Breaking Eggs And Making Omelettes

Topics On Multimedia Technology and Reverse Engineering


Emscripten and Web Audio API

April 28th, 2015 by Multimedia Mike

Ha! They said it couldn’t be done! Well, to be fair, I said it couldn’t be done. Or maybe that I just didn’t have any plans to do it. But I did it– I used Emscripten to cross-compile a CPU-intensive C/C++ codebase (Game Music Emu) to JavaScript. Then I leveraged the Web Audio API to output audio and visualize the audio using an HTML5 canvas.

Want to see it in action? Here’s a demonstration. Perhaps I will be able to expand the reach of my Game Music site when I can drop the odd Native Client plugin. This JS-based player works great on Chrome, Firefox, and Safari across desktop operating systems.

But this endeavor was not without its challenges.

Programmatically Generating Audio
First, I needed to figure out the proper method for procedurally generating audio and making it available to output. Generally, there are 2 approaches for audio output:

  1. Sit in a loop and generate audio, writing it out via a blocking audio call
  2. Implement a callback that the audio system can invoke in order to generate more audio when needed

Option #1 is not a good idea for an event-driven language like JavaScript. So I hunted through the rather flexible Web Audio API for a method that allowed something like approach #2. Callbacks are everywhere, after all.

I eventually found what I was looking for with the ScriptProcessorNode. It seems to be intended to apply post-processing effects to audio streams. A program registers a callback which is passed configurable chunks of audio for processing. I subverted this by simply overwriting the input buffers with the audio generated by the Emscripten-compiled library.

The ScriptProcessorNode interface is fairly well documented and works across multiple browsers. However, it is already marked as deprecated:

Note: As of the August 29 2014 Web Audio API spec publication, this feature has been marked as deprecated, and is soon to be replaced by Audio Workers.

Despite being marked as deprecated for 8 months as of this writing, there exists no appreciable amount of documentation for the successor API, these so-called Audio Workers.

Vive la web standards!

Visualize This
The next problem was visualization. The Web Audio API provides the AnalyzerNode API for accessing both time and frequency domain data from a running audio stream (and fetching the data as both unsigned bytes or floating-point numbers, depending on what the application needs). This is a pretty neat idea. I just wish I could make the API work. The simple demos I could find worked well enough. But when I wired up a prototype to fetch and visualize the time-domain wave, all I got were center-point samples (an array of values that were all 128).

Even if the API did work, I’m not sure if it would have been that useful. Per my reading of the AnalyserNode API, it only returns data as a single channel. Why would I want that? My application supports audio with 2 channels. I want 2 channels of data for visualization.

How To Synchronize
So I rolled my own visualization solution by maintaining a circular buffer of audio when samples were being generated. Then, requestAnimationFrame() provided the rendering callbacks. The next problem was audio-visual sync. But that certainly is not unique to this situation– maintaining proper A/V sync is a perennial puzzle in real-time multimedia programming. I was able to glean enough timing information from the environment to achieve reasonable A/V sync (verify for yourself).

The next problem I encountered with the Web Audio API was pause/resume facilities, or the lack thereof. For all its bells and whistles, the API’s omission of such facilities seems most unusual, as if the design philosophy was, “Once the user starts playing audio, they will never, ever have cause to pause the audio.”

Then again, I must understand that mine is not a use case that the design committee considered and I’m subverting the API in ways the designers didn’t intend. Typical use cases for this API seem to include such workloads as:

  • Downloading, decoding, and playing back a compressed audio stream via the network, applying effects, and visualizing the result
  • Accessing microphone input, applying effects, visualizing, encoding and sending the data across the network
  • Firing sound effects in a gaming application
  • MIDI playback via JavaScript (this honestly amazes me)

What they did not seem to have in mind was what I am trying to do– synthesize audio in real time.

I implemented pause/resume in a sub-par manner: pausing has the effect of generating 0 values when the ScriptProcessorNode callback is invoked, while also canceling any animation callbacks. Thus, audio output is technically still occurring, it’s just that the audio is pure silence. It’s not a great solution because CPU is still being used.

Future Work
I have a lot more player libraries to port to this new system. But I think I have a good framework set up.

