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