problem about generating data section in g++ 4.2

[Ling-hua Tseng]

Here is the example program:
==========
// test.cxx
#include <algorithm>
#include <map>

namespace {
  template <class T>
  struct transformValue {
    size_t operator()(const T &x) const
    {
        return x + 10;
    }
  };
}

extern std::map<int, int, transformValue<int> > *test;
std::map<int, int, transformValue<int> > *test;
==========

If I compile this file with g++ 4.2 by the following command:
  g++ -c test.cxx
and then use this command to check symbol:
  nm test.o
I cannot find the global varible `test' in symbol table:
         U _ZNKSs4sizeEv
         U _ZNKSsixEj
00000000 t _ZSt17__verify_groupingPKcjRKSs
00000000 W _ZSt3minIjERKT_S2_S2_
         U __gxx_personality_v0

I can find the symbol `test' by using older version g++, such as g++ 4.1.x or 3.x:
00000000 r _ZN9__gnu_cxx16__stl_prime_listE
         U _ZNKSs4sizeEv
         U _ZNKSsixEj
00000000 t _ZSt17__verify_groupingPKcjRKSs
00000000 W _ZSt3minIjERKT_S2_S2_
         U __gxx_personality_v0
00000000 B test

The keypoints of this problem are:
  1. struct transformValue<> is defined in anonymous namepsace
  2. transformValue<int> is passed to one of the template argument of std::map<> for instantiating it
  3. declare the global variable (should be a pointer) `test' as a external linkage object
  4. define the global varible `test' (should be a pointer)

If the variable `test' isn't declared/defined as pointer type, such as:
  extern std::map<int, int, transformValue<int> > test;
  std::map<int, int, transformValue<int> > test;
You can find a similar problem: the symbol `test' will become a `static' local variable.
It can be observed by using the tool `nm':
  00000000 b test
Its attribute must be `B', but became to `b'.