Posted in HTML5 | 3 Comments »

Dreamcast Track Sizes

February 28th, 2015 by Multimedia Mike

I’ve been playing around with Sega Dreamcast discs lately. Not playing the games on the DC discs, of course, just studying their structure. To review, the Sega Dreamcast game console used special optical discs named GD-ROMs, where the GD stands for “gigadisc”. They are capable of holding about 1 gigabyte of data.

You know what’s weird about these discs? Each one manages to actually store a gigabyte of data. Each disc has a CD portion and a GD portion. The CD portion occupies the first 45000 sectors and can be read in any standard CD drive. This area is divided between a brief data track and a brief (usually) audio track.

The GD region starts at sector 45000. Sometimes, it’s just one humongous data track that consumes the entire GD region. More often, however, the data track is split between the first track and the last track in the region and there are 1 or more audio tracks in between. But the weird thing is, the GD region is always full. I made a study of it (click for a larger, interactive graph):

Dreamcast Track Sizes

Some discs put special data or audio bonuses in the CD region for players to discover. But every disc manages to fill out the GD region. I checked up on a lot of those audio tracks that divide the GD data and they’re legitimate music tracks. So what’s the motivation? Why would the data track be split in 2 pieces like that?

I eventually realized that I probably answered this question in this blog post from 4 years ago. The read speed from the outside of an optical disc is higher than the inside of the same disc. When I inspect the outer data tracks of some of these discs, sure enough, there seem to be timing-sensitive multimedia FMV files living on the outer stretches.

One day, I’ll write a utility to take apart the split ISO-9660 filesystem offset from a weird sector.

Posted in Sega Dreamcast | 4 Comments »

Dreamcast SD Adapter and DreamShell

December 30th, 2014 by Multimedia Mike

Nope! I’m never going to let go of the Sega Dreamcast hacking. When I was playing around with Dreamcast hacking early last year, I became aware that there is such a thing as an SD card adapter for the DC that plugs into the port normally reserved for the odd DC link cable. Of course I wanted to see what I could do with it.

The primary software that leverages the DC SD adapter is called DreamShell. Working with this adapter and the software requires some skill and guesswork. Searching for these topics tends to turn up results from various forums where people are trying to cargo-cult their way to solutions. I have a strange feeling that this post might become the unofficial English-language documentation on the matter.

Use Cases
What can you do with this thing? Undoubtedly, the primary use is for backing up (ripping) the contents of GD-ROMs (the custom optical format used for the DC) and playing those backed up (ripped) copies. Presumably, users of this device leverage the latter use case more than the former, i.e., download ripped games, load them on the SD card, and launch them using DreamShell.

However, there are other uses such as multimedia playback, system exploration, BIOS reprogramming, high-level programming, and probably a few other things I haven’t figured out yet.

I put in an order via the website and in about 2 short months, the item arrived from China. This marked my third lifetime delivery from China and curiously, all 3 of the shipments have pertained to the Sega Dreamcast.

Dreamcast SD Adapter package

Click for larger image

I thought it was very interesting that this adapter came in such complete packaging. The text is all in Chinese, though the back states “Windows 98 / ME / 2000 / XP, Mac OS 9.1, LINUX2.4″. That’s what tipped me off that they must have just cannibalized some old USB SD card readers and packaging in order to create these. Closer inspection of the internals through the translucent pink case confirms this.

According to its change log, DreamShell has been around for a long time with version 1.0.0 released in February of 2004. The current version is 4.0.0 RC3. There are several downloads available:

  1. DreamShell 4.0 RC 3 CDI Image
  2. DreamShell 4.0 RC 3 + Boot Loader
  3. DreamShell 4.0 RC 3 + Core CDI image

Option #2 worked for me. It contains a CDI disc image and the DreamShell files in a directory named DS/.

Burn the CDI to a CD-R in the normal way you would burn a bootable Dreamcast disc from a CDI image. This is open-ended and left as an exercise to the reader, since there are many procedures depending on platform. On Linux, I used a small script I found once called

Then, copy the contents of the DS/ folder to an SD card. As for filesystem, FAT16 and FAT32 are both known to work. The files in DS/ should land in the root of the SD card; the folder DS/ should not be in the root.

