背景
公司項目使用到了阿里雲的智能語音交互SDK，分布式文件系統Ceph，系統ubuntu，g++版本gcc version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)
問題發現過程
根據需求對比各家語音轉文SDK后，選擇了阿里雲智能語音交互，隨即使用SDK附帶的demo進行准確率測試，測試OK后接入項目，出現鏈接錯誤：
[100%] Linking CXX executable AudioToText
CMakeFiles/AudioToText.dir/ConfigManager.cpp.o: In function `TransConfig::Config::GenerateNewTokenWhenTokenExpire[abi:cxx11]()':
/home/yjk/projects/AudioToText/ConfigManager.cpp:36: undefined reference to `AlibabaNlsCommon::NlsToken::setAccessKeyId(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/home/yjk/projects/AudioToText/ConfigManager.cpp:37: undefined reference to `AlibabaNlsCommon::NlsToken::setKeySecret(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
CMakeFiles/AudioToText.dir/SpeechTranslator.cpp.o: In function `Translation::SpeechTranslator::ParseCallBack(AlibabaNls::NlsEvent*)':
/home/yjk/projects/AudioToText/SpeechTranslator.cpp:199: undefined reference to `AlibabaNls::NlsEvent::getSentenceWordsList[abi:cxx11]()'
collect2: error: ld returned 1 exit status
CMakeFiles/AudioToText.dir/build.make:484: recipe for target 'AudioToText' failed
make[2]: *** [AudioToText] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/AudioToText.dir/all' failed
make[1]: *** [CMakeFiles/AudioToText.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2
終端進程“/bin/bash '-c', 'cmake --build ./ --target all --'”已終止，退出代碼: 2。以為是項目CMakeLists.txt有問題，檢查文件發現確實有指定連接路徑以及庫名
隨即比對SDK附帶的demo中的CMakeLists.txt，發現添加了一個宏定義
把此語句添加到項目項目CMakeLists.txt，編譯成功通過
究其原因，是因為
在GCC5.1發布的同時，為libstdc++添加了新的特性，其中也包括了std::string和std::list的新實現。這個新的實現使得兩者符合了c++11的標准，具體來說是取消了Copy-On-Write。那么，這樣子雖然符合了c++11的標注，舊版不就無法兼容了嗎。為了避免上述混亂，對於舊版而言，GCC5.1添加了__cxx11命名空間，GCC5.1或者說c++11規范下的string和list，實際上是std::__cxx11::string和std::__cxx11::list，所以我們一般的using namespace std就會變成形如using namespace std::__cxx11的樣子。也就是說，有舊版(c++03規范)的libstdc++.so，和新版(c++11規范)的libstdc++.so兩個庫同時存在。
為了避免兩個庫到底選擇哪一個的麻煩，GCC5.1就引入了-D_GLIBCXX_USE_CXX11_ABI來控制編譯器到底鏈接哪一個libstdc++.so，
- D_GLIBCXX_USE_CXX11_ABI=0 鏈接舊版庫
- D_GLIBCXX_USE_CXX11_ABI=1 鏈接新版庫
引用自_GLIBCXX_USE_CXX11_ABI有什么作用
明白了這個之后，添加宏定義之前的連接錯誤就可以解釋了：
連接器在鏈接時，尋找的符號是
`AlibabaNlsCommon::NlsToken::setKeySecret(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'通過nm命令查看下動態庫導出的符號，使用c++filt恢復下函數簽名
得到導出的符號
`AlibabaNlsCommon::NlsToken::setAccessKeyId(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)`符號不匹配，鏈接器找不到需要的符號，鏈接報錯
另一個庫引入的新問題
接入Ceph的庫librados.so后，又發生了鏈接錯誤
[100%] Linking CXX executable AudioToText
CMakeFiles/AudioToText.dir/CephClient.cpp.o: In function `FileSystem::CephWrapper::GetAllPool(std::string&)':
/home/yjk/projects/AudioToText/CephClient.cpp:42: undefined reference to `librados::Rados::pool_list(std::list<std::string, std::allocator<std::string> >&)'
CMakeFiles/AudioToText.dir/CephClient.cpp.o: In function `FileSystem::CephWrapper::ReadObjectToFile(std::string const&, std::string const&, std::string&, std::string&)':
/home/yjk/projects/AudioToText/CephClient.cpp:58: undefined reference to `librados::IoCtx::getxattr(std::string const&, char const*, ceph::buffer::list&)'
/home/yjk/projects/AudioToText/CephClient.cpp:62: undefined reference to `librados::IoCtx::getxattr(std::string const&, char const*, ceph::buffer::list&)'
/home/yjk/projects/AudioToText/CephClient.cpp:73: undefined reference to `librados::IoCtx::aio_read(std::string const&, librados::AioCompletion*, ceph::buffer::list*, unsigned long, unsigned long)'
