same piece of C++ code works in g++ 4.6 compiler but crashes with 5.1 - c++

Question

The following piece of code works with g++ 4.6 compiler but crashes with segmentation fault when compiled with g++ 5.1 compiler. The variable access gString is causing the segmentation fault.
#define _GLIBCXX_DEBUG 1
#define _GLIBCXX_USE_CXX11_ABI 0
#include<string>
#include<iostream>
#include<vector>
static std::string gString("hello");
static void
__attribute__((constructor))
initialize()
{
gString.assign("hello world");
return;
}
static void
__attribute__((destructor))
finalize()
{
return;
}
int main(int ac, char **av)
{
//std::cerr<<gString;
return 0;
}
GDB output:
Reading symbols from /home/rk/str...done.
(gdb) b initialize
Breakpoint 1 at 0x401419: file str.cc, line 15.
(gdb) r
Starting program: /home/rk/str
Breakpoint 1, initialize() () at str.cc:15
15 gString.assign("hello world");
(gdb) n
Program received signal SIGSEGV, Segmentation fault.
0x00000000004018d6 in std::string::size() const () at /usr/include/c++/5/bits/basic_string.h:3118
3118 { return _M_rep()->_M_length; }
(gdb) bt
#0 0x00000000004018d6 in std::string::size() const () at /usr/include/c++/5/bits/basic_string.h:3118
#1 0x00000000004016ff in std::string::assign(char const*, unsigned long) () at /usr/include/c++/5/bits/basic_string.tcc:706
#2 0x000000000040166e in std::string::assign(char const*) () at /usr/include/c++/5/bits/basic_string.h:3542
#3 0x0000000000401428 in initialize() () at str.cc:15
#4 0x00000000004023dd in __libc_csu_init ()
#5 0x00007ffff71ad700 in __libc_start_main () from /lib/x86_64-linux-gnu/libc.so.6
#6 0x0000000000401289 in _start ()

Answer 1

Why are you using __attribute__((constructor)) in C++ instead of simply a global object with a constructor? Those attributes are useful in C code, but redundant in C++.
The problem is that your constructor runs before the standard iostreams have been initialized, which would not be a problem if you used a global object with a constructor.
You could try adding a priority to your constructor, but I don't think it will help in this case:
__attribute__((constructor(999)))

Answer 2

The runtime error also happens with gcc 4.9.2 (see ideone example).
The problem is related to the iostreams which are not yet initialized. Commenting out the cerr line, and everything works fine
Apparently, it's a known issue.
Edit: Additional remarks
This small workaround seems to work, at least with 4.9: use c stdio instead of iostreams:
fprintf(stderr, "_initialize"); // this works
But I fully agree with Jonathan's suggestion of using a global (singleton ?) object relying solely on well defined standard C++ behaviour, unless you really need the constructor being run exactly at the moment of a dynamic library load.