the weakref magic in libgcc/gthr-posix.h is not guaranteed to work which can at least break libstdc++ with static linking and dlopen
there are several bugs here: - fallback code (unknown posix systems) should assume multi-threaded application instead of using a fragile threadedness test - determining threadedness with weak symbols is broken for dynamic loading and static linking as well (dlopened library can pull in pthread dependency at runtime, and with static linking a symbol does not indicate the availability of another) - using symbols through weak references at runtime is wrong with static linking (it just happens to work with hacks that put a single .o into libpthread.a) see this analysis for more details and crashing example code: http://www.openwall.com/lists/musl/2014/10/18/5 the static linking issue there was fixed by unconditionally disabling the weak symbols in libgcc/gthr.h when building the toolchain: #define GTHREAD_USE_WEAK 0 i sent this report to the libstdc++ list first but got redirected here: https://gcc.gnu.org/ml/libstdc++/2014-11/msg00122.html the static linking issue there was worked around by using linker flags '-Wl,--whole-archive -lpthread -Wl,--no-whole-archive' i think upstream should fix this properly
