Bug#882255: libc6-amd64: Multilib causes catastrophic system failure during upgrade to libc 2.25

[Mikulas Patocka <mikulas@twibright.com>]

On Sun, 26 Nov 2017, Aurelien Jarno wrote:

> > > You mean that even now running 'ldconfig' followed by 'ldd /bin/true'
> > > will give you
> > >   libc.so.6 => /lib64/libc.so.6
> > > instead of
> > >   libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6
> > > ?
> > 
> > Yes.
> > # ldd /bin/true
> >         linux-vdso.so.1 (0x00007ffc62b5a000)
> >         libc.so.6 => /lib64/libc.so.6 (0x00007fd870377000)
> >         /lib64/ld-linux-x86-64.so.2 (0x00007fd870921000)
> > 
> > If I use the --inhibit-cache flag, it points to the correct location:
> > # /lib64/ld-linux-x86-64.so.2 --list --inhibit-cache /bin/true
> >         linux-vdso.so.1 (0x00007ffd566e4000)
> >         libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f73026c8000)
> >         /lib64/ld-linux-x86-64.so.2 (0x00007f7302c73000)
> > 
> > Without --inhibit-cache, it points to /lib64/libc.so.6
> > # /lib64/ld-linux-x86-64.so.2 --list /bin/true
> >         linux-vdso.so.1 (0x00007ffd5ad10000)
> >         libc.so.6 => /lib64/libc.so.6 (0x00007fc566092000)
> >         /lib64/ld-linux-x86-64.so.2 (0x00007fc56663c000)
> 
> I am still unable to reproduce this problem. On my system
> lib/x86_64-linux-gnu/ is preferred over lib64. ldconfig uses glob to to
> interpret the "*.conf" in /etc/ld.so.conf, so the files are sorted
> alphabetically and thus the zz_amd64-biarch-compat.conf should appear
> last.
> 
> It would be interesting to check at the order in the cache, using
> "ldconfig -p | grep libc.so". Could you please provide that output?
> 
> Thanks,
> Aurelien

# ldconfig -p | grep libc.so
        libc.so.6 (libc6,x32, ABI OS: Linux 3.4.0) => /lib/x86_64-linux-gnux32/libc.so.6
        libc.so.6 (libc6,x86-64, ABI OS: Linux 3.2.0) => /lib64/libc.so.6
        libc.so.6 (libc6,x86-64, ABI OS: Linux 2.6.32) => /lib/x86_64-linux-gnu/libc.so.6
        libc.so.6 (libc6, ABI OS: Linux 3.2.0) => /lib32/libc.so.6
        libc.so.6 (libc6, ABI OS: Linux 2.6.32) => /lib/i386-linux-gnu/libc.so.6

The problem is caused by the "ABI OS" field - the libraries in /lib64 have 
higher field than the libraries in /lib/x86_64-linux-gnu/

If I comment out this piece of code in the function compare in the file 
glibc/elf/cache.c, the problem goes away and the linker will prefer 
libraries in /lib/x86_64-linux-gnu/ and /lib/i386-linux-gnu/.

/*
      if (e2->osversion > e1->osversion)
        return 1;
      if (e2->osversion < e1->osversion)
        return -1;
*/

Mikulas