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Date:      Fri, 20 Feb 2015 15:09:49 -0600
From:      "Andrew Wilcox" <AWilcox@Wilcox-Tech.com>
To:        "freebsd-current" <freebsd-current@freebsd.org>
Subject:   i386 port no longer bootable on non-SSE CPUs
Message-ID:  <00c401d04d51$905fedc0$b11fc940$@Wilcox-Tech.com>

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Hello,

The i386 port, both 10-STABLE and 11-CURRENT, will not boot on systems =
without SSE support.  This is caused by r273995, as using `svn merge -c =
-273995` (and hacking-and-sloshing through the few compiler errors =
afterwards) makes it once again bootable.

This crash happens very early on in boot, before even mi_startup (as the =
author line is never even printed): http://i.imgur.com/SAty1mT.jpg

This breaks support for all i486, Pentium, Pentium Pro, and Pentium =
II-based CPUs and computers.  These are not only found in older =
computers that are useful as routers and file servers, but there are =
some new SoCs still using these chips:

Intel Galileo board
http://www.frys.com/product/8080584
Pentium core, no MMX/SSE whatsoever.  Released late 2014.

AMD Elan SC520, Geode series
http://www.eurotech.com/en/products/CPU-1421
http://www.amd.com/en-us/products/embedded/processors/lx
While the Elan is no longer manufactured, it still remains popular.  The =
new Geode LX series of processors only implement MMX (so are roughly =
equivalent to a Pentium Pro in terms of instruction set).

Backing out r273995 allows boot to proceed normally, as shown here: =
http://imgur.com/a/WWsa5

I attempted to revert locore.S to see if it was related to the stack =
setup changes found in that commit and it made no difference; the panic =
was the same.

I would be willing to test any patches/diffs on any or all of the =
systems I have, but unfortunately I'm in a bit over my head trying to =
figure out which part of this commit is causing it.

Best,
Andrew

--
Andrew Wilcox, C/C++/Python developer, kernel hacker
Blog:   http://blog.foxkit.us/  WWW: http://foxkit.us/
GitHub:  https://github.com/awilfox





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