MCELFStreamer.cpp revision 249423 
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/MCELFStreamer.h"
15#include "llvm/ADT/SmallPtrSet.h"
16#include "llvm/MC/MCAssembler.h"
17#include "llvm/MC/MCCodeEmitter.h"
18#include "llvm/MC/MCContext.h"
19#include "llvm/MC/MCELF.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
33using namespace llvm;
34
35
36inline void MCELFStreamer::SetSection(StringRef Section, unsigned Type,
37                                      unsigned Flags, SectionKind Kind) {
38  SwitchSection(getContext().getELFSection(Section, Type, Flags, Kind));
39}
40
41inline void MCELFStreamer::SetSectionData() {
42  SetSection(".data",
43             ELF::SHT_PROGBITS,
44             ELF::SHF_WRITE | ELF::SHF_ALLOC,
45             SectionKind::getDataRel());
46  EmitCodeAlignment(4, 0);
47}
48
49inline void MCELFStreamer::SetSectionText() {
50  SetSection(".text",
51             ELF::SHT_PROGBITS,
52             ELF::SHF_EXECINSTR | ELF::SHF_ALLOC,
53             SectionKind::getText());
54  EmitCodeAlignment(4, 0);
55}
56
57inline void MCELFStreamer::SetSectionBss() {
58  SetSection(".bss",
59             ELF::SHT_NOBITS,
60             ELF::SHF_WRITE | ELF::SHF_ALLOC,
61             SectionKind::getBSS());
62  EmitCodeAlignment(4, 0);
63}
64
65MCELFStreamer::~MCELFStreamer() {
66}
67
68void MCELFStreamer::InitToTextSection() {
69  SetSectionText();
70}
71
72void MCELFStreamer::InitSections() {
73  // This emulates the same behavior of GNU as. This makes it easier
74  // to compare the output as the major sections are in the same order.
75  SetSectionText();
76  SetSectionData();
77  SetSectionBss();
78  SetSectionText();
79}
80
81void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
82  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
83
84  MCObjectStreamer::EmitLabel(Symbol);
85
86  const MCSectionELF &Section =
87    static_cast<const MCSectionELF&>(Symbol->getSection());
88  MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
89  if (Section.getFlags() & ELF::SHF_TLS)
90    MCELF::SetType(SD, ELF::STT_TLS);
91}
92
93void MCELFStreamer::EmitDebugLabel(MCSymbol *Symbol) {
94  EmitLabel(Symbol);
95}
96
97void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
98  switch (Flag) {
99  case MCAF_SyntaxUnified: return; // no-op here.
100  case MCAF_Code16: return; // Change parsing mode; no-op here.
101  case MCAF_Code32: return; // Change parsing mode; no-op here.
102  case MCAF_Code64: return; // Change parsing mode; no-op here.
103  case MCAF_SubsectionsViaSymbols:
104    getAssembler().setSubsectionsViaSymbols(true);
105    return;
106  }
107
108  llvm_unreachable("invalid assembler flag!");
109}
110
111void MCELFStreamer::ChangeSection(const MCSection *Section) {
112  MCSectionData *CurSection = getCurrentSectionData();
113  if (CurSection && CurSection->isBundleLocked())
114    report_fatal_error("Unterminated .bundle_lock when changing a section");
115  const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
116  if (Grp)
117    getAssembler().getOrCreateSymbolData(*Grp);
118  this->MCObjectStreamer::ChangeSection(Section);
119}
120
121void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
122  getAssembler().getOrCreateSymbolData(*Symbol);
123  MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
124  AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
125  const MCExpr *Value = MCSymbolRefExpr::Create(Symbol, getContext());
126  Alias->setVariableValue(Value);
127}
128
129void MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
130                                          MCSymbolAttr Attribute) {
131  // Indirect symbols are handled differently, to match how 'as' handles
132  // them. This makes writing matching .o files easier.
133  if (Attribute == MCSA_IndirectSymbol) {
134    // Note that we intentionally cannot use the symbol data here; this is
135    // important for matching the string table that 'as' generates.
