MCMachOStreamer.cpp revision dce4a407a24b04eebc6a376f8e62b41aaa7b071f 
1//===-- MCMachOStreamer.cpp - MachO Streamer ------------------------------===//
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#include "llvm/ADT/DenseMap.h"
12#include "llvm/ADT/SmallVector.h"
13#include "llvm/MC/MCAsmBackend.h"
14#include "llvm/MC/MCAssembler.h"
15#include "llvm/MC/MCCodeEmitter.h"
16#include "llvm/MC/MCContext.h"
17#include "llvm/MC/MCDwarf.h"
18#include "llvm/MC/MCExpr.h"
19#include "llvm/MC/MCInst.h"
20#include "llvm/MC/MCLinkerOptimizationHint.h"
21#include "llvm/MC/MCMachOSymbolFlags.h"
22#include "llvm/MC/MCObjectFileInfo.h"
23#include "llvm/MC/MCObjectStreamer.h"
24#include "llvm/MC/MCSection.h"
25#include "llvm/MC/MCSectionMachO.h"
26#include "llvm/MC/MCSymbol.h"
27#include "llvm/Support/Dwarf.h"
28#include "llvm/Support/ErrorHandling.h"
29#include "llvm/Support/raw_ostream.h"
30
31using namespace llvm;
32
33namespace {
34
35class MCMachOStreamer : public MCObjectStreamer {
36private:
37  /// LabelSections - true if each section change should emit a linker local
38  /// label for use in relocations for assembler local references. Obviates the
39  /// need for local relocations. False by default.
40  bool LabelSections;
41
42  /// HasSectionLabel - map of which sections have already had a non-local
43  /// label emitted to them. Used so we don't emit extraneous linker local
44  /// labels in the middle of the section.
45  DenseMap<const MCSection*, bool> HasSectionLabel;
46
47  void EmitInstToData(const MCInst &Inst, const MCSubtargetInfo &STI) override;
48
49  void EmitDataRegion(DataRegionData::KindTy Kind);
50  void EmitDataRegionEnd();
51
52public:
53  MCMachOStreamer(MCContext &Context, MCAsmBackend &MAB, raw_ostream &OS,
54                  MCCodeEmitter *Emitter, bool label)
55      : MCObjectStreamer(Context, MAB, OS, Emitter),
56        LabelSections(label) {}
57
58  /// @name MCStreamer Interface
59  /// @{
60
61  void ChangeSection(const MCSection *Sect, const MCExpr *Subsect) override;
62  void EmitLabel(MCSymbol *Symbol) override;
63  void EmitDebugLabel(MCSymbol *Symbol) override;
64  void EmitEHSymAttributes(const MCSymbol *Symbol, MCSymbol *EHSymbol) override;
65  void EmitAssemblerFlag(MCAssemblerFlag Flag) override;
66  void EmitLinkerOptions(ArrayRef<std::string> Options) override;
67  void EmitDataRegion(MCDataRegionType Kind) override;
68  void EmitVersionMin(MCVersionMinType Kind, unsigned Major,
69                      unsigned Minor, unsigned Update) override;
70  void EmitThumbFunc(MCSymbol *Func) override;
71  bool EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override;
72  void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) override;
73  void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
74                        unsigned ByteAlignment) override;
75  void BeginCOFFSymbolDef(const MCSymbol *Symbol) override {
76    llvm_unreachable("macho doesn't support this directive");
77  }
78  void EmitCOFFSymbolStorageClass(int StorageClass) override {
79    llvm_unreachable("macho doesn't support this directive");
80  }
81  void EmitCOFFSymbolType(int Type) override {
82    llvm_unreachable("macho doesn't support this directive");
83  }
84  void EndCOFFSymbolDef() override {
85    llvm_unreachable("macho doesn't support this directive");
86  }
87  void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) override {
88    llvm_unreachable("macho doesn't support this directive");
89  }
90  void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
91                             unsigned ByteAlignment) override;
92  void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = nullptr,
93                    uint64_t Size = 0, unsigned ByteAlignment = 0) override;
94  virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
95                      uint64_t Size, unsigned ByteAlignment = 0) override;
96
97  void EmitFileDirective(StringRef Filename) override {
98    // FIXME: Just ignore the .file; it isn't important enough to fail the
99    // entire assembly.
100
101    // report_fatal_error("unsupported directive: '.file'");
102  }
103
104  void EmitIdent(StringRef IdentString) override {
105    llvm_unreachable("macho doesn't support this directive");
106  }
107
108  void EmitLOHDirective(MCLOHType Kind, const MCLOHArgs &Args) override {
109    getAssembler().getLOHContainer().addDirective(Kind, Args);
110  }
111
112  void FinishImpl() override;
113};
114
115} // end anonymous namespace.
