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Message-ID: <87va2f1int.fsf@intel.com>
Date: Wed, 23 Jan 2019 17:46:14 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Edwin Zimmerman <edwin@...mainstreet.net>, 'Greg KH' <gregkh@...uxfoundation.org>, 'Kees Cook' <keescook@...omium.org>
Cc: dev@...nvswitch.org, 'Ard Biesheuvel' <ard.biesheuvel@...aro.org>, netdev@...r.kernel.org, intel-gfx@...ts.freedesktop.org, linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, linux-mm@...ck.org, linux-security-module@...r.kernel.org, kernel-hardening@...ts.openwall.com, intel-wired-lan@...ts.osuosl.org, linux-fsdevel@...r.kernel.org, xen-devel@...ts.xenproject.org, 'Laura Abbott' <labbott@...hat.com>, linux-kbuild@...r.kernel.org, 'Alexander Popov' <alex.popov@...ux.com>
Subject: RE: [Intel-gfx] [PATCH 1/3] treewide: Lift switch variables out of switches
On Wed, 23 Jan 2019, Edwin Zimmerman <edwin@...mainstreet.net> wrote:
> On Wed, 23 Jan 2019, Jani Nikula <jani.nikula@...ux.intel.com> wrote:
>> On Wed, 23 Jan 2019, Greg KH <gregkh@...uxfoundation.org> wrote:
>> > On Wed, Jan 23, 2019 at 03:03:47AM -0800, Kees Cook wrote:
>> >> Variables declared in a switch statement before any case statements
>> >> cannot be initialized, so move all instances out of the switches.
>> >> After this, future always-initialized stack variables will work
>> >> and not throw warnings like this:
>> >>
>> >> fs/fcntl.c: In function ‘send_sigio_to_task’:
>> >> fs/fcntl.c:738:13: warning: statement will never be executed [-Wswitch-unreachable]
>> >> siginfo_t si;
>> >> ^~
>> >
>> > That's a pain, so this means we can't have any new variables in { }
>> > scope except for at the top of a function?
>> >
>> > That's going to be a hard thing to keep from happening over time, as
>> > this is valid C :(
>>
>> Not all valid C is meant to be used! ;)
>
> Very true. The other thing to keep in mind is the burden of enforcing
> a prohibition on a valid C construct like this. It seems to me that
> patch reviewers and maintainers have enough to do without forcing them
> to watch for variable declarations in switch statements. Automating
> this prohibition, should it be accepted, seems like a good idea to me.
Considering that the treewide diffstat to fix this is:
18 files changed, 45 insertions(+), 46 deletions(-)
and using the gcc plugin in question will trigger the switch-unreachable
warning, I think we're good. There'll probably be the occasional
declarations that pass through, and will get fixed afterwards.
BR,
Jani.
--
Jani Nikula, Intel Open Source Graphics Center
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