为什么我得到“未定义的引用”dladdr“”即使使用-ldl这个简单的程序？

需要符号的库包含-lLLVMSupport ，所以-ldl必须在-lLLVMSupport之后。 我改变了这个：

 `llvm-config --ldflags --libs core` 

对此：

 `llvm-config --libs core` `llvm-config --ldflags` 

链接器是成功的。

在通过LLVM教程的时候，我遇到了同样的问题，不幸的是，Matthew的回答没有帮助。 为了将来的参考，我发布了一个新的答案，解决了我遇到的问题以及如何解决问题。

我已经在~/dev/llvm/install安装了LLVM，所以我使用了教程中给出的命令，但用llvm安装的路径替换了llvm-config ：

 clang++ -g -O3 toy.cpp `../llvm/install/bin/llvm-config --cppflags --ldflags --libs core` -o toy 

我得到了很多错误，第一个是：

 filipe@filipe-Kubuntu:~/dev/kaleidoscope$ clang++ -g -O3 toy.cpp `../llvm/install/bin/llvm-config --cppflags --ldflags --libs core` -o toy In file included from toy.cpp:1: In file included from /home/filipe/dev/llvm/install/include/llvm/IR/Verifier.h:24: /home/filipe/dev/llvm/install/include/llvm/ADT/StringRef.h:342:14: error: no template named 'enable_if' in namespace 'std'; did you mean '__gnu_cxx::__enable_if'? typename std::enable_if<std::numeric_limits<T>::is_signed, bool>::type ^~~~~~~~~~~~~~ __gnu_cxx::__enable_if /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/ext/type_traits.h:43:12: note: '__gnu_cxx::__enable_if' declared here struct __enable_if ^ 

这是因为此时LLVM需要一个C ++ 11编译器; 加入-std=c++11来clang++选项解决了它。 但后来我得到了：

 filipe@filipe-Kubuntu:~/dev/kaleidoscope$ clang++ -std=c++11 -g -O3 toy.cpp `../llvm/install/bin/llvm-config --cppflags --ldflags --libs core` -o toy /home/filipe/dev/llvm/install/lib/libLLVMSupport.a(Process.o): In function `terminalHasColors(int)': /home/filipe/dev/llvm/llvm/lib/Support/Unix/Process.inc:273: undefined reference to `setupterm' /home/filipe/dev/llvm/llvm/lib/Support/Unix/Process.inc:291: undefined reference to `tigetnum' /home/filipe/dev/llvm/llvm/lib/Support/Unix/Process.inc:295: undefined reference to `set_curterm' /home/filipe/dev/llvm/llvm/lib/Support/Unix/Process.inc:296: undefined reference to `del_curterm' /home/filipe/dev/llvm/install/lib/libLLVMSupport.a(Signals.o): In function `llvm::sys::PrintStackTrace(_IO_FILE*)': /home/filipe/dev/llvm/llvm/lib/Support/Unix/Signals.inc:278: undefined reference to `dladdr' /home/filipe/dev/llvm/llvm/lib/Support/Unix/Signals.inc:290: undefined reference to `dladdr' /home/filipe/dev/llvm/install/lib/libLLVMSupport.a(Mutex.o): In function `MutexImpl': /home/filipe/dev/llvm/llvm/lib/Support/Mutex.cpp:53: undefined reference to `pthread_mutexattr_init' /home/filipe/dev/llvm/llvm/lib/Support/Mutex.cpp:59: undefined reference to `pthread_mutexattr_settype' /home/filipe/dev/llvm/llvm/lib/Support/Mutex.cpp:67: undefined reference to `pthread_mutexattr_destroy' /home/filipe/dev/llvm/install/lib/libLLVMSupport.a(Mutex.o): In function `llvm::sys::MutexImpl::tryacquire()': /home/filipe/dev/llvm/llvm/lib/Support/Mutex.cpp:109: undefined reference to `pthread_mutex_trylock' /home/filipe/dev/llvm/install/lib/libLLVMSupport.a(RWMutex.o): In function `RWMutexImpl': /home/filipe/dev/llvm/llvm/lib/Support/RWMutex.cpp:59: undefined reference to `pthread_rwlock_init' /home/filipe/dev/llvm/install/lib/libLLVMSupport.a(RWMutex.o): In function `~RWMutexImpl': /home/filipe/dev/llvm/llvm/lib/Support/RWMutex.cpp:72: undefined reference to `pthread_rwlock_destroy' /home/filipe/dev/llvm/install/lib/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::reader_acquire()': /home/filipe/dev/llvm/llvm/lib/Support/RWMutex.cpp:82: undefined reference to `pthread_rwlock_rdlock' /home/filipe/dev/llvm/install/lib/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::reader_release()': /home/filipe/dev/llvm/llvm/lib/Support/RWMutex.cpp:92: undefined reference to `pthread_rwlock_unlock' /home/filipe/dev/llvm/install/lib/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::writer_acquire()': /home/filipe/dev/llvm/llvm/lib/Support/RWMutex.cpp:102: undefined reference to `pthread_rwlock_wrlock' /home/filipe/dev/llvm/install/lib/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::writer_release()': /home/filipe/dev/llvm/llvm/lib/Support/RWMutex.cpp:112: undefined reference to `pthread_rwlock_unlock' /home/filipe/dev/llvm/install/lib/libLLVMSupport.a(ThreadLocal.o): In function `ThreadLocalImpl': /home/filipe/dev/llvm/llvm/lib/Support/ThreadLocal.cpp:56: undefined reference to `pthread_key_create' /home/filipe/dev/llvm/install/lib/libLLVMSupport.a(ThreadLocal.o): In function `~ThreadLocalImpl': /home/filipe/dev/llvm/llvm/lib/Support/ThreadLocal.cpp:63: undefined reference to `pthread_key_delete' /home/filipe/dev/llvm/install/lib/libLLVMSupport.a(ThreadLocal.o): In function `llvm::sys::ThreadLocalImpl::setInstance(void const*)': /home/filipe/dev/llvm/llvm/lib/Support/ThreadLocal.cpp:70: undefined reference to `pthread_setspecific' /home/filipe/dev/llvm/install/lib/libLLVMSupport.a(ThreadLocal.o): In function `llvm::sys::ThreadLocalImpl::getInstance()': /home/filipe/dev/llvm/llvm/lib/Support/ThreadLocal.cpp:77: undefined reference to `pthread_getspecific' /home/filipe/dev/llvm/install/lib/libLLVMSupport.a(Threading.o): In function `llvm::llvm_execute_on_thread(void (*)(void*), void*, unsigned int)': /home/filipe/dev/llvm/llvm/lib/Support/Threading.cpp:91: undefined reference to `pthread_attr_setstacksize' /home/filipe/dev/llvm/llvm/lib/Support/Threading.cpp:96: undefined reference to `pthread_create' /home/filipe/dev/llvm/llvm/lib/Support/Threading.cpp:100: undefined reference to `pthread_join' clang: error: linker command failed with exit code 1 (use -v to see invocation) 

与原始问题的作者发生的情况相反，我注意到llvm-config甚至没有链接到任何系统库。 然后我觉得我需要使用--system-libs来将所需的系统库包含到链接过程中：

 clang++ -std=c++11 -g -O3 toy.cpp `../llvm/install/bin/llvm-config --cppflags --libs core --ldflags --system-libs` -o toy 

总是把--system-libs放到最后，这样所有缺失的依赖都被链接器引入。

经过LLVM 3.4和Kubuntu 14.04的测试