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
32using namespace llvm;
33
34namespace {
35namespace stats {
36STATISTIC(EmittedFragments, "Number of emitted assembler fragments");
37STATISTIC(evaluateFixup, "Number of evaluated fixups");
38STATISTIC(FragmentLayouts, "Number of fragment layouts");
39STATISTIC(ObjectBytes, "Number of emitted object file bytes");
40STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
41STATISTIC(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
52MCAsmLayout::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
64bool 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
73void 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
83void 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
99uint64_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
105uint64_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
137uint64_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
143uint64_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
154MCFragment::MCFragment() : Kind(FragmentType(~0)) {
155}
156
157MCFragment::~MCFragment() {
158}
159
160MCFragment::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
170MCSectionData::MCSectionData() : Section(0) {}
171
172MCSectionData::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
184MCSymbolData::MCSymbolData() : Symbol(0) {}
185
186MCSymbolData::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
199MCAssembler::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
207MCAssembler::~MCAssembler() {
208}
209
210void MCAssembler::setWriter(MCObjectWriter &ObjectWriter) {
211  delete Writer;
212  Writer = &ObjectWriter;
213}
214
215bool 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
228const 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
247bool 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
317uint64_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
369void 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.
391static 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
501void 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
553uint64_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
568void 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
652bool 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
667bool 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
683bool 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
719bool 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
736bool 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
753bool 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
768bool 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
806bool 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
819void 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
828namespace llvm {
829
830raw_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
840void 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
934void 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
946void 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
962void 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
983void MCDataFragment::anchor() { }
984void MCInstFragment::anchor() { }
985void MCAlignFragment::anchor() { }
986void MCFillFragment::anchor() { }
987void MCOrgFragment::anchor() { }
988void MCLEBFragment::anchor() { }
989void MCDwarfLineAddrFragment::anchor() { }
990void MCDwarfCallFrameFragment::anchor() { }
991