On Tue, Jul 31, 2018 at 02:04:40PM +0200, Martin Kletzander wrote: > On Tue, Jul 31, 2018 at 10:26:41AM +0200, Michal Privoznik wrote: > > On 07/30/2018 05:20 PM, Andrea Bolognani wrote: > > > On Sat, 2018-07-28 at 21:56 +0800, Daniel Veillard wrote: > > > > > > > > > > > > Unfortunately I've spotted an issue during my testing of rc1 today: > > > with the libvirt_guest NSS module enabled, Evolution would crash a > > > few seconds after being started. Here's the stack trace: > > > > > > #0 0x00007fffe7b69ba5 in json_object_iter_next () at > > > /lib64/libjson-glib-1.0.so.0 > > > #1 0x00007fffad8e757b in virJSONValueFromJansson () at > > > /lib64/libnss_libvirt_guest.so.2 > > > #2 0x00007fffad8e75d8 in virJSONValueFromJansson () at > > > /lib64/libnss_libvirt_guest.so.2 > > > #3 0x00007fffad8e8994 in virJSONValueFromString () at > > > /lib64/libnss_libvirt_guest.so.2 > > > #4 0x00007fffad8ecb5a in virMacMapNew () at > > > /lib64/libnss_libvirt_guest.so.2 > > > #5 0x00007fffad8cc140 in findLease () at > > > /lib64/libnss_libvirt_guest.so.2 > > > #6 0x00007fffad8ccb1c in _nss_libvirt_guest_gethostbyname4_r () at > > > /lib64/libnss_libvirt_guest.so.2 > > > #7 0x00007fffeb2599d2 in gaih_inet.constprop () at /lib64/libc.so.6 > > > #8 0x00007fffeb25aab4 in getaddrinfo () at /lib64/libc.so.6 > > > #9 0x00007ffff1d41a04 in do_lookup_by_name () at /lib64/libgio-2.0.so.0 > > > #10 0x00007ffff1d3e937 in g_task_thread_pool_thread () at > > > /lib64/libgio-2.0.so.0 > > > #11 0x00007ffff5c39933 in g_thread_pool_thread_proxy () at > > > /lib64/libglib-2.0.so.0 > > > #12 0x00007ffff5c38f2a in g_thread_proxy () at /lib64/libglib-2.0.so.0 > > > #13 0x00007ffff6314594 in start_thread () at /lib64/libpthread.so.0 > > > #14 0x00007fffeb2700df in clone () at /lib64/libc.so.6 > > > > > > I've talked about it with a few colleagues and we believe the issue > > > to be caused by jansson and json-glib both exporting a symbol called > > > json_object_iter_next: Evolution itself (indirectly?) links against > > > the latter library, so when the libvirt_guest NSS module is loaded > > > and attempts to process JSON using the former, it picks up the wrong > > > implementation, leading to a crash. gnome-boxes also crashes with > > > the same stack trace. > > > > Worse. querying gentoo portage I've found some important packages > > requiring json-glib: > > > > x11-libs/gtk > > gnome-base/gnome-shell > > > > So once users of these app update to latest libvirt they will see the > > crashes. > > > > > > > > It seems like a similar issue could affect any application linking > > > both to libvirt and json-glib, regardless of whether or not the NSS > > > plugin has been enabled, which is of course pretty bad. > > > > Yes, any application can crash. > > > > > > > > Unfortunately, I don't have any bright ideas on how to solve this, > > > so anyone who might: please step forward! We're just a few days > > > away from the next release, and if we can't figure out a way around > > > this soon I'm afraid the only reasonable course of action would be > > > to (temporarily) revert the switch from yajl to jansson. > > > > > > > Well, what if we linked with jansson statically? I'm not sure if it is > > possible (and have no idea how to achieve that), but what if our dynamic > > libraries we produce already contained jansson and thus linker would not > > even try to resolve json_* symbols. > > > > It could "help" (quotes for all the disadvantages that approach has). Not > because it would not try to resolve it, but because we would have the `json_` > symbols as 'local' thanks to our src/libvirt.syms. If the lib was added to > our > dynamic lib we would still need to use `-Bsymbolic-functions` so that our > `json_` symbols don't call `json_` symbols from the dynamic one programs where > it is loaded. However that has some issues with `LD_PRELOAD`.
Note there is no jansson static build in Fedora or RHEL, so it is somewhat academic right now. > > Maybe we could utilize the `-Bgroup` linker option, although I'm not sure how > that is supposed to be used. > > In any case, this could be fixed in the respective libraries. The reasoning > behind it is that since C doesn't support namespaces we namespace functions > by a > prefix (`vir` in libvirt), however that "namespace" needs to be unique. They > should switch to `jansson_` or `glib_json_` prefixes and maybe provide macros > for the previous names: > > #define json_auto_t jansson_auto_t > ... > > I know it sounds like too big of a deal, but that's what happens in C world. > The same would happen if libvirt used `json-glib` and some application linking > with libvirt would start using jansson (and also use some specific functions). > Not that we were guarded against that now. I'm not saying the release can go > on, of course not, just that the ultimate fix is not something *we* should do. Changing their API names isn't required unless you need to have separation of namespaces at the #include level, so you can pull in both. For ELF libraries, it would be sufficient to have symbol versioning to get separation. > Querying the fedora repositories I haven't found any similar situation. > Projects that use jansson are separated from those that use json-c and those > that use json-glib. If they want to use each other though, we'll be in the > same > mess as we are now. GNOME control center + NetworkManager hit this problem in Fedora. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
