Date: Thu, 6 Jan 2000 12:02:18 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
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To: Martin Str|mberg <ams AT ludd DOT luth DOT se>
cc: DJGPP <djgpp AT delorie DOT com>
Subject: Re: The endless int31 hooking debugging continued
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On Wed, 5 Jan 100, Martin Str|mberg wrote:

> Is it ok to just overwrite the values that was in ds, es and ss?

No, you need to save and restore them.

> I've
> tried pushing things to be able to restore them, but then I've got
> some _really_ strange crashes (Invalid opcode, Stack fault, EIP
> pointing into the middle of an instruction)!

I don't think it's because of the pushing, but please show the code
which did that.

Once again, I suggest to look at the function _i31_hook in dbgcom.c,
it shows several examples of code that hooks Int 31h and *works*.

> /* Restore segments to valid DJGPP state. */
>         movw %cs:_my_ds, %ds
>         movw _my_ds, %es
>         movw _my_ds, %ss

I don' think you can move values into segment registers directly, I
think you need to use AX as intermediary.