Print Page - Toggling bits in FLAGS ?

Title: Toggling bits in FLAGS ?
Post by: Slugsnack on June 08, 2008, 12:50:46 PM

I was curious as to how I might read and write bits from the EFLAGS register after a certain instruction had executed (at a given virtual address).

I was thinking GetThreadContext/SetThreadContext, have I got my head turned in the right direction ?

Title: Re: Toggling bits in FLAGS ?
Post by: jj2007 on June 08, 2008, 03:30:48 PM

pushfd
pop eax
bt eax, n

Title: Re: Toggling bits in FLAGS ?
Post by: Slugsnack on June 08, 2008, 05:30:14 PM

Thanks, I have not come across bit instructions like this before so I'll need to do a bit of reading ::)

Do you have any idea how I could do this for another thread without "hooking" it with a JMP ?

Title: Re: Toggling bits in FLAGS ?
Post by: jj2007 on June 08, 2008, 05:39:56 PM

OllyDbg shows the flags.

Title: Re: Toggling bits in FLAGS ?
Post by: Slugsnack on June 08, 2008, 05:59:34 PM

Yeap, that's exactly what I want to reproduce. Olly is able to step onto any instruction and then you can change flag states at that point. I was hoping to do the same thing but not sure how to go about doing it.

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General Forums => The Campus => Topic started by: Slugsnack on June 08, 2008, 12:50:46 PM