CMakeFiles/AudioToText.dir/CephClient.cpp.o: In function `FileSystem::CephWrapper::WriteObject(std::string const&, std::string const&, char const*, unsigned int, std::string&)':
/home/yjk/projects/AudioToText/CephClient.cpp:97: undefined reference to `librados::IoCtx::write(std::string const&, ceph::buffer::list&, unsigned long, unsigned long)'
/home/yjk/projects/AudioToText/CephClient.cpp:105: undefined reference to `librados::IoCtx::setxattr(std::string const&, char const*, ceph::buffer::list&)'
/home/yjk/projects/AudioToText/CephClient.cpp:112: undefined reference to `librados::IoCtx::aio_read(std::string const&, librados::AioCompletion*, ceph::buffer::list*, unsigned long, unsigned long)'
/home/yjk/projects/AudioToText/CephClient.cpp:118: undefined reference to `librados::IoCtx::getxattr(std::string const&, char const*, ceph::buffer::list&)'
collect2: error: ld returned 1 exit status
CMakeFiles/AudioToText.dir/build.make:484: recipe for target 'AudioToText' failed
make[2]: *** [AudioToText] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/AudioToText.dir/all' failed
make[1]: *** [CMakeFiles/AudioToText.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2
終端進程“/bin/bash '-c', 'cmake --build ./ --target all --'”已終止，退出代碼: 2。檢查CMakeLists.txt后，將目光鎖定到了之前添加的宏定義
將其修改為
發現依賴的ceph的庫librados.so鏈接成功，阿里雲的庫鏈接失敗
[100%] Linking CXX executable AudioToText
CMakeFiles/AudioToText.dir/ConfigManager.cpp.o: In function `TransConfig::Config::GenerateNewTokenWhenTokenExpire[abi:cxx11]()':
/home/yjk/projects/AudioToText/ConfigManager.cpp:36: undefined reference to `AlibabaNlsCommon::NlsToken::setAccessKeyId(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/home/yjk/projects/AudioToText/ConfigManager.cpp:37: undefined reference to `AlibabaNlsCommon::NlsToken::setKeySecret(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
CMakeFiles/AudioToText.dir/SpeechTranslator.cpp.o: In function `Translation::SpeechTranslator::ParseCallBack(AlibabaNls::NlsEvent*)':
/home/yjk/projects/AudioToText/SpeechTranslator.cpp:199: undefined reference to `AlibabaNls::NlsEvent::getSentenceWordsList[abi:cxx11]()'
collect2: error: ld returned 1 exit status
CMakeFiles/AudioToText.dir/build.make:484: recipe for target 'AudioToText' failed
make[2]: *** [AudioToText] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/AudioToText.dir/all' failed
make[1]: *** [CMakeFiles/AudioToText.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2
終端進程“/bin/bash '-c', 'cmake --build ./ --target all --'”已終止，退出代碼: 2。修改之前。指定的D_GLIBCXX_USE_CXX11_ABI=0，連接器去尋找std::string與std::list時不帶命名空間__cxx11，然而ceph的庫librados.so導出的符號帶了__cxx11
就拿pool_list函數來說，鏈接器鏈接時，試圖鏈接
`librados::Rados::pool_list(std::list<std::string, std::allocator<std::string> >&)'
//相當於連接了 (std::string 就是 std::basic_string<char>)
`librados::Rados::pool_list(std::list<std::basic_string<char, std::char_traits<char>, std::allocator<char> >>&)'然而librados.so導出的卻是
這時阿里雲的庫是鏈接成功了，但是ceph的庫缺鏈接失敗了，兩個庫的ABI是不兼容的，不管指定D_GLIBCXX_USE_CXX11_ABI為0還是1，總有一個會鏈接失敗！！！！！！！！！！！！！！！！！！！！！！！！！！！
目前還在尋找解決辦法，先記一筆，避免遺忘
經驗教訓
- 當項目需要依賴多個三方庫時，在選擇庫時
- 提前通過nm命令與c++filt組合查看下導出的符號，避免導出符號不兼容的情況發生而引起后續的折騰
- 查看動態庫的 .comment段中存儲的編譯器版本信息(不一定有)
readelf -p .comment <lib-name> objdump -s --section=.comment <lib-name>
以GCC5.1版本為分界線檢查，避免ABI不兼容
2.制作庫時，盡量別導出STL符號