116
117void MCMachOStreamer::ChangeSection(const MCSection *Section,
118                                    const MCExpr *Subsection) {
119  // Change the section normally.
120  MCObjectStreamer::ChangeSection(Section, Subsection);
121  // Output a linker-local symbol so we don't need section-relative local
122  // relocations. The linker hates us when we do that.
123  if (LabelSections && !HasSectionLabel[Section]) {
124    MCSymbol *Label = getContext().CreateLinkerPrivateTempSymbol();
125    EmitLabel(Label);
126    HasSectionLabel[Section] = true;
127  }
128}
129
130void MCMachOStreamer::EmitEHSymAttributes(const MCSymbol *Symbol,
131                                          MCSymbol *EHSymbol) {
132  MCSymbolData &SD =
133    getAssembler().getOrCreateSymbolData(*Symbol);
134  if (SD.isExternal())
135    EmitSymbolAttribute(EHSymbol, MCSA_Global);
136  if (SD.getFlags() & SF_WeakDefinition)
137    EmitSymbolAttribute(EHSymbol, MCSA_WeakDefinition);
138  if (SD.isPrivateExtern())
139    EmitSymbolAttribute(EHSymbol, MCSA_PrivateExtern);
140}
141
142void MCMachOStreamer::EmitLabel(MCSymbol *Symbol) {
143  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
144
145  // isSymbolLinkerVisible uses the section.
146  AssignSection(Symbol, getCurrentSection().first);
147  // We have to create a new fragment if this is an atom defining symbol,
148  // fragments cannot span atoms.
149  if (getAssembler().isSymbolLinkerVisible(*Symbol))
150    insert(new MCDataFragment());
151
152  MCObjectStreamer::EmitLabel(Symbol);
153
154  MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
155  // This causes the reference type flag to be cleared. Darwin 'as' was "trying"
156  // to clear the weak reference and weak definition bits too, but the
157  // implementation was buggy. For now we just try to match 'as', for
158  // diffability.
159  //
160  // FIXME: Cleanup this code, these bits should be emitted based on semantic
161  // properties, not on the order of definition, etc.
162  SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeMask);
163}
164
165void MCMachOStreamer::EmitDebugLabel(MCSymbol *Symbol) {
166  EmitLabel(Symbol);
167}
168void MCMachOStreamer::EmitDataRegion(DataRegionData::KindTy Kind) {
169  if (!getAssembler().getBackend().hasDataInCodeSupport())
170    return;
171  // Create a temporary label to mark the start of the data region.
172  MCSymbol *Start = getContext().CreateTempSymbol();
173  EmitLabel(Start);
174  // Record the region for the object writer to use.
175  DataRegionData Data = { Kind, Start, nullptr };
176  std::vector<DataRegionData> &Regions = getAssembler().getDataRegions();
177  Regions.push_back(Data);
178}
179
180void MCMachOStreamer::EmitDataRegionEnd() {
181  if (!getAssembler().getBackend().hasDataInCodeSupport())
182    return;
183  std::vector<DataRegionData> &Regions = getAssembler().getDataRegions();
184  assert(Regions.size() && "Mismatched .end_data_region!");
185  DataRegionData &Data = Regions.back();
186  assert(!Data.End && "Mismatched .end_data_region!");
187  // Create a temporary label to mark the end of the data region.
188  Data.End = getContext().CreateTempSymbol();
189  EmitLabel(Data.End);
190}
191
192void MCMachOStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
193  // Let the target do whatever target specific stuff it needs to do.
194  getAssembler().getBackend().handleAssemblerFlag(Flag);
195  // Do any generic stuff we need to do.
196  switch (Flag) {
197  case MCAF_SyntaxUnified: return; // no-op here.
198  case MCAF_Code16: return; // Change parsing mode; no-op here.
199  case MCAF_Code32: return; // Change parsing mode; no-op here.
200  case MCAF_Code64: return; // Change parsing mode; no-op here.
