LibreOffice unit tests crash when linked with mold

[jmglogow]

So I was able to build LibreOffice (LO) with all unit tests after fixing the '?' glob handling. I've build mold_1.0.0-75-g04ad22d3 as a Debian package. And LO itself seems to run fine. Seems, because I can start it, open Writer etc., but a lot (all?) unit tests crash.

My LO is current master with some additional patches, but mainly https://gerrit.libreoffice.org/c/core/+/127493 to use mold with gcc. It's build in a Ubuntu 20.04 schroot, with updates-repo enabled (AKA libc6:amd64 - 2.31-0ubuntu9.2). If I just switch the linker to gold, and just rebuild the comphelper module (which includes the library and matching unit tests), the crash disappears, so it seems to be a linker problem, from all I can tell.

Example bt starts with (all frames in libtest_comphelper_parallelsort_test_mold.so.bt.txt):

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7fdca80 in _dl_relocate_object (l=0x5555555760c0, scope=0x555555576428, reloc_mode=reloc_mode@entry=0, consider_profiling=consider_profiling@entry=0) at dl-reloc.c:227
227 dl-reloc.c: No such file or directory.
(gdb) bt
#0 0x00007ffff7fdca80 in _dl_relocate_object (l=0x5555555760c0, scope=0x555555576428, reloc_mode=reloc_mode@entry=0, consider_profiling=consider_profiling@entry=0) at dl-reloc.c:227
#1 0x00007ffff7fe4f5c in dl_open_worker (a=a@entry=0x7fffffff0e30) at dl-open.c:688

As the crash happens in some file called relocate, I thought to dump them for the broken and working library with:

$ readelf -Wr libtest_comphelper_parallelsort_test_mold.so | cut -f10 -d' ' | sort > libtest_comphelper_parallelsort_test_mold.so_rel

and I got a longer diff then expected with some __cxa / CXXABI symbols gone: relocations.diff.txt

What is also strange is the fact, that file tells me for both variants:

ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, BuildID[sha1]=..., with debug_info, not stripped

But ldd claims for mold that it's statically linked - WTF?

So my current guess is that something is wrong with the ELF tables / headers in the mold variant.

Link command gold:

ccache g++ -pthread -shared -Wl,-z,noexecstack -Wl,-z,origin '-Wl,-rpath,$ORIGIN/../Library' -Wl,-rpath-link,$I/program -fuse-ld=gold -Wl,-z,defs -fstack-protector-strong -Wl,-rpath-link,/lib:/usr/lib -Wl,-z,combreloc -Wl,--hash-style=gnu -Wl,-Bsymbolic-functions -L$W/LinkTarget/StaticLibrary -L$I/sdk/lib -L$I/program -L$I/program -L$W/LinkTarget/Library -Wl,--gdb-index $W/CxxObject/comphelper/qa/unit/parallelsorttest.o -Wl,--start-group -L$W/UnpackedTarball/cppunit/src/cppunit/.libs -lcppunit -Wl,--end-group -Wl,--no-as-needed -lcomphelper -luno_cppuhelpergcc3 -luno_cppu -luno_sal -ltllo -o $W/LinkTarget/CppunitTest/libtest_comphelper_parallelsort_test.so

Link command with mold as gold:

ccache g++ -pthread -B$S/gcc_linker -shared -Wl,-z,noexecstack -Wl,-z,origin '-Wl,-rpath,$ORIGIN/../Library' -Wl,-rpath-link,$I/program -B$S/gcc_linker -fuse-ld=lld -Wl,-z,defs -fstack-protector-strong -Wl,-rpath-link,/lib:/usr/lib -Wl,-z,combreloc -Wl,--hash-style=gnu -Wl,-Bsymbolic-functions -L$W/LinkTarget/StaticLibrary -L$I/sdk/lib -L$I/program -L$I/program -L$W/LinkTarget/Library -Wl,--gdb-index $W/CxxObject/comphelper/qa/unit/parallelsorttest.o -Wl,--start-group -L$W/UnpackedTarball/cppunit/src/cppunit/.libs -lcppunit -Wl,--end-group -Wl,--no-as-needed -lcomphelper -luno_cppuhelpergcc3 -luno_cppu -luno_sal -ltllo -o $W/LinkTarget/CppunitTest/libtest_comphelper_parallelsort_test.so

gz compressed binaries:

libtest_comphelper_parallelsort_test_gold.so.gz
libtest_comphelper_parallelsort_test_mold.so.gz

