MCMachOStreamer.cpp revision 858143816d43e58b17bfd11cb1b57afbd7f0f893 
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/MC/MCAsmBackend.h"
24#include "llvm/Support/Dwarf.h"
25#include "llvm/Support/ErrorHandling.h"
26#include "llvm/Support/raw_ostream.h"
27
28using namespace llvm;
29
30namespace {
31
32class MCMachOStreamer : public MCObjectStreamer {
33private:
34  virtual void EmitInstToData(const MCInst &Inst);
35
36public:
37  MCMachOStreamer(MCContext &Context, MCAsmBackend &MAB,
38                  raw_ostream &OS, MCCodeEmitter *Emitter)
39    : MCObjectStreamer(Context, MAB, OS, Emitter) {}
40
41  /// @name MCStreamer Interface
42  /// @{
43
44  virtual void InitSections();
45  virtual void EmitLabel(MCSymbol *Symbol);
46  virtual void EmitEHSymAttributes(const MCSymbol *Symbol,
47                                   MCSymbol *EHSymbol);
48  virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
49  virtual void EmitThumbFunc(MCSymbol *Func);
50  virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
51  virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
52  virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue);
53  virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
54                                unsigned ByteAlignment);
55  virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
56    llvm_unreachable("macho doesn't support this directive");
57  }
58  virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
59    llvm_unreachable("macho doesn't support this directive");
60  }
61  virtual void EmitCOFFSymbolType(int Type) {
62    llvm_unreachable("macho doesn't support this directive");
63  }
64  virtual void EndCOFFSymbolDef() {
65    llvm_unreachable("macho doesn't support this directive");
66  }
67  virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
68    llvm_unreachable("macho doesn't support this directive");
69  }
70  virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
71                                     unsigned ByteAlignment) {
72    llvm_unreachable("macho doesn't support this directive");
73  }
74  virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
75                            unsigned Size = 0, unsigned ByteAlignment = 0);
76  virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
77                              uint64_t Size, unsigned ByteAlignment = 0);
78  virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
79  virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
80                                    unsigned ValueSize = 1,
81                                    unsigned MaxBytesToEmit = 0);
82  virtual void EmitCodeAlignment(unsigned ByteAlignment,
83                                 unsigned MaxBytesToEmit = 0);
84
85  virtual void EmitFileDirective(StringRef Filename) {
86    // FIXME: Just ignore the .file; it isn't important enough to fail the
87    // entire assembly.
88
89    //report_fatal_error("unsupported directive: '.file'");
90  }
91
92  virtual void FinishImpl();
93
94  /// @}
95};
96
97} // end anonymous namespace.
98
99void MCMachOStreamer::InitSections() {
100  SwitchSection(getContext().getMachOSection("__TEXT", "__text",
101                                    MCSectionMachO::S_ATTR_PURE_INSTRUCTIONS,
102                                    0, SectionKind::getText()));
103
104}
105
106void MCMachOStreamer::EmitEHSymAttributes(const MCSymbol *Symbol,
107                                          MCSymbol *EHSymbol) {
108  MCSymbolData &SD =
109    getAssembler().getOrCreateSymbolData(*Symbol);
110  if (SD.isExternal())
111    EmitSymbolAttribute(EHSymbol, MCSA_Global);
112  if (SD.getFlags() & SF_WeakDefinition)
113    EmitSymbolAttribute(EHSymbol, MCSA_WeakDefinition);
114  if (SD.isPrivateExtern())
115    EmitSymbolAttribute(EHSymbol, MCSA_PrivateExtern);
116}
117
118void MCMachOStreamer::EmitLabel(MCSymbol *Symbol) {
119  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
120
121  // isSymbolLinkerVisible uses the section.
122  Symbol->setSection(*getCurrentSection());
123  // We have to create a new fragment if this is an atom defining symbol,
124  // fragments cannot span atoms.
125  if (getAssembler().isSymbolLinkerVisible(*Symbol))
126    new MCDataFragment(getCurrentSectionData());
127
128  MCObjectStreamer::EmitLabel(Symbol);
129
130  MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
131  // This causes the reference type flag to be cleared. Darwin 'as' was "trying"
132  // to clear the weak reference and weak definition bits too, but the
133  // implementation was buggy. For now we just try to match 'as', for
134  // diffability.
135  //
136  // FIXME: Cleanup this code, these bits should be emitted based on semantic
137  // properties, not on the order of definition, etc.
138  SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeMask);
139}
140
141void MCMachOStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
142  // Let the target do whatever target specific stuff it needs to do.
143  getAssembler().getBackend().handleAssemblerFlag(Flag);
144  // Do any generic stuff we need to do.
145  switch (Flag) {
146  case MCAF_SyntaxUnified: return; // no-op here.
147  case MCAF_Code16: return; // Change parsing mode; no-op here.
148  case MCAF_Code32: return; // Change parsing mode; no-op here.
