Re: Unsigned widening casts of binary "not" operations..
From: Lin Ming
Date: Wed Apr 24 2013 - 21:13:45 EST
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.
Sorry, but I don't have access to p4 hardware either.
> Still the patch itself is perfectly fine to me
> Reviewed-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
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