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INSTRUCTION SET REFERENCE
SYSENTER—Fast Transition to System Call Entry Point
(Continued)
The presence of this facility is indicated by the SYSENTER Present (SEP) bit 11 of CPUID. An
operating system that detects the presence of the SEP bit must also qualify the processor family
and model to ensure that the SYSENTER/SYSEXIT instructions are actually present. For
example:
IF (CPUID SEP bit is set)
IF (Family == 6) AND (Model < 3) AND (Stepping < 3)
THEN
Fast System Call NOT supported
FI;
ELSE Fast System Call is supported
FI
The Pentium
®
Pro processor (Model = 1) returns a set SEP CPUID feature bit, but does not
support the SYSENTER/SYSEXIT instructions.
