Deterministic Replay of QEMU Emulation

I remember we were working on this exact topic at my University chair ~8-10 years ago. I think it never fully took off. Several Master students worked on it for a while. I like that it's now in QEMU!

Tried to apply it for debugging on my own OS, but couldn’t get it finally running after several days of trial and error…<p><a href="https:&#x2F;&#x2F;github.com&#x2F;jbreu&#x2F;jos?tab=readme-ov-file#reverse-debugging-via-qemu">https:&#x2F;&#x2F;github.com&#x2F;jbreu&#x2F;jos?tab=readme-ov-file#reverse-debu...</a>

This is a big deal. With some tooling around it can be amazing.<p>I can think of using this for testing, and as a vehicle to change a programming paradigm of existing&#x2F;legacy software (run a thing, and roll it back aggressively from outside of a vm)

I think this is awesome.<p>While it might seem like a small feature, it opens a huge door. It&#x27;s similar to what reproducible build infrastructure has done for finding bugs, attestation that binary matches source, immutability, etc.<p>Can imagine this is useful for finding bugs in hardware designs too.

Anyone have clear ideas&#x2F;guidelines for how much ram&#x2F;disk&#x2F;etc this is likely to need for a &quot;reasonable&quot; capture?<p>Say capturing a Qt application as it corrupts its internal state during startup, in order to work out what&#x27;s corrupting its internal state?

Such a casual and low-key introduction of what sounds like an incredible new capability.<p>1 . Would something like this replace packer for creating machine images?<p>2. Curious how quickly the replay log grows and how it compares to a CoW snapshot.<p>3. Will be interesting what the log looks like and what doors could open up creating or generating it by other means.

Seems to me like one of the highest and best uses of this right now would be adding verifiable builds to … literally anything. You no longer need a verifiable-build-capable compiler or language — you can just run the compile and packaging step through a deterministic QEMU session.<p>Does this sound right? I’m trying to figure out where uncontrollable randomness would come in during a compile phase, and coming up blank.

VMware had this many years ago; it was very cool:<p><a href="http:&#x2F;&#x2F;stackframe.blogspot.com&#x2F;2007&#x2F;10&#x2F;configuring-application-debugging-with.html" rel="nofollow">http:&#x2F;&#x2F;stackframe.blogspot.com&#x2F;2007&#x2F;10&#x2F;configuring-applicati...</a><p><a href="http:&#x2F;&#x2F;www.replaydebugging.com&#x2F;2008&#x2F;08&#x2F;vmware-workstation-65-reverse-and.html" rel="nofollow">http:&#x2F;&#x2F;www.replaydebugging.com&#x2F;2008&#x2F;08&#x2F;vmware-workstation-65...</a>