Make use of the `element_count` annotation

[jvoisin]

• clang: https://reviews.llvm.org/D148381
• gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
• https://clang.llvm.org/docs/AttributeReference.html#counted-by
• https://lwn.net/Articles/930943/
• https://medium.com/@boutnaru/the-linux-kernel-macro-journey-counted-by-b1ca212c82dc

[nekopsykose]

something i noticed is that for things like e.g. fread

size_t fread(void ptr[restrict .size * .nmemb],
             size_t size, size_t nmemb,
             FILE *restrict stream);

this case is seemingly not supported (can't element_count(size*nmemb) ?)

[nekopsykose]

actually since it's for fams only it's not useful for that anyway

[nekopsykose]

hm, or is it? all the discussion talks about using it for fams, but if it's just a builtin_object_size complement then it should be usable on function args too...

[jvoisin]

Yeah, the current status of element_count is a bit confusing unfortunately. Let's wait until the dust settles and for the Linux kernel to move forward with it :P

[kees]

counted_by only currently works for flexible array members. https://opensource.googleblog.com/2024/07/bounds-checking-flexible-array-members.html
Coming next will be applying it to pointer members and for function arguments.