XDR related breakage in libvirt v6.6.0 when using libvirt-lxc

Hi, I expect that this falls under the "with meson now everything is different anyway" umbrella but wanted to let you know about this as it affects v6.6 in at least Ubuntu/Debian. The following recent patch has broken libvirt-lxc for us: commit d7147b3797380de2d159ce6324536f3e1f2d97e3 Author: Pavel Hrdina <phrdina(a)redhat.com&gt; Date: Fri Jun 19 00:44:07 2020 +0200 m4: virt-xdr: rewrite XDR check I was tracking that down for [1] since the tests [4] failed on me. [2] holds the backtrace. In Debian the tests are skipped which explains why they were not seen there: smoke-lxc SKIP Test requires machine-level isolation but testbed does not provide that What happens is that the libvirt_lxc segfaults when using XDR functions. dmesg shows: [582093.524644] libvirt_lxc[261446]: segfault at 0 ip 0000000000000000 sp 00007ffdd2345598 error 14 in libvirt_lxc[5587e42aa000+8000] [582093.524650] Code: Bad RIP value. There are quite some uncertainties left, but on the surface it seems that it links with libtirpc but then instead of calling libtirpc: src/xdr.c:929:xdr_uint64_t(xdrs, ullp) it ends (gdb tells us in [2]) in glibc glibc: sunrpc/xdr_intXX_t.c:62:xdr_uint64_t (XDR *xdrs, uint64_t *uip) And the return from that function breaks it badly (instruction pointer at 0x0 -> segfault) Bisecting pointed to the referred commit which brings libtirpc into the mix. The former builds had xdr detected, but not with libtirpc. configure: xdr: yes (CFLAGS='' LIBS='') The new config now does configure: xdr: yes (CFLAGS='-I/usr/include/tirpc' LIBS='-ltirpc') And the resulting libvirt_lxc reflects that v6.0.0 $ lddtree /usr/lib/libvirt/libvirt_lxc | grep tirpc v6.6.0 $ lddtree /usr/lib/libvirt/libvirt_lxc | grep tirpc libtirpc.so.3 => /lib/x86_64-linux-gnu/libtirpc.so.3 This seems to lead to the bad jump and the crash eventually. Meanwhile reverting d7147b37 "m4: virt-xdr: rewrite XDR check" on top of v6.6.0 resolves the issue back to the former state. For anyone that wants to recreate this, I also attached a bisect script [3] which includes the test case you'd need. [1]: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1892826 [2]: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1892826/comments/4 [3]: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1892826/+attachmen... [4]: https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929... -- Christian Ehrhardt Staff Engineer, Ubuntu Server Canonical Ltd