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• Resurrecting SCD

  6 août 2010, par Multimedia Mike — Reverse Engineering

  When I became interested in reverse engineering all the way back in 2000, the first Win32 disassembler I stumbled across was simply called "Win32 Program Disassembler" authored by one Sang Cho. I took to calling it ’scd’ for Sang Cho’s Disassembler. The original program versions and source code are still available for download. I remember being able to compile v0.23 of the source code with gcc under Unix ; 0.25 is no go due to extensive reliance on the Win32 development environment.

  I recently wanted to use scd again but had some trouble compiling. As was the case the first time I tried compiling the source code a decade ago, it’s necessary to transform line endings from DOS -> Unix using ’dos2unix’ (I see that this has been renamed to/replaced by ’fromdos’ on Ubuntu).

  Beyond this, it seems that there are some C constructs that used to be valid but are now rejected by gcc. The first looks like this :

  PLAIN TEXT

  C :

  1. return (int) c = *(PBYTE)((int)lpFile + vCodeOffset) ;

  Ahem, "error : lvalue required as left operand of assignment". Removing the "(int)" before the ’c’ makes the problem go away. It’s a strange way to write a return statement in general. However, ’c’ is a global variable that is apparently part of some YACC/BISON-type output.

  The second issue is when a case-switch block has a default label but with no code inside. Current gcc doesn’t like that. It’s necessary to at least provide a break statement after the default label.

  Finally, the program turns out to not be 64-bit safe. It is necessary to compile it in 32-bit mode (compile and link with the ’-m32’ flag or build on a 32-bit system). The static 32-bit binary should run fine under a 64-bit kernel.

  Alternatively : What are some other Win32 disassemblers that work under Linux ?

• Brute Force Dimensional Analysis

  15 juillet 2010, par Multimedia Mike — Game Hacking, Python

  I was poking at the data files of a really bad (is there any other kind ?) interactive movie video game known simply by one letter : D. The Sega Saturn version of the game is comprised primarily of Sega FILM/CPK files, about which I wrote the book. The second most prolific file type bears the extension ’.dg2’. Cursory examination of sample files revealed an apparently headerless format. Many of the video files are 288x144 in resolution. Multiplying that width by that height and then doubling it (as in, 2 bytes/pixel) yields 82944, which happens to be the size of a number of these DG2 files. Now, if only I had a tool that could take a suspected raw RGB file and convert it to a more standard image format.

  Here’s the FFmpeg conversion recipe I used :

   ffmpeg -f rawvideo -pix_fmt rgb555 -s 288x144 -i raw_file -y output.png
  

  So that covers the files that are suspected to be 288x144 in dimension. But what about other file sizes ? My brute force approach was to try all possible dimensions that would yield a particular file size. The Python code for performing this operation is listed at the end of this post.

  It’s interesting to view the progression as the script compresses to different sizes :

  
  
  

  That ’D’ is supposed to be red. So right away, we see that rgb555(le) is not the correct input format. Annoyingly, FFmpeg cannot handle rgb555be as a raw input format. But this little project worked well enough as a proof of concept.

  If you want to toy around with these files (and I know you do), I have uploaded a selection at : http://multimedia.cx/dg2/.

  Here is my quick Python script for converting one of these files to every acceptable resolution.

  work-out-resolution.py :
  

  PLAIN TEXT

  PYTHON :

  1. # !/usr/bin/python
  2.  
  3. import commands
  4. import math
  5. import os
  6. import sys
  7.  
  8. FFMPEG = "/path/to/ffmpeg"
  9.  
  10. def convert_file(width, height, filename) :
  11.  outfile = "%s-%dx%d.png" % (filename, width, height)
  12.  command = "%s -f rawvideo -pix_fmt rgb555 -s %dx%d -i %s -y %s" % (FFMPEG, width, height, filename, outfile)
  13.  commands.getstatusoutput(command)
  14.  
  15. if len(sys.argv) <2 :
  16.  print "USAGE : work-out-resolution.py <file>"
  17.  sys.exit(1)
  18.  
  19. filename = sys.argv[1]
  20. if not os.path.exists(filename) :
  21.  print filename + " does not exist"
  22.  sys.exit(1)
  23.  
  24. filesize = os.path.getsize(filename) / 2
  25.  
  26. limit = int(math.sqrt(filesize)) + 1
  27. for i in xrange(1, limit) :
  28.  if filesize % i == 0 and filesize & 1 == 0 :
  29.   convert_file(i, filesize / i, filename)
  30.   convert_file(filesize / i, i, filename)

• Monster Battery Power Revisited

  28 mai 2010, par Multimedia Mike — Python, Science Projects

  So I have this new fat netbook battery and I performed an experiment to determine how long it really lasts. In my last post on the matter, it was suggested that I should rely on the information that gnome-power-manager is giving me. However, I have rarely seen GPM report more than about 2 hours of charge ; even on a full battery, it only reports 3h25m when I profiled it as lasting over 5 hours in my typical use. So I started digging to understand how GPM gets its numbers and determine if, perhaps, it’s not getting accurate data from the system.

