MCELFStreamer.cpp revision d80781b98b771d370730ab7c630018f23e202b57 
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/MC/MCAssembler.h"
17#include "llvm/MC/MCContext.h"
18#include "llvm/MC/MCCodeEmitter.h"
19#include "llvm/MC/MCELFSymbolFlags.h"
20#include "llvm/MC/MCExpr.h"
21#include "llvm/MC/MCInst.h"
22#include "llvm/MC/MCObjectStreamer.h"
23#include "llvm/MC/MCSection.h"
24#include "llvm/MC/MCSectionELF.h"
25#include "llvm/MC/MCSymbol.h"
26#include "llvm/Support/Debug.h"
27#include "llvm/Support/ELF.h"
28#include "llvm/Support/ErrorHandling.h"
29#include "llvm/Support/raw_ostream.h"
30#include "llvm/Target/TargetAsmBackend.h"
31
32using namespace llvm;
33
34namespace {
35
36class MCELFStreamer : public MCObjectStreamer {
37  void EmitInstToFragment(const MCInst &Inst);
38  void EmitInstToData(const MCInst &Inst);
39public:
40  MCELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
41                  raw_ostream &OS, MCCodeEmitter *Emitter)
42    : MCObjectStreamer(Context, TAB, OS, Emitter) {}
43
44  ~MCELFStreamer() {}
45
46  /// @name MCStreamer Interface
47  /// @{
48
49  virtual void InitSections();
50  virtual void EmitLabel(MCSymbol *Symbol);
51  virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
52  virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
53  virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
54  virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
55    assert(0 && "ELF doesn't support this directive");
56  }
57  virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
58                                unsigned ByteAlignment);
59  virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
60    assert(0 && "ELF doesn't support this directive");
61  }
62
63  virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
64    assert(0 && "ELF doesn't support this directive");
65  }
66
67  virtual void EmitCOFFSymbolType(int Type) {
68    assert(0 && "ELF doesn't support this directive");
69  }
70
71  virtual void EndCOFFSymbolDef() {
72    assert(0 && "ELF doesn't support this directive");
73  }
74
75  virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
76     MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
77     SD.setSize(Value);
78  }
79
80  virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
81    assert(0 && "ELF doesn't support this directive");
82  }
83  virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
84                            unsigned Size = 0, unsigned ByteAlignment = 0) {
85    assert(0 && "ELF doesn't support this directive");
86  }
87  virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
88                              uint64_t Size, unsigned ByteAlignment = 0) {
89    assert(0 && "ELF doesn't support this directive");
90  }
91  virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
92  virtual void EmitValue(const MCExpr *Value, unsigned Size,unsigned AddrSpace);
93  virtual void EmitGPRel32Value(const MCExpr *Value) {
94    assert(0 && "ELF doesn't support this directive");
95  }
96  virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
97                                    unsigned ValueSize = 1,
98                                    unsigned MaxBytesToEmit = 0);
99  virtual void EmitCodeAlignment(unsigned ByteAlignment,
100                                 unsigned MaxBytesToEmit = 0);
101  virtual void EmitValueToOffset(const MCExpr *Offset,
102                                 unsigned char Value = 0);
103
104  virtual void EmitFileDirective(StringRef Filename);
105  virtual void EmitDwarfFileDirective(unsigned FileNo, StringRef Filename) {
106    DEBUG(dbgs() << "FIXME: MCELFStreamer:EmitDwarfFileDirective not implemented\n");
107  }
108
109  virtual void EmitInstruction(const MCInst &Inst);
110  virtual void Finish();
111
112  /// @}
113  void SetSection(StringRef Section, unsigned Type, unsigned Flags,
114                  SectionKind Kind) {
115    SwitchSection(getContext().getELFSection(Section, Type, Flags, Kind));
116  }
117
118  void SetSectionData() {
119    SetSection(".data", MCSectionELF::SHT_PROGBITS,
120               MCSectionELF::SHF_WRITE |MCSectionELF::SHF_ALLOC,
121               SectionKind::getDataRel());
122    EmitCodeAlignment(4, 0);
123  }
124  void SetSectionText() {
125    SetSection(".text", MCSectionELF::SHT_PROGBITS,
126               MCSectionELF::SHF_EXECINSTR |
127               MCSectionELF::SHF_ALLOC, SectionKind::getText());
128    EmitCodeAlignment(4, 0);
129  }
130  void SetSectionBss() {
131    SetSection(".bss", MCSectionELF::SHT_NOBITS,
132               MCSectionELF::SHF_WRITE |
133               MCSectionELF::SHF_ALLOC, SectionKind::getBSS());
134    EmitCodeAlignment(4, 0);
135  }
136};
137
138} // end anonymous namespace.
