The PROCESS_DEVICEMAP_INFORMATION union has 2 fields, one is a handle, the other one is a structure of 36 bytes (independent of architecture). The handle forces 64 bit alignment on 64 bit builds, making the structure 4 bytes bigger than on 32 bit builds. The site is checked in NtQueryInformationProcess (case ProcessDeviceMap). The expected size on x64 is the size of the Query structure without alignment. autocheck correctly passes the site of the Query union member, while smss passes the full size of PROCESS_DEVICEMAP_INFORMATION. Packing the structure is not an option, since it is defined in public headers without packing. Using the original headers sizeof(PROCESS_DEVICEMAP_INFORMATION) is 0x28, sizeof(PROCESS_DEVICEMAP_INFORMATION::Query) is 0x24.
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