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modrm.c
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#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include "emulator_functions.h"
#include "modrm.h"
#include "util.h"
/*
* Mod R/M: 1 byte
* | 0 1 | 0 0 0 | 1 0 1 |
* | Mod | REG | R/M |
* ________________________________________________________________________
* | REG |EAX |ECX |EDX |EBX |ESP |EBP |ESI |EDI |
* | SREG | ES | CS | SS | DS | FS | GS |rsvd|rsvd|
* | CR |CR0 |CR1 |CR2 |CR3 |CR4 |CR5 |CR6 |CR7 |
* | (r32) |000 |001 |010 |011 |100 |101 |110 |111 |
* | Mod | R/M | Addressing | Mod R/M Value in Hex |
* | 00 | 000 | [eax] | 00 | 08 | 10 | 18 | 20 | 28 | 30 | 38 |
* | | 001 | [ecx] | 01 | 09 | 11 | 19 | 21 | 29 | 31 | 39 |
* | | 010 | [edx] | 02 | 0A | 12 | 1A | 22 | 2A | 32 | 3A |
* | | 011 | [ebx] | 03 | 0B | 13 | 1B | 23 | 2B | 33 | 3B |
* | | 100 | [-][-] | 04 | 0C | 14 | 1C | 24 | 2C | 34 | 3C |
* | | 101 | disp32 | 05 | 0D | 15 | 1D | 25 | 2D | 35 | 3D |
* | | 110 | [esi] | 06 | 0E | 16 | 1E | 26 | 2E | 36 | 3E |
* | | 111 | [edi] | 07 | 0F | 17 | 1F | 27 | 2F | 37 | 3F |
* | 01 | 000 | [eax] + disp8 | 40 | 48 | 50 | 58 | 60 | 68 | 70 | 78 |
* | | 001 | [ecx] + disp8 | 41 | 49 | 51 | 59 | 61 | 69 | 71 | 79 |
* | | 010 | [edx] + disp8 | 42 | 4A | 52 | 5A | 62 | 6A | 72 | 7A |
* | | 011 | [ebx] + disp8 | 43 | 4B | 53 | 5B | 63 | 6B | 73 | 7B |
* | | 100 | [-][-] + disp8 | 44 | 4B | 54 | 5C | 64 | 6C | 74 | 7C |
* | | 101 | [ebp] + disp8 | 45 | 4D | 55 | 5D | 65 | 6D | 75 | 7D |
* | ... |
* | | 111 | [edi] + disp8 | 47 | 4F | 57 | 5F | 67 | 6F | 79 | 7F |
* | 10 | 000 | [eax] + disp32 | 80 | 88 | 90 | 98 | A0 | A8 | B0 | B8 |
* | ... |
* | | 111 | [edi] + disp32 | 87 | 8F | 97 | 9F | A7 | AF | B7 | BF |
* | 11 | 000 | eax | C0 | C8 | D0 | D8 | E0 | E8 | F0 | F8 |
* | ... |
* | | 111 | edi | C7 | CF | D7 | DF | E7 | EF | F7 | FF |
* |______________________________________________________________________|
*
* SIB: 1 byte after ModRM byte: 2 bits: scale | 3 bits: index | 3 bits: base
*
* Examples:
* op eax, [ebx]: 03 (EAX|[EBX])
* op eax, [0x7c00]: 05 007C 0000 (EAX|disp32)
* (op eax, [label1] becomes [0x7c00]: translated by assempler)
*/
ModRM create_modrm()
{
ModRM modrm;
SIB sib = {};
modrm.sib = sib;
return modrm;
}
void parse_modrm(Emulator *emu, ModRM *modrm)
{
uint8_t code;
memset(modrm, 0, sizeof(ModRM));
code = get_code8(emu, 0);
/* Mod (2 bits) Reg (3 bits) R/M (3 bits) */
modrm->mod = ((code & 0xC0) >> 6); /* 1100 0000 */
modrm->opcode = ((code & 0x38) >> 3); /* 0011 1000 */
modrm->rm = code & 0x07; /* 0000 0111 */
emu->eip += 1;
/* Real mode workaround for [disp16] */
if (!emu->is_pe)
{
if (modrm->mod == 0 && modrm->rm == 6)
{
modrm->disp16 = get_sign_code16(emu, 0);
emu->eip += 2;
return;
}
}
/*
* SIB after ModR/M Byte
* mod/RM:
* 00/100: [-][-]
* 01/100: [-][-] + disp8
* 10/100: [-][-] + disp32
*/
if (modrm->mod != 3 && modrm->rm == 4)
{
u_int8_t sib_byte = get_code8(emu, 0);
/* SIB sib; */
modrm->sib.scale = ((sib_byte & 0xC0) >> 6);
modrm->sib.index = ((sib_byte & 0x38) >> 3);
modrm->sib.base = sib_byte & 0x07;
/* modrm->sib = &sib;*/
emu->eip += 1;
}
/*
* Stores disp32.
