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/MCExpr.h"
  15 #include "llvm/MC/MCObjectWriter.h"
  16 #include "llvm/MC/MCSection.h"
  17 #include "llvm/MC/MCSymbol.h"
  18 #include "llvm/MC/MCValue.h"
  19 #include "llvm/MC/MCDwarf.h"
  20 #include "llvm/ADT/OwningPtr.h"
  21 #include "llvm/ADT/Statistic.h"
  22 #include "llvm/ADT/StringExtras.h"
  23 #include "llvm/ADT/Twine.h"
  24 #include "llvm/Support/Debug.h"
  25 #include "llvm/Support/ErrorHandling.h"
  26 #include "llvm/Support/raw_ostream.h"
  27 #include "llvm/Target/TargetRegistry.h"
  28 #include "llvm/Target/TargetAsmBackend.h"
  29
  30 #include <vector>
  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 STATISTIC(SectionLayouts, "Number of section layouts");
  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(0)
  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 (!Asm.getBackend().isVirtualSection(it->getSection()))
  58       SectionOrder.push_back(&*it);
  59   for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
  60     if (Asm.getBackend().isVirtualSection(it->getSection()))
  61       SectionOrder.push_back(&*it);
  62 }
  63
  64 bool MCAsmLayout::isSectionUpToDate(const MCSectionData *SD) const {
  65   // The first section is always up-to-date.
  66   unsigned Index = SD->getLayoutOrder();
  67   if (!Index)
  68     return true;
  69
  70   // Otherwise, sections are always implicitly computed when the preceeding
  71   // fragment is layed out.
  72   const MCSectionData *Prev = getSectionOrder()[Index - 1];
  73   return isFragmentUpToDate(&(Prev->getFragmentList().back()));
  74 }
  75
  76 bool MCAsmLayout::isFragmentUpToDate(const MCFragment *F) const {
  77   return (LastValidFragment &&
  78           F->getLayoutOrder() <= LastValidFragment->getLayoutOrder());
  79 }
  80
  81 void MCAsmLayout::UpdateForSlide(MCFragment *F, int SlideAmount) {
  82   // If this fragment wasn't already up-to-date, we don't need to do anything.
  83   if (!isFragmentUpToDate(F))
  84     return;
  85
  86   // Otherwise, reset the last valid fragment to the predecessor of the
  87   // invalidated fragment.
  88   LastValidFragment = F->getPrevNode();
  89   if (!LastValidFragment) {
  90     unsigned Index = F->getParent()->getLayoutOrder();
  91     if (Index != 0) {
  92       MCSectionData *Prev = getSectionOrder()[Index - 1];
  93       LastValidFragment = &(Prev->getFragmentList().back());
  94     }
  95   }
  96 }
  97
  98 void MCAsmLayout::EnsureValid(const MCFragment *F) const {
  99   // Advance the layout position until the fragment is up-to-date.
 100   while (!isFragmentUpToDate(F)) {
 101     // Advance to the next fragment.
 102     MCFragment *Cur = LastValidFragment;
 103     if (Cur)
 104       Cur = Cur->getNextNode();
 105     if (!Cur) {
 106       unsigned NextIndex = 0;
 107       if (LastValidFragment)
 108         NextIndex = LastValidFragment->getParent()->getLayoutOrder() + 1;
 109       Cur = SectionOrder[NextIndex]->begin();
 110     }
 111
 112     const_cast<MCAsmLayout*>(this)->LayoutFragment(Cur);
 113   }
 114 }
 115
 116 void MCAsmLayout::FragmentReplaced(MCFragment *Src, MCFragment *Dst) {
 117   if (LastValidFragment == Src)
 118     LastValidFragment = Dst;
 119
 120   Dst->Offset = Src->Offset;
 121   Dst->EffectiveSize = Src->EffectiveSize;
 122 }
 123
 124 uint64_t MCAsmLayout::getFragmentAddress(const MCFragment *F) const {
 125   assert(F->getParent() && "Missing section()!");
 126   return getSectionAddress(F->getParent()) + getFragmentOffset(F);
 127 }
 128
 129 uint64_t MCAsmLayout::getFragmentEffectiveSize(const MCFragment *F) const {
 130   EnsureValid(F);
 131   assert(F->EffectiveSize != ~UINT64_C(0) && "Address not set!");
 132   return F->EffectiveSize;
 133 }
 134
 135 uint64_t MCAsmLayout::getFragmentOffset(const MCFragment *F) const {
 136   EnsureValid(F);
 137   assert(F->Offset != ~UINT64_C(0) && "Address not set!");
 138   return F->Offset;
 139 }
 140
 141 uint64_t MCAsmLayout::getSymbolAddress(const MCSymbolData *SD) const {
 142   assert(SD->getFragment() && "Invalid getAddress() on undefined symbol!");
 143   return getFragmentAddress(SD->getFragment()) + SD->getOffset();
 144 }
 145
 146 uint64_t MCAsmLayout::getSectionAddress(const MCSectionData *SD) const {
 147   EnsureValid(SD->begin());
 148   assert(SD->Address != ~UINT64_C(0) && "Address not set!");
 149   return SD->Address;
 150 }
 151
 152 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
 153   // The size is the last fragment's end offset.
