How to use a 64-bit call

Question

The software developer for intelligent software supports call commands:

call r/m64
call m16:32
call m16:64

In user code, if I want to pass ring 0 through a 64-bit call-gate with selector 47. How do I write instructions in an assembly using intel syntax?

Tested:

call far [mem]; wrong
call qword ptr [mem]; wrong

Memory contents:

[mem + 0]: qword 0x00
[mem + 8]: word 47

Answer 1

- fword ptr. m16:32, 64 RIP , . , m16:64, REX, rex64 call fword ptr [mem] rex.w call fword ptr [mem].