Reversible Debugging

Patrick Sabin patrick.just4fun at
Sat Jul 4 10:33:03 CEST 2009

Horace Blegg schrieb:
> You might consider using a VM with 'save-points'. You run the program 
> (in a debugger/ida/what have you) to a certain point (logical point 
> would be if/ifelse/else statements, etc) and save the VM state. Once 
> you've saved, you continue. If you find the path you've taken isn't 
> what you are after, you can reload a previous save point and start 
> over, trying a different path the next time.
That was my idea to implement it. I thought of taking snapshots of the 
current state every time a "unredoable instruction", e.g random number 
generation, is done.  For every other instruction I count the number of 
instructions done since the last snapshot. So I can go back one 
instruction by restoring to the previous state and go the number of 
instructions minus one forward.

> This is also somewhat useful if you're trying to debug an error that 
> happens deep inside of a program, so you can continually jump to the 
> point right before the error happens, instead of needing to run 
> through the entire program each time it crashes. Just beware of tunnel 
> vision.
I think of implementing some snapshot/restore mechanism first. That may 
help in many other situations.

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