<pre>
[0 :15] addr[0:15]
[16:31] segment selector: must point to valid code segment in GDT
[32:39] ist: index into Interrupt Stack Table; only lower 3 bit used,
other bits are reserved to 0
[40:47] attrs: attributes of the call gate:
[0:3] - Gate Type: 0xe for interrupt and 0xf for trap
[ 4 ] - Res0
[5:6] - DPL: allowed privilege levels (via INT)
[ 7 ] - Present (Valid)
[48:63] - addr[16:31]
[64:95] - addr[32:63]