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Re: [RFC patch] spindep: add cross cache lines checking
- From: Alex Shi <alex dot shi at intel dot com>
- To: Arnd Bergmann <arnd at arndb dot de>
- Cc: gcc at gcc dot gnu dot org, Ingo Molnar <mingo at elte dot hu>, 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, 07 Mar 2012 21:13:45 +0800
- 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>
> 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?