Mail Archives: djgpp/1999/09/08/09:14:44
On Tue, 7 Sep 1999, Rez wrote:
> Question, then: I beta-test for a coder who works with DJGPP under
> Win95. I test our app exclusively in real DOS. About half the time when
> there's a bug, the program runs just fine under Win95 in a DOS box (both
> for the coder and my testing partner) but segviols before it even gets
> fully loaded under real DOS with CWSDPMI. Sometimes this happens even
> with trivial bugs, like a wonked menu item. I realise this is vague, but
> anything in particular which causes this dichotomy (bug has no effect
> under Win95, dies spectacularly under DOS) ??? ISTM if we knew what
> sort of things cause this, we (ie. our coder) could avoid 'em up front.
It's all in the DJGPP FAQ: see section 9.1.
In a nutshell: CWSDPMI supports an extension of the DPMI spec that
allows to decommit the null page, and DJGPP uses that extension in the
startup code. Thereafter, every NULL pointer dereference causes a
page fault when you run under CWSDPMI.
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