• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
1 //===- lib/MC/MCAssembler.cpp - Assembler Backend Implementation ----------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #define DEBUG_TYPE "assembler"
11 #include "llvm/MC/MCAssembler.h"
12 #include "llvm/MC/MCAsmLayout.h"
13 #include "llvm/MC/MCCodeEmitter.h"
14 #include "llvm/MC/MCContext.h"
15 #include "llvm/MC/MCExpr.h"
16 #include "llvm/MC/MCObjectWriter.h"
17 #include "llvm/MC/MCSection.h"
18 #include "llvm/MC/MCSymbol.h"
19 #include "llvm/MC/MCValue.h"
20 #include "llvm/MC/MCDwarf.h"
21 #include "llvm/MC/MCAsmBackend.h"
22 #include "llvm/ADT/OwningPtr.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 
31 using namespace llvm;
32 
33 namespace {
34 namespace stats {
35 STATISTIC(EmittedFragments, "Number of emitted assembler fragments");
36 STATISTIC(EvaluateFixup, "Number of evaluated fixups");
37 STATISTIC(FragmentLayouts, "Number of fragment layouts");
38 STATISTIC(ObjectBytes, "Number of emitted object file bytes");
39 STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
40 STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
41 }
42 }
43 
44 // FIXME FIXME FIXME: There are number of places in this file where we convert
45 // what is a 64-bit assembler value used for computation into a value in the
46 // object file, which may truncate it. We should detect that truncation where
47 // invalid and report errors back.
48 
49 /* *** */
50 
MCAsmLayout(MCAssembler & Asm)51 MCAsmLayout::MCAsmLayout(MCAssembler &Asm)
52   : Assembler(Asm), LastValidFragment()
53  {
54   // Compute the section layout order. Virtual sections must go last.
55   for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
56     if (!it->getSection().isVirtualSection())
57       SectionOrder.push_back(&*it);
58   for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
59     if (it->getSection().isVirtualSection())
60       SectionOrder.push_back(&*it);
61 }
62 
isFragmentUpToDate(const MCFragment * F) const63 bool MCAsmLayout::isFragmentUpToDate(const MCFragment *F) const {
64   const MCSectionData &SD = *F->getParent();
65   const MCFragment *LastValid = LastValidFragment.lookup(&SD);
66   if (!LastValid)
67     return false;
68   assert(LastValid->getParent() == F->getParent());
69   return F->getLayoutOrder() <= LastValid->getLayoutOrder();
70 }
71 
Invalidate(MCFragment * F)72 void MCAsmLayout::Invalidate(MCFragment *F) {
73   // If this fragment wasn't already up-to-date, we don't need to do anything.
74   if (!isFragmentUpToDate(F))
75     return;
76 
77   // Otherwise, reset the last valid fragment to this fragment.
78   const MCSectionData &SD = *F->getParent();
79   LastValidFragment[&SD] = F;
80 }
81 
EnsureValid(const MCFragment * F) const82 void MCAsmLayout::EnsureValid(const MCFragment *F) const {
83   MCSectionData &SD = *F->getParent();
84 
85   MCFragment *Cur = LastValidFragment[&SD];
86   if (!Cur)
87     Cur = &*SD.begin();
88   else
89     Cur = Cur->getNextNode();
90 
91   // Advance the layout position until the fragment is up-to-date.
92   while (!isFragmentUpToDate(F)) {
93     const_cast<MCAsmLayout*>(this)->LayoutFragment(Cur);
94     Cur = Cur->getNextNode();
95   }
96 }
97 
getFragmentOffset(const MCFragment * F) const98 uint64_t MCAsmLayout::getFragmentOffset(const MCFragment *F) const {
99   EnsureValid(F);
100   assert(F->Offset != ~UINT64_C(0) && "Address not set!");
101   return F->Offset;
102 }
103 
getSymbolOffset(const MCSymbolData * SD) const104 uint64_t MCAsmLayout::getSymbolOffset(const MCSymbolData *SD) const {
105   const MCSymbol &S = SD->getSymbol();
106 
107   // If this is a variable, then recursively evaluate now.
108   if (S.isVariable()) {
109     MCValue Target;
110     if (!S.getVariableValue()->EvaluateAsRelocatable(Target, *this))
111       report_fatal_error("unable to evaluate offset for variable '" +
112                          S.getName() + "'");
113 
114     // Verify that any used symbols are defined.
