Re: free(3) const void *

[Florian Weimer <fweimer@redhat.com>]

* Russ Allbery:

> Alejandro Colomar <alx@kernel.org> writes:
>
>> Since a `const void *` will accept anything that a `void *` would accept
>> (and more), how about changing the prototype of free() in glibc as an
>> extension to the language?
>
>> I'd like to refor free(3) to be:
>
>> 	void free(const void *p);
>
> Maybe this way of explaining the objection will help.  Right now, if you
> pass a const pointer into a function, you have some assurance from that
> prototype (assisted by compiler diagnostics) that this function will not
> modify *or invalidate* that pointer and you can continue using that
> pointer after that call.  In other words, while C does not have full
> Rust-style lifetime tracking, the const marker on a function approximately
> indicates that the caller is not passing ownership of the pointer to that
> function and the function call will not affect the pointer.

To reinforce that line of argument: GCC can warn if you pass
uninitialized memory to a function using a const void * argument,
assuming that the only reason the you do that is for the called function
to read the uninitialized object, which is probably not what is
intended.

Thanks,
Florian