path: root/lib/MC/MachObjectWriter.cpp

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

#include "llvm/MC/MCMachObjectWriter.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCMachOSymbolFlags.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Object/MachOFormat.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include <vector>
using namespace llvm;
using namespace llvm::object;

void MachObjectWriter::reset() {
  Relocations.clear();
  IndirectSymBase.clear();
  StringTable.clear();
  LocalSymbolData.clear();
  ExternalSymbolData.clear();
  UndefinedSymbolData.clear();
  MCObjectWriter::reset();
}

bool MachObjectWriter::
doesSymbolRequireExternRelocation(const MCSymbolData *SD) {
  // Undefined symbols are always extern.
  if (SD->Symbol->isUndefined())
    return true;

  // References to weak definitions require external relocation entries; the
  // definition may not always be the one in the same object file.
  if (SD->getFlags() & SF_WeakDefinition)
    return true;

  // Otherwise, we can use an internal relocation.
  return false;
}

bool MachObjectWriter::
MachSymbolData::operator<(const MachSymbolData &RHS) const {
  return SymbolData->getSymbol().getName() <
    RHS.SymbolData->getSymbol().getName();
}

bool MachObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
  const MCFixupKindInfo &FKI = Asm.getBackend().getFixupKindInfo(
    (MCFixupKind) Kind);

  return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
}

uint64_t MachObjectWriter::getFragmentAddress(const MCFragment *Fragment,
                                              const MCAsmLayout &Layout) const {
  return getSectionAddress(Fragment->getParent()) +
    Layout.getFragmentOffset(Fragment);
}

uint64_t MachObjectWriter::getSymbolAddress(const MCSymbolData* SD,
                                            const MCAsmLayout &Layout) const {
  const MCSymbol &S = SD->getSymbol();

  // If this is a variable, then recursively evaluate now.
  if (S.isVariable()) {
    if (const MCConstantExpr *C =
          dyn_cast<const MCConstantExpr>(S.getVariableValue()))
      return C->getValue();


    MCValue Target;
    if (!S.getVariableValue()->EvaluateAsRelocatable(Target, Layout))
      report_fatal_error("unable to evaluate offset for variable '" +
                         S.getName() + "'");

    // Verify that any used symbols are defined.
    if (Target.getSymA() && Target.getSymA()->getSymbol().isUndefined())
      report_fatal_error("unable to evaluate offset to undefined symbol '" +
                         Target.getSymA()->getSymbol().getName() + "'");
    if (Target.getSymB() && Target.getSymB()->getSymbol().isUndefined())
      report_fatal_error("unable to evaluate offset to undefined symbol '" +
                         Target.getSymB()->getSymbol().getName() + "'");

    uint64_t Address = Target.getConstant();
    if (Target.getSymA())
      Address += getSymbolAddress(&Layout.getAssembler().getSymbolData(
                                    Target.getSymA()->getSymbol()), Layout);
    if (Target.getSymB())
      Address += getSymbolAddress(&Layout.getAssembler().getSymbolData(
                                    Target.getSymB()->getSymbol()), Layout);
    return Address;
  }

  return getSectionAddress(SD->getFragment()->getParent()) +
    Layout.getSymbolOffset(SD);
}

uint64_t MachObjectWriter::getPaddingSize(const MCSectionData *SD,
                                          const MCAsmLayout &Layout) const {
  uint64_t EndAddr = getSectionAddress(SD) + Layout.getSectionAddressSize(SD);
  unsigned Next = SD->getLayoutOrder() + 1;
  if (Next >= Layout.getSectionOrder().size())
    return 0;

  const MCSectionData &NextSD = *Layout.getSectionOrder()[Next];
  if (NextSD.getSection().isVirtualSection())
    return 0;
  return OffsetToAlignment(EndAddr, NextSD.getAlignment());
}

void MachObjectWriter::WriteHeader(unsigned NumLoadCommands,
                                   unsigned LoadCommandsSize,
                                   bool SubsectionsViaSymbols) {
  uint32_t Flags = 0;

  if (SubsectionsViaSymbols)
    Flags |= macho::HF_SubsectionsViaSymbols;

  // struct mach_header (28 bytes) or