x86 Opcode SYSCALL

Opcode SYSCALL

CPU: AMD K6-2,K6-3
Type of Instruction: User

Instruction: SYSCALL

Description:

if EFER.SCE = 1 then
{ ECX <- EIP
EIP <- STAR[31..0]
IF <- 0
VM <- 0
CS.selector <- STAR[47..32]
SS.selector <- (STAR[47..32]) + 8
CS.base <- 0
SS.base <- 0
CS.limit <- 4G
SS.limit <- 4G
CS.attr <- ReadOnly
SS.attr <- R/W, Expand-Up
CPL <- 0
} else #UD;

Note: Passing control to fixed entry point for faster OS calls.
see RDMSR for description of STAR (SYSCALL Target Address register)

Note: Command opcode equal to 286 LOADALL undocument instruction.

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COP & Times:

SYSCALL 0FH 05H
Am6k86: n/a