MCMachOStreamer.cpp revision ba210243ef7d325ef6954d459091edf580a241f9 
1//===- lib/MC/MCMachOStreamer.cpp - Mach-O Object Output ------------===//
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#include "llvm/MC/MCStreamer.h"
11
12#include "llvm/MC/MCAssembler.h"
13#include "llvm/MC/MCContext.h"
14#include "llvm/MC/MCCodeEmitter.h"
15#include "llvm/MC/MCExpr.h"
16#include "llvm/MC/MCInst.h"
17#include "llvm/MC/MCObjectStreamer.h"
18#include "llvm/MC/MCSection.h"
19#include "llvm/MC/MCSymbol.h"
20#include "llvm/MC/MCMachOSymbolFlags.h"
21#include "llvm/MC/MCSectionMachO.h"
22#include "llvm/MC/MCDwarf.h"
23#include "llvm/Support/Dwarf.h"
24#include "llvm/Support/ErrorHandling.h"
25#include "llvm/Support/raw_ostream.h"
26#include "llvm/Target/TargetAsmBackend.h"
27
28using namespace llvm;
29
30namespace {
31
32class MCMachOStreamer : public MCObjectStreamer {
33private:
34  virtual void EmitInstToFragment(const MCInst &Inst);
35  virtual void EmitInstToData(const MCInst &Inst);
36
37public:
38  MCMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
39                  raw_ostream &OS, MCCodeEmitter *Emitter)
40    : MCObjectStreamer(Context, TAB, OS, Emitter, true) {}
41
42  /// @name MCStreamer Interface
43  /// @{
44
45  virtual void InitSections();
46  virtual void EmitLabel(MCSymbol *Symbol);
47  virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
48  virtual void EmitThumbFunc(MCSymbol *Func);
49  virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
50  virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
51  virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue);
52  virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
53                                unsigned ByteAlignment);
54  virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
55    assert(0 && "macho doesn't support this directive");
56  }
57  virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
58    assert(0 && "macho doesn't support this directive");
59  }
60  virtual void EmitCOFFSymbolType(int Type) {
61    assert(0 && "macho doesn't support this directive");
62  }
63  virtual void EndCOFFSymbolDef() {
64    assert(0 && "macho doesn't support this directive");
65  }
66  virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
67    assert(0 && "macho doesn't support this directive");
68  }
69  virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
70    assert(0 && "macho doesn't support this directive");
71  }
72  virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
73                            unsigned Size = 0, unsigned ByteAlignment = 0);
74  virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
75                              uint64_t Size, unsigned ByteAlignment = 0);
76  virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
77  virtual void EmitValue(const MCExpr *Value, unsigned Size,unsigned AddrSpace);
78  virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
79                                    unsigned ValueSize = 1,
80                                    unsigned MaxBytesToEmit = 0);
81  virtual void EmitCodeAlignment(unsigned ByteAlignment,
82                                 unsigned MaxBytesToEmit = 0);
83  virtual void EmitValueToOffset(const MCExpr *Offset,
84                                 unsigned char Value = 0);
85
86  virtual void EmitFileDirective(StringRef Filename) {
87    // FIXME: Just ignore the .file; it isn't important enough to fail the
88    // entire assembly.
89
90    //report_fatal_error("unsupported directive: '.file'");
91  }
92
93  virtual void Finish();
94
95  /// @}
96};
97
98} // end anonymous namespace.
99
100void MCMachOStreamer::InitSections() {
101  SwitchSection(getContext().getMachOSection("__TEXT", "__text",
102                                    MCSectionMachO::S_ATTR_PURE_INSTRUCTIONS,
103                                    0, SectionKind::getText()));
104
105}
106
107void MCMachOStreamer::EmitLabel(MCSymbol *Symbol) {
108  // TODO: This is almost exactly the same as WinCOFFStreamer. Consider merging
109  // into MCObjectStreamer.
110  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
111  assert(!Symbol->isVariable() && "Cannot emit a variable symbol!");
112  assert(CurSection && "Cannot emit before setting section!");
113
114  Symbol->setSection(*CurSection);
115
116  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
117
118  // We have to create a new fragment if this is an atom defining symbol,
119  // fragments cannot span atoms.
