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Autodesk Visual Lisp Decompilation...

Posted: Mon May 05, 2003 6:13 pm
by gadget
Autodesk Visual Lisp Decompilation...

I know this is a bit off topic, ie non asm but I was wonderin if ne one outhere know of any proggie to do this, any sources, or anything related to the bytecodes etc used in vital/visual lisp *.fas files. Has ne1 looked into this?



Dissecting LISP

Posted: Tue May 06, 2003 1:30 pm
by Rackmount

I am a CAD user and have done some work with LISP. I am currently studying a application based on the ARX file format. ARX is nice in that it is usually coded in C/C++ and so is easily decompiled into the ASM we all love so much. As for decompiling LISP....hmmm.... haven't ever tried it, but I am game on following this line of study as well. I will begin my search for background material to assist the dissection of LISP...surely others have trod this road ahead of us and left their footprints for us to follow...let's go!

Rackmount.... but wait...there's more!!

Found this info already(slightly edited) from site hxxp:// (replace x's -->http):
"It could be possible (so far only theoretically) to retrieve some symbol values (esp. strings) from BI4 or FAS files, if you hack the internal encryption scheme, but it is impossible(?) to get lisp source code. (as hard as getting complete C source code from .EXE files). As far as is currently known, there is no FAS decoder out yet.
Compiled Lisps usually have the extension .BI2, .BI4 or .FAS
Compiled Lisps are not decryptable nor readable.
Compiled Lisps load and run faster than plain AutoLisp, but need a special environment. BI4 files need a special ACADL.EXP/ACADL.EXE, FAS files in Vill 1.0 an external Run-Time System. Vill from version 2.0 on creates single ARX files."

Hmmmm...this could be quite a chore to create a decompiler seems like you would need to
1) decrypt ---> I am only beginning to do cryptography (just reached lvl 1 on Mallatia's site)
2) pattern recognition ---> identify native LISP functions

One thing to test...if you can compile a simple function a few times and compare what it looks like in encrypted form. Is it the same with each compilation? Is it the same when compiled on a different computer? Does this even help...dunno...Im a newbie...why you askin me?


Lisp Decompiler Project (LDP)

Posted: Tue Jun 15, 2004 10:15 pm
by Dead_Loop
Rackmount wrote:Hmmmm...this could be quite a chore to create a decompiler
So you want to write a fas-Decompiler. :yay:
You're welcome to take part in the Lisp Decompiler Project (LDP).
Take a look at:
Most of the reverse engineering work(decrypting the Fasstream and getting format of the Bytecode commands) is already done.
Now it's up to analyse the data from the fas-disassembler and retransform it to real Lisp commands. :sneaky:

Posted: Mon Nov 09, 2015 5:35 am
by cw2k
Sorry to bring up that '10 years old hat' again. However just got an email about some asking for the
Autodesk AutoCAD Lisp Decompiler for *.fas and *.vlx files.

Googled for 'AutoCAD Lisp Decompiler' myself and this is the first place in search result that may allow some update/contribution:

Well old website is down and can be only accessed by '' like this: ...

Reupped it here: ... Decompiler
*VB6(go to parentdir) + source code included*