linux-kernel - Re: [PATCH v4 0/6] Micro-optimize vclock

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Message-ID: <20110517080029.GB22093@elte.hu>
Date:	Tue, 17 May 2011 10:00:29 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Andrew Lutomirski <luto@....edu>, Andi Kleen <andi@...stfloor.org>,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Borislav Petkov <bp@...64.org>
Subject: Re: [PATCH v4 0/6] Micro-optimize vclock_gettime


* Thomas Gleixner <tglx@...utronix.de> wrote:

> > see if I can persuade Uli to take accept a glibc patch to stop calling it 
> > in future static glibc versions.
> 
> How wide spread is this in reality on 64bit systems ?
> 
> IOW, what's the damage if we take a trap and emulate it in the most painful 
> way we can come up with ?

Well, how does that differ from having the real syscall instruction there? How 
are we going to filter real (old-)glibc calls from exploits?

If it can be filtered in a meaningful way then we should just do that and 
perhaps offer a (default enabled) .config COMPAT_VDSO_EMU=y switch to turn the 
emulation off.

That way we keep the ABI and also have a way out for users who *really* need 
this to work in a performant way.

Thanks,

	Ingo
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