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From: Davide Libenzi <davidel@xmailserver.org>
To: "Randy.Dunlap" <rddunlap@osdl.org>
Cc: lkml <linux-kernel@vger.kernel.org>
Subject: Re: asm (lidt) question
Date: Thu, 17 Jul 2003 16:18:06 -0700 (PDT)	[thread overview]
Message-ID: <Pine.LNX.4.55.0307171615580.4845@bigblue.dev.mcafeelabs.com> (raw)
In-Reply-To: <Pine.LNX.4.55.0307171535020.4845@bigblue.dev.mcafeelabs.com>

On Thu, 17 Jul 2003, Davide Libenzi wrote:

> On Thu, 17 Jul 2003, Randy.Dunlap wrote:
>
> >
> > In arch/i386/kernel, inline asm for loading IDT (lidt) is used a few
> > times, but with slightly different constraints and output/input
> > definitions.  Are these OK, equivalent, or what?
> >
> > [rddunlap@dragon kernel]$ findc lidt
> > ./cpu/common.c:484: __asm__ __volatile__("lidt %0": "=m" (idt_descr));
> > ./traps.c:783:	__asm__ __volatile__("lidt %0": "=m" (idt_descr));
> >
> > vs.
> >
> > ./reboot.c:186:	__asm__ __volatile__ ("lidt %0" : : "m" (real_mode_idt));
> > ./reboot.c:261:	__asm__ __volatile__("lidt %0": :"m" (no_idt));
> > ./suspend.c:95:	asm volatile ("lidt %0" :: "m" (saved_context.idt_limit));
>
> I'd have said no looking at the syntax (input/output), but they indeed
> generate the same code (just checked).

Randy, I'd say that this :

__asm__ __volatile__("lidt %0": "=m" (var));

is better then :

__asm__ __volatile__("lidt %0": :"m" (var));

IMHO, since "var" is really an output parameter.



- Davide


  reply	other threads:[~2003-07-17 23:10 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-07-17 22:28 asm (lidt) question Randy.Dunlap
2003-07-17 22:36 ` Davide Libenzi
2003-07-17 23:18   ` Davide Libenzi [this message]
2003-07-17 23:31     ` Randy.Dunlap
2003-07-17 23:36       ` Davide Libenzi
2003-07-22 17:27     ` Jamie Lokier
2003-07-22 17:31       ` Davide Libenzi
2003-07-22 17:50         ` Richard B. Johnson
2003-07-22 17:54           ` Davide Libenzi
2003-07-22 18:58         ` Randy.Dunlap
2003-07-22 18:58           ` Davide Libenzi
2003-07-22 19:04             ` Randy.Dunlap

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