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Reverse Engineering an MPEG Driver
An anonymous reader writes "Following on from the recent spate of reverse engineering articles, there is an interesting summary of the reverse engineering of a binary only Linux driver.
The driver is for the integrated MPEG decoder on VIA's popular EPIA-M boards. At the moment VIA has not publicly released the source code for the MPEG chipset on these boards and will only make the code available under NDA saying that "Typically, only requests from companies developing product for sale will be approved."
As a result this is holding back development of open source tools (e.g. xine, mplayer, vdr) that would be able to make use of the interesting hardware on these boards."
IANAL, but I don't think the source code is legally safe if VIA wants to go after it.
-mse
Fiat Lux.
To me, it just seemed like a general description of the RE process that people able to RE already know. EPIA M boxes are already good for small PVR boxes using mythtv when a Hauppauge PVR card is added (and a larger power supply). If the MPEG decoder can be used, I'm sure that even the lesser models of EPIA will be able to be used.
bananas like monkeys.
Driver code is the biggest liability that a device maker has. It earns no money, it costs quite a bit to make, and it must be written multiple times for multiple platforms and operating systems.
Via's reluctance to free the driver software is pure evil. They sit like slavemasters on the code and hold it hostage as if it were a servant or slave.
Even if the reverse engineering works out and the code runs equally well as the enslaved code, what will become of the original unfree code? Will that unfortunate code be relegated to living out the rest of its days in slavery? Sadly, I think the answer is affirmative.
Who will fight for the rights of software? I only wish the FSF was more vocal about the Freedom of Software that they purportedly base their ideology upon.
But does it ru-- :)
Nevermind, no points to spare
I've setup a mirror for the source at http://43.244.87.231/cle266.tgz
Be nice to it, and check the original site after slashdot effect goes away.
My lil epia box does better than my parents faster Wintel box at playing dvd's and vob's. Sure a lot of that is because MPlayer and Linux are so much better but you're mistaken if you think the epia systems don't have the muscle for the job. If they could enable the hardware decoding it might even make the playback better. They also run much cooler, more energy effecient, and quieter.. something that IMO is a mark of quality.. not of being 'cheap'. Besides, price compare the CPU's.. you'll find they aren't that cheap. :)
At what price learning? At what cost wisdom? The price is a man's peace of mind, and the cost is his life.
The silly thing with all of this is that the drivers and support for this card that result from the reverse engineering will ultimately result in more sales. It seems so counter-intuitive for VIA to resist this.
Let's harass them for not releasing the code, reverse engineer it and post it everywhere, until they get mad and discontinue Linux driver development altogether! Then xine and mplayer will work GREAT!
Why not use a program that automaticlly takes the binary and builds a C program from it? You still have to pick through the logic to give things helpful function/variable names and refactor but it'd save the step discribed here. In the past when I've reverse engineered binaries that is the type of tool I used. Any good reason for doing this by hand?
This still begs the question.. why not just release the damn source? If we can reverse engineer the drivers what would keep the competition from doing so? Why harm your customers for a false sense of security?
At what price learning? At what cost wisdom? The price is a man's peace of mind, and the cost is his life.
From the article:
Oh yeah. Much more readable.
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Hardware decoding allows for much higher resolution video. Furthermore, specialized hardware typically have more accuracy when decoding the stream. There's additional features too: you can allocate, say, more bits for dynamic color range, fractalize regions that have semi-random "noise" distribution (like tree leaves from a distance) and so on that can improve video quality (to help eliminate obvious artifacts). I am not saying all hardware decoders do this, but these are some advantages. It's very analogous to having specialized 3D hardware to handle graphics rather than "letting the CPU do it".
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It won't produce the same code. Different compilers do things different ways. In the end the binary produced will run the hardware the same way and that's the goal.
Very clever, but I thought reverse engineering worked on a functional level.
He did do functional analysis to make it work. He understood what the thing was doing. If he did not, his code would never have worked. He made little doodles and what have you to make it clear to himself. Now it's in C, the diagrams are much easier to make, though we can be sure he's going to share his diagrams as well. That way other people can make nice software too.
IANAL, but I don't think the source code is legally safe if VIA wants to go after it.
I don't know why you think that. He could have had his computer tell him what it was doing instead of using IDC, no? It's not like he dumpster dived code like old Bill Gates did BASIC. He understood what the code did and reimplemented it himself. Even if he did have dumpster dived code, he could use that to make a functional diagram and then use that to write new code and the results would be the same.
