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Re: [RFC patch] spindep: add cross cache lines checking
- From: Ingo Molnar <mingo at elte dot hu>
- To: Alex Shi <alex dot shi at intel dot com>
- Cc: Arnd Bergmann <arnd at arndb dot de>, gcc at gcc dot gnu dot org, tglx at linutronix dot de, "mingo at redhat dot com" <mingo at redhat dot com>, hpa at zytor dot com, akpm at linux-foundation dot org, linux-kernel at vger dot kernel dot org, x86 at kernel dot org, andi dot kleen at intel dot com, gcc-help at gcc dot gnu dot org
- Date: Wed, 7 Mar 2012 14:39:37 +0100
- Subject: Re: [RFC patch] spindep: add cross cache lines checking
- References: <1330917630.18835.44.camel@debian> <201203060932.45223.arnd@arndb.de> <1331108607.18835.343.camel@debian> <201203071154.36059.arnd@arndb.de> <4F575F09.3010107@intel.com>
* Alex Shi <alex.shi@intel.com> wrote:
> > I think the check should be (__alignof__(lock) <
> > __alignof__(rwlock_t)), otherwise it will still pass when
> > you have structure with attribute((packed,aligned(2)))
>
> reasonable!
>
> >> 1, it is alignof bug for default gcc on my fc15 and Ubuntu 11.10 etc?
> >>
> >> struct sub {
> >> int raw_lock;
> >> char a;
> >> };
> >> struct foo {
> >> struct sub z;
> >> int slk;
> >> char y;
> >> }__attribute__((packed));
> >>
> >> struct foo f1;
> >>
> >> __alignof__(f1.z.raw_lock) is 4, but its address actually can align on
> >> one byte.
> >
> > That looks like correct behavior, because the alignment of
> > raw_lock inside of struct sub is still 4. But it does mean
> > that there can be cases where the compile-time check is not
> > sufficient, so we might want the run-time check as well, at
> > least under some config option.
>
> what's your opinion of this, Ingo?
Dunno. How many real bugs have you found via this patch?
Thanks,
Ingo