From:	eplmst AT lu DOT erisoft DOT se (Martin Stromberg)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Question about djgpp's int-wrapper
Date:	9 Jun 2002 19:09:30 GMT
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Lawrence Rust (lvr AT nospam DOT softsystem DOT co DOT uk) wrote:
: If you look at Intel's IA32 architecture manual:

: ftp://download.intel.com/design/pentium4/manuals/24547107.pdf

: you'll see on page 3-49 that in protected mode, iret only restores

Well, I don't. But perhaps you meant page 3-349 or near that?

: EFLAGS(IF) if CPL <= IOPL.  This is also true of popf.  So if the code is
: run on a system such as Windows NT, 2K or XP where CPL is 3 and IOPL is 0
: then the task will be left with virtual interrupts disabled.  The system
: will remain responsive but the task will not receive any more interrupts
: :-(.

Ouch!

: However, sti signals GP(0) if CPL > IOPL, which on NT is handled by the
: NTVDM and will enable virtual interrupts to the task.

: IMHO this is a design fault in the IA32.  The correct action would have been

Yes. I wonder what they were thinking at Intel when they designed
this? Those five pages of pseudo-code showing us what is happening is
impressive (in a baaaad way). I only wish they could have thought it
through a little more before making the chips.


Right,

						MartinS

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