MCELFStreamer.cpp revision 218893 
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#include "llvm/Target/TargetAsmInfo.h"
34
35using namespace llvm;
36
37namespace {
38
39static void SetBinding(MCSymbolData &SD, unsigned Binding) {
40  assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
41         Binding == ELF::STB_WEAK);
42  uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STB_Shift);
43  SD.setFlags(OtherFlags | (Binding << ELF_STB_Shift));
44}
45
46static unsigned GetBinding(const MCSymbolData &SD) {
47  uint32_t Binding = (SD.getFlags() & (0xf << ELF_STB_Shift)) >> ELF_STB_Shift;
48  assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
49         Binding == ELF::STB_WEAK);
50  return Binding;
51}
52
53static void SetType(MCSymbolData &SD, unsigned Type) {
54  assert(Type == ELF::STT_NOTYPE || Type == ELF::STT_OBJECT ||
55         Type == ELF::STT_FUNC || Type == ELF::STT_SECTION ||
56         Type == ELF::STT_FILE || Type == ELF::STT_COMMON ||
57         Type == ELF::STT_TLS);
58
59  uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STT_Shift);
60  SD.setFlags(OtherFlags | (Type << ELF_STT_Shift));
61}
62
63static void SetVisibility(MCSymbolData &SD, unsigned Visibility) {
64  assert(Visibility == ELF::STV_DEFAULT || Visibility == ELF::STV_INTERNAL ||
65         Visibility == ELF::STV_HIDDEN || Visibility == ELF::STV_PROTECTED);
66
67  uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STV_Shift);
68  SD.setFlags(OtherFlags | (Visibility << ELF_STV_Shift));
69}
70
71class MCELFStreamer : public MCObjectStreamer {
72public:
73  MCELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
74                  raw_ostream &OS, MCCodeEmitter *Emitter)
75    : MCObjectStreamer(Context, TAB, OS, Emitter) {}
76
77  ~MCELFStreamer() {}
78
79  /// @name MCStreamer Interface
80  /// @{
81
82  virtual void InitSections();
83  virtual void ChangeSection(const MCSection *Section);
84  virtual void EmitLabel(MCSymbol *Symbol);
85  virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
86  virtual void EmitThumbFunc(MCSymbol *Func);
87  virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
88  virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol);
89  virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
90  virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
91    assert(0 && "ELF doesn't support this directive");
92  }
93  virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
94                                unsigned ByteAlignment);
95  virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
96    assert(0 && "ELF doesn't support this directive");
97  }
98
99  virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
100    assert(0 && "ELF doesn't support this directive");
101  }
102
103  virtual void EmitCOFFSymbolType(int Type) {
104    assert(0 && "ELF doesn't support this directive");
105  }
106
107  virtual void EndCOFFSymbolDef() {
108    assert(0 && "ELF doesn't support this directive");
109  }
110
111  virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
112     MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
113     SD.setSize(Value);
114  }
115
116  virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size);
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", ELF::SHT_PROGBITS,
159               ELF::SHF_WRITE |ELF::SHF_ALLOC,
160               SectionKind::getDataRel());
161    EmitCodeAlignment(4, 0);
162  }
163  void SetSectionText() {
164    SetSection(".text", ELF::SHT_PROGBITS,
165               ELF::SHF_EXECINSTR |
166               ELF::SHF_ALLOC, SectionKind::getText());
167    EmitCodeAlignment(4, 0);
168  }
169  void SetSectionBss() {
170    SetSection(".bss", ELF::SHT_NOBITS,
171               ELF::SHF_WRITE |
172               ELF::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() & ELF::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::ChangeSection(const MCSection *Section) {
226  const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
227  if (Grp)
228    getAssembler().getOrCreateSymbolData(*Grp);
229  this->MCObjectStreamer::ChangeSection(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                                                                    ELF::SHT_NOBITS,
350                                                                    ELF::SHF_WRITE |
351                                                                    ELF::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::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
365  // FIXME: Should this be caught and done earlier?
366  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
367  SetBinding(SD, ELF::STB_LOCAL);
368  SD.setExternal(false);
369  BindingExplicitlySet.insert(Symbol);
370  // FIXME: ByteAlignment is not needed here, but is required.
371  EmitCommonSymbol(Symbol, Size, 1);
372}
373
374void MCELFStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
375  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
376  // MCObjectStreamer.
377  getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
378}
379
380void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
381                                           int64_t Value, unsigned ValueSize,
382                                           unsigned MaxBytesToEmit) {
383  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
384  // MCObjectStreamer.
