Date: Thu, 15 Oct 2009 21:07:20 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Dave Jones <davej@redhat.com>, Linux Kernel <linux-kernel@vger.kernel.org>,
       Thomas Gleixner <tglx@linutronix.de>, esandeen@redhat.com,
       cebbert@redhat.com, Arjan van de Ven <arjan@infradead.org>,
       "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: Unnecessary overhead with stack protector.
Message-ID: <20091015190720.GA19467@elte.hu>
References: <20091015183540.GA8098@redhat.com>
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(Cc:-ed Arjan too.)

* Dave Jones <davej@redhat.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.

Exactly what workload showed overhead, and how much?

	Ingo
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