On Wed, Jun 28, 2017 at 2:24 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> On Wed, 28 Jun 2017, Dmitry Vyukov wrote:
>> On Wed, Jun 28, 2017 at 1:10 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>> > #define cmpxchg_local(ptr, old, new) \
>> > ({ \
>> > - __typeof__(ptr) ____ptr = (ptr); \
>> > - kasan_check_write(____ptr, sizeof(*____ptr)); \
>> > - arch_cmpxchg_local(____ptr, (old), (new)); \
>> > + kasan_check_write((ptr), sizeof(*(ptr))); \
>> > + arch_cmpxchg_local((ptr), (old), (new)); \
>>
>>
>> /\/\/\/\/\/\/\/\/\/\/\/\
>>
>> These are macros.
>> If ptr is foo(), then we will call foo() twice.
>
> If that's true, the foo() will be evaluated a gazillion more times down the
> way to the end of this macro maze.
No. If we do:
__typeof__(ptr) ____ptr = (ptr);
and then only use ____ptr, then ptr is evaluated only once regardless
of what the rest of macros do.
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