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Date: Tue, 17 Dec 2002 10:49:31 -0800 (PST)
From: Linus Torvalds <torvalds@transmeta.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
cc: 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
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On 17 Dec 2002, Alan Cox wrote:
>
> Is there any reason you can't just keep the linker out of the entire
> mess by generating
>
> 	.byte whatever
> 	.dword 0xFFFF0000
>
> instead of call ?

Alan, the problem is that there _is_ no such instruction as a "call
absolute".

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.

			Linus

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