Syscall/Sysret Target Address Register (Star); Figure 4. Syscall/Sysret Target Address Register (Star); Table 11. Syscall/Sysret Target Address Register (Star) Definition (Models 8, 9, And D) - AMD -K6-2/450 - MHz Processor Application Note

Embedded AMD-K6™ Processors BIOS Design Guide

SYSCALL/SYSRET Target Address Register (STAR)

63 48
SYSRET CS Selector and SS
Selector Base
Figure 4. SYSCALL/SYSRET Target Address Register (STAR) (Models 8, 9, and D)

Table 11. SYSCALL/SYSRET Target Address Register (STAR) Definition (Models 8, 9, and D)

Bit Description
SYSRET CS and SS Selector Base
63–48
SYSCALL CS and SS Selector Base
47–32
31–0 Target EIP Address
22
Preliminary Information
Models 8, 9, and D implement the STAR register. This register
contains the target EIP address used by the SYSCALL
instruction and the 16-bit code and stack segment selector
bases used by the SYSCALL and SYSRET instructions.
Figure 4 shows the format of the STAR register, and Table 11
defines the function of each field of the STAR register. The
STAR register is MSR C000_0081h.
For more information about SYSCALL/SYSRET, see the
SYSCALL and SYSRET Instruction Specification Application Note,
order# 21086.
47 32
SYSCALL CS Selector and SS
Selector Base
R/W
R/W
R/W
R/W
31
Target EIP Address
Function
During the SYSRET instruction, this field is copied into the CS
register and the contents of this field, plus 1000b, are copied
into the SS register.
During the SYSCALL instruction, this field is copied into the
CS register and the contents of this field, plus 1000b, are
copied into the SS register.
During the SYSCALL instruction, this address is copied into
the EIP and points to the new starting address.
Model 7 and Model 8/[7:0] Registers
23913A/0—November 2000
0