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November 12, 2018 18:32
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/* (C) Copyright 2012-2014 Semantic Designs, Inc. | |
You may freely use this code provided you retain this copyright message | |
*/ | |
typedef unsigned int natural; | |
natural InstructionLength(BYTE* pc) | |
{ // returns length of instruction at PC | |
natural length=0; | |
natural opcode, opcode2; | |
natural modrm; | |
natural sib; | |
BYTE* p=pc; | |
while (true) | |
{ // scan across prefix bytes | |
opcode=*p++; | |
switch (opcode) | |
{ case 0x64: case 0x65: // FS: GS: prefixes | |
case 0x36: // SS: prefix | |
case 0x66: case 0x67: // operand size overrides | |
case 0xF0: case 0xF2: // LOCK, REPNE prefixes | |
length++; | |
break; | |
case 0x2E: // CS: prefix, used as HNT prefix on jumps | |
case 0x3E: // DS: prefix, used as HT prefix on jumps | |
length++; | |
// goto process relative jmp // tighter check possible here | |
break; | |
default: | |
goto process_instruction_body; | |
} | |
} | |
process_instruction_body: | |
switch(opcode) // switch on main opcode | |
{ | |
// ONE BYTE OPCODE, move to next opcode without remark | |
case 0x27: case 0x2F: | |
case 0x37: case 0x3F: | |
case 0x40: case 0x41: case 0x42: case 0x43: case 0x44: case 0x45: case 0x46: case 0x47: | |
case 0x48: case 0x49: case 0x4A: case 0x4B: case 0x4C: case 0x4D: case 0x4E: case 0x4F: | |
case 0x50: case 0x51: case 0x52: case 0x53: case 0x54: case 0x55: case 0x56: case 0x57: | |
case 0x58: case 0x59: case 0x5A: case 0x5B: case 0x5C: case 0x5D: case 0x5E: case 0x5F: | |
case 0x90: // nop | |
case 0x91: case 0x92: case 0x93: case 0x94: case 0x95: case 0x96: case 0x97: // xchg | |
case 0x98: case 0x99: | |
case 0x9C: case 0x9D: case 0x9E: case 0x9F: | |
case 0xA4: case 0xA5: case 0xA6: case 0xA7: case 0xAA: case 0xAB: // string operators | |
case 0xAC: case 0xAD: case 0xAE: case 0xAF: | |
/* case 0xC3: // RET handled elsewhere */ | |
case 0xC9: | |
case 0xCC: // int3 | |
case 0xF5: case 0xF8: case 0xF9: case 0xFC: case 0xFD: | |
return length+1; // include opcode | |
case 0xC3: // RET | |
if (*p++ != 0xCC) | |
return length+1; | |
if (*p++ != 0xCC) | |
return length+2; | |
if (*p++ == 0xCC | |
&& *p++ == 0xCC) | |
return length+5; | |
goto error; | |
// TWO BYTE INSTRUCTION | |
case 0x04: case 0x0C: case 0x14: case 0x1C: case 0x24: case 0x2C: case 0x34: case 0x3C: | |
case 0x6A: | |
case 0xB0: case 0xB1: case 0xB2: case 0xB3: case 0xB4: case 0xB5: case 0xB6: case 0xB7: | |
case 0xC2: | |
return length+2; | |
// TWO BYTE RELATIVE BRANCH | |
case 0x70: case 0x71: case 0x72: case 0x73: case 0x74: case 0x75: case 0x76: case 0x77: | |
case 0x78: case 0x79: case 0x7A: case 0x7B: case 0x7C: case 0x7D: case 0x7E: case 0x7F: | |
case 0xE0: case 0xE1: case 0xE2: case 0xE3: case 0xEB: | |
return length+2; | |
// THREE BYTE INSTRUCTION (NONE!) | |
// FIVE BYTE INSTRUCTION: | |
case 0x05: case 0x0D: case 0x15: case 0x1D: | |
case 0x25: case 0x2D: case 0x35: case 0x3D: | |
case 0x68: | |
case 0xA9: | |
case 0xB8: case 0xB9: case 0xBA: case 0xBB: case 0xBC: case 0xBD: case 0xBE: case 0xBF: | |
return length+5; | |
// FIVE BYTE RELATIVE CALL | |
case 0xE8: | |
return length+5; | |
// FIVE BYTE RELATIVE BRANCH | |
case 0xE9: | |
if (p[4]==0xCC) | |
return length+6; // <jmp near ptr ... int 3> | |
return length+5; // plain <jmp near ptr> | |
// FIVE BYTE DIRECT ADDRESS | |
case 0xA1: case 0xA2: case 0xA3: // MOV AL,AX,EAX moffset... | |
return length+5; | |
break; | |
// ModR/M with no immediate operand | |
case 0x00: case 0x01: case 0x02: case 0x03: case 0x08: case 0x09: case 0x0A: case 0x0B: | |
case 0x10: case 0x11: case 0x12: case 0x13: case 0x18: case 0x19: case 0x1A: case 0x1B: | |
