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 // Copyright (c) 2012 The Chromium Authors. All rights reserved.

 // Use of this source code is governed by a BSD-style license that can be

 // found in the LICENSE file.

 // Definition of MiniDisassembler.

 #ifndef SANDBOX_SRC_SIDESTEP_MINI_DISASSEMBLER_H__

 #define SANDBOX_SRC_SIDESTEP_MINI_DISASSEMBLER_H__

 #include "sandbox/win/src/sidestep/mini_disassembler_types.h"

 namespace sidestep {

 // This small disassembler is very limited

 // in its functionality, and in fact does only the bare minimum required by the

 // preamble patching utility.  It may be useful for other purposes, however.

 //

 // The limitations include at least the following:

 //  -# No support for coprocessor opcodes, MMX, etc.

 //  -# No machine-readable identification of opcodes or decoding of

 //     assembly parameters. The name of the opcode (as a string) is given,

 //     however, to aid debugging.

 //

 // You may ask what this little disassembler actually does, then?  The answer is

 // that it does the following, which is exactly what the patching utility needs:

 //  -# Indicates if opcode is a jump (any kind) or a return (any kind)

 //     because this is important for the patching utility to determine if

 //     a function is too short or there are jumps too early in it for it

 //     to be preamble patched.

 //  -# The opcode length is always calculated, so that the patching utility

 //     can figure out where the next instruction starts, and whether it

 //     already has enough instructions to replace with the absolute jump

 //     to the patching code.

 //

 // The usage is quite simple; just create a MiniDisassembler and use its

 // Disassemble() method.

 //

 // If you would like to extend this disassembler, please refer to the

 // IA-32 Intel Architecture Software Developer's Manual Volume 2:

 // Instruction Set Reference for information about operand decoding

 // etc.

 class MiniDisassembler {

  public:

   // Creates a new instance and sets defaults.

   //

   // operand_default_32_bits: If true, the default operand size is

   // set to 32 bits, which is the default under Win32. Otherwise it is 16 bits.

   // address_default_32_bits: If true, the default address size is

   // set to 32 bits, which is the default under Win32. Otherwise it is 16 bits.

   MiniDisassembler(bool operand_default_32_bits,

                    bool address_default_32_bits);

   // Equivalent to MiniDisassembler(true, true);

   MiniDisassembler();

   // Attempts to disassemble a single instruction starting from the

   // address in memory it is pointed to.

   //

   // start: Address where disassembly should start.

   // instruction_bytes: Variable that will be incremented by

   // the length in bytes of the instruction.

   // Returns enItJump, enItReturn or enItGeneric on success.  enItUnknown

   // if unable to disassemble, enItUnused if this seems to be an unused

   // opcode. In the last two (error) cases, cbInstruction will be set

   // to 0xffffffff.

   //

   // Postcondition: This instance of the disassembler is ready to be used again,

   // with unchanged defaults from creation time.

   InstructionType Disassemble(unsigned char* start,

                               unsigned int* instruction_bytes);

  private:

   // Makes the disassembler ready for reuse.

   void Initialize();

   // Sets the flags for address and operand sizes.

   // Returns Number of prefix bytes.

   InstructionType ProcessPrefixes(unsigned char* start, unsigned int* size);

   // Sets the flag for whether we have ModR/M, and increments

   // operand_bytes_ if any are specifies by the opcode directly.

   // Returns Number of opcode bytes.

   InstructionType ProcessOpcode(unsigned char* start,

                                 unsigned int table,

                                 unsigned int* size);

   // Checks the type of the supplied operand.  Increments

   // operand_bytes_ if it directly indicates an immediate etc.

   // operand.  Asserts have_modrm_ if the operand specifies

   // a ModR/M byte.

   bool ProcessOperand(int flag_operand);

   // Increments operand_bytes_ by size specified by ModR/M and

   // by SIB if present.

   // Returns 0 in case of error, 1 if there is just a ModR/M byte,

   // 2 if there is a ModR/M byte and a SIB byte.

   bool ProcessModrm(unsigned char* start, unsigned int* size);

   // Processes the SIB byte that it is pointed to.

   // start: Pointer to the SIB byte.

   // mod: The mod field from the ModR/M byte.

   // Returns 1 to indicate success (indicates 1 SIB byte)

   bool ProcessSib(unsigned char* start, unsigned char mod, unsigned int* size);

   // The instruction type we have decoded from the opcode.

   InstructionType instruction_type_;

   // Counts the number of bytes that is occupied by operands in

   // the current instruction (note: we don't care about how large

   // operands stored in registers etc. are).

   unsigned int operand_bytes_;

   // True iff there is a ModR/M byte in this instruction.

   bool have_modrm_;

   // True iff we need to decode the ModR/M byte (sometimes it just

   // points to a register, we can tell by the addressing mode).

   bool should_decode_modrm_;

   // Current operand size is 32 bits if true, 16 bits if false.

   bool operand_is_32_bits_;

   // Default operand size is 32 bits if true, 16 bits if false.

   bool operand_default_is_32_bits_;

   // Current address size is 32 bits if true, 16 bits if false.

   bool address_is_32_bits_;

   // Default address size is 32 bits if true, 16 bits if false.

   bool address_default_is_32_bits_;

   // Huge big opcode table based on the IA-32 manual, defined

   // in Ia32OpcodeMap.cpp

   static const OpcodeTable s_ia32_opcode_map_[];

   // Somewhat smaller table to help with decoding ModR/M bytes

   // when 16-bit addressing mode is being used.  Defined in

   // Ia32ModrmMap.cpp

   static const ModrmEntry s_ia16_modrm_map_[];

   // Somewhat smaller table to help with decoding ModR/M bytes

   // when 32-bit addressing mode is being used.  Defined in

   // Ia32ModrmMap.cpp

   static const ModrmEntry s_ia32_modrm_map_[];

   // Indicators of whether we got certain prefixes that certain

   // silly Intel instructions depend on in nonstandard ways for

   // their behaviors.

   bool got_f2_prefix_, got_f3_prefix_, got_66_prefix_;

 };

 };  // namespace sidestep

 #endif  // SANDBOX_SRC_SIDESTEP_MINI_DISASSEMBLER_H__