It's an AB350 Gaming-ITX/ac. It turns out that not only does it not see fit to tell me the CPU's temperature, it doesn't do fan control on it either. It's entirely running on the basis of a thermistor under the socket. In 2017. On a $110 board. What the hell were they thinking?
If I were more concerned about slow noise changes than reliability, I would be almost OK with this. Instead, I'm interested in low idle noise and spinning the fans way up fast when needed. As is, they take 30+ seconds to respond to 16 threads of prime95, and that's while set to be fully ramped by 9C (nine) over idle.1 Not only that, but the sensor only finds a 17C difference between idle and full-bore prime95. My computer's environment varies seasonally by 10C. If I want anything resembling normal fan spool rate, I'm going to have to adjust my fan curves four or more times per year (and the ramp will have to be compressed into <5C, meaning huge and audibly annoying steps). All of this put together means I'm just going to have to idle my fans much higher than I would like to.
I haven't yet seen a legit temperature from this CPU. Nothing that runs on Linux knows how to ask the CPU itself (for now).
1 I didn't even set it to 16 threads. I had SMT disabled for now due to that one bug (I haven't run into it, just a preemptive measure at least until everything else is set up right), and it for some reason glitched SMT back on at that boot.