linux-kernel - Re: "hwcap 0 nosegneg" doesnt work with paravirt

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Date:	Thu, 29 Nov 2007 01:03:03 +0100
From:	Andres Freund <andres@...razel.de>
To:	Roland McGrath <roland@...hat.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org
Subject: Re: "hwcap 0 nosegneg" doesnt work with paravirt_ops xen as of 2.6.23.9

Hi,

On Wednesday 28 November 2007, Roland McGrath wrote in "Re: "hwcap 0 nosegneg" 
doesnt work with paravirt_ops xen as of 2.6.23.9":
> > > /etc/ld.so.conf.d/xen.conf:
> > > hwcap 0 nosegneg
> >
> > This looks OK. [...]
>
> No, it does not match this:
> 	/* Bit used for the pseudo-hwcap for non-negative segments.  We use
> 	   bit 1 to avoid bugs in some versions of glibc when bit 0 is
> 	   used; the choice is otherwise arbitrary. */
> 	#define VDSO_NOTE_NONEGSEG_BIT	1
> You really want "hwcap 1 nosegneg" given that.
> Yes, we've been over this several times already.
Thanks for the information. I guess it would be nice to document this 
somewhere (except in code)... At least I could not find any information about 
it beside some patch (Not directed at you, Roland). Any idea where?

Besides, it has one Problem: It is not backwards compatible. Using it on 
earlier Xen Versions yields the normal tls versions (xen 3.1). Isnt the 
userbase of existing xen installations bigger than the one of some point in 
FC5 test releases?
Ugh. Leaning a bit far out of the door with that one considering my knowledge 
about it... Sorry about that.

Greetings,

Andres

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