 154   const MCFragment &F = SD->getFragmentList().back();
 155   return getFragmentOffset(&F) + getFragmentEffectiveSize(&F);
 156 }
 157
 158 uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
 159   // Virtual sections have no file size.
 160   if (getAssembler().getBackend().isVirtualSection(SD->getSection()))
 161     return 0;
 162
 163   // Otherwise, the file size is the same as the address space size.
 164   return getSectionAddressSize(SD);
 165 }
 166
 167 uint64_t MCAsmLayout::getSectionSize(const MCSectionData *SD) const {
 168   // The logical size is the address space size minus any tail padding.
 169   uint64_t Size = getSectionAddressSize(SD);
 170   const MCAlignFragment *AF =
 171     dyn_cast<MCAlignFragment>(&(SD->getFragmentList().back()));
 172   if (AF && AF->hasOnlyAlignAddress())
 173     Size -= getFragmentEffectiveSize(AF);
 174
 175   return Size;
 176 }
 177
 178 /* *** */
 179
 180 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
 181 }
 182
 183 MCFragment::~MCFragment() {
 184 }
 185
 186 MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
 187   : Kind(_Kind), Parent(_Parent), Atom(0), Offset(~UINT64_C(0)),
 188     EffectiveSize(~UINT64_C(0))
 189 {
 190   if (Parent)
 191     Parent->getFragmentList().push_back(this);
 192 }
 193
 194 /* *** */
 195
 196 MCSectionData::MCSectionData() : Section(0) {}
 197
 198 MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
 199   : Section(&_Section),
 200     Alignment(1),
 201     Address(~UINT64_C(0)),
 202     HasInstructions(false)
 203 {
 204   if (A)
 205     A->getSectionList().push_back(this);
 206 }
 207
 208 /* *** */
 209
 210 MCSymbolData::MCSymbolData() : Symbol(0) {}
 211
 212 MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
 213                            uint64_t _Offset, MCAssembler *A)
 214   : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
 215     IsExternal(false), IsPrivateExtern(false),
 216     CommonSize(0), SymbolSize(0), CommonAlign(0),
 217     Flags(0), Index(0)
 218 {
 219   if (A)
 220     A->getSymbolList().push_back(this);
 221 }
 222
 223 /* *** */
 224
 225 MCAssembler::MCAssembler(MCContext &_Context, TargetAsmBackend &_Backend,
 226                          MCCodeEmitter &_Emitter, bool _PadSectionToAlignment,
 227                          raw_ostream &_OS)
 228   : Context(_Context), Backend(_Backend), Emitter(_Emitter),
 229     OS(_OS), RelaxAll(false), SubsectionsViaSymbols(false),
 230     PadSectionToAlignment(_PadSectionToAlignment)
 231 {
 232 }
 233
 234 MCAssembler::~MCAssembler() {
 235 }
 236
 237 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
 238   // Non-temporary labels should always be visible to the linker.
 239   if (!Symbol.isTemporary())
 240     return true;
 241
 242   // Absolute temporary labels are never visible.
 243   if (!Symbol.isInSection())
 244     return false;
 245
 246   // Otherwise, check if the section requires symbols even for temporary labels.
 247   return getBackend().doesSectionRequireSymbols(Symbol.getSection());
 248 }
 249
 250 const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
 251   // Linker visible symbols define atoms.
 252   if (isSymbolLinkerVisible(SD->getSymbol()))
 253     return SD;
 254
 255   // Absolute and undefined symbols have no defining atom.
 256   if (!SD->getFragment())
 257     return 0;
 258
 259   // Non-linker visible symbols in sections which can't be atomized have no
 260   // defining atom.
 261   if (!getBackend().isSectionAtomizable(
 262         SD->getFragment()->getParent()->getSection()))
 263     return 0;
 264
 265   // Otherwise, return the atom for the containing fragment.
 266   return SD->getFragment()->getAtom();
 267 }
 268
 269 bool MCAssembler::EvaluateFixup(const MCObjectWriter &Writer,
 270                                 const MCAsmLayout &Layout,
 271                                 const MCFixup &Fixup, const MCFragment *DF,
 272                                 MCValue &Target, uint64_t &Value) const {
 273   ++stats::EvaluateFixup;
 274
 275   if (!Fixup.getValue()->EvaluateAsRelocatable(Target, &Layout))
 276     report_fatal_error("expected relocatable expression");
 277
 278   // FIXME: How do non-scattered symbols work in ELF? I presume the linker
 279   // doesn't support small relocations, but then under what criteria does the
 280   // assembler allow symbol differences?
