linux-kernel - Re: [PATCH v5 4/9] x86-64: Remove kernel.vsyscall64 sysctl

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Date:	Mon, 5 Dec 2011 18:27:09 +0000 (UTC)
From:	Matthew Maurer <maurer@...thewmaurer.org>
To:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/9] x86-64: Remove kernel.vsyscall64 sysctl

Andy Lutomirski <luto <at> MIT.EDU> writes:

> 
> It's unnecessary overhead in code that's supposed to be highly
> optimized.  Removing it allows us to remove one of the two syscall
> instructions in the vsyscall page.
> 
> The only sensible use for it is for UML users, and it doesn't fully
> address inconsistent vsyscall results on UML.  The real fix for UML
> is to stop using vsyscalls entirely.

UML is not the only use case for this. Anybody who wants to be able to
trace _all_ system calls (for debugging, ptrace-based sandboxing, or a
number of other purposes) needs this.

We either need this back, or need another way to make it possible to
trace these system calls.

Apologies for the late reply, I didn't notice this change until it got
into my distribution's kernel.

--Matthew Maurer

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