MCMachOStreamer.cpp   [plain text]

//===- lib/MC/MCMachOStreamer.cpp - Mach-O Object Output ------------===//
//                     The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.

#include "llvm/MC/MCStreamer.h"

#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCMachOSymbolFlags.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetAsmBackend.h"

using namespace llvm;

namespace {

class MCMachOStreamer : public MCStreamer {

  MCAssembler Assembler;
  MCSectionData *CurSectionData;

  /// Track the current atom for each section.
  DenseMap<const MCSectionData*, MCSymbolData*> CurrentAtomMap;

  MCFragment *getCurrentFragment() const {
    assert(CurSectionData && "No current section!");

    if (!CurSectionData->empty())
      return &CurSectionData->getFragmentList().back();

    return 0;

  /// Get a data fragment to write into, creating a new one if the current
  /// fragment is not a data fragment.
  MCDataFragment *getOrCreateDataFragment() const {
    MCDataFragment *F = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
    if (!F)
      F = createDataFragment();
    return F;

  /// Create a new data fragment in the current section.
  MCDataFragment *createDataFragment() const {
    MCDataFragment *DF = new MCDataFragment(CurSectionData);
    return DF;

  MCMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
                  raw_ostream &_OS, MCCodeEmitter *_Emitter)
    : MCStreamer(Context), Assembler(Context, TAB, *_Emitter, _OS),
      CurSectionData(0) {}
  ~MCMachOStreamer() {}

  MCAssembler &getAssembler() { return Assembler; }

  const MCExpr *AddValueSymbols(const MCExpr *Value) {
    switch (Value->getKind()) {
    case MCExpr::Target: assert(0 && "Can't handle target exprs yet!");
    case MCExpr::Constant:

    case MCExpr::Binary: {
      const MCBinaryExpr *BE = cast<MCBinaryExpr>(Value);

    case MCExpr::SymbolRef:

    case MCExpr::Unary:

    return Value;

  /// @name MCStreamer Interface
  /// @{

  virtual void SwitchSection(const MCSection *Section);
  virtual void EmitLabel(MCSymbol *Symbol);
  virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
  virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
  virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
  virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue);
  virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                                unsigned ByteAlignment);
  virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
    assert(0 && "macho doesn't support this directive");
  virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
    assert(0 && "macho doesn't support this directive");
  virtual void EmitCOFFSymbolType(int Type) {
    assert(0 && "macho doesn't support this directive");
  virtual void EndCOFFSymbolDef() {
    assert(0 && "macho doesn't support this directive");
  virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
    assert(0 && "macho doesn't support this directive");
  virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
    assert(0 && "macho doesn't support this directive");
  virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
                            unsigned Size = 0, unsigned ByteAlignment = 0);
  virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
                              uint64_t Size, unsigned ByteAlignment = 0);
  virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
  virtual void EmitValue(const MCExpr *Value, unsigned Size,unsigned AddrSpace);
  virtual void EmitGPRel32Value(const MCExpr *Value) {
    assert(0 && "macho doesn't support this directive");
  virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
                                    unsigned ValueSize = 1,
                                    unsigned MaxBytesToEmit = 0);
  virtual void EmitCodeAlignment(unsigned ByteAlignment,
                                 unsigned MaxBytesToEmit = 0);
  virtual void EmitValueToOffset(const MCExpr *Offset,
                                 unsigned char Value = 0);
  virtual void EmitFileDirective(StringRef Filename) {
    report_fatal_error("unsupported directive: '.file'");
  virtual void EmitDwarfFileDirective(unsigned FileNo, StringRef Filename) {
    report_fatal_error("unsupported directive: '.file'");
  virtual void EmitInstruction(const MCInst &Inst);
  virtual void Finish();

  /// @}

} // end anonymous namespace.

void MCMachOStreamer::SwitchSection(const MCSection *Section) {
  assert(Section && "Cannot switch to a null section!");
  // If already in this section, then this is a noop.
  if (Section == CurSection) return;

  CurSection = Section;
  CurSectionData = &Assembler.getOrCreateSectionData(*Section);

void MCMachOStreamer::EmitLabel(MCSymbol *Symbol) {
  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
  assert(!Symbol->isVariable() && "Cannot emit a variable symbol!");
  assert(CurSection && "Cannot emit before setting section!");