 281
 282   Value = Target.getConstant();
 283
 284   bool IsPCRel = Emitter.getFixupKindInfo(
 285     Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
 286   bool IsResolved = true;
 287   if (const MCSymbolRefExpr *A = Target.getSymA()) {
 288     if (A->getSymbol().isDefined())
 289       Value += Layout.getSymbolAddress(&getSymbolData(A->getSymbol()));
 290     else
 291       IsResolved = false;
 292   }
 293   if (const MCSymbolRefExpr *B = Target.getSymB()) {
 294     if (B->getSymbol().isDefined())
 295       Value -= Layout.getSymbolAddress(&getSymbolData(B->getSymbol()));
 296     else
 297       IsResolved = false;
 298   }
 299
 300   if (IsResolved)
 301     IsResolved = Writer.IsFixupFullyResolved(*this, Target, IsPCRel, DF);
 302
 303   if (IsPCRel)
 304     Value -= Layout.getFragmentAddress(DF) + Fixup.getOffset();
 305
 306   return IsResolved;
 307 }
 308
 309 uint64_t MCAssembler::ComputeFragmentSize(MCAsmLayout &Layout,
 310                                           const MCFragment &F,
 311                                           uint64_t SectionAddress,
 312                                           uint64_t FragmentOffset) const {
 313   switch (F.getKind()) {
 314   case MCFragment::FT_Data:
 315     return cast<MCDataFragment>(F).getContents().size();
 316   case MCFragment::FT_Fill:
 317     return cast<MCFillFragment>(F).getSize();
 318   case MCFragment::FT_Inst:
 319     return cast<MCInstFragment>(F).getInstSize();
 320
 321   case MCFragment::FT_LEB:
 322     return cast<MCLEBFragment>(F).getSize();
 323
 324   case MCFragment::FT_Align: {
 325     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
 326
 327     assert((!AF.hasOnlyAlignAddress() || !AF.getNextNode()) &&
 328            "Invalid OnlyAlignAddress bit, not the last fragment!");
 329
 330     uint64_t Size = OffsetToAlignment(SectionAddress + FragmentOffset,
 331                                       AF.getAlignment());
 332
 333     // Honor MaxBytesToEmit.
 334     if (Size > AF.getMaxBytesToEmit())
 335       return 0;
 336
 337     return Size;
 338   }
 339
 340   case MCFragment::FT_Org:
 341     return cast<MCOrgFragment>(F).getSize();
 342
 343   case MCFragment::FT_Dwarf: {
 344     const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
 345
 346     // The AddrDelta is really unsigned and it can only increase.
 347     int64_t AddrDelta;
 348
 349     OF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, &Layout);
 350
 351     int64_t LineDelta;
 352     LineDelta = OF.getLineDelta();
 353
 354     return MCDwarfLineAddr::ComputeSize(LineDelta, AddrDelta);
 355   }
 356   }
 357
 358   assert(0 && "invalid fragment kind");
 359   return 0;
 360 }
 361
 362 void MCAsmLayout::LayoutFile() {
 363   // Initialize the first section and set the valid fragment layout point. All
 364   // actual layout computations are done lazily.
 365   LastValidFragment = 0;
 366   if (!getSectionOrder().empty())
 367     getSectionOrder().front()->Address = 0;
 368 }
 369
 370 void MCAsmLayout::LayoutFragment(MCFragment *F) {
 371   MCFragment *Prev = F->getPrevNode();
 372
 373   // We should never try to recompute something which is up-to-date.
 374   assert(!isFragmentUpToDate(F) && "Attempt to recompute up-to-date fragment!");
 375   // We should never try to compute the fragment layout if the section isn't
 376   // up-to-date.
 377   assert(isSectionUpToDate(F->getParent()) &&
 378          "Attempt to compute fragment before it's section!");
 379   // We should never try to compute the fragment layout if it's predecessor
 380   // isn't up-to-date.
 381   assert((!Prev || isFragmentUpToDate(Prev)) &&
 382          "Attempt to compute fragment before it's predecessor!");
 383
 384   ++stats::FragmentLayouts;
 385
 386   // Compute the fragment start address.
 387   uint64_t StartAddress = F->getParent()->Address;
 388   uint64_t Address = StartAddress;
 389   if (Prev)
 390     Address += Prev->Offset + Prev->EffectiveSize;
 391
 392   // Compute fragment offset and size.
 393   F->Offset = Address - StartAddress;
 394   F->EffectiveSize = getAssembler().ComputeFragmentSize(*this, *F, StartAddress,
 395                                                         F->Offset);
 396   LastValidFragment = F;
 397
 398   // If this is the last fragment in a section, update the next section address.
 399   if (!F->getNextNode()) {
 400     unsigned NextIndex = F->getParent()->getLayoutOrder() + 1;
 401     if (NextIndex != getSectionOrder().size())
 402       LayoutSection(getSectionOrder()[NextIndex]);
 403   }
 404 }
 405
 406 void MCAsmLayout::LayoutSection(MCSectionData *SD) {
 407   unsigned SectionOrderIndex = SD->getLayoutOrder();
 408
 409   ++stats::SectionLayouts;
 410
 411   // Compute the section start address.
 412   uint64_t StartAddress = 0;
 413   if (SectionOrderIndex) {
 414     MCSectionData *Prev = getSectionOrder()[SectionOrderIndex - 1];
 415     StartAddress = getSectionAddress(Prev) + getSectionAddressSize(Prev);
 416   }
 417
 418   // Honor the section alignment requirements.
 419   StartAddress = RoundUpToAlignment(StartAddress, SD->getAlignment());
 420
 421   // Set the section address.
 422   SD->Address = StartAddress;
 423 }
 424
 425 /// WriteFragmentData - Write the \arg F data to the output file.
