Thanks to igorsk for informing me that DataRescue has made an updated version of IDA Pro available as freeware. No longer must we suffer the quirks of the old freeware version 4.3– we get to learn a whole new set of idiosyncrasies with 4.9.
The sales folks at DataRescue told me that this freeware release was in the works– to pacify me when they refused to sell me a license for the full version of IDA Pro. Interesting business model.
Dear Nano: You know I love you. You are the GPL’d heir to the old UW-Pine-derived Pico editor, my text-editing savior when I was unceremoniously thrust onto the Unix command line early in my computer science education and told to write a program.
However, clever error messages may seem funny to you but are actually aggravating to the end user due to their failure to actually articulate what went wrong:
This is not helpful when a user is trying to be productive and honestly has no idea what misstep just occurred. Fortunately, I have been using using GNU Nano long enough to know that “Come on, be reasonable” usually means that, rather than pressing Ctrl-W to search for text, I mistakenly pressed Ctrl-/ (go to line number) and entered a non-numeric value.
I wonder if non-English-speaking users have to put up with the same error message? Using my limited ability to interpret non-English languages, I delved into the .po files in the Nano source. Well, what do you know?
de.po:
msgid "Come on, be reasonable" msgstr "Komm schon, sei vernünftig"
fr.po:
msgid "Come on, be reasonable" msgstr "Allez, soyez raisonnable"
it.po:
msgid "Come on, be reasonable" msgstr "Avanti, sii ragionevole"
This is especially egregious since “come on” is literally translated and I doubt that the idiom has the same connotation in other languages.
Thankfully, a brief perusal of the other msgid strings does not immediately reveal any other unintuitive errors. As a bonus, I just figured out that Nano must have a bracket-matching feature due the presence of such strings as “Not a bracket” and “No matching bracket”.
Here’s the complete, do-it-yourself instructions and code for that re-targeting experiment. First, the files:
The re-targeter wants to process code like that found in function.txt. This is the disassembly format output by my favorite Win32 PE disassembler, Sang Cho’s Disassembler. I knew in advance that the function expects 4 parameters, and that fact is hardcoded in the re-targeter along with the file name. The testbench.c file contains the opcodes for the original function and allows the programmer to switch between the original opcodes and the re-targeted code for verification.
To run this experiment:
The testbench.c program simulates the data structure that the re-targeted bitreading function expects, along with a bitstream that looks like 0xA5, 0x5A repeated. Running the program should result in:
12 bits = A55 4 bits = A
If compiling on x86_32, you can switch the “#if 0” to “#if 1” in order to test the original opcodes.
I took a stab at making the re-targeter portable to a big endian platform, as brainstormed last night. However, I soon realized what my hastily scrawled, year-old note about that task’s difficulty must have warned about– the outlined approach works for source arguments, but is not as straightforward for destination arguments.
I don’t have immediate access to an x86_64/Linux environment, but I would like to know if the re-targeted code compiles on that platform. The entire point of a re-targeter is to run code on a different platform, though I suppose alternate operating systems on the same CPU architecture is another interpretation.
So, of course the re-targeter is super-naive in its current form. It only implements enough instructions to handle that one function in function.txt. It does not handle branching at all. In order to do so, each of the instruction emitters would also need to output the code that adjusts the appropriate flags after each arithmetic instruction. Then, a branch would map to a simple goto with the correct address label.
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It was nearly a year ago that I tried my hand at writing a re-targeter — a program that can take machine opcodes and automatically translate them into a portable C program, which certainly sounds simple and intuitive enough. I was really quite busy last year about this time and I don’t remember how I found time for the re-targeter experiment in the first place. But it looks like I had time to write up some notes that I never fleshed out and published. It was hard enough just to locate the old source code. I was completely surprised to find that I had actually managed to write the re-targeter in Python; I had no idea I knew so much of that language (which, granted, isn’t much).
Here are some of the problems I encountered when I took a stab at writing a re-targeter; let’s see if I can remember the specifics a year later: