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To: "Ying Chu" <xjtuychu@gmail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: sysenter cause a segmentation fault.
References: <b965e8580703180108t6bc50b0eg895c5464463ab09@mail.gmail.com>
From: Andi Kleen <andi@firstfloor.org>
Date: 18 Mar 2007 16:51:21 +0100
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"Ying Chu" <xjtuychu@gmail.com> writes:

> A simple code running on PIII 800,kernel 2.6.20 with SEP enabled
> causes  a  segmentation fault.

SYSENTER has a hardcoded return address, that is why you cannot be used
anywhere but in the vsyscall trampoline.  In addition it doesn't work
on x86-64 for 32bit processes for AMD. The only system call method
supported without the vDSO is int 0x80. Better you just use the vDSO.

> More, when i enabled Kdb and set "bp sysenter_entry",it went with a
> catastrophic error errupted.

The stack and some other kernel state are not set up yet at this point.

-Andi