139
140void MCELFStreamer::InitSections() {
141  // This emulates the same behavior of GNU as. This makes it easier
142  // to compare the output as the major sections are in the same order.
143  SetSectionText();
144  SetSectionData();
145  SetSectionBss();
146  SetSectionText();
147}
148
149void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
150  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
151
152  // FIXME: This is wasteful, we don't necessarily need to create a data
153  // fragment. Instead, we should mark the symbol as pointing into the data
154  // fragment if it exists, otherwise we should just queue the label and set its
155  // fragment pointer when we emit the next fragment.
156  MCDataFragment *F = getOrCreateDataFragment();
157  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
158  assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
159  SD.setFragment(F);
160  SD.setOffset(F->getContents().size());
161
162  Symbol->setSection(*CurSection);
163}
164
165void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
166  switch (Flag) {
167  case MCAF_SubsectionsViaSymbols:
168    getAssembler().setSubsectionsViaSymbols(true);
169    return;
170  }
171
172  assert(0 && "invalid assembler flag!");
173}
174
175void MCELFStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
176  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
177  // MCObjectStreamer.
178  // FIXME: Lift context changes into super class.
179  getAssembler().getOrCreateSymbolData(*Symbol);
180  Symbol->setVariableValue(AddValueSymbols(Value));
181}
182
183static void SetBinding(MCSymbolData &SD, unsigned Binding) {
184  assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
185         Binding == ELF::STB_WEAK);
186  uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STB_Shift);
187  SD.setFlags(OtherFlags | (Binding << ELF_STB_Shift));
188}
189
190static void SetType(MCSymbolData &SD, unsigned Type) {
191  assert(Type == ELF::STT_NOTYPE || Type == ELF::STT_OBJECT ||
192         Type == ELF::STT_FUNC || Type == ELF::STT_SECTION ||
193         Type == ELF::STT_FILE || Type == ELF::STT_COMMON ||
194         Type == ELF::STT_TLS);
195
196  uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STT_Shift);
197  SD.setFlags(OtherFlags | (Type << ELF_STT_Shift));
198}
199
200static void SetVisibility(MCSymbolData &SD, unsigned Visibility) {
201  assert(Visibility == ELF::STV_DEFAULT || Visibility == ELF::STV_INTERNAL ||
202         Visibility == ELF::STV_HIDDEN || Visibility == ELF::STV_PROTECTED);
203
204  uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STV_Shift);
205  SD.setFlags(OtherFlags | (Visibility << ELF_STV_Shift));
206}
207
208void MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
209                                          MCSymbolAttr Attribute) {
210  // Indirect symbols are handled differently, to match how 'as' handles
211  // them. This makes writing matching .o files easier.
212  if (Attribute == MCSA_IndirectSymbol) {
213    // Note that we intentionally cannot use the symbol data here; this is
214    // important for matching the string table that 'as' generates.
215    IndirectSymbolData ISD;
216    ISD.Symbol = Symbol;
217    ISD.SectionData = getCurrentSectionData();
218    getAssembler().getIndirectSymbols().push_back(ISD);
219    return;
220  }
221
222  // Adding a symbol attribute always introduces the symbol, note that an
223  // important side effect of calling getOrCreateSymbolData here is to register
224  // the symbol with the assembler.
225  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
226
227  // The implementation of symbol attributes is designed to match 'as', but it
228  // leaves much to desired. It doesn't really make sense to arbitrarily add and
229  // remove flags, but 'as' allows this (in particular, see .desc).
