与共享库链接时未定义的引用

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我正在尝试编写一个链接到共享库（* .so）的小程序。但是当我尝试编译程序时，我收到错误，说“未定义引用”到“函数”

程序文件的内容。

user@ubuntu:~/Perforce/user_ubuntu_3105/wp/eng/main/src/libfc/37D03B6/bin$ cat test.cpp 
#include <iostream>
#include <vector>
#include <memory>
#include "InfoModel.h"

int main() 
{
    libfc::InfoModel & model = libfc::InfoModel::instance();
    return 0;
}

编译这个我得到错误'未定义引用'

user@ubuntu:~/Perforce/user_ubuntu_3105/wp/eng/main/src/libfc/37D03B6/bin$ g++ -Wall -W -std=c++0x test.cpp -L. -lfc -o rst
test.cpp: In function ‘int main()’:
test.cpp:9:21: warning: unused variable ‘model’ [-Wunused-variable]
libfc::InfoModel & model = libfc::InfoModel::instance();
                 ^
/tmp/ccFtLDxc.o: In function `main':
test.cpp:(.text+0x9): undefined reference to `libfc::InfoModel::instance()'
collect2: error: ld returned 1 exit status

但是当我查看.so文件中的符号时，我会在那里看到符号。

user@ubuntu:~/Perforce/user_ubuntu_3105/wp/eng/main/src/libfc/37D03B6/bin$ nm --demangle libfc.so | grep InfoModel 
0000000000007e40 t _GLOBAL__sub_I_InfoModel.cpp
00000000002464a0 b guard variable for libfc::InfoModel::instance()::instance_
0000000000010260 t libfc::InfoModel::add_unknown(unsigned int, unsigned short, unsigned short)
0000000000010520 t libfc::InfoModel::registerIEType(libfc::IEType const*)
000000000000f550 t libfc::InfoModel::add(libfc::InfoElement const&)
0000000000012980 t libfc::InfoModel::add(std::string const&)
0000000000010a60 t libfc::InfoModel::instance()
00000000000106f0 t libfc::InfoModel::initTypes()
00000000000108f0 t libfc::InfoModel::InfoModel()
00000000000108f0 t libfc::InfoModel::InfoModel()
0000000000027ae0 t libfc::InfoModel::~InfoModel()
0000000000027ae0 t libfc::InfoModel::~InfoModel()
0000000000010b00 t libfc::InfoModel::parseIESpec(std::string const&) const
000000000000ee80 t libfc::InfoModel::lookupIEType(unsigned int) const
000000000000ed40 t libfc::InfoModel::lookupIEType(std::string const&) const
000000000000ef20 t libfc::InfoModel::dump(std::ostream&) const
000000000000f0c0 t libfc::InfoModel::lookupIE(unsigned int, unsigned short, unsigned short) const
000000000000f1b0 t libfc::InfoModel::lookupIE(libfc::InfoElement const&) const
0000000000012840 t libfc::InfoModel::lookupIE(std::string const&) const
000000000000f410 t libfc::InfoModel::lookupIE2(unsigned int, std::string const&, unsigned short, unsigned short) const
00000000002463a0 b libfc::InfoModel::instance()::instance_

我也这样做了。

user@ubuntu:~/Perforce/user_ubuntu_3105/wp/eng/main/src/libfc/37D03B6/bin$ readelf -s libfc.so | grep FILE 
34: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS EncodePlan.cpp
43: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS InfoElement.cpp
49: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS FileExportDestination.cpp
53: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS IETemplate.cpp
58: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS IEType.cpp
104: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS InfoModel.cpp
113: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS libfc.cpp
118: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS PlacementExporter2.cpp
124: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS PlacementTemplate.cpp
129: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS TemplateState.cpp
135: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS test.cpp
141: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS UdpSocketExportDestinatio
149: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS crtstuff.c
158: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS BasicOctetArray.cpp
159: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS Exception.cpp
160: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS ExportError.cpp
161: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS FormatError.cpp
162: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS IESpecError.cpp
163: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS error_code.cpp
187: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS crtstuff.c
190: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS

