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Date: Tue, 17 Dec 2002 16:34:58 -0500
From: Benjamin LaHaise <bcrl@redhat.com>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, Ulrich Drepper <drepper@redhat.com>,
       Dave Jones <davej@codemonkey.org.uk>, Ingo Molnar <mingo@elte.hu>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       hpa@transmeta.com
Subject: Re: Intel P6 vs P7 system call performance
Message-ID: <20021217163458.B10781@redhat.com>
References: <1040153030.20804.8.camel@irongate.swansea.linux.org.uk> <Pine.LNX.4.44.0212171046550.1095-100000@home.transmeta.com>
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In-Reply-To: <Pine.LNX.4.44.0212171046550.1095-100000@home.transmeta.com>; from torvalds@transmeta.com on Tue, Dec 17, 2002 at 10:49:31AM -0800
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On Tue, Dec 17, 2002 at 10:49:31AM -0800, Linus Torvalds wrote:
> There is only a "call relative" or "call indirect-absolute". So you either
> have to indirect through memory or a register, or you have to fix up the
> call at link-time.
> 
> Yeah, I know it sounds strange, but it makes sense. Absolute calls are
> actually very unusual, and using relative calls is _usually_ the right
> thing to do. It's only in cases like this that we really want to call a
> specific address.

The stubs I used for the vsyscall bits just did an absolute jump to 
the vsyscall page, which would then do a ret to the original calling 
userspace code (since that provided library symbols for the user to 
bind against).

		-ben
-- 
"Do you seek knowledge in time travel?"
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