DOS MZ executable: JavaScript parsing library

DOS MZ file format is a traditional format for executables in MS-DOS environment. Many modern formats (i.e. Windows PE) still maintain compatibility stub with this format.

As opposed to .com file format (which basically sports one 64K code segment of raw CPU instructions), DOS MZ .exe file format allowed more flexible memory management, loading of larger programs and added support for relocations.

File extension

["exe", "ovl"]

KS implementation details

License: CC0-1.0
Minimal Kaitai Struct required: 0.9

References

This page hosts a formal specification of DOS MZ executable using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Usage

Runtime library

All parsing code for JavaScript generated by Kaitai Struct depends on the JavaScript runtime library. You have to install it before you can parse data.

The JavaScript runtime library is available at npm:

npm install kaitai-struct

Code

See the usage examples in the JavaScript notes.

Parse structure from an ArrayBuffer:

var arrayBuffer = ...;
var data = new DosMz(new KaitaiStream(arrayBuffer));

After that, one can get various attributes from the structure by accessing fields or properties like:

data.header // => get header

JavaScript source code to parse DOS MZ executable

DosMz.js

// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

(function (root, factory) {
  if (typeof define === 'function' && define.amd) {
    define(['kaitai-struct/KaitaiStream'], factory);
  } else if (typeof module === 'object' && module.exports) {
    module.exports = factory(require('kaitai-struct/KaitaiStream'));
  } else {
    root.DosMz = factory(root.KaitaiStream);
  }
}(typeof self !== 'undefined' ? self : this, function (KaitaiStream) {
/**
 * DOS MZ file format is a traditional format for executables in MS-DOS
 * environment. Many modern formats (i.e. Windows PE) still maintain
 * compatibility stub with this format.
 * 
 * As opposed to .com file format (which basically sports one 64K code
 * segment of raw CPU instructions), DOS MZ .exe file format allowed
 * more flexible memory management, loading of larger programs and
 * added support for relocations.
 * @see {@link http://www.delorie.com/djgpp/doc/exe/|Source}
 */

var DosMz = (function() {
  function DosMz(_io, _parent, _root) {
    this._io = _io;
    this._parent = _parent;
    this._root = _root || this;

    this._read();
  }
  DosMz.prototype._read = function() {
    this.header = new ExeHeader(this._io, this, this._root);
    this.body = this._io.readBytes(this.header.lenBody);
  }

  var ExeHeader = DosMz.ExeHeader = (function() {
    function ExeHeader(_io, _parent, _root) {
      this._io = _io;
      this._parent = _parent;
      this._root = _root || this;

      this._read();
    }
    ExeHeader.prototype._read = function() {
      this.mz = new MzHeader(this._io, this, this._root);
      this.restOfHeader = this._io.readBytes((this.mz.lenHeader - 28));
    }
    Object.defineProperty(ExeHeader.prototype, 'lenBody', {
      get: function() {
        if (this._m_lenBody !== undefined)
          return this._m_lenBody;
        this._m_lenBody = ((this.mz.lastPageExtraBytes == 0 ? (this.mz.numPages * 512) : (((this.mz.numPages - 1) * 512) + this.mz.lastPageExtraBytes)) - this.mz.lenHeader);
        return this._m_lenBody;
      }
    });

    return ExeHeader;
  })();

  var MzHeader = DosMz.MzHeader = (function() {
    function MzHeader(_io, _parent, _root) {
      this._io = _io;
      this._parent = _parent;
      this._root = _root || this;

      this._read();
    }
    MzHeader.prototype._read = function() {
      this.magic = KaitaiStream.bytesToStr(this._io.readBytes(2), "ASCII");
      if (!( ((this.magic == "MZ") || (this.magic == "ZM")) )) {
        throw new KaitaiStream.ValidationNotAnyOfError(this.magic, this._io, "/types/mz_header/seq/0");
      }
      this.lastPageExtraBytes = this._io.readU2le();
      this.numPages = this._io.readU2le();
      this.numRelocations = this._io.readU2le();
      this.headerSize = this._io.readU2le();
      this.minAllocation = this._io.readU2le();
      this.maxAllocation = this._io.readU2le();
      this.initialSs = this._io.readU2le();
      this.initialSp = this._io.readU2le();
      this.checksum = this._io.readU2le();
      this.initialIp = this._io.readU2le();
      this.initialCs = this._io.readU2le();
      this.ofsRelocations = this._io.readU2le();
      this.overlayId = this._io.readU2le();
    }
    Object.defineProperty(MzHeader.prototype, 'lenHeader', {
      get: function() {
        if (this._m_lenHeader !== undefined)
          return this._m_lenHeader;
        this._m_lenHeader = (this.headerSize * 16);
        return this._m_lenHeader;
      }
    });

    return MzHeader;
  })();

  var Relocation = DosMz.Relocation = (function() {
    function Relocation(_io, _parent, _root) {
      this._io = _io;
      this._parent = _parent;
      this._root = _root || this;

      this._read();
    }
    Relocation.prototype._read = function() {
      this.ofs = this._io.readU2le();
      this.seg = this._io.readU2le();
    }

    return Relocation;
  })();
  Object.defineProperty(DosMz.prototype, 'relocations', {
    get: function() {
      if (this._m_relocations !== undefined)
        return this._m_relocations;
      if (this.header.mz.ofsRelocations != 0) {
        var io = this.header._io;
        var _pos = io.pos;
        io.seek(this.header.mz.ofsRelocations);
        this._m_relocations = [];
        for (var i = 0; i < this.header.mz.numRelocations; i++) {
          this._m_relocations.push(new Relocation(io, this, this._root));
        }
        io.seek(_pos);
      }
      return this._m_relocations;
    }
  });

  return DosMz;
})();
return DosMz;
}));