slow emulation warning when loading libgomp.so.1

[Kostas Chatzikokolakis]

The issue happens on lucid instances running on ec2. Loading /usr/lib/libgomp.so.1 takes a long time (~10 seconds) and the following warning appears in dmesg:

** 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 **

To reproduce:
 - launch a lucid instance from ami-a403f7cd
 - apt-get install libgomp1
 - load /usr/lib/libgomp.so.1, eg
     perl -MDynaLoader -e 'DynaLoader::dl_load_file("/usr/lib/libgomp.so.1")'
  or run an executable that uses it, eg 'convert' from the imagemagick package.

A weird thing is that libgomp1 seems to be normally using the nosegneg version:

ldd /usr/lib/libgomp.so.1
 linux-gate.so.1 => (0xb77e2000)
 librt.so.1 => /lib/tls/i686/nosegneg/librt.so.1 (0xb77c1000)
 libpthread.so.0 => /lib/tls/i686/nosegneg/libpthread.so.0 (0xb77a8000)
 libc.so.6 => /lib/tls/i686/nosegneg/libc.so.6 (0xb764a000)
 /lib/ld-linux.so.2 (0xb77e3000)

Is it a false warning? Deleting /lib/tls does not help.

Note also that on maverick (ami-1a837773) this issue does _not_ exist, and ldd output is different:

ldd /usr/lib/libgomp.so.1
 linux-gate.so.1 => (0xb779f000)
 librt.so.1 => /lib/librt.so.1 (0xb7780000)
 libpthread.so.0 => /lib/libpthread.so.0 (0xb7766000)
 libc.so.6 => /lib/libc.so.6 (0xb7608000)
 /lib/ld-linux.so.2 (0xb77a0000)

ProblemType: Bug
DistroRelease: Ubuntu 10.04
Package: libc6-xen 2.11.1-0ubuntu7.5
ProcVersionSignature: Ubuntu 2.6.32-309.18-ec2 2.6.32.21+drm33.7
Uname: Linux 2.6.32-309-ec2 i686
Architecture: i386
Date: Sun Oct 31 16:52:41 2010
Ec2AMI: ami-a403f7cd
Ec2AMIManifest: ubuntu-images-us/ubuntu-lucid-10.04-i386-server-20101020.manifest.xml
Ec2AvailabilityZone: us-east-1b
Ec2InstanceType: m1.small
Ec2Kernel: aki-6603f70f
Ec2Ramdisk: unavailable
ProcEnviron:
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: eglibc

[Scott Moser (smoser)]

Possibly related to bug 427288 and/or bug 432718. I'm really just mentioning them here for reference, I haven't looked much deeper.

[Scott Moser (smoser)]

I've just now reproduced:

ec2run-instances --region us-east-1 --instance-type m1.small ami-a403f7cd --key mykey

then
sudo apt-get update && sudo apt-get install libgomp1

$ time perl -MDynaLoader -e 'DynaLoader::dl_load_file("/usr/lib/libgomp.so.1")'

that took ~ 13 seconds, and I see the messages in dmesg.

[Scott Moser (smoser)]

Other interesting piece of info, I can't reproduce this on a t1.micro of ami-480df921
  us-east-1 ami-480df921 canonical ebs/ubuntu-lucid-10.04-i386-server-20101020

[Kostas Chatzikokolakis (kostas-chatzi)]

The other bugs are about the same warning indeed, but for different executables (init and dbus-uuidgen). Both bugs seem fixed in my instances. One interesting difference is that in bug 432718 dbus-uuidgen uses libraries under /lib/tls/i686/cmov/, while ldd /usr/lib/libgomp.so.1 shows only the nosegneg versions.

[dino99 (9d9)]

This is no more a supported version now