Since updating archlinux i've been unable to build bitcoin-qt from git HEAD.

The error is as follows:

$ make g++ -m64 -Wl,-O1,--sort-common,--as-needed,-z,relro,--hash-style=gnu -fstack-protector -Wl,-O1 -o bitcoin-qt build/bitcoin.o [...] build/qrc_bitcoin.o -L/usr/lib -lqrencode -lminiupnpc -lssl -lcrypto -ldb_cxx -lboost_system -lboost_filesystem -lboost_program_options -lboost_thread -lQtGui -lQtCore -lpthread /usr/bin/ld: build/qtipcserver.o: undefined reference to symbol 'shm_unlink@@GLIBC_2.2.5' /usr/bin/ld: note: 'shm_unlink@@GLIBC_2.2.5' is defined in DSO /lib/librt.so.1 so try adding it to the linker command line /lib/librt.so.1: could not read symbols: Invalid operation collect2: ld returned 1 exit status make: *** [bitcoin-qt] Error 1 $

I made the following change to bitcoin-qt.pro and the problem went away:

LIBS += $$join(BOOST_LIB_PATH,,-L,) $$join(BDB_LIB_PATH,,-L,) $$join(OPENSSL_LIB_PATH,,-L,) $$join(QRENCODE_LIB_PATH,,-L,) -LIBS += -lssl -lcrypto -ldb_cxx$$BDB_LIB_SUFFIX +LIBS += -lssl -lcrypto -ldb_cxx$$BDB_LIB_SUFFIX -lrt

-lgdi32 has to happen after -lcrypto (see #681)

I don't know enough about what's going on to say whether that's a good idea, but it worked for me...

Adding -rt should be done only for Linux, I suppose? It's strange that we'd have to link against it directly, as we don't use shm_open/shm_unlink directly, it is at most Boost using it.

When trying to understand the change I found a link: http://fedoraproject.org/wiki/UnderstandingDSOLinkChange that claims to explain it.

Hope that helps!

The undefined symbol is referenced on line 374 of /usr/include/boost/interprocess/shared_memory_object.hpp, included by /usr/include/boost/interprocess/ipc/message_queue.hpp, included by bitcoin/src/qt/qtipcserver.cpp

Yes, that makes it fully clear. We must link to -lrt on Linux, as previously we were using it indirectly through some other lib and that's no longer allowed...

On Fedora You fix help too.

Is that some kind of a stack-based language?

Does changing "LIBS += -lssl -lcrypto -ldb_cxx$$BDB_LIB_SUFFIX" to "LIBS += -lssl -lcrypto -ldb_cxx$$BDB_LIB_SUFFIX -lrt" in bitcoin-qt.pro fix it on Fedora?

Fixed now.