From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jani Nikula Subject: RE: [Intel-gfx] [PATCH 1/3] treewide: Lift switch variables out of switches In-Reply-To: <000001d4b32a$845e06e0$8d1a14a0$@211mainstreet.net> References: <20190123110349.35882-1-keescook@chromium.org> <20190123110349.35882-2-keescook@chromium.org> <20190123115829.GA31385@kroah.com> <874l9z31c5.fsf@intel.com> <000001d4b32a$845e06e0$8d1a14a0$@211mainstreet.net> Date: Wed, 23 Jan 2019 17:46:14 +0200 Message-ID: <87va2f1int.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable To: Edwin Zimmerman , 'Greg KH' , 'Kees Cook' Cc: dev@openvswitch.org, 'Ard Biesheuvel' , 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' , linux-kbuild@vger.kernel.org, 'Alexander Popov' List-ID: On Wed, 23 Jan 2019, Edwin Zimmerman wrote: > On Wed, 23 Jan 2019, Jani Nikula wrote: >> On Wed, 23 Jan 2019, Greg KH 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 =E2=80=98send_sigio_to_task=E2=80=99: >> >> fs/fcntl.c:738:13: warning: statement will never be executed [-Wswitc= h-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 :( >>=20 >> 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. --=20 Jani Nikula, Intel Open Source Graphics Center