On 04/26, H. Peter Anvin wrote:
>
> On 04/26/2013 09:38 AM, Oleg Nesterov wrote:
> >
> > - do_debug:
> >
> > dr6 &= ~DR6_RESERVED;
> >
> > this also wrongly clears 32-63 bits. Fortunately these
> > bits are reserved and must be zero.
>
> I don't think this is wrongly at all.
OK, I meant that it also clears the bits that are not specified in
DR6_RESERVED mask.
> The whole point is to mask out
> the bits that the handler doesn't want to deal with, so masking out the
> reserved bits [63:32] seems reasonable to me.
Then we should do
- #define DR6_RESERVED 0xFFFF0FF0
+ #define DR6_RESERVED 0xFFFFFFFFFFFF0FF0
?
or what? (just in case, I will happily agree with "do nothing" ;)
> The comment should probably be corrected, though.
Which one?
/* Define reserved bits in DR6 which are always set to 1 */
#define DR6_RESERVED (0xFFFF0FF0UL)
/* Filter out all the reserved bits which are preset to 1 */
dr6 &= ~DR6_RESERVED;
I guess both should be updated then. But if I read the doc correctly
the lower reserved bits are set to 1.
However do_debug() does set_debugreg(0, 6) and this looks correct, the
doc says "debug handlers should clear the register before returning to
the interrupted task".
Oleg.
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