 426 static void WriteFragmentData(const MCAssembler &Asm, const MCAsmLayout &Layout,
 427                               const MCFragment &F, MCObjectWriter *OW) {
 428   uint64_t Start = OW->getStream().tell();
 429   (void) Start;
 430
 431   ++stats::EmittedFragments;
 432
 433   // FIXME: Embed in fragments instead?
 434   uint64_t FragmentSize = Layout.getFragmentEffectiveSize(&F);
 435   switch (F.getKind()) {
 436   case MCFragment::FT_Align: {
 437     MCAlignFragment &AF = cast<MCAlignFragment>(F);
 438     uint64_t Count = FragmentSize / AF.getValueSize();
 439
 440     assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
 441
 442     // FIXME: This error shouldn't actually occur (the front end should emit
 443     // multiple .align directives to enforce the semantics it wants), but is
 444     // severe enough that we want to report it. How to handle this?
 445     if (Count * AF.getValueSize() != FragmentSize)
 446       report_fatal_error("undefined .align directive, value size '" +
 447                         Twine(AF.getValueSize()) +
 448                         "' is not a divisor of padding size '" +
 449                         Twine(FragmentSize) + "'");
 450
 451     // See if we are aligning with nops, and if so do that first to try to fill
 452     // the Count bytes.  Then if that did not fill any bytes or there are any
 453     // bytes left to fill use the the Value and ValueSize to fill the rest.
 454     // If we are aligning with nops, ask that target to emit the right data.
 455     if (AF.hasEmitNops()) {
 456       if (!Asm.getBackend().WriteNopData(Count, OW))
 457         report_fatal_error("unable to write nop sequence of " +
 458                           Twine(Count) + " bytes");
 459       break;
 460     }
 461
 462     // Otherwise, write out in multiples of the value size.
 463     for (uint64_t i = 0; i != Count; ++i) {
 464       switch (AF.getValueSize()) {
 465       default:
 466         assert(0 && "Invalid size!");
 467       case 1: OW->Write8 (uint8_t (AF.getValue())); break;
 468       case 2: OW->Write16(uint16_t(AF.getValue())); break;
 469       case 4: OW->Write32(uint32_t(AF.getValue())); break;
 470       case 8: OW->Write64(uint64_t(AF.getValue())); break;
 471       }
 472     }
 473     break;
 474   }
 475
 476   case MCFragment::FT_Data: {
 477     MCDataFragment &DF = cast<MCDataFragment>(F);
 478     assert(FragmentSize == DF.getContents().size() && "Invalid size!");
 479     OW->WriteBytes(DF.getContents().str());
 480     break;
 481   }
 482
 483   case MCFragment::FT_Fill: {
 484     MCFillFragment &FF = cast<MCFillFragment>(F);
 485
 486     assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
 487
 488     for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
 489       switch (FF.getValueSize()) {
 490       default:
 491         assert(0 && "Invalid size!");
 492       case 1: OW->Write8 (uint8_t (FF.getValue())); break;
 493       case 2: OW->Write16(uint16_t(FF.getValue())); break;
 494       case 4: OW->Write32(uint32_t(FF.getValue())); break;
 495       case 8: OW->Write64(uint64_t(FF.getValue())); break;
 496       }
 497     }
 498     break;
 499   }
 500
 501   case MCFragment::FT_Inst:
 502     llvm_unreachable("unexpected inst fragment after lowering");
 503     break;
 504
 505   case MCFragment::FT_LEB: {
 506     MCLEBFragment &LF = cast<MCLEBFragment>(F);
 507
 508     // FIXME: It is probably better if we don't call EvaluateAsAbsolute in
 509     // here.
 510     int64_t Value;
 511     LF.getValue().EvaluateAsAbsolute(Value, &Layout);
 512     SmallString<32> Tmp;
 513     raw_svector_ostream OSE(Tmp);
 514     if (LF.isSigned())
 515       MCObjectWriter::EncodeSLEB128(Value, OSE);
 516     else
 517       MCObjectWriter::EncodeULEB128(Value, OSE);
 518     OW->WriteBytes(OSE.str());
 519     break;
 520   }
 521
 522   case MCFragment::FT_Org: {
 523     MCOrgFragment &OF = cast<MCOrgFragment>(F);
 524
 525     for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
 526       OW->Write8(uint8_t(OF.getValue()));
 527
 528     break;
 529   }
 530
 531   case MCFragment::FT_Dwarf: {
 532     const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
 533
 534     // The AddrDelta is really unsigned and it can only increase.
 535     int64_t AddrDelta;
 536     OF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, &Layout);
 537
 538     int64_t LineDelta;
 539     LineDelta = OF.getLineDelta();
 540
 541     MCDwarfLineAddr::Write(OW, LineDelta, (uint64_t)AddrDelta);
 542     break;
 543   }
 544   }
 545
 546   assert(OW->getStream().tell() - Start == FragmentSize);
 547 }
 548
 549 void MCAssembler::WriteSectionData(const MCSectionData *SD,
 550                                    const MCAsmLayout &Layout,
 551                                    MCObjectWriter *OW) const {
 552   // Ignore virtual sections.
 553   if (getBackend().isVirtualSection(SD->getSection())) {
 554     assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
 555
 556     // Check that contents are only things legal inside a virtual section.
