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// Copyright (c) 2006-2008 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/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__
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