From: andrey mirtchovski <andrey@lanl.gov>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] calculating the gdt pointer in 32 bit (protected) mode
Date: Wed, 23 Jan 2002 18:16:29 -0700 [thread overview]
Message-ID: <20020124011654.DEFF419A1C@mail.cse.psu.edu> (raw)
the instruction is:
BYTE $0x0f
BYTE $0x01
BYTE $0x16
LONG $tgdptr-KZERO(SB)
when traced it resembles:
MOVL ([ESI]+($tgdptr-KZERO(SB))), GDTR
(the 0x16 tells it that the address if offset from ESI)
if instead one assembles:
MOVL $tgdptr-KZERO(SB), GDTR
(as it is written in the comments above the original
instruction) then the third byte becomes 0x15 and
it starts thinking that the pointer is actually a 32 bit
displacement, which is even less correct (i think)..
i'm going to start debugging using the proven trial-
error method and will see which takes me to the
correct GDT pointer..
am i correct in my assumption that i am unable to
modify the ESI register? otherwise i'd be tempted
to put the pointer value in ESI and execute the
instruction with 0 displacement from ESI..
i could of course be terribly wrong in everything i've
done so far...
andrey
next reply other threads:[~2002-01-24 1:16 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-01-24 1:16 andrey mirtchovski [this message]
-- strict thread matches above, loose matches on Subject: below --
2002-01-24 3:32 jmk
2002-01-24 2:23 Russ Cox
2002-01-24 3:14 ` Ronald G Minnich
2002-01-24 0:42 jmk
2002-01-24 0:21 andrey mirtchovski
2002-01-23 23:51 Russ Cox
2002-01-23 23:43 andrey mirtchovski
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