A.5.313 SYSCALL: Call Operating System
SYSCALL ; 0F 05 [P6,AMD]
SYSCALL provides a fast method of transferring control to a fixed entry
point in an operating system.
- The EIP register is copied into the ECX register.
- Bits [31-0] of the 64-bit SYSCALL/SYSRET Target Address Register
(STAR) are copied into the EIP register.
- Bits [47-32] of the STAR register specify the selector that is
copied into the CS register.
- Bits [47-32]+1000b of the STAR register specify the selector that is
copied into the SS register.
The CS and SS registers should not be modified by the operating system
between the execution of the SYSCALL instruction and its corresponding
SYSRET instruction.
For more information, see the
"SYSCALL and SYSRET Instruction Specification" (AMD document number
21086.pdf).