Path: utzoo!attcan!uunet!zephyr.ens.tek.com!uw-beaver!cornell!rochester!pt.cs.cmu.edu!b.gp.cs.cmu.edu!Ralf.Brown@B.GP.CS.CMU.EDU
From: Ralf.Brown@B.GP.CS.CMU.EDU
Newsgroups: comp.os.msdos.programmer
Subject: Re: Need info on 286/386 exceptions and int handling under DOS
Message-ID: <2715b473@ralf>
Date: 12 Oct 90 12:17:55 GMT
Sender: ralf@b.gp.cs.cmu.edu
Organization: Carnegie Mellon University School of Computer Science
Lines: 24
In-Reply-To: <1990Oct11.161231.261@Octopus.COM>

In article <1990Oct11.161231.261@Octopus.COM>, stever@Octopus.COM (Steve Resnick ) wrote:
}I got all that, so far. The interrupt vector table (in real mode) is located
}at 0000:0000. IRQ12's vector should be located at 0000:0030. This is all well
}and fine, but there are processor exceptions which map to hardware interrupts.
}I cannot find where INT 12 is mapped to an exception. My default BIOS int 12
}handler does not deal with processor exceptions, and my own int 12 handler for
}dealing with serial interrupts does not either. Normally, exception 12 (stack
}fault exception) will not occur in real mode, unless you have a SP of 1 and
}push a word on the stack. Then SP = -1 = FFFFH which is not real good. 
}What I want to know, is how that gets handled independantly of my serial
}interrupts. 

If you are running a 386 memory manager such as QEMM-386 or 386^MAX, the
memory manager gets any CPU exceptions first, and decides whether or not
to pass them down to the virtual86-mode program via the real-mode interrupt
vector table.  BTW, an exception 12 will also occur on a 386 when attempting
to access the word at FFFFh in the stack segment (any other segment gets you
an exception 13).

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