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Date: Mon, 22 Aug 2011 05:26:05 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Lutomirski <luto@mit.edu>, mingo@redhat.com,
        Richard Weinberger <richard@nod.at>,
        user-mode-linux-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org
Subject: Re: SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird
 crap with vdso on uml/i386)
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On Sun, Aug 21, 2011 at 09:11:54PM -0700, H. Peter Anvin wrote:
> > lack of point - the *only* CPU where it would matter would be K6-2, IIRC,
> > and (again, IIRC) it had some differences in SYSCALL semantics compared to
> > K7 (which supports SYSENTER as well).  Bugger if I remember what those
> > differences might've been...  Some flag not cleared?
> 
> The most likely reason for a binary to execute a stray SYSCALL is
> because they read it out of the vdso.  Totally daft, but we certainly
> see a lot of stupid things as evidenced by the JIT thread earlier this
> month.

Um...  What, blindly, no matter what surrounds it in there?  What will
happen to the same eager JIT when it steps on SYSENTER?