115     if (Target.getSymA() && Target.getSymA()->getSymbol().isUndefined())
116       report_fatal_error("unable to evaluate offset to undefined symbol '" +
117                          Target.getSymA()->getSymbol().getName() + "'");
118     if (Target.getSymB() && Target.getSymB()->getSymbol().isUndefined())
119       report_fatal_error("unable to evaluate offset to undefined symbol '" +
120                          Target.getSymB()->getSymbol().getName() + "'");
121 
122     uint64_t Offset = Target.getConstant();
123     if (Target.getSymA())
124       Offset += getSymbolOffset(&Assembler.getSymbolData(
125                                   Target.getSymA()->getSymbol()));
126     if (Target.getSymB())
127       Offset -= getSymbolOffset(&Assembler.getSymbolData(
128                                   Target.getSymB()->getSymbol()));
129     return Offset;
130   }
131 
132   assert(SD->getFragment() && "Invalid getOffset() on undefined symbol!");
133   return getFragmentOffset(SD->getFragment()) + SD->getOffset();
134 }
135 
getSectionAddressSize(const MCSectionData * SD) const136 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
137   // The size is the last fragment's end offset.
138   const MCFragment &F = SD->getFragmentList().back();
139   return getFragmentOffset(&F) + getAssembler().ComputeFragmentSize(*this, F);
140 }
141 
getSectionFileSize(const MCSectionData * SD) const142 uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
143   // Virtual sections have no file size.
144   if (SD->getSection().isVirtualSection())
145     return 0;
146 
147   // Otherwise, the file size is the same as the address space size.
148   return getSectionAddressSize(SD);
149 }
150 
151 /* *** */
152 
MCFragment()153 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
154 }
155 
~MCFragment()156 MCFragment::~MCFragment() {
157 }
158 
MCFragment(FragmentType _Kind,MCSectionData * _Parent)159 MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
160   : Kind(_Kind), Parent(_Parent), Atom(0), Offset(~UINT64_C(0))
161 {
162   if (Parent)
163     Parent->getFragmentList().push_back(this);
164 }
165 
166 /* *** */
167 
MCSectionData()168 MCSectionData::MCSectionData() : Section(0) {}
169 
MCSectionData(const MCSection & _Section,MCAssembler * A)170 MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
171   : Section(&_Section),
172     Ordinal(~UINT32_C(0)),
173     Alignment(1),
174     HasInstructions(false)
175 {
176   if (A)
177     A->getSectionList().push_back(this);
178 }
179 
180 /* *** */
181 
MCSymbolData()182 MCSymbolData::MCSymbolData() : Symbol(0) {}
183 
MCSymbolData(const MCSymbol & _Symbol,MCFragment * _Fragment,uint64_t _Offset,MCAssembler * A)184 MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
185                            uint64_t _Offset, MCAssembler *A)
186   : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
187     IsExternal(false), IsPrivateExtern(false),
188     CommonSize(0), SymbolSize(0), CommonAlign(0),
189     Flags(0), Index(0)
190 {
191   if (A)
192     A->getSymbolList().push_back(this);
193 }
194 
195 /* *** */
196 
MCAssembler(MCContext & Context_,MCAsmBackend & Backend_,MCCodeEmitter & Emitter_,MCObjectWriter & Writer_,raw_ostream & OS_)197 MCAssembler::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 
~MCAssembler()205 MCAssembler::~MCAssembler() {
206 }
207 
isSymbolLinkerVisible(const MCSymbol & Symbol) const208 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
209   // Non-temporary labels should always be visible to the linker.
210   if (!Symbol.isTemporary())
211     return true;
212 
213   // Absolute temporary labels are never visible.
214   if (!Symbol.isInSection())
215     return false;
216 
217   // Otherwise, check if the section requires symbols even for temporary labels.
218   return getBackend().doesSectionRequireSymbols(Symbol.getSection());
219 }
220 
getAtom(const MCSymbolData * SD) const221 const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
222   // Linker visible symbols define atoms.
223   if (isSymbolLinkerVisible(SD->getSymbol()))
224     return SD;
225 
226   // Absolute and undefined symbols have no defining atom.
227   if (!SD->getFragment())
228     return 0;
229 
230   // Non-linker visible symbols in sections which can't be atomized have no
231   // defining atom.
232   if (!getBackend().isSectionAtomizable(
233         SD->getFragment()->getParent()->getSection()))
234     return 0;
235 
236   // Otherwise, return the atom for the containing fragment.
