I have verified that creating a new DriverKit project in Xcode 12.5, adding a single .cpp file, with a single #include , fails to build with the same errors. This worked in previous Xcode versions (version 11, and version 12.4).

This appears to have been fixed in a subsequent release of Big Sur.

Can you provide a pointer to documentation on how to package an application for the app store? I'm building the app bundle outside of Xcode because the installation application and driverkit extension are separate projects. I can build either pkg or dmg for ad hoc distribution and get them notarized. What difference in that for doing an App Store submission?

A diff between the .iig.cpp files generated by Xcode 11 and Xcode 12 show that there is a substantial change at the lines where the error is indicated from the build log: 				case Comm_TxAvailable_ID: 				 {						union { 								void (Comm::*fIn)(IODataQueueDispatchSource_DataAvailable_Args); 								IODataQueueDispatchSource::DataAvailable_Handler handler; 						} map; 						map.fIn = &Comm::TxAvailable_Impl; 						ret = IODataQueueDispatchSource::DataAvailable_Invoke(rpc, self, map.handler); 						ret = IODataQueueDispatchSource::DataAvailable_Invoke(rpc, self, SimpleMemberFunctionCast(IODataQueueDispatchSource::DataAvailable_Handler, *self, &Comm::TxAvailable_Impl), OSTypeID(OSAction_Comm_TxAvailable)); 						 break; 				 } The creation of the iig.cpp files is automatic. The base class iig file is unchanged. From my perspective the only change is Xcode 11 was automatically updated to Xcode 12 and I can no longer build or test. I have verified the same behaviour on both my Catalina based development system and my Big Sur (on Intel) development system.

GetDataLength() has been deprecated, look at the DriverKit-20 API, you'll find getDataLength(). Unfortunately, Catalina does not (currently) support DriverKit-20, so you will need to compile with GetDataLength() for Catalina and getDataLength() for Big Sur. I assume that it is a bug that Big Sur returns an error for GetDataLength() as it is marked as deprecated not removed in the documentation.