Re: System call support in reversible debugging

[Sean Chen <sean.chen1234@gmail.com>]

On Thu, Dec 3, 2009 at 1:16 AM, Jakob Engblom <jakob@virtutech.com> wrote:
>> >> Hi Michael and Hui,
>> >>
>> >> I am sorry for my late response.
>> >>
>> >> Thanks for your explanation. So we can't treat the system calls as a
>> >> black box and have to understand the detailed implementation of each
>> >> system call. I think we need to understand every lines of the code in
>> >> the system calls carefully enough, and care about the difference of
>> >> the Linux kernel since the code of system calls might change
>> >> frequently. Do we have any good ways to do it?
>> >
>> > To really do this right, you should use a full-system simulator that lets
> you
>> > debug OS and user code at the same time, as it is attacking the system at
> the
>> > hardware/software interface level.
>>
>> It all depends what you want to do.
>>
>> If you want to debug kernel code, then absolutely you need a full system
>> approach, such as Simics or VMware offers.  Similarly if you want to
>> debug the whole host.  But if you're debugging just a process (i.e. the
>> classic use-case of gdb), you may not want to wind back the state of the
>> entire (virtual) machine.  In which case, something like UndoDB or prec
>> is more appropriate.
>>
>> I don't claim either approach is superior.  It's a bit like native
>> debugging versus remote debugging.  Which one makes most sense all
>> depends on what it is you're trying to debug.
>
> Couldn't agree more.  The full-system approach is a bit more gnarly, but it
> gives you more insight.  It depends on the problem.
>
> /jakob
>
>

Hi Jakob and Greg,

You are both right. These two solutions focus on different problems.
If you want to debug a user space process and don’t care what’s going
on in the system call at all, Michael’s solution is OK. If you want to
look more closely into the kernel, a full-system simulator is
absolutely the best one.

-- 
Best Regards,
Sean Chen