385  if (MaxBytesToEmit == 0)
386    MaxBytesToEmit = ByteAlignment;
387  new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
388                      getCurrentSectionData());
389
390  // Update the maximum alignment on the current section if necessary.
391  if (ByteAlignment > getCurrentSectionData()->getAlignment())
392    getCurrentSectionData()->setAlignment(ByteAlignment);
393}
394
395void MCELFStreamer::EmitCodeAlignment(unsigned ByteAlignment,
396                                        unsigned MaxBytesToEmit) {
397  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
398  // MCObjectStreamer.
399  if (MaxBytesToEmit == 0)
400    MaxBytesToEmit = ByteAlignment;
401  MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
402                                           getCurrentSectionData());
403  F->setEmitNops(true);
404
405  // Update the maximum alignment on the current section if necessary.
406  if (ByteAlignment > getCurrentSectionData()->getAlignment())
407    getCurrentSectionData()->setAlignment(ByteAlignment);
408}
409
410// Add a symbol for the file name of this module. This is the second
411// entry in the module's symbol table (the first being the null symbol).
412void MCELFStreamer::EmitFileDirective(StringRef Filename) {
413  MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
414  Symbol->setSection(*getCurrentSection());
415  Symbol->setAbsolute();
416
417  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
418
419  SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
420}
421
422void  MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
423  switch (expr->getKind()) {
424  case MCExpr::Target: llvm_unreachable("Can't handle target exprs yet!");
425  case MCExpr::Constant:
426    break;
427
428  case MCExpr::Binary: {
429    const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
430    fixSymbolsInTLSFixups(be->getLHS());
431    fixSymbolsInTLSFixups(be->getRHS());
432    break;
433  }
434
435  case MCExpr::SymbolRef: {
436    const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
437    switch (symRef.getKind()) {
438    default:
439      return;
440    case MCSymbolRefExpr::VK_NTPOFF:
441    case MCSymbolRefExpr::VK_GOTNTPOFF:
442    case MCSymbolRefExpr::VK_TLSGD:
443    case MCSymbolRefExpr::VK_TLSLDM:
444    case MCSymbolRefExpr::VK_TPOFF:
445    case MCSymbolRefExpr::VK_DTPOFF:
446    case MCSymbolRefExpr::VK_GOTTPOFF:
447    case MCSymbolRefExpr::VK_TLSLD:
448    case MCSymbolRefExpr::VK_ARM_TLSGD:
449      break;
450    }
451    MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
452    SetType(SD, ELF::STT_TLS);
453    break;
454  }
455
456  case MCExpr::Unary:
457    fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
458    break;
459  }
460}
461
462void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
463  this->MCObjectStreamer::EmitInstToFragment(Inst);
464  MCInstFragment &F = *cast<MCInstFragment>(getCurrentFragment());
465
466  for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
467    fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
468}
469
470void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
471  MCDataFragment *DF = getOrCreateDataFragment();
472
473  SmallVector<MCFixup, 4> Fixups;
474  SmallString<256> Code;
475  raw_svector_ostream VecOS(Code);
476  getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
477  VecOS.flush();
478
479  for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
480    fixSymbolsInTLSFixups(Fixups[i].getValue());
481
482  // Add the fixups and data.
483  for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
484    Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
485    DF->addFixup(Fixups[i]);
486  }
487  DF->getContents().append(Code.begin(), Code.end());
488}
489
490void MCELFStreamer::Finish() {
491  if (getNumFrameInfos())
492    MCDwarfFrameEmitter::Emit(*this);
493
494  for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
495                                                e = LocalCommons.end();
496       i != e; ++i) {
497    MCSymbolData *SD = i->SD;
498    uint64_t Size = i->Size;
499    unsigned ByteAlignment = i->ByteAlignment;
500    const MCSymbol &Symbol = SD->getSymbol();
501    const MCSection &Section = Symbol.getSection();
502
503    MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
504    new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
505
506    MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
507    SD->setFragment(F);
508
509    // Update the maximum alignment of the section if necessary.
510    if (ByteAlignment > SectData.getAlignment())
511      SectData.setAlignment(ByteAlignment);
512  }
513
514  this->MCObjectStreamer::Finish();
515}
516
517MCStreamer *llvm::createELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
518                                    raw_ostream &OS, MCCodeEmitter *CE,
519                                    bool RelaxAll, bool NoExecStack) {
520  MCELFStreamer *S = new MCELFStreamer(Context, TAB, OS, CE);
521  if (RelaxAll)
522    S->getAssembler().setRelaxAll(true);
523  if (NoExecStack)
524    S->getAssembler().setNoExecStack(true);
525  return S;
526}
527