This content has not been validated; it was AI-generated following the x86-64 ISA Documentation generation process to maintain high quality. However, as no human has verified this data, errors may exist. If the accuracy of this data is critical, please consult the Intel SDM. The model used to generate this is gemma4:31b

SYSENTER

SYSENTER transfers execution to the system entry point specified by the MSR_SYSENTER_CS, MSR_SYSENTER_EIP, and MSR_SYSENTER_ESP Model Specific Registers. It switches the processor to the privilege level specified in MSR_SYSENTER_CS and sets the instruction pointer to the value in MSR_SYSENTER_EIP.

The table after the description covers what the source and destinations can be.

DO NOT support LOCK

In x86-64 architecture, SYSENTER is ONLY available in compatibility mode. It SHALL NOT be used in 64-bit mode; the SYSCALL instruction MUST be used instead for fast system calls in 64-bit mode.

The instruction DOES NOT save the return address (RIP) or the current stack pointer (RSP) to the stack or a register. The software MUST implement a mechanism to save the return address if it is required. Because it relies on Model Specific Registers, the OS MUST properly initialize MSR_SYSENTER_CS, MSR_SYSENTER_EIP, and MSR_SYSENTER_ESP before the instruction is executed to avoid unpredictable behavior or processor faults.