A question about TLS libraries in case of Xen integration in Linux

A question about TLS libraries in case of Xen integration in Linux

[Philippe Berthault]

The current Xen hypervisor (v3.0.1) doesn't support TLS library.
In case of an hypothetical integration of Xen in Linux and also in 
distributions
such as RHEL5, SuSE, etc... this restriction becomes unacceptable.

So my question is:
There is a plan to support TLS library in the future or there is a plan
to integrate a Xen compatible TLS library in Linux ?

Philippe Berthault.

Re: A question about TLS libraries in case of Xen integration in Linux

[Rik van Riel]

On Tue, 21 Feb 2006, Philippe Berthault wrote:

> The current Xen hypervisor (v3.0.1) doesn't support TLS library.

Are you sure?  ISTR it just flipping the segment on every fault,
and incurring a slowdown.

> There is a plan to support TLS library in the future or there is a plan
> to integrate a Xen compatible TLS library in Linux ?

Fedora Core 4 and 5 have such a glibc variant.  Other distributions
may have it too.

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Re: A question about TLS libraries in case of Xen integration in Linux

[Mark Williamson]

Sorry if this was already replied to by someone...

> > The current Xen hypervisor (v3.0.1) doesn't support TLS library.
>
> Are you sure?  ISTR it just flipping the segment on every fault,
> and incurring a slowdown.

Yep.

> > There is a plan to support TLS library in the future or there is a plan
> > to integrate a Xen compatible TLS library in Linux ?
>
> Fedora Core 4 and 5 have such a glibc variant.  Other distributions
> may have it too.

Fedora's glibc switches off the TLS negative segment accesses (and uses 
conventional accesses) when running on Xen.  SuSE's glibc variant just 
doesn't implement TLS accesses using negative segment offsets on any system, 
so it also supports Xen just fine. [the SuSE guys don't think using negative 
segment offsets gives a significant performance increase for them, so they 
chose to avoid the inconvenience entirely]

On 64-bit systems, the TLS implementations used by Linux are a non-issue 
anyhow.

Cheers,
Mark

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