MCMachOStreamer.cpp revision 205407 
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/MCSection.h"
18#include "llvm/MC/MCSymbol.h"
19#include "llvm/Support/ErrorHandling.h"
20#include "llvm/Support/raw_ostream.h"
21using namespace llvm;
22
23namespace {
24
25class MCMachOStreamer : public MCStreamer {
26  /// SymbolFlags - We store the value for the 'desc' symbol field in the lowest
27  /// 16 bits of the implementation defined flags.
28  enum SymbolFlags { // See <mach-o/nlist.h>.
29    SF_DescFlagsMask                        = 0xFFFF,
30
31    // Reference type flags.
32    SF_ReferenceTypeMask                    = 0x0007,
33    SF_ReferenceTypeUndefinedNonLazy        = 0x0000,
34    SF_ReferenceTypeUndefinedLazy           = 0x0001,
35    SF_ReferenceTypeDefined                 = 0x0002,
36    SF_ReferenceTypePrivateDefined          = 0x0003,
37    SF_ReferenceTypePrivateUndefinedNonLazy = 0x0004,
38    SF_ReferenceTypePrivateUndefinedLazy    = 0x0005,
39
40    // Other 'desc' flags.
41    SF_NoDeadStrip                          = 0x0020,
42    SF_WeakReference                        = 0x0040,
43    SF_WeakDefinition                       = 0x0080
44  };
45
46private:
47  MCAssembler Assembler;
48  MCSectionData *CurSectionData;
49
50private:
51  MCFragment *getCurrentFragment() const {
52    assert(CurSectionData && "No current section!");
53
54    if (!CurSectionData->empty())
55      return &CurSectionData->getFragmentList().back();
56
57    return 0;
58  }
59
60public:
61  MCMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
62                  raw_ostream &_OS, MCCodeEmitter *_Emitter)
63    : MCStreamer(Context), Assembler(Context, TAB, *_Emitter, _OS),
64      CurSectionData(0) {}
65  ~MCMachOStreamer() {}
66
67  const MCExpr *AddValueSymbols(const MCExpr *Value) {
68    switch (Value->getKind()) {
69    case MCExpr::Target: assert(0 && "Can't handle target exprs yet!");
70    case MCExpr::Constant:
71      break;
72
73    case MCExpr::Binary: {
74      const MCBinaryExpr *BE = cast<MCBinaryExpr>(Value);
75      AddValueSymbols(BE->getLHS());
76      AddValueSymbols(BE->getRHS());
77      break;
78    }
79
80    case MCExpr::SymbolRef:
81      Assembler.getOrCreateSymbolData(
82        cast<MCSymbolRefExpr>(Value)->getSymbol());
83      break;
84
85    case MCExpr::Unary:
86      AddValueSymbols(cast<MCUnaryExpr>(Value)->getSubExpr());
87      break;
88    }
89
90    return Value;
91  }
92
93  /// @name MCStreamer Interface
94  /// @{
95
96  virtual void SwitchSection(const MCSection *Section);
97  virtual void EmitLabel(MCSymbol *Symbol);
98  virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
99  virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
100  virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
101  virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue);
102  virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
103                                unsigned ByteAlignment);
104  virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
105    assert(0 && "macho doesn't support this directive");
106  }
107  virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
108    assert(0 && "macho doesn't support this directive");
109  }
110  virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
111                            unsigned Size = 0, unsigned ByteAlignment = 0);
112  virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
113  virtual void EmitValue(const MCExpr *Value, unsigned Size,unsigned AddrSpace);
114  virtual void EmitGPRel32Value(const MCExpr *Value) {
115    assert(0 && "macho doesn't support this directive");
116  }
117  virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
118                                    unsigned ValueSize = 1,
119                                    unsigned MaxBytesToEmit = 0);
120  virtual void EmitCodeAlignment(unsigned ByteAlignment,
121                                 unsigned MaxBytesToEmit = 0);
122  virtual void EmitValueToOffset(const MCExpr *Offset,
123                                 unsigned char Value = 0);
124
125  virtual void EmitFileDirective(StringRef Filename) {
126    errs() << "FIXME: MCMachoStreamer:EmitFileDirective not implemented\n";
127  }
128  virtual void EmitDwarfFileDirective(unsigned FileNo, StringRef Filename) {
129    errs() << "FIXME: MCMachoStreamer:EmitDwarfFileDirective not implemented\n";
130  }
131
132  virtual void EmitInstruction(const MCInst &Inst);
133  virtual void Finish();
134
135  /// @}
136};
137
138} // end anonymous namespace.
139
140void MCMachOStreamer::SwitchSection(const MCSection *Section) {
141  assert(Section && "Cannot switch to a null section!");
142
143  // If already in this section, then this is a noop.
