On Mon, Oct 28, 2013 at 7:11 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
If copying takes place between objects that overlap, the behavior is undefined.
Both gcc and glibc have been moving steadily in the direction of aggressively exploiting "undefined behavior" cases for optimization purposes. I don't know if there is yet a platform where strncpy with src == dest behaves oddly, but we'd be foolish to imagine that it's not going to happen eventually. If anything, Apple is probably doing us a service by making it obvious where we're failing to adhere to spec.
However ... I still can't replicate this here, and as you say, there's about zero chance of keeping our code clean of this problem unless we can set up a buildfarm member that will catch it.