237   return SD->getFragment()->getAtom();
238 }
239 
EvaluateFixup(const MCAsmLayout & Layout,const MCFixup & Fixup,const MCFragment * DF,MCValue & Target,uint64_t & Value) const240 bool MCAssembler::EvaluateFixup(const MCAsmLayout &Layout,
241                                 const MCFixup &Fixup, const MCFragment *DF,
242                                 MCValue &Target, uint64_t &Value) const {
243   ++stats::EvaluateFixup;
244 
245   if (!Fixup.getValue()->EvaluateAsRelocatable(Target, Layout))
246     report_fatal_error("expected relocatable expression");
247 
248   bool IsPCRel = Backend.getFixupKindInfo(
249     Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
250 
251   bool IsResolved;
252   if (IsPCRel) {
253     if (Target.getSymB()) {
254       IsResolved = false;
255     } else if (!Target.getSymA()) {
256       IsResolved = false;
257     } else {
258       const MCSymbolRefExpr *A = Target.getSymA();
259       const MCSymbol &SA = A->getSymbol();
260       if (A->getKind() != MCSymbolRefExpr::VK_None ||
261           SA.AliasedSymbol().isUndefined()) {
262         IsResolved = false;
263       } else {
264         const MCSymbolData &DataA = getSymbolData(SA);
265         IsResolved =
266           getWriter().IsSymbolRefDifferenceFullyResolvedImpl(*this, DataA,
267                                                              *DF, false, true);
268       }
269     }
270   } else {
271     IsResolved = Target.isAbsolute();
272   }
273 
274   Value = Target.getConstant();
275 
276   bool IsThumb = false;
277   if (const MCSymbolRefExpr *A = Target.getSymA()) {
278     const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
279     if (Sym.isDefined())
280       Value += Layout.getSymbolOffset(&getSymbolData(Sym));
281     if (isThumbFunc(&Sym))
282       IsThumb = true;
283   }
284   if (const MCSymbolRefExpr *B = Target.getSymB()) {
285     const MCSymbol &Sym = B->getSymbol().AliasedSymbol();
286     if (Sym.isDefined())
287       Value -= Layout.getSymbolOffset(&getSymbolData(Sym));
288   }
289 
290 
291   bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
292                          MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
293   assert((ShouldAlignPC ? IsPCRel : true) &&
294     "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
295 
296   if (IsPCRel) {
297     uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
298 
299     // A number of ARM fixups in Thumb mode require that the effective PC
300     // address be determined as the 32-bit aligned version of the actual offset.
301     if (ShouldAlignPC) Offset &= ~0x3;
302     Value -= Offset;
303   }
304 
305   // ARM fixups based from a thumb function address need to have the low
306   // bit set. The actual value is always at least 16-bit aligned, so the
307   // low bit is normally clear and available for use as an ISA flag for
308   // interworking.
309   if (IsThumb)
310     Value |= 1;
311 
312   return IsResolved;
313 }
314 
ComputeFragmentSize(const MCAsmLayout & Layout,const MCFragment & F) const315 uint64_t MCAssembler::ComputeFragmentSize(const MCAsmLayout &Layout,
316                                           const MCFragment &F) const {
317   switch (F.getKind()) {
318   case MCFragment::FT_Data:
319     return cast<MCDataFragment>(F).getContents().size();
320   case MCFragment::FT_Fill:
321     return cast<MCFillFragment>(F).getSize();
322   case MCFragment::FT_Inst:
323     return cast<MCInstFragment>(F).getInstSize();
324 
325   case MCFragment::FT_LEB:
326     return cast<MCLEBFragment>(F).getContents().size();
327 
328   case MCFragment::FT_Align: {
329     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
330     unsigned Offset = Layout.getFragmentOffset(&AF);
331     unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
332     if (Size > AF.getMaxBytesToEmit())
333       return 0;
334     return Size;
335   }
336 
337   case MCFragment::FT_Org: {
338     MCOrgFragment &OF = cast<MCOrgFragment>(F);
339     int64_t TargetLocation;
340     if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, Layout))
341       report_fatal_error("expected assembly-time absolute expression");
342 
343     // FIXME: We need a way to communicate this error.
344     uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
345     int64_t Size = TargetLocation - FragmentOffset;
346     if (Size < 0 || Size >= 0x40000000)
347       report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
348                          "' (at offset '" + Twine(FragmentOffset) + "')");
349     return Size;
350   }
351 
352   case MCFragment::FT_Dwarf:
353     return cast<MCDwarfLineAddrFragment>(F).getContents().size();
354   case MCFragment::FT_DwarfFrame:
355     return cast<MCDwarfCallFrameFragment>(F).getContents().size();
356   }
357 
358   assert(0 && "invalid fragment kind");
359   return 0;
360 }
361 
LayoutFragment(MCFragment * F)362 void MCAsmLayout::LayoutFragment(MCFragment *F) {
363   MCFragment *Prev = F->getPrevNode();
364 
365   // We should never try to recompute something which is up-to-date.
366   assert(!isFragmentUpToDate(F) && "Attempt to recompute up-to-date fragment!");
367   // We should never try to compute the fragment layout if it's predecessor
368   // isn't up-to-date.
