From: Tom Lane <tgl@sss.pgh.pa.us>
To: James Hilliard <james.hilliard1@gmail.com>
cc: pgsql-hackers@lists.postgresql.org,
        Sergey Shinderuk <s.shinderuk@postgrespro.ru>,
        Thomas Munro <thomas.munro@gmail.com>
Subject: Re: [PATCH v2 1/1] Fix detection of pwritev support for OSX.
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Comments: In-reply-to James Hilliard <james.hilliard1@gmail.com>
	message dated "Tue, 19 Jan 2021 10:55:46 -0700"
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Date: Tue, 19 Jan 2021 16:00:08 -0500
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James Hilliard <james.hilliard1@gmail.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