 557     for (MCSectionData::const_iterator it = SD->begin(),
 558            ie = SD->end(); it != ie; ++it) {
 559       switch (it->getKind()) {
 560       default:
 561         assert(0 && "Invalid fragment in virtual section!");
 562       case MCFragment::FT_Data: {
 563         // Check that we aren't trying to write a non-zero contents (or fixups)
 564         // into a virtual section. This is to support clients which use standard
 565         // directives to fill the contents of virtual sections.
 566         MCDataFragment &DF = cast<MCDataFragment>(*it);
 567         assert(DF.fixup_begin() == DF.fixup_end() &&
 568                "Cannot have fixups in virtual section!");
 569         for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
 570           assert(DF.getContents()[i] == 0 &&
 571                  "Invalid data value for virtual section!");
 572         break;
 573       }
 574       case MCFragment::FT_Align:
 575         // Check that we aren't trying to write a non-zero value into a virtual
 576         // section.
 577         assert((!cast<MCAlignFragment>(it)->getValueSize() ||
 578                 !cast<MCAlignFragment>(it)->getValue()) &&
 579                "Invalid align in virtual section!");
 580         break;
 581       case MCFragment::FT_Fill:
 582         assert(!cast<MCFillFragment>(it)->getValueSize() &&
 583                "Invalid fill in virtual section!");
 584         break;
 585       }
 586     }
 587
 588     return;
 589   }
 590
 591   uint64_t Start = OW->getStream().tell();
 592   (void) Start;
 593
 594   for (MCSectionData::const_iterator it = SD->begin(),
 595          ie = SD->end(); it != ie; ++it)
 596     WriteFragmentData(*this, Layout, *it, OW);
 597
 598   assert(OW->getStream().tell() - Start == Layout.getSectionFileSize(SD));
 599 }
 600
 601 void MCAssembler::AddSectionToTheEnd(const MCObjectWriter &Writer,
 602                                      MCSectionData &SD, MCAsmLayout &Layout) {
 603   // Create dummy fragments and assign section ordinals.
 604   unsigned SectionIndex = 0;
 605   for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it)
 606     SectionIndex++;
 607
 608   SD.setOrdinal(SectionIndex);
 609
 610   // Assign layout order indices to sections and fragments.
 611   unsigned FragmentIndex = 0;
 612   unsigned i = 0;
 613   for (unsigned e = Layout.getSectionOrder().size(); i != e; ++i) {
 614     MCSectionData *SD = Layout.getSectionOrder()[i];
 615
 616     for (MCSectionData::iterator it2 = SD->begin(),
 617            ie2 = SD->end(); it2 != ie2; ++it2)
 618       FragmentIndex++;
 619   }
 620
 621   SD.setLayoutOrder(i);
 622   for (MCSectionData::iterator it2 = SD.begin(),
 623          ie2 = SD.end(); it2 != ie2; ++it2) {
 624     it2->setLayoutOrder(FragmentIndex++);
 625   }
 626   Layout.getSectionOrder().push_back(&SD);
 627
 628   Layout.LayoutSection(&SD);
 629
 630   // Layout until everything fits.
 631   while (LayoutOnce(Writer, Layout))
 632     continue;
 633
 634 }
 635
 636 void MCAssembler::Finish(MCObjectWriter *Writer) {
 637   DEBUG_WITH_TYPE("mc-dump", {
 638       llvm::errs() << "assembler backend - pre-layout\n--\n";
 639       dump(); });
 640
 641   // Create the layout object.
 642   MCAsmLayout Layout(*this);
 643
 644   // Insert additional align fragments for concrete sections to explicitly pad
 645   // the previous section to match their alignment requirements. This is for
 646   // 'gas' compatibility, it shouldn't strictly be necessary.
 647   if (PadSectionToAlignment) {
 648     for (unsigned i = 1, e = Layout.getSectionOrder().size(); i < e; ++i) {
 649       MCSectionData *SD = Layout.getSectionOrder()[i];
 650
 651       // Ignore sections without alignment requirements.
 652       unsigned Align = SD->getAlignment();
 653       if (Align <= 1)
 654         continue;
 655
 656       // Ignore virtual sections, they don't cause file size modifications.
 657       if (getBackend().isVirtualSection(SD->getSection()))
 658         continue;
 659
 660       // Otherwise, create a new align fragment at the end of the previous
 661       // section.
 662       MCAlignFragment *AF = new MCAlignFragment(Align, 0, 1, Align,
 663                                                 Layout.getSectionOrder()[i - 1]);
 664       AF->setOnlyAlignAddress(true);
 665     }
 666   }
 667
 668   // Create dummy fragments and assign section ordinals.
 669   unsigned SectionIndex = 0;
 670   for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
 671     // Create dummy fragments to eliminate any empty sections, this simplifies
 672     // layout.
 673     if (it->getFragmentList().empty())
 674       new MCDataFragment(it);
 675
 676     it->setOrdinal(SectionIndex++);
 677   }
 678
 679   // Assign layout order indices to sections and fragments.
