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

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Date:	Wed, 28 Nov 2007 18:29:24 +0100
From:	Andres Freund <andres@...razel.de>
To:	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: "hwcap 0 nosegneg" doesnt work with paravirt_ops xen as of 2.6.23.9

Hi all,

after converting a host from using a ubuntu patched 2.6.22 domU to using 
2.6.23 xen via paravirt_ops (no configuration change except devicename change 
in fstab, and another getty running) ldconfig no longer picks up the nosegneg 
libc leading to segfaults for some programs.

/etc/ld.so.conf.d/xen.conf:
hwcap 0 nosegneg

On ubuntu's 2.6.22-xen:
ldd /usr/bin/perl
        linux-gate.so.1 =>  (0xf57fe000)
        libdl.so.2 => /lib/tls/i686/nosegneg/libdl.so.2 (0xb7f90000)
        libm.so.6 => /lib/tls/i686/nosegneg/libm.so.6 (0xb7f6b000)
        libpthread.so.0 => /lib/tls/i686/nosegneg/libpthread.so.0 (0xb7f53000)
        libc.so.6 => /lib/tls/i686/nosegneg/libc.so.6 (0xb7e05000)
        libcrypt.so.1 => /lib/tls/i686/nosegneg/libcrypt.so.1 (0xb7dd7000)
        /lib/ld-linux.so.2 (0xb7f9d000)

On selfcompiled 2.6.23.9:
ldd /usr/bin/perl
        linux-gate.so.1 =>  (0xf57fc000)
        libdl.so.2 => /lib/tls/i686/cmov/libdl.so.2 (0xb7f3b000)
        libm.so.6 => /lib/tls/i686/cmov/libm.so.6 (0xb7f16000)
        libpthread.so.0 => /lib/tls/i686/cmov/libpthread.so.0 (0xb7efe000)
        libc.so.6 => /lib/tls/i686/cmov/libc.so.6 (0xb7db3000)
        libcrypt.so.1 => /lib/tls/i686/cmov/libcrypt.so.1 (0xb7d85000)
        /lib/ld-linux.so.2 (0xb7f46000)

I now discover, that after some playing around (during discovering what the 
problem is) i must have changed something, because ldd still shows the use of 
the i686/cmov libraries, but applications reliably causing crashes earlier, 
dont do so anymore.

Perhaps Im all wrong, and paravirt_ops doesnt need the nosegneg versions and 
just a ldconfig or so (which seems strange because the result before and 
after the ldconfig were the same).

Greetings, 

Andres Freund

PS: I did this conversion mainly, because I was getting quite random crashes 
inside the domU. I guess, as this was a vendor kernel + xensource xen kernel, 
this isnt appropriate for lkml? As well as the crashes of the Dom0 (ubuntu 
again)?

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