I ran into a weird problem in one of our build scripts at work today. We compile our tools across a number of platforms and architectures, and I ran across this issue on one of our oldest boxes, running RedHat 9. Here's the horrible error that I got when linking:

/usr/bin/ld: myFile.so: undefined versioned symbol name std::basic_string<char, std::char_traits<char>, std::allocator<char> >& std::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_replace_safe<char const*>(__gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, char const*, char const*)@@GLIBCPP_3.2 /usr/bin/ld: failed to set dynamic section sizes: Bad value

It seems as if the standard C++ libraries on this system were compiled with gcc 3.2, while the version we're using to build our tools is 3.2.3. Unfortunately, the 3.2 compiler isn't installed on the system, and I'm not sure where we would find it for RH9 anyway. Thankfully, I found a workaround for this problem. Our link step originally looked like this:

gcc -shared -fPIC -lstdc++ -lrt -lpthread -o myFile.so {list_of_object_files}

I found out that by moving the standard libraries to the end of the line, the problem disappeared. Here's the new link step:

gcc -shared -fPIC -o myFile.so {list_of_object_files} -lstdc++ -lrt -lpthread

I don't fully understand why ordering should matter during the link step, but by putting the standard libraries last, we were able to get rid of this error. If you understand the root cause of this, please leave a comment explaining. I'd love to know more about why changing the order makes a difference.