230  //
231  // In the future it might be worth trying to make these operations more well
232  // defined.
233  switch (Attribute) {
234  case MCSA_LazyReference:
235  case MCSA_Reference:
236  case MCSA_NoDeadStrip:
237  case MCSA_PrivateExtern:
238  case MCSA_WeakDefinition:
239  case MCSA_WeakDefAutoPrivate:
240  case MCSA_Invalid:
241  case MCSA_ELF_TypeIndFunction:
242  case MCSA_IndirectSymbol:
243    assert(0 && "Invalid symbol attribute for ELF!");
244    break;
245
246  case MCSA_Global:
247    SetBinding(SD, ELF::STB_GLOBAL);
248    SD.setExternal(true);
249    break;
250
251  case MCSA_WeakReference:
252  case MCSA_Weak:
253    SetBinding(SD, ELF::STB_WEAK);
254    break;
255
256  case MCSA_Local:
257    SetBinding(SD, ELF::STB_LOCAL);
258    break;
259
260  case MCSA_ELF_TypeFunction:
261    SetType(SD, ELF::STT_FUNC);
262    break;
263
264  case MCSA_ELF_TypeObject:
265    SetType(SD, ELF::STT_OBJECT);
266    break;
267
268  case MCSA_ELF_TypeTLS:
269    SetType(SD, ELF::STT_TLS);
270    break;
271
272  case MCSA_ELF_TypeCommon:
273    SetType(SD, ELF::STT_COMMON);
274    break;
275
276  case MCSA_ELF_TypeNoType:
277    SetType(SD, ELF::STT_NOTYPE);
278    break;
279
280  case MCSA_Protected:
281    SetVisibility(SD, ELF::STV_PROTECTED);
282    break;
283
284  case MCSA_Hidden:
285    SetVisibility(SD, ELF::STV_HIDDEN);
286    break;
287
288  case MCSA_Internal:
289    SetVisibility(SD, ELF::STV_INTERNAL);
290    break;
291  }
292}
293
294void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
295                                       unsigned ByteAlignment) {
296  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
297
298  if ((SD.getFlags() & (0xf << ELF_STB_Shift)) == ELF_STB_Local) {
299    const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
300                                                                    MCSectionELF::SHT_NOBITS,
301                                                                    MCSectionELF::SHF_WRITE |
302                                                                    MCSectionELF::SHF_ALLOC,
303                                                                    SectionKind::getBSS());
304
305    MCSectionData &SectData = getAssembler().getOrCreateSectionData(*Section);
306    MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
307    SD.setFragment(F);
308    Symbol->setSection(*Section);
309    SD.setSize(MCConstantExpr::Create(Size, getContext()));
310  }
311
312  SetBinding(SD, ELF::STB_GLOBAL);
313  SD.setExternal(true);
314
315  SD.setCommon(Size, ByteAlignment);
316}
317
318void MCELFStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
319  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
320  // MCObjectStreamer.
321  getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
322}
323
324void MCELFStreamer::EmitValue(const MCExpr *Value, unsigned Size,
325                                unsigned AddrSpace) {
326  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
327  // MCObjectStreamer.
328  MCDataFragment *DF = getOrCreateDataFragment();
329
330  // Avoid fixups when possible.
331  int64_t AbsValue;
332  if (AddValueSymbols(Value)->EvaluateAsAbsolute(AbsValue)) {
333    // FIXME: Endianness assumption.
334    for (unsigned i = 0; i != Size; ++i)
335      DF->getContents().push_back(uint8_t(AbsValue >> (i * 8)));
336  } else {
337    DF->addFixup(MCFixup::Create(DF->getContents().size(), AddValueSymbols(Value),
338                                 MCFixup::getKindForSize(Size)));
339    DF->getContents().resize(DF->getContents().size() + Size, 0);
340  }
341}
342
343void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
344                                           int64_t Value, unsigned ValueSize,
345                                           unsigned MaxBytesToEmit) {
346  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
347  // MCObjectStreamer.
348  if (MaxBytesToEmit == 0)
349    MaxBytesToEmit = ByteAlignment;
350  new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
351                      getCurrentSectionData());
352
353  // Update the maximum alignment on the current section if necessary.
