------- Additional Comments From joseph at codesourcery dot com 2004-11-10
01:41 -------
Subject: Re: Warning not legitimate
On Wed, 10 Nov 2004, manus at eiffel dot com wrote:
> I believe we do not have the right definition of unspecified behavior. Going
We're talking about undefined behavior (e.g. your computer, or the whole
universe, may blow up) rather than unspecified (bounded variation on what
may happen).
> extern void f();
> Knowing that actually `f' has been declared in some other module as:
> extern void f(char){...}
Those types are incompatible, 6.7.5.3#15, so you have undefined behavior
by 6.2.7#2. In that case - if the compiler can see both the declaration
and definition in different translation units at once - it is compile-time
undefined (a property of the program, rather than of some execution path,
is undefined), so the program can be rejected. But when compiling only
the translation unit with the unprototyped declaration, it's possible that
(a) the call through the cast pointer is never executed, (b) the real
definition is of a compatible type e.g. void f(void) { ... } so there is
only undefined behavior on execution, not compilation. What is true is
that given the first translation unit with call through a cast to an
incompatible type, the behavior on execution of the call is guaranteed to
be undefined if the behavior on translation wasn't already.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18411