136    IndirectSymbolData ISD;
137    ISD.Symbol = Symbol;
138    ISD.SectionData = getCurrentSectionData();
139    getAssembler().getIndirectSymbols().push_back(ISD);
140    return;
141  }
142
143  // Adding a symbol attribute always introduces the symbol, note that an
144  // important side effect of calling getOrCreateSymbolData here is to register
145  // the symbol with the assembler.
146  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
147
148  // The implementation of symbol attributes is designed to match 'as', but it
149  // leaves much to desired. It doesn't really make sense to arbitrarily add and
150  // remove flags, but 'as' allows this (in particular, see .desc).
151  //
152  // In the future it might be worth trying to make these operations more well
153  // defined.
154  switch (Attribute) {
155  case MCSA_LazyReference:
156  case MCSA_Reference:
157  case MCSA_SymbolResolver:
158  case MCSA_PrivateExtern:
159  case MCSA_WeakDefinition:
160  case MCSA_WeakDefAutoPrivate:
161  case MCSA_Invalid:
162  case MCSA_IndirectSymbol:
163    llvm_unreachable("Invalid symbol attribute for ELF!");
164
165  case MCSA_NoDeadStrip:
166  case MCSA_ELF_TypeGnuUniqueObject:
167    // Ignore for now.
168    break;
169
170  case MCSA_Global:
171    MCELF::SetBinding(SD, ELF::STB_GLOBAL);
172    SD.setExternal(true);
173    BindingExplicitlySet.insert(Symbol);
174    break;
175
176  case MCSA_WeakReference:
177  case MCSA_Weak:
178    MCELF::SetBinding(SD, ELF::STB_WEAK);
179    SD.setExternal(true);
180    BindingExplicitlySet.insert(Symbol);
181    break;
182
183  case MCSA_Local:
184    MCELF::SetBinding(SD, ELF::STB_LOCAL);
185    SD.setExternal(false);
186    BindingExplicitlySet.insert(Symbol);
187    break;
188
189  case MCSA_ELF_TypeFunction:
190    MCELF::SetType(SD, ELF::STT_FUNC);
191    break;
192
193  case MCSA_ELF_TypeIndFunction:
194    MCELF::SetType(SD, ELF::STT_GNU_IFUNC);
195    break;
196
197  case MCSA_ELF_TypeObject:
198    MCELF::SetType(SD, ELF::STT_OBJECT);
199    break;
200
201  case MCSA_ELF_TypeTLS:
202    MCELF::SetType(SD, ELF::STT_TLS);
203    break;
204
205  case MCSA_ELF_TypeCommon:
206    MCELF::SetType(SD, ELF::STT_COMMON);
207    break;
208
209  case MCSA_ELF_TypeNoType:
210    MCELF::SetType(SD, ELF::STT_NOTYPE);
211    break;
212
213  case MCSA_Protected:
214    MCELF::SetVisibility(SD, ELF::STV_PROTECTED);
215    break;
216
217  case MCSA_Hidden:
218    MCELF::SetVisibility(SD, ELF::STV_HIDDEN);
219    break;
220
221  case MCSA_Internal:
222    MCELF::SetVisibility(SD, ELF::STV_INTERNAL);
223    break;
224  }
225}
226
227void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
228                                       unsigned ByteAlignment) {
229  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
230
231  if (!BindingExplicitlySet.count(Symbol)) {
232    MCELF::SetBinding(SD, ELF::STB_GLOBAL);
233    SD.setExternal(true);
234  }
235
236  MCELF::SetType(SD, ELF::STT_OBJECT);
237
238  if (MCELF::GetBinding(SD) == ELF_STB_Local) {
239    const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
240                                                         ELF::SHT_NOBITS,
241                                                         ELF::SHF_WRITE |
242                                                         ELF::SHF_ALLOC,
243                                                         SectionKind::getBSS());
244    Symbol->setSection(*Section);
245
246    struct LocalCommon L = {&SD, Size, ByteAlignment};
247    LocalCommons.push_back(L);
248  } else {
249    SD.setCommon(Size, ByteAlignment);
250  }
251
252  SD.setSize(MCConstantExpr::Create(Size, getContext()));
253}
254
255void MCELFStreamer::EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
256  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
257  SD.setSize(Value);
258}
259
260void MCELFStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
261                                          unsigned ByteAlignment) {
262  // FIXME: Should this be caught and done earlier?
