src/arm/constants-arm.h

// Copyright 2010 the V8 project authors. All rights reserved.
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#ifndef V8_ARM_CONSTANTS_ARM_H_
#define V8_ARM_CONSTANTS_ARM_H_

// The simulator emulates the EABI so we define the USE_ARM_EABI macro if we
// are not running on real ARM hardware.  One reason for this is that the
// old ABI uses fp registers in the calling convention and the simulator does
// not simulate fp registers or coroutine instructions.
#if defined(__ARM_EABI__) || !defined(__arm__)
# define USE_ARM_EABI 1
#endif

// This means that interwork-compatible jump instructions are generated.  We
// want to generate them on the simulator too so it makes snapshots that can
// be used on real hardware.
#if defined(__THUMB_INTERWORK__) || !defined(__arm__)
# define USE_THUMB_INTERWORK 1
#endif

#if defined(__ARM_ARCH_7A__) || \
    defined(__ARM_ARCH_7R__) || \
    defined(__ARM_ARCH_7__)
# define CAN_USE_ARMV7_INSTRUCTIONS 1
#endif

#if defined(__ARM_ARCH_6__) ||   \
    defined(__ARM_ARCH_6J__) ||  \
    defined(__ARM_ARCH_6K__) ||  \
    defined(__ARM_ARCH_6Z__) ||  \
    defined(__ARM_ARCH_6ZK__) || \
    defined(__ARM_ARCH_6T2__) || \
    defined(CAN_USE_ARMV7_INSTRUCTIONS)
# define CAN_USE_ARMV6_INSTRUCTIONS 1
#endif

#if defined(__ARM_ARCH_5T__)            || \
    defined(__ARM_ARCH_5TE__)           || \
    defined(CAN_USE_ARMV6_INSTRUCTIONS)
# define CAN_USE_ARMV5_INSTRUCTIONS 1
# define CAN_USE_THUMB_INSTRUCTIONS 1
#endif

// Simulator should support ARM5 instructions and unaligned access by default.
#if !defined(__arm__)
# define CAN_USE_ARMV5_INSTRUCTIONS 1
# define CAN_USE_THUMB_INSTRUCTIONS 1

# ifndef CAN_USE_UNALIGNED_ACCESSES
#  define CAN_USE_UNALIGNED_ACCESSES 1
# endif

#endif

#if CAN_USE_UNALIGNED_ACCESSES
#define V8_TARGET_CAN_READ_UNALIGNED 1
#endif

// Using blx may yield better code, so use it when required or when available
#if defined(USE_THUMB_INTERWORK) || defined(CAN_USE_ARMV5_INSTRUCTIONS)
#define USE_BLX 1
#endif

namespace assembler {
namespace arm {

// Number of registers in normal ARM mode.
static const int kNumRegisters = 16;

// VFP support.
static const int kNumVFPSingleRegisters = 32;
static const int kNumVFPDoubleRegisters = 16;
static const int kNumVFPRegisters =
    kNumVFPSingleRegisters + kNumVFPDoubleRegisters;

// PC is register 15.
static const int kPCRegister = 15;
static const int kNoRegister = -1;

// Defines constants and accessor classes to assemble, disassemble and
// simulate ARM instructions.
//
// Section references in the code refer to the "ARM Architecture Reference
// Manual" from July 2005 (available at http://www.arm.com/miscPDFs/14128.pdf)
//
// Constants for specific fields are defined in their respective named enums.
// General constants are in an anonymous enum in class Instr.

typedef unsigned char byte;

// Values for the condition field as defined in section A3.2
enum Condition {
  no_condition = -1,
  EQ =  0,  // equal
  NE =  1,  // not equal
  CS =  2,  // carry set/unsigned higher or same
  CC =  3,  // carry clear/unsigned lower
  MI =  4,  // minus/negative
  PL =  5,  // plus/positive or zero
  VS =  6,  // overflow
  VC =  7,  // no overflow
  HI =  8,  // unsigned higher
  LS =  9,  // unsigned lower or same
  GE = 10,  // signed greater than or equal
  LT = 11,  // signed less than
  GT = 12,  // signed greater than
  LE = 13,  // signed less than or equal
  AL = 14,  // always (unconditional)
  special_condition = 15,  // special condition (refer to section A3.2.1)
  max_condition = 16
};


