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[Win32 C++] How to set a hardware breakpoint?
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Dark Byte
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PostPosted: Thu Jan 25, 2018 11:01 am    Post subject: Reply with quote

dr0 to dr3 contain addresses (or IO ports but let's not go into that for now...)

and dr7 is a bitfield split up into 4 sections (of 6 bits) and 8 bits for other features (global debug, break on TRAP, debug type handing, and old stuff used for before pentium cpus)

each debugreg section specifies if it's enabled or not, and if it should keep enabled when going through intel taskswitches or not.
And it contains the length of the breakpoint (1,2,4 or 8 bytes) and the type (execute, write, read/write, io port)

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OldCheatEngineUser
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PostPosted: Thu Jan 25, 2018 11:18 am    Post subject: Reply with quote

thats interesting, i wanna read more about it.
which volume/chapter contain infos about this, im pointing to intel architecture software developers manual (ia-sdm)

also a question here about io-ports, did you meant hardware level? ie motherboard io?
if so then that means the user can also debug io's from HW-Ports?

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Dark Byte
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PostPosted: Thu Jan 25, 2018 11:31 am    Post subject: Reply with quote

Intel® 64 and IA-32 Architectures Software Developer’s Manual chapter 17

As for io-ports, no idea, I never used them, but i'm sure that windows will prevent you from setting them in usermode (just like you can't set GD)
Talking about windows, it uses the obsolete GE/LE bits for access to the debugcontrol MSR to enable single stepping to branches only

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OldCheatEngineUser
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PostPosted: Thu Jan 25, 2018 11:47 am    Post subject: Reply with quote

tons of thanks db.
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toffler
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PostPosted: Fri Jan 26, 2018 4:54 am    Post subject: Reply with quote

I finally made HWBP work, thanks Dark Byte!

To my surprise, it turned out HWBP take a lot heavier toll on the debugee than SWBP, the cost of broadcasting debug register states to all threads outweighs the punishment for flushing CPU cache in case of SWBPs, at least when you have a couple dozen threads.
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