[Bug c/108896] provide "element_count" attribute to give more context to __builtin_dynamic_object_size() and -fsanitize=bounds

[muecker at gwdg dot de via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896

--- Comment #34 from Martin Uecker <muecker at gwdg dot de> ---
Created attachment 54787
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54787&action=edit
patch for C FE to add size expressions to VM types in structs


Here is a preliminary patch for C FE just to see how this could work
look like VM-types in structs.

struct foo {
  int n;
  int (*buf)[.n];
};

It works with UBSan, but it isn't clear how this could pass the
information to the object size pass. This also does not work for
parameters: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109334

So it seems for an attribute it might make sense to implement
it differently.