gistfile1.js

//--------------------------------------------------------------------------------------------------
//
// stage 2 of 3
//
// challenge:
//   reveal the solution within VM.mem
//
// disclaimer:
//   tested in ie 9, firefox 6, chrome 14 and v8 shell (http://code.google.com/apis/v8/build.html),
//   other javascript implementations may or may not work.
//
//--------------------------------------------------------------------------------------------------

var VM = {

    mem: [
        0x31, 0x04, 0x33, 0xaa, 0x40, 0x02, 0x80, 0x03, 0x52, 0x00, 0x72, 0x01, 0x73, 0x01, 0xb2, 0x50,
        0x30, 0x14, 0xc0, 0x01, 0x80, 0x00, 0x10, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,

        0x98, 0xab, 0xd9, 0xa1, 0x9f, 0xa7, 0x83, 0x83, 0xf2, 0xb1, 0x34, 0xb6, 0xe4, 0xb7, 0xca, 0xb8,
        0xc9, 0xb8, 0x0e, 0xbd, 0x7d, 0x0f, 0xc0, 0xf1, 0xd9, 0x03, 0xc5, 0x3a, 0xc6, 0xc7, 0xc8, 0xc9,
        0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf, 0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9,
        0xda, 0xdb, 0xa9, 0xcd, 0xdf, 0xdf, 0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9,
        0x26, 0xeb, 0xec, 0xed, 0xee, 0xef, 0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9,
        0x7d, 0x1f, 0x15, 0x60, 0x4d, 0x4d, 0x52, 0x7d, 0x0e, 0x27, 0x6d, 0x10, 0x6d, 0x5a, 0x06, 0x56,
        0x47, 0x14, 0x42, 0x0e, 0xb6, 0xb2, 0xb2, 0xe6, 0xeb, 0xb4, 0x83, 0x8e, 0xd7, 0xe5, 0xd4, 0xd9,
        0xc3, 0xf0, 0x80, 0x95, 0xf1, 0x82, 0x82, 0x9a, 0xbd, 0x95, 0xa4, 0x8d, 0x9a, 0x2b, 0x30, 0x69,
        0x4a, 0x69, 0x65, 0x55, 0x1c, 0x7b, 0x69, 0x1c, 0x6e, 0x04, 0x74, 0x35, 0x21, 0x26, 0x2f, 0x60,
        0x03, 0x4e, 0x37, 0x1e, 0x33, 0x54, 0x39, 0xe6, 0xba, 0xb4, 0xa2, 0xad, 0xa4, 0xc5, 0x95, 0xc8,
        0xc1, 0xe4, 0x8a, 0xec, 0xe7, 0x92, 0x8b, 0xe8, 0x81, 0xf0, 0xad, 0x98, 0xa4, 0xd0, 0xc0, 0x8d,
        0xac, 0x22, 0x52, 0x65, 0x7e, 0x27, 0x2b, 0x5a, 0x12, 0x61, 0x0a, 0x01, 0x7a, 0x6b, 0x1d, 0x67,
        0x75, 0x70, 0x6c, 0x1b, 0x11, 0x25, 0x25, 0x70, 0x7f, 0x7e, 0x67, 0x63, 0x30, 0x3c, 0x6d, 0x6a,
        0x01, 0x51, 0x59, 0x5f, 0x56, 0x13, 0x10, 0x43, 0x19, 0x18, 0xe5, 0xe0, 0xbe, 0xbf, 0xbd, 0xe9,
        0xf0, 0xf1, 0xf9, 0xfa, 0xab, 0x8f, 0xc1, 0xdf, 0xcf, 0x8d, 0xf8, 0xe7, 0xe2, 0xe9, 0x93, 0x8e,
        0xec, 0xf5, 0xc8, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,

