llvm/lib/MC/MCObjectStreamer.cpp

//===- lib/MC/MCObjectStreamer.cpp - Object File MCStreamer Interface -----===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "llvm/MC/MCObjectStreamer.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCDwarf.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/TargetRegistry.h"
using namespace llvm;

MCObjectStreamer::MCObjectStreamer(MCContext &Context, MCAsmBackend &TAB,
                                   raw_pwrite_stream &OS,
                                   MCCodeEmitter *Emitter_)
    : MCStreamer(Context),
      Assembler(new MCAssembler(Context, TAB, *Emitter_,
                                *TAB.createObjectWriter(OS), OS)),
      EmitEHFrame(true), EmitDebugFrame(false) {}

MCObjectStreamer::~MCObjectStreamer() {
  delete &Assembler->getBackend();
  delete &Assembler->getEmitter();
  delete &Assembler->getWriter();
  delete Assembler;
}

void MCObjectStreamer::flushPendingLabels(MCFragment *F, uint64_t FOffset) {
  if (PendingLabels.size()) {
    if (!F) {
      F = new MCDataFragment();
      MCSection *CurSection = getCurrentSectionOnly();
      CurSection->getFragmentList().insert(CurInsertionPoint, F);
      F->setParent(CurSection);
    }
    for (MCSymbol *Sym : PendingLabels) {
      Sym->setFragment(F);
      Sym->setOffset(FOffset);
    }
    PendingLabels.clear();
  }
}

void MCObjectStreamer::emitAbsoluteSymbolDiff(const MCSymbol *Hi,
                                              const MCSymbol *Lo,
                                              unsigned Size) {
  // If not assigned to the same (valid) fragment, fallback.
  if (!Hi->getFragment() || Hi->getFragment() != Lo->getFragment()) {
    MCStreamer::emitAbsoluteSymbolDiff(Hi, Lo, Size);
    return;
  }

  assert(Hi->getOffset() >= Lo->getOffset() &&
         "Expected Hi to be greater than Lo");
  EmitIntValue(Hi->getOffset() - Lo->getOffset(), Size);
}

void MCObjectStreamer::reset() {
  if (Assembler)
    Assembler->reset();
  CurInsertionPoint = MCSection::iterator();
  EmitEHFrame = true;
  EmitDebugFrame = false;
  PendingLabels.clear();
  MCStreamer::reset();
}

void MCObjectStreamer::EmitFrames(MCAsmBackend *MAB) {
  if (!getNumFrameInfos())
    return;

  if (EmitEHFrame)
    MCDwarfFrameEmitter::Emit(*this, MAB, true);

  if (EmitDebugFrame)
    MCDwarfFrameEmitter::Emit(*this, MAB, false);
}

MCFragment *MCObjectStreamer::getCurrentFragment() const {
  assert(getCurrentSectionOnly() && "No current section!");

  if (CurInsertionPoint != getCurrentSectionOnly()->getFragmentList().begin())
    return std::prev(CurInsertionPoint);

  return nullptr;
}

MCDataFragment *MCObjectStreamer::getOrCreateDataFragment() {
  MCDataFragment *F = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
  // When bundling is enabled, we don't want to add data to a fragment that
  // already has instructions (see MCELFStreamer::EmitInstToData for details)
  if (!F || (Assembler->isBundlingEnabled() && !Assembler->getRelaxAll() &&
             F->hasInstructions())) {
    F = new MCDataFragment();
    insert(F);
  }
  return F;
}

void MCObjectStreamer::visitUsedSymbol(const MCSymbol &Sym) {
  Assembler->registerSymbol(Sym);
}

void MCObjectStreamer::EmitCFISections(bool EH, bool Debug) {
  MCStreamer::EmitCFISections(EH, Debug);
  EmitEHFrame = EH;
  EmitDebugFrame = Debug;
}

void MCObjectStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
                                     const SMLoc &Loc) {
  MCStreamer::EmitValueImpl(Value, Size, Loc);
  MCDataFragment *DF = getOrCreateDataFragment();

  MCLineEntry::Make(this, getCurrentSection().first);