354  if (ByteAlignment > getCurrentSectionData()->getAlignment())
355    getCurrentSectionData()->setAlignment(ByteAlignment);
356}
357
358void MCELFStreamer::EmitCodeAlignment(unsigned ByteAlignment,
359                                        unsigned MaxBytesToEmit) {
360  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
361  // MCObjectStreamer.
362  if (MaxBytesToEmit == 0)
363    MaxBytesToEmit = ByteAlignment;
364  MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
365                                           getCurrentSectionData());
366  F->setEmitNops(true);
367
368  // Update the maximum alignment on the current section if necessary.
369  if (ByteAlignment > getCurrentSectionData()->getAlignment())
370    getCurrentSectionData()->setAlignment(ByteAlignment);
371}
372
373void MCELFStreamer::EmitValueToOffset(const MCExpr *Offset,
374                                        unsigned char Value) {
375  // TODO: This is exactly the same as MCMachOStreamer. Consider merging into
376  // MCObjectStreamer.
377  new MCOrgFragment(*Offset, Value, getCurrentSectionData());
378}
379
380// Add a symbol for the file name of this module. This is the second
381// entry in the module's symbol table (the first being the null symbol).
382void MCELFStreamer::EmitFileDirective(StringRef Filename) {
383  MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
384  Symbol->setSection(*CurSection);
385  Symbol->setAbsolute();
386
387  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
388
389  SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
390}
391
392void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
393  MCInstFragment *IF = new MCInstFragment(Inst, getCurrentSectionData());
394
395  // Add the fixups and data.
396  //
397  // FIXME: Revisit this design decision when relaxation is done, we may be
398  // able to get away with not storing any extra data in the MCInst.
399  SmallVector<MCFixup, 4> Fixups;
400  SmallString<256> Code;
401  raw_svector_ostream VecOS(Code);
402  getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
403  VecOS.flush();
404
405  IF->getCode() = Code;
406  IF->getFixups() = Fixups;
407}
408
409void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
410  MCDataFragment *DF = getOrCreateDataFragment();
411
412  SmallVector<MCFixup, 4> Fixups;
413  SmallString<256> Code;
414  raw_svector_ostream VecOS(Code);
415  getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
416  VecOS.flush();
417
418  // Add the fixups and data.
419  for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
420    Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
421    DF->addFixup(Fixups[i]);
422  }
423  DF->getContents().append(Code.begin(), Code.end());
424}
425
426void MCELFStreamer::EmitInstruction(const MCInst &Inst) {
427  // Scan for values.
428  for (unsigned i = 0; i != Inst.getNumOperands(); ++i)
429    if (Inst.getOperand(i).isExpr())
430      AddValueSymbols(Inst.getOperand(i).getExpr());
431
432  getCurrentSectionData()->setHasInstructions(true);
433
434  // If this instruction doesn't need relaxation, just emit it as data.
435  if (!getAssembler().getBackend().MayNeedRelaxation(Inst)) {
436    EmitInstToData(Inst);
437    return;
438  }
439
440  // Otherwise, if we are relaxing everything, relax the instruction as much as
441  // possible and emit it as data.
442  if (getAssembler().getRelaxAll()) {
443    MCInst Relaxed;
444    getAssembler().getBackend().RelaxInstruction(Inst, Relaxed);
445    while (getAssembler().getBackend().MayNeedRelaxation(Relaxed))
446      getAssembler().getBackend().RelaxInstruction(Relaxed, Relaxed);
447    EmitInstToData(Relaxed);
448    return;
449  }
450
451  // Otherwise emit to a separate fragment.
452  EmitInstToFragment(Inst);
453}
454
455void MCELFStreamer::Finish() {
456  getAssembler().Finish();
457}
458
459MCStreamer *llvm::createELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
460                                      raw_ostream &OS, MCCodeEmitter *CE,
461                                      bool RelaxAll) {
462  MCELFStreamer *S = new MCELFStreamer(Context, TAB, OS, CE);
463  if (RelaxAll)
464    S->getAssembler().setRelaxAll(true);
465  return S;
466}
467