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/OwningPtr.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCMachOSymbolFlags.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Object/MachOFormat.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Target/TargetAsmBackend.h"

// FIXME: Gross.
#include "../Target/X86/X86FixupKinds.h"

#include <vector>
using namespace llvm;
using namespace llvm::object;

// FIXME: this has been copied from (or to) X86AsmBackend.cpp
static unsigned getFixupKindLog2Size(unsigned Kind) {
  switch (Kind) {
  // FIXME: Until ARM has it's own relocation stuff spun off, it comes
  // through here and we don't want it to puke all over. Any reasonable
  // values will only come when ARM relocation support gets added, at which
  // point this will be X86 only again and the llvm_unreachable can be
  // re-enabled.
  default: return 0;// llvm_unreachable("invalid fixup kind!");
  case FK_PCRel_1:
  case FK_Data_1: return 0;
  case FK_PCRel_2:
  case FK_Data_2: return 1;
  case FK_PCRel_4:
  case X86::reloc_riprel_4byte:
  case X86::reloc_riprel_4byte_movq_load:
  case X86::reloc_signed_4byte:
  case FK_Data_4: return 2;
  case FK_Data_8: return 3;
  }
}

static bool doesSymbolRequireExternRelocation(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;
}

static bool isScatteredFixupFullyResolved(const MCAssembler &Asm,
                                          const MCValue Target,
                                          const MCSymbolData *BaseSymbol) {
  // The effective fixup address is
  //     addr(atom(A)) + offset(A)
  //   - addr(atom(B)) - offset(B)
  //   - addr(BaseSymbol) + <fixup offset from base symbol>
  // and the offsets are not relocatable, so the fixup is fully resolved when
  //  addr(atom(A)) - addr(atom(B)) - addr(BaseSymbol) == 0.
  //
  // Note that "false" is almost always conservatively correct (it means we emit
  // a relocation which is unnecessary), except when it would force us to emit a
  // relocation which the target cannot encode.

  const MCSymbolData *A_Base = 0, *B_Base = 0;