On Wed, 23 Apr 2003, Andrew Kirilenko wrote:
> 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
> <---
>
> Any ideas? I've spent two days, trying to understand what's going on
> - no luck
> at all...
>
> Best regards,
> Andrew.
Cheers,
Dick Johnson
Penguin : Linux version 2.4.20 on an i686 machine (797.90 BogoMips).
Why is the government concerned about the lunatic fringe? Think about it.
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This archive was generated by hypermail 2b29 : Wed Apr 23 2003 - 22:00:36 EST