On Windows targets, weak symbols have not supported in GCC, and have never been supported. However, they have been supported in binutils for years, with varying degrees of quality. They are probably now reliable enough to be supported by GCC.
-- Summary: Weak symbols are unimplemented on Windows Product: gcc Version: 4.0.0 Status: UNCONFIRMED Severity: enhancement Priority: P2 Component: target AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: aaronavay62 at aaronwl dot com CC: gcc-bugs at gcc dot gnu dot org GCC target triplet: i686-pc-mingw32 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18106