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Difference between revisions of "HOWTO-Reverse Engineering"
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HOWTO-Reverse Engineering (view source)
Revision as of 19:48, 20 January 2018
, 19:48, 20 January 2018Added a miscellaneous section
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The 2> causes a redirection of the stderr output to a file. Afterwards, I was able to compare the result with a similar output from ScummVM. With differences identified, I could set up a conditional breakpoint in ScummVM in the engine's adlib write method for the last call before wrong values started being written, and stepped through the code until I figured out what the engine was doing incorrectly. | The 2> causes a redirection of the stderr output to a file. Afterwards, I was able to compare the result with a similar output from ScummVM. With differences identified, I could set up a conditional breakpoint in ScummVM in the engine's adlib write method for the last call before wrong values started being written, and stepped through the code until I figured out what the engine was doing incorrectly. | ||
== Miscellaneous == | |||
This is a small section of miscellaneous tips and musings to help you as you reverse engineer games | |||
* Don't get too bogged down in the minutiae of what methods do.. it's sometimes best to just get a high level understanding and then implement your own code from scratch. For example, several games I've reversed had complicated logic as part of loading resources to allocate memory handles and reserve space in extended/expanded memory. Obviously this isn't something you need to worry about in your reimplementation anyway. It was enough to know the resource method returned a pointer to the data, and callers were responsible for calling a free method when they were done with it. So all the extra logic could be ignored in favor of simple C new byte[..] and delete[] calls. | |||
* In a similar vein, drawing code in EGA or earlier based games can be particularly labyrinthine. Since you'd be more likely to set up an 8-bit per pixel graphics surface when reimplementing such games, it may be simpler for you to experiment with your own implementation of drawing methods based on examining the raw data. EGA in particular had a nasty graphic layout, with single bytes represent parts of multiple pixels, and port usage to control what portion of the pixels' values were modified. This can make it complex to understand what original drawing code is. And frequently data will be passed to such drawing methods using one pixel per byte, or two pixels per byte in any case. So taking a stab at it yourself first may end up saving time. | |||
* Visual Studio (but alas not IDA) has a nice feature where if you hold down Alt whilst dragging the cursor, you can select a square area of text to copy. I've found this very helping when copying arrays of static data to create arrays. If you've copied a raw block of memory from DosBox, you can paste it into Visual Studio and then Alt-drag the cursor down along the start of all the lines. Then when you can start putting sequences of ', 0x' between the byte values and have it be applied on all the lines. This saves a lot of time converting the data to a properly formatted C array. | |||
== Final Words == | == Final Words == | ||