MCELFStreamer.cpp revision 6c1d4972cf1cd6b6072e31c05f97abb1ed7a8497 
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::InitSections() {
69  // This emulates the same behavior of GNU as. This makes it easier
70  // to compare the output as the major sections are in the same order.
71  SetSectionText();
72  SetSectionData();
73  SetSectionBss();
74  SetSectionText();
75}
76
77void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
78  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
79
80  MCObjectStreamer::EmitLabel(Symbol);
81
82  const MCSectionELF &Section =
83    static_cast<const MCSectionELF&>(Symbol->getSection());
84  MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
85  if (Section.getFlags() & ELF::SHF_TLS)
86    MCELF::SetType(SD, ELF::STT_TLS);
87}
88
89void MCELFStreamer::EmitDebugLabel(MCSymbol *Symbol) {
90  EmitLabel(Symbol);
91}
92
93void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
94  switch (Flag) {
95  case MCAF_SyntaxUnified: return; // no-op here.
96  case MCAF_Code16: return; // Change parsing mode; no-op here.
97  case MCAF_Code32: return; // Change parsing mode; no-op here.
98  case MCAF_Code64: return; // Change parsing mode; no-op here.
99  case MCAF_SubsectionsViaSymbols:
100    getAssembler().setSubsectionsViaSymbols(true);
101    return;
102  }
103
104  llvm_unreachable("invalid assembler flag!");
105}
106
107void MCELFStreamer::ChangeSection(const MCSection *Section) {
108  MCSectionData *CurSection = getCurrentSectionData();
109  if (CurSection && CurSection->isBundleLocked())
110    report_fatal_error("Unterminated .bundle_lock when changing a section");
111  const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
112  if (Grp)
113    getAssembler().getOrCreateSymbolData(*Grp);
114  this->MCObjectStreamer::ChangeSection(Section);
115}
116
117void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
118  getAssembler().getOrCreateSymbolData(*Symbol);
119  MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
120  AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
121  const MCExpr *Value = MCSymbolRefExpr::Create(Symbol, getContext());
122  Alias->setVariableValue(Value);
123}
124
125void MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
126                                          MCSymbolAttr Attribute) {
127  // Indirect symbols are handled differently, to match how 'as' handles
128  // them. This makes writing matching .o files easier.
129  if (Attribute == MCSA_IndirectSymbol) {
130    // Note that we intentionally cannot use the symbol data here; this is
131    // important for matching the string table that 'as' generates.
132    IndirectSymbolData ISD;
133    ISD.Symbol = Symbol;
134    ISD.SectionData = getCurrentSectionData();
135    getAssembler().getIndirectSymbols().push_back(ISD);
136    return;
137  }
138
139  // Adding a symbol attribute always introduces the symbol, note that an
140  // important side effect of calling getOrCreateSymbolData here is to register
141  // the symbol with the assembler.
142  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
143
144  // The implementation of symbol attributes is designed to match 'as', but it
145  // leaves much to desired. It doesn't really make sense to arbitrarily add and
146  // remove flags, but 'as' allows this (in particular, see .desc).
147  //
148  // In the future it might be worth trying to make these operations more well
149  // defined.
150  switch (Attribute) {
151  case MCSA_LazyReference:
152  case MCSA_Reference:
153  case MCSA_SymbolResolver:
154  case MCSA_PrivateExtern:
155  case MCSA_WeakDefinition:
156  case MCSA_WeakDefAutoPrivate:
157  case MCSA_Invalid:
158  case MCSA_IndirectSymbol:
159    llvm_unreachable("Invalid symbol attribute for ELF!");
160
161  case MCSA_NoDeadStrip:
162  case MCSA_ELF_TypeGnuUniqueObject:
163    // Ignore for now.
