It'd be an API change, sort of? Although POSIX doesn't seem to say anything about ownership of the pointer, beyond thou-shalt-not modify the data it points to.

It'd be an API change, sort of? Although POSIX doesn't seem to say anything about ownership of the pointer, beyond thou-shalt-not modify the data it points to. Doesn't seem to specify calling free as valid or invalid. But honestly, it seems like one might as well do exactly that (strdup & return)? At worst, nothing calls free(), and it is equivalent to the macOS strategy of "just leak the memory" to make it threadsafe. But at best, a program could #ifdef its way into "oh, this semi-sorta-nonstandard-behavior on this particular OS" and call free(), getting both a thread-safe & non-leaking implementation.