RE: reverse for GDB/MI

Marc Khouzam
2009-01-20T18:22:27Z

Hi,

I am hoping this request can help restart the process
of getting the reverse MI commands approved.

I have applied the patches of Process Record and Replay
and have built myself a nice GDB that can do reverse debugging
on Linux.

I then implemented the corresponding support in DSF-GDB
(soon to be committed.) However, I ran into some MI limitations
(explanation below for those interested) which make me need
the MI Commands for Reverse debugging.

A patch for these commands was submitted in
http://sourceware.org/ml/gdb-patches/2008-12/msg00276.html
but there were many discussions after, which did not seem to
conclude.

The details of my troubles follow:

With no MI commands for Reverse I tried to use CLI commands
but ran into a bug causing incomplete MI *stopped event when using CLI commands.
http://sourceware.org/ml/gdb/2008-12/msg00058.html

As per Nick's finding, I tried Async mode to work around *stopped event bug but
realized Process Record and Replay does not support Async.

So, the solution I currently have is to use "set execution-direction" and the
MI commands for execution. For example, to perform a 'reverse-continue' from
DSF-GDB I have to do the set of three commands:

set execution-direction reverse
-exec-continue
set execution-direction forward

It would be nice to have the reverse MI commands :-)

Thanks

Marc

> -----Original Message-----
> From: gdb-patches-owner@sourceware.org
> [mailto:gdb-patches-owner@sourceware.org] On Behalf Of Jakob Engblom
> Sent: Saturday, January 03, 2009 1:09 PM
> To: gdb-patches@sources.redhat.com
> Subject: RE: reverse for GDB/MI
>
>
> > Hi,
> >
> > It was pointed out to me that people who have been doing reversible
> > debug for a while seems to
> > have specific commands for reverse debugging and they do
> have a command
> > for "go to time point P".
> > For example http://www.undo-software.com/undodb_man.html:
> >
> > bgoton <number>
> > Move forwards or backwards to the specified time, in simulated
> > nanoseconds.
> > bgoton +<number> | -<number>
> > Step forward/backward the specified number of simulated nanoseconds.
>
> Simics has it to, in some different ways:
>
> skip-to <bookmark>
> reverse n time units
> continue n time units
>
> I think this is a good example of the kind of new commands
> and abilities that
> come with having a reverse ability in the first place, like
> Marc said.
>
> And as the later discussion evolved, it would be jolly nice
> to have an idea of
> time in gdb. I think that is needed anyway to handle
> multicore, multiprocessor,
> and multithreaded debug: when things happen in disparate
> locations under the
> control of a single debugger quickly gets very interesting...
>
> Best regards,
>
> /jakob
>
> _______________________________________________________
>
> Jakob Engblom, PhD, Technical Marketing Manager
>
> Virtutech Direct: +46 8 690 07 47
> Drottningholmsvägen 14 Mobile: +46 709 242 646
> 11243 Stockholm Web: www.virtutech.com
> Sweden
> ________________________________________________________
>
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>