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Re: [RFC] reverse-step, reverse-next
- From: Michael Snyder <msnyder at redhat dot com>
- To: Stan Shebs <shebs at apple dot com>
- Cc: GDB Patches <gdb-patches at sources dot redhat dot com>, jrydberg at virtutech dot com
- Date: Fri, 09 Sep 2005 15:39:36 -0700
- Subject: Re: [RFC] reverse-step, reverse-next
- References: <431F6D55.firstname.lastname@example.org> <4320AFFE.email@example.com>
Stan Shebs wrote:
Michael Snyder wrote:
This isn't for submission, just for discussion. This is something
that Johan Rydberg (of Virtutech) and I have been working on.
I'd like to hear what everybody thinks about this
bit of infrun implementation for the reverse debugging
that we discussed a few months ago.
Seems plausible to me. I've actually been experimenting with
a reverse execution prototype based on GDB managing all the
checkpoints, rather than pushing them down into the target as
Simics apparently does, and while GDB-managed checkpoints are
more powerful in some ways (random access to arbitrary states,
general undo), it's also looking rather more complicated.
Yeah, I consider this sort of abstract and modular.
My patch here makes no assumptions about how a backend
does reverse execution. The backend could, for instance,
call into a separate module such as yours that manages
checkpoints. Another backend might do it by direct request
to the target -- a la Simics.
This part is enough to get step and next to work in reverse,
based solely on the assumption that the backend (or someone)
provides an interface "get_exec_direction ()", which returns
forward or reverse. It's also assumed that the backend will
know which direction to go (leaving user-interface issues
out of the picture). One can imagine either a "set direction"
interface, or a "reverse-step/reverse-continue".
Presumably there is a set_exec_direction,
and both it and
get_exec_direction are target vector entries?
For instance. But again, this infrun code makes no assumptions.
So that decision is orthogonal -- an implementation detail.
This code would be equally useful whether
(a) the direction was set by a modal "set direction" command,
(b) the direction was set by a "reverse-step" command.
BTW, I have a little discussion of usage models for reverse
execution that I'm planning to post on Monday.
Looking forward to it.
I, in turn, have a patch to implement "reverse-finish",
which I thought I'd post a little while after this one.