Plug the SD card into the DC SD adapter and plug the adapter in the link cable port on the back of the Dreamcast. Then, boot the disc. If it works, you will see this minor corruption of the usual Sega licensing screen:

DreamShell logo on Dreamcast startup

Then, there will be a brief white-on-black text screen that explains the booting process:
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Posted in Sega Dreamcast | 3 Comments »

Saying Goodbye To Old Machines

November 30th, 2014 by Multimedia Mike

I recently sent a few old machines off for recycling. Both had relevance to the early days of the FATE testing effort. As is my custom, I photographed them (poorly, of course).

First, there’s the PowerPC-based Mac Mini I procured thanks to a Craigslist ad in late 2006. I had plans to develop automated FFmpeg building and testing and was already looking ahead toward testing multiple CPU architectures. Again, this was 2006 and PowerPC wasn’t completely on the outs yet– although Apple’s MacTel transition was in full swing, the entire new generation of video game consoles was based on PowerPC.

PPC Mac Mini pieces

Click for larger image

I remember trying to find a Mac Mini PPC on Craigslist. Many were to be found, but all asked more than the price of even a new Mac Mini Intel, always because the seller was leaving all of last year’s applications and perhaps including a monitor, neither of which I needed. Fortunately, I found this bare Mac Mini. Also fortunate was the fact that it was far easier to install Linux on it than the first PowerPC machine I owned.

After FATE operation transitioned away from me, I still kept the machine in service as an edge server and automated backup machine. That is, until the hard drive failed on reboot one day. Thus, when it was finally time to recycle the computer, I felt it necessary to disassemble the machine and remove the hard drive for possible salvage and then for destruction.
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Posted in General | 3 Comments »

Evolution of Multimedia Fiefdoms

September 30th, 2014 by Multimedia Mike

I want to examine how multimedia fiefdoms have risen and fallen through the years.

Medieval Castle

Back in the day, the multimedia fiefdoms were built around the formats put forth by competing companies: there was Microsoft/WMV, Apple/MOV, and Real/RM as the big contenders. On2 always wanted to be a player in this arena but could never quite catch a break. A few brave contenders held the line for open source and also for the power users who desired one application that could handle everything (my original motivation for wanting to get into multimedia hacking).

The computer desktop was the battleground for internet-based media stream. Whatever happened to those days? Actually, if memory serves, Flash-based video streaming stepped on all of them.

Over the last 6-7 years, the battleground has expanded to cover mobile devices, where Flash’s impact has… lessened. During this time, multimedia technology pretty well standardized on a particular stack, namely, the MPEG (MP4/H.264/AAC) stack.

The belligerents in this war tried for years to effectively penetrate new territory, namely, the living room where the television lived. This had been slowgoing for years due to various user interface and content issues, but steadily improved.

Last April, Amazon announced their entry into the set-top box market with the Fire TV. That was when it suddenly crystallized for me that the multimedia ecosystem has radically shifted. Now, the multimedia fiefdoms revolve around access to content via streaming services.

Off the top of my head, here are some of the fiefdoms these days (fiefdoms I have experience using):

  • Netflix (subscription streaming)
  • Amazon (subscription, rental, and purchased streaming)
  • Hulu Plus (subscription streaming)
  • Apple (rental and purchased media)

I checked some results on Can I Stream.It? (which I refer to often) and found a bunch more streaming fiefdoms such as Google (both Play and YouTube, which are separate services), Sony, Xbox 360, Crackle, Redbox Instant, Vudu, Target Ticket, Epix, Sony, SnagFilms, and XFINITY StreamPix. And surely, these are probably just services available in the United States; I know other geographical regions have their own fiefdoms.

What happened?

When I got into multimedia hacking, there were all these disparate, competing ecosystems. As a consumer, I didn’t care where the media came from, I just wanted to play it. That’s what inspired me to work on open source multimedia projects. Now I realize that I have the same problem 10-15 years later: there are multiple competing ecosystems. I might subscribe to fiefdoms X and Y, but am frustrated to learn that something I’d like to watch is only available through fiefdom Z. Very few of these fiefdoms can be penetrated using open source technology.