144  if (Section == CurSection) return;
145
146  CurSection = Section;
147  CurSectionData = &Assembler.getOrCreateSectionData(*Section);
148}
149
150void MCMachOStreamer::EmitLabel(MCSymbol *Symbol) {
151  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
152
153  // FIXME: We should also use offsets into Fill fragments.
154  MCDataFragment *F = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
155  if (!F)
156    F = new MCDataFragment(CurSectionData);
157
158  MCSymbolData &SD = Assembler.getOrCreateSymbolData(*Symbol);
159  assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
160  SD.setFragment(F);
161  SD.setOffset(F->getContents().size());
162
163  // This causes the reference type and weak reference flags to be cleared.
164  SD.setFlags(SD.getFlags() & ~(SF_WeakReference | SF_ReferenceTypeMask));
165
166  Symbol->setSection(*CurSection);
167}
168
169void MCMachOStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
170  switch (Flag) {
171  case MCAF_SubsectionsViaSymbols:
172    Assembler.setSubsectionsViaSymbols(true);
173    return;
174  }
175
176  assert(0 && "invalid assembler flag!");
177}
178
179void MCMachOStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
180  // Only absolute symbols can be redefined.
181  assert((Symbol->isUndefined() || Symbol->isAbsolute()) &&
182         "Cannot define a symbol twice!");
183
184  // FIXME: Lift context changes into super class.
185  // FIXME: Set associated section.
186  Symbol->setValue(AddValueSymbols(Value));
187}
188
189void MCMachOStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
190                                          MCSymbolAttr Attribute) {
191  // Indirect symbols are handled differently, to match how 'as' handles
192  // them. This makes writing matching .o files easier.
193  if (Attribute == MCSA_IndirectSymbol) {
194    // Note that we intentionally cannot use the symbol data here; this is
195    // important for matching the string table that 'as' generates.
196    IndirectSymbolData ISD;
197    ISD.Symbol = Symbol;
198    ISD.SectionData = CurSectionData;
199    Assembler.getIndirectSymbols().push_back(ISD);
200    return;
201  }
202
203  // Adding a symbol attribute always introduces the symbol, note that an
204  // important side effect of calling getOrCreateSymbolData here is to register
205  // the symbol with the assembler.
206  MCSymbolData &SD = Assembler.getOrCreateSymbolData(*Symbol);
207
208  // The implementation of symbol attributes is designed to match 'as', but it
209  // leaves much to desired. It doesn't really make sense to arbitrarily add and
210  // remove flags, but 'as' allows this (in particular, see .desc).
211  //
212  // In the future it might be worth trying to make these operations more well
213  // defined.
214  switch (Attribute) {
215  case MCSA_Invalid:
216  case MCSA_ELF_TypeFunction:
217  case MCSA_ELF_TypeIndFunction:
218  case MCSA_ELF_TypeObject:
219  case MCSA_ELF_TypeTLS:
220  case MCSA_ELF_TypeCommon:
221  case MCSA_ELF_TypeNoType:
222  case MCSA_IndirectSymbol:
223  case MCSA_Hidden:
224  case MCSA_Internal:
225  case MCSA_Protected:
226  case MCSA_Weak:
227  case MCSA_Local:
228    assert(0 && "Invalid symbol attribute for Mach-O!");
229    break;
230
231  case MCSA_Global:
232    SD.setExternal(true);
233    break;
234
235  case MCSA_LazyReference:
236    // FIXME: This requires -dynamic.
237    SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
238    if (Symbol->isUndefined())
239      SD.setFlags(SD.getFlags() | SF_ReferenceTypeUndefinedLazy);
240    break;
241
242    // Since .reference sets the no dead strip bit, it is equivalent to
243    // .no_dead_strip in practice.
244  case MCSA_Reference:
245  case MCSA_NoDeadStrip:
246    SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
247    break;
248
249  case MCSA_PrivateExtern:
250    SD.setExternal(true);
251    SD.setPrivateExtern(true);
252    break;
253
254  case MCSA_WeakReference:
255    // FIXME: This requires -dynamic.
256    if (Symbol->isUndefined())
257      SD.setFlags(SD.getFlags() | SF_WeakReference);
258    break;
259
260  case MCSA_WeakDefinition:
261    // FIXME: 'as' enforces that this is defined and global. The manual claims
262    // it has to be in a coalesced section, but this isn't enforced.
263    SD.setFlags(SD.getFlags() | SF_WeakDefinition);
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  Assembler.getOrCreateSymbolData(*Symbol).setFlags(DescValue&SF_DescFlagsMask);
273}
274
275void MCMachOStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
276                                       unsigned ByteAlignment) {
277  // FIXME: Darwin 'as' does appear to allow redef of a .comm by itself.
