[Bug lto/65239] New: typeinfo / VTT for some classes not visibile in shared library when LTO is used

[jana at saout dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65239

            Bug ID: 65239
           Summary: typeinfo / VTT for some classes not visibile in shared
                    library when LTO is used
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jana at saout dot de

I am seeing a possible issue with LTO that just seems to have appeared in GCC
5.

When trying to link against the shared library "libgtkmm-2.4.so.1" from gtkmm
2.4 with -flto, I sometimes get complaints that the vtable or VTT for
"Gtk::TreeViewColumn" cannot be found.

In fact:

nm -C .libs/libgtkmm-2.4.so.1.1.0 | egrep '(vtable|VTT) for
Gtk::TreeViewColumn'
00000000002fa8c8 d VTT for Gtk::TreeViewColumn [clone .lto_priv.731]
0000000000323410 d vtable for Gtk::TreeViewColumn [clone .lto_priv.732]

objdump -tC .libs/libgtkmm-2.4.so.1.1.0 | egrep '(vtable|VTT) for
Gtk::TreeViewColumn'
00000000002fa8c8 l     O .data.rel.ro.local    0000000000000038             
.hidden VTT for Gtk::TreeViewColumn [clone .lto_priv.731]
0000000000323410 l     O .data.rel.ro    00000000000000b8              .hidden
vtable for Gtk::TreeViewColumn [clone .lto_priv.732]

(-T comes back empty)


Not using LTO everything is fine (as is LTO with 4.9.2):

objdump -TC /usr/lib64/libgtkmm-2.4.so.1.1.0 | egrep '(vtable|VTT) for
Gtk::TreeViewColumn'
000000319a72b7e8  w   DO .data.rel.ro    0000000000000038  Base        VTT for
Gtk::TreeViewColumn
000000319a72b820  w   DO .data.rel.ro    00000000000000b8  Base        vtable
for Gtk::TreeViewColumn



The symbols are from here:

gcc-nm -C .libs/treeviewcolumn.o | egrep '(vtable|VTT) for Gtk::TreeViewColumn'
00000000 W VTT for Gtk::TreeViewColumn
00000000 W vtable for Gtk::TreeViewColumn



Note that if I create a shared library just from that single (slim LTO) object
file, the vtable/VTT are there:

g++ -shared -o x.so -flto -save-temps .libs/treeviewcolumn.o 
objdump -tC x.so | egrep '(vtable|VTT) for Gtk::TreeViewColumn'
00000000000097e0 l     O .data.rel.ro    00000000000000b8              vtable
for Gtk::TreeViewColumn
00000000000098b8 l     O .data.rel.ro.local    0000000000000038             
VTT for Gtk::TreeViewColumn

If I

g++ -shared -o x.so -flto -save-temps .libs/*.o (whole bunch of object files)

I am getting the shared library where the vtable/VTT are missing (or rather
just have hidden clones). Note that all other vtable/VTT are there, it's just
the Gtk::TreeViewVolumn ones that are missing.



Tested with the latest (20150226) SVN version.


The .res file says:

grep ZT.\*TreeViewColumnE\$ -- -lm.res 
10602 218553227c96204c RESOLVED_IR _ZTTN3Gtk14TreeViewColumnE
4750 218553227c96204c RESOLVED_IR _ZTVN3Gtk14TreeViewColumnE
9268 751c477e728966a5 PREVAILING_DEF_IRONLY_EXP _ZTIN3Gtk14TreeViewColumnE
4192 751c477e728966a5 PREVAILING_DEF_IRONLY_EXP _ZTVN3Gtk14TreeViewColumnE
9270 751c477e728966a5 PREVAILING_DEF_IRONLY_EXP _ZTTN3Gtk14TreeViewColumnE
9287 751c477e728966a5 PREVAILING_DEF_IRONLY_EXP _ZTSN3Gtk14TreeViewColumnE
14067 f3ebcd2e3bf3a025 RESOLVED_IR _ZTIN3Gtk14TreeViewColumnE


(the shared library where the vtable/VTT aren't missing doesn't contain the
RESOLVED_IR lines, just the four PREVAILING_DEF_IRONLY_EXP ones)

This happens with just "-O2 -flto" on an x86_64 system.

I'm not sure how to reduce the testcase or provide further information but can
try to provide further information if you can tell me what you need.

I've uploaded the object files here:
https://www.dropbox.com/s/0rmzoxtpbdq8lc7/objectfiles.tar.gz?dl=0

( g++ -shared -o x.so *.o )