MCAssembler.cpp revision f1d0f7781e766df878bec4e7977fa3204374f394 
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
31using namespace llvm;
32
33namespace {
34namespace stats {
35STATISTIC(EmittedFragments, "Number of emitted assembler fragments");
36STATISTIC(evaluateFixup, "Number of evaluated fixups");
37STATISTIC(FragmentLayouts, "Number of fragment layouts");
38STATISTIC(ObjectBytes, "Number of emitted object file bytes");
39STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
40STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
41}
42}
43
44// FIXME FIXME FIXME: There are number of places in this file where we convert
45// what is a 64-bit assembler value used for computation into a value in the
46// object file, which may truncate it. We should detect that truncation where
47// invalid and report errors back.
48
49/* *** */
50
51MCAsmLayout::MCAsmLayout(MCAssembler &Asm)
52  : Assembler(Asm), LastValidFragment()
53 {
54  // Compute the section layout order. Virtual sections must go last.
55  for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
56    if (!it->getSection().isVirtualSection())
57      SectionOrder.push_back(&*it);
58  for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
59    if (it->getSection().isVirtualSection())
60      SectionOrder.push_back(&*it);
61}
62
63bool MCAsmLayout::isFragmentUpToDate(const MCFragment *F) const {
64  const MCSectionData &SD = *F->getParent();
65  const MCFragment *LastValid = LastValidFragment.lookup(&SD);
66  if (!LastValid)
67    return false;
68  assert(LastValid->getParent() == F->getParent());
69  return F->getLayoutOrder() <= LastValid->getLayoutOrder();
70}
71
72void MCAsmLayout::Invalidate(MCFragment *F) {
73  // If this fragment wasn't already up-to-date, we don't need to do anything.
74  if (!isFragmentUpToDate(F))
75    return;
76
77  // Otherwise, reset the last valid fragment to this fragment.
78  const MCSectionData &SD = *F->getParent();
79  LastValidFragment[&SD] = F;
80}
81
82void MCAsmLayout::EnsureValid(const MCFragment *F) const {
83  MCSectionData &SD = *F->getParent();
84
85  MCFragment *Cur = LastValidFragment[&SD];
86  if (!Cur)
87    Cur = &*SD.begin();
88  else
89    Cur = Cur->getNextNode();
90
91  // Advance the layout position until the fragment is up-to-date.
92  while (!isFragmentUpToDate(F)) {
93    const_cast<MCAsmLayout*>(this)->LayoutFragment(Cur);
94    Cur = Cur->getNextNode();
95  }
96}
97
98uint64_t MCAsmLayout::getFragmentOffset(const MCFragment *F) const {
99  EnsureValid(F);
100  assert(F->Offset != ~UINT64_C(0) && "Address not set!");
101  return F->Offset;
102}
103
104uint64_t MCAsmLayout::getSymbolOffset(const MCSymbolData *SD) const {
105  const MCSymbol &S = SD->getSymbol();
106
107  // If this is a variable, then recursively evaluate now.
108  if (S.isVariable()) {
109    MCValue Target;
110    if (!S.getVariableValue()->EvaluateAsRelocatable(Target, *this))
111      report_fatal_error("unable to evaluate offset for variable '" +
112                         S.getName() + "'");
113
114    // Verify that any used symbols are defined.
115    if (Target.getSymA() && Target.getSymA()->getSymbol().isUndefined())
116      report_fatal_error("unable to evaluate offset to undefined symbol '" +
117                         Target.getSymA()->getSymbol().getName() + "'");
118    if (Target.getSymB() && Target.getSymB()->getSymbol().isUndefined())
119      report_fatal_error("unable to evaluate offset to undefined symbol '" +
120                         Target.getSymB()->getSymbol().getName() + "'");
121
122    uint64_t Offset = Target.getConstant();
123    if (Target.getSymA())
124      Offset += getSymbolOffset(&Assembler.getSymbolData(
125                                  Target.getSymA()->getSymbol()));
126    if (Target.getSymB())
127      Offset -= getSymbolOffset(&Assembler.getSymbolData(
128                                  Target.getSymB()->getSymbol()));
129    return Offset;
130  }
131
132  assert(SD->getFragment() && "Invalid getOffset() on undefined symbol!");
133  return getFragmentOffset(SD->getFragment()) + SD->getOffset();
134}
135
136uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
137  // The size is the last fragment's end offset.