263  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
264  MCELF::SetBinding(SD, ELF::STB_LOCAL);
265  SD.setExternal(false);
266  BindingExplicitlySet.insert(Symbol);
267  EmitCommonSymbol(Symbol, Size, ByteAlignment);
268}
269
270void MCELFStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
271                                  unsigned AddrSpace) {
272  if (getCurrentSectionData()->isBundleLocked())
273    report_fatal_error("Emitting values inside a locked bundle is forbidden");
274  fixSymbolsInTLSFixups(Value);
275  MCObjectStreamer::EmitValueImpl(Value, Size, AddrSpace);
276}
277
278void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
279                                         int64_t Value,
280                                         unsigned ValueSize,
281                                         unsigned MaxBytesToEmit) {
282  if (getCurrentSectionData()->isBundleLocked())
283    report_fatal_error("Emitting values inside a locked bundle is forbidden");
284  MCObjectStreamer::EmitValueToAlignment(ByteAlignment, Value,
285                                         ValueSize, MaxBytesToEmit);
286}
287
288
289// Add a symbol for the file name of this module. This is the second
290// entry in the module's symbol table (the first being the null symbol).
291void MCELFStreamer::EmitFileDirective(StringRef Filename) {
292  MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
293  Symbol->setSection(*getCurrentSection());
294  Symbol->setAbsolute();
295
296  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
297
298  SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
299}
300
301void  MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
302  switch (expr->getKind()) {
303  case MCExpr::Target:
304    cast<MCTargetExpr>(expr)->fixELFSymbolsInTLSFixups(getAssembler());
305    break;
306  case MCExpr::Constant:
307    break;
308
309  case MCExpr::Binary: {
310    const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
311    fixSymbolsInTLSFixups(be->getLHS());
312    fixSymbolsInTLSFixups(be->getRHS());
313    break;
314  }
315
316  case MCExpr::SymbolRef: {
317    const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
318    switch (symRef.getKind()) {
319    default:
320      return;
321    case MCSymbolRefExpr::VK_GOTTPOFF:
322    case MCSymbolRefExpr::VK_INDNTPOFF:
323    case MCSymbolRefExpr::VK_NTPOFF:
324    case MCSymbolRefExpr::VK_GOTNTPOFF:
325    case MCSymbolRefExpr::VK_TLSGD:
326    case MCSymbolRefExpr::VK_TLSLD:
327    case MCSymbolRefExpr::VK_TLSLDM:
328    case MCSymbolRefExpr::VK_TPOFF:
329    case MCSymbolRefExpr::VK_DTPOFF:
330    case MCSymbolRefExpr::VK_ARM_TLSGD:
331    case MCSymbolRefExpr::VK_ARM_TPOFF:
332    case MCSymbolRefExpr::VK_ARM_GOTTPOFF:
333    case MCSymbolRefExpr::VK_Mips_TLSGD:
334    case MCSymbolRefExpr::VK_Mips_GOTTPREL:
335    case MCSymbolRefExpr::VK_Mips_TPREL_HI:
336    case MCSymbolRefExpr::VK_Mips_TPREL_LO:
337    case MCSymbolRefExpr::VK_PPC_TPREL16_HA:
338    case MCSymbolRefExpr::VK_PPC_TPREL16_LO:
339    case MCSymbolRefExpr::VK_PPC_DTPREL16_HA:
340    case MCSymbolRefExpr::VK_PPC_DTPREL16_LO:
341    case MCSymbolRefExpr::VK_PPC_GOT_TPREL16_HA:
342    case MCSymbolRefExpr::VK_PPC_GOT_TPREL16_LO:
343    case MCSymbolRefExpr::VK_PPC_TLS:
344    case MCSymbolRefExpr::VK_PPC_GOT_TLSGD16_HA:
345    case MCSymbolRefExpr::VK_PPC_GOT_TLSGD16_LO:
346    case MCSymbolRefExpr::VK_PPC_TLSGD:
