Re: [PATCH v2 1/1] Fix detection of pwritev support for OSX.

James Hilliard <james(dot)hilliard1(at)gmail(dot)com> writes:
> I also don't think this is a weak symbol.

> From the header file it is not have __attribute__((weak_import)):
> ssize_t pwritev(int, const struct iovec *, int, off_t)
> __DARWIN_NOCANCEL(pwritev) __API_AVAILABLE(macos(11.0), ios(14.0),
> watchos(7.0), tvos(14.0));

See the other thread. I found by looking at the asm output that
what __API_AVAILABLE actually does is cause the compiler to emit
a ".weak_reference" directive when calling a function it thinks
might not be available. So there's some sort of weak linking
going on, though it's certainly possible that it's not shaped
in a way that'd help us do this the way we'd prefer.

regards, tom lane