201  case MCAF_SubsectionsViaSymbols:
202    getAssembler().setSubsectionsViaSymbols(true);
203    return;
204  }
205}
206
207void MCMachOStreamer::EmitLinkerOptions(ArrayRef<std::string> Options) {
208  getAssembler().getLinkerOptions().push_back(Options);
209}
210
211void MCMachOStreamer::EmitDataRegion(MCDataRegionType Kind) {
212  switch (Kind) {
213  case MCDR_DataRegion:
214    EmitDataRegion(DataRegionData::Data);
215    return;
216  case MCDR_DataRegionJT8:
217    EmitDataRegion(DataRegionData::JumpTable8);
218    return;
219  case MCDR_DataRegionJT16:
220    EmitDataRegion(DataRegionData::JumpTable16);
221    return;
222  case MCDR_DataRegionJT32:
223    EmitDataRegion(DataRegionData::JumpTable32);
224    return;
225  case MCDR_DataRegionEnd:
226    EmitDataRegionEnd();
227    return;
228  }
229}
230
231void MCMachOStreamer::EmitVersionMin(MCVersionMinType Kind, unsigned Major,
232                                     unsigned Minor, unsigned Update) {
233  getAssembler().setVersionMinInfo(Kind, Major, Minor, Update);
234}
235
236void MCMachOStreamer::EmitThumbFunc(MCSymbol *Symbol) {
237  // Remember that the function is a thumb function. Fixup and relocation
238  // values will need adjusted.
239  getAssembler().setIsThumbFunc(Symbol);
240}
241
242bool MCMachOStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
243                                          MCSymbolAttr Attribute) {
244  // Indirect symbols are handled differently, to match how 'as' handles
245  // them. This makes writing matching .o files easier.
246  if (Attribute == MCSA_IndirectSymbol) {
247    // Note that we intentionally cannot use the symbol data here; this is
248    // important for matching the string table that 'as' generates.
249    IndirectSymbolData ISD;
250    ISD.Symbol = Symbol;
251    ISD.SectionData = getCurrentSectionData();
252    getAssembler().getIndirectSymbols().push_back(ISD);
253    return true;
254  }
255
256  // Adding a symbol attribute always introduces the symbol, note that an
257  // important side effect of calling getOrCreateSymbolData here is to register
258  // the symbol with the assembler.
259  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
260
261  // The implementation of symbol attributes is designed to match 'as', but it
262  // leaves much to desired. It doesn't really make sense to arbitrarily add and
263  // remove flags, but 'as' allows this (in particular, see .desc).
264  //
265  // In the future it might be worth trying to make these operations more well
266  // defined.
267  switch (Attribute) {
268  case MCSA_Invalid:
269  case MCSA_ELF_TypeFunction:
270  case MCSA_ELF_TypeIndFunction:
271  case MCSA_ELF_TypeObject:
272  case MCSA_ELF_TypeTLS:
273  case MCSA_ELF_TypeCommon:
274  case MCSA_ELF_TypeNoType:
275  case MCSA_ELF_TypeGnuUniqueObject:
276  case MCSA_Hidden:
277  case MCSA_IndirectSymbol:
278  case MCSA_Internal:
279  case MCSA_Protected:
280  case MCSA_Weak:
281  case MCSA_Local:
282    return false;
283
284  case MCSA_Global:
285    SD.setExternal(true);
286    // This effectively clears the undefined lazy bit, in Darwin 'as', although
287    // it isn't very consistent because it implements this as part of symbol
288    // lookup.
289    //
290    // FIXME: Cleanup this code, these bits should be emitted based on semantic
291    // properties, not on the order of definition, etc.
292    SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeUndefinedLazy);
293    break;
294
295  case MCSA_LazyReference:
296    // FIXME: This requires -dynamic.
297    SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
298    if (Symbol->isUndefined())
299      SD.setFlags(SD.getFlags() | SF_ReferenceTypeUndefinedLazy);
300    break;
301
302    // Since .reference sets the no dead strip bit, it is equivalent to
303    // .no_dead_strip in practice.
304  case MCSA_Reference:
305  case MCSA_NoDeadStrip:
306    SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
307    break;
308
309  case MCSA_SymbolResolver:
310    SD.setFlags(SD.getFlags() | SF_SymbolResolver);
311    break;
312
313  case MCSA_PrivateExtern:
314    SD.setExternal(true);
315    SD.setPrivateExtern(true);
316    break;
317
318  case MCSA_WeakReference:
319    // FIXME: This requires -dynamic.
320    if (Symbol->isUndefined())
321      SD.setFlags(SD.getFlags() | SF_WeakReference);
322    break;
323
324  case MCSA_WeakDefinition:
325    // FIXME: 'as' enforces that this is defined and global. The manual claims
326    // it has to be in a coalesced section, but this isn't enforced.
327    SD.setFlags(SD.getFlags() | SF_WeakDefinition);
328    break;
329
330  case MCSA_WeakDefAutoPrivate:
331    SD.setFlags(SD.getFlags() | SF_WeakDefinition | SF_WeakReference);
332    break;
333  }
334
335  return true;
336}
337
338void MCMachOStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
339  // Encode the 'desc' value into the lowest implementation defined bits.