347    case MCSymbolRefExpr::VK_PPC_GOT_TLSLD16_HA:
348    case MCSymbolRefExpr::VK_PPC_GOT_TLSLD16_LO:
349    case MCSymbolRefExpr::VK_PPC_TLSLD:
350      break;
351    }
352    MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
353    MCELF::SetType(SD, ELF::STT_TLS);
354    break;
355  }
356
357  case MCExpr::Unary:
358    fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
359    break;
360  }
361}
362
363void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
364  this->MCObjectStreamer::EmitInstToFragment(Inst);
365  MCRelaxableFragment &F = *cast<MCRelaxableFragment>(getCurrentFragment());
366
367  for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
368    fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
369}
370
371void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
372  MCAssembler &Assembler = getAssembler();
373  SmallVector<MCFixup, 4> Fixups;
374  SmallString<256> Code;
375  raw_svector_ostream VecOS(Code);
376  Assembler.getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
377  VecOS.flush();
378
379  for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
380    fixSymbolsInTLSFixups(Fixups[i].getValue());
381
382  // There are several possibilities here:
383  //
384  // If bundling is disabled, append the encoded instruction to the current data
385  // fragment (or create a new such fragment if the current fragment is not a
386  // data fragment).
387  //
388  // If bundling is enabled:
389  // - If we're not in a bundle-locked group, emit the instruction into a
390  //   fragment of its own. If there are no fixups registered for the
391  //   instruction, emit a MCCompactEncodedInstFragment. Otherwise, emit a
392  //   MCDataFragment.
393  // - If we're in a bundle-locked group, append the instruction to the current
394  //   data fragment because we want all the instructions in a group to get into
395  //   the same fragment. Be careful not to do that for the first instruction in
396  //   the group, though.
397  MCDataFragment *DF;
398
399  if (Assembler.isBundlingEnabled()) {
400    MCSectionData *SD = getCurrentSectionData();
401    if (SD->isBundleLocked() && !SD->isBundleGroupBeforeFirstInst())
402      // If we are bundle-locked, we re-use the current fragment.
403      // The bundle-locking directive ensures this is a new data fragment.
404      DF = cast<MCDataFragment>(getCurrentFragment());
405    else if (!SD->isBundleLocked() && Fixups.size() == 0) {
406      // Optimize memory usage by emitting the instruction to a
407      // MCCompactEncodedInstFragment when not in a bundle-locked group and
408      // there are no fixups registered.
409      MCCompactEncodedInstFragment *CEIF = new MCCompactEncodedInstFragment(SD);
410      CEIF->getContents().append(Code.begin(), Code.end());
411      return;
412    } else {
413      DF = new MCDataFragment(SD);
414      if (SD->getBundleLockState() == MCSectionData::BundleLockedAlignToEnd) {
415        // If this is a new fragment created for a bundle-locked group, and the
416        // group was marked as "align_to_end", set a flag in the fragment.
417        DF->setAlignToBundleEnd(true);
418      }
419    }
420
421    // We're now emitting an instruction in a bundle group, so this flag has
422    // to be turned off.
423    SD->setBundleGroupBeforeFirstInst(false);
424  } else {
425    DF = getOrCreateDataFragment();
426  }
427
428  // Add the fixups and data.