case 0x20: case 0x21: case 0x22: case 0x23: case 0x28: case 0x29: case 0x2A: case 0x2B: | |
case 0x30: case 0x31: case 0x32: case 0x33: case 0x38: case 0x39: case 0x3A: case 0x3B: | |
case 0x84: case 0x85: case 0x86: case 0x87: case 0x88: case 0x89: case 0x8A: case 0x8B: case 0x8D: case 0x8F: | |
case 0xD1: case 0xD2: case 0xD3: | |
case 0xFE: case 0xFF: // misinterprets JMP far and CALL far, not worth fixing | |
length++; // count opcode | |
goto modrm; | |
// ModR/M with immediate 8 bit value | |
case 0x80: case 0x82: case 0x83: | |
case 0xC0: case 0xC1: | |
case 0xC6: // with r=0? | |
length+=2; // count opcode and immediate byte | |
goto modrm; | |
// ModR/M with immediate 32 bit value | |
case 0x81: | |
case 0xC7: // with r=0? | |
length+=5; // count opcode and immediate byte | |
goto modrm; | |
case 0x9B: // FSTSW AX = 9B DF E0 | |
if (*p++==0xDF) | |
{ if (*p++==0xE0) | |
return length+3; | |
printf("InstructionLength: Unimplemented 0x9B tertiary opcode %2x at %x\n",*p,p); | |
goto error; | |
} | |
else { printf("InstructionLength: Unimplemented 0x9B secondary opcode %2x at %x\n",*p,p); | |
goto error; | |
} | |
case 0xD9: // various FP instructions | |
modrm=*p++; | |
length++; // account for FP prefix | |
switch (modrm) | |
{ case 0xC9: case 0xD0: | |
case 0xE0: case 0xE1: case 0xE4: case 0xE5: | |
case 0xE8: case 0xE9: case 0xEA: case 0xEB: case 0xEC: case 0xED: case 0xEE: | |
case 0xF8: case 0xF9: case 0xFA: case 0xFB: case 0xFC: case 0xFD: case 0xFE: case 0xFF: | |
return length+1; | |
default: // r bits matter if not one of the above specific opcodes | |
switch((modrm&0x38)>>3) | |
{ case 0: goto modrm_fetched; // fld | |
case 1: return length+1; // fxch | |
case 2: goto modrm_fetched; // fst | |
case 3: goto modrm_fetched; // fstp | |
case 4: goto modrm_fetched; // fldenv | |
case 5: goto modrm_fetched; // fldcw | |
case 6: goto modrm_fetched; // fnstenv | |
case 7: goto modrm_fetched; // fnstcw | |
} | |
goto error; // unrecognized 2nd byte | |
} | |
case 0xDB: // various FP instructions | |
modrm=*p++; | |
length++; // account for FP prefix | |
switch (modrm) | |
{ case 0xE3: | |
return length+1; | |
default: // r bits matter if not one of the above specific opcodes | |
#if 0 | |
switch((modrm&0x38)>>3) | |
{ case 0: goto modrm_fetched; // fld | |
case 1: return length+1; // fxch | |
case 2: goto modrm_fetched; // fst | |
case 3: goto modrm_fetched; // fstp | |
case 4: goto modrm_fetched; // fldenv | |
case 5: goto modrm_fetched; // fldcw | |
case 6: goto modrm_fetched; // fnstenv | |
case 7: goto modrm_fetched; // fnstcw | |
} | |
#endif | |
goto error; // unrecognized 2nd byte | |
} | |
case 0xDD: // various FP instructions | |
modrm=*p++; | |
length++; // account for FP prefix | |
switch (modrm) | |
{ case 0xE1: case 0xE9: | |
return length+1; | |
default: // r bits matter if not one of the above specific opcodes | |
switch((modrm&0x38)>>3) | |
{ case 0: goto modrm_fetched; // fld | |
// case 1: return length+1; // fisttp | |
case 2: goto modrm_fetched; // fst | |
case 3: goto modrm_fetched; // fstp | |
case 4: return length+1; // frstor | |
case 5: return length+1; // fucomp | |
case 6: goto modrm_fetched; // fnsav | |
case 7: goto modrm_fetched; // fnstsw | |
} | |
goto error; // unrecognized 2nd byte | |
} | |
case 0xF3: // funny prefix REPE | |
opcode2=*p++; // get second opcode byte | |
switch (opcode2) | |
{ case 0x90: // == PAUSE | |
case 0xA4: case 0xA5: case 0xA6: case 0xA7: case 0xAA: case 0xAB: // string operators | |
return length+2; | |
case 0xC3: // (REP) RET | |
if (*p++ != 0xCC) | |
return length+2; // only (REP) RET | |
if (*p++ != 0xCC) | |
goto error; | |
if (*p++ == 0xCC) | |
return length+5; // (REP) RET CLONE IS LONG JUMP RELATIVE | |
goto error; | |
