llvm-project/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"
using namespace llvm;

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

MCObjectStreamer::MCObjectStreamer(MCContext &Context, MCAsmBackend &TAB,
                                   raw_ostream &OS, MCCodeEmitter *Emitter_,
                                   MCAssembler *_Assembler)
    : MCStreamer(Context), Assembler(_Assembler), CurSectionData(nullptr),
      EmitEHFrame(true), EmitDebugFrame(false) {}

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

void MCObjectStreamer::reset() {
  if (Assembler)
    Assembler->reset();
  CurSectionData = nullptr;
  CurInsertionPoint = MCSectionData::iterator();
  EmitEHFrame = true;
  EmitDebugFrame = false;
  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(getCurrentSectionData() && "No current section!");

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

  return nullptr;
}

MCDataFragment *MCObjectStreamer::getOrCreateDataFragment() const {
  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() && F->hasInstructions())) {
    F = new MCDataFragment();
    insert(F);
  }
  return F;
}

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

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

  // 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 = getOrCreateDataFragment();
  assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
  SD.setFragment(F);
  SD.setOffset(F->getContents().size());
}

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(const MCSection *Section,
                                     const MCExpr *Subsection) {
  assert(Section && "Cannot switch to a null section!");

  CurSectionData = &getAssembler().getOrCreateSectionData(*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 =
    CurSectionData->getSubsectionInsertionPoint(unsigned(IntSubsection));
}

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

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

  MCSectionData *SD = getCurrentSectionData();
  SD->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() && SD->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) {
  // 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.
  if (ByteAlignment > getCurrentSectionData()->getAlignment())
    getCurrentSectionData()->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) {
  unsigned ItemSize = getCurrentSection().first->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);

  getAssembler().Finish();
}