On Tue, 28 Nov 2017, Thomas Gleixner wrote:
> On Tue, 28 Nov 2017, Gustavo A. R. Silva wrote:
> > Quoting Thomas Gleixner <t...@linutronix.de>:
> >
> > > On Mon, 27 Nov 2017, Gustavo A. R. Silva wrote:
> > >
> > > > In preparation to enabling -Wimplicit-fallthrough, mark switch cases
> > > > where we are expecting to fall through.
> > >
> > > > case 0:
> > > > if (!n--) break;
> > > > *args++ = regs->bx;
> > > > + /* fall through */
> > >
> > > And these gazillions of pointless comments help enabling of
> > > -Wimplicit-fallthrough in which way?
> > >
> >
> > The -Wimplicit-fallthrough option was added to GCC 7. We want to add that
> > option to the top-level Makefile so we can have the compiler help us not
> > make
> > mistakes as missing "break"s or "continue"s. This also documents the
> > intention
> > for humans and provides a way for analyzers to report issues or ignore False
> > Positives.
> >
> > So prior to adding such option to the Makefile, we have to properly add a
> > code
> > comment wherever the code is intended to fall through.
> >
> > During the process of placing these comments I have identified actual bugs
> > (missing "break"s/"continue"s) in a variety of components in the kernel, so
> > I
> > think this effort is valuable. Lastly, such a simple comment in the code can
> > save a person plenty of time during a code review.
>
> To be honest, such comments annoy me during a code review especially when
> the fallthrough is so obvious as in this case. There might be cases where
> its worth to document because it's non obvious, but documenting the obvious
> just for the sake of documenting it is just wrong.
And _IF_ at all then you want a fixed macro for this and not a comment
which will be formatted as people see it fit.
GCC supports: __attribute__ ((fallthrough)) which we can wrap into a macro,
e.g. falltrough()
That'd be useful, but adding all these comments and then having to chase a
gazillion of warning instances to figure out whether there is a comment or
not is just backwards.
Sure, but slapping a comment everywhere is just simpler than reading the
documentation and make something useful and understandable.
Thanks,
tglx