369   assert((!Prev || isFragmentUpToDate(Prev)) &&
370          "Attempt to compute fragment before it's predecessor!");
371 
372   ++stats::FragmentLayouts;
373 
374   // Compute fragment offset and size.
375   uint64_t Offset = 0;
376   if (Prev)
377     Offset += Prev->Offset + getAssembler().ComputeFragmentSize(*this, *Prev);
378 
379   F->Offset = Offset;
380   LastValidFragment[F->getParent()] = F;
381 }
382 
383 /// WriteFragmentData - Write the \arg F data to the output file.
WriteFragmentData(const MCAssembler & Asm,const MCAsmLayout & Layout,const MCFragment & F)384 static void WriteFragmentData(const MCAssembler &Asm, const MCAsmLayout &Layout,
385                               const MCFragment &F) {
386   MCObjectWriter *OW = &Asm.getWriter();
387   uint64_t Start = OW->getStream().tell();
388   (void) Start;
389 
390   ++stats::EmittedFragments;
391 
392   // FIXME: Embed in fragments instead?
393   uint64_t FragmentSize = Asm.ComputeFragmentSize(Layout, F);
394   switch (F.getKind()) {
395   case MCFragment::FT_Align: {
396     MCAlignFragment &AF = cast<MCAlignFragment>(F);
397     uint64_t Count = FragmentSize / AF.getValueSize();
398 
399     assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
400 
401     // FIXME: This error shouldn't actually occur (the front end should emit
402     // multiple .align directives to enforce the semantics it wants), but is
403     // severe enough that we want to report it. How to handle this?
404     if (Count * AF.getValueSize() != FragmentSize)
405       report_fatal_error("undefined .align directive, value size '" +
406                         Twine(AF.getValueSize()) +
407                         "' is not a divisor of padding size '" +
408                         Twine(FragmentSize) + "'");
409 
410     // See if we are aligning with nops, and if so do that first to try to fill
411     // the Count bytes.  Then if that did not fill any bytes or there are any
412     // bytes left to fill use the the Value and ValueSize to fill the rest.
413     // If we are aligning with nops, ask that target to emit the right data.
414     if (AF.hasEmitNops()) {
415       if (!Asm.getBackend().WriteNopData(Count, OW))
416         report_fatal_error("unable to write nop sequence of " +
417                           Twine(Count) + " bytes");
418       break;
419     }
420 
421     // Otherwise, write out in multiples of the value size.
422     for (uint64_t i = 0; i != Count; ++i) {
423       switch (AF.getValueSize()) {
424       default:
425         assert(0 && "Invalid size!");
426       case 1: OW->Write8 (uint8_t (AF.getValue())); break;
427       case 2: OW->Write16(uint16_t(AF.getValue())); break;
428       case 4: OW->Write32(uint32_t(AF.getValue())); break;
429       case 8: OW->Write64(uint64_t(AF.getValue())); break;
430       }
431     }
432     break;
433   }
434 
435   case MCFragment::FT_Data: {
436     MCDataFragment &DF = cast<MCDataFragment>(F);
437     assert(FragmentSize == DF.getContents().size() && "Invalid size!");
438     OW->WriteBytes(DF.getContents().str());
439     break;
440   }
441 
442   case MCFragment::FT_Fill: {
443     MCFillFragment &FF = cast<MCFillFragment>(F);
444 
445     assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
446 
447     for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
448       switch (FF.getValueSize()) {
449       default:
450         assert(0 && "Invalid size!");
451       case 1: OW->Write8 (uint8_t (FF.getValue())); break;
452       case 2: OW->Write16(uint16_t(FF.getValue())); break;
453       case 4: OW->Write32(uint32_t(FF.getValue())); break;
454       case 8: OW->Write64(uint64_t(FF.getValue())); break;
455       }
456     }
457     break;
458   }
459 
460   case MCFragment::FT_Inst: {
461     MCInstFragment &IF = cast<MCInstFragment>(F);
462     OW->WriteBytes(StringRef(IF.getCode().begin(), IF.getCode().size()));
463     break;
464   }
465 
466   case MCFragment::FT_LEB: {
467     MCLEBFragment &LF = cast<MCLEBFragment>(F);
468     OW->WriteBytes(LF.getContents().str());
469     break;
470   }
471 
472   case MCFragment::FT_Org: {
473     MCOrgFragment &OF = cast<MCOrgFragment>(F);
474 
475     for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
476       OW->Write8(uint8_t(OF.getValue()));
477 
478     break;
479   }
480 
481   case MCFragment::FT_Dwarf: {
482     const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
483     OW->WriteBytes(OF.getContents().str());
484     break;
485   }
486   case MCFragment::FT_DwarfFrame: {
487     const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
488     OW->WriteBytes(CF.getContents().str());
489     break;
490   }
491   }
492 
493   assert(OW->getStream().tell() - Start == FragmentSize);
494 }
495 
WriteSectionData(const MCSectionData * SD,const MCAsmLayout & Layout) const496 void MCAssembler::WriteSectionData(const MCSectionData *SD,
497                                    const MCAsmLayout &Layout) const {
498   // Ignore virtual sections.
