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

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Message-ID: <4E51D597.3060800@zytor.com>
Date:	Sun, 21 Aug 2011 21:05:43 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andrew Lutomirski <luto@....edu>, Borislav Petkov <bp@...64.org>
CC:	Al Viro <viro@...iv.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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)

Borislav,

We're tracking down an issue with the way system call arguments are
handled on 32 bits.  We have a solution for SYSENTER but not SYSCALL;
fixing SYSCALL "properly" appears to be very difficult at best.

So the question is: how much overhead would it be to simply fall back to
int $0x80 or some other legacy-style domain crossing instruction for
32-bit system calls on AMD64 processors?  We don't ever use SYSCALL in
legacy mode, so native i386 kernels are unaffected.

	-hpa

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

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