How can Autoconf help with the transition to stricter compilation defaults?

[Michael Matz via cfe-commits]

Hello,

On Wed, 16 Nov 2022, Paul Eggert wrote:

> On 2022-11-16 06:26, Michael Matz wrote:
> > char foobar(void);
> > int main(void) {
> >    return &foobar != 0;
> > }
> 
> That still has undefined behavior according to draft C23,

This is correct (and also holds for the actually working variant later, 
with a volatile variable).  If your argument is then that as both 
solutions for the link-test problem are relying on undefined behaviour 
they are equivalent and hence no change is needed, you have a point, but I 
disagree.  In practice one (with the call) will cause more problems than 
the other (with address taking).

> If Clang's threatened pickiness were of some real use elsewhere, it 
> might be justifiable for default Clang to break Autoconf. But so far we 
> haven't seen real-world uses that would justify this pickiness for 
> Autoconf's use of 'char memset_explicit(void);'.

Note that both, GCC and clang, already warn (not error out!) about the 
mismatching decl, even without any headers.  So we are in the pickiness 
era already.

I.e. a C file containing just a single line "char printf(void);" will be 
warned about, by default.  There is about nothing that autoconf could do 
to rectify this, except containing a long list of prototypes for 
well-known functions, with the associated maintenance hassle.  But 
autoconf _can_ do something about how the decls are used in the 
link-tests.


Ciao,
Michael.