120  if (getAssembler().isSymbolLinkerVisible(SD.getSymbol()))
121    new MCDataFragment(getCurrentSectionData());
122
123  // FIXME: This is wasteful, we don't necessarily need to create a data
124  // fragment. Instead, we should mark the symbol as pointing into the data
125  // fragment if it exists, otherwise we should just queue the label and set its
126  // fragment pointer when we emit the next fragment.
127  MCDataFragment *F = getOrCreateDataFragment();
128  assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
129  SD.setFragment(F);
130  SD.setOffset(F->getContents().size());
131
132  // This causes the reference type flag to be cleared. Darwin 'as' was "trying"
133  // to clear the weak reference and weak definition bits too, but the
134  // implementation was buggy. For now we just try to match 'as', for
135  // diffability.
136  //
137  // FIXME: Cleanup this code, these bits should be emitted based on semantic
138  // properties, not on the order of definition, etc.
139  SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeMask);
140}
141
142void MCMachOStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
143  switch (Flag) {
144  case MCAF_SyntaxUnified: return; // no-op here.
145  case MCAF_Code16: return; // no-op here.
146  case MCAF_Code32: return; // no-op here.
147  case MCAF_SubsectionsViaSymbols:
148    getAssembler().setSubsectionsViaSymbols(true);
149    return;
150  default:
151    llvm_unreachable("invalid assembler flag!");
152  }
153}
154
155void MCMachOStreamer::EmitThumbFunc(MCSymbol *Func) {
156  // FIXME: Flag the function ISA as thumb with DW_AT_APPLE_isa.
157}
158
159void MCMachOStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
160  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
161  // MCObjectStreamer.
162  // FIXME: Lift context changes into super class.
163  getAssembler().getOrCreateSymbolData(*Symbol);
164  Symbol->setVariableValue(AddValueSymbols(Value));
165}
166
167void MCMachOStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
168                                          MCSymbolAttr Attribute) {
169  // Indirect symbols are handled differently, to match how 'as' handles
170  // them. This makes writing matching .o files easier.
171  if (Attribute == MCSA_IndirectSymbol) {
172    // Note that we intentionally cannot use the symbol data here; this is
173    // important for matching the string table that 'as' generates.
174    IndirectSymbolData ISD;
175    ISD.Symbol = Symbol;
176    ISD.SectionData = getCurrentSectionData();
177    getAssembler().getIndirectSymbols().push_back(ISD);
178    return;
179  }
180
181  // Adding a symbol attribute always introduces the symbol, note that an
182  // important side effect of calling getOrCreateSymbolData here is to register
183  // the symbol with the assembler.
184  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
185
186  // The implementation of symbol attributes is designed to match 'as', but it
187  // leaves much to desired. It doesn't really make sense to arbitrarily add and
188  // remove flags, but 'as' allows this (in particular, see .desc).
189  //
190  // In the future it might be worth trying to make these operations more well
191  // defined.
192  switch (Attribute) {
193  case MCSA_Invalid:
194  case MCSA_ELF_TypeFunction:
195  case MCSA_ELF_TypeIndFunction:
196  case MCSA_ELF_TypeObject:
197  case MCSA_ELF_TypeTLS:
198  case MCSA_ELF_TypeCommon:
199  case MCSA_ELF_TypeNoType:
200  case MCSA_ELF_TypeGnuUniqueObject:
201  case MCSA_IndirectSymbol:
202  case MCSA_Hidden:
203  case MCSA_Internal:
204  case MCSA_Protected:
205  case MCSA_Weak:
206  case MCSA_Local:
207    assert(0 && "Invalid symbol attribute for Mach-O!");
208    break;
209
210  case MCSA_Global:
211    SD.setExternal(true);
212    // This effectively clears the undefined lazy bit, in Darwin 'as', although
213    // it isn't very consistent because it implements this as part of symbol
214    // lookup.
215    //
216    // FIXME: Cleanup this code, these bits should be emitted based on semantic
217    // properties, not on the order of definition, etc.
218    SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeUndefinedLazy);
219    break;
220
221  case MCSA_LazyReference:
222    // FIXME: This requires -dynamic.
223    SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
224    if (Symbol->isUndefined())
225      SD.setFlags(SD.getFlags() | SF_ReferenceTypeUndefinedLazy);
226    break;
227
228    // Since .reference sets the no dead strip bit, it is equivalent to
229    // .no_dead_strip in practice.
