On Tue, Jul 26, 2016 at 10:32 AM, kefu chai <tchaikov@xxxxxxxxx> wrote: > Hey Cephers, > > we are almost finished the transition to cmake. but we are also facing > some problems which did not exist in autotools. > > last time i asked help on static library versus dynamic library in > this mailing list. and the consensus was we should just build and > package dynamic libraries. but this time, i ran into a more difficult > one: http://tracker.ceph.com/issues/16686. I strongly suspect that http://tracker.ceph.com/issues/16556 is caused by the same problem with the symbols in lockdep.cc, although in this instance it is only causing a problem when we fork. I have a patch (https://github.com/ceph/ceph/pull/10452) which demonstrates that the issue goes away when we don't load librados and libcephfs into the same process. John > a little bit background: we have a convenience library named libcommon > which wraps some of the class/methods shared across the Ceph project, > messenger among the other things. and in tracker#16686, i found that > in AsyncMessenger.cc, we have a static member variable named > WorkerPool::name. it is a std::string. see > https://github.com/ceph/ceph/blob/master/src/msg/async/AsyncMessenger.cc#L346 > > if we load both libceph.so and librados.so in the same process, when > the process exists, this variable will be destructed twice. hence the > double free. because the linker thinks that the symbols the two copies > of libcommon in libcephfs and librados are the same ones. while the > two libraries destruct the variable individually. that's why we have > this problem. > > you might want to ask, "it works in autotools!". i asked myself the > same question. and i found that we don't pass > "-Wl,--exclude-libs=libcommon.a" or "-Wl,--exclude-libs,ALL" to linker > when linking libcephfs and librados, as we did in automake. this > confuses the run-time linker. yeah, we can do the same in cmake. but > this breaks the build. see > http://gitbuilder.sepia.ceph.com/gitbuilder-ceph-deb-trusty-amd64-basic/log.cgi?log=87ff7617bf2c07d43b6a6b7d116ea61f9ea6e905: > > ``` > /srv/autobuild-ceph/gitbuilder.git/build/out~/ceph-11.0.0-902-g87ff761/src/common/Formatter.h:92: > undefined reference to `ceph::Formatter::~Formatter()' > > error: collect2: ld returned 1 exit status > > make[4]: *** [bin/ceph_test_rados_api_c_read_operations] Error 1 > ``` > > some librados tests (maybe more of them) are using the non-public > symbols. so we have two solutions: > > - extract the .cc files which are used by these tests into a > convenience library and link the tests against it *and* librados. but > again this introduces the risk of double free. the extracted .cc files > should be non-POD static variable free. > - compile a static librados and link the tests against it. this > actually mimics the behavior of autotools. but this approach > complicates the cmake file, as we discussed before. > > > so, maybe we should just forbid the non-POD static variables in > libcommon? if you have better solution, or i am completely wrong (i > wish so), please let me know. > > thanks, > > -- > Regards > Kefu Chai > -- > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