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

  // Update the current atom map, if necessary.
  bool MustCreateFragment = false;
  if (Assembler.isSymbolLinkerVisible(&SD)) {
    CurrentAtomMap[CurSectionData] = &SD;

    // We have to create a new fragment, fragments cannot span atoms.
    MustCreateFragment = true;

  // FIXME: This is wasteful, we don't necessarily need to create a data
  // fragment. Instead, we should mark the symbol as pointing into the data
  // fragment if it exists, otherwise we should just queue the label and set its
  // fragment pointer when we emit the next fragment.
  MCDataFragment *F =
    MustCreateFragment ? createDataFragment() : getOrCreateDataFragment();
  assert(!SD.getFragment() && "Unexpected fragment on symbol data!");

  // This causes the reference type flag to be cleared. Darwin 'as' was "trying"
  // to clear the weak reference and weak definition bits too, but the
  // implementation was buggy. For now we just try to match 'as', for
  // diffability.
  // FIXME: Cleanup this code, these bits should be emitted based on semantic
  // properties, not on the order of definition, etc.
  SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeMask);

void MCMachOStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
  switch (Flag) {
  case MCAF_SubsectionsViaSymbols:

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

void MCMachOStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
  // FIXME: Lift context changes into super class.

void MCMachOStreamer::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 = CurSectionData;

  // 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 = Assembler.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_Invalid:
  case MCSA_ELF_TypeFunction:
  case MCSA_ELF_TypeIndFunction:
  case MCSA_ELF_TypeObject:
  case MCSA_ELF_TypeTLS:
  case MCSA_ELF_TypeCommon:
  case MCSA_ELF_TypeNoType:
  case MCSA_IndirectSymbol:
  case MCSA_Hidden:
  case MCSA_Internal:
  case MCSA_Protected:
  case MCSA_Weak:
  case MCSA_Local:
    assert(0 && "Invalid symbol attribute for Mach-O!");

  case MCSA_Global:
    // This effectively clears the undefined lazy bit, in Darwin 'as', although
    // it isn't very consistent because it implements this as part of symbol
    // lookup.
    // FIXME: Cleanup this code, these bits should be emitted based on semantic
    // properties, not on the order of definition, etc.
    SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeUndefinedLazy);

  case MCSA_LazyReference:
    // FIXME: This requires -dynamic.
    SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
    if (Symbol->isUndefined())
      SD.setFlags(SD.getFlags() | SF_ReferenceTypeUndefinedLazy);

    // Since .reference sets the no dead strip bit, it is equivalent to
    // .no_dead_strip in practice.
  case MCSA_Reference:
  case MCSA_NoDeadStrip:
    SD.setFlags(SD.getFlags() | SF_NoDeadStrip);

  case MCSA_PrivateExtern:

  case MCSA_WeakReference:
    // FIXME: This requires -dynamic.
    if (Symbol->isUndefined())
      SD.setFlags(SD.getFlags() | SF_WeakReference);

  case MCSA_WeakDefinition:
    // FIXME: 'as' enforces that this is defined and global. The manual claims
    // it has to be in a coalesced section, but this isn't enforced.
    SD.setFlags(SD.getFlags() | SF_WeakDefinition);

void MCMachOStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
  // Encode the 'desc' value into the lowest implementation defined bits.
  assert(DescValue == (DescValue & SF_DescFlagsMask) && 
         "Invalid .desc value!");

void MCMachOStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                                       unsigned ByteAlignment) {
  // FIXME: Darwin 'as' does appear to allow redef of a .comm by itself.
  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");

  MCSymbolData &SD = Assembler.getOrCreateSymbolData(*Symbol);
  SD.setCommon(Size, ByteAlignment);

void MCMachOStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
                                   unsigned Size, unsigned ByteAlignment) {
  MCSectionData &SectData = Assembler.getOrCreateSectionData(*Section);

  // The symbol may not be present, which only creates the section.
  if (!Symbol)

  // FIXME: Assert that this section has the zerofill type.