230  case MCSA_Reference:
231  case MCSA_NoDeadStrip:
232    SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
233    break;
234
235  case MCSA_SymbolResolver:
236    SD.setFlags(SD.getFlags() | SF_SymbolResolver);
237    break;
238
239  case MCSA_PrivateExtern:
240    SD.setExternal(true);
241    SD.setPrivateExtern(true);
242    break;
243
244  case MCSA_WeakReference:
245    // FIXME: This requires -dynamic.
246    if (Symbol->isUndefined())
247      SD.setFlags(SD.getFlags() | SF_WeakReference);
248    break;
249
250  case MCSA_WeakDefinition:
251    // FIXME: 'as' enforces that this is defined and global. The manual claims
252    // it has to be in a coalesced section, but this isn't enforced.
253    SD.setFlags(SD.getFlags() | SF_WeakDefinition);
254    break;
255
256  case MCSA_WeakDefAutoPrivate:
257    SD.setFlags(SD.getFlags() | SF_WeakDefinition | SF_WeakReference);
258    break;
259  }
260}
261
262void MCMachOStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
263  // Encode the 'desc' value into the lowest implementation defined bits.
264  assert(DescValue == (DescValue & SF_DescFlagsMask) &&
265         "Invalid .desc value!");
266  getAssembler().getOrCreateSymbolData(*Symbol).setFlags(
267    DescValue & SF_DescFlagsMask);
268}
269
270void MCMachOStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
271                                       unsigned ByteAlignment) {
272  // FIXME: Darwin 'as' does appear to allow redef of a .comm by itself.
273  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
274
275  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
276  SD.setExternal(true);
277  SD.setCommon(Size, ByteAlignment);
278}
279
280void MCMachOStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
281                                   unsigned Size, unsigned ByteAlignment) {
282  MCSectionData &SectData = getAssembler().getOrCreateSectionData(*Section);
283
284  // The symbol may not be present, which only creates the section.
285  if (!Symbol)
286    return;
287
288  // FIXME: Assert that this section has the zerofill type.
289
290  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
291
292  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
293
294  // Emit an align fragment if necessary.
295  if (ByteAlignment != 1)
296    new MCAlignFragment(ByteAlignment, 0, 0, ByteAlignment, &SectData);
297
298  MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
299  SD.setFragment(F);
300
301  Symbol->setSection(*Section);
302
303  // Update the maximum alignment on the zero fill section if necessary.
304  if (ByteAlignment > SectData.getAlignment())
305    SectData.setAlignment(ByteAlignment);
306}
307
308// This should always be called with the thread local bss section.  Like the
309// .zerofill directive this doesn't actually switch sections on us.
310void MCMachOStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
311                                     uint64_t Size, unsigned ByteAlignment) {
312  EmitZerofill(Section, Symbol, Size, ByteAlignment);
313  return;
314}
315
316void MCMachOStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
317  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
318  // MCObjectStreamer.
319  getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
320}
321
322void MCMachOStreamer::EmitValue(const MCExpr *Value, unsigned Size,
323                                unsigned AddrSpace) {
324  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
325  // MCObjectStreamer.
326  MCDataFragment *DF = getOrCreateDataFragment();
327
328  // Avoid fixups when possible.
329  int64_t AbsValue;
330  if (AddValueSymbols(Value)->EvaluateAsAbsolute(AbsValue)) {
331    // FIXME: Endianness assumption.
332    for (unsigned i = 0; i != Size; ++i)
333      DF->getContents().push_back(uint8_t(AbsValue >> (i * 8)));
334  } else {
335    DF->addFixup(MCFixup::Create(DF->getContents().size(),
336                                 AddValueSymbols(Value),
337                                 MCFixup::getKindForSize(Size, false)));
338    DF->getContents().resize(DF->getContents().size() + Size, 0);
339  }
340}
341
342void MCMachOStreamer::EmitValueToAlignment(unsigned ByteAlignment,
343                                           int64_t Value, unsigned ValueSize,
344                                           unsigned MaxBytesToEmit) {
345  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
346  // MCObjectStreamer.
347  if (MaxBytesToEmit == 0)
348    MaxBytesToEmit = ByteAlignment;
349  new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
350                      getCurrentSectionData());
351
352  // Update the maximum alignment on the current section if necessary.
353  if (ByteAlignment > getCurrentSectionData()->getAlignment())
354    getCurrentSectionData()->setAlignment(ByteAlignment);
355}
356
357void MCMachOStreamer::EmitCodeAlignment(unsigned ByteAlignment,
358                                        unsigned MaxBytesToEmit) {
359  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
360  // MCObjectStreamer.
