Dr7 Setting

[What]

I have been looking into setting hardware breakpoints, I googled the hell out of it, anyway, every site I go to says set dr7 to 101, which although it works, it isnt very helpful, I was wondering if anyone could explain how to set the dr7 right especially when there is more then 1 hardware breakpoint and where to put the settings for type (access, write, execute) for each breakpoint. Thank you for you time.

[GaBoR]

See Intel 64 and IA-32 Architectures Software Developer’s Manual, System Programming Guide:

http://www.intel.com/design/processor/manuals/253668.pdf

http://download.intel.com/design/processor...uals/253669.pdf

[Killboy]

Found a pretty good source in C++ which doesnt seem to edit DR7 just hardcoded but somehow calculates it.

I dont have a clue about that myself so I couldnt tell you why it is done which way.

http://www.morearty.com/code/breakpoint/breakpoint.zip

Especially look at that piece of code:

SetBits(cxt.Dr7, 16 + (m_index*4), 2, when);
SetBits(cxt.Dr7, 18 + (m_index*4), 2, len);
SetBits(cxt.Dr7, m_index*2, 1, 1);

where 'when' decides whether its hwbp on write (3) or read (1).

Not sure about execute, should be either 2 or 0

Look at breakpoint.h for the implementation of SetBits

[What]

Well, that was confusing as hell, but I think I got it, I guess you have to place 32 bits of info into 1 dword and reset the regflag. For instance if you just want to set all for breakpoints to execute on execution, you set dr7 to 257. Still a little confused. Thanks for the Intel manual and example.

Edited March 8, 2008 by What