I'm trying to assemble debug.exe/com from the [MS-DOS 2.0 source code](https://github.com/microsoft/MS-DOS/tree/master/v2.0/source), at first it wasn't working but I've been changing some filenames and I've managed to get an .obj file, using link(16-bit version) there is an error (error L2029: unresolved external) on some commands, and I don't know what to do, do I need to add some libraries?

Here's the errors and commands where it fails:

```
batch
C:\Users\<my_username>\Desktop\Assembly>link16.exe

Microsoft (R) Segmented Executable Linker  Version 5.60.339 Dec  5 1994
Copyright (C) Microsoft Corp 1984-1993.  All rights reserved.

Object Modules [.obj]: debug.obj
Run File [debug.exe]: 
List File [nul.map]:
Libraries [.lib]:
Definitions File [nul.def]:
LINK : warning L4021: no stack segment

debug.obj(DEBUGGER) : error L2029: 'PARSERR' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'GO' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'REG' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'NAME' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'BYTEBUF' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'RELEASEPARITY' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'DUMP' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'FILL' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'DEFIO' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'LINEBUF' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'COMPARE' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'DSIZ' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'MOVE' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'LOAD' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'DEFDUMP' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'PARITYMES' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'DISPB' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'TRACE' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'TRAPPARITY' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'PERR' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'HEADSAVE' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'BADVER' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'DATAEND' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'ASSEM' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'LBUFSIZ' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'SPSAVE' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'ENDMES' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'BACMES' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'ASMADD' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'SKIP_FILE' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'PREPNAME' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'NEWEXEC' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'ZTRACE' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'DSSAVE' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'DISADD' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'DWRITE' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'DEBUG_FOUND' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'STACK' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'SEARCH' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'ENTER' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'QFLAG' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'INPUT' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'PARITYFLAG' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'UNASSEM' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'GETHEX' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'GETEOL' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'CSSAVE' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'CARRET' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'NOREGL' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'OUTPUT' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'USER_PROC_PDB' : unresolved external
debug.obj(DEBUGGER) : error L2029: 'IPSAVE' : unresolved external

There were 52 errors detected

```

The code, tools, and other dependencies I've used can be downloaded from [here](https://mega.nz/#!hioDTYIL!hUSrTreGZI7u--OeBDJiR24ed8SQnGiWeXyZgrkwT2s).

How can I fix these unresolved errors?