----- On Oct 5, 2021, at 3:40 PM, rostedt rostedt@xxxxxxxxxxx wrote:
> On Tue, 5 Oct 2021 21:06:36 +0200 (CEST)
> Jan Engelhardt <jengelh@xxxxxxx> wrote:
>
>> On Tuesday 2021-10-05 20:40, Steven Rostedt wrote:
>> >>
>> >> >>>> typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p);
>> >>
>> >> #define static_cast(type, expr) ((struct { type x; }){(expr)}.x)
>> >> typeof(p) p1 = (typeof(p) __force)static_cast(void *, READ_ONCE(p));
>> >>
>> >> Let the name not fool you; it's absolutely _not_ the same as C++'s
>> >> static_cast, but still: it does emit a warning when you do pass an
>> >> integer, which is better than no warning at all in that case.
>> >>
>> >> *flies away*
>> >
>> >Are you suggesting I should continue this exercise ;-)
>>
>> “After all, why not?”
>>
>> typeof(p) p1 = (typeof(p) __force)READ_ONCE(p) +
>> BUILD_BUG_ON_EXPR(__builtin_classify_type(p) != 5);
>
> I may try it, because exposing the structure I want to hide, is pulling out
> a lot of other crap with it :-p
I like the static_cast() approach above. It is neat way to validate that the
argument is a pointer without need to dereference the pointer.
I would also be open to consider this trick for liburcu's userspace API.
About the other proposed solution based on __builtin_classify_type, I am
reluctant to use something designed specifically for varargs in a context
where they are not used.
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