  // Avoid fixups when possible.
  int64_t AbsValue;
  if (Value->evaluateAsAbsolute(AbsValue, getAssembler())) {
    EmitIntValue(AbsValue, Size);
    return;
  }
  DF->getFixups().push_back(
      MCFixup::create(DF->getContents().size(), Value,
                      MCFixup::getKindForSize(Size, false), Loc));
  DF->getContents().resize(DF->getContents().size() + Size, 0);
}

void MCObjectStreamer::EmitCFIStartProcImpl(MCDwarfFrameInfo &Frame) {
  // We need to create a local symbol to avoid relocations.
  Frame.Begin = getContext().createTempSymbol();
  EmitLabel(Frame.Begin);
}

void MCObjectStreamer::EmitCFIEndProcImpl(MCDwarfFrameInfo &Frame) {
  Frame.End = getContext().createTempSymbol();
  EmitLabel(Frame.End);
}

void MCObjectStreamer::EmitLabel(MCSymbol *Symbol) {
  MCStreamer::EmitLabel(Symbol);

  getAssembler().registerSymbol(*Symbol);
  assert(!Symbol->getFragment() && "Unexpected fragment on symbol data!");

  // If there is a current fragment, mark the symbol as pointing into it.
  // Otherwise queue the label and set its fragment pointer when we emit the
  // next fragment.
  auto *F = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
  if (F && !(getAssembler().isBundlingEnabled() &&
             getAssembler().getRelaxAll())) {
    Symbol->setFragment(F);
    Symbol->setOffset(F->getContents().size());
  } else {
    PendingLabels.push_back(Symbol);
  }
}

void MCObjectStreamer::EmitULEB128Value(const MCExpr *Value) {
  int64_t IntValue;
  if (Value->evaluateAsAbsolute(IntValue, getAssembler())) {
    EmitULEB128IntValue(IntValue);
    return;
  }
  insert(new MCLEBFragment(*Value, false));
}

void MCObjectStreamer::EmitSLEB128Value(const MCExpr *Value) {
  int64_t IntValue;
  if (Value->evaluateAsAbsolute(IntValue, getAssembler())) {
    EmitSLEB128IntValue(IntValue);
    return;
  }
  insert(new MCLEBFragment(*Value, true));
}

void MCObjectStreamer::EmitWeakReference(MCSymbol *Alias,
                                         const MCSymbol *Symbol) {
  report_fatal_error("This file format doesn't support weak aliases.");
}

void MCObjectStreamer::ChangeSection(MCSection *Section,
                                     const MCExpr *Subsection) {
  changeSectionImpl(Section, Subsection);
}

bool MCObjectStreamer::changeSectionImpl(MCSection *Section,
                                         const MCExpr *Subsection) {
  assert(Section && "Cannot switch to a null section!");
  flushPendingLabels(nullptr);

  bool Created = getAssembler().registerSection(*Section);

  int64_t IntSubsection = 0;
  if (Subsection &&
      !Subsection->evaluateAsAbsolute(IntSubsection, getAssembler()))
    report_fatal_error("Cannot evaluate subsection number");
  if (IntSubsection < 0 || IntSubsection > 8192)
    report_fatal_error("Subsection number out of range");
  CurInsertionPoint =
      Section->getSubsectionInsertionPoint(unsigned(IntSubsection));
  return Created;
}

void MCObjectStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
  getAssembler().registerSymbol(*Symbol);
  MCStreamer::EmitAssignment(Symbol, Value);
}

bool MCObjectStreamer::mayHaveInstructions(MCSection &Sec) const {
  return Sec.hasInstructions();
}

void MCObjectStreamer::EmitInstruction(const MCInst &Inst,
                                       const MCSubtargetInfo &STI) {
  MCStreamer::EmitInstruction(Inst, STI);

  MCSection *Sec = getCurrentSectionOnly();
  Sec->setHasInstructions(true);

  // Now that a machine instruction has been assembled into this section, make
  // a line entry for any .loc directive that has been seen.
  MCLineEntry::Make(this, getCurrentSection().first);

  // If this instruction doesn't need relaxation, just emit it as data.
  MCAssembler &Assembler = getAssembler();
  if (!Assembler.getBackend().mayNeedRelaxation(Inst)) {
    EmitInstToData(Inst, STI);
    return;
  }

