linux-kernel - Re: SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird crap with vdso on uml/i386)

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Date:	Sun, 21 Aug 2011 22:03:33 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Al Viro <viro@...IV.linux.org.uk>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Lutomirski <luto@....edu>, mingo@...hat.com,
	Richard Weinberger <richard@....at>,
	user-mode-linux-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird
 crap with vdso on uml/i386)

On 08/21/2011 09:26 PM, Al Viro wrote:
> 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?

The JIT will have had to manage SYSENTER already.  It's not a change,
whereas SYSCALL would be.  We could just try it, and see if anything
breaks, of course.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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