 680   unsigned FragmentIndex = 0;
 681   for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
 682     MCSectionData *SD = Layout.getSectionOrder()[i];
 683     SD->setLayoutOrder(i);
 684
 685     for (MCSectionData::iterator it2 = SD->begin(),
 686            ie2 = SD->end(); it2 != ie2; ++it2)
 687       it2->setLayoutOrder(FragmentIndex++);
 688   }
 689
 690   llvm::OwningPtr<MCObjectWriter> OwnWriter(0);
 691   if (Writer == 0) {
 692     //no custom Writer_ : create the default one life-managed by OwningPtr
 693     OwnWriter.reset(getBackend().createObjectWriter(OS));
 694     Writer = OwnWriter.get();
 695     if (!Writer)
 696       report_fatal_error("unable to create object writer!");
 697   }
 698
 699   // Layout until everything fits.
 700   while (LayoutOnce(*Writer, Layout))
 701     continue;
 702
 703   DEBUG_WITH_TYPE("mc-dump", {
 704       llvm::errs() << "assembler backend - post-relaxation\n--\n";
 705       dump(); });
 706
 707   // Finalize the layout, including fragment lowering.
 708   FinishLayout(Layout);
 709
 710   DEBUG_WITH_TYPE("mc-dump", {
 711       llvm::errs() << "assembler backend - final-layout\n--\n";
 712       dump(); });
 713
 714   uint64_t StartOffset = OS.tell();
 715
 716   // Allow the object writer a chance to perform post-layout binding (for
 717   // example, to set the index fields in the symbol data).
 718   Writer->ExecutePostLayoutBinding(*this);
 719
 720   // Evaluate and apply the fixups, generating relocation entries as necessary.
 721   for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
 722     for (MCSectionData::iterator it2 = it->begin(),
 723            ie2 = it->end(); it2 != ie2; ++it2) {
 724       MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
 725       if (!DF)
 726         continue;
 727
 728       for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
 729              ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
 730         MCFixup &Fixup = *it3;
 731
 732         // Evaluate the fixup.
 733         MCValue Target;
 734         uint64_t FixedValue;
 735         if (!EvaluateFixup(*Writer, Layout, Fixup, DF, Target, FixedValue)) {
 736           // The fixup was unresolved, we need a relocation. Inform the object
 737           // writer of the relocation, and give it an opportunity to adjust the
 738           // fixup value if need be.
 739           Writer->RecordRelocation(*this, Layout, DF, Fixup, Target,FixedValue);
 740         }
 741
 742         getBackend().ApplyFixup(Fixup, *DF, FixedValue);
 743       }
 744     }
 745   }
 746
 747   // Write the object file.
 748   Writer->WriteObject(*this, Layout);
 749
 750   stats::ObjectBytes += OS.tell() - StartOffset;
 751 }
 752
 753 bool MCAssembler::FixupNeedsRelaxation(const MCObjectWriter &Writer,
 754                                        const MCFixup &Fixup,
 755                                        const MCFragment *DF,
 756                                        const MCAsmLayout &Layout) const {
 757   if (getRelaxAll())
 758     return true;
 759
 760   // If we cannot resolve the fixup value, it requires relaxation.
 761   MCValue Target;
 762   uint64_t Value;
 763   if (!EvaluateFixup(Writer, Layout, Fixup, DF, Target, Value))
 764     return true;
 765
 766   // Otherwise, relax if the value is too big for a (signed) i8.
 767   //
 768   // FIXME: This is target dependent!
 769   return int64_t(Value) != int64_t(int8_t(Value));
 770 }
 771
 772 bool MCAssembler::FragmentNeedsRelaxation(const MCObjectWriter &Writer,
 773                                           const MCInstFragment *IF,
 774                                           const MCAsmLayout &Layout) const {
 775   // If this inst doesn't ever need relaxation, ignore it. This occurs when we
 776   // are intentionally pushing out inst fragments, or because we relaxed a
 777   // previous instruction to one that doesn't need relaxation.
 778   if (!getBackend().MayNeedRelaxation(IF->getInst()))
 779     return false;
 780
 781   for (MCInstFragment::const_fixup_iterator it = IF->fixup_begin(),
 782          ie = IF->fixup_end(); it != ie; ++it)
 783     if (FixupNeedsRelaxation(Writer, *it, IF, Layout))
 784       return true;
 785
 786   return false;
 787 }
 788
 789 bool MCAssembler::RelaxInstruction(const MCObjectWriter &Writer,
 790                                    MCAsmLayout &Layout,
 791                                    MCInstFragment &IF) {
 792   if (!FragmentNeedsRelaxation(Writer, &IF, Layout))
 793     return false;
 794
 795   ++stats::RelaxedInstructions;
 796
 797   // FIXME-PERF: We could immediately lower out instructions if we can tell
 798   // they are fully resolved, to avoid retesting on later passes.
 799
 800   // Relax the fragment.
 801
 802   MCInst Relaxed;
 803   getBackend().RelaxInstruction(IF.getInst(), Relaxed);
 804
 805   // Encode the new instruction.
 806   //
 807   // FIXME-PERF: If it matters, we could let the target do this. It can
 808   // probably do so more efficiently in many cases.
 809   SmallVector<MCFixup, 4> Fixups;
 810   SmallString<256> Code;
 811   raw_svector_ostream VecOS(Code);
 812   getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups);
 813   VecOS.flush();
 814
 815   // Update the instruction fragment.
