Re: [PATCH] Use correct x86 reboot vector

[wingel@zoo.weinigel.se]

[following up to myself]

Christer Weinigel <christer@weinigel.se> writes:

> 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

better add the following too:

        move.l   %cr0, %eax
        and.l    $~1, %eax
        move.l   %eax, %cr0

> reset_gdt_end:
> 
>         lgdt    %cs:reset_gdt
>         ljmp    $ROM_CODE_SEG, 0xfff0

BTW, what does Windows do here?  Whatever Windows is using should work
with Linux too.

  /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