Re: Unsigned widening casts of binary "not" operations..

[Lin Ming]

On Wed, Apr 24, 2013 at 3:47 PM, Cyrill Gorcunov <gorcunov@xxxxxxxxxx> wrote:
> On Wed, Apr 24, 2013 at 09:26:30AM +0200, Ingo Molnar wrote:
>>
>> * Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>>
>> > And there's quite a lot of them. Even in my (fairly small) config I use on
>> > my desktop. And the first warnings I see are in x86 code:
>> >
>> >     arch/x86/kernel/traps.c:405:16: warning: implicit unsigned widening
>> > cast of a '~' expression
>> >     arch/x86/kernel/cpu/perf_event_p4.c:912:15: warning: implicit unsigned
>> > widening cast of a '~' expression
>>
>> Hm, the perf_event_p4.c code is indeed confused.
>>
>> I think the bug is real but probably benign in effect: we allow narrower
>> values into the MSR register than probably intended. Only a couple of low
>> bits are reserved AFAICS.
>>
>> Here's an (untested!) patch that tries to untangle it all: it just moves
>> to clean 64-bit types everywhere - these MSRs are 64-bit wide regardless
>> of whether we run on 32-bit or not.
>>
>> Would be nice if someone with a working P4 could test it - Cyrill? [It
>> should also be double checked whether the high words are really not
>> reserved and can be written to ...]
>
> Hi Ingo! Ufortunately I don't have access to real p4 hardware,
> thus I'm CC'ing Ming who has been helping a lot in testing
> this code pieces.

Hi,

Sorry, but I don't have access to p4 hardware either.

Lin Ming

>
> Still the patch itself is perfectly fine to me
>
> Reviewed-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
> --
> To unsubscribe from this list: send the line "unsubscribe netdev" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/