Re: [PATCH] libnsl: Turn remaining symbols into compat symbols [BZ #22701]

[Szabolcs Nagy <szabolcs dot nagy at arm dot com>]

On 31/01/18 15:07, Szabolcs Nagy wrote:
> On 31/01/18 12:53, Florian Weimer wrote:
> > On 01/31/2018 12:21 PM, Szabolcs Nagy wrote:
> > > if i install glibc-2.27 on top of an earlier glibc install
> > > without removing the previous libnss_nis.so.2, which references
> > > _nsl_default_nss, then the new libnsl.so.1 will not have that
> > > symbol so old libnss_nis.so.2 no longer works.
> > >
> > > either i have to --enable-obsolete-nsl in the new libc or
> > > remove the old libnss_nis.so.2 (and hope nothing needs it)
> > > before i run the new ldconfig.
> > >
> > > i thought 'installing over' previous libc is a valid use
> > > (i do this when testing in chroot)
> >
> > A similar thing happens if you install a glibc over another glibc with different build flags, e.g. one that is using AT_PLATFORM directories.
> >
> > We can certainly revert the change and reapply it for 2.28, maybe this time with a change which loads the NSS modules with RTLD_NOW, so that 
> > the missing GLIBC_PRIVATE symbol is detected at dlopen time and the NSS module is ignored (at least for now).
>
> i think RTLD_NOW wont help me, i run ldconfig in the
> chroot with mixed old and new glibc libs and ldconfig
> fails to process libnss_nis.so.2
>
> chroot /tmp/tmp6YjWM3/chroot sudo /sbin/ldconfig
> sudo: relocation error: /lib/aarch64-linux-gnu/libnss_nis.so.2: symbol _nsl_default_nss version GLIBC_PRIVATE not defined in file libnsl.so.1 
> with link time reference

sorry you were right, it's sudo that fails, so RTLD_NOW
would make the dlopen fail and then there would be no
runtime failure.

(i thought it's ldconfig that tries to load the library somehow)

anyway i'll have a workaround for this so either way is
fine for me (revert or keep).

> i guess i will work this around in the chroot build script.
> (i assume it's enough to remove the obsolete nss libs
> and potentially update the /etc/nsswitch.conf if things
> dont work with the old one)