I hope this is enough info, so you don't need to build LO. I certainly don't have a simple test case. I'll happily provide more info as needed.

[rui314]

Thank you for your report! I tried to build LibreOffice on my machine and confirmed that the test crashes. Here is the stack trace.

(gdb) bt
#0  0x00007ffff7fdca80 in _dl_relocate_object (l=0x220d00, scope=0x221068, reloc_mode=reloc_mode@entry=0, consider_profiling=consider_profiling@entry=0) at dl-reloc.c:227
#1  0x00007ffff7fe4f5c in dl_open_worker (a=a@entry=0x7fffffffd120) at dl-open.c:688
#2  0x00007ffff7a548b8 in __GI__dl_catch_exception (exception=<optimized out>, operate=<optimized out>, args=<optimized out>) at dl-error-skeleton.c:208
#3  0x00007ffff7fe45fa in _dl_open (file=0x220790 "/home/ruiu/libreoffice/workdir/LinkTarget/CppunitTest.good/libtest_comphelper_parallelsort_test.so", mode=-2147483390, caller_dlopen=<optimized out>, nsid=-2, argc=8, argv=0x7fffffffdc48, env=0x7fffffffdc90) at dl-open.c:837
#4  0x00007ffff78ec34c in dlopen_doit (a=a@entry=0x7fffffffd340) at dlopen.c:66
#5  0x00007ffff7a548b8 in __GI__dl_catch_exception (exception=exception@entry=0x7fffffffd2e0, operate=<optimized out>, args=<optimized out>) at dl-error-skeleton.c:208
#6  0x00007ffff7a54983 in __GI__dl_catch_error (objname=0x220c70, errstring=0x220c78, mallocedp=0x220c68, operate=<optimized out>, args=<optimized out>) at dl-error-skeleton.c:227
#7  0x00007ffff78ecb59 in _dlerror_run (operate=operate@entry=0x7ffff78ec2f0 <dlopen_doit>, args=args@entry=0x7fffffffd340) at dlerror.c:170
#8  0x00007ffff78ec3da in __dlopen (file=<optimized out>, mode=<optimized out>) at dlopen.c:87
#9  0x00007ffff7f9afe6 in CppUnit::DynamicLibraryManager::doLoadLibrary(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) () from /home/ruiu/libreoffice/workdir/UnpackedTarball/cppunit/src/cppunit/.libs/libcppunit-1.15.so.1
#10 0x00007ffff7f753af in CppUnit::DynamicLibraryManager::loadLibrary(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) () from /home/ruiu/libreoffice/workdir/UnpackedTarball/cppunit/src/cppunit/.libs/libcppunit-1.15.so.1
#11 0x00007ffff7f7534d in CppUnit::DynamicLibraryManager::DynamicLibraryManager(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) () from /home/ruiu/libreoffice/workdir/UnpackedTarball/cppunit/src/cppunit/.libs/libcppunit-1.15.so.1
#12 0x00007ffff7f7c1ed in CppUnit::PlugInManager::load(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, CppUnit::PlugInParameters const&) () from /home/ruiu/libreoffice/workdir/UnpackedTarball/cppunit/src/cppunit/.libs/libcppunit-1.15.so.1
#13 0x0000000000205632 in (anonymous namespace)::ProtectedFixtureFunctor::run() const ()
#14 0x0000000000204c12 in main ()

I'll investigate and fix the issue.

[rui314]

It looks like this is a regression caused by 5c35d2a. I reverted it, so it should be fine now.