linux-fsdevel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Kees Cook <keescook@chromium.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Jani Nikula <jani.nikula@linux.intel.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	dev@openvswitch.org, Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Network Development <netdev@vger.kernel.org>,
	intel-gfx@lists.freedesktop.org, linux-usb@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	Maling list - DRI developers  <dri-devel@lists.freedesktop.org>,
	Linux-MM <linux-mm@kvack.org>,
	linux-security-module <linux-security-module@vger.kernel.org>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	intel-wired-lan@lists.osuosl.org,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Laura Abbott <labbott@redhat.com>,
	linux-kbuild <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: Thu, 24 Jan 2019 09:36:11 +1300	[thread overview]
Message-ID: <CAGXu5jLNvHVhbyr5Cbyoe8o0ARv52sU-NEpD+u2UYfESM3ofCw@mail.gmail.com> (raw)
In-Reply-To: <20190123191802.GB15311@bombadil.infradead.org>

On Thu, Jan 24, 2019 at 8:18 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Wed, Jan 23, 2019 at 04:17:30PM +0200, Jani Nikula wrote:
> > Can't have:
> >
> >       switch (i) {
> >               int j;
> >       case 0:
> >               /* ... */
> >       }
> >
> > because it can't be turned into:
> >
> >       switch (i) {
> >               int j = 0; /* not valid C */
> >       case 0:
> >               /* ... */
> >       }
> >
> > but can have e.g.:
> >
> >       switch (i) {
> >       case 0:
> >               {
> >                       int j = 0;
> >                       /* ... */
> >               }
> >       }
> >
> > I think Kees' approach of moving such variable declarations to the
> > enclosing block scope is better than adding another nesting block.
>
> Another nesting level would be bad, but I think this is OK:
>
>         switch (i) {
>         case 0: {
>                 int j = 0;
>                 /* ... */
>         }
>         case 1: {
>                 void *p = q;
>                 /* ... */
>         }
>         }
>
> I can imagine Kees' patch might have a bad effect on stack consumption,
> unless GCC can be relied on to be smart enough to notice the
> non-overlapping liveness of the vriables and use the same stack slots
> for both.

GCC is reasonable at this. The main issue, though, was most of these
places were using the variables in multiple case statements, so they
couldn't be limited to a single block (or they'd need to be manually
repeated in each block, which is even more ugly, IMO).

Whatever the consensus, I'm happy to tweak the patch.

Thanks!

-- 
Kees Cook

  reply	other threads:[~2019-01-23 20:36 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
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 [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAGXu5jLNvHVhbyr5Cbyoe8o0ARv52sU-NEpD+u2UYfESM3ofCw@mail.gmail.com \
    --to=keescook@chromium.org \
    --cc=alex.popov@linux.com \
    --cc=ard.biesheuvel@linaro.org \
    --cc=dev@openvswitch.org \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=gregkh@linuxfoundation.org \
    --cc=intel-gfx@lists.freedesktop.org \
    --cc=intel-wired-lan@lists.osuosl.org \
    --cc=jani.nikula@linux.intel.com \
    --cc=kernel-hardening@lists.openwall.com \
    --cc=labbott@redhat.com \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kbuild@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linux-security-module@vger.kernel.org \
    --cc=linux-usb@vger.kernel.org \
    --cc=netdev@vger.kernel.org \
    --cc=willy@infradead.org \
    --cc=xen-devel@lists.xenproject.org \
    --subject='Re: [Intel-gfx] [PATCH 1/3] treewide: Lift switch variables out of switches' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
on how to clone and mirror all data and code used for this inbox