linux-kernel - Re: Unnecessary overhead with stack protector.

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Message-Id: <20091026093706.c6416715.akpm@linux-foundation.org>
Date:	Mon, 26 Oct 2009 09:37:06 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Chuck Ebbert <cebbert@...hat.com>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>, esandeen@...hat.com
Subject: Re: Unnecessary overhead with stack protector.

On Mon, 26 Oct 2009 12:30:04 -0400 Chuck Ebbert <cebbert@...hat.com> wrote:

> On Wed, 21 Oct 2009 18:26:36 -0700
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Thu, 15 Oct 2009 14:35:41 -0400 Dave Jones <davej@...hat.com> wrote:
> > 
> > > 113c5413cf9051cc50b88befdc42e3402bb92115 introduced a change that
> > > made CC_STACKPROTECTOR_ALL not-selectable if someone enables CC_STACKPROTECTOR.
> > > 
> > > We've noticed in Fedora that this has introduced noticable overhead on
> > > some functions, including those which don't even have any on-stack variables.
> > > 
> > > According to the gcc manpage, -fstack-protector will protect functions with
> > > as little as 8 bytes of stack usage. So we're introducing a huge amount
> > > of overhead, to close a small amount of vulnerability (the >0 && <8 case).
> > > 
> > > The overhead as it stands right now means this whole option is unusable for
> > > a distro kernel without reverting the above commit.
> > > 
> > 
> > This looks like a fairly serious problem to me, but I'm confused by the
> > commit ID.  February 2008 - is this correct?
> > 
> 
> That date is pure fiction AFAICT. And the Mercurial kernel repo says May 2008...
> Is there some way to get the date a change was merged into the official tree as
> opposed to the date it was created in some other tree?

oh, so someone _did_ read my email!


git show --pretty=fuller 113c5413cf9051cc50b88befdc42e3402bb92115

commit 113c5413cf9051cc50b88befdc42e3402bb92115
Author:     Ingo Molnar <mingo@...e.hu>
AuthorDate: Thu Feb 14 10:36:03 2008 +0100
Commit:     Thomas Gleixner <tglx@...utronix.de>
CommitDate: Mon May 26 16:15:32 2008 +0200

I think the CommitDate is when it hit mainline.
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