138  const MCFragment &F = SD->getFragmentList().back();
139  return getFragmentOffset(&F) + getAssembler().computeFragmentSize(*this, F);
140}
141
142uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
143  // Virtual sections have no file size.
144  if (SD->getSection().isVirtualSection())
145    return 0;
146
147  // Otherwise, the file size is the same as the address space size.
148  return getSectionAddressSize(SD);
149}
150
151/* *** */
152
153MCFragment::MCFragment() : Kind(FragmentType(~0)) {
154}
155
156MCFragment::~MCFragment() {
157}
158
159MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
160  : Kind(_Kind), Parent(_Parent), Atom(0), Offset(~UINT64_C(0))
161{
162  if (Parent)
163    Parent->getFragmentList().push_back(this);
164}
165
166/* *** */
167
168MCSectionData::MCSectionData() : Section(0) {}
169
170MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
171  : Section(&_Section),
172    Ordinal(~UINT32_C(0)),
173    Alignment(1),
174    HasInstructions(false)
175{
176  if (A)
177    A->getSectionList().push_back(this);
178}
179
180/* *** */
181
182MCSymbolData::MCSymbolData() : Symbol(0) {}
183
184MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
185                           uint64_t _Offset, MCAssembler *A)
186  : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
187    IsExternal(false), IsPrivateExtern(false),
188    CommonSize(0), SymbolSize(0), CommonAlign(0),
189    Flags(0), Index(0)
190{
191  if (A)
192    A->getSymbolList().push_back(this);
193}
194
195/* *** */
196
197MCAssembler::MCAssembler(MCContext &Context_, MCAsmBackend &Backend_,
198                         MCCodeEmitter &Emitter_, MCObjectWriter &Writer_,
199                         raw_ostream &OS_)
200  : Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(Writer_),
201    OS(OS_), RelaxAll(false), NoExecStack(false), SubsectionsViaSymbols(false)
202{
203}
204
205MCAssembler::~MCAssembler() {
206}
207
208bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
209  // Non-temporary labels should always be visible to the linker.
210  if (!Symbol.isTemporary())
211    return true;
212
213  // Absolute temporary labels are never visible.
214  if (!Symbol.isInSection())
215    return false;
216
217  // Otherwise, check if the section requires symbols even for temporary labels.
218  return getBackend().doesSectionRequireSymbols(Symbol.getSection());
219}
220
221const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
222  // Linker visible symbols define atoms.
223  if (isSymbolLinkerVisible(SD->getSymbol()))
224    return SD;
225
226  // Absolute and undefined symbols have no defining atom.
227  if (!SD->getFragment())
228    return 0;
229
230  // Non-linker visible symbols in sections which can't be atomized have no
231  // defining atom.
232  if (!getBackend().isSectionAtomizable(
233        SD->getFragment()->getParent()->getSection()))
234    return 0;
235
236  // Otherwise, return the atom for the containing fragment.
237  return SD->getFragment()->getAtom();
238}
239
240bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
241                                const MCFixup &Fixup, const MCFragment *DF,
242                                MCValue &Target, uint64_t &Value) const {
243  ++stats::evaluateFixup;
244
245  if (!Fixup.getValue()->EvaluateAsRelocatable(Target, Layout))
246    getContext().FatalError(Fixup.getLoc(), "expected relocatable expression");
247
248  bool IsPCRel = Backend.getFixupKindInfo(
249    Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
250
251  bool IsResolved;
252  if (IsPCRel) {
253    if (Target.getSymB()) {
254      IsResolved = false;
255    } else if (!Target.getSymA()) {
256      IsResolved = false;
257    } else {
258      const MCSymbolRefExpr *A = Target.getSymA();
259      const MCSymbol &SA = A->getSymbol();
260      if (A->getKind() != MCSymbolRefExpr::VK_None ||
261          SA.AliasedSymbol().isUndefined()) {
262        IsResolved = false;
263      } else {
264        const MCSymbolData &DataA = getSymbolData(SA);
265        IsResolved =
266          getWriter().IsSymbolRefDifferenceFullyResolvedImpl(*this, DataA,
267                                                             *DF, false, true);
268      }
269    }
270  } else {
271    IsResolved = Target.isAbsolute();
272  }
273
274  Value = Target.getConstant();
275
276  if (const MCSymbolRefExpr *A = Target.getSymA()) {
277    const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
278    if (Sym.isDefined())
279      Value += Layout.getSymbolOffset(&getSymbolData(Sym));
280  }
281  if (const MCSymbolRefExpr *B = Target.getSymB()) {
282    const MCSymbol &Sym = B->getSymbol().AliasedSymbol();
283    if (Sym.isDefined())
284      Value -= Layout.getSymbolOffset(&getSymbolData(Sym));
285  }
286
287
288  bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
289                         MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
290  assert((ShouldAlignPC ? IsPCRel : true) &&
291    "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
292
293  if (IsPCRel) {
294    uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
295
296    // A number of ARM fixups in Thumb mode require that the effective PC
297    // address be determined as the 32-bit aligned version of the actual offset.
