lib/MC/MCELFStreamer.cpp

//===- lib/MC/MCELFStreamer.cpp - ELF Object Output ------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file assembles .s files and emits ELF .o object files.
//
//===----------------------------------------------------------------------===//

#include "MCELFStreamer.h"
#include "MCELF.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCELFSymbolFlags.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCValue.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ELF.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"

using namespace llvm;

void MCELFStreamer::InitSections() {
  // This emulates the same behavior of GNU as. This makes it easier
  // to compare the output as the major sections are in the same order.
  SetSectionText();
  SetSectionData();
  SetSectionBss();
  SetSectionText();
}

void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");

  MCObjectStreamer::EmitLabel(Symbol);

  const MCSectionELF &Section =
    static_cast<const MCSectionELF&>(Symbol->getSection());
  MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
  if (Section.getFlags() & ELF::SHF_TLS)
    MCELF::SetType(SD, ELF::STT_TLS);
}

void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
  switch (Flag) {
  case MCAF_SyntaxUnified: return; // no-op here.
  case MCAF_Code16: return; // no-op here.
  case MCAF_Code32: return; // no-op here.
  case MCAF_SubsectionsViaSymbols:
    getAssembler().setSubsectionsViaSymbols(true);
    return;
  }

  assert(0 && "invalid assembler flag!");
}

void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
  // FIXME: Anything needed here to flag the function as thumb?

  getAssembler().setIsThumbFunc(Func);

  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Func);
  SD.setFlags(SD.getFlags() | ELF_Other_ThumbFunc);
}

void MCELFStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
  // MCObjectStreamer.
  // FIXME: Lift context changes into super class.
  getAssembler().getOrCreateSymbolData(*Symbol);
  Symbol->setVariableValue(AddValueSymbols(Value));
}

void MCELFStreamer::ChangeSection(const MCSection *Section) {
  const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
  if (Grp)
    getAssembler().getOrCreateSymbolData(*Grp);
  this->MCObjectStreamer::ChangeSection(Section);
}

void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
  getAssembler().getOrCreateSymbolData(*Symbol);
  MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
  AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
  const MCExpr *Value = MCSymbolRefExpr::Create(Symbol, getContext());
  Alias->setVariableValue(Value);
}

void MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
                                          MCSymbolAttr Attribute) {
  // Indirect symbols are handled differently, to match how 'as' handles
  // them. This makes writing matching .o files easier.
  if (Attribute == MCSA_IndirectSymbol) {
    // Note that we intentionally cannot use the symbol data here; this is
    // important for matching the string table that 'as' generates.
    IndirectSymbolData ISD;
    ISD.Symbol = Symbol;
    ISD.SectionData = getCurrentSectionData();
    getAssembler().getIndirectSymbols().push_back(ISD);
    return;
  }

  // Adding a symbol attribute always introduces the symbol, note that an
  // important side effect of calling getOrCreateSymbolData here is to register
  // the symbol with the assembler.
  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);

  // The implementation of symbol attributes is designed to match 'as', but it
  // leaves much to desired. It doesn't really make sense to arbitrarily add and
  // remove flags, but 'as' allows this (in particular, see .desc).
  //
  // In the future it might be worth trying to make these operations more well
  // defined.
  switch (Attribute) {
  case MCSA_LazyReference:
  case MCSA_Reference:
  case MCSA_NoDeadStrip:
  case MCSA_SymbolResolver:
  case MCSA_PrivateExtern:
  case MCSA_WeakDefinition:
  case MCSA_WeakDefAutoPrivate:
  case MCSA_Invalid:
  case MCSA_ELF_TypeIndFunction:
  case MCSA_IndirectSymbol:
    assert(0 && "Invalid symbol attribute for ELF!");
    break;

  case MCSA_ELF_TypeGnuUniqueObject:
    // Ignore for now.
    break;

  case MCSA_Global:
    MCELF::SetBinding(SD, ELF::STB_GLOBAL);
    SD.setExternal(true);
    BindingExplicitlySet.insert(Symbol);
    break;

  case MCSA_WeakReference:
  case MCSA_Weak:
    MCELF::SetBinding(SD, ELF::STB_WEAK);
    SD.setExternal(true);
    BindingExplicitlySet.insert(Symbol);
    break;

  case MCSA_Local:
    MCELF::SetBinding(SD, ELF::STB_LOCAL);
    SD.setExternal(false);
    BindingExplicitlySet.insert(Symbol);
    break;

  case MCSA_ELF_TypeFunction:
    MCELF::SetType(SD, ELF::STT_FUNC);
    break;

  case MCSA_ELF_TypeObject:
    MCELF::SetType(SD, ELF::STT_OBJECT);
    break;

  case MCSA_ELF_TypeTLS:
    MCELF::SetType(SD, ELF::STT_TLS);
    break;

  case MCSA_ELF_TypeCommon:
    MCELF::SetType(SD, ELF::STT_COMMON);
    break;

  case MCSA_ELF_TypeNoType:
    MCELF::SetType(SD, ELF::STT_NOTYPE);
    break;

  case MCSA_Protected:
    MCELF::SetVisibility(SD, ELF::STV_PROTECTED);
    break;

  case MCSA_Hidden:
    MCELF::SetVisibility(SD, ELF::STV_HIDDEN);
    break;

  case MCSA_Internal:
    MCELF::SetVisibility(SD, ELF::STV_INTERNAL);
    break;
  }
}

void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                                       unsigned ByteAlignment) {
  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);

  if (!BindingExplicitlySet.count(Symbol)) {
    MCELF::SetBinding(SD, ELF::STB_GLOBAL);
    SD.setExternal(true);
  }

