我正在使用LLVM Tutorial，但我在编译时遇到了问题。我写了一个重现问题的最小例子：
#include "llvm/Module.h"
#include "llvm/LLVMContext.h"
int main(int argc, char **argv) {
llvm::Module *module = new llvm::Module("test", llvm::getGlobalContext());
return 0;
}
当我尝试编译时，我得到了一堆'未定义的引用'错误：
clang++ `llvm-config --cxxflags` -c -o test.o test.cpp
clang++ test.o `llvm-config --ldflags --libs core` -o test
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(Signals.o): In function `PrintStackTrace(void*)':
(.text+0x6c): undefined reference to `dladdr'
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(Signals.o): In function `PrintStackTrace(void*)':
(.text+0x1f6): undefined reference to `dladdr'
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(Mutex.o): In function `llvm::sys::MutexImpl::MutexImpl(bool)':
(.text+0x53): undefined reference to `pthread_mutexattr_init'
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(Mutex.o): In function `llvm::sys::MutexImpl::MutexImpl(bool)':
(.text+0x64): undefined reference to `pthread_mutexattr_settype'
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(Mutex.o): In function `llvm::sys::MutexImpl::MutexImpl(bool)':
(.text+0x74): undefined reference to `pthread_mutexattr_setpshared'
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(Mutex.o): In function `llvm::sys::MutexImpl::MutexImpl(bool)':
(.text+0x88): undefined reference to `pthread_mutexattr_destroy'
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(Mutex.o): In function `llvm::sys::MutexImpl::tryacquire()':
(.text+0x179): undefined reference to `pthread_mutex_trylock'
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::RWMutexImpl()':
(.text+0x3e): undefined reference to `pthread_rwlock_init'
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::~RWMutexImpl()':
(.text+0x80): undefined reference to `pthread_rwlock_destroy'
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::reader_acquire()':
(.text+0xb9): undefined reference to `pthread_rwlock_rdlock'
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::reader_release()':
(.text+0xe9): undefined reference to `pthread_rwlock_unlock'
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::writer_acquire()':
(.text+0x119): undefined reference to `pthread_rwlock_wrlock'
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::writer_release()':
(.text+0x149): undefined reference to `pthread_rwlock_unlock'
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(Threading.o): In function `llvm::llvm_execute_on_thread(void (*)(void*), void*, unsigned int)':
(.text+0x1cc): undefined reference to `pthread_create'
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(Threading.o): In function `llvm::llvm_execute_on_thread(void (*)(void*), void*, unsigned int)':
(.text+0x208): undefined reference to `pthread_attr_setstacksize'
/usr/lib/llvm-2.9/lib/libLLVMSupport.a(Threading.o): In function `llvm::llvm_execute_on_thread(void (*)(void*), void*, unsigned int)':
(.text+0x228): undefined reference to `pthread_join'
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [test] Error 1
如果我查看了dladdr的联机帮助页，则说我需要与-ldl链接。但我已经使用llvm-config：
$ llvm-config --ldflags --libs core
-L/usr/lib/llvm-2.9/lib -lpthread -lffi -ldl -lm
-lLLVMCore -lLLVMSupport -L/usr/lib/llvm-2.9/lib
此外，-ldl按正确的顺序出现（即在需要符号的.o文件之后）。
我对调试此问题的下一步感到茫然。谁能指出我正确的方向？我在Ubuntu 12.04上运行LVVM 2.9-7。
答案 0 :(得分：34)
-lLLVMSupport包含需要符号的库，因此-ldl必须位于-lLLVMSupport之后。我改变了这个：
`llvm-config --ldflags --libs core`
对此：
`llvm-config --libs core` `llvm-config --ldflags`
连接器成功了。
答案 1 :(得分：11)
在浏览llvm-3.4的LLVM教程时我遇到了同样的问题，不幸的是，Matthew的答案并没有帮助。为了将来的参考，我发布了一个新答案，其中包含了我遇到的问题以及我是如何修复它的。
我已经在~/dev/llvm/install中安装了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
我遇到了很多错误，第一个错误是：
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;将-std=c++11添加到clang++个选项即可解决问题。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。然后我想我需要使用--system-libs才能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
始终将--system-libs放在最后是很重要的，这样所有缺少的依赖关系都会被链接器引入。
使用LLVM 3.4和Kubuntu 14.04进行测试