149  case MCAF_Code64: return; // Change parsing mode; no-op here.
150  case MCAF_SubsectionsViaSymbols:
151    getAssembler().setSubsectionsViaSymbols(true);
152    return;
153  }
154}
155
156void MCMachOStreamer::EmitThumbFunc(MCSymbol *Symbol) {
157  // Remember that the function is a thumb function. Fixup and relocation
158  // values will need adjusted.
159  getAssembler().setIsThumbFunc(Symbol);
160
161  // Mark the thumb bit on the symbol.
162  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
163  SD.setFlags(SD.getFlags() | SF_ThumbFunc);
164}
165
166void MCMachOStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
167  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
168  // MCObjectStreamer.
169  // FIXME: Lift context changes into super class.
170  getAssembler().getOrCreateSymbolData(*Symbol);
171  Symbol->setVariableValue(AddValueSymbols(Value));
172}
173
174void MCMachOStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
175                                          MCSymbolAttr Attribute) {
176  // Indirect symbols are handled differently, to match how 'as' handles
177  // them. This makes writing matching .o files easier.
178  if (Attribute == MCSA_IndirectSymbol) {
179    // Note that we intentionally cannot use the symbol data here; this is
180    // important for matching the string table that 'as' generates.
181    IndirectSymbolData ISD;
182    ISD.Symbol = Symbol;
183    ISD.SectionData = getCurrentSectionData();
184    getAssembler().getIndirectSymbols().push_back(ISD);
185    return;
186  }
187
188  // Adding a symbol attribute always introduces the symbol, note that an
189  // important side effect of calling getOrCreateSymbolData here is to register
190  // the symbol with the assembler.
191  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
192
193  // The implementation of symbol attributes is designed to match 'as', but it
194  // leaves much to desired. It doesn't really make sense to arbitrarily add and
195  // remove flags, but 'as' allows this (in particular, see .desc).
196  //
197  // In the future it might be worth trying to make these operations more well
198  // defined.
199  switch (Attribute) {
200  case MCSA_Invalid:
201  case MCSA_ELF_TypeFunction:
202  case MCSA_ELF_TypeIndFunction:
203  case MCSA_ELF_TypeObject:
204  case MCSA_ELF_TypeTLS:
205  case MCSA_ELF_TypeCommon:
206  case MCSA_ELF_TypeNoType:
207  case MCSA_ELF_TypeGnuUniqueObject:
208  case MCSA_Hidden:
209  case MCSA_IndirectSymbol:
210  case MCSA_Internal:
211  case MCSA_Protected:
212  case MCSA_Weak:
213  case MCSA_Local:
214    llvm_unreachable("Invalid symbol attribute for Mach-O!");
215
216  case MCSA_Global:
217    SD.setExternal(true);
218    // This effectively clears the undefined lazy bit, in Darwin 'as', although
219    // it isn't very consistent because it implements this as part of symbol
220    // lookup.
221    //
222    // FIXME: Cleanup this code, these bits should be emitted based on semantic
223    // properties, not on the order of definition, etc.
224    SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeUndefinedLazy);
225    break;
226
227  case MCSA_LazyReference:
228    // FIXME: This requires -dynamic.
229    SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
230    if (Symbol->isUndefined())
231      SD.setFlags(SD.getFlags() | SF_ReferenceTypeUndefinedLazy);
232    break;
233
234    // Since .reference sets the no dead strip bit, it is equivalent to
235    // .no_dead_strip in practice.
236  case MCSA_Reference:
237  case MCSA_NoDeadStrip:
238    SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
239    break;
240
241  case MCSA_SymbolResolver:
242    SD.setFlags(SD.getFlags() | SF_SymbolResolver);
243    break;
244
245  case MCSA_PrivateExtern:
246    SD.setExternal(true);
247    SD.setPrivateExtern(true);
248    break;
249
250  case MCSA_WeakReference:
251    // FIXME: This requires -dynamic.
252    if (Symbol->isUndefined())
253      SD.setFlags(SD.getFlags() | SF_WeakReference);
254    break;
255
256  case MCSA_WeakDefinition:
257    // FIXME: 'as' enforces that this is defined and global. The manual claims
258    // it has to be in a coalesced section, but this isn't enforced.
259    SD.setFlags(SD.getFlags() | SF_WeakDefinition);
260    break;
261
262  case MCSA_WeakDefAutoPrivate:
263    SD.setFlags(SD.getFlags() | SF_WeakDefinition | SF_WeakReference);
264    break;
265  }
266}
267
268void MCMachOStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
269  // Encode the 'desc' value into the lowest implementation defined bits.
270  assert(DescValue == (DescValue & SF_DescFlagsMask) &&
271         "Invalid .desc value!");
272  getAssembler().getOrCreateSymbolData(*Symbol).setFlags(
273    DescValue & SF_DescFlagsMask);
274}
275
276void MCMachOStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
277                                       unsigned ByteAlignment) {
278  // FIXME: Darwin 'as' does appear to allow redef of a .comm by itself.