  // Otherwise, relax and emit it as data if either:
  // - The RelaxAll flag was passed
  // - Bundling is enabled and this instruction is inside a bundle-locked
  //   group. We want to emit all such instructions into the same data
  //   fragment.
  if (Assembler.getRelaxAll() ||
      (Assembler.isBundlingEnabled() && Sec->isBundleLocked())) {
    MCInst Relaxed;
    getAssembler().getBackend().relaxInstruction(Inst, Relaxed);
    while (getAssembler().getBackend().mayNeedRelaxation(Relaxed))
      getAssembler().getBackend().relaxInstruction(Relaxed, Relaxed);
    EmitInstToData(Relaxed, STI);
    return;
  }

  // Otherwise emit to a separate fragment.
  EmitInstToFragment(Inst, STI);
}

void MCObjectStreamer::EmitInstToFragment(const MCInst &Inst,
                                          const MCSubtargetInfo &STI) {
  if (getAssembler().getRelaxAll() && getAssembler().isBundlingEnabled())
    llvm_unreachable("All instructions should have already been relaxed");

  // Always create a new, separate fragment here, because its size can change
  // during relaxation.
  MCRelaxableFragment *IF = new MCRelaxableFragment(Inst, STI);
  insert(IF);

  SmallString<128> Code;
  raw_svector_ostream VecOS(Code);
  getAssembler().getEmitter().encodeInstruction(Inst, VecOS, IF->getFixups(),
                                                STI);
  VecOS.flush();
  IF->getContents().append(Code.begin(), Code.end());
}

#ifndef NDEBUG
static const char *const BundlingNotImplementedMsg =
  "Aligned bundling is not implemented for this object format";
#endif

void MCObjectStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
  llvm_unreachable(BundlingNotImplementedMsg);
}

void MCObjectStreamer::EmitBundleLock(bool AlignToEnd) {
  llvm_unreachable(BundlingNotImplementedMsg);
}

void MCObjectStreamer::EmitBundleUnlock() {
  llvm_unreachable(BundlingNotImplementedMsg);
}

void MCObjectStreamer::EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
                                             unsigned Column, unsigned Flags,
                                             unsigned Isa,
                                             unsigned Discriminator,
                                             StringRef FileName) {
  // In case we see two .loc directives in a row, make sure the
  // first one gets a line entry.
  MCLineEntry::Make(this, getCurrentSection().first);

  this->MCStreamer::EmitDwarfLocDirective(FileNo, Line, Column, Flags,
                                          Isa, Discriminator, FileName);
}

static const MCExpr *buildSymbolDiff(MCObjectStreamer &OS, const MCSymbol *A,
                                     const MCSymbol *B) {
  MCContext &Context = OS.getContext();
  MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
  const MCExpr *ARef = MCSymbolRefExpr::create(A, Variant, Context);
  const MCExpr *BRef = MCSymbolRefExpr::create(B, Variant, Context);
  const MCExpr *AddrDelta =
      MCBinaryExpr::create(MCBinaryExpr::Sub, ARef, BRef, Context);
  return AddrDelta;
}

static void emitDwarfSetLineAddr(MCObjectStreamer &OS, int64_t LineDelta,
                                 const MCSymbol *Label, int PointerSize) {
  // emit the sequence to set the address
  OS.EmitIntValue(dwarf::DW_LNS_extended_op, 1);
  OS.EmitULEB128IntValue(PointerSize + 1);
  OS.EmitIntValue(dwarf::DW_LNE_set_address, 1);
  OS.EmitSymbolValue(Label, PointerSize);

  // emit the sequence for the LineDelta (from 1) and a zero address delta.
  MCDwarfLineAddr::Emit(&OS, LineDelta, 0);
}

void MCObjectStreamer::EmitDwarfAdvanceLineAddr(int64_t LineDelta,
                                                const MCSymbol *LastLabel,
                                                const MCSymbol *Label,
                                                unsigned PointerSize) {
  if (!LastLabel) {
    emitDwarfSetLineAddr(*this, LineDelta, Label, PointerSize);
    return;
  }
  const MCExpr *AddrDelta = buildSymbolDiff(*this, Label, LastLabel);
  int64_t Res;
  if (AddrDelta->evaluateAsAbsolute(Res, getAssembler())) {
    MCDwarfLineAddr::Emit(this, LineDelta, Res);
    return;
  }
  insert(new MCDwarfLineAddrFragment(LineDelta, *AddrDelta));
}

