https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50584
--- Comment #11 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- On Fri, 3 Jul 2015, sergei.ivn+bugzilla at gmail dot com wrote: > Some excerpts from the C11 standard: > > /----- > If the keyword static also appears within the [ and ] of the array type > derivation, then for each call to the function, the value of the corresponding > actual argument shall provide access to the first element of an array with at > least as many elements as specified by the size expression. > \----- This is in a Semantics section, not Constraints. > I'm not sure about warnings (the meaning of the word "shall" is unclear for > me), but IMO according to the standard null-pointers should issue an *error*. "shall" is defined in clause 4, paragraph 2: 'If a "shall" or "shall not" requirement that appears outside of a constraint or runtime-constraint is violated, the behavior is undefined.' In this case, the "shall" relates to a property of an execution of a program, not a property of the program itself. Thus, undefined behavior only occurs on such an execution. In particular, a program with such a call inside if (0) - or in any code that the compiler cannot prove will always be executed for all executions of the program - must *not* produce an error at compile time. To quote the response to DR#109, "A conforming implementation must not fail to translate a strictly conforming program simply because some possible execution of that program would result in undefined behavior.". Some such cases of runtime-undefined behavior get compiled into aborts, but this is only valid if the abort only occurs when the undefined function call would definitely be executed - not, for example, before the evaluation of another argument to the function that might exit the program or call longjmp (see previous bug fixes in this regard).
