linux-kernel - Re: [RFC 00/15] x86_64: Optimize percpu accesses

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Date:	Wed, 9 Jul 2008 22:15:01 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Mike Travis <travis@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC 00/15] x86_64: Optimize percpu accesses

* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

>> Further -fstack-protector-all only seems to detect against buffer 
>> overflows and thus corruption of the stack.  Not stack overflows.  So 
>> it doesn't appear especially useful.
>
> It's a bit useful.  But at the cost of preventing a pile of more 
> useful unification work, not to mention making all access to per-cpu 
> variables more expensive.

well, stackprotector is near zero maintenance trouble. It mostly binds 
in places that are fundamentally non-unifiable anyway. (nobody is going 
to unify the assembly code in switch_to())

i had zero-based percpu problems (early crashes) with a 4.2.3 gcc that 
had --fstack-protect compiled out, so there's no connection there.

In its fixed form in tip/core/stackprotector it can catch the splice 
exploit which makes it quite a bit useful. It would be rather silly to 
not offer that feature.

	Ingo
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