164    break;
165
166  case MCSA_Global:
167    MCELF::SetBinding(SD, ELF::STB_GLOBAL);
168    SD.setExternal(true);
169    BindingExplicitlySet.insert(Symbol);
170    break;
171
172  case MCSA_WeakReference:
173  case MCSA_Weak:
174    MCELF::SetBinding(SD, ELF::STB_WEAK);
175    SD.setExternal(true);
176    BindingExplicitlySet.insert(Symbol);
177    break;
178
179  case MCSA_Local:
180    MCELF::SetBinding(SD, ELF::STB_LOCAL);
181    SD.setExternal(false);
182    BindingExplicitlySet.insert(Symbol);
183    break;
184
185  case MCSA_ELF_TypeFunction:
186    MCELF::SetType(SD, ELF::STT_FUNC);
187    break;
188
189  case MCSA_ELF_TypeIndFunction:
190    MCELF::SetType(SD, ELF::STT_GNU_IFUNC);
191    break;
192
193  case MCSA_ELF_TypeObject:
194    MCELF::SetType(SD, ELF::STT_OBJECT);
195    break;
196
197  case MCSA_ELF_TypeTLS:
198    MCELF::SetType(SD, ELF::STT_TLS);
199    break;
200
201  case MCSA_ELF_TypeCommon:
202    MCELF::SetType(SD, ELF::STT_COMMON);
203    break;
204
205  case MCSA_ELF_TypeNoType:
206    MCELF::SetType(SD, ELF::STT_NOTYPE);
207    break;
208
209  case MCSA_Protected:
210    MCELF::SetVisibility(SD, ELF::STV_PROTECTED);
211    break;
212
213  case MCSA_Hidden:
214    MCELF::SetVisibility(SD, ELF::STV_HIDDEN);
215    break;
216
217  case MCSA_Internal:
218    MCELF::SetVisibility(SD, ELF::STV_INTERNAL);
219    break;
220  }
221}
222
223void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
224                                       unsigned ByteAlignment) {
225  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
226
227  if (!BindingExplicitlySet.count(Symbol)) {
228    MCELF::SetBinding(SD, ELF::STB_GLOBAL);
229    SD.setExternal(true);
230  }
231
232  MCELF::SetType(SD, ELF::STT_OBJECT);
233
234  if (MCELF::GetBinding(SD) == ELF_STB_Local) {
235    const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
236                                                         ELF::SHT_NOBITS,
237                                                         ELF::SHF_WRITE |
238                                                         ELF::SHF_ALLOC,
239                                                         SectionKind::getBSS());
240    Symbol->setSection(*Section);
241
242    struct LocalCommon L = {&SD, Size, ByteAlignment};
243    LocalCommons.push_back(L);
244  } else {
245    SD.setCommon(Size, ByteAlignment);
246  }
247
248  SD.setSize(MCConstantExpr::Create(Size, getContext()));
249}
250
251void MCELFStreamer::EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
252  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
253  SD.setSize(Value);
254}
255
256void MCELFStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
257                                          unsigned ByteAlignment) {
258  // FIXME: Should this be caught and done earlier?
259  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
260  MCELF::SetBinding(SD, ELF::STB_LOCAL);
261  SD.setExternal(false);
262  BindingExplicitlySet.insert(Symbol);
263  EmitCommonSymbol(Symbol, Size, ByteAlignment);
264}
265
266void MCELFStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
267                                  unsigned AddrSpace) {
268  if (getCurrentSectionData()->isBundleLocked())
269    report_fatal_error("Emitting values inside a locked bundle is forbidden");
270  fixSymbolsInTLSFixups(Value);
271  MCObjectStreamer::EmitValueImpl(Value, Size, AddrSpace);
272}
273
274void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
275                                         int64_t Value,
276                                         unsigned ValueSize,
277                                         unsigned MaxBytesToEmit) {
278  if (getCurrentSectionData()->isBundleLocked())
279    report_fatal_error("Emitting values inside a locked bundle is forbidden");
280  MCObjectStreamer::EmitValueToAlignment(ByteAlignment, Value,
281                                         ValueSize, MaxBytesToEmit);
282}
283
284
285// Add a symbol for the file name of this module. This is the second
286// entry in the module's symbol table (the first being the null symbol).