298    if (ShouldAlignPC) Offset &= ~0x3;
299    Value -= Offset;
300  }
301
302  // Let the backend adjust the fixup value if necessary, including whether
303  // we need a relocation.
304  Backend.processFixupValue(*this, Layout, Fixup, DF, Target, Value,
305                            IsResolved);
306
307  return IsResolved;
308}
309
310uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
311                                          const MCFragment &F) const {
312  switch (F.getKind()) {
313  case MCFragment::FT_Data:
314    return cast<MCDataFragment>(F).getContents().size();
315  case MCFragment::FT_Fill:
316    return cast<MCFillFragment>(F).getSize();
317  case MCFragment::FT_Inst:
318    return cast<MCInstFragment>(F).getInstSize();
319
320  case MCFragment::FT_LEB:
321    return cast<MCLEBFragment>(F).getContents().size();
322
323  case MCFragment::FT_Align: {
324    const MCAlignFragment &AF = cast<MCAlignFragment>(F);
325    unsigned Offset = Layout.getFragmentOffset(&AF);
326    unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
327    if (Size > AF.getMaxBytesToEmit())
328      return 0;
329    return Size;
330  }
331
332  case MCFragment::FT_Org: {
333    MCOrgFragment &OF = cast<MCOrgFragment>(F);
334    int64_t TargetLocation;
335    if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, Layout))
336      report_fatal_error("expected assembly-time absolute expression");
337
338    // FIXME: We need a way to communicate this error.
339    uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
340    int64_t Size = TargetLocation - FragmentOffset;
341    if (Size < 0 || Size >= 0x40000000)
342      report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
343                         "' (at offset '" + Twine(FragmentOffset) + "')");
344    return Size;
345  }
346
347  case MCFragment::FT_Dwarf:
348    return cast<MCDwarfLineAddrFragment>(F).getContents().size();
349  case MCFragment::FT_DwarfFrame:
350    return cast<MCDwarfCallFrameFragment>(F).getContents().size();
351  }
352
353  llvm_unreachable("invalid fragment kind");
354}
355
356void MCAsmLayout::LayoutFragment(MCFragment *F) {
357  MCFragment *Prev = F->getPrevNode();
358
359  // We should never try to recompute something which is up-to-date.
360  assert(!isFragmentUpToDate(F) && "Attempt to recompute up-to-date fragment!");
361  // We should never try to compute the fragment layout if it's predecessor
362  // isn't up-to-date.
363  assert((!Prev || isFragmentUpToDate(Prev)) &&
364         "Attempt to compute fragment before it's predecessor!");
365
366  ++stats::FragmentLayouts;
367
368  // Compute fragment offset and size.
369  uint64_t Offset = 0;
370  if (Prev)
371    Offset += Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
372
373  F->Offset = Offset;
374  LastValidFragment[F->getParent()] = F;
375}
376
377/// WriteFragmentData - Write the \arg F data to the output file.
378static void WriteFragmentData(const MCAssembler &Asm, const MCAsmLayout &Layout,
379                              const MCFragment &F) {
380  MCObjectWriter *OW = &Asm.getWriter();
381  uint64_t Start = OW->getStream().tell();
382  (void) Start;
383
384  ++stats::EmittedFragments;
385
386  // FIXME: Embed in fragments instead?
