I just ran flashrom against what I believe is a
XM25QU64A and SFDP worked just fine but I got a message saying to email the output of `flashrom -VV` -- please find it attached. It's worth noting that the device I'm reading from uses XM25QU64A and GD25LQ64CWIG interchangeably so you could likely add support for the entire family.
Thanks for writing such a nifty tool.