From: Andrew Kirilenko <icedank@gmx.net>
To: linux-kernel@vger.kernel.org
Subject: Re: Stored data missed in setup.S
Date: Wed, 23 Apr 2003 16:39:57 +0300 [thread overview]
Message-ID: <200304231639.57148.icedank@gmx.net> (raw)
In-Reply-To: <Pine.LNX.4.53.0304230925150.23037@chaos>
Hello!
> > I feel myself stupid, when fighting against setup.S. Here is small piece
> > of code (/arch/i386/boot/setup.S)
> >
> > --->
> > start_of_setup: # line 160
> > # bla bla bla - some checking code
> > movb $1, %al
> > movb %al, (0x100)
> > ....
> > ....
> > pushw %ax
> > movb (0x100), %al
>
> You put something from offset 0x100 into %al.
>
> > cmpb $1, %al
>
> Then you compared it against 1. This is where the comparaison
> occurred.
>
> > popw %ax # pop don't change any flags - 386 asm reference
>
> Then you put something else into %ax. Whatever it is, doesn't count.
>
> > je bail820 # and it don't jump -- al != 1
>
> Then you jumped based upon the comparison you made before you
> destroyed the contents of %al by poping %eax (%eax is (%ah << 8) | %al).
>
> If you don't want to muck with registers, just do:
>
> cmpb $1, (0x100)
> jz wherever
>
> You don't need to put memory oprands into registers to compare.
>
> > meme820: # line 300
> > <---
OK. And now code looks like:
-->
start_of_setup: # line 160
# bla bla bla - some checking code
movb $1, %al
movb %al, (0x100)
....
....
cmpb $1, (0x100)
je bail820 # and it DON'T jump here
<--
I'm sure, I'm doing something wrong. But what???
Best regards,
Andrew.
next prev parent reply other threads:[~2003-04-23 13:27 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-04-23 13:17 Stored data missed in setup.S Andrew Kirilenko
2003-04-23 13:33 ` Richard B. Johnson
2003-04-23 13:39 ` Andrew Kirilenko [this message]
2003-04-23 14:36 ` Richard B. Johnson
2003-04-23 14:50 ` Andrew Kirilenko
2003-04-23 15:06 ` Richard B. Johnson
2003-04-23 14:51 ` Randy.Dunlap
2003-04-23 15:11 ` Richard B. Johnson
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