        0x37, 0x7a, 0x07, 0x11, 0x1f, 0x1d, 0x68, 0x25, 0x32, 0x77, 0x1e, 0x62, 0x23, 0x5b, 0x47, 0x55,
        0x53, 0x30, 0x11, 0x42, 0xf6, 0xf1, 0xb1, 0xe6, 0xc3, 0xcc, 0xf8, 0xc5, 0xe4, 0xcc, 0xc0, 0xd3,
        0x85, 0xfd, 0x9a, 0xe3, 0xe6, 0x81, 0xb5, 0xbb, 0xd7, 0xcd, 0x87, 0xa3, 0xd3, 0x6b, 0x36, 0x6f,
        0x6f, 0x66, 0x55, 0x30, 0x16, 0x45, 0x5e, 0x09, 0x74, 0x5c, 0x3f, 0x29, 0x2b, 0x66, 0x3d, 0x0d,
        0x02, 0x30, 0x28, 0x35, 0x15, 0x09, 0x15, 0xdd, 0xec, 0xb8, 0xe2, 0xfb, 0xd8, 0xcb, 0xd8, 0xd1,
        0x8b, 0xd5, 0x82, 0xd9, 0x9a, 0xf1, 0x92, 0xab, 0xe8, 0xa6, 0xd6, 0xd0, 0x8c, 0xaa, 0xd2, 0x94,
        0xcf, 0x45, 0x46, 0x67, 0x20, 0x7d, 0x44, 0x14, 0x6b, 0x45, 0x6d, 0x54, 0x03, 0x17, 0x60, 0x62,
        0x55, 0x5a, 0x4a, 0x66, 0x61, 0x11, 0x57, 0x68, 0x75, 0x05, 0x62, 0x36, 0x7d, 0x02, 0x10, 0x4b,
        0x08, 0x22, 0x42, 0x32, 0xba, 0xe2, 0xb9, 0xe2, 0xd6, 0xb9, 0xff, 0xc3, 0xe9, 0x8a, 0x8f, 0xc1,
        0x8f, 0xe1, 0xb8, 0xa4, 0x96, 0xf1, 0x8f, 0x81, 0xb1, 0x8d, 0x89, 0xcc, 0xd4, 0x78, 0x76, 0x61,
        0x72, 0x3e, 0x37, 0x23, 0x56, 0x73, 0x71, 0x79, 0x63, 0x7c, 0x08, 0x11, 0x20, 0x69, 0x7a, 0x14,
        0x68, 0x05, 0x21, 0x1e, 0x32, 0x27, 0x59, 0xb7, 0xcf, 0xab, 0xdd, 0xd5, 0xcc, 0x97, 0x93, 0xf2,
        0xe7, 0xc0, 0xeb, 0xff, 0xe9, 0xa3, 0xbf, 0xa1, 0xab, 0x8b, 0xbb, 0x9e, 0x9e, 0x8c, 0xa0, 0xc1,
        0x9b, 0x5a, 0x2f, 0x2f, 0x4e, 0x4e, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
    ],

    s_seg: 2, // segment size

    cpu: {
        ip: 0x00, // instruction pointer

        r0: 0x00,
        r1: 0x00,
        r2: 0x00,
        r3: 0x00,

        cs: 0x00,
        ds: 0x10,

        fl: 0x00,

        firmware: [0xd2ab1f05, 0xda13f110],
        
        is_halted: false
    },

    exec: function()
    {
        // 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

        while (!this.cpu.is_halted) {
            this.cpu.ip = this.dispatch(this.mem.slice(this.cpu.ip, this.cpu.ip+2))
        }
    },

    dispatch: function(segment) {
        advance = 0;
        ins = this.instruction_set[this.get_opcode(segment[0])];;
        mod = this.get_mod(segment[0]);

        // print some nice info
        this.dump();

        print('=>',
              ('0x0' + ins.code),
              ins.name,
              '([', ('0x' + segment[0].toString(16)), ',',
              ('0x' + segment[1].toString(16)),
              '])');

        // execute the instruction and add
        // its return value to the cpu's internal
        // pointer
        this.cpu.ip += ins.op((segment.length == 2 ? segment : segment[0]), mod, this)
        this.dump();
        print("\n");

        // return the cpu's current pointer
        return this.cpu.ip
    },

    dump: function() {
        print('ip:', this.cpu.ip,
              ', r0:', this.cpu.r0,
              ', r1:', this.cpu.r1,
              ', r2:', this.cpu.r2,
              ', r3:', this.cpu.r3,
              ', ds:', this.cpu.ds,
              ', cs:', this.cpu.cs,
              ', fl:', this.cpu.fl);
    },

    addr: function(segment_index, offset) {
        // 16-byte segments + any offset given
        return (this.cpu[segment_index] * 16) + offset;
    },

    instruction_set: [
        {
            'code': 0x00,
            'name': 'jmp',
            'op': function(ins, mod, inst) {
                print(' (ip)', inst.cpu.ip, ':', this.name, mod);
                op1 = inst.get_register(inst.get_opand1(ins[0]));

                if (!mod) {
                    addr = inst.addr('cs', inst.cpu[op1]);
                    print('  (!mod)', op1, addr, inst.cpu[op1]);
                    inst.cpu.ip = addr;
                }
                else {
                    op2 = ins[1];
                    print('  (mod)', op2, ':', op1);
                    addr = op2 * 0x10 + inst.cpu[op1];
                    inst.cpu.cs = op2;
                    inst.cpu.ip = addr;
                }

                return 0;
            },
        },
        {
            'code': 0x01,
            'name': 'movr',
            'op': function(ins, mod, inst) {
                op1 = inst.get_register(inst.get_opand1(ins[0]));

                if (!mod) {
                    // take value from op2
                    op2 = inst.get_register(ins[1]);
                    print(' (!mod) (ip)', inst.cpu.ip, ':', this.name, op2, ',', this.cpu[op2]);
                    inst.cpu[op1] = inst.cpu[op2]
                }
                else {
                    // take immediate value
                    print(' (mod) (ip)', inst.cpu.ip, ':', this.name, op1, ',', ins[1]);
                    inst.cpu[op1] = ins[1];
                    print(' ', op1, '=', inst.cpu[op1]);
                }