279  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
280
281  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
282  SD.setExternal(true);
283  SD.setCommon(Size, ByteAlignment);
284}
285
286void MCMachOStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
287                                   unsigned Size, unsigned ByteAlignment) {
288  MCSectionData &SectData = getAssembler().getOrCreateSectionData(*Section);
289
290  // The symbol may not be present, which only creates the section.
291  if (!Symbol)
292    return;
293
294  // FIXME: Assert that this section has the zerofill type.
295
296  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
297
298  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
299
300  // Emit an align fragment if necessary.
301  if (ByteAlignment != 1)
302    new MCAlignFragment(ByteAlignment, 0, 0, ByteAlignment, &SectData);
303
304  MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
305  SD.setFragment(F);
306
307  Symbol->setSection(*Section);
308
309  // Update the maximum alignment on the zero fill section if necessary.
310  if (ByteAlignment > SectData.getAlignment())
311    SectData.setAlignment(ByteAlignment);
312}
313
314// This should always be called with the thread local bss section.  Like the
315// .zerofill directive this doesn't actually switch sections on us.
316void MCMachOStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
317                                     uint64_t Size, unsigned ByteAlignment) {
318  EmitZerofill(Section, Symbol, Size, ByteAlignment);
319  return;
320}
321
322void MCMachOStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
323  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
324  // MCObjectStreamer.
325  getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
326}
327
328void MCMachOStreamer::EmitValueToAlignment(unsigned ByteAlignment,
329                                           int64_t Value, unsigned ValueSize,
330                                           unsigned MaxBytesToEmit) {
331  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
332  // MCObjectStreamer.
333  if (MaxBytesToEmit == 0)
334    MaxBytesToEmit = ByteAlignment;
335  new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
336                      getCurrentSectionData());
337
338  // Update the maximum alignment on the current section if necessary.
339  if (ByteAlignment > getCurrentSectionData()->getAlignment())
340    getCurrentSectionData()->setAlignment(ByteAlignment);
341}
342
343void MCMachOStreamer::EmitCodeAlignment(unsigned ByteAlignment,
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  MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
350                                           getCurrentSectionData());
351  F->setEmitNops(true);
352
353  // Update the maximum alignment on the current section if necessary.
354  if (ByteAlignment > getCurrentSectionData()->getAlignment())
355    getCurrentSectionData()->setAlignment(ByteAlignment);
356}
357
358void MCMachOStreamer::EmitInstToData(const MCInst &Inst) {
359  MCDataFragment *DF = getOrCreateDataFragment();
360
361  SmallVector<MCFixup, 4> Fixups;
362  SmallString<256> Code;
363  raw_svector_ostream VecOS(Code);
364  getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
365  VecOS.flush();
366
367  // Add the fixups and data.
368  for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
369    Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
370    DF->addFixup(Fixups[i]);
371  }
372  DF->getContents().append(Code.begin(), Code.end());
373}
374
375void MCMachOStreamer::FinishImpl() {
376  EmitFrames(true);
377
378  // We have to set the fragment atom associations so we can relax properly for
379  // Mach-O.
380
381  // First, scan the symbol table to build a lookup table from fragments to
382  // defining symbols.
383  DenseMap<const MCFragment*, MCSymbolData*> DefiningSymbolMap;
384  for (MCAssembler::symbol_iterator it = getAssembler().symbol_begin(),
385         ie = getAssembler().symbol_end(); it != ie; ++it) {
386    if (getAssembler().isSymbolLinkerVisible(it->getSymbol()) &&
387        it->getFragment()) {
388      // An atom defining symbol should never be internal to a fragment.
389      assert(it->getOffset() == 0 && "Invalid offset in atom defining symbol!");
390      DefiningSymbolMap[it->getFragment()] = it;
391    }
392  }
393
394  // Set the fragment atom associations by tracking the last seen atom defining
395  // symbol.
396  for (MCAssembler::iterator it = getAssembler().begin(),
397         ie = getAssembler().end(); it != ie; ++it) {
398    MCSymbolData *CurrentAtom = 0;
399    for (MCSectionData::iterator it2 = it->begin(),
400           ie2 = it->end(); it2 != ie2; ++it2) {
401      if (MCSymbolData *SD = DefiningSymbolMap.lookup(it2))
402        CurrentAtom = SD;
403      it2->setAtom(CurrentAtom);
404    }
405  }
406
407  this->MCObjectStreamer::FinishImpl();
408}
409
410MCStreamer *llvm::createMachOStreamer(MCContext &Context, MCAsmBackend &MAB,
411                                      raw_ostream &OS, MCCodeEmitter *CE,
412                                      bool RelaxAll) {
413  MCMachOStreamer *S = new MCMachOStreamer(Context, MAB, OS, CE);
414  if (RelaxAll)
415    S->getAssembler().setRelaxAll(true);
416  return S;
417}
418