MCELFStreamer.cpp revision f7fd4aa2610f46467369de07f3ec669561d79be0 
1//===- lib/MC/MCELFStreamer.cpp - ELF 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// This file assembles .s files and emits ELF .o object files.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/MC/MCStreamer.h"
15
16#include "llvm/ADT/SmallPtrSet.h"
17#include "llvm/MC/MCAssembler.h"
18#include "llvm/MC/MCContext.h"
19#include "llvm/MC/MCCodeEmitter.h"
20#include "llvm/MC/MCELFSymbolFlags.h"
21#include "llvm/MC/MCExpr.h"
22#include "llvm/MC/MCInst.h"
23#include "llvm/MC/MCObjectStreamer.h"
24#include "llvm/MC/MCSection.h"
25#include "llvm/MC/MCSectionELF.h"
26#include "llvm/MC/MCSymbol.h"
27#include "llvm/MC/MCValue.h"
28#include "llvm/Support/Debug.h"
29#include "llvm/Support/ELF.h"
30#include "llvm/Support/ErrorHandling.h"
31#include "llvm/Support/raw_ostream.h"
32#include "llvm/Target/TargetAsmBackend.h"
33
34using namespace llvm;
35
36namespace {
37
38static void SetBinding(MCSymbolData &SD, unsigned Binding) {
39  assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
40         Binding == ELF::STB_WEAK);
41  uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STB_Shift);
42  SD.setFlags(OtherFlags | (Binding << ELF_STB_Shift));
43}
44
45static unsigned GetBinding(const MCSymbolData &SD) {
46  uint32_t Binding = (SD.getFlags() & (0xf << ELF_STB_Shift)) >> ELF_STB_Shift;
47  assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
48         Binding == ELF::STB_WEAK);
49  return Binding;
50}
51
52static void SetType(MCSymbolData &SD, unsigned Type) {
53  assert(Type == ELF::STT_NOTYPE || Type == ELF::STT_OBJECT ||
54         Type == ELF::STT_FUNC || Type == ELF::STT_SECTION ||
55         Type == ELF::STT_FILE || Type == ELF::STT_COMMON ||
56         Type == ELF::STT_TLS);
57
58  uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STT_Shift);
59  SD.setFlags(OtherFlags | (Type << ELF_STT_Shift));
60}
61
62static void SetVisibility(MCSymbolData &SD, unsigned Visibility) {
63  assert(Visibility == ELF::STV_DEFAULT || Visibility == ELF::STV_INTERNAL ||
64         Visibility == ELF::STV_HIDDEN || Visibility == ELF::STV_PROTECTED);
65
66  uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STV_Shift);
67  SD.setFlags(OtherFlags | (Visibility << ELF_STV_Shift));
68}
69
70class MCELFStreamer : public MCObjectStreamer {
71public:
72  MCELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
73                  raw_ostream &OS, MCCodeEmitter *Emitter)
74    : MCObjectStreamer(Context, TAB, OS, Emitter) {}
75
76  ~MCELFStreamer() {}
77
78  /// @name MCStreamer Interface
79  /// @{
80
81  virtual void InitSections();
82  virtual void EmitLabel(MCSymbol *Symbol);
83  virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
84  virtual void EmitThumbFunc(MCSymbol *Func);
85  virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
86  virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol);
87  virtual void SwitchSection(const MCSection *Section);
88  virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
89  virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
90    assert(0 && "ELF doesn't support this directive");
91  }
92  virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
93                                unsigned ByteAlignment);
94  virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
95    assert(0 && "ELF doesn't support this directive");
96  }
97
98  virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
99    assert(0 && "ELF doesn't support this directive");
100  }
101
102  virtual void EmitCOFFSymbolType(int Type) {
103    assert(0 && "ELF doesn't support this directive");
104  }
105
106  virtual void EndCOFFSymbolDef() {
107    assert(0 && "ELF doesn't support this directive");
108  }
109
110  virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
111     MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
112     SD.setSize(Value);
113  }
114
115  virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
116    assert(0 && "ELF doesn't support this directive");
117  }
118  virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
119                            unsigned Size = 0, unsigned ByteAlignment = 0) {
120    assert(0 && "ELF doesn't support this directive");
121  }
122  virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
123                              uint64_t Size, unsigned ByteAlignment = 0) {
124    assert(0 && "ELF doesn't support this directive");
125  }