387  uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
388  switch (F.getKind()) {
389  case MCFragment::FT_Align: {
390    MCAlignFragment &AF = cast<MCAlignFragment>(F);
391    uint64_t Count = FragmentSize / AF.getValueSize();
392
393    assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
394
395    // FIXME: This error shouldn't actually occur (the front end should emit
396    // multiple .align directives to enforce the semantics it wants), but is
397    // severe enough that we want to report it. How to handle this?
398    if (Count * AF.getValueSize() != FragmentSize)
399      report_fatal_error("undefined .align directive, value size '" +
400                        Twine(AF.getValueSize()) +
401                        "' is not a divisor of padding size '" +
402                        Twine(FragmentSize) + "'");
403
404    // See if we are aligning with nops, and if so do that first to try to fill
405    // the Count bytes.  Then if that did not fill any bytes or there are any
406    // bytes left to fill use the the Value and ValueSize to fill the rest.
407    // If we are aligning with nops, ask that target to emit the right data.
408    if (AF.hasEmitNops()) {
409      if (!Asm.getBackend().writeNopData(Count, OW))
410        report_fatal_error("unable to write nop sequence of " +
411                          Twine(Count) + " bytes");
412      break;
413    }
414
415    // Otherwise, write out in multiples of the value size.
416    for (uint64_t i = 0; i != Count; ++i) {
417      switch (AF.getValueSize()) {
418      default: llvm_unreachable("Invalid size!");
419      case 1: OW->Write8 (uint8_t (AF.getValue())); break;
420      case 2: OW->Write16(uint16_t(AF.getValue())); break;
421      case 4: OW->Write32(uint32_t(AF.getValue())); break;
422      case 8: OW->Write64(uint64_t(AF.getValue())); break;
423      }
424    }
425    break;
426  }
427
428  case MCFragment::FT_Data: {
429    MCDataFragment &DF = cast<MCDataFragment>(F);
430    assert(FragmentSize == DF.getContents().size() && "Invalid size!");
431    OW->WriteBytes(DF.getContents().str());
432    break;
433  }
434
435  case MCFragment::FT_Fill: {
436    MCFillFragment &FF = cast<MCFillFragment>(F);
437
438    assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
439
440    for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
441      switch (FF.getValueSize()) {
442      default: llvm_unreachable("Invalid size!");
443      case 1: OW->Write8 (uint8_t (FF.getValue())); break;
444      case 2: OW->Write16(uint16_t(FF.getValue())); break;
445      case 4: OW->Write32(uint32_t(FF.getValue())); break;
446      case 8: OW->Write64(uint64_t(FF.getValue())); break;
447      }
448    }
449    break;
450  }
451
452  case MCFragment::FT_Inst: {
453    MCInstFragment &IF = cast<MCInstFragment>(F);
454    OW->WriteBytes(StringRef(IF.getCode().begin(), IF.getCode().size()));
455    break;
456  }
457
458  case MCFragment::FT_LEB: {
459    MCLEBFragment &LF = cast<MCLEBFragment>(F);
460    OW->WriteBytes(LF.getContents().str());
461    break;
462  }
463
464  case MCFragment::FT_Org: {
465    MCOrgFragment &OF = cast<MCOrgFragment>(F);
466
467    for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
468      OW->Write8(uint8_t(OF.getValue()));
469
470    break;
471  }
472
473  case MCFragment::FT_Dwarf: {
474    const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
475    OW->WriteBytes(OF.getContents().str());
476    break;
477  }
478  case MCFragment::FT_DwarfFrame: {
479    const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
480    OW->WriteBytes(CF.getContents().str());
481    break;
482  }
483  }
484
485  assert(OW->getStream().tell() - Start == FragmentSize);
486}
487
488void MCAssembler::writeSectionData(const MCSectionData *SD,
489                                   const MCAsmLayout &Layout) const {
490  // Ignore virtual sections.
491  if (SD->getSection().isVirtualSection()) {
492    assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
493
494    // Check that contents are only things legal inside a virtual section.
