what's the xor stuff that's happening in rc0.12? can I turn it off, or is it needed for the pre check script?

It is xoring the gds streamed by magic versus the gds streamed by klayout. I think

RUN_KLAYOUT_XOR

should disable it. And, it isn't needed for the precheck.

right, so openlane is currently generating gds with both magic and klayout. Then the xor is just comparing the 2 to make sure they're the same.