I’m not really sure about the point about this whole post. Multimedia technology seems really standardized these days. But that’s probably just my perspective because I have spent way too long focusing on a few areas of multimedia technology such as audio and video coding. It’s interesting that all these services probably leverage the same limited number of codecs. Their differentiation comes from the catalog of content that each is able to license for streaming. There are different problems to solve in the multimedia arena now.

Posted in General | 1 Comment »

Visualizing Call Graphs Using Gephi

August 31st, 2014 by Multimedia Mike

When I was at university studying computer science, I took a basic chemistry course. During an accompanying lab, the teaching assistant chatted me up and asked about my major. He then said, “Computer science? Well, that’s just typing stuff, right?”

My impulsive retort: “Sure, and chemistry is just about mixing together liquids and coming up with different colored liquids, as seen on the cover of my high school chemistry textbook, right?”

Chemistry fun

In fact, pure computer science has precious little to do with typing (as is joked in CS circles, computer science is about computers in the same way that astronomy is about telescopes). However, people who study computer science often pursue careers as programmers, or to put it in fancier professional language, software engineers.

So, what’s a software engineer’s job? Isn’t it just typing? That’s where I’ve been going with this overly long setup. After thinking about it for long enough, I like to say that a software engineer’s trade is managing complexity.

A few years ago, I discovered Gephi, an open source tool for graph and data visualization. It looked neat but I didn’t have much use for it at the time. Recently, however, I was trying to get a better handle on a large codebase. I.e., I was trying to manage the project’s complexity. And then I thought of Gephi again.

Prior Work
One way to get a grip on a large C codebase is to instrument it for profiling and extract details from the profiler. On Linux systems, this means compiling and linking the code using the -pg flag. After running the executable, there will be a gmon.out file which is post-processed using the gprof command.

GNU software development tools have a reputation for being rather powerful and flexible, but also extremely raw. This first hit home when I was learning how to use the GNU tool for code coverage — gcov — and the way it outputs very raw data that you need to massage with other tools in order to get really useful intelligence.

And so it is with gprof output. The output gives you a list of functions sorted by the amount of processing time spent in each. Then it gives you a flattened call tree. This is arranged as “during the profiled executions, function c was called by functions a and b and called functions d, e, and f; function d was called by function c and called functions g and h”.

How can this call tree data be represented in a more instructive manner that is easier to navigate? My first impulse (and I don’t think I’m alone in this) is to convert the gprof call tree into a representation suitable for interpretation by Graphviz. Unfortunately, doing so tends to generate some enormous and unwieldy static images.

Feeding gprof Data To Gephi
I learned of Gephi a few years ago and recalled it when I developed an interest in gaining better perspective on a large base of alien C code. To understand what this codebase is doing for a particular use case, instrument it with gprof, gather execution data, and then study the code paths.

How could I feed the gprof data into Gephi? Gephi supports numerous graphing formats including an XML-based format named GEXF.

Thus, the challenge becomes converting gprof output to GEXF.

Which I did.

I have been absent from FFmpeg development for a long time, which is a pity because a lot of interesting development has occurred over the last 2-3 years after a troubling period of stagnation. I know that 2 big video codec developments have been HEVC (next in the line of MPEG codecs) and VP9 (heir to VP8’s throne). FFmpeg implements them both now.

I decided I wanted to study the code flow of VP9. So I got the latest FFmpeg code from git and built it using the options "--extra-cflags=-pg --extra-ldflags=-pg". Annoyingly, I also needed to specify "--disable-asm" because gcc complains of some register allocation snafus when compiling inline ASM in profiling mode (and this is on x86_64). No matter; ASM isn’t necessary for understanding overall code flow.

After compiling, the binary ‘ffmpeg_g’ will have symbols and be instrumented for profiling. I grabbed a sample from this VP9 test vector set and went to work.

./ffmpeg_g -i vp90-2-00-quantizer-00.webm -f null /dev/null
gprof ./ffmpeg_g > vp9decode.txt vp9decode.txt > ~/bigdisk/vp9decode.gexf

Gephi loads vp9decode.gexf with no problem. Using Gephi, however, can be a bit challenging if one is not versed in any data exploration jargon. I recommend this Gephi getting starting guide in slide deck form. Here’s what the default graph looks like:


Not very pretty or helpful. BTW, that beefy arrow running from mid-top to lower-right is the call from decode_coeffs_b -> iwht_iwht_4x4_add_c. There were 18774 from the former to the latter in this execution. Right now, the edge thicknesses correlate to number of calls between the nodes, which I’m not sure is the best representation.