495    for (MCSectionData::const_iterator it = SD->begin(),
496           ie = SD->end(); it != ie; ++it) {
497      switch (it->getKind()) {
498      default: llvm_unreachable("Invalid fragment in virtual section!");
499      case MCFragment::FT_Data: {
500        // Check that we aren't trying to write a non-zero contents (or fixups)
501        // into a virtual section. This is to support clients which use standard
502        // directives to fill the contents of virtual sections.
503        MCDataFragment &DF = cast<MCDataFragment>(*it);
504        assert(DF.fixup_begin() == DF.fixup_end() &&
505               "Cannot have fixups in virtual section!");
506        for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
507          assert(DF.getContents()[i] == 0 &&
508                 "Invalid data value for virtual section!");
509        break;
510      }
511      case MCFragment::FT_Align:
512        // Check that we aren't trying to write a non-zero value into a virtual
513        // section.
514        assert((!cast<MCAlignFragment>(it)->getValueSize() ||
515                !cast<MCAlignFragment>(it)->getValue()) &&
516               "Invalid align in virtual section!");
517        break;
518      case MCFragment::FT_Fill:
519        assert(!cast<MCFillFragment>(it)->getValueSize() &&
520               "Invalid fill in virtual section!");
521        break;
522      }
523    }
524
525    return;
526  }
527
528  uint64_t Start = getWriter().getStream().tell();
529  (void) Start;
530
531  for (MCSectionData::const_iterator it = SD->begin(),
532         ie = SD->end(); it != ie; ++it)
533    WriteFragmentData(*this, Layout, *it);
534
535  assert(getWriter().getStream().tell() - Start ==
536         Layout.getSectionAddressSize(SD));
537}
538
539
540uint64_t MCAssembler::handleFixup(const MCAsmLayout &Layout,
541                                  MCFragment &F,
542                                  const MCFixup &Fixup) {
543   // Evaluate the fixup.
544   MCValue Target;
545   uint64_t FixedValue;
546   if (!evaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
547     // The fixup was unresolved, we need a relocation. Inform the object
548     // writer of the relocation, and give it an opportunity to adjust the
549     // fixup value if need be.
550     getWriter().RecordRelocation(*this, Layout, &F, Fixup, Target, FixedValue);
551   }
552   return FixedValue;
553 }
554
555void MCAssembler::Finish() {
556  DEBUG_WITH_TYPE("mc-dump", {
557      llvm::errs() << "assembler backend - pre-layout\n--\n";
558      dump(); });
559
560  // Create the layout object.
561  MCAsmLayout Layout(*this);
562
563  // Create dummy fragments and assign section ordinals.
564  unsigned SectionIndex = 0;
565  for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
566    // Create dummy fragments to eliminate any empty sections, this simplifies
567    // layout.
568    if (it->getFragmentList().empty())
569      new MCDataFragment(it);
570
571    it->setOrdinal(SectionIndex++);
572  }
573
574  // Assign layout order indices to sections and fragments.
575  for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
576    MCSectionData *SD = Layout.getSectionOrder()[i];
577    SD->setLayoutOrder(i);
578
579    unsigned FragmentIndex = 0;
580    for (MCSectionData::iterator it2 = SD->begin(),
581           ie2 = SD->end(); it2 != ie2; ++it2)
582      it2->setLayoutOrder(FragmentIndex++);
583  }
584
585  // Layout until everything fits.
586  while (layoutOnce(Layout))
587    continue;
588
589  DEBUG_WITH_TYPE("mc-dump", {
590      llvm::errs() << "assembler backend - post-relaxation\n--\n";
591      dump(); });
592
593  // Finalize the layout, including fragment lowering.
594  finishLayout(Layout);
595
596  DEBUG_WITH_TYPE("mc-dump", {
597      llvm::errs() << "assembler backend - final-layout\n--\n";
598      dump(); });
599
600  uint64_t StartOffset = OS.tell();
601
602  // Allow the object writer a chance to perform post-layout binding (for
603  // example, to set the index fields in the symbol data).
604  getWriter().ExecutePostLayoutBinding(*this, Layout);
605
606  // Evaluate and apply the fixups, generating relocation entries as necessary.