  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");

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

  // Emit an align fragment if necessary.
  if (ByteAlignment != 1)
    new MCAlignFragment(ByteAlignment, 0, 0, ByteAlignment, &SectData);

  MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
  if (Assembler.isSymbolLinkerVisible(&SD))


  // Update the maximum alignment on the zero fill section if necessary.
  if (ByteAlignment > SectData.getAlignment())

// This should always be called with the thread local bss section.
void MCMachOStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
                                     uint64_t Size, unsigned ByteAlignment) {
  EmitZerofill(Section, Symbol, Size, ByteAlignment);

void MCMachOStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
  getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());

void MCMachOStreamer::EmitValue(const MCExpr *Value, unsigned Size,
                                unsigned AddrSpace) {
  MCDataFragment *DF = getOrCreateDataFragment();

  // Avoid fixups when possible.
  int64_t AbsValue;
  if (AddValueSymbols(Value)->EvaluateAsAbsolute(AbsValue)) {
    // FIXME: Endianness assumption.
    for (unsigned i = 0; i != Size; ++i)
      DF->getContents().push_back(uint8_t(AbsValue >> (i * 8)));
  } else {
    DF->addFixup(MCAsmFixup(DF->getContents().size(), *AddValueSymbols(Value),
    DF->getContents().resize(DF->getContents().size() + Size, 0);

void MCMachOStreamer::EmitValueToAlignment(unsigned ByteAlignment,
                                           int64_t Value, unsigned ValueSize,
                                           unsigned MaxBytesToEmit) {
  if (MaxBytesToEmit == 0)
    MaxBytesToEmit = ByteAlignment;
  MCFragment *F = new MCAlignFragment(ByteAlignment, Value, ValueSize,
                                      MaxBytesToEmit, CurSectionData);

  // Update the maximum alignment on the current section if necessary.
  if (ByteAlignment > CurSectionData->getAlignment())

void MCMachOStreamer::EmitCodeAlignment(unsigned ByteAlignment,
                                        unsigned MaxBytesToEmit) {
  if (MaxBytesToEmit == 0)
    MaxBytesToEmit = ByteAlignment;
  MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,

  // Update the maximum alignment on the current section if necessary.
  if (ByteAlignment > CurSectionData->getAlignment())

void MCMachOStreamer::EmitValueToOffset(const MCExpr *Offset,
                                        unsigned char Value) {
  MCFragment *F = new MCOrgFragment(*Offset, Value, CurSectionData);

void MCMachOStreamer::EmitInstruction(const MCInst &Inst) {
  // Scan for values.
  for (unsigned i = Inst.getNumOperands(); i--; )
    if (Inst.getOperand(i).isExpr())


  // FIXME-PERF: Common case is that we don't need to relax, encode directly
  // onto the data fragments buffers.

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

  // FIXME: Eliminate this copy.
  SmallVector<MCAsmFixup, 4> AsmFixups;
  for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
    MCFixup &F = Fixups[i];
    AsmFixups.push_back(MCAsmFixup(F.getOffset(), *F.getValue(),

  // See if we might need to relax this instruction, if so it needs its own
  // fragment.
  // FIXME-PERF: Support target hook to do a fast path that avoids the encoder,
  // when we can immediately tell that we will get something which might need
  // relaxation (and compute its size).
  // FIXME-PERF: We should also be smart about immediately relaxing instructions
  // which we can already show will never possibly fit (we can also do a very
  // good job of this before we do the first relaxation pass, because we have
  // total knowledge about undefined symbols at that point). Even now, though,
  // we can do a decent job, especially on Darwin where scattering means that we
  // are going to often know that we can never fully resolve a fixup.
  if (Assembler.getBackend().MayNeedRelaxation(Inst, AsmFixups)) {
    MCInstFragment *IF = new MCInstFragment(Inst, CurSectionData);

    // Add the fixups and data.
    // FIXME: Revisit this design decision when relaxation is done, we may be
    // able to get away with not storing any extra data in the MCInst.
    IF->getCode() = Code;
    IF->getFixups() = AsmFixups;


  // Add the fixups and data.
  MCDataFragment *DF = getOrCreateDataFragment();
  for (unsigned i = 0, e = AsmFixups.size(); i != e; ++i) {
    AsmFixups[i].Offset += DF->getContents().size();
  DF->getContents().append(Code.begin(), Code.end());

void MCMachOStreamer::Finish() {

MCStreamer *llvm::createMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
                                      raw_ostream &OS, MCCodeEmitter *CE,
                                      bool RelaxAll) {
  MCMachOStreamer *S = new MCMachOStreamer(Context, TAB, OS, CE);
  if (RelaxAll)
  return S;