 816   int SlideAmount = Code.size() - IF.getInstSize();
 817   IF.setInst(Relaxed);
 818   IF.getCode() = Code;
 819   IF.getFixups().clear();
 820   // FIXME: Eliminate copy.
 821   for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
 822     IF.getFixups().push_back(Fixups[i]);
 823
 824   // Update the layout, and remember that we relaxed.
 825   Layout.UpdateForSlide(&IF, SlideAmount);
 826   return true;
 827 }
 828
 829 bool MCAssembler::RelaxOrg(const MCObjectWriter &Writer,
 830                            MCAsmLayout &Layout,
 831                            MCOrgFragment &OF) {
 832   int64_t TargetLocation;
 833   if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, &Layout))
 834     report_fatal_error("expected assembly-time absolute expression");
 835
 836   // FIXME: We need a way to communicate this error.
 837   uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
 838   int64_t Offset = TargetLocation - FragmentOffset;
 839   if (Offset < 0 || Offset >= 0x40000000)
 840     report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
 841                        "' (at offset '" + Twine(FragmentOffset) + "')");
 842
 843   unsigned OldSize = OF.getSize();
 844   OF.setSize(Offset);
 845   return OldSize != OF.getSize();
 846 }
 847
 848 bool MCAssembler::RelaxLEB(const MCObjectWriter &Writer,
 849                            MCAsmLayout &Layout,
 850                            MCLEBFragment &LF) {
 851   int64_t Value;
 852   LF.getValue().EvaluateAsAbsolute(Value, &Layout);
 853   SmallString<32> Tmp;
 854   raw_svector_ostream OSE(Tmp);
 855   if (LF.isSigned())
 856     MCObjectWriter::EncodeSLEB128(Value, OSE);
 857   else
 858     MCObjectWriter::EncodeULEB128(Value, OSE);
 859   uint64_t OldSize = LF.getSize();
 860   LF.setSize(OSE.GetNumBytesInBuffer());
 861   return OldSize != LF.getSize();
 862 }
 863
 864 bool MCAssembler::LayoutOnce(const MCObjectWriter &Writer,
 865                              MCAsmLayout &Layout) {
 866   ++stats::RelaxationSteps;
 867
 868   // Layout the sections in order.
 869   Layout.LayoutFile();
 870
 871   // Scan for fragments that need relaxation.
 872   bool WasRelaxed = false;
 873   for (iterator it = begin(), ie = end(); it != ie; ++it) {
 874     MCSectionData &SD = *it;
 875
 876     for (MCSectionData::iterator it2 = SD.begin(),
 877            ie2 = SD.end(); it2 != ie2; ++it2) {
 878       // Check if this is an fragment that needs relaxation.
 879       switch(it2->getKind()) {
 880       default:
 881         break;
 882       case MCFragment::FT_Inst:
 883         WasRelaxed |= RelaxInstruction(Writer, Layout,
 884                                        *cast<MCInstFragment>(it2));
 885         break;
 886       case MCFragment::FT_Org:
 887         WasRelaxed |= RelaxOrg(Writer, Layout, *cast<MCOrgFragment>(it2));
 888         break;
 889       case MCFragment::FT_LEB:
 890         WasRelaxed |= RelaxLEB(Writer, Layout, *cast<MCLEBFragment>(it2));
 891         break;
 892       }
 893     }
 894   }
 895
 896   return WasRelaxed;
 897 }
 898
 899 void MCAssembler::FinishLayout(MCAsmLayout &Layout) {
 900   // Lower out any instruction fragments, to simplify the fixup application and
 901   // output.
 902   //
 903   // FIXME-PERF: We don't have to do this, but the assumption is that it is
 904   // cheap (we will mostly end up eliminating fragments and appending on to data
 905   // fragments), so the extra complexity downstream isn't worth it. Evaluate
 906   // this assumption.
 907   for (iterator it = begin(), ie = end(); it != ie; ++it) {
 908     MCSectionData &SD = *it;
 909
 910     for (MCSectionData::iterator it2 = SD.begin(),
 911            ie2 = SD.end(); it2 != ie2; ++it2) {
 912       MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
 913       if (!IF)
 914         continue;
 915
 916       // Create a new data fragment for the instruction.
 917       //
 918       // FIXME-PERF: Reuse previous data fragment if possible.
 919       MCDataFragment *DF = new MCDataFragment();
 920       SD.getFragmentList().insert(it2, DF);
 921
 922       // Update the data fragments layout data.
 923       DF->setParent(IF->getParent());
 924       DF->setAtom(IF->getAtom());
 925       DF->setLayoutOrder(IF->getLayoutOrder());
 926       Layout.FragmentReplaced(IF, DF);
 927
 928       // Copy in the data and the fixups.
 929       DF->getContents().append(IF->getCode().begin(), IF->getCode().end());
 930       for (unsigned i = 0, e = IF->getFixups().size(); i != e; ++i)
 931         DF->getFixups().push_back(IF->getFixups()[i]);
 932
 933       // Delete the instruction fragment and update the iterator.
