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From: "Edwin Zimmerman" <edwin@211mainstreet.net>
To: "'Jani Nikula'" <jani.nikula@linux.intel.com>,
	"'Greg KH'" <gregkh@linuxfoundation.org>,
	"'Kees Cook'" <keescook@chromium.org>
Cc: <dev@openvswitch.org>,
	"'Ard Biesheuvel'" <ard.biesheuvel@linaro.org>,
	<netdev@vger.kernel.org>, <intel-gfx@lists.freedesktop.org>,
	<linux-usb@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<dri-devel@lists.freedesktop.org>, <linux-mm@kvack.org>,
	<linux-security-module@vger.kernel.org>,
	<kernel-hardening@lists.openwall.com>,
	<intel-wired-lan@lists.osuosl.org>,
	<linux-fsdevel@vger.kernel.org>, <xen-devel@lists.xenproject.org>,
	"'Laura Abbott'" <labbott@redhat.com>,
	<linux-kbuild@vger.kernel.org>,
	"'Alexander Popov'" <alex.popov@linux.com>
Subject: RE: [Intel-gfx] [PATCH 1/3] treewide: Lift switch variables out of switches
Date: Wed, 23 Jan 2019 09:47:06 -0500	[thread overview]
Message-ID: <000001d4b32a$845e06e0$8d1a14a0$@211mainstreet.net> (raw)
In-Reply-To: <874l9z31c5.fsf@intel.com>

On Wed, 23 Jan 2019, Jani Nikula <jani.nikula@linux.intel.com> wrote:
> On Wed, 23 Jan 2019, Greg KH <gregkh@linuxfoundation.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.

-Edwin Zimmerman


  parent reply	other threads:[~2019-01-23 14:59 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-23 11:03 [PATCH 0/3] gcc-plugins: Introduce stackinit plugin Kees Cook
2019-01-23 11:03 ` [PATCH 1/3] treewide: Lift switch variables out of switches Kees Cook
2019-01-23 11:58   ` Greg KH
2019-01-23 12:09     ` Jann Horn
2019-01-23 12:12       ` Ard Biesheuvel
2019-01-23 13:21       ` William Kucharski
2019-01-23 14:17     ` [Intel-gfx] " Jani Nikula
2019-01-23 14:23       ` Jani Nikula
2019-01-23 14:47       ` Edwin Zimmerman [this message]
2019-01-23 15:46         ` Jani Nikula
2019-01-23 18:55           ` Kees Cook
2019-01-24  8:10             ` Greg KH
2019-01-23 19:18       ` Matthew Wilcox
2019-01-23 20:36         ` Kees Cook
2019-01-23 16:51   ` [Intel-wired-lan] " Jeff Kirsher
2019-01-24 12:58   ` Edwin Zimmerman
2019-01-23 11:03 ` [PATCH 2/3] gcc-plugins: Introduce stackinit plugin Kees Cook
2019-01-23 11:03 ` [PATCH 3/3] lib: Introduce test_stackinit module Kees Cook
2019-01-29  0:12 ` [PATCH 0/3] gcc-plugins: Introduce stackinit plugin Alexander Popov
2019-02-12 17:54   ` Kees Cook

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