Stack-Smashing Protector
The Stack-Smashing Protector (sometimes called SSP, formerly known as ProPolice) is an extension to the GNU Compiler Collection that helps mitigate the damage that can be done by buffer overflow-based attacks. In particular, it provides stack-smashing protection.
The Stack-Smashing Protector was originally written, and is still maintained, by Hiroaki Etoh of IBM.
So far it remains a patch external to GCC, and must be added to GCC by developers wishing to employ stack-smashing protection in their programs. At this time, only a small number of operating system developers utilize the Stack-Smashing Protector in their projects by default: OpenBSD and DragonFly BSD. Gentoo Linux also has a version of their software distribution (Hardened Gentoo) that contains the Stack-Smashing Protector patch, but as Gentoo is primarily a source-based meta-distribution, this cannot be considered "out of the box" support. IPCop 1.4.0+ also includes SSP and libsafe as hardening measures.