glibc/debug/Versions

libc {
  GLIBC_2.1 {
    # functions used in other libraries
    __backtrace; __backtrace_symbols; __backtrace_symbols_fd;

    # b*
    backtrace; backtrace_symbols; backtrace_symbols_fd;
  }
  GLIBC_2.2 {
    # These are to support some gcc features.
    __cyg_profile_func_enter; __cyg_profile_func_exit;
  }
}