Re: [uml-devel] UML and Execution Replay

["Oliver Oppitz" <o.oppitz@web.de>]

"Patrick \"Petschge\" Kilian" <petschge@web.de> 
> The only problem is, that you have to replay the input with the exact 
> correct timing.

Yes, indeed that is the more tricky part. However, there are known techniques for handling this. One involves a hardware instruction counter. Using this you can record exactly in what moment some input (e.g. an interrupt) was received. Hardware instruction counters in current CPUs are however pretty imprecise, in particular in x86. Motorola PowerPC 7410 is pretty precise.

An alternative technique is called "unique marker". When there is an interrupt you record some checksums over the register file, parts of the stack etc. For the replay you insert breakpoint instructions at all places where an interrupt had occured in the execution phase. By comparing the stored checksum with the current register file/stack you can determine "where" in the program flow you are. Obviously there is potential for ambiguity but not much. It works in practice. Henrik Thane at the MRTC (Mälardalen Real Time Research Center, http://www.mrtc.mdh.se/) works on this. 

Because I want to work on x86 I favour the latter approach. 

Regards, Oliver

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