429  for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
430    Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
431    DF->getFixups().push_back(Fixups[i]);
432  }
433  DF->setHasInstructions(true);
434  DF->getContents().append(Code.begin(), Code.end());
435}
436
437void MCELFStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
438  assert(AlignPow2 <= 30 && "Invalid bundle alignment");
439  MCAssembler &Assembler = getAssembler();
440  if (Assembler.getBundleAlignSize() == 0 && AlignPow2 > 0)
441    Assembler.setBundleAlignSize(1 << AlignPow2);
442  else
443    report_fatal_error(".bundle_align_mode should be only set once per file");
444}
445
446void MCELFStreamer::EmitBundleLock(bool AlignToEnd) {
447  MCSectionData *SD = getCurrentSectionData();
448
449  // Sanity checks
450  //
451  if (!getAssembler().isBundlingEnabled())
452    report_fatal_error(".bundle_lock forbidden when bundling is disabled");
453  else if (SD->isBundleLocked())
454    report_fatal_error("Nesting of .bundle_lock is forbidden");
455
456  SD->setBundleLockState(AlignToEnd ? MCSectionData::BundleLockedAlignToEnd :
457                                      MCSectionData::BundleLocked);
458  SD->setBundleGroupBeforeFirstInst(true);
459}
460
461void MCELFStreamer::EmitBundleUnlock() {
462  MCSectionData *SD = getCurrentSectionData();
463
464  // Sanity checks
465  if (!getAssembler().isBundlingEnabled())
466    report_fatal_error(".bundle_unlock forbidden when bundling is disabled");
467  else if (!SD->isBundleLocked())
468    report_fatal_error(".bundle_unlock without matching lock");
469  else if (SD->isBundleGroupBeforeFirstInst())
470    report_fatal_error("Empty bundle-locked group is forbidden");
471
472  SD->setBundleLockState(MCSectionData::NotBundleLocked);
473}
474
475void MCELFStreamer::FinishImpl() {
476  EmitFrames(true);
477
478  for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
479                                                e = LocalCommons.end();
480       i != e; ++i) {
481    MCSymbolData *SD = i->SD;
482    uint64_t Size = i->Size;
483    unsigned ByteAlignment = i->ByteAlignment;
484    const MCSymbol &Symbol = SD->getSymbol();
485    const MCSection &Section = Symbol.getSection();
486
487    MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
488    new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
489
490    MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
491    SD->setFragment(F);
492
493    // Update the maximum alignment of the section if necessary.
494    if (ByteAlignment > SectData.getAlignment())
495      SectData.setAlignment(ByteAlignment);
496  }
497
498  this->MCObjectStreamer::FinishImpl();
499}
500void MCELFStreamer::EmitTCEntry(const MCSymbol &S) {
501  // Creates a R_PPC64_TOC relocation
502  MCObjectStreamer::EmitSymbolValue(&S, 8);
503}
504
505MCStreamer *llvm::createELFStreamer(MCContext &Context, MCAsmBackend &MAB,
506                                    raw_ostream &OS, MCCodeEmitter *CE,
507                                    bool RelaxAll, bool NoExecStack) {
508  MCELFStreamer *S = new MCELFStreamer(Context, MAB, OS, CE);
509  if (RelaxAll)
510    S->getAssembler().setRelaxAll(true);
511  if (NoExecStack)
512    S->getAssembler().setNoExecStack(true);
513  return S;
514}
515
516void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
517  llvm_unreachable("Generic ELF doesn't support this directive");
518}
519
520MCSymbolData &MCELFStreamer::getOrCreateSymbolData(MCSymbol *Symbol) {
521  return getAssembler().getOrCreateSymbolData(*Symbol);
522}
523
524void MCELFStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
525  llvm_unreachable("ELF doesn't support this directive");
526}
527
528void MCELFStreamer::BeginCOFFSymbolDef(const MCSymbol *Symbol) {
529  llvm_unreachable("ELF doesn't support this directive");
530}
531
532void MCELFStreamer::EmitCOFFSymbolStorageClass(int StorageClass) {
533  llvm_unreachable("ELF doesn't support this directive");
534}
535
536void MCELFStreamer::EmitCOFFSymbolType(int Type) {
537  llvm_unreachable("ELF doesn't support this directive");
538}
539
540void MCELFStreamer::EndCOFFSymbolDef() {
541  llvm_unreachable("ELF doesn't support this directive");
542}
543
544void MCELFStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
545                                 uint64_t Size, unsigned ByteAlignment) {
546  llvm_unreachable("ELF doesn't support this directive");
547}
548
549void MCELFStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
550                                   uint64_t Size, unsigned ByteAlignment) {
551  llvm_unreachable("ELF doesn't support this directive");
552}
553