499   if (SD->getSection().isVirtualSection()) {
500     assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
501 
502     // Check that contents are only things legal inside a virtual section.
503     for (MCSectionData::const_iterator it = SD->begin(),
504            ie = SD->end(); it != ie; ++it) {
505       switch (it->getKind()) {
506       default:
507         assert(0 && "Invalid fragment in virtual section!");
508       case MCFragment::FT_Data: {
509         // Check that we aren't trying to write a non-zero contents (or fixups)
510         // into a virtual section. This is to support clients which use standard
511         // directives to fill the contents of virtual sections.
512         MCDataFragment &DF = cast<MCDataFragment>(*it);
513         assert(DF.fixup_begin() == DF.fixup_end() &&
514                "Cannot have fixups in virtual section!");
515         for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
516           assert(DF.getContents()[i] == 0 &&
517                  "Invalid data value for virtual section!");
518         break;
519       }
520       case MCFragment::FT_Align:
521         // Check that we aren't trying to write a non-zero value into a virtual
522         // section.
523         assert((!cast<MCAlignFragment>(it)->getValueSize() ||
524                 !cast<MCAlignFragment>(it)->getValue()) &&
525                "Invalid align in virtual section!");
526         break;
527       case MCFragment::FT_Fill:
528         assert(!cast<MCFillFragment>(it)->getValueSize() &&
529                "Invalid fill in virtual section!");
530         break;
531       }
532     }
533 
534     return;
535   }
536 
537   uint64_t Start = getWriter().getStream().tell();
538   (void) Start;
539 
540   for (MCSectionData::const_iterator it = SD->begin(),
541          ie = SD->end(); it != ie; ++it)
542     WriteFragmentData(*this, Layout, *it);
543 
544   assert(getWriter().getStream().tell() - Start ==
545          Layout.getSectionAddressSize(SD));
546 }
547 
548 
HandleFixup(const MCAsmLayout & Layout,MCFragment & F,const MCFixup & Fixup)549 uint64_t MCAssembler::HandleFixup(const MCAsmLayout &Layout,
550                                   MCFragment &F,
551                                   const MCFixup &Fixup) {
552    // Evaluate the fixup.
553    MCValue Target;
554    uint64_t FixedValue;
555    if (!EvaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
556      // The fixup was unresolved, we need a relocation. Inform the object
557      // writer of the relocation, and give it an opportunity to adjust the
558      // fixup value if need be.
559      getWriter().RecordRelocation(*this, Layout, &F, Fixup, Target, FixedValue);
560    }
561    return FixedValue;
562  }
563 
Finish()564 void MCAssembler::Finish() {
565   DEBUG_WITH_TYPE("mc-dump", {
566       llvm::errs() << "assembler backend - pre-layout\n--\n";
567       dump(); });
568 
569   // Create the layout object.
570   MCAsmLayout Layout(*this);
571 
572   // Create dummy fragments and assign section ordinals.
573   unsigned SectionIndex = 0;
574   for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
575     // Create dummy fragments to eliminate any empty sections, this simplifies
576     // layout.
577     if (it->getFragmentList().empty())
578       new MCDataFragment(it);
579 
580     it->setOrdinal(SectionIndex++);
581   }
582 
583   // Assign layout order indices to sections and fragments.
584   for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
585     MCSectionData *SD = Layout.getSectionOrder()[i];
586     SD->setLayoutOrder(i);
587 
588     unsigned FragmentIndex = 0;
589     for (MCSectionData::iterator it2 = SD->begin(),
590            ie2 = SD->end(); it2 != ie2; ++it2)
591       it2->setLayoutOrder(FragmentIndex++);
592   }
593 
594   // Layout until everything fits.
595   while (LayoutOnce(Layout))
596     continue;
597 
598   DEBUG_WITH_TYPE("mc-dump", {
599       llvm::errs() << "assembler backend - post-relaxation\n--\n";
600       dump(); });
601 
602   // Finalize the layout, including fragment lowering.
603   FinishLayout(Layout);
604 
605   DEBUG_WITH_TYPE("mc-dump", {
606       llvm::errs() << "assembler backend - final-layout\n--\n";
607       dump(); });
608 
609   uint64_t StartOffset = OS.tell();
610 
611   // Allow the object writer a chance to perform post-layout binding (for
612   // example, to set the index fields in the symbol data).
