[Bug analyzer/106854] [[gnu::malloc(deallocator)]] for non-pointer functions (e.g., fd)

[colomar.6.4.3 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106854

--- Comment #4 from Alejandro Colomar <colomar.6.4.3 at gmail dot com> ---
Hi David,

I was missing that this is to be introduced in GCC 13, which of course I still
don't have; but thanks!  It'll be a great improvement.

Still, this doesn't seem to cover all cases.  See for example the case of

       int timer_create(clockid_t clockid, struct sigevent *restrict sevp,
                        timer_t *restrict timerid);
       int timer_delete(timer_t timerid);

One needs to pair those two functions.

The case with these functions has another problem: the initialized object
(which is an arithmetic type; check clockid_t(3type) --or clockid_t(3) in older
systems--) is returned via a parameter, instead of the return value.

It would be good if a more generic attribute could be used to mark such cases. 
We would need to be careful to accept both pointers and integers, to not
unnecessarily make it unusable in some future use cases, so it could be used
for malloc(3), for open(2), for timer_create(3), and for any other functions
that one may create.

I think the following syntax would make sense:

       [[gnu::init(3, timer_delete, 1)]]
       int timer_create(clockid_t clockid, struct sigevent *restrict sevp,
                        timer_t *restrict timerid);

Where the first argument, 3, refers to the position of the parameter that is
initialized to a unique value; the second refers to the function that
deinitializes it; and the third (optional), refers to the position in the
deinitializer function where the parameter is expected.  For a function like
malloc(3) or open(2), where the initialized value is returned via the return
value, the first argument should be 0.

Does this make sense?

This would superseed the [[gnu::malloc(...)]] attribute, which would be less
confusing (having two different attributes with the same name is confusing,
IMHO).