MCELFStreamer.cpp revision 224145 
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 "MCELFStreamer.h"
15#include "MCELF.h"
16#include "llvm/MC/MCStreamer.h"
17#include "llvm/MC/MCCodeEmitter.h"
18#include "llvm/MC/MCELFSymbolFlags.h"
19#include "llvm/MC/MCExpr.h"
20#include "llvm/MC/MCInst.h"
21#include "llvm/MC/MCSection.h"
22#include "llvm/MC/MCSymbol.h"
23#include "llvm/MC/MCValue.h"
24#include "llvm/Support/Debug.h"
25#include "llvm/Support/ELF.h"
26#include "llvm/Support/ErrorHandling.h"
27#include "llvm/Support/raw_ostream.h"
28#include "llvm/Target/TargetAsmBackend.h"
29
30using namespace llvm;
31
32void MCELFStreamer::InitSections() {
33  // This emulates the same behavior of GNU as. This makes it easier
34  // to compare the output as the major sections are in the same order.
35  SetSectionText();
36  SetSectionData();
37  SetSectionBss();
38  SetSectionText();
39}
40
41void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
42  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
43
44  MCObjectStreamer::EmitLabel(Symbol);
45
46  const MCSectionELF &Section =
47    static_cast<const MCSectionELF&>(Symbol->getSection());
48  MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
49  if (Section.getFlags() & ELF::SHF_TLS)
50    MCELF::SetType(SD, ELF::STT_TLS);
51}
52
53void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
54  switch (Flag) {
55  case MCAF_SyntaxUnified: return; // no-op here.
56  case MCAF_Code16: return; // no-op here.
57  case MCAF_Code32: return; // no-op here.
58  case MCAF_SubsectionsViaSymbols:
59    getAssembler().setSubsectionsViaSymbols(true);
60    return;
61  }
62
63  assert(0 && "invalid assembler flag!");
64}
65
66void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
67  // FIXME: Anything needed here to flag the function as thumb?
68
69  getAssembler().setIsThumbFunc(Func);
70
71  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Func);
72  SD.setFlags(SD.getFlags() | ELF_Other_ThumbFunc);
73}
74
75void MCELFStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
76  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
77  // MCObjectStreamer.
78  // FIXME: Lift context changes into super class.
79  getAssembler().getOrCreateSymbolData(*Symbol);
80  Symbol->setVariableValue(AddValueSymbols(Value));
81}
82
83void MCELFStreamer::ChangeSection(const MCSection *Section) {
84  const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
85  if (Grp)
86    getAssembler().getOrCreateSymbolData(*Grp);
87  this->MCObjectStreamer::ChangeSection(Section);
88}
89
90void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
91  getAssembler().getOrCreateSymbolData(*Symbol);
92  MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
93  AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
94  const MCExpr *Value = MCSymbolRefExpr::Create(Symbol, getContext());
95  Alias->setVariableValue(Value);
96}
97
98void MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
99                                          MCSymbolAttr Attribute) {
100  // Indirect symbols are handled differently, to match how 'as' handles
101  // them. This makes writing matching .o files easier.
102  if (Attribute == MCSA_IndirectSymbol) {
103    // Note that we intentionally cannot use the symbol data here; this is
104    // important for matching the string table that 'as' generates.
105    IndirectSymbolData ISD;
106    ISD.Symbol = Symbol;
107    ISD.SectionData = getCurrentSectionData();
108    getAssembler().getIndirectSymbols().push_back(ISD);
109    return;
110  }
111
112  // Adding a symbol attribute always introduces the symbol, note that an
113  // important side effect of calling getOrCreateSymbolData here is to register
114  // the symbol with the assembler.
115  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
116
117  // The implementation of symbol attributes is designed to match 'as', but it
118  // leaves much to desired. It doesn't really make sense to arbitrarily add and
119  // remove flags, but 'as' allows this (in particular, see .desc).
120  //
121  // In the future it might be worth trying to make these operations more well
122  // defined.