// Opcodes for Data-processing instructions (instructions with a type 0 and 1)
// as defined in section A3.4
enum Opcode {
  no_operand = -1,
  AND =  0,  // Logical AND
  EOR =  1,  // Logical Exclusive OR
  SUB =  2,  // Subtract
  RSB =  3,  // Reverse Subtract
  ADD =  4,  // Add
  ADC =  5,  // Add with Carry
  SBC =  6,  // Subtract with Carry
  RSC =  7,  // Reverse Subtract with Carry
  TST =  8,  // Test
  TEQ =  9,  // Test Equivalence
  CMP = 10,  // Compare
  CMN = 11,  // Compare Negated
  ORR = 12,  // Logical (inclusive) OR
  MOV = 13,  // Move
  BIC = 14,  // Bit Clear
  MVN = 15,  // Move Not
  max_operand = 16
};


// The bits for bit 7-4 for some type 0 miscellaneous instructions.
enum MiscInstructionsBits74 {
  // With bits 22-21 01.
  BX   =  1,
  BXJ  =  2,
  BLX  =  3,
  BKPT =  7,

  // With bits 22-21 11.
  CLZ  =  1
};


// Shifter types for Data-processing operands as defined in section A5.1.2.
enum Shift {
  no_shift = -1,
  LSL = 0,  // Logical shift left
  LSR = 1,  // Logical shift right
  ASR = 2,  // Arithmetic shift right
  ROR = 3,  // Rotate right
  max_shift = 4
};


// Special Software Interrupt codes when used in the presence of the ARM
// simulator.
enum SoftwareInterruptCodes {
  // transition to C code
  call_rt_redirected = 0x10,
  // break point
  break_point = 0x20
};


// Type of VFP register. Determines register encoding.
enum VFPRegPrecision {
  kSinglePrecision = 0,
  kDoublePrecision = 1
};


typedef int32_t instr_t;


// The class Instr enables access to individual fields defined in the ARM
// architecture instruction set encoding as described in figure A3-1.
//
// Example: Test whether the instruction at ptr does set the condition code
// bits.
//
// bool InstructionSetsConditionCodes(byte* ptr) {
//   Instr* instr = Instr::At(ptr);
//   int type = instr->TypeField();
//   return ((type == 0) || (type == 1)) && instr->HasS();
// }
//
class Instr {
 public:
  enum {
    kInstrSize = 4,
    kInstrSizeLog2 = 2,
    kPCReadOffset = 8
  };

  // Get the raw instruction bits.
  inline instr_t InstructionBits() const {
    return *reinterpret_cast<const instr_t*>(this);
  }

  // Set the raw instruction bits to value.
  inline void SetInstructionBits(instr_t value) {
    *reinterpret_cast<instr_t*>(this) = value;
  }

  // Read one particular bit out of the instruction bits.
  inline int Bit(int nr) const {
    return (InstructionBits() >> nr) & 1;
  }

  // Read a bit field out of the instruction bits.
  inline int Bits(int hi, int lo) const {
    return (InstructionBits() >> lo) & ((2 << (hi - lo)) - 1);
  }


  // Accessors for the different named fields used in the ARM encoding.
  // The naming of these accessor corresponds to figure A3-1.
  // Generally applicable fields
  inline Condition ConditionField() const {
    return static_cast<Condition>(Bits(31, 28));
  }
  inline int TypeField() const { return Bits(27, 25); }

  inline int RnField() const { return Bits(19, 16); }
  inline int RdField() const { return Bits(15, 12); }

  inline int CoprocessorField() const { return Bits(11, 8); }
  // Support for VFP.
  // Vn(19-16) | Vd(15-12) |  Vm(3-0)
  inline int VnField() const { return Bits(19, 16); }
  inline int VmField() const { return Bits(3, 0); }
  inline int VdField() const { return Bits(15, 12); }
  inline int NField() const { return Bit(7); }
  inline int MField() const { return Bit(5); }
  inline int DField() const { return Bit(22); }
  inline int RtField() const { return Bits(15, 12); }
  inline int PField() const { return Bit(24); }
  inline int UField() const { return Bit(23); }
  inline int Opc1Field() const { return (Bit(23) << 2) | Bits(21, 20); }
  inline int Opc2Field() const { return Bits(19, 16); }
  inline int Opc3Field() const { return Bits(7, 6); }
  inline int SzField() const { return Bit(8); }
  inline int VLField() const { return Bit(20); }
  inline int VCField() const { return Bit(8); }
  inline int VAField() const { return Bits(23, 21); }
  inline int VBField() const { return Bits(6, 5); }
  inline int VFPNRegCode(VFPRegPrecision pre) {
    return VFPGlueRegCode(pre, 16, 7);
  }
  inline int VFPMRegCode(VFPRegPrecision pre) {
    return VFPGlueRegCode(pre, 0, 5);
  }
  inline int VFPDRegCode(VFPRegPrecision pre) {
    return VFPGlueRegCode(pre, 12, 22);
  }

