This is the mail archive of the
gdb@sourceware.org
mailing list for the GDB project.
Re: System call support in reversible debugging
- From: Sean Chen <sean dot chen1234 at gmail dot com>
- To: Jakob Engblom <jakob at virtutech dot com>
- Cc: Greg Law <glaw at undo-software dot com>, Hui Zhu <teawater at gmail dot com>, gdb at sourceware dot org
- Date: Thu, 3 Dec 2009 11:05:05 +0800
- Subject: Re: System call support in reversible debugging
- References: <5e81cb500911262231g57f693dwc885576172e016e1@mail.gmail.com> <5e81cb500911270742j546062f2jca7441a912ffad87@mail.gmail.com> <4B10154F.7070902@vmware.com> <5e81cb500911271745t1a119520l4944919d2139e8ae@mail.gmail.com> <4B11607C.7000500@vmware.com> <daef60380911300427p20b2e9bege4087bbcd18bc82a@mail.gmail.com> <5e81cb500911300539r52e8be5dva54d32c734978021@mail.gmail.com> <00a701ca7279$f1a03c60$d4e0b520$@com> <4B157A21.9020603@undo-software.com> <003201ca7373$29b6f590$7d24e0b0$@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