613   getWriter().ExecutePostLayoutBinding(*this, Layout);
614 
615   // Evaluate and apply the fixups, generating relocation entries as necessary.
616   for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
617     for (MCSectionData::iterator it2 = it->begin(),
618            ie2 = it->end(); it2 != ie2; ++it2) {
619       MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
620       if (DF) {
621         for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
622                ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
623           MCFixup &Fixup = *it3;
624           uint64_t FixedValue = HandleFixup(Layout, *DF, Fixup);
625           getBackend().ApplyFixup(Fixup, DF->getContents().data(),
626                                   DF->getContents().size(), FixedValue);
627         }
628       }
629       MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
630       if (IF) {
631         for (MCInstFragment::fixup_iterator it3 = IF->fixup_begin(),
632                ie3 = IF->fixup_end(); it3 != ie3; ++it3) {
633           MCFixup &Fixup = *it3;
634           uint64_t FixedValue = HandleFixup(Layout, *IF, Fixup);
635           getBackend().ApplyFixup(Fixup, IF->getCode().data(),
636                                   IF->getCode().size(), FixedValue);
637         }
638       }
639     }
640   }
641 
642   // Write the object file.
643   getWriter().WriteObject(*this, Layout);
644 
645   stats::ObjectBytes += OS.tell() - StartOffset;
646 }
647 
FixupNeedsRelaxation(const MCFixup & Fixup,const MCFragment * DF,const MCAsmLayout & Layout) const648 bool MCAssembler::FixupNeedsRelaxation(const MCFixup &Fixup,
649                                        const MCFragment *DF,
650                                        const MCAsmLayout &Layout) const {
651   if (getRelaxAll())
652     return true;
653 
654   // If we cannot resolve the fixup value, it requires relaxation.
655   MCValue Target;
656   uint64_t Value;
657   if (!EvaluateFixup(Layout, Fixup, DF, Target, Value))
658     return true;
659 
660   // Otherwise, relax if the value is too big for a (signed) i8.
661   //
662   // FIXME: This is target dependent!
663   return int64_t(Value) != int64_t(int8_t(Value));
664 }
665 
FragmentNeedsRelaxation(const MCInstFragment * IF,const MCAsmLayout & Layout) const666 bool MCAssembler::FragmentNeedsRelaxation(const MCInstFragment *IF,
667                                           const MCAsmLayout &Layout) const {
668   // If this inst doesn't ever need relaxation, ignore it. This occurs when we
669   // are intentionally pushing out inst fragments, or because we relaxed a
670   // previous instruction to one that doesn't need relaxation.
671   if (!getBackend().MayNeedRelaxation(IF->getInst()))
672     return false;
673 
674   for (MCInstFragment::const_fixup_iterator it = IF->fixup_begin(),
675          ie = IF->fixup_end(); it != ie; ++it)
676     if (FixupNeedsRelaxation(*it, IF, Layout))
677       return true;
678 
679   return false;
680 }
681 
RelaxInstruction(MCAsmLayout & Layout,MCInstFragment & IF)682 bool MCAssembler::RelaxInstruction(MCAsmLayout &Layout,
683                                    MCInstFragment &IF) {
684   if (!FragmentNeedsRelaxation(&IF, Layout))
685     return false;
686 
687   ++stats::RelaxedInstructions;
688 
689   // FIXME-PERF: We could immediately lower out instructions if we can tell
690   // they are fully resolved, to avoid retesting on later passes.
691 
692   // Relax the fragment.
693 
694   MCInst Relaxed;
695   getBackend().RelaxInstruction(IF.getInst(), Relaxed);
696 
697   // Encode the new instruction.
698   //
699   // FIXME-PERF: If it matters, we could let the target do this. It can
700   // probably do so more efficiently in many cases.
701   SmallVector<MCFixup, 4> Fixups;
702   SmallString<256> Code;
703   raw_svector_ostream VecOS(Code);
704   getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups);
705   VecOS.flush();
706 
707   // Update the instruction fragment.
708   IF.setInst(Relaxed);
709   IF.getCode() = Code;
710   IF.getFixups().clear();
711   // FIXME: Eliminate copy.