278  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
279
280  MCSymbolData &SD = Assembler.getOrCreateSymbolData(*Symbol);
281  SD.setExternal(true);
282  SD.setCommon(Size, ByteAlignment);
283}
284
285void MCMachOStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
286                                   unsigned Size, unsigned ByteAlignment) {
287  MCSectionData &SectData = Assembler.getOrCreateSectionData(*Section);
288
289  // The symbol may not be present, which only creates the section.
290  if (!Symbol)
291    return;
292
293  // FIXME: Assert that this section has the zerofill type.
294
295  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
296
297  MCSymbolData &SD = Assembler.getOrCreateSymbolData(*Symbol);
298
299  MCFragment *F = new MCZeroFillFragment(Size, ByteAlignment, &SectData);
300  SD.setFragment(F);
301
302  Symbol->setSection(*Section);
303
304  // Update the maximum alignment on the zero fill section if necessary.
305  if (ByteAlignment > SectData.getAlignment())
306    SectData.setAlignment(ByteAlignment);
307}
308
309void MCMachOStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
310  MCDataFragment *DF = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
311  if (!DF)
312    DF = new MCDataFragment(CurSectionData);
313  DF->getContents().append(Data.begin(), Data.end());
314}
315
316void MCMachOStreamer::EmitValue(const MCExpr *Value, unsigned Size,
317                                unsigned AddrSpace) {
318  MCDataFragment *DF = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
319  if (!DF)
320    DF = new MCDataFragment(CurSectionData);
321
322  // Avoid fixups when possible.
323  int64_t AbsValue;
324  if (AddValueSymbols(Value)->EvaluateAsAbsolute(AbsValue)) {
325    // FIXME: Endianness assumption.
326    for (unsigned i = 0; i != Size; ++i)
327      DF->getContents().push_back(uint8_t(AbsValue >> (i * 8)));
328  } else {
329    DF->addFixup(MCAsmFixup(DF->getContents().size(), *AddValueSymbols(Value),
330                            MCFixup::getKindForSize(Size)));
331    DF->getContents().resize(DF->getContents().size() + Size, 0);
332  }
333}
334
335void MCMachOStreamer::EmitValueToAlignment(unsigned ByteAlignment,
336                                           int64_t Value, unsigned ValueSize,
337                                           unsigned MaxBytesToEmit) {
338  if (MaxBytesToEmit == 0)
339    MaxBytesToEmit = ByteAlignment;
340  new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
341                      false /* EmitNops */, CurSectionData);
342
343  // Update the maximum alignment on the current section if necessary.
344  if (ByteAlignment > CurSectionData->getAlignment())
345    CurSectionData->setAlignment(ByteAlignment);
346}
347
348void MCMachOStreamer::EmitCodeAlignment(unsigned ByteAlignment,
349                                        unsigned MaxBytesToEmit) {
350  if (MaxBytesToEmit == 0)
351    MaxBytesToEmit = ByteAlignment;
352  // FIXME the 0x90 is the default x86 1 byte nop opcode.
353  new MCAlignFragment(ByteAlignment, 0x90, 1, MaxBytesToEmit,
354                      true /* EmitNops */, CurSectionData);
355
356  // Update the maximum alignment on the current section if necessary.
357  if (ByteAlignment > CurSectionData->getAlignment())
358    CurSectionData->setAlignment(ByteAlignment);
359}
360
361void MCMachOStreamer::EmitValueToOffset(const MCExpr *Offset,
362                                        unsigned char Value) {
363  new MCOrgFragment(*Offset, Value, CurSectionData);
364}
365
366void MCMachOStreamer::EmitInstruction(const MCInst &Inst) {
367  // Scan for values.
368  for (unsigned i = 0; i != Inst.getNumOperands(); ++i)
369    if (Inst.getOperand(i).isExpr())
370      AddValueSymbols(Inst.getOperand(i).getExpr());
371
372  CurSectionData->setHasInstructions(true);
373
374  SmallVector<MCFixup, 4> Fixups;
375  SmallString<256> Code;
376  raw_svector_ostream VecOS(Code);
377  Assembler.getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
378  VecOS.flush();
379
380  // Add the fixups and data.
381  MCDataFragment *DF = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
382  if (!DF)
383    DF = new MCDataFragment(CurSectionData);
384  for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
385    MCFixup &F = Fixups[i];
386    DF->addFixup(MCAsmFixup(DF->getContents().size()+F.getOffset(),
387                            *F.getValue(), F.getKind()));
388  }
389  DF->getContents().append(Code.begin(), Code.end());
390}
391
392void MCMachOStreamer::Finish() {
393  Assembler.Finish();
394}
395
396MCStreamer *llvm::createMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
397                                      raw_ostream &OS, MCCodeEmitter *CE) {
398  return new MCMachOStreamer(Context, TAB, OS, CE);
399}
400