
    921     OS << " AddrDelta:" << CF->getAddrDelta();
    922     break;
    923   }
    924   case MCFragment::FT_LEB: {
    925     const MCLEBFragment *LF = cast<MCLEBFragment>(this);
    926     OS << "\n       ";
    927     OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
    928     break;
    929   }
    930   }
    931   OS << ">";
    932 }
    933 
    934 void MCSectionData::dump() {
    935   raw_ostream &OS = llvm::errs();
    936 
    937   OS << "<MCSectionData";
    938   OS << " Alignment:" << getAlignment() << " Fragments:[\n      ";
    939   for (iterator it = begin(), ie = end(); it != ie; ++it) {
    940     if (it != begin()) OS << ",\n      ";
    941     it->dump();
    942   }
    943   OS << "]>";
    944 }
    945 
    946 void MCSymbolData::dump() {
    947   raw_ostream &OS = llvm::errs();
    948 
    949   OS << "<MCSymbolData Symbol:" << getSymbol()
    950      << " Fragment:" << getFragment() << " Offset:" << getOffset()
    951      << " Flags:" << getFlags() << " Index:" << getIndex();
    952   if (isCommon())
    953     OS << " (common, size:" << getCommonSize()
    954        << " align: " << getCommonAlignment() << ")";
    955   if (isExternal())
    956     OS << " (external)";
    957   if (isPrivateExtern())
    958     OS << " (private extern)";
    959   OS << ">";
    960 }
    961 
    962 void MCAssembler::dump() {
    963   raw_ostream &OS = llvm::errs();
    964 
    965   OS << "<MCAssembler\n";
    966   OS << "  Sections:[\n    ";
    967   for (iterator it = begin(), ie = end(); it != ie; ++it) {
    968     if (it != begin()) OS << ",\n    ";
    969     it->dump();
    970   }
    971   OS << "],\n";
    972   OS << "  Symbols:[";
    973 
    974   for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
    975     if (it != symbol_begin()) OS << ",\n           ";
    976     it->dump();
    977   }
    978   OS << "]>\n";
    979 }
    980 #endif
    981 
    982 // anchors for MC*Fragment vtables
    983 void MCDataFragment::anchor() { }
    984 void MCInstFragment::anchor() { }
    985 void MCAlignFragment::anchor() { }
    986 void MCFillFragment::anchor() { }
    987 void MCOrgFragment::anchor() { }
    988 void MCLEBFragment::anchor() { }
    989 void MCDwarfLineAddrFragment::anchor() { }
    990 void MCDwarfCallFrameFragment::anchor() { }
    991