Re: [PATCH] x86: make DR*_RESERVED unsigned long

From: H. Peter Anvin
Date: Wed Apr 24 2013 - 21:21:31 EST

On 04/24/2013 04:31 PM, Frederic Weisbecker wrote:
>> Now, DR6 is a bit special in that a bunch of the reserved bits are
>> hardwired to 1, not 0; I don't know offhand if that is true for bits
>> [63:32].
> Hmm, good point, could it be a problem given that we clear the
> reserved dr6 bits on do_trap() and write that 'cleaned up" value back
> to "tsk->thread.debugreg6"? Probably not if those hardwired reserved
> bits are set to "1" on dr6 physical write whether those bits are
> cleared or not in their storage in thread struct before resuming the
> task?

OK, the SDM states that DR6[63:32] are reserved and must be written as
zero (not one).

So the quiescent 64-bit value of DR6 is 0x0000_0000_FFFF_0FF0.


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