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From: Christer Weinigel <christer@weinigel.se>
To: ebiederm@xmission.com (Eric W. Biederman)
Cc: Davide Libenzi <davidel@xmailserver.org>,
	Jamie Lokier <jamie@shareable.org>, Jos Hulzink <josh@stack.nl>,
	Linus Torvalds <torvalds@transmeta.com>, Andi Kleen <ak@muc.de>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Use correct x86 reboot vector
Date: 11 May 2003 20:43:26 +0200	[thread overview]
Message-ID: <m3wugxz5m9.fsf@zoo.weinigel.se> (raw)
In-Reply-To: <m1fznl74f9.fsf@frodo.biederman.org>

ebiederm@xmission.com (Eric W. Biederman) writes:

> Davide Libenzi <davidel@xmailserver.org> writes:
> Now if someone could tell me how to do a jump to 0xffff0000:0xfff0 in real
> mode I would find that very interesting.

Well, it should be possible to use a trick similar to the BIG REAL or
UNREAL mode.  Just load CS with a segment that has a base of
0xffff0000 in protected mode and then jump back to real mode.
Something like this, completely untested of course, should do it:

        .align  4
reset_gdt:
        .word   reset_gdt_end - reset_gdt -1
        .long   reset_gdt
        .word   0

/* 16 bit code segment starting at 0xffff0000 */
        .word   0xffff, 0x0000
        .byte   0xff, 0x9b, 0x00, 0xff
#endif

reset_gdt_end:

        lgdt    %cs:reset_gdt
        ljmp    $ROM_CODE_SEG, 0xfff0

  /Christer

-- 
"Just how much can I get away with and still go to heaven?"

Freelance consultant specializing in device driver programming for Linux 
Christer Weinigel <christer@weinigel.se>  http://www.weinigel.se

  parent reply	other threads:[~2003-05-11 18:23 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-05-10  2:56 [PATCH] Use correct x86 reboot vector Andi Kleen
2003-05-10  3:35 ` CaT
2003-05-10  3:58   ` H. Peter Anvin
2003-05-10 14:49   ` Alan Cox
2003-05-10 16:17     ` Jamie Lokier
2003-05-10 18:47       ` Jos Hulzink
2003-05-11 18:01     ` Eric W. Biederman
2003-05-11 17:24       ` Alan Cox
2003-05-11 19:04         ` Eric W. Biederman
2003-05-12  5:48         ` [PATCH] always shutdown on the bootstrap processor Eric W. Biederman
2003-05-10 16:15 ` [PATCH] Use correct x86 reboot vector Jamie Lokier
2003-05-10 17:09   ` Randy.Dunlap
2003-05-10 19:41   ` Jos Hulzink
2003-05-10 18:10     ` Jamie Lokier
2003-05-10 20:55       ` Jos Hulzink
2003-05-11  3:50       ` Linus Torvalds
2003-05-11  9:37         ` Jos Hulzink
2003-05-11 14:01           ` Jamie Lokier
2003-05-11 17:38             ` Davide Libenzi
2003-05-11 17:56               ` Eric W. Biederman
2003-05-11 18:23                 ` Davide Libenzi
2003-05-11 19:12                   ` Eric W. Biederman
2003-05-12 15:36                     ` Maciej W. Rozycki
2003-05-13  6:35                     ` H. Peter Anvin
2003-05-11 18:38                 ` Linus Torvalds
2003-05-11 19:00                   ` Matt Mackall
2003-05-11 19:16                     ` Eric W. Biederman
2003-05-12  1:07                     ` H. Peter Anvin
2003-05-11 19:10                   ` Eric W. Biederman
2003-05-11 18:43                 ` Christer Weinigel [this message]
2003-05-11 20:22                   ` wingel
2003-05-11 20:26                     ` Davide Libenzi
2003-05-11 17:54         ` Eric W. Biederman
2003-05-13 12:49 Chuck Ebbert
2003-05-13 18:45 ` H. Peter Anvin
2003-05-13 19:04   ` Richard B. Johnson
2003-05-13 19:27     ` H. Peter Anvin

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