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operating-systemkernel-mode

Does Instruction Decoder check a mode bit and makes a interrupt?

I learned that a Privileged Instruction is only executed when current privileged level(CPL) is kernel mode and if not a interrupt is occurred.

And the way to check the current CPL is looking up some mode bit in registers.

I think there should be some process that check a instruction with a mode bit using some special table. And I read this process is on decode state in an unverified blog.

It is true? If not where this process is done?

I wonder where mode bits be checked.

Solution

  • Privileged Instructions are defined by CPU but operating-system.It uses a different branch to run,and hardware will do it.To be honest,you should check Intel Software Developer's Manual,but internel process is not public.