From: j.neuschaefer@gmx.net (Jonathan Neuschäfer)
To: kernelnewbies@lists.kernelnewbies.org
Subject: What's the value of %cs before jump in pm32 on booting?
Date: Thu, 11 Aug 2011 18:29:25 +0200 [thread overview]
Message-ID: <20110811162924.GI29043@debian.debian> (raw)
In-Reply-To: <CAGdaadaYBKLgJ9S-XPy6T4BL+XaF70oCt3BGRURo8qGYm46XGQ@mail.gmail.com>
On Thu, Aug 11, 2011 at 09:53:10PM +0700, Mulyadi Santosa wrote:
> On Thu, Aug 11, 2011 at 18:18, jiangtao.jit <jiangtao.jit@gmail.com> wrote:
> > Hi all:
> >
> > on booting of x86
> > top of file arch/x86/boot/pmjump.S
> > there is code
> > -------------------
> > GLOBAL(protected_mode_jump)
> > ? ? ? ?movl ? ?%edx, %esi
> > ? ? ? ?xorl ? ?%ebx, %ebx
>
> i think it's zeroing bx (l--> low I suppose)
Long, actually, i.e. 32-bit.
>
> > ? ? ? ?movw ? ?%cs, %bx
>
> then, it should zero the content of cs. Quite likely, it means to jump
> to cpu ring level 0 and do something there..
No, this is written in AT&T syntax, where the source comes first, and
then the destination. IOW, the code means: Copy the 16 bit register CS
into the lower 16 bit of EBX (which is BX).
CMIIW,
Jonathan Neusch?fer
prev parent reply other threads:[~2011-08-11 16:29 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-11 11:18 What's the value of %cs before jump in pm32 on booting? jiangtao.jit
2011-08-11 14:53 ` Mulyadi Santosa
2011-08-11 16:29 ` Jonathan Neuschäfer [this message]
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