Re: Simulating memory-mapped registers with SEH

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.language

Date:

Fri, 29 Aug 2008 09:18:17 -0400

Message-ID:

<eWhC2mdCJHA.1816@TK2MSFTNGP06.phx.gbl>

"Ulrich Eckhardt" <eckhardt@satorlaser.com> wrote in message
news:st7lo5-fuo.ln1@satorlaser.homedns.org

I'd like to simulate a register, similar to the memory-mapped IO
registers used by many embedded CPUs. Those are registers that are
connected to an integrated device but can be accessed by the normal
memory access methods for RAM.

For that, I thought I'd simply allocate a piece of virtual address
space without connecting any RAM to it. Then, when some code accesses
that address, I would expect to get an SEH notification caused by the
access violation. I would then perform the action according to the
read or write access and let the program continue. However, from what
I have seen so far, I could only let the program continue if I
actually remove the cause for the violation, i.e. connect some
storage to the virtual address, but that means that the next access
will also be able to use that storage and I don't get a second
notification.

If you feel really adventurous, you could get IP (instruction pointer)
from CONTEXT structure you get with GetExceptionInformation, emulate the
assembly instruction found at this address, and adjust IP to point to
the next instruction before returning.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925