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动态库依赖于可执行文件(依赖项反转)

dynamic-library linux c++

Aubin · 技术社区 · 4 年前

插件是通过 dlopen

插件使用主程序提供的一些符号,但在加载时,它们不会被库看到。

这是密码 Main.cpp :

#include "SampleMain.h"

#include <dlfcn.h>
#include <iostream>
#include <map>
#include <string>

typedef std::map<std::string, Service> Services;

static Services services;

extern "C" void AddService( const char * name, Service service ) {
   std::cerr << "AddService( " << name << " )" << std::endl;
   services[name] = service;
}

int main( void ) {
   void * hLib = dlopen( "lib/libsample.so", RTLD_LAZY );
   if( hLib ) {
      typedef bool ( * RegisterServices )( void );
      RegisterServices registerServices =
         (RegisterServices)dlsym( hLib, "RegisterServices" );
      if( registerServices ) {
         if( registerServices()) {
            Services::iterator it = services.find( "MyService" );
            if( it != services.end()) {
               Service service = it->second;
               int retCode = service( 0 );
               std::cerr << "'MyService' returns " << retCode << std::endl;
            }
            else {
               std::cerr << "'MyService' not found!" << std::endl;
            }
         }
         else {
            std::cerr << "Registration failed" << std::endl;
         }
      }
      else {
         std::cerr << "dlsym error: " << dlerror() << std::endl;
      }
      dlclose( hLib );
   }
   else {
      std::cerr << "dlopen error: " << dlerror() << std::endl;
   }
   return 0;
}

这是密码 SampleLib.cpp

#include "SampleMain.h"

#if defined __linux__
#  define API extern "C" __attribute((visibility("default")))
#elif defined WIN32
#  define API extern "C" __declspec(dllexport)
#else
#  error Unsupported platform
#endif

#include <iostream>
#include <vector>

static int ServiceOffer( void * arg ) {
   std::cerr << "ServiceOffer|entry" << std::endl;
   std::vector<void *> v;
   v.push_back( arg );
   v.push_back( arg );
   v.push_back( arg );
   size_t val = v.size();
   std::cerr << "ServiceOffer|exit, val: " << val << std::endl;
   return 0;
}

API bool RegisterServices( void ) {
   AddService( "MyService", ServiceOffer );
   return true;
}

这是你的名字 Makefile :

run: Main lib/libsample.so
    LD_LIBRARY_PATH=./lib ./Main

lib/libsample.so: SampleLib.cpp
    g++ -fPIC -shared -o $@ $<

Main: SampleMain.cpp
    g++ -fPIC -o $@ $< -ldl

这是执行日志 RTLD_NOW :

$ make run
g++ -fPIC -o Main SampleMain.cpp -ldl
g++ -fPIC -shared -o lib/libsample.so SampleLib.cpp
LD_LIBRARY_PATH=./lib ./Main
dlopen error: lib/libsample.so: undefined symbol: AddService

这是执行日志 RTLD_LAZY

$ make run
g++ -fPIC -o Main SampleMain.cpp -ldl
LD_LIBRARY_PATH=./lib ./Main
./Main: symbol lookup error: lib/libsample.so: undefined symbol: AddService

我该怎么办出口 AddService ?

0 回复 | 直到 4 年前

Aubin 4 年前

以下是 Makefile :

.PHONY: all clean

all: Main lib/libsample.so
    LD_LIBRARY_PATH=./lib ./Main

clean:
    rm -f lib/libsample.so Main

Main: SampleMain.cpp
    g++ -o $@ $< -rdynamic -Wl,--dynamic-list=main-api -ldl

lib/libsample.so: SampleLib.cpp
    g++ -o $@ $< -fvisibility=hidden -fpic -shared

以下是 main-api 文本文件:

{
   extern "C" {
      AddService;
   };
};

执行日志变成:

$ make run
g++ -o Main SampleMain.cpp -rdynamic -Wl,--dynamic-list=main-api -ldl
g++ -o lib/libsample.so SampleLib.cpp -fvisibility=hidden -fpic -shared
LD_LIBRARY_PATH=./lib ./Main
AddService( MyService )
ServiceOffer|entry
ServiceOffer|exit, val: 3
'MyService' returns 0

under GitHub .