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SubjectRe: Possible bug in arch/i386/kernel/process.c for reloading of debug registers (DRx)?
> 	- However, DR6 bit B0 is now set.

You cannot detect it. Linux offers no way to read DR6 from user space
as far as I can see. The only way to handle break points is to catch
the signals caused by the debug exceptions.

Yo access debug registers you need to use ptrace from another process.
ptrace only ever returns cached values in tsk->thread, but the register is
never stored in there.

So in fact __switch_to could drop the loaddebug(next, 6) because it is
useless.

-Andi
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