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Posted in General | 2 Comments »

Vedanti and Max Sound vs. Google

August 13th, 2014 by Multimedia Mike

Vedanti Systems Limited (VSL) and Max Sound Coporation filed a lawsuit against Google recently. Ordinarily, I wouldn’t care about corporate legal battles. However, this one interests me because it’s multimedia-related. I’m curious to know how coding technology patents might hold up in a real court case.

Here’s the most entertaining complaint in the lawsuit:

Despite Google’s well-publicized Code of Conduct — “Don’t be Evil” — which it explains is “about doing the right thing,” “following the law,” and “acting honorably,” Google, in fact, has an established pattern of conduct which is the exact opposite of its claimed piety.

I wonder if this is the first known case in which Google has been sued over its long-obsoleted “Don’t be evil” mantra?

Researching The Plaintiffs
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Posted in Legal/Ethical | 14 Comments »

Server Move For

July 31st, 2014 by Multimedia Mike

I made a big change to last week: I moved hosting from a shared web hosting plan that I had been using for 10 years to a dedicated virtual private server (VPS). In short, I now have no one to blame but myself for any server problems I experience from here on out.

The tipping point occurred a few months ago when my game music search engine kept breaking regardless of what technology I was using. First, I had an admittedly odd C-based CGI solution which broke due to mysterious binary compatibility issues, the sort that are bound to occur when trying to make a Linux binary run on heterogeneous distributions. The second solution was an SQLite-based solution. Like the first solution, this worked great until it didn’t work anymore. Something else mysteriously broke vis-à-vis PHP and SQLite on my server. I started investigating a MySQL-based full text search solution but couldn’t make it work, and decided that I shouldn’t have to either.

Ironically, just before I finished this entire move operation, I noticed that my SQLite-based FTS solution was working again on the old shared host. I’m not sure when that problem went away. No matter, I had already thrown the switch.

How Hard Could It Be?
We all have thresholds for the type of chores we’re willing to put up with and which we’d rather pay someone else to perform. For the past 10 years, I felt that administering a website’s underlying software is something that I would rather pay someone else to worry about. To be fair, 10 years ago, I don’t think VPSs were a thing, or at least a viable thing in the consumer space, and I wouldn’t have been competent enough to properly administer one. Though I would have been a full-time Linux user for 5 years at that point, I was still the type to build all of my own packages from source (I may have still been running Linux From Scratch 10 years ago) which might not be the most tractable solution for server stability.

These days, VPSs are a much more affordable option (easily competitive with shared web hosting). I also realized I know exactly how to install and configure all the software that runs the main components of the various sites, having done it on local setups just to ensure that my automated backups would actually be useful in the event of catastrophe.

All I needed was the will to do it.

The Switchover Process
Here’s the rough plan:

  • Investigate options for both VPS providers and mail hosts– I might be willing to run a web server but NOT a mail server
  • Start plotting several months in advance of my yearly shared hosting renewal date
  • Screw around for several months, playing video games and generally finding reasons to put off the move
  • Panic when realizing there are only a few days left before the yearly renewal comes due

So that’s the planning phase. BTW, I chose Digital Ocean for VPS and Zoho for email hosting. Here’s the execution phase I did last week:

  • Register with Digital Ocean and set up DNS entries to point to the old shared host for the time being
  • Once the D-O DNS servers respond correctly using a manual ‘dig’ command, use their servers as the authoritative ones for
  • Create a new Droplet (D-O VPS), install all the right software, move the databases, upload the files; and exhaustively document each step, gotcha, and pitfall; treat a VPS as necessarily disposable and have an eye towards iterating the process with a new VPS
  • Use /etc/hosts on a local machine to point DNS to the new server and verify that each site is working correctly
  • After everything looks all right, update the DNS records to point to the new server

Finally, flip the switch on the MX record by pointing it to the new email provider.

Improvements and Problems
Hosting on Digital Ocean is quite amazing so far. Maybe it’s the SSDs. Whatever it is, all the sites are performing far better than on the old shared web host. People who edit the MultimediaWiki report that changes get saved in less than the 10 or so seconds required on the old server.

