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Open Source and information security mailing list archives
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Date: Sat, 23 Jun 2007 01:00:17 +0200 From: Bodo Eggert <7eggert@....de> To: Rene Herman <rene.herman@...il.com>, "H. Peter Anvin" <hpa@...or.com>, Bart Trojanowski <bart@...ie.net>, linux-kernel@...r.kernel.org Subject: Re: how to tell linux (on x86) to ignore 1M or memory Rene Herman <rene.herman@...il.com> wrote: > The point was that real mode could only access the first 1M, not > the first 16... :-) The real mode on i386+ can actually access the whole 4GB address range due to a former-bug-now-feature in the i386+. This "bug" causes the segment limit to not be reset on return to real mode, but only on subsequent assigns to the segment registers/selectors. Using a rarely used segment register like GS, you could use extended memory in your program. Obviously this needs 1) Entering and returning from protected mode, 2) all programs to agree not to clobber GS and 3) not using v86 mode (EMM386.exe). Therefore and because it was discovered in the late days of DOS it was not in widespread use. Some DOS extenders were reported to use it ... http://www.programmersheaven.com/mb/x86_asm/344953/344953/readmessage.aspx -- The programmer's National Anthem is 'AAAAAAAAHHHHHHHH' Friß, Spammer: vO9EZegbA@...pA.7eggert.dyndns.org maFsnwE@...nj.7eggert.dyndns.org mhF-@...Rjk.7eggert.dyndns.org - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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