linux-kernel - Re: Is 386 processor still supported?

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Date:	Thu, 15 Jan 2009 15:17:34 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Jan-Benedict Glaw <jbglaw@...-owl.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Kosina <jkosina@...e.cz>, Adam Osuchowski <adwol@...k.pl>,
	linux-kernel@...r.kernel.org, Nick Piggin <npiggin@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: Is 386 processor still supported?


* Maciej W. Rozycki <macro@...ux-mips.org> wrote:

> On Thu, 15 Jan 2009, Alan Cox wrote:
> 
> > >  UP emulation of CMPXCHG and XADD for userland should be rather trivial, 
> > > so why not include it like with LL/SC for MIPS?
> > 
> > Why not just ship an additional libc with the right options ?
> 
>  Does not work for MIPS as glibc has no equivalent code for pre-LL/SC 
> CPUs and LL/SC is always used.  For the i386 the situation seems worse 
> yet as for pre-i486 CPUs a generic C implementation of 
> compare-and-exchange is used guaranteeing silent thread unsafety. :(
> 
>  IMO, a kernel emulation of CMPXCHG and XADD (both are used by 
> sysdeps/i386/i486/bits/atomic.h in glibc) with an optional LOCK prefix, 
> guaranteeing UP atomicity would be a cheap way to provide long-term i386 
> userland support with little burden for both Linux and respective user 
> software maintainers.  Certainly it adds some bloat to the kernel, but I 
> think it is not an option that should be outright dismissed without 
> consideration.

patches are welcome ...

	Ingo
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