path: root/lib/MC/MCAssembler.cpp

//===- lib/MC/MCAssembler.cpp - Assembler Backend Implementation ----------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "assembler"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/Target/TargetMachOWriterInfo.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <vector>
using namespace llvm;

class MachObjectWriter;

STATISTIC(EmittedFragments, "Number of emitted assembler fragments");

static void WriteFileData(raw_ostream &OS, const MCSectionData &SD,
                          MachObjectWriter &MOW);

class MachObjectWriter {
  // See <mach-o/loader.h>.
  enum {
    Header_Magic32 = 0xFEEDFACE,
    Header_Magic64 = 0xFEEDFACF
  };
  
  static const unsigned Header32Size = 28;
  static const unsigned Header64Size = 32;
  static const unsigned SegmentLoadCommand32Size = 56;
  static const unsigned Section32Size = 68;
  static const unsigned SymtabLoadCommandSize = 24;
  static const unsigned DysymtabLoadCommandSize = 80;
  static const unsigned Nlist32Size = 12;

  enum HeaderFileType {
    HFT_Object = 0x1
  };

  enum LoadCommandType {
    LCT_Segment = 0x1,
    LCT_Symtab = 0x2,
    LCT_Dysymtab = 0xb
  };

  // See <mach-o/nlist.h>.
  enum SymbolTypeType {
    STT_Undefined = 0x00,
    STT_Absolute  = 0x02,
    STT_Section   = 0x0e
  };

  enum SymbolTypeFlags {
    // If any of these bits are set, then the entry is a stab entry number (see
    // <mach-o/stab.h>. Otherwise the other masks apply.
    STF_StabsEntryMask = 0xe0,

    STF_TypeMask       = 0x0e,
    STF_External       = 0x01,
    STF_PrivateExtern  = 0x10
  };

  /// IndirectSymbolFlags - Flags for encoding special values in the indirect
  /// symbol entry.
  enum IndirectSymbolFlags {
    ISF_Local    = 0x80000000,
    ISF_Absolute = 0x40000000
  };

  /// MachSymbolData - Helper struct for containing some precomputed information
  /// on symbols.
  struct MachSymbolData {
    MCSymbolData *SymbolData;
    uint64_t StringIndex;
    uint8_t SectionIndex;

    // Support lexicographic sorting.
    bool operator<(const MachSymbolData &RHS) const {
      const std::string &Name = SymbolData->getSymbol().getName();
      return Name < RHS.SymbolData->getSymbol().getName();
    }
  };

  raw_ostream &OS;
  bool IsLSB;

public:
  MachObjectWriter(raw_ostream &_OS, bool _IsLSB = true) 
    : OS(_OS), IsLSB(_IsLSB) {
  }

  /// @name Helper Methods
  /// @{

  void Write8(uint8_t Value) {
    OS << char(Value);
  }

  void Write16(uint16_t Value) {
    if (IsLSB) {
      Write8(uint8_t(Value >> 0));
      Write8(uint8_t(Value >> 8));
    } else {
      Write8(uint8_t(Value >> 8));
      Write8(uint8_t(Value >> 0));
    }
  }

  void Write32(uint32_t Value) {
    if (IsLSB) {
      Write16(uint16_t(Value >> 0));
      Write16(uint16_t(Value >> 16));
    } else {
      Write16(uint16_t(Value >> 16));
      Write16(uint16_t(Value >> 0));
    }
  }

  void Write64(uint64_t Value) {
    if (IsLSB) {
      Write32(uint32_t(Value >> 0));
      Write32(uint32_t(Value >> 32));
    } else {
      Write32(uint32_t(Value >> 32));
      Write32(uint32_t(Value >> 0));
    }
  }

  void WriteZeros(unsigned N) {
    const char Zeros[16] = { 0 };
    
    for (unsigned i = 0, e = N / 16; i != e; ++i)
      OS << StringRef(Zeros, 16);
    
    OS << StringRef(Zeros, N % 16);
  }

  void WriteString(const StringRef &Str, unsigned ZeroFillSize = 0) {
    OS << Str;
    if (ZeroFillSize)
      WriteZeros(ZeroFillSize - Str.size());
  }

  /// @}
  
  void WriteHeader32(unsigned NumLoadCommands, unsigned LoadCommandsSize) {
    // struct mach_header (28 bytes)

    uint64_t Start = OS.tell();
    (void) Start;

    Write32(Header_Magic32);

    // FIXME: Support cputype.
    Write32(TargetMachOWriterInfo::HDR_CPU_TYPE_I386);

    // FIXME: Support cpusubtype.
    Write32(TargetMachOWriterInfo::HDR_CPU_SUBTYPE_I386_ALL);

    Write32(HFT_Object);

    // Object files have a single load command, the segment.
    Write32(NumLoadCommands);
    Write32(LoadCommandsSize);
    Write32(0); // Flags

    assert(OS.tell() - Start