* mod/RM:
* 00/101: disp32
* 10/[000 - 111]: [reg] + disp32
*/
if ((modrm->mod == 0 && modrm->rm == 5) || (modrm->mod == 0 && modrm->sib.base == 5) || modrm->mod == 2)
{
modrm->disp32 = get_sign_code32(emu, 0);
emu->eip += 4;
}
else if (modrm->mod == 1)
{
/*
* Stores disp8.
* mod/RM:
* 01/[000 - 111]: [reg] + disp8
*/
modrm->disp8 = get_sign_code8(emu, 0);
emu->eip += 1;
}
}
/*
* _Mod:00________________________________________________________________________________
* | Scale | Index REG | Base REG | |
* | 00: 1 | | 000: eax | 001 | 010 | 011 | 100 | 101 (ebp) | 110 | 111 |
* | 01: 2 | 000: eax | | | |
* | 10: 4 | 001: ecx | [Base + (Index * Scale)] | [(I * S) | [Base + (I * S)] |
* | 11: 8 | 010: edx | | + disp32] | |
* |_______| 011: ebx |__________________________________|____________|___________________|
* | 100: esp |_____________[base]_______________|__[disp32]__|_____[base]________|
* | 101: ebp | | | |
* | 110: esi | [Base + (Index + Scale)] | [(I * S) | [Base + (I * S)] |
* | 111: edi | | + disp32] | |
* |___________|__________________________________|____________|___________________|
* _Mod:01________________________________________________________________________________
* | Scale | Index REG | Base REG | |
* | 00: 1 | | 000: eax | 001 | 010 | 011 | 100 | 101 | 110 | 111 |
* | 01: 2 | 000: eax | |
* | 10: 4 | 001: ecx | [Base + (Index * Scale) + disp8] |
* | 11: 8 | 010: edx | |
* |_______| 011: ebx |___________________________________________________________________|
* | 100: esp |________________________[base + disp8]_____________________________|
* | 101: ebp | |
* | 110: esi | [Base + (Index * Scale) + disp8] |
* | 111: edi | |
* |___________|___________________________________________________________________|
* _Mod:10________________________________________________________________________________
* | Scale | Index REG | Base REG | |
* | 00: 1 | | 000: eax | 001 | 010 | 011 | 100 | 101 | 110 | 111 |
* | 01: 2 | 000: eax | |
* | 10: 4 | 001: ecx | [Base + (Index * Scale) + disp32] |
* | 11: 8 | 010: edx | |
* |_______| 011: ebx |___________________________________________________________________|
* | 100: esp |________________________[base + disp32]____________________________|
* | 101: ebp | |
* | 110: esi | [Base + (Index * Scale) + disp32] |
* | 111: edi | |
* |___________|___________________________________________________________________|
*/
uint32_t calc_cib_address(Emulator *emu, ModRM *modrm)
{
uint32_t base_val = get_register32(emu, modrm->sib.base);
uint32_t scale = pow(2, modrm->sib.scale);
uint32_t index_val = get_register32(emu, modrm->sib.index);
// printf("modrm sib mod %d index: %d base %d\n", modrm->mod, modrm->sib.index, modrm->sib.base);
if (modrm->mod == 0)
{
if (modrm->sib.index == 4 && modrm->sib.base == 5)
return modrm->disp32;
if (modrm->sib.index == 4)
return base_val;
if (modrm->sib.base == 5)
return (index_val * scale) + modrm->disp32;
return index_val * scale + base_val;
}
if (modrm->mod == 1)
{
if (modrm->sib.index == 4)
return base_val + modrm->disp8;
return base_val + (index_val * scale) + modrm->disp8;
}
if (modrm->mod == 2)
{
if (modrm->sib.index == 4)
return base_val + modrm->disp32;
return base_val + (index_val * scale) + modrm->disp32;
}
printf("Invalid Mod value for SIB");
panic_exit(emu);
}
uint32_t calc_memory_address(Emulator *emu, ModRM *modrm)
{
/* Real mode workaround for [disp16] */
if (!emu->is_pe)
{
if (modrm->mod == 0 && modrm->rm == 6)
{
return modrm->disp16;
}
}
/* Mod:0 [reg] */
if (modrm->mod == 0)
{
