https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68065
--- Comment #20 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- Undefined behavior when the type is created (not when an object of that type is declared or when sizeof is used) seems entirely in accordance with normal C practice in areas such as stack overflow[*] (that is, where the C standard fails to recognize limits in such areas but all implementations in practice have such limits, that's a defect in the C standard). [*] The existence of stack limits cannot be deduced from the argument that all objects in C are required by the C standard to have addresses, because you can recurse, and even do Turing-complete computation, without creating any new objects. Cf. <http://www.open-std.org/jtc1/sc22/wg14/12727>. One way (for C) to get a check that is evaluated at the point where the size of the type is evaluated is to hook into how grokdeclarator stores array size expressions in *expr (other parts of the front end then ensure that *expr is evaluated at exactly the right time). Instead of storing plain size expressions, it would be necessary to store a more complicated expression containing the checks. *And* it would be necessary to put checks in there for the case where a constant-size array is declared but the elements of that array are of variable size, to make sure that overflow in the multiplication is detected in that case (right now, *expr is used only for variable size expressions, because they might have side effects so the time of evaluation matters). This applies regardless of what the conditions are for when to enable such a check.