126  virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
127  virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
128                                    unsigned ValueSize = 1,
129                                    unsigned MaxBytesToEmit = 0);
130  virtual void EmitCodeAlignment(unsigned ByteAlignment,
131                                 unsigned MaxBytesToEmit = 0);
132
133  virtual void EmitFileDirective(StringRef Filename);
134
135  virtual void Finish();
136
137private:
138  virtual void EmitInstToFragment(const MCInst &Inst);
139  virtual void EmitInstToData(const MCInst &Inst);
140
141  void fixSymbolsInTLSFixups(const MCExpr *expr);
142
143  struct LocalCommon {
144    MCSymbolData *SD;
145    uint64_t Size;
146    unsigned ByteAlignment;
147  };
148  std::vector<LocalCommon> LocalCommons;
149
150  SmallPtrSet<MCSymbol *, 16> BindingExplicitlySet;
151  /// @}
152  void SetSection(StringRef Section, unsigned Type, unsigned Flags,
153                  SectionKind Kind) {
154    SwitchSection(getContext().getELFSection(Section, Type, Flags, Kind));
155  }
156
157  void SetSectionData() {
158    SetSection(".data", MCSectionELF::SHT_PROGBITS,
159               MCSectionELF::SHF_WRITE |MCSectionELF::SHF_ALLOC,
160               SectionKind::getDataRel());
161    EmitCodeAlignment(4, 0);
162  }
163  void SetSectionText() {
164    SetSection(".text", MCSectionELF::SHT_PROGBITS,
165               MCSectionELF::SHF_EXECINSTR |
166               MCSectionELF::SHF_ALLOC, SectionKind::getText());
167    EmitCodeAlignment(4, 0);
168  }
169  void SetSectionBss() {
170    SetSection(".bss", MCSectionELF::SHT_NOBITS,
171               MCSectionELF::SHF_WRITE |
172               MCSectionELF::SHF_ALLOC, SectionKind::getBSS());
173    EmitCodeAlignment(4, 0);
174  }
175};
176
177} // end anonymous namespace.
178
179void MCELFStreamer::InitSections() {
180  // This emulates the same behavior of GNU as. This makes it easier
181  // to compare the output as the major sections are in the same order.
182  SetSectionText();
183  SetSectionData();
184  SetSectionBss();
185  SetSectionText();
186}
187
188void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
189  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
190
191  MCObjectStreamer::EmitLabel(Symbol);
192
193  const MCSectionELF &Section =
194    static_cast<const MCSectionELF&>(Symbol->getSection());
195  MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
196  if (Section.getFlags() & MCSectionELF::SHF_TLS)
197    SetType(SD, ELF::STT_TLS);
198}
199
200void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
201  switch (Flag) {
202  case MCAF_SyntaxUnified: return; // no-op here.
203  case MCAF_Code16: return; // no-op here.
204  case MCAF_Code32: return; // no-op here.
205  case MCAF_SubsectionsViaSymbols:
206    getAssembler().setSubsectionsViaSymbols(true);
207    return;
208  }
209
210  assert(0 && "invalid assembler flag!");
211}
212
213void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
214  // FIXME: Anything needed here to flag the function as thumb?
215}
216
217void MCELFStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
218  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
219  // MCObjectStreamer.
220  // FIXME: Lift context changes into super class.
221  getAssembler().getOrCreateSymbolData(*Symbol);
222  Symbol->setVariableValue(AddValueSymbols(Value));
223}
224
225void MCELFStreamer::SwitchSection(const MCSection *Section) {
226  const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
227  if (Grp)
228    getAssembler().getOrCreateSymbolData(*Grp);
229  this->MCObjectStreamer::SwitchSection(Section);
230}
231
232void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
233  getAssembler().getOrCreateSymbolData(*Symbol);
234  MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
235  AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
236  const MCExpr *Value = MCSymbolRefExpr::Create(Symbol, getContext());
237  Alias->setVariableValue(Value);
238}
239
240void MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
241                                          MCSymbolAttr Attribute) {
242  // Indirect symbols are handled differently, to match how 'as' handles
243  // them. This makes writing matching .o files easier.
244  if (Attribute == MCSA_IndirectSymbol) {
245    // Note that we intentionally cannot use the symbol data here; this is
246    // important for matching the string table that 'as' generates.
