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

Fixes:
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -Wno-unused-command-line-argument -O2 -I../../../../src/include -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk -c -o fd.o fd.c
fd.c:3661:10: warning: 'pwritev' is only available on macOS 11.0 or newer [-Wunguarded-availability-new]
part = pg_pwritev(fd, iov, iovcnt, offset);
^~~~~~~~~~
../../../../src/include/port/pg_iovec.h:49:20: note: expanded from macro 'pg_pwritev'
^~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk/usr/include/sys/uio.h:104:9: note: 'pwritev' has been marked as being introduced in macOS 11.0
here, but the deployment target is macOS 10.15.0
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));
^
fd.c:3661:10: note: enclose 'pwritev' in a __builtin_available check to silence this warning
part = pg_pwritev(fd, iov, iovcnt, offset);
^~~~~~~~~~
../../../../src/include/port/pg_iovec.h:49:20: note: expanded from macro 'pg_pwritev'
^~~~~~~
1 warning generated.

This results in a runtime error:
running bootstrap script ... dyld: lazy symbol binding failed: Symbol not found: _pwritev
Referenced from: /usr/local/pgsql/bin/postgres
Expected in: /usr/lib/libSystem.B.dylib

dyld: Symbol not found: _pwritev
Referenced from: /usr/local/pgsql/bin/postgres
Expected in: /usr/lib/libSystem.B.dylib

child process was terminated by signal 6: Abort trap: 6

To fix this we set -Werror=unguarded-availability-new so that a compile
test for pwritev will fail if the symbol is unavailable on the requested
SDK version.
---
configure | 88 ++++++++++++++++++++++++++++++++++++++++++++--------
configure.ac | 19 +++++++++++-
2 files changed, 93 insertions(+), 14 deletions(-)

diff --git a/configure b/configure
index 8af4b99021..503b0d27e6 100755
--- a/configure
+++ b/configure
@@ -5373,6 +5373,47 @@ if test x"$pgac_cv_prog_CC_cflags__Werror_vla" = x"yes"; then
fi


+ # Prevent usage of symbols marked as newer than our target.
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Werror=unguarded-availability-new, for CFLAGS" >&5
+$as_echo_n "checking whether ${CC} supports -Werror=unguarded-availability-new, for CFLAGS... " >&6; }
+if ${pgac_cv_prog_CC_cflags__Werror_unguarded_availability_new+:} false; then :
+ $as_echo_n "(cached) " >&6
+else
+ pgac_save_CFLAGS=$CFLAGS
+pgac_save_CC=$CC
+CC=${CC}
+CFLAGS="${CFLAGS} -Werror=unguarded-availability-new"
+ac_save_c_werror_flag=$ac_c_werror_flag
+ac_c_werror_flag=yes
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h. */
+
+int
+main ()
+{
+
+ ;
+ return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+ pgac_cv_prog_CC_cflags__Werror_unguarded_availability_new=yes
+else
+ pgac_cv_prog_CC_cflags__Werror_unguarded_availability_new=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ac_c_werror_flag=$ac_save_c_werror_flag
+CFLAGS="$pgac_save_CFLAGS"
+CC="$pgac_save_CC"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CC_cflags__Werror_unguarded_availability_new" >&5
+$as_echo "$pgac_cv_prog_CC_cflags__Werror_unguarded_availability_new" >&6; }
+if test x"$pgac_cv_prog_CC_cflags__Werror_unguarded_availability_new" = x"yes"; then
+ CFLAGS="${CFLAGS} -Werror=unguarded-availability-new"
+fi
+
+
# -Wvla is not applicable for C++

{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Wendif-labels, for CFLAGS" >&5
@@ -15715,6 +15756,40 @@ $as_echo "#define HAVE_PS_STRINGS 1" >>confdefs.h

fi

+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for pwritev" >&5
+$as_echo_n "checking for pwritev... " >&6; }
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h. */
+#ifdef HAVE_SYS_TYPES_H
+#include <sys/types.h>
+#endif
+#ifdef HAVE_SYS_UIO_H
+#include <sys/uio.h>
+#endif
+int
+main ()
+{
+struct iovec *iov;
+off_t offset;
+offset = 0;
+pwritev(0, iov, 0, offset);
+
+ ;
+ return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+ { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+
+$as_echo "#define HAVE_PWRITEV 1" >>confdefs.h
+
+else
+ { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+
ac_fn_c_check_func "$LINENO" "dlopen" "ac_cv_func_dlopen"
if test "x$ac_cv_func_dlopen" = xyes; then :
$as_echo "#define HAVE_DLOPEN 1" >>confdefs.h
@@ -15871,19 +15946,6 @@ esac

fi

-ac_fn_c_check_func "$LINENO" "pwritev" "ac_cv_func_pwritev"
-if test "x$ac_cv_func_pwritev" = xyes; then :
- $as_echo "#define HAVE_PWRITEV 1" >>confdefs.h
-
-else
- case " $LIBOBJS " in
- *" pwritev.$ac_objext "* ) ;;
- *) LIBOBJS="$LIBOBJS pwritev.$ac_objext"
- ;;
-esac
-
-fi
-
ac_fn_c_check_func "$LINENO" "random" "ac_cv_func_random"
if test "x$ac_cv_func_random" = xyes; then :
$as_echo "#define HAVE_RANDOM 1" >>confdefs.h
diff --git a/configure.ac b/configure.ac
index 868a94c9ba..30fa39c859 100644
--- a/configure.ac
+++ b/configure.ac
@@ -494,6 +494,8 @@ if test "$GCC" = yes -a "$ICC" = no; then
AC_SUBST(PERMIT_DECLARATION_AFTER_STATEMENT)
# Really don't want VLAs to be used in our dialect of C
PGAC_PROG_CC_CFLAGS_OPT([-Werror=vla])
+ # Prevent usage of symbols marked as newer than our target.
+ PGAC_PROG_CC_CFLAGS_OPT([-Werror=unguarded-availability-new])
# -Wvla is not applicable for C++
PGAC_PROG_CC_CFLAGS_OPT([-Wendif-labels])
PGAC_PROG_CXX_CFLAGS_OPT([-Wendif-labels])
@@ -1726,6 +1728,22 @@ if test "$pgac_cv_var_PS_STRINGS" = yes ; then
AC_DEFINE([HAVE_PS_STRINGS], 1, [Define to 1 if the PS_STRINGS thing exists.])
fi

+AC_MSG_CHECKING([for pwritev])
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
+[#ifdef HAVE_SYS_TYPES_H
+#include <sys/types.h>
+#endif
+#ifdef HAVE_SYS_UIO_H
+#include <sys/uio.h>
+#endif],
+[struct iovec *iov;
+off_t offset;
+offset = 0;
+pwritev(0, iov, 0, offset);
+])], [AC_MSG_RESULT(yes)
+AC_DEFINE([HAVE_PWRITEV], 1, [Define to 1 if you have the `pwritev' function.])],
+[AC_MSG_RESULT(no)])
+
AC_REPLACE_FUNCS(m4_normalize([
dlopen
explicit_bzero
@@ -1739,7 +1757,6 @@ AC_REPLACE_FUNCS(m4_normalize([
pread
preadv
pwrite
- pwritev
random
srandom
strlcat
--
2.30.0