712   for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
713     IF.getFixups().push_back(Fixups[i]);
714 
715   return true;
716 }
717 
RelaxLEB(MCAsmLayout & Layout,MCLEBFragment & LF)718 bool MCAssembler::RelaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
719   int64_t Value = 0;
720   uint64_t OldSize = LF.getContents().size();
721   bool IsAbs = LF.getValue().EvaluateAsAbsolute(Value, Layout);
722   (void)IsAbs;
723   assert(IsAbs);
724   SmallString<8> &Data = LF.getContents();
725   Data.clear();
726   raw_svector_ostream OSE(Data);
727   if (LF.isSigned())
728     MCObjectWriter::EncodeSLEB128(Value, OSE);
729   else
730     MCObjectWriter::EncodeULEB128(Value, OSE);
731   OSE.flush();
732   return OldSize != LF.getContents().size();
733 }
734 
RelaxDwarfLineAddr(MCAsmLayout & Layout,MCDwarfLineAddrFragment & DF)735 bool MCAssembler::RelaxDwarfLineAddr(MCAsmLayout &Layout,
736 				     MCDwarfLineAddrFragment &DF) {
737   int64_t AddrDelta = 0;
738   uint64_t OldSize = DF.getContents().size();
739   bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
740   (void)IsAbs;
741   assert(IsAbs);
742   int64_t LineDelta;
743   LineDelta = DF.getLineDelta();
744   SmallString<8> &Data = DF.getContents();
745   Data.clear();
746   raw_svector_ostream OSE(Data);
747   MCDwarfLineAddr::Encode(LineDelta, AddrDelta, OSE);
748   OSE.flush();
749   return OldSize != Data.size();
750 }
751 
RelaxDwarfCallFrameFragment(MCAsmLayout & Layout,MCDwarfCallFrameFragment & DF)752 bool MCAssembler::RelaxDwarfCallFrameFragment(MCAsmLayout &Layout,
753                                               MCDwarfCallFrameFragment &DF) {
754   int64_t AddrDelta = 0;
755   uint64_t OldSize = DF.getContents().size();
756   bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
757   (void)IsAbs;
758   assert(IsAbs);
759   SmallString<8> &Data = DF.getContents();
760   Data.clear();
761   raw_svector_ostream OSE(Data);
762   MCDwarfFrameEmitter::EncodeAdvanceLoc(AddrDelta, OSE);
763   OSE.flush();
764   return OldSize != Data.size();
765 }
766 
LayoutSectionOnce(MCAsmLayout & Layout,MCSectionData & SD)767 bool MCAssembler::LayoutSectionOnce(MCAsmLayout &Layout,
768                                     MCSectionData &SD) {
769   MCFragment *FirstInvalidFragment = NULL;
770   // Scan for fragments that need relaxation.
771   for (MCSectionData::iterator it2 = SD.begin(),
772          ie2 = SD.end(); it2 != ie2; ++it2) {
773     // Check if this is an fragment that needs relaxation.
774     bool relaxedFrag = false;
775     switch(it2->getKind()) {
776     default:
777           break;
778     case MCFragment::FT_Inst:
779       relaxedFrag = RelaxInstruction(Layout, *cast<MCInstFragment>(it2));
780       break;
781     case MCFragment::FT_Dwarf:
782       relaxedFrag = RelaxDwarfLineAddr(Layout,
783                                        *cast<MCDwarfLineAddrFragment>(it2));
784       break;
785     case MCFragment::FT_DwarfFrame:
786       relaxedFrag =
787         RelaxDwarfCallFrameFragment(Layout,
788                                     *cast<MCDwarfCallFrameFragment>(it2));
789       break;
790     case MCFragment::FT_LEB:
791       relaxedFrag = RelaxLEB(Layout, *cast<MCLEBFragment>(it2));
792       break;
793     }
794     // Update the layout, and remember that we relaxed.
795     if (relaxedFrag && !FirstInvalidFragment)
796       FirstInvalidFragment = it2;
797   }
798   if (FirstInvalidFragment) {
799     Layout.Invalidate(FirstInvalidFragment);
800     return true;
801   }
802   return false;
803 }
804 
LayoutOnce(MCAsmLayout & Layout)805 bool MCAssembler::LayoutOnce(MCAsmLayout &Layout) {
806   ++stats::RelaxationSteps;
807 
808   bool WasRelaxed = false;
809   for (iterator it = begin(), ie = end(); it != ie; ++it) {
810     MCSectionData &SD = *it;
811     while(LayoutSectionOnce(Layout, SD))
812       WasRelaxed = true;
813   }
814 
815   return WasRelaxed;
816 }
817 
FinishLayout(MCAsmLayout & Layout)818 void MCAssembler::FinishLayout(MCAsmLayout &Layout) {
819   // The layout is done. Mark every fragment as valid.
