Carrez: The real problem with Java in Linux distros

Posted Sep 24, 2010 22:49 UTC (Fri) by Lennie (subscriber, #49641)
In reply to: Carrez: The real problem with Java in Linux distros by jonabbey
Parent article: Carrez: The real problem with Java in Linux distros

I've been wondering about that, why do they include java with blu-ray ?

Carrez: The real problem with Java in Linux distros

Posted Sep 24, 2010 23:33 UTC (Fri) by cesarb (subscriber, #6266) [Link] (5 responses)

It is part of the DRM.

If I recall correctly, I read a long time ago a thread on doom9.org where people were reverse-engineering the VM used by BD+ (one of the several parts of the Blu-ray specification written to make copying harder). They found out it was a heavily-obfuscated variant of the DLX architecture, and reverse-engineered most of the system calls programs written on it could use. An open-source emulator was written which could emulate the programs from the discs they had.

However, they had a problem with newer discs, because one of the system calls on the code found in these newer discs called into the Java code, which they did not emulate. I do not know how or even if they worked around it; I did not follow the developments or even the thread (I just read it once).

You can probably read more about it on some thread linked to by http://en.wikipedia.org/wiki/BD%2B .

Carrez: The real problem with Java in Linux distros

Posted Sep 26, 2010 18:01 UTC (Sun) by elanthis (guest, #6227) [Link] (4 responses)

It has nothing to do with the DRM. It's what they use for the interactive programs found on some Blu-ray discs. Think of the DVD menus you're used to, but now add actual Turing-complete language, some small bit of data storage, and an Internet connection. Someone thought it would be neat to include that kind of interactive content on a movie. (I disagree and think it's stupid as hell, but that's not particularly relevant.)

Carrez: The real problem with Java in Linux distros

Posted Sep 27, 2010 13:15 UTC (Mon) by cesarb (subscriber, #6266) [Link]

Yes, it has to do with the DRM. I looked again at the long (38 pages) thread (it was easy to find again, it is one of the references from that Wikipedia article), and at the related threads that branch from it. This is from the first post on one of the branched threads:

> BD-J does not only provide the menu/gui for convenient movie playback. The BD-J applications (Xlets) also interact with the content code (BD+) via TRAP_ApplicationLayer. A basic BD-J platform implementation is therefor required to properly repair BD+ corrupted movies.

http://forum.doom9.org/showpost.php?p=1254307&postcou...

Carrez: The real problem with Java in Linux distros

Posted Sep 27, 2010 13:56 UTC (Mon) by sorpigal (guest, #36106) [Link]

I think they think that this whole web site fad will go away if they can deliver similarly dynamic content to people's TVs in a manner that is slick and (most importantly) under studio control.

Just imagine! Why get a computer and a web browser and all that complication if you can just insert your Info-Acces Blueray and get a sanitized subset of available information!

Carrez: The real problem with Java in Linux distros

Posted Sep 30, 2010 15:09 UTC (Thu) by BenHutchings (subscriber, #37955) [Link] (1 responses)

DVD menus are also controlled by a program running on a virtual machine. The VM is Turing-complete but is limited to 128 instructions per menu, 16 16-bit general-purpose registers and no memory.

Sorry, but this is NOT Turing-complete VM

Posted Oct 2, 2010 22:35 UTC (Sat) by khim (subscriber, #9252) [Link]

For Turing-completeness you need some kind of ENDLESS memory. It may be tape (as in Turing or Post machines), memory (well, most CPUs have finite memory so they are fully not Turing-complete - yet 2^64 is usually "good enough") or just a few counters (three is enough - but they must be unbound!).

DVD VM has very limited memory so it's not Turing-complete...

Carrez: The real problem with Java in Linux distros

Posted Sep 24, 2010 23:38 UTC (Fri) by Kamilion (subscriber, #42576) [Link]

Disc menus, online content, various other things. Occasionally, updating the AACS keys or player firmware image.