From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f199.google.com (mail-pl1-f199.google.com [209.85.214.199]) by kanga.kvack.org (Postfix) with ESMTP id 5DA468E001A for ; Wed, 23 Jan 2019 09:22:02 -0500 (EST) Received: by mail-pl1-f199.google.com with SMTP id v2so1557065plg.6 for ; Wed, 23 Jan 2019 06:22:02 -0800 (PST) Received: from mga11.intel.com (mga11.intel.com. [192.55.52.93]) by mx.google.com with ESMTPS id j3si18527568plk.199.2019.01.23.06.22.01 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 23 Jan 2019 06:22:01 -0800 (PST) From: Jani Nikula Subject: Re: [Intel-gfx] [PATCH 1/3] treewide: Lift switch variables out of switches In-Reply-To: <874l9z31c5.fsf@intel.com> References: <20190123110349.35882-1-keescook@chromium.org> <20190123110349.35882-2-keescook@chromium.org> <20190123115829.GA31385@kroah.com> <874l9z31c5.fsf@intel.com> Date: Wed, 23 Jan 2019 16:23:39 +0200 Message-ID: <871s53311w.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: 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 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: >>>=20 >>> 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 [-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! ;) > > Anyway, I think you're mistaking the limitation to arbitrary blocks > while it's only about the switch block IIUC. > > Can't have: > > switch (i) { > int j; > case 0: > /* ... */ > } > > because it can't be turned into: > > switch (i) { > int j =3D 0; /* not valid C */ > case 0: > /* ... */ > } > > but can have e.g.: > > switch (i) { > case 0: > { > int j =3D 0; > /* ... */ > } > } > > I think Kees' approach of moving such variable declarations to the > enclosing block scope is better than adding another nesting block. PS. The patch is Reviewed-by: Jani Nikula and the drivers/gpu/drm/i915/* parts are Acked-by: Jani Nikula for merging via whichever tree is appropriate. (There'll be minor conflicts with in-flight work in our -next tree, but no biggie.) --=20 Jani Nikula, Intel Open Source Graphics Center