http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56977
Bastiaan Jacques <bastiaan at bjacques dot org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |bastiaan at bjacques dot org --- Comment #7 from Bastiaan Jacques <bastiaan at bjacques dot org> --- The following program fd.cc: #include <sys/select.h> int some_socket = 0; void foo() { fd_set fdset; struct timeval tval; FD_ZERO(&fdset); FD_SET(some_socket, &fdset); } When compiled with: g++ -c -o fd.o fd.cc -D_FORTIFY_SOURCE=2 -Og Generates the following warning: fd.cc:12:219: warning: call to ‘__fdelt_warn’ declared with attribute warning: bit outside of fd_set selected [enabled by default] FD_SET(some_socket, &fdset); I think this might be another instance of this bug, because it goes away when switching to -O2 (but I don't have a 4.8 branch handy to test whether the fix also resolved this case).