From: "Gustavo A. R. Silva" <garsilva@embeddedor.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, LKML <linux-kernel@vger.kernel.org>,
Kees Cook <keescook@chromium.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] x86/syscalls: Mark expected switch fall-throughs
Date: Tue, 28 Nov 2017 12:53:31 -0600 [thread overview]
Message-ID: <20171128125331.Horde.XUXRWEiZ7FMJv6yoDylZxN8@gator4166.hostgator.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1711281944010.2222@nanos>
Quoting Thomas Gleixner <tglx@linutronix.de>:
> On Tue, 28 Nov 2017, Thomas Gleixner wrote:
>
> +CC Linus.
>
>> On Tue, 28 Nov 2017, Thomas Gleixner wrote:
>>
>> > On Tue, 28 Nov 2017, Gustavo A. R. Silva wrote:
>> > > Quoting Thomas Gleixner <tglx@linutronix.de>:
>> > > > > 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.
>> > > >
>> > >
>> > > I understand that and I agree that in this particular case it
>> is just obvious.
>> > > The thing is that if we want to benefit from having the
>> compiler help us to
>> > > spot these kind of issues before committing our code, we have
>> to address every
>> > > place in the whole code-base.
>> > >
>> > > > 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.
>> > > >
>> > >
>> > > I have run into this before and people find what you suggest
>> even uglier.
>> >
>> > It's not about ugly. It's about _USEFULL_.
>> >
>> > The comments are ugly AND completely useless for the compiler and they are
>> > going to be malformatted so checker tools can't differentiate the false
>> > positives.
>> >
>> > The macro, in which more or less ugly form written, is both documentation
>> > and helps the compiler NOT to emit the same crap over and over.
>>
>> Just checked and GCC really supports analyzing the comment to some extent.
>>
>> But just look at
>>
>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77817
>>
>> " It is not really possible. __attribute__((fallthrough)) has precise
>> rules on where it can appear, while /* FALLTHRU */ comments, being
>> comments, can appear anywhere. Especially with -Wimplicit-fallthrough=1
>> when all comments are considered fallthru comments... "
>>
This is what we want to add:
# Warn about missing switch break or fall-through comment.
KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough)
>> I have no idea who came up with that brilliant idea of parsing comments in
>> the code. It's so simple to make this parser completely fail that it's not
>> even funny anymore.
>>
I don't get why someone would want to do that to himself. :/
>> I don't care what other people prefer. The code base I'm responsible for
>> gets either proper annotations or nothing.
>
> And in fact we want ONE solution for the whole kernel. And comments are
> obviously the wrong one.
>
OK. I'll discuss this and see how we can come up with the best solution.
Thank you for your feedback
--
Gustavo A. R. Silva
next prev parent reply other threads:[~2017-11-28 18:53 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-27 23:52 [PATCH] x86/syscalls: Mark expected switch fall-throughs Gustavo A. R. Silva
2017-11-28 13:49 ` Thomas Gleixner
2017-11-28 18:05 ` Gustavo A. R. Silva
2017-11-28 18:10 ` Thomas Gleixner
2017-11-28 18:17 ` Thomas Gleixner
2017-11-28 18:22 ` Gustavo A. R. Silva
2017-11-28 18:27 ` Thomas Gleixner
2017-11-28 18:35 ` Thomas Gleixner
2017-11-28 18:45 ` Thomas Gleixner
2017-11-28 18:53 ` Gustavo A. R. Silva [this message]
2017-11-28 19:48 ` Thomas Gleixner
2017-11-28 19:00 ` Alan Cox
2017-11-28 19:10 ` Linus Torvalds
2017-11-28 19:59 ` Joe Perches
2017-11-28 20:08 ` Thomas Gleixner
2017-11-28 20:34 ` Kees Cook
2017-11-28 20:37 ` Gustavo A. R. Silva
2017-11-29 1:07 ` Joe Perches
2017-11-29 8:20 ` Geert Uytterhoeven
2017-11-28 20:11 ` Thomas Gleixner
2017-11-28 20:25 ` Gustavo A. R. Silva
2017-11-28 21:25 ` Thomas Gleixner
2017-11-29 15:10 ` Gustavo A. R. Silva
2017-11-29 15:14 ` Thomas Gleixner
2017-11-30 0:21 ` Kees Cook
2019-01-29 23:56 Gustavo A. R. Silva
2019-01-30 0:14 ` Thomas Gleixner
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