340  assert(DescValue == (DescValue & SF_DescFlagsMask) &&
341         "Invalid .desc value!");
342  getAssembler().getOrCreateSymbolData(*Symbol).setFlags(
343    DescValue & SF_DescFlagsMask);
344}
345
346void MCMachOStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
347                                       unsigned ByteAlignment) {
348  // FIXME: Darwin 'as' does appear to allow redef of a .comm by itself.
349  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
350
351  AssignSection(Symbol, nullptr);
352
353  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
354  SD.setExternal(true);
355  SD.setCommon(Size, ByteAlignment);
356}
357
358void MCMachOStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
359                                            unsigned ByteAlignment) {
360  // '.lcomm' is equivalent to '.zerofill'.
361  return EmitZerofill(getContext().getObjectFileInfo()->getDataBSSSection(),
362                      Symbol, Size, ByteAlignment);
363}
364
365void MCMachOStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
366                                   uint64_t Size, unsigned ByteAlignment) {
367  MCSectionData &SectData = getAssembler().getOrCreateSectionData(*Section);
368
369  // The symbol may not be present, which only creates the section.
370  if (!Symbol)
371    return;
372
373  // On darwin all virtual sections have zerofill type.
374  assert(Section->isVirtualSection() && "Section does not have zerofill type!");
375
376  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
377
378  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
379
380  // Emit an align fragment if necessary.
381  if (ByteAlignment != 1)
382    new MCAlignFragment(ByteAlignment, 0, 0, ByteAlignment, &SectData);
383
384  MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
385  SD.setFragment(F);
386
387  AssignSection(Symbol, Section);
388
389  // Update the maximum alignment on the zero fill section if necessary.
390  if (ByteAlignment > SectData.getAlignment())
391    SectData.setAlignment(ByteAlignment);
392}
393
394// This should always be called with the thread local bss section.  Like the
395// .zerofill directive this doesn't actually switch sections on us.
396void MCMachOStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
397                                     uint64_t Size, unsigned ByteAlignment) {
398  EmitZerofill(Section, Symbol, Size, ByteAlignment);
399  return;
400}
401
402void MCMachOStreamer::EmitInstToData(const MCInst &Inst,
403                                     const MCSubtargetInfo &STI) {
404  MCDataFragment *DF = getOrCreateDataFragment();
405
406  SmallVector<MCFixup, 4> Fixups;
407  SmallString<256> Code;
408  raw_svector_ostream VecOS(Code);
409  getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups, STI);
410  VecOS.flush();
411
412  // Add the fixups and data.
413  for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
414    Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
415    DF->getFixups().push_back(Fixups[i]);
416  }
417  DF->getContents().append(Code.begin(), Code.end());
418}
419
420void MCMachOStreamer::FinishImpl() {
421  EmitFrames(&getAssembler().getBackend());
422
423  // We have to set the fragment atom associations so we can relax properly for
424  // Mach-O.
425
426  // First, scan the symbol table to build a lookup table from fragments to
427  // defining symbols.
428  DenseMap<const MCFragment*, MCSymbolData*> DefiningSymbolMap;
429  for (MCSymbolData &SD : getAssembler().symbols()) {
430    if (getAssembler().isSymbolLinkerVisible(SD.getSymbol()) &&
431        SD.getFragment()) {
432      // An atom defining symbol should never be internal to a fragment.
433      assert(SD.getOffset() == 0 && "Invalid offset in atom defining symbol!");
434      DefiningSymbolMap[SD.getFragment()] = &SD;
435    }
436  }
437
438  // Set the fragment atom associations by tracking the last seen atom defining
439  // symbol.
440  for (MCAssembler::iterator it = getAssembler().begin(),
441         ie = getAssembler().end(); it != ie; ++it) {
442    MCSymbolData *CurrentAtom = nullptr;
443    for (MCSectionData::iterator it2 = it->begin(),
444           ie2 = it->end(); it2 != ie2; ++it2) {
445      if (MCSymbolData *SD = DefiningSymbolMap.lookup(it2))
446        CurrentAtom = SD;
447      it2->setAtom(CurrentAtom);
448    }
449  }
450
451  this->MCObjectStreamer::FinishImpl();
452}
453
454MCStreamer *llvm::createMachOStreamer(MCContext &Context, MCAsmBackend &MAB,
455                                      raw_ostream &OS, MCCodeEmitter *CE,
456                                      bool RelaxAll,
457                                      bool LabelSections) {
458  MCMachOStreamer *S = new MCMachOStreamer(Context, MAB, OS, CE, LabelSections);
459  if (RelaxAll)
460    S->getAssembler().setRelaxAll(true);
461  return S;
462}
463