Messages in this thread | | | Date | Fri, 26 Apr 2013 19:15:26 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v2] x86: make DR*_RESERVED unsigned long |
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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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