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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__