Again, all problems are now my problems. A sore spot with the shared web host was general poor performance. The hosting company would sometimes complain that my sites were using too much CPU. I would have loved to try to optimize things. However, the cPanel interface found on many shared hosts don’t give you a great deal of data for debugging performance problems. However, same sites, same software, same load on the VPS is considerably more performant.

Problem: I’ve already had the MySQL database die due to a spike in usage. I had to manually restart it. I was considering a cron-based solution to check if the server is running and restart it if not. In response to my analysis that my databases are mostly read and not often modified, so db crashes shouldn’t be too disastrous, a friend helpfully reminded me that, “You would not make a good sysadmin with attitudes like ‘an occasional crash is okay’.”

To this end, I am planning to migrate the database server to a separate VPS. This is a strategy that even Digital Ocean recommends. I’m hoping that the MySQL server isn’t subject to such memory spikes, but I’ll continue to monitor it after I set it up.

Overall, the server continues to get modest amounts of traffic. I predict it will remain that way unless Dark Shikari resurrects the x264dev blog. The biggest spike that ever saw was when Steve Jobs linked to this WebM post.

Dropped Sites
There are a bunch of subdomains I dropped because I hadn’t done anything with them for years and I doubt anyone will notice they’re gone. One notable section that I decided to drop is the archive. It will live on, but it will be hosted by, which had a full mirror anyway. The lower-end VPS instances don’t have the 53 GB necessary.

Going Forward
Here’s to another 10 years of, even if multimedia isn’t as exciting as it was 10 years ago (personal opinion; I’ll have another post on this later). But at least I can get working on some other projects now that this is done. For the past 4 months or so, whenever I think of doing some other project, I always remembered that this server move took priority over everything else.

Posted in General | 3 Comments »

Reverse Engineering Italian Literature

June 30th, 2014 by Multimedia Mike

Some time ago, Diego “Flameeyes” Pettenò tried his hand at reverse engineering a set of really old CD-ROMs containing even older Italian literature. The goal of this RE endeavor would be to extract the useful literature along with any structural metadata (chapters, etc.) and convert it to a more open format suitable for publication at, e.g., Project Gutenberg or

Unfortunately, the structure of the data thwarted the more simplistic analysis attempts (like inspecting for blocks of textual data). This will require deeper RE techniques. Further frustrating the effort, however, is the fact that the binaries that implement the reading program are written for the now-archaic Windows 3.1 operating system.

In pursuit of this RE goal, I recently thought of a way to glean more intelligence using DOSBox.

Prior Work
There are 6 discs in the full set (distributed along with 6 sequential issues of a print magazine named L’Espresso). Analysis of the contents of the various discs reveals that many of the files are the same on each disc. It was straightforward to identify the set of files which are unique on each disc. This set of files all end with the extension “LZn”, where n = 1..6 depending on the disc number. Further, the root directory of each disc has a file indicating the sequence number (1..6) of the CD. Obviously, these are the interesting targets.

The LZ file extensions stand out to an individual skilled in the art of compression– could it be a variation of the venerable LZ compression? That’s actually unlikely because LZ — also seen as LIZ — stands for Letteratura Italiana Zanichelli (Zanichelli’s Italian Literature).

The Unix ‘file’ command was of limited utility, unable to plausibly identify any of the files.

Progress was stalled.

Saying Hello To An Old Frenemy
I have been showing this screenshot to younger coworkers to see if any of them recognize it:

DOSBox running Window 3.1

Not a single one has seen it before. Senior computer citizen status: Confirmed.

I recently watched an Ancient DOS Games video about Windows 3.1 games. This episode showed Windows 3.1 running under DOSBox. I had heard this was possible but that it took a little work to get running. I had a hunch that someone else had probably already done the hard stuff so I took to the BitTorrent networks and quickly found a download that had the goods ready to go– a directory of Windows 3.1 files that just had to be dropped into a DOSBox directory and they would be ready to run.

Aside: Running OS software procured from a BitTorrent network? Isn’t that an insane security nightmare? I’m not too worried since it effectively runs under a sandboxed virtual machine, courtesy of DOSBox. I suppose there’s the risk of trojan’d OS software infecting binaries that eventually leave the sandbox.