  MCELF::SetType(SD, ELF::STT_OBJECT);

  if (MCELF::GetBinding(SD) == ELF_STB_Local) {
    const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
                                                                    ELF::SHT_NOBITS,
                                                                    ELF::SHF_WRITE |
                                                                    ELF::SHF_ALLOC,
                                                                    SectionKind::getBSS());
    Symbol->setSection(*Section);

    struct LocalCommon L = {&SD, Size, ByteAlignment};
    LocalCommons.push_back(L);
  } else {
    SD.setCommon(Size, ByteAlignment);
  }

  SD.setSize(MCConstantExpr::Create(Size, getContext()));
}

void MCELFStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
  // FIXME: Should this be caught and done earlier?
  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
  MCELF::SetBinding(SD, ELF::STB_LOCAL);
  SD.setExternal(false);
  BindingExplicitlySet.insert(Symbol);
  // FIXME: ByteAlignment is not needed here, but is required.
  EmitCommonSymbol(Symbol, Size, 1);
}

void MCELFStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
  // MCObjectStreamer.
  getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
}

void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
                                           int64_t Value, unsigned ValueSize,
                                           unsigned MaxBytesToEmit) {
  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
  // MCObjectStreamer.
  if (MaxBytesToEmit == 0)
    MaxBytesToEmit = ByteAlignment;
  new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
                      getCurrentSectionData());

  // Update the maximum alignment on the current section if necessary.
  if (ByteAlignment > getCurrentSectionData()->getAlignment())
    getCurrentSectionData()->setAlignment(ByteAlignment);
}

void MCELFStreamer::EmitCodeAlignment(unsigned ByteAlignment,
                                        unsigned MaxBytesToEmit) {
  // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
  // MCObjectStreamer.
  if (MaxBytesToEmit == 0)
    MaxBytesToEmit = ByteAlignment;
  MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
                                           getCurrentSectionData());
  F->setEmitNops(true);

  // Update the maximum alignment on the current section if necessary.
  if (ByteAlignment > getCurrentSectionData()->getAlignment())
    getCurrentSectionData()->setAlignment(ByteAlignment);
}

// Add a symbol for the file name of this module. This is the second
// entry in the module's symbol table (the first being the null symbol).
void MCELFStreamer::EmitFileDirective(StringRef Filename) {
  MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
  Symbol->setSection(*getCurrentSection());
  Symbol->setAbsolute();

  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);

  SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
}

void  MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
  switch (expr->getKind()) {
  case MCExpr::Target: llvm_unreachable("Can't handle target exprs yet!");
  case MCExpr::Constant:
    break;

  case MCExpr::Binary: {
    const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
    fixSymbolsInTLSFixups(be->getLHS());
    fixSymbolsInTLSFixups(be->getRHS());
    break;
  }

  case MCExpr::SymbolRef: {
    const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
    switch (symRef.getKind()) {
    default:
      return;
    case MCSymbolRefExpr::VK_GOTTPOFF:
    case MCSymbolRefExpr::VK_INDNTPOFF:
    case MCSymbolRefExpr::VK_NTPOFF:
    case MCSymbolRefExpr::VK_GOTNTPOFF:
    case MCSymbolRefExpr::VK_TLSGD:
    case MCSymbolRefExpr::VK_TLSLD:
    case MCSymbolRefExpr::VK_TLSLDM:
    case MCSymbolRefExpr::VK_TPOFF:
    case MCSymbolRefExpr::VK_DTPOFF:
    case MCSymbolRefExpr::VK_ARM_TLSGD:
    case MCSymbolRefExpr::VK_ARM_TPOFF:
    case MCSymbolRefExpr::VK_ARM_GOTTPOFF:
      break;
    }
    MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
    MCELF::SetType(SD, ELF::STT_TLS);
    break;
  }

  case MCExpr::Unary:
    fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
    break;
  }
}

void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
  this->MCObjectStreamer::EmitInstToFragment(Inst);
  MCInstFragment &F = *cast<MCInstFragment>(getCurrentFragment());

  for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
    fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
}

void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
  MCDataFragment *DF = getOrCreateDataFragment();

  SmallVector<MCFixup, 4> Fixups;
  SmallString<256> Code;
  raw_svector_ostream VecOS(Code);
  getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
  VecOS.flush();

  for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
    fixSymbolsInTLSFixups(Fixups[i].getValue());

  // Add the fixups and data.
  for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
    Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
    DF->addFixup(Fixups[i]);
  }
  DF->getContents().append(Code.begin(), Code.end());
}

void MCELFStreamer::Finish() {
  EmitFrames(true);

  for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
                                                e = LocalCommons.end();
       i != e; ++i) {
    MCSymbolData *SD = i->SD;
    uint64_t Size = i->Size;
    unsigned ByteAlignment = i->ByteAlignment;
    const MCSymbol &Symbol = SD->getSymbol();
    const MCSection &Section = Symbol.getSection();

    MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
    new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);

    MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
    SD->setFragment(F);

    // Update the maximum alignment of the section if necessary.
    if (ByteAlignment > SectData.getAlignment())
      SectData.setAlignment(ByteAlignment);
  }

  this->MCObjectStreamer::Finish();
}

MCStreamer *llvm::createELFStreamer(MCContext &Context, MCAsmBackend &MAB,
                                    raw_ostream &OS, MCCodeEmitter *CE,
                                    bool RelaxAll, bool NoExecStack) {
  MCELFStreamer *S = new MCELFStreamer(Context, MAB, OS, CE);
  if (RelaxAll)
    S->getAssembler().setRelaxAll(true);
  if (NoExecStack)
    S->getAssembler().setNoExecStack(true);
  return S;
}