386 brokenes

Pavel Machek (pavel@atrey.karlin.mff.cuni.cz)
Tue, 29 Jul 1997 14:54:46 +0200


> >> Not really. Except for BSWAP the 386/486/586 user mode stuff is basically
> >> all down to how you order instructions and how you align them not to new
> >> instructions
> >
> >I thought there was some problem with 386s not write faulting
> >correctly when you had kernel level privileges? Hence the 386/486
> >differences in verify_area.
> Well, Alan did say "user mode stuff".
> The i386 is indeed very very broken when it comes to read-only pages in
> kernel space. The kernel tries to handle this, but the i386 braindamage
> does result in threads being inherently unsafe because there are various
> nasty race conditions that a thread library could hit.

You just said that only kernel is hit by this. But is not threads
library part of userland? Why does especialy threads library care
about wp bit being broken?

> This is fixed in the i486 and up, and the threads race problem only
> shows up for code that tries to be malicious on purpose, so it is mostly
> harmless (hint: if you're using a 386 as a server that accepts logins,
> you should probably try to hit somebody for a 486 - there must be tons
> of them lying around).

I do not think so. Not here :-(. BTW such warnings should be better
written out somewhere, I always thought that 386s are expected to
work... And btw replacing board is somehow non-trivial for portable
computers... Bad, bad, bad.


I'm really pavel@atrey.karlin.mff.cuni.cz. 	   Pavel
Look at http://atrey.karlin.mff.cuni.cz/~pavel/ ;-).


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This is my little buggy signature...				Pavel
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