361  if (MaxBytesToEmit == 0)
362    MaxBytesToEmit = ByteAlignment;
363  MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
364                                           getCurrentSectionData());
365  F->setEmitNops(true);
366
367  // Update the maximum alignment on the current section if necessary.
368  if (ByteAlignment > getCurrentSectionData()->getAlignment())
369    getCurrentSectionData()->setAlignment(ByteAlignment);
370}
371
372void MCMachOStreamer::EmitValueToOffset(const MCExpr *Offset,
373                                        unsigned char Value) {
374  new MCOrgFragment(*Offset, Value, getCurrentSectionData());
375}
376
377void MCMachOStreamer::EmitInstToFragment(const MCInst &Inst) {
378  MCInstFragment *IF = new MCInstFragment(Inst, getCurrentSectionData());
379
380  // Add the fixups and data.
381  //
382  // FIXME: Revisit this design decision when relaxation is done, we may be
383  // able to get away with not storing any extra data in the MCInst.
384  SmallVector<MCFixup, 4> Fixups;
385  SmallString<256> Code;
386  raw_svector_ostream VecOS(Code);
387  getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
388  VecOS.flush();
389
390  IF->getCode() = Code;
391  IF->getFixups() = Fixups;
392}
393
394void MCMachOStreamer::EmitInstToData(const MCInst &Inst) {
395  MCDataFragment *DF = getOrCreateDataFragment();
396
397  SmallVector<MCFixup, 4> Fixups;
398  SmallString<256> Code;
399  raw_svector_ostream VecOS(Code);
400  getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
401  VecOS.flush();
402
403  // Add the fixups and data.
404  for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
405    Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
406    DF->addFixup(Fixups[i]);
407  }
408  DF->getContents().append(Code.begin(), Code.end());
409}
410
411void MCMachOStreamer::Finish() {
412  // Dump out the dwarf file & directory tables and line tables.
413  if (getContext().hasDwarfFiles()) {
414    const MCSection *DwarfLineSection = getContext().getMachOSection("__DWARF",
415                                         "__debug_line",
416                                         MCSectionMachO::S_ATTR_DEBUG,
417                                         0, SectionKind::getDataRelLocal());
418    MCSectionData &DLS =
419      getAssembler().getOrCreateSectionData(*DwarfLineSection);
420    int PointerSize = getAssembler().getBackend().getPointerSize();
421    MCDwarfFileTable::Emit(this, DwarfLineSection, &DLS, PointerSize);
422  }
423
424  // We have to set the fragment atom associations so we can relax properly for
425  // Mach-O.
426
427  // First, scan the symbol table to build a lookup table from fragments to
428  // defining symbols.
429  DenseMap<const MCFragment*, MCSymbolData*> DefiningSymbolMap;
430  for (MCAssembler::symbol_iterator it = getAssembler().symbol_begin(),
431         ie = getAssembler().symbol_end(); it != ie; ++it) {
432    if (getAssembler().isSymbolLinkerVisible(it->getSymbol()) &&
433        it->getFragment()) {
434      // An atom defining symbol should never be internal to a fragment.
435      assert(it->getOffset() == 0 && "Invalid offset in atom defining symbol!");
436      DefiningSymbolMap[it->getFragment()] = it;
437    }
438  }
439
440  // Set the fragment atom associations by tracking the last seen atom defining
441  // symbol.
442  for (MCAssembler::iterator it = getAssembler().begin(),
443         ie = getAssembler().end(); it != ie; ++it) {
444    MCSymbolData *CurrentAtom = 0;
445    for (MCSectionData::iterator it2 = it->begin(),
446           ie2 = it->end(); it2 != ie2; ++it2) {
447      if (MCSymbolData *SD = DefiningSymbolMap.lookup(it2))
448        CurrentAtom = SD;
449      it2->setAtom(CurrentAtom);
450    }
451  }
452
453  this->MCObjectStreamer::Finish();
454}
455
456MCStreamer *llvm::createMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
457                                      raw_ostream &OS, MCCodeEmitter *CE,
458                                      bool RelaxAll) {
459  MCMachOStreamer *S = new MCMachOStreamer(Context, TAB, OS, CE);
460  if (RelaxAll)
461    S->getAssembler().setRelaxAll(true);
462  return S;
463}
464