Re: [PATCH] Use correct x86 reboot vector

Christer Weinigel (christer@weinigel.se)
11 May 2003 20:43:26 +0200


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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/