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

--Apple-Mail=_6CBEB47A-2714-479D-B040-A29DC401D735
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain;
	charset=us-ascii



> On 16 Nov 2022, at 15:27, Richard Biener <[email protected]> =
wrote:
>=20
> On Wed, Nov 16, 2022 at 4:02 PM Michael Matz via Gcc <[email protected]> =
wrote:
>>=20
>> Hey,
>>=20
>> On Wed, 16 Nov 2022, Alexander Monakov wrote:
>>=20
>>>> The idea is so obvious that I'm probably missing something, why =
autoconf
>>>> can't use that idiom instead.  But perhaps the (historic?) reasons =
why it
>>>> couldn't be used are gone now?
>>>=20
>>> Ironically, modern GCC and LLVM optimize '&foobar !=3D 0' to '1' =
even at -O0,
>>> and thus no symbol reference remains in the resulting assembly.
>>=20
>> Err, right, *head-->table*.
>> Playing with volatile should help:
>>=20
>> char foobar(void);
>> char (* volatile ptr)(void);
>> int main(void) {
>>    ptr =3D foobar;
>>    return ptr !=3D 0;
>> }
>=20
> using printf for foobar this works even with GCC 2.95.2 and with trunk
> and -Wall diagnoses
>=20
> t.c:1:6: warning: conflicting types for built-in function 'printf';
> expected 'int(const char *, ...)' [-Wbuiltin-declaration-mismatch]
>    1 | char printf(void);
>      |      ^~~~~~
> t.c:1:1: note: 'printf' is declared in header '<stdio.h>'
>  +++ |+#include <stdio.h>
>    1 | char printf(void);
>=20
> so without -Werror this should be fine.
>=20
Unrelated but I was a bit tempted to ask for throwing in =
-Wbuiltin-declaration-mismatch
to default -Werror while Clang 16 was at it, but I suppose we don't want =
the world to
burn too much, and it's got a very obvious usecase (this one) whereas =
implicit
func decls are too hard to justify.

> Richard.

--Apple-Mail=_6CBEB47A-2714-479D-B040-A29DC401D735
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
	filename=signature.asc
Content-Type: application/pgp-signature;
	name=signature.asc
Content-Description: Message signed with OpenPGP

-----BEGIN PGP SIGNATURE-----

iNUEARYKAH0WIQQlpruI3Zt2TGtVQcJzhAn1IN+RkAUCY3UDLF8UgAAAAAAuAChp
c3N1ZXItZnByQG5vdGF0aW9ucy5vcGVucGdwLmZpZnRoaG9yc2VtYW4ubmV0MjVB
NkJCODhERDlCNzY0QzZCNTU0MUMyNzM4NDA5RjUyMERGOTE5MAAKCRBzhAn1IN+R
kBCXAP9BdX2hjbcXRqMriNr3kyJZDWBGzB3la2YEKTaQudXIrgD/evpVBl5ulRGC
YyuE53QVS/jN7AtnhcodJFt0q5cJJg8=
=3Llf
-----END PGP SIGNATURE-----

--Apple-Mail=_6CBEB47A-2714-479D-B040-A29DC401D735--