A debug register substitute?

I was reading some old articles about debugging, and one of them mentioned the debug registers. Reading some more about these registers and what they can do made me incredibly eager to have some fun with them. However when I tried looking for some more information about how to actually use them I read that they can only be accessed from ring 0 in windows.

I thought that that was the end then, since I'm not going to write a kernel driver just to play with a few registers. But then I thought about the memory editing tool I used to play around with. Cheat engine it's called, and one of the various options of the program was to specify to break on instructions/data that was being executed/accessed/read. That is exactly the same as the debug registers do. So I was wondering: Is there a substitute/replacement for the debug registers in windows? Since I'm s开发者_运维技巧ure that the program (cheat engine) doesn't use a kernel driver to set these values.

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Thats not true at all, you can set HW debug register from ring3, indirectly (ollydbg does this), for this you need to use SetThreadContext under windows (example).

if you still want a substitute for HW registers, you can use INT3 for code break points and single step trapping for checking if a varibale has changed(highly inefficient).

a good reference is GDB and its source: http://developer.apple.com/library/mac/#documentation/DeveloperTools/gdb/gdbint/gdbint_3.html