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From: Nick Desaulniers <ndesaulniers@google.com>
To: Tom Rix <trix@redhat.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
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	clang-built-linux <clang-built-linux@googlegroups.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	George Burgess <gbiv@google.com>
Subject: Re: [RFC] treewide: cleanup unreachable breaks
Date: Mon, 19 Oct 2020 12:42:15 -0700
Message-ID: <CAKwvOdkR_Ttfo7_JKUiZFVqr=Uh=4b05KCPCSuzwk=zaWtA2_Q@mail.gmail.com> (raw)
In-Reply-To: <20201018054332.GB593954@kroah.com>

On Sat, Oct 17, 2020 at 10:43 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Sat, Oct 17, 2020 at 09:09:28AM -0700, trix@redhat.com wrote:
> > From: Tom Rix <trix@redhat.com>
> >
> > This is a upcoming change to clean up a new warning treewide.
> > I am wondering if the change could be one mega patch (see below) or
> > normal patch per file about 100 patches or somewhere half way by collecting
> > early acks.
>
> Please break it up into one-patch-per-subsystem, like normal, and get it
> merged that way.
>
> Sending us a patch, without even a diffstat to review, isn't going to
> get you very far...

Tom,
If you're able to automate this cleanup, I suggest checking in a
script that can be run on a directory.  Then for each subsystem you
can say in your commit "I ran scripts/fix_whatever.py on this subdir."
 Then others can help you drive the tree wide cleanup.  Then we can
enable -Wunreachable-code-break either by default, or W=2 right now
might be a good idea.

Ah, George (gbiv@, cc'ed), did an analysis recently of
`-Wunreachable-code-loop-increment`, `-Wunreachable-code-break`, and
`-Wunreachable-code-return` for Android userspace.  From the review:
```
Spoilers: of these, it seems useful to turn on
-Wunreachable-code-loop-increment and -Wunreachable-code-return by
default for Android
...
While these conventions about always having break arguably became
obsolete when we enabled -Wfallthrough, my sample turned up zero
potential bugs caught by this warning, and we'd need to put a lot of
effort into getting a clean tree. So this warning doesn't seem to be
worth it.
```
Looks like there's an order of magnitude of `-Wunreachable-code-break`
than the other two.

We probably should add all 3 to W=2 builds (wrapped in cc-option).
I've filed https://github.com/ClangBuiltLinux/linux/issues/1180 to
follow up on.
-- 
Thanks,
~Nick Desaulniers

  parent reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-17 16:09 trix
2020-10-17 16:24 ` Joe Perches
2020-10-17 18:21   ` [Cocci] " Julia Lawall
2020-10-17 19:00     ` Joe Perches
2020-10-17 21:01 ` Dan Williams
2020-10-18  5:43 ` Greg KH
2020-10-18 14:04   ` Tom Rix
2020-10-19 19:42   ` Nick Desaulniers [this message]
2020-10-19 23:05     ` Jason Gunthorpe
2020-10-20 14:09       ` Tom Rix
2020-10-20  8:47     ` [Ocfs2-devel] " John Haxby
2020-10-20 13:55     ` Tom Rix
2020-10-20 18:42     ` Joe Perches
2020-10-18  9:29 ` Hans de Goede
2020-10-18 18:59 ` [Ocfs2-devel] " Matthew Wilcox
2020-10-18 19:06   ` Joe Perches
2020-10-18 19:13   ` James Bottomley
2020-10-18 19:16     ` Matthew Wilcox
2020-10-18 19:17       ` James Bottomley

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