System call support in reversible debugging

Greg Law glaw@undo-software.com
Tue Dec 1 20:21:00 GMT 2009


Ok, I can't resist jumping in :)

Jakob Engblom wrote:
>  
>> Hi Michael and Hui,
>>
>> I am sorry for my late response.
>>
>> Thanks for your explanation. So we canÂ’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.

Greg
-- 
Greg Law, Undo Software                       http://undo-software.com/



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