247    IndirectSymbolData ISD;
248    ISD.Symbol = Symbol;
249    ISD.SectionData = getCurrentSectionData();
250    getAssembler().getIndirectSymbols().push_back(ISD);
251    return;
252  }
253
254  // Adding a symbol attribute always introduces the symbol, note that an
255  // important side effect of calling getOrCreateSymbolData here is to register
256  // the symbol with the assembler.
257  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
258
259  // The implementation of symbol attributes is designed to match 'as', but it
260  // leaves much to desired. It doesn't really make sense to arbitrarily add and
261  // remove flags, but 'as' allows this (in particular, see .desc).
262  //
263  // In the future it might be worth trying to make these operations more well
264  // defined.
265  switch (Attribute) {
266  case MCSA_LazyReference:
267  case MCSA_Reference:
268  case MCSA_NoDeadStrip:
269  case MCSA_SymbolResolver:
270  case MCSA_PrivateExtern:
271  case MCSA_WeakDefinition:
272  case MCSA_WeakDefAutoPrivate:
273  case MCSA_Invalid:
274  case MCSA_ELF_TypeIndFunction:
275  case MCSA_IndirectSymbol:
276    assert(0 && "Invalid symbol attribute for ELF!");
277    break;
278
279  case MCSA_ELF_TypeGnuUniqueObject:
280    // Ignore for now.
281    break;
282
283  case MCSA_Global:
284    SetBinding(SD, ELF::STB_GLOBAL);
285    SD.setExternal(true);
286    BindingExplicitlySet.insert(Symbol);
287    break;
288
289  case MCSA_WeakReference:
290  case MCSA_Weak:
291    SetBinding(SD, ELF::STB_WEAK);
292    SD.setExternal(true);
293    BindingExplicitlySet.insert(Symbol);
294    break;
295
296  case MCSA_Local:
297    SetBinding(SD, ELF::STB_LOCAL);
298    SD.setExternal(false);
299    BindingExplicitlySet.insert(Symbol);
300    break;
301
302  case MCSA_ELF_TypeFunction:
303    SetType(SD, ELF::STT_FUNC);
304    break;
305
306  case MCSA_ELF_TypeObject:
307    SetType(SD, ELF::STT_OBJECT);
308    break;
309
310  case MCSA_ELF_TypeTLS:
311    SetType(SD, ELF::STT_TLS);
312    break;
313
314  case MCSA_ELF_TypeCommon:
315    SetType(SD, ELF::STT_COMMON);
316    break;
317
318  case MCSA_ELF_TypeNoType:
319    SetType(SD, ELF::STT_NOTYPE);
320    break;
321
322  case MCSA_Protected:
323    SetVisibility(SD, ELF::STV_PROTECTED);
324    break;
325
326  case MCSA_Hidden:
327    SetVisibility(SD, ELF::STV_HIDDEN);
328    break;
329
330  case MCSA_Internal:
331    SetVisibility(SD, ELF::STV_INTERNAL);
332    break;
333  }
334}
335
336void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
337                                       unsigned ByteAlignment) {
338  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
339
340  if (!BindingExplicitlySet.count(Symbol)) {
341    SetBinding(SD, ELF::STB_GLOBAL);
342    SD.setExternal(true);
343  }
344
345  SetType(SD, ELF::STT_OBJECT);
346
347  if (GetBinding(SD) == ELF_STB_Local) {
348    const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
349                                                                    MCSectionELF::SHT_NOBITS,
350                                                                    MCSectionELF::SHF_WRITE |
351                                                                    MCSectionELF::SHF_ALLOC,
352                                                                    SectionKind::getBSS());
353    Symbol->setSection(*Section);
354
355    struct LocalCommon L = {&SD, Size, ByteAlignment};
356    LocalCommons.push_back(L);
357  } else {
358    SD.setCommon(Size, ByteAlignment);
359  }
360
361  SD.setSize(MCConstantExpr::Create(Size, getContext()));
362}
363
364void MCELFStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
365  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
366  // MCObjectStreamer.
367  getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
368}
369
370void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
371                                           int64_t Value, unsigned ValueSize,
372                                           unsigned MaxBytesToEmit) {
373  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
374  // MCObjectStreamer.
375  if (MaxBytesToEmit == 0)
376    MaxBytesToEmit = ByteAlignment;
377  new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
378                      getCurrentSectionData());
379
380  // Update the maximum alignment on the current section if necessary.
381  if (ByteAlignment > getCurrentSectionData()->getAlignment())
382    getCurrentSectionData()->setAlignment(ByteAlignment);
383}
384
385void MCELFStreamer::EmitCodeAlignment(unsigned ByteAlignment,
386                                        unsigned MaxBytesToEmit) {
387  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
388  // MCObjectStreamer.