  I started poking around /proc for the data I wanted. You can learn a lot in /proc as long as you know the right question to ask. I had to remember what the power subsystem is called — ACPI — and this led me to /proc/acpi/battery/BAT0/state which has data such as :

  present :                 yes
  capacity state :          ok
  charging state :          charged
  present rate :            unknown
  remaining capacity :      100 mAh
  present voltage :         8326 mV
  

  "Remaining capacity" rated in mAh is a little odd ; I would later determine that this should actually be expressed as a percentage (i.e., 100% charge at the time of this reading). Examining the GPM source code, it seems to determine as a function of the current CPU load (queried via /proc/stat) and the battery state queried via a facility called devicekit. I couldn’t immediately find any source code to the latter but I was able to install a utility called ’devkit-power’. Mostly, it appears to rehash data already found in the above /proc file.

  Curiously, the file /proc/acpi/battery/BAT0/info, which displays essential information about the battery, reports the design capacity of my battery as only 4400 mAh which is true for the original battery ; the new monster battery is supposed to be 10400 mAh. I can imagine that all of these data points could be conspiring to under-report my remaining battery life.

  Science project : Repeat the previous power-related science project but also parse and track the remaining capacity and present voltage fields from the battery state proc file.

  Let’s skip straight to the results (which are consistent with my last set of results in terms of longevity) :

  
  
  

  So there is definitely something strange going on with the reporting— the 4400 mAh battery reports discharge at a linear rate while the 10400 mAh battery reports precipitous dropoff after 60%.

  Another curious item is that my script broke at first when there was 20% power remaining which, as you can imagine, is a really annoying time to discover such a bug. At that point, the "time to empty" reported by devkit-power jumped from 0 seconds to 20 hours (the first state change observed for that field).

  Here’s my script, this time elevated from Bash script to Python. It requires xdotool and devkit-power to be installed (both should be available in the package manager for a distro).
  

  PLAIN TEXT

  PYTHON :

  1. # !/usr/bin/python
  2.  
  3. import commands
  4. import random
  5. import sys
  6. import time
  7.  
  8. XDOTOOL = "/usr/bin/xdotool"
  9. BATTERY_STATE = "/proc/acpi/battery/BAT0/state"
  10. DEVKIT_POWER = "/usr/bin/devkit-power -i /org/freedesktop/DeviceKit/Power/devices/battery_BAT0"
  11.  
  12. print "count, unixtime, proc_remaining_capacity, proc_present_voltage, devkit_percentage, devkit_voltage"
  13.  
  14. count = 0
  15. while 1 :
  16.   commands.getstatusoutput("%s mousemove %d %d" % (XDOTOOL, random.randrange(0,800), random.randrange(0, 480)))
  17.   battery_state = open(BATTERY_STATE).read().splitlines()
  18.   for line in battery_state :
  19.     if line.startswith("remaining capacity :") :
  20.       proc_remaining_capacity = int(line.lstrip("remaining capacity : ").rstrip("mAh"))
  21.     elif line.startswith("present voltage :") :
  22.       proc_present_voltage = int(line.lstrip("present voltage : ").rstrip("mV"))
  23.   devkit_state = commands.getoutput(DEVKIT_POWER).splitlines()
  24.   for line in devkit_state :
  25.     line = line.strip()
  26.     if line.startswith("percentage :") :
  27.       devkit_percentage = int(line.lstrip("percentage :").rstrip(’\%’))
  28.     elif line.startswith("voltage :") :
  29.       devkit_voltage = float(line.lstrip("voltage :").rstrip(’V’)) * 1000
  30.   print "%d, %d, %d, %d, %d, %d" % (count, time.time(), proc_remaining_capacity, proc_present_voltage, devkit_percentage, devkit_voltage)
  31.   sys.stdout.flush()
  32.   time.sleep(60)
  33.   count += 1