I'm puzzled by the following on Linux, where I don't understand what
causes it that a given symbol is exported as "u" (when viewed with nm,
which documents "u" as "a unique global symbol. This is a GNU
extension...") or not:
* On an older toolchain (SLED 11 with GCC 4.3.4 and binutils 2.21.1), we
have
$ nm -D /usr/lib64/libstdc++.so.6.0.16 | grep empty_rep_storage
00000000002f7660 u _ZNSbIwSt11char_traitsIwESaIwEE4_Rep20_S_empty_rep_storageE
00000000002f7580 B _ZNSs4_Rep20_S_empty_rep_storageE
where the latter (aka "std::basic_string<char, std::char_traits<char>,
std::allocator<char> >::_Rep::_S_empty_rep_storage") is not exported as
"u" while the former (aka "std::basic_string<wchar_t,
std::char_traits<wchar_t>, std::allocator<wchar_t>
>::_Rep::_S_empty_rep_storage") is. Also, in other dynamic libraries
linked with that toolchain, _ZNSs4_Rep20_S_empty_rep_storageE is
exported as "V", and:
** If libstdc++.so.6 is loaded after one of those other libraries, all
libraries consistently bind to that other libraries' symbol, and
everything works well.
** However, if libstdc++.so.6 is loaded first, it binds to its symbol,
but all those other libraries loaded later bind to one of those other
libaries' symbol, and there is an invalid delete on an address "0 bytes
inside data symbol '_ZNSs4_Rep20_S_empty_rep_storageE'" from
std::basic_stringbuf<char, std::char_traits<char>, std::allocator<char>
>::overflow(int) (in /usr/lib64/libstdc++.so.6.0.16), as reported by
valgrind.
* But on a more recent toolchain (F18 with GCC 4.7.2 and binutils
2.23.51), we have
$ nm -D /usr/lib64/libstdc++.so.6.0.17 | grep empty_rep_storage
0000003c831024e0 u _ZNSbIwSt11char_traitsIwESaIwEE4_Rep20_S_empty_rep_storageE
0000003c831024c0 u _ZNSs4_Rep20_S_empty_rep_storageE
Also, in dynamic libraries linked with that toolchain,
_ZNSs4_Rep20_S_empty_rep_storageE is also exported as "u" and runtime
behavior is just fine.
Now, why is _ZNSs4_Rep20_S_empty_rep_storageE exported as "B" resp. "V"
in the first case, while it is consistently "u" in the second?
Stephan
