* 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/44168c0d8e4c059ea51c8bc98a10784a74454b54>
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
--
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