123  switch (Attribute) {
124  case MCSA_LazyReference:
125  case MCSA_Reference:
126  case MCSA_NoDeadStrip:
127  case MCSA_SymbolResolver:
128  case MCSA_PrivateExtern:
129  case MCSA_WeakDefinition:
130  case MCSA_WeakDefAutoPrivate:
131  case MCSA_Invalid:
132  case MCSA_ELF_TypeIndFunction:
133  case MCSA_IndirectSymbol:
134    assert(0 && "Invalid symbol attribute for ELF!");
135    break;
136
137  case MCSA_ELF_TypeGnuUniqueObject:
138    // Ignore for now.
139    break;
140
141  case MCSA_Global:
142    MCELF::SetBinding(SD, ELF::STB_GLOBAL);
143    SD.setExternal(true);
144    BindingExplicitlySet.insert(Symbol);
145    break;
146
147  case MCSA_WeakReference:
148  case MCSA_Weak:
149    MCELF::SetBinding(SD, ELF::STB_WEAK);
150    SD.setExternal(true);
151    BindingExplicitlySet.insert(Symbol);
152    break;
153
154  case MCSA_Local:
155    MCELF::SetBinding(SD, ELF::STB_LOCAL);
156    SD.setExternal(false);
157    BindingExplicitlySet.insert(Symbol);
158    break;
159
160  case MCSA_ELF_TypeFunction:
161    MCELF::SetType(SD, ELF::STT_FUNC);
162    break;
163
164  case MCSA_ELF_TypeObject:
165    MCELF::SetType(SD, ELF::STT_OBJECT);
166    break;
167
168  case MCSA_ELF_TypeTLS:
169    MCELF::SetType(SD, ELF::STT_TLS);
170    break;
171
172  case MCSA_ELF_TypeCommon:
173    MCELF::SetType(SD, ELF::STT_COMMON);
174    break;
175
176  case MCSA_ELF_TypeNoType:
177    MCELF::SetType(SD, ELF::STT_NOTYPE);
178    break;
179
180  case MCSA_Protected:
181    MCELF::SetVisibility(SD, ELF::STV_PROTECTED);
182    break;
183
184  case MCSA_Hidden:
185    MCELF::SetVisibility(SD, ELF::STV_HIDDEN);
186    break;
187
188  case MCSA_Internal:
189    MCELF::SetVisibility(SD, ELF::STV_INTERNAL);
190    break;
191  }
192}
193
194void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
195                                       unsigned ByteAlignment) {
196  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
197
198  if (!BindingExplicitlySet.count(Symbol)) {
199    MCELF::SetBinding(SD, ELF::STB_GLOBAL);
200    SD.setExternal(true);
201  }
202
203  MCELF::SetType(SD, ELF::STT_OBJECT);
204
205  if (MCELF::GetBinding(SD) == ELF_STB_Local) {
206    const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
207                                                                    ELF::SHT_NOBITS,
208                                                                    ELF::SHF_WRITE |
209                                                                    ELF::SHF_ALLOC,
210                                                                    SectionKind::getBSS());
211    Symbol->setSection(*Section);
212
213    struct LocalCommon L = {&SD, Size, ByteAlignment};
214    LocalCommons.push_back(L);
215  } else {
216    SD.setCommon(Size, ByteAlignment);
217  }
218
219  SD.setSize(MCConstantExpr::Create(Size, getContext()));
220}
221
222void MCELFStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
223  // FIXME: Should this be caught and done earlier?
224  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
225  MCELF::SetBinding(SD, ELF::STB_LOCAL);
226  SD.setExternal(false);
227  BindingExplicitlySet.insert(Symbol);
228  // FIXME: ByteAlignment is not needed here, but is required.
229  EmitCommonSymbol(Symbol, Size, 1);
230}
231
232void MCELFStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
233  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
234  // MCObjectStreamer.
235  getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
236}
237
238void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
239                                           int64_t Value, unsigned ValueSize,
240                                           unsigned MaxBytesToEmit) {
241  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
242  // MCObjectStreamer.
243  if (MaxBytesToEmit == 0)
244    MaxBytesToEmit = ByteAlignment;
245  new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
246                      getCurrentSectionData());
247
248  // Update the maximum alignment on the current section if necessary.
249  if (ByteAlignment > getCurrentSectionData()->getAlignment())
250    getCurrentSectionData()->setAlignment(ByteAlignment);
251}
252
253void MCELFStreamer::EmitCodeAlignment(unsigned ByteAlignment,
254                                        unsigned MaxBytesToEmit) {
255  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
256  // MCObjectStreamer.
