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7-22 Vol. 3
TASK MANAGEMENT
7.7 TASK MANAGEMENT IN 64-BIT MODE
In 64-bit mode, task structure and task state are similar to those in protected mode.
However, the task switching mechanism available in protected mode is not supported
in 64-bit mode. Task management and switching must be performed by software.
The processor issues a general-protection exception (#GP) if the following is
attempted in 64-bit mode:
• Control transfer to a TSS or a task gate using JMP, CALL, INTn, or interrupt.
• An IRET with EFLAGS.NT (nested task) set to 1.
Figure 7-10. 16-Bit TSS Format
Task LDT Selector
DS Selector
SS Selector
CS Selector
ES Selector
DI
SI
BP
SP
BX
DX
CX
AX
FLAG Word
IP (Entry Point)
SS2
SP2
SS1
SP1
SS0
SP0
Previous Task Link
15
0
42
40
36
34
32
30
38
28
26
24
22
20
18
16
14
12
10
8
6
4
2
0