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From:	"japheth" <mail AT japheth DOT de>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: LWP & hw_exception under DJGPP
Date:	6 Dec 2006 06:05:34 -0800
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>     2. My program crashes, with SIGSEGV, when it tries to 'pop'
> something from the stack, while SS points to segment with limit=0000FFF
> and ESP=1000. What is that segment? I was sure, that DJGPP uses the flat
> memory model - all data and code are sharing the same linear space, but
> during the crash SS points to segment with different base address (which
> differs from the base address pointed by CS, for example). Could you
> explain what is the purpose of this weird segment?

it is the "locked" protected-mode stack. The dpmi host switches to this
stack to handle hardware interrupts, real-mode callbacks and
exceptions. The selector contained in SS might even be a GDT selector,
that is, you won't get it's linear base address by calling int 31h,
ax=0006.

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