287void MCELFStreamer::EmitFileDirective(StringRef Filename) {
288  MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
289  Symbol->setSection(*getCurrentSection());
290  Symbol->setAbsolute();
291
292  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
293
294  SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
295}
296
297void  MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
298  switch (expr->getKind()) {
299  case MCExpr::Target: llvm_unreachable("Can't handle target exprs yet!");
300  case MCExpr::Constant:
301    break;
302
303  case MCExpr::Binary: {
304    const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
305    fixSymbolsInTLSFixups(be->getLHS());
306    fixSymbolsInTLSFixups(be->getRHS());
307    break;
308  }
309
310  case MCExpr::SymbolRef: {
311    const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
312    switch (symRef.getKind()) {
313    default:
314      return;
315    case MCSymbolRefExpr::VK_GOTTPOFF:
316    case MCSymbolRefExpr::VK_INDNTPOFF:
317    case MCSymbolRefExpr::VK_NTPOFF:
318    case MCSymbolRefExpr::VK_GOTNTPOFF:
319    case MCSymbolRefExpr::VK_TLSGD:
320    case MCSymbolRefExpr::VK_TLSLD:
321    case MCSymbolRefExpr::VK_TLSLDM:
322    case MCSymbolRefExpr::VK_TPOFF:
323    case MCSymbolRefExpr::VK_DTPOFF:
324    case MCSymbolRefExpr::VK_ARM_TLSGD:
325    case MCSymbolRefExpr::VK_ARM_TPOFF:
326    case MCSymbolRefExpr::VK_ARM_GOTTPOFF:
327    case MCSymbolRefExpr::VK_Mips_TLSGD:
328    case MCSymbolRefExpr::VK_Mips_GOTTPREL:
329    case MCSymbolRefExpr::VK_Mips_TPREL_HI:
330    case MCSymbolRefExpr::VK_Mips_TPREL_LO:
331      break;
332    }
333    MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
334    MCELF::SetType(SD, ELF::STT_TLS);
335    break;
336  }
337
338  case MCExpr::Unary:
339    fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
340    break;
341  }
342}
343
344void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
345  this->MCObjectStreamer::EmitInstToFragment(Inst);
346  MCInstFragment &F = *cast<MCInstFragment>(getCurrentFragment());
347
348  for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
349    fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
350}
351
352void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
353  MCAssembler &Assembler = getAssembler();
354  SmallVector<MCFixup, 4> Fixups;
355  SmallString<256> Code;
356  raw_svector_ostream VecOS(Code);
357  Assembler.getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
358  VecOS.flush();
359
360  for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
361    fixSymbolsInTLSFixups(Fixups[i].getValue());
362
363  // There are several possibilities here:
364  //
365  // If bundling is disabled, append the encoded instruction to the current data
366  // fragment (or create a new such fragment if the current fragment is not a
367  // data fragment).
368  //
369  // If bundling is enabled:
370  // - If we're not in a bundle-locked group, emit the instruction into a data
371  //   fragment of its own.
372  // - If we're in a bundle-locked group, append the instruction to the current
373  //   data fragment because we want all the instructions in a group to get into
374  //   the same fragment. Be careful not to do that for the first instruction in
375  //   the group, though.
376  MCDataFragment *DF;
377
378  if (Assembler.isBundlingEnabled()) {
379    MCSectionData *SD = getCurrentSectionData();
380    if (SD->isBundleLocked() && !SD->isBundleGroupBeforeFirstInst())
381      DF = getOrCreateDataFragment();
382    else {
383      DF = new MCDataFragment(SD);
384      if (SD->getBundleLockState() == MCSectionData::BundleLockedAlignToEnd) {
385        // If this is a new fragment created for a bundle-locked group, and the
386        // group was marked as "align_to_end", set a flag in the fragment.
387        DF->setAlignToBundleEnd(true);
388      }
389    }
390
391    // We're now emitting an instruction in a bundle group, so this flag has
392    // to be turned off.
393    SD->setBundleGroupBeforeFirstInst(false);
394  } else {
395    DF = getOrCreateDataFragment();
396  }
397
398  // Add the fixups and data.
