pub fn stac()Expand description
Set AC flag in RFLAGS to temporarily disable SMAP.
Must be paired with clac() after the user-memory access is complete.
Only needed when CR4.SMAP is set.
#CPUID guard: QEMU TCG raises #UD on CLAC/STAC when the CPU model does
not advertise CPUID.(7,0):EBX.SMAP (e.g. plain -cpu qemu64), even
though real Ivy Bridge+ CPUs execute them unconditionally. Gate both
instructions on the detected feature so kernels built with SMAP-aware
user accessors boot on any CPU model.