607  for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
608    for (MCSectionData::iterator it2 = it->begin(),
609           ie2 = it->end(); it2 != ie2; ++it2) {
610      MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
611      if (DF) {
612        for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
613               ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
614          MCFixup &Fixup = *it3;
615          uint64_t FixedValue = handleFixup(Layout, *DF, Fixup);
616          getBackend().applyFixup(Fixup, DF->getContents().data(),
617                                  DF->getContents().size(), FixedValue);
618        }
619      }
620      MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
621      if (IF) {
622        for (MCInstFragment::fixup_iterator it3 = IF->fixup_begin(),
623               ie3 = IF->fixup_end(); it3 != ie3; ++it3) {
624          MCFixup &Fixup = *it3;
625          uint64_t FixedValue = handleFixup(Layout, *IF, Fixup);
626          getBackend().applyFixup(Fixup, IF->getCode().data(),
627                                  IF->getCode().size(), FixedValue);
628        }
629      }
630    }
631  }
632
633  // Write the object file.
634  getWriter().WriteObject(*this, Layout);
635
636  stats::ObjectBytes += OS.tell() - StartOffset;
637}
638
639bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
640                                       const MCInstFragment *DF,
641                                       const MCAsmLayout &Layout) const {
642  if (getRelaxAll())
643    return true;
644
645  // If we cannot resolve the fixup value, it requires relaxation.
646  MCValue Target;
647  uint64_t Value;
648  if (!evaluateFixup(Layout, Fixup, DF, Target, Value))
649    return true;
650
651  return getBackend().fixupNeedsRelaxation(Fixup, Value, DF, Layout);
652}
653
654bool MCAssembler::fragmentNeedsRelaxation(const MCInstFragment *IF,
655                                          const MCAsmLayout &Layout) const {
656  // If this inst doesn't ever need relaxation, ignore it. This occurs when we
657  // are intentionally pushing out inst fragments, or because we relaxed a
658  // previous instruction to one that doesn't need relaxation.
659  if (!getBackend().mayNeedRelaxation(IF->getInst()))
660    return false;
661
662  for (MCInstFragment::const_fixup_iterator it = IF->fixup_begin(),
663         ie = IF->fixup_end(); it != ie; ++it)
664    if (fixupNeedsRelaxation(*it, IF, Layout))
665      return true;
666
667  return false;
668}
669
670bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
671                                   MCInstFragment &IF) {
672  if (!fragmentNeedsRelaxation(&IF, Layout))
673    return false;
674
675  ++stats::RelaxedInstructions;
676
677  // FIXME-PERF: We could immediately lower out instructions if we can tell
678  // they are fully resolved, to avoid retesting on later passes.
679
680  // Relax the fragment.
681
682  MCInst Relaxed;
683  getBackend().relaxInstruction(IF.getInst(), Relaxed);
684
685  // Encode the new instruction.
686  //
687  // FIXME-PERF: If it matters, we could let the target do this. It can
688  // probably do so more efficiently in many cases.
689  SmallVector<MCFixup, 4> Fixups;
690  SmallString<256> Code;
691  raw_svector_ostream VecOS(Code);
692  getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups);
693  VecOS.flush();
694
695  // Update the instruction fragment.
696  IF.setInst(Relaxed);
697  IF.getCode() = Code;
698  IF.getFixups().clear();
699  // FIXME: Eliminate copy.