399  for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
400    Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
401    DF->getFixups().push_back(Fixups[i]);
402  }
403  DF->setHasInstructions(true);
404  DF->getContents().append(Code.begin(), Code.end());
405}
406
407void MCELFStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
408  assert(AlignPow2 <= 30 && "Invalid bundle alignment");
409  MCAssembler &Assembler = getAssembler();
410  if (Assembler.getBundleAlignSize() == 0 && AlignPow2 > 0)
411    Assembler.setBundleAlignSize(1 << AlignPow2);
412  else
413    report_fatal_error(".bundle_align_mode should be only set once per file");
414}
415
416void MCELFStreamer::EmitBundleLock(bool AlignToEnd) {
417  MCSectionData *SD = getCurrentSectionData();
418
419  // Sanity checks
420  //
421  if (!getAssembler().isBundlingEnabled())
422    report_fatal_error(".bundle_lock forbidden when bundling is disabled");
423  else if (SD->isBundleLocked())
424    report_fatal_error("Nesting of .bundle_lock is forbidden");
425
426  SD->setBundleLockState(AlignToEnd ? MCSectionData::BundleLockedAlignToEnd :
427                                      MCSectionData::BundleLocked);
428  SD->setBundleGroupBeforeFirstInst(true);
429}
430
431void MCELFStreamer::EmitBundleUnlock() {
432  MCSectionData *SD = getCurrentSectionData();
433
434  // Sanity checks
435  if (!getAssembler().isBundlingEnabled())
436    report_fatal_error(".bundle_unlock forbidden when bundling is disabled");
437  else if (!SD->isBundleLocked())
438    report_fatal_error(".bundle_unlock without matching lock");
439  else if (SD->isBundleGroupBeforeFirstInst())
440    report_fatal_error("Empty bundle-locked group is forbidden");
441
442  SD->setBundleLockState(MCSectionData::NotBundleLocked);
443}
444
445void MCELFStreamer::FinishImpl() {
446  EmitFrames(true);
447
448  for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
449                                                e = LocalCommons.end();
450       i != e; ++i) {
451    MCSymbolData *SD = i->SD;
452    uint64_t Size = i->Size;
453    unsigned ByteAlignment = i->ByteAlignment;
454    const MCSymbol &Symbol = SD->getSymbol();
455    const MCSection &Section = Symbol.getSection();
456
457    MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
458    new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
459
460    MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
461    SD->setFragment(F);
462
463    // Update the maximum alignment of the section if necessary.
464    if (ByteAlignment > SectData.getAlignment())
465      SectData.setAlignment(ByteAlignment);
466  }
467
468  this->MCObjectStreamer::FinishImpl();
469}
470void MCELFStreamer::EmitTCEntry(const MCSymbol &S) {
471  // Creates a R_PPC64_TOC relocation
472  MCObjectStreamer::EmitSymbolValue(&S, 8, 0);
473}
474
475MCStreamer *llvm::createELFStreamer(MCContext &Context, MCAsmBackend &MAB,
476                                    raw_ostream &OS, MCCodeEmitter *CE,
477                                    bool RelaxAll, bool NoExecStack) {
478  MCELFStreamer *S = new MCELFStreamer(Context, MAB, OS, CE);
479  if (RelaxAll)
480    S->getAssembler().setRelaxAll(true);
481  if (NoExecStack)
482    S->getAssembler().setNoExecStack(true);
483  return S;
484}
485
486void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
487  llvm_unreachable("Generic ELF doesn't support this directive");
488}
489
490void MCELFStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
491  llvm_unreachable("ELF doesn't support this directive");
492}
493
494void MCELFStreamer::BeginCOFFSymbolDef(const MCSymbol *Symbol) {
495  llvm_unreachable("ELF doesn't support this directive");
496}
497
498void MCELFStreamer::EmitCOFFSymbolStorageClass(int StorageClass) {
499  llvm_unreachable("ELF doesn't support this directive");
500}
501
502void MCELFStreamer::EmitCOFFSymbolType(int Type) {
503  llvm_unreachable("ELF doesn't support this directive");
504}
505
506void MCELFStreamer::EndCOFFSymbolDef() {
507  llvm_unreachable("ELF doesn't support this directive");
508}
509
510void MCELFStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
511                                 uint64_t Size, unsigned ByteAlignment) {
512  llvm_unreachable("ELF doesn't support this directive");
513}
514
515void MCELFStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
516                                   uint64_t Size, unsigned ByteAlignment) {
517  llvm_unreachable("ELF doesn't support this directive");
518}
519