389  if (MaxBytesToEmit == 0)
390    MaxBytesToEmit = ByteAlignment;
391  MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
392                                           getCurrentSectionData());
393  F->setEmitNops(true);
394
395  // Update the maximum alignment on the current section if necessary.
396  if (ByteAlignment > getCurrentSectionData()->getAlignment())
397    getCurrentSectionData()->setAlignment(ByteAlignment);
398}
399
400// Add a symbol for the file name of this module. This is the second
401// entry in the module's symbol table (the first being the null symbol).
402void MCELFStreamer::EmitFileDirective(StringRef Filename) {
403  MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
404  Symbol->setSection(*CurSection);
405  Symbol->setAbsolute();
406
407  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
408
409  SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
410}
411
412void  MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
413  switch (expr->getKind()) {
414  case MCExpr::Target: llvm_unreachable("Can't handle target exprs yet!");
415  case MCExpr::Constant:
416    break;
417
418  case MCExpr::Binary: {
419    const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
420    fixSymbolsInTLSFixups(be->getLHS());
421    fixSymbolsInTLSFixups(be->getRHS());
422    break;
423  }
424
425  case MCExpr::SymbolRef: {
426    const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
427    switch (symRef.getKind()) {
428    default:
429      return;
430    case MCSymbolRefExpr::VK_NTPOFF:
431    case MCSymbolRefExpr::VK_GOTNTPOFF:
432    case MCSymbolRefExpr::VK_TLSGD:
433    case MCSymbolRefExpr::VK_TLSLDM:
434    case MCSymbolRefExpr::VK_TPOFF:
435    case MCSymbolRefExpr::VK_DTPOFF:
436    case MCSymbolRefExpr::VK_GOTTPOFF:
437    case MCSymbolRefExpr::VK_TLSLD:
438    case MCSymbolRefExpr::VK_ARM_TLSGD:
439      break;
440    }
441    MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
442    SetType(SD, ELF::STT_TLS);
443    break;
444  }
445
446  case MCExpr::Unary:
447    fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
448    break;
449  }
450}
451
452void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
453  this->MCObjectStreamer::EmitInstToFragment(Inst);
454  MCInstFragment &F = *cast<MCInstFragment>(getCurrentFragment());
455
456  for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
457    fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
458}
459
460void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
461  MCDataFragment *DF = getOrCreateDataFragment();
462
463  SmallVector<MCFixup, 4> Fixups;
464  SmallString<256> Code;
465  raw_svector_ostream VecOS(Code);
466  getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
467  VecOS.flush();
468
469  for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
470    fixSymbolsInTLSFixups(Fixups[i].getValue());
471
472  // Add the fixups and data.
473  for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
474    Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
475    DF->addFixup(Fixups[i]);
476  }
477  DF->getContents().append(Code.begin(), Code.end());
478}
479
480void MCELFStreamer::Finish() {
481  // FIXME: duplicated code with the MachO streamer.
482  // Dump out the dwarf file & directory tables and line tables.
483  if (getContext().hasDwarfFiles()) {
484    const MCSection *DwarfLineSection =
485      getContext().getELFSection(".debug_line", 0, 0,
486                                 SectionKind::getDataRelLocal());
487    MCDwarfFileTable::Emit(this, DwarfLineSection);
488  }
489
490  for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
491                                                e = LocalCommons.end();
492       i != e; ++i) {
493    MCSymbolData *SD = i->SD;
494    uint64_t Size = i->Size;
495    unsigned ByteAlignment = i->ByteAlignment;
496    const MCSymbol &Symbol = SD->getSymbol();
497    const MCSection &Section = Symbol.getSection();
498
499    MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
500    new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
501
502    MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
503    SD->setFragment(F);
504
505    // Update the maximum alignment of the section if necessary.
506    if (ByteAlignment > SectData.getAlignment())
507      SectData.setAlignment(ByteAlignment);
508  }
509
510  this->MCObjectStreamer::Finish();
511}
512
513MCStreamer *llvm::createELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
514                                      raw_ostream &OS, MCCodeEmitter *CE,
515                                      bool RelaxAll) {
516  MCELFStreamer *S = new MCELFStreamer(Context, TAB, OS, CE);
517  if (RelaxAll)
518    S->getAssembler().setRelaxAll(true);
519  return S;
520}
521