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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.09.15 at 10:57, <feng.wu@xxxxxxxxx> wrote:

> 
>> -----Original Message-----
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: Tuesday, September 08, 2015 4:52 PM
>> To: Wu, Feng
>> Cc: Andrew Cooper; xen-devel@xxxxxxxxxxxxx; Keir Fraser
>> Subject: RE: [PATCH v6 02/18] Add cmpxchg16b support for x86-64
>> 
>> >>> On 08.09.15 at 09:37, <feng.wu@xxxxxxxxx> wrote:
>> > Thanks for your suggestion. How about this?
>> >
>> > #define cmpxchg16b(ptr,o,n)
>> \
>> >     ( ({ ASSERT(((unsigned long)ptr & 0xF) == 0); }),                  \
>> >       BUILD_BUG_ON(sizeof(*o) != sizeof(__uint128_t)),
>> \
>> >       BUILD_BUG_ON(sizeof(*n) != sizeof(__uint128_t)),
>> \
>> >       __cmpxchg16b((ptr), (__uint128_t *)(o), (__uint128_t *)(n)) )
>> 
>> Yes (properly parenthesized and the ({ }) either removed or extended
> 
> We need the ({ }) for the ASSERT statement, or we will meet build error.

And note that I didn't unconditionally say drop it, I provided the
alternative of making it cover the entire expression (at once allowing
you to convert the comma expressions to more conventional individual
statements).

Jan


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