Look into finding a stable counter for determining when asynchronous events are delivered.

kallsyms / warpspeed

macOS Record Replay Debugger

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Look into finding a stable counter for determining when asynchronous events are delivered. #20

Open pmarkowsky opened 1 year ago

pmarkowsky commented 1 year ago

We need a stable counter / measurement to say when an asynchronous signal was delivered. Additionally the mechanism needs to allow us to inject an interrupt when the counter / measurement is hit for replay.

Potential Options

Use a PMU counter like retired branches like they do in RR
Use a homegrown stable timer and burn a thread like they do in the PacMan attack.

Option 1. May be easily exposed via kperf.

Resources

The PacMan Talk highlights some of the different counters in the M1.

kallsyms commented 1 year ago

thought: is the 24(?)Mhz timer accessible from userland? we can't get interrupted by it but it should be more consistent than a while(1) thread