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Jemm v5.66 : exception 09 on Intel P4 w/ Ultra IDE BIOS ext. (DOSX)

posted by Japheth Homepage, Germany (South), 06.09.2007, 07:50

> I was moving back and forth on the cmdline words via Ctrl-Left and
> Ctrl-Right, then I wanted to see if (unlike FreeCOM 0.82, disk #2) it
> deleted to end of cmdline via Ctrl-End, but that resulted in *crash*! This
> is via the default setup of disk #1: "JEMM386 SB X=C000-CFFF I=TEST
> VERBOSE" (5.66).
>
> > Jemm386: exception 09 occured at CS:EIP=3206:00000008
> > SS:ESP=0010:f8004E04 EBP=00000A5E
> > EFL=4B415453 CR0=80000011
> > CR2=00000000 EAX=0A400200
> > EBX=00000A6A ECX=00000A6A
> > EDX=00000006 ESI=00000001
> > EDI=00003629
this dump is interesting:

EFL=4B415453 is "impossible". In ASCII it is "STAK".

OTOH, 3206 for CS is also very unlikely, but 3206 is a very common value for the flags register (and this value also tells that interrupts are enabled).

So I guess that an IRQ 1 (keyboard interrupt) is occuring in ring 0 protected mode which Jemm seems unable to handle properly. CS in fact is 0008, which is the Jemm ring 0 code selector, but unfortunately the true EIP is not displayed because of Jemm's stack mess.

What's important to know in this context is that Jemm's ring 0 code usually runs with interrupts disabled.

There is a chance that loading 386SWAT can show more details (the EIP register content). Or, if 386SWAT cannot help, a slight modification in Jemm will display this register.

---
MS-DOS forever!

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