700  for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
701    IF.getFixups().push_back(Fixups[i]);
702
703  return true;
704}
705
706bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
707  int64_t Value = 0;
708  uint64_t OldSize = LF.getContents().size();
709  bool IsAbs = LF.getValue().EvaluateAsAbsolute(Value, Layout);
710  (void)IsAbs;
711  assert(IsAbs);
712  SmallString<8> &Data = LF.getContents();
713  Data.clear();
714  raw_svector_ostream OSE(Data);
715  if (LF.isSigned())
716    MCObjectWriter::EncodeSLEB128(Value, OSE);
717  else
718    MCObjectWriter::EncodeULEB128(Value, OSE);
719  OSE.flush();
720  return OldSize != LF.getContents().size();
721}
722
723bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
724                                     MCDwarfLineAddrFragment &DF) {
725  int64_t AddrDelta = 0;
726  uint64_t OldSize = DF.getContents().size();
727  bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
728  (void)IsAbs;
729  assert(IsAbs);
730  int64_t LineDelta;
731  LineDelta = DF.getLineDelta();
732  SmallString<8> &Data = DF.getContents();
733  Data.clear();
734  raw_svector_ostream OSE(Data);
735  MCDwarfLineAddr::Encode(LineDelta, AddrDelta, OSE);
736  OSE.flush();
737  return OldSize != Data.size();
738}
739
740bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
741                                              MCDwarfCallFrameFragment &DF) {
742  int64_t AddrDelta = 0;
743  uint64_t OldSize = DF.getContents().size();
744  bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
745  (void)IsAbs;
746  assert(IsAbs);
747  SmallString<8> &Data = DF.getContents();
748  Data.clear();
749  raw_svector_ostream OSE(Data);
750  MCDwarfFrameEmitter::EncodeAdvanceLoc(AddrDelta, OSE);
751  OSE.flush();
752  return OldSize != Data.size();
753}
754
755bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout,
756                                    MCSectionData &SD) {
757  MCFragment *FirstInvalidFragment = NULL;
758  // Scan for fragments that need relaxation.
759  for (MCSectionData::iterator it2 = SD.begin(),
760         ie2 = SD.end(); it2 != ie2; ++it2) {
761    // Check if this is an fragment that needs relaxation.
762    bool relaxedFrag = false;
763    switch(it2->getKind()) {
764    default:
765          break;
766    case MCFragment::FT_Inst:
767      relaxedFrag = relaxInstruction(Layout, *cast<MCInstFragment>(it2));
768      break;
769    case MCFragment::FT_Dwarf:
770      relaxedFrag = relaxDwarfLineAddr(Layout,
771                                       *cast<MCDwarfLineAddrFragment>(it2));
772      break;
773    case MCFragment::FT_DwarfFrame:
774      relaxedFrag =
775        relaxDwarfCallFrameFragment(Layout,
776                                    *cast<MCDwarfCallFrameFragment>(it2));
777      break;
778    case MCFragment::FT_LEB:
779      relaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(it2));
780      break;
781    }
782    // Update the layout, and remember that we relaxed.
783    if (relaxedFrag && !FirstInvalidFragment)
784      FirstInvalidFragment = it2;
785  }
786  if (FirstInvalidFragment) {
787    Layout.Invalidate(FirstInvalidFragment);
788    return true;
789  }
790  return false;
791}
792
793bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
794  ++stats::RelaxationSteps;
795
796  bool WasRelaxed = false;
797  for (iterator it = begin(), ie = end(); it != ie; ++it) {
798    MCSectionData &SD = *it;
799    while(layoutSectionOnce(Layout, SD))
800      WasRelaxed = true;
801  }
802
803  return WasRelaxed;
804}
805
806void MCAssembler::finishLayout(MCAsmLayout &Layout) {
807  // The layout is done. Mark every fragment as valid.
