* Jakub Jelinek:
On Tue, Dec 05, 2023 at 04:38:55AM +0100, Kevin Kofler via devel
wrote:
> Florian Weimer wrote:
> > The final patches for GCC 14 are currently under upstream review and
> > should land very soon. Earlier, I had received feedback that the larger
> > community desires just one transition, so we end up with the following
> > warnings which turn into errors by default:
> >
> > -Wimplicit-function-declaration
> > -Wimplicit-int
> > -Wint-conversion
> > -Wreturn-mismatch (new, previously part of -Wreturn-types)
> > -Wdeclaration-missing-parameter-type (new, previously unnamed)
> > -Wincompatible-pointer-types
> >
> > Only the first two were covered in the initial Fedora conversion work.
>
> As much as I understand the point of -Werror=implicit-function-declaration
> (since implicit function declarations can cause several subtle bugs), and
> implicit int is obscure enough for its removal to not be a big problem (even
> though its potential for causing bugs is much lower), as much I have to
> wonder about the others. Especially the incompatible pointer types sound
> more like nitpicking than actual bugs (though I guess strict aliasing can
> cause issues with those, but then I would expect to see -Wstrict-aliasing
> warnings).
Look at the gimp case, where a function prototype was expecting double *
argument but caller was calling it with address of float.
void foo (double *);
void
bar ()
{
float f = 5.0f;
foo (&f);
}
While this resulted in a warning even without -Wall, clearly nobody
noticed
until this was made an error:
And this results in an out-of-bounds write and potential memory
corruption.
That's actually not uncommon for such bugs. Here's a similar issue for
python-tables:
<
https://github.com/PyTables/PyTables/commit/44168c0d8e4c059ea51c8bc98a107...
Although the critical type size mismatch happens on 32-bit architectures
and Windows only. Problems like these are the reason why I don't think
the Clang approach of restricting to incompatible-function-pointer-types
only makes much sense.
Thanks,
Florian