更新：构建此共享库的make文件是

PLUGIN          = libfc
OUTPUT_DIR      = bin
OUTPUT          = $(OUTPUT_DIR)/$(PLUGIN).so
PLUG_SRC        = src
EXCEPTION_SRC   = src/exceptions
CPP             = g++
THIRD_PARTY_DIR = ../../../../../third-party
BOOST_DIR       = $(THIRD_PARTY_DIR)/boost/1.66.0
G3LOG_DIR       = $(THIRD_PARTY_DIR)/g3log/2017-07-18_g3log
FLAGS           = -c -std=c++0x -fvisibility-inlines-hidden -pthread 
              -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive 
MACROS          = -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_
INCLUDES        = -I$(PLUG_SRC) 
              -I$(EXCEPTION_SRC) 
              -I$(BOOST_DIR) 
              -I$(G3LOG_DIR)/src 
              -I$(G3LOG_DIR)/include
LFLAGS          = -shared -lpthread -L$(G3LOG_DIR)/build -lg3logger
CPPFLAGS     = $(FLAGS) $(MACROS) $(INCLUDES)  
LDFLAGS      = $(LFLAGS)
ifeq ($(BUILD),DEBUG)
CPPFLAGS += -ggdb3 -O0 
else
CPPFLAGS += -g -Wall -O2 -D NDEBUG
LDFLAGS += -flto 
endif

# compile static boost lib as
# ./bjam --toolset=gcc address-model=64 cxxflags=-fPIC cflags=-fPIC 
variant=release threading=multi link=static --with-system stage
BOOST_LIBS      = $(BOOST_DIR)/stage/lib/libboost_system.a
OBJ_DIR         = obj
PLUG_OBJS       = $(patsubst %.cpp,$(OBJ_DIR)/%.o,$(subst 
$(PLUG_SRC)/,,$(wildcard $(PLUG_SRC)/*.cpp)))
FRAME_OBJS      = $(patsubst %.cpp,$(OBJ_DIR)/%.o,$(subst 
$(EXCEPTION_SRC)/,,$(wildcard $(EXCEPTION_SRC)/*.cpp)))
VPATH           = $(PLUG_SRC) $(EXCEPTION_SRC)

all: $(PLUGIN)
$(PLUG_OBJS): $(OBJ_DIR)/%.o: %.cpp
   $(CPP) $(CPPFLAGS) -o $@ $<
$(FRAME_OBJS): $(OBJ_DIR)/%.o: %.cpp
   $(CPP) $(CPPFLAGS) -o $@ $<
$(PLUG_OBJS) $(FRAME_OBJS): | $(OBJ_DIR)
$(OBJ_DIR):
   mkdir $(OBJ_DIR)
$(OUTPUT): | $(OUTPUT_DIR)
$(OUTPUT_DIR):
   mkdir $(OUTPUT_DIR)
$(PLUGIN): $(PLUG_OBJS) $(FRAME_OBJS) $(OUTPUT)
   $(CPP) $(LDFLAGS) -o $(OUTPUT)  $(PLUG_OBJS) $(FRAME_OBJS) $(BOOST_LIBS)

.PHONY: clean
clean:
   rm -f $(PLUG_OBJS) $(FRAME_OBJS) $(OUTPUT)
   rm -rf $(OBJ_DIR)
   rm -rf $(OUTPUT_DIR)