void MCObjectStreamer::EmitDwarfAdvanceFrameAddr(const MCSymbol *LastLabel,
                                                 const MCSymbol *Label) {
  const MCExpr *AddrDelta = buildSymbolDiff(*this, Label, LastLabel);
  int64_t Res;
  if (AddrDelta->evaluateAsAbsolute(Res, getAssembler())) {
    MCDwarfFrameEmitter::EmitAdvanceLoc(*this, Res);
    return;
  }
  insert(new MCDwarfCallFrameFragment(*AddrDelta));
}

void MCObjectStreamer::EmitBytes(StringRef Data) {
  MCLineEntry::Make(this, getCurrentSection().first);
  getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
}

void MCObjectStreamer::EmitValueToAlignment(unsigned ByteAlignment,
                                            int64_t Value,
                                            unsigned ValueSize,
                                            unsigned MaxBytesToEmit) {
  if (MaxBytesToEmit == 0)
    MaxBytesToEmit = ByteAlignment;
  insert(new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit));

  // Update the maximum alignment on the current section if necessary.
  MCSection *CurSec = getCurrentSection().first;
  if (ByteAlignment > CurSec->getAlignment())
    CurSec->setAlignment(ByteAlignment);
}

void MCObjectStreamer::EmitCodeAlignment(unsigned ByteAlignment,
                                         unsigned MaxBytesToEmit) {
  EmitValueToAlignment(ByteAlignment, 0, 1, MaxBytesToEmit);
  cast<MCAlignFragment>(getCurrentFragment())->setEmitNops(true);
}

bool MCObjectStreamer::EmitValueToOffset(const MCExpr *Offset,
                                         unsigned char Value) {
  int64_t Res;
  if (Offset->evaluateAsAbsolute(Res, getAssembler())) {
    insert(new MCOrgFragment(*Offset, Value));
    return false;
  }

  MCSymbol *CurrentPos = getContext().createTempSymbol();
  EmitLabel(CurrentPos);
  MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
  const MCExpr *Ref =
    MCSymbolRefExpr::create(CurrentPos, Variant, getContext());
  const MCExpr *Delta =
    MCBinaryExpr::create(MCBinaryExpr::Sub, Offset, Ref, getContext());

  if (!Delta->evaluateAsAbsolute(Res, getAssembler()))
    return true;
  EmitFill(Res, Value);
  return false;
}

// Associate GPRel32 fixup with data and resize data area
void MCObjectStreamer::EmitGPRel32Value(const MCExpr *Value) {
  MCDataFragment *DF = getOrCreateDataFragment();

  DF->getFixups().push_back(MCFixup::create(DF->getContents().size(), 
                                            Value, FK_GPRel_4));
  DF->getContents().resize(DF->getContents().size() + 4, 0);
}

// Associate GPRel32 fixup with data and resize data area
void MCObjectStreamer::EmitGPRel64Value(const MCExpr *Value) {
  MCDataFragment *DF = getOrCreateDataFragment();

  DF->getFixups().push_back(MCFixup::create(DF->getContents().size(), 
                                            Value, FK_GPRel_4));
  DF->getContents().resize(DF->getContents().size() + 8, 0);
}

void MCObjectStreamer::EmitFill(uint64_t NumBytes, uint8_t FillValue) {
  // FIXME: A MCFillFragment would be more memory efficient but MCExpr has
  //        problems evaluating expressions across multiple fragments.
  getOrCreateDataFragment()->getContents().append(NumBytes, FillValue);
}

void MCObjectStreamer::EmitZeros(uint64_t NumBytes) {
  const MCSection *Sec = getCurrentSection().first;
  assert(Sec && "need a section");
  unsigned ItemSize = Sec->isVirtualSection() ? 0 : 1;
  insert(new MCFillFragment(0, ItemSize, NumBytes));
}

void MCObjectStreamer::FinishImpl() {
  // If we are generating dwarf for assembly source files dump out the sections.
  if (getContext().getGenDwarfForAssembly())
    MCGenDwarfInfo::Emit(this);

  // Dump out the dwarf file & directory tables and line tables.
  MCDwarfLineTable::Emit(this);

  flushPendingLabels(nullptr);
  getAssembler().Finish();
}