Using DOSBox Like ‘strace’
strace is a tool available on some Unix systems, including Linux, which is able to monitor the system calls that a program makes. In reverse engineering contexts, it can be useful to monitor an opaque, binary program to see the names of the files it opens and how many bytes it reads, and from which locations. I have written examples of this before (wow, almost 10 years ago to the day; now I feel old for the second time in this post).

Here’s the pitch: Make DOSBox perform as strace in order to serve as a platform for reverse engineering Windows 3.1 applications. I formed a mental model about how DOSBox operates — abstracted file system classes with methods for opening and reading files — and then jumped into the source code. Sure enough, the code was exactly as I suspected and a few strategic print statements gave me the data I was looking for.

Eventually, I even took to running DOSBox under the GNU Debugger (GDB). This hasn’t proven especially useful yet, but it has led to an absurd level of nesting:

GDB runs DOSBox runs Windows 3.1

The target application runs under Windows 3.1, which is running under DOSBox, which is running under GDB. This led to a crazy situation in which DOSBox had the mouse focus when a GDB breakpoint was triggered. At this point, DOSBox had all desktop input focus and couldn’t surrender it because it wasn’t running. I had no way to interact with the Linux desktop and had to reboot the computer. The next time, I took care to only use the keyboard to navigate the application and trigger the breakpoint and not allow DOSBox to consume the mouse focus.

New Intelligence
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Posted in Reverse Engineering | 15 Comments »

Playing With Emscripten and ASM.js

February 28th, 2014 by Multimedia Mike

The last 5 years or so have provided a tremendous amount of hype about the capabilities of JavaScript. I think it really kicked off when Google announced their Chrome web browser in September, 2008 along with its V8 JS engine. This seemed to spark an arms race in JS engine performance along with much hyperbole that eventually all software could, would, and/or should be written in straight JavaScript for maximum portability and future-proofing, perhaps aided by Emscripten, a tool which magically transforms C and C++ code into JS. The latest round of rhetoric comes courtesy of something called asm.js which purports to narrow the gap between JS and native code performance.

I haven’t been a believer, to express it charitably. But I wanted to be certain, so I set out to devise my own experiment to test modern JS performance.

Up Front Summary
I was extremely surprised that my experiment demonstrated JS performance FAR beyond my expectations. There might be something to these claims of magnficent JS speed in numerical applications. Basically, here were my thoughts during the process:

  • There’s no way that JavaScript can come anywhere close to C performance for a numerically intensive operation; a simple experiment should demonstrate this.
  • Here’s a straightforward C program to perform a simple yet numerically intensive operation.
  • Let’s compile the C program on gcc and get some baseline performance numbers.
  • Let’s use Emscripten to convert the C program to JavaScript and run it under Chrome.
  • Ha! Pitiful JS performance, just as I expected!
  • Try the same program under Firefox, since Firefox is supposed to have some crazy optimization for asm.js code, allegedly emitted by Emscripten.
  • LOL! Firefox performs even worse than Chrome!
  • Wait a minute… the Emscripten documentation mentioned using optimization levels for generating higher performance JS, so try ‘-O1′.
  • Umm… wow: Chrome’s performance increased dramatically! What about Firefox? Not only is Firefox faster than Chrome, it’s faster than the gcc-generated code!
  • As my faith in C is suddenly shaken to its core, I remembered to compile the gcc version with an explicit optimization level. The native C version pulled ahead of Firefox again, but the Firefox code is still close.
  • Aha! This is just desktop– but what about mobile? One of the leading arguments for converting everything to pure JavaScript is that such programs will magically run perfectly in mobile browsers. So I wager that this is where the experiment will fall over.
  • I proceed to try the same converted program on a variety of mobile platforms.
  • The mobile platforms perform rather admirably as well.
  • I am surprised.

The Experiment
I wanted to run a simple yet numerically-intensive and relevant benchmark, and something I am familiar with. I settled on JPEG image decoding. Again, I wanted to keep this simple, ideally in a single file because I didn’t know how hard it might be to deal with Emscripten. I found NanoJPEG, which is a straightforward JPEG decoder contained in a single C file.
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