820   for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
821     Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
822   }
823 }
824 
825 // Debugging methods
826 
827 namespace llvm {
828 
operator <<(raw_ostream & OS,const MCFixup & AF)829 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
830   OS << "<MCFixup" << " Offset:" << AF.getOffset()
831      << " Value:" << *AF.getValue()
832      << " Kind:" << AF.getKind() << ">";
833   return OS;
834 }
835 
836 }
837 
dump()838 void MCFragment::dump() {
839   raw_ostream &OS = llvm::errs();
840 
841   OS << "<";
842   switch (getKind()) {
843   case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
844   case MCFragment::FT_Data:  OS << "MCDataFragment"; break;
845   case MCFragment::FT_Fill:  OS << "MCFillFragment"; break;
846   case MCFragment::FT_Inst:  OS << "MCInstFragment"; break;
847   case MCFragment::FT_Org:   OS << "MCOrgFragment"; break;
848   case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
849   case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
850   case MCFragment::FT_LEB:   OS << "MCLEBFragment"; break;
851   }
852 
853   OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
854      << " Offset:" << Offset << ">";
855 
856   switch (getKind()) {
857   case MCFragment::FT_Align: {
858     const MCAlignFragment *AF = cast<MCAlignFragment>(this);
859     if (AF->hasEmitNops())
860       OS << " (emit nops)";
861     OS << "\n       ";
862     OS << " Alignment:" << AF->getAlignment()
863        << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
864        << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
865     break;
866   }
867   case MCFragment::FT_Data:  {
868     const MCDataFragment *DF = cast<MCDataFragment>(this);
869     OS << "\n       ";
870     OS << " Contents:[";
871     const SmallVectorImpl<char> &Contents = DF->getContents();
872     for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
873       if (i) OS << ",";
874       OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
875     }
876     OS << "] (" << Contents.size() << " bytes)";
877 
878     if (!DF->getFixups().empty()) {
879       OS << ",\n       ";
880       OS << " Fixups:[";
881       for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
882              ie = DF->fixup_end(); it != ie; ++it) {
883         if (it != DF->fixup_begin()) OS << ",\n                ";
884         OS << *it;
885       }
886       OS << "]";
887     }
888     break;
889   }
890   case MCFragment::FT_Fill:  {
891     const MCFillFragment *FF = cast<MCFillFragment>(this);
892     OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
893        << " Size:" << FF->getSize();
894     break;
895   }
896   case MCFragment::FT_Inst:  {
897     const MCInstFragment *IF = cast<MCInstFragment>(this);
898     OS << "\n       ";
899     OS << " Inst:";
900     IF->getInst().dump_pretty(OS);
901     break;
902   }
903   case MCFragment::FT_Org:  {
904     const MCOrgFragment *OF = cast<MCOrgFragment>(this);
905     OS << "\n       ";
906     OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
907     break;
908   }
909   case MCFragment::FT_Dwarf:  {
910     const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
911     OS << "\n       ";
912     OS << " AddrDelta:" << OF->getAddrDelta()
913        << " LineDelta:" << OF->getLineDelta();
914     break;
915   }
916   case MCFragment::FT_DwarfFrame:  {
917     const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
918     OS << "\n       ";
919     OS << " AddrDelta:" << CF->getAddrDelta();
920     break;
921   }
922   case MCFragment::FT_LEB: {
923     const MCLEBFragment *LF = cast<MCLEBFragment>(this);
924     OS << "\n       ";
925     OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
926     break;
927   }
928   }
929   OS << ">";
930 }
931 
dump()932 void MCSectionData::dump() {
933   raw_ostream &OS = llvm::errs();
934 
935   OS << "<MCSectionData";
936   OS << " Alignment:" << getAlignment() << " Fragments:[\n      ";
937   for (iterator it = begin(), ie = end(); it != ie; ++it) {
938     if (it != begin()) OS << ",\n      ";
939     it->dump();
940   }
941   OS << "]>";
942 }
943 
dump()944 void MCSymbolData::dump() {
945   raw_ostream &OS = llvm::errs();
946 
947   OS << "<MCSymbolData Symbol:" << getSymbol()
948      << " Fragment:" << getFragment() << " Offset:" << getOffset()
949      << " Flags:" << getFlags() << " Index:" << getIndex();
950   if (isCommon())
951     OS << " (common, size:" << getCommonSize()
952        << " align: " << getCommonAlignment() << ")";
953   if (isExternal())
954     OS << " (external)";
955   if (isPrivateExtern())
956     OS << " (private extern)";
957   OS << ">";
958 }
959 
dump()960 void MCAssembler::dump() {
961   raw_ostream &OS = llvm::errs();
962 
963   OS << "<MCAssembler\n";
964   OS << "  Sections:[\n    ";
965   for (iterator it = begin(), ie = end(); it != ie; ++it) {
966     if (it != begin()) OS << ",\n    ";
967     it->dump();
968   }
969   OS << "],\n";
970   OS << "  Symbols:[";
971 
972   for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
973     if (it != symbol_begin()) OS << ",\n           ";
974     it->dump();
975   }
976   OS << "]>\n";
977 }
978