From: andrey mirtchovski <andrey@lanl.gov>
To: 9fans@cse.psu.edu
Subject: [9fans] calculating the gdt pointer in 32 bit (protected) mode
Date: Wed, 23 Jan 2002 16:43:46 -0700 [thread overview]
Message-ID: <20020123234412.1ABFF19A02@mail.cse.psu.edu> (raw)
hello,
i'm trying to understand how the gdt pointer is calculated in
/sys/src/boot/pc/l.s .. the exercise includes calculating this
pointer when already in 32 bit mode and i'm kind of lost at this
point...
here's the relevant code snippet:
/*
* pointer to initial gdt
*/ TEXT tgdtptr(SB),$0
WORD $(3*8)
LONG $tgdt-KZERO(SB) /*
* goto protected mode
*/ /* MOVL tgdtptr(SB),GDTR /**/
BYTE $0x0f
BYTE $0x01
BYTE $0x16
WORD $tgdtptr(SB)
MOVL CR0,AX
ORL $1,AX
MOVL AX,CR0
using MOVL tgdtptr(SB),GDTR to calculate the gdt pointer when already
in protected mode crashes the machine, although not immediately...
thanx, andrey
next reply other threads:[~2002-01-23 23:43 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-01-23 23:43 andrey mirtchovski [this message]
2002-01-23 23:51 Russ Cox
2002-01-24 0:21 andrey mirtchovski
2002-01-24 0:42 jmk
2002-01-24 1:16 andrey mirtchovski
2002-01-24 2:23 Russ Cox
2002-01-24 3:14 ` Ronald G Minnich
2002-01-24 3:32 jmk
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