Hi!
On Thu, May 20, 2021 at 05:37:20PM +1000, Michael Ellerman wrote:
> Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx> writes:
> > On Tue, May 18, 2021 at 07:45:14PM -0500, Segher Boessenkool wrote:
> >> On Wed, May 19, 2021 at 10:26:22AM +1000, Michael Ellerman wrote:
> >> > Guenter Roeck <linux@xxxxxxxxxxxx> writes:
> >> > > Ah, sorry. I wasn't aware that the following is valid C code
> >> > >
> >> > > void f1()
> >> > > {
> >> > > return f2();
> >> > > ^^^^^^
> >> > > }
> >> > >
> >> > > as long as f2() is void as well. Confusing, but we live and learn.
> >> >
> >> > It might be valid, but it's still bad IMHO.
> >> >
> >> > It's confusing to readers, and serves no useful purpose.
> >>
> >> And it actually explicitly is undefined behaviour in C90 already
> >> (3.6.6.4 in C90, 6.8.6.4 in C99 and later).
>
> We use gnu89, which presumably does not make it UB.
Indeed. That is kind of implied by the "as a GNU extension" below, but
some explicit statement would be better, yup.
> > ... but there is a GCC extension that allows this by default:
> > <https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wreturn-type>
> > For C only, warn about a 'return' statement with an expression in a
> > function whose return type is 'void', unless the expression type is
> > also 'void'. As a GNU extension, the latter case is accepted
> > without a warning unless '-Wpedantic' is used.
>
> There's no chance we'll ever enable -Wpedantic,
Good, because -pedantic adds a lot of much more annoying warnings as
well. I find this extension questionable (like Guenter says it is
confusing and has no purpose), so the only thing it is "good" for is it
causes long email threads ;-)
Other than those things it is harmless though.
> so I guess it's allowed
> for practical purposes. I guess clang must accept it too or we'd be
> seeing warnings from it.
Yup.
Segher
