.LTHUNK symbols are surviving

I encountered the issue when compiling Qt 4.8.0 using -O0. It causes qdbusviewer fail to link:

`.LTHUNK0' referenced in section `.text._ZN14PropertyDialogD1Ev[PropertyDialog::~PropertyDialog()]' of .obj/release-shared-emb-arm/moc_propertydialog.o: defined in discarded section `.text._ZN14PropertyDialogD2Ev[_ZN14PropertyDialogD5Ev]' of .obj/release-shared-emb-arm/moc_propertydialog.o
collect2: ld returned 1 exit status

I noticed that as soon as the main.o (the user of that property dialog) gets built with -O1 (or higher) the link succeeds. I guess that most people who are using the multiple inheritance feature of C++ don't build their sources with -O0 usually. Tha might explain why we didn't see this issue earlier.

However, the .THUNK symbols survive regardless of the optimization level or the mode (arm/thumb). I've checked various GCC versions and the latest binutils (20120131) with the following results:
affected:
 * gcc-linaro-4.6-2012.01
 * Linaro binary toolchain (gcc-linaro-arm-linux-gnueabi-2012.01-20120125_linux)
 * g++-arm-linux-gnueabi 4.6.0-8 shipped with Ubunut 11.10 (Oneiric)
 * ARM CSL 2011.03

not affected:
 * FSF GCC 4.7 trunk (r183767)
 * FSF GCC gcc-4_6-branch (r183768)
 * FSF GCC gcc_4_6_0_release (r183772)

Tarball containing the preprocessed source, assembler output and object files.

The gcc-linaro head (revno: 106865) is also affected.

Thank you for the bug report. I've confirmed this with gcc-linaro-4.6-2012.01 on ARM:

asa-san@ursa4:~/bugs/ken$ /scratch/asa-san/cbuild/slaves/ursa4/gcc-linaro-4.6-20
12.0
gcc-linaro-4.6-2012.01/ gcc-linaro-4.6-2012.02/
asa-san@ursa4:~/bugs/ken$ /scratch/asa-san/cbuild/slaves/ursa4/gcc-linaro-4.6-20
12.01/gcc-binary/bin/g++ -c test.cpp
asa-san@ursa4:~/bugs/ken$ readelf -s test.o|grep THUNK
    13: 00000001 72 FUNC LOCAL DEFAULT 29 .LTHUNK0
    32: 00000001 68 FUNC LOCAL DEFAULT 44 .LTHUNK2
    51: 00000001 68 FUNC LOCAL DEFAULT 59 .LTHUNK4

Ken has investigated for which other toolchains the problems does and does not exist, see previous comments.

I have set the priority to Medium, since there is a work around - the error only happens when compiling at -O0.

This bug is also present upstream in Debian Wheezy on armel (package builds perfectly under i386 and amd64).

Build failure: http://quickbuild.pearsoncomputing.net:58080/2553357/buildlog_ubuntu-wheezy-armel.tdebase-trinity_4%3A14.0.0-0debian3%2Br492%2Bpr21~wheezy_FAILEDTOBUILD.txt.gz

Linking CXX shared library libtdeinit_kicker.so
cd /build/buildd/tdebase-trinity-14.0.0/obj-arm-linux-gnueabi/kicker/kicker && /usr/bin/cmake -E cmake_link_script CMakeFiles/tdeinit_kicker-shared.dir/link.txt --verbose=1
/usr/bin/g++ -fPIC -DSMB_CTX_FLAG_USE_KERBEROS -DSMB_CTX_FLAG_FALLBACK_AFTER_KERBEROS -g -Wall -fvisibility=hidden -fvisibility-inlines-hidden -DQT_NO_ASCII_CAST -DQT_CLEAN_NAMESPACE -DQT_NO_STL -DQT_NO_COMPAT -DQT_NO_TRANSLATION -DQT_THREAD_SUPPORT -D_REENTRANT -include tqt.h -Wl,--no-undefined -shared -Wl,-soname,libtdeinit_kicker.so -o libtdeinit_kicker.so CMakeFiles/tdeinit_kicker-shared.dir/dummy.cpp.o -Wl,-whole-archive core/libkicker_core.a -Wl,-no-whole-archive buttons/libkicker_buttons.a ui/libkicker_ui.a ../libkicker/libkickermain.so.1.0.0 /opt/trinity/lib/libkabc.so.1.2.0 /opt/trinity/lib/libkutils.so.1.2.0 ../../libkonq/libkonq.so.4.2.0 ../../tdmlib/libdmctl.a -lXau interfaces/libkickoffsearch_interfaces.so.0.0.0 /opt/trinity/lib/libvcard.so.0.0.0 /opt/trinity/lib/libkresources.so.1.2.0 /opt/trinity/lib/libkparts.so.2.1.0 /opt/trinity/lib/libkio.so.4.2.0 /opt/trinity/lib/libtdeui.so.4.2.0 -lfreetype -lfontconfig /opt/trinity/lib/libtdesu.so.4.2.0 -lutil /opt/trinity/lib/libkwalletclient.so.1.0.1 /opt/trinity/lib/libtdecore.so.4.2.0 /opt/trinity/lib/libDCOP.so.4.2.0 /opt/trinity/lib/libtdefx.so.4.2.0 -ltqt -ltqt-mt -lXrender -lX11 -lz -lidn -lXcomposite -lICE -lSM -lr -Wl,-rpath,/build/buildd/tdebase-trinity-14.0.0/obj-arm-linux-gnueabi/kicker/libkicker:/opt/trinity/lib:/build/buildd/tdebase-trinity-14.0.0/obj-arm-linux-gnueabi/libkonq:/build/buildd/tdebase-trinity-14.0.0/obj-arm-linux-gnueabi/kicker/kicker/interfaces:
`.LTHUNK4' referenced in section `.text._ZN16PanelDirDropMenuD1Ev[PanelDirDropMenu::~PanelDirDropMenu()]' of ui/libkicker_ui.a(dirdrop_mnu.cpp.o): defined in discarded section `.text._ZN16PanelDirDropMenuD2Ev[_ZN16PanelDirDropMenuD5Ev]' of ui/libkicker_ui.a(dirdrop_mnu.cpp.o)
`.LTHUNK5' referenced in section `.text._ZN16PanelDirDropMenuD1Ev[PanelDirDropMenu::~PanelDirDropMenu()]' of ui/libkicker_ui.a(dirdrop_mnu.cpp.o): defined in discarded section `.text._ZN16PanelDirDropMenuD2Ev[_ZN16PanelDirDropMenuD5Ev]' of ui/libkicker_ui.a(dirdrop_mnu.cpp.o)
collect2: ld returned 1 exit status

This may need to be reported and fixed upstream before it can be fixed in Ubuntu.

Now tracked at https://bugs.linaro.org/show_bug.cgi?id=539