                return inst.s_seg; // advance ip by two
            }
        },
        {
            'code': 0x02,
            'name': 'movm',
            'op': function(ins, mod, inst) {
                op1 = inst.get_register(inst.get_opand1(ins[0]));
                op2 = inst.get_register(ins[1]);
                print(' (ip)', inst.cpu.ip, ':', this.name, mod, op1, op2);
                if (!mod) {
                    addr = inst.addr('ds', inst.cpu[op2]);
                    print('  (!mod)', op1, ',', '[ds:', op2, ']', addr, inst.mem[addr]);
                    inst.cpu[op1] = inst.mem[addr];
                    print('  ', op1, '=', inst.cpu[op1]);
                }
                else {
                    addr = inst.addr('ds', inst.cpu[op1]);
                    print('  (mod)', '[ds:', op1, '],', op2, addr, inst.mem[addr]);
                    inst.mem[addr] = inst.cpu[op2]
                    print('  mem:', addr, '=', inst.mem[addr]);
                }

                return inst.s_seg; // done, advance by two
            }
        },
        {
            'code': 0x03,
            'name': 'add',
            'op': function(ins, mod, inst) {
                op1 = inst.get_register(inst.get_opand1(ins[0]));
                print(' (ip)', inst.cpu.ip, ':', this.name, op1, mod);
                // & 0xff to ensure val no larger than 1 byte
                if (!mod) {
                    print('  (!mod)', op1, op2, inst.cpu[op1], inst.cpu[op2]);
                    op2 = inst.get_register(ins[1]);
                    // add both registers together
                    inst.cpu[op1] = (inst.cpu[op1] + inst.cpu[op2]) & 0xff;
                    print('  ', op1, inst.cpu[op1]);
                }
                else {
                    print('  (mod)', ins[1], op2, ',', inst.cpu[op1]);
                    // add the value in ins[1]
                    inst.cpu[op1] = (inst.cpu[op1] + ins[1]) & 0xff;
                    print('  ', op1, '=', inst.cpu[op1]);
                }

                return inst.s_seg;
            }
        },
        {
            'code': 0x04,
            'name': 'xor',
            'op': function(ins, mod, inst) {
                op1 = inst.get_register(inst.get_opand1(ins[0]));
                print(' (ip)', inst.cpu.ip, ':', this.name, mod, ',', op1);
                if (!mod) {
                    op2 = inst.get_register(ins[1]);
                    print('  (!mod)', op1, op2, inst.cpu[op1], inst.cpu[op2]);
                    inst.cpu[op1] = inst.cpu[op1] ^ inst.cpu[op2];
                    print('  ', op1, '=', inst.cpu[op1]);
                }
                else {
                    print('  (mod)', ins[1]);
                    inst.cpu[op1] = (inst.cpu[op1] ^ ins[1]);
                }

                return inst.s_seg;
            },
        },
        {
            'code': 0x05,
            'name': 'cmp',
            'op': function(ins, mod, inst) {
                op1_register = inst.get_register(inst.get_opand1(ins[0]));
                op1 = inst.cpu[op1_register];
                print(' ', inst.cpu.ip, ':', this.name, mod, op1_register, ',');
                op2 = ''
                if (!mod) {
                    op2_regiser = inst.get_register(ins[1]);
                    print('  (!mod)', op2_register);
                    op2 = inst.cpu[op2_register];
                }
                else {
                    op2 = ins[1];
                    print('  (mod)', op2);
                }
                d = op1 - op2;
                if (d == 0) {
                    inst.cpu.fl = 0;
                }
                else if (d > 0) {
                    inst.cpu.fl = 1;
                }
                else {
                    inst.cpu.fl = -1;
                }
                print('  cpu.fl =', inst.cpu.fl);
                return inst.s_seg;
            }
        },
        {
            'code': 0x06,
            'name': 'jmpe',
            'op': function(ins, mod, inst) {
                print(' (ip)', inst.cpu.ip, mod);
                if (inst.cpu.fl == 0) {
                    return inst.instruction_set[0].op(ins, mod, ins);
                }
                print('  [!] Not taken');
                return mod+1;
            }
        },
        {
            'code': 0x07,
            'name': 'hlt',
            'op': function(ins, mod, inst) {
                inst.cpu.is_halted = true;
                print('hlt')
                print('[!] Halting.');
                return 0;
            }
        }
    ],

    get_register: function(ins) {
        // return a register to use for each opcode.
        // note halt (HLT) has no register
        return ['r0', 'r1', 'r2', 'r3', 'cs', 'ds'][ins];
    },

    get_opcode: function(w) {
        // shift bits 5 to the right to get the value of the 3 leftmost bits
        return (w >> 5) & 0xff;
    },

    get_mod: function(w) {
        // filter by 0x0f to figure out 
        return (w >> 4) & 0x01;
    },

    get_opand1: function(w) {
        // filter for 4 rightmost bits
        return w & ((1 << 4) - 1);
    },

    get_opand2: function(w) {
        // pass-thru
        return w;
    },
};

//--------------------------------------------------------------------------------------------------

try
{
    VM.exec();
}
catch(e)
{
    print(e);
}

//--------------------------------------------------------------------------------------------------