Re: [Xen-devel] [PATCH v6 02/18] Add cmpxchg16b support for x86-64

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.09.15 at 08:07, <feng.wu@xxxxxxxxx> wrote:
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: Friday, September 04, 2015 10:23 PM
>> >>> On 25.08.15 at 03:57, <feng.wu@xxxxxxxxx> wrote:
>> > ---
>> > v6:
>> > - Fix a typo
>> >
>> > v5:
>> > - Change back the parameters of __cmpxchg16b() to __uint128_t *
>> > - Remove pointless cast for 'ptr'
>> > - Remove pointless parentheses
>> > - Use A constraint for the output
>> 
>> There are a few comments I had on v4 which neither have been
>> addressed verbally nor have got incorporated into the patch. See
>> http://lists.xenproject.org/archives/html/xen-devel/2015-07/msg04694.html 
> 
> Do you mean I missed the following part in the above link?
> 
> " But I think now I recall that it may have been me asking for using
> void pointers here: That way one can pass pointers to other types.
> But then you would better cast to void * here, and have the inline
> function have properly typed pointers. And it should go without
> saying that if you cast (or implicitly convert to void), you should
> validate that what your caller handed you is at least the size of a
> __uint128_t (and for "ptr" perhaps also, as I think Andrew already
> pointed out, that it is suitably aligned). "
> 
> If that is the case, what about the changes below?
> 
> #define cmpxchg16b(ptr,o,n)                                          \
>     ASSERT((unsigned long)ptr & 0xF == 0);                              \
>     ASSERT(sizeof(*o) == sizeof(__uint128_t))                            \
>     ASSERT(sizeof(*n) == sizeof(__uint128_t))                            \
>     __cmpxchg16b((ptr), (void *)(o), (void *)(n))

Along those lines, but with BUILD_BUG_ON() and properly
parenthesized please.

Jan


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