case 0x66: // operand size override (32->16 bits) | |
if (*p++ == 0xA5) // "rep movsw" | |
return length+3; | |
goto error; | |
default: goto error; | |
} | |
case 0xF6: // funny subblock of opcodes | |
modrm=*p++; | |
if ((modrm & 0x20) == 0) | |
length++; // 8 bit immediate operand | |
goto modrm_fetched; | |
case 0xF7: // funny subblock of opcodes | |
modrm=*p++; | |
if ((modrm & 0x30) == 0) | |
length+=4; // 32 bit immediate operand | |
goto modrm_fetched; | |
// Intel's special prefix opcode | |
case 0x0F: | |
length+=2; // add one for special prefix, and one for following opcode | |
opcode2=*p++; | |
switch(opcode2) | |
{ case 0x31: // RDTSC | |
return length; | |
// CMOVxx | |
case 0x40: case 0x41: case 0x42: case 0x43: case 0x44: case 0x45: case 0x46: case 0x47: | |
case 0x48: case 0x49: case 0x4A: case 0x4B: case 0x4C: case 0x4D: case 0x4E: case 0x4F: | |
goto modrm; | |
// JC relative 32 bits | |
case 0x80: case 0x81: case 0x82: case 0x83: case 0x84: case 0x85: case 0x86: case 0x87: | |
case 0x88: case 0x89: case 0x8A: case 0x8B: case 0x8C: case 0x8D: case 0x8E: case 0x8F: | |
return length+4; // account for subopcode and displacement | |
// SETxx rm32 | |
case 0x90: case 0x91: case 0x92: case 0x93: case 0x94: case 0x95: case 0x96: case 0x97: | |
case 0x98: case 0x99: case 0x9A: case 0x9B: case 0x9C: case 0x9D: case 0x9E: case 0x9F: | |
goto modrm; | |
case 0xA2: // CPUID | |
return length+2; | |
case 0xAE: // LFENCE, SFENCE, MFENCE | |
opcode2=*p++; | |
switch (opcode2) | |
{ case 0xE8: // LFENCE | |
case 0xF0: // MFENCE | |
case 0xF8: // SFENCE | |
return length+1; | |
default: | |
printf("InstructionLength: Unimplemented 0x0F, 0xAE tertiary opcode in clone %2x at %x\n",opcode2,p-1); | |
goto error; | |
} | |
case 0xAF: // imul | |
case 0xB0: // cmpxchg 8 bits | |
goto error; | |
case 0xB1: // cmpxchg 32 bits | |
case 0xB6: case 0xB7: // movzx | |
case 0xBC: /* bsf */ case 0xBD: // bsr | |
// case 0xBE: case 0xBF: // movsx | |
case 0xC1: // xadd | |
case 0xC7: // cmpxchg8b | |
goto modrm; | |
default: | |
printf("InstructionLength: Unimplemented 0x0F secondary opcode in clone %2x at %x\n",opcode,p-1); | |
goto error; | |
} // switch | |
// ALL THE THE REST OF THE INSTRUCTIONS; these are instructions that runtime system shouldn't ever use | |
default: | |
/* case 0x26: case 0x36: // ES: SS: prefixes | |
case 0x9A: | |
case 0xC8: case 0xCA: case 0xCB: case 0xCD: case 0xCE: case 0xCF: | |
case 0xD6: case 0xD7: | |
case 0xE4: case 0xE5: case 0xE6: case 0xE7: case 0xEA: case 0xEB: case 0xEC: case 0xED: case 0xEF: | |
case 0xF4: case 0xFA: case 0xFB: | |
*/ | |
printf("InstructionLength: Unexpected opcode %2x\n",opcode); | |
goto error; | |
} | |
modrm: | |
modrm=*p++; | |
modrm_fetched: | |
if (trace_clone_checking) | |
printf("InstructionLength: ModR/M byte %x %2x\n",pc,modrm); | |
if (modrm >= 0xC0) | |
return length+1; // account for modrm opcode | |
else | |
{ /* memory access */ | |
if ((modrm & 0x7) == 0x04) | |
{ /* instruction with SIB byte */ | |
length++; // account for SIB byte | |
sib=*p++; // fetch the sib byte | |
if ((sib & 0x7) == 0x05) | |
{ if ((modrm & 0xC0) == 0x40) | |
return length+1+1; // account for MOD + byte displacment | |
else return length+1+4; // account for MOD + dword displacement | |
} | |
} | |
switch(modrm & 0xC0) | |
{ case 0x0: | |
if ( (modrm & 0x07) == 0x05) | |
return length+5; // 4 byte displacement | |
else return length+1; // zero length offset | |
case 0x80: | |
return length+5; // 4 byte offset | |
default: | |
return length+2; // one byte offset | |
} | |
} | |
error: | |
{ printf("InstructionLength: unhandled opcode at %8x with opcode %2x\n",pc,opcode); | |
} | |
return 0; // can't actually execute this | |
} |
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