Xref: utzoo comp.os.msdos.programmer:4624 comp.os.os2.programmer:619
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!batcomputer!cornell!rochester!pt.cs.cmu.edu!o.gp.cs.cmu.edu!ralf
From: ralf+@cs.cmu.edu (Ralf Brown)
Newsgroups: comp.os.msdos.programmer,comp.os.os2.programmer
Subject: Re: Info on Changing Stacks in protected mode
Message-ID: <1991Apr13.153517.10767@cs.cmu.edu>
Date: 13 Apr 91 15:35:17 GMT
References: <1991Mar29.155840.2626@netcom.COM> <71689@microsoft.UUCP>
Sender: netnews@cs.cmu.edu (USENET News Group Software)
Organization: School of Computer Science, Carnegie Mellon
Lines: 21

In article <71689@microsoft.UUCP> donh@microsoft.UUCP (Don HACHERL) writes:
}In article <1991Mar29.155840.2626@netcom.COM> resnicks@netcom.COM (Steve Resnick) writes:
}>Everything works great until I run this under OS/2 rather than MS DOS.
}>OS/2 will not let me clear interrupts while changing SS:SP.  My question:
}>Is it necessary to disable interrupts while switching stacks in protected 
}
}Not only do you not need an IOPL segment, you don't even need to
}disable interrupts, under DOS or OS/2, because the chip will do it for
}you.  To quote from my handy Intel refernce manual "A MOV into SS
}instruction inhibits all interrupts until after the execution of the
}next instruction (which is presumably a MOV into SP instruction)."

The reason why everybody disables interrupts during a stack switch is that
the early 8088s had a microcode bug which caused interrupts to remain
enabled after a MOV into SS.  If your code can't run on an 8088/8086, you
won't need the CLI.
--
{backbone}!cs.cmu.edu!ralf  ARPA: RALF@CS.CMU.EDU   FIDO: Ralf Brown 1:129/3.1
BITnet: RALF%CS.CMU.EDU@CMUCCVMA   AT&Tnet: (412)268-3053 (school)   FAX: ask
DISCLAIMER?  Did  | It isn't what we don't know that gives us trouble, it's
I claim something?| what we know that ain't so.  --Will Rogers