From: "Gustavo A. R. Silva" <email@example.com> To: Thomas Gleixner <firstname.lastname@example.org> Cc: Ingo Molnar <email@example.com>, "H. Peter Anvin" <firstname.lastname@example.org>, email@example.com, LKML <firstname.lastname@example.org>, Kees Cook <email@example.com>, Linus Torvalds <firstname.lastname@example.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 <email@example.com>: > 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 <firstname.lastname@example.org>: >> > > > > 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 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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