linux C++. Link shared objects and main -

i write simple testing program in c++, tell hello, alex , exit. here it's code: main.cpp:

#include <iostream> #include <dlfcn.h>   int main() {     void* descriptor = dlopen("dll.so", rtld_lazy);     std::string (*fun)(const std::string name) = (std::string (*)(const std::string)) dlsym(descriptor, "sayhello");      std::cout << fun("alex") << std::endl;      dlclose(descriptor);     return 0; } 

dll.h:

#ifndef untitled_dll_h #define untitled_dll_h  #include <string>     std::string sayhello(const std::string name); #endif 

dll.cpp:

#include "dll.h"  std::string sayhello(const std::string name) {     return ("hello, " + name); } 

makefile:

build_all : main dll.so  main : main.cpp     $(cxx) -c main.cpp     $(cxx) -o main main.o -ldl  dll.so : dll.h dll.cpp     $(cxx) -c dll.cpp     $(cxx) -shared -o dll dll.o 

but when build code make, have such error:

/usr/bin/ld: dll.o: relocation r_x86_64_32 against `.rodata' can not used when making shared object; recompile -fpic
dll.o: error adding symbols: bad value
collect2: error: ld returned 1 exit status
makefile:8: recipe target 'dll.so' failed
make: *** [dll.so] error 1

what did make not correct?
p.s. use gnu make 3.81 on ubuntu server 14.04.3 gnu gcc 4.8.4

update
if link dll.so file -fpic param, have same error

firstly, bit off topic, in makefile, better specify build_all phony target

.phony: build_all 

next, compiling dll.cpp without relocatable code. need add -fpic or -fpic (see here explanation of difference).

$(cxx) -c dll.cpp -fpic 

lastly, unix doesn't automatically add file suffixes, here need specify .so:

$(cxx) -shared -o dll.so dll.o