Messages in this thread | | | Subject | Re: Fetching a value of control registers from user space | From | Josip Gracin <> | Date | 05 Jan 1999 20:11:25 +0100 |
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Thanks everybody who responsed to my question.
Richard B. Johnson (root@chaos.analogic.com) wrote: > Quote: (Intel 26-212) > MOV to/from Special Registers. > #GP(0) if current privilege level is not 0. > This is a general protection violation. No user-mode program would > (should) ever use these instructions.
Oh, I see.
I thought otherwise because of the following paragraph in the Intel Programmer's Manual for i486 which I've downloaded perhaps a year ago from Intel's site:
Chapter 2, System Architecture Overview
2.5. CONTROL REGISTERS ... In protected mode, the move-to-or-from-control-registers forms of the MOV instruction allow the control registers to be read (at any privilege level) or loaded (at privilege level 0 only). This restriction means that application programs (running at privilege levels 1, 2, or 3) are prevented from loading the control registers; however, application programs can read these registers. For example, an application might need to read register CR0 to determine if an FPU is present. ...
Regards, -- | Josip Gracin | Zagreb, Croatia
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