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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Sergey Shinderuk <s.shinderuk@postgrespro.ru>
cc: Thomas Munro <thomas.munro@gmail.com>,
        pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: pg_preadv() and pg_pwritev()
In-reply-to: <1286060.1610558607@sss.pgh.pa.us>
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Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Wed, 13 Jan 2021 12:23:27 -0500"
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Date: Wed, 13 Jan 2021 13:20:46 -0500
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Hmmm ... I can further report that on Catalina + Xcode 12.0,
everything seems fine.  configure correctly detects that preadv
and pwritev aren't there:

configure:15161: checking for preadv
configure:15161: ccache gcc -o conftest -Wall -Wmissing-prototypes -Wpoint=
er-ar\
ith -Wdeclaration-after-statement -Werror=3Dvla -Wendif-labels -Wmissing-f=
ormat-a\
ttribute -Wformat-security -fno-strict-aliasing -fwrapv -Wno-unused-comman=
d-lin\
e-argument -g -O2 -isysroot /Applications/Xcode.app/Contents/Developer/Pla=
tform\
s/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk   -isysroot /Applications=
/Xcod\
e.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10=
.15.s\
dk   conftest.c -lz  -lm  >&5
Undefined symbols for architecture x86_64:
  "_preadv", referenced from:
      _main in conftest-fca7e9.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invoca=
tion)
configure:15161: $? =3D 1

So I'm a little confused as to why this test is failing to fail
with (I assume) newer Xcode.  Can we see the relevant part of
config.log on your machine?

			regards, tom lane