lib/MC/MCELFStreamer.cpp

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