To: linux-kernel@vger.kernel.org
From: Stephen Hemminger <shemminger@osdl.org>
Subject: Re: Calling syscalls from x86-64 kernel results in a crash on
 Opteron machines
Date: Mon, 13 Sep 2004 09:41:48 -0700
Organization: Open Source Development Lab
Message-ID: <20040913094148.45509d9c@dell_ss3.pdx.osdl.net>
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On Mon, 13 Sep 2004 18:17:36 +0200
Andrea Arcangeli <andrea@novell.com> wrote:

> Hi Constantine,
> 
> On Mon, Sep 13, 2004 at 06:05:52PM +0300, Constantine Gavrilov wrote:
> > And BTW, kernel-space applications have their own place even if the 
> > concept seems foreign to you.
> 
> I avoided to do like i386 that inefficiently calls int 0x80 when you can
> call sys_read/sys_write etc.. by hand.
> 
> the syscall is only meaningful if you're not in kernel space. Once
> you're in kernel space if you ever try to invoke a syscall again (either
> via int 0x80, syscall, sysenter, call gate, whatever) then you're just
> going slower than you should for no good reason. 
> 
> The only point of calling int 0x80 and friends is to change mode from
> user space to kernel space, and you're in kernel space already so you
> should just call sys_read/sys_write etc.. by hand which will not waste
> precious cycles and it'll be a lot simpler too.
> 
> Note also that int 0x80 will bring you into the 32bit emulation layer,
> the only 64bit entry point is reacheable only via syscall.
> 
> Hope this helps.


Actually, the fact that system calls work in kernel space I would consider
a BUG.  The int 0x80 handler should oops or at least kill the offending
thread for security and robustness reasons.

-- 
Stephen Hemminger 		mailto:shemminger@osdl.org
Open Source Development Lab	http://developer.osdl.org/shemminger
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