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Date:      Wed, 2 Sep 1998 07:23:23 +0000 (GMT)
From:      Terry Lambert <tlambert@primenet.com>
To:        dawes@rf900.physics.usyd.edu.au (David Dawes)
Cc:        joki@kuebart.stuttgart.netsurf.de, roberto@keltia.freenix.fr, freebsd-current@FreeBSD.ORG
Subject:   Re: XFree86 and ELF
Message-ID:  <199809020723.AAA22823@usr02.primenet.com>
In-Reply-To: <19980902123708.A21469@rf900.physics.usyd.edu.au> from "David Dawes" at Sep 2, 98 12:37:08 pm

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> Can I ask a naive question?  Is there any reason the FreeBSD/ELF rules
> need to be different from those used for Linux/ELF (see lnxLib.cf)?  Also,
> please keep in mind that bsdLib.rules is used for NetBSD and OpenBSD too.

Linux uses a call-gate based kernel entry, which is TSS based, and
therefore takes more CPU cycles on a contect switch than strictly
required.  The FreeBSD mechanism for kernel entry (and subsequet
context switch) is threfore more efficient than that used by Linux.

In addition, Linux has gratuitous differences between the BSD 4.4
system cal table and the Linux system call table that result in
ABI incompatabilities.

Realisitcally, the Linux ABI is not static enough to be considered an
ABI standard, and thus the BSD ABI is preferred (being both more
static and more orthogonal).

You could argue that this was a religious difference, if you were
willing to orphan legacy applications.  If not, you would regard
this as a bug in the Linux method of ABI update.


> I see you submitted a patch to XFree86 -- thanks.  Maybe it would be a good
> idea to wait a little while until everything is resolved, then send another
> patch?  I don't have a box running 3.0 ELF yet, but I'm planning to set one
> up in the next week or two.

The patch is not useful unless you are micro-tracking the FreeBSD -current
sources, which the XFree86 project is not.

The eventual FreeBSD ABI should (hopefully) match at least two of the
other BSD 4.4 derivative ABI's.

In an ideal world, given that the Solaris ABI changes at a slower rate
than all others, FreeBSD (and the other BSD's) would adopt the Solaris
ABI for ABI compatability...

And then monkeys fly out my butt.


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.

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