808  for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
809    Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
810  }
811}
812
813// Debugging methods
814
815namespace llvm {
816
817raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
818  OS << "<MCFixup" << " Offset:" << AF.getOffset()
819     << " Value:" << *AF.getValue()
820     << " Kind:" << AF.getKind() << ">";
821  return OS;
822}
823
824}
825
826void MCFragment::dump() {
827  raw_ostream &OS = llvm::errs();
828
829  OS << "<";
830  switch (getKind()) {
831  case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
832  case MCFragment::FT_Data:  OS << "MCDataFragment"; break;
833  case MCFragment::FT_Fill:  OS << "MCFillFragment"; break;
834  case MCFragment::FT_Inst:  OS << "MCInstFragment"; break;
835  case MCFragment::FT_Org:   OS << "MCOrgFragment"; break;
836  case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
837  case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
838  case MCFragment::FT_LEB:   OS << "MCLEBFragment"; break;
839  }
840
841  OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
842     << " Offset:" << Offset << ">";
843
844  switch (getKind()) {
845  case MCFragment::FT_Align: {
846    const MCAlignFragment *AF = cast<MCAlignFragment>(this);
847    if (AF->hasEmitNops())
848      OS << " (emit nops)";
849    OS << "\n       ";
850    OS << " Alignment:" << AF->getAlignment()
851       << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
852       << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
853    break;
854  }
855  case MCFragment::FT_Data:  {
856    const MCDataFragment *DF = cast<MCDataFragment>(this);
857    OS << "\n       ";
858    OS << " Contents:[";
859    const SmallVectorImpl<char> &Contents = DF->getContents();
860    for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
861      if (i) OS << ",";
862      OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
863    }
864    OS << "] (" << Contents.size() << " bytes)";
865
866    if (!DF->getFixups().empty()) {
867      OS << ",\n       ";
868      OS << " Fixups:[";
869      for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
870             ie = DF->fixup_end(); it != ie; ++it) {
871        if (it != DF->fixup_begin()) OS << ",\n                ";
872        OS << *it;
873      }
874      OS << "]";
875    }
876    break;
877  }
878  case MCFragment::FT_Fill:  {
879    const MCFillFragment *FF = cast<MCFillFragment>(this);
880    OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
881       << " Size:" << FF->getSize();
882    break;
883  }
884  case MCFragment::FT_Inst:  {
885    const MCInstFragment *IF = cast<MCInstFragment>(this);
886    OS << "\n       ";
887    OS << " Inst:";
888    IF->getInst().dump_pretty(OS);
889    break;
890  }
891  case MCFragment::FT_Org:  {
892    const MCOrgFragment *OF = cast<MCOrgFragment>(this);
893    OS << "\n       ";
894    OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
895    break;
896  }
897  case MCFragment::FT_Dwarf:  {
898    const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
899    OS << "\n       ";
900    OS << " AddrDelta:" << OF->getAddrDelta()
901       << " LineDelta:" << OF->getLineDelta();
902    break;
903  }
904  case MCFragment::FT_DwarfFrame:  {
905    const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
906    OS << "\n       ";
907    OS << " AddrDelta:" << CF->getAddrDelta();
908    break;
909  }
910  case MCFragment::FT_LEB: {
911    const MCLEBFragment *LF = cast<MCLEBFragment>(this);
912    OS << "\n       ";
913    OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
914    break;
915  }
916  }
917  OS << ">";
918}
919
920void MCSectionData::dump() {
921  raw_ostream &OS = llvm::errs();
922
923  OS << "<MCSectionData";
924  OS << " Alignment:" << getAlignment() << " Fragments:[\n      ";
925  for (iterator it = begin(), ie = end(); it != ie; ++it) {
926    if (it != begin()) OS << ",\n      ";
927    it->dump();
928  }
929  OS << "]>";
930}
931
932void MCSymbolData::dump() {
933  raw_ostream &OS = llvm::errs();
934
935  OS << "<MCSymbolData Symbol:" << getSymbol()
936     << " Fragment:" << getFragment() << " Offset:" << getOffset()
937     << " Flags:" << getFlags() << " Index:" << getIndex();
938  if (isCommon())
939    OS << " (common, size:" << getCommonSize()
940       << " align: " << getCommonAlignment() << ")";
941  if (isExternal())
942    OS << " (external)";
943  if (isPrivateExtern())
944    OS << " (private extern)";
945  OS << ">";
946}
947
948void MCAssembler::dump() {
949  raw_ostream &OS = llvm::errs();
950
951  OS << "<MCAssembler\n";
952  OS << "  Sections:[\n    ";
953  for (iterator it = begin(), ie = end(); it != ie; ++it) {
954    if (it != begin()) OS << ",\n    ";
955    it->dump();
956  }
957  OS << "],\n";
958  OS << "  Symbols:[";
959
960  for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
961    if (it != symbol_begin()) OS << ",\n           ";
962    it->dump();
963  }
964  OS << "]>\n";
965}
966
967// anchors for MC*Fragment vtables
968void MCDataFragment::anchor() { }
969void MCInstFragment::anchor() { }
970void MCAlignFragment::anchor() { }
971void MCFillFragment::anchor() { }
972void MCOrgFragment::anchor() { }
973void MCLEBFragment::anchor() { }
974void MCDwarfLineAddrFragment::anchor() { }
975void MCDwarfCallFrameFragment::anchor() { }
976