  // Fields used in Data processing instructions
  inline Opcode OpcodeField() const {
    return static_cast<Opcode>(Bits(24, 21));
  }
  inline int SField() const { return Bit(20); }
    // with register
  inline int RmField() const { return Bits(3, 0); }
  inline Shift ShiftField() const { return static_cast<Shift>(Bits(6, 5)); }
  inline int RegShiftField() const { return Bit(4); }
  inline int RsField() const { return Bits(11, 8); }
  inline int ShiftAmountField() const { return Bits(11, 7); }
    // with immediate
  inline int RotateField() const { return Bits(11, 8); }
  inline int Immed8Field() const { return Bits(7, 0); }
  inline int Immed4Field() const { return Bits(19, 16); }
  inline int ImmedMovwMovtField() const {
      return Immed4Field() << 12 | Offset12Field(); }

  // Fields used in Load/Store instructions
  inline int PUField() const { return Bits(24, 23); }
  inline int  BField() const { return Bit(22); }
  inline int  WField() const { return Bit(21); }
  inline int  LField() const { return Bit(20); }
    // with register uses same fields as Data processing instructions above
    // with immediate
  inline int Offset12Field() const { return Bits(11, 0); }
    // multiple
  inline int RlistField() const { return Bits(15, 0); }
    // extra loads and stores
  inline int SignField() const { return Bit(6); }
  inline int HField() const { return Bit(5); }
  inline int ImmedHField() const { return Bits(11, 8); }
  inline int ImmedLField() const { return Bits(3, 0); }

  // Fields used in Branch instructions
  inline int LinkField() const { return Bit(24); }
  inline int SImmed24Field() const { return ((InstructionBits() << 8) >> 8); }

  // Fields used in Software interrupt instructions
  inline SoftwareInterruptCodes SwiField() const {
    return static_cast<SoftwareInterruptCodes>(Bits(23, 0));
  }

  // Test for special encodings of type 0 instructions (extra loads and stores,
  // as well as multiplications).
  inline bool IsSpecialType0() const { return (Bit(7) == 1) && (Bit(4) == 1); }

  // Test for miscellaneous instructions encodings of type 0 instructions.
  inline bool IsMiscType0() const { return (Bit(24) == 1)
                                           && (Bit(23) == 0)
                                           && (Bit(20) == 0)
                                           && ((Bit(7) == 0)); }

  // Special accessors that test for existence of a value.
  inline bool HasS()    const { return SField() == 1; }
  inline bool HasB()    const { return BField() == 1; }
  inline bool HasW()    const { return WField() == 1; }
  inline bool HasL()    const { return LField() == 1; }
  inline bool HasU()    const { return UField() == 1; }
  inline bool HasSign() const { return SignField() == 1; }
  inline bool HasH()    const { return HField() == 1; }
  inline bool HasLink() const { return LinkField() == 1; }

  // Decoding the double immediate in the vmov instruction.
  double DoubleImmedVmov() const;

  // Instructions are read of out a code stream. The only way to get a
  // reference to an instruction is to convert a pointer. There is no way
  // to allocate or create instances of class Instr.
  // Use the At(pc) function to create references to Instr.
  static Instr* At(byte* pc) { return reinterpret_cast<Instr*>(pc); }

 private:
  // Join split register codes, depending on single or double precision.
  // four_bit is the position of the least-significant bit of the four
  // bit specifier. one_bit is the position of the additional single bit
  // specifier.
  inline int VFPGlueRegCode(VFPRegPrecision pre, int four_bit, int one_bit) {
    if (pre == kSinglePrecision) {
      return (Bits(four_bit + 3, four_bit) << 1) | Bit(one_bit);
    }
    return (Bit(one_bit) << 4) | Bits(four_bit + 3, four_bit);
  }

  // We need to prevent the creation of instances of class Instr.
  DISALLOW_IMPLICIT_CONSTRUCTORS(Instr);
};


// Helper functions for converting between register numbers and names.
class Registers {
 public:
  // Return the name of the register.
  static const char* Name(int reg);

  // Lookup the register number for the name provided.
  static int Number(const char* name);

  struct RegisterAlias {
    int reg;
    const char* name;
  };

 private:
  static const char* names_[kNumRegisters];
  static const RegisterAlias aliases_[];
};

// Helper functions for converting between VFP register numbers and names.
class VFPRegisters {
 public:
  // Return the name of the register.
  static const char* Name(int reg, bool is_double);

  // Lookup the register number for the name provided.
  // Set flag pointed by is_double to true if register
  // is double-precision.
  static int Number(const char* name, bool* is_double);

 private:
  static const char* names_[kNumVFPRegisters];
};


} }  // namespace assembler::arm

#endif  // V8_ARM_CONSTANTS_ARM_H_