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RE: System call support in reversible debugging
- From: "Jakob Engblom" <jakob at virtutech dot com>
- To: "'Greg Law'" <glaw at undo-software dot com>
- Cc: "'Sean Chen'" <sean dot chen1234 at gmail dot com>, "'Hui Zhu'" <teawater at gmail dot com>, <gdb at sourceware dot org>
- Date: Wed, 2 Dec 2009 18:16:18 +0100
- Subject: RE: System call support in reversible debugging
- References: <5e81cb500911262231g57f693dwc885576172e016e1@mail.gmail.com> <daef60380911270004p52c53a54k53ddab9c639db066@mail.gmail.com> <5e81cb500911270711wb99d531i111d064f05ef03b4@mail.gmail.com> <daef60380911270716r44fe2efcr79930beacc1f38ed@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>
> >> 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