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Re: [Xen-users] Debian lenny and the TLS warning

To: Robert Dunkley <Robert@xxxxxxxxx>, Xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Debian lenny and the TLS warning
From: Andreas Sommer <AndiDog@xxxxxx>
Date: Fri, 21 Aug 2009 11:39:31 +0100
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The nosegneg setting is only valid for dynamically linked programs, I guess. It is automatically restored to "1" (probably by libc6-xen) when rebooting the domain.

You're right, it does not make a difference with the init process.

Robert Dunkley wrote:

Hi Andreas,


Sorry ignore my last reply, I just noticed the offending process is different.



This is a neat fix for this problem with RHEL/Centos, might work with Debian (?):


create a file called /etc/ld.so.conf.d/nosegneg.conf that contains this:


# This directive teaches ldconfig to search in nosegneg subdirectories

# and cache the DSOs there with extra bit 0 set in their hwcap match

# fields.  In Xen guest kernels, the vDSO tells the dynamic linker to

# search in nosegneg subdirectories and to match this extra hwcap bit

# in the ld.so.cache file.

hwcap 0 nosegneg






From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Andreas Sommer
Sent: 21 August 2009 09:52
To: Xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Debian lenny and the TLS warning


I have set up Debian lenny domains using debootstrap (similar to the tutorial on http://www.option-c.com/xwiki/Create_a_Debian_VM_with_debootstrap). As most tutorials say, /lib/tls should be renamed to /lib/tls.disabled - but that file doesn't even exist on Lenny?! Anyway, this shouldn't be a problem because I installed libc6-xen on the guest domain, but I still get this warning:

  ** WARNING: Currently emulating unsupported memory accesses  **
  **          in /lib/tls glibc libraries. The emulation is    **
  **          slow. To ensure full performance you should      **
  **          install a 'xen-friendly' (nosegneg) version of   **
  **          the library, or disable tls support by executing **
  **          the following as root:                           **
  **          mv /lib/tls /lib/tls.disabled                    **
  ** Offending process:
init (pid=701)                         **

I guess the init process is statically linked against a normal xen-unfriendly libc?? If yes, how do I replace it with a xen-friendly init and does that prevent my dom0 mouse cursor from stuttering when I start/shutdown domains (i.e. is there a performance difference ;-) ?

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