If there is a legal problem with this, there should not be. Why should people be afraid to understand what their machines do and then share that information? So someone else can make money of evryone else's ignorance? Shit, no one would be able to get anything done that way.
Friends don't help friends install M$ junk.
Well, he has done the first part of a reverse engineering process - he has worked out, by inspection of the target, what is being done.
However, he now needs to write the specifications for the hardware, and publish THAT, so that somebody else, somebody who has not seen the binary driver, can write a program based upon the specifications.
Should this not be done, then this code, while interesting to individuals, would be pure poison to anybody who has any intention of distributing this code in a commercial way (e.g. a distro).
And writing a specification for the chip, by inspecting the code, is far more difficult than simply reverse compiling the binary.
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With the ever-increasing clock speed of our CPUs, what is the point of having a hardware MPEG decoder? I understand that p2-400 is sufficient to play DVD-quality movies. The amount you spend on the hardware decoder could have been better spent on memory or video card or CPU or whatever. Now, a hardware encoder would certainly be useful as encoding is still very CPU-intensive. I was contemplating a tivo-like box with a hardware encoder. Does anyone know if hardware MPEG encoders are supported on Linux?
___
If you think big enough, you'll never have to do it.
Just to prove it exists:
Reverse Engineering Compiler
Obviously you've never used VIA processors before. They are notorious for their slow FPU's. In fact, before their latest top-of-the line model - the Nehemiah, their FPU's of previous models always ran at HALF CLOCK. Ouchy.
:O
But, even at full speed a similarly clocked Celeron kicks it's ass in every which way. That said, high performance is not the stated purpose of the Centaur/Via CPU. Its low watts, coupled with the decoder make for an excellent all-around box. I've built around 7 or 8 of these myself and they are excellent for what they are designed for (think: mom and dad or net terminals, not Half Life 2).
I have a few of these floating around the school here now as basic net access / workstation terminals and they are hugely popular - especially in light of what they replaced (AMD 300's). There's nothing like tearing apart some ancient computer and putting one of these boards in it. 90% of the time, it's simply cavernous in there (so much space!)
Last week I put one in an Aptiva and realized that if I was an enterprising person (read: man with a Dremel) I could have fit TWO of them in there as a dual workstation!
So to sum up, they're small as hell (you have to see it to believe it), simple, fun, easy to configure, but don't plan of using them at the next Fragfest 2003 (c)
"...Well, there's egg and bacon; egg sausage and bacon; egg and spam; egg bacon and spam; egg bacon sausage and spam..."
This is not reverse engineering, he dissassembled the code and pretty much copied/ported the result to C. I don't think this meets any cleanroom standards and the code is dangerously contaminated. To use this work you would have to get someone else to reimplement the driver without looking at this contaminated code base. That means they need to be passed a description of the hardware interface inferred from observations of how this driver works, and the code produced by dissassebling the driver needs to be tossed in the garbage can.
Who taught anyone that dissassembling someone's proprietary code and doing a line for line port then publishing the result was in any way legitimate?
First of all, it's just a small wrapper library that is comparatively easy to reverse engineer.
Second of all, there is a library we can reverse engineer.
Third of all, the guy is using the VIA forums to spread the word, so VIA obviously knows about this, and they haven't sued.
To me this rather looks like they were waiting for someone to reverse engineer this, because they couldn't release the sources themselves for contractual reasons. Don't just assume people are evil, maybe they didn't have a choice and did what was in their power to give you the means to help yourself.
I believe this is the TV encoder chip used by the EPIA-M and the VT1622M is the one that supports Macrovision.
I believe that distribution of this code would be illegal, since it is a derivative work based on VIA's library. I haven't seen VIA's license, by typically those licenses prohibit redistribution, reverse engineering, and disclosure of any trade secrets.
The reverse engineering itself is probably still legal, arguably, if it is done to enable someone to write software that interoperates with the decoder. To be safe, I would assume that it's probably better to write such software for an operating system that VIA doesn't support - QNX, for example. (One could argue that the BSDs' ability to run Linux binaries voids the interoperability argument if one were to write a BSD driver, but what do I know?).
You should also make sure that the person writing the final open source code hasn't seen VIA's decompiled source. Typically this is done by having one person or team reverse engineer the code, document the hardware, and toss the hardware documentation over the wall to the driver team.
Lets not forget the hardware mpeg2 decoder - dxr3. A lot of people have worked on this and it has resulted in a very decent driver. It has had absolutely zero help from sigma. There is even hacks to make it display rgb directly to your tv, bypassing the crappy composite and svideo.