x86.js

registers = ["eax", "ebx", "ecx", "edx", "esi", "edi", "esp", "ebp"];

function hex(v) {
    var parts = new Array(8);
    for (var i = 0; i < 8; i++) {
       parts[8 - i] = (v & 0xf).toString(16);
       v >>= 4
    }
    return "0x" + parts.join("");
}

var MAX_STACK = 10;

function State (prevState) {
    this.prevState = prevState;
    self = this;
    if (prevState) {
    this.stack = prevState.stack.slice(0)
	registers.forEach(function (reg) {
	    self[reg] = prevState[reg];
	});
    } else {
        this.stack = new Array(MAX_STACK);
	for (var i = 0; i < MAX_STACK; i++) {
	    this.stack[i] = 0;
	}
	this.eax = 0; this.ebx = 0; this.ecx = 0; this.esi = 0; this.edi = 0;
	this.esp = this.stackBase; this.ebp = this.stackBase;
    }
}
State.prototype.stackBase = 0xfffffe00
State.prototype.toString = function () {
    var self = this;
    var ret = "";
    for (var stackIndex = 0; stackIndex < this.stack.length; stackIndex++) {
	ret += hex(self.stackBase - (stackIndex << 2));
	ret += ": " + hex(self.stack[stackIndex]) + "\n"
    }
    registers.slice(0,4).forEach(function (v) {
	ret += v + ": " + hex(self[v]) + " ";
    });
    ret += "\n";
    registers.slice(4).forEach(function (v) {
	ret += v + ": " + hex(self[v]) + " ";
    });
    return ret;
}

function Command(regex, callback) {
    regex = regex.replace("REG", "%(" + registers.join("|") + ")");
    regex = regex.replace("IMM", "\\$(0x\\d+|\\d+)");
    regex = "^" + regex + "$";
    this.regex = new RegExp(regex, "i");
    this.callback = callback;
}

var commands = [
    new Command("pushl? REG", function (state, reg) {
	stackIndex = (state.stackBase - state.esp) >> 2;
	state.stack[stackIndex] = state[reg]
	state.esp -= 4;
    }),
    new Command("pushl? IMM", function (state, imm) {
	stackIndex = (state.stackBase - state.esp) >> 2;
	state.stack[stackIndex] = parseInt(imm);
	state.esp -= 4;
    }),
    new Command("popl? REG", function (state, reg) {
	stackIndex = (state.stackBase - state.esp) >> 2;
	state[reg] = state.stack[stackIndex]
	state.esp += 4;
    }),
    new Command("movl? IMM, ?REG", function(state, imm, reg) {
	state[reg] = parseInt(imm);
    }),
    new Command("movl? REG, ?REG", function(state, src, dst) {
	state[dst] = parseInt(src);
    }),

]

State.prototype.eval = function (string) {
    var newState = new State(this);
    var matched = commands.some(function (command) {
	var found = string.match(command.regex);
	if (found) {
	    var args = [newState];
	    args.push.apply(args, found.slice(1));
            command.callback.apply(this, args);
	    return true;
	}
	return false;
    });
    if (matched) {
	return newState;
    } else {
        throw "No matching command for " + string;
    }
}