而make的输出是

user@ubuntu:~/Perforce/sselvam_ubuntu_3105/wp/eng/main/src/libfc/37D03B6$ make all 
mkdir obj
g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/BasicOctetArray.o src/BasicOctetArray.cpp
g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/EncodePlan.o src/EncodePlan.cpp
src/EncodePlan.cpp: In constructor ‘libfc::EncodePlan2::EncodePlan2(const libfc::PlacementTemplate*)’:
src/EncodePlan.cpp:90:9: warning: unused variable ‘ie_present’ [-Wunused-variable]
bool ie_present
     ^
g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/FileExportDestination.o src/FileExportDestination.cpp
g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/IETemplate.o src/IETemplate.cpp
 g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/IEType.o src/IEType.cpp
 g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/InfoElement.o src/InfoElement.cpp
g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/InfoModel.o src/InfoModel.cpp
g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/libfc.o src/libfc.cpp
g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/PlacementExporter2.o src/PlacementExporter2.cpp
g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/PlacementTemplate.o src/PlacementTemplate.cpp
g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/TemplateState.o src/TemplateState.cpp
g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/UdpSocketExportDestination.o src/UdpSocketExportDestination.cpp
g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/Exception.o src/exceptions/Exception.cpp
g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/ExportError.o src/exceptions/ExportError.cpp
g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/FormatError.o src/exceptions/FormatError.cpp
g++ -c -std=c++0x -fvisibility-inlines-hidden -pthread -fPIC -fvisibility=hidden -fno-omit-frame-pointer -fpermissive  -D_libfc_HAVE_NIXIO -U_libfc_HAVE_LOG4CPLUS_ -U_libfc_HAVE_WANDIO_ -Isrc -Isrc/exceptions -I../../../../../third-party/boost/1.66.0 -I../../../../../third-party/g3log/2017-07-18_g3log/src -I../../../../../third-party/g3log/2017-07-18_g3log/include -g -Wall -O2 -D NDEBUG -o obj/IESpecError.o src/exceptions/IESpecError.cpp
mkdir bin
g++ -shared -lpthread -L../../../../../third-party/g3log/2017-07-18_g3log/build -lg3logger -flto  -o bin/libfc.so  obj/BasicOctetArray.o obj/EncodePlan.o obj/FileExportDestination.o obj/IETemplate.o obj/IEType.o obj/InfoElement.o obj/InfoModel.o obj/libfc.o obj/PlacementExporter2.o obj/PlacementTemplate.o obj/TemplateState.o obj/UdpSocketExportDestination.o obj/Exception.o obj/ExportError.o obj/FormatError.o obj/IESpecError.o ../../../../../third-party/boost/1.66.0/stage/lib/libboost_system.a

任何帮助都会非常有帮助。

答案
libfc::InfoModel & model = libfc::InfoModel::instance();
                 ^
/tmp/ccFtLDxc.o: In function `main':
test.cpp:(.text+0x9): undefined reference to `libfc::InfoModel::instance()'
collect2: error: ld returned 1 exit status

与-fvisibility=hidden（和朋友）结合：

$ nm -gCD ...

0000000000012980 t libfc::InfoModel::add(std::string const&)
0000000000010a60 t libfc::InfoModel::instance()
00000000000106f0 t libfc::InfoModel::initTypes()
...

我相信所有这些意味着你已经隐藏了你的InfoModel类，它不再可见。我猜你手动添加-fvisibility=hidden（和朋友）但没有编辑源文件并添加DLL_PUBLIC（根据GCC Visibility维基）。

我认为最简单的解决方法是在没有可见性的情况下构建静态存档。即，不要使用-fvisibility=hidden（和朋友）。然后，当您构建使用静态存档的共享对象/插件时，请使用-fvisibility=hidden（和朋友）并包含-Wl,--exclude-libs,ALL链接器标志。额外的链接器标志将确保您不会从静态存档重新导出符号。

你的插件的源文件将使用DLL_PUBLIC（根据GCC Visibility wiki）。 makefile配方将使用如下内容：

$(PLUGIN): $(PLUG_OBJS) $(FRAME_OBJS) $(OUTPUT)
   $(CXX) -shared -o $(OUTPUT) $(CXXFLAGS) $(PLUG_OBJS) $(FRAME_OBJS) $(BOOST_LIBS) $(LDFLAGS) -Wl,--exclude-libs,ALL

然后，您可以检查从共享对象/插件导出的内容，例如：

nm -gCD libplugin.so | grep ' T '

不幸的是，没有办法避免nm -gCD libplugin.so | grep ' T '疣。我刚刚在Binutils邮件列表上寻找更好的方式来显示出口。

最近针对Issue 87190, Feedback on documentation for symbol visibility的知名度文件开设了海湾合作委员会问题报告。另请参阅Binutils邮件列表中的Linker exposing private symbols。

一些额外的快速评论......

CPP = g++

CPP是预处理器。使用CXX。

FLAGS = ...

使用CXXFLAGS进行C ++项目。您的C ++配方可能如下所示：

SRCS = $(sort $(wildcard *.cpp))
OBJS = $(SRCS:.cpp=.o)

%.o : %.cpp
    $(CXX) $(CPPFLAGS) $(CXXFLAGS) -c $<

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