RtlLocateExtendedFeature

char *__fastcall RtlLocateExtendedFeature(_DWORD *a1, unsigned int a2, _DWORD *a3){
  return RtlLocateExtendedFeature2(a1, a2, 0xFFFFF780000003D8ui64, a3);
}

Referenced by:

PspAllocateThread
PspSetupUserShadowStack