x86 Opcode SYSRET

Opcode SYSRET

CPU: AMD K6-2,K6-3
Type of Instruction: Privelege (CPL =0)

Instruction: SYSRET

Description:

if EFER.SCE == 1
{
if CPL == 0
{
EIP <- ECX
IF <- 1
CS.selector <- STAR[47..32] OR 3H
CS.base <- 0
CS.limit <- 4GB
CS.attr <- ReadOnly
SS <- (STAR[47..32]) + 16) OR 3H
} else #GP(0);
} else #UD;

Note: Passing control from OS entry point back to ring 3 client.
see RDMSR for description of STAR (SYSCALL Target Address register)

Note: Command opcode equal to 386/486 LOADALL undocument instruction.

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COP & Times:

SYSRET 0FH 07H
Am6k86: n/a