/* * Implementation of Virtual Machine (VM) * * by Adam 'pi3' Zabrocki * * * This code was written to solve this challenge: * http://www.canyoucrackit.co.uk/15b436de1f9107f3778aad525e5d0b20.js * * * The main page for challenge is: * http://canyoucrackit.co.uk * Organized by the Government Communications Headquarters (GCHQ). * * *************************************************************************************** *************************************************************************************** * * virtual machine architecture * ++++++++++++++++++++++++++++ * * segmented memory model with 16-byte segment size (notation seg:offset) * * 4 general-purpose registers (r0-r3) * 2 segment registers (cs, ds equiv. to r4, r5) * 1 flags register (fl) * * instruction encoding * ++++++++++++++++++++ * * byte 1 byte 2 (optional) * bits [ 7 6 5 4 3 2 1 0 ] [ 7 6 5 4 3 2 1 0 ] * opcode - - - * mod - * operand1 - - - - * operand2 - - - - - - - - * * operand1 is always a register index * operand2 is optional, depending upon the instruction set specified below * the value of mod alters the meaning of any operand2 * 0: operand2 = reg ix * 1: operand2 = fixed immediate value or target segment (depending on instruction) * * instruction set * +++++++++++++++ * * Notes: * * r1, r2 => operand 1 is register 1, operand 2 is register 2 * * movr r1, r2 => move contents of register r2 into register r1 * * opcode | instruction | operands (mod 0) | operands (mod 1) * -------+-------------+------------------+----------------- * 0x00 | jmp | r1 | r2:r1 * 0x01 | movr | r1, r2 | rx, imm * 0x02 | movm | r1, [ds:r2] | [ds:r1], r2 * 0x03 | add | r1, r2 | r1, imm * 0x04 | xor | r1, r2 | r1, imm * 0x05 | cmp | r1, r2 | r1, imm * 0x06 | jmpe | r1 | r2:r1 * 0x07 | hlt | N/A | N/A * * flags * +++++ * * cmp r1, r2 instruction results in: * r1 == r2 => fl = 0 * r1 < r2 => fl = 0xff * r1 > r2 => fl = 1 * * jmpe r1 * => if (fl == 0) jmp r1 * else nop * *************************************************************************************** *************************************************************************************** */ #include #include #include #define SEGMENT 0x10 #define MOD_FLAG(x) ((x >> 4) & 0x1) #define OPCODE(x) ((x >> 5) & 0x7) #define OPERAND_ONE(x) x & 0xF #define DUMP(x) \ do { \ unsigned int i; \ \ printf("\n--- DUMP ---\n"); \ for (i=0;i "); switch (opc) { /* jmp */ case 0x0: if (m_flag) { if (opr2 >= 0x10) regs[0x4] = 0x10; printf("%s' r%d:r%d\n",instr[opc],opr1,opr2); ip = regs[0x4]*SEGMENT+(opr2-regs[0x4])*SEGMENT+regs[opr1]; } else { printf("%s r%d\n",instr[opc],opr1); ip = regs[0x4]*SEGMENT+regs[opr1]; } break; /* movr */ case 0x1: if (m_flag) { printf("%s' r%d,%X\n",instr[opc],opr1,opr2); regs[opr1] = opr2; } else { printf("%s r%d,r%d\n",instr[opc],opr1,opr2); regs[opr1] = regs[opr2]; /* MAM ODWROTENIE */ } break; /* movm */ case 0x2: if (m_flag) { printf("%s' [ds:r%d],r%d\n",instr[opc],opr1,opr2); mem[regs[0x5]*SEGMENT+regs[opr1]] = regs[opr2]; } else { printf("%s r%d,[ds:r%d]\n",instr[opc],opr1,opr2); regs[opr1] = mem[regs[0x5]*SEGMENT+regs[opr2]]; } break; /* add */ case 0x3: if (m_flag) { printf("%s' r%d,%X\n",instr[opc],opr1,opr2); regs[opr1] += opr2; } else { printf("%s' r%d,r%d\n",instr[opc],opr1,opr2); regs[opr1] += regs[opr2]; } break; /* xor */ case 0x4: if (m_flag) { printf("%s' r%d,%X\n",instr[opc],opr1,opr2); regs[opr1] ^= opr2; } else { printf("%s r%d,r%d\n",instr[opc],opr1,opr2); regs[opr1] ^= regs[opr2]; } break; /* cmp */ case 0x5: if (m_flag) { printf("%s' r%d,%X\n",instr[opc],opr1,opr2); if (regs[opr1] == opr2) flag = 0x0; else if (regs[opr1] < opr2) flag = 0xFF; else if (regs[opr1] > opr2) flag = 0x1; else { printf("This is grey area... I'll never bere here ;) - mod = 1\n"); exit(-1); } } else { printf("%s r%d,r%d\n",instr[opc],opr1,opr2); if (regs[opr1] == regs[opr2]) flag = 0x0; else if (regs[opr1] < regs[opr2]) flag = 0xFF; else if (regs[opr1] > regs[opr2]) flag = 0x1; else { printf("This is grey area... I'll never bere here ;) - mod = 0\n"); exit(-1); } } break; /* jmpe */ case 0x6: if (m_flag) { printf("%s' r%d,%X\n",instr[opc],opr1,opr2); if (!flag) { if (opr2 >= 0x10) regs[0x4] = 0x10; ip = regs[0x4]*SEGMENT+(opr2-regs[0x4])*SEGMENT+regs[opr1]; } } else { printf("%s r%d\n",instr[opc],opr1); if (!flag) ip = regs[0x4]*SEGMENT+regs[opr1]; else ip -= 1; } break; /* hlt */ case 0x7: printf("%s\n",instr[opc]); DUMP(mem); exit(0); break; default: printf("WTF?!?!\n"); exit(-1); break; } // exit(-1); }