How to change the entry point of a g++ generated Linux shared library compiled from multiple source files?

Question

Today, I read the web blog article , How to make executable shared libraries. In this article it states that if one types at a Linux command prompt:

gcc -shared service.c -o libservice.so -Wl,-soname,libservice.so -W1,-e lib_entry

followed by

./libservice.so, then we can directly executer the lib_entry function.

However, when I run a similar g++ command:

g++ -shared one.cpp two.cpp three.cpp -o libservice.so -Wl,-soname,libservice.so -W1,-e lib_entry

where lib_entry is a C function defined in two.cpp I get the warning message:

No entry point lib_entry point found.

How do I fix this warning message so I can directly run the entry point, lib_entry ? Should I enclose the implementation of the C function foo with extern "C" linkage to resolve this problem?

Answer 1

This is my answer: Missing include "bits/c++config.h" when cross compiling 64 bit program on 32 bit in Ubuntu

sudo apt-get install gcc-4.9-multilib g++-4.9-multilib

Answer 2

Please disregard the previous answer. The answer below was tested successfully. Thank you for your patience. Step 1

#include <stdio.h>
#include <unistd.h>

#ifdef __LP64__
const char service_interp[] __attribute__((section(".interp"))) = "/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2";
#else
const char service_interp[] __attribute__((section(".interp"))) = "/lib/ld-linux.so.2";
#endif


void lib_service(void)
{

  printf("This is a service of the shared library\n");

} // lib_service
void lib_entry(void)
{
  printf("Entry point of the service library\n");
 _exit(0);
}

Step 2.

vendor@clickit:~/Downloads/DataServerLib$ g++   -shared -fPIC -DLINUX -Wl,-soname,libdataserver.so -efunc  -I /home/vendor/Downloads/waitForMultipleObjects -I /home/vendor/development/Test/Include  DataServer.cpp DataServerLib.cpp DataTransferClient.cpp CWinEventHandle.cpp WinEvent.cpp -o libDataServer.so -lpthread -lrt
maryych@uwash.edu:~/Downloads/DataServerLib$ chmod 777 libDataServer.so
maryych@uwash.edu:~/Downloads/DataServerLib$ ./libDataServer.so

Inside entry point tester 1 AddUser