 934       SD.getFragmentList().erase(IF);
 935       it2 = DF;
 936     }
 937   }
 938 }
 939
 940 // Debugging methods
 941
 942 namespace llvm {
 943
 944 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
 945   OS << "<MCFixup" << " Offset:" << AF.getOffset()
 946      << " Value:" << *AF.getValue()
 947      << " Kind:" << AF.getKind() << ">";
 948   return OS;
 949 }
 950
 951 }
 952
 953 void MCFragment::dump() {
 954   raw_ostream &OS = llvm::errs();
 955
 956   OS << "<";
 957   switch (getKind()) {
 958   case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
 959   case MCFragment::FT_Data:  OS << "MCDataFragment"; break;
 960   case MCFragment::FT_Fill:  OS << "MCFillFragment"; break;
 961   case MCFragment::FT_Inst:  OS << "MCInstFragment"; break;
 962   case MCFragment::FT_Org:   OS << "MCOrgFragment"; break;
 963   case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
 964   case MCFragment::FT_LEB:   OS << "MCLEBFragment"; break;
 965   }
 966
 967   OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
 968      << " Offset:" << Offset << " EffectiveSize:" << EffectiveSize << ">";
 969
 970   switch (getKind()) {
 971   case MCFragment::FT_Align: {
 972     const MCAlignFragment *AF = cast<MCAlignFragment>(this);
 973     if (AF->hasEmitNops())
 974       OS << " (emit nops)";
 975     if (AF->hasOnlyAlignAddress())
 976       OS << " (only align section)";
 977     OS << "\n       ";
 978     OS << " Alignment:" << AF->getAlignment()
 979        << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
 980        << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
 981     break;
 982   }
 983   case MCFragment::FT_Data:  {
 984     const MCDataFragment *DF = cast<MCDataFragment>(this);
 985     OS << "\n       ";
 986     OS << " Contents:[";
 987     const SmallVectorImpl<char> &Contents = DF->getContents();
 988     for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
 989       if (i) OS << ",";
 990       OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
 991     }
 992     OS << "] (" << Contents.size() << " bytes)";
 993
 994     if (!DF->getFixups().empty()) {
 995       OS << ",\n       ";
 996       OS << " Fixups:[";
 997       for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
 998              ie = DF->fixup_end(); it != ie; ++it) {
 999         if (it != DF->fixup_begin()) OS << ",\n                ";
1000         OS << *it;
1001       }
1002       OS << "]";
1003     }
1004     break;
1005   }
1006   case MCFragment::FT_Fill:  {
1007     const MCFillFragment *FF = cast<MCFillFragment>(this);
1008     OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
1009        << " Size:" << FF->getSize();
1010     break;
1011   }
1012   case MCFragment::FT_Inst:  {
1013     const MCInstFragment *IF = cast<MCInstFragment>(this);
1014     OS << "\n       ";
1015     OS << " Inst:";
1016     IF->getInst().dump_pretty(OS);
1017     break;
1018   }
1019   case MCFragment::FT_Org:  {
1020     const MCOrgFragment *OF = cast<MCOrgFragment>(this);
1021     OS << "\n       ";
1022     OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
1023     break;
1024   }
1025   case MCFragment::FT_Dwarf:  {
1026     const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
1027     OS << "\n       ";
1028     OS << " AddrDelta:" << OF->getAddrDelta()
1029        << " LineDelta:" << OF->getLineDelta();
1030     break;
1031   }
1032   case MCFragment::FT_LEB: {
1033     const MCLEBFragment *LF = cast<MCLEBFragment>(this);
1034     OS << "\n       ";
1035     OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
1036     break;
1037   }
1038   }
1039   OS << ">";
1040 }
1041
1042 void MCSectionData::dump() {
1043   raw_ostream &OS = llvm::errs();
1044
1045   OS << "<MCSectionData";
1046   OS << " Alignment:" << getAlignment() << " Address:" << Address
1047      << " Fragments:[\n      ";
1048   for (iterator it = begin(), ie = end(); it != ie; ++it) {
1049     if (it != begin()) OS << ",\n      ";
1050     it->dump();
1051   }
1052   OS << "]>";
1053 }
1054
1055 void MCSymbolData::dump() {
1056   raw_ostream &OS = llvm::errs();
1057
1058   OS << "<MCSymbolData Symbol:" << getSymbol()
1059      << " Fragment:" << getFragment() << " Offset:" << getOffset()
1060      << " Flags:" << getFlags() << " Index:" << getIndex();
1061   if (isCommon())
1062     OS << " (common, size:" << getCommonSize()
1063        << " align: " << getCommonAlignment() << ")";
1064   if (isExternal())
1065     OS << " (external)";
1066   if (isPrivateExtern())
1067     OS << " (private extern)";
1068   OS << ">";
1069 }
1070
1071 void MCAssembler::dump() {
1072   raw_ostream &OS = llvm::errs();
1073
1074   OS << "<MCAssembler\n";
1075   OS << "  Sections:[\n    ";
1076   for (iterator it = begin(), ie = end(); it != ie; ++it) {
1077     if (it != begin()) OS << ",\n    ";
1078     it->dump();
1079   }
1080   OS << "],\n";
1081   OS << "  Symbols:[";
1082
1083   for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1084     if (it != symbol_begin()) OS << ",\n           ";
1085     it->dump();
1086   }
1087   OS << "]>\n";
1088 }