257  if (MaxBytesToEmit == 0)
258    MaxBytesToEmit = ByteAlignment;
259  MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
260                                           getCurrentSectionData());
261  F->setEmitNops(true);
262
263  // Update the maximum alignment on the current section if necessary.
264  if (ByteAlignment > getCurrentSectionData()->getAlignment())
265    getCurrentSectionData()->setAlignment(ByteAlignment);
266}
267
268// Add a symbol for the file name of this module. This is the second
269// entry in the module's symbol table (the first being the null symbol).
270void MCELFStreamer::EmitFileDirective(StringRef Filename) {
271  MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
272  Symbol->setSection(*getCurrentSection());
273  Symbol->setAbsolute();
274
275  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
276
277  SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
278}
279
280void  MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
281  switch (expr->getKind()) {
282  case MCExpr::Target: llvm_unreachable("Can't handle target exprs yet!");
283  case MCExpr::Constant:
284    break;
285
286  case MCExpr::Binary: {
287    const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
288    fixSymbolsInTLSFixups(be->getLHS());
289    fixSymbolsInTLSFixups(be->getRHS());
290    break;
291  }
292
293  case MCExpr::SymbolRef: {
294    const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
295    switch (symRef.getKind()) {
296    default:
297      return;
298    case MCSymbolRefExpr::VK_GOTTPOFF:
299    case MCSymbolRefExpr::VK_INDNTPOFF:
300    case MCSymbolRefExpr::VK_NTPOFF:
301    case MCSymbolRefExpr::VK_GOTNTPOFF:
302    case MCSymbolRefExpr::VK_TLSGD:
303    case MCSymbolRefExpr::VK_TLSLD:
304    case MCSymbolRefExpr::VK_TLSLDM:
305    case MCSymbolRefExpr::VK_TPOFF:
306    case MCSymbolRefExpr::VK_DTPOFF:
307    case MCSymbolRefExpr::VK_ARM_TLSGD:
308    case MCSymbolRefExpr::VK_ARM_TPOFF:
309    case MCSymbolRefExpr::VK_ARM_GOTTPOFF:
310      break;
311    }
312    MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
313    MCELF::SetType(SD, ELF::STT_TLS);
314    break;
315  }
316
317  case MCExpr::Unary:
318    fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
319    break;
320  }
321}
322
323void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
324  this->MCObjectStreamer::EmitInstToFragment(Inst);
325  MCInstFragment &F = *cast<MCInstFragment>(getCurrentFragment());
326
327  for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
328    fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
329}
330
331void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
332  MCDataFragment *DF = getOrCreateDataFragment();
333
334  SmallVector<MCFixup, 4> Fixups;
335  SmallString<256> Code;
336  raw_svector_ostream VecOS(Code);
337  getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
338  VecOS.flush();
339
340  for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
341    fixSymbolsInTLSFixups(Fixups[i].getValue());
342
343  // Add the fixups and data.
344  for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
345    Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
346    DF->addFixup(Fixups[i]);
347  }
348  DF->getContents().append(Code.begin(), Code.end());
349}
350
351void MCELFStreamer::Finish() {
352  EmitFrames(true);
353
354  for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
355                                                e = LocalCommons.end();
356       i != e; ++i) {
357    MCSymbolData *SD = i->SD;
358    uint64_t Size = i->Size;
359    unsigned ByteAlignment = i->ByteAlignment;
360    const MCSymbol &Symbol = SD->getSymbol();
361    const MCSection &Section = Symbol.getSection();
362
363    MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
364    new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
365
366    MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
367    SD->setFragment(F);
368
369    // Update the maximum alignment of the section if necessary.
370    if (ByteAlignment > SectData.getAlignment())
371      SectData.setAlignment(ByteAlignment);
372  }
373
374  this->MCObjectStreamer::Finish();
375}
376
377MCStreamer *llvm::createELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
378                                    raw_ostream &OS, MCCodeEmitter *CE,
379                                    bool RelaxAll, bool NoExecStack) {
380  MCELFStreamer *S = new MCELFStreamer(Context, TAB, OS, CE);
381  if (RelaxAll)
382    S->getAssembler().setRelaxAll(true);
383  if (NoExecStack)
384    S->getAssembler().setNoExecStack(true);
385  return S;
386}
387