The Oracle blog has a lengthy article on enhancements to GCC to help detect overflows of flexible array members (FAMs) in C programs.

We describe here two new GNU extensions which specify size information for FAMs. These are a new attribute, "counted_by" and a new builtin function, "__builtin_counted_by_ref". Both extensions can be used in GNU C applications to specify size information for FAMs, improving the buffer overflow detection for FAMs in general.

This work has been covered on LWN as well.