/* SIB (Mod: 00 R/M: 100) */
if (modrm->rm == 4)
{
return calc_cib_address(emu, modrm);
}
/* Mod:0 R/M: 101 uses disp32 as memory address. */
else if (modrm->rm == 5)
{
return modrm->disp32;
}
/* Mod:0 R/M: 000 - 011, 110, 111 uses [reg] */
else
{
return get_register32(emu, modrm->rm);
}
}
/* Mod: 01 [reg] + disp8 */
else if (modrm->mod == 1)
{
/* SIB (Mod: 01 R/M: 100) */
if (modrm->rm == 4)
{
return calc_cib_address(emu, modrm);
}
/* Mod: 1 R/M: 000 - 011, 101 - 111 uses [reg] + disp8 */
else
{
return get_register32(emu, modrm->rm) + modrm->disp8;
}
}
/* Mod: 10 [reg] + disp32 */
else if (modrm->mod == 2)
{
/* SIB (MOD: 10 R/M: 100) */
if (modrm->rm == 4)
{
return calc_cib_address(emu, modrm);
}
/* Mod: 10 R/M: 000 - 011, 101 - 111 uses [reg] + disp32 */
else
{
return get_register32(emu, modrm->rm) + modrm->disp32;
}
}
else
{
printf("ModRM with mod: 00 - 10 are only implemented.");
panic_exit(emu);
}
}
void set_rm8(Emulator *emu, ModRM *modrm, uint8_t value)
{
/* Mod:11 is for registers directly. */
if (modrm->mod == 3)
{
set_register8(emu, modrm->rm, value);
}
else
{
/*
* Mod: Pattern
* 00: [eax], [ecx]...
* 01: [eax] + disp8, [ecx] + disp8...
* 10: [eax] + disp32 etc, [ecx] + disp32...
*/
uint32_t address = calc_memory_address(emu, modrm);
set_memory8(emu, DS, address, value);
}
}
uint8_t get_rm8(Emulator *emu, ModRM *modrm)
{
if (modrm->mod == 3)
{
return get_register8(emu, modrm->rm);
}
else
{
uint32_t address = calc_memory_address(emu, modrm);
return get_memory8(emu, DS, address);
}
}
void set_rm16(Emulator *emu, ModRM *modrm, uint16_t value)
{
/* Mod:11 is for registers directly. */
if (modrm->mod == 3)
{
set_register16(emu, modrm->rm, value);
}
else
{
/*
* Mod: Pattern
* 00: [eax], [ecx]...
* 01: [eax] + disp8, [ecx] + disp8...
* 10: [eax] + disp32 etc, [ecx] + disp32...
*/
uint32_t address = calc_memory_address(emu, modrm);
set_memory16(emu, DS, address, value);
}
}
uint16_t get_rm16(Emulator *emu, ModRM *modrm)
{
if (modrm->mod == 3)
{
return get_register16(emu, modrm->rm);
}
else
{
uint32_t address = calc_memory_address(emu, modrm);
return get_memory16(emu, DS, address);
}
}
void set_rm32(Emulator *emu, ModRM *modrm, uint32_t value)
{
/* Mod:11 is for registers directly. */
if (modrm->mod == 3)
{
set_register32(emu, modrm->rm, value);
}
else
{
/*
* Mod: Pattern
* 00: [eax], [ecx]...
* 01: [eax] + disp8, [ecx] + disp8...
* 10: [eax] + disp32 etc, [ecx] + disp32...
*/
uint32_t address = calc_memory_address(emu, modrm);
set_memory32(emu, DS, address, value);
}
}
uint32_t get_rm32(Emulator *emu, ModRM *modrm)
{
if (modrm->mod == 3)
{
return get_register32(emu, modrm->rm);
}
else
{
uint32_t address = calc_memory_address(emu, modrm);
return get_memory32(emu, DS, address);
}
}
void set_r8(Emulator *emu, ModRM *modrm, uint8_t value)
{
set_register8(emu, modrm->reg_index, value);
}
uint8_t get_r8(Emulator *emu, ModRM *modrm)
{
return get_register8(emu, modrm->reg_index);
}
void set_r16(Emulator *emu, ModRM *modrm, uint16_t value)
{
set_register16(emu, modrm->reg_index, value);
}
uint16_t get_r16(Emulator *emu, ModRM *modrm)
{
return get_register16(emu, modrm->reg_index);
}
void set_r32(Emulator *emu, ModRM *modrm, uint32_t value)
{
set_register32(emu, modrm->reg_index, value);
}
uint32_t get_r32(Emulator *emu, ModRM *modrm)
{
return get_register32(emu, modrm->reg_index);
}
void set_seg_r(Emulator *emu, ModRM *modrm, uint16_t value)
{
set_seg_register16(emu, modrm->reg_index, value);
}
uint16_t get_seg_r(Emulator *emu, ModRM *modrm)
{
return get_seg_register16(emu, modrm->reg_index);
}