Linux Kernel Module Cheat

Analogous to QEMU’s Snapshot, but better since it can be started from inside the guest, so we can easily checkpoint after a specific guest event, e.g. just before init is done.

Documentation: http://gem5.org/Checkpoints

To see it in action try:

In the guest, wait for the boot to end and run:

where gem5 m5 executable is a guest utility present inside the gem5 tree which we cross-compiled and installed into the guest.

To restore the checkpoint, kill the VM and run:

The --gem5-restore option restores the checkpoint that was created most recently.

Let’s create a second checkpoint to see how it works, in guest:

Kill the VM, and try it out:

Here we use --gem5-restore 1 again, since the second snapshot we took is now the most recent one

Now in the guest:

contains the date. The file f wouldn’t exist had we used the first checkpoint with --gem5-restore 2, which is the second most recent snapshot taken.

If you automate things with Kernel command line parameters as in:

Then there is no need to pass the kernel command line again to gem5 for replay:

since boot has already happened, and the parameters are already in the RAM of the snapshot.