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
struct trace_pid_list {
raw_spinlock_t lock;
struct irq_work refill_irqwork;
union upper_chunk *upper[UPPER1_SIZE]; // 1 or 2K in size
union upper_chunk *upper_list;
union lower_chunk *lower_list;
int free_upper_chunks;
int free_lower_chunks;
};
I can still abstract out the unions, but this means I need to also pull out
the define of "UPPER1_SIZE". Not to mention, I need to make sure irq_work
and spin locks are defined.
Another approach is to have it return:
struct trace_pid_list {
unsigned long ignore;
};
Rename the above struct trace_pid_list to struct trace_pid_internal.
And internally have:
union trace_pid_data {
struct trace_pid_list external;
struct trace_pid_internal internal;
};
Then use the internal version within the C file that modifies it, and just
return a pointer to the external part.
That should follow the "C standard".
-- Steve
